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Wednesday.
1506.08820
Cosmic star formation history and AGN evolution near and far: from AKARI to SPICA
Goto, et al
IR luminosity is fundamental to understanding the cosmic SFH and AGN evolution, since their most intense stages are often obscured by dust. AKARI provided unique data sets to probe these both at low and high z. AKARI performed an all-sky survey in 6 IR bands (9,18,65,90,140, and 160um) with 3-10x better spatial resolution, AKARI can measure the total L_TIR of individual galaxies much more precisely, and thus, the total IR L density of the local universe. In the AKARI NEP deep field, construct rest frame 8um, 12um and total IR (TIR) LFs at 0.15<z<2.2 using 4128 IR sources. A continuous filter coverage in the MIR wavelength (2.4, 3.2, 4.1, 7,9,11,15,18 and 24 um) by the AKARI satellite allows estimation of rest frame 8 and 12 um luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. By combining these two results, reveal dust-hidden cosmic SFH and AGN evolution from z=0 to 2.2, all probed by the AKARI satellite. The next generation space IR telescope, SPICA, will revolutionize the view of the IR universe with superb sensitivity of the cooled 3m space telescope. Conclude with a survey proposal and future prospects with SPICA.
1506.08821
Evolution of mid-infrared galaxy luminosity functions from the entire AKARI NEP-deep field with new CFHT photometry
Goto, et al
Present IR galaxy LFs in the AKARI North Ecliptic Pole (NEP) deep field using the wider CFHT optical/NIR images. ... The resulting rest frame 8um, 12um and TIR LFs at 0.15<z<2.2 are consistent with previous works, but with reduced uncertainties, especially at the high luminosity-end, thanks to the wide field coverage. In terms of cosmic infrared luminosity density, found that it evolves as ~(1+z)^4.2±0.4.
1506.09156
The ERA method with idealizing PSF for precise weak gravitational lensing shear analysis
Okura, Futamase
Generalize ERA method of PSF correction for more realistic situations. The method re-smears the observed galaxy image and PSF image by an appropriate function called Re-Smearing Function (RSF) to make new images with have the same ellipticity with the lensed (i.e., intrinsic) galaxy image. It has been shown that the method avoids a systematic error arising from an approximation in the usual PSF correction in moment method such as KSB for simple PSF shape. By adopting an idealized PSF, generalize ERA method applicable for arbitrary PSF. This is confirmed with simulated complex PSF shapes. Also consider the effect of pixel noise and found that the effect causes systematic overestimation.
Tuesday.
1506.08222
Galaxy and mass assembly (GAMA): end of survey report and data release 2
Liske, et al
The GAMA survey is one of the largest contemporary spectroscopic surveys of low-z galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r<19.8 mag, they have collected spectra and reliable redshifts for 238k objects using the AAOmega spectrograph on the AAT. In addition, they have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm-1m. Report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. Also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of UV, optical and NIR photometry. Finally, present the second public release of GAMA data. In this release, provide input catalogue and targeting information, spectra, z, UV, optical and NIR photometry, single-component Sersic fits, stellar masses, Ha-derived SFRs, environment information, and group properties for all galaxies with r<19.0 mag in two of the survey regions, and for all galaxies with r<19.4 mag in a 3rd region (72,225 objects in total). The database serving these data is available online.
1506.08359
Detecting stellar spots through polarimetry observations of microlensing events in caustic-crossing
Sajadian
Investigate if gravitational microlensing can magnify the polarization signal of a stellar spot and make it be observable. A stellar spot on a source star of microlensing makes polarization signal through two channels of Zeeman effect and breaking circular symmetry of the source surface brightness due to its temperature contrast. First explore the characteristics of perturbations in polarimetric microlensing during caustic-crossing of a binary lensing as follows: (a) the cooler spots over the Galactic bulge sources have the smaller contributions in the total flux, although they have stronger B-fields. (b) the maximum deviation in the polarimetry curve due to the spot happens when the spot is located near the source edge and the source spot is first entering the caustic whereas the maximum photometric deviation occurs for the spots located at the source center. (c) There is a (partial) degeneracy for indicating spot's size, its temperature contrast and its magnetic induction from the deviations in light or polarimetric curves. (d) if the time when the photometric deviation due to spot becomes zero (between positive and negative deviations) is inferred from microlensing light curves, the magnification factor of the spot can be indicated, characterizing the spot properties except its temperature contrast. The stellar spots alter the polarization degree as well as strongly change its orientation which gives some information about the spot position. Although, the photometry observations are more efficient in detecting stellar spots than the polarimetry ones, but polarimetry observations can specify the magnetic field of the source spots.
1506.08642
Galactic archeology - requirements on survey spectrographs
Feltzing
Galactic archeology is about exploring the MW as a galaxy by, mainly, using its (old) stars as tracers of past events and thus figure out the formation and evolution of the Galaxy. Briefly outline some of the key scientific aspects of Galactic Archeology and then discuss the associated instrumentations. Gaia will forever change the way this subject is approached. However, Gaia on its own is not enough. Ground-based complementary spectroscopy is necessary to obtain full phase-space information and elemental abundances for stars fainter than the top few percent of the bright part of the Gaia catalogue. Review the requirement on instrumentation for Gaia follow-up that Galactic Archeology sets. In particular, discuss the requirement on radial velocity and elemental abundance determination, including a brief look at potential pit-falls in the abundance analysis (e.g., NLTE, atomic diffusion). This contribution also provides a non-exhaustive comparison of the various current and future spectrographs for Galactic Archeology. Finally, discuss the needs for astrophysical calibrations for the surveys and inter-survey calibrations.
1506.08730
The impact of intrinsic alignment on current and future cosmic shear surveys
Krause, Eifler, Blazek
IA of source galaxies is one of the major astrophysical systematics for ongoing and future WL surveys. This paper presents the first forecasts of the impact of IA on cosmic shear measurements for current and future surveys (DES, Euclid, LSST, WFIRST) using simulated likelihood analyses and realistic covariances that include higher-order moments of the density field in the computation. Consider a range of possible IA scenarios and test mitigation schemes, which parameterize IA by the fraction of red galaxies, normalization, luminosity and redshift dependence of the IA signal (for a subset, consider joint IA and photo-z uncertainties). Compared to previous studies, find smaller biases in time-dependent DE models if IA is ignored in the anslysis; the amplitude and significance of these biases vary as a function of survey properties (depth, statistical uncertainties), luminosity function, and IA scenario: due to its small statistical errors and relatively shallow observing strategy Euclid is significantly impacted by IA. LSST and WFIRST benefit from their increased survey depth, while the larger statistical errors for DES increase IA's relative impact on cosmological parameters. The proposed IA mitigation scheme removes parameter biases due to IA for DES, LSST, and WFIRST even if the shape of the IA PS is only poorly known; successful IA mitigation for Euclid requires more prior information. Explore several alternative IA mitigation strategies for Euclid; in the absence of alignment of blue galaxies, recommend the exclusion of red (IA contaminated) galaxies in cosmic shear analyses. Find that even a reduction of 20% fin the number density of galaxies only leads to a 4-10% loss in cosmological constraining power.
Monday.
1506.07891
Discovery of low-metallicity stars in the central parsec of the Milky Way
Do, et al
Wide variety of metallicity, with 6% of the stars (out of 83 late-type giants) within the central 1pc of the MW, have [M/H]<-0.5, in contrast to previous observations. These low metallicity stars are consistent with that of globular clusters in the MW, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the MW nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, the results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.
