J. Kurk

Multiwavelength Study of Massive Galaxies at z~2. I. Star Formation and Galaxy Growth

Examining a sample of massive galaxies at 1.4 10 11 L⊙, 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 24µm-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 order of magnitude, but give better agreement for z > 1.4 quiescent galaxies. Subject headings: galaxies: evolution — galaxies: formation — cosmology: observations — galaxies: starbursts — galaxies: high-redshift

zCOSMOS: A large VLT/VIMOS redshift survey covering 0 < z < 3 in the COSMOS field

zCOSMOS is a large-redshift survey that is being undertaken in the COSMOS field using 600 hr of observation with the VIMOS spectrograph on the 8 m VLT. The survey is designed to characterize 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: (1) zCOSMOSbright, a magnitude-limited I-band I_(AB) < 22.5 sample of about 20,000 galaxies with 0.1 < z < 1.2 covering the whole 1.7 deg^2 COSMOS ACS field, for which the survey parameters at z ~ 0.7 are designed to be directly comparable to those of the 2dFGRS at z ~ 0.1; and (2) zCOSMOS-deep, a survey of approximately 10,000 galaxies selected through color-selection criteria to have 1.4 < z < 3.0, within the central 1 deg^2. This paper describes the survey design and the construction of the target catalogs and briefly outlines the observational program and the data pipeline. In the first observing season, spectra of 1303 zCOSMOS-bright targets and 977 zCOSMOS-deep targets have been obtained. These are briefly analyzed to demonstrate the characteristics that may be expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally completed between 2008 and 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. These techniques bring the overall success rate in the zCOSMOS-bright so far to almost 90% and to above 97% in the 0.5 < z < 0.8 redshift range. Our zCOSMOS-deep spectra demonstrate the power 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.

GMASS ultradeep spectroscopy of galaxies at z ~ 2 - II. Superdense passive galaxies: How did they form and evolve?

Aims. The aim of this work is to investigate the physical, structur al and evolutionary properties of old, passive galaxies at z> 1.4 and to place new constraints on massive galaxy formation and evolution. Methods. We combine ultradeep optical spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band (optical to mid‐infrared) photometry and HST imaging to study a sample of spectroscopically identified passive galaxies at 1.39 2. No X-ray emission was found neither from individual galaxies nor from a stacking analysis of the sample. Only one galaxy shows a marginal detection at 24� m. These galaxies have morphologies that are predominantly compact and spheroidal. However, their sizes (Re. 1 kpc) are much smaller than those of spheroids in the present‐day Universe. Their stellar mass surface densities are consequently hig her 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 Korme ndy 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 Re≈ 1 kpc are extremely rare at z≈ 0 with respect to z> 1, and absent if Re 2. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution.

THE SINS SURVEY OF z ∼ 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS ∗

We have studied the properties of giant star-forming clumps in five z ~ 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H?/[N II] line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km s?1 kpc?1, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.

Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges

Approximately 20‐30% of 1.4 6.2 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 NH > ∼ 10 24 cm −2 and an average, unobscured X-ray luminosity L2−8keV ≈(1‐4) × 10 43 erg s −1 . Their sky density (∼ 3200 deg −2 ) and space density (∼ 2.6 × 10 −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⊙, an effect likely connected with downsizing in galaxy formation. The ratio of the inferred 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 in local s pheroids, implying concurrent growth of both within the precursors of today’s massive galaxies. Subject headings:galaxies: evolution — galaxies: formation — galaxies: active — X-rays: galaxies

THE SINS SURVEY: MODELING THE DYNAMICS OF z ∼ 2 GALAXIES AND THE HIGH-z TULLY-FISHER RELATION*

We present the modeling of SINFONI integral field dynamics of 18 star-forming galaxies at z ~ 2 from Hα line emission. The galaxies are selected from the larger sample of the SINS survey, based on the prominence of ordered rotational motions with respect to more complex merger-induced dynamics. The quality of the data allows us to carefully select systems with kinematics dominated by rotation, and to model the gas dynamics across the whole galaxy using suitable exponential disk models. We obtain a good correlation between the dynamical mass and the stellar mass, finding that large gas fractions (M gas ≈ M *) are required to explain the difference between the two quantities. We use the derived stellar mass and maximum rotational velocity V max from the modeling to construct for the first time the stellar mass Tully-Fisher relation at z ~ 2.2. The relation obtained shows a slope similar to what is observed at lower redshift, but we detect an evolution of the zero point. We find that at z ~ 2.2 there is an offset in log(M *) for a given rotational velocity of 0.41 ± 0.11 with respect to the local universe. This result is consistent with the predictions of the latest N-body/hydrodynamical simulations of disk formation and evolution, which invoke gas accretion onto the forming disk in filaments and cooling flows. This scenario is in agreement with other dynamical evidence from SINS, where gas accretion from the halo is required to reproduce the observed properties of a large fraction of the z ~ 2 galaxies. Based on observations obtained at the Very Large Telescope (VLT) of the European Southern Observatory, Paranal, Chile, in the context of guaranteed time programs 073.B-9018, 074.A-9011, 075.A-0466, 076.A-0527, 077.A-0576, 078.A-0600, 078.A-0055, 079.A-0341, 080.A-0330, and 080.A-0635.

