[en] We present sensitive near-infrared (NIR) VLT ISAAC spectroscopic observations of the z = 6.08 quasar SDSS J030331.40-001912.9. This quasi-stellar object (QSO) is more than a magnitude fainter than other QSOs at z ∼ 6 for which NIR spectroscopy has been obtained to date and is therefore presumably more representative of the QSO population at the end of cosmic reionization. Combining rest-frame UV continuum luminosity with the width measurements of the Mg II and C IV lines, we derive a black hole mass of 2^+1.0_-0.5 x 10⁸ M _sun, the lowest mass observed for z ∼ 6 QSOs to date, and derive an Eddington ratio of 1.6^+0.4_-0.6, among the highest value derived for QSOs at any redshift. The Spitzer 24 μm nondetection of this QSO does not leave space for a significant hot dust component in its optical/NIR spectral energy distribution, in common with one other faint QSO at z = 6, but in contrast to more than 20 more z = 6 QSOs and all known lower redshift QSOs with sufficiently deep multiwavelength photometry. We conclude that we have found evidence for differences in the intrinsic properties of at least one z ∼ 6 QSO as compared to the lower redshift population.

[en] Quasars (QSOs) at the highest known redshift (z ∼ 6) are unique probes of the early growth of supermassive black holes (BHs). Until now, only the most luminous QSOs have been studied, often one object at a time. Here we present the most extensive consistent analysis to date of 4 < z < 6.5 QSOs with observed near-infrared spectra, combining three new z ∼ 6 objects from our ongoing Very Large Telescope-Infrared Spectrometer And Array Camera program with nineteen sources from the literature. The new sources extend the existing Sloan Digital Sky Survey (SDSS) sample toward the faint end of the QSO luminosity function. Using a maximum likelihood fitting routine optimized for our spectral decomposition, we estimate the BH mass (M_BH), the Eddington ratio (defined as L_bol/L_Edd), and the Fe II/Mg II line ratio, a proxy for the chemical abundance, to characterize both the central object and the broad-line region gas. The QSOs in our sample host BHs with masses of ∼10⁹ M_sun that are accreting close to the Eddington luminosity, consistent with earlier results. We find that the distribution of observed Eddington ratios is significantly different than that of a luminosity-matched comparison sample of SDSS QSOs at lower redshift (0.35 < z < 2.25): the average (log (L_bol/L_Edd)) = -0.37 (L_bol/L_Edd ∼ 0.43) with a scatter of 0.20 dex for the z > 4 sample and the (log (L_bol/L_Edd)) = -0.80 (L_bol/L_Edd ∼ 0.16) with a scatter of 0.24 dex for the 0.35 < z < 2.25 sample. This implies that, at a given luminosity, the M_BH at high-z is typically lower than the average M_BH of the lower-redshift population, i.e., the z > 4 sources are accreting significantly faster than the lower-redshift ones. We show that the derived Fe II/Mg II ratios depend sensitively on the analysis performed: our self-consistent, homogeneous analysis significantly reduces the Fe II/Mg II scatter found in previous studies. The measured Fe II/Mg II line ratios show no sign of evolution with cosmic time in the redshift range 4 < z < 6.5. If the Fe II/Mg II line ratio is used as a secondary proxy of the Fe/Mg abundance ratio, this implies that the QSOs in our sample have undergone a major episode of Fe enrichment in the few 100 Myr preceding the cosmic age at which they are observed.

[en] In this paper, we follow up on our previous detection of nuclear ionized outflows in the most massive (log(M _*/M _☉) ≥ 10.9) z ∼ 1-3 star-forming galaxies by increasing the sample size by a factor of six (to 44 galaxies above log(M _*/M _☉) ≥ 10.9) from a combination of the SINS/zC-SINF, LUCI, GNIRS, and KMOS^3Dspectroscopic surveys. We find a fairly sharp onset of the incidence of broad nuclear emission (FWHM in the Hα, [N II], and [S II] lines ∼450-5300 km s^–1), with large [N II]/Hα ratios, above log(M _*/M _☉) ∼ 10.9, with about two-thirds of the galaxies in this mass range exhibiting this component. Broad nuclear components near and above the Schechter mass are similarly prevalent above and below the main sequence of star-forming galaxies, and at z ∼ 1 and ∼2. The line ratios of the nuclear component are fit by excitation from active galactic nuclei (AGNs), or by a combination of shocks and photoionization. The incidence of the most massive galaxies with broad nuclear components is at least as large as that of AGNs identified by X-ray, optical, infrared, or radio indicators. The mass loading of the nuclear outflows is near unity. Our findings provide compelling evidence for powerful, high-duty cycle, AGN-driven outflows near the Schechter mass, and acting across the peak of cosmic galaxy formation.

