AAS 197, January 2001
Session 58. Barred and Edge-on Galaxies
Oral, Tuesday, January 9, 2001, 10:30am-12:00noon, Pacific One

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[58.06] CO Detections of Edge-On Low Surface Brightness Galaxies

L. D. Matthews (NRAO), Y. Gao (IPAC)

We present the results of deep CO (1-0) observations of 8 edge-on, low surface brightness (LSB) spiral galaxies observed with the NRAO 12-m telescope. We have detected 3 of these galaxies at >4\sigma level, representing some of the first direct detections of molecular gas in late-type, LSB spirals. Using a Galactic CO-to-H2 conversion factor, we derive MH2~107~M\odot and MHI/MH2~0.02 for the detected galaxies, and comparable upper limits for the undetected objects. Thus LSB spirals appear to be deficient in molecular material relative to their atomic gas contents by roughly an order of magnitude compared with higher surface brightness spirals of similar Hubble type unless the CO-to-H2 conversion factor appropriate for LSB systems is drastically different from the Galactic value. We find that LSB spirals appear to follow the same LFIR versus MH2 correlation as brighter galaxies, but deviate significantly from the normal LFIR versus total gas (MHI+MH2) correlation.

Although we can tell little about the detailed distribution of CO in our target galaxies from our present observations, the velocity widths of the detected lines suggest that the CO is spread over a several kpc region near the centers of the galaxies, as seen in high surface brightness, very late-type spirals. From optical images we have identified dark cloud candidates in some of our target galaxies that may be the sites of at least some of the CO-emitting gas.

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