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Filling the gap in the extragalactic census: A study at 21 cm and in the near -infrared

Jessica Langer Rosenberg, University of Massachusetts Amherst


Fundamental to a complete understanding of galaxy properties, formation, and evolution is a thorough knowledge of the local galaxy population. Until we understand the nearest, most easily detectable galaxies in the Universe it will be impossible to deduce galaxy history. The reliance on optical detection of galaxies has biased most surveys against the lowest mass, lowest luminosity, and lowest surface brightness systems. The primary goal of this thesis is to fill this gap in the extragalactic census. We use the 21 cm line of neutral hydrogen to search for galaxies in the local universe. The Arecibo DualBeam Survey (ADBS) has detected 265 galaxies, only half of which have previously identified optical counterparts. These detections are used in the calculation of the HI mass function for which the low mass end is better determined than any previous survey. We find a faint end slope of α = −1.6 in the field, but α = −1.2 in the Virgo Cluster region. The difference in the slopes is an indication that the slope of the mass function is not universal but is environmentally dependent. The steep slope of the HI mass function demonstrates that we have identified a population of galaxies missed in optical surveys. We use near infrared observations from 2-Micron All-Sky Survey (2MASS) and optical images from the digitized POSS data, in conjunction with the HI data, to study the relationships between gas and stars in this unique sample. The combination of HI, near infrared, and optical data allow us to examine the detailed characteristics of the galaxy profiles for a subsample of the ADBS galaxies as well as to study the global inter-relations of galaxy properties at these wavelengths. We use the measurements such as galaxy color, luminosity, and gas-to-star ratio to probe differences in the evolutionary state of galaxies and examine how observational properties of galaxies such as surface brightness affect the fraction of a galaxy's mass in gas, stars, and dark matter.

Subject Area


Recommended Citation

Rosenberg, Jessica Langer, "Filling the gap in the extragalactic census: A study at 21 cm and in the near -infrared" (2000). Doctoral Dissertations Available from Proquest. AAI9988837.