[en] We present the KMOS^3D survey, a new integral field survey of over 600 galaxies at 0.7 < z < 2.7 using KMOS at the Very Large Telescope. The KMOS^3D survey utilizes synergies with multi-wavelength ground- and space-based surveys to trace the evolution of spatially resolved kinematics and star formation from a homogeneous sample over 5 Gyr of cosmic history. Targets, drawn from a mass-selected parent sample from the 3D-HST survey, cover the star formation-stellar mass (M _*) and rest-frame (U – V) – M _* planes uniformly. We describe the selection of targets, the observations, and the data reduction. In the first-year of data we detect Hα emission in 191 M _* = 3 × 10⁹-7 × 10¹¹ M _☉ galaxies at z = 0.7-1.1 and z = 1.9-2.7. In the current sample 83% of the resolved galaxies are rotation dominated, determined from a continuous velocity gradient and v _rot/σ₀ > 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

[en] The kinematics of distant galaxies from z = 0.1 to z > 2 play a key role in our understanding of galaxy evolution from early times to the present. One of the important parameters is the intrinsic, or local, velocity dispersion of a galaxy, which allows one to quantify the degree of non-circular motions such as pressure support. However, this is difficult to measure because the observed dispersion includes the effects of (often severe) beam smearing on the velocity gradient. Here we investigate four methods of measuring the dispersion that have been used in the literature, to assess their effectiveness at recovering the intrinsic dispersion. We discuss the biases inherent in each method, and apply them to model disk galaxies in order to determine which methods yield meaningful quantities and under what conditions. All the mean-weighted dispersion estimators are affected by (residual) beam smearing. In contrast, the dispersion recovered by fitting a spatially and spectrally convolved disk model to the data is unbiased by the beam smearing it is trying to compensate. Because of this, and because the bias it does exhibit depends only on the signal-to-noise ratio (S/N), it can be considered reliable. However, at very low S/N, all methods should be used with caution.

[en] We present the analysis of Hubble Space Telescope (HST) J- and H-band imaging for 29 galaxies on the star-forming main sequence at z ∼ 2, which have adaptive optics Very Large Telescope SINFONI integral field spectroscopy from our SINS/zC-SINF program. The SINFONI Hα data resolve the ongoing star formation and the ionized gas kinematics on scales of 1–2 kpc; the near-IR images trace the galaxies’ rest-frame optical morphologies and distributions of stellar mass in old stellar populations at a similar resolution. The global light profiles of most galaxies show disk-like properties well described by a single Sérsic profile with $n\sim <!--\; ???\; -->1$, with only $\sim <!--\; ???\; -->15\mathrm{\%<!--\; \%\; -->}$ requiring a high $n><!--\; >\; -->3$ Sérsic index, all more massive than ${10}^{10}{M}_{\odot <!--\; ???\; -->}$. In bulge+disk fits, about 40% of galaxies have a measurable bulge component in the light profiles, with $\sim <!--\; ???\; -->15\mathrm{\%<!--\; \%\; -->}$ showing a substantial bulge-to-total ratio (B/T) $B/T\gtrsim <!--\; ???\; -->0.3$. This is a lower limit to the frequency of z ∼ 2 massive galaxies with a developed bulge component in stellar mass because it could be hidden by dust and/or outshined by a thick actively star-forming disk component. The galaxies’ rest-optical half-light radii range between 1 and 7 kpc, with a median of 2.1 kpc, and lie slightly above the size–mass relation at these epochs reported in the literature. This is attributed to differences in sample selection and definitions of size and/or mass measurements. The ${(u-<!--\; ???\; -->g)}_{\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{t}}$ color gradient and scatter within individual z ∼ 2 massive galaxies with $\gtrsim <!--\; ???\; -->{10}^{11}{M}_{\odot <!--\; ???\; -->}$ are as high as in z = 0 low-mass, late-type galaxies and are consistent with the high star formation rates of massive z ∼ 2 galaxies being sustained at large galactocentric distances.

[en] We analyze the size evolution of H II regions around 27 quasars between z = 5.7 and 6.4 ('quasar near zones' or NZs). We include more sources than previous studies, and we use more accurate redshifts for the host galaxies, with eight CO molecular line redshifts and nine Mg II redshifts. We confirm the trend for an increase in NZ size with decreasing redshift, with the luminosity-normalized proper size evolving as R_NZ,corrected = (7.4 ± 0.3) - (8.0 ± 1.1) x (z - 6) Mpc. While derivation of the absolute neutral fraction remains difficult with this technique, the evolution of the NZ sizes suggests a decrease in the neutral fraction of intergalactic hydrogen by a factor ∼9.4 from z = 6.4 to 5.7, in its simplest interpretation. Alternatively, recent numerical simulations suggest that this rapid increase in NZ size from z = 6.4 to 5.7 is due to the rapid increase in the background photo-ionization rate at the end of the percolation or overlap phase, when the average mean-free path of ionizing photons increases dramatically. In either case, the results are consistent with the idea that z ∼ 6-7 corresponds to the tail end of cosmic reionization. The scatter in the normalized NZ sizes is larger than expected simply from measurement errors, and likely reflects intrinsic differences in the quasars or their environments. We find that the NZ sizes increase with quasar UV luminosity, as expected for photo-ionization dominated by quasar radiation.

