Integral Field spectroscopy of two HI rich E+A galaxies

TL;DR

This study uses integral field spectroscopy to investigate two nearby HI-rich E+A galaxies, revealing ongoing star formation in their outer regions despite post-starburst signatures in the core, highlighting aperture effects in galaxy classification.

Contribution

It provides spatially resolved evidence that star formation can occur outside the central regions of HI-rich E+A galaxies, challenging previous single-fiber spectroscopic classifications.

Findings

Outer regions show strong optical emission lines indicating ongoing star formation.

Central regions are consistent with post-starburst populations with little emission.

Aperture effects can misclassify galaxies by missing peripheral star-forming activity.

Abstract

Approximately half of the nearby E+A galaxies followed up with 21-cm observations have detectable HI emission. The optical spectra of these galaxies show strong post-starburst stellar populations but no optical emission lines implying star-formation is not ongoing despite the presence of significant gas reservoirs. We have obtained integral field spectroscopic follow up observations of the two brightest, and nearest, of the six E+A galaxies with HI 21-cm emission in the recent sample of Zwaan et al. (2013). In the central regions of both galaxies the observations are consistent with a post-starburst population with little emission. However, outside the central regions both galaxies have strong optical emission lines, with a clumpy or knot-like distribution, indicating ongoing star-formation. We conclude that in these two cases the presence of optical spectra lacking evidence for star-formation while a large gas mass is present can be explained by an aperture effect in selecting the nearby E+A galaxies using single-fibre spectroscopy that probes only the galaxy core.