Friday.
1506.07523
Accurate and efficient halo-based galaxy clustering modeling with simulations
Zheng, Guo
Small- and intermediate-scale galaxy clustering can be used to establish the galaxy-halo connection to study galaxy formation and evolution and to tighten constraints on cosmological parameters. With the increasing precision of galaxy clustering measurements from ongoing and forthcoming large galaxy surveys, accurate models are required to interpret the data and extract relevant information. Introduce a method based on high-resolution N-body simulations to accurately and efficiently model the galaxy 2PCFs in projected and redshift spaces. The basic idea is to tabulate all information of haloes in the simulations necessary for computing the galaxy 2PCFs within the framework of halo occupation distribution or conditional luminosity function. It is equivalent to populating galaxies to DM haloes and using the mock 2PCF measurements as the model predictions. Besides the accurate 2PCF calculations, this method is also fast and therefore enables an efficient exploration of the parameter space. As an example of the method, decompose the redshift-space galaxy 2PCF into different components based on the type of galaxy pairs and show the z-space distortion effect in each component. The generalizations and limitations of the method are discussed.
1506.07524
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses XV. Assessing th achievability and precision of time-delay measurements
Bonvin, Tewes, Courbin, Kuntzer, Sluse, Meylan
COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed QSOs aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H0. Given long and well sampled light curves of strongly lensed QSOs, time-delay measurements require numerical techniques whose quality must be assessed. To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named the Time Delay Challenge 1 (TDC1) was held in 2014. The aim of the present paper, which is based on the simulated light urges from the TDC1, is double. First, test the performance of the time-delay measurement techniques currently used in COSMOGRAIL. Second, analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations. To achieve these goals, first discover time delays through a careful inspection of the light curves via a dedicated visual interface. The measurement algorithms can then be applied to the data in an automated way. Show that the techniques have no significant bases, and yield adequate uncertainty estimates resulting in reduced chi2 values between 0.5 and 1.0. Prove estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay. Make the blind measurements on the TDC1 data publicly available.
1506.07526
Redshift-space distortions in massive neutrino and evolving dark energy cosmologies
Upadhye, et al
Large-scale structure surveys in the coming years will measure the redshift-space power spectrum to unprecedented accuracy, allowing for powerful new tests of the LCDM picture as well as measurements of particle physics parameters such as the neutrino masses. Extend the Time-RG perturbative framework to redshift space, computing the power spectrum P_s(k, mu) in massive neutrino cosmologies with time-dependent DE EoS w(z). Time-RG is uniquely capable of incorporating scale-dependent growth into the P_s(k,mu) computations, which is important for massive neutrinos as well as modified gravity models. Although changes to w(z) and the neutrino mass fraction both affect the late-time scale-dependence of the non-linear power spectrum, find that the two effects depend differently on the LoS angle mu. Finally, use the HACC N-body code to quantify errors in the perturbative calculations. For a LCDM model at z=1, the procedure predicts the monopole (quadrupole) to 1% accuracy up to a wave number 0.19h/Mpc (0.28h/Mpc), compared to 0.08h/Mpc (0.07h/Mpc) for the Kaiser approximation and 0.19h/Mpc (0.16h/Mpc) for the current state-of-the-art perturbation scheme. The calculation agrees with the simulated redshift-space PS even for neutrino masses Sum m_nu~1eV, several times the current bound, as well as rapidly-evolving DE EoS, |dw/dz|~1. Along with this article, make the z-space Time-RG implementation publicly available as the code redTime.
1506.07640
Precision cosmology with time delay lenses: high resolution imaging requirements
Meng, Treu,... Marshall, et al
Lens time delays are a powerful probe of cosmology, provided that the gravitational potential of the main deflector can be modeled with sufficient precision. Recent work has shown that this can be achieved by detailed modeling of the host galaxies of lensed quasars, which appear as "Einstein Rings" in high resolution images. Carry out a systematic exploration of the high resolution imaging required to exploit the thousands of lensed quasars that will be discovered by current and upcoming surveys with the next decade. Specifically, simulate realistic lens systems as imaged by HST, JWST, and ground-based adaptive optics images taken with Keck or the Thirty Meter Telescope (TMT). Compare the performance of these pointed observations with that of images taken by Euclid (VIS), WFIRST and LSST surveys. Use as the metric the precision with which the slope gamma' of the total mass density profile rho_tot~r^{-gamma') for the main deflector can be measured. Ideally, require that the statistical error on gamma' be less than 0.02, such that it is subdominant to other sources of random and systematic uncertainties. Find that survey data will likely have sufficient depth and resolution to meet the target only for the brighter gravitational lens systems, comparable to those discovered by the SDSS survey. For fainter systems that will be discovered by current and future surveys, targeted follow-up with be required. However, the exposure time required with upcoming facilities such as JWST, the Keck Next Generation Adaptive Optics System, and TMT, will only be of order a few minutes per system, thus making the follow-up of hundreds of systems a practical and efficient cosmological probe.
1506.07831
How well can Charge Transfer Inefficiency be corrected? A parameter sensitivity study for iterative correction
Israel, Massey, Prod'homme, Cropper, Cordes, Gow, Kohley, Margrraf, Niemi, Rhodes, Shot, Verhoeve
Radiation damage to space-based CCD detectors creates defects which result in an increasing CTI that causes spurious image trailing. Most of the trailing can be corrected during post-processing, by modeling the charge trapping and moving electrons back to where they belong. However, such correction is not perfect -- and damage is continuing to accumulate in orbit. To aid future development, quantify the limitations of current approaches, and determine where imperfect knowledge of model parameters most degrade measurements of photometry and morphology. As a concrete application, simulate 1.5e9 "worst case" galaxy and1.5e8 star images to test the performance of the Euclid visual instrument detectors. There are two separable challenges: if the model used to correct CTI is perfectly the same as that used to add CTI, 99.68% of spurious ellipticity is corrected in the setup. This is because readout noise is not subject to CTI, but gets over-corrected during correction. Second, if the first issue is solved, knowledge of the charge trap density within Delta rho/rho=(0.0272±0.0005)%, and the characteristic release time of the dominant species to be known within Delta tau/tau=(0.0400±0.0004)% will be required. This work presents the next level of definition of in-orbit CTI calibration procedures for Euclid.
Thursday.
1506.07173
The brightest Ly$\alpha$ emitter: Pop III or Black Hole?
Pallottini, et al
CR7 is the brightest z-6.6 LAE known to date, and spectroscopic follow-up by Sobral+2015 suggests that CR7 might host Pop III stars. Examine this interpretation using cosmo hydro sims. Several simulated galaxies show the same "Pop III wave" pattern observed in CR7. However, to reproduce the extreme CR7 Lya/HeII 1640 line luminosities (L_alpha/HeII) a top-heavy IMF and a massive (>1e7 Msun) PopIII burst with age <2Myr are required. Assuming that the observed properties of Lya and HeII emission are typical for Pop III, predict that in the COSMOS/UDS/SA22 fields, 14 out of the 30 LAEs at z=6.6 with L_a>1e43.3 erg/s should also host Pop III stars producing an observable L_HeII>1e42.7 erg/s. As an alternate explanation, explore the possibility that CR7 is instead powered by accretion onto a Direct Collapse Black Hole (DCBH). The model predicts L_a, L_HeII, and X-ray luminosities that are in agreement with the observations. In any case, the observed properties of CR7 in ideate that this galaxy is most likely powered by sources formed from pristine gas. Propose that further X-ray observations can distinguish between the two above scenarios.
