Heavily reddened z ~ 2 Type 1 quasars - II. H α star formation constraints from SINFONI IFU observations

Abstract

We use near infrared integral field unit (IFU) spectroscopy to search for H$\alpha$ emission associated with star formation in a sample of 28 heavily reddened ($E(B-V)\simeq$0.5-1.9), hyperluminous ($log(L_{bol}/ergs^{-1})\simeq$47-48) broad-line quasars at $z\simeq$1.4-2.7. Sixteen of the 28 quasars show evidence for star formation with an average extinction-corrected star formation rate (SFR) of 320$\pm$70M$_\odot$yr$^{-1}$. A stacked spectrum of the detections shows weak [NII], consistent with star formation as the origin of the narrow H$\alpha$ emission. The star-forming regions are spatially unresolved in 11 of the 16 detections and constrained to lie within $\sim$6kpc of the quasar emission. In the five resolved detections we find the star-forming regions are extended on scales of $\sim$8kpc around the quasar emission. The prevalence of high SFRs is consistent with the identification of the heavily reddened quasar population as representing a transitional phase from apparent `starburst galaxies' to optically-luminous quasars. Upper limits are determined for 10 quasars in which star formation is undetected. In two of the quasars the SFR is constrained to be relatively modest, $<$50M$_\odot$yr$^{-1}$, but significantly higher levels of star formation could be present in the other eight quasars. The combination of the 16 strong star formation detections and the eight high SFR limits means that high levels of star formation may be present in the majority of the sample. Higher spatial resolution data, of multiple emission lines, will allow us to better understand the interplay between star formation and Active Galactic Nucleus (AGN) activity in these transitioning quasars.The authors thank the Science and Technology Facilities Council (STFC) via the Consolidated Grant awarded to the Institute of Astronomy, Cambridge. SA-Z acknowledges the support from Peterhouse, Cambridge, and the Institute of Astronomy, Cambridge. The narrow-band imaging study is based on observations made with ESO Telescopes at the La Sill a Paranal Observatory under programme ID: 290.A-5062. The IFU study is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs:383.A-0573 (PI:McMahon) and 091.A-0341 (PI:Banerji).This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw68