Friday.
1502.07346
A primordial origin for the composition similarity between the Earth and the Moon
Mastrobuono-Battisti, Perets, Raymond
Most of the Earth-moon system can be explained by a collision between a planetary embryo and the growing Earth late in the accretion process. Simulations show that most of the material that eventually aggregates to form the Moon originates from the impactor. However, analysis of the terrestrial and lunar isotopic composition show them to be highly similar. In contrast, the compositions of other solar system bodies are significantly different than the Earth and Moon. This poses a major challenge to the giant impact scenario since the Moon-forming impactor is then thought to also have differed in composition from the proto-Earth. Track the feeding zones of growing planets in a suite of simulations of planetary accretion, in order to measure the composition of Moon-forming impactors. Find that different planets formed in the same simulation have distinct compositions, but the compositions of giant impactors are systematically more similar to the planets they impact. A significant fraction of planet-impactor pairs have virtually identical compositions. Thus, the similarity in composition between the Earth and Moon could be a natural consequence of a late giant impact.
1502.07347
Galaxy cluster mass reconstruction project: II. quantifying scatter and bias using contrasting mock catalogues
Old, ... Rozo, Rykoff, et al
An comparison of various galaxy-based cluster mass estimation techniques that utilise the positions, velocities and colors of galaxies. Aim: quantify the scatter, systematic bias and completeness of cluster masses derived from a diverse set of 25 galaxy-based methods using two contrasting mock galaxy catalogues based on a sophisticated halo occupation model and a SAM. Analyzing 968 clusters, find a wide range in the RMS errors in log M200c delivered by the different methods (0.18 to 1.08 dex, or a factor of ~1.5 to 12), with abundance matching and richness methods providing the best results, irrespective of the input model assumptions. In addition, certain methods produce a significant number of catastrophic cases where the mass is under- or over-estimated by a factor grater than 10. Given the steeply falling high-mass end of the cluster MF, recommend that richness or abundance matching-based methods are used in conjunction with these methods as sanity check for studies selecting high mass clusters. See a stronger correlation of the recovered to input number of galaxies for both catalogues in comparison with the group/cluster mass, however, this does not guarantee that the correct member galaxies are being selected. Do not observe significantly higher scatter for either mock galaxy catalogues. Results have implications for cosmo analysis that utilize the masses, richness or abundances of clusters, which have different uncertainties when different methods are used.
1502.07356
Milking the spherical cow: on aspherical dynamics in spherical coordinates
Pontzen, ... Roth et al
Galaxies and DM haloes that host them are not spherically symmetric, yet spherical symmetry is a helpful simplifying approximation for idealised calculations and analysis of observational data. The assumption leads to an exact conservation of angular momentum for every particle, making the dynamics unrealistic. But how much does that inaccuracy matter in practice for analysis of stellar distribution functions, collisions relaxation, or DM core-creation? Prove a general answer to this question for a wide class of aspherical systems; specifically, consider distribution functions that are "maximally stable", i.e., that do not evolve at first order when external potentials (which arise from baryons, large scale tidal fields or inflating substructure) are applied. Show that a spherically-symmetric analysis of such systems gives rise to the case conclusion that the density of particles in phase space is ergodic (a function of energy alone). Using this idea, able to demonstrate that: (a) observational analyses that falsely assume spherical symmetry are made more accurate by imposing a strong prior preference for near-isotropic velocity dispersions in the center of spheroids; (b) numerical simulations that use an idealized spherical-symmetric setup can yield misleading results and should be avoided where possible; and (c) triaxial DM haloes (formed in collisions cosmo sims) nearly attain the maximally-stable limit, but their evolution freezes out before reaching it.
1502.07357
Baryon impact on the halo mass function: fitting formula and implications for cluster cosmology
Bocquet, Saro, Dolag, Mohr
Calibrate the halo MF accounting for halo baryons and present fitting formulae for spherical overdensity masses M500c, M200c, and M200m. Use the hydrodynamical Magneticum simulations, suited because of their high resolution nan large cosmo volumes up to ~2 Gpc^3. Baryonic effects globally decrease the masses of galaxy clusters, which at given mass, results in a decrease of their number density. This effect vanishes at high z (~2) and for high masses >5e14 Msun. Perform cosmo analyses of 3 idealized approximations to the cluster surveys by SPT, Planck, and eROSITA. For the SPT-like and the Planck-like samples, find that the impact of baryons on the cosmo results is negligible. In the eROSITA-like case, find that neglecting the baryonic impact leads to an underestimate of Omega_m by about 0.01, which is comparable to the expected uncertainty from eROSITA. Compare MF fits with the literature. In the analysis of the Planck-like sample, results obtained using MF are shifted by Delta(sigma_8)~0.05 with respect to results obtained using the Tinker+2008 fit. This shift represent a large fraction of the observed difference between the latest results from Planck clusters and CMB anisotropies, and the tension is essentially removed. Discuss biases that can be introduced through inadequate MF parameterizations that introduce false cosmo sensitivity. Additional work to calibrate the halo MF is crucial for progress in cluster cosmology.
1502.07442
ngravs: distinct gravitational interactions in GADGET-2
Croker
Discuss an extension of the massively parallel cosmo sim code GADGET-2, which enables investigations of distinct gravitational force laws between particle species. In addition to simplifying investigations of a universally modified force law, the graves extension allows state-of-the-art collisions cosmo sims of quite exotic gravitational scenarios. Briefly review the algorithms used by GADGET-2, and present extension to multiple gravitates, highlighting additional features that facilitate consideration of exotic force laws. Discuss the accuracy and performance of the graves extension, both internally and with an unaltered GADGET-2, under all relevant operational modes. The graves extension is publicly released .
1502.07696
Why are dense planetary rings only found between 8AU and 20AU?
Hedman
Recent discovery reveals that complete dense planetary rings are not only found around Saturn and Uranus, but also found small bodies orbiting in the vicinity of these giant planets. This report examines whether there could be a physical process that would make rings more likely to form or persist in this particular part of the outer Solar System. Specifically, the ring material orbiting Saturn and Uranus appears to be much weaker than the material forming the innermost moons of Jupiter and Neptune. Also, the mean surface temperatures of Saturn's, Uranus' and Chariklo's rings are all close to 70K. Thus the restricted distribution of dense rings in our SS may arise because icy materials are particularly weak around that temperature.
Friday, February 27, 2015
Thursday, February 26, 2015
Day 841
Thursday.
Nature 518
An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
Wu, et al
Cosmic redshifts of between 6 and 7 represent a time when the IGM was in transition from a neutral state to being completely ionized. Report the discovery of an UL quasar at z=6.30 that has optical and NIR luminosity several times greater than previously known quasars at redshift beyond z=6. Based on NIR spectral data, the authors estimate a mass of approximately twelve-billion Msun for the associated BH, consistent with the 13 billion Msun derived by assuming an Eddington-limited accretion rate, where the force of radiation acting outwards and the gravitational force acting inward are in balance. As the most luminous quasar known to date at z=6, this object will be a useful resource for the study of galaxy formation around massive BHs at the end of the epoch of cosmic reionization.
1502.07024
Hiding in plain sight: an abundance of compact massive spheroids in the local universe
Graham, Dullo, Savorgnan
...This abundance of compact, massive spheroids in our own backyard - with a number density of 6.9e-6 Mpc^-3 (or 3.5e-5 Mpc^-3 per unit dec in stellar mass) - and with the same physical properties as the high-redshift galaxies, had been over-looked because they are encased in stellar disks which usually result in 'galaxy' sizes notably larger than 2 kpc. Moreover, this number density is a lower limit because it has not come from a volume-limited sample. The actual density may be closer to 1e-4 Mpc^-3, although further work is required to confirm this. Conclude that not all massive 'spheroids' have undergone dramatic structural and size evolution since z~2pm0.6. Given that the bulges of local early-type disk galaxies are known to consist of predominantly old stars which existed at z~2, it seems likely that some of the observed high-z spheroids did not increase in size by building 3d triaxial envelopes as commonly advocated, and that the growth of 2d disks has also been important over the past 9-11 billion years.
Nature 518
An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
Wu, et al
Cosmic redshifts of between 6 and 7 represent a time when the IGM was in transition from a neutral state to being completely ionized. Report the discovery of an UL quasar at z=6.30 that has optical and NIR luminosity several times greater than previously known quasars at redshift beyond z=6. Based on NIR spectral data, the authors estimate a mass of approximately twelve-billion Msun for the associated BH, consistent with the 13 billion Msun derived by assuming an Eddington-limited accretion rate, where the force of radiation acting outwards and the gravitational force acting inward are in balance. As the most luminous quasar known to date at z=6, this object will be a useful resource for the study of galaxy formation around massive BHs at the end of the epoch of cosmic reionization.
1502.07024
Hiding in plain sight: an abundance of compact massive spheroids in the local universe
Graham, Dullo, Savorgnan
...This abundance of compact, massive spheroids in our own backyard - with a number density of 6.9e-6 Mpc^-3 (or 3.5e-5 Mpc^-3 per unit dec in stellar mass) - and with the same physical properties as the high-redshift galaxies, had been over-looked because they are encased in stellar disks which usually result in 'galaxy' sizes notably larger than 2 kpc. Moreover, this number density is a lower limit because it has not come from a volume-limited sample. The actual density may be closer to 1e-4 Mpc^-3, although further work is required to confirm this. Conclude that not all massive 'spheroids' have undergone dramatic structural and size evolution since z~2pm0.6. Given that the bulges of local early-type disk galaxies are known to consist of predominantly old stars which existed at z~2, it seems likely that some of the observed high-z spheroids did not increase in size by building 3d triaxial envelopes as commonly advocated, and that the growth of 2d disks has also been important over the past 9-11 billion years.
Wednesday, February 25, 2015
Day 840
Wednesday.
1502.06604
Can we use weak lensing to measure total mass profiles of galaxies on 20 kilo parsec scales?
Kobayashi, Leauthaud, More, Okabe, Laigle, Rhodes, Takeuchi
Current constraints on DM density profiles from WL are typically limited to radial scales greater than 50-100 kpc. In this paper, explore the possibility of probing the very inner regions of galaxy/halo density profiles by measuring stacked WL on scales of only a few tens of kpc. The forecasts focus on scales smaller than the equality radius (Req) where the stellar component and the DM component contribute equally to the lensing signal. Compute the evolution of Req as a function of lens stellar mass and redshift and show that Req=7-34 kpc for galaxies with the stellar mass of 1e9.5-11.5 Msun. Unbiased shear measurement will be challenging on these scales. Introduce a simple metric to quantify how many source galaxies overlap with their neighbors and for which shear measurement will be challenging. Rejecting source galaxies with close-by companions results in about a 20% decrease in the overall source density. Despite this decrease, show that Euclid and WFIRST will be able to constrain galaxy/halo density profiles at Req with S/N >20 for M* >1e10 Msun. WL measurements at Req, in combination with stellar kinematics on small scales, will be a powerful means by which to constrain both the inner slope of the DM density profile as well as the mass and z dependence of the stellar IMF.
1502.06614
The galaxy - dark matter halo connection: which galaxy properties are correlated with the host halo mass?
Contreras, Baugh, Norberg, Padilla
Demonstrate how the properties of a galaxy depend on the mass of its host dark matter sub halo, using two independent models of galaxy formation. For the cases of stellar mass and BH mass, the median property value displays a monotonic dependence on sub halo mass. The slope of the relation changes for sub halo masses for which heating by AGN becomes important. The median property values are predicted to be remarkably similar for central and satellite galaxies. The two models predict considerable scatter around the median property value, though the size of the scatter is model dependent. There is only modest evolution with z in the median galaxy property at a fixed sub halo mass. Properties such as cold gas mass and SFR, however, are predicted to have a complex dependence on sub halo mass. In these cases sub halo mass is not a good indicator of the value of the galaxy property. Illustrate how the predictions in the galaxy property - sub halo mass plane differ from the assumptions made in empirical models of galaxy clustering by reconstruction the model output using a sub halo abundance matching scheme. In its simplest form, abundance matching generally does not reproduce the clustering predicted by the models, typically resulting in an overproduction of the clustering signal. Show how the basic abundance matching scheme can be extended to reproduce the model predictions more faithfully, which has implications for the analysis of galaxy clustering, particularly for low abundance samples.
1502.06604
Can we use weak lensing to measure total mass profiles of galaxies on 20 kilo parsec scales?
Kobayashi, Leauthaud, More, Okabe, Laigle, Rhodes, Takeuchi
Current constraints on DM density profiles from WL are typically limited to radial scales greater than 50-100 kpc. In this paper, explore the possibility of probing the very inner regions of galaxy/halo density profiles by measuring stacked WL on scales of only a few tens of kpc. The forecasts focus on scales smaller than the equality radius (Req) where the stellar component and the DM component contribute equally to the lensing signal. Compute the evolution of Req as a function of lens stellar mass and redshift and show that Req=7-34 kpc for galaxies with the stellar mass of 1e9.5-11.5 Msun. Unbiased shear measurement will be challenging on these scales. Introduce a simple metric to quantify how many source galaxies overlap with their neighbors and for which shear measurement will be challenging. Rejecting source galaxies with close-by companions results in about a 20% decrease in the overall source density. Despite this decrease, show that Euclid and WFIRST will be able to constrain galaxy/halo density profiles at Req with S/N >20 for M* >1e10 Msun. WL measurements at Req, in combination with stellar kinematics on small scales, will be a powerful means by which to constrain both the inner slope of the DM density profile as well as the mass and z dependence of the stellar IMF.
1502.06614
The galaxy - dark matter halo connection: which galaxy properties are correlated with the host halo mass?
Contreras, Baugh, Norberg, Padilla
Demonstrate how the properties of a galaxy depend on the mass of its host dark matter sub halo, using two independent models of galaxy formation. For the cases of stellar mass and BH mass, the median property value displays a monotonic dependence on sub halo mass. The slope of the relation changes for sub halo masses for which heating by AGN becomes important. The median property values are predicted to be remarkably similar for central and satellite galaxies. The two models predict considerable scatter around the median property value, though the size of the scatter is model dependent. There is only modest evolution with z in the median galaxy property at a fixed sub halo mass. Properties such as cold gas mass and SFR, however, are predicted to have a complex dependence on sub halo mass. In these cases sub halo mass is not a good indicator of the value of the galaxy property. Illustrate how the predictions in the galaxy property - sub halo mass plane differ from the assumptions made in empirical models of galaxy clustering by reconstruction the model output using a sub halo abundance matching scheme. In its simplest form, abundance matching generally does not reproduce the clustering predicted by the models, typically resulting in an overproduction of the clustering signal. Show how the basic abundance matching scheme can be extended to reproduce the model predictions more faithfully, which has implications for the analysis of galaxy clustering, particularly for low abundance samples.
