Heavily Reddened z~2 Type 1 Quasars II: H-alpha Star Formation Constraints from SINFONI IFU Observations

TL;DR

This study uses near-infrared IFU spectroscopy to detect and analyze star formation in heavily reddened, hyperluminous quasars at redshifts 1.4-2.7, revealing high star formation rates and spatial characteristics of star-forming regions.

Contribution

It provides the first detailed spatially-resolved measurements of star formation in heavily reddened quasars at high redshift, linking star formation activity to quasar evolution.

Findings

16 of 28 quasars show significant star formation with an average SFR of 320 M_sun/yr.

Star-forming regions are mostly unresolved or within 6 kpc, some extending to 8 kpc.

High SFRs support the idea that these quasars are in a transitional phase from starburst galaxies to luminous quasars.

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.