Density profiles of galaxy bulges and nuclei

¹ Instituto de Astrofsica de Canarias, 38200 La Laguna, Tenerife, Spain
² Mount Stromlo and Siding Spring Observatories, Australian National University, Private Bag, Weston Creek, ACT 2611, Australia
³ Kapteyn Astronomical Institute, Postbus 800, 9700 AV, Groningen, The Netherlands

Abstract

The bulge contribution to the inner density profile of a galaxy is well traced by the bulge's NIR surface brightness profile. We map the surface brightness profiles of bulges using HST/NICMOS imaging. Most bulges show nuclear components of 20–200 pc scales, and frequently also unresolved nuclear star clusters (<20 pc). These nuclear components are the densest parts of bulges, and gave bulges the “reputation” of having high stellar concentration. Actually, the Sérsic r^1/n bulges typically have low concentrations, 1 < n < 2.5. We cannot confirm the bi-modal distribution of bulge profile slopes reported by others, and suggest that the alleged bi-modality is related to selectively excluding/including nuclear components in low/high-n bulges.