1506.07185
The importance of 56Ni in shaping the light curves of type II supernovae
Nakar, Poznanski, Katz
What intrinsic property shape the light curves of Type II SNe [core-collapse SNe]? To address this question, derive observational measures that are robust (i.e., insensitive to detailed radiative transfer) and constrain the contribution from 56Ni, as well as a combination of the ejecta mass, progenitor radius, and explosion energy. By applying the methods to a sample of type II SNe from the literature, find that 56Ni contribution is often significant. It is typically the source of about 20% of the radiated energy during the photospheric phase, and in extreme cases it even dominates. Find that the 56Ni relative contribution is anti-correlated with the luminosity decline rate, while it is not significantly correlated with other properties of the light curve. When added to other clues, this in turn suggests that the flat plateaus often observed i type II SNe are not a generic feature of the cooling envelope emission, and that without 56Ni many of the SNe that are classified as II-P would have shown a decline rate that is steeper by up to 1 mag/100 d. Furthermore, contrary to previous suggestions, find that SNe with faster decline have at least comparable, and possibly larger, ejecta mass compared to those with flat plateaus.
1506.07366
Angular spectra of the intrinsic galaxy ellipticity field, their observability and their impact on lensing in tomographic surveys
Schaefer, Merkel
Subject of this paper: intrinsic ellipticity correlations between galaxies, their statistical properties, their observability with future surveys and their interference with WL measurements. Using an angular momentum-based, quadratic intrinsic alignment model, derive correlation functions of the ellipticity components and project them to yield the four non-zero angular ellipticity spectra C_E(ell), C_B(ell), C_C(ell) and C_S(ell) in their generalization to tomographic surveys. For a Euclid-like survey, these spectra would have amplitudes smaller than the WL effect on nonlinear structures, but would constitute an important systematic. Computing estimation basis for cosmological parameters derived from an alignment-contaminated survey suggests biases of +5sigma_w for the DE EoS parameter w, -20sigma_Omega_m for the matter density Omega_m and -12sigma_sigma8 for the spectrum normalization sigma_8. IA yield a signal which is easily observable with a survey similar to Euclid: while not independent, significances for estimates of each of the four spectra reach values of tens of sigma if WL and shape noise are considered as noise sources, which suggests relative uncertainties on alignment parameters at the percent level.
Wednesday.
1506.06867
A metallicity recipe for rocky planets
Dawson, Chiang, Lee
Planets with sizes between those of Earth and Neptune divide into two populations: purely rocky bodies whose atmospheres contribute negligibly to their sizes, and large gas-enveloped planets possessing voluminous and optically thick atmospheres. Show that whether a plant forms rocky or gas-enveloped depends on the solid surface density of its parent disk. Assembly times for rocky cores are sensitive to disk solid surface density. Lower surface densities spawn smaller planetary embryos; to assemble a core of given mass, smaller embryos require more mergers between bodies farther apart and therefore exponentially longer formation times. Gas accretion simulations yield a rule of thumb that a rocky core must be at least 2M_earth before it can acquire a volumetrically significant atmosphere from its parent nebula. In disks of low solid surface density, cores of such mass appear only after the gas disk has dissipated, and so remain purely rocky. Higher surface density disks breed massive cores more quickly, within the gas disk lifetime, and so produce gas-enveloped planets. Test model predictions against observations, using planet radius as an observational proxy for gas-to-rock content and host star metallicity as a proxy for disk solid surface density. Theory can explain the observation that metal-rich stars host predominantly gags-enveloped planets.
1506.07135
Planck 2015 resuits. XVI. Isotropy and statistics of the CMB
Planck Collaboration
Test the statistical isotropy and Gaussianity of the CMB anisotropies using observations made by the Planck satellite. Results are based mainly on the full Planck mission for temperature, but also include some polarization measurements. In particular, consider the CMB anisotropy maps derived from the multi-frequency Planck data by several component-separation methods. For the temperature anisotropies, find excellent agreement between results based on these sky maps over both a very large fraction of the sky and a broad range of angular scales, establishing that potential foreground residuals do not affect the studies. Tests of skewness, kurtosis, multi-normality, N-point functions, and Minkowski functionals indicate consistency with Gaussianity, while a power deficit at large angle scales is manifested in several ways, for example low map variance. The results of a peak statistics analysis are consistent with the expectations of a Gaussian random field. The "Cold Spot" is detected with several methods, including map kurtosis, peak statistics, and mean temperature profile. Thoroughly probe the large-scale dipolar power asymmetry, detecting it with several independent tests, and address the subject of a posteriori correction. Tests of directionality suggest the presence of angular clustering from large to small scales, but at a significance that is dependent on the details of the approach. Perform the first examination of polarization data, finding the morphology of stacked peaks to be consistent with the expectations of statistically isotropic simulations. Where they overlap, these results are consistent with the Planck 2013 analysis based on the nominal mission data and provide the most thorough view of the statistics of the CMB fluctuations to date.
Tuesday.
1506.06135
Evidence of halo assembly bias in massive clusters
Miyatake, More, Takada, Spergel, Mandelbaum, Rykoff, Rozo
Present significant evidence of halo assembly bias for redMaPPer galaxy clusters in 0.1<z<0.33. By dividing the 8,648 clusters into two subsamples based on the average member galaxy separation from the cluster center, first show that the two subsamples have very similar halo mass of M_200m~1.9e14 Msun/h based on the WL signals at small radii R<~10 Mpc/h. However, their halo bias inferred from both the large-scale WL and the projected auto-correlation functions differs by a factor of ~1.5, which is a signature of assembly bias. The same bias hypothesis for the two subsamples is excluded at 2.5 sigma in the WL and 4.6 sigma in the auto-correlation data, respectively.
1506.06313
Testing modified gravity with cosmic shear
Harnois-Déraps, Munshi, Valageas, van Waerbeke, Brax, Coles, Rizzo
Use cosmic shear data from CFHTLenS to place constraints on f(R) and Generalized Dilaton models of modified gravity. This is highly complimentary to other probes since the constraints mainly come from the NL scales: maximal deviations with respect to GR+LCDM scenario occurs at k~1 h/Mpc. At these scales, it becomes necessary to account for known degeneracies with baryon feedback and massive neutrinos, hence place constraints jointly on these three physical effects. To achieve this, formulate these modified gravity theories within a common tomographic parameterization, compute their impact on the clustering properties relative to a GR universe, and propagate the observed modifications into the WL xi_± quantity. Confronted against the cosmic shear data, reject the f(R) {|f_R0|=1e-4, n=1} model with more than 99.9% CI when assuming a LCDM DM only model. In the presence of baryonic feedback processes and massive neutrinos with total mass up to 0.2 eV, the model is disfavored with at least 94% CI in all different combinations studied. Constraints on the {|f_R0|=1e-4, n=2} model are weaker, but nevertheless disfavored with at least 89% CI. Identify several specific combinations of neutrino mass, baryon feedback and f(R) or Dilaton gravity models that are excluded by the current cosmic shear data. Notably, universes with 3 massless neutrinos and no baryon feedback are strongly disfavored in all modified gravity scenarios studied. These results indicate that competitive constraints may be achieved with future cosmic shear data.
Monday.
