The Globular Cluster System of the Spiral Galaxy NGC7814

We present the results of a wide-field photometric study of the globular cluster (GC) system of the edge-on Sab spiral NGC7814. This is the first spiral to be fully analyzed from our survey of the GC systems of a large sample of galaxies beyond the Local Group. NGC7814 is of particular interest because a previous study estimated that it has 500-1000 GCs, giving it the largest specific frequency (S_N) known for a spiral. Understanding this galaxy's GC system is important in terms of our understanding of the GC populations of spirals in general and has implications for the formation of massive galaxies. We observed the galaxy in BVR filters with the WIYN 3.5-m telescope, and used image classification and three-color photometry to select GC candidates. We also analyzed archival HST WFPC2 images of NGC7814, both to help quantify the contamination level of the WIYN GC candidate list and to detect GCs in the inner part of the galaxy halo. Combining HST data with high-quality ground-based images allows us to trace the entire radial extent of this galaxy's GC system and determine the total number of GCs directly through observation. We find that rather than being an especially high-S_N spiral, NGC7814 has <200 GCs and S_N ~ 1, making it comparable to the two most well-studied spirals, the Milky Way and M31. We explore the implications of these results for models of the formation of galaxies and their GC systems. The initial results from our survey suggest that the GC systems of typical ellipticals can be accounted for by the merger of two or more spirals, but that for highly-luminous ellipticals, additional physical processes may be needed.Comment: 28 pages, incl. 4 figures; accepted for publication in The Astronomical Journal, November 2003 issu

Dynamical Evolution of Globular Clusters in Hierarchical Cosmology

We probe the evolution of globular clusters that could form in giant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that the large and dense enough gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution.Comment: 5 pages, proceedings of IAU 246 "Dynamical Evolution of Dense Stellar Systems", eds. Vesperini, Giersz, Sill

Formation and evolution of clumpy tidal tails around globular clusters

We present some results of numerical simulations of a globular cluster orbiting in the central region of a triaxial galaxy on a set of 'loop' orbits. Tails start forming after about a quarter of the globular cluster orbital period and develop, in most cases, along the cluster orbit, showing clumpy substructures as observed, for example, in Palomar 5. If completely detectable, clumps can contain about 7,000 solar masses each, i.e. about 10% of the cluster mass at that epoch. The morphology of tails and clumps and the kinematical properties of stars in the tails are studied and compared with available observational data. Our finding is that the stellar velocity dispersion tends to level off at large radii, in agreement to that found for M15 and Omega Centauri.Comment: LaTeX 2e, uses AASTeX v5.x, 40 pages with 18 figures. Submitted to The Astronomical Journa

Modeling the dynamical evolution of the M87 globular cluster system

We study the dynamical evolution of the M87 globular cluster system (GCS) with a number of numerical simulations. We explore a range of different initial conditions for the GCS mass function (GCMF), for the GCS spatial distribution and for the GCS velocity distribution. We confirm that an initial power-law GCMF like that observed in young cluster systems can be readily transformed through dynamical processes into a bell-shaped GCMF. However,only models with initial velocity distributions characterized by a strong radial anisotropy increasing with the galactocentric distance are able to reproduce the observed constancy of the GCMF at all radii.We show that such strongly radial orbital distributions are inconsistent with the observed kinematics of the M87 GCS. The evolution of models with a bell-shaped GCMF with a turnover similar to that currently observed in old GCS is also investigated. We show that models with this initial GCMF can satisfy all the observational constraints currently available on the GCS spatial distribution,the GCS velocity distribution and on the GCMF properties.In particular these models successfully reproduce both the lack of a radial gradient of the GCS mean mass recently found in an analysis of HST images of M87 at multiple locations, and the observed kinematics of the M87 GCS.Our simulations also show that evolutionary processes significantly affect the initial GCS properties by leading to the disruption of many clusters and changing the masses of those which survive.The preferential disruption of inner clusters flattens the initial GCS number density profile and it can explain the rising specific frequency with radius; we show that the inner flattening observed in the M87 GCS spatial distribution can be the result of the effects of dynamical evolution on an initially steep density profile. (abridged)Comment: 15 pages,14 figures;accepted for publication in The Astrophysical Journa

