The Color-Dependent Frequency of XUV Disks In Low-Mass E/S0s

TL;DR

This study finds a high frequency of Type 1 XUV disks in low-mass E/S0 galaxies, especially in dwarfs, suggesting these disks are linked to weak star formation rather than significant disk growth.

Contribution

It reveals a higher occurrence of XUV disks in low-mass E/S0s than in late-type galaxies, highlighting a potential link to inefficient star formation in dwarf galaxies.

Findings

~40% of low-mass E/S0s have XUV disks, double the rate in late-type galaxies.

In dwarf E/S0s, red-sequence galaxies show ~70% XUV disk occurrence, blue-sequence ~20%.

XUV disks in dwarfs may relate to weak star formation, not substantial disk growth.

Abstract

We identify a high frequency of Type 1 XUV disks, reflecting recent outer disk star formation, in a sample of 31 E/S0s with stellar masses primarily below M_* ~ 4 x 10^10 M_sun. Our ~40% identification rate is roughly twice the 20% fraction reported for late-type galaxies. Intriguingly, in the dwarf mass regime (below M_* ~ 5 x 10^9 M_sun) where gas fractions clearly rise, Type 1 XUV disks occur in ~70% of red-sequence E/S0s but only ~20% of blue-sequence E/S0s, a population recently linked to active disk rebuilding, especially in the dwarf regime. Our statistics are preliminary, but could indicate that for dwarf E/S0s Type 1 XUV disks are primarily related to weak or inefficient outer-disk star formation rather than to star formation capable of driving substantial disk growth. Substantial growth may instead be associated with populations that have low XUV-disk frequency, possibly explaining the similar ~20% frequencies for normal late types and low-mass blue-sequence E/S0s.