paper

Hubble Space Telescope Captures UGC~12591: Bulge/Disc Properties, Star Formation and `Missing Baryons' Census in a Very Massive and Fast Spinning Hybrid Galaxy

arXiv:2203.02885 · doi:10.1093/mnras/stac2683

Abstract

We present Hubble Space Telescope (HST) observations of the nearby, massive, highly rotating hybrid galaxy UGC~12591, along with observations in UV to FIR bands. HST data in V, I, and H bands is used to disentangle the structural components. Surface photometry shows a dominance of the bulge over the disc with H-band B/D ratio of . The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of , exceptionally low for the galaxy's huge stellar mass of , implying a strong quenching of its SFR with star formation efficiency of . For at least the past years, the galaxy has remained in a quiescent state as a sterile, `red and dead' galaxy. UGC~12591 hosts a supermassive black hole (SMBH) of which is possibly quiescent at present, i.e. neither we see large () radio jets nor is the SMBH contributing significantly to the mid-IR SED, ruling out strong radiative feedback of AGN. We obtained a detailed census of all observable baryons with a total mass of within the virial radius, amounting to a baryonic deficiency of relative to the cosmological mean. Only a small fraction of these baryons resides in a warm/hot circum-galactic X-ray halo, while the majority are still unobservable. We discussed various astrophysical scenarios to explain its unusual properties. Our work is a major step forward in understanding the assembly history of such extremely massive, isolated galaxies.

19 pages, 8 figures, 8 Tables, Accepted for publication in MNRAS

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