Young stellar clusters and associations in M 33

Grossi, M.; Corbelli, E.; Giovanardi, C.; Magrini, L.

doi:10.1051/0004-6361/200913513

Cited by 13 publications

(15 citation statements)

References 77 publications

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“…We may thus arrive at the conclusion that the YSCs display average characteristics reminiscent of the protocluster environment from which they were born. A similar conclusion was also drawn by Grossi et al (2010) from the analysis of stellar clusters and complexes.…”

Section: Ysc Propertiessupporting

confidence: 83%

The population of young stellar clusters throughout the disk of M 33

Sharma

Corbelli

Giovanardi

et al. 2011

A&A

Self Cite

105

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Aims. The properties of young stellar clusters (YSCs) in M 33, identified from the center out to about twice the size of the bright star-forming disk, are investigated to determine possible spatial and time variations of the star formation process in this Local Group blue galaxy. Methods. 915 MIR sources have been extracted from the Spitzer 24 μm image. Upon inspection of Hα and GALEX images and exclusion of evolved AGB stars, a sample of 648 objects is selected as candidate YSCs and their luminosity function is examined. The spectral energy distribution of each object, based on aperture photometry, is compared with Starburst99 models to derive age, mass and A V of individual clusters. In the analysis we allow for different values of the upper mass cutoff of the stellar initial mass function (IMF), the porosity of the ISM, and the dustiness of HII regions. We also examine the influence of different dust models and include corrections for incompleteness of the IMF. Results. We find discrete MIR sources as far as the extent of the warped HI disk, i.e. 16 kpc from the galaxy center. Their surface density has a steep radial decline beyond 4.5 kpc, and flattens out beyond the optical radius at 8.5 kpc. We are able to identify YSCs out to 12 kpc. At large galactocentric radii, the paucity of luminous clusters and the relevance of hot dust emission become evident from the analysis of the bolometric and MIR luminosity functions. The YSC mass and size are correlated with a log-log slope of 2.09±0.01, similar to that measured for giant molecular clouds in M 33 and the Milky Way, which represent the protocluster environment. Most of the YSCs in our sample have A V ∼ 0−1 mag and ages between 3 and 10 Myr. In the inner regions of M 33 the clusters span a wide range of mass (10 2 < M < 3 × 10 5 M ) and luminosity (10 38 < L bol < 3 × 10 41 erg s −1 ), while at galactocentric radii larger than ∼4 kpc we find a deficiency of massive clusters. Beyond 7 kpc, where the Hα surface brightness drops significantly, the dominant YSC population has M < 10 3 M and a slightly older age (10 Myr). This implies the occurrence of star formation events about 10 Myr ago as far as 10−12 kpc from the center of M 33. The cluster L FUV vs. L Hα relation is non-linear for L FUV < 10 39 erg s −1 , in agreement with randomly sampled models of the IMF which, furthermore, shows no appreciable variation throughout the M 33 disk.

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Section: Ysc Propertiessupporting

confidence: 83%

The population of young stellar clusters throughout the disk of M 33

Sharma

Corbelli

Giovanardi

et al. 2011

A&A

Self Cite

105

View full text Add to dashboard Cite

show abstract

“…A radio-selected sample of sources in M 33 has been analyzed by Buckalew et al (2006), who found optically visible counterparts with ages between 2-10 Myr. Similar ages have been derived by Grossi et al (2010) by analyzing the spectral energy distribution of a sample of compact HII regions. These results point out the paucity of embedded clusters, which might be a short-lived phase of the cluster lifetime.…”

