Cold Gas in Blue-Sequence E/S0s: Galaxies in Transition

TL;DR

This study investigates the gas content and star formation activity in blue-sequence early-type galaxies, suggesting many are in transition and capable of disk regrowth through gas accretion and minor mergers.

Contribution

It provides new observational evidence that blue-sequence E/S0 galaxies contain significant gas reservoirs and exhibit disk-like molecular gas rotation, indicating potential for morphological transformation.

Findings

Blue-sequence E/S0s have gas-to-stellar mass ratios comparable to spirals.

Molecular gas shows disk-like rotation, supporting disk regrowth.

Many galaxies can exhaust their gas in less than 3 Gyr, enabling stellar growth.

Abstract

We examine the HI+H_2 content of blue-sequence E/S0s -- a recently identified population of galaxies that are morphologically early type, but reside alongside spiral galaxies in color vs. stellar mass space. We test the idea that the majority of low-to-intermediate mass blue-sequence E/S0s may be settled products of past mergers evolving toward later-type morphology via disk regrowth. We find that blue-sequence E/S0s with stellar masses <= 4 x 10^10 M_{\odot} have atomic gas-to-stellar mass ratios of 0.1 to > 1.0, comparable to those of spiral galaxies. Preliminary CO(1-0) maps reveal disk-like rotation of molecular gas in the inner regions of several of our blue-sequence E/S0s, which suggests that they may have gas disks suitable for stellar disk regrowth. At the current rate of star formation, many of our blue-sequence E/S0s will exhaust their atomic gas reservoirs in <~ 3 Gyr. Over the same time period, most of these galaxies are capable of substantial growth in the stellar component. Star formation in blue-sequence E/S0s appears to be bursty, and likely involves inflow triggered by minor mergers and/or interactions.