The black holes of radio galaxies during the "Quasar Era": Masses, accretion rates, and evolutionary stage

We present an analysis of the AGN broad-line regions of 6 powerful radio galaxies at z>~2 (HzRGs) with rest-frame optical imaging spectroscopy obtained at the VLT. All galaxies have luminous (L(H-alpha)=few x 10^44 erg s^-1), spatially unresolved H-alpha line emission with FWHM>= 10,000 km s^-1 at the position of the nucleus, suggesting their AGN are powered by supermassive black holes with masses of few x 10^9 M_sun and accretion luminosities of a few percent of the Eddington luminosity. In two galaxies we also detect the BLRs in H-beta, suggesting relatively low extinction of A_V~1 mag, which agrees with constraints from X-ray observations. By relating black hole and bulge mass, we find a possible offset towards higher black-hole masses of at most ~0.6 dex relative to nearby galaxies at a given host mass, although each individual galaxy is within the scatter of the local relationship. If not entirely from systematic effects, this would then suggest that the masses of the host galaxies have increased by at most a factor ~4 since z~2 relative to the black-hole masses, perhaps through accretion of satellite galaxies or because of a time lag between star formation in the host galaxy and AGN fueling. We also compare the radiative and mechanical energy output (from jets) of our targets with predictions of recent models of "synthesis" or "grand unified" AGN feedback, which postulate that AGN with similar radiative and mechanical energy output rates to those found in our HzRGs may be nearing the end of their period of active growth. We discuss evidence that they may reach this stage at the same time as their host galaxies.Comment: A&A in pres

Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326: Evidence for negative AGN feedback

We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation rate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors 10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 326 N in the optical suggests an outflow with a terminal velocity of ~−1800 km s^(−1) and a mass outflow rate of 30−40 M_⊙ yr^(−1), which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times are of order 10^(7−8) yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2 luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback

Defying jet-gas alignment in two radio galaxies at z~2 with extended light profiles: Similarities to brightest cluster galaxies

We report the detection of extended warm ionized gas in two powerful high-redshift radio galaxies, NVSS J210626-314003 at z=2.10 and TXS 2353-003 at z=1.49, that does not appear to be associated with the radio jets. This is contrary to what would be expected from the alignment effect, a characteristic feature of distant, powerful radio galaxies at z> 0.6. The gas also has smaller velocity gradients and line widths than most other high-z radio galaxies with similar data. Both galaxies are part of a systematic study of 50 high-redshift radio galaxies with SINFONI, and are the only two that are characterized by the presence of high surface-brightness gas not associated with the jet axis and by the absence of such gas aligned with the jet. Both galaxies are spatially resolved with ISAAC broadband imaging covering the rest-frame R band, and have extended wings that cannot be attributed to line contamination. We argue that the gas and stellar properties of these galaxies are more akin to gas-rich brightest cluster galaxies in cool-core clusters than the general population of high-redshift radio galaxies at z>2. In support of this interpretation, one of our sources, TXS 2353-003, for which we have H\alpha\ narrowband imaging, is associated with an overdensity of candidate H\alpha\ emitters by a factor of 8 relative to the field at z=1.5. We discuss possible scenarios of the evolutionary state of these galaxies and the nature of their emission line gas within the context of cyclical AGN feedback.Comment: A&A in pres

The dynamics of the ionized and molecular ISM in powerful obscured quasars at z>=3.5

We present an analysis of the kinematics and excitation of the warm ionized gas in two obscured, powerful quasars at z>=3.5 from the SWIRE survey, SWIRE J022513.90-043419.9 and SWIRE J022550.67-042142, based on imaging spectroscopy on the VLT. Line ratios in both targets are consistent with luminous narrow-line regions of AGN. SWIRE J022550.67-042142 has very broad (FWHM=2000 km/s), spatially compact [OIII] line emission. SWIRE J022513.90-043419.9 is spatially resolved, has complex line profiles of H-beta and [OIII], including broad wings with blueshifts of up to -1500 km/s relative to the narrow [OIII]5007 component, and widths of up to FWHM=5000 km/s. Estimating the systemic redshift from the narrow H-beta line, as is standard for AGN host galaxies, implies that a significant fraction of the molecular gas is blueshifted by up to ~ -1000 km/s relative to the systemic velocity. Thus the molecular gas could be participating in the outflow. Significant fractions of the ionized and molecular gas reach velocities greater than the escape velocity. We compare empirical and modeling constraints for different energy injection mechanisms, such as merging, star formation, and momentum-driven AGN winds. We argue that the radio source is the most likely culprit, in spite of the sources rather modest radio power of 10^25 W/Hz. Such a radio power is not uncommon for intense starburst galaxies at z~2. We discuss these results in light of the co-evolution of AGN and their host galaxy.Comment: Accepted by MNRA

The Average Optical Spectra of Intense Starbursts at z~2: Outflows and the Pressurization of the ISM

