The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf Galaxies as Revealed by RR Lyrae Variables (original) (raw)

Chemical Properties of Star Forming Dwarf Galaxies

2007

Recent studies of the near-infrared (NIR) properties of dwarf irregular galaxies (dIs) and blue compact dwarfs (BCDs) have provided improved estimates for the NIR luminosity of old stellar populations in these galaxies. These can be used to derive gas fractions, and thereby to evaluate how BCDs have evolved with respect to dIs. Oxygen abundances have been derived for four BCDs in the Virgo Cluster from a run at Gemini-North in 2003. Combining these new abundances with published values, we study the correlations among the metallicity, Ks luminosity, gas mass, baryonic mass, and gas fraction. Within errors, the two types of dwarfs appear to share a common relation between the oxygen abundance and the luminosity in Ks. The correlation between metallicity and the gas fraction is the same for BCDs as for dIs, indicating that BCD evolution has been similar to dIs. Since dIs appear to have evolved as isolated systems, the BCD bursts are unlikely to be a consequence of gas infall or merging.

Chemical enrichment and star formation in the Milky Way disk. II. Star formation history

Astronomy and Astrophysics, 2000

A chromospheric age distribution of 552 late-type dwarfs is transformed into a star formation history by the ap- plication of scale height corrections, stellar evolutionary cor- rections and volume corrections. We show that the disk of our Galaxy has experienced enhanced episodes of star formation at 0-1 Gyr, 2-5 Gyr and 7-9 Gyr ago, although the reality of the latter burst is still uncertain. The star sample birthsites are dis- tributed over a very large range of distances because of orbital diffusion, and so give an estimate of the global star formation rate. These results are compared with the metal-enrichment rate, given by the age-metallicity relation, with the expected epochs of close encounters between our Galaxy and the Magellanic Clouds, and with previous determinations of the star forma- tion history. Simulations are used to examine the age-dependent smearing of the star formation history due to age uncertainties, and the broadening of the recovered features, as well as to...