Monday, February 23, 2015
Day 839
Tuesday.
1502.06001
Detection and localization of single-source gravitational waves with pulsar timing arrays
Zhu, et al
PTAs can be used to search for very low frequency (1e-9 to 1e-7 Hz) GWs. Present a general method for the detection and localization of single-source GWs using PTAs. Demonstrate the effectiveness of this new method for 3 types of signals: monochromatic waves as expected from individual SMBH binaries in circular orbits, GWs from eccentric binaries and GW bursts. Also test its implementation in realistic data sets that include effects such as uneven sampling and heterogeneous data spans and measurement precision. It is shown that the method, which works in the frequency domain, performs as well as published time-domain methods. Find it equivalent to the P_e-statistic proposed in Ellis+2012 for monochromatic waves. Also discuss the construction of null streams --- data streams that have null response to GWs and the prospect of using tunnel streams as a consistency check in the case of detected GW signals. Finally, present sensitivities to individual SMBH binaries in eccentric orbits. Find that a monochromatic search that is designed for circular binaries can efficiently detect eccentric binaries with both high and low eccentricities, while a harmonic summing technique provides greater sensitivities only for binaries with moderate eccentricities.
1502.06016
PAPER-64 constraints on reionization: the 21cm power spectrum at z=8.4
Ali, Parsons, ... Pober, Liu, Aguirre, et al
Report new limits on 21 cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the D.C.Backer Precision Array for probing the epoch of reionization (PAPER) in South Africa. This work extends the Parsons+2014 with more collection area, a longer observing periods, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optical quadratic estimators. The result is a new 2sigma upper limit on Delta^2(k) of (22.4 mK)^2 in the range 0.15<k<0.5 h/Mpc at z=8.4. This represent a three-fold improvement over the previous best upper limit. This upper limit supports and extends previous evidence against extremely cold reionization scenarios. Conclude with a discussion of implications for future 21cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array (HERA).
1502.06020
Cosmology and astrophysics from relaxed galaxy clusters I: sample selection
Mantz, Allen, Morris, Schmidt, von der Linden, Urban
First in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Present a new, automated method for identifying relaxed clusters based on their morphologies in X-ray imaging data. While broadly similar to others in the literature, the morphological quantities that are measured are specifically designed to provide a fair basis for comparison across a range of data quality and cluster redshifts, to be robust against missing data due to point-source masks and gaps between detectors, and to avoid strong assumptions about the cosmological background and cluster masses. Based on 3 morphological indicators - Symmetry, Peakiness and Alignment - develop the SPA criterion for relaxation. This analysis was applied to a large sample of cluster observations from the Chandra and ROSAT archives. Of the 361 clusters which received the SPA treatment, 57 (16%) were subsequently found to be relaxed according to this criterion. Compare measurements to similar estimators in the literature, as well as projected ellipticity and other image measures, and comment on trends in the relaxed cluster fraction with z, temperature, and survey selection method. Code implementing the morphological analysis will be made available on the web.
1502.06456
The Atacama cosmology telescope: measuring radio galaxy bias through cross-correlation with lensing
Allison, ... Sherwin, ... Devlin, ... Hlozek, Jarvis, ... et al
Correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from ACT over 470 sq deg to determine the bias of these galaxies. Remove optically cross-matched sources below z=0.2 to preferentially select AGN. Measure the angular cross-power spectrum C^{kappa g}_ell at 4.4 sigma significance in the multipole range 100<l<3000, corresponding to physical scales between 2-60Mpc at an effective z=1.5. Modeling the AGN population with a z-dependent bias, the cross-spectrum is well fit by the Planck best-fit LCDM cosmological model. Fixing the cosmology, fit for the overall bias model normalization, finding b(z_eff)=3.5pm0.8 for the full galaxy sample, and b(z_eff)=4.0pm1.1(3.0pm1.1) for source brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radio-loud AGN: find log(M_halo/M_sun)=13.6pm0.3.
1502.06001
Detection and localization of single-source gravitational waves with pulsar timing arrays
Zhu, et al
PTAs can be used to search for very low frequency (1e-9 to 1e-7 Hz) GWs. Present a general method for the detection and localization of single-source GWs using PTAs. Demonstrate the effectiveness of this new method for 3 types of signals: monochromatic waves as expected from individual SMBH binaries in circular orbits, GWs from eccentric binaries and GW bursts. Also test its implementation in realistic data sets that include effects such as uneven sampling and heterogeneous data spans and measurement precision. It is shown that the method, which works in the frequency domain, performs as well as published time-domain methods. Find it equivalent to the P_e-statistic proposed in Ellis+2012 for monochromatic waves. Also discuss the construction of null streams --- data streams that have null response to GWs and the prospect of using tunnel streams as a consistency check in the case of detected GW signals. Finally, present sensitivities to individual SMBH binaries in eccentric orbits. Find that a monochromatic search that is designed for circular binaries can efficiently detect eccentric binaries with both high and low eccentricities, while a harmonic summing technique provides greater sensitivities only for binaries with moderate eccentricities.
1502.06016
PAPER-64 constraints on reionization: the 21cm power spectrum at z=8.4
Ali, Parsons, ... Pober, Liu, Aguirre, et al
Report new limits on 21 cm emission from cosmic reionization based on a 135-day observing campaign with a 64-element deployment of the D.C.Backer Precision Array for probing the epoch of reionization (PAPER) in South Africa. This work extends the Parsons+2014 with more collection area, a longer observing periods, improved redundancy-based calibration, optimal fringe-rate filtering, and improved power-spectral analysis using optical quadratic estimators. The result is a new 2sigma upper limit on Delta^2(k) of (22.4 mK)^2 in the range 0.15<k<0.5 h/Mpc at z=8.4. This represent a three-fold improvement over the previous best upper limit. This upper limit supports and extends previous evidence against extremely cold reionization scenarios. Conclude with a discussion of implications for future 21cm reionization experiments, including the newly funded Hydrogen Epoch of Reionization Array (HERA).
1502.06020
Cosmology and astrophysics from relaxed galaxy clusters I: sample selection
Mantz, Allen, Morris, Schmidt, von der Linden, Urban
First in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Present a new, automated method for identifying relaxed clusters based on their morphologies in X-ray imaging data. While broadly similar to others in the literature, the morphological quantities that are measured are specifically designed to provide a fair basis for comparison across a range of data quality and cluster redshifts, to be robust against missing data due to point-source masks and gaps between detectors, and to avoid strong assumptions about the cosmological background and cluster masses. Based on 3 morphological indicators - Symmetry, Peakiness and Alignment - develop the SPA criterion for relaxation. This analysis was applied to a large sample of cluster observations from the Chandra and ROSAT archives. Of the 361 clusters which received the SPA treatment, 57 (16%) were subsequently found to be relaxed according to this criterion. Compare measurements to similar estimators in the literature, as well as projected ellipticity and other image measures, and comment on trends in the relaxed cluster fraction with z, temperature, and survey selection method. Code implementing the morphological analysis will be made available on the web.
1502.06456
The Atacama cosmology telescope: measuring radio galaxy bias through cross-correlation with lensing
Allison, ... Sherwin, ... Devlin, ... Hlozek, Jarvis, ... et al
Correlate the positions of radio galaxies in the FIRST survey with the CMB lensing convergence estimated from ACT over 470 sq deg to determine the bias of these galaxies. Remove optically cross-matched sources below z=0.2 to preferentially select AGN. Measure the angular cross-power spectrum C^{kappa g}_ell at 4.4 sigma significance in the multipole range 100<l<3000, corresponding to physical scales between 2-60Mpc at an effective z=1.5. Modeling the AGN population with a z-dependent bias, the cross-spectrum is well fit by the Planck best-fit LCDM cosmological model. Fixing the cosmology, fit for the overall bias model normalization, finding b(z_eff)=3.5pm0.8 for the full galaxy sample, and b(z_eff)=4.0pm1.1(3.0pm1.1) for source brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radio-loud AGN: find log(M_halo/M_sun)=13.6pm0.3.
Sunday, February 22, 2015
Day 838
Monday.
1502.05709
Test for radial mixing of stars in M31
Gould, Rix
Effective radial migration and mixing of orbits throughout the stellar disk has been definitely established in the MW, but not in any other galaxy. Show how such radial mixing can be measured (or strongly constrained) in M31 using a combination of existing data and readily available facilities.
1502.05733
The observational status of cosmic inflation after Planck
Martin
These pedagogical lecture notes are intended to serve as a technical guide filling the gap between the theoretical articles on inflation and the experimental works on astrophysical and cosmological data. After a short discussion of the central tenets at the basis of inflation (negative self-gravitating pressure) and its experimental verifications, it reviews how the most recent CBM anisotropy measurements constrain cosmic inflation. The fact that vanilla inflationary models are, so far, preferred by the observations is discussed and the reason why plateau-like potential versions of inflation are favored within this subclass of scenarios is explained. Finally, how well the future measurements, in particular of B-mode CMB polarization or primordial gravity waves, will help to improve the knowledge about inflation is also investigated.
1502.05872
Weak lensing reconstructions in 2D & 3D: implications for cluster studies
Leonard, Lanusse, Starck
Compare the efficiency with which 2D and 3D weak lensing mass mapping techniques are able to detect clusters of galaxies using 2 state-of-the-art mass reconstruction techniques: MRLens in 2D and GLIMPSE in 3D. Simulate otherwise-empty cluster fields for 96 different virial mass-redshift combinations spanning the ranges 3e13 Msun/h<M_vir<1e15 Msun/h and 0.05<z_cl<0.75, and for each generate 1000 realizations of noisy shear data in 2d and 3d. For each field, compute the cluster (false) detection rate as the mean number of cluster (false) detections per reconstruction over the sample of 1000 reconstructions. Show that both MRLens and GLIMPSE are effective tools for the detection of clusters from WL measurements, and provide comparable quality reconstructions at low redshift. At high z, GLIMPSE reconstructions offer increased sensitivity in the detection of clusters, yielding cluster detection rates up to a factor of 10x that seen in 2d reconstructions using MRLens. Conclude that 3d mass mapping techniques are more efficient for the detection of clusters of galaxies in WL surveys than 2d methods, particularly since 3d reconstructions yield unbiased estimators of both the mass and z of the detected clusters directly.
1502.05709
Test for radial mixing of stars in M31
Gould, Rix
Effective radial migration and mixing of orbits throughout the stellar disk has been definitely established in the MW, but not in any other galaxy. Show how such radial mixing can be measured (or strongly constrained) in M31 using a combination of existing data and readily available facilities.
1502.05733
The observational status of cosmic inflation after Planck
Martin
These pedagogical lecture notes are intended to serve as a technical guide filling the gap between the theoretical articles on inflation and the experimental works on astrophysical and cosmological data. After a short discussion of the central tenets at the basis of inflation (negative self-gravitating pressure) and its experimental verifications, it reviews how the most recent CBM anisotropy measurements constrain cosmic inflation. The fact that vanilla inflationary models are, so far, preferred by the observations is discussed and the reason why plateau-like potential versions of inflation are favored within this subclass of scenarios is explained. Finally, how well the future measurements, in particular of B-mode CMB polarization or primordial gravity waves, will help to improve the knowledge about inflation is also investigated.
1502.05872
Weak lensing reconstructions in 2D & 3D: implications for cluster studies
Leonard, Lanusse, Starck
Compare the efficiency with which 2D and 3D weak lensing mass mapping techniques are able to detect clusters of galaxies using 2 state-of-the-art mass reconstruction techniques: MRLens in 2D and GLIMPSE in 3D. Simulate otherwise-empty cluster fields for 96 different virial mass-redshift combinations spanning the ranges 3e13 Msun/h<M_vir<1e15 Msun/h and 0.05<z_cl<0.75, and for each generate 1000 realizations of noisy shear data in 2d and 3d. For each field, compute the cluster (false) detection rate as the mean number of cluster (false) detections per reconstruction over the sample of 1000 reconstructions. Show that both MRLens and GLIMPSE are effective tools for the detection of clusters from WL measurements, and provide comparable quality reconstructions at low redshift. At high z, GLIMPSE reconstructions offer increased sensitivity in the detection of clusters, yielding cluster detection rates up to a factor of 10x that seen in 2d reconstructions using MRLens. Conclude that 3d mass mapping techniques are more efficient for the detection of clusters of galaxies in WL surveys than 2d methods, particularly since 3d reconstructions yield unbiased estimators of both the mass and z of the detected clusters directly.
Friday, February 20, 2015
Day 837
Friday.
1502.05432
The VLT survey telescope ATLAS
Shanks, Metcalfe, ... et al
The VLT Survey Telescope (VST) ATLAS is an optical ugriz survey aiming to cover ~4700 sq deg of the Southern sky to similar depths as SDSS. From reduced images and object catalogues provided by Cambridge Astronomical Surveys Unit (CASU), first find that the median seeing ranges from 0.8" FWHM in i to 1.0" in u, significantly better than the 1.2-1.5" seeing for SDSS. The 5 sigma magnitude limit for stellar sources is r_AB=22.7 and in all bands these limits are at least as faint as SDSS. SDSS and ATLAS are more equivalent for galaxy photometry except in the z band where ATLAS has significantly higher throughput. Improved the original ESO magnitude zero points by comparing m<16 star magnitudes with APASS in gri, also extrapolating into u and z, resulting in zero points accurate to ~pm0.02 mag. Finally compare star and galaxy number counts in a 250 sqdeg area with SDSS and other count data and find good agreement. ATLAS data products can be retrieved from the ESO science archive, while support for survey science analysis is provided by the OmegaCAM Science Archive (OSA), operated by the Wide-Field Astronomy Unit in Edinburgh.