1506.05803
Mapping metals at high redshift with far-infrared lines
Pallottini, et al
Hard to detect metals at high z; absorption line experiments at z~6 become increasingly difficult because of instrumental limitations and the paucity of background quasars. with ALMA, FIR emission lines provide a novel tool to study early metal enrichment. Among these, the [CII] line at 157.74 um is the most luminous line emitted by the ISM of galaxies; it can also resonant scatter CMB photons near the peak of the CMB spectrum, thus allowing to probe the low-density IGM. Compute both [CII] galaxy emission and metal induced CMB fluctuations at z~6 by using AMR cosmo hydro sims and produce mock observations to be directly compared with ALMA BAND6 data. Calculated relation is in very good agreement with recent ALMA observations of M_UV<-20 galaxies. Predict that M_UV=-19 (-18) galaxy can be detected at 4 sigma in ~40 (2000) hours. CMB resonant scattering can produce ~±0.1 uJy/beam emission/absorptions features that are currently very challenging to be detected with current facilities. The best strategy to detect these signals consists in the stacking of deep ALMA observations pointing fields with known M_UV~=-19 galaxies. This would allow to simultaneously detect both [CII] emission from galactic reionization sources and CMB fluctuations produced by z~6 metals.
1506.05814
Galaxy power spectrum in redshift space: combining perturbation theory with the halo model
Okumura, Hand, Seljak, Vlah, Desjacques
Theoretical modeling of the z-space PS of galaxies is crucially important to correctly extract cosmological information from z surveys. The task is complicated by the nonlinear biasing and z space distortion effects, which change with halo mass, and by the wide distribution of halo masses and their occupations by galaxies. One of the main modeling challenges is the existence of satellite galaxies that have both radial distribution and large viral velocities inside haloes, a phenomenon known as the FoG effect. Present a model for the galaxy PS of in which a given galaxy sample is decomposed into central and satellite galaxies and relate different contributions to 1- and 2-halo terms in a halo model. The primary goal is to ensure that any parameters that are introduced have physically meaningful values, and are not just fitting parameters. For the 2-halo terms, use the previously developed RSD modeling of haloes in the context of distribution function and perturbation theory approach. This term needs to be multiplied by the effect of radial distances and velocities of satellites inside the halo. To this one needs to add the 1-halo terms, which are non-perturbative. Show that the real space 1-halo terms can be modeled as almost constant, with the finite extent of the satellites inside the halo inducing a small k^2 R^2 P(k) term, where R is related to the size of the halo. Adopt a similar model for FoG in redshift space, ensuring that FoG velocity dispersion is related to the halo mass. For FoG k^2 type expansions do not work and FoG resummation must be used instead.
Friday. Saturday. Sunday.
1506.05459
ALMA and Herschel reveal that AGN and main-sequence galaxies have different star formation rate distributions
Mullaney, et al
Investigate SFR distributions of X-ray AGN host galaxies at 0.5<z<1.5 and 1.5<z<4, comparing them to that of normal, SF (MS) galaxies. Find 34-55% of AGNs have SFRs at least a factor of 2 below that of the average MS galaxy, compared to ~15% of all MS galaxies, suggesting significantly different SFR distributions. Indeed, when both are modeled as log-normal distributions, the mass and z-normalized SFR distributions of AGNs are roughly twice as broad, and peak ~0.4 dex lower, than that of MS galaxies. However, like MS galaxies, the normalized SFR distribution of AGNs appears not to evolve with redshift. Despite AGNs and MS galaxies having different SFR distributions, the linear-mean SFR of AGNs derived from our distributions is remarkably consistent with that of MS galaxies, and thus with previous results derived from stacked Herschel data. This apparent contradiction is due to the linear-mean SFR being biased by bright outliers, and thus does not necessarily represent a true characterization of the typical SFR of AGNs.
1506.05466
H-ATLAS/GAMA: quantifying the morphological evolution of the galaxy population using cosmic calorimetry
Eales, et al
Using results from H-ATLAS/GAMA, show that, for galaxy masses above approximately 1e8 Msun, 51% of the stellar mass-density in the local Uinverse is in early-type galaxies (ETGs: Sersic n>2.5) while 89% of the rate of production of stellar mass-density is occurring in late-type galaxies (LTGs: Sersic n<2.5). From this zero-redshift benchmark, use a calorimetric technique to quantify the importance of the morphological transformation of galaxies over the history of the Universe. The extragalactic background radiation contains all the energy generated by nuclear fusion in stars since the BB. By resolving this BG radiation into individual galaxies using the deepest FIR survey with Herschel and a deep NIR/optical survey with HST, and using measurements of the Sersic index of these galaxies derived from the HST images, estimate that approximately 83% of the stellar mass-density formed over the history of the universe occurred in LTGs. The difference between this and the fraction of the stellar mass-density that is in LTGs today implies there must have been a major transformation of LTGs into ETGs after the formation of most of the stars.
1506.05537
Baryonic impact on the dark matter distribution in Milky Way-size galaxies and their satellites
Zhu, ... Springel, Hernquist, et al
Study the impact of baryons on the distribution of dark matter in a MW-size halo by comparing a high-resolution, moving-mesh cosmological simulation with its DM-only counterpart. Identify 3 main processes related to baryons -- adiabatic contraction, tidal disruption and reionization -- which jointly shape the DM distribution in both the main halo and its subclass. The relative effect of each baryonic process depends strongly on the sub halo mass. For massive sub-haloes with maximum circular velocity v_max>35 km/s, adiabatic contraction increases the DM concentration, making these haloes less susceptible to tidal disruption. For low-mass subhalos with v_max<20 km/s, reionization effectively reduces their mass on average by ~30% and v_max by ~20%. For intermediate sub haloes with 20km/s<v_max<35 km/s, which share a similar mass range as the classical dSphs, strong tidal truncation induced by the main galaxy reduces their v_max. Moreover, the stellar disk of the main galaxy effectively depletes sub-haloes near the central region. As a combined result of reionization and increased tidal disruption, the total number of low-mass sub haloes in the hydrodynamic simulation is nearly halved compared to that of the N-body simulation. No DM cores in dwarf galaxies found, unlike previous studies that employed bursty feedback-driven outflows. The substantial impact of baryons on the abundance and internal structure of sub haloes suggests that galaxy formation and evolution models based on N-body sims should include these physical processes as major components.
Thursday.
1506.05251
Primordial power spectrum features and $f_{NL}$ constraints
Gariazzo, Lopez-Honorez, Mena
The simplest models of inflation predict small non-gaussianities and a featureless PS. However, there exist a large number of well-motivated theoretical scenarios in which large non-gaussianities could be generated. In general, in these scenarios the primordial PS will deviate from its standard power law shape. Study, in a model-independent manner, the constraints from future large scale structure surveys on the local non-gaussianity parameter f_NL when the standard power law assumption for the primordial PS is relaxed. If the analyses are restricted to the large scale-dependent bias induced in the linear matter power spectrum by non-gaussianities, the errors on the fNL parameter could be increased by 60% when exploiting data from the future DESI survey, if dealing with only one possible DM tracer. In the same context, a nontrivial bias |delta f_NL|~2.5 could be induced if future data are fitted to the wrong primordial PS. Combining all the possible DESI objects slightly ameliorates the problem, as the forecasted errors on f_NL would be degraded by 40% when relaxing the assumptions concerning the primordial PS shape. Also the shift on the non-gaussianity parameter is reduced in this case, |delta f_NL|~1.6. The addition of CMB priors ensure robust future f_NL bounds, as the forecasted errors obtained including these measurements are almost independent on the primordial PS features, and |delta f_NL|~0.2, close to the standard single-field slow-roll paradigm prediction.
