Further constraints on the evolution of Ks-selected galaxies in the GOODS/CDFS field

We have selected and analysed the properties of a sample of 2905 Ks<21.5 galaxies in ~ 131 sq.arcmin of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of Ks-selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5 micron bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimised redshift catalogue for our galaxy sample. We computed the Ks-band LF and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from z=0 to =2.5. We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (~ 85-90%) of the most massive (M>2.5x10^11 Msun) local galaxies appear to be in place before redshift z ~1. Around 65-70% of the total assemble between redshifts z=1 and z=3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-timescale bursts. The remaining fraction (up to ~ 20%) could be in place at even higher redshifts z=3-4, pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys.Comment: Accepted for publication in MNRAS. 16 pages, 15 figure

Number counts and clustering properties of bright Distant Red Galaxies in the UKIDSS Ultra Deep Survey Early Data Release

We describe the number counts and spatial distribution of 239 Distant Red Galaxies (DRGs), selected from the Early Data Release of the UKIDSS Ultra Deep Survey. The DRGs are identified by their very red infrared colours with (J-K)AB>1.3, selected over 0.62 sq degree to a 90% completeness limit of KAB~20.7. This is the first time a large sample of bright DRGs has been studied within a contiguous area, and we provide the first measurements of their number counts and clustering. The population shows strong angular clustering, intermediate between those of K-selected field galaxies and optical/infrared-selected Extremely Red Galaxies. Adopting the redshift distributions determined from other recent studies, we infer a high correlation length of r0~11 h-1 Mpc. Such strong clustering could imply that our galaxies are hosted by very massive dark matter halos, consistent with the progenitors of present-day L>L* elliptical galaxies.Comment: 5 pages, 4 figures, revised version accepted to MNRAS. Higher-resolution figures available from the authors on reques

Galaxy formation in the Planck cosmology - III. The high-redshift universe

We present high-redshift predictions of the star formation rate distribution function (SFRDF), UV luminosity function (UVLF), galactic stellar mass function (GSMF), and specific star formation rates (sSFRs) of galaxies from the latest version of the Munich semi-analytic model L-GALAXIES. We find a good fit to both the shape and normalization of the SFRDF at z = 4–7, apart from a slight underprediction at the low-SFR end at z = 4. Likewise, we find a good fit to the faint number counts for the observed UVLF at brighter magnitudes our predictions lie below the observations, increasingly so at higher redshifts. At all redshifts and magnitudes, the raw (unattenuated) number counts for the UVLF lie above the observations. Because of the good agreement with the SFR we interpret our underprediction as an overestimate of the amount of dust in the model for the brightest galaxies, especially at high redshift. While the shape of our GSMF matches that of the observations, we lie between (conflicting) observations at z = 4–5, and underpredict at z = 6–7. The sSFRs of our model galaxies show the observed trend of increasing normalization with redshift, but do not reproduce the observed mass dependence. Overall, we conclude that the latest version of L-GALAXIES, which is tuned to match observations at z ≤ 3, does a fair job of reproducing the observed properties of galaxies at z ≥ 4. More work needs to be done on understanding observational bias at high redshift, and upon the dust model, before strong conclusions can be drawn on how to interpret remaining discrepancies between the model and observations

A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr

Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3; ref. 1). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ~ 8 galaxies that, together with reports of a gamma-ray burst at z ~ 8.2 (refs 10, 11), constitute the earliest objects reliably reported to date. Observations of z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200 Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest galaxies.Comment: 41 pages, 14 figures, 2 tables, Nature, in pres

Old elliptical galaxies at z=1.5 and the Kormendy relation

Deep spectroscopy of the two mJy radio galaxies LBDS 53W069 and 53W091 has previously shown them to have old (>3 Gyr) stellar populations at z=1.5. Here we present the results of HST observations of these galaxies. 53W069 has an r^1/4 profile in both the F814W & F110W data with an effective radius of 0.30 arcsec (2.7 kpc). The restframe U-B colour gradient requires a stellar population of super-solar (3Z_sun) metallicity that formed on a very short timescale at high redshift (z>5). 53W091 has a regular r^1/4 profile in F110W with an effective radius of 0.32 arcsec (2.9 kpc). The F814W profile is more extended and is consistent with a blue exponential disk that contributes 20% of the flux within r_e. The restframe U-B colour gradient is significantly larger than that observed in field ellipticals at z<1, implying a stellar population of mixed metallicity (1-3Z_sun) that formed in a high-redshift rapid burst. We have compared these two LBDS radio galaxies with the Kormendy relation of ten 3CR radio galaxies at z=0.8. The LBDS galaxies follow the same relation as the more radio-luminous 3CR galaxies, assuming passive evolution of their stellar populations, although they are smaller than the 3CR galaxies whose mean effective radius is 12 kpc. Their sizes and radio luminosities are consistent with scaling relations applied to the 3CR galaxies, in which both radio power and effective radius scale with galaxy mass. Compared with a sample of z=0.4 cluster ellipticals, 53W069 & 53W091 lie well within the scatter of the Kormendy relation. We conclude that the hosts of these mJy radio sources at z=1.5 are passively-evolving elliptical galaxies that will evolve into ordinary L* ellipticals by the present day. (Abridged)Comment: Accepted for publication in MNRAS. 11 pages including 7 figure

