Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: Galaxies in the Coma I Cloud

The membership of some galaxies in the nearby (d ~ 12 Mpc) Coma I cloud is uncertain. Here we present globular cluster luminosity functions (GCLFs) from the HST for two bright ellipticals which may belong to this group. After fitting the GCLF, we find a turnover magnitude of m_V^0 = 23.23 +/- 0.11 for NGC 4278 and m_V^0 = 23.07 +/- 0.13 for NGC 4494. Our limiting magnitude is about two magnitudes fainter than these values, making this data among the most complete GCLFs published to date. The fitted GCLF dispersions (~ 1.1 mag.) are somewhat smaller than typical values for other ellipticals. Assuming an absolute turnover magnitude of M_V^0 = -7.62, and after applying a small metallicity correction, we derive distance modulii of (m -- M) = 30.61 +/- 0.14 for NGC 4278 and 30.50 +/- 0.15 for NGC 4494. These distance estimates are compared to other methods, and lie within the published range of values. We conclude that both galaxies lie at the same distance and are both members of the Coma I cloud.Comment: 13 pages, Latex. Full paper also available at http://www.ucolick.org/~forbes/home.htm

Radial Kinematics of Isolated Elliptical Galaxies

Ellipticals in very low density environments are extremely rare but hold important clues about galaxy formation and evolution. In this paper we continue our study of isolated elliptical galaxies, presenting results on the radial stellar kinematics for 13 isolated early-type galaxies. We derive radial rotation velocity, velocity dispersion and hermite terms to ~1 effective radius. We observe a dichotomy in kinematic properties similar to that in the elliptical population as a whole, where low luminosity ellipticals tend to be rotationally supported. For all galaxies the V/sigma ratio increases with radius. We find kinematically distinct cores (KDCs), or velocity substructure, in ~40% of the galaxies for which we have major axis spectra. Such a fraction is similar to that observed for ellipticals in higher density environments. Most galaxies in the sample reveal kinematic evidence for a nuclear disk. The non-relaxed kinematics in several galaxies suggests that they have undergone a merger or accretion event. Isolated ellipticals generally follow the fundamental plane defined by cluster ellipticals -- exceptions being those galaxies with evidence for young stellar populations. Overall, we find isolated ellipticals have similar kinematic properties to their counterparts in higher density environments.Comment: 11 pages, 6 figures, MNRAS accepte

High-Precision Dark Halo Virial Masses from Globular Cluster Numbers: Implications for Globular Cluster Formation and Galaxy Assembly

We confirm that the number of globular clusters (GCs), N$_{GC}$, is an excellent tracer of their host galaxy's halo virial mass M$_{vir}$. The simple linear relation M$_{vir} = 5 \times 10^9$ M$_{\odot} \times$ N$_{GC}$ fits the data perfectly from M$_{vir} = 10^{10}$ M$_{\odot}$ to M$_{vir} = 2 \times 10^{15}$ M$_{\odot}$. This result is independent of galaxy morphology and extends statistically into the dwarf galaxy regime with M$_{vir} = 10^8 - 10^{10}$ M$_{\odot}$, including the extreme ultra diffuse galaxy DF44. As this correlation does not depend on GC mass it is ideally suited for high-precision determinations of M$_{vir}$. The linearity is most simply explained by cosmological merging of a high-redshift halo seed population that hosted on average one GC per $5 \times 10^8$ M$_{\odot}$ of dark matter. We show that hierarchical merging is also extremely powerful in restoring a linear correlation and erasing signatures of even a strong secular evolution of GC systems. The cosmological merging scenario also implies a strong decline of the scatter in $N_{GC}$ with increasing virial mass $\delta N_{GC}/N_{GC} \sim M_{vir}^{-1/2}$ in contrast with the observations that show a roughly constant scatter, independent of virial mass. This discrepancy can be explained if errors in determining virial masses from kinematical tracers and gravitational lensing are on the order of a factor of 2. GCs in dwarf satellite galaxies pose a serious problem for high-redshift GC formation scenarios; the dark halo masses of dwarf galaxies hosting GCs therefore might need to be an order of magnitude larger than currently estimated.Comment: 11 pages, 4 figures, ApJ in pres

Star Formation in Southern Seyfert Galaxies

We have produced radio maps, using the ATCA, of the central regions of six southern Seyfert 2 galaxies (NGC 1365, 4945, 6221, 6810, 7582, and Circinus) with circumnuclear star formation, to estimate the relative contribution of star formation activity compared to activity from the active galactic nucleus (AGN). The radio morphologies range from extended diffuse structures to compact nuclear emission, with no evidence, even in the relatively compact sources, for synchrotron self--absorption. In each case the radio to far--infrared (FIR) ratio has a value consistent with star formation, and in all but one case the radio to [FeII] ratio is also consistent with star formation. We derive supernova rates and conclude that, despite the presence of a Seyfert nucleus in these galaxies, the radio, FIR, and [FeII] line emission are dominated by processes associated with the circumnuclear star formation (i.e. supernova remnants and HII regions) rather than with the AGN.Comment: 26 pages, Latex, 13 figures, submitted to MNRA

Constraints on the Merger Models of Elliptical Galaxies from their Globular Cluster Systems

The discovery of proto-globular cluster candidates in many current-day mergers allows us to better understand the possible effects of a merger event on the globular cluster system of a galaxy, and to foresee the properties of the end-product. By comparing these expectations to the properties of globular cluster systems of today's elliptical galaxies we can constrain merger models. The observational data indicate that i) every gaseous merger induces the formation of new star clusters, ii) the number of new clusters formed in such a merger increases with the gas content of the progenitor galaxies. Low-luminosity (about M_V>-21), disky ellipticals are generally thought to be the result of a gaseous merger. As such, new globular clusters are expected to form but have not been detected to date. We investigate various reasons for the non-detection of sub-populations in low-luminosity ellipticals, i.e. absence of an old population, absence of a new population, destruction of one of the populations, and finally, an age-metallicity conspiracy that allows old and new globular clusters to appear indistinguishable at the present epoch. All of these possibilities lead us to a similar conclusion, namely that low-luminosity ellipticals did not form recently (z<1) in a gas-rich merger, and might not have formed in a major merger of stellar systems at all. High-luminosity ellipticals do reveal globular cluster sub-populations. However, it is difficult to account for the two populations in terms of mergers alone, and in particular, we can rule out scenarios in which the second sub-population is the product of a recent, gas-poor merger.Comment: 11 pages (MNRAS style, two columns, including 2 figures, mn.sty included), accepted for publication in the MNRAS, also available at http://www.ucolick.org/~mkissle