Hysteresis in one-dimensional reaction-diffusion systems

We introduce a simple nonequilibrium model for a driven diffusive system with nonconservative reaction kinetics which exhibits ergodicity breaking and hysteresis in one dimension. These phenomena can be understood through a description of the dominant stochastic many-body dynamics in terms of an equilibrium single-particle problem, viz. the random motion of a shock in an effective potential. This picture also leads to the exact phase diagram of the system and suggests a new generic mechanism for "freezing by heating".Comment: 4 Pages, 5 figure

Cluster Populations in A115 and A2283

This paper presents four color narrow-band photometry of clusters A115 ($z=0.191$) and A2283 ($z=0.182$) in order to follow the star formation history of various galaxy types. Although located at similar redshifts, the two clusters display very different fractions of blue galaxies (i.e. the Butcher-Oemler effect, $f_B = 0.13$ for A115, $f_B = 0.30$ for A2283). A system of photometric classification is applied to the cluster members that divides the cluster population into four classes based on their recent levels of star formation. It is shown that the blue population of each cluster is primarily composed of normal starforming (SFR < 1 M_{\sun} yrs$^{-1}$) galaxies at the high luminosity end, but with an increasing contribution from a dwarf starburst population below $M_{5500}= -20$. This dwarf starburst population appears to be the same population of low mass galaxies identified in recent HST imaging (Koo et al 1997), possible progenitors to present-day cluster dwarf ellipticals, irregulars and BCD's. Deviations in the color-magnitude relationship for the red galaxies in each cluster suggest that a population of blue S0's is evolving into present-day S0 colors at this epoch. The radial distribution of the blue population supports the prediction of galaxy harassment mechanisms for tidally induced star formation operating on an infalling set of gas-rich galaxies.Comment: 28 pages including 2 tables and 9 figures, AASTeX v4.0. Accepted by Ap.J. Data, referee report and response are avaliable from http://zebu.uoregon.edu/~j

The Butcher-Oemler Effect in Abell 2317

This paper presents deep narrow band photometry of the cluster A2317 (z=0.211) carried out using KPNO 4 m and Steward 2.3 m telescopes. Using rest frame Stromgren photometry, it is determined that A2317 has an unusually high fraction of blue galaxies (the Butcher-Oemler effect) for its redshift (f_B=0.35). We demonstrate that the ratio of blue to red galaxies has a strong dependence on absolute magnitude such that blue galaxies dominate the top of the luminosity function. Spectrophotometric classification shows that a majority of the red galaxies are E/S0's, with a small number of reddened starburst galaxies. Butcher-Oemler galaxies are shown to be galaxies with star formation rates typical of late-type spirals and irregular. Starburst systems were typically found to be on the lower end of the cluster luminosity function. In addition, blue galaxies are preferentially found in the outer edges of the cluster, whereas the red galaxies are concentrated in the cluster core.Comment: 23 pages including 1 table and 6 figures, AASTeX v4.0. Accepted by Ap.J. Data, referee report and response are avaliable from http://zebu.uoregon.edu/~j

The Ages of Dwarf Ellipticals

We present narrow band photometry of 91 dwarf ellipticals in the Coma and Fornax clusters taken through the Stromgren (uvby) filter system. Dividing the sample by dwarf morphology into nucleated (dEN) and non-nucleated (dE) dwarfs reveals two distinct populations of early-type systems based on integrated colors. The class of dEN galaxies are redder in their continuum colors as compared to bright cluster ellipticals and dE type dwarfs, and their position in multi-color diagrams can only be explained by an older mean age for their underlying stellar populations. By comparison with the narrow band photometry of the M87 globular cluster system (Jordan et al. 2002), we find that dENs are a higher metallicity continuation of the old, metal-poor color sequence of galactic globulars and the blue population of M87 globulars. Bright ellipticals and dE dwarfs, on the other hand, follow the color sequence of the metal-rich, red population of M87 globulars. A comparison to SED models, convolved to a simple metallicity model, finds that dENs and blue globulars are 3 to 4 Gyrs older than cluster ellipticals and 5 Gyrs older than dE type galaxies. The implication is that globulars and dEN galaxies are primordial and have metallicities set by external constraints such as the enrichment of their formation clouds. Bright ellipticals and dE galaxies have metallicities and ages that suggest an extended phase of initial star formation to produce a younger mean age, even if their formation epoch is similar to that of dENs and blue globulars, and an internally driven chemical evolutionary history.Comment: 13 pages AAS LaTeX, 6 figures, accepted for publication in A

