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

Shankar Ray, J. Bagchi+5 more|arXiv (Cornell University)|Mar 6, 2022

Astronomy and Astrophysical Research5 citations

TL;DR

This study uses Hubble Space Telescope and multiwavelength data to analyze UGC 12591, a massive, fast-spinning hybrid galaxy with a dominant bulge (H-band B/D = 69%) and extremely low star formation (SFR ≈ 0.1–0.2 M☉ yr⁻¹). Despite its high stellar mass (1.6×10¹¹ M☉), it is quiescent, with only 15% of baryons accounted for, revealing a 85% baryonic deficiency and suggesting non-gravitational processes like AGN feedback or inefficient cooling may disrupt standard scaling relations like the Baryonic Tully-Fisher relation.

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 $69\%$. The spectral energy distribution (SED) fitting reveals an extremely low global star formation rate (SFR) of $ m\sim0.1-0.2 M_\odot yr^{-1}$, exceptionally low for the galaxy's huge stellar mass of $ m 1.6 imes10^{11}M_\odot$, implying a strong quenching of its SFR with star formation efficiency of $3-5\%$. For at least the past $ m 10^{8}$ 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 $ m 6.18 imes 10^{8} M_\odot$ which is possibly quiescent at present, i.e. neither we see large ($ m>1 kpc$) 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 $ m 6.46 imes10^{11} M_\odot$ within the virial radius, amounting to a baryonic deficiency of $\sim$$85\%$ 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.

Motivation & Objective

• To investigate the structural components (bulge/disc) and star formation properties of UGC 12591 using Hubble Space Telescope imaging.
• To perform a comprehensive census of all observable baryons within the virial radius to assess baryonic deficiency.
• To evaluate the role of AGN feedback in quenching star formation in this massive, isolated galaxy.
• To test the robustness of the Baryonic Tully-Fisher Relation (BTFR) in extreme systems like UGC 12591.
• To understand the evolutionary mechanisms behind the formation of massive, quiescent, fast-rotating hybrid galaxies.

Proposed method

• Conducted surface photometry on HST ACS data in V, I, and H bands to decompose bulge and disc components.
• Fitted the spectral energy distribution (SED) using multiwavelength data from UV to FIR to derive global star formation rate and stellar mass.
• Estimated the total baryonic mass within the virial radius by summing stellar mass, cold/warm/hot gas, and dark matter halo mass.
• Used X-ray observations to estimate the mass of the circum-galactic medium (CGM) in the form of hot gas.
• Compared the galaxy’s dynamical mass and baryonic mass to the cosmological mean to quantify baryonic deficiency.
• Analyzed radio and mid-IR data to assess the presence and impact of active galactic nucleus (AGN) feedback.

Experimental results

Research questions

• RQ1 What are the structural properties of the bulge and disc in UGC 12591, and what fraction of the light is contributed by each component?
• RQ2 Why is the star formation rate in UGC 12591 so exceptionally low (0.1–0.2 M☉ yr⁻¹) given its high stellar mass of 1.6×10¹¹ M☉?
• RQ3 To what extent is the baryonic mass in UGC 12591 accounted for, and what fraction remains unobserved, indicating baryonic deficiency?
• RQ4 Does the Baryonic Tully-Fisher Relation (BTFR) hold for UGC 12591, especially after including hot halo gas mass?
• RQ5 Could past AGN feedback or other non-gravitational processes explain the quiescent state and baryonic deficiency in this massive galaxy?

Key findings

• UGC 12591 exhibits a dominant bulge with an H-band B/D ratio of 69%, indicating a strongly bulge-dominated morphology.
• The galaxy has an extremely low global star formation rate of 0.1–0.2 M☉ yr⁻¹, corresponding to a star formation efficiency of only 3–5%, despite its massive stellar content of 1.6×10¹¹ M☉.
• The galaxy has been in a quiescent state for at least 10⁸ years, classified as a 'red and dead' galaxy with no significant ongoing star formation.
• A total baryonic mass of 6.46×10¹¹ M☉ is found within the virial radius, but this represents only 15% of the cosmological mean, indicating a baryonic deficiency of ~85%.
• Only a small fraction of the baryons reside in a hot circum-galactic X-ray halo, while the majority remain unobservable, suggesting missing baryons are not in the expected phases.
• Despite inclusion of extrapolated hot halo gas mass, UGC 12591 still lies far below the standard Baryonic Tully-Fisher relation (slope ~4), indicating a potential breakdown of self-similar scaling due to non-gravitational processes such as AGN feedback or inefficient cooling.