Age and Mass Studies for Young Star Clusters in M31 From Seds-Fit

Abstract

In this paper, we present photometry for young star clusters in M31, which are selected from Caldwell et al. These star clusters have been observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March. The BATC images including these star clusters are taken with 15 intermediate-band filters covering 3000-10000Å. Combined with photometry in the GALEX far-and near-ultraviolet, broad-band U BV RI, SDSS ugriz, and infrared JHK s of Two Micron All Sky Survey, we obtain their accurate spectral energy distributions (SEDs) from 1538 − 20000Å. We derive these star clusters' ages and masses by comparing their SEDs with stellar population synthesis models. Our results are in good agreement with previous determinations. The mean value of age and mass of young clusters (< 2 Gyr) is about 385 Myr and 2 × 10 4 M ⊙ , respectively. There are two distinct peaks in the age distribution, a highest peak at age ∼ 60 Myr and a secondary peak around 250 Myr, while the mass distribution shows a single peak around 10 4 M ⊙ . A few young star clusters have two-body relaxation times greater than their ages, indicating that those clusters have not been well dynamically relaxed and therefore have not established the thermal equilibrium. There are several regions showing aggregations of young star clusters around the 10 kpc ring and the outer ring, indicating that the distribution of the young star clusters is well correlated with M31's star-forming regions. The young massive star clusters (age ≤ 100 Myr and mass ≥ 10 4 M ⊙ ) show apparent concentration around the ring splitting region, suggesting a recent passage of a satellite galaxy (M32) through M31 disk.

Hubble Space Telescope Spectroscopy of a Planetary Nebula in an M31 Open Cluster: Hot-bottom Burning at 3.4 M⊙*

“…Kang et al (2012) obtained ultraviolet (UV) measurements of the cluster and used the system's full far-UV to near-infrared spectral-energy distribution (SED) to derive a smaller cluster reddening of E(B − V ) = 0.08, but nearly the same age of 325 Myr. However, a similar SED analysis by Wang et al (2012) gave an age of only 62 Myr, and a reddening of E(B−V ) = 0.30. Chen et al (2015) independently determined the cluster's RV using the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), finding −123 ± 12 km s −1 .…”

The Ages of M31 Star Clusters: Spectral Energy Distribution versus Color–Magnitude Diagram

“…For BC03 SSP models, GALEV models and the ASPS ss-SSPs/bs-SSPs models, the theoretical spectra have been convolved into the AB system with the transmission of filters in the FUV, NUV, UBV RIJHK, W 1, and W 2 bands (Jarrett et al 2011). The AB magnitudes of the models are calculated in the formula (see, e.g., Fan et al 2006;Ma et al 2007Ma et al , 2009Ma et al , 2011Ma et al , 2012Wang et al 2010Wang et al , 2012…”

“…Previously, de Grijs et al (2003) derive the ages, metallicities, and reddening of the star clusters associated with NGC 3310 by the SED-fitting method with the photometry of the ultraviolet (UV), optical, and near-infrared (NIR) observations obtained with the Hubble Space Telescope (HST). Fan et al (2006); Ma et al (2007Ma et al ( , 2009Ma et al ( , 2011Ma et al ( , 2012; Wang et al (2010Wang et al ( , 2012 have done a series of SED-fitting works of M31 star clusters, based on the Beijing-Arizona-Taiwan-Connecticut (BATC) multi-color photometry system, with a 60/90cm Schmidt telescope. The simple stellar population (SSP) models applied are the Bruzual & Charlot (2003, henceforth BC03) and the Galaxy Evolutionary Synthesis Models (GALEV; Lilly & Fritze-v. Alvensleben 2006;Kotulla et al 2009).…”

Comparisons of Different Fitting Methods for the Physical Parameters of A Star Cluster Sample of M33 with Spectroscopy and Photometry

“…de Grijs et al (2003) derive the ages, metallicities, and reddening of the star clusters associated with NGC 3310 by the SED-fitting method with the photometry of the ultraviolet (UV), optical, and near-infrared (NIR) observations obtained with the HST. Fan et al (2006); Ma et al (2007Ma et al ( , 2009Ma et al ( , 2011Ma et al ( , 2012; Wang et al (2010Wang et al ( , 2012 have done a series of SED-fitting works targeting M31 star clusters, based on the Beijing-Arizona-Taiwan-Connecticut (BATC) multi-color photometry system, with a 60/90cm Schmidt telescope. They applied the simple stellar population (SSP) models, Bruzual & Charlot (2003, henceforth BC03) and the Galaxy Evolutionary Synthesis Models (GALEV; Lilly & Fritze-v. Alvensleben 2006;Kotulla et al 2009).…”