Red, Gas Rich Low Surface Brightness Galaxies And Enigmatic Deviations from the Tully-Fisher Relation

Authors: Karen O'Neil, G. D. Bothun, & J. Schombert

Published:The Astronomical Journal, Vol. 119, pg 136 (2000)


Using the refurbished 305m Arecibo Gregorian Telescope, we detected 43 low surface brightness (LSB) galaxies from the catalog of O'Neil, Bothun, & Cornell (1997a). The detected galaxies range from 22.0 mag/ arcsec² < Bµ < 25.0 mag/arcsec², with colors ranging from the blue through the first detection of a very red LSB galaxies (B-V = -0.7 to 1.7). The MHI/LB of these galaxies ranges from 0.1 Msol/Lsol - 50 Msol/Lsol, showing this sample to range from very gas poor to possibly the most gas rich galaxies ever detected.

One of the more intriguing results of this survey is that the galaxies with the highest MHI/LB correspond to some of the reddest (optically) galaxies in the survey, raising the question of why star formation has not continued in these galaxies. Since the average H I column density in these systems is above the threshold for massive star formation, the lack of such may indicate that these galaxies form some kind of ``optical core'' which trace a much more extended distribution of neutral hydrogen. Alternatively, a model in which no stars more massive than two solar masses form in these systems can explain the presence of both blue and red gas rich LSB galaxies. Moreover, under this model the baryonic mass fraction (fb) of LSB galaxies is the same as for galaxies of higher surface brightness, thus perhaps escaping the dilemma proposed by McGaugh & de Blok (1997a, 1997b) with respect to LSB and high surface brightness galaxies defining the same Tully-Fisher relation.

A subset of the detected LSB galaxies have rotational velocities > 200 km s-1 and yet are at least an order of magnitude below L* in total luminosity. As such, they represent extreme departures from the standard Tully-Fisher relation. In fact, our sample does not appear to have any significant correlation between the velocity widths and absolute magnitudes, with only 40% of the galaxies falling within the 1 sigma low surface brightness galaxy Tully-Fisher relation. Overall, the discovery of very red, sub-L* but very gas rich LSB galaxies in the nearby Universe has increased, once again, the overall parameter space occupied by disk galaxies.

Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the central surface brightness distribution (phi(µ(0))) of galaxies in the 22.0 < µ(0) < 25.0 B mag/arcsec² range. Taking advantage of having a catalog in which each galaxy has a known central surface brightness, scale length, and redshift, we apply a bi-variate volume correction to the data and extend the surface brightness distribution function by one magnitude, to 25.0 B mag/arcsec². The result is a flat (slope = 0) surface brightness distribution function from the Freeman value of 21.65 +\- 0.30 to the survey limit of 25.0 mag arcsec², more than 11 sigma away. This indicates that a significant percentage of the baryonic content of the universe is likely in potentials only dimly lit by the embedded galaxy.

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Figure 4a (9 kb)
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Figure 5a (24 kb)
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Figure 7a (21 kb)
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Table 1 (20 kb)
Table 2 (27 kb)
Table 3 (15 kb)
Table 4 (18 kb)
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