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Title:
Stochastic Star Formation in Low Mass Galaxies: A case study of DDO 210
Authors:
Tremonti, Christina A.; Lee, J. C.; van Zee, L.; Kennicutt, R. C.; Gil de Paz, A.; Sakai, S.; Funes, J.; Akiyama, S.
Affiliation:
AA(Univ. of Arizona), AB(Carnegie Obs), AC(Univ. of Indiana), AD(Univ. of Cambridge, United Kingdom), AE(Univ. Complutense, Spain), AF(UCLA), AG(Vatican Obs., Italy), AH(Univ. of Arizona)
Publication:
American Astronomical Society, AAS Meeting #211, #95.03; Bulletin of the American Astronomical Society, Vol. 39, p.894
Publication Date:
12/2007
Origin:
AAS
Bibliographic Code:
2007AAS...211.9503T

Abstract

To address the longstanding question of whether dwarf galaxies have bursty star formation histories requires a large sample of dwarf galaxies and an accurate tracer of star formation. Here we explore the utility of using two common tracers, H-alpha and the ultraviolet (UV). H-alpha and UV photons are primarily produced by massive stars, so stochastic effects come into play when the star formation rate (SFR) is so low that the upper mass end of the initial mass function (IMF) is not fully populated. We use Monte-Carlo simulations to explore these effects at a range of SFRs for a standard Chabrier IMF. We do not impose the restriction that stars form primarily in low mass clusters as explored by Kroupa and Weidner. Here we simply consider Poisson fluctuations in the number of massive stars when star formation occurs at a constant low rate. We find that above SFRs of 0.001 Msun/yr both the far-UV and H-alpha are reliable tracers of SFR. Below this value both indicators begin to show deviations, with H-alpha being more strongly affected. We explore the implications of these findings for the 11 Mpc H-alpha UV Galaxy Survey (11HUGS), a GALEX Legacy program designed to characterize the star formation properties of a local volume-limited sample. We highlight the dwarf galaxy DDO 210, which has a UV luminosity of 270 L_sun, but no nebular H-alpha emission. While we cannot rule out a truncated star formation history for this galaxy, our simulations demonstrate that this H-alpha deficient galaxy could be forming stars at a constant rate of 0.0001 Msun/yr.
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