The Rest-frame Optical Colors of 99,000 SDSS Galaxies

We synthesize the rest-frame Stroemgren colors using SDSS spectra for 99,088 galaxies selected from Data Release 1. This narrow-band ~200 AA photometric system (uz, vz, bz, yz), first designed for the determination of effective temperature, metallicity and gravity of stars, measures the continuum spectral slope of galaxies in the rest-frame 3200-5800 AA wavelength range. Galaxies form a remarkably narrow locus (~0.03 mag) in the resulting color-color diagram. The Bruzual & Charlot population synthesis models suggest that the position of a galaxy along this locus is controlled by a degenerate combination of metallicity and age of the dominant stellar population. Galaxy distribution along the locus is bimodal, with the local minimum corresponding to an ~1 Gyr old single stellar population. The position perpendicular to the locus is independent of metallicity and age, and reflects the galaxy's dust content, as implied by both the models and the statistics of IRAS detections. A comparison of this locus with the galaxy locus in the H_delta-D_n(4000) diagram, utilized by Kauffmann et al. (2003) to estimate stellar masses, reveals a tight correlation, although the two analyzed spectral ranges barely overlap. Overall, the galaxy spectral energy distribution in the entire UV to near-IR range can be described as a single-parameter family with an accuracy of 0.1 mag, or better. This nearly one-dimensional distribution of galaxies in the multi-dimensional space of measured parameters strongly supports the conclusion of Yip et al. (2004), based on a principal component analysis, that SDSS galaxy spectra can be described by a small number of eigenspectra. Apparently, the contributions of stellar populations that dominate the optical emission from galaxies are combined in a simple and well-defined way.Comment: Accepted for publication in MNRAS; 19 pages, 28 color figure

The Galaxy Population of Abell 1367: The Stellar Mass-Metallicity Relation

Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red sequence lenticular galaxies and blue cloud galaxies, low mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally-driven gas flows toward the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red sequence or blue cloud galaxies, at fixed stellar mass, with location within the cluster.Comment: 15 pages, 10 figures, MNRAS in pres

The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations

We have observed three fields of the Coma cluster of galaxies with a narrow band (modified Stromgren) filter system. Observed galaxies include 31 in the vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839 complete to M_5500=-18 in all three subclusters. Spectrophotometric classification finds all three subclusters of Coma to be dominated by red, E type (ellipticals/S0's) galaxies with a mean blue fraction, f_B, of 0.10. The blue fraction increases to fainter luminosities, possible remnants of dwarf starburst population or the effects of dynamical friction removing bright, blue galaxies from the cluster population by mergers. We find the color-magnitude (CM) relation to be well defined and linear over the range of M_5500=-13 to -22. After calibration to multi-metallicity models, bright ellipticals are found to have luminosity weighted mean [Fe/H] values between -0.5 and +0.5, whereas low luminosity ellipticals have [Fe/H] values ranging from -2 to solar. The lack of CM relation in our continuum color suggests that a systematic age effect cancels the metallicity effects in this bandpass. This is confirmed with our age index which finds a weak correlation between luminosity and mean stellar age in ellipticals such that the stellar populations of bright ellipticals are 2 to 3 Gyrs younger than low luminosity ellipticals.Comment: 26 pages AAS LaTeX, 6 figures, accepted for publication in A

Geometric Universality of Currents

We discuss a non-equilibrium statistical system on a graph or network. Identical particles are injected, interact with each other, traverse, and leave the graph in a stochastic manner described in terms of Poisson rates, possibly dependent on time and instantaneous occupation numbers at the nodes of the graph. We show that under the assumption of constancy of the relative rates, the system demonstrates a profound statistical symmetry, resulting in geometric universality of the statistics of the particle currents. This phenomenon applies broadly to many man-made and natural open stochastic systems, such as queuing of packages over the internet, transport of electrons and quasi-particles in mesoscopic systems, and chains of reactions in bio-chemical networks. We illustrate the utility of our general approach using two enabling examples from the two latter disciplines.Comment: 15 pages, 5 figure

SOCIEDADE CIVIL E CONTROLE SOCIAL DEMOCRÁTICO: profícuo campo de extensão universitária

RESUMO: O artigo socializa a prática extensionista da Universidade Federal de Santa Catarina – por meio do Núcleo de Estudos da Criança, Adolescente e Família – junto às instâncias de controle social municipal e estadual na área da criança e adolescente em Santa Catarina. O estreitamento das relações, entre universidade e sociedade, acontece por meio da assessoria sistemática à sociedade civil. As principais atividades desenvolvidas foram: a participação nas reuniões mensais do fórum e plenárias mensais dos conselhos de direitos da criança e do adolescente municipal de Florianópolis e estadual de Santa Catarina; desenvolvimento de estudos, elaboração do Plano Decenal, documentos, projetos e pareceres; capacitações de conselheiros. Conclui-se que as ações extensionistas têm contribuído na qualificação e fortalecimento da representação da sociedade civil, contudo ainda existem desafios importantes como o de responsabilizar os representantes governamentais para maior presença nesses espaços democráticos de controle social voltado à política da infância e adolescência