Piecing together the X-ray background : bolometric corrections for active galactic nuclei

By R. Vasudevan, A. C. Fabian. 2007

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The X-ray background can be used to constrain the accretion history of supermassive black holes (SMBHs) in active galactic nuclei (AGN), with the SMBH mass density related to the energy density due to accretion. A knowledge of the hard X-ray bolometric correction, K 2-10 kev , is a vital input into these studies, as it allows us to constrain the parameters of the accretion responsible for SMBH growth. Earlier studies assumed a constant bolometric correction for all AGN, and more recent work has suggested accounting for a dependence on AGN luminosity. Until recently, the variations in the disc emission in the ultraviolet (UV) have not been taken into account in this calculation; we show that such variations are important by construction of optical-to-X-ray spectral energy distributions for 54 AGN. In particular, we use Far Ultraviolet Spectroscopic Explorer (FUSE) UV and X-ray data from the literature to constrain the disc emission as well as possible. We find evidence for very significant spread in the bolometric corrections, with no simple dependence on luminosity being evident. Populations of AGN such as narrow-line Seyfert 1 nuclei, radio-loud and X-ray-weak AGN may have bolometric corrections which differ systematically from the rest of the AGN population. We identify other sources of uncertainty including intrinsic extinction in the optical-UV, X-ray and UV variability and uncertainties in SMBH mass estimates. Our results suggest a more well-defined relationship between the bolometric correction and Eddington ratio in AGN, with a transitional region at an Eddington ratio of ∼0.1, below which the bolometric correction is typically 15-25, and above which it is typically 40-70. We consider the potential-implied parallels with the low/hard and high/soft states in Galactic black hole (GBH) accretion, and present bolometric corrections for the GBH binary GX 339-4 for comparison. Our findings reinforce previous studies proposing a multistate description of AGN accretion analogous to that for GBH binaries. Future calculations of the SMBH mass density may need to take into account the possible dependence of K 2-10 kev on the Eddington ratio.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/fce4e1dffda464f057a2dbd63c657102966cac24