1506.05356
Non-Gaussian forecasts of weak lensing with and without priors
Sellentin, Schäfer
Assuming a Euclid-like WL data set, compare different methods of dealing with its inherent parameter degeneracies. Including priors into a data analysis can mask the information content of a given data set alone. However, since the information content of a data set is usually estimated with the Fisher matrix, priors are added in order to enforce an approximately Gaussian likelihood. Here, compare priories forecasts to more conventional forecasts that use priors. Find strongly non-G likelihoods for 2d-WL if no priors are used, which is approximated with the DALI-expansion. Without priors, the Fisher matrix of the 2d-WL likelihood includes unphysical values of Omega_m and h, since it does not capture the shape of the likelihood well. The Cramer-Rao inequality then does not need to apply. Find that DALI and MCMC predict the presence of a DE with high significance, whereas a Fisher forecast of the same data set also allows decelerated expansion. Also find that a 2d-WL analysis provides a sharp lower limit on the Hubble constant of h>0.4, even if the equation of state of DE is jointly constrained by the data. This is not predicted by the Fisher matrix and usually amused in other works by a sharp prior on h. Additionally, find that DALI estimates FoM in the presence of non-G better than the Fisher matrix. Additionally demonstrate how DALI allows switching to a Hamiltonian MC sampling of a highly curved likelihood with acceptance rates of ~0.5, an effective covering of the parameter space, and numerically effectively costless leapfrog steps. This shows how quick forecasts can be upgraded to accurate forecasts whenever needed. Results were gained with the public code from github/DALI.
Wednesday.
1506.04151
Please of satellite galaxies: when exceptions are the rule
Cautun, et al
The detection of planar structures within the satellite systems of both MW and M31 has been reported as being in stark contradiction to the predictions of LCDM. Given the ambiguity in defining a planar configurations, it is unclear how to interpret the low incidence of the MW and M31 planes in LCDM. Investigate the prevalence of satellite planes around galactic mass haloes identified in high resolution cosmo sims. Find that planar structures are very common, and that ~10% of LCDM haloes have even more prominent planes than those present in the Local Group. While ubiquitous, the planes of satellite galaxies show a large diversity in their properties. This precludes using one or two systems as small scale probes of cosmology, since a large sample of satellite systems is needed to obtain a good measure of the object-to-object variation. This very diversity has been misinterpreted as a discrepancy between the satellite planes observed in the LG and LCDM predictions. In fact, ~10% of LCDM galactic halos have planes of satellites that are as infrequent as the MW and M31 planes. The look-elsewhere effect plays an important role in assessing the detection significance of satellite planes and accounting for it leads to overestimating the significance level by a factor of 30 and 100 for the MW and the M31 systems, respectively.
1506.04156
The radial variation of HI velocity dispersions in dwarfs and spirals
Ianjamasimanana, et al
Gas velocity dispersions provide important diagnostics of the forces counteracting gravity to prevent collapse of the gas. Use the 21 cm line of neutral HI to study HI velocity dispersion and HI phases as a function of galaxy morphology in 22 galaxies from the THINGS survey. Stack individual HI velocity profiles and decompose them into broad and narrow gaussian components. Study the HI velocity dispersion and the HI surface density, as a function of radius. For spirals, the velocity dispersions of the narrow and broad components decline with radius and their radial profiles are well described by an exponential function. For dwarfs, however, the profiles are much flatter. The single Gaussian dispersions profiles are, in general, flatter than those of the narrow and broad components. In most cases, the dispersion profiles in the outer disks do not drop as fast fast the SF profiles, derived in the literature. This indicates the importance of other energy sources in driving HI velocity dispersion in the outer disks. The radial surface density profiles of spirals and dwarfs are similar. The surface density profiles of the narrow component decline more steeply than those of the broad component, but not as steep as what was found previously for the molecular component. As a consequence, the surface density ratio between the narrow and broad components, an estimate of the mass ratio between cold HI and warm HI, tends to decrease with radius. On average, this ratio is lower in dwarfs than in spirals. This lack of a narrow, cold HI component in dwarfs may explain their low star formation activity.
1506.04166
Impact of the geo-synchronous orbit radiation environment on the design of astronomical observatories
Kruk, ... Hirata, et al
Geosynchronous orbits are appealing for Solar or astrophysical observatories because they permit continuous data downlink at high rats. The radiation environment in these orbits presents unique challenges, however. This paper describes the characteristics of the radiation environment in Geo-synchronous orbit and the implications for instrument design. Radiation-induced BG event rates are given for some simplified shielding models, and for a detailed model of the proposed WFIRST.
1506.04746
Accelerating the 2-point and 3-point galaxy correlation functions using Fourier transforms
Slepian, Eisenstein
Though FTs are a common technique for finding correlation functions, they are not typically used in computations of the anisotropy of the 2PCF about the LoS in wide-angle surveys because the LoS direction is not constant on the Cartesian grid. Show how FTs can be used to compute the multipole moments of the anisotropic 2PCF. Also show how FTs can be used to accelerate the 3PCF algorithm of Slepian & Eisenstein 2015. In both cases, these FT methods allow one to avoid the computational cost of pair counting, which scales as the square of the number density of objects in the survey. With the upcoming large datasets of DESI, Euclid, and LSST, FT techniques will therefore offer an important complement to simple pair or triplet counts.
Friday. Monday. Tuesday.
1506.03453
A bright year for tidal disruptions?
Metzger, Stone
When a star is tidally disrupted by a SMBH, roughly half of its mass falls back to the BH at super-Eddington rates. Being tenuously gravitationally bound and unable to cool radiatively, only a small fraction f_in<<1 of the returning debris will likely be incorporated into the disk and accrete, with the vast majority instead becoming unbound in an outflow of velocity ~1e4 km/s. This slow outflow spreads laterally, encasing the BH. For months or longer, the outflow remains sufficiently neutral to block hard EUV and X-ray radiation from the hot inner disk, which instead become trapped in a radiation-dominated nebula. Ionizing nebular radiation heats the inner edge of the ejecta to temperatures of T>few 1e4 K, converting the emission to optical/near-UV wavelengths where photons more readily escape due to the lower opacity. This can explain the unexpectedly low and temporally constant effective temperatures of optically-discovered TDE flares. For BHs with relatively high masses M_BH>1e7 Msun the ejecta can become ionized at an earlier stage, or for a wider range of viewing angles, producing a TDE flare which is instead dominated by thermal X-ray emission. Predict total radiated energies consistent with those of observed TDE flares, and ejecta velocities that agree with the measured emission line widths. The peak optical luminosity for M_BH<1e6 Msun is suppressed due to adiabatic losses in the inner disk wind, possibly contributing to the unexpected dearth of optical TDEs in galaxies with low mass BHs. In the classical picture, where f_in~1, TDEs de-spin SMBHs and cap their maximum spins well below theoretical accretion physics limits. This cap is greatly relaxed in the model, and existing Fe K-alpha spin measurements provide suggestive preliminary evidence that f_in<1.
