35 research outputs found
Structural Parameters of Star Clusters: Signal to Noise Effects
We study the impact of photometric signal to noise on the accuracy of derived
structural parameters of unresolved star clusters using MCMC model fitting
techniques. Star cluster images were simulated as a smooth surface brightness
distribution following a King profile convolved with a point spread function.
The simulation grid was constructed by varying the levels of sky background and
adjusting the cluster's flux to a specified signal to noise. Poisson noise was
introduced to a set of cluster images with the same input parameters at each
node of the grid. Model fitting was performed using emcee algorithm. The
presented posterior distributions of the parameters illustrate their
uncertainty and degeneracies as a function of signal to noise. By defining the
photometric aperture containing 80% of the cluster's flux, we find that in all
realistic sky background level conditions a signal to noise ratio of 50
is necessary to constrain the cluster's half-light radius to an accuracy better
than 20%. The presented technique can be applied to synthetic images
simulating various observations of extragalactic star clusters.Comment: 9 pages, 5 figure
Compact Star Clusters in the M31 Disk
We have carried out a survey of compact star clusters (apparent size <3
arcsec) in the southwest part of the M31 galaxy, based on the high-resolution
Suprime-Cam images (17.5 arcmin x 28.5 arcmin), covering ~15% of the
deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V
< 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The
final sample, containing 238 high probability star cluster candidates (typical
half-light radius r_h ~ 1.5 pc), was selected by specifying a lower limit of
r_h > 0.15 arcsec (>0.6 pc). We derived cluster parameters based on the
photometric data and multiband images by employing simple stellar population
models. The clusters have a wide range of ages from ~5 Myr (young objects
associated with 24 um and/or Ha emission) to ~10 Gyr (globular cluster
candidates), and possess mass in a range of 3.0 < log(m/M_sol) < 4.3 peaking at
m ~ 4000 M_sol. Typical age of these intermediate-mass clusters is in the range
of 30 Myr < t < 3 Gyr, with a prominent peak at ~70 Myr. These findings suggest
a rich intermediate-mass star cluster population in M31, which appears to be
scarce in the Milky Way galaxy.Comment: 16 pages, 8 figures, 1 table, accepted for publication in Ap