We present new optical and radio spectroscopic observations of the remarkable galaxy
Malin 1. This galaxy has unique features that include an extremely low surface brightness
disk with an enormous mass of neutral hydrogen, and a low luminosity Seyfert nucleus.
Malin 1 is exceptional in its values of MHO, LB, and MHI /Ln, and modest in its surface
mass density of gas and stars. Spirals with large Min /LB tend to have low mean column
densities of HI, and are close to the threshold for star formation due to instabilities in
a rotating gas disk. In these terms, Malin 1 has a disk with extremely inefficient star
formation. The bulge spectrum is dominated by the absorption features of an old, metal
rich stellar population, although there is some evidence for hot (young) stars. The emission
line excitations and widths in the nucleus are typical of a Seyfert galaxy; but Malin 1 is in
the lowest 5% of the luminosity function of Seyferts, despite a copious fuel supply. Malin 1
is in a low density region of the universe. We propose it as an unevolving disk galaxy, where
the surface mass density is so low that the chemical composition and mass fraction in gas
change very slowly over a Hubble time. Its properties are similar to those of the damped
Lyman -a absorption systems seen in the spectra of high redshift quasars. We emphasize
that there are strong observational selection effects against finding gas -rich galaxies that
are both massive and diffuse. Finally, we suggest that large and massive HI disks may
have formed as early as z - 2, and remained quiescent to the present day.
Subject headings : individual (Malin 1) - galaxies : photometry - galaxies : Seyfert -
galaxies : stellar content - radio sources : 21 cm radiation - stars : formation
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/623912 |
| Date | 11 1900 |
| Creators | Impey, C. D., Bothun, G. D. |
| Contributors | Univ Arizona, Steward Observ |
| Publisher | Steward Observatory, The University of Arizona (Tucson, Arizona) |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Article |
| Source | Steward Observatory Parker Library SO QB 4 .S752 ARCH |
| Rights | Copyright © All Rights Reserved. |
| Relation | Preprints of the Steward Observatory #844, http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1989ApJ...341...89I&db_key=AST&data_type=HTML&format=&high=3ed65e9cd007589 |
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