PGC 38025: A Star-forming Lenticular Galaxy With an Off-nuclear Star-forming Core

TL;DR

This study investigates a unique star-forming lenticular galaxy with an off-nuclear blue core, revealing that minor mergers can trigger star formation in such galaxies, challenging the traditional passive view of S0s.

Contribution

It provides detailed observations of PGC 38025, demonstrating star formation driven by minor mergers in a field S0 galaxy, which is a novel insight into galaxy evolution.

Findings

Star formation rate of 0.446 M_sun/yr in PGC 38025

Gaseous metallicity of 12 + log(O/H) = 8.42

Misaligned rotation of gas and stars indicating recent merger activity

Abstract

Lenticular galaxies (S0s) were considered mainly as passive evolved spirals due to environmental effects for a long time; however, most S0s in the field cannot fit into this common scenario. In this work, we study one special case, SDSS J120237.07+642235.3 (PGC 38025), a star-forming field S0 galaxy with an off-nuclear blue core. We present optical integral field spectroscopic (IFS) observation with the 3.5 meter telescope at Calar Alto (CAHA) Observatory, and high-resolution millimeter observation with the NOrthern Extended Millimeter Array (NOEMA). We estimated the star formation rate (SFR = 0.446 $M_\odot yr^{-1}$) and gaseous metallicity (12 + log(O/H) = 8.42) for PGC 38025, which follows the star formation main sequence and stellar mass - metallicity relation. We found that the ionized gas and cold molecular gas in PGC 38025 show the same spatial distribution and kinematics, whilst rotating misaligned with stellar component. The off-nuclear blue core is locating at the same redshift as PGC 38025 and its optical spectrum suggest it is \rm H\,{\sc ii} region. We suggest that the star formation in PGC 38025 is triggered by a gas-rich minor merger, and the off-nuclear blue core might be a local star-formation happened during the accretion/merger process.