John J. Salzer

ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. I. H I OBSERVATIONS

The discovery of a previously unknown 21 cm H I line source identified as an ultra-compact high velocity cloud in the ALFALFA survey is reported. The H I detection is barely resolved by the Arecibo 305 m telescope {approx}4 beam and has a narrow H I linewidth (half-power full width of 24 km s{sup -1}). Further H I observations at Arecibo and with the Very Large Array corroborate the ALFALFA H I detection, provide an estimate of the H I radius, {approx}1 at the 5 Multiplication-Sign 10{sup 19} cm{sup -2} isophote, and show the cloud to exhibit a velocity field which, if interpreted as disk rotation, has an amplitude of {approx_equal}9.0 {+-} 1.5 km s{sup -1}. In other papers, Rhode et al. show the H I source to have a resolved stellar counterpart and ongoing star forming activity, while Skillman et al. reveal it as having extremely low metallicity: 12 + log (O/H) = 7.16 {+-} 0.04. The H I mass to stellar mass ratio of the object is found to be 2.6. We use the Tully-Fisher template relation in its baryonic form to obtain a distance estimate D{sub Mpc}=1.3{sup +0.9}{sub -0.5}. Additional constraints on the distance are also providedmorexa0» by the optical data of Rhode et al. and McQuinn et al., both indicating a distance in the range of 1.5 to 2.0 Mpc. The three estimates are compatible within their errors. The object appears to be located beyond the dynamical boundaries of, but still in close proximity to the Local Group. Its pristine properties are consistent with the sedate environment of its location. At a nominal distance of 1.75 Mpc, it would have an H I mass of {approx_equal} 1.0 Multiplication-Sign 10{sup 6} M {sub Sun }, a stellar mass of {approx_equal} 3.6 Multiplication-Sign 10{sup 5} M {sub Sun }, and a dynamical mass within the H I radius of {approx_equal} 1.5 Multiplication-Sign 10{sup 7} M {sub Sun }. This discovery supports the idea that optically faint-or altogether dark-low mass halos may be detectable through their non-stellar baryons.«xa0less

Observations of a complete sample of emission-line galaxies. III. Spatial and luminosity distributions of the UM galaxies

A study of the luminosity and spatial distributions of a deep, complete sample of emission-line galaxies (ELGs) is presented. The luminosity function (LF) is found to be flatter than that of normal galaxies at low luminosities, and the integrated LFs show that ELGs contribute 6.7 + or - 2.0 percent to the overall galaxy LF. Space densities of the various types of ELGs found in the survey are also derived. The ELGs are found to follow for the most part the structures defined by the luminous galaxies in the Catalog of Galaxies and Clusters of Galaxies. However, the ELGs strongly avoid regions of very high galactic density and a number of low-luminosity ELGs reside in regions otherwise devoid of normal galaxies. The overall density environments within which the ELGs are found are significantly lower than those of the normal galaxies. 82 refs.

The survey of H i in extremely low-mass dwarfs (SHIELD)

We present first results from the Survey of H I in Extremely Low-mass Dwarfs (SHIELD), a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas contents and dynamics of galaxies with H I masses in the 106-107 M ? range detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We describe the survey motivation and concept demonstration using Very Large Array imaging of six low-mass galaxies detected in early ALFALFA data products. We then describe the primary scientific goals of SHIELD and present preliminary EVLA and WIYN 3.5 m imaging of the 12 SHIELD galaxies. With only a few exceptions, the neutral gas distributions of these extremely low-mass galaxies are centrally concentrated. In only one system have we detected H I column densities higher than 1021?cm?2. Despite this, the stellar populations of all of these systems are dominated by blue stars. Further, we find ongoing star formation as traced by H? emission in 10 of the 11 galaxies with H? imaging obtained to date. Taken together these results suggest that extremely low-mass galaxies are forming stars in conditions different from those found in more massive systems. While detailed dynamical analysis requires the completion of data acquisition, the most well-resolved system is amenable to meaningful position-velocity analysis. For AGC 749237, we find well-ordered rotation of 30?km?s?1 at ~40 distance from the dynamical center. At the adopted distance of 3.2 Mpc, this implies the presence of a 1 ? 108 M ? dark matter halo and a baryon fraction 0.1.

