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3rd of April 2018
ALMA and ATCA observations of the Spiderweb galaxy
The Spiderweb Galaxy is a massive conglomerate of merging proto-cluster galaxies at a redshift of z=2.2 (about 10.6 billion light years away). The circumgalactic medium forms an enriched interface where feedback and recycling act on accreted gas, however the origin of this gas has not been clear. Emonts et al. have studied circumgalactic medium using the molecular tracers carbon and carbon monoxide. Carbon, [CI], emits at a rest frequency of 492.2 GHz, and carbon monoxide has molecular transitions at rest frequencies of CO(1-0) 115.3 GHz and CO(4-3) 461.04 GHz. Due to the expansion of the Universe, these frequencies are shifted to observed frequencies a factor of 3.2 lower for this galaxy, placing the CO(1-0) emission in the ATCA's 7mm band. ALMA detcted [C I] and CO(4-3) across ∼50 kpc, following the distribution of low-surface-brightness CO(1-0) previously detected with the ATCA by this team, confirming their previous results on the presence of a cold molecular halo. A study of molecular abundance ratios indicates that the molecular circumgalactic medium is metal-rich and not diffuse, confirming a link between the cold gas and in-situ star formation. Thus, the Spiderweb Galaxy is not growing through accretion of gas directly from the cosmic web, but from recycled gas in the circumgalactic medium,

The figure above shows the mission on 17-70 kpc scales in the Spiderweb’s circumgalactic medium based on ATCA CO(1-0) and ALMA CO(4-3) and CI data. The horizontal bar indicates the conservative velocity range over which we detect all three tracers in the circumgalactic medium, which were used to determine intensities and ratios. The botton histogram shows velocities of satellite galaxies that lie within the molecular halo, based on other observations. Results are presented in the preprint of the paper.

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