1506.03536
Lensing measurements of the ellipticity of LRG dark matter halos
Clampitt, Jain
Lensing measurements of the shapes of DM haloes can provide tests of gravity theories and possible DM interactions. Measure the quadrupole WL signal from the elliptical halos of 70k SDSS LRGs. Use a new estimator that nulls the spherical halo lensing signal, isolating the shear due to anisotropy in the DM distribution. One of the two Cartesian components of the estimator is insensitive to the primary systematic, a spurious alignment of lens and source ellipticities, allowing to make robust measurements of halo ellipticity. The best-fit value for the ellipticity of the surface mass density is 0.24, which translates to an axis ratio of 0.78. Rule out the hypothesis of no ellipticity at the 4-sigma confidence level, and ellipticity <0.12 (axis ratio > 0.89) at the 2-sigma level. Discuss how the measurement of halo ellipticity are revised to higher values using estimates of the misalignment of mass and light from simulations. Finally, apply the same techniques to a smaller sample of redMaPPer galaxy clusters and obtain a 3-sigma measurement of cluster ellipticity. Discuss how the improved signal to noise properties of the estimator can enable studies of halo shapes for different galaxy populations with upcoming surveys.
1506.03715
Records of sunspot and aurora during CE 960-1279 in the Chinese chronicle of the Song dynasty
Hayakawa, et al
The Songshi chronicle contains a record of continuous observations with well-formatted reports conducted as a policy of the government; a brief comparison of the frequency of observations of sunspots and auroras and the observations of radioisotopes as an indicator of the solar activity during corresponding periods is provided. This paper is the first step of the project in which they survey and compile the records of sunspots and aurora in historical documents from various locations and languages, ultimately providing it to the science community as online data.
1506.03817
Weak-lensing-iferred scaling realtions of galaxy clusters in the RCS2: mass-richness, mass-concentration, mass-bias and more
van Uitert, Gilbank, Hoekstra, Semboloni, Gladders, Yee
Study a sample of ~1e4 galaxy clusters in 0.2<z<0.8 with masses M_200>5e13 Msun/h_70, discovered in RCS2. The depth and excellent image quality of the RCS2 enables detection of the cluster-mass cross-correlation up to z~0.7. To obtain cluster masses, concentrations and halo biases, fit a cluster halo model simultaneously to the lensing signal and to the projected density profile of RCS members, as the latter provides tight constraints on the cluster miscentering distribution. Parameterize the mass-richness relation as M_200=A (N_200/20)^alpha, and find A=(16.7±1.2)e13 Msun/h_70 and alpha=0.73±0.09 at low z (0.2<z<0.35). At intermediate redshift (0.35<z<0.55), find a higher normalization, which points at a fractional increase of the richness towards lower z caused by the build-up of the red-sequence. The miscentering distribution is well constrained. Only ~30% of the BCGs coincide with the peak of the DM distribution. The distribution of the remaining BCGs are modeled with a 2d-Gaussian, whose width increases from 0.2 to 0.4 Mpc/h_70 towards higher masses; the ratio of width and r_200 is constant with mass and has an average value of 0.43±0.01. The mass-concentration and mass-bias relation agree fairly well with literature results at low z, but have a higher normalization at higher redshifts, which may be due to selection and projection effects. The concentration of the satellite distribution decreases with mass and is correlated with the concentration of the halo.
1506.03823
Galaxy clusters and groups in the ALHAMBRA survey
Ascaso, et al
Present a catalogue of 348 galaxy clusters and groups with 0.2<z<1.2 selected in the 2.78 deg^2 ALHAMBRA survey. The high precision of the photometric redshifts, close to 1%, and the wide spread of the seven ALHAMBRA pointing ensure that this catalogue has better mass sensitivity and is less affected by cosmic variance than comparable samples. The detection has been carried out with the Bayesian Cluster Finder (BCF), whose performance has been checked in ALHAMBRA-like light-cone mock catalogues. Great care has been taken to ensure that the observable properties of the mocks photometry accurately correspond to those of real catalogues. From the simulations, expect to detect galaxy clusters and groups with both 70% completeness and purity down to dark matter halo masses of Mh~3e13Msun for z<0.85. Cluster redshifts are expected to be recovered with ~0.6% precision for z<1. Also expect to measure cluster masses with sigma_Mh|M*_CL~0.25-0.35 dex precision down to ~3e13Msun, masses which are 50% smaller than those reached by similar work. Compare these detections with previous optical, spectroscopic and X-rays work, finding an excellent agreement with the rates reported from the simulations. Also explored the overall properties of these detections such as the presence of a color-magnitude relation, the evolution of the photometric blue fraction and the clustering of these sources in the different ALHAMBRA fields. Despite the small numbers, observe tentative evidence that, for a fixed stellar mass, the environment is playing a crucial role at lower redshifts (z<0.5).
1506.03900
The BOSS-WIggleZ overlap region I: Baryon Acoustic Oscillations
Beutler, Blake, Koda, Marin, Seo, Cuesta, Schneider
Study the large-scale clustering of galaxies in the overlap region of the BOSS CMASS sample and the WIggleZ Dark Energy Survey. Calculate the auto-correlation and cross-correlation functions in the overlap region of he two datasets and detect BAO final in each of them. The BAO measurement from the cross-correlation function represents the first such detection between 2 different galaxy surveys. After applying density-field reconstruction, report distance-scale measurements D_V r^fid_s/r_s = (1970±47, 2132±67, 2100±200) Mpc from CMASS, the cross-correlation and WiggleZ, respectively. Use correlated mock realizations to calculate the covariance between the 2 BAO constraints. The distance scales derived from the 2 datasets are consistent, and are also robust against switching the displacement fields used for reconstruction between the 2 surveys. This approach can be used to construct a correlation matrix, permitting for the first time a rigorous combination of WiggleZ and CMASS BAO measurements. Using a volume-scaling technique, the result can also be used to combine WiggleZ and future CMASS DR12 results. Finally, use the cross-correlation function measurements to show that the relative velocity effect, a possible source of systematic uncertainty for the BAO technique is consistent with zero for the samples.
1506.03901
The BOSS-WIggleZ overlap region II: dependence of cosmic growth on galaxy type
Marin, Beutler, Blake, Koda, Kazin, Schneider
The anisotropic galaxy 2PCF allows measurement of the growth of large-scale structures from the effect of peculiar velocities on the clustering pattern. Present new measurements of the auto- and cross-correlation function multipoles of 69180 WiggleZ and 46380 BOSS-CMASS galaxies sharing an overlapping volume of ~0.2 (Gpc/h)^3. Analyzing the RSD of galaxy 2pt statistics for these two galaxy tracers, test for systematic errors in the modeling depending on galaxy type and investigate potential improvements in cosmological constraints. Build a large number of mock galaxy catalogues to examine the limits of different RSD models in terms of fitting scales and galaxy type, and to study the covariance of the measurements when performing joint fits. For the galaxy data, fitting the monopole and quadrupole of the WiggleZ 2PCF on scales 24<s<80 Mpc/h produces a measurement of the normalized growth rate f sigma_8(z=0.54)=0.409±0.059, whereas for the CMASS galaxies find a consistent constraint of f sigma8 (z=0.54)=0.413±0.054, in agreement with the LCDM-GR model of structure growth and with other survey measurements.
Thursday.
1506.02729
Fast estimators for redshift-space clustering
Scoccimarro
Redshift-space distortions in galaxy surveys happen along the radial directions, breaking statistical translation invariance. Construct estimators for radial distortions that, using only 7 FFTs of the overdensity fields for a given survey geometry, compute the PS monopole, quadrupole and hexadecapole, and generalize such estimators to the bispectrum. The resulting algorithm is very efficient, e.g., for the BOSS survey requires about 3 minutes for ell=0,2,4 PS for scales up to k=0.3 h/Mpc and about 10 minutes for ell=0,2 bispectra for all scales and triangle shapes up to k=0.2 h/Mpc on a single core. The speed and these estimators is essential as it makes possible to compute covariance matrices from large number of realizations of mock catalogs with realistic survey characteiristics, and paves the way for improved constraints of gravity on cosmo scales, inflation and galaxy bias.
