Faint Fuzzy Star Clusters in NGC 1023 as Remnants of Merged Star Cluster Complexes

Brüns, R. C.; Kroupa, Pavel; Fellhauer, M.

doi:10.1088/0004-637x/702/2/1268

Cited by 24 publications

(36 citation statements)

References 28 publications

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“…Kroupa 1998;Fellhauer & Kroupa 2002aBekki et al 2004;Brüns et al 2009. These studies demonstrated that the merging star cluster scenario provides a mechanism for the formation of EOs.…”

Section: An Eo Formation Scenariomentioning

confidence: 71%

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A catalog of extended clusters and ultra-compact dwarf galaxies

Kroupa

2012

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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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“…Kroupa 1998;Fellhauer & Kroupa 2002aBekki et al 2004;Brüns et al 2009. These studies demonstrated that the merging star cluster scenario provides a mechanism for the formation of EOs.…”

Section: An Eo Formation Scenariomentioning

confidence: 71%

“…In addition, Brüns et al (2009) discussed the origin of the EOs, or faint fuzzies, associated with the disk of NGC 1023 in the context of merged cluster scenario and demonstrated that the observed structural parameters of the faint fuzzies are in excellent agreement with the modeled merger objects.…”

Section: An Eo Formation Scenariomentioning

confidence: 90%

A catalog of extended clusters and ultra-compact dwarf galaxies

Kroupa

2012

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“…Burkert et al (2005) analyzed the kinematics of the faint fuzzies and concluded that they form a ring-like structure within the galactic disk of NGC 1023 and that this ring was probably formed during a galaxy-galaxy interaction comparable to the Cartwheel galaxy. A detailed discussion of faint fuzzies in the context of merged CCs is given in Brüns et al (2009), who demonstrated that the observed structural parameters of the faint fuzzies are in excellent agreement with the merged CC scenario.…”

Section: Discussionmentioning

confidence: 89%

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

Brüns

Kroupa

Fellhauer

et al. 2011

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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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“…Recent mergers of star clusters in star cluster complexes can host a variety of substructures in the form of faint envelopes, tidal tails, and nonmerged companion GCs (e.g., Brüns et al 2011Brüns et al , 2009Fellhauer & Kroupa 2005). Whereas in some simulations of UCD-like objects the surrounding GC companions have merged into the central object within the first Gyr (Brüns et al 2011), and thus the merging process is finished.…”

Section: Spatial Correlation Of Gcs With Ucdsmentioning

confidence: 99%

“…An alternative explanation for the clustering of GCs around UCDs could be that those UCDs initially formed in a star cluster complex that then subsequently merged to create a UCD (see, e.g., Fellhauer & Kroupa 2002;Brüns et al 2009Brüns et al , 2011. Massive star cluster complexes are common in gas-rich mergers (e.g., The Antennae, Whitmore et al 1999).…”

Section: Spatial Correlation Of Ucds With Globular Clustersmentioning

confidence: 99%

Globular cluster clustering and tidal features around ultra-compact dwarf galaxies in the halo of NGC 1399

Voggel¹,

Hilker²,

Richtler³

2016

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We present a novel approach to constrain the formation channels of ultra-compact dwarf galaxies (UCDs). They most probably are an inhomogeneous class of objects, composed of remnants of tidally stripped dwarf elliptical galaxies and star clusters that occupy the high mass end of the globular cluster luminosity function. We use three methods to unravel their nature: 1) we analyzed their surface brightness profiles; 2) we carried out a direct search for tidal features around UCDs; and 3) we compared the spatial distribution of GCs and UCDs in the halo of their host galaxy. Based on FORS2 observations under excellent seeing conditions, we studied the detailed structural composition of a large sample of 97 UCDs in the halo of NGC 1399, the central galaxy of the Fornax cluster, by analyzing their surface brightness profiles. We found that 13 of the UCDs were resolved above the resolution limit of 23 pc and we derived their structural parameters fitting a single Sérsic function. When decomposing their profiles into composite King and Sérsic profiles, we find evidence for faint stellar envelopes at µ =∼ 26 mag arcsec −2 , surrounding the UCDs up to an extension of 90 pc in radius. We also show new evidence for faint asymmetric structures and tidal tail-like features surrounding several of these UCDs, a possible tracer of their origin and assembly history within their host galaxy halos. In particular, we present evidence for the first discovery of a significant tidal tail with an extension of ∼350 pc around UCD-FORS 2. Finally, we studied the local overdensities in the spatial distribution of globular clusters within the halo of NGC 1399 out to 110 kpc to see if they are related to the positions of the UCDs. We found a local overabundance of globular clusters on a scale of ≤1 kpc around UCDs, when we compared it to the distribution of globulars from the host galaxy. This effect is strongest for the metal-poor blue GCs. We discuss how likely it is that these clustered globulars were originally associated with the UCD, either as globular cluster systems of a nucleated dwarf galaxy that was stripped down to its nucleus, or as a surviving member of a merged super star cluster complex.

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Faint Fuzzy Star Clusters in NGC 1023 as Remnants of Merged Star Cluster Complexes

Cited by 24 publications

References 28 publications

A catalog of extended clusters and ultra-compact dwarf galaxies

A catalog of extended clusters and ultra-compact dwarf galaxies

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

Globular cluster clustering and tidal features around ultra-compact dwarf galaxies in the halo of NGC 1399

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