Small Bites: Star formation recipes in extreme dwarfs

Abstract

We study the relationship between the gas column density (Sigma_HI) and the star formation rate surface density (Sigma_SFR) for a sample of extremely small (M_B ~ -13, Delta V_50 ~ 30 km/s) dwarf irregular galaxies. We find a clear stochasticity in the relation between the gas column density and star formation. All gas with Sigma_HI >~ 10 M_sun/pc^2 has some ongoing star formation, but the fraction of gas with ongoing star formation decreases as the gas column density decreases, and falls to about 50% at Sigma_HI ~ 3 M_sun/pc^2. Further, even for the most dense gas, the star formation efficiency is at least a factor of ~ 2 smaller than typical of star forming regions in spirals. We also find that the ratio of H-alpha emission to FUV emission increases with increasing gas column density. This is unlikely to be due to increasing dust extinction because the required dust to gas ratios are too high. We suggest instead that this correlation arises because massive (i.e. H-alpha producing) stars are formed preferentially in regions with high gas density.

5 pages, 5 figures, 1 table. Accepted for publication in MNRAS Letters. The definitive version is available at www.blackwell- synergy.com

References in corpus (7)

• Extremely Inefficient Star Formation in the Outer Disks of Nearby Galaxies
• FIGGS: Faint Irregular Galaxies GMRT Survey - Overview, observations and first results
• Converting H$\alpha$ Luminosities into Star Formation Rates
• Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
• Baryonic Tully-Fisher Relation for Extremely Low Mass Galaxies
• A view of the M81 galaxy group via the H-alpha window
• Canes Venatici I cloud of galaxies seen in the H-alpha line

Cited by in corpus (18)

• The stellar and sub-stellar IMF of simple and composite populations
• The State of the Gas and the Relation Between Gas and Star Formation at Low Metallicity: the Small Magellanic Cloud
• The Survey of HI in Extremely Low-mass Dwarfs (SHIELD)
• The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
• Star formation histories of the LEGUS dwarf galaxies (III): the non-bursty nature of 23 star forming dwarf galaxies
• SHIELD: Comparing Gas and Star Formation in Low Mass Galaxies
• The relation between atomic gas and star formation rate densities in faint irregular galaxies
• The Kennicutt-Schmidt Relation in Extremely Metal-Poor Dwarf Galaxies
• The Metallicity Dependence of the HI Shielding Layers in Nearby Galaxies
• The radio - far infrared correlation in the faintest star forming dwarf galaxies
• Dwarf Spheroidal Satellite Formation in a Reionized Local Group
• Extended Schmidt law holds for faint dwarf irregular galaxies
• WALLABY pre-pilot survey: Two dark clouds in the vicinity of NGC 1395
• Atomic hydrogen, star formation and feedback in the lowest mass Blue Compact Dwarf galaxies
• Modeling HI distribution and kinematics in the edge-on dwarf irregular galaxy KK250
• Probing galaxy evolution through HI 21-cm emission and absorption: current status and prospects with the Square Kilometre Array
• The HI Structure of the Local Volume Dwarf Galaxy Pisces A
• Dynamics of Starbursting Dwarf Galaxies. III. A HI study of 18 nearby objects