Search

We calculate the major pair fraction and derive the major merger fraction and rate for 82 massive ($M_{*}>10^{11}M_{\odot}$) galaxies at $1.7 < z < 3.0$ utilising deep HST NICMOS data taken in the GOODS North and South fields. For the first time, our NICMOS data provides imaging with sufficient angular resolution and depth to collate a sufficiently large sample of massive galaxies at z $>$ 1.5 to reliably measure their pair fraction history. We find strong evidence that the pair fraction of massive galaxies evolves with redshift. We calculate a pair fraction of $f_{m}$ = 0.29 +/- 0.06 for our whole sample at $1.7 < z < 3.0$. Specifically, we fit a power law function of the form $f_{m}=f_{0}(1+z)^{m}$ to a combined sample of low redshift data from Conselice et al. (2007) and recently acquired high redshift data from the GOODS NICMOS Survey. We find a best fit to the free parameters of $f_{0}$ = 0.008 +/- 0.003 and $m$ = 3.0 +/- 0.4. We go on to fit a theoretically motivated Press-Schechter curve to this data. This Press-Schechter fit, and the data, show no sign of levelling off or turning over, implying that the merger fraction of massive galaxies continues to rise with redshift out to z $\sim$ 3. Since previous work has established that the merger fraction for lower mass galaxies turns over at z $\sim$ 1.5 - 2.0, this is evidence that higher mass galaxies experience more mergers earlier than their lower mass counterparts, i.e. a galaxy assembly downsizing. Finally, we calculate a merger rate at z = 2.6 of $\Re$ $<$ 5 $\times$ 10$^{5}$ Gpc$^{-3}$ Gyr$^{-1}$, which experiences no significant change to $\Re$ $<$ 1.2 $\times$ 10$^{5}$ Gpc$^{-3}$ Gyr$^{-1}$ at z = 0.5. This corresponds to an average $M_{*}>10^{11}M_{\odot}$ galaxy experiencing 1.7 +/- 0.5 mergers between z = 3 and z = 0., Comment: 5 pages, 3 figures, accepted to MNRAS

We study the spatial clustering of 538 X-ray selected AGN in the 2 deg^2 XMM-COSMOS field that are spectroscopically identified to I_{AB}<23 and span the redshift range z=0.2-3.0. The median redshift and luminosity of the sample are z = 0.98 and L_{0.5-10}=6.3 x 10^{43} erg/s, respectively. A strong clustering signal is detected at ~18sigma level, which is the most significant measurement obtained to date for clustering of X-ray selected AGN. By fitting the projected correlation function w(r_p) with a power law on scales of r_p=0.3-40 Mpc/h, we derive a best fit comoving correlation length of r_0 = 8.6 +- 0.5 Mpc/h and slope of gamma=1.88 +- 0.07 (Poissonian errors; bootstrap errors are about a factor of 2 larger). An excess signal is observed in the range r_p~5-15 Mpc/h, which is due to a large scale structure at z ~ 0.36 containing about 40 AGN. When removing the z ~ 0.36 structure, or computing w(r_p) in a narrower range around the peak of the redshift distribution (e.g. z=0.4-1.6), the correlation length decreases to r_0 ~ 5-6 Mpc/h, which is consistent with that observed for bright optical QSOs at the same redshift. We investigate the clustering properties of obscured and unobscured AGN separately. Within the statistical uncertainties, we do not find evidence that AGN with broad optical lines (BLAGN) cluster differently from AGN without broad optical lines (non-BLAGN). The correlation length measured for XMM-COSMOS AGN at z~1 is similar to that of massive galaxies (stellar mass M_*> 3 x 10^{10} M_sun) at the same redshift. This suggests that AGN at z~1 are preferentially hosted by massive galaxies, as observed both in the local and in the distant (z~2) Universe. (shortened), Comment: 16 pages, 11 figures; accepted for publication in A&A. Language edited version

We present the serendipitous discovery of z=4.05 molecular gas CO emission lines with the IRAM Plateau de Bure interferometer coincident with GN20 and GN20.2, two luminous submillimeter galaxies (SMGs) in the Great Observatories Origins Deep Survey North field (GOODS-N). These are among the most distant submillimeter-selected galaxies reliably identified through CO emission and also some of the most luminous known. In terms of CO to bolometric luminosities, stellar mass and star formation rates (SFRs), these newly discovered z>4 SMGs are similar to z~1.5-3 SMGs studied to date. These z~4 SMGs have much higher specific SFRs than typical B-band dropout Lyman break galaxies at the same redshift. The stellar mass-SFR correlation for normal galaxies does not seem to evolve much further, between z~2 and z~4. A significant z=4.05 spectroscopic redshift spike is observed in GOODS-N, and a strong spatial overdensity of B-band dropouts and IRAC selected z>3.5 galaxies appears to be centered on the GN20 and GN20.2 galaxies. This suggests a proto-cluster structure with total mass ~10^14 Msun. Using photometry at mid-IR, submm and radio wavelengths, we show that reliable photometric redshifts (Dz/(1+z)~0.1) can be derived for SMGs over 13.5 starbursts, regardless of their submm/mm emission [abridged]., Comment: 23 pages, 16 figures. Version accepted for publication in ApJ

