2009A&A...500..785K


C.D.S. - SIMBAD4 rel 1.7 - 2019.11.18CET16:28:15

2009A&A...500..785K - Astronomy and Astrophysics, volume 500, 785-799 (2009/6-3)

Dissolution is the solution: on the reduced mass-to-light ratios of galactic globular clusters.

KRUIJSSEN J.M.D. and MIESKE S.

Abstract (from CDS):

The observed dynamical mass-to-light (M/L) ratios of globular clusters (GCs) are systematically lower than the value expected from ``canonical'' simple stellar population models, which do not account for dynamical effects such as the preferential loss of low-mass stars due to energy equipartition. It has recently been shown that low-mass star depletion can qualitatively explain this discrepancy for globular clusters in several galaxies. To verify whether low-mass star depletion is indeed the driving mechanism behind the M/L decrease, we aim to predict the M/LV ratios of individual GCs for which orbital parameters and dynamical V-band mass-to-light ratios M/LV are known. There is a sample of 24 Galactic GCs for which this is possible. We used the SPACE cluster models, which include dynamical dissolution, low-mass star depletion, stellar evolution, stellar remnants, and various metallicities. We derived the dissolution timescales due to two-body relaxation and disc shocking from the orbital parameters of our GC sample and used these to predict the M/LV ratios of the individual GCs. To verify our findings, we also predicted the slopes of their low-mass stellar mass functions. The computed dissolution timescales agree well with earlier empirical studies. The predicted M/LV are in 1σ agreement with the observations for 12 out of 24 GCs. The discrepancy for the other GCs probably arises because our predictions give global M/L ratios, while the observations represent extrapolated central values that are different from global ones in the case of mass segregation and a long dissolution timescale. The GCs in our sample that likely have dissimilar global and central M/L ratios can be excluded by imposing limits on the dissolution timescale and King parameter. For the remaining GCs, the observed and predicted average M/LV are 78+9–11% and 78±2% of the canonically expected values, while the values are 74+6–7% and 85±1% for the entire sample. The predicted correlation between the slope of the low-mass stellar mass function and M/LV drop is found to be qualitatively consistent with observed mass function slopes. The dissolution timescales of Galactic GCs are such that the ∼20% gap between canonically expected and observed M/LV ratios is bridged by accounting for the preferential loss of low-mass stars, also when considering individual clusters. It is concluded that the variation in M/L ratio due to dissolution and low-mass star depletion is a plausible explanation for the discrepancy between the observed and canonically expected M/L ratios of GCs.

Abstract Copyright:

Journal keyword(s): Galaxy: globular clusters: general - Galaxy: stellar content - galaxies: star clusters

CDS comments: Paragraph. 6.3 NGC 2808 is a probable misprint for NGC 288.

Simbad objects: 24

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Number of rows : 24

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3472 0
2 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 890 0
3 NGC 1851 GlC 05 14 06.76 -40 02 47.6   8.80 7.23     ~ 1209 0
4 M 79 GlC 05 24 10.59 -24 31 27.3   9.21 8.16     ~ 693 0
5 NGC 4147 GlC 12 10 06.149 +18 32 31.78   11.45 10.74     ~ 482 0
6 M 68 GlC 12 39 27.98 -26 44 38.6   10.26 7.96     ~ 856 0
7 NGC 5139 GlC 13 26 47.28 -47 28 46.1   6.12 5.33     ~ 2920 0
8 M 3 GlC 13 42 11.62 +28 22 38.2     6.39     ~ 2225 0
9 NGC 5466 GlC 14 05 27.29 +28 32 04.0   10.5 9.70     ~ 699 0
10 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1725 0
11 M 80 GlC 16 17 02.41 -22 58 33.9           ~ 595 0
12 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1636 0
13 M 107 GlC 16 32 31.86 -13 03 13.6   9.96 8.85     ~ 681 0
14 M 13 GlC 16 41 41.634 +36 27 40.75     5.8     ~ 1970 0
15 M 12 GlC 16 47 14.18 -01 56 54.7   8.52 6.07     ~ 557 0
16 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 654 0
17 M 92 GlC 17 17 07.39 +43 08 09.4     6.52     ~ 1870 0
18 NGC 6362 GlC 17 31 54.99 -67 02 54.0   9.72 8.86     ~ 462 0
19 M 22 GlC 18 36 23.94 -23 54 17.1   7.16 6.17     ~ 1177 0
20 NGC 6712 GlC 18 53 04.32 -08 42 21.5   9.85 8.69     ~ 458 0
21 M 56 GlC 19 16 35.57 +30 11 00.5   8.90       ~ 346 0
22 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 734 0
23 NGC 6934 GlC 20 34 11.37 +07 24 16.1   10.48 9.75     ~ 347 0
24 M 2 GlC 21 33 27.02 -00 49 23.7     6.25     ~ 861 1

    Equat.    Gal    SGal    Ecl

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2019.11.18-16:28:15

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