V. Vikram

The massive end of the luminosity and stellar mass functions: dependence on the fit to the light profile

In addition to the large systematic differences arising from assumptions about the stellar mass-to-light ratio, the massive end of the stellar mass function is rather sensitive to how one fits the light profiles of the most luminous galaxies. We quantify this by comparing the luminosity and stellar mass functions based on SDSS cmodel magnitudes, and PyMorph single-Sersic and Sersic-Exponential fits to the surface brightness profiles of galaxies in the SDSS. The PyMorph fits return more light, so that the predicted masses are larger than when cmodel magnitudes are used. As a result, the total stellar mass density at z~0.1 is about 1.2x larger than in our previous analysis of the SDSS. The differences are most pronounced at the massive end, where the measured number density of objects having M* > 6 x 10^{11} Msun is ~5x larger. Alternatively, at number densities of 10^{-6} Mpc^{-3}, the limiting stellar mass is 2x larger. The differences with respect to fits by other authors, typically based on Petrosian-like magnitudes, are even more dramatic, although some of these differences are due to sky-subtraction problems, and are sometimes masked by large differences in the assumed

Size evolution of spheroids in a hierarchical Universe

M_*/L

Mass and galaxy distributions of four massive galaxy clusters from Dark Energy Survey Science Verification data

(even after scaling to the same IMF). Our results impact studies of the growth and assembly of stellar mass in galaxies, and of the relation between stellar and halo mass, so we provide simple analytic fits to these new luminosity and stellar mass functions and quantify how they depend on morphology, as well as the binned counts in electronic format.

Astrophysical Tests of Modified Gravity: the Morphology and Kinematics of Dwarf Galaxies

Unveiling the structural evolution of spheroids, and in particular the origin of the tight size- stellar mass relation, has become one of the hottest topics in cosmology in the last years and it is still largely debated. To this purpose, we present and discuss basic predictions of an updated version of the latest release of the Munich semi-analytic hierarchical galaxy formation model that grows bulges via mergers and disc instabilities. We find that while spheroids below a characteristic mass Ms ∼ 10 11 Mgrow their sizes via a mixture of disc instability and mergers, galaxies above it mainly evolve via dry mergers. Including gas dissipation in major mergers efficiently shrinks galaxies, especially those with final mass Ms 10 11 Mthat are the most gas-rich, improving the match with different observables. We find that the predicted scatter in sizes at fixed stellar mass is still larger than the observed one by up to 40 per cent. Spheroids are, on average, more compact at higher redshifts at fixed stellar mass, and at fixed redshift and stellar mass larger galaxies tend to be more star forming. More specifically, while for bulge-dominated galaxies the model envisages a nearly mass-independent decrease in sizes, the predicted size evolution for intermediate-mass galaxies is more complex. The z = 2 progenitors of massive galaxies with Mstar ∼ (1-2) × 10 11 Mand B/T > 0. 7a tz = 0a re found to be mostly disc-dominated galaxies with a median B/T ∼ 0.3, with only ∼20 per cent remaining bulge-dominated. The model also predicts that central spheroids living in more massive haloes tend to have larger sizes at fixed stellar mass. Including host halo mass dependence in computing velocity dispersions allows the model to properly reproduce the correlations with stellar mass. We also discuss the Fundamental Plane, the correlations with galaxy age, the structural properties of pseudo-bulges and the correlations with central black holes.

Weak lensing analysis of RXC J2248.7−4431

We measure the weak-lensing masses and galaxy distributions of four massive galaxy clusters observed during the Science Verification phase of the Dark Energy Survey. This pathfinder study is meant to 1) validate the DECam imager for the task of measuring weak-lensing shapes, and 2) utilize DECams large field of view to map out the clusters and their environments over 90 arcmin. We conduct a series of rigorous tests on astrometry, photometry, image quality, PSF modeling, and shear measurement accuracy to single out flaws in the data and also to identify the optimal data processing steps and parameters. We find Science Verification data from DECam to be suitable for the lensing analysis described in this paper. The PSF is generally well-behaved, but the modeling is rendered difficult by a flux-dependent PSF width and ellipticity. We employ photometric redshifts to distinguish between foreground and background galaxies, and a red-sequence cluster finder to provide cluster richness estimates and cluster-galaxy distributions. By fitting NFW profiles to the clusters in this study, we determine weak-lensing masses that are in agreement with previous work. For Abell 3261, we provide the first estimates of redshift, weak-lensing mass, and richness. In addition, the cluster-galaxy distributions indicate the presence of filamentary structures attached to 1E 0657-56 and RXC J2248.7-4431, stretching out as far as 1 degree (approximately 20 Mpc), showcasing the potential of DECam and DES for detailed studies of degree-scale features on the sky.

On the Intermediate-redshift Central Stellar Mass-Halo Mass Relation, and Implications for the Evolution of the Most Massive Galaxies Since z ~ 1

This paper is the third in a series on tests of gravity using observations of stars and nearby dwarf galaxies. We carry out four distinct tests using published data on the kinematics and morphology of dwarf galaxies, motivated by the theoretical work of Hui et al. (2009) and Jain & Vanderplas (2011). In a wide class of gravity theories a scalar field couples to matter and provides an attractive fifth force. Due to their different self-gravity, stars and gas may respond differently to the scalar force leading to several observable deviations from standard gravity. HI gas, red giant stars and main sequence stars can be displaced relative to each other, and the stellar disk can display warps or asymmetric rotation curves aligned with external potential gradients. To distinguish the effects of modified gravity from standard astrophysical phenomena, we use a control sample of galaxies that are expected to be screened from the fifth force. In all cases we find no significant deviation from the null hypothesis of general relativity. The limits obtained from dwarf galaxies are not yet competitive with the limits from cepheids obtained in our first paper, but can be improved to probe regions of parameter space that are inaccessible using other tests. We discuss how our methodology can be applied to new radio and optical observations of nearby galaxies.