1506.03085
Forming compact massive galaxies at z~2
van Dokkum, et al
Study a key phase in the formation of massive galaxies: the transition of SF galaxies into massive (M*~1e11 Msun), compact (r_e~1kpc) quiescent galaxies, which takes place from z~3 to z~1.5. Use HST grim redshifts and extensive photometry in all 5 3D-HST/CANDELS fields, more than doubling the area used previously for such studies, and combine these data with Keck MOSFIRE and NIRSPEC spectroscopy. First confirm that a population of massive, compact, SF galaxies exists at z~2, using K-band spectroscopy of 25 of these objects at 2.0<z<2.5. They have a median NII/Halpha ratio of 0.6, are highly obscured with SFR(tot)/SFR(Halpha)~10, and have a large range of observe velocity dispersions. Infer from the kinematics and spatial distribution of Halpha that the galaxies have rotating disks of ionized gas that are a factor of ~2 more extended than the stellar distribution. By combining measurements of individual galaxies, find that the kinematics are consistent with a Keplerian fall-off from V_rot~500 km/s at 1 kpc to V_rot~250 km/s at 7kpc, and that the total mass out to this radius is dominated by the dense stellar component. Next, study the size and mass evolution of the progenitors of compact massive galaxies. Even though individual galaxies may have had complex histories with periods of compaction and mergers, show that the population of progenitors likely followed a simple inside-out growth track in the size-mass plane of d(log r_e) ~0.3 d(log (M_stars). This mode of growth gradually increases the stellar mass within a fixed physical radius, and galaxies quench when they reach a stellar density or velocity dispersion threshold. As shown in other studies, the mode of growth changes after quenching, as dry mergers take the galaxies on a relatively steep track in the size-mass plane.
Wednesday.
1506.02671
Imprint of inflation on galaxy shape correlations
Schmidt, Chisari, Dvorkin
Show that intrinsic (not lensing-induced) correlations between galaxy shapes offer a new probe of primordial non-Gaussianity and inflationary physics which is complementary to galaxy number counts. Specifically, intrinsic assignment correlations are sensitive to an anisotropic squeezed limit bispectrum of the primordial perturbations. Such a feature arises in solid inflation, as well as more broadly in the presence of light higher spin fields during inflation (as pointed out recently by Arkani-Hamed and Maldacena). Present a derivation of the all-sky 2pt correlations of intrinsic shapes and number counts in the presence of non-Gausiannity with general angular dependence, and show that a quadrupolar (spin-2) anisotropy leads to the analog in galaxy shapes of the well-known scale-dependent bias induced in number counts by isotropic (spin-0) non-G. Moreover, in presence of non-zero anisotropic non-G, the quadruple of galaxy shapes becomes sensitive to far super horizon modes. These effects come about because long-wavelength modes induce a local anisotropy in the initial PS, with which galaxies will correlate. Forecast that future imaging surveys could provide constraints on the amplitude of anisotropic non-Gaussianity that are comparable to those from the CMB. These are complementary as they probe different physical scales. The constraints, however, depend on the sensitivity of galaxy shapes to the ICs which are only roughly estimated from observed tidal alignments.
1506.02720
High resolution imaging and spectroscopy of the gravitational lens SDSJ1206+4332: a natural coronagraph at $z=1.789$ and a standard ruler at $z=0.745$
Agnello, ... Suyu, Treu, Fassnacht, .. .Bradac, et al
Present spectroscopy and laser guide star adaptive optics (LGSAO) images of the double imaged lensed quasar SDSS J1206+4332. Revise the deflector redshift proposed previously to z_d=0.745, and measure for the first time its velocity dispersion sigma=(290±30) km/s. The LGSAO data show the lensed quasar host galaxy stretching over the astroid caustic thus forming an extra pair of merging images, which was previously thought to be an unrelated galaxy in seeing limited data. Owing to the peculiar geometry, the lens acts as a natural coronagraph on the broad-one region of the quasar so that only narrow [OIII] emission is found in the fold arc. Use the data to reconstruct the source structure and deflector potential, including nearby potential perturbers. Reconstruct the PSF from the quasar images themselves, since no additional point source is present in the field of view. From gravitational lensing and stellar dynamics, find the slope of the total mass density profile to be gamma'=-log rho/log r = 1.93±0.09. Discuss the potential of this system for measuring time delay distance (and thus H0 and other cosmo params), r as a standard ruler, in combination with the time delay published by the COSMOGRAIL collaboration. Conclude that this system is very promising for cosmography. However, in order to achieve competitive precision and accuracy, and independent characterization of the PSF is needed. Spatially resolved kinematics of the deflector would reduce the uncertainties further. Both are within the reach of current observational facilities.
Tuesday.
1506.02036
An analytical model for galaxy metallicity: what do metallicity relations tell us about star formation and outflow?
Lu, Blanc, Benson
Develop a simple analytical model that tracks galactic metallicities governed by star formation and feedback to gain insight from the observed galaxy stellar mass-metallicity relations over a large range of stellar masses and redshifts. The model reveals the following implications of star formation and feedback processes in galaxy formation. First, the observed metallicity relations provide a stringent upper limit for the averaged outflow mass-loading factors of local galaxies, which is ~20 for M*~1e9 Msun galaxies and monotonically decreases to ~1 for M*~1e11 Msun galaxies. Second, the inferred upper-limit for the outflow mass-loading factor sensitively depends on whether the outflow is metal-enriched with respect to the ISM metallicity. In half of the metals ejected from SNe leave the galaxy in metal-enrihed winds, the outflow mass-loading factor for galaxies at any mass can barely be higher than ~10, which puts strong constraints on galaxy formation models. Third, the relatively lower stellar-phase to gas-phase metallicity ratio for lower-mass galaxies indicate that low-mass galaxies are still rapidly enriching their metallicities in recent times, while high-mass galaxies are more settled, which seems to show a downsizing effect in the metallicity evolution of galaxies. The analysis presented in the paper demonstrates the importance of accurate measurements of galaxy metallicities and the cold gas fraction of galaxies at different redshifts for constraining star formation and feedback processes, and demonstrates the power of these relations in constraining the physics of galaxy formation.
1506.02040
Computing the three-point correlation function of galaxies in $\mathcal{O}(N^2)$ time
Slepian, Eisenstein
Present an algorithm that computes the multipole coefficients of the galaxy 3PCF without explicitly considering triplets of galaxies. Rather, centering on each galaxy in the survey, it expands the radially-binned density field in spherical harmonics and combines these to form the multiples without ever requiring the relative angle between a pair about the central. This approach scales with number and number density in the same way as the 2PCF, allowing runtimes that are comparable, and 500x faster than a naive triple count. It is exact in angle and easily handles edge correction. Demonstrate the algorithm on the LasDamas SDSS-DR7 mock catalogs, computing an edge corrected 3PCF out to 90 Mpc/h in under an hour on modest computing resources. Expect this algorithm will render it possible to obtain the large-scale 3PCF for upcoming surveys such as Euclid, LSST, and DESI.
