Heavily reddenedz∼ 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 Hα emission associated with star formation in a sample of 28 heavily reddened (E(B − V ) ≃ 0.5 − 1.9), hyperluminous (log(L bol /ergs −1 ) ≃ 47 − 48) broad-line quasars at z ≃ 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 ± 70 M ⊙ yr −1 . A stacked spectrum of the detections shows weak [NII], consistent with star formation as the origin of the narrow Hα emission. The star-forming regions are spatially unresolved in 11 of the 16 detections and constrained to lie within ∼6 kpc of the quasar emission. In the five resolved detections we find the star-forming regions are extended on scales of ∼8 kpc 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, <50 M ⊙ 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 impact of ionized outflows from z ∼ 2.5 quasars is not through instantaneous in situ quenching: the evidence from ALMA and VLT/SINFONI

“…Hao et al 2011;Murphy et al 2011), it is sensitive to dust obscuration and can be contaminated by AGN photo-ionisation. Indeed, most of the star formation in high-redshift galaxies is obscured (Madau et al 1996;Casey et al 2014;Whitaker et al 2014) and, although obscuration corrections can help (Alaghband-Zadeh et al 2016), sometimes the H emission can be completely hidden (e.g., Hodge et al 2016;Chen et al 2017Chen et al , 2020. This dust absorbed emission is re-radiated at far-infrared (8-1000 m; FIR) wavelengths and, consequently, the FIR emission is sensitive to on-going obscured star formation (for reviews see Kennicutt & Evans 2012;Calzetti 2013).…”

UV-luminous, star-forming hosts of z ∼ 2 reddened quasars in the Dark Energy Survey

“…Fifteen of the reddened quasars in our sample overlap with those in Alaghband-Zadeh et al (2016), who look for narrow Hα emission that could be associated with star formation in the NIR spectra. Narrow Hα emission is detected in nine of the 15 quasars in their sample, from which AlaghbandZadeh et al (2016) derive extinction-corrected SFRs assuming a Calzetti dust extinction law (Calzetti et al 2000) and a dust attenuation towards the star-forming regions equal to that towards the quasar continuum.…”

“…In our analysis, one of these nine quasars -VHSJ2100-5820 -does not show an excess of rest-frame UV emission relative to that expected from a reddened quasar and so is not considered further in our comparisons to Hα-derived SFRs. Similarly, we do not include the six quasars with no evidence of narrow Hα emission, for which Alaghband-Zadeh et al (2016) derive only upper limits on the SFR, assuming the star-forming regions to be located within the PSF of the SINFONI data (FWHM ∼0.5-0.8 arcsec). As we clearly see evidence for rest-frame UV emission on larger scales than this across our sample, the Hα SFR limits for these six quasars are not directly comparable to our work.…”

“…This lack of a one-to-one correspondence between the two SFR measures is expected however, as several assumptions have been made regarding the quasar host galaxy and the dust attenuation affecting both the UV-and Hα-emitting regions. We also note that Alaghband-Zadeh et al (2016) restrict their search for narrow Hα emission to ∼0.5-0.8 arcsec regions (corresponding to the size of the PSF in their observations), meaning their study is not sensitive to extended emission on larger scales. Given that the rest-frame UV emission in our sample typically extends 1 arcsec, we expect the SFRs we derive from the spatially-integrated UV flux to generally be higher than those measured from Hα by Alaghband-Zadeh et al (2016), which is exactly what we see in Fig.…”

Imaging Spectroscopy of Ionized Gaseous Nebulae around Optically Faint AGNs at Redshift z ∼ 2

“…10 10 47 48  ñ~n erg s −1 ) broad-line QSOs (e.g., Cano-Díaz et al 2012;Glikman et al 2015;Bischetti et al 2017;Nesvadba et al 2017), finding evidence of substantial star formation in the host galaxies (e.g., Alaghband-Zadeh et al 2016;Carniani et al 2016) and suggesting that while AGN feedback may quench star formation in some regions of the galaxy, this quenching may be incomplete (or indeed, trigger enhanced star formation near the edges of the outflows; Cresci et al 2015). Although large integral field unit (IFU) surveys (e.g., Förster Schreiber et al 2009 serendipitously contain some fainter narrow-line AGNs (especially at stellar masses M M 10 ;…”