Vladimir Marsakov Publication List

2000, in Stellar dynamics: from classic to modern. Int.Conf. - Saint Petersburg, August, 2000.

A catalogue of homogeneous fundamental astrophysical parameters for 145 globular clusters is composed on the base of the data of compilative catalogue by Harris (1997) and from another literature. The connections between chemical compositions, horizontal branch morphology, space position, orbit elements, ages, and other physical parameters of globular clusters are investigated based on this catalogue. It is shown that all population of globular clusters is divided by the gap on their metallicity function at [Fe/H]=-1.0 dex into two discrete groups with distinct peaks at [Fe/H]=-1.60±0.03 dex, and -0.60±0.04 dex. Simultaneously, the mean values and dispersions of space-kinematical parameters are changed sharply by crossing the border quantity of metallicity. So it turns out that the metal poor clusters occupy approximately spherical volume and has appreciable concentration to the galactic center. The population of metal rich globular clusters (thick disk subsystem) has size less than metal poor one, and concentrates not only to the galactic center but to the galactic plane too. It has considerable rotation velocity (V_rot=165±28 km/s), great negative vertical metallicity gradient with infinitesimal radial metallicity gradient, the smallest mean age, and consists of clusters with extremely red horizontal branch only. The by Zinn (1993) effect that population of spherical subsystem is also non uniform and it is divided on two discrete groups by horizontal branch morphology is confirmed. The subsystem of globular clusters with extremely blue horizontal branches occupies spherical volume with radius approximately equals 9 kpc. In addition, it has large rotation velocity (V_rot=77±33 km/s), appreciable radial and vertical metallicity gradients equal by value, and has the oldest average age (subsystem of the old halo). The population of clusters with intermediate type of horizontal branches occupies the volume close to spherical form with radius (for overwhelming majority) rovn;

18 kpc and slightly flattened along the axis perpendicular to Z and directed at the angle 30^O along X-coordinate, is some younger in comparison with the old halo clusters (subsystem of young halo) in average. It has values of the metallicity gradients, coinciding with ones in the old halo, so as a result the metallicity of the younger halo clusters are systematically greater by delt;

[Fe/H]

0.3 dex for the same galactocentric radius and distance from the galactic plane. The subsystem of the young halo, consisting, most likely, of the clusters captured by the Galaxy at different periods, contains a large number of clusters with retrograde orbits therefore its rotational velocity is small, and its value is calculated with large uncertainty (-23±54 km/s). The characteristic parameters of all separated subsystems and the weighted mean parameters of globular clusters included in it are determined. Reasons stand for the different nature of the thick disk and the old halo clusters on the one hand, and the young halo - on the other, are given. The scenario of the Galactic evolution is suggested, supposing that only clusters of the first two subsystems are genetically connected with the Galaxy. We found that old halo globular clusters have the ages distribution with dispersion equal to the uncertainty of age determination whereas the thick disk clusters show the real age spread. There is an age gap between thick disk and old halo samples. We found the statistically significant correlation of cluster ages with the metallicity, the distance from the galactic plane, and galactocentric distance for whole the Galaxy. However, no convincing evidence was found for the same relationships in each subsystem separately. It is declared that the process of enrichment of interstellar matter by heavy elements and its collaps were occurred mainly during the period between formation of the old halo and thick disk subsystems.

Characteristic parameter of globular cluster subsystems.

Parameters	Thinck disk	Old halo	Young halo
<[Fe/H]>	-0.56±0.05	-1.71±0.05	-1.56±0.07
_[Fe/H]	0.28±0.03	0.26±0.03	0.38±0.05
<(B-R)/(B+V+R)>	-0.95±0.03	0.95±0/01	0.06±0.10
X₀, kpc	3.0±0.5	3.5±1.0	7.0±3.0
Y₀, kpc	2.0±0.5	2.5±0.5	6.5±1.5
Z₀, kpc	1.0±0.2	2.5±0.5	8.5±1.5
<\|V_r\|>, km/s	72±9	113±15	144±23
<R_a>, kpc	7±0	12±3	24±5
<e>	0.13±0.04	0.53±0.06	0.59±0.06
V_rec, km/s	165±38	77±33	-23±54
_V, km/s	88±15	129±19	140±18
d([Fe/H])/dR	0.01±0.02	-0.03±0.02	-0.04±0.01
d([Fe/H])/d\|Z\|	0.16±0.06	-0.03±0.03	-0.03±0.01
<r^*_h>, pc	2.6±0.3	3.4±0.3	4.0±0.4
<lg(M/M)>	5.2±0.1	5.4±0.1	5.5±0.1
<t>, Gyr	12.5±0.5	15.5±0.5	14.1±0.3
<C>	1.7±0.1	1.6±0.1	1.5±0.1
<log(₀>	3.5±0.7	3.8±0.3	3.2±0.3

Inspection of calculated properties of globular clusters brings us to the following scenario for early history of the Milky Way Galaxy. The first globular clusters was formed when protogalactic cloud collapsed already up to modern sizes rovn;

12 kpc. (Here, however, it is remains indefinite the question of belonging slightly reddened most metal-poor old globular clusters, to the old halo - which lies on galactocentric distance 15÷25 kpc.) The old halo subsystem was formed for a short period of time, so we are not able to reveal a changing with an age neither sizes, nor metallicity in this subsystem. Existence of radial and vertical metallicity gradients inside of this mostly old galactic subsystem evidences that most probably the first acts of the enrichment of the proto-galaxy by heavy elements had occurred before the formation of the clusters of this subsystem else. Moreover an activity of these processes was stronger nearer the galactic center. (Notice that clusters save orbits of parent protoclouds. In particular, the existence of great number of sufficiently old and simultaneously very distant young halo clusters points absence of relaxation processes in the Galaxy.) Spatial and chemical characteristics of globular clusters are suddenly changed when turning to the thick disk subsystem. Probably it was sufficiently long delay between formation of these subsystems. Delay had allowed the gaseous protogalactic cloud greatly enriched by heavy elements and had time to mix up them and cloud contracted up to vastly smaller size. As a result it was formed rather flat, metal-rich thick disk subsystem. Thick disk rotates faster, than old halo, and its line-of-site velocity dispersion is less. Neither mean metallicity, nor thickness of thick disk did not change with a time. Star formation in protoclusters of this subsystem has began on the most distant galactocentric distances. Then process become to spread to the galactic center. Significant contraction of the protodisk cloud after formation of the halo subsystem led to increasing of rotation velocity and hence to quick flattening of it. Interstellar matter herewith, probably, was not deeply mixed, as far as under the full absence of the radial metallicity gradient in the thick disk we observe strong negative vertical metallicity gradient in it. In other words, performed analysis shows that quick contraction of gaseous matter to the galactic plane with simultaneous enrichment by heavy elements and partial homogenization of it had occurred basically for a period between the formation end of the old halo and the beginning of the thick disk formation. Presented scenario requires further revision as far as modern quality observation data does not allow to advance deeper into understanding of the processes, occurred inside each globular clusters subsystems of the Galaxy for a period of its formation.