The nature of LoBAL QSOs. I. SEDs and mid-infrared spectral properties

Mariana S. Lazarova, Gabriela Canalizo, Mark Lacy, Anna Sajina

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Abstract

We have obtained Spitzer Infrared Spectrograph spectra and MIPS 24, 70, and 160 μm photometry for a volume-limited sample of 22 Sloan Digital Sky Survey selected low-ionization broad absorption line (LoBALs) QSOs at 0.5 < z < 0.6. By comparing their mid-IR spectral properties and far-IR spectral energy distributions (SEDs) with those of a control sample of 35 non-LoBALs matched in Mi , we investigate the differences between the two populations in terms of their infrared emission and star formation (SF) activity. Twenty-five percent of the LoBALs show polycyclic aromatic hydrocarbon features and 45% have weak 9.7μm silicate dust emission. We model the SEDs and decouple the active galactic nucleus (AGN) and starburst contributions to the far-infrared luminosity in LoBALs and in non-LoBALs. Their median total, starburst, and AGN infrared luminosities are comparable. Twenty percent (but no more than 60%) of the LoBALs and 26% of the non-LoBALs are ultraluminous infrared galaxies (L IR > 1012 L). We estimate star formation rates (SFRs) corrected for the AGN contribution to the FIR flux and find that LoBALs have comparable levels of SF activity to non-LoBALs when considering the entire samples. However, the SFRs of the IR-luminous LoBALs are 80% higher than those of their counterparts in the control sample. The median contribution of SF to the total far-infrared flux in LoBALs and in non-LoBALs is estimated to be 40%-50%, in agreement with previous results for Palomar-Green (PG) QSOs. Overall, our results show that there is no strong evidence from the mid- and far-IR properties that LoBALs are drawn from a different parent population than non-LoBALs.

Original languageEnglish (US)
Article number29
JournalAstrophysical Journal
Volume755
Issue number1
DOIs
StatePublished - Aug 10 2012

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Keywords

  • galaxies: active
  • galaxies: evolution
  • infrared: galaxies
  • quasars: absorption lines
  • quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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