Recent work has identified a population of low-redshift E/S0 galaxies that lie on the blue sequence in color vs. stellar mass parameter space , where spiral galaxies typically reside .
While high-mass blue-sequence E/S0s often resemble young merger or interaction remnants likely to fade to the red sequence , we focus on blue-sequence E/S0s with lower stellar masses ( { M _ { * } } < a few \times 10 ^ { 10 } M _ { \odot } ) , which are characterized by fairly regular morphologies and low-density field environments where fresh gas infall is possible .
This population may provide an evolutionary link between early-type galaxies and spirals through disk regrowth .
Focusing on atomic gas reservoirs , we present new GBT HI data for 27 E/S0s on both sequences as well as a complete tabulation of archival HI data for other galaxies in the Nearby Field Galaxy Survey .
Normalized to stellar mass , the atomic gas masses for 12 of the 14 blue-sequence E/S0s range from 0.1 to > 1.0 , demonstrating that morphological transformation is possible if the detected gas can be converted into stars .
These gas-to-stellar mass ratios are comparable to those of spiral and irregular galaxies and have a similar dependence on stellar mass .
Assuming that the HI is accessible for star formation , we find that many of our blue-sequence E/S0s can increase in stellar mass by 10–60 % in 3 Gyr in both of two limiting scenarios , exponentially declining star formation ( i.e. , closed box ) and constant star formation ( i.e. , allowing gas infall ) .
In a constant star formation scenario , about half of the blue-sequence E/S0s require fresh gas infall on a timescale of \lesssim 3 Gyr to avoid exhausting their atomic gas reservoirs and evolving to the red sequence .
We present evidence that star formation in these galaxies is bursty and likely involves externally triggered gas inflows .
Our analysis suggests that most blue-sequence E/S0s are indeed capable of substantial stellar disk growth on relatively short timescales .