Early-type galaxies at large galactocentric radii - I. Stellar kinematics and photometric properties
Abstract
We present the results of a combined analysis of the kinematic and photometric properties at large galactocentric radii of a sample of 14 low-luminosity early-type galaxies in the Fornax and Virgo clusters. From Gemini South GMOS long-slit spectroscopic data, we measure radial profiles of the kinematic parameters vrot, σ, h3 and h4 out to ~1-3 effective radii. Multiband imaging data from the Hubble Space Telescope/ACS are employed to evaluate surface brightness profiles and isophotal shape parameters of ellipticity, position angle and discyness/boxiness. The galaxies are found to host a cold and old stellar component which extend to the largest observed radii and that is the dominant source of their dynamical support. The prevalence of discy-shaped isophotes and the radial variation of their ellipticity are signatures of a gradual gas dissipation. An early star-forming collapse appears to be the main mechanism acting in the formation of these objects. Major mergers are unlikely to have occurred in these galaxies. We cannot rule out a minor merging origin for these galaxies, but a comparison of our results with model predictions of different merger categories places some constraints on the possible merger progenitors. These merger events are required to happen at high-redshift (i.e. z >= 1), between progenitors of different mass ratio (at least 3:1) and containing a significant amount of gas (i.e. >=10 per cent). A further scenario is that the low-luminosity galaxies were originally late-type galaxies, whose star formation has been truncated by removal of gas and subsequently the disc has been dynamically heated by high-speed encounters in the cluster environment.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2010
- DOI:
- 10.1111/j.1365-2966.2010.17282.x
- arXiv:
- arXiv:1007.0599
- Bibcode:
- 2010MNRAS.408..254S
- Keywords:
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- galaxies: dwarf;
- galaxies: elliptical and lenticular;
- cD;
- galaxies: evolution;
- galaxies: formation;
- galaxies: kinematics and dynamics;
- galaxies: photometry;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 19 pages, 16 figures (Contact author for high resolution version of figures 1,2,3), MNRAS, accepted. The second paper of the series "Early-type galaxies at large galactocentric radii - II. Metallicity gradients and the [Z/H]-mass, [alpha/Fe] mass relations" can be found at arXiv:1006.1698