Star Formation Properties of HIPASS Galaxies I: Sample Characteristics

Astronomy and Astrophysics – Astronomy

Scientific paper

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Scientific paper

Any sample of galaxies selected according to optical properties will be biased by the night sky towards higher surface brightness. This implies that so called low surface brightness (LSB) galaxies are under represented in many studies. This is of some concern when trying to understand the star formation properties of a given sample since LSB galaxies appear to have significantly different star formation histories that HSB galaxies. A sample of ~120 galaxies was chosen from the Hi Parkes All Sky Survey (HiPASS) to be imaged in B and R band and in Hα to deduce details about star formation in nearby disk galaxies while avoiding such surface brightness selection effects. ~65 of these HiPASS galaxies have been imaged in all three bandpasses for this paper. The sample is dominated by late-type, dwarf disks (mostly Sc and Sm galaxies) with exponential disk scalelengths around 1 kpc or less. They inhabit a range in colors over all values of central surface brightness and exhibit a weak trend between Hα flux per unit area and B-band surface brightness. Hii regions were detected in all but one of the galaxies; many galaxies had as few as 2-5 which is what would be expected for a large sample of late-type galaxies. Calculation of the star formation rates (SFRs) using the integrated Hα luminosities shows that most of the galaxies have SFRs ~0.01-0.1 Msun yr-1, which is typical for LSB and dwarf galaxies. It should be noted that such low SFRs cannot produce the amount of stars typically observed in such systems, implying that the SFRs were higher at some point in the past.

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