Metallicities of galaxies in the nearby Lynx-Cancer void

Does the void environment have a sizable effect on the evolution of dwarf galaxies? If yes, the best probes should be the most fragile least massive dwarfs. We compiled a sample of about one hundred dwarfs with M_B in the range -12 to -18 mag, falling within the nearby Lynx-Cancer void. The goal is to study their evolutionary parameters -- gas metallicity and gas mass-fraction, and to address the epoch of the first substantial episode of Star Formation. Here we present and discuss the results of O/H measurements in 38 void galaxies, among which several the most metal-poor galaxies are found with the oxygen abundances of 12+log(O/H)=7.12-7.3 dex.Comment: 2 pages, one figure. To appear in proceedings of 'Environment and the Formation of Galaxies: 30 years later,' (Lisbon, September 2010), published by Springer-Verla

Neutral Gas Distributions and Kinematics of Five Blue Compact Dwarf Galaxies

We present the results of high spatial resolution HI observations of five intrinsically compact dwarf galaxies which are currently experiencing a strong burst of star formation. The HI maps indicate that these systems have a complex and clumpy interstellar medium. Unlike typical dwarf irregular galaxies, these Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in their neutral gas distributions which may provide a clue to the origin of their strong star-burst activity. Furthermore, while all of the systems do appear to be rotating, based on observed velocity gradients, the kinematics are complex. All systems have non-ordered kinematic structure at some level; some of the extended gas is not necessarily kinematically connected to the main system. The observed gas distributions and kinematics place constraints on evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf irregulars, and dwarf ellipticals have been postulated to explain their high star formation rates and low luminosity, low metallicity nature. The BCDs appear to have higher central mass concentrations in both gas and stellar content than the dwarf irregulars, indicating that evolutionary scenarios connecting these two classes will require mass redistribution. In addition, the fact that BCDs are rotationally supported systems indicates that BCDs are unlikely to evolve into dwarf ellipticals without substantial loss of angular momentum. Thus, while such evolutionary scenarios may still be possible with the aid of mergers or tidal interactions, the isolated nature of BCDs suggests that the majority of BCDs will not fade to become objects similar to the present day dwarf ellipticals.Comment: 19 pages, 15 figures. To appear in A

A Serendipitous Search for High-Redshift Lyman alpha Emission: Two Primeval Galaxy Candidates at z~3

In the course of our ongoing search for serendipitous high-redshift Lyman alpha (LyA) Emissionin deep archival Keck spectra, we discovered two very high equivalent width (W_{obs} ~ 450A, 2-sigma) LyA emission line candidates at z ~3 in a moderate dispersion (R~1200) spectrogram. Both lines have low velocity dispersions (sigma_v ~ 60 km/s) and deconvolved radii r ~ 1 kpc (h = 0.5). We argue that the lines are LyA, and are powered by stellar ionization. The surface density of robust, high equivalent width LyA candidates is estimated to be ~3 \pm 2 per arcmin^2 per unit redshift at z ~ 3, consistent with the estimate of Cowie etal (1998). The LyA emission line source characteristics are consistent with the galaxies undergoing their first burst of star formation, ie, with being primeval. Source sizes and velocity dispersions are comparable to the theoretical primeval galaxy model of Lin and Murray (1992) based on the inside-out, self-similar collapse of an isothermal sphere. In this model, star formation among field galaxies is a protracted process. Galaxies are thought to be able to display high equivalent widths for only the first few x 10 Myr. This time is short in relation to the difference in look back times between z=3 and z=4, and implies that a substantial fraction of strong line-emitting galaxies at z=3 were formed at redshifts z < 4. We discuss the significance of high-equivalent width LyA-emitting galaxies in terms of the emerging picture of the environment, and the specific characteristics of primeval galaxy formation at high redshift.Comment: 17 pages, 3 figures, one table. To appear in the Astrophysical Journa

Total Infrared Luminosity Estimation of Resolved and Unresolved Galaxies

The total infrared (TIR) luminosity from galaxies can be used to examine both star formation and dust physics. We provide here new relations to estimate the TIR luminosity from various Spitzer bands, in particular from the 8 micron and 24 micron bands. To do so, we use 45" subregions within a subsample of nearby face-on spiral galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) that have known oxygen abundances as well as integrated galaxy data from the SINGS, the Local Volume Legacy Survey (LVL) and Engelbracht et al. (2008) samples. Taking into account the oxygen abundances of the subregions, the star formation rate intensity, and the relative emission of the polycyclic aromatic hydrocarbons at 8 micron, the warm dust at 24 micron and the cold dust at 70 micron and 160 micron we derive new relations to estimate the TIR luminosity from just one or two of the Spitzer bands. We also show that the metallicity and the star formation intensity must be taken into account when estimating the TIR luminosity from two wave bands, especially when data longward of 24 micron are not available.Comment: 11 pages, 10 figures, accepted for publication in Ap