http://arxiv.org/abs/2001.05776
Brightest cluster galaxies (BCG) are today passive and very massive galaxies at the center of their clusters, still accreting mass through swallowing companions, and gas from cooling flows. However their formation history is not well known. We report CO(4$\rightarrow$3) and continuum map observations of the SpARCS1049+56 BCG at $z=1.709$, one of the most distant known BCGs. Our observations yield $M_{{\rm H}2}<1.1\times10^{10}M\odot$ for the BCG, while we detect in CO(4$\rightarrow$3) two gas-rich companions at the north-east and south-east of the BCG, within 20 kpc, with a total $L^\prime_{\rm CO(4\rightarrow3)}=(3.2\pm0.5)\times10^{10}$ K km s$^{-1}$ pc$^2$. The northern companion is associated with a pair of merging cluster galaxies, while the { southern one} shows a southern tail in CO(4$\rightarrow$3), detected also in continuum, and we suggest it to be the most distant jellyfish galaxy, for which ram pressure stripping is effectively able to strip off its dense molecular gas. This study probes the presence of rare gas-rich systems in the very central region of a distant cluster core, which will potentially merge into the BCG itself. We may thus be seeing the reversal of the star formation vs. density relation at play in the distant universe. This is the first time the assembly of high-$z$ progenitors of our local BCGs can be studied in such a great detail.
G. Castignani, F. Combes and P. Salomé
Fri, 17 Jan 20
56/60
Comments: 6 pages, 3 figures, submitted to A&A Letters
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