We present a survey of star clusters in the halo of IC 10, a starburst galaxy in the Local Group, based on Subaru R-band images and NOAO Local Group Survey UBVRI images. We find five new star clusters. All of these star clusters are located far from the center of IC 10, while previously known star clusters are mostly located in the main body. Interestingly, the distribution of these star clusters shows an asymmetrical structure elongated along the east and southwest directions. We derive UBVRI photometry of 66 star clusters, including these new star clusters, as well as previously known star clusters. Ages of the star clusters are estimated from a comparison of their UBVRI spectral energy distribution with the simple stellar population models. We find that the star clusters in the halo are all older than 1Gyr, while those in the main body have various ages, from very young (several Myr) to old (>1Gyr). The young clusters (<10Myr) are mostly located in the H{alpha} emission regions and are concentrated on a small region at 2" in the southeast direction from the galaxy center, while the old clusters are distributed in a wider area than the disk. Intermediate-age clusters (~100 Myr) are found in two groups. One is close to the location of the young clusters and the other is at ~ 4" from the location of the young clusters. The latter may be related to past mergers or tidal interaction.
In this paper we present the discovery of 60 star clusters in 20 multiband Hubble Space Telescope (HST) WFPC2 fields in M33. The fields sample a variety of environments, from outer regions to spiral arms and central regions, as well as a range of galactocentric distances. The HST spatial resolution allowed us to penetrate the crowded, spiral arm regions of M33 yielding the first unbiased, representative sample of star clusters for this galaxy. We discuss the separation of clusters from stellar sources, and from other extended sources such as star-forming regions, H II regions, and supernova remnants. For the clusters we present multiband images and discuss morphology, location, and integrated photometry. Measured cluster colors and magnitudes are presented. The cluster density in our sample as a function of galactocentric distance yields an estimate of 690 total clusters in M33.
A new survey of star clusters in the southwest field of the M31 disk based on the high-resolution Subaru Suprime-Cam observations is presented. The UBVRI aperture CCD photometry catalog of 285 objects (V<~20.5mag; 169 of them identified for the first time) is provided. Each object is supplemented with multiband color maps presented in the electronic edition of the Astrophysical Journal Supplement. Seventy-seven star cluster candidates from the catalog are located in the Hubble Space Telescope archive frames.
In this paper we derive ages and masses for 276 clusters in the merger galaxy NGC 3256. This was achieved by taking accurate photometry in four wavebands from archival Hubble Space Telescope images. Photometric measurements are compared to synthetic stellar population (SSP) models to find the most probable age, mass and extinction. The cluster population of NGC 3256 reveals an increase in the star formation rate (SFR) over the last 100Myr and the initial cluster mass function (ICMF) is best described by a power-law relation with slope alpha=1.85+/-0.12.
We present deep near-infrared images of the Antennae galaxies, taken with the Palomar Wide-Field Infrared Camera (WIRC). The images cover a 4.33'x4'33' (24.7x24.7kpc) area around the galaxy interaction zone. We derive J- and K_s_-band photometric fluxes for 172 infrared star clusters and discuss details of the two galactic nuclei and the overlap region.
To produce an homogeneous catalog of astrophysical parameters of 239 resolved star clusters located in the Small and Large Magellanic Clouds, observed in the Washington photometric system. The cluster sample was processed with the recently introduced Automated Stellar Cluster Analysis (ASteCA) package, which ensures both an automatized and a fully reproducible treatment, together with a statistically based analysis of their fundamental parameters and associated uncertainties. The fundamental parameters determined with this tool for each cluster, via a color-magnitude diagram (CMD) analysis, are: metallicity, age, reddening, distance modulus, and total mass. We generated an homogeneous catalog of structural and fundamental parameters for the studied cluster sample, and performed a detailed internal error analysis along with a thorough comparison with values taken from twenty-six published articles. We studied the distribution of cluster fundamental parameters in both Clouds, and obtained their age-metallicity relationships. The ASteCA package can be applied to an unsupervised determination of fundamental cluster parameters; a task of increasing relevance as more data becomes available through upcoming surveys.
We present a database of structural and dynamical properties for 153 spatially resolved star clusters in the Milky Way, the Large and Small Magellanic Clouds, and the Fornax dwarf spheroidal. This database complements and extends others in the literature, such as those of Harris (Cat. <VII/202>) and Mackey & Gilmore (2003MNRAS.338...85M, 2003MNRAS.338..120M, 2003MNRAS.340..175M). Our cluster sample comprises 50 "young massive clusters" in the LMC and SMC, and 103 old globular clusters between the four galaxies. The parameters we list include central and half-light-averaged surface brightnesses and mass densities; core and effective radii; central potentials, concentration parameters, and tidal radii; predicted central velocity dispersions and escape velocities; total luminosities, masses, and binding energies; central phase-space densities; half-mass relaxation times; and "{kappa}-space" parameters.
We present H{alpha} narrow-band imaging of 17 dwarf irregular (dI) galaxies in the nearby Centaurus A Group. Although all large galaxies of the group are or recently have been through a period of enhanced star formation, the dIs have normal star formation rates (SFRs) and do not contain a larger fraction of dwarf starbursts than other nearby groups such as the Sculptor Group or the Local Group. Most of the galaxies in the group now have fairly accurately known distances, which enables us to obtain relative distances between dIs and larger galaxies of the group. We find four transition dwarfs in the Group, dwarfs that show characteristics of both dE/dSphs and dIs, and which contain cold gas but no current star formation.
A sample of 69 galaxies with radial velocities of less than 2500km/s was selected from the HI Parkes All-Sky Survey (HIPASS, Cat. <VIII/73>) and imaged in broadband B and R and narrowband H{alpha}, to deduce details about star formation in nearby disk galaxies while avoiding surface brightness selection effects.
We present results from a photometric H{alpha} survey of 22 nuclear rings, aiming to provide insight into their star formation properties, including age distribution, dynamical timescales, star formation rates, and galactic bar influence. We find a clear relationship between the position angles and ellipticities of the rings and those of their host galaxies, which indicates the rings are in the same plane as the disk and circular. We use population synthesis models to estimate ages of each H{alpha}-emitting (HII) region, which range from 1 to 10Myr throughout the rings. We find that approximately half of the rings contain azimuthal age gradients that encompass at least 25% of the ring, although there is no apparent relationship between the presence or absence of age gradients and the morphology of the rings or their host galaxies. NGC 1343, NGC 1530, and NGC 4321 show clear bipolar age gradients, where the youngest HII regions are located near the two contact points of the bar and ring. We speculate in these cases that the gradients are related to an increased mass inflow rate and/or an overall higher gas density in the ring, which would allow for massive star formation to occur on short timescales, after which the galactic rotation would transport the HII regions around the ring as they age. Two-thirds of the barred galaxies show correlation between the locations of the youngest HII region(s) in the ring and the location of the contact points, which is consistent with predictions from numerical modeling.
