An Application of Multi-band Forced Photometry to One Square Degree of SERVS: Accurate Photometric Redshifts and Implications for Future Science

We apply The Tractor image modeling code to improve upon existing multi-band photometry for the Spitzer Extragalactic Representative Volume Survey (SERVS). SERVS consists of post-cryogenic Spitzer observations at 3.6 and 4.5 micron over five well-studied deep fields spanning 18 square degrees. In concert with data from ground-based near-infrared (NIR) and optical surveys, SERVS aims to provide a census of the properties of massive galaxies out to z ~ 5. To accomplish this, we are using The Tractor to perform "forced photometry." This technique employs prior measurements of source positions and surface brightness profiles from a high-resolution fiducial band from the VISTA Deep Extragalactic Observations (VIDEO) survey to model and fit the fluxes at lower-resolution bands. We discuss our implementation of The Tractor over a square degree test region within the XMM-LSS field with deep imaging in 12 NIR/optical bands. Our new multi-band source catalogs offer a number of advantages over traditional position-matched catalogs, including 1) consistent source cross-identification between bands, 2) de-blending of sources that are clearly resolved in the fiducial band but blended in the lower-resolution SERVS data, 3) a higher source detection fraction in each band, 4) a larger number of candidate galaxies in the redshift range 5 < z < 6, and 5) a statistically significant improvement in the photometric redshift accuracy as evidenced by the significant decrease in the fraction of outliers compared to spectroscopic redshifts. Thus, forced photometry using The Tractor offers a means of improving the accuracy of multi-band extragalactic surveys designed for galaxy evolution studies. We will extend our application of this technique to the full SERVS footprint in the future.Comment: accepted to ApJ, 22 pages, 12 figure

The environmental dependence of the stellar mass-size relation in STAGES galaxies

We present the stellar mass-size relations for elliptical, lenticular, and spiral galaxies in the field and cluster environments using HST/ACS imaging and data from the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). We use a large sample of ~1200 field and cluster galaxies, and a sub-sample of cluster core galaxies, and quantify the significance of any putative environmental dependence on the stellar mass-size relation. For elliptical, lenticular, and high-mass (log M*/M_sun > 10) spiral galaxies we find no evidence to suggest any such environmental dependence, implying that internal drivers are governing their size evolution. For intermediate/low-mass spirals (log M*/M_sun < 10) we find evidence, significant at the 2-sigma level, for a possible environmental dependence on galaxy sizes: the mean effective radius a_e for lower-mass spirals is ~15-20 per cent larger in the field than in the cluster. This is due to a population of low-mass large-a_e field spirals that are largely absent from the cluster environments. These large-a_e field spirals contain extended stellar discs not present in their cluster counterparts. This suggests the fragile extended stellar discs of these spiral galaxies may not survive the environmental conditions in the cluster. Our results suggest that internal physical processes are the main drivers governing the size evolution of galaxies, with the environment possibly playing a role affecting only the discs of intermediate/low-mass spirals.Comment: 16 pages, 10 figures, accepted to MNRA

GEMS Survey Data and Catalog

We describe the data reduction and object cataloging for the GEMS survey, a large-area (800 arcmin(2)) two-band (F606W and F850LP) imaging survey with the Advanced Camera for Surveys on the Hubble Space Telescope, centered on the Chandra Deep Field-South.STScI HST-GO-9500.01NASA GO-9500, NAS5-26555, NAG5-13063, NAG5-13102European Community’s Human Potential Programunder contractHPRN-CT-2002-00316, HPRN-CT-2002-00305McDonald Observator

Evidence for a correlation between the sizes of quiescent galaxies and local environment to z ~ 2

We present evidence for a strong relationship between galaxy size and environment for the quiescent population in the redshift range 1 < z < 2. Environments were measured using projected galaxy overdensities on a scale of 400 kpc, as determined from ~ 96,000 K-band selected galaxies from the UKIDSS Ultra Deep Survey (UDS). Sizes were determined from ground-based K-band imaging, calibrated using space-based CANDELS HST observations in the centre of the UDS field, with photometric redshifts and stellar masses derived from 11-band photometric fitting. From the resulting size-mass relation, we confirm that quiescent galaxies at a given stellar mass were typically ~ 50 % smaller at z ~ 1.4 compared to the present day. At a given epoch, however, we find that passive galaxies in denser environments are on average significantly larger at a given stellar mass. The most massive quiescent galaxies (M_stellar > 2 x 10^11 M_sun) at z > 1 are typically 50 % larger in the highest density environments compared to those in the lowest density environments. Using Monte Carlo simulations, we reject the null hypothesis that the size-mass relation is independent of environment at a significance > 4.8 sigma for the redshift range 1 < z < 2. In contrast, the evidence for a relationship between size and environment is much weaker for star-forming galaxies.Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 6 table

Observations of the initial formation and evolution of spiral galaxies at 1 < z < 3 in the CANDELS fields

