Growth of galactic bulges by mergers

I. Dense satellites

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Canary Islands, Spain
² Astronomisches Institut der Universitat Basel, 4102 Binningen, Switzerland
³ School of Physics and Astronomy, University of Nottingham, NG7 2RD, UK e-mail: jalfonso@astro.unibas.ch; balcells@ll.iac.es; Reynier.Peletier@nottingham.ac.uk

Corresponding author: J. A. L. Aguerri, jalfonso@astro.unibas.ch

Received: 21 September 2000
Accepted: 1 December 2000

Abstract

Andredakis et al. ([CITE]) fit Sersic's law to the bulges of the Balcells & Peletier ([CITE]) galaxy sample, and infer that n drops with morphological type T from 4-6 for S0 to (exponential) for Sc's. We use collisionless N body simulations to test the assumption that initially the surface brightness profiles of all bulges were exponential, and that the steepening of the profiles toward the early-types is due to satellite accretion. The results are positive. After the accretion of a satellite, bulge-disk fits show that the bulge grows and that the bulge profile index n increases proportional to the satellite mass. For a satellite as massive as the bulge, n rises from 1 to 4. We present kinematic diagnostics on the remnants and disk thickening. The latter suggests that the bulge growth must have occurred before the last formation of a thin disk in the galaxy. The thick disks created by the merger are reminiscent of thick disks seen in early-type edge-on galaxies. The efficiency of the process suggests that present day bulges of late-type spirals showing exponential profiles cannot have grown significantly by collisionless mergers.