Marc Balcells

The central mass distribution in dwarf and low surface brightness galaxies

We present high-resolution Hrotation curves for a sample of 15 dwarf and low surface brightness galaxies. From these we derive limits on the slopes of the central mass distributions, using both a direct inversion of the rotation curves and detailed mass models. Assuming that the density distributions of dark matter halos follow a power law at small radii, � ðr Þ/ r � � , we find inner slopes in the range 0dd1 for most galaxies. Thus, even with the relatively high spatial resolution of the Hrotation curves presented here, the inner slopes are poorly constrained. In general halos with constant density cores (� ¼ 0) provide somewhat better fits, but the majority of our galaxies (� 75%) are also consistent with � ¼ 1, as long as the R-band stellar mass-to-light ratios are smaller than about 2. Halos with � ¼ 1:5, however, are ruled out in virtually every case. In order to investigate the robustness of these results we discuss and model several possi- ble causes of systematic errors, including noncircular motions, galaxy inclination, slit width, seeing, and slit alignment errors. Taking the associated uncertainties into account, we conclude that even for the � 25% of the cases where � ¼ 1 seems inconsistent with the rotation curves, we cannot rule out cusp slopes this steep. Inclusion of literature samples similar to the one presented here leads to the same conclusion when the possibility of systematic errors is taken into account. In the ongoing debate on whether the rotation curves of dwarf and low surface brightness galaxies are consistent with predictions for a cold dark matter universe, we argue that our sample and the literature samples discussed in this paper provide insufficient evidence to rule out halos with � ¼ 1. At the same time, we note that none of the galaxies in these samples require halos with steep cusps, as most are equally well or better explained by halos with constant density cores. Subject headings: galaxies: dwarf — galaxies: halos — galaxies: kinematics and dynamics

Proceedings of the SPIE

Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take advantage of a future prime-focus corrector and atmospheric-dispersion corrector (Agocs et al, this conf.) that will deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions (R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner technologies are considered. Several options for the spectrograph are discussed, building in part on published design studies for E-ELT spectrographs. Indeed, a WHT MOS will not only efficiently deliver data for exploitation of important imaging surveys planned for the coming decade, but will also serve as a test-bed to optimize the design of MOS instruments for the future E-ELT.

Ages of galaxy bulges and disks from optical and near-infrared colors

We compare optical and near-infrared colors of disks and bulges in a diameter-limited sample of inclined, bright, nearby, early-type spirals. Color profiles along wedge apertures at 15 degrees from the major axis and on the minor axis on the side of the galaxy opposite to the dust lane are used to assign nominal colors for the inner disks (at 2 scale length) and for the bulges (similar to 0.5r(eff)), respectively. We estimate that the effects of dust reddening and the cross-talk between the colors of the two components is negligible. We find that color differences (bulge - disk) are very small: Delta(U-R)=0.126+/-0.165, Delta(R-K)=0.078+/-0.165. Disks tend to be bluer by an amount three times smaller than that reported by Bothun & Gregg [ApJ, 350, 73 (1990)] for S0s. Color variations from galaxy to galaxy are much larger than color differences between disk and bulge in each galaxy. Probably, the underlying old population of disks and bulges is much more similar than the population paradigm would lead us to believe. Implied age differences, assuming identical metallicities, are less than 30%

Growth of galactic bulges by mergers - I. Dense satellites

Andredakis et al. ([CITE]) fit Sersics law

Galactic bulges from Hubble Space Telescope NICMOS observations : ages and dust

\mu(r) \sim r^{1/n}

Colors and color gradients in bulges of galaxies

to the bulges of the Balcells & Peletier ([CITE]) galaxy sample, and infer that n drops with morphological type T from

The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

n \approx

THE HST/ACS COMA CLUSTER SURVEY. II. DATA DESCRIPTION AND SOURCE CATALOGS ∗

4-6 for S0 to

The Westerbork HI survey of spiral and irregular galaxies - II. R-band surface photometry of late-type dwarf galaxies

n=1

The formation of counterrotating cores in elliptical galaxies

(exponential) for Scs. We use collisionless N body simulations to test the assumption that initially the surface brightness profiles of all bulges were exponential, and that the steepening of the profiles toward the early-types is due to satellite accretion. The results are positive. After the accretion of a satellite, bulge-disk fits show that the bulge grows and that the bulge profile index n increases proportional to the satellite mass. For a satellite as massive as the bulge, n rises from 1 to 4. We present kinematic diagnostics on the remnants and disk thickening. The latter suggests that the bulge growth must have occurred before the last formation of a thin disk in the galaxy. The thick disks created by the merger are reminiscent of thick disks seen in early-type edge-on galaxies. The efficiency of the process suggests that present day bulges of late-type spirals showing exponential profiles cannot have grown significantly by collisionless mergers.