STAR FORMATION AND GAS KINEMATICS OF QUASAR HOST GALAXIES ATz∼ 6: NEW INSIGHTS FROM ALMA

Abstract

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 158 µm fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z=6.00 quasar SDSS J231038.88+185519.7 using the IRAM facilities. The ALMA observations were carried out in the extended array at 0. −4 , which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0.3 ′′ to 0.6 ′′ (i.e., 1.7 to 3.5 kpc) for the [C II] line emission and 0.2 ′′ to 0.4 ′′ (i.e., 1.2 to 2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the star-forming gas in the nuclear region. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [C II]-emitting regions are of order 10 10 to 10 11 M ⊙ . Given these estimates, the mass ratios between the SMBHs and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars.

Dusty star-forming galaxies at high redshift

“…The high-z points that show a deficit in this study tended to host an AGN. Wang et al (2013a) found that the [CII]/FIR deficit also persisted in their sample of five z ∼ 6 quasars detected by ALMA, and Rawle et al (2013) found a deficit for an extreme starburst SMG at z ∼ 5. Similarly, Iono et al (2006) Decarli et al (2012).…”

“…Further X-ray analysis of SMGs estimate AGN fractions of 20-29(±7)% (Laird et al, 2010), <26±9% (Georgantopoulos et al, 2011), 14-28% and 17( +16 −6 )% . The Wang et al (2013a) work is of particular note since its sample is the ∼100 ALMA-confirmed 870µm-selected sources in CDFS with unambiguous counterparts, enabling effectively more precise measurements in both X-ray and FIR. An important follow-up to these X-ray studies of SMGs came in Alexander et al (2008).…”

“…Similar compact sizes were derived for two z ∼ 4 quasar host galaxies by Gallerani et al (2012) and Carniani et al (2013), who also detected companion galaxies potentially due to merge with the quasar host. Carniani et al (2013) and Wang et al (2013a) displayed the power of using ALMA to examine the dynamics of [CII]-emitting gas in quasar host galaxies, and showed that a number of galaxies in their sample potentially exhibited rotating gas disks. This all said, there have been a number of notable non-detections of [CII] at high-z that have called into question the reliability of [CII] as a gas tracer in high-z galaxies.…”

The nature of the [C ii] emission in dusty star-forming galaxies from the SPT survey

“…Seventeen have been added to the number of z > 4 [CII] detections in the past decade (Maiolino et al 2005(Maiolino et al , 2009Iono et al 2006;Wagg et al 2010;Ivison et al 2010;De Breuck et al 2011;Cox et al 2011;Swinbank et al 2012;Venemans et al 2012;Walter et al 2012;Riechers et al 2013;Wang et al 2013;Rawle et al 2014;De Breuck et al 2014;Neri et al 2014). Many of these objects have been selected based on the presence of a luminous active galactic nuclei (AGN; e.g.…”

“…Many of these objects have been selected based on the presence of a luminous active galactic nuclei (AGN; e.g. Maiolino et al 2005;Stacey et al 2010;Wang et al 2013), while others have been selected as starburst galaxies (e.g. Ivison et al 2010;Hailey-Dunsheath et al 2010;Stacey et al 2010;Cox et al 2011;Swinbank et al 2012;Walter et al 2012;Riechers et al 2013;Brisbin et al 2015).…”