DWARF GALAXY STARBURST STATISTICS IN THE LOCAL VOLUME

By Janice C. Lee, Robert C. Kennicutt Jr., J. G. F. S.J., S. Sakai, Sanae Akiyama. 2008

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An unresolved question in galaxy evolution is whether the star formation histories (SFHs) of low-mass systems are preferentially dominated by starbursts or modes that are more quiescent and continuous. Here, we quantify the prevalence of global starbursts in dwarf galaxies at the present epoch and infer their characteristic durations and amplitudes. The analysis is based on the Hα component of the 11 Mpc Hα UV Galaxy Survey (11HUGS), which provides Hα and Galaxy Evolution Explorer UV imaging for an approximately volume-limited sample of ∼ 300 star-forming galaxies within 11 Mpc. We first examine the completeness properties of the sample, and then directly tally the number of bursting dwarfs and compute the fraction of star formation that is concentrated in such systems. To identify starbursting dwarfs, we use an integrated Hα equivalent width (EW) threshold of 100 Å, which corresponds to a stellar birthrate of ∼ 2.5, and also explore the use of empirical starburst definitions based on σ thresholds of the observed logarithmic EW distributions. Our results are robust to the exact choice of the threshold, and are consistent with a picture where dwarfs that are currently experiencing massive global bursts are just the ∼ 6% tip of a low-mass galaxy iceberg. Moreover, bursts are only responsible for about a quarter of the total star formation in the overall dwarf population, so the majority of stars in low-mass systems are not formed in this mode today. Spirals and irregulars devoid of Hα emission are rare, indicating that the complete cessation of star formation generally does not occur in such galaxies and is not characteristic of the interburst state, at least for the more luminous systems with MB < −15. The starburst statistics presented here directly constrain the duty cycle and the average burst amplitude under the simplest assumptions where all dwarf irregulars share a common SFH and undergo similar burst cycles with equal probability. Uncertainties in such assumptions are discussed in the context of previous work.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/df7ac5c19ad7885f623d4b70c57f71a4dc72cbd6

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Citations in the corpus

THE SPITZER LOCAL VOLUME LEGACY: SURVEY DESCRIPTION AND INFRARED PHOTOMETRY (2009, methodology): “The outer tier of LVL is derived from the larger 11 Mpc narrowband Hα imaging survey of Kennicutt et al. (2008), and GALEX ultraviolet follow-up observations of a subsample which avoids the Galactic plane (|b| > 30◦) (Lee et al. 2009a).”
Galaxy evolution in cosmological simulations with outflows ― I. Stellar masses and star formation rates (2011, methodology): “Lee et al. (2009) used the volume-limited 11HUGS sample to show that the burst fraction, defined as having birthrate> 2.5, is only 6+4−2% in dwarfs (typically .”
COMPARISON OF Hα AND UV STAR FORMATION RATES IN THE LOCAL VOLUME: SYSTEMATIC DISCREPANCIES FOR DWARF GALAXIES (2009, methodology): “…is being further augmented by Spitzer IRAC mid-infrared and MIPS far-infrared observations through the composite Local Volume Legacy1 (LVL) program (Lee et al. 2008; Dale et al. 2009), which is delivering the overall multi-wavelength dataset to the community.2 The ensemble of observations enables…”
A GALEX ULTRAVIOLET IMAGING SURVEY OF GALAXIES IN THE LOCAL VOLUME (2010, methodology): “As discussed in Paper I and Lee et al. (2009a), late-type galaxies that are completely devoid of star formation as traced by Hα emission are rare.”
THE NATURE OF STARBURSTS. I. THE STAR FORMATION HISTORIES OF EIGHTEEN NEARBY STARBURST DWARF GALAXIES (2010, methodology): “…over the past decade have used these different wavelength observations to study the properties of both nearby and distant actively bursting systems (e.g., Colless et al. 1994; Babul & Ferguson 1996; Meurer et al. 1997; Heckman et al. 2005; Oey et al. 2007; Lee et al. 2009, among many others).”
THE EMISSION BY DUST AND STARS OF NEARBY GALAXIES IN THE HERSCHEL KINGFISH SURVEY (2011, background): “For example, some S0 and Sa galaxies have similar specific SFRs and fdust/f∗, but the S0s have slightly warmer dust and lower dust masses.”
LOW CO LUMINOSITIES IN DWARF GALAXIES (2012, background): “Such variations are strongest in the smallest dwarf galaxies (MB > −15) and are less common and weaker in (more) massive dwarfs and spirals (Lee et al. 2009).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “Lee et al. (2009b) analyzed the statistics of the SFRs in more depth and confirmed a larger fraction of stars formed in bursts in low-mass galaxies (∼25%), but these still represent only a small fraction of the total stars formed– even in the dwarfs the majority of stars appear to form in extended…”