An important property of star-forming galaxies at z~1-2 is the high local star-formation intensities they maintain over tens of kiloparsecs at levels that are only observed in the nearby Universe in the most powerful nuclear starbursts. To investigate how these high star-formation intensities affect the warm ionized medium, we present an analysis of the average spectra of about 50 such galaxies at z~1.2-2.6 and of subsamples selected according to their local and global star-formation intensity. Stacking allows us to probe relatively weak lines like [SII]\lambda \lambda 6716,6731 and [OI]\lambda 6300, which are tracers of the conditions of the ISM and are undetectable in most individual targets. We find higher gas densities (hence pressures) in intensely star-forming regions compared to fainter diffuse gas and, overall, values that are comparable to starburst regions and the diffuse ISM in nearby galaxies. By modeling the H\alpha\ surface brightnesses and [SII]/H\alpha\ line ratios with the Cloudy photoionization code, we find that our galaxies continue trends observed in local galaxies, where gas pressures scale with star-formation intensity. We discuss these results in the context of models of self-regulated star formation, where star formation determines the average thermal and turbulent pressure in the ISM, which in turn determines the rate at which stars can form, finding good agreement with our data. We also confirm the detection of broad, faint lines underlying H\alpha\ and [NII], which have previously been considered evidence of either outflows or active galactic nuclei. Finding that the broad component is only significantly detected in stacks with the highest average local and global star-formation intensities strongly supports the outflow interpretation, and further emphasizes the importance of star-formation feedback and self-regulation in the early Universe.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and Astrophysic

CO line emission in the halo of a radio galaxy at z=2.6

We report the detection of luminous CO(3-2) line emission in the halo of the z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun and relatively low star-formation rates. With the IRAM PdBI we find two CO emission line components at the same position at ~80 kpc distance from the HzRG along the axis of the radio jet, with different blueshifts of few 100 km s^-1 relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected at 8 sigma significance. HzRGs have significant galaxy overdensities and extended halos of metal-enriched gas often with embedded clouds or filaments of denser material, and likely trace very massive dark-matter halos. The CO emission may be associated with a gas-rich, low-mass satellite galaxy with little on-going star formation, in contrast to all previous CO detections of galaxies at similar redshifts. Alternatively, the CO may be related to a gas cloud or filament and perhaps jet-induced gas cooling in the outer halo, somewhat in analogy with extended CO emission found in low-redshift galaxy clusters.Comment: MNRAS Letters, accepte

On the self-regulation of intense star-formation in galaxies at z=1-3

(abridged) We have analyzed the properties of the rest-frame optical emission lines of a sample of 53 intensely star forming galaxies at z=1.3 to 2.7 observed with SINFONI on the ESO-VLT. We find large velocity dispersions in the lines, sigma=30-250 km/s. Our data agree well with simulations where we applied beam-smearing and assumed a scaling relation of the form: velocity dispersion is proportional to the square root of the star-formation intensity (star-formation rate per unit area). We conclude that the dispersions are primarily driven by star formation. To explain the high surface brightness and optical line ratios, high thermal pressures in the warm ionized medium, WIM, are required (log P/k (K/cm^3)>~6-7). Such thermal pressures in the WIM are similar to those observed in nearby starburst galaxies, but occur over much larger physical scales. Moreover, the relatively low ionization parameters necessary to fit the high surface brightnesses and optical line ratios suggest that the gas is not only directly associated with regions of star formation, but is wide spread throughout the general ISM. Thus the optical emission line gas is a tracer of the large scale dynamics of the bulk of the ISM. We present a simple model for the energy input from young stars in an accreting galaxy, to argue that the intense star-formation is supporting high turbulent pressure, which roughly balances the gravitational pressure and thus enables distant gas accreting disks to maintain a Toomre disk instability parameter Q~1. For a star formation efficiency of 3%, only 5-15% of the mechanical energy from young stars that is deposited in the ISM is needed to support the level of turbulence required for maintaining this balance. Since this balance is maintained by energy injected into the ISM by the young stars themselves, this suggests that star formation in high redshift galaxies is self-regulating.Comment: A&A in press; 15 figure

Integral-field spectroscopy of a Lyman-Break Galaxy at z=3.2: evidence for merging

We present spatially-resolved, rest-frame optical spectroscopy of a z~3 Lyman-break galaxy (LBG), Q0347-383 C5, obtained with SINFONI on the VLT. This galaxy, among the ~10% brightest LBGs, is only the second z~3 LBG observed with an integral-field spectrograph. It was first described by Pettini et al. (2001), who obtained WFPC2 F702W imaging and longslit spectroscopy in the K-band. We find that the emission line morphology is dominated by two unresolved blobs at a projected distance of ~5 kpc with a velocity offset of ~33 km s^-1. Velocity dispersions suggest that each blob has a mass of ~10^10 M_sun. Unlike Pettini et al. (2001), our spectra are deep enough to detect H-beta, and we derive star-formation rates of ~20-40 M_sun yr^-1, and use the H-beta/[OIII] ratio to crudely estimate an oxygen abundance 12+[O/H]=7.9-8.6, which is in the range typically observed for LBGs. We compare the properties of Q0347-383 C5 with what is found for other LBGs, including the gravitationally lensed ``arc+core'' galaxy (Nesvadba et al. 2006), and discuss possible scenarios for the nature of the source, namely disk rotation, a starburst-driven wind, disk fragmentation, and merging of two LBGs. We favor the merging interpretation or bright, extended LBGs like Q0347-383C5, in broad agreement with predicted merger rates from hierarchical models.Comment: A&A accepte