Journal Article

Metallicity and far-infrared luminosity of high-redshift quasars

Leah E. Simon and Fred Hamann

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 407, issue 3, pages 1826-1834
Published in print September 2010 | ISSN: 0035-8711
Published online September 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.17022.x
Metallicity and far-infrared luminosity of high-redshift quasars

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We present the results of an exploratory study of broad-line region (BLR) metallicity in 34 2.2 ≤z≤ 4.6 quasars with far-infrared (FIR) luminosities (LFIR) from 1013.4 to ≤1012.1 L. Quasar samples sorted by LFIR might represent an evolutionary sequence if the star formation rates (SFRs) in quasar hosts generally diminish across quasar lifetimes. We use rest-frame ultraviolet spectra from the Sloan Digital Sky Survey to construct three composite spectra sorted by LFIR, corresponding to average SFRs of 4980, 2130 and ≤340 M yr−1 after correcting for a nominal quasar FIR contribution. The measured N vλ1240/C ivλ1550 and Si ivλ1397+O iv] λ1402/C ivλ1550 emission line ratios indicate supersolar BLR metallicities in all three composites, with no evidence for a trend with the star formation rate. The formal derived metallicities, Z∼ 5–9 Z, are similar to those derived for the BLRs of other quasars at similar redshifts and luminosities. These results suggest that the ongoing star formation in the host is not responsible for the metal enrichment of the BLR gas. Instead, the BLR gas must have been enriched before the visible quasar phase. These results for high quasar metallicities, regardless of LFIR, are consistent with evolution scenarios wherein visibly bright quasars appear after the main episode(s) of star formation and metal enrichment in the host galaxies. Finally, young quasars, those more closely associated with a recent merger or a blowout of gas and dust, may exhibit tracers of these events, such as redder continuum slopes and higher incidence of narrow absorption lines. With the caveat of small sample sizes, we find no relation between LFIR and the reddening or the incidence of absorption lines.

Keywords: galaxies: evolution; quasars: emission lines; quasars: general

Journal Article.  6586 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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