Characterization and correction of charge-induced pixel shifts in DECam

ABSTRACT We present a weak lensing analysis of the cluster of galaxies RXC J2248.7-4431,a mas-sive system at z = 0.3475 with prominent strong lensing features covered by the Clus-ter Lensing And Supernova survey with Hubble (CLASH). Based on UBVRIZ imagingfrom the Wide-Field Imager camera at the MPG/ESO 2.2-m telescope, we measurephotometric redshifts and shapes of background galaxies. The cluster is detected asa mass peak at 5σ significance. Its density can be parametrized as a Navarro-Frenk-White (NFW) profile with two free parameters, the mass M 200m = 33.1 +9.6−6.8 ×10 14 M⊙and concentration c 200m = 2.6 +1.5−1.0 . We discover a second cluster inside the field of viewat a photometric redshift of z ≈0.6, with an NFW mass of M 200m = 4.0 +3.7−2.6 ×10 14 M⊙.Key words: gravitational lensing: strong – gravitational lensing: weak – galaxies:clusters: individual: RXC J2248.7–4431 – dark matter 1 INTRODUCTIONClusters of galaxies, such as RXC J2248.7-4431 (cf. Fig. 1)studied in this work, are the most massive gravitationallybound objects that have formed in the Universe to date.What makes them interesting for cosmology is that theylie at an intersection of the two potentially most importantunresolved questions: their mass content is dominated bydark matter - and their formation and evolution is stronglyinfluenced by the interplay of matter density and dark en-ergy. For this reason, studying clusters of galaxies is also apowerful probe of cosmological parameters and models (e.g.Wang & Steinhardt 1998; Holder et al. 2001; Weller et al.2002).Perhaps the most important property of a cluster ofgalaxies with respect to cosmology is its virial mass, whichcan be determined in several different ways. The num-ber and the velocity dispersion of cluster member galax-ies are related to the total mass of the system. Onecan use larger fractions of the overall mass as a proxyby observing the hot intracluster gas, which emits X-rayradiation (e.g. B¨ohringer et al. 2004; Sahlen et al. 2009;Piffaretti et al. 2011) and changes the cosmic microwavebackground spectrum due to inverse Compton scattering(Sunyaev-Zel’dovich, SZ, effect; cf. Sunyaev & Zel’dovich

Astrophysical tests of gravity: a screening map of the nearby universe

The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z ~ 1 for stellar masses M_(star)≳2 × 10^(11) M_☉. Specifically, we find significant evidence for a high-mass end slope of β ≳ 0.35-0.70 instead of the usual β ≾ 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (≾ 0.15 dex) in stellar mass at fixed halo mass, in the redshift range z 3 × 10^(11) M_☉, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z ~ 1.

The high mass end of the stellar mass function: Dependence on stellar population models and agreement between fits to the light profile

Interaction of charges in CCDs with the already accumulated charge distribution causes both a flux dependence of the point-spread function (an increase of observed size with flux, also known as the brighter/fatter effect) and pixel-to-pixel correlations of the {Poissonian} noise in flat fields. We describe these effects in the Dark Energy Camera (DECam) with charge dependent shifts of effective pixel borders, i.e. the Antilogus et al. (2014) model, which we fit to measurements of flat-field {Poissonian} noise correlations. The latter fall off approximately as a power-law r−2.5 with pixel separation r, are isotropic except for an asymmetry in the direct neighbors along rows and columns, are stable in time, and are weakly dependent on wavelength. They show variations from chip to chip at the 20% level that correlate with the silicon resistivity. The charge shifts predicted by the model cause biased shape measurements, primarily due to their effect on bright stars, at levels exceeding weak lensing science requirements. We measure the flux dependence of star images and show that the effect can be mitigated by applying the reverse charge shifts at the pixel level during image processing. Differences in stellar size, however, remain significant due to residuals at larger distance from the centroid.

The massive end of the luminosity and stellar mass functions and clustering from CMASS to SDSS: evidence for and against passive evolution

Astrophysical tests of modified gravity theories in the nearby universe have been emphasized recently by Hui 2009 and Jain 2011. A key element of such tests is the screening mechanism whereby general relativity is restored in massive halos or high density environments like the Milky Way. In chameleon theories of gravity, including all f(R) models, field dwarf galaxies may be unscreened and therefore feel an extra force, as opposed to screened galaxies. The first step to study differences between screened and unscreened galaxies is to create a 3D screening map. We use N-body simulations to test and calibrate simple approximations to determine the level of screening in galaxy catalogs. Sources of systematic errors in the screening map due to observational inaccuracies are modeled and their contamination is estimated. We then apply our methods to create a map out to 200 Mpc in the Sloan Digital Sky Survey footprint using data from the Sloan survey and other sources. In two companion papers this map will be used to carry out new tests of gravity using distance indicators and the disks of dwarf galaxies. We also make our screening map publicly available.