Investigating evidence for different black hole accretion modes since redshift z~1

Chandra data in the COSMOS, AEGIS-XD and 4Ms CDFS are combined with optical/near-IR photometry to determine the rest-frame U-V vs V-J colours of X-ray AGN hosts at mean redshifts 0.40 and 0.85. This combination of colours (UVJ) provides an efficient means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasises differences between AGN split by their UVJ colours. AGN in quiescent galaxies are dominated by spheroids, while star-forming hosts are split between bulges and disks. The UVJ diagram of AGN hosts is then used to set limits on the accretion density associated with evolved and star-forming systems. Most of the black hole growth since z~1 is associated with star-forming hosts. Nevertheless, ~15-20% of the X-ray luminosity density since z~1, is taking place in the quiescent region of the UVJ diagram. For the z~0.40 subsample, there is tentative evidence (2sigma significance), that AGN split by their UVJ colours differ in Eddington ratio. AGN in star-forming hosts dominate at high Eddington ratios, while AGN in quiescent hosts become increasingly important as a fraction of the total population toward low Eddington ratios. At higher redshift, z~0.8, such differences are significant at the 2sigma level only at Eddington ratios >1e-3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of SMBHs at the centres of galaxies. We compare our results with the GALFORM semi-analytic model, which postulates two black hole fuelling modes, the first linked to star-formation and the second occuring in passive galaxies. GALFORM predicts a larger fraction of black hole growth in quiescent galaxies at z<1, compared to the data. Relaxing the strong assumption of the model that passive AGN hosts have zero star-formation rate could reconcile this disagreement.Comment: MNRAS accepte

Investigating Evidence for Different Black Hole Accretion Modes since Redshift \u3cem\u3ez\u3c/em\u3e ∼ 1

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U − V versus V − J colours of X-ray AGN hosts in the redshift intervals 0.1 \u3c z \u3c 0.6 (mean z¯=0.40) and 0.6 \u3c z \u3c 1.2 (mean z¯=0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by theirU − V versus V − J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U − V versusV − J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z ≈ 0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15–20 per cent, at both z¯=0.40 and 0.85, is taking place in galaxies in the quiescent region of the U − V versus V − J diagram. For the low-redshift sub-sample, 0.1 \u3c z \u3c 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U − V and V − J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift, z \u3e 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≳ 10− 3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies. We compare these results with the predictions of theGALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z \u3c 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data

Disk, merger, or outflow ? Molecular gas kinematics in two powerful obscured QSOs at z>3.4

We report on the detection of bright CO(4-3) line emission in two powerful, obscured quasars discovered in the SWIRE survey, SW022513 and SW022550 at z>3.4. We analyze the line strength and profile to determine the gas mass, dynamical mass and the gas dynamics for both galaxies. In SW022513 we may have found the first evidence for a molecular, AGN-driven wind in the early Universe. The line profile in SW022513 is broad (FWHM = 1000 km/s) and blueshifted by -200 km/s relative to systemic (where the systemic velocity is estimated from the narrow components of ionized gas lines, as is commonly done for AGN at low and high redshifts). SW022550 has a more regular, double-peaked profile, which is marginally spatially resolved in our data, consistent with either a merger or an extended disk. The molecular gas masses, 4x10^10 Msun, are large and account for <30% of the stellar mass, making these obscured QSOs as gas rich as other powerful CO emitting galaxies at high redshift, i.e., submillimeter galaxies. Our sources exhibit relatively lower star-formation efficiencies compared to other dusty, powerful starburst galaxies at high redshift. We speculate that this could be a consequence of the AGN perturbing the molecular gas.Comment: Accepted for publication in A&

The deepest view of radio AGN in COSMOS: a two­fold population

The 3 GHz VLA­COSMOS surve

Constraining Dynamical Dark Energy Models through the Abundance of High-Redshift Supermassive Black Holes

We compute the number density of massive Black Holes (BHs) at the centre of galaxies at z=6 in different Dynamical Dark Energy (DDE) cosmologies, and compare it with existing observational lower limits, to derive constraints on the evolution of the Dark Energy equation of state parameter w. Our approach only assumes the canonical scenario for structure formation from the collapse of overdense regions of the Dark Matter dominated primordial density field on progressively larger scales; the Black Hole accretion and merging rate have been maximized in the computation so as to obtain robust constraints on w and on its look-back time derivative w_a. Our results provide independent constraints complementary to those obtained by combining Supernovae, Cosmic Microwave Background and Baryonic Acoustic Oscillations; while the latter concern combinations of w_0 and w_a leaving the time evolution of the state parameter w_a highly unconstrained, the BH abundance mainly provide upper limits on w_a, only weakly depending on w_0. Combined with the existing constraints, our results significantly restrict the allowed region in DDE parameter space, ruling out DDE models not providing cosmic time and fast growth factor large enough to allow for the building up of the observed abundance of BHs; in particular, models with -1.2 \leq w_0 \leq -1 and positive redshift evolution w_a > 0.8 - completely consistent with previous constraints - are strongly disfavoured by our independent constraints from BH abundance. Such range of parameters corresponds to "Quintom" DDE models, with w crossing -1 starting from larger values.Comment: 19 pages, 6 figures, accepted to MNRA

