Broadband Optical and Near-Infrared Imaging of Massive, \\Gas-Rich Low Surface Brightness Galaxies
Session 77 -- Spirals II
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

## [77.13] Broadband Optical and Near-Infrared Imaging of Massive, \\Gas-Rich Low Surface Brightness Galaxies

P.Knezek, J.Wroten (UMich)

One of the more surprising discoveries in the recent work on low surface brightness galaxies (LSBs) is that a significant number are massive and possess significant quantities of atomic gas. Disk galaxies with sizes approaching that of Malin 1 (M$_{\rm HI}$ $\sim$ 2x10$^{11}$ M$_{\sun}$; D $\sim$ 147 kpc, H$_{0}$ = 75 km s$^{-1}$ Mpc$^{-1}$; Impey and Bothun 1989) have been identified through the use of the Palomar Sky Surveys, with follow-up studies in HI. While many of these galaxies have large amounts of atomic gas and unusually blue disk colors, they have only weak regions of H$\alpha$ emission, indicating little ongoing massive star formation, and their low surface brightnesses suggest extremely low stellar surface densities. The blue disk colors have ruled out the hypothesis that LSBs are faded galaxies, but the difficulty in disentangling the difference between low metallicity and young stellar populations based on broadband optical colors has hindered understanding their stellar evolutionary history. It has been suggested (McGaugh 1992) that some LSBs may, in fact, be undergoing their first episodes of star formation since there is little evidence of a difference in the distribution of light in $UBVRI$ images. The LSBs in his sample are largely dwarf systems, however, and the situation is not necessarily comparable for more massive LSBs. In fact, the optical morphology of massive LSBs in $B$ and $R$ is consistent with the idea that many of these systems have undergone previous episodes of star formation. We present both broadband optical ($UBVRI$) and some near-infrared ($JHK$) imaging of a sample of LSBs which are gas-rich (M$_{HI} \geq$\kern.03em 5x10$^{10}$\kern.03emM$_{\sun}$) and of similar size to giant spiral galaxies (D$_{25} \geq$\kern.03em25\kern.03emkpc). We compare their long baseline colors to models of stellar populations (Worthey 1992) in order to deconvolve the age and metallicity effects.