Sweep the dust away: infrared kinematics of nearby galaxies

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Silge, Julia Dorothea

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In this dissertation, I have conducted a study of the near-infrared kinematics of a well-defined sample of nearby galaxies. I use the CO bandhead at 2.29 microns to measure the internal stellar kinematics of this sample. Observing in the near-infrared allows us to address possible biases or problems in our current kinematic understanding of galaxies (based on optical kinematics alone) and extend our knowledge to galaxies often excluded from kinematic analyses. This spectral region minimizes the effects of dust in galaxies; it is long enough to minimize dust absorption but short enough to avoid dilution of the continuum by emission from vii hot dust. Also, observing at these longer wavelengths traces the older, redder stellar population and minimizes effects due to recent star formation. I have chosen a sample of nearby early-type galaxies which are well-studied in optical wavelengths to first calibrate the CO bandhead for kinematic analysis, finding that for the galaxies which have the least dust and are the best-studied, optical and near-IR kinematics are consistent. I then apply this observational treatment to study the Fundmental Plane (FP) of galaxies in an unbiased way, as well as to measure the central black hole (BH) mass of Centaurus A, a galaxy so dusty that it is inaccessible to optical kinematic techniques. For a sample of early-type galaxies, I find a FP scaling relation different from the optical relation, indicating that systematic variation in mass-to-light ratio is important in the shape of the FP. For a sample of bulge galaxies, I find a FP scaling relation moderately different from the early-type FP, pointing to relative structural differences between these families of galaxies. I find a high value for the central BH of Centaurus A, five to ten times higher than that predicted by correlations between BH mass and global galaxy properties. This result implies that galaxy bulge growth and central BH growth are not coeval. Together, these results illustrate the power of using near-infrared kinematics.





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