REVEALING THE HEAVILY OBSCURED ACTIVE GALACTIC NUCLEUS POPULATION OF HIGH-REDSHIFT 3CRR SOURCES WITHCHANDRAX-RAY OBSERVATIONS

Abstract

Chandra observations of a complete, flux-limited sample of 38 high-redshift (1<z<2), lowfrequency 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 L R (5 GHz)∼ 44 − 45). The quasars have high radio core-fraction, high X-ray luminosities (log L X ∼ 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 L X ∼ 43 − 45) and mostly hard X-ray hardness ratios (HR> 0) indicating obscuration (N H ∼ 10 22−24 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 high [OIII] 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 NGC1068). The ratios of unobscured to Compton-thin (10 22 < N H (int) < 1.5 × 10 24 cm −2 ) to CT (N H (int)> 1.5 × 10 24 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 AGN 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 o and the obscuring material covers 30 o of which ∼ 12 o is Compton thick. 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 L X values are ∼10-100× larger than the hardness-ratio absorption corrections would indicate.

The Chandra Cosmos Legacy Survey: Overview and Point Source Catalog

“…Using the HR we measure a fraction of obscured sources of 50 16 17 -+ %, defined as sources with HR > -0.2, that correspond to column density >10 22 cm −2 at all redshifts despite the uncertainties on the classification due to complex spectral modeling not taken into account in this work (see Wilkes et al 2009Wilkes et al , 2013. For the first time, we computed the number counts for obscured and unobscured sources separately using the HR as an indication for obscuration (HR=-0.2 corresponding to the separation between > and <10 22 cm…”

Star formation inz> 1 3CR host galaxies as seen byHerschel

“…The high-z 3CR sample has been observed with many space telescopes (including Hubble, Spitzer, and Chandra; Best et al 1998;Haas et al 2008;Leipski et al 2010;Wilkes et al 2013): objects from this sample represent landmarks in our study of active galaxies through cosmic time.…”

Composite Spectral Energy Distributions and Infrared–Optical Colors of Type 1 and Type 2 Quasars

“…It has long been known that BH growth can occur behind large columns of gas and dust (e.g., Setti & Woltjer 1989;Comastri et al 1995). Such obscured ("type 2") active galactic nuclei (AGNs) can be identified from narrow optical emission lines (Zakamska et al 2003(Zakamska et al , 2004(Zakamska et al , 2005Reyes et al 2008;Yuan et al 2016), radio luminosity (e.g., McCarthy 1993Martínez-Sansigre et al 2006;Seymour et al 2007;Wilkes et al 2013), or X-ray properties (e.g Alexander et al 2001;Stern et al 2002;Treister et al 2004;Vignali et al 2006Vignali et al , 2009Del Moro et al 2014). In addition, pioneering work with the Spitzer Space Telescope demonstrated that obscured quasars have similar mid-infrared (MIR) SEDs to their unobscured counterparts but are dominated by host galaxy light in the optical (Lacy et al 2004;Rowan-Robinson et al 2005;Stern et al 2005;Alonso-Herrero et al 2006;Martínez-Sansigre et al 2006;Polletta et al 2006;Hickox et al 2007;Donley et al 2008;Lacy et al 2013Lacy et al , 2015Dai et al 2014).…”