Galaxy formation and evolution

Abstract:

We report on the discovery of a double nucleus in M 83, based on measurements of the line of sight velocity distribution of stars observed at near infrared wavelengths with the VLT ISAAC spectrograph. We observe two peaks separated by 2.7" in the velocity dispersion profile of light from late-type stars measured along a slit 0.6" wide, centered on the peak of K band emission and with P.A. 51.7 degrees. The first peak coincides with the peak of the K band light distribution, widely assumed to be the galaxy nucleus. The second peak, of almost equal strength, almost coincides with the center of symmetry of the outer isophotes of the galaxy. The secondary peak location has little K band emission, and appears to be significantly extincted, even at near infrared wavelengths. It also lies along a mid-infrared bar, previously identified by Gallais et al. (1991) and shows strong hydrogen recombination emission at 1.875 microns. If we interpret the observed stellar velocity dispersion as coming from a virialized system, the two nuclei would each contain an enclosed mass of 13.2 x 10^6 M_sun within a radius of 5.4pc. These could either be massive star clusters, or supermassive dark objects.

Abstract:

The Lin and Pringle model (1987) of galactic disk formation postulates that if star formation proceeds on the same timescale as the viscous redistribution of mass and angular momentum in disk galaxies, then the stars attain an exponential density profile. Their claim is that this result holds generally: regardless of the disk galaxy's initial gas and dark matter distribution and independent of the nature of the viscous processes acting in the disk. We present new results from a set of 2D hydro-simulations which investigate their analytic result.