- ID:
- ivo://CDS.VizieR/J/ApJ/845/56
- Title:
- Star clusters automatically detected in the LMC
- Short Name:
- J/ApJ/845/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our new, fully automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia+ (2017, in prep.), estimates the ages of the clusters. Comparisons of our estimates with those from other surveys show the superiority of our method to extract and measure the ages of star clusters, even in the most crowded fields. An application of our method is shown for the high-resolution, multiband imaging of the Large Magellanic Cloud. We detect 4850 clusters in the 7deg^2^ we surveyed, 3451 of which have not been reported before. Our findings suggest multiple epochs of star cluster formation, with the most probable occurring ~310Myr ago. Several of these events are consistent with the epochs of the interactions among the Large and Small Magellanic Clouds, and the Galaxy, as predicted by N-body numerical simulations. Finally, the spatially resolved star cluster formation history may suggest an inside-out cluster formation scenario throughout the LMC, for the past 1Gyr.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/436/1465
- Title:
- Star clusters distances and extinctions
- Short Name:
- J/MNRAS/436/1465
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Determining star cluster distances is essential to analyse their properties and distribution in the Galaxy. In particular, it is desirable to have a reliable, purely photometric distance estimation method for large samples of newly discovered cluster candidates e.g. from the Two Micron All Sky Survey, the UK Infrared Deep Sky Survey Galactic Plane Survey and VVV. Here, we establish an automatic method to estimate distances and reddening from near-infrared photometry alone, without the use of isochrone fitting. We employ a decontamination procedure of JHK photometry to determine the density of stars foreground to clusters and a galactic model to estimate distances. We then calibrate the method using clusters with known properties. This allows us to establish distance estimates with better than 40 percent accuracy. We apply our method to determine the extinction and distance values to 378 known open clusters and 397 cluster candidates from the list of Froebrich, Scholz & Raftery (2007MNRAS.374..399F, Cat. J/MNRAS/374/399). We find that the sample is biased towards clusters of a distance of approximately 3kpc, with typical distances between 2 and 6kpc. Using the cluster distances and extinction values, we investigate how the average extinction per kiloparsec distance changes as a function of the Galactic longitude. We find a systematic dependence that can be approximated by A_H_(l)[mag/kpc]=0.10+0.001x|l-180{deg}|/{deg} for regions more than 60{deg} from the Galactic Centre.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/290
- Title:
- Star clusters distances and extinctions. II.
- Short Name:
- J/MNRAS/444/290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Until now, it has been impossible to observationally measure how star cluster scaleheight evolves beyond 1Gyr as only small samples have been available. Here, we establish a novel method to determine the scaleheight of a cluster sample using modelled distributions and Kolmogorov-Smirnov tests. This allows us to determine the scaleheight with a 25% accuracy for samples of 38 clusters or more. We apply our method to investigate the temporal evolution of cluster scaleheight, using homogeneously selected sub-samples of Kharchenko et al. (MWSC, 2012, Cat. J/A+A/543/A156, 2013, J/A+A/558/A53 ), Dias et al. (DAML02, 2002A&A...389..871D, Cat. B/ocl), WEBDA, and Froebrich et al. (FSR, 2007MNRAS.374..399F, Cat. J/MNRAS/374/399). We identify a linear relationship between scaleheight and log(age/yr) of clusters, considerably different from field stars. The scaleheight increases from about 40pc at 1Myr to 75pc at 1Gyr, most likely due to internal evolution and external scattering events. After 1Gyr, there is a marked change of the behaviour, with the scaleheight linearly increasing with log(age/yr) to about 550pc at 3.5Gyr. The most likely interpretation is that the surviving clusters are only observable because they have been scattered away from the mid-plane in their past. A detailed understanding of this observational evidence can only be achieved with numerical simulations of the evolution of cluster samples in the Galactic disc. Furthermore, we find a weak trend of an age-independent increase in scaleheight with Galactocentric distance. There are no significant temporal or spatial variations of the cluster distribution zero-point. We determine the Sun's vertical displacement from the Galactic plane as Z_{sun}_=18.5+/-1.2pc.