Residual star formation at late times in early-type galaxies and their progenitors must be suppressed in order to explain the population of red, passively evolving systems we see today. Likewise, residual or newly accreted reservoirs of molecular gas that are fuelling star formation must be destroyed. This suppression of star formation in early-type galaxies is now commonly attributed to AGN feedback wherein the reservoir of gas is heated and expelled during a phase of accretion onto the central supermassive black hole. However, direct observational evidence for a link between the destruction of this molecular gas and an AGN phase has been missing so far. We present new mm-wavelength observations from the IRAM 30m telescope of a sample of low redshift SDSS early-type galaxies currently undergoing this process of quenching of late-time star formation. Our observations show that the disappearance of the molecular gas coincides within less than 100 Myr with the onset of accretion onto the black hole and is too rapid to be due to star formation alone. Since our sample galaxies are not associated to powerful quasar activity or radio jets, we conclude that low-luminosity AGN episodes are sufficient to suppress residual star formation in early-type galaxies. This `suppression mode' of AGN feedback is very different from the `truncation mode' linked to powerful quasar activity during early phases of galaxy formation., Comment: Accepted for publication in ApJ, 10 pages, 5 figures. A version with full-resolution figures is available at http://www.astro.yale.edu/ks57/papers/obs_action.pdf

Population III stars, the first generation of stars formed from primordial Big Bang material with a top-heavy IMF, should contribute substantially to the Universe reionization and they are crucial for understanding the early metal enrichment of galaxies. Therefore it is very important that these objects, foreseen by theories, are detected by observations. However PopIII stars, searched through the HeII 1640A line signature, have remained elusive. We report about the search for the HeII line in a galaxy at z=6.5, which is a very promising candidate. Unfortunately we are not yet able to show the results of this search. However we call attention to the possible detection of PopIII stars in a lensed HII dwarf galaxy at z=3.4, which appeared in the literature some years ago, but has been overlooked., Comment: Contribution for the Proceedings of the IAU Symposium No. 255 on "Low-Metallicity Star Formation: From the First Stars to Dwarf Galaxies"

We present Ha integral field spectroscopy of well resolved, UV/optically selected z~2 star-forming galaxies as part of the SINS survey with SINFONI on the ESO VLT. Our laser guide star adaptive optics and good seeing data show the presence of turbulent rotating star forming rings/disks, plus central bulge/inner disk components, whose mass fractions relative to total dynamical mass appears to scale with [NII]/Ha flux ratio and star formation age. We propose that the buildup of the central disks and bulges of massive galaxies at z~2 can be driven by the early secular evolution of gas-rich proto-disks. High redshift disks exhibit large random motions. This turbulence may in part be stirred up by the release of gravitational energy in the rapid cold accretion flows along the filaments of the cosmic web. As a result dynamical friction and viscous processes proceed on a time scale of <1 Gyr, at least an order of magnitude faster than in z~0 disk galaxies. Early secular evolution thus drives gas and stars into the central regions and can build up exponential disks and massive bulges, even without major mergers. Secular evolution along with increased efficiency of star formation at high surface densities may also help to account for the short time scales of the stellar buildup observed in massive galaxies at z~2., Comment: accepted Astrophysical Journal, main July 8 2008

Preliminary site testing datasets suggest that Dome C in Antarctica is one of the best sites on Earth for astronomical observations in the 200 to 500 micron regime, i.e. for far-infrared (FIR) and submillimetre (submm) astronomy. We present an overview of potential science cases that could be addressed with a large telescope facility at Dome C. This paper also includes a presentation of the current knowledge about the site characterics in terms of atmospheric transmission, stability, sky noise and polar constraints on telescopes. Current and future site testing campaigns are finally described., Comment: 20

Following an episode of star formation, Type Ia supernova events occur over an extended period of time, following a distribution of delay times (DDT). We critically discuss some empirically-based DDT functions that have been proposed in recent years, some favoring very early (prompt) events, other very late (tardy) ones, and therefore being mutually exclusive. We point out that in both cases the derived DDT functions are affected by dubious assumptions, and therefore there is currently no ground for claiming either a DDT strongly peaked at early times, or at late ones. Theoretical DDT functions are known to accommodate both prompt as well as late SNIa events, and can account for all available observational constraints. Recent observational evidence exists that both single degenerate and double degenerate precursors may be able of producing SNIa events. We then explore on the basis of plausible theoretical models the possible variation with cosmic time of the mix between the events produced by the two different channels, which in principle could lead to systematics effects on the SNIa properties with redshift., Comment: 9 pages, 7 figures, submitted to MNRAS March 20, accepted May 9, 2008. New version is identical to previous one apart from a "Note added in proof"

We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015-2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0

The Galaxy Mass Assembly ultra-deep Spectroscopic Survey samples a part of the CDFS to unprecedented depth. The resulting distribution of 150 z>1.4 redshifts reveals a significant peak at z=1.6, part of a larger overdensity found at this redshift. The 42 spectroscopic members of this structure, called Cl 0332-2742, form an overdensity in redshift of a factor 11+/-3 and have a velocity dispersion of 450 km/s. We derive a total mass for Cl 0332-2742 of ~7x10^14 Msol. The colours of its early-type galaxies are consistent with a theoretical red sequence of galaxies with stars formed at z=3.0. In addition, there are more massive, passive and older, but less star forming galaxies in CL 0332-2742 than in the field. We conclude that this structure is a cluster under assembly at z=1.6., Comment: 4 pages, 1 figure, proceedings of the first Subaru International Conference: "Panoramic Views of Galaxy Formation and Evolution", in Hayama, Japan, December 2007

