CO line emission in the halo of a radio galaxy at z=2.6

TL;DR

This paper reports the detection of luminous CO(3-2) emission in the halo of a high-redshift radio galaxy, suggesting the presence of gas-rich satellites or jet-induced cooling in the galaxy's extended halo.

Contribution

First detection of CO emission in the halo of a z=2.6 radio galaxy, indicating possible gas-rich satellites or jet-induced cooling mechanisms.

Findings

CO emission detected at 80 kpc from the galaxy

Two components with different blueshifts observed

Possible association with a low-mass satellite or gas filament

Abstract

We report the detection of luminous CO(3-2) line emission in the halo of the z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun and relatively low star-formation rates. With the IRAM PdBI we find two CO emission line components at the same position at ~80 kpc distance from the HzRG along the axis of the radio jet, with different blueshifts of few 100 km s^-1 relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected at 8 sigma significance. HzRGs have significant galaxy overdensities and extended halos of metal-enriched gas often with embedded clouds or filaments of denser material, and likely trace very massive dark-matter halos. The CO emission may be associated with a gas-rich, low-mass satellite galaxy with little on-going star formation, in contrast to all previous CO detections of galaxies at similar redshifts. Alternatively, the CO may be related to a gas cloud or filament and perhaps jet-induced gas cooling in the outer halo, somewhat in analogy with extended CO emission found in low-redshift galaxy clusters.