Star Clusters in Pseudo-bulges of Spiral Galaxies

We present a study of the properties of the star-cluster systems around pseudo-bulges of late-type spiral galaxies using a sample of 11 galaxies with distances from 17 to 37 Mpc. Star clusters are identified from multiband HST ACS and WFPC2 imaging data by combining detections in 3 bands (F435W and F814W with ACS and F606W with WFPC2). The photometric data are then compared to population synthesis models to infer the masses and ages of the star clusters. Photometric errors and completeness are estimated by means of artificial source Monte Carlo simulations. Dust extinction is estimated by considering F160W NICMOS observations of the central regions of the galaxies, augmenting our wavelength coverage. In all galaxies we identify star clusters with a wide range of ages, from young (age . 8 Myr) blue clusters, with typical mass of 10 M⊙ to older (age > 100-250 Myr), more massive, red clusters. Some of the latter might likely evolve into objects similar to the Milky Way’s globular clusters. We compute the specific frequencies for the older clusters with respect to the galaxy Based on observation with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA CICLOPS, Space Science Institute, 4750 Walnut St., Boulder, CO 80301, USA Center for Astrophysics and Space Astronomy, University of Colorado, 389 UCB, Boulder, CO 80309, USA ETH Zurich, Physics Department, CH-8033 Switzerland Spitzer Science Center, Caltech, 1200 East California Boulevard, Pasadena, CA 91125, USA Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK