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Tuesday.
1510.07040
A multiwavelength study of tadpole galaxies in the Hubble ultra deep field
Straughn, et al
Multiwavelength dat are essential in order to provide a complete picture of galaxy evolution and to inform studies of galaxies' morphological properties across cosmic time. Present realists of a multi wavelength investigation of the morphologies of "tadpole" galaxies at intermediate redshift (0.314<z<3.175) in the HUDF. These galaxies were previeously selected from deep HST F774W data based on their distinct asymmetric knot-plug-tail morphologies (Sraughn+2006). Use deep WFC3 NIR imaging in addition to the HST optical data in order to study the rest-frame UV/optical morphologies of these galaxies across the redshift range 0.3<z<3.2. This study reveals that the majority of these galaxies do retain the general asymmetric morphology in the rest-frame optical over this redshift range, if not the district "tadpole" shape. The average stellar mass of tadpole galaxies is lower than field galaxies, with the effect being slightly greater at higher redshift within the errors. Estimated from SED fits, the average age of tadpole galaxies is younger than field galaxies in the lower redshift bin, and the average metallicity is lower (whereas the sSFR for tadpoles is roughly the same as field galaxies across the redshift range probed here). These average effects combined support the conclusion that this subset of galaxies is in an active phase of assembly, either late-stage merging or cold gas accretion causing localized clumpy star-formation.
1510.07574
A daytime measurement of the lunar contribution to the night sky brightness in LSST's ugrizy bands-- initial results
Coughlin, Stubbs, Claver
Report measurements from which the spatial structure of the lunar contribution to nigh sky brightness is determined. Taken at the LSST site on Cerro Pachon in Chile. Use an array of six photodiodes with filters that approximate the LSST's ugriz and y bands. Use the sun as a proxy for the moon, and measure sky brightness as a function of zenith angle of the point on sky, zenith angle of the sun, and angular distance between the sun and the point on sky. Make a correction for the difference between the illumination spectrum of the sun and the moon. Since scattered sunlight totally dominates the daytime sky brightness, this technique allows clean determination of the contribution to the (cloudless) night sky from backscattered moonlight, without contamination from other sources of night sky brightness. Estimate the uncertainty in the relative lunar night sky brightness vs. zenith and lunar angle to be 10%. This information is useful in planning the optimal execution of the LSST survey, and perhaps for other astronomical observations as well. Although the primary objective is to map out the angular structure and spectrum of the scattered light form the atmosphere and particulates, also make an estimate of the expected number of scattered lunar photons per pixel per second in LSST, and find values that are in overall agreement with previous estimates.
Monday.
1510.06738
Cold-gas outflows in typical low-redshift galaxies are driven by stars formation, not AGN
Sarzi, Kaviraj, Nedelchev, Tiffany, Shabala, Deller, Niddleberg
Energetic feedback from AGN is an important ingredient for regulating the SFH of galaxies in models of galaxy formation, which makes it important to study how AGN feedback actually occurs in practice. In order to catch AGNs in the act of quenching SF, use the interstellar NaD absorption lines to look for cold-gas outflows in a sample of 456 nearby galaxies for which the presence of radio AGN activity can be unambiguously ascertained, thanks to radio imaging at milli-arcsecond scales. While compact radio emission indicating a radio AGN was found in 103 galaxies (23% of the sample), and 23 objects (5%) exhibited NaD absorption-line kinematics suggested of cold-gas outflows, not one object showed evidence of a radio AGN and of a cold-gas outflow simultaneously. Radio AGN activity was found predominantly in early-type galaxies, while cold-gas outflows were mainly seen in spiral galaxies with central SF or composite SF/AGN activity. Optical AGNs also do not seem capable of driving galactic winds in the sample. The work adds to a picture of the low-z Universe where cold-gas outflows in massive galaxies are generally driven by SF and where radio-AGN activity occurs most often in systems in which the gas reservoir has already been significantly depleted.
1510.06744
First results from COPSS: the CO power spectrum survey
Keating, Bower, et al
Present constraints on the abundance of CO in the early Universe from COPSS. Utilize a dataset collected between 2005 and 2008 using SZA, which were previously used to measured arcminute-scale fluctuations of the CMB. This data set features observations of 44 fields, covering an effective area of 1.7 sq.deg., over a frequency range of 27 to 35 GHz. Using the technique of intensity mapping, it is possible to probe the CO(1-0) transition, with sensitivity to spatial modes between k=0.5-2 h/Mpc over a range in redshift of z-2.3-3.3, spanning a comoving volume of 3.6e6 h^-3 Mpc^3. Demonstrate the ability to mitigate foregrounds, and present estimates of the impact of continuum sources on the measurement. Constrain the CO PS to P_CO<2.6e4 muK^2(Mpc/h)^3 at 95% CL. This limit resides near optimistic predictions for the CO PS. Under the assumption that CO emission is proportional to halo mass during bursts of active SF, this corresponds to a limit on the ratio of CO(1-0) luminosity to host halo mass of A_CO<1.2e-5 Lsun/Msun. Further assuming a MW-like conversion factor between CO luminosity and molecular gas mass (a_CO-4.3Msun(K km/s /pc^2)^-1), constrain the global density of molecular gas to rho_{z~3}(M_H2)<2.8e8Msun/Mpc^3.
1510.06752
Intrinsic alignments of BOSS LOWZ galaxies II: impact of shape measurement methods
Singh, Mandelbaum
Measurements of IA of galaxy shapes with the LS density field, and the inferred IA model parameters, are sensitive to the shape measurement methods used. In this paper, measure the IA of SDSS-III BOSS LOWZ galaxies using 3 different shape measurement methods (re-Gaussianization, isophotal, and deVaucouleurs), identifying a variation in the inferred IA amplitude at the 40% level between these methods, independent of the galaxy luminosity or other properties. Also carry out a suite of systematics tests on the shapes and their 2PCFs, identifying a pronounced contribution from additive PSF systematics in the deV shapes. Since different methods measure galaxy shapes at different effective radii, the trends identified in the IA amplitude are consistent with the interpretation that the outer regions of galaxy shapes are more responsive to tidal fields, resulting in isophote twisting and stronger alignments for isophotal shapes. Observe environmental dependence of ellipticity, with brightest galaxies in groups being rounder on average compared to satellite and field galaxies. Also study the anisotropy in IA measurements introduced by projected shapes, finding effects consistent with predictions of the nonlinear alignment model and hydrodynamic simulations. The large variations seen using the different shape measurement methods have important implications for IA forecasting and mitigation with future surveys.
1510.07024
Intrinsic alignments of disk and elliptical galaxies in the Massive Black-II and Illustris simulations
Tenneti, Mandelbaum, Di Matteo
Study the shapes and IA of disks and elliptical galaxies in MBII and Illustris cosmo hydro sims, with volumes of (100Mpc/h)^3 and (75Mpc/h)^3, respectively. Find that simulated disk galaxies are more oblate in shape and more misaligned with the shape of their host DM sub halo when compared with ellipticals. The disk major axis is found to be oriented towards the location of nearby elliptical galaxies. Also find that the disks are thinner in MBII and misalignments with DM halo orientations are smaller in both disks and ellipticals when compared with Illustris. As a result, the IA correlation functions at fixed mass have a higher amplitude in MBII than in Illustris. Despite significant differences in the treatments of hydrodynamics and baryonic physics in the simulations, find that the correlation function scale similarly with transverse separation (yet both have a different scale dependence to the correlation functions of the shapes of DM sub haloes within the same simulation). This is true for both disks and ellipticals. This results makes it likely that we should be able to use information from hydro sims to understand IA 2pt stats. Finally in scales above ~0.1 Mpc/h, the intrinsic alignment 2PCF for disk galaxies in both simulations are consistent with a null detection, unlike those for ellipticals.
Friday.
Nature (2015)
Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres
Hansen et al.
More than 50 years ago. John Bell proved that no theory of nature that obeys locality and realism can reproduce all the predictions of quantum theory: in any local-realist theory, the correlations between outcomes of measurements on distant particles satisfy an inequality that can be violated if the particles are entangled. Numerous Bell inequality tests have been reported; however, all experiments reported so far required additional assumption to obtain a contradiction with local realism, resulting in 'loopholes'. Here, report a Bell experiment that is free of any such additional assumption and thus directly tests the principles underlying Bell's inequality. [...] Data imply statistically significant rejection of the local-realist null hypothesis.
1510.06442
Evidence for the kinematic Sunyaev-Zeldovich effect with ACTPol and velocity reconstruction from BOSS
Schaan, et al
Stack the CMB temperature at the halo, weighted by the corresponding reconstructed velocity. The resulting best fit kSZ model is preferred over the no-kSZ hypothesis at 3.3 sigma and 2.9 sigma for 2 independent velocity reconstruction methods, using 25537 galaxies over 660 square degrees.
1510.06665
Efficient construction of mock catalogs for Baryon Acoustic Oscillation surveys
Sunayama, Padmanabhan, Heitmann, Habib, Rangel
Precision measurements of the LSS of the universe require large numbers of high fidelity mock catalogs to accurately assess, and account for, the presence of systematic effects. Introduce and test a scheme for generating mock catalogs rapidly using suitable derated N-body sims. The aim is to reproduce the LSS and the gross properties of DM haloes with high accuracy, while sacrificing the details of the internal structure of the halos. By adjusting global and local time-steps in an N-body code, demonstrate that halo masses are recovered to better than 2% and the power spectrum (both in real and redshift space, for k=1h/Mpc) to better than 1%, while requiring a factor of 4 less CPU time. Also calibrate the redshift spacing of outputs required to generate simulated light cones. Find that outputs separated by every z=0.05 allow interpolation of particle positions and velocities to reproduce the real and redshift space power spectra to better than 1% (out to k-1h/Mpc). Apply the ideas to generate a suite of simulations spanning a range of cosmologies, motivated by BOSS but broadly applicable to future LSS surveys including eBOSS and DESI. As an initial demonstration of the utility of such simulations, calibrate the shift in the BAO peak position as a function of galaxy bias with higher precision than has been possible so far. This paper also serves to document the simulations, which is made publicly available.
Thursday.
MNRAS 2015 454
Periodic impact cratering and extinction events over the last 260 million years
Rampino, Caldeira
The claims of periodicity in impact cratering and biological extinction events are controversial. A newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8±0.6 Myr cycle. Using the same method, find a significant 27.0±0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 1 apparent peaks in the last 260 Myr, at least 5 of which correlated closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.
1510.06034
A new method to quantify the effects of baryons on the matter power spectrum
Schneider, Teyssier
Future large-scale galaxy surveys have the potential to become leading probes for cosmology provided the influence of baryons on the total mass distribution is understood well enough. As hydrodynamical simulations strongly depend on details in the feedback implementations, no unique and robust predictions for baryonic effects currently exist. In this paper, propose a baryonic correction model that modifies the density field of DM-only N-body sims to mimic the effects of baryons from any underlying adopted feedback recipe. The model assumes haloes to consist of 4 components: 1) hot gas in hydro equilibrium, 2) ejected gas from feedback processes, 3) central galaxy stars, and 4) adiabatically relaxed dark matter, which all modify the initial DM-only density profiles. This altered mass profiles allow definition of a displacement field for particles in N-body sims and to modify the total density field accordingly. The main advantage of the baryonic correction model is to connect the total matter density field to the observable distribution of gas and stars in haloes, making it possible to parametric baryonic effects on the matter power spectrum. Show that the most crucial quantities are the mass fraction of ejected gas and its corresponding ejection radius. The former controls how strongly baryons suppress the power spectrum, while the latter provides a measure of the scale where baryonic effects become important. A comparison with X-ray and Sunyaev-Zel'dovich cluster observations suggests that baryons suppress wave modes above k~0.5 h/Mpc with a maximum suppression of 10-25 percent around k~2 h/Mpc. More detailed observations of the gas in the outskirts of groups and clusters are required to decrease the large uncertainties of these numbers.
1510.06387
A disintegrating minor planet transiting a white dwarf
Vanderburg, Johnson, et al
WDs are the end state of most stars, including the Sun, after they exhaust their nuclear fuel. Between 1/4 and 1/2 of WDs have elements heavier than He in their atmospheres, even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished. The abundance ratios of heavy elements in WD atmospheres are similar to rocky bodies in the Solar system. This and the existence of warm dusty debris disks around about 4% of WDs suggest that rocky debris from WD progenitors' planetary systems occasionally pollute the stars' atmospheres. The total accreted mass can be comparable to that of large asteroids the solar system. However, the process of disrupting planetary material has not yet been observed. Here, report observations of a WD being transited by at least one and likely multiple disintegrating planetesimals with periods ranging from 4.5 hrs to 4.9 hours. The strongest transit signal occur every 4.5 hours and exhibit varying depths up to 40% and asymmetric profiles, indicative of a small object with a cometary tail of dust effluent material. The star hosts a dusty debris disk and the star's spectrum shows prominent lines from heavy elements like Mg, Al, Si, Ca, Fe, and Ni. This system provides evidence that heavy element pollution of WDs can originate from disrupted rocky bodies such as asteroids and minor planets.
Wednesday.
1510.05645
Size evolution of normal and compact galaxies in the EAGLE simulation
Furlong, Bower, et al
Present the evolution of galaxy sizes, from redshift 2 to 0 , for actively SF and passive galaxies in the cosmo hydro 1003 cMpc3 simulation of the EAGLE project. Find that the sizes increase with stellar mass, but that the relation weakens with increasing redshift. Separating galaxies by their SF activity, find that passive galaxies are typically smaller than active galaxies at fixed stellar mass. These trends are consistent with those found in observations and the level of agreement between the predicted and observed size-mass relation is of order 0.1 dex for z<1 and 0.2-0.3 dex from redshift 1 to 2. Use the simulation to compare the evolution of individual galaxies to that of the population as a whole. While the evolution of the size-stellar mass relation for active galaxies provides a good proxy for the evolution of individual galaxies, the evolution of the individual passive galaxies is not well represented by the observed size-mass relation due to the evolving number density of passive galaxies. Observations of z~2 galaxies have revealed an abundance of massive red compact galaxies, that depletes below z~1. Find that a similar population forms naturally in the simulation. Comparing these galaxies to their z=0 descendants, find that all compact galaxies grow in size due to the high-redshift stars migrating outwards. Approximately 60% of the compact galaxies increase in size further due to renewed star formation and/or mergers.
1510.05650
How stellar feedback simultaneously regulates star formation and drives outflows
Hayward, Hopkins
Present an analytic model for how momentum deposition from stellar feedback simultaneously regulates SF and drives outflows in a turbulent ISM. Because the ISM is turbulent, a given patch of ISM exhibits sub-patches with a range of surface densities. The high-density patches are 'pushed' by feedback, thereby driving turbulence and self-regulating local SF. Sufficiently low-density patches, however, are accelerated to above the escape velocity before the region can self-adjust and are thus vented as outflows. In the turbulent-pressure-supported regime, when the gas fraction is >0.3, the ratio of the turbulent velocity dispersion to the circular velocity is sufficiently high that at any given time, of order half of the ISM has surface density less than the critical value and thus can be blown out on a dynamical time. The resulting outflows have a mass-loading factor (eta==Mout/M*) that is inversely proportional to the gas fraction times the circular velocity. At low gas fractions, the star formation rate needed to local self-regulation, and corresponding turbulent Mach number, decline rapidly; the ISM is 'smoother', and it is actually more difficult to drive winds with large mass-loading factors. Crucially, the model predicts that stellar-feedback-driven outflows should be suppressed at z<1 in M*>1e10 Msun galaxies. This mechanism allows massive galaxies to exhibit violent outflows at high redshifts and then 'shut down' those outflows at late times, thereby enabling the formation of a smooth, extended thin stellar disk. Provide simple fitting functions for eta that should be useful for sub-resolution and semi-analytic models.
1510.05651
The concentration dependence of the galaxy-halo connection
Lehmann, Mao, Becker, Skillman, Wechsler
Empirical methods for connecting galaxies to their DM haloes have become essential in interpreting measurements of the spatial statistics of galaxies. Among the most successful of these methods is the technique of sub halo abundance matching, which has to date been used to associated galaxy properties with a small set of halo properties. Generalize this set of halo properties to allow variable dependence on halo concentration, and parameterize the degree of concentration dependence with a single parameter. This parameter provides a smooth interpolation between abundance matching to peak halo mass and to peak halo circular velocity. Characterize the influence of this parameter on two-point clustering, the satellite fraction, and the degree of galaxy assembly bias. Also evaluate the degeneracies between the concentration dependence and the scatter in the abundance matching relation. Show that low redshift clustering measurements from SDSS prefer a moderate amount of concentration dependence --- more than would be indicated by matching galaxy luminosity to the peak halo mass, and less than would be indicated by matching to the peak halo circular velocity. Also show that these results are robust to moderate changes in cosmo params, and that the best-fit model from 2pt clustering agrees with previous measurements of the satellite fraction. Note that statistical constraints on these models have been (and still are, in most regimes) limited primarily by sample variance in the limited-size simulations, and not in the data. Discuss physical interpretations of these results and their implications for the galaxy-halo connection.
1510.05750
`Refsdal' meets Popper: comparing predictions of the re-apearance of the multiply imaged supernova behind MACS1149.5+2223
Treu et al
Supernova `Refsdal', multiply imaged by cluster MACS1149.5+2223, represents a rare opportunity to make a true blind test of model predictions in extragalactic astronomy, on a time scale that is short compared to a human lifetime In order to take advantage of this event, produce 7 GL models with 5 independent methods, based on HST Hubble Frontier Field images, along with extensive spectroscopic follow-up from HST and form the VLT. Compare the model predictions and shout that they agree reasonably well with the measured time delays and magnification ratios between the known images, even though these quantities were not used as input. This agreement is encouraging, considering that the models only provide statistical uncertainties, and do not include additional sources of uncertainties such as structure along the line of sight, cosmology, and the mass sheet degeneracy. Then present the model predictions for the other appearances of SN `Refsdal'. A further image will reach its peak in the first half of 2016, while another image appeared between 1994 and 2004. The past image would have been too faint to be detected in archival images. The future image should be approximately 1/3 as bright as the brightest known images and thus detectable in HST images, as soon as the cluster can be targeted again (beginning 2015 October 30). Soon to find out whether the predictions are correct.
Tuesday.
1510.00004
Search for extended gamma-ray emission from the Virgo galaxy cluster with Fermi-LAT
Ackermann et al
Galaxy clusters are one of the prime sites to search for DM annihilation signals. Depending on the substructure of the DM halo of a galaxy cluster and the cross sections for DM annihilation channels, these signals might be detectable by the latest generation of gamma-ray telescopes. Use 3 years of Fermi LAT data, which are the most suitable for searching for very extended emission in the vicinity of nearby Virgo galaxy cluster. Analysis reveals statistically significant extended emission which can be well characterized by a uniformly emitting disk profile with a radius of 3 deg that moreover is offset from the cluster center. Demonstrate that the significance of this extended emission strongly depends on the adopted interstellar emission model (IEM) and is most likely an artifact of the incomplete description of the IEM in this region. Also search for and find new point source candidates in the region. Then derive conservative upper limits on the velocity-averaged DM pair annihilation cross section from Virgo. Take into account the potential gamma-ray flux enhancement due to DM sub-haloes and its complex morphology as a merging cluster. For DM annihilating into bb-bar, assuming a conservative sub-halo model setup, find limits that are between 1 and 1.5 orders of magnitude above the expectation from the thermal cross section for m_DM<100 GeV. In a more optimistic scenario, exclude <sigma nu>~3e-26 cm^3/s for m_DM<40 GeV for the same channel. Finally, derive upper limits on the gamma-rya flux produced by hadronic cosmic-ray interactions in the ICM. Find that the volume-averaged cosmic-ray-to-thermal pressure ratio is less than ~6%.
1510.01359
Probing star formation in the dense environments of z~1 lensing halos aligned with dusty star-forming galaxies detected with the South Pole Telescope
Welikala, et al
Probe SF in the environments of massive ~1e13 Msun DM haloes at z~1. This SF is linked to a sub-millimeter clustering signal which is detected in maps of Planck HFI that are stacked at the positions of a sample of high-z (>2) strongly-lensed dusty SF galaxies (DSFGs) selected from the SPT 2500 deg2 survey. The clustering signal has sub-millimeter colors which are consistent wit the mean redshift of the foreground lensing haloes (z~1). Report a mean excess of SFR compared to the field, of (2700±700) Msun/yr from all galaxies contributing to this clustering signal within a radius of 3.5' from the SPT DSFGs. The magnitude of the Planck excess is in broad agreement with predictions of a current model of the CIB. The model predicts that 80% of the excess emission measured by Planck originates from galaxies lying in the neighboring haloes of the lensing halo. Using Herschel maps of the same fields, find a clear excess, relative to the field, of individual sources which contribute to the Planck excess. The mean excess SFR compared to the field is measured to be (370±40) Msun/yr per resolved, clustered source. The findings suggest that the environments around these massive z~1 lensing haloes host intense SF out to about 2Mpc. The flux enhancement due to clustering should also be considered when measuring flux densities of galaxies in Planck data.
