The Nuclear Reddening Curve for Active Galactic Nuclei and the Shape of the Infrared to X-Ray Spectral Energy Distribution

By C. Gaskell, R. Goosmann, R. Antonucci, D. Whysong. 2003

135 citations recorded by the source corpus.

We present extinction curves derived from the broad emission lines and continua of samples of 72 radio-loud and 1018 radio-quiet active galactic nuclei (AGNs). The curves are significantly flatter in the UV than curves for the local interstellar medium. The reddening curves for the radio-quiet Large Bright Quasar Survey quasars are slightly steeper than those of the radio-loud quasars in the UV, probably because of additional reddening by dust farther out in the host galaxies of the former. The UV extinction curves for the radio-loud AGNs are very flat. This is explicable with slight modifications to standard Mathis-Rumpl-Nordsieck dust models: there is a relative lack of small grains in the nuclear dust. Our continuum and broad emission line reddening curves agree in both shape and amplitude, confirming that the continuum shape is indeed profoundly affected by reddening for all but the bluest AGNs. With correction by our generic extinction curve, all of the radio-loud AGNs have optical-UV continuous spectra consistent with a single shape. We show that radio-quiet AGNs have very similar intrinsic UV to optical shape over orders of magnitude in luminosity. We also argue that radio-loud and radio-quiet AGNs probably share the same underlying continuum shape and that most of the systematic differences between their observed continuum shapes are due to higher nuclear reddening in radio-selected AGNs and additional reddening from dust farther out in the host galaxies in radio-quiet AGNs. Our conclusions have important implications for the modeling of quasar continua and the analysis of quasar demographics.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/42e90520349267578f7298479366e75d9d4b0ffa

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Citations in the corpus

THE RADIATIVE EFFICIENCY OF ACCRETION FLOWS IN INDIVIDUAL ACTIVE GALACTIC NUCLEI (2010, unknown): “We consider several different reddening curves, including SMC-like (Richards et al. 2003) and those of Czerny et al. (2004) and Gaskell et al. (2004).”
The innermost region of AGN tori: implications from the HST/NICMOS type 1 point sources and near-IR reverberation (2007, background): “Note that a dominance of large grains in AGN tori has been suggested and discussed on different grounds (e.g. Maiolino et al. 2001a,b; Gaskell et al. 2004).”
The Relationship between Luminosity and Broad-Line Region Size in Active Galactic Nuclei (2005, result): “Recent studies (e.g., Gaskell et al. 2004; Hopkins et al. 2004) indicate that AGNs have reddening in addition to the Galactic reddening, probably due to gas in their host galaxy or the intergalactic medium.”
REVERBERATION MEASUREMENTS OF THE INNER RADIUS OF THE DUST TORUS IN 17 SEYFERT GALAXIES (2014, background): “In addition, a larger grain size of a ≈ 0.1 µm could be adopted on the basis of the analysis of reddening curves for quasars (Gaskell et al. 2004).”
ANALYSIS OF OPTICAL Fe ii EMISSION IN A SAMPLE OF ACTIVE GALACTIC NUCLEUS SPECTRA (2010, background): “The observed correlation between the G/S group ratio and Hβ FWHM may be caused by intrinsic reddening since reddening increases as objects get more edge-on (Gaskell et al. 2004) and the Hβ FWHM also increases (Wills & Browne 1986).”
REVERBERATION MAPPING MEASUREMENTS OF BLACK HOLE MASSES IN SIX LOCAL SEYFERT GALAXIES (2010, background): “Gaskell et al. (2004) argue that the UV-optical continua of AGNs are all very similar, so that the reddening can be estimated by dividing the spectrum of a reddened AGN by the spectrum of an unreddened AGN.”
The Hard X-Ray Spectrum as a Probe for Black Hole Growth in Radio-Quiet Active Galactic Nuclei (2008, background): “We also checked whether theαox-Lν(2500Å) correlation is induced by luminosity-dependent obscuration (e.g., Lawrence 1991; Gaskell et al. 2004).”
The Cosmic Evolution of Hard X-Ray-selected Active Galactic Nuclei (2004, result): “This behavior is similar to that seen in samples divided by optical luminosity, in which the extinctions are higher at lower luminosities (e.g., Gaskell et al. 2004).”
Testing thermal reprocessing in active galactic nuclei accretion discs (2007, methodology): “Further reddening due to extinction intrinsic to the AGN is included using the AGN reddening curve of Gaskell et al. (2004) (see Fig.”
Piecing together the X-ray background : bolometric corrections for active galactic nuclei (2007, methodology): “Hopkins et al. (2004) find that an SMC-type extinction curve best accounts for the reddening in a sampleof Sloan Digital Sky Survey (SDSS) quasars, in preference to Mikly Way-type or Gaskell et al. (2004)-type reddening.”