Galaxy formation and evolution

Abstract:

The study of the physical properties of high-redshift galaxies has become one of the major goals of extragalactic astronomy. In particular the massassembly histories of galaxies have been the focus of many studies at redshifts 1 to 3. In the purpose of probing the dynamics of intermediate and high-redshift galaxies, we have designed a research program to carry out a near-infrared spectroscopic follow up of spatially resolved distant galaxies. Here, we present the results for A370-A5 (z=1.341), an arc behind the lens cluster Abell 370 (z=0.374), observed in the case of science verification programme of SINFONI/VLT. The natural magni fication due to massive galaxy clusters allows to spatially resolve and constrain the dynamics of young star forming galaxies 1 to 3 magnitudes fainter than those selected in blank fields. Thus, the study of lensed galaxies allows to probe a low mass regime of galaxies not accessible in standard observation. In this particular case, we found that the gas distribution and kinematics are consistent with a bipolar outflow with a range of velocities of v ∼ 100km/s. © 2007 Springer-Verlag Berlin Heidelberg.

Abstract:

We have studied ∼2100 early-type galaxies in the SDSS DR3 which have been detected by the GALEX Medium Imaging Survey (MIS), in the redshift range O < z < 0.1.1. Combining GALEXUV photometry with corollary optical data from the SDSS, we find that, at a 95% confidence level, at least ∼30% of galaxies in this sample have UV to optical colors consistent with some recent star formation within the last Gyr. In particular, galaxies with an NUV - r color less than 5.5 are very likely to have experienced such recent star formation, taking into account the possibility of a contribution to NUV flux from the UV upturn phenomenon. We find quantitative agreement between the observations and the predictions of a semianalytical ACDM hierarchical merger model and deduce that early-type galaxies in the redshift range 0 < z < 0.11 have ∼ 1 % -3 % of their stellar mass in stars less than 1 Gyr old. The average age of this recently formed population is ∼300-500 Myr. We also find that "monolithically" evolving galaxies, where recent star formation can be driven solely by recycled gas from stellar mass loss, cannot exhibit the blue colors (NUV - r < 5.5) seen in a significant fraction (∼30%) of our observed sample. © 2007. The American Astronomical Society. All rights reserved.