SAO RAS 6-m telescope spectroscopic observations of globular clusters in nearby galaxies

Шарина, М. Е.; Chandar, Rupali; Puzia, Thomas H.; Goudfrooij, Paul; Davoust, E.

doi:10.1111/j.1365-2966.2010.16510.x

Cited by 25 publications

(41 citation statements)

References 123 publications

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“…Similar differences have also been observed for dwarf galaxies (e.g. Beasley et al 2008;Mackey & Gilmore 2004;Sharina et al 2010) 1 . The most extreme example was found in the Fornax dSph where the stars have a broad metallicity distribution with −2.5 < [M/H] < −0.2 with a peak at [M/H] = −1.0 while the globular clusters are all metal-poor with −2.6 < [M/H] < −1.4 (Larsen et al 2012b).…”

Section: Introductionsupporting

confidence: 84%

“…Globular clusters in dwarf galaxies are in general very metalpoor, mostly even more metal-poor than the peak metallicity of the dwarf's stellar MDF (e.g. Mackey & Gilmore (2004); Sharina et al (2010)). The Fornax dSph, for example, contains four GCs with [M/H] ∼ −2.5 to -1.9 and one more metalrich GC at [M/H] ∼ −1.5 dex, whereas its stellar MDF peaks at [M/H] ∼ −1.0 with a long tail towards lower metallicities (Strader et al 2003;Helmi et al 2006;Larsen et al 2012b).…”

Section: The Mdf Of Globular Clusters In Dwarf Galaxiesmentioning

confidence: 99%

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The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type

Lamers

Kruijssen

Bastian

et al. 2017

A&A

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Context. Observations of globular clusters (GCs) and field stars in the halos of the giant elliptical galaxy Cen A and the spiral galaxy M31 show a large range of cluster-to-star number ratios (or 'specific frequencies'). The cluster-to-star ratio decreases with increasing metallicity by over a factor of 100-1000, at all galactocentric radii and with a slope that does not seem to depend on radius. In dwarf galaxies, the GCs are also more metal-poor than the field stars on average. These observations indicate a strong dependence of either the cluster formation efficiency and/or the cluster destruction rate on metallicity and environment. Aims. We aim to explain the observed trends by considering the various effects that influence the cluster-to-star ratio as a function of metallicity, environment and cosmological history. Methods. We discuss the following effects that may influence the observed cluster-to-star ratio: (a) the formation efficiency of GCs; (b) the destruction of embedded GCs by gas expulsion; (c) the maximum masses of GCs; (d) the destruction of GCs by tidal stripping, dynamical friction, and tidal shocks as a function of environment; (e) the hierarchical assembly of GC systems during galaxy formation and the dependence on metallicity. Results. We show that both the cluster formation efficiency and the maximum cluster mass increase with metallicity, so they cannot explain the observed trend. Destruction of GCs by tidal stripping and dynamical friction destroy clusters mostly within the inner few kpc, whereas the cluster-to-star ratio trend is observed over a much larger range of galactocentric radii. We show that cluster destruction by tidal shocks from giant molecular clouds in the high-density formation environments of GCs becomes increasingly efficient towards high galaxy masses and, hence, towards high metallicities. The predicted cluster-to-star ratio decreases by a factor 100-1000 towards high metallicities and should only weakly depend on galactocentric radius due to orbital mixing during hierarchical galaxy merging, consistent with the observations. Conclusions. The observed, strong dependence of the cluster-to-star ratio on metallicity and the independence of its slope on galactocentric radius can be explained by cluster destruction and hierarchical galaxy growth. During galaxy assembly, GC metallicities remain a good tracer of the host galaxy masses in which the GCs formed and experienced most of their destruction. As a result, we find that the metallicity-dependence of the cluster-to-star ratio does not reflect a GC formation efficiency, but a survival fraction.