The aim of this work is to study the evolution of the rest frame color distribution of galaxies with the redshift, in particular in the critical interval 1.410.1, and we study their morphological and spectro-photometric properties. We show that the contribution to this sample of early-type galaxies, defined as galaxies with a spheroidal morphology and no star formation, decreases from 60-70% at z<0.5 down to ~50% at redshift z=2. At z>2 we still find red galaxies in the mass complete sample, even if the bimodality is not seen any more. About 25% of these red galaxies at z>2 are passively evolving, with the bulk of their stars formed at redshift z>`3., Comment: to appear on A&A letters, 4 pages, 3 figures

In a recent multiwavelength study of galaxies at redshift ~ 2 by Daddi et al. (2007a,b) it is shown that galaxies with a Mid-IR excess most likely harbor a Compton-thick AGN, thus bringing to about 1/3 the fraction of z ~ 2 galaxies hosting an AGN. This finding opens a number of intriguing issues concerning the concomitant growth of galaxies and supermassive black holes, AGN feedback, and downsizing, at the cosmic epoch of most intense star formation and nuclear activity., Comment: 6 pages, 5 figures, to appear on the proceedings of the conference "Panoramic Views of Galaxy Formation and Evolution", Hayama, Japan, December 11-16, 2007; Ed. Tadayuki Kodama, ASP Conf. Ser. New version (v2) with figure numbering corrected

We investigate the properties of a clump-cluster galaxy at redshift 1.57. The morphology of this galaxy is dominated by eight star-forming clumps in optical observations, and has photometric properties typical of most clump-cluster and chain galaxies. Its complex asymmetrical morphology has led to the suggestion that this system is a group merger of several initially separate proto-galaxies. We performed H_alpha integral field spectroscopy of this system using SINFONI on VLT UT4. These observations reveal a large-scale velocity gradient throughout the system, but with large local kinematic disturbances. Using a numerical model of gas-rich disk fragmentation, we find that clump interactions and migration can account for the observed disturbed rotation. On the other hand, the global rotation would not be expected for a multiply merging system. We further find that this system follows the stellar mass vs. metallicity, star formation rate and size relations expected for a disk at this redshift, and exhibits a disk-like radial metallicity gradient, so that the scenario of internal disk fragmentation is the most likely one. A red and metallic central concentration appears to be a bulge in this proto-spiral clumpy galaxy. A chain galaxy at redshift 2.07 in the same field also shows disk-like rotation. Such systems are likely progenitors of the present-day bright spiral galaxies, forming their exponential disks through clump migration and disruption and fueling their bulges. Our present results show that disturbed morphologies and kinematics are not necessarily signs of galaxy mergers and interactions, and can instead result from the internal evolution of primordial disks., Comment: A&A, accepted. Version with full resolution figures available at http://aramis.obspm.fr/~bournaud/udfr2.pdf -- Animation of clumpy galaxy models available at http://aramis.obspm.fr/~bournaud/cc/cc.html

Many models that seek to explain the origin of the unresolved X-ray background predict that Compton-thick Active Galactic Nuclei (AGNs) are ubiquitious at high redshift. However, few distant Compton-thick AGNs have been reliably identified to date. Here we present Spitzer-IRS spectroscopy and 3.6-70um photometry of a z=2.2 optically identified AGN (HDF-oMD49) that is formally undetected in the 2Ms Chandra Deep Field-North (CDF-N) survey. The Spitzer-IRS spectrum and spectral energy distribution of this object is AGN dominated, and a comparison of the energetics at X-ray wavelengths to those derived from mid-infrared (mid-IR) and optical spectroscopy shows that the AGN is intrinsically luminous (L_X~3x10^44 erg/s) but heavily absorbed by Compton-thick material (N_H>>10^24 cm^{-2}); i.e., this object is a Compton-thick quasar. Adopting the same approach that we applied to HDF-oMD49, we found a further six objects at z~2-2.5 in the literature that are also X-ray weak/undetected but have evidence for AGN activity from optical and/or mid-IR spectroscopy, and show that all of these sources are also Compton-thick quasars with L_X>10^44 erg/s. On the basis of the definition of Daddi etal. (2007), these Compton-thick quasars would be classified as mid-IR excess galaxies, and our study provides the first spectroscopic confirmation of Compton-thick AGN activity in a subsample of these z~2 mid-IR bright galaxies. Using the four objects that lie in the CDF-N field, we estimate the space-density of Compton-thick quasars [Phi~(0.7-2.5)x10^-5 Mpc^-3 for L_X>10^44 erg/s objects at z~2-2.5] and show that Compton-thick accretion is as ubiquitious as unobscured accretion in the distant Universe., Comment: ApJ in press; 13 pages, 7 figures, 1 table. Paper updated to take account of feedback, predominantly exploring other X-ray-mid-IR relationships, providing an N_H constraint from the X-ray data, and adding a second panel to Fig 1 to compare to the composite mid-IR spectrum of X-ray obscured Compton-thin quasars. Results and conclusions are unchanged

