Constraints on the Merger Models of Elliptical Galaxies from their Globular Cluster Systems

The discovery of proto-globular cluster candidates in many current-day mergers allows us to better understand the possible effects of a merger event on the globular cluster system of a galaxy, and to foresee the properties of the end-product. By comparing these expectations to the properties of globular cluster systems of today's elliptical galaxies we can constrain merger models. The observational data indicate that i) every gaseous merger induces the formation of new star clusters, ii) the number of new clusters formed in such a merger increases with the gas content of the progenitor galaxies. Low-luminosity (about M_V>-21), disky ellipticals are generally thought to be the result of a gaseous merger. As such, new globular clusters are expected to form but have not been detected to date. We investigate various reasons for the non-detection of sub-populations in low-luminosity ellipticals, i.e. absence of an old population, absence of a new population, destruction of one of the populations, and finally, an age-metallicity conspiracy that allows old and new globular clusters to appear indistinguishable at the present epoch. All of these possibilities lead us to a similar conclusion, namely that low-luminosity ellipticals did not form recently (z<1) in a gas-rich merger, and might not have formed in a major merger of stellar systems at all. High-luminosity ellipticals do reveal globular cluster sub-populations. However, it is difficult to account for the two populations in terms of mergers alone, and in particular, we can rule out scenarios in which the second sub-population is the product of a recent, gas-poor merger.Comment: 11 pages (MNRAS style, two columns, including 2 figures, mn.sty included), accepted for publication in the MNRAS, also available at http://www.ucolick.org/~mkissle

Is demagnetization an efficient optimization method?

Demagnetization, commonly employed to study ferromagnets, has been proposed as the basis for an optimization tool, a method to find the ground state of a disordered system. Here we present a detailed comparison between the ground state and the demagnetized state in the random field Ising model, combing exact results in $d=1$ and numerical solutions in $d=3$. We show that there are important differences between the two states that persist in the thermodynamic limit and thus conclude that AC demagnetization is not an efficient optimization method.Comment: 2 pages, 1 figur

Noise-induced memory in extended excitable systems

We describe a form of memory exhibited by extended excitable systems driven by stochastic fluctuations. Under such conditions, the system self-organizes into a state characterized by power-law correlations thus retaining long-term memory of previous states. The exponents are robust and model-independent. We discuss novel implications of these results for the functioning of cortical neurons as well as for networks of neurons.Comment: 4 pages, latex + 5 eps figure

Immune Response Modulation by Tumor-Secreted Glycosphingolipids

Although originally considered merely structural components of cellular membranes, glycosphingolipids (GSL) arenow recognized as having critical effects on cellular physiology, including proliferation, differentiation, viraltransformation and ontogenesis. In addition, a vast majority of human cancers have modified GSL compositioncompared to parental normal cells. These modifications may contribute to both tumor survival and exert strikingeffects on anti-tumor immunity. In this review, we discuss mechanisms of immune modulation by tumor-secreted GSL.Fil: Lardone, Ricardo Dante. John Wayne Cancer Institute at Providence Saint John’s Health Center. Santa Monica; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Cely, Ingrid. John Wayne Cancer Institute at Providence Saint John’s Health Center. Santa Monica; Estados UnidosFil: Sieling, Peter A.. John Wayne Cancer Institute at Providence Saint John’s Health Center. Santa Monica; Estados UnidosFil: Lee, Delphine. John Wayne Cancer Institute at Providence Saint John’s Health Center. Santa Monica; Estados Unido

The Elliptical Galaxy formerly known as the Local Group: Merging the Globular Cluster Systems

Prompted by a new catalogue of M31 globular clusters, we have collected together individual metallicity values for globular clusters in the Local Group. Although we briefly describe the globular cluster systems of the individual Local Group galaxies, the main thrust of our paper is to examine the collective properties. In this way we are simulating the dissipationless merger of the Local Group, into presumably an elliptical galaxy. Such a merger is dominated by the Milky Way and M31, which appear to be fairly typical examples of globular cluster systems of spiral galaxies. The Local Group `Elliptical' has about 700 +/- 125 globular clusters, with a luminosity function resembling the `universal' one. The metallicity distribution has peaks at [Fe/H] ~ -1.55 and -0.64 with a metal-poor to metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical is initially about 1 but rises to about 3, when the young stellar populations fade and the galaxy resembles an old elliptical. The metallicity distribution and stellar population corrected specific frequency are similar to that of some known early type galaxies. Based on our results, we briefly speculate on the origin of globular cluster systems in galaxies.Comment: 22 pages, Latex, 4 figures, 5 tables, submitted to A &