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Section: Introductionsupporting

confidence: 84%

Section: The Mdf Of Globular Clusters In Dwarf Galaxiesmentioning

confidence: 99%

The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type

Lamers

Kruijssen

Bastian

et al. 2017

A&A

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“…For U49, our metallicity determination agrees with the previous spectroscopic metallicity estimate by Brodie & Huchra (1991) within the (large) uncertainty on their measurement. For R12, our new metallicity is 0.22 dex lower than the spectroscopic estimate of [Fe/H] = −0.73 ± 0.01 of Sharina et al (2010), although the 0.01 dex uncertainty on that measurement appears somewhat optimistic (the same paper quotes an overall metallicity of [Z/H] = −0.6 ± 0.2). Our measurements generally agree with those based on the RGB slope from Sarajedini et al (1998), within the 0.1-0.3 dex uncertainties on those estimates.…”

Section: Metallicities: Comparisons With Previous Workcontrasting

confidence: 54%

Detailed abundance analysis of globular clusters in the Local Group

Larsen

Brodie

Wasserman

et al. 2018

A&A

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Context. Globular clusters (GCs) are emerging as powerful tracers of the chemical composition of extragalactic stellar populations. Aims. We present new abundance measurements for eleven GCs in the Local Group galaxies NGC 147, NGC 6822, and Messier 33. These are combined with previously published observations of four GCs in the Fornax and WLM galaxies. Methods. The abundances were determined from analysis of integrated-light spectra, obtained with the HIRES spectrograph on the Keck I telescope and with UVES on the VLT. We used our analysis technique that has been developed for this purpose and tested on Milky Way GCs. Results. We find that the clusters with [Fe/H] < −1.5 are all α-enhanced at about the same level as Milky Way GCs. Their Na abundances are also generally enhanced relative to Milky Way halo stars, suggesting that these extragalactic GCs resemble their Milky Way counterparts in containing significant fractions of Na-rich stars. For [Fe/H] > −1.5, the GCs in M33 are also α-enhanced, while the GCs that belong to dwarfs (NGC 6822 SC7 and Fornax 4) have closer to Solar-scaled α-element abundances. The abundance patterns in SC7 are remarkably similar to those in the Galactic GC Ruprecht 106, including significantly sub-solar [Na/Fe] and [Ni/Fe] ratios. In NGC 147, the GCs with [Fe/H] < −2.0 account for about 6% of the total luminosity of stars in the same metallicity range, a lower fraction than those previously found in the Fornax and WLM galaxies, but substantially higher than in the Milky Way halo. Conclusions. At low metallicities, the abundance patterns suggest that GCs in the Milky Way, dwarf galaxies, and M33 experienced similar enrichment histories and/or processes. At higher metallicities, the lower levels of α-enhancement in the GCs found in dwarf galaxies resemble the abundance patterns observed in field stars in nearby dwarfs. Constraining the presence of multiple populations in the GCs is complicated by the lack of information about detailed abundances in field stars of the corresponding metallicities. We suggest that correlations such as [Na/Fe] vs. [Ni/Fe] may prove useful for this purpose if an accuracy of ∼ 0.1 dex or better can be reached for the integrated-light measurements.

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“…Puzia et al (2005) finds an [α/Fe] ∼ +0.4 for their sample of extragalactic GCs. In the recent study of Sharina et al (2010) it is found that the [α/Fe] ratios of GCs tend to be higher on average for giants than for dwarf galaxies. If a gE has recently accreted nearby dwarfs with its GCs, they should have therefore lower [α/Fe] ratios than the GCs formed within the protogalaxy.…”

Section: α-Enhanced Vs Solar-scaled Tracksmentioning

confidence: 99%

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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SAO RAS 6-m telescope spectroscopic observations of globular clusters in nearby galaxies

Cited by 25 publications

References 123 publications

The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type

The difference in metallicity distribution functions of halo stars and globular clusters as a function of galaxy type

Detailed abundance analysis of globular clusters in the Local Group

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

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