Ph.D. Thesis

Calibration of the Tully-Fisher Relation for Use with Carbon Monoxide Line Widths, With Applications

by Tracy Ellen Lavezzi

Under the supervision of Professor John M. Dickey

ABSTRACT

This work investigates whether 12CO (J= 1-0) emission lines from galaxies can be used in lieu of 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 measures the full velocity of disk rotation, despite their confined gas distributions. We find that the profile shape for 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 with horns is produced, that measures the full rotation velocity of the disk. We also determine that the corrections to the line width of Tully & Fouque (1985) most exactly correct the measured line width to twice the disk rotation velocity. We then construct a sample of galaxies appropriate to the Tully-Fisher surveys, with the added requirement that the galaxies are IRAS sources with strong 60 micro flux densities. We observe 44 of these galaxies in the 2.6mm (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 HI data, provided one rejects spectra with specified shape characteristics.

Master's Thesis

The Tully-Fisher Relation and Carbon Monoxide: A Feasibility Study

by Tracy Ellen Lavezzi

Under the supervision of Professor John M. Dickey

ABSTRACT

We consider the feasibility of using the emission from carbon monoxide's rotational J= 1-0 and J = 2-1 transitions at 115 GHz and 230 GHz in the Tully-Fisher relation, rather than atomic hydrogen emission, as is usually done. The effects of environment on galaxies in clusters are reviewed as motivation, including the stripping and distortion of their HI spectra. We present new observations of 28 galaxies in the Hercules cluster (z = 0.03) at both 115 GHz and 230 GHz. We gather HI spectra for 18 of the sources form the literature. The line widths and photometric data are corrected for inclination and extinction according to the treatment of Tully & Fouque (1985). Comparison of the corrected HI and CO line widths indicates that while the CO does reach the flat part of the rotation curve, the smaller beam size at 230 GHz does not extend far enough to adequately measure the rotation velocity. The HI and CO (J = 1-0) widths are them used for Tully-Fisher distance calculations; the average distance modulus for the Hercules cluster is found to be <u>CO = 35.10 ± 0.49 mag and <u>HI = 35.05 ± 0.77 mag. The smaller dispersion in CO implies that Co may minimize the intrinsic scatter in the TFR, particularly if used with and infrar-red Tully-Fisher calibration, although the small sample size of this work makes premature a statement that CO is superior to HI for TF calculations. Finally, some additional uses for the CO J = 1-0 and J = 2-1 lines are explored, including determining the molecular mass in galaxies, and finding the point of turn-over in rotation curves. The spectra from a disk of uniformly emitting gas are modeled for a variety of beam sizes, and the radius at which the rotation curve flattens is varied as well. We find that the 12CO J = 1-0 and J = 2-1 lines, because of their two-to-one ratio of beam sizes, could be used to find the maximum solid bony radius for a galactic disk through a comparison of the emission line widths.