Star formation in bulgeless late type galaxies: clues to their evolution

TL;DR

This study investigates star formation and evolution in bulgeless late-type galaxies using radio and optical observations, highlighting the role of tidal interactions in triggering star formation and bulge development.

Contribution

It provides new insights into how tidal interactions influence star formation and bulge formation in bulgeless galaxies through combined radio and optical data analysis.

Findings

Radio emission detected in 5 of 12 galaxies, mainly from disk star formation.

Tidal interactions trigger star formation and possibly pseudobulge development.

Bulgeless galaxies can evolve into bulge-containing systems through external interactions.

Abstract

We present GMRT 1280 MHz radio continuum observations and follow-up optical studies of the disk and nuclear star formation in a sample of low luminosity bulgeless galaxies. The main aim is to understand bulge formation and overall disk evolution in these late type galaxies. We detected radio continuum from five of the twelve galaxies in our sample; the emission is mainly associated with disk star formation. Only two of the detected galaxies had extended radio emission; the others had patchy disk emission. In the former two galaxies, NGC3445 and NGC4027, the radio continuum is associated with star formation triggered by tidal interactions with nearby companion galaxies. We did follow-up Halpha imaging and nuclear spectroscopy of both galaxies using the Himalayan Chandra Telescope (HCT). The Halpha emission is mainly associated with the strong spiral arms. The nuclear spectra indicate ongoing nuclear star formation in NGC3445 and NGC4027 which maybe associated with nuclear star clusters. No obvious signs of AGN activity were detected. Although nearly bulgeless, both galaxies appear to have central oval distortions in the R band images; these could represent pseudobulges that may later evolve into large bulges. We thus conclude that tidal interactions are an important means of bulge formation and disk evolution in bulgeless galaxies; without such triggers these galaxies appear to be low in star formation and overall disk evolution.