We present the first results of the VIsible Multiobject Spectrograph (VIMOS) ESO/GOODS program of spectroscopy of faint galaxies in the Chandra Deep Field South (CDF-S). The program complements the FORS2 ESO/GOODS campaign. 3312 spectra have been obtained in service mode with VIMOS at the ESO/VLT UT3. The VIMOS LR-Blue and MR grisms have been used to cover different redshift ranges. Galaxies at 1.8 < z < 3.5 have been observed in the GOODS VIMOS-LR-Blue campaign. Galaxies at z < 1 and Lyman Break Galaxies at z > 3.5 have been observed in the VIMOS MR survey. Here we report results for the first 6 masks (out of 10 total) that have been analyzed from each of the LR-Blue and MR grisms. Spectra of 2344 spectra have been extracted from these 6 LR-Blue masks and 968 from 6 MR masks. 33% of the LR-Blue and 18% of the MR spectra are serendipitous observations. We obtained 1481 redshifts in the LR-Blue campaign and 656 in the MR campaign for a total success rate of 63% and 68%, respectively, which increase to 70% and 75% when only the primary targets are considered. By complementing our VIMOS spectroscopic catalog with all existing spectroscopic redshifts publicly available in the CDF-S, we created a redshift master catalog. By comparing this redshift compilation with different photometric redshift catalogs we estimate the completeness level of the CDF-S spectroscopic coverage in several redshift bins. The completeness level is very high, > 60%, at z < 3.5, and it is very uncertain at higher redshift. The master catalog has been used also to estimate completeness and contamination levels of different galaxy photometric selection techniques, such as the BzK, the so called 'sub'-U-dropout and the drop-out methods and to identify large scale structures in the field., Comment: 16 pages, 12 figures, A&A submitted

We present a simple set of kinematic criteria that can distinguish between galaxies dominated by ordered rotational motion and those involved in major merger events. Our criteria are based on the dynamics of the warm ionized gas (as traced by H-alpha) within galaxies, making this analysis accessible to high-redshift systems, whose kinematics are primarily traceable through emission features. Using the method of kinemetry (developed by Krajnovic and co-workers), we quantify asymmetries in both the velocity and velocity dispersion maps of the warm gas, and the resulting criteria enable us to empirically differentiate between non-merging and merging systems at high redshift. We apply these criteria to 11 of our best-studied rest-frame UV/optical-selected z~2 galaxies for which we have near infrared integral field spectroscopic data from SINFONI on the VLT. Of these 11 systems, we find that >50% have kinematics consistent with a single rotating disk interpretation, while the remaining systems are more likely undergoing major mergers. This result, combined with the short formation timescales of these systems, provides evidence that rapid, smooth accretion of gas plays a significant role in galaxy formation at high redshift., Comment: Accepted for publication in the Astrophysical Journal. 24 pages, 14 figures

We report sub-arcsecond resolution IRAM PdBI millimeter CO interferometry of four z~2 submillimeter galaxies (SMGs), and sensitive CO (3-2) flux limits toward three z~2 UV-/optically selected star forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of ~500 km/s across 0.2 arcsec (1.6 kpc) diameter regions, suggesting that the star forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived 'maximum' star forming events in highly dissipative mergers of gas rich galaxies. The resulting high mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range, and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion time scales and stellar ages, we estimate that the SMG phase duration is about 100 Myrs. Our analysis of SMGs and optically/UV selected high redshift star forming galaxies supports a 'universal' Chabrier IMF as being valid over the star forming history of these galaxies. We find that the 12CO luminosity to total gas mass conversion factors at z~2-3 are probably similar to those assumed at z~0. The implied gas fractions in our sample galaxies range from 20 to 50%., Comment: 61 pages, 10 figures, Accepted for publication in ApJ

Context: Galaxy metallicities have been measured to redshift z~2 by gas-phase oxygen abundances of the interstellar medium using the R23 and N2 methods. Galaxy stellar metallicities provide crucial data for chemical evolution models but have not been assessed reliably much outside the local Universe. Aims: We determine the iron-abundance, stellar metallicity of star-forming galaxies (SFGs) at redshift z~2, observed as part of the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS). Methods: We compute the equivalent width of a rest-frame mid-ultraviolet, photospheric absorption-line index, the 1978 index found to vary monotonically with stellar metallicity by Rix and collaborators. We normalise and combine 75 SFG spectra from the GMASS survey to produce a spectrum corresponding to a total integration time 1652.5 hours (and a signal-to-noise ratio ~100 for our 1.5 angstrom binning) of FORS2 spectroscopic observations at the Very Large Telescope. Results: We measure an iron-abundance, stellar metallicity of log (Z/Zsolar) = -0.574+/-0.159 for our spectrum representative of a galaxy of stellar mass 9.4 x 10^9 Msolar assuming a Chabrier IMF. We find that the R04 model SFG spectrum for log (Z/Zsolar) = -0.699 solar metallicity provides the best description of our GMASS coadded spectrum. For similar galaxy stellar mass, our stellar metallicity is ~0.25 dex lower than the oxygen-abundance, gas-phase metallicity quantified by Erb and collaborators for UV-selected star-forming galaxies at z=2. Conclusions: We conclude that we are witnessing the establishment of a light-element overabundance in galaxies as they are being formed at redshift z~2. Our measurements are reminiscent of the alpha-element enhancement seen in low-redshift, galactic bulges and early-type galaxies. (Abridged), Comment: Accepted for publication in Astronomy and Astrophysics on 18 December 2007, 9 pages, 8 figures, aa.bst and aa.cls A&A style files

