Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21915410l&link_type=abstract
American Astronomical Society, AAS Meeting #219, #154.10
Astronomy and Astrophysics
Astronomy
Scientific paper
Quasar broad lines exhibit several trends, including the Baldwin effect, an anticorrelation between the emission line equivalent width and continuum luminosity. There is suggestive evidence that the Baldwin effect is driven by the spectral energy distribution (SED).
We test this assertion and the efficacy of the locally-optimally-emitting cloud (LOC) model using large-scale Cloudy modeling. We investigate the effect of the SED by constructing a grid of continua in which αox and the temperature of the UV cutoff are varied independently. We also vary the LOC radial- and density-distribution indices. We constrain the results using three sets of results: the relationship between αox and CIV equivalent width observed by Wu et al. 2009, the relationship between luminosity and αox parameterized by Just et al. 2007, and the Baldwin effect results from 19 lines measured in luminosity-sorted quasar composite spectra by Dietrich et al. 2002. We investigate the baseline LOC (column density log(NH)=23.5) as well as high column density log(NH)=24.5, enhanced abundances (Z=5), and alternative SEDs that have a power law in the EUV rather than an exponential cutoff.
Our preliminary results show that, for the baseline model, the Baldwin effect is explained by a softening of the SED as well as a decrease of the covering fraction at higher luminosities. The radial and density indices are independent of luminosity and lie near the standard values of -1 and -1. In contrast, the high column model explains the Baldwin effect principally as a softening of the SED with no trend in covering fraction. Both the high metallicity and alternative SED models provide poorer fits. The LOC fails to model some emission lines well, and some evidence for two zones is found. Additional results will be described.
This work is funded by NSF AST-0707703.
Hemantha Maddumage Don P.
Leighly Karen
Richards Geordie
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