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GALEX ULTRAVIOLET IMAGING OF DWARF GALAXIES AND STAR FORMATION RATES

机译:GALEX ULTRAVIOLET IMAGING OF DWARF GALAXIES AND STAR FORMATION RATES

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摘要

We present ultraviolet-integrated and azimuthally averaged surface photometric properties of a sample of 44dwarf irregular (dIm), blue compact dwarf, and Sm galaxies measured from archival near-ultraviolet (NUV)and far-ultraviolet (FUV) images obtained with the Galaxy Evolution Explorer (GALEX). We compare the UVto Ha and V-band properties and convert FUV, Ha, and V-band luminosities into star formation rates (SFRs).We also model the star formation history from colors and compare the integrated SFRs and SFR profiles withradius for these methods. In most galaxies, the UV photometry extends beyond Ha in radius, providing abetter measure of the star formation activity in the outer disks. The Ha appears to be lacking in the outerdisk because of faintness in low-density gas. The FUV and V-band profiles are continuous with radius, althoughthey sometimes have a kink from a double exponential disk. There is no obvious difference in star formationproperties between the inner and outer disks. No disk edges have been observed, even to stellar surface densitiesas low as 0.1 M⊙ pc~(-2)and SFRs as low as10~(-4)M⊙yr~(-1)kpc~(-2). Galaxies with H i to luminosity ratios haverelatively low FUV compared to V-band emission in the outer parts, suggesting a cessation of star formationthere. Galaxies with relatively high H I apparently have fluctuating star formation with a gigayear timescale.

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