1506.02192
Constraining cosmology with shear peak statistics: tomographic analysis
Martinet, Bartlett, Kiessling, Sartoris
The abundance of peaks in WL maps is a potentially powerful cosmo tool, complementary to measurements of the shear power spectrum. Study peaks detected directly in shear maps, rather than convergence maps, an approach that has the advantage of working directly with the observable quantity, the galaxy ellipticity catalog. Using large numbers of numerical simulations to accurately predict the abundance of peaks and their covariance, quantify the cosmo constraints attainable by a large-area survey similar to that expected from the Euclid mission, focusing on the density parameter Omega_m, and on the PS normalization sigma8, for illustration. Present a tomographic peak counting method that improves the conditional (marginal) constraints by a factor 1.2(2) over those from a 2d (i.e., non-tomographic) peak-count analysis. Find that peak statistics provide constraints an order of magnitude less accurate than those from the cluster sample in the ideal situation of a perfectly known observable-mass relation, however, when the scaling relation is not known a priori, the constraints are comparable and orthogonal in the parameter plane, highlighting the value of using both clusters and shear-peak statistics.
Monday.
1506.01712
Approximately a thousand ultra diffuse galaxies in the Coma cluster
Koda, Yagi, Yamanoi, Komiyama
Report the discovery of 854 ultra diffuse galaxies (UDGs) in the Coma cluster using deep R band images, with partial B, i, and Halpha band coverage, obtained with Subaru. Many of them (332) are MW-sized with very large effective radii of r_e>1.5 kpc. This study was motivated by the recent discovery of 47 UDGs by van Dokkum+(2015); this discovery suggests >1000 UDGs after accounting for the small Subaru fields. The new UDGs show a distribution concentrated around the cluster center, strongly suggesting that the great majority are (likely longtime) cluster members. They are a passively evolving population, lying along the red sequence in the CM diagram with no Halpha signatures. Star formation was, therefore, quenched in the past. They have exponential light profiles, effective radii re~800 pc-5 kpc, effective surface brightnesses mu_e(R)=25-28 mag/arcsec^-2, and stellar masses ~1e7-5e8 Msun. There is also a population of nucleated UDGs. Some MW-sized UDGs appear closer to the cluster center than previously reported; their survival in the strong tidal field, despite their large sizes, possibly indicates a large dark matter fraction protecting the diffuse stellar component. The indicated baryon fraction ~<1% is less than the cosmic average, and thus the gas must have been removed from the possibly massive dark halo. The UDG population appears to be elevated in the Coma cluster compared to the field, indicating that the gas removal mechanism is related primarily to the cluster environment.
1506.01800
Radial alignment of elliptical galaxies by the tidal force of a cluster of galaxies
Rong, et al
Unlike the random radial orientation distribution of field elliptical galaxies, galaxies in a cluster are expected to point preferentially towards the center of the cluster, as a result of the cluster's tidal force on its member galaxies. In this work an analytic model is formulated to simulate this effect. The deformation time scale of a galaxy in a cluster is usually much shorter than the time scale of change of the tidal force; the dynamical process of the tidal interaction within the galaxy can thus be ignored. An equilibrium shape of a galaxy is then assumed to be in the surface of equipotential, which is the sum of the self-gravitational potential of the galaxy and the tidal potential of the cluster at this location. Use a MC method to calculate the radial orientation distribution of these galaxies, by assuming the NFW mass profile of the cluster and the initial ellipticity of field galaxies. The radial angles show a single peak distribution centered at zero. The MC simulations also show that a shift of the reference center from the real cluster center weakens the anisotropy of the radial angle distribution. Therefore, the expected radial alignment cannot be revealed if the distribution of spatial position angle is used instead of that of radial angle. The observed radial orientations of elliptical galaxies in cluster A2744 are consistent with the simulated distribution.
1506.01405
Major mergers going Notts: challenges for modern halo finders
Behroozi, et al
Merging haloes with similar masses (i.e., major mergers) pose significant challenges for halo finders. Compare 5 halo finding algorithms (AHF, HBT, Rockstar, SubFind, and VELOCIraptor) recovery of halo properties for both isolated and cosmo major mergers. Find that halo positions and velocities are often robust, but mass biases exist for every technique. The algorithms also show strong disagreement in the prevalence and duration of major mergers, especially at high redshifts (z>1). This raises significant uncertainties for theoretical models that require major mergers for, e.g., galaxy morphology changes, size changes, or BH growth, as well as for finding Bullet Cluster analogues. All finders not using temporal information also show host halo and sub halo relationship swaps over successive time steps, requiring careful merger tree construction to avoid problematic mass accretion histories. Suggest that future algorithms should combine phase-space and temporal information to avoid the issues presented.
1506.01653
Missing stellar mass in SED fitting: spatially unresolved photometry can underestimate galaxy masses
Sorba, Sawicki
Fit model SED to each pixel in 67 nearby (<z>=0.0057) galaxies using broadband photometry from the SDSS and GALEX. For each galaxy, compare the stellar mass derived by summing the mass of each pixel to that found from fitting the entire galaxy treated as an unresolved point source. Find that, while the pixel-by-pixel and unresolved masses of galaxies with low sSFRs (such as ellipticals and lenticular) are in rough agreement, the unresolved mass estimate for SF galaxies is systematically lower than the measurement from spatially-resolved photometry. The discrepancy is strongly correlated with sSFR, with the highest sSFRs in the sample having masses underestimated by 25% (0.12 dex) when treated as point sources. Found a simple relation to statistically correct mass estimates derived from unresolved broadband SED fitting to the resoled mass estimates: m_resolved = m_unresolved/(-0.0057log(sSFR)+0.34) where sSFR is in units of yr^-1. Study the effect of varying spatial resolution by degrading the image resolution of the largest images and find a sharp decrease in the pixel-by-pixel mass estimate at a physical scale of approximately 3 kpc, which is comparable to spiral arm widths. The effects observed are consistent with the "outshining" idea which posits that the youngest stellar populations mask more massive, older -- and thus fainter -- stellar populations. Although the presence of strong dust lanes can also lead to a drastic difference between resolved and unresolved mass estimates (up to 45% or 0.3 dex) for any individual galaxy, found that resolving dust does not affect mass estimates on average. The strong correlation between mass discrepancy and sSFR is thus most likely due to the outshining systematic bias.
1506.07475
Probing the role of the galactic environment in the formation of stellar clusters; using M83 as a test-bench
Adamo, et al
Present a study of the M83 cluster population, covering the disc of the galaxy between radii of 0.45 and 4.5 kpc. Aim to probe the properties of the cluster population as a function of distance from the galactic center. Observe a net decline in cluster formation efficiency (Gamma, i.e., the amount of star formation happening in bound clusters) from about 19% in the inner region to 7% in the outer part of the galaxy. The recovered Gamma values within different regions of M83 follow the same Gamma versus SFR density relation observed for entire galaxies. Also probe the initial cluster mass function (ICMF) as a function of galactocentric distance. Observe a significant steepening of the ICMF in the outer regions (from -1.90±0.11 to -1.70±0.14) and for the whole galactic cluster population (slope of -2.18±0.07) of M83. Show that this change of slope reflects a more fundamental change of the 'truncation mass' at the high-mass end of the distribution. This can be modeled as a Schechter function slope -2 with an exponential cut-off mass (M_c) that decreases significantly from the inner to the outer regions (from 4.00 to 0.25e5 Msun) while the galactic M_c is ~1.6e5 Msun. The trends in Gamma and ICMF are consistent with the observed radial decrease of the Sigma (H_2), hence in gas pressure. As gas pressure declines, cluster formation becomes less efficient. Conclude that the host galaxy environment appears to regulate 1) the fraction of stars locked in clusters; 2) the upper mass limit of the ICMF, consistently described by a near-universal slope -2 truncated at the high-mass end.