ALFALFA Discovery of the nearby Gas-rich Dwarf Galaxy Leo P. III. An Extremely Metal Deficient Galaxy

We present KPNO 4 m and LBT/MODS spectroscopic observations of an H II region in the nearby dwarf irregular galaxy Leo P discovered recently in the Arecibo ALFALFA survey. In both observations, we are able to accurately measure the temperature sensitive [O III] {lambda}4363 line and determine a direct oxygen abundance of 12 + log(O/H) = 7.17 {+-} 0.04. Thus, Leo P is an extremely metal deficient (XMD) galaxy, and, indeed, one of the most metal deficient star-forming galaxies ever observed. For its estimated luminosity, Leo P is consistent with the relationship between luminosity and oxygen abundance seen in nearby dwarf galaxies. Leo P shows normal {alpha} element abundance ratios (Ne/O, S/O, and Ar/O) when compared to other XMD galaxies, but elevated N/O, consistent with the delayed release hypothesis for N/O abundances. We derive a helium mass fraction of 0.2509{sup +0.0184}{sub -0.0123}, which compares well with the WMAP + BBN prediction of 0.2483 {+-} 0.0002 for the primordial helium abundance. We suggest that surveys of very low mass galaxies compete well with emission line galaxy surveys for finding XMD galaxies. It is possible that XMD galaxies may be divided into two classes: the relatively rare XMD emission line galaxies whichmorexa0» are associated with starbursts triggered by infall of low-metallicity gas and the more common, relatively quiescent XMD galaxies like Leo P, with very low chemical abundances due to their intrinsically small masses.«xa0less

Observations of a complete sample of emission-line galaxies. II: Properties of the UM survey galaxies

Une classification des galaxies a raies demission du UM survey (Salzer J.J., Mc Alpine G.M., Boroson T.A., 1989, Ap. J. Suppl., 70) est effectuee en 10 groupes naturels de galaxies actives. Les proprietes physiques et les diagrammes diagnostiques de ces galaxies et les diagrammes diagnostiques des raies demission sont analyses

A Critical Look at the Mass-Metallicity-Star Formation Rate Relation in the Local Universe. I. An Improved Analysis Framework and Confounding Systematics

It has been proposed that the (stellar) mass-(gas) metallicity relation of galaxies exhibits a secondary dependence on star formation rate (SFR), and that the resulting Stellar Mass-Z-SFR relation may be redshift-invariant, i.e., fundamental. However, conflicting results on the character of the SFR dependence, and whether it exists, have been reported. To gain insight into the origins of the conflicting results, we (1) devise a non-parametric, astrophysically motivated analysis framework based on the offset from the star-forming (main) sequence at a given Stellar Mass (relative specific SFR); (2) apply this methodology and perform a comprehensive re-analysis of the local Stellar Mass-Z-SFR relation, based on SDSS, GALEX, and WISE data; and (3) study the impact of sample selection and of using different metallicity and SFR indicators. We show that metallicity is anti-correlated with specific SFR regardless of the indicators used. We do not find that the relation is spurious due to correlations arising from biased metallicity measurements or fiber aperture effects. We emphasize that the dependence is weak/absent for massive galaxies (logStellar Mass greater than 10.5), and that the overall scatter in the Stellar Mass-Z-SFR relation does not greatly decrease from the Stellar Mass-Z relation. We find that the dependence is stronger for the highest SSFR galaxies above the star-forming sequence. This two-mode behavior can be described with a broken linear fit in 12+log(O/H) versus log (SFR/Stellar Mass), at a given Stellar Mass. Previous parameterizations used for comparative analysis with higher redshift samples that do not account for the more detailed behavior of the local Stellar Mass-Z-SFR relation may incorrectly lead to the conclusion that those samples follow a different relationship.

