Abundant Molecular Gas in the Central Region of Lenticular Galaxy PGC 39535

TL;DR

This study reveals abundant molecular gas and ongoing central star formation in the lenticular galaxy PGC 39535, challenging the typical view of S0 galaxies as gas-poor and inactive.

Contribution

First detailed molecular gas mapping of a star-forming S0 galaxy showing central gas structures and kinematics similar to stars and ionized gas.

Findings

Molecular gas mainly in the galaxy's center as a bar and ring.

Star formation rate of 1.57 solar masses per year.

Galaxy's star formation efficiency is suppressed compared to spiral galaxies.

Abstract

Lenticular galaxies (S0s) in the local universe are generally absent of recent star formation and lack molecular gas. In this paper, we investigate one massive ($M_*$$\sim$5$\times10^{10}$ M$_\odot$) star-forming S0, PGC 39535, with the Northern Extended Millimeter Array (NOEMA). Using optical data from SDSS-IV MaNGA survey, we find star formation mainly concentrates in the central region of PGC 39535. The total star formation rate estimated using extinction-corrected H$\alpha$ flux is 1.57 M$_\odot$ yr$^{-1}$. Results of NOEMA observation suggest that the molecular gas mainly concentrates in the central regions as a gaseous bar and a ring-like structure, and shows similar kinematics as the stellar and ionized gas components. The total molecular gas mass estimated from CO(1-0) is (5.42$\pm$1.52)$\times$10$^{9}$ M$_{\odot}$. We find PGC 39535 lies on the star-forming main sequence, but falls below Kennicutt-Schmidt relation of spiral galaxies, suggesting that the star formation efficiency may be suppressed by the massive bulge. The existence of a second Gaussian component in the CO spectrum of the central region indicates possible gas flows. Furthermore, our analyses suggest that PGC 39535 resides in the center of a massive group and the derived star formation history indicates it may experience a series of gas-rich mergers over the past 2$\sim$7 Gyr.