[Paper Review] The H alpha Galaxy Survey. IV. Star formation in the local Universe

P. A. James, J. H. Knapen+3 more|ArXiv.org|Feb 29, 2008

Stellar, planetary, and galactic studies27 citations

TL;DR

This study presents a comprehensive analysis of star formation in field galaxies within the local Universe (out to 3000 km s⁻¹) using H𝛼 imaging from the H𝛼 Galaxy Survey. By calibrating B-band luminosity to star formation rate and applying Monte Carlo simulations to a sample of 327 galaxies, it finds a total star formation rate density of 0.016–0.023 M⊙ yr⁻¹ Mpc⁻³, with 75–80% occurring in disk regions (>1 kpc from galactic centers), and shows that bright spirals (MB ≈ –20 mag) dominate the star formation, while faint dwarfs contribute less than 10%.

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.

Motivation & Objective

• To determine the total star formation rate density (SFRD) in the local Universe using a volume-limited sample of field galaxies.
• To assess the contribution of galaxies of different luminosities and Hubble types to the total SFRD.
• To quantify the spatial distribution of star formation within galaxies, distinguishing between bulge and disk regions.
• To compare SFRD estimates derived from the H𝛼 Galaxy Survey with those from other large surveys using different indicators and samples.
• To correct for incompleteness in the sample due to magnitude, diameter, and velocity selection criteria to enable robust statistical analysis.

Proposed method

• A parent sample of 863 star-forming galaxies was selected from the UGC catalog based on magnitude, diameter, and recession velocity limits (v < 3000 km s⁻¹).
• A B-band luminosity function was derived from the parent sample to model the overall galaxy population distribution.
• A calibration was established between B-band luminosity and star formation rate using H𝛼 fluxes from a subsample of 327 galaxies.
• A Monte Carlo simulation was used to extrapolate SFR information from the observed subsample to the full parent population, accounting for statistical sampling uncertainty.
• Internal extinction corrections were applied to H𝛼 fluxes to convert observed line fluxes into intrinsic star formation rates.
• Spatially resolved star formation was analyzed by dividing galaxies into central (≤1 kpc) and disk (>1 kpc) regions to assess where most SF occurs.

Experimental results

Research questions

• RQ1 What is the total star formation rate density in the local Universe as derived from the H𝛼 Galaxy Survey, and how does it compare to other literature estimates?
• RQ2 Which galaxy luminosities and morphological types contribute most significantly to the total star formation rate density?
• RQ3 What fraction of star formation in local field galaxies occurs in disk regions (>1 kpc from the center) versus bulge regions?
• RQ4 How do different extinction correction assumptions affect the derived star formation rate density?
• RQ5 How does the SFRD estimate change when using an external luminosity function (e.g., from SDSS) instead of the internally derived one?

Key findings

• The total star formation rate density in the local Universe is estimated at 0.016–0.023 M⊙ yr⁻¹ Mpc⁻³, with uncertainties primarily driven by internal extinction corrections.
• When using the SDSS blue sequence luminosity function instead of the internally derived one, the SFRD drops to approximately 60% of the original estimate, yielding 0.0130 M⊙ yr⁻¹ Mpc⁻³.
• Galaxies with MB ≈ –20 mag (L* spirals) contribute the largest share to the total SFRD, while galaxies fainter than MB = –15.5 mag contribute less than 10%.
• Approximately 60% of the total SFRD comes from galaxies of Hubble types Sb, Sbc, or Sc; 33% from later types (Scd and later); and 9% from earlier types (Sa and earlier).
• Between 75% and 80% of the total star formation in the local Universe occurs in disk regions (>1 kpc from galactic centers), indicating that most SF is not concentrated in the central bulges.
• The SFRD estimates are consistent with values from other recent surveys using diverse star formation indicators, such as UV, H𝛼, and emission-line surveys, supporting the robustness of the findings.