Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...19112203l&link_type=abstract
American Astronomical Society, 191st AAS Meeting, #122.03; Bulletin of the American Astronomical Society, Vol. 29, p.1405
Astronomy and Astrophysics
Astronomy
Scientific paper
This work investigates whether (12) CO(J=1-> 0) emission lines from galaxies can be used in lieu of lambda 21 cm emission in the Tully-Fisher distance indicator as a measure of disk rotation velocity. We begin by simulating extragalactic emission spectra in order to determine whether the spectra of molecular gas measure the full velocity of disk rotation, despite centralized molecular gas distributions. We find that the profile shape from confined gas distributions depends mainly on opacity and the degree to which the telescope beam resolves the solid body rotation region of the galaxy disk. In all cases where the optical depth is moderate and the beam sees some portion of the differentially rotating disk, a line profile is produced that measures the full rotation velocity of the disk. We then construct a sample of galaxies appropriate to Tully-Fisher surveys, with the added requirement that the galaxies are IRAS sources with strong 60mu flux densities. We observe 44 of these galaxies in the lambda 2.6 mm (115 GHz) CO line. From this data we determine molecular gas masses and star formation efficiencies, and find that the survey galaxies are neither ultra-luminous in the FIR nor particularly molecular-gas-rich. We find good agreement overall between the CO spectra and the existing Hi data for these galaxies. We also perform I-band CCD photometry on 72 of the galaxies. This sample includes 21 galaxies at very high redshift for which CO spectra are available. Finally, we perform luminosity-linewidth analyses on the 51 cluster galaxies for which we have photometry and spectra, and find that the results are indistinguishable from those found using the Hi data, provided one rejects spectra with specified shape characteristics.
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