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Register a new userCO Emission from z>3 Radio Galaxies
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Carlos De Breuck
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We report on the detection of the CO(4-3) line with the IRAM Plateau de Bure Interferometer in two z>3 radio galaxies, doubling the number of successful detections in such objects. A comparison of the CO and Ly-alpha velocity profiles indicates that in at least half of the cases, the CO is coincident in velocity with associated HI absorption seen against the Ly-alpha emission. This strongly suggests that the CO and HI originate from the same gas reservoir, and could explain the observed redshift differences between the optical narrow emission lines and the CO. The CO emission traces a mass of H_2 100-1000 times larger than the HI and HII mass traced by Ly-alpha, providing sufficient gas to supply the massive starbursts suggested by their strong thermal dust emission.
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We present results of a comprehensive multi-frequency study of the radio galaxy B3 J2330+3927. The 1.9 wide radio source, consisting of 3 components, is bracketed by 2 objects in our Keck K-band image. Optical and near-IR Keck spectroscopy of these two objects yield z=3.087+-0.004. The brightest (K=18.8) object has a standard type II AGN spectrum, and is the most likely location of the AGN, which implies a one-sided jet radio morphology. Deep 113 GHz observations with the IRAM Plateau de Bure Interferometer reveal CO J=4-3 emission, which peaks at the position of the AGN. The CO line is offset by 500 km/s from the systemic redshift of the AGN, but corresponds very closely to the velocity shift of an associated HI absorber seen in Lya. This strongly suggests that both originate from the same gas reservoir surrounding the AGN host galaxy. Simultaneous 230 GHz interferometer observations find a ~3x lower integrated flux density when compared to single dish 250 GHz observations with MAMBO at the IRAM 30m telescope. This can be interpreted as spatially resolved thermal dust emission at scales of 0.5 to 6. Finally, we present a tau <1.3% limit to the HI 21 cm absorption against the radio source, which represents the seventh non-detection out of 8 z>2 radio galaxies observed to date with the WSRT. We present mass estimates for the atomic, neutral, and ionized hydrogen, and for the dust, ranging from M(HI)=2x10^7 M_Sun derived from the associated HI absorber in Lya up to M(H_2)=7x10^{10} M_Sun derived from the CO emission. This indicates that the host galaxy is surrounded by a massive reservoir of gas and dust. The K-band companion objects may be concentrations within this reservoir, which will eventually merge with the central galaxy hosting the AGN.
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We investigate the nature of CO emission from z~6 quasars by combining non-LTE radiative transfer calculations with merger-driven models of z~6 quasar formation that arise naturally in LCDM cosmological simulations. We consider four model quasars formed in 10^12-10^13 M_sun halos from different merging histories. Our main results follow. Owing to massive starbursts and funneling of dense gas into the nuclear regions of merging galaxies, the CO is highly excited and the flux density peaks between J=5-8. The CO morphology of z~6 quasars often exhibits multiple emission peaks which arise from H2 concentrations which have not yet fully coalesced. Quasars at z~6 display a large range of sightline dependent line widths such that the lines are narrowest when the rotating H2 gas associated with the quasar is viewed face-on (when L_B is largest), and broadest when the gas is seen edge-on (when L_B is lowest). Thus for all models selection effects exist such that quasars selected for optical luminosity are preferentially face-on which may result in detected CO line widths narrower than the median. The sightline averaged line width is reflective of the circular velocity (V_c) of the host halo, and ranges from sigma~300-650 km/s. For optically selected QSOs, 10-25% (halo-mass dependant) of sightlines have narrow line widths compatible with the sole CO detection at z>6, J1148+5251. When accounting for both the temporal evolution of CO line widths, as well as the redshift evolution of halo V_c, these models self-consistently account for the CO line widths of both z~2 sub-mm galaxies and QSOs. Finally, the dynamical mass derived from the sightline averaged line widths provides a good estimate of the total mass, and allows for a stellar bulge and SMBH consistent with the local M_BH-M_bulge relation. [abridged]
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