We present observations obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope of the "fossil" starburst region B in the nearby starburst galaxy M82. By comparing UBVI photometry with models, we derive ages and extinctions for 35 U-band-selected star clusters. We find that the peak epoch of cluster formation occurred ~150Myr ago, in contrast to earlier work that found a peak formation age of 1.1Gyr. The difference is most likely due to our inclusion of U-band data, which are essential for accurate age determinations of young cluster populations. We further show that the previously reported turnover in the cluster luminosity function is probably due to the neglect of the effect of extended sources on the detection limit. The much younger cluster ages we derive clarifies the evolution of the M82 starburst. The M82-B age distribution now overlaps with the ages of the nuclear starburst, the clusters formed on the opposite side of the disk, and the last encounter with M81, some 220Myr ago.
We have used deep ACS/WFC images of M33 to check the nature of extended objects detected by the ground based survey of Zloczewski et al. (2008, Cat. J/AcA/58/23). A total of 24 candidates turned out to be genuine compact stellar clusters. In addition we detected 91 new clusters. Equatorial coordinates, integrated magnitudes and angular sizes are listed for all 115 objects. Forty-two clusters have sufficiently red colors to be candidates for old globulars. For four clusters we extracted resolved stellar photometry. Object 33-3-018 located in the outer disk of M33 turned out to be a young cluster with an age estimated at 200-350Myr. Cluster ZK-90 has an age of 3-5Gyr. The remaining two clusters have intermediate ages ranging from one to a few Gyr.
We present a study of the star cluster population in the starburst irregular galaxy NGC 4449 based on B, V, I, and H{alpha} images taken with the Advanced Camera for Surveys on the Hubble Space Telescope. We derive cluster properties such as size, ellipticity, and total magnitude. Cluster ages and masses are derived fitting the observed spectral energy distributions with different population synthesis models.
We perform a detailed study of the globular cluster (GC) system in the galaxy NGC 5866 based on F435W, F555W, and F625W (~B, V, and R) Hubble Space Telescope Advanced Camera for Surveys images. Adopting color, size, and shape selection criteria, the final list of GC candidates comprises 109 objects, with small estimated contamination from background galaxies, and foreground stars.
We focus on the resolved stellar populations of one early-type and four transition-type dwarf galaxies in the Sculptor group, with the aim to examine the potential presence of population gradients and place constraints on their mean metallicities. We use deep Hubble Space Telescope images to construct color-magnitude diagrams, from which we select stellar populations that trace different evolutionary phases in order to constrain their range of ages and metallicities, as well as to examine their spatial distribution. In addition, we use the resolved stars in the red giant branch in order to derive photometric metallicities.
We present a photometric study of star clusters in the nearby starburst galaxy M82 based on the UBVI-, YJ- and H-band Hubble Space Telescope images. We find 1105 star clusters with V<23mag. Of those, 1070 are located in the disk region, while 35 star clusters are in the halo region. The star clusters in the disk are composed of a dominant blue population with a color peak at (B-V)_0_~0.45, and a weaker red population. The luminosity function of the disk clusters shows a power-law distribution with a power-law index {alpha}=-2.04+/-0.03, and the scale height of their distribution is h_z_=9.64"+/-0.40" (164+/-7pc), similar to that of the stellar thin disk of M82. We have derived the ages of ~630 star clusters using the spectral energy distribution fit method by comparing UBVI(YJ)H-band photometric data with the simple stellar population models. The age distribution of the disk clusters shows that the most dominant cluster population has ages ranging from 100Myr to 1Gyr, with a peak at about 500Myr. This suggests that M82 has undergone a disk-wide star formation about 500Myr ago, probably through the interaction with M81. The brightest star clusters in the nuclear region are much brighter than those in other regions, indicating that more massive star clusters are formed in the denser environments. On the other hand, the colors of the halo clusters are similar to those of globular clusters in the Milky Way, and their ages are estimated to be older than 1Gyr. These are probably genuine old globular clusters in M82.
We present a photometric catalog of 45 massive star clusters in the nuclear starburst of M83 (NGC 5236), observed with the Hubble Space Telescope Wide Field Planetary Camera 2, in both broadband (F300W, F547M, and F814W) and narrowband (F656N and F487N) filters, in two separate visits one week apart during April and May 2000 .
We present deep HST ACS observations in g_475_r_625_i_775_z_850_ toward the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Ly{alpha} emitters (LAEs). We select 66 g_475_ band dropouts to z_850,5sigma_=27, 6 of which are also LAEs.
We present the data and methods that we have used to perform a detailed UV-optical study of the nearby dwarf starburst galaxy NGC 4214 using multifilter Hubble Space Telescope WFPC2 and STIS photometry. We explain the process followed to obtain high-quality photometry and astrometry of the stellar and cluster populations of this galaxy. We describe the procedure used to transform magnitudes and colors into physical parameters using spectral energy distributions. The data show the existence of both young and old stellar populations that can be resolved at the distance of NGC 4214 (2.94Mpc), and we perform a general description of those populations.
Utilizing the F814W and F300W filters, Hubble Space Telescope Wide Field Planetary Camera-2 (WFPC2) images were taken of four low surface brightness galaxies in the direction of the Virgo Cluster - V7L3, V2L8, V1L4, and Malin 1. The high resolution of the WFPC2 combined with the extremely diffuse nature of the four galaxies makes them essentially transparent, allowing for the serendipitous discovery of 139 background galaxies visible through both the disks and nuclei of the foreground galaxies. Surface photometry was done on the newly discovered galaxies through the F814W (I-band) filter. The detected galaxies have both r1/4 and exponential-type profiles with radii (to the {mu}_F814W_=25.0mag/arcsec^2^ limit) less than 5.0". Their total magnitudes range from 18.9 through the survey cutoff at 25.0 in the F814W filter.