The H alpha Galaxy Survey. IV. Star formation in the local Universe

TL;DR

This study analyzes star formation in local field galaxies, estimating the total star formation rate density and its dependence on galaxy luminosity, type, and location within galaxies, using H alpha imaging and luminosity functions.

Contribution

It provides a new calibration of star formation rates from B-band luminosity and a Monte Carlo method to estimate local universe star formation density.

Findings

Total star formation rate density is between 0.016 and 0.023 MSun/yr/cubic Mpc.

Bright galaxies contribute the most to star formation; faint galaxies contribute less than 10%.

Most star formation occurs in disk regions more than 1 kpc from galaxy centers.

Abstract

We present an analysis of the star formation properties of field galaxies within the local volume out to a recession velocity limit of 3000 km/s. A parent sample of 863 star-forming galaxies is used to calculate a B-band luminosity function. This is then populated with star formation information from a subsample of 327 galaxies, for which we have H alpha imaging, firstly by calibrating a relationship between galaxy B-band luminosity and star formation rate, and secondly by a Monte Carlo simulation of a representative sample of galaxies, in which star formation information is randomly sampled from the observed subset. The total star formation rate density of the local Universe is found to be between 0.016 and 0.023 MSun/yr/cubic Mpc, with the uncertainties being dominated by the internal extinction correction used in converting measured H alpha fluxes to star formation rates. If our internally derived B-band luminosity function is replaced by one from the Sloan Digital Sky Survey blue sequence, the star formation rate densities are approx. 60% of the above values. We also calculate the contribution to the total star formation rate density from galaxies of different luminosities and Hubble T-types. The largest contribution comes from bright galaxies with B absolute mag of approx. -20 mag, and the total contribution from galaxies fainter than -15.5 mag is less than 10%. Almost 60% of the star formation rate density comes from galaxies of types Sb, Sbc or Sc; 9% from galaxies earlier than Sb and 33% from galaxies later than Sc. Finally, 75 - 80% of the total star formation in the local Universe is shown to be occurring in disk regions, defined as being >1 kpc from the centres of galaxies.