Global Mass Function Research Articles

The assembly of matter in galaxy clusters

We study the merging history of dark matter haloes that end up in rich clusters, using N-body simulations of a scale-free universe. We compare the predictions of the extended Press & Schechter (PS) formalism (Bond et al. 1991; Bower 1991; Lacey & Cole 1993) with several conditional statistics of the proto-cluster matter: the mass distribution and relative abundance of progenitor haloes at different redshifts, the infall rate of progenitors within the proto-cluster, the formation redshift of the most massive cluster progenitor, and the accretion rates of other haloes onto it. The high quality of our simulations allows an unprecedented resolution in the mass range of the studied distributions. We also present the global mass function for the same cosmological model. We find that the PS formalism and its extensions cannot simultaneously describe the global evolution of clustering and its evolution in a proto-cluster environment. The best-fit PS model for the global mass function is a poor fit to the statistics of cluster progenitors. This discrepancy is in the sense of underpredicting the number of high-mass progenitors at high redshift. Although the PS formalism can provide a good qualitative description of the global evolution of hierarchical clustering, particular attention is needed when applying the theory to the mass distribution of progenitor objects at high redshift.

Palomar 1: Another Young Galactic Halo Globular Cluster?

?????Deep V and I CCD images of the loosely populated Galactic globular cluster Pal 1 and the surrounding field have been obtained with the Isaac Newton Telescope. A color-magnitude diagram (CMD) down to Vlim ~ 24 and a luminosity function down to Vlim = 23.25 have been constructed. Adopting a reddening E(V - I) = 0.20 ? 0.04 and comparing the CMD of Pal 1 with that of 47 Tucanae, we obtain a distance modulus (m - M)0 = 15.25 ? 0.25, indicating that Pal 1 is located 3.7 ? 0.4 kpc above the Galactic disc and 17.3 ? 1.6 kpc from the Galactic center. Comparison with 47 Tuc and M71 shows that Pal 1 must be significantly younger. The best-fitting isochrones, as listed by Bertelli et al., yield an age between 6.3 and 8 Gyr, which would make Pal 1 the youngest Galactic globular cluster identified thus far, casting some doubt on the real nature of this object. The luminosity function shows some evidence of mass segregation, consistent with the very short relaxation time. The global mass function can be fitted with a power law of slope x = -1.4 ? 0.7. This mass function is anomalously flat, suggesting either a strong dynamical evolution or an initial mass function significantly different from most other halo globular clusters. A discussion of the possible nature of Pal 1 is presented.

On the effects of dynamical evolution on the initial mass function of globular clusters

In this paper we show the results of a large set of N-body simulations modelling the evolution of globular clusters driven by relaxation,stellar evolution,disk shocking and including the effects of the tidal field of the Galaxy. We investigate the evolution of multi-mass models with a power-law initial mass function (IMF) starting with different initial masses, concentrations, slopes of the IMF and located at different galactocentric distances. We show to what extent the effects of the various evolutionary processes alter the shape of the IMF and to what extent these changes depend on the position of the cluster in the Galaxy. Both the changes in the global mass function and in the local one (measured at different distances from the cluster center) are investigated showing whether and where the local mass function keeps memory of the IMF and where it provides a good indication of the current global mass function. The evolution of the population of white dwarfs is also followed in detail and we supply an estimate of the fraction of the current value of the total mass expected to be in white dwarfs depending on the main initial conditions for the cluster (mass and position in the Galaxy).Simple analytical expression by which it is possible to calculate the main quantities of interest (total mass, fraction of white dwarfs, slope of the mass function) at any time t for a larger number of different initial conditions than those investigated numerically have been derived.

Effect of prolonged inotropic stimulation on ventricular remodeling during healing after myocardial infarction in the dog: Mechanistic insights

Objectives. We hypothesized that positive inotropic stimulation during healing after myocardial infarction might increase contractile pull on the infarct segment, increase expansion and promote ventricular dilation.Background. The effect of prolonged inotropic stimulation on left ventricular remodeling during healing after myocardial infarction has not been studied.Methods. The effects of 6 weeks of inotropic stimulation on in vivo changes in left ventricular topography, function and mass (serial two-dimensional echocardiograms), hemodynamic variables, postmortem topography (planimetry) and collagen (hydroxyproline content) were studied in 36 chronically instrumented dogs randomized, 2 days after small anterior infarction, to digoxin (0.125 mg daily) and no digoxin (control group).Results. Heart rate and arterial and left atrial pressures were similar in the two groups, but the first derivative of left ventricular pressure (peak dP/dt), systolic thickening of the noninfarct wall and systolic thinning of the infarct wall were higher in the digoxin group during the 6 weeks. At 6 weeks, infarct scar size and collagen content were similar in both groups, but the digoxin group had more infarct expansion and thinning. Between 2 days and 6 weeks, the digoxin group showed more in vivo diastolic infarct expansion, thinning and bulging; more aneurysm but less global dilation and increase in mass; and no change in ejection fraction. The effects of inotropic stimulation on remodeling were more marked in infarcts with 100% than 85% transmurality.Conclusions. Prolonged inotropic stimulation with digoxin during healing after small anterior infarction increases infarct bulging without decreasing infarct collagen content and preserves global ventricular size, mass and systolic function.