1510.05040
The necessity of feedback physics in setting the peak of the initial mass function
Guszejnov, Krumholz, Hopkins
A popular theory of SF is gravitoturbulent fragmentation, in which self-gravitating structures are created by turbulence-driven density fluctuations. Simple theories of isothermal fragmentation successfully reproduce the core mass function (CMF) which has a very similar shape to the IMF of stars. However, numerical sims of isothermal turbulent fragmentation thus far have not succeeded in identifying a fragment mass scale that is independent of the simulation resolution. Moreover, the fluid equations for magnetized, self-gravitating, isothermal turbulence are scale-free, and do not predict any characteristic mass. In this paper, show that although an isothermal self-gravitating flow does produce a CMF with a mass scale imposed by the ICs, this scale changes as the parent cloud evolves. In addition, the cores that form undergo further fragmentation and after sufficient time forget about their ICs, yielding a scale-free pure power-law distribution dN/dM~M^-2 for the stellar IMF. Show that this problem can be alleviated by introducing a simple model for stellar radiation feedback. Radiative heating, powered by accretion onto forming stars, arrests the fragmentation cascade and imposes a characteristic mass scale that is nearly independent of the time-evolution or ICs in the SF cloud, and that agrees well wit the peak of the observed IMF. In contrast, models that introduce a stiff equation of state for denser clouds but that do not explicitly include the effects of feedback do not yield an invariant IMF.
1510.05388
Penetrating gas streams generate unrelaxed, non-cool-core clusters of galaxies
Zinger, Dekel, Birnboim, Kravtsov, Nagai
Utilize cosmo sims of 16 galaxy clusters at z=0 and 0.6 to study the effect of inflowing streams on the properties of the inner ICM. Find that the mass accretion occurs predominantly along streams that originate from the cosmic web and consist of heated gas. Clusters that are unrelaxed in terms of their X-ray morphology are characterized by higher mass inflow rates and deeper penetration of the streams, typically in the inner third of the viral radius. The penetrating streams generate elevated random motions, bulk flows, cold fronts and metal mixing, thus producing non-cool-core clusters. The degree of penetration of the streams may change over time such that clusters can switch from being unrelated to relaxed over a time-scale of several Gyrs. The stream properties thus help us understand the distinction between cool-core and non-cool-core clusters.
Monday.
1510.04696
Beyond 31 mag/arcsec^2: the low surface brightness frontier with the largest optical telescopes
Trujillo, Fliri
The detection of optical surface brightness structures in the sky with magnitudes fainter than 30 mag/arcsec^2 (3 sigma in 10x10 arcsec boxes; r-band) has remained elusive in current photometric deep surveys. Show how present-day 10m class telescopes can provide broadband imaging 1.5-2 mag deeper than most previous results within a reasonable amount of time (i.e., <10h on sources integration). In particular, illustrate the ability of the 10.4 Gran Telescopio de Canaries (GTC) telescope to produce imaging with a limiting surface brightness of 31.5 mag/arcsec^2 (3 sigma in 10x10 arcsec boxes; 4-band) using 8.1 hours on source. Apply this power to explore the stellar halo of the galaxy UGC00180, a galaxy analogous to M31 located at ~150 Mpc, by obtaining a surface brightness radial profile down to mu_r~33 mag/arcsec^2. This depth is similar to that obtained using star counts techniques of Local Group galaxies, but is achieved at a distance where this technique is unfeasible. Find that the mass of the stellar halo of this galaxy is ~4e9 Msun, i.e., 3±1% of the total stellar mass of the whole system. This amount of mass in the stellar halo is in agreement with current theoretical expectations for galaxies of this kind.
1510.04809
A new look at lines of sight: using Fourier methods for the wide-angle anisotropic 2-point correlation function
Slepian, Eisenstein
The anisotropic 2PCF of galaxies measures pairwise clustering as a function of the pair separation's angle to the line of sight. The latter is often defined as either the angle bisector of the observer-galaxy-pair triangle or the vector from the observer to the separation midpoint. Show how to accelerate either of these measurements with Fourier Transforms, using a slight generalization of the Yamamoto+2006 estimator in which each member of the pair is used successively as the line of sight. Also present perturbation theory predictions for the generalized estimator including wide-angle corrections.
Friday.
1510.04270
Chandra Measurements of a complete sample of X-ray luminous galaxy clusters: the Luminosity-mass relation
Giles, et al
Statistically complete sample of 34 galaxy clusters in 0.15<z<0.3 observed with Chandra. Present the mass-temperature calibration relation using hydrostatic mass estimates for the most relaxed clusters, and use this relation as a mass proxy for the full cluster sample. Slope of the MT relation follows the self-similar expectation, and is consistent with previously published relations. Investigate the LM relation for the cluster sample, utilising a method to fully account for selection bias. Find that the difference in normalization of the LM relation with and without accounting for selection effects is ~2. For a cluster of luminosity 1e45 erg/s, find that the mass estimated from the LM relation when we account for selection effects is ~40% higher compared to the sample LM relation (not accounting for selection effects.
1510.04287
Testing gravity with $E_G$: mapping theory onto observations
Leonard, Ferreira, Heymans
Present a complete derivation of the observationally motivated definition of the modified gravity statistic E_G. Using this expression, investigate how variations to theory and survey parameters may introduce uncertainty in the GR prediction of E_G. Forecast errors on E_G for measurements using 2 combinations of upcoming surveys, and find that theoretical uncertainties may dominate for a futuristic measurement. Finally, compute predictions of E_G under modifications to GR in the quasi static regime, and comment on the pros and cons of using E_G to test gravity with future surveys.
1510.04307
Dissecting the multiphase circumgalactic medium around three massive lensing galaxies at z =0.4-0.7
Zahedi et al
Present multi-sightline absorption spectroscopy of the inner gaseous halo around 3 lensing galaxies at z=0.4-0.7. Their spectral and photometric properties are characteristic of nearby passive elliptical galaxies with half-light radii of r_e=2.6-8 kpc and estimated total stellar masses of log M*/Ms=10.6-11.2. The lensed QSO sight lines pass through the gaseous halo of the lensing galaxy at projected distances d=3-15 kpc or (1-2) r_e. The absorption-line search reveals a diverse range of cool (T~1e4 K) halo gas properties among the 3 lensing galaxies. Specifically, while the quadruple lens for HE0435-1223 shows no trace of associated Mg II or other ionic absorption features to very sensitive limit in all 4 sightlines, strong MgII absorbers are found along both sightlines at the redshift of the double lens for HE0047-1756, and in one of the two sightlines at the redshift of the lens for HE1104-1805. In addition to Mg II, associated FeII, MgI, and CaII absorption transitions are detected. The absorbers are resolved into 8-15 individual components with a line-of-sight velocity spread of dv~300-600 km/s. The large ionic column densities observed in a few of the components suggest a significant neutral gas fraction comparable to what is expected for Lyman limit or daped Lya absorbers. The majority of the absorbing components exhibit a super solar Fe/Me ratio, whose pattern is remarkably uniform with a scatter of <0.1 dex across the full dv. Given a predominantly old stellar population in these lensing galaxies, argue that the Fe-rich gas (which dominates the total absorption width) originates in the SNe Ia enriched inner regions at radius r~d. The study demonstrates that combining spatially resolved gas kinematics and relative (Fe/Mg) abundance pattern provides a powerful tool to resolve the origin of chemically-enriched cool gas in massive halos.
