The JCMT Nearby Galaxies Legacy Survey VII: H\alpha{} imaging and massive star formation properties

TL;DR

This study provides H extalpha{} fluxes and star formation rates for 156 nearby galaxies, revealing their properties and correlations, and introduces new measurements and methods for analyzing star formation in galaxies.

Contribution

It offers new H extalpha{} imaging data for 72 galaxies and refines star formation rate estimates, emphasizing an HI-selected sample with lower internal absorption corrections.

Findings

SFRs range from 0.1 to 11 Msun/yr with median 0.2 Msun/yr

Weak correlation between EWs and luminosity, stronger in late-type galaxies

Internal absorption A(H extalpha{}) is lower than in previous studies

Abstract

We present H\alpha{} fluxes, star formation rates (SFRs) and equivalent widths (EWs) for a sample of 156 nearby galaxies observed in the 12CO J=3-2 line as part of the James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey. These are derived from images and values in the literature and from new H\alpha{} images for 72 galaxies which we publish here. We describe the sample, observations and procedures to extract the H\alpha{} fluxes and related quantities. We discuss the SFR properties of our sample and confirm the well-known correlation with galaxy luminosity, albeit with high dispersion. Our SFRs range from 0.1 to 11 Msun yr-1 with a median SFR value for the complete sample of 0.2 Msun yr-1. This median values is somewhat lower than similar published measurements, which we attribute, in part, to our sample being HI-selected and, thus, not biased towards high SFRs as has frequently been the case in previous studies. Additionally, we calculate internal absorptions for the H\alpha{} line, A(H\alpha{}), which are lower than many of those used in previous studies. Our derived EWs, which range from 1 to 880\AA{} with a median value of 27\AA{}, show little dependence with luminosity but rise by a factor of five from early- to late-type galaxies. This paper is the first in a series aimed at comparing SFRs obtained from H\alpha{} imaging of galaxies with information derived from other tracers of star formation and atomic and molecular gas.