Soft X-Ray and Ultraviolet Emission Relations in Optically Selected AGN Samples

By I. Strateva, N. Brandt, D. Schneider, D. V. vanden Berk, Cristian Vignali Penn State, U. Bologna. 2005

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Using a sample of 228 optically selected active galactic nuclei (AGNs) in the 0.01–6.3 redshift range with a high fraction of X-ray detections (81%–86%), we study the relation between rest-frame UV and soft X-ray emission and its evolution with cosmic time. The majority of the AGNs in our sample (155 objects) have been selected from the Sloan Digital Sky Survey (SDSS) in an unbiased way, rendering the sample results representative of all SDSS AGNs. The addition of two heterogeneous samples of 36 high-redshift and 37 low-redshift AGNs further supports and extends our conclusions. We confirm that the X-ray emission from AGNs is correlated with their UV emission and that the ratio of the monochromatic luminosity emitted at 2 keV compared to 2500 Å decreases with increasing luminosity (αox = -0.136lUV + 2.616, where lUV is in log units) but does not change with cosmic time. These results apply to intrinsic AGN emission, as we correct or control for the effects of the host galaxy, UV/X-ray absorption, and any X-ray emission associated with radio emission in AGNs. We investigate a variety of systematic errors and can thereby state with confidence that (1) the αox-lUV anticorrelation is real and not a result of accumulated systematic errors and (2) any αox dependence on redshift is negligible in comparison. We provide the best quantification of the αox-lUV relation to date for normal radio-quiet AGNs; this should be of utility for researchers pursuing a variety of studies.

Subfields: Astronomy and Astrophysics, Instrumentation, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/20406dee9e410eaee08a5a8a4465060a1bc3c071

