Physics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt.........6p&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF VIRGINIA, 1995.Source: Dissertation Abstracts International, Volume: 56-04, Section: B, page: 207
Physics
2
Scientific paper
CCD B- and I-band surface photometry is presented for a sample of 51 dwarf and low surface brightness galaxies. The main selection criterion was their extremely narrow HI linewidths (Delta V2<100 {rm km}{rm s}^{ -1}), chosen in order to examine the Tully -Fisher (TF) relation between linewidth and absolute magnitude at the low-luminosity end. In this regime, a substantial fraction of the linewidth is attributable to turbulent rather than rotational motion. Therefore, it is not surprising that the original TF relation, an expression of the scaling relation between mass (from the linewidth due to rotation) and luminosity, does not hold in this regime. If we assume the linewidth is due to both turbulent and rotation motion, we obtain a mass for the dwarfs which does correlate with luminosity. However, the relation is distinct from the TF relation for spirals, and indicates the presence of an increasing amount of dark matter at low luminosities. We find that the locus of dwarf galaxies in the mass/luminosity plane is well fit by the theoretical prediction of Dekel & Silk (1986, ApJ, 303, 39), M/L ~ L^{-0.37}, where M/L decreases with increasing L, while the spirals follow a relation in which M/L increases with increasing L (M/L ~ L^{0.2}), which corresponds to the observed slope (~7) of the TF relation for spirals. For dwarfs fainter that L B/L_odot~10^7, the observed M/L is ~ 20, while it drops to unity for LB/L _odot~10^{9.5}.. The Dekel-Silk relation arises in low mass systems with massive dark halos which undergo extensive mass loss due to supernova-driven winds. The halo allows the galaxy to remain bound even as most of the gas is removed, drastically reducing the rate of star formation. The trend towards higher M/L at lower L is the result of the lower escape velocity of the less massive systems, allowing the gas to be removed more efficiently. The same relation has previously been seen to hold for dwarf Spheroidal galaxies, providing further evidence for a common evolutionary history of these two types of dwarfs systems, radically different from "normal" early - and late-type galaxies.
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