A Census of Object Types and Redshift Estimates in the SDSS Photometric Catalog from a Trained Decision-Tree Classifier

We have applied ClassX, an oblique decision tree classifier optimized for astronomical analysis, to the homogeneous multicolor imaging data base of the Sloan Digital Sky Survey (SDSS), training the software on subsets of SDSS objects whose nature is precisely known via spectroscopy. We find that the software, using photometric data only, correctly classifies a very large fraction of the objects with existing SDSS spectra, both stellar and extragalactic. ClassX also accurately predicts the redshifts of both normal and active galaxies in SDSS. To illustrate ClassX applications in SDSS research, we (a) derive the object content of the SDSS DR2 photometric catalog and (b) provide a sample catalog of resolved SDSS objects that contains a large number of candidate AGN galaxies, 27,000, along with 63,000 candidate normal galaxies at magnitudes substantially fainter than typical magnitudes of SDSS spectroscopic objects. The surface density of AGN selected by ClassX to i~19 is in agreement with that quoted by SDSS. When ClassX is applied to the photometric data fainter than the SDSS spectroscopic limit, the inferred surface density of AGN rises sharply, as expected. The ability of the classifier to accurately constrain the redshifts of huge numbers (ultimately ~ 10^7) of active galaxies in the photometric data base promises new insights into fundamental issues of AGN research, such as the evolution of the AGN luminosity function with cosmic time, the starburst--AGN connection, and AGN--galactic morphology relationships.Comment: Accepted for publication in The Astronomical Journal, Vol. 130, 2005; 33 pages, 10 figures, 5 tables, AASTeX v5.0. Table 5 will be electronic in the published journal, but available now at http://www-int.stsci.edu/~margon/table5.ascii and http://www-int.stsci.edu/~margon/table5.ascii.g

Running a distributed virtual observatory: US Virtual Astronomical Observatory operations

Operation of the US Virtual Astronomical Observatory shares some issues with modern physical observatories, e.g., intimidating data volumes and rapid technological change, and must also address unique concerns like the lack of direct control of the underlying and scattered data resources, and the distributed nature of the observatory itself. In this paper we discuss how the VAO has addressed these challenges to provide the astronomical community with a coherent set of science-enabling tools and services. The distributed nature of our virtual observatory-with data and personnel spanning geographic, institutional and regime boundaries-is simultaneously a major operational headache and the primary science motivation for the VAO. Most astronomy today uses data from many resources. Facilitation of matching heterogeneous datasets is a fundamental reason for the virtual observatory. Key aspects of our approach include continuous monitoring and validation of VAO and VO services and the datasets provided by the community, monitoring of user requests to optimize access, caching for large datasets, and providing distributed storage services that allow user to collect results near large data repositories. Some elements are now fully implemented, while others are planned for subsequent years. The distributed nature of the VAO requires careful attention to what can be a straightforward operation at a conventional observatory, e.g., the organization of the web site or the collection and combined analysis of logs. Many of these strategies use and extend protocols developed by the international virtual observatory community.Comment: 7 pages with 2 figures included within PD

Phase diagram and magnetic collective excitations of the Hubbard model in graphene sheets and layers

We discuss the magnetic phases of the Hubbard model for the honeycomb lattice both in two and three spatial dimensions. A ground state phase diagram is obtained depending on the interaction strength U and electronic density n. We find a first order phase transition between ferromagnetic regions where the spin is maximally polarized (Nagaoka ferromagnetism) and regions with smaller magnetization (weak ferromagnetism). When taking into account the possibility of spiral states, we find that the lowest critical U is obtained for an ordering momentum different from zero. The evolution of the ordering momentum with doping is discussed. The magnetic excitations (spin waves) in the antiferromagnetic insulating phase are calculated from the random-phase-approximation for the spin susceptibility. We also compute the spin fluctuation correction to the mean field magnetization by virtual emission/absorpion of spin waves. In the large $U$ limit, the renormalized magnetization agrees qualitatively with the Holstein-Primakoff theory of the Heisenberg antiferromagnet, although the latter approach produces a larger renormalization

