Kinematics & stellar populations of nearby bulges

• Main Author: Falcon Barroso, Jesus
• Published: University of Nottingham 2003
• Subjects: 523; QB Astronomy
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514599

In this thesis, we investigate the internal kinematics and stellar populations of a subsample of the bulges of nearby galaxies defined by Balcells & Peletier (1994). To do that we have analysed minor axis spectroscopic data of the sample together with Integral Field observations of one the most interesting galaxies in it (NGC7332). We introduce, for the first time, the use of single-burst stellar population models to obtain stellar velocities, velocity dispersions and higher order Gauss-Hermite moments (h_3, h_4) from galaxy spectra in the near-infrared Ca II triplet region. We detect small-amplitude minor-axis rotation, generally due to inner isophotal twists as a result of slightly triaxial bulges or misaligned inner disks. Velocity dispersion profiles, which extend well into the disk region, show a wide range of slopes. Flattened bulges tend to have shallower velocity dispersion profiles. The inferred similarity of radial velocity dispersion profiles of bulge and disk supports the interpretation of these bulges as thickened disks. We also investigate the position of our sample on the fundamental plane of early-type galaxies. We find that bulges, both in the B and K band, lie close to but slightly below the relation defined by ellipticals and S0s. The most deviant point is NGC7332, whose offset w.r.t the FP cannot be explained by measurement errors. Besides, there are hints that bulges of later morphological type are situated below the other bulges in our sample. The fact that bulges lie so close to the FP of ellipticals and S0s implies that their formation epoch must have been similar to that of cluster Es and S0s. We then proceed to present measurements of near-IR Ca triplet (CaT, CaT*), Paschen (PaT) and Magnesium (MgI) indices for the same sample. We find that CaT* decreases with central velocity dispersion (sigma) with small scatter, unlike other metal indices that generally increase. Our result shows that the CaT* - sigma relation is independent of galaxy type from ellipticals to intermediate-type spirals. Finally we have made use of SAURON observations to unravel the origin of peculiar features in the S0 galaxy NGC7332. We have discovered a Kinematically Decoupled Core, found kinematic evidence for a central disk and mapped a rather disturbed gas distribution counter-rotating w.r.t the stellar body of the galaxy. 2D stellar populations maps reveal that NGC7332 is young everywhere. The fact that we see gas inflow now, together with many features indicates that there must have been gas infall for Gyrs in a row, leading to a continuum formation of this galaxy.