Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aj....114.2437l&link_type=abstract
Astronomical Journal v.114, p.2437
Astronomy and Astrophysics
Astronomy
10
Galaxy: Kinematics And Dynamics, Galaxies: Ism
Scientific paper
We simulate extragalactic emission spectra in order to determine whether the spectra of molecular gas measure the full velocity of disk rotation, despite their confined gas distributions. We present synthetic emission profiles to determine the effects on profile shapes due to factors such as telescope beam size. gas distribution, opacity, and pointing errors. We find that linewidths cease to be useful if the telescope beam resolves the solid body rotation region of the galaxy disk, or if the disk is very optically thick. Opacity is more problematic for edge-on galaxies; at lower optical depths, we find that very often a trough is created in the center of the emission line. We establish guidelines for rejecting spectra as unreliable disk-velocity indicators, and determine what corrections to the measured line widths at 20% and 50% of the peak intensity are best to recover twice the disk rotation velocity. Following the procedure of Bicay & Giovanelli (1986, AJ, 91, 705) we find that the 50% of peak intensity threshold for measuring linewidths (W50p, or FWHM) is the most robust, yielding the smallest measurement errors as a function of signal to noise, and requires the smallest turbulence corrections.
Dickey John M.
Lavezzi T. E.
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