1502.05432
The VLT survey telescope ATLAS
Shanks, Metcalfe, ... et al
The VLT Survey Telescope (VST) ATLAS is an optical ugriz survey aiming to cover ~4700 sq deg of the Southern sky to similar depths as SDSS. From reduced images and object catalogues provided by Cambridge Astronomical Surveys Unit (CASU), first find that the median seeing ranges from 0.8" FWHM in i to 1.0" in u, significantly better than the 1.2-1.5" seeing for SDSS. The 5 sigma magnitude limit for stellar sources is r_AB=22.7 and in all bands these limits are at least as faint as SDSS. SDSS and ATLAS are more equivalent for galaxy photometry except in the z band where ATLAS has significantly higher throughput. Improved the original ESO magnitude zero points by comparing m<16 star magnitudes with APASS in gri, also extrapolating into u and z, resulting in zero points accurate to ~pm0.02 mag. Finally compare star and galaxy number counts in a 250 sqdeg area with SDSS and other count data and find good agreement. ATLAS data products can be retrieved from the ESO science archive, while support for survey science analysis is provided by the OmegaCAM Science Archive (OSA), operated by the Wide-Field Astronomy Unit in Edinburgh.
Thursday, February 19, 2015
Day 836
Wednesday. Thursday.
1502.04710
The influence of wavelength, flux, and lensing selection effects on the redshift distribution of dusty, star-forming galaxies
Béthermin, De Breudk, Sargent, Daddi
Interpret the large variety of z distributions of galaxies found by FIR and (sub-)mm deep surveys depending on their depth and wavelength using a phenomenological model of galaxy evolution. This model reproduces without any new parameter tuning the observed z distributions from 100um to 1.4mm, and especially the increase of the median z with survey wavelength. This median redshift varies also significantly with the depth of the surveys, and deeper surveys do necessarily not probe higher redshifts. Paradoxically, at fixed wavelength and flux limit, the lensed sources are not always at higher z. Found that the higher z of 1.4mm-selected SPT sources compared to other SMG surveys is not only caused by the lensing selection, but also by the longer wavelength. This SPT sample is expected to be dominated by a population of lensed MS galaxies and a minor contribution (~10%) of unlensed extreme starbursts.
1502.04984
Predictions for the abundance and colors of galaxies in high redshift clusters in hierarchical models
Merson, Baugh, Abdalla, et al
High-z galaxy clusters allows examination of galaxy formation in extreme environments. Compile data for z>1 galaxy clusters to test the predictions from one of the latest semi-analytical models of galaxy formation. The model gives a good match to the slope and zero-point of the cluster red sequence. The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but underestimates the number of galaxies around the break in the LF. Find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy LF, but worsened the predictions for the red sequence at bright magnitudes. Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is very large due to these galaxies having large reservoirs of cold gas as well as small radii. Find that matching the LF and colors of high z cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models. Results highlight the need to consider observations beyond the local Universe, as well as for different environments, when calibrating the parameters of galaxy formation models.
1502.05043
Connecting dark matter halos with the galaxy center and the supermassive black hole
Bogdan, Goulding
Correlation between central SMBHs and properties of the host galaxies (i.e., stellar bulge mass or central stellar velocity dispersion) observed; models of BH and bulge co-evolution emerged. Coevolution challenged by observational and theoretical studies, hinted that the fundamental connection may be between BHs and DM halos, and not necessarily their host galaxies. Based on a study of 3130 elliptical galaxies -- selected from SDSS and ROSAT All Sky Surveys -- demonstrate that the central stellar velocity dispersion exhibits a significantly tighter correlation with the total gravitating mass, traced by the X-ray luminosity of the hot gas, than with the stellar mass. This hints that the central stellar velocity dispersion, and hence the central gravitational potential, may be the fundamental property of elliptical galaxies that is most tightly connected to the larger-scale DM halo. Furthermore, using the central stellar velocity dispersion as a surrogate for the BH mass, find that in elliptical galaxies the inferred BH mass and inferred total gravitating mass within the viral radius (or within 5 effective radii) can be expressed as M_BH propto M_tot^1.6 (or M_5r_eff^1.8). These results are consistent with a picture in which the BH mass is directly set by the central stellar velocity dispersion, which, in turn, is determined by the total gravitating mass of the system.
1502.05356
Delousing the CMB with the cosmic infrared background
Sherwin, Schmittfull
Robust delensing of CMB polarization will help with search of B-mode polarization. Investigate in detail the possibility of delensing the CMB with CIB, emission from dusty SF galaxies that is an excellent tracer of the CMB lensing signal, in order to improve constraints on the tensor-to-scalar ratio r. Find that the maps of the CIB, such as current Planck satellite maps at 545 GHz, can be used to remove more than half of the lensing B-mode power. Calculating optimal combinations of different large-scale-structure tracers for delensing, find that co-adding CIB data and external arcminute-resolution CMB lensing reconstruction can lead to significant additional improvements in delensing performance. Investigate whether measurement uncertainty in the CIB spectra will degrade the delensing performance if no model of the CIB spectra is assumed, and instead the CIB spectra are marginalized over, when constraining r. Find that such uncertainty does not significantly affect B-mode surveys smaller than a few thousand degrees. Even for larger surveys, it causes only a moderate reduction in CIB delousing performance, especially if the surveys have high (arcmin) resolution, which allows self-calibration of the delensing procedure. Though further work on the impact of FG residuals is required, the overall conclusions for delensing with current CIB data are optimistic: this delensing method can tighten constraints on r by a factor up to ~2.2, and by a factor up to ~4 when combined with external ~3uK-arcmin lensing reconstruction, without requiring the modeling of CIB properties. CIB delensing is thus a promising method for the upcoming generation of CMB polarization surveys.
1502.04710
The influence of wavelength, flux, and lensing selection effects on the redshift distribution of dusty, star-forming galaxies
Béthermin, De Breudk, Sargent, Daddi
Interpret the large variety of z distributions of galaxies found by FIR and (sub-)mm deep surveys depending on their depth and wavelength using a phenomenological model of galaxy evolution. This model reproduces without any new parameter tuning the observed z distributions from 100um to 1.4mm, and especially the increase of the median z with survey wavelength. This median redshift varies also significantly with the depth of the surveys, and deeper surveys do necessarily not probe higher redshifts. Paradoxically, at fixed wavelength and flux limit, the lensed sources are not always at higher z. Found that the higher z of 1.4mm-selected SPT sources compared to other SMG surveys is not only caused by the lensing selection, but also by the longer wavelength. This SPT sample is expected to be dominated by a population of lensed MS galaxies and a minor contribution (~10%) of unlensed extreme starbursts.
1502.04984
Predictions for the abundance and colors of galaxies in high redshift clusters in hierarchical models
Merson, Baugh, Abdalla, et al
High-z galaxy clusters allows examination of galaxy formation in extreme environments. Compile data for z>1 galaxy clusters to test the predictions from one of the latest semi-analytical models of galaxy formation. The model gives a good match to the slope and zero-point of the cluster red sequence. The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but underestimates the number of galaxies around the break in the LF. Find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy LF, but worsened the predictions for the red sequence at bright magnitudes. Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is very large due to these galaxies having large reservoirs of cold gas as well as small radii. Find that matching the LF and colors of high z cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models. Results highlight the need to consider observations beyond the local Universe, as well as for different environments, when calibrating the parameters of galaxy formation models.
1502.05043
Connecting dark matter halos with the galaxy center and the supermassive black hole
Bogdan, Goulding
Correlation between central SMBHs and properties of the host galaxies (i.e., stellar bulge mass or central stellar velocity dispersion) observed; models of BH and bulge co-evolution emerged. Coevolution challenged by observational and theoretical studies, hinted that the fundamental connection may be between BHs and DM halos, and not necessarily their host galaxies. Based on a study of 3130 elliptical galaxies -- selected from SDSS and ROSAT All Sky Surveys -- demonstrate that the central stellar velocity dispersion exhibits a significantly tighter correlation with the total gravitating mass, traced by the X-ray luminosity of the hot gas, than with the stellar mass. This hints that the central stellar velocity dispersion, and hence the central gravitational potential, may be the fundamental property of elliptical galaxies that is most tightly connected to the larger-scale DM halo. Furthermore, using the central stellar velocity dispersion as a surrogate for the BH mass, find that in elliptical galaxies the inferred BH mass and inferred total gravitating mass within the viral radius (or within 5 effective radii) can be expressed as M_BH propto M_tot^1.6 (or M_5r_eff^1.8). These results are consistent with a picture in which the BH mass is directly set by the central stellar velocity dispersion, which, in turn, is determined by the total gravitating mass of the system.
1502.05356
Delousing the CMB with the cosmic infrared background
Sherwin, Schmittfull
Robust delensing of CMB polarization will help with search of B-mode polarization. Investigate in detail the possibility of delensing the CMB with CIB, emission from dusty SF galaxies that is an excellent tracer of the CMB lensing signal, in order to improve constraints on the tensor-to-scalar ratio r. Find that the maps of the CIB, such as current Planck satellite maps at 545 GHz, can be used to remove more than half of the lensing B-mode power. Calculating optimal combinations of different large-scale-structure tracers for delensing, find that co-adding CIB data and external arcminute-resolution CMB lensing reconstruction can lead to significant additional improvements in delensing performance. Investigate whether measurement uncertainty in the CIB spectra will degrade the delensing performance if no model of the CIB spectra is assumed, and instead the CIB spectra are marginalized over, when constraining r. Find that such uncertainty does not significantly affect B-mode surveys smaller than a few thousand degrees. Even for larger surveys, it causes only a moderate reduction in CIB delousing performance, especially if the surveys have high (arcmin) resolution, which allows self-calibration of the delensing procedure. Though further work on the impact of FG residuals is required, the overall conclusions for delensing with current CIB data are optimistic: this delensing method can tighten constraints on r by a factor up to ~2.2, and by a factor up to ~4 when combined with external ~3uK-arcmin lensing reconstruction, without requiring the modeling of CIB properties. CIB delensing is thus a promising method for the upcoming generation of CMB polarization surveys.
Tuesday, February 17, 2015
Day 835
Tuesday.
1502.04166
The extragalactic background light, the Hubble constant, and anomalies: conclusions from 20 years of TeV gamma-ray observations
Biteau, Williams
Ground-based observatories have been collecting 0.2-20 TeV gamma rays from blazers for about twenty years. These gamma rays can experience absorption along the line of sight due to interactions with the extragalactic background light (EBL). In this paper, investigate the most extensive set of TeV spectra from blazers collected so far, twice as large as any other studied. First show that the gamma-ray optical depth can be reduced to the convolution product of an EBL kernel with the EBL intensity. Extract the EBL intensity from the gamma-ray spectra, show that it is preferred at 11 sigma to a null intensity, and unveil the broad-band spectrum of the EBL from mid-UV to far IR. The measurement shows that the total radiative content of the universe between 0.1 and 1000 microns represents 6.5pm1.2% of the brightness of the CMB. This is slightly above the accumulated emission of stars and galaxies and constrains the unresolved sources that could have recognized the universe. Also propose a data-driven method to estimate the Hubble constant based on the comparison of local and gamma-ray measurements of the EBL, yielding H0=88pm8(stat)pm13(sys) km/s/Mpc. After setting the most stringent upper-limits on the redshift of four TeV blazers, investigate the 106 intrinsic gamma-ray spectra in the sample and find no significant evidence for anomalies. Do not find evidence for the so-called "pair-production anomaly" at large optical depths, which has been used previously to place lower limits on the coupling of TeV gamma rays with axion-like particles. Finally, investigate the impact of a modification of the pair-creation threshold due to a Lorenz invariance violation. A mild excess prevents the ruling out of an effect at the Planck energy; constrain for the first time the energy scale of the modification to values larger than 60% of the Planck energy.
1502.04198
Effective destruction of CO by cosmic rays: implications for tracing H$_2$ gas in the Universe
Bisbas, Papadopoulos, Viti
[CO is a H2 tracer.] Conclude that the CR-induced destruction of CO in molecular clouds, unhindered by dust absorption, is perhaps the single most important factor controlling the CO-vilibility of molecular gas in vigorously SF galaxies. The second-order effect of this CO destruction mechanism will be to make the H2 distribution in the gas-rich disks of such galaxies appear much clumpier in CO J=1-0, 2-1 line emission than it actually is. Give an analytical approximation of the CO/H2 abundance ratio as a function of gas density and CR energy density for use in galaxy-size or cosmo hydro sims, and propose some key observational tests.
1502.04491
Constrained correlation functions from the Millennium Simulation
Wilking, Röseler, Schneider
In previous work, developed a quasi-Gaussian approximation for the likelihood of correlation functions, which, in contrast to the usual Gaussian approach, incorporates fundamental mathematical constraints on correlation functions. The analytical computation of these constraints is only feasible in the case of correlation functions of 1-d random fields. In this work, aim to obtain corresponding constraints in the case of higher-dimensional random fields and test them in a more realistic context. Develop numerical methods to compute the constraints on correlation functions which are also applicable for 2- and 3-d fields. In order to test the accuracy of the numerically obtained constraints, compare them to the analytical results for the 1-d case. Finally, compute correlation functions from the halo catalog of the Millennium Simulation, check whether they obey the constraints, and examine the performance of the transformation used in the construction of the quasi-Gaussian likelihood. Find that the numerical methods of computing the constraints are robust and that the correlation functions measured from the Millennium Simulation obey them. Despite the fact that the measured correlation functions lie well inside the allowed region of parameter space, i.e., far away from the boundaries of the allowed volume defined by the constraints, find strong indications that the quasi-Gaussian likelihood yields a substantial more accurate description than the Gaussian one.
