An updated catalog of M33 clusters and candidates: $UBVRI$ photometry, and some statistical results

TL;DR

This paper provides an updated catalog of 392 M33 star clusters with $UBVRI$ photometry, correcting positions, comparing with previous data, and analyzing cluster properties and formation history.

Contribution

It offers new photometric data for many clusters lacking previous measurements and presents statistical analysis of their masses, ages, and formation continuity.

Findings

No young clusters (~10^7 yr) have masses near 10^5 M_sun

Approximately half the clusters have masses between 10^4 and 10^5 M_sun

Star clusters in M33 formed continuously from early times to recent epochs

Abstract

We present $UBVRI$ photometry for 392 star clusters and candidates in the field of M33, which are selected from the most recent star cluster catalog. In this catalog, the authors listed star clusters' parameters such as cluster positions, magnitudes and colors in the $UBVRIJHK_s$ filters, and so on. However, a large fraction of objects in this catalog do not have previously published photometry. Photometry is performed using archival images from the Local Group Galaxies Survey, which covers 0.8 deg$^2$ along the major axis of M33. Detailed comparisons show that, in general, our photometry is consistent with previous measurements. Positions (right ascension and declination) for some clusters are corrected here. Combined with previous literature, we constitute a large sample of M33 star clusters. Based on this cluster sample, we present some statistical results: none of the M33 youngest clusters ($\sim 10^7$ yr) have masses approaching $10^5$ $M_{\odot}$; roughly half the star clusters are consistent with the $10^4$ to $10^5$ $M_{\odot}$ mass models; the continuous distribution of star clusters along the model line indicates that M33 star clusters have been formed continuously from the epoch of the first star cluster formation until recent times; there are $\sim 50$ star clusters which being overlapped with the Galactic globular clusters on the color-color diagram, and these clusters are old globular clusters candidates in M33.