Spectral Energy Distributions and Age Estimates of 78 Star Clusters in M33

Ma, Jun; Zhou, Xu; Chen, Jiansheng; Wu, Hong; Jiang, Zhongjing; Xue, Suijian; Zhu, Jin

doi:10.1086/340361

Cited by 27 publications

(22 citation statements)

References 34 publications

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“…To study the integrated properties of the stellar populations in M 81 and clusters in M 33, Kong (2000) and Ma (2001Ma ( , 2002a used the simple stellar populations (SSPs) of the Galaxy Isochrone Synthesis Spectra Evolution Library (Bruzual & Charlot 1996). An SSP is defined as a single generation of coeval stars with fixed parameters, such as metallicity, IMF, etc.…”

Section: Fitting Algorithm and Resultsmentioning

confidence: 99%

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SED, age distribution and evolutionary history of M 33

et al. 2004

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Abstract. We present CCD spectrophotometry of the nearby spiral galaxy M 33 using images obtained with National Astronomical Observatories of China (NAOC) 60/90 cm Schmidt telescope in a broad U-band and 13 intermediate-band filters from 4000 to 10 000 Å. The observations cover the whole area of M 33, with a total integration of 39.08 h from September 23, 1995 to August 28, 2000. The spectral energy distributions (SEDs) for each area of M 33 are obtained. With the aid of an evolutionary synthesis model, PEGASE (Fioc & Rocca-Volmerange 1997, we compute theoretical SEDs for three kinds of star formation rate (SFR) histories. From best fits on templates of PEGASE and observed SEDs by the χ 2 -minimization procedure, we find that both the constant and exponentially decreasing (hereafter Exp, τ = 12 Gyr) SFR give good agreement between models and observations. We then obtain age distributions (when the observed stellar population formation began) and evolutionary histories of M 33 for the two models. For the constant SFR, an age gradient is clearly found between stellar populations of the central regions and of the outer regions. The stellar populations in its central regions are older than 10 Gyr; stars in the outer regions are younger, about 7 Gyr and the youngest components in the spiral arms are less than 5 Gyr. The Exp SFR gives a similar age distribution, but with absolute ages that are smaller by ∼2 Gyr. We conclude that M 33 has been forming stars continuously for most of its lifetime, with the interior having built up its stellar populations several Gyr earlier than the outer parts.

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Section: Fitting Algorithm and Resultsmentioning

confidence: 99%

“…For convenience, as we do in our series of work on galactic structure (Kong et al 2000;Ma et al 2001Ma et al , 2002a, we use flux ratios that are independent of distance. We calculate the flux ratio of PEGASE, the integrated luminosity of BATC i relative to that of BATC08 (λ 8 = 6075 Å) (thereafter the flux ratio),…”

Section: Flux Ratios Of Pegasementioning

confidence: 99%

SED, age distribution and evolutionary history of M 33

et al. 2004

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“…Also, cluster 54 in Chandar et al (1999a) is U137 in Christian & Schommer (1982). In Ma et al (2002b), there are 22 clusters older than 1 Gyr. However, the ratios of signal-to-noise of 11 clusters are not high enough, and are not included in this sample.…”

Section: Sample Of Old Star Clustersmentioning

confidence: 97%

Metallicity estimates for old star clusters in M 33

Zhou

Chen

2003

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Abstract. Using the theoretical stellar population synthesis models of BC96, Kong et al. (2003) showed that some BATC colors and color indices could be used to disentangle the age and metallicity effect. They found that there is a very good relation between the flux ratio of L 8510 /L 9170 and the metallicity for stellar populations older than 1 Gyr. In this paper, based on the Kong et al. results and on the multicolor spectrophotometry of Ma et al. (2001Ma et al. ( , 2002a, we estimate the metallicities of 31 old star clusters in the nearby spiral galaxy M 33, 23 of which are "true" globular clusters. The results show that most of these old clusters are metal poor. We also find that the ages and metal abundance for these old star clusters of M 33 do not vary with deprojected radial position.

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“…A number of studies have analysed the cluster population of M 33 both from space (Chandar et al 1999(Chandar et al , 2001 and from the ground (Ma et al 2001(Ma et al , 2002(Ma et al , 2004, although they have mainly concentrated on rather evolved stellar systems with ages between a few tens of Myr and few Gyrs. Nonetheless, the population of young stellar systems ( ∼ <10 Myr) in M 33 has not been thoroughly investigated, and only a few studies have been dedicated to such young star-forming systems.…”

Section: Introductionmentioning

confidence: 99%

Young stellar clusters and associations in M 33

Grossi

Corbelli

Giovanardi

et al. 2010

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Aims. We analyse multi-wavelength observations of 32 young star clusters and associations in M 33 with known oxygen abundance (8 < 12 + log(O/H) < 8.7). The data set includes ultraviolet (UV), optical, mid-infrared (MIR), CO (1-0) and 21-cm line (Hi) observations. We derive the spectral energy distribution (SED) of these systems and the properties of their gaseous environment to investigate the process of star formation and the interplay with the interstellar medium (ISM). Methods. We determine age, bolometric luminosities, masses, and the extinction by comparing the multi-band integrated photometry to single-age stellar population models. The best-fit solutions have been obtained using the Large Magellanic Cloud (LMC) extinction curves.Results. The stellar system ages range between 2 and 15 Myr, masses are between 3 × 10 2 and 4 × 10 4 M , and the intrinsic extinction, A V , varies from 0.3 to 1 mag. We find a correlation between age and extinction (young clusters being more reddened than older ones), and between the cluster mass and size. From the MIR emission we infer the presence of a dust component around the clusters whose fractional luminosity at 24 μm, L 24 /L Bol , decreases with the galactocentric distance. However, the total infrared luminosity inferred from L 24 is smaller than what we derive from the extinction corrections. We also find that the Hα luminosity predicted by population synthesis models is higher than the observed one, especially for low-mass systems (M < 10 4 M ). This difference is reduced, but not erased, when the incomplete sampling of the initial mass function (IMF) at the high-mass end is taken into account. Conclusions. Our results suggest that a non-negligible fraction of UV ionising and non-ionising radiation is leaking into the ISM outside the Hii regions. This agrees with the large UV and Hα diffuse fractions observed in M 33, but it implies that stellar systems younger than 3 Myr retain, on average, only 30% of their Lyman-continuum photons. However, the uncertainties in cluster ages and the stochastic fluctuations of the IMF do not allow us to accurately quantify this issue. We also consider the possibility that this discrepancy is the consequence of a suppressed or delayed formation of the most massive stars, given that it mainly affects the young and less massive clusters. We do not find any clear correlation between the cluster mass and the gas surface density or metallicity.

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Spectral Energy Distributions and Age Estimates of 78 Star Clusters in M33

Cited by 27 publications

References 34 publications

SED, age distribution and evolutionary history of M 33

SED, age distribution and evolutionary history of M 33

Metallicity estimates for old star clusters in M 33

Young stellar clusters and associations in M 33

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