Why z > 1 radio-loud galaxies are commonly located in protoclusters

Distant powerful radio-loud active galactic nuclei (RLAGN) tend to reside in dense environments and are commonly found in protoclusters at z > 1.3. We examine whether this occurs because RLAGN are hosted by massive galaxies, which preferentially reside in rich environments. We compare the environments of powerful RLAGN at 1.3 1014M cluster having experienced powerful radio-loud feedback of duration ~60 Myr during 1.3<z<3.2. This feedback could heat the intracluster medium to the extent of 0.5–1 keV per gas particle, which could limit the amount of gas available for further star formation in the protocluster galaxies

The environments of luminous radio galaxies and type-2 quasars

We present the results of a comparison between the environments of (1) a complete sample of 46 southern 2-Jy radio galaxies at intermediate redshifts (0.05 < z < 0.7), (2) a complete sample of 20 radio-quiet type-2 quasars (0.3 ≤ z ≤ 0.41), and (3) a control sample of 107 quiescent early-type galaxies at 0.2 ≤ z < 0.7 in the Extended Groth Strip. The environments have been quantified using angular clustering amplitudes (Bgq) derived from deep optical imaging data. Based on these comparisons, we discuss the role of the environment in the triggering of powerful radio-loud and radio-quiet quasars. When we compare the Bgq distributions of the type-2 quasars and quiescent early-type galaxies, we find no significant difference between them. This is consistent with the radio-quiet quasar phase being a short-lived but ubiquitous stage in the formation of all massive early-type galaxies. On the other hand, powerful radio galaxies are in denser environments than the quiescent population, and this difference between distributions of Bgq is significant at the 3σ level. This result supports a physical origin of radio loudness, with high-density gas environments favouring the transformation of active galactic nucleus (AGN) power into radio luminosity, or alternatively, affecting the properties of the supermassive black holes themselves. Finally, focusing on the radio-loud sources only, we find that the clustering of weak-line radio galaxies (WLRGs) is higher than the strong-line radio galaxies (SLRGs), constituting a 3σ result. 82 per cent of the 2-Jy WLRGs are in clusters, according to our definition (Bgq ≳ 400), versus only 31 per cent of the SLRGs

Faint high-redshift AGN in the Chandra Deep Field South: the evolution of the AGN luminosity function and black hole demography

We present detection and analysis of faint X-ray sources in the Chandra deep field south (CDFS) using the 4 Msec Chandra observation and adopting a new detection algorithm, based on a targeted search at the position of known high-z galaxies. This optimized technique results in the identification of 54 z>3 AGNs, 29 of which are new detections. Applying stringent completeness criteria, we derive AGN luminosity functions in the redshift bins 3-4, 4-5 and >5.8 and for 42.75<log L(2-10 keV)<44.5. We join this data with the luminous AGN luminosity functions from optical surveys and find that the evolution of the high-z, wide luminosity range luminosity function can be best modeled by pure luminosity evolution with L* decreasing from 6x10^44 ergs/s at z=3 to L*=2x10^44 ergs/s at z=6. We compare the high-z luminosity function with the prediction of theoretical models using galaxy interactions as AGN triggering mechanism. We find that these models are broadly able to reproduce the high-z AGN luminosity functions. A better agreement is found assuming a minimum Dark Matter halo mass for black hole formation and growth. We compare our AGN luminosity functions with galaxy mass functions to derive high-z AGN duty cycle using observed Eddington ratio distributions to derive black hole masses. We find that the duty cycle increases with galaxy stellar mass and redshift by a factor 10-30 from z=0.25 to z=4-5. We also report on the detection of a large fraction of highly obscured, Compton thick AGN at z>3 (18+17-10%). Their optical counterparts are not strongly reddened and we thus conclude that the size of the X-ray absorber is likely smaller than the dust sublimation radius. We finally report the discovery of a highly star-forming galaxy at z=3.47. If confirmed, this would be one of the farthest objects in which stellar sources are detected in X-rays.Comment: A&A in pres