Multiwavelength study of massive galaxies at z similar to 2. II. Widespread compton-thick active galactic nuclei and the concurrent growth of black holes and bulges

Approximately 20‐30% of 1.4 6.2 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 NH > ∼ 10 24 cm −2 and an average, unobscured X-ray luminosity L2−8keV ≈(1‐4) × 10 43 erg s −1 . Their sky density (∼ 3200 deg −2 ) and space density (∼ 2.6 × 10 −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⊙, an effect likely connected with downsizing in galaxy formation. The ratio of the inferred 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 in local s pheroids, implying concurrent growth of both within the precursors of today’s massive galaxies. Subject headings:galaxies: evolution — galaxies: formation — galaxies: active — X-rays: galaxies

A large Hα survey at z = 2.23, 1.47, 0.84 and 0.40: the 11 Gyr evolution of star-forming galaxies from HiZELS

This paper presents new deep and wide narrow-band surveys undertaken with United Kingdom Infrared Telescope (UKIRT), Subaru and the Very Large Telescope (VLT), a unique combined effort to select large, robust samples of Hα star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyr) in a uniform manner over ∼2 deg^2 in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch Hα surveys reach a matched 3σ flux limit of ≈3 M_⊙ yr^(−1) out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow us to greatly overcome cosmic variance and assemble by far the largest samples of Hα emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Hα emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the Hα luminosity function and its evolution. The faint-end slope of the Hα luminosity function is found to be α = −1.60 ± 0.08 over z = 0–2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L*_Hα, evolves significantly as log  L*_Hα(z) = 0.45z + log  L*_z = 0. This is the first time Hα has been used to trace star formation activity with a single homogeneous survey at z = 0.4–2.23. Overall, the evolution seen with Hα is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as far-infrared and ultraviolet, jointly pointing towards the bulk of the evolution in the last 11 Gyr being driven by a statistically similar star-forming population across cosmic time, but with a strong luminosity increase from z ∼ 0 to ∼2.2. Our uniform analysis allows us to derive the Hα star formation history (SFRH) of the Universe, showing a clear rise up to z ∼ 2.2, for which the simple parametrization log_10ρSFR = −2.1(1 + z)^(−1) is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalization of the Hα SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Hα SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last ∼11 Gyr is responsible for producing ∼95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past ∼11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value.

The KMOS3D survey: design, first results, and the evolution of galaxy kinematics from 0.7 ≤ z ≤ 2.7

We present the KMOS3D survey, a new integral field survey of over 600 galaxies at 0.7 1, implying that the star-forming main sequence is primarily composed of rotating galaxies at both redshift regimes. When considering additional stricter criteria, the Hα kinematic maps indicate that at least ~70% of the resolved galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated velocity dispersions reported in previous integral field spectroscopy studies at z 0.7. For rotation-dominated disks, the average intrinsic velocity dispersion decreases by a factor of two from 50 km s–1at z ~ 2.3 to 25 km s–1at z ~ 0.9. Combined with existing results spanning z ~ 0-3, we show that disk velocity dispersions follow an evolution that is consistent with the dependence of velocity dispersion on gas fractions predicted by marginally stable disk theory.

Black Hole Masses and Enrichment of z ~ 6 SDSS Quasars*

We present sensitive near-infrared spectroscopic observations for a sample of five z ~ 6 quasars. These quasars are among the most distant, currently known quasars in the universe. The spectra have been obtained using ISAAC at the VLT and include the C IV, Mg II, and Fe II lines. We measure the Fe II/Mg II line ratio, as an observational proxy for the Fe/α-element ratio. We derive a ratio of 2.7 ± 0.8 for our sample, which is similar to that found for lower redshift quasars; i.e., we provide additional evidence for the lack of evolution in the Fe II/Mg II line ratio of quasars up to the highest redshifts. This result demonstrates that star formation must have commenced at z ≥ 8 in the quasar hosts. The line widths of the Mg II and C IV lines give two estimates for the black hole masses. A third estimate is given by assuming that the quasars emit at their Eddington luminosity. The derived masses using these three methods agree well, implying that the quasars are not likely to be strongly lensed. We derive central black hole masses of (0.3-5.2) × 109 M☉. We use the difference between the redshift of Mg II (a proxy for the systemic redshift of the quasar) and the onset of the Gunn-Peterson trough to derive the extent of the ionized Stromgren spheres around our target quasars. The derived physical radii are about 5 Mpc. Using a simple ionization model, the emission of the central quasars would need of order 106-108 yr to create these cavities. As the e-folding timescale for the central accreting black hole is on the order of a few times 107 yr, it can grow by one e-folding or less within this time span.