1502.04575
CFHTLenS: a gaussian likelihood is a sufficient approximation for a cosmological analysis of third-order cosmic shear statistics
Simon, Semboloni, van Waerbeke, Hoekstra, Erben, .. et al
Study the correlations of the shear signal between triplets of sources in the CFHTLenS to probe cosmo params via the matter bispectrum. In contrast to previous studies, adopt a non-Gaussian model of the data likelihood which is supported by simulations of the survey. Find that for state-of-the-art surveys, similar to CFHTLenS, a Gaussian likelihood analysis is a reasonable approximation, albeit small differences in the parameter constraints are already visible. For future surveys, expect that a Gaussian model becomes inaccurate. Algorithm for a refined non-Gaussian analysis and data compression is then of great utility especially because it is not much more elaborate if simulated data are available. Applying this algorithm to the third-order correlations of shear alone in a blind analysis, find a good agreement with the standard cosmo model: Sigma_8=sigma8(Omega_m/0.27)^0.64=0.79+0.08-0.11 for a flat LCDM cosmology with h=0.7pm0.04 (68% CL). Nevertheless, models provide only moderately good fits as indicated by chi2/dof=2.9, including a 20 rms uncertainty in the predicted signal amplitude. The models cannot explain a signal drop on scales around 15 arcmin, which may be caused by systematics. It is unclear whether the discrepancy can be fully explained by residual PSF systematics of which evidence is found at least on scales of a few arcmin. Therefore need a better understanding of higher-order correlations of cosmic shear and their systematics to confidently apply them as cosmo probes.
1502.04584
On the definition of superclusters
Chon, Boehringer, Zaroubi
Propose to select superclusters with an overdenesity criterion that selects only those objects that will collapse in the future, including those that are at a turn-around in the present epoch. Present numerical values for these criteria for range os cosmo models. Express these criteria in terms of a density ratio, or as an infall velocity and show that these two criteria give almost identical results. Applied the criteria to some prominent structures in the local universe: the Local supercluster, Shapley supercluster, and Laniakea supercluster. Find that for the Local and Shapley superclusters, only the central regions will collapse in the future, while Laniakea does not constitute a significant over density and will disperse in the future. Finally, suggest that those superclusters that will survive the accelerating cosmic expansion and collapse in the future be called "superstes-clusters", where "superstes" means surviver in Latin, to distinguish them from traditional superclusters.
1502.04166
The extragalactic background light, the Hubble constant, and anomalies: conclusions from 20 years of TeV gamma-ray observations
Biteau, Williams
Ground-based observatories have been collecting 0.2-20 TeV gamma rays from blazers for about twenty years. These gamma rays can experience absorption along the line of sight due to interactions with the extragalactic background light (EBL). In this paper, investigate the most extensive set of TeV spectra from blazers collected so far, twice as large as any other studied. First show that the gamma-ray optical depth can be reduced to the convolution product of an EBL kernel with the EBL intensity. Extract the EBL intensity from the gamma-ray spectra, show that it is preferred at 11 sigma to a null intensity, and unveil the broad-band spectrum of the EBL from mid-UV to far IR. The measurement shows that the total radiative content of the universe between 0.1 and 1000 microns represents 6.5pm1.2% of the brightness of the CMB. This is slightly above the accumulated emission of stars and galaxies and constrains the unresolved sources that could have recognized the universe. Also propose a data-driven method to estimate the Hubble constant based on the comparison of local and gamma-ray measurements of the EBL, yielding H0=88pm8(stat)pm13(sys) km/s/Mpc. After setting the most stringent upper-limits on the redshift of four TeV blazers, investigate the 106 intrinsic gamma-ray spectra in the sample and find no significant evidence for anomalies. Do not find evidence for the so-called "pair-production anomaly" at large optical depths, which has been used previously to place lower limits on the coupling of TeV gamma rays with axion-like particles. Finally, investigate the impact of a modification of the pair-creation threshold due to a Lorenz invariance violation. A mild excess prevents the ruling out of an effect at the Planck energy; constrain for the first time the energy scale of the modification to values larger than 60% of the Planck energy.
1502.04198
Effective destruction of CO by cosmic rays: implications for tracing H$_2$ gas in the Universe
Bisbas, Papadopoulos, Viti
[CO is a H2 tracer.] Conclude that the CR-induced destruction of CO in molecular clouds, unhindered by dust absorption, is perhaps the single most important factor controlling the CO-vilibility of molecular gas in vigorously SF galaxies. The second-order effect of this CO destruction mechanism will be to make the H2 distribution in the gas-rich disks of such galaxies appear much clumpier in CO J=1-0, 2-1 line emission than it actually is. Give an analytical approximation of the CO/H2 abundance ratio as a function of gas density and CR energy density for use in galaxy-size or cosmo hydro sims, and propose some key observational tests.
1502.04491
Constrained correlation functions from the Millennium Simulation
Wilking, Röseler, Schneider
In previous work, developed a quasi-Gaussian approximation for the likelihood of correlation functions, which, in contrast to the usual Gaussian approach, incorporates fundamental mathematical constraints on correlation functions. The analytical computation of these constraints is only feasible in the case of correlation functions of 1-d random fields. In this work, aim to obtain corresponding constraints in the case of higher-dimensional random fields and test them in a more realistic context. Develop numerical methods to compute the constraints on correlation functions which are also applicable for 2- and 3-d fields. In order to test the accuracy of the numerically obtained constraints, compare them to the analytical results for the 1-d case. Finally, compute correlation functions from the halo catalog of the Millennium Simulation, check whether they obey the constraints, and examine the performance of the transformation used in the construction of the quasi-Gaussian likelihood. Find that the numerical methods of computing the constraints are robust and that the correlation functions measured from the Millennium Simulation obey them. Despite the fact that the measured correlation functions lie well inside the allowed region of parameter space, i.e., far away from the boundaries of the allowed volume defined by the constraints, find strong indications that the quasi-Gaussian likelihood yields a substantial more accurate description than the Gaussian one.
1502.04575
CFHTLenS: a gaussian likelihood is a sufficient approximation for a cosmological analysis of third-order cosmic shear statistics
Simon, Semboloni, van Waerbeke, Hoekstra, Erben, .. et al
Study the correlations of the shear signal between triplets of sources in the CFHTLenS to probe cosmo params via the matter bispectrum. In contrast to previous studies, adopt a non-Gaussian model of the data likelihood which is supported by simulations of the survey. Find that for state-of-the-art surveys, similar to CFHTLenS, a Gaussian likelihood analysis is a reasonable approximation, albeit small differences in the parameter constraints are already visible. For future surveys, expect that a Gaussian model becomes inaccurate. Algorithm for a refined non-Gaussian analysis and data compression is then of great utility especially because it is not much more elaborate if simulated data are available. Applying this algorithm to the third-order correlations of shear alone in a blind analysis, find a good agreement with the standard cosmo model: Sigma_8=sigma8(Omega_m/0.27)^0.64=0.79+0.08-0.11 for a flat LCDM cosmology with h=0.7pm0.04 (68% CL). Nevertheless, models provide only moderately good fits as indicated by chi2/dof=2.9, including a 20 rms uncertainty in the predicted signal amplitude. The models cannot explain a signal drop on scales around 15 arcmin, which may be caused by systematics. It is unclear whether the discrepancy can be fully explained by residual PSF systematics of which evidence is found at least on scales of a few arcmin. Therefore need a better understanding of higher-order correlations of cosmic shear and their systematics to confidently apply them as cosmo probes.
1502.04584
On the definition of superclusters
Chon, Boehringer, Zaroubi
Propose to select superclusters with an overdenesity criterion that selects only those objects that will collapse in the future, including those that are at a turn-around in the present epoch. Present numerical values for these criteria for range os cosmo models. Express these criteria in terms of a density ratio, or as an infall velocity and show that these two criteria give almost identical results. Applied the criteria to some prominent structures in the local universe: the Local supercluster, Shapley supercluster, and Laniakea supercluster. Find that for the Local and Shapley superclusters, only the central regions will collapse in the future, while Laniakea does not constitute a significant over density and will disperse in the future. Finally, suggest that those superclusters that will survive the accelerating cosmic expansion and collapse in the future be called "superstes-clusters", where "superstes" means surviver in Latin, to distinguish them from traditional superclusters.
Monday, February 16, 2015
Day 834
Monday.
1502.03820
A clear age-velocity dispersion correlation in Andromeda's stellar disk
Dorman, ... Dalcanton, et al
The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. Measure (for the first time) the stellar age-velocity dispersion correlation in the inner 20 kpc (3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the MW. Use optical Hubble ACS photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and Keck/DEIMOS radial velocity measurements of the same stars from the SPLASH survey. Show that the average line-of-sight velocity dispersion is a steadily increasing function of stellar age exterior to R=10kpc, increasing from 30 km/s for the young upper MS stars to 90 km/s for the old red giant branch stars. This monotonic increase implies that a continuous or recurring process contributed to the evolution of the disk. Both the slope and normalization of the dispersion vs. age relation are significantly larger than in the MW, allowing for the possibility that the disk of M31 has had a more violent history than the disk of the MW, more in line with cosmological predictions. Also find evidence for an inhomogeneous distribution of stars from a second kinematical component in addition to the dominant disk component. One of the largest and hottest high-dispersion patches is present in all age bins, and may be the signature of the end of the long bar.
1502.03821
Evidence for DM in the inner Milky Way
Iocco, Pato, Bertone
The ubiquitous presence of DM in the universe is today a central tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies to the observable universe, the evidence for DM is compelling in dwarfs, spirals, galaxy clusters, as well as at cosmological scales. However, it has been historically difficult to pin down the DM contribution to the total mass density of the MW, particularly in the innermost regions of the Galaxy and in the solar neighborhood. Present an up-to-date compilation of MW rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. Show that current data strongly disfavor baryons as the sole contribution to the galactic mass budget, even inside the solar circle. These findings demonstrate the existence of DM in the inner Galaxy while making no assumptions on its distribution. Anticipate that this result will compel new model-independent constraints on the DM local density and profile, thus reducing uncertainties on direct and indirect DM searches, and will shed new light on the structure and evolution of the Galaxy.
1502.03887
The impact of strong gravitational lensing on observed Lyman-break galaxy numbers at 4<z<8 in the GOODS and the XDF blank fields
Barone-Nugent, ... Treu, Oesch, et al
Detection of LBGs at high-z can be affected by GL induced by FG deflectors not only in galaxy clusters, but also in blank fields. Quantify the impact of strong magnification in the samples of B,V,i,z,&Y LBGs (4<z<8) observed in the XDF and GOODS/CANDELS fields, by investigating the proximity of dropouts to FG objects. Find that ~6% of bright LBGs (m_H160<26) at z~7 have been strongly lensed (mu>2) by FG objects. This fraction decreases from ~3.5% at z~6 to ~1.5% at z~4. Since the observed fraction of strongly lensed galaxies is a function of the shape of the LF, it can be used to derive Schechter parameters, alpha and M*, independently from galaxy number counts. The magnification bias analysis yields Shcechter-function parameters in close agreement with those determined from galaxy counts albeit with larger uncertainties. Extrapolation of the analysis to z>8 suggest that future surveys with JSWT, WFIRST and EUCLID should find excess LBGs at the bright-end, even if there is an intrinsic exponential cutoff of number counts. Finally, highlight how the magnification bias measurement near the detection limit can be used as probe of the population of galaxies too faint to be detected. Preliminary results using this novel idea suggest that the magnification bias at M_UV~-18 is not as strong as expected if alpha<-1.7 extends well below the current detection limits in the XDF. At face value this implies a flattening of the LF at M_UV-16.5. However, selection effects and completeness estimates are difficult to quantify precisely. Thus, no ruling out a steep LF extending to M_UV>-15.
1502.03972
Combining spectroscopic and photometric surveys using angular cross-correlations II: parameter constraints from different physical effects
Eriksen, Gaztanaga
In the previous paper, studied the effects of RSD, BAO and WL using angular cross-correlation. Provide a new forecast that explores the contribution in including different observables, physical effects (galaxy bias, WL, RSD, BAO) and approximations (non-linearities, Limber approximation, covariance between probes). The radial information is included by using the cross-correlation of separate narrow redshift bins. For the auto correlation the separation of galaxy pairs is mostly transverse, while the cross-correlations also includes a radial component. Study how this information adds to the FoM, which includes the DE EoS w(z) and the growth history, parameterized by gamma. Show that the Limber approximation and galaxy bias are the most critical ingredients to the modelling of correlations. Adding WL increases the FoM by 4.8, RSD by 2.1 and BAO by 1.3. Also explore how overlapping surveys perform under the different assumption and for different FoM. Qualitative conclusions depend on the survey choices and scales included, but find some clear tendencies that highlight the importance of combining different probes and can be used to guid and optimism survey strategies.
1502.03994
Cnostraints on a scale-depedent bias from galaxy clustering
Amendola, ... Branchini
Forecast the future constraints on scale-dependent parameterizations of galaxy bias and their impact on the estimate of cosmo params from the PS of galaxies measured in a spectroscopic redshift survey. For the latter, assume a wide survey at relatively large z, similar to the planned Euclid survey, as baseline for future experiments. To assess the impact of the bias, perform a Fisher matrix analysis and adopt two different parameterizations of scale-dependent bias. The fiducial model for galaxy bias are calibrated using a mock catalogs of Ha emitting galaxies mimicking the expected properties of the objects that will be targeted by the Euclid survey. In the analysis, obtained 2 main results: (1) allowing for a scale-dependent bias does not significantly increase the errors on the other cosmo params apart from the RMS amplitude of density fluctuations, sigma_8 and the growth index gamma, whose uncertainties increase by a factor up to two, depending on the bias model adopted. (2) find that the accuracy in the linear bias parameter b_0 can be estimated to within 1-2% at various z regardless of the fiducial model. The NL bias parameters have significantly large errors that depend on the model adopted. Despite this, in the more realistic scenarios departs from the simple linear bias prescription can be detected with a ~2 sigma significance at each z explored.
1502.03820
A clear age-velocity dispersion correlation in Andromeda's stellar disk
Dorman, ... Dalcanton, et al
The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. Measure (for the first time) the stellar age-velocity dispersion correlation in the inner 20 kpc (3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the MW. Use optical Hubble ACS photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and Keck/DEIMOS radial velocity measurements of the same stars from the SPLASH survey. Show that the average line-of-sight velocity dispersion is a steadily increasing function of stellar age exterior to R=10kpc, increasing from 30 km/s for the young upper MS stars to 90 km/s for the old red giant branch stars. This monotonic increase implies that a continuous or recurring process contributed to the evolution of the disk. Both the slope and normalization of the dispersion vs. age relation are significantly larger than in the MW, allowing for the possibility that the disk of M31 has had a more violent history than the disk of the MW, more in line with cosmological predictions. Also find evidence for an inhomogeneous distribution of stars from a second kinematical component in addition to the dominant disk component. One of the largest and hottest high-dispersion patches is present in all age bins, and may be the signature of the end of the long bar.
