CO(1–0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources★

Abstract

We present a CO(1-0) survey for cold molecular gas in a representative sample of 13 high-z radio galaxies (HzRGs) at 1.4 < z < 2.8, using the Australia Telescope Compact Array. We detect CO(1-0) emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1-0) luminosities are in the range L CO ∼ (5 − 9) × 10 10 K km s −1 pc 2 . For MRC 0152-209 and MRC 1138-262 part of the CO(1-0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M H2 ∼ 6 × 10 10 M (M H2 /L CO = 0.8). For the remaining three CO-detected sources, the CO(1-0) emission is located in the halo (∼50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases the CO(1-0) is aligned along the radio axis and found beyond the brightest radio hot-spot, in a region devoid of 4.5µm emission in Spitzer imaging. The CO(1-0) profiles are broad, with velocity widths of ∼ 1000 -3600 km s −1 . We discuss several possible scenarios to explain these halo reservoirs of CO(1-0). Following these results, we complement our CO(1-0) study with detections of extended CO from the literature and find at marginal statistical significance (95% level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1-0), we set realistic upper limits of L CO ∼ 3 − 4 × 10 10 K km s −1 pc 2 . Our survey reveals a CO(1-0) detection rate of 38%, allowing us to compare the CO(1-0) content of HzRGs with that of other types of high-z galaxies.

Witnessing the transformation of a quasar host galaxy at z = 1.6

“…Though it is not unusual for powerful radio galaxies to show ionized nebulae extending tens or even a hundred kpc from the AGN (e.g., McCarthy et al 1995;Reuland et al 2003), the case of 5C 7.245 is quite unusual in that the spatial peak of the nebular emission does not occur at the position of the AGN (or the peak in the stellar light). It instead resembles detections of cold molecular CO-emitting gas found just beyond the brightest edge of the radio source in several HzRGs (Nesvadba et al 2009, Emonts et al 2014.…”

A free-form mass model of the Hubble Frontier Fields cluster AS1063 (RXC J2248.7−4431) with over one hundred constraints

“…A second is a series of massive CO clumps aligned along a quasar jet at z=4.3, providing triggering of molecular gas (on scales up to ≈ 15 kpc), the essential prerequisite for star formation, in Klamer et al (2004). Such offsets or alignments are inferred to be a common phenomenon in CO-detected high redshift radio sources (Emonts et al 2014). Finally, we note that theoretical simulations of positive feedback by nuclear jets (Gaibler et al 2012) and winds (Wagner, Umemura & Bicknell 2013) 14.4?…”

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

“…This could imply that they do not represent a distinct structure, but are merely part of a population of ambient clouds that are distributed over large solid angles, and of which a subset is being lit up as it intercepts the quasar ionization cone. Filaments of neutral gas have also been observed around some HzRGs (van Ojik et al 1997;Jarvis et al 2003;Wilman et al 2004;De Breuck et al 2005;Nesvadba et al 2009;Emonts et al 2014).…”

“…This is remarkable, given that the general population of passively evolving early-type galaxies at high redshift tends to be more compact than their local analogs (e.g., Daddi et al 2005;van Dokkum et al 2008;Schawinski et al 2011;Whitaker et al 2012). Furthermore, although about 1/3 of HzRGs are still actively starforming (Drouart et al 2014), their molecular gas reservoirs of a few 10 10 M (e.g., Emonts et al 2014) compared to few 10 11 M of stellar mass (Seymour et al 2007;De Breuck et al 2010) suggest that most of their stellar mass growth has already been completed. Targett et al (2011) found extended broadband emission when stacking 13 HzRGs at redshifts between z = 1.5 and 2.0 (as did Best et al 1998, at slightly lower redshifts).…”

“…They follow the low-redshift Kormendy relation of powerful radio and brightest cluster galaxies when allowing for passive luminosity evolution (Targett et al 2011). Many HzRGs are themselves gas rich (e.g., van Ojik et al 1997;Nesvadba et al 2008;Ogle et al 2012;Emonts et al 2014), and while they have no well established, virialized halos of hot gas (Overzier et al 2005), HzRGs do have extended (few 100 kpc) reservoirs of diffuse warm ionized gas (Villar-Martín et al 2003) with embedded clouds or filaments of neutral (van Ojik et al 1997;Adams et al 2009) and molecular gas De Breuck et al 2003;Emonts et al 2014). As suggested by, e.g., Villar-Martín et al (2003) these could be the vestiges of the gaseous reservoirs from which the brightest cluster and other galaxies formed.…”