We combine ultradeep optical spectroscopy from the GMASS project ("Galaxy Mass Assembly ultradeep Spectroscopic Survey") with GOODS multi-band photometry and HST imaging to study a sample of passive galaxiesat 1.392. These galaxies have morphologies that are predominantly compact and spheroidal.However, their sizes (R_e <~ 1 kpc) are much smaller than those of spheroids in the present--day Universe. Their stellar mass surface densities are consequently higher by ~1 dex if compared to spheroids at z~0 with the same mass. Their rest-frame B-band surface brightness scales with the effective radius, but the offset with respect to the surface brightness of the local Kormendy relation is too large to be explained by simple passive evolution. At z~1, a larger fraction of passive galaxies follows the z~0 size -- mass relation. Superdense relics with R_e~1 kpc are extremely rare at z~0 with respect to z>1, and absent if R_e<1 kpc. Because of the similar sizes and mass densities, we suggest that the superdense passive galaxies at 12. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution., Comment: 22 pages, 23 figures, Astronomy & Astrophysics, in press

We present the first detection of molecular gas cooling CO emission lines from ordinary massive galaxies at z=1.5. Two sources were observed with the IRAM Plateau de Bure Interferometer, selected to lie in the mass-star formation rate correlation at their redshift, thus being representative of massive high-z galaxies. Both sources were detected with high confidence, yielding L'_CO~10^{10}K km/s pc^2. For one of the sources we find evidence for velocity shear, implying CO sizes of ~10 kpc. With an infrared luminosity of L_FIR~10^{12}L_sun, these disk-like galaxies are borderline ULIRGs but with star formation efficiency similar to that of local spirals, and an order of magnitude lower than that in submm galaxies. This suggests a CO to total gas conversion factor similar to local spirals, gas consumption timescales approaching 1 Gyr or longer and molecular gas masses reaching ~10^11 M_sun, comparable to or larger than the estimated stellar masses. These results support a major role of 'in situ' gas consumption over cosmological timescales and with relatively low star formation efficiency, analogous to that of local spiral disks, for the formation of today's most massive galaxies and their central black holes. Given the high space density of similar galaxies, ~10^{-4}/Mpc^3, this implies a widespread presence of gas rich galaxies in the early Universe, many of which might be within reach of detailed investigations of current and planned facilities., Comment: 4 pages, 3 figures. ApJ Letters in press

We present the first spatial clustering measurements of z~1, 24um-selected, star forming galaxies in the Great Observatories Origins Deep Survey (GOODS). The sample under investigation includes 495 objects in GOODS-South and 811 objects in GOODS-North selected down to flux densities of f_24>20 uJy and z_AB<23.5 mag, for which spectroscopic redshifts are available. The median redshift, IR luminosity and star formation rate (SFR) of the samples are z~0.8, L_IR~4.4 x 10^10 L_sun, and SFR~7.6 M_sun/yr, respectively. We measure the projected correlation function w(r_p) on scales of r_p=0.06-10 h^-1 Mpc, from which we derive a best fit comoving correlation length of r_0 = 4.0 +- 0.4 h^-1 Mpc and slope of gamma=1.5 +- 0.1 for the whole f_24>20uJy sample after combining the two fields. We find indications of a larger correlation length for objects of higher luminosity, with Luminous Infrared Galaxies (LIRGs, L_IR>10^11 L_sun) reaching r_0~5.1 h^-1 Mpc. This would imply that galaxies with larger SFRs are hosted in progressively more massive halos, reaching minimum halo masses of ~3 x 10^12 M_sun for LIRGs. We compare our measurements with the predictions from semi-analytic models based on the Millennium simulation. The variance in the models is used to estimate the errors in our GOODS clustering measurements, which are dominated by cosmic variance. The measurements from the two GOODS fields are found to be consistent within the errors. On scales of the GOODS fields, the real sources appear more strongly clustered than objects in the Millennium-simulation based catalogs, if the selection function is applied consistently. This suggests that star formation at z~0.5-1 is being hosted in more massive halos and denser environments than currently predicted by galaxy formation models.[truncated], Comment: 19 pages, 15 figures. Accepted for publication in A&A. Style and English improved

We present the first comparison of the dynamical properties of different samples of z~1.4-3.4 star forming galaxies from spatially resolved imaging spectroscopy from SINFONI/VLT integral field spectroscopy and IRAM CO millimeter interferometry. Our samples include 16 rest-frame UV-selected, 16 rest-frame optically-selected and 13 submillimeter galaxies (SMGs). We find that restframe UV- and optically bright (K<20) z~2 star forming galaxies are dynamically similar, and follow the same velocity-size relation as disk galaxies at z~0. In the theoretical framework of rotating disks forming from dissipative collapse in dark matter halos, the two samples require a spin parameter ranging from 0.06 to 0.2. In contrast bright SMGs have larger velocity widths and are much more compact. Hence, SMGs have lower angular momenta and higher matter densities than either of the UV- or optically selected populations. This indicates that dissipative major mergers may dominate the SMGs population, resulting in early spheroids, and that the majority of UV/optically bright galaxies have evolved less violently [...]. These early disks may later evolve into spheroids via disk instabilities or mergers. Because of their small sizes and large densities, SMGs lie at the high surface density end of a universal (out to z=2.5) "Schmidt-Kennicutt" relation between gas surface density and star formation rate surface density with a slope of ~1.7., Comment: 14 pages, 3 figures, accepted for publication in ApJ, minor typos corrected