1502.03821
Evidence for DM in the inner Milky Way
Iocco, Pato, Bertone
The ubiquitous presence of DM in the universe is today a central tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies to the observable universe, the evidence for DM is compelling in dwarfs, spirals, galaxy clusters, as well as at cosmological scales. However, it has been historically difficult to pin down the DM contribution to the total mass density of the MW, particularly in the innermost regions of the Galaxy and in the solar neighborhood. Present an up-to-date compilation of MW rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. Show that current data strongly disfavor baryons as the sole contribution to the galactic mass budget, even inside the solar circle. These findings demonstrate the existence of DM in the inner Galaxy while making no assumptions on its distribution. Anticipate that this result will compel new model-independent constraints on the DM local density and profile, thus reducing uncertainties on direct and indirect DM searches, and will shed new light on the structure and evolution of the Galaxy.
1502.03887
The impact of strong gravitational lensing on observed Lyman-break galaxy numbers at 4<z<8 in the GOODS and the XDF blank fields
Barone-Nugent, ... Treu, Oesch, et al
Detection of LBGs at high-z can be affected by GL induced by FG deflectors not only in galaxy clusters, but also in blank fields. Quantify the impact of strong magnification in the samples of B,V,i,z,&Y LBGs (4<z<8) observed in the XDF and GOODS/CANDELS fields, by investigating the proximity of dropouts to FG objects. Find that ~6% of bright LBGs (m_H160<26) at z~7 have been strongly lensed (mu>2) by FG objects. This fraction decreases from ~3.5% at z~6 to ~1.5% at z~4. Since the observed fraction of strongly lensed galaxies is a function of the shape of the LF, it can be used to derive Schechter parameters, alpha and M*, independently from galaxy number counts. The magnification bias analysis yields Shcechter-function parameters in close agreement with those determined from galaxy counts albeit with larger uncertainties. Extrapolation of the analysis to z>8 suggest that future surveys with JSWT, WFIRST and EUCLID should find excess LBGs at the bright-end, even if there is an intrinsic exponential cutoff of number counts. Finally, highlight how the magnification bias measurement near the detection limit can be used as probe of the population of galaxies too faint to be detected. Preliminary results using this novel idea suggest that the magnification bias at M_UV~-18 is not as strong as expected if alpha<-1.7 extends well below the current detection limits in the XDF. At face value this implies a flattening of the LF at M_UV-16.5. However, selection effects and completeness estimates are difficult to quantify precisely. Thus, no ruling out a steep LF extending to M_UV>-15.
1502.03972
Combining spectroscopic and photometric surveys using angular cross-correlations II: parameter constraints from different physical effects
Eriksen, Gaztanaga
In the previous paper, studied the effects of RSD, BAO and WL using angular cross-correlation. Provide a new forecast that explores the contribution in including different observables, physical effects (galaxy bias, WL, RSD, BAO) and approximations (non-linearities, Limber approximation, covariance between probes). The radial information is included by using the cross-correlation of separate narrow redshift bins. For the auto correlation the separation of galaxy pairs is mostly transverse, while the cross-correlations also includes a radial component. Study how this information adds to the FoM, which includes the DE EoS w(z) and the growth history, parameterized by gamma. Show that the Limber approximation and galaxy bias are the most critical ingredients to the modelling of correlations. Adding WL increases the FoM by 4.8, RSD by 2.1 and BAO by 1.3. Also explore how overlapping surveys perform under the different assumption and for different FoM. Qualitative conclusions depend on the survey choices and scales included, but find some clear tendencies that highlight the importance of combining different probes and can be used to guid and optimism survey strategies.
1502.03994
Cnostraints on a scale-depedent bias from galaxy clustering
Amendola, ... Branchini
Forecast the future constraints on scale-dependent parameterizations of galaxy bias and their impact on the estimate of cosmo params from the PS of galaxies measured in a spectroscopic redshift survey. For the latter, assume a wide survey at relatively large z, similar to the planned Euclid survey, as baseline for future experiments. To assess the impact of the bias, perform a Fisher matrix analysis and adopt two different parameterizations of scale-dependent bias. The fiducial model for galaxy bias are calibrated using a mock catalogs of Ha emitting galaxies mimicking the expected properties of the objects that will be targeted by the Euclid survey. In the analysis, obtained 2 main results: (1) allowing for a scale-dependent bias does not significantly increase the errors on the other cosmo params apart from the RMS amplitude of density fluctuations, sigma_8 and the growth index gamma, whose uncertainties increase by a factor up to two, depending on the bias model adopted. (2) find that the accuracy in the linear bias parameter b_0 can be estimated to within 1-2% at various z regardless of the fiducial model. The NL bias parameters have significantly large errors that depend on the model adopted. Despite this, in the more realistic scenarios departs from the simple linear bias prescription can be detected with a ~2 sigma significance at each z explored.
Friday, February 13, 2015
Day 833
Friday.
1502.03442
Disentangling dark sector models using weak lensing statistics
Giocoli, Metcalf, .. Meneghetti, ... et al
Perofrm multi-plen ray-tracing using GLAMER GL code within high-res light-cones extracted from CoDECS sims: a suite of cosmo runs featuring a coupling between DE and CDM. Show that the presence of the coupling is evident not only in the z evolution of the normalization of the convergence PS, but also in differences in NL structure formation wrt LCDM. Using a tomographic approach under the assumption of LCDM cosmology, demonstrate that WL measurements would result in a sigma8 value that changes with the source z if the true underlying cosmology is a coupled DE one. This provides a generic null test for these types of models. Also find that different models of coupled DE can show either an enhanced or a suppressed correlation between convergence maps with differing source z as compared to LCDM. This would provide a direct way to discriminate between different possible realisations of the coupled DE scenario. Finally, discuss the impact of the coupling on several lensing observables for different source z and angular scales with realistic source z distributions for current ground-based and future space-based lensing surveys.
1502.03545
Catalog of visually classified galaxies in the local ($z\sim0.01$) universe
Ann, Seo, Ha
The morphological types of 5840 galaxies were classified by visual inspection of color images using SDSS DR7 to produce a morphology catalog of a representative sample of local galaxies with z<0.01. The sample galaxies are almost complete for galaxies brighter than r_pet=17.77. The classification system is basically the same as that of the Third Reference Catalog of Bright Galaxies with some simplification for giant galaxies. On the other hand, fine features of dwarf elliptical-like galaxies are distinguished to classify 5 sub-types: dwarf ellipticals (dE), blue-cored dwarf ellipticals (dE_bc), dwarf spheroidals (dSph), blue dwarf elliptical (dE_blue), and dwarf lenticulars (dS0). In addition, denote the presence of nucleation in dE, dSph, and dS0. Elliptical galaxies and lenticular galaxies contribute only ~1.5% and 4.9% of the local galaxies, respectively, whereas spirals and irregulars contribute ~32.1% and ~42.8%, respectively. The dE_blue galaxies, which are recently found populations of galaxies, contribute a significant fraction to the dwarf galaxies. There seems to be structural difference between dSph and dE galaxies. The dSph galaxies are fainter and bluer with shallower surface brightness garden than dE galaxies. They also have lower fraction of galaxies with small axis ratios (b/a<~0.4) than dE galaxies. The mean projected distances to the nearest neighbor galaxy is ~260kpc. About 1% of local galaxies have no neighbors with comparable luminosity within a projected distance of 2Mpc.
1502.03795
Correcting the z~8 galaxy luminosity function for gravitational lensing magnification bias
Mason, Treu, ... Marshall, et al
Present a Bayesian framework to account for the magnification bias from both SL and WL in estimates of high-z galaxy LFs. Illustrate the method by estimating the z~8 UV LF using a sample of 97 Y-band dropouts (Lyman-break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the literature. Find the LF is well described by a Schechter function with characteristic magnitude of M*=-19.8, faint-end slope of alpha=-1.7, and number density of log10 Psi*[Mpc^-3] = -3.0. These parameters are consistent within the uncertainties with those inferred from the same sample without accounting for the magnification bias demonstrating that the effect is small for current surveys at z~8, and cannot account for the apparent over density of bright galaxies found recently. Estimate that the probability of finding a strongly lensed z~8 source in the sample is in the range ~3-15% depending on limiting magnitude. Identify one strongly-lensed candidate and 3 cases of intermediate lensing in BoRG (estimated magnification mu>1.4) in addition to the previously known candidate group-scale strong lens. Using a range of theoretical LFs, conclude that magnification bias will dominate wide field surveys (e.g., Euclid and WFIRST), especially at z>10. Magnification bias will need to be accounted for in order to derive accurate estimates of high-z LFs in these surveys and to distinguish between galaxy formation models.
1502.03442
Disentangling dark sector models using weak lensing statistics
Giocoli, Metcalf, .. Meneghetti, ... et al
Perofrm multi-plen ray-tracing using GLAMER GL code within high-res light-cones extracted from CoDECS sims: a suite of cosmo runs featuring a coupling between DE and CDM. Show that the presence of the coupling is evident not only in the z evolution of the normalization of the convergence PS, but also in differences in NL structure formation wrt LCDM. Using a tomographic approach under the assumption of LCDM cosmology, demonstrate that WL measurements would result in a sigma8 value that changes with the source z if the true underlying cosmology is a coupled DE one. This provides a generic null test for these types of models. Also find that different models of coupled DE can show either an enhanced or a suppressed correlation between convergence maps with differing source z as compared to LCDM. This would provide a direct way to discriminate between different possible realisations of the coupled DE scenario. Finally, discuss the impact of the coupling on several lensing observables for different source z and angular scales with realistic source z distributions for current ground-based and future space-based lensing surveys.
1502.03545
Catalog of visually classified galaxies in the local ($z\sim0.01$) universe
Ann, Seo, Ha
The morphological types of 5840 galaxies were classified by visual inspection of color images using SDSS DR7 to produce a morphology catalog of a representative sample of local galaxies with z<0.01. The sample galaxies are almost complete for galaxies brighter than r_pet=17.77. The classification system is basically the same as that of the Third Reference Catalog of Bright Galaxies with some simplification for giant galaxies. On the other hand, fine features of dwarf elliptical-like galaxies are distinguished to classify 5 sub-types: dwarf ellipticals (dE), blue-cored dwarf ellipticals (dE_bc), dwarf spheroidals (dSph), blue dwarf elliptical (dE_blue), and dwarf lenticulars (dS0). In addition, denote the presence of nucleation in dE, dSph, and dS0. Elliptical galaxies and lenticular galaxies contribute only ~1.5% and 4.9% of the local galaxies, respectively, whereas spirals and irregulars contribute ~32.1% and ~42.8%, respectively. The dE_blue galaxies, which are recently found populations of galaxies, contribute a significant fraction to the dwarf galaxies. There seems to be structural difference between dSph and dE galaxies. The dSph galaxies are fainter and bluer with shallower surface brightness garden than dE galaxies. They also have lower fraction of galaxies with small axis ratios (b/a<~0.4) than dE galaxies. The mean projected distances to the nearest neighbor galaxy is ~260kpc. About 1% of local galaxies have no neighbors with comparable luminosity within a projected distance of 2Mpc.
1502.03795
Correcting the z~8 galaxy luminosity function for gravitational lensing magnification bias
Mason, Treu, ... Marshall, et al
Present a Bayesian framework to account for the magnification bias from both SL and WL in estimates of high-z galaxy LFs. Illustrate the method by estimating the z~8 UV LF using a sample of 97 Y-band dropouts (Lyman-break galaxies) found in the Brightest of Reionizing Galaxies (BoRG) survey and from the literature. Find the LF is well described by a Schechter function with characteristic magnitude of M*=-19.8, faint-end slope of alpha=-1.7, and number density of log10 Psi*[Mpc^-3] = -3.0. These parameters are consistent within the uncertainties with those inferred from the same sample without accounting for the magnification bias demonstrating that the effect is small for current surveys at z~8, and cannot account for the apparent over density of bright galaxies found recently. Estimate that the probability of finding a strongly lensed z~8 source in the sample is in the range ~3-15% depending on limiting magnitude. Identify one strongly-lensed candidate and 3 cases of intermediate lensing in BoRG (estimated magnification mu>1.4) in addition to the previously known candidate group-scale strong lens. Using a range of theoretical LFs, conclude that magnification bias will dominate wide field surveys (e.g., Euclid and WFIRST), especially at z>10. Magnification bias will need to be accounted for in order to derive accurate estimates of high-z LFs in these surveys and to distinguish between galaxy formation models.
Thursday, February 12, 2015
Day 832
Thursday, Karneval started.
1502.03099
Cosmology with anisotropic galaxy clustering from the combination of power spectrum and bispectrum
Song, Taruya, Oka
The apparent anisotropies of the galaxy clustering in observable z-space provide a unique opportunity to simultaneously probe cosmic expansion and gravity on cosmological scales via the Alcock-Paczynski effect and z-space distortions. While the improved theoretical models have been proposed and developed to describe the apparent anisotropic clustering at weakly NL scales, the applicability of these models is still limited in the presence of the non-perturbative smearing effect caused by the randomness of the relative velocities. Although the cosmological constraint from the anisotropic clustering will be certainly improved with a more elaborate theoretical model, consider an alternative way by using the statistical power of both the power spectrum and bispectrum at large scales. Based on the Fisher matrix analysis, estimate the benefit of combining the power spectra and bispectra, finding that the constraints on the cosmic expansion and growth of structure will be improved by a a factor of two. This compensates for the loss of constraining power using the PS alone due to the randomness of the relative velocities.
1502.03107
Detecting the integrated Sachs-Wolfe effect with high-redshift 21-cm surveys
Raccanelli, Kovetz, Dai, Kamionkowski
Investigate the possibility to detect ISW by cross-correlating 21-cm surveys at high z with galaxies, in a way similar to the CMB-galaxy X-correlation. The high-z 21-cm signal is dominated by CMB photons that travel freely without interacting with the intervening matter, and hence its late-time ISW signature should correlate extremely well with that of the CMB at its peak frequencies. Using the 21-cm temperature brightness instead of the CMB would thus be a further check on the detection of the ISW effect, measured by different instruments at different frequencies and suffering from different systematics. Also study the ISW effect on the photons that are scattered by HI clouds. Show that a detection of the unscathed photons is achievable with planned radio arrays, while one using scattered photons will require advanced radio interferometer, either an extended version of the planned Square Kilometer Array or futuristic experiments such as a lunar radio array.