The estimation of black-hole masses in distant radio galaxies

We have estimated the masses of the central supermassive black holes of 2442 radio galaxies froma catalog compiled using data from the NED, SDSS, and CATS databases. Mass estimates based on optical photometry and radio data are compared. Relationships between the mass of the central black hole $M_p^{bh}$ and the redshift $z_p$ are constructed for both wavelength ranges. The distribution of the galaxies in these diagrams and systematic effects influencing estimation of the black-hole parameters are discussed. Upperenvelope cubic regression fits are obtained using the maximum estimates of the black-hole masses. The optical and radio upper envelopes show similar behavior, and have very similar peaks in position, $z_p \simeq 1.9$, and amplitude, $\log M_p^{bh}$ = 9.4. This is consistent with a model in which the growth of the supermassive black holes is self-regulating, with this redshift corresponding to the epoch when the accretion-flow phase begins to end and the nuclear activity falls off.Comment: 8 pages, 6 figure

Host galaxies of luminous quasars: population synthesis of optical off-axis spectra

There is increasing evidence of a connection between AGN activity and galaxy evolution. To obtain further insight into this potentially important evolutionary phase, we analyse the properties of quasar host galaxies. In this paper, we present a population synthesis modeling technique for off-axis spectra, the results of which constrain host colour and the stellar ages of luminous quasars (M_V(nuc)<-23). Our technique is similar to well established quiescent-galaxy models, modified to accommodate scattered nuclear light (a combination of atmospheric, instrumental and host galaxy scattered light) observed off axis. In our model, subtraction of residual scattered quasar light is performed, while simultaneously modeling the constituent stellar populations of the host galaxy. The reliability of this technique is tested via a Monte-Carlo routine in which the correspondence between synthetic spectra with known parameters and the model output is determined. Application of this model to a preliminary sample of 10 objects is presented and compared to previous studies. Spectroscopic data was obtained via long-slit and integral-field unit observations on the Keck and WIYN telescopes. We confirm that elliptical quasar hosts are distinguishable (bluer) from inactive ellipticals in rest frame B-V colour. Additionally, we note a trend for radio luminous (L_5GHz > 10^40 erg s^-1) quasars to be located in redder host galaxies in comparison to their less luminous radio counterparts. While the host colour and age of our radio luminous sample is in close proximity to the green valley, our radio faint sample is consistent with quiescent star-forming galaxies. However, further observations are needed to confirm these results. Finally, we discuss future applications for our technique on a larger sample of objects being obtained via SALT and WIYN telescope observing campaigns.Comment: 18 pages, 10 figures, accepted for publication in MNRA

Very blue UV-continuum slopes of low luminosity z~7 galaxies from WFC3/IR: Evidence for extremely low metallicities?

We use the ultra-deep WFC3/IR data over the HUDF and the Early Release Science WFC3/IR data over the CDF-South GOODS field to quantify the broadband spectral properties of candidate star-forming galaxies at z~7. We determine the UV-continuum slope beta in these galaxies, and compare the slopes with galaxies at later times to measure the evolution in beta. For luminous L*(z=3) galaxies, we measure a mean UV-continuum slope beta of -2.0+/-0.2, which is comparable to the beta~-2 derived at similar luminosities at z~5-6. However, for the lower luminosity 0.1L*(z=3) galaxies, we measure a mean beta of -3.0+/-0.2. This is substantially bluer than is found for similar luminosity galaxies at z~4, just 800 Myr later, and even at z~5-6. In principle, the observed beta of -3.0 can be matched by a very young, dust-free stellar population, but when nebular emission is included the expected beta becomes >~-2.7. To produce these very blue beta's (i.e., beta~-3), extremely low metallicities and mechanisms to reduce the red nebular emission are likely required. For example, a large escape fraction (i.e., f_{esc}>~0.3) could minimize the contribution from this red nebular emission. If this is correct and the escape fraction in faint z~7 galaxies is >~0.3, it may help to explain how galaxies reionize the universe.Comment: 5 pages, 5 figures, accepted for publication in Astrophysical Journal Letter

CANDELS Observations Of The Structural Properties Of Cluster Galaxies At Z=1.62

We discuss the structural and morphological properties of galaxies in a z = 1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (less than or similar to 1 kpc), massive galaxies compared to CANDELS field galaxies at z = 1.6. As a result, the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z similar or equal to 1.6 to the present, growing as (1 + z)(-0.6 +/- 0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seem to have caused accelerated size growth in quiescent galaxies prior to z = 1.6 and slower subsequent growth at z < 1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z = 1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue that the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z < 1 clusters.NASA NAS5-26555HST GO-12060NASA through from the Space Telescope Science Institute GO-12060European Research CouncilRoyal SocietyTexas AM UniversityGeorge P. and Cynthia Woods Institute for Fundamental Physics and AstronomyAstronom

Galaxies in Southern Bright Star Fields I. Near-infrared imaging

As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of K_s imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations 60" from candidate guide stars in the magnitude range 9.0 R 12.4. When analyzed as a "discrete deep field" with 131 arcmin^2 area, our dataset gives galaxy number counts that agree with those derived previously over the range 16 K_s 20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.Comment: 10 pages, 7 figures, accepted by A&A; Table 3 is available at http://www.rzg.mpg.de/~ajb/data.html pending upload to CD