Examining a sample of massive galaxies at 1.410^{11}L_sun, show a mid-IR excess which is likely due to the presence of obscured active nuclei, as shown in a companion paper. There is a tight and roughly linear correlation between stellar mass and SFR for 24um-detected galaxies. For a given mass, the SFR at z=2 was larger by a factor of ~4 and ~30 relative to that in star forming galaxies at z=1 and z=0, respectively. Typical ultraluminous infrared galaxies (ULIRGs) at z=2 are relatively 'transparent' to ultraviolet light, and their activity is long lived (~400 Myr), unlike that in local ULIRGs and high redshift submillimeter-selected galaxies. ULIRGs are the common mode of star formation in massive galaxies at z=2, and the high duty cycle suggests that major mergers are not the dominant trigger for this activity.Current galaxy formation models underpredict the normalization of the mass-SFR correlation by about a factor of 4, and the space density of ULIRGs by an orderof magnitude, but give better agreement for z>1.4 quiescent galaxies., Comment: 19 pages, 18 figures. ApJ in press. A figure added. See also the companion paper arXiv:0705.2832

Approximately 20-30% of 1.46.2 keV. The stacked X-ray spectrum rises steeply at >10 keV, suggesting that these sources host Compton-thick Active Galactic Nuclei (AGNs) with column densities N_H~10^{24} cm^-2 and an average, unobscured X-ray luminosity L_{2-8 keV}~(1-4)x10^43 erg/s. Their sky density(~3200 deg^-2) and space density (~2.6x10^-4 Mpc^-3) are twice those of X-ray detected AGNs at z~2, and much larger than those of previously-known Compton thick sources at similar redshifts. The mid-IR excess galaxies are part of the long sought-after population of distant heavily obscured AGNs predicted by synthesis models of the X-ray background. The fraction of mid-IR excess objects increases with galaxy mass, reaching ~50-60% for M~10^11 M_sun, an effect likely connected with downsizing in galaxy formation. The ratio of theinferred black hole growth rate from these Compton-thick sources to the global star formation rate at z=2 is similar to the mass ratio of black holes to stars inlocal spheroids, implying concurrent growth of both within the precursors oftoday's massive galaxies., Comment: 18 pages, 10 figures. ApJ in press. Minor changes only. See also the companion paper arXiv:0705.2831

We study the relationship between the local environment of galaxies and their star formation rate (SFR) in the Great Observatories Origins Deep Survey, GOODS, at z~1, from ultradeep imaging at 24 microns with the MIPS camera onboard Spitzer. We show that the star formation-density relation observed locally was reversed at z~1: the average SFR of an individual galaxy increased with local galaxy density when the universe was less than half its present age. Hierarchical galaxy formation models (simulated lightcones from the Millennium model) predicted such a reversal to occur only at only at earlier epochs (z>2) and at a lower level. We present a remarkable structure at z~1.016, containing X-ray traced galaxy concentrations, which will eventually merge into a Virgo-like cluster. This structure illustrates how the individual SFR of galaxies increases with density at the ~1-2 Mpc scale. The SFR of z~1 galaxies is found to correlate with stellar mass suggesting that mass plays a role in the observed star formation-density trend. However the specific SFR (=SFR/M*) decreases with stellar mass while it increases with galaxy density, which implies that the environment does directly affect the star formation activity of galaxies. Major mergers do not appear to be the unique or even major cause for this effect since nearly half (46%) of the luminous infrared galaxies (LIRGs) at z~1 present the HST-ACS morphology of spirals, while only a third present a clear signature of major mergers. The remaining galaxies are divided into compact (9%) and irregular (14%) galaxies. Moreover, the specific SFR of major mergers is only marginally stronger than that of spirals. Reproducing the SFR-density relation at z ~ 1 is a new challenge for models, requiring a correct balance between mergers and in-situ star formation at early epochs., Comment: Accepted for publication in Astronomy & Astrophysics, 17 pages, 29 figures (same as previous version except for a few typos). For a version of this paper with higher resolution figures, go to http://david.elbaz3.free.fr/papers.html

We present redshifts for 115 emission line objects in the Hubble Ultra Deep Field (HUDF) identified through the GRism ACS Program for Extragalactic Science (GRAPES) project using the slitless grism spectroscopy mode of the ACS Camera on the Hubble Space Telescope (HST). The sample was selected by an emission line search on all extracted 1-dimensional GRAPES spectra. We identify the emission lines using line wavelength ratios where multiple lines are detected in the grism wavelength range (5800A < lambda < 9600A), and using photometric redshift information where multiple lines are unavailable. We then derive redshifts using the identified lines. Our redshifts are accurate to delta(z) = 0.009, based on both statistical uncertainty estimates and comparison with published ground-based spectra. Over 40% of our sample is fainter than typical magnitude limits for ground-based spectroscopy (with i_{AB}>25 mag). Such emission lines would likely remain undiscovered without our deep survey. The emission line objects fall into 3 categories: 1) Most are low to moderate redshift galaxies (0 < z < 2), including many actively star forming galaxies with strong HII regions; 2) 9 are high redshift (4 < z < 7) Lyman-alpha emitters; and 3) at least 3 are candidate AGNs., Comment: 30 pages, 5 figures. Accepted for publication in The Astronomical Journal

