Hubble Space Telescope imaging of globular cluster candidates in low surface brightness dwarf galaxies

Free access article

Issue		A&A Volume 442, Number 1, October IV 2005


Page(s)		85 - 95
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20052921

A&A 442, 85-95 (2005)
DOI: 10.1051/0004-6361:20052921

Hubble Space Telescope imaging of globular cluster candidates in low surface brightness dwarf galaxies

M. E. Sharina^{1, 2}, T. H. Puzia³ and D. I. Makarov^{1, 2}

¹ Special Astrophysical Observatory, Russian Academy of Sciences, N. Arkhyz, KChR, 369167, Russia
² Isaac Newton Institute, Chile, SAO Branch
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD21218, USA
e-mail: tpuzia@stsci.edu

(Received 22 February 2005 / Accepted 26 May 2005 )

Abstract
Fifty-seven nearby low surface brightness dwarf galaxies ( $-10\ga M_{V}\ga -16$ ) were searched for globular cluster candidates (GCCs) using Hubble Space Telescope WFPC2 imaging in V and I. The sample consists of 18 dwarf spheroidal (dSph), 36 irregular (dIrr), and 3 "transition" type (dIrr/dSph) galaxies with angular sizes less than 3.7 kpc situated at distances 2-6 Mpc in the field and in the nearby groups: M 81, Centaurus A, Sculptor, Canes Venatici I cloud. We find that ~50% of dSph, dIrr/dSph, and dIrr galaxies contain GCCs. The fraction of GCCs located near the center of dwarf spheroidal galaxies is $\ga$ 2 times higher than for dIrrs. The mean integral color of GCCs in dSphs, $(V-I)_0=1.04\pm0.16$ mag, coincides with the corresponding value for Galactic globular clusters and is similar to the blue globular cluster sub-populations in massive early-type galaxies. The color distribution for GCCs in dIrrs shows a clear bimodality with peaks near (V-I)₀ = 0.5 and 1.0 mag. Blue GCCs are presumably young with ages $t\la1$ Gyr, while the red GCC population is likely to be older. The detected GCCs have absolute visual magnitudes between M_V=-10 and -5 mag. We find indications for an excess population of faint GCCs with $M_{V}\ga-6.5$ mag in both dSph and dIrr galaxies, reminiscent of excess populations of faint globular clusters in nearby Local Group spiral galaxies. The measurement of structural parameters using King-profile fitting reveals that most GCCs have structural parameters similar to extended outer halo globular clusters in the Milky Way and M 31, as well as the recently discovered population of "faint fuzzy" clusters in nearby lenticular galaxies.

Key words: galaxies: dwarf -- galaxies: star clusters

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