Effect of the Milky Way on Magellanic Cloud structure

A combination of analytic models and n-body simulations implies that the structural evolution of the Large Magellanic Cloud (LMC) is dominated by its dynamical interaction with the Milky Way. Although expected at some level, the scope of the involvement has significant observational consequences. First, LMC disk orbits are torqued out of the disk plane, thickening the disk and populating a spheroid. The torque results from direct forcing by the Milky Way tide and, indirectly, from the drag between the LMC disk and its halo resulting from the induced precession of the LMC disk. The latter is a newly reported mechanism that can affect all satellite interations. However, the overall torque can not isotropize the stellar orbits and their kinematics remains disk-like. Such a kinematic signature is observed for nearly all LMC populations. The extended disk distribution is predicted to increase the microlensing toward the LMC. Second, the disk's binding energy slowly decreases during this process, puffing up and priming the outer regions for subsequent tidal stripping. Because the tidally stripped debris will be spatially extended, the distribution of stripped stars is much more extended than the HI Magellanic Stream. This is consistent with upper limits to stellar densities in the gas stream and suggests a different strategy for detecting the stripped stars. And, finally, the mass loss over several LMC orbits is predicted by n-body simulation and the debris extends to tens of kiloparsecs from the tidal boundary. Although the overall space density of the stripped stars is low, possible existence of such intervening populations have been recently reported and may be detectable using 2MASS.Comment: 15 pages, color Postscript figures, uses emulateapj.sty. Also available from http://www-astro.phast.umass.edu/~weinberg/weinberg-pubs.htm

Dynamical Evolution of the Mass Function of Globular Star Clusters

We present a series of simple, largely analytical models to compute the effects of disruption on the mass function of star clusters. Our calculations include evaporation by two-body relaxation and gravitational shocks and mass loss by stellar evolution. We find that, for a wide variety of initial conditions, the mass function develops a turnover or peak and that, after 12 Gyr, this is remarkably close to the observed peak for globular clusters, at M_p = 2 10^5 solar masses. Below the peak, the evolution is dominated by two-body relaxation, and the mass function always develops a tail of the form psi(M) = const, reflecting that the masses of tidally limited clusters decrease linearly with time just before they are destroyed. This also agrees well with the empirical mass function of globular clusters in the Milky Way. Above the peak, the evolution is dominated by stellar evolution at early times and gravitational shocks at late times. These processes shift the mass function to lower masses while nearly preserving its shape. The radial variation of the mass function within a galaxy depends on the initial position-velocity distribution of the clusters. We find that some radial anisotropy in the initial velocity distribution, especially when this increases outward, is needed to account for the observed near-uniformity of the mass functions of globular clusters. This may be consistent with the observed near-isotropy of the present velocity distributions because clusters on elongated orbits are preferentially destroyed. These results are based on models with static, spherical galactic potentials. We point out that there would be even more radial mixing of the orbits and hence more uniformity of the mass function if the galactic potentials were time-dependent and/or non-spherical.Comment: 39 pages including 13 figures; scheduled for publication in the Astrophysical Journal (issue of 10 Nov 2001); Minor revisions to improve clarity; no changes to equations, figures, or conclusion

Analyzing the Information Sharing Practices and Barriers in Supply Chain of Automotive Industries

Information sharing and technology remain one of the key factors of coordination amongst the parties in a supply chain. Supply chain efficiency is highly important as today�s competition is no longer between companies, but between supply chains. Information sharing can increase supply chain efficiency by reducing inventories and smoothing the production. The purpose of this study is to assess the status of the supply chain information sharing practices in Indian automotive industries. This study is focused on identifying the types of information shared, determining the level of information sharing , usage of Information Technology (IT) tools and identifying the barriers of information sharing. Data for this study is collected from the respondents of Original Equipment Manufacturer (OEM), Tier 1, Tier 2 and Tier 3 Indian automobile industries. Frequency analysis is employed to derive the results from the survey