ABRIDGED: We study the evolution since z~1 of the rest-frame B luminosity function of the early-type galaxies (ETGs) in ~0.7 deg^2 in the COSMOS field. In order to identify ALL progenitors of local ETGs we construct the sample of high-z galaxies using two complementary criteria: (i) A morphological selection based on the Zurich Estimator of Structural Types, and (ii) A photometric selection based on the galaxy properties in the (U-V)-M_V color-magnitude diagram. We furthermore constrain both samples so as to ensure that the selected progenitors of ETGs are compatible with evolving into systems which obey the mu_B-r_{hl} Kormendy relation. Assuming the luminosity evolution derived from studies of the fundamental plane for high-z ETGs, our analysis shows no evidence for a decrease in the number density of the most massive ETGs out to z~ 0.7: Both the morphologically- and the photometrically-selected sub-samples show no evolution in the number density of bright (~L>2.5L*) ETGs. Allowing for different star formation histories, and cosmic variance, we estimate a maximum decrease in the number density of massive galaxies at that redshift of ~30%. We observe, however, in both the photometrical and morphological samples, a deficit of up to ~2-3 of fainter ETGs over the same cosmic period. Our results argue against a significant contribution of recent dissipationless ``dry'' mergers to the formation of the most massive ETGs. We suggest that the mass growth in low luminosity ETGs can be explained with a conversion from z~0.7 to z=0 of blue, irregular and disk galaxies into low- and intermediate-mass ``red'' ETGs, possibly also through gas rich mergers., Comment: Replaced with accepted version (ApJ COSMOS special issue)

The Spitzer-COSMOS survey (S-COSMOS) is a Legacy program (Cycles 2+3) designed to carry out a uniform deep survey of the full 2 sq deg COSMOS field in all seven Spitzer bands (3.6, 4.5, 5.6, 8.0, 24.0, 70.0, 160.0 u). This paper describes the survey parameters, mapping strategy, data reduction procedures, achieved sensitivities to date, and the complete data set for future reference. We show that the observed infrared backgrounds in the S-COSMOS field are within 10% of the predicted background levels. The fluctuations in the background at 24u have been measured and do not show any significant contribution from cirrus, as expected. In addition, we report on the number of asteroid detections in the low galactic latitude COSMOS field. We use the Cycle 2 S-COSMOS data to determine preliminary number counts, and compare our results with those from previous Spitzer Legacy surveys (e.g. SWIRE, GOODS). The results from this "first analysis" confirm that the S-COSMOS survey will have sufficient sensitivity with IRAC to detect ~ L* disks and spheroids out to z ~ 3, and with MIPS to detect ultraluminous starbursts and AGN out to z ~3 at 24u and out to z ~1.5-2 at 70u and 160u., Comment: 21 pages including 4 tables and 9 figures. Accepted for Publication on ApJS COSMOS special Issue

The Cosmic Evolution Survey (COSMOS) was initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope (HST) for high resolution imaging. Here we review the characteristics of the HST imaging with the Advanced Camera for Surveys (ACS) and parallel observations with NICMOS and WFPC2. A square field (1.8$\sq$\deg) has been imaged with single-orbit ACS I-F814W exposures with 50% completeness for sources 0.5\arcsec in diameter at I$_{AB} $ = 26.0 mag. The ACS imaging is a key part of the COSMOS survey, providing very high sensitivity and high resolution (0.09\arcsec FWHM, 0.05\arcsec pixels) imaging and detecting 1.2 million objects to a limiting magnitude of 26.5 (AB). These images yield resolved morphologies for several hundred thousand galaxies. The small HST PSF also provides greatly enhanced sensitivity for weak lensing investigations of the dark matter distribution., Comment: 21 pages, 6 figures -- to appear in COSMOS ApJ Suppl. special issue

zCOSMOS is a large redshift survey that is being undertaken in the COSMOS field using 600 hours of observation with the VIMOS spectrograph on the 8-m VLT. The survey is designed to characterise the environments of COSMOS galaxies from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic web and to produce diagnostic information on galaxies and active galactic nuclei. The zCOSMOS survey consists of two parts: (a) zCOSMOS-bright, a magnitude-limited I-band IAB < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole 1.7 deg2 COSMOS ACS field and designed to mimic the parameters of the 2dfGRS; and (b) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through colour-selection criteria to have 1.4 < z < 3.0, within the central 1 deg2. This paper describes the survey design and the construction of the target catalogues, and briefly outlines the observational program and the data pipeline. In the first observing season, spectra of 1303 zCOSMOS-bright targets and of 977 zCOSMOS-deep targets have been obtained. These are briefly analysed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally completed between 2008-2009. The power of combining spectroscopic and photometric redshifts is demonstrated, especially in correctly identifying the emission line in single-line spectra and in determining which of the less reliable spectroscopic redshifts are correct and which are incorrect. Our zCOSMOS-deep spectra demonstrate the effectiveness of our selection techniques to isolate high redshift galaxies at 1.4 < z < 3.0 and of VIMOS to measure their redshifts using ultraviolet absorption lines., Comment: 24 pages plus 16 figures. Accepted, to appear in the ApJ Supplement COSMOS Special Issue

