An optical/NIR survey of globular clusters in early-type galaxies

Chies-Santos, Ana L.; Larsen, S. S.; Wehner, E. M.; Küntschner, H.; Strader, Jay; Brodie, Jean P.

doi:10.1051/0004-6361/201015681

Cited by 22 publications

(26 citation statements)

References 86 publications

(127 reference statements)

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“…The accuracy of the LIRIS K-band photometric calibration is estimated to be ∼0.03−0.05 mag -(see Sect. 3.2 of Chies- Santos et al 2011). There are cases where the mean δ reaches values as large as three times the values of the uncertainty on the photometric calibration.…”

Section: Relative Comparison Without Ssp Modelsmentioning

confidence: 97%

“…One might think that the relation shown in Fig. 12 might be an artefact of our sky subtraction method through ellipse model fits (see Chies-Santos et al 2011). Even though the direction the morphology becomes more complicated is the same direction the ellipse model fits became more difficult, Fig.…”

Section: Investigating Effects Other Than Age and Metallicity In The mentioning

confidence: 98%

“…Because the photometric errors are dominated by the K-band photometry, the scatter in (g − K) will be very nearly proportional to the scatter in δ if photometric errors are the only cause of offsets from the line defining the δ parameter. It is immediately seen that the scatter varies among different systems and that in most cases it is larger than the 1σ of ∼±0.4 permitted (Chies- Santos et al 2011) from observational uncertainties. Analogously the scatter of δ blue and δ red along (g − K) as function of galaxy morphology are shown in the middle and in the bottom panels respectively.…”

Section: Investigating Effects Other Than Age and Metallicity In The mentioning

confidence: 98%

“…The homogeneous survey of extragalactic GCs that we carried out with optical and NIR photometry was presented in Chies- Santos et al (2011). In the same article the data reduction techniques were described in detail, and we will only briefly mention them here.…”

Section: Observations and Datamentioning

confidence: 99%

“…Puzia et al 2004). We note that a careful visual inspection was performed removing obvious background galaxies and blends (see Chies-Santos et al 2011). There could still be some contaminants left, but only spectroscopic analysis of such objects would give clearer answers.…”

Section: Blue and Red Peak Agesmentioning

confidence: 99%

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An optical/NIR survey of globular clusters in early-type galaxies

Chies-Santos

Larsen

Küntschner

et al. 2010

A&A

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Context. Some photometric studies of extragalactic globular cluster (GC) systems using the optical and near-infrared colour combination have suggested the presence of a large fraction of intermediate-age (2−8 Gyr) GCs. Aims. We investigate the age distributions of GC systems in 14 E/S0 galaxies. Methods. We carried out a differential comparison of the (g − z) vs. (g − K) two-colour diagrams for GC systems in the different galaxies in order to see whether there are any indications of age differences. We also compared the different GC systems with a few simple stellar population models. Results. No significant difference is detected in the mean ages of GCs among elliptical galaxies. S0 galaxies, on the other hand, show evidence for younger GCs. Surprisingly, this appears to be driven by the more metal-poor clusters. The age distribution of GCs in NGC 4365 seems to be similar to that of other large ellipticals (e.g. NGC 4486, NGC 4649). Padova SSPs with recently released isochrones for old ages (14 Gyr) show less of an offset with respect to the photometry than previously published models. Conclusions. We suggest that E type galaxies assembled most of their GCs in a shorter and earlier period than S0 type galaxies. The latter galaxy type seems to have a more extended period of GC formation/assembly.

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Section: Relative Comparison Without Ssp Modelsmentioning

confidence: 97%

Section: Investigating Effects Other Than Age and Metallicity In The mentioning

confidence: 98%

Section: Investigating Effects Other Than Age and Metallicity In The mentioning

confidence: 98%

Section: Observations and Datamentioning

confidence: 99%

Section: Blue and Red Peak Agesmentioning

confidence: 99%

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An optical/NIR survey of globular clusters in early-type galaxies

Chies-Santos

Larsen

Küntschner

et al. 2010

A&A

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An optical/NIR survey of globular clusters in early-type galaxies

Chies-Santos

Larsen

Cantiello

et al. 2012

A&A

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Context. The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused for example by the horizontal branch (HB) stars may be responsible for transforming a unimodal metallicity distribution into a bimodal (optical) colour distribution. Aims. We study optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0 galaxies. Methods. We test whether the bimodal feature, generally present in optical colour distributions, remains in the optical/NIR ones. The latter colour combination is a better metallicity proxy than the former. We use KMM and GMM tests to quantify the probability that different colour distributions are better described by a bimodal, as opposed to a unimodal distribution. Results. We find that double-peaked colour distributions are more commonly seen in optical than in optical/NIR colours. For some of the galaxies where the optical (g − z) distribution is clearly bimodal, a bimodal distribution is not preferred over a unimodal one at a statistically significant level for the (g − K) and (z − K) distributions. The two most cluster-rich galaxies in our sample, NGC 4486 and NGC 4649, show some interesting differences. The (g − K) distribution of NGC 4649 is better described by a bimodal distribution, while this is true for the (g − K) distribution of NGC 4486 GCs only if restricted to a brighter sub-sample with small K-band errors (<0.05 mag). Formally, the K-band photometric errors cannot be responsible for blurring bimodal metallicity distributions to unimodal (g − K) colour distributions. However, simulations including the extra scatter in the colour-colour diagrams (not fully accounted for in the photometric errors) show that such scatter may contribute to the disappearance of bimodality in (g − K) for the full NGC 4486 sample. For the less cluster-rich galaxies results are inconclusive due to poorer statistics. Conclusions. A bimodal optical colour distribution is not necessarily an indication of an underlying bimodal metallicity distribution. Horizontal branch morphology may play an important role in shaping some of the optical GC colour distributions. However, we find tentative evidence that the (g − K) colour distributions remain bimodal in the two cluster-rich galaxies in our sample (NGC 4486 and NGC 4649) when restricted to clusters with small K-band photometric errors. This bimodality becomes less pronounced when including objects with larger errors, or for the (z − K) colour distributions. Deeper observations of large numbers of GCs will be required to reach more secure conclusions.

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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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An optical/NIR survey of globular clusters in early-type galaxies

Cited by 22 publications

References 86 publications

An optical/NIR survey of globular clusters in early-type galaxies

An optical/NIR survey of globular clusters in early-type galaxies

An optical/NIR survey of globular clusters in early-type galaxies

A catalog of extended clusters and ultra-compact dwarf galaxies

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