1510.04388
Formation of ultra-compact blue dwarf galaxies and their evolution into nucleated dwarfs
Bekki
Propose that there is an evolutionary link between UCBDs (ultra-compact blue dwarfs) with active SF and nucleated dwarfs based on the results of numerical simulations of dwarf-dwarf merging. Consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf-dwarf mergers. Find that the remnants of dwarf-dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z~[0.2-1] Zsun). Also find that the remnants of these mergers can have rather high mass-densities (1e4 Msun/pc^3) within the central 10 pc and small half-light radii (40-100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. SF can continue in nuclear gas disks (R<100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after fading of young stars. Discuss these results in the context of the origins of metal-rich ultra-compact dwarfs (UCDs) and SGNs.
Thursday.
1510.03870
The bulge-disk decomposition of AGN host galaxies
Bruce et al
... Find no strong corruption between the point-source component and AGN activity, and that these point-source components are best modeled physically by nuclear starbursts. The analysis of the bulge and disk fractions of these AGN hosts in comparison to a mass-matched control sample reveals a similar morphological evolutionary track for both the active and non-active populations, providing evidence in favor of a model where AGN activity is triggered by secular processes.
1510.03962
Cosmic shear results from the deep lens survey - II: full cosmological parameter constraints from tomography
Jee, Tyson, Hilbert, Schneider, Schmidt, Witman
Present a tomographic cosmic shear study from DLS, which, providing a limiting magnitude r_lm~27 (5 sigma), is designed as a pre-cursor LSST survey with an emphasis on depth. Using 5 tomographic redshift bins, study their auto-and cross-correlations to constrain cosmo parameters. Use a luminosity-dependent nonlinear model to account for the astrophysical systematics originating form IA of galaxy shapes. Find that the cosmo leverage of the DLS is among the highest among existing >10 sq.deg comic shear surveys. Combining the DLS tomography with the 9yr results of the WMAP9 gives Omega_m=0.293±0.014, sigma_8=0.833±0.018, H0=68.6±1.3 km/s/Mpc, and Ombea_b=0.0475±0.0012 for LCDM, reducing the uncertainties of the WMAP9-only constraints by ~50%. When flatness is not assumed for LCDM, obtain the curvature constraint Omega_k=-0.010±0.014 from the DLS+WMAP9 combination, which however is not well constrained when WMAP9 is used alone. The DE EoS parameter w is highly constrained when BAO data are added, yielding w=-1.02±0.10 with the DLS+@MAP9+BAO joint probe. The addition of SN constraints further tightens the parameter to w=-1.03±0.03. The joint constraints are fully consistent with the final Planck results and also the predictions of a LCDM universe.
Wednesday.
1510.03426
Dynamics of stream-subhalo interactions
Sanders, Bovy, Erkal
Develop a formalism for modeling the impact of DM subhalos on cold thin streams. The formalism models the formation of a gap in a stream in angle-frequency space and is able to handle general stream and impact geometry. Analyse an N-body simulation of a cold stream formed from a progenitor on an eccentric orbit in an axisymmetric potential, which is perturbed by a direct impact from a 1e8 Msun sub halo, and produce a complete generative model of the perturbed stream that matches the simulation well at a range of times. Show how the results in angle-frequency space can be related to physical properties of the gaps and that previous results for more constrained simulations are recovered. Demonstrate how the results are dependent upon the mass of the sub halo and the location of the impact along the stream. Find that gaps formed far downstream grow more rapidly than those closer to the progenitor due to the more ordered nature of the stream members far from the progenitor. Additionally, show that the minimum gap density plateaus in time at a value that decreases with increasing sub halo mass.
1510.03431
Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation
Neyrinck
Discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest-possible fully 3-D halo collapse in the 'origami approximation,' in which voids are irrotational, and the DM sheet out of which DM structures form is allowed to fold in position-velocity phase space, but not stretch (i.e., it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only 3 other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighboring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.
1510.03486
Mapping the dark matter distribution of the "Toothbrush" cluster RX J0603.3+4214 with Hubble Space Telescope and Subaru Weak-lensing
Jee, Dawson, Stroe, Wittman,et al
The galaxy cluster at z=0.225 is one of the rarest clusters boasting an extremely large (~2Mpc) radio-relic. Because of the remarkable morphology of the relic, the cluster is nicknamed "Toothbrush Cluster". Although the cluster's underlying mass distribution is one of the critical pieces of information needed to reconstruct the merger scenario responsible for the puzzling radio-relic morphology, its proximity to the Galactic plane b~10 deg has imposed significant observational challenges. Present a high-resolution WL study of the cluster with Subaru/Suprime Cam and HST imaging data. The mass reconstruction reveals that the cluster is comprised of complicated DM substructures closely tracing the galaxy distribution, however in contrast with the relatively simple binary X-ray morphology. Nevertheless, find that the cluster mass is still dominated by the two most massive clumps aligned NS with a ~3:1 mass ratio (M200=6.29e14 Msun and 1.98e14 Msun for N/S clumps, respectively). The southern mass peak is ~2' offset toward the south with respect to the corresponding X-ray peak, which has a "bullet"-like morphology pointing south. Comparison of the current WL result with the X-ray, galaxy, and radio-relic suggests that perhaps the dominant mechanism responsible for the observed relic may be a high-speed collision of the two most massive subclusters, although the peculiarity of the morphology necessitates involvement of additional sub-clusters. Careful numerical simulations should follow in order to obtain more complete understanding of the merger scenario utilizing all existing observations.
1510.03489
The rotation of galaxy clusters
Tovmassian
Propose a method for detection of the galaxy cluster rotation based on the study of distribution of member galaxies with velocities higher and lower of the cluster mean velocity over the cluster image. The search for rotation is made for flat cluster with a/b>1.8and BMI type [?] clusters which are expected to be rotating. For comparison, studied also round clusters and clusters of NBMI type, the second by brightness galaxy in which does not differ significantly from the cluster cD galaxy. 17/65 clusters are found to be rotating. Found that the detection rate is sufficiently high for flat clusters, over 60%, and clusters of BMI type with dominant cD galaxy, ~35%. The obtained results show that clusters were formed from the huge primordial gas clouds and preserved the rotation of the primordial clouds, unless they did not have merging with other clusters and groups of galaxies, in the result of chic the rotation has been prevented.
1510.03554
Streaming velocities and the baryon-acoustic oscillation scale
Blazek, McEwen, Hirata
At the epoch of decoupling, cosmic baryons had supersonic velocities relative to the DM that were coherent on large scales. These velocities subsequently slow the growth of small-scale structures and, via feedback processes, can influence the formation of larger galaxies. Examine the effect of streaming velocities on the galaxy correlation function, including all leading-order contributions for the first time. Find that the impact on the BAO peak is dramatically enhanced (by a factor of ~5) over the results of previous investigations, with the primary new effect due to advection: if a galaxy retains memory of the primordial streaming velocity, it does so at its Lagrangian, rather than Eulerian, position. Since correlations in the streaming velocity change rapidly at the BAO scale, this advection term can cause a significant shift in the observed BAO position. If streaming velocities impact tracer density at the 1% level, compared to the linear bias, the recovered BAO scale is shifted by approximately 0.5%. This new effect greatly increases the importance of including streaming velocities in the analysis of upcoming BAO measurements and opens a new window to the astrophysics of galaxy formation.