1502.03141
Distortion of the luminosity function of high-redshift galaxies by gravitation lensing
Fialkov, Loeb
The observed properties of high-z galaxies depend on the underlying FG distribution of LSS, which distorts their intrinsic properties via GL. Focus on the regime where the dominant contribution originates from a single lens and examine the statistics of GL by a population of virtualized and non-vilrialized structures using sub-mm galaxies at z~2.6 and Lyman-break galaxies at z~6-15 as the BG sources. Quantify the effect of lensing on the LF of the high-z sources, focusing on the intermediate and small magnifications (mu<3) which affect the majority of the background galaxies. Show that depending on the intrinsic properties of the FG galaxies, GL can significantly affect the observed LF even when no obvious SLs are present. Find that in the case of the Lyman-break galaxies, it is important to account for the surface brightness profiles of both the FG and BG galaxies when computing the lensing statistics, which introduces a selection criterion for the BG galaxies that can actually be observed. Not taking this criterion into account leads to an overestimation of the number densities of very bright galaxies by nearly 2 orders of magnitude.
1502.03405
Cross-correlation of CFHTLenS galaxy number density and Planck CMB lensing
Omori, Holder
Measure the X-PS between galaxy density from CFHTLenS catalogues and gravitational lensing convergence from Planck DR1 (2013) and DR2 (2015). Investigate 3 main galaxy samples: 18.0<i_AB<22.0, 18.0<i_AB<23.0, 18.0<i_AB<24.0, in 0.2<z<1.3 in each of the 4 CFHTLenS wide fields. By comparing the measured X-spectrum with model predictions, linear galaxy-DM basis of b=0.82, 0.83, 0.82 are inferred at significances of 3.5, 4.5, 5.6 sigma using the Planck 2015 release. These measurements are marginally consistent with biases derived from g-g auto-correlations: b=1.15, 1.08, and 0.96 respectively. Using the 2013 Planck release, obtain biases of b=1.33, 1.19, 1.16, showing significant differences between the releases.
1502.03429
Internal alignments of red versus blue disks in dark matter halos
Debattista, van den Bosch, Roskar, Quinn, Moore, Cole
Large surveys have shown that red galaxies are preferentially aligned with their haloes while blue galaxies have a more isotropic distribution. Since haloes generally align with their filaments, this introduces a bias in the measurement of the cosmic shear from WL. It is therefore vitally important to understand why this difference arises. Explore the stability of different disc orientations within triaxial haloes. Show that, in the absence of gas, the disc orientation is most stable when its spin is along the minor axis of the halo. Instead when gas cools onto a disc, it is able to form in almost arbitrary orientation, including off the main planes of the halo (but avoiding an orientation perpendicular to the halo's intermediate axis). Substructure helps gases galaxies reach alignment with the halo faster, but have less effect on galaxies when gas is cooling onto the disc. Results provide a novel and natural interpretation for why red, gas poor galaxies are preferentially aligned with their halo, while blue, SF, galaxies have nearly random orientations, without requiring a connection between galaxies' current SFR and their merger history.
1502.03099
Cosmology with anisotropic galaxy clustering from the combination of power spectrum and bispectrum
Song, Taruya, Oka
The apparent anisotropies of the galaxy clustering in observable z-space provide a unique opportunity to simultaneously probe cosmic expansion and gravity on cosmological scales via the Alcock-Paczynski effect and z-space distortions. While the improved theoretical models have been proposed and developed to describe the apparent anisotropic clustering at weakly NL scales, the applicability of these models is still limited in the presence of the non-perturbative smearing effect caused by the randomness of the relative velocities. Although the cosmological constraint from the anisotropic clustering will be certainly improved with a more elaborate theoretical model, consider an alternative way by using the statistical power of both the power spectrum and bispectrum at large scales. Based on the Fisher matrix analysis, estimate the benefit of combining the power spectra and bispectra, finding that the constraints on the cosmic expansion and growth of structure will be improved by a a factor of two. This compensates for the loss of constraining power using the PS alone due to the randomness of the relative velocities.
1502.03107
Detecting the integrated Sachs-Wolfe effect with high-redshift 21-cm surveys
Raccanelli, Kovetz, Dai, Kamionkowski
Investigate the possibility to detect ISW by cross-correlating 21-cm surveys at high z with galaxies, in a way similar to the CMB-galaxy X-correlation. The high-z 21-cm signal is dominated by CMB photons that travel freely without interacting with the intervening matter, and hence its late-time ISW signature should correlate extremely well with that of the CMB at its peak frequencies. Using the 21-cm temperature brightness instead of the CMB would thus be a further check on the detection of the ISW effect, measured by different instruments at different frequencies and suffering from different systematics. Also study the ISW effect on the photons that are scattered by HI clouds. Show that a detection of the unscathed photons is achievable with planned radio arrays, while one using scattered photons will require advanced radio interferometer, either an extended version of the planned Square Kilometer Array or futuristic experiments such as a lunar radio array.
1502.03141
Distortion of the luminosity function of high-redshift galaxies by gravitation lensing
Fialkov, Loeb
The observed properties of high-z galaxies depend on the underlying FG distribution of LSS, which distorts their intrinsic properties via GL. Focus on the regime where the dominant contribution originates from a single lens and examine the statistics of GL by a population of virtualized and non-vilrialized structures using sub-mm galaxies at z~2.6 and Lyman-break galaxies at z~6-15 as the BG sources. Quantify the effect of lensing on the LF of the high-z sources, focusing on the intermediate and small magnifications (mu<3) which affect the majority of the background galaxies. Show that depending on the intrinsic properties of the FG galaxies, GL can significantly affect the observed LF even when no obvious SLs are present. Find that in the case of the Lyman-break galaxies, it is important to account for the surface brightness profiles of both the FG and BG galaxies when computing the lensing statistics, which introduces a selection criterion for the BG galaxies that can actually be observed. Not taking this criterion into account leads to an overestimation of the number densities of very bright galaxies by nearly 2 orders of magnitude.
1502.03405
Cross-correlation of CFHTLenS galaxy number density and Planck CMB lensing
Omori, Holder
Measure the X-PS between galaxy density from CFHTLenS catalogues and gravitational lensing convergence from Planck DR1 (2013) and DR2 (2015). Investigate 3 main galaxy samples: 18.0<i_AB<22.0, 18.0<i_AB<23.0, 18.0<i_AB<24.0, in 0.2<z<1.3 in each of the 4 CFHTLenS wide fields. By comparing the measured X-spectrum with model predictions, linear galaxy-DM basis of b=0.82, 0.83, 0.82 are inferred at significances of 3.5, 4.5, 5.6 sigma using the Planck 2015 release. These measurements are marginally consistent with biases derived from g-g auto-correlations: b=1.15, 1.08, and 0.96 respectively. Using the 2013 Planck release, obtain biases of b=1.33, 1.19, 1.16, showing significant differences between the releases.
1502.03429
Internal alignments of red versus blue disks in dark matter halos
Debattista, van den Bosch, Roskar, Quinn, Moore, Cole
Large surveys have shown that red galaxies are preferentially aligned with their haloes while blue galaxies have a more isotropic distribution. Since haloes generally align with their filaments, this introduces a bias in the measurement of the cosmic shear from WL. It is therefore vitally important to understand why this difference arises. Explore the stability of different disc orientations within triaxial haloes. Show that, in the absence of gas, the disc orientation is most stable when its spin is along the minor axis of the halo. Instead when gas cools onto a disc, it is able to form in almost arbitrary orientation, including off the main planes of the halo (but avoiding an orientation perpendicular to the halo's intermediate axis). Substructure helps gases galaxies reach alignment with the halo faster, but have less effect on galaxies when gas is cooling onto the disc. Results provide a novel and natural interpretation for why red, gas poor galaxies are preferentially aligned with their halo, while blue, SF, galaxies have nearly random orientations, without requiring a connection between galaxies' current SFR and their merger history.
Wednesday, February 11, 2015
Day 831
Wednesday.
1502.02661
The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kalpha line emission in Type 1 AGN
Gandhi, Hoenig, Kishimoto
The Fe Kalpha emission lines is the most ubiquitous feature in the X-ray spectra of AGN, but the origin of its narrow core remains uncertain. Investigate the connection between the sizes of the Fe Kalpha core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGN. The observed Fe Kalpha emission radii (R_fe) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (R_dust) are measured either from optical/NIR reverberation time lags or from resolved NIR interferometric data. This direct comparison shows that the dust sublimation raids forms an outer envelope to the bulk of the Fe Kalpha emission. R_fe matches R_dust well in the AGN with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, R_fe is similar to, or smaller than the radius of the optical broad line region. These facts place important constraints on the torus geometries for the sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. Also test for luminosity scalings of R_fe, finding that Eddington ratio is not a prime driver in determining the line location in the sample. Large uncertainties on the line core widths preclude more detailed investigations at present, a limitation which Astro-H will help to overcome.
1502.02681
On the cosmic evolution of the specific star formation rate
Lehnert et al
The apparent correlation between the sSFR and the total stellar mass M* of galaxies is a fundamental relationship indicating how they formed their stellar populations. To attempt to understand this relation, hypothesize that the relation and its evolution is regulated by the increase in the stellar and gas mass surface density in galaxies with redshift, which is itself governed by the angular momentum of the accreted gas, the amount of available gas, and by self-regulation of star formation. This model can reproduce the sSFR-M* relations at z~1-2 by assuming gas fractions and gas mass surface densities similar to those observed for z=1-2 galaxies. Further argue that it is the increasing angular momentum with cosmic time that causes a decrease in the surface density of accreted gas. The gas mass surface densities in galaxies are controlled by the centrifugal support (i.e., angular momentum), and the sSFR is predicted to increase as, sSFR(z)=(1+z)^3/t_H0, as observed (where t_H0 is the Hubble time and no free parameters are necessary) . At z>~2, argue that SF is self-regulated by high pressures generated by the intense SF itself. The SF intensity must be high enough to either balance the hydrostatic pressure (a rather extreme assumption) or to generate high turbulent pressure in the molecular medium which maintains galaxies near the line of instability (i.e., Toomre Q~1). The most important factor is the increase in stellar and gas mass surface density with redshift, which allows distant galaxies to maintain high levels of sSFR. Without a strong feedback from massive stars, such galaxies would likely reach very high sSFR levels, have high SF efficiencies, and because strong feedback drives outflows, ultimately have an excess of stellar baryons.
1502.02867
The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field
Coupon, et al
Present new constraints on the relationship between galaxies and their host DM haloes, measured from the location of the peak of the stellar-to-halo mass ratio (SMHR), up to the most massive galaxy clusters at z~0.8 and over a volume of nearly 0.1 Gpc^3. Use a unique combination of deep observations in the CFHTLenS/VIPERS field from the near-UV to the near-IR, supplemented by ~60k secure spec-z, analyzing galaxy clustering, gg lensing and the stellar MF. Interpret measurements within the HOD framework, separating the contributions from central and satellite galaxies. Find that the SHMR for the central galaxies peaks at M_h,peak = 1.9e12 Msun with an amplitude of 0.025, which decreases to ~0.001 for massive haloes (M_h>1e14 Msun). Compared to central galaxies only the total SHMR (including satellites) is boosted by a factor 10 in the high-mass regime (cluster-size halos), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modeling, compare results with a large number of results from the literature up to z=1: find good general agreement, independently of the method used, within the typical stellar-mass systematic errors at low to intermediate mass (M*<1e11 Msun) and the statistical errors above. Have also compared SHMR results to semi-analytic simulations and found that the SHMR is tilted compared to measurements in such a way that they over-(under-) predict SF efficiency in central (satellite) galaxies.
1502.02661
The dust sublimation radius as an outer envelope to the bulk of the narrow Fe Kalpha line emission in Type 1 AGN
Gandhi, Hoenig, Kishimoto
The Fe Kalpha emission lines is the most ubiquitous feature in the X-ray spectra of AGN, but the origin of its narrow core remains uncertain. Investigate the connection between the sizes of the Fe Kalpha core emission regions and the measured sizes of the dusty tori in 13 local Type 1 AGN. The observed Fe Kalpha emission radii (R_fe) are determined from spectrally resolved line widths in X-ray grating spectra, and the dust sublimation radii (R_dust) are measured either from optical/NIR reverberation time lags or from resolved NIR interferometric data. This direct comparison shows that the dust sublimation raids forms an outer envelope to the bulk of the Fe Kalpha emission. R_fe matches R_dust well in the AGN with the best constrained line widths currently. In a significant fraction of objects without a clear narrow line core, R_fe is similar to, or smaller than the radius of the optical broad line region. These facts place important constraints on the torus geometries for the sample. Extended tori in which the solid angle of fluorescing gas peaks at well beyond the dust sublimation radius can be ruled out. Also test for luminosity scalings of R_fe, finding that Eddington ratio is not a prime driver in determining the line location in the sample. Large uncertainties on the line core widths preclude more detailed investigations at present, a limitation which Astro-H will help to overcome.
1502.02681
On the cosmic evolution of the specific star formation rate
Lehnert et al
The apparent correlation between the sSFR and the total stellar mass M* of galaxies is a fundamental relationship indicating how they formed their stellar populations. To attempt to understand this relation, hypothesize that the relation and its evolution is regulated by the increase in the stellar and gas mass surface density in galaxies with redshift, which is itself governed by the angular momentum of the accreted gas, the amount of available gas, and by self-regulation of star formation. This model can reproduce the sSFR-M* relations at z~1-2 by assuming gas fractions and gas mass surface densities similar to those observed for z=1-2 galaxies. Further argue that it is the increasing angular momentum with cosmic time that causes a decrease in the surface density of accreted gas. The gas mass surface densities in galaxies are controlled by the centrifugal support (i.e., angular momentum), and the sSFR is predicted to increase as, sSFR(z)=(1+z)^3/t_H0, as observed (where t_H0 is the Hubble time and no free parameters are necessary) . At z>~2, argue that SF is self-regulated by high pressures generated by the intense SF itself. The SF intensity must be high enough to either balance the hydrostatic pressure (a rather extreme assumption) or to generate high turbulent pressure in the molecular medium which maintains galaxies near the line of instability (i.e., Toomre Q~1). The most important factor is the increase in stellar and gas mass surface density with redshift, which allows distant galaxies to maintain high levels of sSFR. Without a strong feedback from massive stars, such galaxies would likely reach very high sSFR levels, have high SF efficiencies, and because strong feedback drives outflows, ultimately have an excess of stellar baryons.
1502.02867
The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field
Coupon, et al
Present new constraints on the relationship between galaxies and their host DM haloes, measured from the location of the peak of the stellar-to-halo mass ratio (SMHR), up to the most massive galaxy clusters at z~0.8 and over a volume of nearly 0.1 Gpc^3. Use a unique combination of deep observations in the CFHTLenS/VIPERS field from the near-UV to the near-IR, supplemented by ~60k secure spec-z, analyzing galaxy clustering, gg lensing and the stellar MF. Interpret measurements within the HOD framework, separating the contributions from central and satellite galaxies. Find that the SHMR for the central galaxies peaks at M_h,peak = 1.9e12 Msun with an amplitude of 0.025, which decreases to ~0.001 for massive haloes (M_h>1e14 Msun). Compared to central galaxies only the total SHMR (including satellites) is boosted by a factor 10 in the high-mass regime (cluster-size halos), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modeling, compare results with a large number of results from the literature up to z=1: find good general agreement, independently of the method used, within the typical stellar-mass systematic errors at low to intermediate mass (M*<1e11 Msun) and the statistical errors above. Have also compared SHMR results to semi-analytic simulations and found that the SHMR is tilted compared to measurements in such a way that they over-(under-) predict SF efficiency in central (satellite) galaxies.
Tuesday, February 10, 2015
Day 830
Tuesday.
Nature Letters
Evidence for dark matter in the inner Milky Way
Iocco, Pato, Bertone
The ubiquitous presence of dark matter in the Universe is today a central tenet in modern cosmology and astrophysics. Throughout the universe, the evidence for DM is compelling in dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales. However, it has been historically difficult to pin down the DM contribution to the total mass density in the MW, particularly in the innermost regions of the Galaxy and in the solar neighborhood. Present an up-to-date compilation of MW rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. Show that current data strongly disfavor baryons as the sole contribution to the Galactic mass budge, even inside the solar circle. Findings demonstrate the existence of DM in the inner Galaxy without making any assumptions about it distribution. Anticipate that this result will compel new model-independent constraints on the DM local density and profile, thus reduction uncertainties on direct and indirect DM searches, and will help reveal the structure and evolution of the Galaxy.
1502.02046
The alignment of satellite galaxies and cosmic filaments: observations and simulations
Tempel, Guo, Kipper, Libeskind
The accretion of satellite onto central galaxies along vast cosmic filaments is an apparent outcome of the anisotropic collapse of structure in the Universe. Numerical work (based on N-body sims) indicates that satellites are beamed towards hosts along preferred directions imprinted by the velocity shear field. Use the SDSS to observationally test this claim. Construct 3D filaments and sheets and examine the relative position of satellites galaxies. A statistical significant alignment between satellite galaxy position and filament axis is confirmed. Find a similar (but stronger) signal by examining satellites and filaments similarly identified in the Millennium simulation, semi-analytical galaxy catalogue. Also examine the dependence of the alignment strength on galaxy properties such as color, magnitude and (relative) satellite magnitude, finding that the alignment is strongest for the reddest and brightest central and satellite galaxies. Results confirm the theoretical picture and the old of the cosmic web in satellite accretion. Furthermore, the results suggest that filaments identified on larger scales can be reflected in the positions of satellite galaxies that are quite close to their hosts.
Nature Letters
Evidence for dark matter in the inner Milky Way
Iocco, Pato, Bertone
The ubiquitous presence of dark matter in the Universe is today a central tenet in modern cosmology and astrophysics. Throughout the universe, the evidence for DM is compelling in dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales. However, it has been historically difficult to pin down the DM contribution to the total mass density in the MW, particularly in the innermost regions of the Galaxy and in the solar neighborhood. Present an up-to-date compilation of MW rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. Show that current data strongly disfavor baryons as the sole contribution to the Galactic mass budge, even inside the solar circle. Findings demonstrate the existence of DM in the inner Galaxy without making any assumptions about it distribution. Anticipate that this result will compel new model-independent constraints on the DM local density and profile, thus reduction uncertainties on direct and indirect DM searches, and will help reveal the structure and evolution of the Galaxy.
1502.02046
The alignment of satellite galaxies and cosmic filaments: observations and simulations
Tempel, Guo, Kipper, Libeskind
The accretion of satellite onto central galaxies along vast cosmic filaments is an apparent outcome of the anisotropic collapse of structure in the Universe. Numerical work (based on N-body sims) indicates that satellites are beamed towards hosts along preferred directions imprinted by the velocity shear field. Use the SDSS to observationally test this claim. Construct 3D filaments and sheets and examine the relative position of satellites galaxies. A statistical significant alignment between satellite galaxy position and filament axis is confirmed. Find a similar (but stronger) signal by examining satellites and filaments similarly identified in the Millennium simulation, semi-analytical galaxy catalogue. Also examine the dependence of the alignment strength on galaxy properties such as color, magnitude and (relative) satellite magnitude, finding that the alignment is strongest for the reddest and brightest central and satellite galaxies. Results confirm the theoretical picture and the old of the cosmic web in satellite accretion. Furthermore, the results suggest that filaments identified on larger scales can be reflected in the positions of satellite galaxies that are quite close to their hosts.
Monday, February 9, 2015
Day 829
Monday.
1502.01883
The Canadian Cluster Comparison Project: detailed study of systematic and updated weak lensing masses
Hoekstra, Herbonnet, Muzzin, Babul, Mahdavi, Viola, Cacciato
Masses of clusters of galaxies from WL analyses of ever larger samples are increasingly used as the reference to which baryonic scaling relations are compared. In this paper, revisit the analysis of a sample of 50 clusters studied as part of the Canadian Cluster comparison Project. Examine the key sources of systematic error in cluster masses. Quantify the robustness of shape measurements and calibrate the algorithm empirically using extensive image simulations. The source redshift distribution is revised using the latest state-of-the-art photometric redshift catalogs that include new deep NIR observations. Nonetheless find that the uncertainty in the determination of photometric redshifts is the largest source of systematic error for the mass estimates. Use updated masses to determine b, the bias in the hydrostatic mass, for the clusters detected by Planck. Results suggest 1-b = 0.76pm0.05(stat)pm0.06(sys), which does not resolve the tension with the measurements from the primary cosmic microwave background.
1502.01883
The Canadian Cluster Comparison Project: detailed study of systematic and updated weak lensing masses
Hoekstra, Herbonnet, Muzzin, Babul, Mahdavi, Viola, Cacciato
Masses of clusters of galaxies from WL analyses of ever larger samples are increasingly used as the reference to which baryonic scaling relations are compared. In this paper, revisit the analysis of a sample of 50 clusters studied as part of the Canadian Cluster comparison Project. Examine the key sources of systematic error in cluster masses. Quantify the robustness of shape measurements and calibrate the algorithm empirically using extensive image simulations. The source redshift distribution is revised using the latest state-of-the-art photometric redshift catalogs that include new deep NIR observations. Nonetheless find that the uncertainty in the determination of photometric redshifts is the largest source of systematic error for the mass estimates. Use updated masses to determine b, the bias in the hydrostatic mass, for the clusters detected by Planck. Results suggest 1-b = 0.76pm0.05(stat)pm0.06(sys), which does not resolve the tension with the measurements from the primary cosmic microwave background.
Saturday, February 7, 2015
Day 828
Thursday. Friday.
1502.01349
On the diffuse Lyman-alpha halo around Lyman-alpha emitting galaxies
Lake et al
Lya photons scattered by neutral H atoms in the circumgalactic media or produced in the halos of SF galaxies are expected to lead to extended Lya emission around galaxies. Such low surface brightness Lya halos (LAHs) have been detected by stacking Lya images of high-z SF galaxies. Study the origin of LAHs by performing radiative transfer modeling of 9 z=3.1 LAEs in a high-res hydro galaxy formation sim. Develop a method of computing the mean Lya surface brightness profile of each LAE by effectively integrating over many different observing directions. Without adjusting any parameters, the model yields an average Lya surface brightness profile in remarkable agreement with observations. Find that observed LAHs can not be accounted for solely by photons originating from the central LAE and scattered to large radii by hydrogen atoms in the circumgalactic gas. Instead, Lya emission from regions in the outer halo is primarily responsible for producing the extended LAHs seen in observations, which potentially includes both SF and cooling radiation. The contribution from SF in the outer halo regions can be strongly constrained to be negligible by the observed absence of an extended UV halo. The results therefore suggest that cooling radiation from the outer halo regions of LAEs plays a major role in forming their extended LAHs. Discuss the implications and caveats of such a picture.
1502.01353
Tailoring strong lensing cosmographic observations
Linder
SL time delay cosmography has excellent complementarity with other DE probes, and will soon have abundant systems detected. Investigate two issues in the imaging and spectroscopic followup required to obtain the time delay distance. The first is optimization of spectroscopic resources. Develop a code to optimize the cosmo leverage under the constrain of constant spectroscopic time, and find that sculpting the lens system redshift distribution can deliver a 40% improvement in DE FoM. The second is the role of systematics, correlated between different quantities of a given system or model errors common to all systems. Show how the levels of different systematics affect the cosmological parameter estimation, and derive guidance for the fraction of double image vs quad image systems to follow as a function of differing systematics between them.
1502.01589
Planck 2015 results. XIII. Cosmological parameters
Planck Collaboration
Present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology find a Hubble constant, H0=67pm0.9 km/s/Mpc, a matter density parameter Omega_m=0.38pm0.012, and a scalar spectral index with n_s=0.968pm0.006 (quote 68% errors on measured parameters and 95% limits on other parameters). Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a deionization optical depth of tau=0.066pm0.016. Combining Planck with other astrophysical data, find N_eff = 3.15pm0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to <0.23 eV. Spatial curvature is found to be |Omega_K|<0.005. For LCDM find a limit on the tensor-to-scalar ratio of r<0.11 consistent wit the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r<0.09. Find no evidence for isocurvature perturbations or cosmic defects. The equation of state of DE is constrained to w=-1.006pm0.045. Standard BB nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. Investigate annihilating DM and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However, the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
1502.01591
Planck 2015 results. XV. Gravitational lensing
Planck Collaboration, et al
Present the most significant measurement of the CMB lensing potential to date (40 sigma), using temperature and polarization data from the Planck 2015 full-mission release. Using a polarization-only estimator, detect lensing at a significance of 5 sigma. Cross-check the accuracy of the measurement using the wide frequency coverage and complementarity of the temperature and polarization measurements. Public products based on this measurement include an estimate of the lensing potential over approximately 70% of the sky, and estimate of the lensing potential power spectrum in band powers for the multipole range 40<L<400 and an associated likelihood for cosmological parameter constraints. Find good agreement between measurement of the lensing potential PS and that found in the best-fitting LCDM model based on the Planck temperature and polarization power spectra. Using the lensing likelihood alone, obtain a percent-level measurement of the parameter combination Sigma_8 Omega_m^0.25 = 0.591pm0.021. Combine determination of the lensing potential with the E-mode polarization also measured by Planck to generate an estimate of the lensing B-mode. Show that this lensing B-mode estimate is correlated with the B-modes observed directly by Planck at the expected level and with a statistical significance of 10 sigma, confirming Planck's sensitivity to this known sky signal. Also correlate lensing potential estimate with the LS temperature anisotropies, detecting a cross-correlation at the 3 sigma level, as expected due to DE in the concordance LCDM model.
1502.01349
On the diffuse Lyman-alpha halo around Lyman-alpha emitting galaxies
Lake et al
Lya photons scattered by neutral H atoms in the circumgalactic media or produced in the halos of SF galaxies are expected to lead to extended Lya emission around galaxies. Such low surface brightness Lya halos (LAHs) have been detected by stacking Lya images of high-z SF galaxies. Study the origin of LAHs by performing radiative transfer modeling of 9 z=3.1 LAEs in a high-res hydro galaxy formation sim. Develop a method of computing the mean Lya surface brightness profile of each LAE by effectively integrating over many different observing directions. Without adjusting any parameters, the model yields an average Lya surface brightness profile in remarkable agreement with observations. Find that observed LAHs can not be accounted for solely by photons originating from the central LAE and scattered to large radii by hydrogen atoms in the circumgalactic gas. Instead, Lya emission from regions in the outer halo is primarily responsible for producing the extended LAHs seen in observations, which potentially includes both SF and cooling radiation. The contribution from SF in the outer halo regions can be strongly constrained to be negligible by the observed absence of an extended UV halo. The results therefore suggest that cooling radiation from the outer halo regions of LAEs plays a major role in forming their extended LAHs. Discuss the implications and caveats of such a picture.
1502.01353
Tailoring strong lensing cosmographic observations
Linder
SL time delay cosmography has excellent complementarity with other DE probes, and will soon have abundant systems detected. Investigate two issues in the imaging and spectroscopic followup required to obtain the time delay distance. The first is optimization of spectroscopic resources. Develop a code to optimize the cosmo leverage under the constrain of constant spectroscopic time, and find that sculpting the lens system redshift distribution can deliver a 40% improvement in DE FoM. The second is the role of systematics, correlated between different quantities of a given system or model errors common to all systems. Show how the levels of different systematics affect the cosmological parameter estimation, and derive guidance for the fraction of double image vs quad image systems to follow as a function of differing systematics between them.