(Abbrev.) This paper prepares a series of papers analysing the Intermediate MAss Galaxy Evolution Sequence (IMAGES) up to z=1. Intermediate mass galaxies (MJ <=-20.3) are selected from the Chandra Deep Field South (CDFS) for which we identify a serious lack of spectroscopically determined redshifts..... We have spectroscopically identified 691 objects including 580 gal., 7 QSOs, and 104 stars. This study provides 531 new redshifts in the CDFS. It confirms the presence of several large scale structures in the CDFS. To test the impact of these structures in the GOODS-South field, we ... compare the evolution of rest-frame U, B, V and K galaxy luminosity densities to that derived from the CFRS. The CDFS field shows a significant excess of luminosity densities in the z=0.5-0.75 range, which increases with the wavelength, reaching up to 0.5 dex at 2.1 um. Stellar mass and specific star formation evolutions might be significantly affected by the presence of the peculiar large scale structures at z= 0.668 and at z= 0.735, that contain a significant excess of evolved, massive galaxies when compared to other fields. This leads to a clear warning to results based on the CDFS/GOODS South fields, especially those related to the evolution of red luminosity densities, i.e. stellar mass density and specific star formation rate. Photometric redshift techniques, when applied to that field, are producing quantities which are apparently less affected by cosmic variance (0.25 dex at 2.1 um), however at the cost of the difficulty in disentangling between evolutionary and cosmic variance effects., Comment: Accepted for publication in A&A, 19 pages, 13 figures

We present deep, high angular-resolution HST/NICMOS imaging in the Hubble Deep Field South (HDF-S), focusing on a subset of 14 Distant Red Galaxies (DRGs) at z ~ 2.5 galaxies that have been pre-selected to have J-K > 2.3. We find a clear trend between the rest-frame optical sizes of these sources and their luminosity-weighted stellar ages as inferred from their broad-band spectral energy distributions (SEDs). Galaxies whose SEDs are consistent with being dusty and actively star forming generally show extended morphologies in the NICMOS images (r_e >~ 2 kpc), while the 5 sources which are not vigorously forming stars are extremely compact (r_e <~ 1 kpc). This trend suggests a direct link between the mean ages of the stars and the size and density of the galaxies and supports the conjecture that early events quench star-formation and leave compact remnants. Furthermore, the compact galaxies have stellar surface mass densities which exceed those of local galaxies by more than an order of magnitude. The existence of such massive dense galaxies presents a problem for models of early-type galaxy formation and evolution. Larger samples of DRGs and higher spatial resolution imaging will allow us to determine the universality of the results presented here for a small sample., Comment: Accepted to The Astrophysical Journal, 8 pages, 5 figures

[Abridged] Over the past two decades observations and theoretical simulations have established a global frame-work of galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark matter halos. Mergers of halos led to the build up of galaxy mass. A major step forward in understanding these issues requires well resolved physical information on individual galaxies at high redshift. Here we report adaptive optics, spectroscopic observations of a representative luminous star forming galaxy when the Universe was only twenty percent of its age. The superior angular resolution of these data reveals the physical and dynamical properties of a high redshift galaxy in unprecedented detail. A large and massive rotating proto-disk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole., Comment: Narure, accepted (Released Aug 17th)

We present SEDs, Spitzer colours, and IR luminosities for 850 micron selected galaxies in the GOODS-N field. Using the deep Spitzer Legacy images and new data and reductions of the VLA-HDF radio data, we find statistically secure counterparts for 60 per cent (21/35) of our submm sample, and identify tentative counterparts for another 12 objects. This is the largest sample of submm galaxies with statistically secure counterparts detected in the radio and with Spitzer. We find that in most cases the 850 micron emission is dominated by a single 24 micron source. A composite rest-frame SED shows that the submm sources peak at longer wavelengths than those of local ULIRGs of the same luminosity and therefore appear to be cooler. The SEDs of submm galaxies are also different from those of their high redshift neighbours, the near-IR selected BzK galaxies, whose mid-IR to radio SEDs are more like those of local ULIRGs. Using 24 micron. 850 micron and 1.4 GHz observations, we fit templates that span the mid-IR through radio to derived the integrated IR luminosity of the submm galaxies. By themselves, 24 micron and radio fluxes are able to predict LIR reasonably well because they are relatively insensitive to temperature. However, the submm flux by itself consistently overpredicts LIR when using spectral templates which obey the local ULIRG temperature-luminosity relation. The shorter Spitzer wavelengths sample the stellar bump at the redshifts of the submm sources, and we find that the Spitzer photometry alone provides a model independent estimate of the redshift. Using X-ray and mid-IR data, only 5 per cent of our secure counterparts show strong evidence for an active galactic nucleus dominating the IR luminosity., Comment: 24 pages, 11 eps figures. Accepted for publication in MNRAS 2006. Full resolution paper available from http://www.phas.ubc.ca/~pope/MF1289rv2.pdf