Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy

Larsen, S. S.; Forbes, Duncan A.; Brodie, Jean P.

doi:10.1046/j.1365-8711.2001.04797.x

Cited by 46 publications

(49 citation statements)

References 49 publications

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“…Outside the Local Group, EOs were detected in the spiral galaxies M 81 (Chandar et al 2004;Nantais et al 2011), M 83 (Chandar et al 2004), M 51 (Chandar et al 2004;Hwang & Lee 2008), NGC 891 (Harris et al 2009), NGC 3370 (Cantiello et al 2009), and in the Sombrero Galaxy M 104 (Larsen et al 2001;Hau et al 2009). In addition, EOs were found in the dwarf irregular and the magellanic type dwarf galaxies UGCA 86, UGC 8638, NGC 247, NGC 5237, ESO269-58, NGC 784, NGC 4605, UGC 3974, and NGC 1311 (Georgiev et al 2009), UGC 7605, KK 065, UGC 3755, KK 112, and UGC 4115 (Sharina et al 2005;van den Bergh 2006), and NGC 4449 (Strader et al 2012).…”

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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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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“…Observations at optical wavelengths have identified globular clusters and planetary nebulae in M104 (VanDalfsen et al 2001;Larsen, Forbes, & Brodie 2001;Ford et al 1996). We searched for coincidences between these catalogs and our Chandra sources.…”

Section: Source Identificationmentioning

confidence: 99%

“…There are 640 GCs identified from the ground (VanDalfsen et al 2001) in the field of view of S3. Moreover, 72 additional GCs were found by using the Hubble Space Telescope (HST; Larsen et al 2001). It is worth noting that the astrometry of the HST image (Larsen et al 2001) was not well calibrated, and we therefore corrected the astrometry by using the 2MASS catalog in our analysis.…”

Section: Source Identificationmentioning

confidence: 99%

“…Moreover, 72 additional GCs were found by using the Hubble Space Telescope (HST; Larsen et al 2001). It is worth noting that the astrometry of the HST image (Larsen et al 2001) was not well calibrated, and we therefore corrected the astrometry by using the 2MASS catalog in our analysis. In addition, we also checked the USNO-B1.0 (Monet et al 2003) and 2MASS (Cutri et al 2000) catalogs.…”

Section: Source Identificationmentioning

confidence: 99%

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X‐Ray Point Sources in the Sombrero Galaxy: Very Soft Sources, the Globular Cluster/Low‐Mass X‐Ray Binary Connection, and an Overview

Stefano¹,

Kong²,

VanDalfsen³

et al. 2003

ApJ

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We report on the population of point sources discovered during an 18.5 ks Chandra ACIS-S observation of the Sombrero galaxy. We present the luminosity function and the spectra of the six brightest sources, consider correlations with globular clusters (GCs) and with planetary nebulae, and study the galaxy's population of very soft sources. We detected 122 sources. Twenty-two sources are identified as very soft; of these, five appear to be classical luminous supersoft X-ray sources (SSSs), while 17 may belong to the slightly harder class referred to as quasi-soft (QSSs). There is an overdensity of very soft sources within 2 kpc of the nucleus, which is itself the brightest X-ray source. Very soft sources are also found in the disk and halo, with one QSS in a globular cluster (GC). This source is somewhat harder than most SSSs; the energy distribution of its photons is consistent with what is expected from an accreting intermediate-mass black hole. Several sources in the Sombrero's halo are good candidates for SSS models in which the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are associated with GCs. The majority of sources with luminosity greater than 10 38 ergs s À1 are in GCs. These results for M104, an Sa galaxy, are similar to what has been found for elliptical galaxies and for the latetype spiral M31. We find that those optically bright GCs with X-ray sources house only the brightest X-ray sources. We find that, in common with other galaxies, there appears to be a positive connection between young (metal-rich) GCs and X-ray sources but that the brightest X-ray sources are equally likely to be in metal-poor GCs. The luminosity function of X-ray sources in GCs has a cut-off near the Eddington luminosity for a 1.4 M object. We propose a model that can explain the trends seen in the data sets from the Sombrero and other galaxies. Thermal timescale mass transfer can occur in some of the younger clusters in which the turnoff mass is slightly greater than 0.8 M ; multiplicity may play a role in some of the most massive clusters; accretion from giant stars may be the dominant mechanism in some older, less massive and less centrally concentrated clusters. Key elements of the model can be tested.

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“…In such cases, visual inspection of the images and measurements of their FWHM values with the imexamine task in IRAF would generally support the ishape measurements. For a detailed description of ishape and tests of its performance, we refer to Larsen (1999) and Larsen, Forbes, & Brodie (2001).…”

Section: Data Reductionmentioning

confidence: 99%

Hubble Space Telescope Imaging of a Peculiar Stellar Complex in NGC 6946*

Larsen¹,

Efremov²,

Elmegreen³

et al. 2002

ApJ

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The stellar populations in a stellar complex in NGC 6946 are analyzed on images taken with the Wide Field Planetary Camera 2 on board the Hubble Space T elescope. The complex is peculiar because of its very high density of stars and clusters and semicircular shape. Its physical dimensions are about the same as for the local Gould Belt, but the stellar density is 1È2 orders of magnitude higher. In addition to an extremely luminous, D15 Myr old cluster discussed in an earlier paper, accounting for about 17% of the integrated V -band light, we identify 18 stellar clusters within the complex with luminosities similar to the brightest open clusters in the Milky Way. The color-magnitude diagram of individual stars in the complex shows a paucity of red supergiants compared to model predictions in the 10È20 Myr age range for a uniform star formation rate. We thus Ðnd tentative evidence for a gap in the dispersed star formation history, with a concentration of star formation into a young globular cluster during this gap. ConÐrmation of this result must, however, await a better understanding of the late evolution of stars in the corresponding mass range A reddening map based on individual reddenings for 373 early-(Z12 M _ ). type stars is presented, showing signiÐcant variations in the absorption across the complex. These may be responsible for some of the arclike structures previously identiÐed on ground-based images. We Ðnally discuss various formation scenarios for the complex and the star clusters within it.

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Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy

Cited by 46 publications

References 49 publications

A catalog of extended clusters and ultra-compact dwarf galaxies

A catalog of extended clusters and ultra-compact dwarf galaxies

X‐Ray Point Sources in the Sombrero Galaxy: Very Soft Sources, the Globular Cluster/Low‐Mass X‐Ray Binary Connection, and an Overview

Hubble Space Telescope Imaging of a Peculiar Stellar Complex in NGC 6946*

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