The X-ray to optical-UV luminosity ratio of X-ray selected type 1 AGN in XMM-COSMOS

Abstract

We present a study of the X-ray to optical properties of a sample of 545 X-ray selected type 1 AGN, from the XMM-COSMOS survey, over a wide range of redshifts (0.04 < z < 4.25) and X-ray luminosities (40.6 ≤ Log L [2−10] keV ≤ 45.3). About 60% of them are spectroscopically identified type 1 AGN, while the others have a reliable photometric redshift and are classified as type 1 AGN on the basis of their multi-band Spectral Energy Distributions. We discuss the relationship between UV and X-ray luminosity, as parameterized by the α ox spectral slope, and its dependence on redshift and luminosity. We compare our findings with previous investigations of optically selected broad-line AGN (mostly from SDSS). A highly significant correlation between α ox and L 2500 Å is found, in agreement with previous investigations of optically selected samples. We calculate bolometric corrections, k bol , for the whole sample using hard X-ray luminosities (L [2−10] keV ), and the Eddington ratios for a subsample of 150 objects for which black hole mass estimates are available. We confirm the trend of increasing bolometric correction with increasing Eddington ratio as proposed in previous works. A tight correlation is found between α ox and k bol , which can be used to estimate accurate bolometric corrections using only optical and X-ray data. We find a significant correlation between α ox and Eddington ratio, in which the ratio between X-ray and optical flux decreases with increasing Eddington ratio.

The Illustris simulation: the evolving population of black holes across cosmic time

“…We find that the black hole X-ray luminosities (direct proxies of the accretion rates) are correlated with the host galaxy star formation rate -in accordance with the similar shapes of the cosmic star formation and black hole accretion rate density -albeit with a large scatter. Current observations probe a too narrow dynamic range in X-ray luminosities to see this correlation, even though it can be inferred if the spectroscopically confirmed COSMOS data (Lusso et al 2010(Lusso et al , 2011Brusa et al 2010;Bongiorno et al 2012) at all redshifts are combined together. Large scatter seen in the simulated SF R -L 2−10keV relation demonstrates that the physical link between star formation and black hole accretion triggering is more complex than previously envisaged.…”

“…We compare the Illustris results with the recent study by Azadi et al (2014) based on the PRIMUS survey (green diamonds) and with the COSMOS data compilation (Lusso et al 2010(Lusso et al , 2011, with stellar masses and star formation rates from Bongiorno et al 2012 and redshifts from Brusa et al 2010; red circles). The three panels are for different redshift intervals probed by the surveys while we plot the Illustris data at the mean redshift of each redshift bin.…”

“…Even though we probe somewhat smaller luminosities than Hickox et al (2014) this is in qualitative agreement with their findings (see also Azadi et al 2014), further corroborating the idea that also due to the underlying short-timescale AGN variability star formation and AGN activity do not appear correlated, while in fact there is time-averaged correlation. Illustris results at z = 1, 0.65 and 0.35 are shown with 2D histograms (colours indicate number density), while the data points (green diamonds) are for the PRIMUS galaxies from Azadi et al (2014) and COSMOS galaxy compilation (red circles) from Lusso et al (2010Lusso et al ( , 2011Brusa et al (2010); Bongiorno et al (2012) for the redshift ranges 0.2 < z < 0.5, 0.5 < z < 0.8 and 0.8 < z < 1.2, respectively. Bottom panels: Stellar mass within the stellar half-mass radius versus the hard X-ray luminosity of the central AGN for the Illustris galaxies (2D histograms), PRIMUS galaxies from Azadi et al (2014) (green diamonds), and COSMOS galaxies (red circles).…”

The X-Ray and Mid-infrared Luminosities in Luminous Type 1 Quasars

“…However, it is not clear whether such a linear relation holds for more luminous AGNs (i.e.,quasars 14 ). Notably, studies comparing L X to the UV luminosity for AGNs found that the ratio between the X-ray and UV luminosities rapidly decreases with increasing UV luminosity for type 1 AGNs (e.g., Tananbaum et al 1979;Strateva et al 2005;Lusso et al 2010). Since the rest-frame mid-IR emission of AGNs originates from the hot dust heated by the UV photons from the SMBH accretion disk, understanding the L L X MIR -relation for luminous AGNs is also crucial for understanding the structure of the hot dust surrounding the central SMBH, as well as the AGN accretion physics.…”

“…We use type 1 AGN samples from the AGN and Galaxy Evolution Survey (AGES; Kochanek et al 2012) in the Boötes survey region, the publicly available AGN samples from the XMM-COSMOS survey (Lusso et al 2010), the XMM-XXL-North survey (Liu et al 2016;Menzel et al 2016;Pierre et al 2016), and the SDSS DR5 quasars with serendipitous Swift/XRT observations (Wu et al 2012a). …”