Evaporation of stars from isolated, truncated globular clusters

We have analyzed the escape rate of stars from model clusters versus the concentration and the global mass function. We performed a detailed calculation of the number of stars escaping throughout the model cluster taking into account the variation in the potential and the stellar number density, and accumulating the escapes from progressively larger radii. For single- and multi-mass models we find that the fraction of stars evaporating per half-mass relaxation time decreases with increasing concentration until c∼1.5, after which it increases. For multi-mass clusters the escape rate of low-mass stars is significantly higher than the escape rate of high-mass stars

Young stars between the Magellanic Clouds. III - Overall properties of associations: A shallow mass function

We present CCD B, V photometry of three more groups of blue stars located in the bridge of the Magellanic Clouds (MC). Two associations near the SMC Wing tip are members of large complexes of blue stars. The other one, located at equal angular distance between the SMC and the LMC, is isolated. ZAMS fittings yield distances to the Sun that are intermediate between the ones of the LMC and the SMC. We find that the stellar bridge has a large line-of-sight depth near the eastern tip of the SMC Wing. A difference in distance modulus of 12 +/- 8 kpc is observed for two associations separated by only 17 arcmin. Isochrone fittings revealed that the inter-Cloud associations are as young as 16 million years. The global mass function of the associations is much flatter than the one obtained by Mateo [ApJ, 331, 261(1988)] for MC's clusters. These associations are characterized by an IMF slope x = 1.3+/-0.1 [Ξ(M) is proportional to (M)^-(1+x)^] for masses in the 1.5-12 M_sun_ range. We also confirm that there is no halo population in the Magellanic Bridge, eastwards of the SMC Wing tip; the halos of the Magellanic Clouds do not touch each other.

Mass segregation in the globular cluster M30

view Abstract Citations (75) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass Segregation in the Globular Cluster M30 Bolte, Michael Abstract The main-sequence LFs are derived for three fields at different radial distances from the center of the globular cluster M30. It is found that the LFs become flatter with decreasing radius. The observed radial dependence of the slope of the LF is compared with the predictions of mass segregation from the multi-mass component King (1966) models computed by Pryor et al. (1986). The models are shown to be consistent within the errors with an equipartition model with a global mass function slope of x = 0.9, confirming the validity of the mass segregation corrections of Pryor et al. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167481 Bibcode: 1989ApJ...341..168B Keywords: Globular Clusters; Stellar Luminosity; Astronomical Photometry; Charge Coupled Devices; Astrophysics; CLUSTERS: GLOBULAR; LUMINOSITY FUNCTION; STARS: STELLAR DYNAMICS full text sources ADS | data products SIMBAD (1)

Global Versus Local Mass Functions

Multimass dynamical models are used to study the difference between a mass function determined in an outer field and the global mass function of the cluster. The differences are small.

Dynamical studies of globular clusters based on photoelectric radial velocities of individual stars and on the observed mass function. II - M13

We have measured radial velocities for 147 stars in the globular cluster M13 with typical errors of about 1 km s<SUP>-1</SUP>. Six of these are probable new velocity variables. The one-dimensional central velocity dispersion in the giants is about 7 km s<SUP>-1</SUP> , and the cluster is rotating with a maximum rotational velocity of about 5 km s<SUP>-1</SUP>. We have constructed truncated Maxwellian models of M13, using the observations of Lupton and Gunn to constrain the mass function in the region 0.5-0.8 M<SUB>sun</SUB>. In order to reconcile the mass-to-light ratio derived from the dynamics with that of the assumed mass spectrum, we had to assume that half the mass of the cluster was not observed. This mass cannot be present as heavy remnants, and the expected mass in white dwarfs is too low by a factor of about 20. If we assume that this mass takes the form of low-mass stars, the global mass function has a maximum at about 0.65 M<SUB>sun</SUB>, a minimum at about 0.5 M<SUB>sun</SUB> ,and then a very sharp rise towards lower masses. We see no evidence for any truncation of the mass function. There is no evidence for any heavy remnants not accounted for by the adopted mass function. We find that isotropic models of the velocity dispersion do not fit our velocity measurements, and that the transition to anisotropy occurs at 3-5 core radii. We use the proper-motion data of Cudworth and Monet in conjunction with our models to derive a distance of 6.5 kpc to the cluster, with formal errors of + 9%, - 6%.