ALFALFA DISCOVERY OF THE NEARBY GAS-RICH DWARF GALAXY LEO P. II. OPTICAL IMAGING OBSERVATIONS

We present results from ground-based optical imaging of a low-mass dwarf galaxy discovered by the ALFALFA 21?cm H I survey. Broadband (BVR) data obtained with the WIYN 3.5?m telescope at Kitt Peak National Observatory (KPNO) are used to construct color-magnitude diagrams of the galaxys stellar population down to Vo ~ 25. We also use narrowband H? imaging from the KPNO 2.1?m telescope to identify a H II region in the galaxy. We use these data to constrain the distance to the galaxy to be between 1.5 and 2.0?Mpc. This places Leo P within the Local Volume but beyond the Local Group. Its properties are extreme: it is the lowest-mass system known that contains significant amounts of gas and is currently forming stars.

Observations of a complete sample of emission-line galaxies. I. CCD imaging and spectroscopy of galaxies in UM lists IV and V. II. Properties of the UM survey galaxies

Letude dun echantillon complet de galaxies a raies demission, observees en imagerie CCD et par spectroscopie, est presentee. Les donnees observationnelles concernent les positions, la classe spectrale, les couleurs, le diametre apparent et la spectrometrie. Les diagrammes de contours et les spectres des galaxies de Seyfert sont rapportes

Lyα ESCAPE FROM z ∼ 0.03 STAR-FORMING GALAXIES: THE DOMINANT ROLE OF OUTFLOWS

The usefulness of H I Ly? photons for characterizing star formation in the distant universe is limited by our understanding of the astrophysical processes that regulate their escape from galaxies. These processes can only be observed in detail out to a few ? 100?Mpc. Past nearby (z =0.03. The galaxies cover a broad range of luminosity, oxygen abundance, and reddening. In this paper, we characterize the observed Ly? lines and establish correlations with fundamental galaxy properties. We find seven emitters. These host young (?10?Myr) stellar populations have rest-frame equivalent widths in the range 1-12??, and have Ly? escape fractions within the COS aperture in the range 1%-12%. One emitter has a double-peaked Ly? with peaks 370?km s?1 apart and a stronger blue peak. Excluding this object, the emitters have Ly? and O I ?1302 offsets from H? in agreement with expanding-shell models and Lyman break galaxies observations. The absorbers have offsets that are almost consistent with a static medium. We find no one-to-one correspondence between Ly? emission and age, metallicity, or reddening. Thus, we confirm that Ly? is enhanced by outflows and is regulated by the dust and H I column density surrounding the hot stars.

ALFALFA Discovery of the Nearby Gas-rich Dwarf Galaxy Leo P. IV. Distance Measurement from LBT Optical Imaging

Leo P is a low-luminosity dwarf galaxy discovered through the blind H I Arecibo Legacy Fast ALFA survey. The H I and follow-up optical observations have shown that Leo P is a gas-rich dwarf galaxy with both active star formation and an underlying older population, as well as an extremely low oxygen abundance. Here, we measure the distance to Leo P by applying the tip of the red giant branch (TRGB) distance method to photometry of the resolved stellar population from new Large Binocular Telescope V and I band imaging. We measure a distance modulus of 26.19{sub −0.50}{sup +0.17} mag corresponding to a distance of 1.72{sub −0.40}{sup +0.14} Mpc. Although our photometry reaches 3 mag below the TRGB, the sparseness of the red giant branch yields higher uncertainties on the lower limit of the distance. Leo P is outside the Local Group with a distance and velocity consistent with the local Hubble flow. While located in a very low-density environment, Leo P lies within ∼0.5 Mpc of a loose association of dwarf galaxies which include NGC 3109, Antlia, Sextans A, and Sextans B, and 1.1 Mpc away from its next nearest neighbor, Leo A. Leo P is one of themorexa0» lowest metallicity star-forming galaxies known in the nearby universe, comparable in metallicity to I Zw 18 and DDO 68, but with stellar characteristics similar to dwarf spheriodals (dSphs) in the Local Volume such as Carina, Sextans, and Leo II. Given its physical properties and isolation, Leo P may provide an evolutionary link between gas-rich dwarf irregular galaxies and dSphs that have fallen into a Local Group environment and been stripped of their gas.«xa0less