Person: Fazio, Giovanni
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Fazio
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Giovanni
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Fazio, Giovanni
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Publication Near‐ and Mid‐Infrared Photometry of High‐Redshift 3CR Sources(IOP Publishing, 2008) Haas, Martin; Willner, Steven; Heymann, Frank; Ashby, Matthew; Fazio, Giovanni; Wilkes, Belinda; Chini, Rolf; Siebenmorgen, RalfUsing 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.Publication Revealing the Heavily Obscured Active Galactic Nucleus Population of High-Redshift 3crr Sources With Chandra X-Ray Observations(IOP Publishing, 2013) Wilkes, Belinda; Kuraszkiewicz, Joanna; Haas, Martin; Barthel, Peter; Leipski, Christian; Willner, Steven; Worrall, Diana; Birkinshaw, Mark; Antonucci, Robert; Ashby, Matthew; Chini, Rolf; Fazio, Giovanni; Lawrence, Charles; Ogle, Patrick; Schulz, BernhardChandra observations of a complete, flux-limited sample of 38 high-redshift (1 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.Publication Mid-Infrared Spectroscopy of High-Redshift 3crr Sources(IOP Publishing, 2010) Leipski, C.; Haas, Mary Elizabeth; Willner, Steven; Ashby, Matthew; Wilkes, Belinda; Fazio, Giovanni; Antonucci, R.; Barthel, P.; Chini, R.; Siebenmorgen, R.; Ogle, P.; Heymann, F.Using the Spitzer Space Telescope, we have obtained rest-frame 9–16 μm spectra of 11 quasars and 9 radio galaxies from the 3CRR catalog at redshifts 1.0Publication Clustering of Red Galaxies around the Z = 1.53 Quasar 3C 270.1(IOP Publishing, 2009) Haas, Martin; Willner, Steven; Heymann, Frank; Ashby, Matthew; Fazio, Giovanni; Wilkes, Belinda; Chini, Rolf; Siebenmorgen, Ralf; Stern, DanielIn 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).Publication Simulated Galaxy Interactions as Probes of Merger Spectral Energy Distributions(IOP Publishing, 2014) Lanz, Lauranne; Hayward, Christopher C.; Zezas, Andreas; Smith, Howard; Ashby, Matthew; Brassington, Nicola; Fazio, Giovanni; Hernquist, LarsWe present the first systematic comparison of ultraviolet-millimeter spectral energy distributions (SEDs) of observed and simulated interacting galaxies. Our sample is drawn from the Spitzer Interacting Galaxy Survey and probes a range of galaxy interaction parameters. We use 31 galaxies in 14 systems which have been observed with Herschel, Spitzer, GALEX, and 2MASS. We create a suite of GADGET-3 hydrodynamic simulations of isolated and interacting galaxies with stellar masses comparable to those in our sample of interacting galaxies. Photometry for the simulated systems is then calculated with the SUNRISE radiative transfer code for comparison with the observed systems. For most of the observed systems, one or more of the simulated SEDs match reasonably well. The best matches recover the infrared luminosity and the star formation rate of the observed systems, and the more massive systems preferentially match SEDs from simulations of more massive galaxies. The most morphologically distorted systems in our sample are best matched to the simulated SEDs that are close to coalescence, while less evolved systems match well with the SEDs over a wide range of interaction stages, suggesting that an SED alone is insufficient for identifying the interaction stage except during the most active phases in strongly interacting systems. This result is supported by our finding that the SEDs calculated for simulated systems vary little over the interaction sequence.Publication Star formation in z > 1 3CR host galaxies as seen by Herschel(EDP Sciences, 2015) Podigachoski, P.; Barthel, P. D.; Haas, Mary Elizabeth; Leipski, C.; Wilkes, Belinda; Kuraszkiewicz, Joanna; Westhues, C.; Willner, Steven; Ashby, Matthew; Chini, R.; Clements, D. L.; Fazio, Giovanni; Labiano, A.; Lawrence, C.; Meisenheimer, K.; Peletier, R. F.; Siebenmorgen, R.; Verdoes Kleijn, G.We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a complete sample of z> 1 3CR sources, from the Herschel guaranteed time project The Herschel Legacy of distant radio-loud AGN. Combining these with existing Spitzer photometric data, we perform an infrared (IR) spectral energy distribution (SED) analysis of these landmark objects in extragalactic research to study the star formation in the hosts of some of the brightest active galactic nuclei (AGN) known at any epoch. Accounting for the contribution from an AGN-powered warm dust component to the IR SED, about 40% of our objects undergo