Tuesday.
1510.02796
Advanced data visualization in astrophysics: the X3D pathway
Vogt, et al
Introduce the concept of the "X3D pathway" as a mean of simplifying and easing the access to data visualization and publication via 3D diagrams. Argue that X3D standard is an ideal vector for sharing multi-dimensional datasets, as it provides direct access to a range of different data visualization techniques, is fully-open source, and is a well defined ISO standard. Is compatible wit ha range of open-source software already in use by the community. Detailed set of practical astrophysical examples given.
1510.02985
Shocks in the early universe
Pen, Turok
A consequence of the usually assumed ICs for cosmological perturbations: a scale invariant spectrum of Gaussian, linear, adiabatic, scalar, growing mode perturbations not only creates acoustic oscillations, of the kind observed in great detail on large scales today, it also leads to the production of shock waves in the radiation fluid of the very early universe. At very early epochs, 1 GeV<T<1e7 GeV, assuming standard model physics, viscous damping is negligible and NL effects turn acoustic waves into shocks after ~1e4 oscillations. The resulting scale-invariant network of shocks provides a natural mechanism for creating significant departures from local thermal equilibrium as well as primordial vorticity and gravitational waves.
1510.03171
Model-independent characterization of strong gravitational lenses
Wagner, Bartelmann
Develop a new approach to extracting model-independent information from observations of strong gravitational lenses. The approach is based on the generic properties of images near the fold and cusp catastrophes in caustics and critical curves. Observables used are the relative image positions, the magnification ratios and ellipticities of extended images, and time delays between images with temporally varying intensity. Show how these observables constrain derivatives and ratios of derivatives of the lensing potential near a critical curve. Based on these measured properties of the lensing potential, classes of parametric lens models can then easily be restricted to such parameter values compatible with the measurements, thus allowing fast scans of large varieties of models. Applying the approach to a representative galaxy and a galaxy cluster lens, show which model-independent information can be extracted in those cases and demonstrate that the parameters obtained by the approach for known parametric lens models agree well with those found by detailed model fitting.
Monday.
1510.02471
Accretion-induced variability links young stellar objects, white dwarfs, and black holes
Scaringi, et al
The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretion mass, size or type. Examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting WDs and young stellar objects (YSOs). Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (mrs-flux relation) and obeys the same quantitative scaling relation as stellar-mass BHs and AGN. Also show that the most important parameter in this scaling relation is the physical size of the accreting objects. This establishes the universality of accretion physics from protostars still in the star-forming process to the SMBHs at the centers of galaxies.
1510.02475
Unveiling a rich system of faint dwarf galaxies in the Next Generation Fornax Survey
Munoz, et al
Report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded u, g, and i-band image obtained with the DECam wide-field camera mounted o the 4-m Blanco telescope at CTIO as part of the NGFS. The new dwarf galaxies have quasi-exponential light profiles, effective radii 0.1<re<2.8 kpc and average effective surface brightness values 22.0<mu_i<28.0 mag arcs^-2. Confirm the existence of ultra-diffuse galaxies (UDGs) in the Fornax core regions that resemble counterparts recently discovered in the Virgo and Coma galaxy clusters. Also find extremely low surface brightness NGFS dwarfs, which are several magnitudes fainter than the classical UDGs. The faintest dwarf candidate in the NGFS sample has an absolute magnitude of M_i=-8.0mag. The nucleation fraction of the NGFS dwarf galaxy sample appears to decrease as a function of their total luminosity, reaching from a nucleation fraction of >75% at luminosities brighter than M_i~-15.0 mag to 0% at luminosities fainter than M_i~-10.0 mag. The 2PCF analysis of the NGFS dwarf sample shows an excess on length scales below ~100 kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.
1510.02617
Intrinsic alignment contamination to CMB lensing-galaxy weak lensing correlations from tidal torquing
Larsen, Challinor
Correlations of galaxy ellipticities with large-scale structure, due to galactic tidal interactions, provide a potentially significant contaminant to measurements of cosmic shear. However, these intrinsics alignments are still poorly understood for galaxies at the redshifts typically used in cosmic shear analyses. For spiral galaxies, it is thought that tidal torquing is significant in determining alignments resulting in zero correlation between the intrinsic ellipticity and the gravitational potential in linear theory. Here, calculate the leading-order correction to this result in the tidal-torque model from non-linear evolution, using second-order perturbation theory, and relate this to the contamination from intrinsic alignments to the recently-measured cross-correlation between galaxy ellipticities and the CMB lensing potential. Find that the angular cross-correlation from tidal torquing has a very similar scale dependence as in the linear alignment model (believed to be appropriate for elliptical galaxies), but the opposite sign and so increases the observable correlation between CMB lensing and spiral galaxies. The amplitude of the cross-correlation is predicted to depend strongly on the formation redshift, being smaller for galaxies that formed at higher redshift when the bispectrum of the gravitational potential was smaller. Finally, make simple forecasts for constrains on IAs from the correlation of forthcoming cosmic shear measurements with current CMB lensing measurements.
Friday.
1510.02097
Mass measurements of isolated objects from spaced-based microlensing
Zhu, ... Gould, et al
Report on the mass and distance measurements of 2 single-lens events from 2015 Spitzer microlensing campaign. With both finite-source effect and microlens parallax measurements, find that the lens of OGLE-2015-BLG1268 is a 47±7 M_J brown dwarf at 5.4±1.0 kpc, and that the lens of -0763 is a 0.50±0.04 Msun star at 6.9±1.0 kpc. Show that the probability to definitively measure the mass of isolated micro lenses, including isolated stellar mass BHs and free floating planets, is dramatically increased once simultaneous ground- and space-based observations are conducted.
1510.02101
Detectability of local group dwarf galaxy analogues at high redshifts
Patej, Loeb
The dwarf galaxies of the Local Group are believed to be similar to the most abundant galaxies during the epoch of reionization (z>6). As a result of their proximity, there is a wealth of information that can be obtained about these galaxies; however, due to their low surface brightnesses, detecting their progenitors at high redshifts is challenging. Compare the physical properties of these dwarf galaxies to those of galaxies detected at high redshifts using HST and Spitzer observations and consider the promise of the upcoming JWST on the prospects for detecting high redshift analogues of these galaxies.
