Galaxy formation and evolution

Abstract:

We present a mid-infrared (MIR) spectroscopic survey of starburst galaxies as an example of analysis of scientifically focused samples selected from the ISO Data Archive (IDA). We use fine structure lines (FSL) ratios of Ne, Ar and S to construct diagnostic excitation diagrams and, in combination with hydrogen recombination lines (HRL), we determine their elemental abundances. For Ne and Ar, we find that excitation indicators are positively correlated with each other and negatively with abundance. On comparison with a complementary sample of galactic H II regions we find that starbursts are generally of lower excitation. Starbursts exhibiting Wolf-Rayet (WR) features are separated both in excitation and abundance from the remaining starbursts. Most surprisingly, S is found to be underabundant by a factor of ∼ 3 in our low excitation starbursts with respect to the Ne and Ar, contrary to expectations from nucleosynthesis theory. Our results are combined with those of a related sub-sample of Seyfert galaxies (Sturm et al. 2002) to derive diagnostic diagrams discriminating the two types of activity on the basis of excitation traced by MIR lines. The data presented will be useful as a reference for observations of fainter and/or higher redshift sources with future IR observatories such as SIRTF, SOFIA and Herschel.

Abstract:

We present axisymmetric, orbit superposition models for 12 galaxies using data taken with the Hubble Space Telescope (HST) and ground-based observatories. In each galaxy, we detect a central black hole (BH) and measure its mass to accuracies ranging from 10% to 70%. We demonstrate that in most cases the BH detection requires both the HST and ground-based data. Using the ground-based data alone does provide an unbiased measure of the BH mass (provided that they are fitted with fully general models), but at a greatly reduced significance. The most significant correlation with host galaxy properties is the relation between the BH mass and the velocity dispersion of the host galaxy; we find no other equally strong correlation and no second parameter that improves the quality of the mass-dispersion relation. We are also able to measure the stellar orbital properties from these general models. The most massive galaxies are strongly biased to tangential orbits near the BH, consistent with binary BH models, while lower mass galaxies have a range of anisotropies, consistent with an adiabatic growth of the BH.

Abstract:

As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of Ks imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations Δθ ≤ 60″ from candidate guide stars in the magnitude range 9.0 ≤ R ≤ 12.4. When analyzed as a "discrete deep field" with 131 arcmin² area, our dataset gives galaxy number counts that agree with those derived previously over the range 16 ≤ Ks < 20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.