Person:

Fazio, Giovanni

We provide a catalog of 391 mid-infrared-selected (MIR; 24 μm) broad-emission-line (BEL; type 1) quasars in the 22 deg2 SWIRE Lockman Hole field. This quasar sample is selected in the MIR from Spitzer MIPS with S 24 > 400 μJy, jointly with an optical magnitude limit of r (AB) < 22.5 for broad line identification. The catalog is based on MMT and Sloan Digital Sky Survey (SDSS) spectroscopy to select BEL quasars, extending the SDSS coverage to fainter magnitudes and lower redshifts, and recovers a more complete quasar population. The MIR-selected quasar sample peaks at z ~ 1.4 and recovers a significant and constant (20%) fraction of extended objects with SDSS photometry across magnitudes, which were not included in the SDSS quasar survey dominated by point sources. This sample also recovers a significant population of z < 3 quasars at i > 19.1. We then investigate the continuum luminosity and line profiles of these MIR quasars, and estimate their virial black hole masses and the Eddington ratios. The supermassive black hole mass shows evidence of downsizing, although the Eddington ratios remain constant at 1 < z < 4. Compared to point sources in the same redshift range, extended sources at z < 1 show systematically lower Eddington ratios. The catalog and spectra are publicly available online.

Using the Spitzer Space Telescope, we have obtained 3.6-24 μm photometry of 38 radio galaxies and 24 quasars from the 3CR (Third Cambridge Revised Catalog of Radio Sources) at redshift 1 < z < 2.5. This 178 MHz selected sample is unbiased with respect to orientation and therefore suited to study orientation-dependent effects in the most powerful active galactic nuclei (AGNs). Quasar and radio galaxy subsamples matched in isotropic radio luminosity are compared. The quasars all have similar spectral energy distributions (SEDs), nearly constant in νFν through the rest 1.6-10 μm range, consistent with a centrally heated dust distribution that outshines the host galaxy contribution. The radio galaxy SEDs show larger dispersion, but the mean radio galaxy SED declines from rest 1.6 to 3 μm and then rises from 3 to 8 μm. The radio galaxies are on average a factor 3-10 less luminous in this spectral range than the quasars. These characteristics are consistent with composite emission from a heavily reddened AGN plus starlight from the host galaxy. The mid-infrared colors and radio to mid-infrared spectral slopes of individual galaxies are also consistent with this picture. Individual galaxies show different amounts of extinction and host galaxy starlight, consistent with the orientation-dependent unified scheme.

In the paradigm of hierarchical galaxy formation, luminous radio galaxies mark mass assembly peaks that should contain clusters of galaxies. Observations of the z = 1.53 quasar 3C 270.1 with the Spitzer Space Telescope at 3.6–24 μm and with the 6.5 m MMT in the z and Y bands allow the detection of potential cluster members via photometric redshifts. Compared with nearby control fields, there is an excess of ∼11 extremely red objects (EROs) at 1.33 zphot 1.73, consistent with a protocluster around the quasar. The spectral energy distributions of 3/4 of the EROs are better fitted with passive elliptical galaxies than with dust-reddened starbursts, and of four sources well detected on an archival Hubble Space Telescope (HST) snapshot image, all have undisturbed morphologies. However, one ERO, not covered by the HST image, is a double source with 0.8 separation on the z image and a marginal (2σ) 24 μm detection indicating a dust-enshrouded starburst. The EROs are more luminous than L (H = −23.6 AB mag at z ≈ 1.5).

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 <z< 2), low-frequency-selected (and so unbiased in orientation) 3CRR radio sources are reported. The sample includes 21 quasars (=broad-line radio galaxies) and 17 narrow-line radio galaxies (NLRGs) with matched 178 MHz radio luminosity (log LR(5 GHz) ∼ 44–45). The quasars have high radio core fraction, high X-ray luminosities (log LX ∼ 45–46), and soft X-ray hardness ratios (HR ∼ −0.5) indicating low obscuration. The NLRGs have lower core fraction, lower apparent X-ray luminosities (log LX ∼ 43–45), and mostly hard X-ray hardness ratios (HR > 0) indicating obscuration (NH ∼ 1022–1024 cm−2). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [O iii] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (1022 cm−2 < NH(int) < 1.5 × 1024 cm−2) to CT (NH(int) > 1.5 × 1024 cm−2) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1–0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is ∼60◦ and the obscuring material covers 30◦, ∼12◦ of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10–1000× higher than indicated by their X-ray hardness ratios, and their true LX values are ∼10–100× larger than the hardness-ratio absorption corrections would indicate.