2005A&A...439..997P


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.02CET13:08:08

2005A&A...439..997P - Astronomy and Astrophysics, volume 439, 997-1011 (2005/9-1)

VLT spectroscopy of globular cluster systems. II. Spectroscopic ages, metallicities, and [α/Fe] ratios of globular clusters in early-type galaxies.

PUZIA T.H., KISSLER-PATIG M., THOMAS D., MARASTON C., SAGLIA R.P., BENDER R., GOUDFROOIJ P. and HEMPEL M.

Abstract (from CDS):

An analysis of ages, metallicities, and [α/Fe] ratios of globular cluster systems in early-type galaxies is presented, based on Lick index measurements summarized in Puzia et al. (2004A&A...415..123P, Paper I of this series). In the light of calibration and measurement uncertainties, age-metallicity degeneracy, and the relative dynamic range of Lick indices, as well as systematics introduced by abundance ratio variations (in particular variations of [α/Fe] ratios), we find that the most reliable age indicator for our dataset is a combination of the Lick Balmer-line indices HγA, Hβ, and HδA. [MgFe]' is used as a spectroscopic metallicity indicator which is least affected by [α/Fe] variations. We introduce an interpolation routine to simultaneously derive ages, metallicities, and [α/Fe] ratios from diagnostic grids constructed from Lick indices. From a comparison of high-quality data with SSP model predictions, we find that ∼2/3 of the globular clusters in early-type galaxies are older than 10Gyr, up to 1/3 have ages in the range ∼5-10Gyr, and only a few cluster are younger than ∼5Gyr. Our sample of globular clusters covers metallicities from [Z/H]≃-1.3 up to ∼0.5dex. We find that metal-rich globular clusters show on average a smaller mean age and a larger age scatter than their metal-poor counterparts. [α/Fe] diagnostic plots show that globular cluster systems in early-type galaxies have super-solar α/Fe abundance ratios with a mean [α/Fe]=0.47±0.06dex and a dispersion of ∼0.3dex. We find evidence for a correlation between [α/Fe] and metallicity, in the sense that more metal-rich clusters exhibit lower α-element enhancements. A discussion of systematics related to the Lick index system shows that the method suffers to some extent from uncertainties due to unknown horizontal branch morphologies at high metallicities. However, these systematics still allow us to make good qualitative statements. A detailed investigation of indices as a function of data quality reveals that the scatter in Balmer index values decreases for higher-quality data. In particular, extremely low Balmer index values that are lower than any SSP model prediction tend to disappear. Furthermore, we find that observed photometric colors are in good agreement with computed SSP colors using ages and metallicities as derived from the spectroscopic line indices.

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Journal keyword(s): galaxies: star clusters - galaxies: general

Simbad objects: 19

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Number of rows : 19

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 M 32 IG 00 42 41.825 +40 51 54.61 9.51 9.03 8.08     ~ 2034 2
2 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 11209 1
3 NGC 1380 GiP 03 36 27.590 -34 58 34.68 11.32 10.94 9.93 9.37   ~ 382 1
4 NGC 1399 BiC 03 38 29.083 -35 27 02.67 11.05 9.74 9.59 8.12   ~ 1473 1
5 NGC 2434 GiG 07 34 51.1487209121 -69 17 03.008825858 12.82 12.50 11.26 10.84   ~ 177 1
6 NGC 3115 GiG 10 05 13.978 -07 43 06.89   11   9.37   ~ 943 2
7 M 105 LIN 10 47 49.600 +12 34 53.87   10.56 9.76 9.12 8.18 ~ 1392 0
8 NGC 3585 GiG 11 13 17.109 -26 45 17.96   10.64   9.22   ~ 267 0
9 M 49 Sy2 12 29 46.798 +08 00 01.48   13.21 12.17     ~ 1985 2
10 M 87 BiC 12 30 49.42338230 +12 23 28.0438581 10.16 9.59 8.63   7.49 ~ 6351 3
11 M 104 LIN 12 39 59.43185 -11 37 22.9954 9.51 9.55 8.00 8.05   ~ 1295 3
12 NAME Centaurus A Sy2 13 25 27.61509104 -43 01 08.8056025   8.18 6.84 6.66   ~ 4076 3
13 NGC 5846 BiC 15 06 29.253 +01 36 20.29   11.9   9.74   ~ 786 1
14 NGC 6284 GlC 17 04 28.747 -24 45 51.22   10.72 7.43     ~ 245 0
15 NGC 6356 GlC 17 23 34.99 -17 48 46.9   10.01 7.42     ~ 324 1
16 NGC 6388 GlC 17 36 17.461 -44 44 08.34   7.40       ~ 827 1
17 NGC 6441 GlC 17 50 13.06 -37 03 05.2   9.26 8.00     ~ 788 0
18 M 69 GlC 18 31 23.10 -32 20 53.1   9.32 8.31     ~ 416 1
19 NGC 7192 GiG 22 06 50.178 -64 18 58.38   12.21 11.21 10.77   ~ 135 0

    Equat.    Gal    SGal    Ecl

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2021.03.02-13:08:08

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