1502.01589
Planck 2015 results. XIII. Cosmological parameters
Planck Collaboration
Present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology find a Hubble constant, H0=67pm0.9 km/s/Mpc, a matter density parameter Omega_m=0.38pm0.012, and a scalar spectral index with n_s=0.968pm0.006 (quote 68% errors on measured parameters and 95% limits on other parameters). Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a deionization optical depth of tau=0.066pm0.016. Combining Planck with other astrophysical data, find N_eff = 3.15pm0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to <0.23 eV. Spatial curvature is found to be |Omega_K|<0.005. For LCDM find a limit on the tensor-to-scalar ratio of r<0.11 consistent wit the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r<0.09. Find no evidence for isocurvature perturbations or cosmic defects. The equation of state of DE is constrained to w=-1.006pm0.045. Standard BB nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. Investigate annihilating DM and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However, the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
1502.01591
Planck 2015 results. XV. Gravitational lensing
Planck Collaboration, et al
Present the most significant measurement of the CMB lensing potential to date (40 sigma), using temperature and polarization data from the Planck 2015 full-mission release. Using a polarization-only estimator, detect lensing at a significance of 5 sigma. Cross-check the accuracy of the measurement using the wide frequency coverage and complementarity of the temperature and polarization measurements. Public products based on this measurement include an estimate of the lensing potential over approximately 70% of the sky, and estimate of the lensing potential power spectrum in band powers for the multipole range 40<L<400 and an associated likelihood for cosmological parameter constraints. Find good agreement between measurement of the lensing potential PS and that found in the best-fitting LCDM model based on the Planck temperature and polarization power spectra. Using the lensing likelihood alone, obtain a percent-level measurement of the parameter combination Sigma_8 Omega_m^0.25 = 0.591pm0.021. Combine determination of the lensing potential with the E-mode polarization also measured by Planck to generate an estimate of the lensing B-mode. Show that this lensing B-mode estimate is correlated with the B-modes observed directly by Planck at the expected level and with a statistical significance of 10 sigma, confirming Planck's sensitivity to this known sky signal. Also correlate lensing potential estimate with the LS temperature anisotropies, detecting a cross-correlation at the 3 sigma level, as expected due to DE in the concordance LCDM model.
Tuesday, February 3, 2015
Day 827
Wednesday.
15002.00003
A direct onstraint on the gas content of a massive, passively evolving elliptical galaxy at z=1.43
Sargent et al
In comparison to gas and dust in SF galaxies at the peak epoch of galaxy assembly, little is known about the ISM of distant, passively evolving galaxies. Report on a deep 3mm band search with IRAM/PdBI for molecular gas in a massive (M*~6e11 Msun) elliptical galaxy at z=1.4277, the first observation of this kind ever attempted. Place a 3 sigma upper limit of 0.30Jy km/s on the flux of the CO(J=2-1) line of L'_CO<8.3e9 K km/s pc^2, assuming a line width in accordance with the stellar velocity dispersion of sigma*~330 km/s. This translates to a molecular gas mass of <3.6e10 (alpha_CO/4.4)M_sun or a gas fraction of <5% assuming a Saltpeter IMF and an ISM dominated by molecular gas, as observed in local ETGs. This low gas fraction approaches that of local ETGs, suggesting that the low SF activity in massive, high-z passive galaxies reflects a true dearth of gas and a secondary role for inhibitive mechanisms like morphological quenching.
1502.00008
Gravitational lens modelling in a citizen science context
Küng, Saha, et al
Develop a method to enable collaborative modeling of gravitational lenses and lens candidates, that could be used by non-professional lens enthusiasts. Uses and existing free-form modeling program (glass), but enables the input to this code to be provided in a novel way, via a user-generated diagram that is essentially a sketch of an arrival-time surface. Report on an implementation of this method, SpaghettiLens, which has been tested in a modeling challenge using 29 simulated lenses drawn from a larger set created for the Space Warps citizen science SL search. Find that volunteers from this online community asserted the image parities and time ordering consistently in some lenses, but made errors in other lenses depending on the image morphology. While errors in image parity and time ordering lead to large errors in the mass distribution, the enclosed mass was found to be more robust: the model-derived Einstein radii found by the volunteers were consistent with those produced by one of the professional team, suggesting that given the appropriate tools, gravitational lens modeling is a data analysis activity that can be crowd-sourced to good effect. Ideas for improvement are discussed, these include (a) overcoming the tendency of the models to be shallower than the correct answer in test cases, leading to systematic overestimation of the Einstein radius by 10% at present, and (b) detailed modeling of arcs.
1502.00292
Giant disk galaxies : where environment trumps mass in galaxy evolution
Courtois, Zaritsky, Sorce, Pomarede
Identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6 um photometry obtained with the Spitzer Space Telescope, with which stellar mass can be measured, use the baryonic Tully-Fisher (BTF) relationship to explore whether these massive galaxies are distinct. Discuss several results, but the most striking is the systematic offset of the HI-massive sample above the BTF. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The "condensed" baryon fraction, f_C, the fraction of the baryons in a DM halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases, suggesting that the most extreme of these galaxies have little in the way of a hot baryonic component or cold baryons distributed well outside the disk. In contrast, the SFE, measured as the ratio lf the mass in stars to that in both stars and gas, shows no difference between the HI-massive sample and the typical disk galaxies. Conclude that the SFE is driven by an internal, self-regulating process, while f_C is affected by external factors. Also found that the most massive HI detected galaxies are located preferentially in filaments. Present the first evidence of an environmental effect on galaxy evolution using a dynamical definition of a filament.
1502.00313
The mass-concenration relation and the stellar-to-halo mass ratio in the CFHT Stripe 82 survey
Shan, Kneib, Li, Comparat, Erben, ... Van Waerbeke, et al
A new measurement of M-c relation and the stellar-to-halo mass ratio over 5e12 to 2e14 Msun range galaxy clusters. Used stacked lensing signals from CS82, combined with clusters from SDSS DR10. Measure for 0.2<z<0.4 and 0.4<z<0.6. Conclude that the amplitude A and slope B are both consistent with the simulation predictions by Klypin+2014 within errors. Also measure the stellar-to-halo mass ratio and find it to be flatter than previous measurement for high stellar masses because of the complex structures and merger history in massive DM haloes.
1502.00394
Probing the DM radial profile in lens galaxies and the size of X-ray emitting region in quasars with mircolensing
Jiménez-Vicente, Mediavilla, Kochanik, Muñoz
Use X-ray and optical microlensing measurements of 47 image pairs in 18 lens systems to study the shape of the DM density profile in the lens galaxies and the size of the (soft) X-ray emission region. Show that single epoch X-ray microlensing is sensitive to the source size. These results, in good agreement with previous estimates, show that the X-ray size scales roughly linearly with the BH mass, with a HLR of R_1/2~(20pm12)r_g (r_g=GM_BH/c^2). This corresponds to a size of ~1 light dat for a black hole mass of M_BH=1e9Msun. Simultaneously estimate the fraction of the local surface mass density in stars, finding that the stellar mass fraction is alpha=0.20pm0.05 at an average radius of ~1.9 R_e, where R_e is the effective radius of the lens. This stellar mass fraction is insensitive to the X-ray source size and in excellent agreement with earlier results based on optical data. By combining the X-ray and optical microlensing data, divide this larger sample into two radial binds. Find that the surface mass density in the form of stars is alpha=0.31pm0.15 and alpha=0.13pm0.05 at (1.3pm0.3) R_e and (2.3mp0.3) R_e, respectively, in good agreement with expectations and some previous results.
1502.00709
How to collect matches that will catch fire
Loeb
How can we select a cohort of promising astrophysicists before they have made their discoveries? This is a fundamental challenge of academic planning. Argue that science can only blossom if young researches are rewarded for acquired skills and growth rather than inherited academic ancestry.
1502.00806
Exoplanets: Gaia and the importance of ground based spectroscopy follow-up
Benamati et al
Thanks to Gaia, high-accuracy astrometric orbits of thousands of new low-mass celestial objects will be collected, such as extra-solar planets and brown dwarfs. These measurements in combination with spectroscopy and with present day and future extrasolar planet search programs (HARPS, ESPRESSO) will have a crucial contribution to several aspects of planetary astrophysics (formation theories, dynamical evolution, etc). Moreover, Gaia will have a strong contribution on the stellar chemical and kinematic characterization studies. In this paper, preset a shirt overview of the importance of Gaia in the context of exoplanet research. As preparatory work for Gaia, then present a study where derived stellar parameters for a sample of field giant stars are derived. [???]
15002.00003
A direct onstraint on the gas content of a massive, passively evolving elliptical galaxy at z=1.43
Sargent et al
In comparison to gas and dust in SF galaxies at the peak epoch of galaxy assembly, little is known about the ISM of distant, passively evolving galaxies. Report on a deep 3mm band search with IRAM/PdBI for molecular gas in a massive (M*~6e11 Msun) elliptical galaxy at z=1.4277, the first observation of this kind ever attempted. Place a 3 sigma upper limit of 0.30Jy km/s on the flux of the CO(J=2-1) line of L'_CO<8.3e9 K km/s pc^2, assuming a line width in accordance with the stellar velocity dispersion of sigma*~330 km/s. This translates to a molecular gas mass of <3.6e10 (alpha_CO/4.4)M_sun or a gas fraction of <5% assuming a Saltpeter IMF and an ISM dominated by molecular gas, as observed in local ETGs. This low gas fraction approaches that of local ETGs, suggesting that the low SF activity in massive, high-z passive galaxies reflects a true dearth of gas and a secondary role for inhibitive mechanisms like morphological quenching.
1502.00008
Gravitational lens modelling in a citizen science context
Küng, Saha, et al
Develop a method to enable collaborative modeling of gravitational lenses and lens candidates, that could be used by non-professional lens enthusiasts. Uses and existing free-form modeling program (glass), but enables the input to this code to be provided in a novel way, via a user-generated diagram that is essentially a sketch of an arrival-time surface. Report on an implementation of this method, SpaghettiLens, which has been tested in a modeling challenge using 29 simulated lenses drawn from a larger set created for the Space Warps citizen science SL search. Find that volunteers from this online community asserted the image parities and time ordering consistently in some lenses, but made errors in other lenses depending on the image morphology. While errors in image parity and time ordering lead to large errors in the mass distribution, the enclosed mass was found to be more robust: the model-derived Einstein radii found by the volunteers were consistent with those produced by one of the professional team, suggesting that given the appropriate tools, gravitational lens modeling is a data analysis activity that can be crowd-sourced to good effect. Ideas for improvement are discussed, these include (a) overcoming the tendency of the models to be shallower than the correct answer in test cases, leading to systematic overestimation of the Einstein radius by 10% at present, and (b) detailed modeling of arcs.
1502.00292
Giant disk galaxies : where environment trumps mass in galaxy evolution
Courtois, Zaritsky, Sorce, Pomarede
Identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6 um photometry obtained with the Spitzer Space Telescope, with which stellar mass can be measured, use the baryonic Tully-Fisher (BTF) relationship to explore whether these massive galaxies are distinct. Discuss several results, but the most striking is the systematic offset of the HI-massive sample above the BTF. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The "condensed" baryon fraction, f_C, the fraction of the baryons in a DM halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases, suggesting that the most extreme of these galaxies have little in the way of a hot baryonic component or cold baryons distributed well outside the disk. In contrast, the SFE, measured as the ratio lf the mass in stars to that in both stars and gas, shows no difference between the HI-massive sample and the typical disk galaxies. Conclude that the SFE is driven by an internal, self-regulating process, while f_C is affected by external factors. Also found that the most massive HI detected galaxies are located preferentially in filaments. Present the first evidence of an environmental effect on galaxy evolution using a dynamical definition of a filament.
1502.00313
The mass-concenration relation and the stellar-to-halo mass ratio in the CFHT Stripe 82 survey
Shan, Kneib, Li, Comparat, Erben, ... Van Waerbeke, et al
A new measurement of M-c relation and the stellar-to-halo mass ratio over 5e12 to 2e14 Msun range galaxy clusters. Used stacked lensing signals from CS82, combined with clusters from SDSS DR10. Measure for 0.2<z<0.4 and 0.4<z<0.6. Conclude that the amplitude A and slope B are both consistent with the simulation predictions by Klypin+2014 within errors. Also measure the stellar-to-halo mass ratio and find it to be flatter than previous measurement for high stellar masses because of the complex structures and merger history in massive DM haloes.
1502.00394
Probing the DM radial profile in lens galaxies and the size of X-ray emitting region in quasars with mircolensing
Jiménez-Vicente, Mediavilla, Kochanik, Muñoz
Use X-ray and optical microlensing measurements of 47 image pairs in 18 lens systems to study the shape of the DM density profile in the lens galaxies and the size of the (soft) X-ray emission region. Show that single epoch X-ray microlensing is sensitive to the source size. These results, in good agreement with previous estimates, show that the X-ray size scales roughly linearly with the BH mass, with a HLR of R_1/2~(20pm12)r_g (r_g=GM_BH/c^2). This corresponds to a size of ~1 light dat for a black hole mass of M_BH=1e9Msun. Simultaneously estimate the fraction of the local surface mass density in stars, finding that the stellar mass fraction is alpha=0.20pm0.05 at an average radius of ~1.9 R_e, where R_e is the effective radius of the lens. This stellar mass fraction is insensitive to the X-ray source size and in excellent agreement with earlier results based on optical data. By combining the X-ray and optical microlensing data, divide this larger sample into two radial binds. Find that the surface mass density in the form of stars is alpha=0.31pm0.15 and alpha=0.13pm0.05 at (1.3pm0.3) R_e and (2.3mp0.3) R_e, respectively, in good agreement with expectations and some previous results.
1502.00709
How to collect matches that will catch fire
Loeb
How can we select a cohort of promising astrophysicists before they have made their discoveries? This is a fundamental challenge of academic planning. Argue that science can only blossom if young researches are rewarded for acquired skills and growth rather than inherited academic ancestry.
1502.00806
Exoplanets: Gaia and the importance of ground based spectroscopy follow-up
Benamati et al
Thanks to Gaia, high-accuracy astrometric orbits of thousands of new low-mass celestial objects will be collected, such as extra-solar planets and brown dwarfs. These measurements in combination with spectroscopy and with present day and future extrasolar planet search programs (HARPS, ESPRESSO) will have a crucial contribution to several aspects of planetary astrophysics (formation theories, dynamical evolution, etc). Moreover, Gaia will have a strong contribution on the stellar chemical and kinematic characterization studies. In this paper, preset a shirt overview of the importance of Gaia in the context of exoplanet research. As preparatory work for Gaia, then present a study where derived stellar parameters for a sample of field giant stars are derived. [???]
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