1510.02106
The 3D-HST survey: Hubble Space Telescope WFC3/G141 grism spectra, redshifts, and emission line measurements from $/sim 100,000$ galaxies
Momcheva, Bramer, van Dokkum, ... et al
Present reduced data and data products from the 3D-HST survey, a 248-orbit HST Treasury program. The survey obtained WFC3 G141 grism spectrosocopy in four of the five CANDELS fields: AEGIS, COSMOS, GOODS-S, and UDS, along with WFC3 H_140 imaging, parallel ACS G800L spectroscopy, and parallel I_814 imaging. A previous paper (Skelton+ 2014) presented photometric catalogs in these 4 fields and in GOODS-N, the fifth CANDELS field. Describe and present the WFC3 G141 spectroscopic data, again augmented with data from GO-1600 in GOODS-N. The data analysis is complicated by the fact that no slits are used: all objects in the WFC3 field are dispersed, and many spectra overlap. Developed software to automatically and optimally extract interlaced 2d and 1d spectra for all objects in the Skelton+2014 photometric catalogs. The 2d spectra and the multi-band photometry were fit simultaneously to determine redshifts and emission line strengths, making the morphology of the galaxies explicitly into account. The resulting catalog has 98,663 measured redshifts and line strengths down to JH_IR<26 and 22,548 with JH_IR<24, where continuum emission is comfortably detected. Of this sample 5,459 galaxies are at z>1.5 and 9.621 are at 0.7<z<1.5, where Ha falls in the G141 wavelength coverage. Based on comparisons with ground-based spec-z's, and on analyses of paired galaxies and repeat observations, the typical redshift error for JH_IR<24 galaxies in the catalog is sigma_z~0.003(1+z), i.e., one native WFPC3 pixel. The 3sigma limit for emission line fluxes of point sources is 1.5e-17 erg/s/cm2. Show various representations of the full dataset, as well as individual examples that highlight the range of spectra that is found in the survey.
1510.02296
Detailed modeling of the 21-cm forest
Semelin
The 21-cm forest is a promising probe of the Epoch of Reionization. The local state of the IGM is encoded in the spectrum of a background source (radio-loud quasars or gamma ray burst afterglow) by absorption at the local 21-cm wavelength, resulting in a continuous and fluctuating absorption level. Small-scale structures (filaments and minihaloes) in the IGM are responsible for the strongest absorption features. The absorption can also be modulated on large scales by inhomogeneous heating and Wouthuysen-Field coupling. Present the results from a simulation that attempts to preserve the cosmological environment while resolving some of the small-scale structures (a few kpc resolution in a 50 Mpc/h box). The simulation couples the dynamics and the ionizing radiative transfer and includes X-ray and Lyman lines radiative transfer for a detailed physical modeling. As a result, find that soft X-ray self-sheidling, Lyman-alpha self-sheilding and shock heating all have an impact on the predicted values of the 21-cm optical depth of moderately overdense structures like filaments. A correct treatment of the peculiar velocities is also critical. Modeling these processes seems necessary for accurate predictions and can be done only at high enough resolution. As a result, based on the fiducial model, estimate that LOFAR should be abe to detect a few (strong) absorption features in a frequency range of a few tens of MHz for a 20 mJy source located at z=10, while the SKA would extract a large fraction of the absorption information for the same source.
Thursday.
1510.01733
Detecting direct collapse black holes: making the case for CR7
Agarwal, Johnson, Zackrisson, Labbe, van den Bosch, Natarajan, Khochfar
Propose that one of the sources in the recently detected system CR7 by Sobral+2015 through spectro-photometric measurements at z=6.6 harbors a direct collapse black hole (DCBH). Argue that the LW radiation field required for direct collapse in source A is provided by sources B and C. By tracing the LW production history and SFR over cosmic time for the halo hosting CR7 in a LCDM universe, demonstrate that a DCBH could have formed at z~20. The spectrum of source A is well fit by nebular emission from primordial gas around a BH with MBH~4.4e6 Msun accreting at a 40% of the Eddington rate, which strongly supports the interpretation of the data. Combining these lines of evidence, argue that CR7 might well be the first DCBH candidate.
1510.01737
Quantifying the color-dependent stochasticity of large-scale structure
Patej, Eisenstein
Address the question of weather massive red and blue galaxies trace the same LSS at z~0.6 using the CMASS sample of galaxies from SDSS DR12. After splitting the catalog into subsamples of red ad blue galaxies using a simple color cut, measure the clustering of both subsamples and construct the correlation coefficient, r, using two statistics. The correlation coefficient quantifies the stochasticity between the two subsamples, which is examined over intermediate scales (20<R<100 Mpc/h). Find that on these intermediate scales, the correlation coefficient is consistent with 1; in particular, find r>0.95 taking into account both statistics and r>0.974 using the favored statistic.
1510.01740
Large covariance matrices: smooth models from the 2-point correlation function
O'Connell, Eisenstein, Vargas, Ho, Padmanabhan
Introduce a new method for estimating the covariance matrix for the galaxy correlation function in surveys of LSS. The method combines simple theoretical results with a realistic characterization of the survey to dramatically reduce noise in the covariance matrix. For example, an investment of only ~1000 CPU hours can produce a model covariance matrix with noise levels that would otherwise require ~35000 mocks. Non-Gaussian contributions to the model are calibrated against mock catalogs, after which the model covariance is found to be in impressive agreement with the mock covariance matrix. Since calibration of this method requires fewer mocks than brute force approaches, believe that it could dramatically reduce the number of mocks required to analyse future surveys.
1510.01745
Detection of enhancement in Number densities of background galaxies due to magnification by massive galaxy clusters
Chiu, Dietrich, Mohr, Applegate, ... et al
Present a detection of the enhancement of the number densities of background galaxies induced from lensing magnification and use it to test the SZE inferred masses in a sample of 19 galaxy clusters with median redshift z~0.42 selected from the SPT-SZ survey. Two background galaxy populations are selected for tis study through their photometric colors; they have median redshifts z_median~0.9 (low-z background) and z_median~1.8 (high-z background). Stacking these populations, detect the magnification bias effect at 3.3 sigma and 1.3 sigma for the low- and high-z backgrounds, respectively. Fit NFW models simultaneously to all observed magnification bias profiles to estimate the multiplicative factor eta that describes the ratio of the weak lensening mass to the mass inferred from the SZE observable-mass relation. Further quantify systematic uncertainties in eta resulting from the photometric noise and bias, the cluster galaxy contamination and the estimations of the background properties. The resulting eta for the combined background populations with 1 sigma uncertainties is 0.83±0.24 (stat)±0.074(sys), indicating good consistency between the lensing and the SZE-inferred masses. Use the best-fit eta to predict the weak lensing shear profiles and compare these predictions with observations, showing agreement between the magnification and shear mass constraints. This work demonstrate the promise of using the magnification as a complementary method to estimate cluster masses in large surveys.
1510.01961
The galaxy cluster concentration-mass scaling relation
Groener, Goldberg, Sereno
Scaling relation of clusters make clusters important cosmo probes of structure formation. In this work, present a comprehensive study of the relation between two profile observables, c_vir and M_vir. Collect the largest known sample of measurements from lituerature which make use of one or more or the following reconstruction methods: WL, SL, WL+SL, Caustic method (CM), LoS velocity dispersion (LOSVD), and X-ray. Find that the c-M relation is highly variable depending upon the reconstruction technique used. Also find concentrations derived from DM only sims (at approximately Mvir~1e14 Msun) to be inconsistent with the WL and WL+SL relations at the 1 sigma level, even after the projection of triaxial haloes is taken into account. However, to fully determine consistency between simulations and observations, a volume-limited sample of clusters is required, as selection effects become increasingly more important in answering this. Also find evidence for a steeper WL+SL relation as compared to WL alone, a result which could perhaps be caused by the varying shape of cluster isodensities, though most likely reflects differences in selection effects caused by these two techniques. Lastly, compare concentration and mass measurements of individual clusters made using more than one technique, highlighting the magnitude of the potential bias which could exist in such observational samples.