episodes of prodigious, ULIRG-strength star formation, with rates of hundreds of solar masses per year, coeval with the growth of the central supermassive black hole. Median SEDs imply that the quasar and radio galaxy hosts have similar FIR properties, in agreement with the orientation-based unification for radio-loud AGN. The star-forming properties of the AGN hosts are similar to those of the general population of equally massive non-AGN galaxies at comparable redshifts, thus there is no strong evidence of universal quenching of star formation (negative feedback) within this sample. Massive galaxies at high redshift may be forming stars prodigiously, regardless of whether their supermassive black holes are accreting or not.Publication Chandra X-Ray Observations of the Redshift 1.53 Radio-Loud Quasar 3c 270.1(IOP Publishing, 2012) Wilkes, Belinda; Lal, Dharam V.; Worrall, Diana; Birkinshaw, Mark; Haas, Martin; Willner, Steven; Antonucci, Robert; Ashby, Matthew; Avara, Mark; Barthel, Peter; Chini, Rolf; Fazio, Giovanni; Hardcastle, Martin; Lawrence, Charles; Leipski, Christian; Ogle, Patrick; Schulz, BernhardChandra X-ray observations of the high redshift (z = 1.532) radio-loud quasar 3C 270.1 in 2008 February show the nucleus to have a power-law spectrum, Γ = 1.66 ± 0.08, typical of a radio-loud quasar, and a marginally detected Fe Kα emission line. The data also reveal extended X-ray emission, about half of which is associated with the radio emission from this source. The southern emission is co-spatial with the radio lobe and peaks at the position of the double radio hot spot. Modeling this hot spot, including Spitzer upper limits, rules out synchrotron emission from a single power-law population of electrons, favoring inverse Compton emission with a field of ∼11 nT, roughly a third of the equipartition value. The northern emission is concentrated close to the location of a 40◦ bend where the radio jet is presumed to encounter an external medium. It can be explained by inverse Compton emission involving cosmic microwave background photons with a field of ∼3 nT, a factor of 7–10 below the equipartition value. The remaining, more diffuse X-ray emission is harder (HR = −0.09 ± 0.22). With only 22.8 ± 5.6 counts, the spectral form cannot be constrained. Assuming thermal emission with a temperature of 4 keV yields an estimate for the luminosity of 1.8×1044 erg s−1, consistent with the luminosity–temperature relation of lower-redshift clusters. However, deeper Chandra X-ray observations are required to delineate the spatial distribution and better constrain the spectrum of the diffuse emission to verify that we have detected X-ray emission from a high-redshift cluster.Publication Mid-Infrared-Selected Quasars. I. Virial Black Hole Mass and Eddington Ratios(IOP Publishing, 2014) Dai, Y. Sophia; Elvis, Martin; Bergeron, Jacqueline; Fazio, Giovanni; Huang, Jia-Sheng; Wilkes, Belinda; Willmer, Christopher N. A.; Omont, Alain; Papovich, CaseyWe 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.Publication The total infrared luminosity may significantly overestimate the star formation rate of quenching and recently quenched galaxies(Oxford University Press (OUP), 2014) Hayward, C. C.; Lanz, L.; Ashby, Matthew; Fazio, Giovanni; Hernquist, Lars; Martinez-Galarza, J. R.; Noeske, K.; Smith, Howard; Wuyts, S.; Zezas, AndreasThe total infrared (IR) luminosity is very useful for estimating the star formation rate (SFR) of galaxies, but converting the IR luminosity into an SFR relies on assumptions that do not hold for all galaxies. We test the effectiveness of the IR luminosity as an SFR indicator by applying it to synthetic spectral energy distributions generated from three-dimensional hydrodynamical simulations of isolated disc galaxies and galaxy mergers. In general, the SFR inferred from the IR luminosity agrees well with the true instantaneous SFR of the simulated galaxies. However, for the major mergers in which a strong starburst is induced, the SFR inferred from the IR luminosity can overestimate the instantaneous SFR during the post-starburst phase by greater than two orders of magnitude. Even though the instantaneous SFR decreases rapidly after the starburst, the stars that were formed in the starburst can remain dust-obscured and thus produce significant IR luminosity. Consequently, use of the IR luminosity as an SFR indicator may cause one to conclude that post-starburst galaxies are still star forming, whereas in reality, star formation was recently quenched.