Section: Introductionsupporting

confidence: 58%

On the nature of faint mid-infrared sources in M 33

Corbelli

Giovanardi

Palla

et al. 2011

A&A

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Aims. We investigate the nature of 24 μm sources in M 33 that have weak or no associated Hα emission. Both bright evolved stars and embedded star-forming regions are visible as compact infrared sources in the 8 and 24 μm Spitzer maps of M 33 and contribute to the more diffuse and faint emission in these bands. Can we distinguish the two populations? Methods. We carry out deep CO J = 2-1 and J = 1-0 line searches at the location of 18 compact mid-IR sources and two optically selected ones to unveil an ongoing star formation process throughout the disk of M 33. In the absence of high-resolution CO maps we use different assumptions to estimate cloud masses from pointed observations. We also analyze if the spectral energy distribution and mid-IR colors can be used to discriminate between evolved stars and star-forming regions.Results. Molecular emission is detected at the location of 17 sources at the level of 0.3 K km s −1 or higher in at least one of the CO rotational lines. Even though the number of giant molecular clouds drops beyond 4 kpc in M 33, our deep observations reveal that clouds of smaller mass are common out to 6.8 kpc. Estimated cloud masses range between 10 4 and 10 5 M , assuming likely values of the CO-to-H 2 conversion factor and virial equilibrium. Sources that are known to be evolved variable stars show weaker or undetectable CO lines. Evolved stars occupy a well defined region of the IRAC color-color diagrams. Star-forming regions are scattered throughout a larger area, even though the bulk of the distribution has different IRAC colors than evolved variable stars. We estimate that about half of the 24 μm sources without an Hα counterpart are genuine embedded star-forming regions. Sources with faint but compact Hα emission have an incomplete Initial Mass Function (IMF) at the high-mass end and are compatible with a population of young clusters with a stochastically sampled, universal IMF.

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“…All of the objects have oxygen abundances of 8 < 12 + log(O/H) < 8.7 and have 24 μm counterparts in the Spitzer/MIPS map. Comparison of the Grossi et al (2010) catalog with ours reveals 10 common objects, all of them associated with the previously mentioned "finger" feature. Table 2 provides a crossidentification of the common objects and includes the ages, extinctions, and reddenings obtained from their spectral energy distribution fitting technique.…”

Section: Color-color Diagramsmentioning

confidence: 67%

“…The recent work of Grossi et al (2010) analyzes multiwavelength observations of 32 young SCs and associations in M33. The sample was selected from catalogs of emission line objects based on their round shape and their position in regions of the galaxy that are not too crowded in the Hα map.…”

Section: Color-color Diagramsmentioning

confidence: 99%

Photometric Properties of the M33 Star Cluster System

Roman

Sarajedini

Aparicio

2010

ApJ

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We present a catalog of 2990 extended sources in a 1• × 1 • area centered on M33 using the MegaCam camera on the 3.6 m Canada-France-Hawaii Telescope. The catalog includes 599 new candidate stellar clusters, 204 previously confirmed clusters, 1969 likely background galaxies, and 218 unknown extended objects. We present ugriz integrated magnitudes of the candidates and confirmed star clusters (SCs) as well as the full width at half maximum, ellipticity, and stellarity. Based on the properties of the confirmed SCs, we select a sub-sample of highly probable clusters composed of 246 objects. The integrated photometry of the complete cluster catalog reveals a wide range of colors of −0.4 < (g − r) < 1.5 and −1.0 < (r − i) < 1.0 with no obvious cluster subpopulations. Comparisons with models of simple stellar populations suggest a large range of ages some as old as ∼10 Gyr. In addition, we find a sequence in the color-color diagrams that deviates from the expected direction of evolution. This feature could be associated with very young clusters (<10 7 yr) possessing significant nebular emission. Analysis of the radial density distribution suggests that the cluster system of M33 has suffered from significant depletion possibly due to interactions with M31. We also detect a gap in the cluster distribution in the color-color diagram at (g − r) 0.3 and (u − g) 0.8. This gap could be interpreted as an evolutionary effect. This complete catalog provides promising targets for deep photometry and high-resolution spectroscopy to study the structure and star formation history of M33.

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Young stellar clusters and associations in M 33

Cited by 13 publications

References 77 publications

The population of young stellar clusters throughout the disk of M 33

The population of young stellar clusters throughout the disk of M 33

On the nature of faint mid-infrared sources in M 33

Photometric Properties of the M33 Star Cluster System

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