Metallicity Gradients in Early-type Galaxies

Collaborators: R.L.C. Ogando (IF/UFRJ), P.S.Pellegrini (GEA/OV/UFRJ) and many others.

Two scenarios compete to explain the formation of early-type galaxies: the monolithical dissipative collapse of a gas cloud, or through the coalescence of small, possibly gaseous, galaxies. Models based on the first scenario predict the existence of a radial metallicity gradient which would correlate with galaxy mass. Differently, gradients in the merger hypothesis should be shallower, when present, and not correlated to mass due to mixing processes involved. Recent works steered a middle course, claiming that both scenarios participate, the resultant galaxy characteristics depending on the relative weight that each scenario played. Therefore, it is interesting to gather a large sample and try to quantify this weight and its dependence on environmental effects, for example.

So far, observational studies have tackled the subject with relatively small samples, 30 in Carollo, Danziger e Buson (1993) work, and 35 galaxies in the Coma cluster in Mehlert et al. (2003). We intent to examine the question using more than 100 galaxies from the ENEAR survey (da Costa et al. 2000). This project is the subject of Ricardo L. C. Ogando PhD thesis. Thus, we have somebody to help us with the hard labor.

Spectroscopic observations were carried out at ESO1.52m in Chile. We measure Lick system Mg2 index, velocity dispersion and rotational velocity for spectra extracted radially.

Below, we present a few examples of Mg2, velocity dispersion and rotational velocity profiles, along with its DSS images, for NGC 1404 (E), NGC 3115 (S0) and NGC 7507 (E). Click on the image to get a better view.

The work is still in progress. The next step is to publish... or perish before the Dark Lord.

Preliminary results were presented at the X Reunião Latino-Americana de Astronomia; published at Revista Mexicana de Astronomía y Astrofísica (2002) (pdf file 64K)

The undergraduate monograph of R. Ogando is available in PDF format (pdf file 1.8M)