The Globular Cluster System in the Inner Region of M87

1057 globular cluster candidates have been identified in a WFPC2 image of the inner region of M87. The Globular Cluster Luminosity Function (GCLF) can be well fit by a Gaussian profile with a mean value of m_V^0=23.67 +/- 0.07 mag and sigma=1.39 +/- 0.06 mag (compared to m_V^0=23.74 mag and sigma=1.44 mag from an earlier study using the same data by Whitmore it et al. 1995). The GCLF in five radial bins is found to be statistically the same at all points, showing no clear evidence of dynamical destruction processes based on the luminosity function (LF), in contradiction to the claim by Gnedin (1997). Similarly, there is no obvious correlation between the half light radius of the clusters and the galactocentric distance. The core radius of the globular cluster density distribution is R_c=56'', considerably larger than the core of the stellar component (R_c=6.8''). The mean color of the cluster candidates is V-I=1.09 mag which corresponds to an average metallicity of Fe/H = -0.74 dex. The color distribution is bimodal everywhere, with a blue peak at V-I=0.95 mag and a red peak at V-I=1.20 mag. The red population is only 0.1 magnitude bluer than the underlying galaxy, indicating that these clusters formed late in the metal enrichment history of the galaxy and were possibly created in a burst of star/cluster formation 3-6 Gyr after the blue population. We also find that both the red and the blue cluster distributions have a more elliptical shape (Hubble type E3.5) than the nearly spherical galaxy. The average half light radius of the clusters is ~2.5 pc which is comparable to the 3 pc average effective radius of the Milky Way clusters, though the red candidates are ~20% smaller than the blue ones.Comment: 40 pages, 17 figures, 4 tables, latex, accepted for publication in the Ap

New mixed ligand complexes of ruthenium(II) that incorporate a modified phenanthroline ligand: synthesis, spectral characterization and DNA binding

The hexafluorophosphate and chloride salts of two ruthenium(II) complexes, viz. [Ru(phen)(ptzo)2]2 and [Ru(ptzo)3]2+, where ptzo = 1,10-phenanthrolino[5,6-e]1,2,4-triazine-3-one (ptzo) - a new modified phenanthroline (phen) ligand, have been synthesised. These complexes have been characterised by infrared, UV-Vis, steady-state emission and1H NMR spectroscopic methods. Results of absorption and fluorescence titration as well as thermal denaturation studies reveal that both thebis- and tris-complexes of ptzo show moderately strong affinity for binding with calf thymus (CT) DNA with the binding constants being close to 105M-1 in each case. An intercalative mode of DNA binding has been suggested for both the complexes. Emission studies carried out in non-aqueous solvents and in aqueous media without DNA reveal that both [Ru(phen)(ptzo)2]2+ and [Ru(ptzo)3]2+ are weakly luminescent under these solution conditions. Successive addition of CT DNA to buffered aqueous solutions containing [Ru(phen)(ptzo)2]2+results in an enhancement of the emission. These results have been discussed in the light of the dependence of the structure-specific deactivation processes of the MLCT state of the metallo-intercalator with the characteristic features of its DNA interaction. In doing so, attempts have been made to compare and contrast its properties with those of the analogous phenanthroline-based complexes including the ones reported by us previously

The Upper Asymptotic Giant Branch of the Elliptical Galaxy Maffei 1, and Comparisons with M32 and NGC 5128

Deep near-infrared images obtained with adaptive optics systems on the Gemini North and Canada-France-Hawaii telescopes are used to investigate the bright stellar content and central regions of the nearby elliptical galaxy Maffei 1. Stars evolving on the upper asymptotic giant branch (AGB) are resolved in a field 3 arcmin from the center of the galaxy. The locus of bright giants on the (K, H-K) color-magnitude diagram is consistent with a population of stars like those in Baade's Window reddened by E(H-K) = 0.28 +/- 0.05 mag. This corresponds to A_V = 4.5 +/- 0.8 mag, and is consistent with previous estimates of the line of sight extinction computed from the integrated properties of Maffei 1. The AGB-tip occurs at K = 20.0, which correponds to M_K = -8.7; hence, the AGB-tip brightness in Maffei 1 is comparable to that in M32, NGC 5128, and the bulges of M31 and the Milky-Way. The near-infrared luminosity functions (LFs) of bright AGB stars in Maffei 1, M32, and NGC 5128 are also in excellent agreement, both in terms of overall shape and the relative density of infrared-bright stars with respect to the fainter stars that dominate the light at visible and red wavelengths. It is concluded that the brightest AGB stars in Maffei 1, NGC 5128, M32, and the bulge of M31 trace an old, metal-rich population, rather than an intermediate age population. It is also demonstrated that Maffei 1 contains a distinct red nucleus, and this is likely the optical signature of low-level nuclear activity and/or a distinct central stellar population. Finally, there is an absence of globular clusters brighter than the peak of the globular cluster LF in the central 700 x 700 parsecs of Maffei 1.Comment: 22 pages of text and 9 postscript figures; to appear in the Astronomical Journa