[en] The relationship between galaxies of intermediate stellar mass and moderate luminosity active galactic nuclei (AGNs) at 1 < z < 3 is investigated with a Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample complemented with public data in the GOODS-South field. Using X-ray data, hidden AGNs are identified in unsuspected star-forming galaxies with no apparent signs of non-stellar activity. In the color-mass plane, two parallel trends emerge during the ∼2 Gyr between the average redshifts z ∼ 2.2 and z ∼ 1.3: while the red sequence becomes significantly more populated by ellipticals, the majority of AGNs with L(2-10 keV) > 10^42.3 erg s^–1 disappear from the blue cloud/green valley where they were hosted predominantly by star-forming systems with disk and irregular morphologies. These results are even clearer when the rest-frame colors are corrected for dust reddening. At z ∼ 2.2, the ultraviolet spectra of active galaxies (including two Type 1 AGNs) show possible gas outflows with velocities up to about –500 km s^–1, which are observed neither in inactive systems at the same redshift, nor at lower redshifts. Such outflows indicate the presence of gas that can move faster than the escape velocities of active galaxies. These results suggest that feedback from moderately luminous AGNs (log L_X < 44.5 erg s^–1) played a key role at z ≳ 2 by contributing to outflows capable of ejecting part of the interstellar medium and leading to a rapid decrease in star formation in host galaxies with stellar masses 10 < log(M/M_⊙)< 11

[en] As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive the radial distributions of Hα surface brightness, stellar mass surface density, and dynamical mass at ∼2 kpc resolution in 19 z ∼ 2 star-forming disks with deep SINFONI adaptive optics spectroscopy at the ESO Very Large Telescope. From these data we infer the radial distribution of the Toomre Q-parameter for these main-sequence star-forming galaxies (SFGs), covering almost two decades of stellar mass (10^9.6-10^11.5 M _☉). In more than half of our SFGs, the Hα distributions cannot be fit by a centrally peaked distribution, such as an exponential, but are better described by a ring, or the combination of a ring and an exponential. At the same time the kinematic data indicate the presence of a mass distribution more centrally concentrated than a single exponential distribution for 5 of the 19 galaxies. The resulting Q-distributions are centrally peaked for all, and significantly exceed unity there for three-quarters of the SFGs. The occurrence of Hα rings and of large nuclear Q-values appears to be more common for the more massive SFGs. While our sample is small and biased to larger SFGs, and there remain uncertainties and caveats, our observations are consistent with a scenario in which cloud fragmentation and global star formation are secularly suppressed in gas-rich high-z disks from the inside out, as the central stellar mass density of the disks grows.

[en] We measured stellar velocity dispersions σ and derived dynamical masses of nine massive (M ∼ 10¹¹ M_sun) early-type galaxies (ETGs) from the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample at redshift 1.4 ∼< z ∼< 2.0. The σ are based on individual spectra for two galaxies at z ∼ 1.4 and on a stacked spectrum for seven galaxies with 1.6 < z < 2.0, with 202 hr of exposure at the ESO Very Large Telescope. We constructed detailed axisymmetric dynamical models for the objects, based on the Jeans equations, taking the observed surface brightness (from deep HST/ACS observations), point-spread function, and slit effects into account. Our dynamical masses M_Jeans agree within ∼<30% with virial estimates M_vir = 5 x R_eσ²/G, although the latter tend to be smaller. Our M_Jeans also agrees within a factor ∼<2 with the M_pop previously derived using stellar population models and 11 bands photometry. This confirms that the galaxies are intrinsically massive. The inferred mass-to-light ratios (M/L) _U in the very age-sensitive rest-frame U band are consistent with passive evolution in the past ∼1 Gyr (formation redshift z_f ∼ 3). A 'bottom-light' stellar initial mass function appears to be required to ensure close agreement between M_Jeans and M _pop at z ∼ 2, as it does at z ∼ 0. The GMASS ETGs are on average more dense than their local counterpart. However, a few percent of local ETGs of similar dynamical masses also have comparable σ and mass surface density Σ₅₀ inside R_e.