An Extended Star Cluster at the Outer Edge of the Spiral Galaxy M 33

Stonkutė, R.; Vansevičius, Vladas; Arimoto, N.; Hasegawa, Takashi; Narbutis, D.; Tamura, Naoyuki; Jablonka, P.; Ohta, Kouji; Yamada, Yoshiyuki

doi:10.1088/0004-6256/135/4/1482

Cited by 47 publications

(69 citation statements)

References 40 publications

(55 reference statements)

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“…The only massive EC (M EC ≈ 10 6 M and r eff ≈ 20 pc) of the Milky Way, NGC 2419, is located at a distance of about 92 kpc. A similar trend has been shown for the other two disk galaxies in the Local Group: 12 out of 13 ECs associated with M 31 and both ECs found in M 33 have projected distances well outside the optical disks of these galaxies (Huxor et al 2008;Stonkutė et al 2008;Huxor et al 2009). While halo ECs might be found by chance in projection to the main body of a galaxy, the probability is relatively low: if a survey covers a projected area of 20 kpc by 20 kpc and a line-of-sight of ±100 kpc is considered, the resulting volume, which is covered by the survey, is only about two percent of the volume of a sphere of radius 100 kpc, wherein the ECs would be distributed.…”

Section: Discussionsupporting

confidence: 80%

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A parametric study on the formation of extended star clusters and ultra-compact dwarf galaxies

Brüns

Kroupa

Fellhauer

et al. 2011

A&A

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Context. In the last decade, very extended old stellar clusters with masses in the range from a few 10 4 to 10 8 M have been found in various types of galaxies in different environments. Objects with masses comparable to normal globular clusters (GCs) are called extended clusters (ECs), while objects with masses in the dwarf galaxy regime are called ultra-compact dwarf galaxies (UCDs). In heavily interacting galaxies star clusters tend to form in larger conglomerations called star cluster complexes (CCs). The individual star clusters in a CC can merge and form a variety of spheroidal stellar objects. Aims. The parametric study aims to analyze how the structural parameters of the final merger objects correlate with the underlying CC parameter space. Methods. In this work we systematically scan a suitable parameter space for CCs and perform numerical simulations to study their further fate. The varied sizes and masses of the CCs cover a matrix of 5 × 6 values with CC Plummer radii between 10-160 pc and CC masses between 10 5.5 -10 8 M , which are consistent with observed CC parameters. The CCs of the parametric study are on orbits with galactocentric distances between 20 kpc and 60 kpc. In addition, we studied also the evolution of CCs on a circular orbit at a galactocentric distance of 60 kpc to verify that also extremely extended ECs and UCDs can be explained by our formation scenario. Results. All 54 simulations end up with stable merger objects, wherein 26 to 97% of the initial CC mass is bound. The objects show a general trend of increasing effective radii with increasing mass. Despite the large range of input Plummer radii of the CCs (10 to 160 pc) the effective radii of the merger objects are constrained to values between 10 and 20 pc at the low mass end and to values between 15 and 55 pc at the high mass end. The structural parameters of the models are comparable to those of the observed ECs and UCDs. The results of the circular orbits demonstrate that even very extended objects like the M 31 ECs found by Huxor in 2005 and the very extended (r eff > 80 pc), high-mass UCDs can be explained by merged cluster complexes in regions with low gravitational fields at large galactocentric radii. Conclusions. We conclude that the observed ECs and UCDs can be well explained as evolved star cluster complexes.

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Section: Discussionsupporting

confidence: 80%

“…ECs are now detected in all types of galaxies from dwarfs to ellipticals (e.g. Larsen & Brodie 2000;Harris et al 2002;Lee et al 2005;Peng et al 2006;Chies-Santos et al 2007;Stonkutė et al 2008;Georgiev et al 2009;Da Costa et al 2009). …”

Section: Introductionmentioning

confidence: 99%

A parametric study on the formation of extended star clusters and ultra-compact dwarf galaxies

Brüns

Kroupa

Fellhauer

et al. 2011

A&A

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“…For M 31 five out of 20 EOs have projected distances smaller than 10 kpc and 11 EOs have projected distances larger than 20 kpc (Peacock et al 2009;Huxor et al 2008). The two EOs associated with M 33 have projected distances of 12.5 and 28.4 kpc (Stonkutė et al 2008;Huxor et al 2009). …”