Wednesday.
1510.00718
RHAPSODY-G simulations II - Baryonic growth and metal enrichment in massive galaxy clusters
Martizzi, Hahn, Wu, Evard, Teyssier, Wechsler
Study the evolution of the stellar component and the metallicity of both the ICM and of stars in massive (Mvir~6e14 Msun) simulated galaxy clusters for the RHAPSODY-G suite in detail and compare them to observational results. The simulations were performed with the AMR code RAMSES and include the effect of AGN feedback at the sub-grid level. AGN feedback is required to produce realistic galaxy and cluster properties and plays a role in mixing material in the central regions and regulating SF in the central galaxy. In the low resolution runs with fiducial stellar yields, find that stellar and ICM metallicities are a factor of two lower than in observations, however they tend to converge to the observed values ~0.3 Zsun as the resolution is increased. Find that cool core clusters exhibit steeper metallicity gradients than non-cool core clusters, in qualitative agreement with observations. Verify that the ICM metallicities measured in the simulation can be explained by a simple "regulator" model in which the metallicity is set by a balance of stellar yield and gas accretion. The analytical model also predicts that the metallicities are proportional to the stellar yield. The realists thus indicate that a combination of higher resolution and higher metal yield in AMR simulation would allow the metallicity of simulated clusters to match observed values. Comparison to recent literature highlights that results concerning the metallicity of clusters and cluster galaxies might depend severely on the scheme chosen to solve the hydrodynamics.
NSF report
Impact of declining proposal success rates on scientific productivity
Cushman, Hoeksema, Kouveliotou, Lowenthal, Peterson, Stassun, von Hippel
Over the last decade proposal success rates in the fundamental sciences have dropped significantly. Astronomy and related fields funded by NASA and NSF are no exception. Data across agencies show that this is not principally the result of a decline in proposal merit (the proportion of proposals receiving high ranking is largely unchanged), nor of a shift in proposer demographics (seniority, gender, and institutional affiliation have all remained unchanged), nor of an increase (beyond inflation) in the average requested funding per proposal, nor of an increase in the number of proposals per investigator in any one year. Rather, the statistics are consistent with a scenario in which agency budgets for competed research are flat or decreasing in inflation-adjusted dollars, the overall population of investigators has grown, and a larger proportion of these investigators are resubmitting meritorious but unfunded proposals, likely in response to the decreased success rates. Recent research on the time cost of proposal writing versus that of producing publishable results show that a funding rate of ~6% represents the tipping point below which proposal writing prevents more papers than grants produce. This is close to the success rate experienced by new investigators against an overall average funding rate of 20%, due to treating bias against PIs without recent funding. At this 20% average selection threshold, the opportunity cost is still significant (2-3 papers per successful proposal) even for established researchers. Unfortunately, even an investigator submitting a proposal rated "very good" can expect, with three attempts, only a ~58% chance of funding. A 20% overall funding rate is thus unhealthy for the field, since it precludes stable, long-term support for students, postdocs, or researchers on soft money, and it preferentially discourages young researchers from remaining in the field. Yet, as demonstrated below, we are currently in exactly this situation. Conclude that an aspirational proposal success rate of 30-35% would still provide a healthily competitive environment for researchers, would more fully utilize the scientific capacity of the community's facilities and missions, and provide relief to the funding agencies who face the logistics of alarming volumes of proposals.
1510.01321
Interstellar extinction curve variations toward the inner Milky Way: a challenge to observation cosmology
Nataf, et al
Investigate interstellar extinction curve variations toward ~4 deg2 of the inner MW in VIJKs photometry from the OGLE-III and VVVs surveys, with supporting evidence from diffuse interstellar bands and F435W,F625W photometry. Obtain independent measurements toward ~2000 sightless of A_I, E(V-I), E(I-J), and E(J-Ks), with median precision and accuracy of 2%. Find that the variations in the extinction ratios A_I/E(V-I), E(I-J)/E(V-I) and E(J-Ks)/E(V-I) are large (exceeding 20%), significant, and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how R_V is varied. Furthermore, demonstrate the variations in the shape of the extinction curve has at least 2 degrees of freedom, and not one (e.g., R_V), which is confirmed with a principal component analysis. Derive a median value of <A_V/A_Ks>=13.44, which is ~60% higher than the "standard" value. Show that the Wesenheit magnitude W_I=I-1.61(I-J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, argue that systematic errors in the distance ladder from studies of type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ~100%, and lack sensitivity to extinction curve variations.
1510.01326
Is Draco II one of the faintest dwarf galaxies? First evidence from Keck/DEIMOS spectroscopy
Martin, Geha, et al
Present the first spectroscopic analysis of the faint and compact stellar system Draco II (Dra II, M_V=-2.9±0.8, r_h=19±7 pc), recently discovered in the Pan-STARRS1 3pi survey. The observations, conducted with DEIMOS on the Kick II telescope, reveal a cold velocity peak with 9 member stars at a systemic heliocentric velocity <v_r>=-347.6±1.7 km/s, thereby confirming Dra II is a satellite of the MW. Infer a marginally resolved velocity dispersion with sigma_vr=2.9±2.1 km/s which hints that this system is kinematically hotter than implied from its baryonic mass alone and potential y dark-matter-dominated (log10(M_1/2)=5.5±0.5 and log10((M/L)_(1/2))=2.7±0.6, in Solar units). Furthermore, very weak Calcium triplet lines in the spectra of the high S/N member stars indicate that its metallicity is likely lower than that of the globular cluster NGC 2419 ([Fe/H]<-2.1). Finally, variations in the line strengths of two stars with similar colors and magnitudes suggest the presence of a metallicity spread in Dra II. Taken together, these 3 pieces of evidence lead us to conclude that Dra II is likely to be among the faintest, most compact, and closest dwarf galaxies. However, emphasize that this conclusion needs to be strengthened through a more systematic spectroscopic campaign.
1510.01586
On the segregation of dark matter substructure
van den Bosch, Jiang, Campbell, Behroozi
Present the first comprehensive analysis of the segregation of DM sub haloes in their host halos. Using numerical sims, examine the segregation of 12 different sub halo properties with respect to both orbital energy and halo-centric radius (in real space as well as in projection). Sub haloes are strongly segregated by accretion redshift, which is an outcome of the inside-out assembly of their host halos. Since sub haloes that were accreted earlier have experienced more tidal stripping, sub haloes that have lost a larger fraction of their mass at infall are on more bound orbits. Sub haloes are also strongly segregated in their masses and maximum circular velocities at accretion. Demonstrate that part of this segregation is already imprinted in the infall conditions. For massive sub haloes it is subsequently boosted by dynamical friction, but only during their first radial orbit. The impact of these two effects is counterbalanced, though, by the fact that sub haloes with larger accretion masses are accreted later. Because of tidal stripping, sub haloes reveal little to no segregation by present-day mass or maximum circular velocity, while the corresponding torques cause subhalos on more bound orbits to have smaller spin. There is a weak tendency for sub haloes that formed earlier to be segregated towards the center of their host halo, which is an indirect consequence of the fact hat (sub)halo formation time is correlated with other, strongly segregated properties. Discuss the implications of the results for the segregation of satellite galaxies in galaxy groups and clusters.