Many aspects concerning the formation of spiral and disc galaxies remain unresolved, despite their discovery and detailed study over the past 150 years. As such, we present the results of an observational search for proto-spiral galaxies and their earliest formation, including the discovery of a significant population of spiral-like and clumpy galaxies at z &gt; 1 in deep Hubble Space Telescope CANDELS imaging. We carry out a detailed analysis of this population, characterizing their number density evolution, masses, star formation rates and sizes. Overall, we find a surprisingly high overall number density of massive M* &gt; 1010 M⊙ spiral-like galaxies (including clumpy spirals) at z &gt; 1 of 0.18 per arcmin−2. We measure and characterise the decline in the number of these systems at higher redshift using simulations to correct for redshift effects in identifications, finding that the true fraction of spiral-like galaxies grows at lower redshifts as ∼ (1 + z)−1.1. This is such that the absolute numbers of spirals increases by a factor of ∼10 between z = 2.5 and z = 0.5. We also demonstrate that these spiral-like systems have large sizes at z &gt; 2, and high star formation rates, above the main-sequence, These galaxies represent a major mode of galaxy formation in the early universe, perhaps driven by the spiral structure itself. We finally discuss the origin of these systems, including their likely formation through gas accretion and minor mergers, but conclude that major mergers are an unlikely cause

Formation of S0s in extreme environments I: clues from kinematics and stellar populations

Despite numerous efforts, it is still unclear whether lenticular galaxies (S0s) evolve from spirals whose star formation was suppressed, or formed trough mergers or disk instabilities. In this paper we present a pilot study of 21 S0 galaxies in extreme environments (field and cluster), and compare their spatially-resolved kinematics and global stellar populations. Our aim is to identify whether there are different mechanisms that form S0s in different environments. Our results show that the kinematics of S0 galaxies in field and cluster are, indeed, different. Lenticulars in the cluster are more rotationally supported, suggesting that they are formed through processes that involve the rapid consumption or removal of gas (e.g. starvation, ram pressure stripping). In contrast, S0s in the field are more pressure supported, suggesting that minor mergers served mostly to shape their kinematic properties. These results are independent of total mass, luminosity, or disk-to-bulge ratio. On the other hand, the mass-weighted age, metallicity, and star formation time-scale of the galaxies correlate more with mass than with environment, in agreement with known relations from previous work such as the one between mass and metallicity. Overall, our results re-enforce the idea that there are multiple mechanisms that produce S0s, and that both mass and environment play key roles. A larger sample is highly desirable to confirm or refute the results and the interpretation of this pilot study

A weak lensing estimate from GEMS of the virial to stellar mass ratio in massive galaxies to z~0.8

We present constraints on the evolution of the virial to stellar mass ratio of galaxies with high stellar masses in the redshift range 0.2<z<0.8, by comparing weak lensing measurements of virial mass M_vir to estimates of stellar mass M_star from COMBO-17. For a complete sample of galaxies with log(M_star/ M_\odot) > 10.5, where the majority show an early-type morphology, we find that the virial mass to stellar mass ratio is given by M_vir/M_star = 53^{+13}_{-16}. Assuming a baryon fraction from the concordance cosmology, this corresponds to a stellar fraction of baryons in massive galaxies of Omega_b^*/\Omega_b = 0.10 +/- 0.03. Analysing the galaxy sample in different redshift slices, we find little or no evolution in the virial to stellar mass ratio, and place an upper limit of ~2.5 on the growth of massive galaxies through the conversion of gas into stars from z=0.8 to the present day.Comment: 5 pages, 2 figures, to appear in MNRAS Letters. Version includes referee comment

Dissecting the Transcriptional Regulatory Properties of Human Chromosome 16 Highly Conserved Non-Coding Regions

Non-coding DNA conservation across species has been often used as a predictor for transcriptional enhancer activity. However, only a few systematic analyses of the function of these highly conserved non-coding regions (HCNRs) have been performed. Here we use zebrafish transgenic assays to perform a systematic study of 113 HCNRs from human chromosome 16. By comparing transient and stable transgenesis, we show that the first method is highly inefficient, leading to 40% of false positives and 20% of false negatives. When analyzed in stable transgenic lines, a great majority of HCNRs were active in the central nervous system, although some of them drove expression in other organs such as the eye and the excretory system. Finally, by testing a fraction of the HCNRs lacking enhancer activity for in vivo insulator activity, we find that 20% of them may contain enhancer-blocking function. Altogether our data indicate that HCNRs may contain different types of cis-regulatory activity, including enhancer, insulators as well as other not yet discovered functions

The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey

We present a high-resolution dark matter reconstruction of the z = 0.165 Abell 901/902 supercluster from a weak lensing analysis of the Hubble Space Telescope STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901 alpha. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'

Alliances and the innovation performance of corporate and public research spin-off firms

We explore the innovation performance benefits of alliances for spin-off firms, in particular spin-offs either from other firms or from public research organizations. During the early years of the emerging combinatorial chemistry industry, the industry on which our empirical analysis focuses, spin-offs engaged in alliances with large and established partners, partners of similar type and size, and with public research organizations, often for different reasons. We seek to understand to what extent alliances of spin-offs with other firms (either large- or small- and medium-sized firms) affected their innovation performance and also how this performance may have been affected by their corporate or public research background. We find evidence that in general alliances of spin-offs with other firms, in particular alliances with large firms, increased their innovation performance. Corporate spin-offs that formed alliances with other firms outperformed public research spin-offs with such alliances. This suggests that, in terms of their innovation performance, corporate spin-offs that engaged in alliances with other firms seemed to have benefitted from their prior corporate background. Interestingly, it turns out that the negative impact of alliances on the innovation performance of public research spin-offs was largely affected by their alliances with small- and medium-sized firms