Growth of galactic bulges by mergers

Free access article

Issue		A&A Volume 367, Number 2, February IV 2001


Page(s)		428 - 442
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20000441

A&A 367, 428-442 (2001)
DOI: 10.1051/0004-6361:20000441

I. Dense satellites

J. A. L. Aguerri^{1, 2}, M. Balcells¹ and R. F. Peletier³

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

(Received 21 September 2000 / Accepted 1 December 2000)

Abstract
Andredakis et al. (1995) fit Sersic's law $\mu(r) \sim r^{1/n}$ to the bulges of the Balcells & Peletier (1994) galaxy sample, and infer that n drops with morphological type T from $n \approx$ 4-6 for S0 to n=1 (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.

Key words: galaxies: evolution -- galaxies: interactions -- galaxies: kinematics and dynamics -- galaxies: nuclei -- galaxies: spiral -- galaxies: structure

Offprint request: J. A. L. Aguerri, jalfonso@astro.unibas.ch

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