| Abstrakt: |
We present Hubble Space Telescope (HST) observations of the nearby, massive, highly rotating hybrid galaxy UGC 12591, along with observations in the 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 an H -band B / D ratio of |$69{{\,\rm per\,cent}}$|. The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of |$\rm \sim 0.1\!-\!0.2\, M_\odot \, yr^{-1}$| , exceptionally low for the galaxy's huge stellar mass of |$\rm 1.6\times 10^{11}M_\odot$| , implying a strong quenching of its SFR with a star formation efficiency of 3–5 per cent. For at least the past |$\rm 10^{8}$| yr, the galaxy has remained in a quiescent state as a sterile, 'red and dead' galaxy. UGC 12591 hosts a supermassive black hole (SMBH) of |$\rm 6.18\times 10^{8} \, M_\odot$| , which is possibly quiescent at present, i.e. we neither see large (|$\rm \gt 1 kpc$|) radio jets nor 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 |$\rm 6.46\times 10^{11} \, M_\odot$| within the virial radius, amounting to a baryonic deficiency of |${\sim }85{{\,\rm per\,cent}}$| relative to the cosmological mean. Only a small fraction of these baryons reside in a warm/hot circumgalactic 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. [ABSTRACT FROM AUTHOR] |