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Citations in the corpus

Radiative efficiency, variability and Bondi accretion on to massive black holes: the transition from radio AGN to quasars in brightest cluster galaxies (2012, methodology): “Vasudevan & Fabian (2007) find a typical bolometric correction for low luminosity sources of order∼ 10, however for ease of comparison we adopt the same value as Merloni & Heinz (2007).”
RADIATIVELY INEFFICIENT ACCRETION IN NEARBY GALAXIES (2009, result): “This is consistent with the analysis of Vasudevan & Fabian (2007).”
The Hard X-Ray Spectrum as a Probe for Black Hole Growth in Radio-Quiet Active Galactic Nuclei (2008, background): “Since Compton-thin type 2 AGNs comprise a significant fraction of the AGN population, tracing the growth of the supermassive BHs in their centers using the X-ray-based method is crucial for testing models of the evolution of BH growth and accretion luminosity in the Universe in an unbiased way.”
ARE THE VARIATIONS IN QUASAR OPTICAL FLUX DRIVEN BY THERMAL FLUCTUATIONS? (2009, background): “However, we stress that a constant bolometric correction can introduce significant error in the Eddington ratio (e.g., Vasudevan & Fabian 2007; Kelly et al. 2008), and that our use of Cbol = 10 is only suggestive.”
A UNIFIED EMPIRICAL MODEL FOR INFRARED GALAXY COUNTS BASED ON THE OBSERVED PHYSICAL EVOLUTION OF DISTANT GALAXIES (2012, methodology): “This scaling relation assumes a mean ratio between black hole and stellar mass of 0.0015 (Mullaney et al. 2012), plus a mean ratio betweenLAGNIR andL AGN bol calibrated from Mullaney et al. (2011), Lutz et al. (2004) and Vasudevan & Fabian (2007).”
Bolometric luminosities and Eddington ratios of X-ray selected active galactic nuclei in the XMM-COSMOS survey (2012, background): “…and the optical luminosity (Tananbaum et al. 1979; Zamorani et al. 1981; Vignali et al. 2003; Steffen et al. 2006; Just et al. 2007; Young et al. 2009; Lusso et al. 2010; Marchese et al. 2012), or betweenαox and the Eddington ratio (Vasudevan & Fabian 2007; Kelly et al. 2008; Vasudevan etal.”
GOODS-Herschel: the far-infrared view of star formation in active galactic nucleus host galaxies since z ≈ 3 (2011, background): “5−8keV, though Vasudevan & Fabian (2007) argue against such a simpleluminositydependent bolometric correction factor.”
A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES (2013, background): “3 is derived fromLX with a constant bolometric correction factor of 22.4 (the mean bolometric correction factor from Vasudevan & Fabian 2007, which is based on a sample of local,LX=1041−46 erg s−1 AGN.)”
What drives the growth of black holes (2011, background): “Indeed by fitting the X-ray–optical SEDs of nearby AGNs, interpolating at UV wavelengths, Vasudevan & Fabian (2007, 2009) have shown that the AGN bolometric correction may be a strong function of the Eddington ratio: the X-ray–bolometric conversion factors change from ≈ 15–60 for Eddington ratios…”
MASS FUNCTIONS OF THE ACTIVE BLACK HOLES IN DISTANT QUASARS FROM THE LARGE BRIGHT QUASAR SURVEY, THE BRIGHT QUASAR SURVEY, AND THE COLOR-SELECTED SAMPLE OF THE SDSS FALL EQUATORIAL STRIPE (2009, background): “5 Note, the bolometric correction factors are suggested to depend on both black hole mass (Kelly et al. 2008b) and ’Eddington luminosity ratio’ (Vasudevan & Fabian 2007) which may introduce systematic uncertainties in the derived Lbol/LEdd values in addition to those stemming from assuming a…”
THE HIDDEN “AGN MAIN SEQUENCE”: EVIDENCE FOR A UNIVERSAL BLACK HOLE ACCRETION TO STAR FORMATION RATE RATIO SINCE z ∼ 2 PRODUCING AN MBH–M* RELATION (2012, methodology): “For simplicity, we derive our main results using a constant bolometric correction factor of 22.4 to convert LX to LBol (the median bolometric correction factor of a sample of local, LX= 10 41−46 ergs s−1 AGN from Vasudevan & Fabian 2007).”
Accretion and star formation rates in low‐redshift type II active galactic nuclei (2009, background): “While potentially insensitive to reddening and other complications, the exact bolometric correction factor required to convert the 2–10 keV luminosity to Lbol depends on the global SED and is still debatable (see e.g. the differences between Marconi et al. 2004 and Vasudevan and Fabian 2007).”
A global look at X-ray time lags in seyfert galaxies (2016, methodology): “The Eddington ratio was calculated using the bolometric luminosities calculated from the SEDs in Vasudevan & Fabian (2007, 2009); Vasudevan et al. (2010), and Wang et al. (2004).”
CONSTRAINTS ON BLACK HOLE GROWTH, QUASAR LIFETIMES, AND EDDINGTON RATIO DISTRIBUTIONS FROM THE SDSS BROAD-LINE QUASAR BLACK HOLE MASS FUNCTION (2010, background): “There is evidence that the bolometric correction depends on both Eddington ratio (Vasudevan & Fabian 2007; Young et al. 2010) and black hole mass (Kelly et al. 2008), and the increase of L/LEdd with MBH we find may instead be a reflection of a decrease in the bolometric correction with MBH.”
PRIMUS: THE DEPENDENCE OF AGN ACCRETION ON HOST STELLAR MASS AND COLOR (2011, background): “…of recent studies, however, have used observed multiband SEDs of unobscured AGNs to accurately measure bolometric luminosities and propose that k2−10keV may be more closely correlated with the Eddington ratio, albeit with significant scatter (Vasudevan & Fabian 2007, 2009; Lusso et al. 2010).”
Simultaneous X-ray/optical/UV snapshots of active galactic nuclei from XMM–Newton: spectral energy distributions for the reverberation mapped sample (2008, background): “The work of Vasudevan & Fabian (2007) (‘VF07’ hereafter) presents observationally determined AGN SEDs for 54 AGN for which optical, c© 0000 RAS ar X iv :0 81 0.”
A synthesis model for AGN evolution: supermassive black holes growth and feedback modes (2008, methodology): “In order to account for the measurement uncertainties in 2 This conclusion, however, has been recently challenged by Vasudevan & Fabian (2007), who ague that the 2-10 keV X-ray bolometric correction is better correlated with Eddington ratio rather than with luminosity. a simple and straightforward…”
Universal bolometric corrections for active galactic nuclei over seven luminosity decades (2020, background): “Many authors have found a correlation (although with a huge scatter) between the bolometric correction and either the Eddington ratio (λEDD = LBOL/LEDD) or the BH mass (e.g., A73, page 9 of 16 Vasudevan & Fabian 2007; Vasudevan et al. 2009; Lusso et al. 2010).”
A Combined Optical and X-ray Study of Unobscured Type 1 AGN. I. Optical Spectra and SED Modeling (2011, background): “Vasudevan & Fabian (2007) (hereinafter VF07) combined a disc and a broken power-law model to fit optical, far-UV and X-ray data for 54 AGNs.”
Intrinsic disc emission and the soft X‐ray excess in active galactic nuclei (2011, background): “The amount of power in the soft excess compared to the higher energy emission drops slightly, but the decrease inrcorona means that both hard and soft X-ray components carry a smaller fraction of the bolometricluminosity (see also Vasudevan & Fabian 2007).”