A SCUBA-2 survey of FeLoBAL QSOs. Are FeLoBALs in a ‘transition phase’ between ULIRGs and QSOs?

Abstract

It is thought that a class of broad absorption line (BAL) QSOs, characterised by Fe absorption features in their UV spectra (called 'FeLoBALs'), could mark a transition stage between the end of an obscured starburst event and a youthful QSO beginning to shed its dust cocoon, where Fe has been injected into the interstellar medium by the starburst. To test this hypothesis we have undertaken deep SCUBA-2 850 µm observations of a sample of 17 FeLoBAL QSOs with 0.89 z 2.78 and -23.31 M B -28.50 to directly detect an excess in the thermal emission of the dust which would probe enhanced star-formation activity. We find that FeLoBALs are not luminous sources in the submillimetre, none of them are individually detected at 850 µm, nor as a population through stacking (F s = 1.14 ± 0.58 mJy). Statistical and survival analyses reveal that FeLoBALs have sub-mm properties consistent with BAL and non-BAL QSOs with matched redshifts and magnitudes. An SED fitting analysis shows that the FIR emission is dominated by AGN activity, and a starburst component is required only in 6/17 sources of our sample; moreover the integrated total luminosity of 16/17 sources is L 10 12 L , high enough to classify FeLoBALs as infrared luminous.In conclusion, we do not find any evidence in support of FeLoBAL QSOs being a transition population between a ULIRG and an unobscured QSO; in particular, FeLoBALs are not characterized by a cold starburst which would support this hypothesis.

The host galaxies of FeLoBAL quasars atz∼ 0.9 are not dominated by recent major mergers

“…Cisternas et al 2011;Kocevski et al 2012;Schawinski et al 2012;Villforth et al 2014Villforth et al , 2017Boehm et al 2012;Gabor et al 2009;Hewlett et al 2017;Grogin et al 2005) This suggest that unlike extremely red quasars (Urrutia et al 2008;Glikman et al 2015) or heavily obscured AGN (Kocevski et al 2015), FeLoBALs are consistent with the population of host galaxies of quasars of similar luminosities. This also matches findings by (Violino et al 2016) who compared the star forming properties of FeLoBAL quasars to the general quasar population and found them to be consistent.…”

“…We analyze the host galaxies of a sample of FeLoBAL quasars and compare them to a sample of blue quasars from Villforth et al (2017). FeLoBALs, which have Fe II and other low-ionization broad absorption lines (LoBALs) (Becker et al 1997;Hall et al 2002), have been proposed as transition objects based on their typically dust-reddened colors (Dunn et al 2015) and large far-IR luminosities (indicating high star formation rates (SFRs)) (Farrah et al 2010(Farrah et al , 2012, although Violino et al (2016) found no enhanced star formation rates when compared to the general quasar population. Samples of extremely red quasars, which show high incidences of FeLoBALs, have also been found to have extremely high merger rates Urrutia et al 2008).…”

Extreme star formation events in quasar hosts over 0.5 <z< 4

“…Instead, our results are consistent with HiBAL quasars being normal quasars observed along a particular line of sight, with the outflows in HiBAL quasars not having any measurable effect on the star formation in their hosts (see also e.g. Violino et al 2016).…”

Discovery of Strong Balmer Line Absorption in Two Luminous LoBAL Quasars at z ∼ 1.5

“…Bruni et al 2012;DiPompeo et al 2012DiPompeo et al , 2013. For LoBALs more frequently an evolution scenario is advocated (Boroson & Meyers 1992;Voit et al 1993), in which they constitute an early, short-lived transition phase of AGN activity, with observational support for (Boroson & Meyers 1992;Canalizo & Stockton 2002;Farrah et al 2007) and against this scenario (Lazarova et al 2012;Violino et al 2016;). The evolution scenario has been most strongly argued for the rare sub-population within the LoBAL class of FeLoBALs, which in addition also show absorption troughs in the metastable Fe II line (Hazard et al 1987;Becker et al 1997;Hall et al 2002).…”