Section: Spatial Distribution Of Eosmentioning

confidence: 96%

“…The other two Local Group spiral A65, page 2 of 17 galaxies M 31 and M 33 have 20 (Huxor et al 2008;Peacock et al 2009;Huxor et al 2011a) and 2 (Stonkutė et al 2008;Cockcroft et al 2011) EOs, respectively. EOs were also found in the LMC (van den Bergh & Mackey 2004), and the dwarf irregular galaxy NGC 6822 (Hwang et al 2011).…”

Section: Eos In Late-type Galaxiesmentioning

confidence: 99%

A catalog of extended clusters and ultra-compact dwarf galaxies

Kroupa

2012

A&A

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Context. In the past decade, very extended old stellar clusters with masses in the range from a few 10 4 to 10 8 M and effective radii larger than 10 pc have been found in various types of galaxies in different environments. Objects with masses comparable to normal globular clusters (GCs) are called extended clusters (ECs), while objects with masses in the dwarf galaxy regime are called ultra-compact dwarf galaxies (UCDs). Aims. The paper analyses the observational parameters total luminosity, M V , effective radius, r eff , and projected distance to the host galaxy, R proj , of all known ECs and UCDs and the dependence of these parameters on the type and the total luminosity of their host galaxy. Methods. We searched the available literature to compile a catalog of star clusters with effective radii larger than 10 pc. As there is no clear distinction between ECs and UCDs, both types of objects will be called extended stellar objects -abbreviated "EOs" -in this paper.Results. In total, we found 813 EOs of which 171 are associated with late-type galaxies and 642 EOs associated with early-type galaxies. EOs cover a luminosity range from about M V = −4 to −14 mag. However, the vast majority of EOs brighter than M V = −10 mag are associated with giant elliptical galaxies. At each magnitude extended objects are found with effective radii between 10 pc and an upper size limit, which shows a clear trend: the more luminous the object the larger is the upper size limit. For EOs associated with early-and late-type galaxies, the EO luminosity functions peak at −6.40 mag and −6.47 mag, respectively, which is about one magnitude fainter than the peak of the GC luminosity function. EOs and GCs form a coherent structure in the r eff vs. M V parameter space, while there is a clear gap between EOs and early-type dwarf galaxies. However, there is a small potential overlap at the high-mass end, where the most extended EOs are close to the parameters of some compact elliptical galaxies. We compare the EO sample with the numerical models of a previous paper and conclude that the parameters of the EO sample as a whole can be very well explained by a star cluster origin, where EOs are the results of merged star clusters of cluster complexes.

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“…However, they have a resolution limit, and split unresolved cores of clusters into several artificial point sources. Hence, they are suitable for construction of color−magnitude diagrams of the brightest stars only in the outer parts of semi-resolved clusters, e.g., an extended object studied by Stonkutė et al (2008) or clusters measured in HST frames by Larsen et al (2011).…”

Section: Introductionmentioning

confidence: 99%

Deriving structural parameters of semi-resolved star clusters

Narbutis

Semionov

Stonkutė

et al. 2014

A&A

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Context. An automatic tool to derive structural parameters of semi-resolved star clusters located in crowded stellar fields in nearby galaxies is needed for homogeneous processing of archival frames. Aims. We have developed a program that automatically derives the structural parameters of star clusters and estimates errors by accounting for individual stars and variable sky background. Methods. Models of observed frames consist of the cluster's surface brightness distribution, convolved with a point spread function; the stars, represented by the same point spread function; and a smoothly variable sky background. The cluster's model is fitted within a large radius by using the Levenberg-Marquardt and Markov chain Monte Carlo algorithms to derive structural parameters, the flux of the cluster, and individual fluxes of all well-resolved stars. Results. FitClust, a program to derive structural parameters of semi-resolved clusters in crowded stellar fields, was developed and is available for free use. The program was tested on simulated cluster frames, and was used to measure clusters of the M31 galaxy in Subaru Suprime-Cam frames. Conclusions. Accounting for bright resolved stars and variable sky background significantly improves the accuracy of derived structural parameters of star clusters. However, their uncertainty remains dominated by the stochastic noise of unresolved stars.

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An Extended Star Cluster at the Outer Edge of the Spiral Galaxy M 33

Cited by 47 publications

References 40 publications

A parametric study on the formation of extended star clusters and ultra-compact dwarf galaxies

A parametric study on the formation of extended star clusters and ultra-compact dwarf galaxies

A catalog of extended clusters and ultra-compact dwarf galaxies

Deriving structural parameters of semi-resolved star clusters

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