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Citations in the corpus

Reverberation Mapping of High-Luminosity Quasars: First Results (2006, background): “It is well known that some other AGN properties, such as the opticalYtoYX-ray spectral slope and emission-line equivalent widths (EWs), depend on luminosity (e.g., Baldwin 1977; Strateva et al. 2005; Steffen et al. 2006).”
A Survey of z > 5.7 Quasars in the Sloan Digital Sky Survey. IV. Discovery of Seven Additional Quasars (2004, background): “The relatively short exposures and significant off-axis angles of these two quasars do not allow physically tight constraints to be placed upon their X-ray-to-optical flux ratios (see Strateva et al. 2005).”
THE NEXT GENERATION ATLAS OF QUASAR SPECTRAL ENERGY DISTRIBUTIONS FROM RADIO TO X-RAYS (2011, methodology): “Our SEDs show relatively much higher X-ray emission, indicating that our sample (and that of Elvis et al. (1994)) is not representative of the SDSS quasars in this region and probably does not follow the LUV (2500Å)-LX relationship found in SDSS quasars (Strateva et al. 2005).”
The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity (2006, background): “…emission-line regions as found in low-redshift quasars (e.g., Hamann& Ferland 1999; Dietrich et al. 2003;Maiolino et al. 2003), and the opticalYtoYX-ray flux ratios and X-ray continuum shapes show little evolution with redshift (e.g., Strateva et al. 2005; Steffen et al. 2006; Shemmer et al. 2006).”
LOW-RESOLUTION SPECTRAL TEMPLATES FOR ACTIVE GALACTIC NUCLEI AND GALAXIES FROM 0.03 TO 30 μm (2010, background): “Since the flux in X-rays is generally significantly lower than the UV emission in AGNs, as determined by the values of αOX (e.g., Tananbaum et al. 1979; Strateva et al. 2005), we know the spectrum must turn down at some wavelength shortward of Lyα.”
A CATALOG OF BROAD ABSORPTION LINE QUASARS IN SLOAN DIGITAL SKY SURVEY DATA RELEASE 5 (2008, background): “Recent studies have carefully quantified the UV/X-ray luminosity relation across ≈ 5 orders of magnitude in UV luminosity (e.g., Strateva et al. 2005; Steffen et al. 2006; Just et al. 2007).”
The X-Ray Properties of the Most Luminous Quasars from the Sloan Digital Sky Survey (2007, methodology): “…measuring a relationship between X-ray and UV luminosities of the formLX ∝ L β UV have found bothβ ≃ 0.7– 0.8 (e.g., Avni & Tananbaum 1982, 1986; Kriss & Canizares 1985; Anderson & Margon 1987; Wilkes et al. 1994; Vignali et al. 2003; Strateva et al. 2005; S06) andβ = 1 (La Franca et al. 1995).”
The Hard X-Ray Spectrum as a Probe for Black Hole Growth in Radio-Quiet Active Galactic Nuclei (2008, background): “The αox parameter is known to have a strong anticorrelation with optical–UV luminosity at 2500̊A [hereafter Lν(2500Å)], and it shows no significant dependence on redshift (e.g., Vignali et al. 2003; Strateva et al. 2005; Steffen et al. 2006; Just et al. 2007; but see also Kelly et al. 2007).”
A New Sample of Low-Mass Black Holes in Active Galaxies (2007, background): “Exactly this trend has been seen in the X-ray to optical slopes of broad-line AGNs over a wide range in luminosity (e.g., Strateva et al. 2005), includingfor a subset of the GH sample (Greene & Ho 2007a).”
The Relation between Quasar and Merging Galaxy Luminosity Functions and the Merger-driven Star Formation History of the Universe (2006, result): “…of the optical–to–X-ray luminosity ratio on luminosity (e.g., Wilkes et al. 1994; Green et al. 1995; Vignali et al. 2003; Risaliti & Elvis 2005; Strateva et al. 2005), but for our purposes adopting the mean observed quasar SED from Richards et al. (2006b) yields a similar result (for a…”
A HUBBLE DIAGRAM FOR QUASARS (2015, background): “Optically Selected Samples The Steffen et al. sample (333 sources) contains 155 objects from the SDSS-DR2 quasar catalog (Abazajian et al. 2004; Strateva et al. 2005).”
THE SLOAN DIGITAL SKY SURVEY QUASAR CATALOG. V. SEVENTH DATA RELEASE (2010, background): “For example, to construct an optically selected set of quasars (e.g., Strateva et al. 2005), one can either require that the low-redshift or high-redshift target selection flag is set, or, alternatively, require that the object was not chosen solely by radio/X-ray criteria (depending on whether or…”
The Mass Function of Active Black Holes in the Local Universe (2007, methodology): “We employ the Greene & Ho (2005b) conversion between Hα luminosity andL5100, and then, assuming a spectral slope ofα = 0.44 (fν ∝ ν−α; see, e.g., Vanden Berk et al. 2001; Greene & Ho 2005b), the relation betweenαox andL2500 from Strateva et al. (2005).”
The Sloan Digital Sky Survey Quasar Survey: Quasar Luminosity Function from Data Release 3 (2006, background): “2500Å is also the canonical wavelength used to determine the spectral index between optical and X-rays in quasars (Tananbaum et al. 1979; Strateva et al. 2005).”
THE SIMULTANEOUS OPTICAL-TO-X-RAY SPECTRAL ENERGY DISTRIBUTION OF SOFT X-RAY SELECTED ACTIVE GALACTIC NUCLEI OBSERVED BY SWIFT (2010, background): “Also our sample shows the well-known relation found by e.g. Yuan et al. (1998); Strateva et al. (2005); Just et al. (2007); Gibson et al. (2008) that AGN with higher luminosity density at 2500Å appear to be X-ray weaker at 2 keV.”
Piecing together the X-ray background : bolometric corrections for active galactic nuclei (2007, methodology): “Strateva et al. (2005) used 228 optically selected AGN across a range of redshifts (0.01 < z < 6.3) to provide a robust characterisation of this relation.”
The X-Ray-to-Optical Properties of Optically Selected Active Galaxies over Wide Luminosity and Redshift Ranges (2006, methodology): “We extend the work f Strateva et al. (2005), that analyzed optically-selected AGNs from the Sloan Digital Sky Survey (SDSS), by including 52 moderate-luminosity, optically-selected AGNs from the COMBO-17 survey with corresponding deep (≈ 250 ks to 1 Ms) X-ray observations from the…”
An Observational Determination of the Bolometric Quasar Luminosity Function (2006, methodology): “…self-consistently reproduce the observed QLFs in different wave bands; it is necessary to account for the dependence of spectral shape on luminosity seen inWilkes et al. (1994),Green et al. (1995),Vignali et al. (2003), Strateva et al. (2005), Richards et al. (2006c), and Steffen et al. (2006).”
A Unified, Merger-driven Model of the Origin of Starbursts, Quasars, the Cosmic X-Ray Background, Supermassive Black Holes, and Galaxy Spheroids (2005, background): “…of Elvis et al. (1994) are X-ray bright (Elvis et al. 2002), whereas it has been well-established that the ratio of bolometric luminosity to hard or soft X-ray luminosity increases with increasing luminosity (e.g., Wilkes et al. 1994; Green et al. 1995; Vignali et al. 2003; Strateva et al. 2005).”