Igor O. Drozdovsky

Star Formation Rates of Local Blue Compact Dwarf Galaxies. I. 1.4 GHz and 60 Micron Luminosities

We determine and examine the star formation rates of 50 well-known, local blue compact dwarf (BCD) galaxies based on their 1.4 GHz and 60 μm luminosities. We find that in cases for which both radio and far-infrared luminosities are available, the resulting star formation rates agree extremely well with one another. We determine that the star formation rates of the BCD galaxies in our sample span nearly 5 orders of magnitude, from approximately a few times 10-3 to several times 101 M⊙ yr-1, with a median SFR of about 0.3 M⊙ yr-1. We discuss trends of metallicity (primarily oxygen abundance) with star formation rate and explore the connections between SFR and galaxy mass estimates.

A Near-Infrared Stellar Census of Blue Compact Dwarf Galaxies: The Wolf-Rayet Galaxy I Zw 36*

We report the results of near-IR imaging in J and H, of I Zw 36 (≈Z⊙/14) with the Hubble Space Telescope. Whereas imaging with the pre-COSTAR Faint Object Camera (FOC) previously resolved hot and massive stars in the near-UV, the NICMOS data furnish a census of the cool, intermediate- and low-mass stars. There clearly was star formation in I Zw 36 prior to the activity which earned it its blue compact dwarf/Wolf-Rayet galaxy classification. The detection of luminous, asymptotic giant branch stars requires that stars formed vigorously several hundred megayears ago. The well-populated red giant branch indicates stars with ages of at least 1–2 Gyr (and possibly older than 10 Gyr). We use the tip-of-the-red-giant-branch method to derive a distance of ≥5.8 Mpc. This is the third in a series of papers on near-IR–resolved blue compact dwarf galaxies. We notice that the color-magnitude diagrams of VII Zw 403, Mrk 178, and I Zw 36 do not exhibit the gaps expected from an episodic mode of star formation. Using simulated color-magnitude diagrams we demonstrate for I Zw 36 that star formation did not stop for more than a few 108 yr over the past 109 yr, and we discuss the implications of this result.

The Stellar Content of NGC 6789, A Blue Compact Dwarf Galaxy in the Local Void*

We find that NGC 6789 is the most nearby example of a blue compact dwarf galaxy known to date. With the help of the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope, we resolve NGC 6789 into over 15,000 point sources in the V and I bands. The young stars of NGC 6789 are found exclusively near the center of the galaxy. The red giant population identified at large galactocentric radii yields a distance of about 3.6 Mpc, a stellar metallicity [Fe/H] of about -2, and a minimum age of about 1 Gyr. Despite its isolated location in the Local Void, its low metallicity, and its active star formation, the properties of NGC 6789 are clearly not those of a galaxy in formation.

Emission-Line Spectroscopy of Damped Lyα Systems: The Case of SBS 1543+593/HS 1543+5921

We report HST/STIS spectroscopy and Gemini/GMOS-N imaging of the Damped Lyα (DLA) system toward HS 1543+5921 caused by the host star-forming galaxy (SFG) SBS 1543+593. The Gemini image shows new morphological details of this well-resolved DLA galaxy. In combination with previous optical spectra, the new UV spectra enable us to compare, for the first time, ionized and neutral gas-phase α-element abundances derived from emission- and absorption-line spectroscopy, in a bona fide DLA galaxy. The abundances we determine using emission-line diagnostics agree with those from absorption-line diagnostics. We present our results on a metallicity versus redshift diagram that combines local H II regions and SFGs with high-redshift DLAs, and discuss implications for the chemical evolution of galaxies.

The H II Regions of the Damped Lyα Absorber SBS 1543+593*

We report new imaging and spectroscopic observations of the damped Ly alpha (DLA) galaxy SBS 1543+593, a nearby dwarf galaxy whose stellar disk is intersected by the sightline to the bright background QSO HS 1543+5921. Hubble Space Telescope imaging observations with WFPC2 in the F450W and F702W bands are used to measure the DLA galaxys properties and compile a catalog of its (candidate) HII regions. Ground-based long-slit spectroscopy of the brightest HII region in the galaxy yields estimates of the star formation rate (SFR) and of chemical abundances in the galaxys interstellar medium. We find that SBS 1543+593 exhibits a SFR

The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A

\approx 0.006 h^{-2}_{70} M_{\odot}

The Stellar Content of the Polar Rings in the Galaxies NGC 2685 and NGC 4650A

yr

The Hubble Space Telescope ACS Grism Parallel Survey. II. First Results and a Catalog of Faint Emission-Line Galaxies at z ≤ 1.6

^{-1}

The Resolved Red Giant Branches of E/S0 Galaxies

, or a SFR per unit area of

The Dwarf Irregular/Wolf-Rayet Galaxy NGC 4214. I. A New Distance, Stellar Content, and Global Parameters*

\approx 1.4 \times 10^{-4} h^{-2}_{70} M_\odot