- ID:
- ivo://CDS.VizieR/J/PAZh/35/829
- Title:
- Star clusters in IC 10
- Short Name:
- J/PAZh/35/829
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on our observations with the 6-m BTA telescope at the Special Astrophysical Observatory, the Russian Academy of Sciences, and archival Hubble Space Telescope images, we have performed stellar photometry for several regions of the irregular galaxy IC 10, a member of the Local Group. Distance moduli with a median value of m-M=24.47, D=780+/-4kpc, have been obtained by the TRGB method for several regions of IC 10. We have revealed 57 star clusters with various masses and ages within the fields used. Comparison of the Hertzsprung-Russell diagrams for star clusters in IC 10 with theoretical isochrones has shown that this galaxy has an enhanced metallicity, which probably explains the high ratio of the numbers of carbon and nitrogen Wolf-Rayet stars (WC/WN). The size of the galaxy's thick disk along its minor axis is 10.5' and a more extended halo is observed outside this disk.
325. Star clusters in M31
- ID:
- ivo://CDS.VizieR/J/AJ/137/94
- Title:
- Star clusters in M31
- Short Name:
- J/AJ/137/94
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an updated catalog of 1300 objects in the field of M31, including 670 likely star clusters of various types, the rest being stars or background galaxies once thought to be clusters. The coordinates in the catalog are accurate to 0.2", and are based on images from the Local Group Survey (LGS) or from the Digitized Sky Survey (DSS). Archival Hubble Space Telescope (HST) images and the LGS were inspected to confirm cluster classifications where possible, but most of the classifications are based on spectra taken of ~1000 objects with the Hectospec fiber positioner and spectrograph on the 6.5m MMT.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/1446
- Title:
- Star clusters in Magellanic Clouds
- Short Name:
- J/MNRAS/463/1446
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have introduced a semi-automated quantitative method to estimate the age and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study brings out 308 newly parameterised clusters. In a first of its kind, the LMC clusters are classified into groups based on richness/mass as very poor, poor, moderate and rich clusters, similar to the classification scheme of open clusters in the Galaxy. A major cluster formation episode is found to happen at 125+/-25Myr in the inner LMC. The bar region of the LMC appears prominently in the age range 60-250Myr and is found to have a relatively higher concentration of poor and moderate clusters. The eastern and the western ends of the bar are found to form clusters initially, which later propagates to the central part. We demonstrate that there is a significant difference in the distribution of clusters as a function of mass, using a movie based on the propagation (in space and time) of cluster formation in various groups. The importance of including the low mass clusters in the cluster formation history is demonstrated. The catalog with parameters, classification, and cleaned and isochrone fitted CMDs of 1072 clusters, which are available as online material, can be further used to understand the hierarchical formation of clusters in selected regions of the LMC.
- ID:
- ivo://CDS.VizieR/J/AJ/141/61
- Title:
- Star clusters in M31. II.
- Short Name:
- J/AJ/141/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new high signal-to-noise spectroscopic data on the M31 globular cluster (GC) system, obtained with the Hectospec multifiber spectrograph on the 6.5m MMT. More than 300 clusters have been observed at a resolution of 5{AA} and with a median S/N of 75 per{AA}, providing velocities with a median uncertainty of 6km/s. The primary focus of this paper is the determination of mean cluster metallicities, ages, and reddenings. Metallicities were estimated using a calibration of Lick indices with [Fe/H] provided by Galactic GCs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/405/857
- Title:
- Star clusters in NGC 3256
- Short Name:
- J/MNRAS/405/857
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/635/280
- Title:
- Star clusters in the Antennae galaxies
- Short Name:
- J/ApJ/635/280
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/556/A98
- Title:
- Star-forming rings in NGC5248
- Short Name:
- J/A+A/556/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of gas in the central kiloparsec of a galaxy has a dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of the galactic disk, such as a large scale stellar bar or spiral, can lead to significant radial motion of gaseous material from larger radii to the central region. The large influx of gas and the subsequent star formation keep the central region constantly changing. However, the ability of gas to reach the nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted at a circumnuclear star forming ring several hundred parsec away. The nearby galaxy NGC5248 is especially interesting in this sense since it is said to host 2 circumnuclear star forming rings at 100pc and 370pc from its quiescent nucleus. Here we present new subarcsecond PdBI+30m CO(2-1) emission line observations of the central region. For the first time the molecular gas distribution at the smallest stellar ring is resolved into a gas ring, consistent with the presence of a quiescent nucleus. However, the molecular gas shows no ring structure at the larger ring. We combine analyses of the gaseous and stellar content in the central kiloparsec of this galaxy to understand the gas distribution and dynamics of this star forming central region. We discuss the probability of two scenarios leading to the current observations, given our full understanding of this system, and discuss whether there are really two circumnuclear star forming rings in this galaxy.
