Mathematics – Logic
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21331702s&link_type=abstract
American Astronomical Society, AAS Meeting #213, #317.02; Bulletin of the American Astronomical Society, Vol. 41, p.295
Mathematics
Logic
Scientific paper
In 20% of its intended coverage, the ongoing, blind HI survey ALFALFA has already made >300 detections with log(MHI)<8.0, many of which are very low surface brightness and were previously uncatalogued. Superior sensitivity and spectral resolution enable ALFALFA to increase dramatically the number of known dwarf galaxies in the local universe. The survey probes the low-mass end of the HI mass function (HIMF) using the lowest mass galaxies detectable outside the Local Group. At 10.5 Mpc, the Leo I group presents a nearby, loose group environment well-suited for finding these low-mass objects believed to be the building blocks of galaxy formation. Compared with an optically-selected sample, ALFALFA uncovered more dwarfs without the need for additional spectroscopic followup to verify group membership. We derive the only HIMF to date dominated by low-mass systems from the complete ALFALFA sample in Leo I which includes 45 galaxies with log(MHI)<8.0, and compare with HIMFs previously derived for other nearby groups. We derive a shallower low-mass slope than that predicted by simulations of dark matter halo formation which suggests a population of gas-rich, low surface brightness galaxies does not solve the discrepancy between simulations and observations. Leo I is the nearest group to contain both E/S0 and spiral galaxies and is characterized by a low velocity dispersion ( 175 km/s) despite the presence of early-type galaxies more typical of dense clusters. The group's proximity and intermediate density offer a unique basis for comparison of observed trends among Local Group dwarfs that offer key information to our understanding of dwarf galaxy evolution. An investigation of such trends, like morphological segregation, metallicity-luminosity relation, and gas fraction versus color, for the HI-selected gas-rich, yet still very low-mass dwarfs of the Leo I group will be presented. This work has been supported by NSF grant AST-0607007 and the Brinson Foundation.
ALFALFA Team
Giovanelli Riccardo
Haynes Martha P.
Stierwalt Sabrina
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