C. M. Carollo

Dark Matter in Elliptical Galaxies

We present measurements of the shape of the stellar line-of-sight velocity distribution out to two effective radii along the major axes of the four elliptical galaxies NGC 2434, 2663, 3706, and 5018. The velocity dispersion profiles are flat or decline gently with radius. We compare the data to the predictions of f=f(E,L_z) axisymmetric models with and without dark matter. Strong tangential anisotropy is ruled out at large radii. We conclude from our measurements that massive dark halos must be present in three of the four galaxies, while for the fourth galaxy (NGC 2663) the case is inconclusive.

HST Optical-NIR Colors of Nearby

We have analyzed V, H, and J Hubble Space Telescope (HST) images for a sample of early- to late-type spiral galaxies and have reported elsewhere the statistical frequency of R1/4-law and exponential bulges in our sample as a function of Hubble type and the frequency of occurrence and structural properties of the resolved central nuclei hosted by intermediate- to late-type bulges and disks (see references in the text). Here we use these data to show the following: The V-H color distribution of the R1/4 bulge peaks around V-H ~ 1.3, with a sigma Δ(V-H) ~ 0.1 mag. Assuming a solar metallicity, these values correspond to stellar ages of ≈ 6 ± 3 Gyr. In contrast, the V-H color distribution of the exponential bulges peaks at V-H ~ 0.9 and has a sigma Δ(V-H) ~ 0.4 mag. This likely implies significantly smaller ages and/or lower metallicities for (a significant fraction of the stars in) the exponential bulges compared to the R1/4-law spheroids. Most of the central nuclei hosted by the exponential bulges have V-H and J-H colors that are compatible with relatively unobscured stellar populations. Assuming no or little dust effects, ages 1 Gyr are suggested for these nuclei, which in turn imply masses of about a few 106 to a few 107 M☉, i.e., sufficient to dissolve progenitor bars with masses consistent with those inferred for the exponential bulges by their luminosities. While different bulge-nucleus pairs cover a large range of V-H colors, each bulge-nucleus pair has quite similar V-H colors and thus possibly similar stellar populations. The HST photometric analysis suggests that exponential-type bulge formation is taking place in the local universe and that this process is consistent with being the outcome of secular evolution processes within the disks. The structures that are currently formed inside the disks are quite dissimilar from the old elliptical-like spheroids that are hosted by the early-type disks.We have analysed

R^{1/4}

V

and Exponential Bulges

,

Nuclear Properties of a Sample of Nearby Spiral Galaxies from Hubble Space Telescope STIS Imaging

H

Nuclear Properties of Nearby Spiral Galaxies from Hubble Space Telescope NICMOS Imaging and STIS Spectroscopy

and

SAURON: integral-field spectroscopy of galaxies

J

Dynamical Constraints on the Formation of Elliptical Galaxies

HST images for a sample of early- to late-type spiral galaxies, and reported elsewhere the statistical frequency of

Spiral Galaxies with WFPC2.I.Nuclear Morphology, Bulges, Star Clusters, and Surface Brightness Profiles

R^{1/4}

A family of triaxial mass models with central cusps

-law and exponential bulges in our sample as a function of Hubble type, and the frequency of occurrence and structural properties of the resolved central nuclei hosted by intermediate- to late-type bulges and disks (see references in the text). Here we use these data to show that: {\it (i)} The