SDSS AGNs with X-ray Emission from ROSAT PSPC Pointed Observations

We present a sample of 1744 type 1 active galactic nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS DR4) spectroscopic catalog with X-ray counterparts in the White-Giommi-Angelini Catalog (WGACAT) of ROSAT PSPC pointed observations. Of 1744 X-ray sources, 1410 (80.9%) are new AGN identifications. Of 4574 SDSS DR4 AGNs for which we found radio matches in the catalog of radio sources from the FIRST catalog, 224 turned up in our sample of SDSS X-ray AGNs. The sample objects are given in a catalog that contains optical and X-ray parameters along with radio emission parameters where available. We illustrate the content of our catalog and its potential for AGN science by providing statistical relationships for the catalog data. The potential of the morphological information is emphasized by confronting the statistics of optically resolved and unresolved AGNs. The immediate properties of the catalog objects include significant correlation of X-ray and optical fluxes, which is consistent with expectations. Also expected is the decrease of X-ray flux toward higher redshifts. The X-ray to optical flux ratio for the unresolved AGNs exhibits a decline toward higher redshifts, in agreement with previous results. The resolved AGNs, however, display the opposite trend. At a given optical brightness, X-ray fluxes of radio-quiet AGNs by a factor of 2. We caution, however, that because of the variety of selection effects present in both the WGACAT and the SDSS, the interpretation of any relationships based on our sample of X-ray AGNs requires a careful analysis of these effects.Comment: 34 pages, 18 figure

Extreme Ultraviolet Emission from Clusters of Galaxies: Inverse Compton Radiation from a Relic Population of Cosmic Ray Electrons?

We suggest that the luminous extreme ultraviolet (EUV) emission which has been detected recently from clusters of galaxies is Inverse Compton (IC) scattering of Cosmic Microwave Background (CMB) radiation by low energy cosmic ray electrons in the intracluster medium. The cosmic ray electrons would have Lorentz factors of gamma ~ 300, and would lose energy primarily by emitting EUV radiation. These particles have lifetimes comparable to the Hubble time; thus, the electrons might represent a relic population of cosmic rays produced by nonthermal activity over the history of the cluster. The IC model naturally explains the observed increase in the ratio of EUV to X-ray emission with radius in clusters. The required energy in cosmic ray electrons is typically 1--10% of the thermal energy content of the intracluster gas. We suggest that the cosmic ray electrons might have been produced by supernovae in galaxies, by radio galaxies, or by particle acceleration in intracluster shocks.Comment: ApJ Letters, in press, 4 pages with 1 embedded figure, Latex in emulateapj styl

Check list of ground-dwelling ant diversity (Hymenoptera: Formicidae) of the Iguazú National Park with a comparison at regional scale

We describe the ant fauna of Iguazú National Park (INP), a region of high biodiversity andendemism in northeastern Argentina that includes the southernmost protected area ofthe Atlantic Forest (AF). Ants were sampled over seven periods from 1998 to 2011 usinga variety of techniques. We also surveyed museum collections and the scientific literatureto obtain additional records of ants from INP. In addition to providing a species list, wecompare ant composition of INP to other sites in the Upper Paraná, Serra do Mar CoastalForest and Araucaria ecoregion of AF. A total of 172 ant species belonging to 56 genera arereported; 56 species are new records for Misiones Province and 39 species are reportedfrom Argentina for the first time. Alto Paraná and Canindeyú departments in Paraguaypresent the most similar ant fauna to INP. Serra da Bodoquena in Brazil and Pilcomayoin Argentina showed higher similarity with the Upper Paraná AF ecoregion, despite thatSerra da Bodoquena is composed of a mix of ecoregions. Ant diversity was lower in UpperParaná than in Serra do Mar Coastal Forest ecoregion. This difference may result fromhigher primary productivity and a greater altitudinal variation in the coastal region.Fil: Hanisch, Priscila Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; ArgentinaFil: Calcaterra, Luis Alberto. Fundación para el Estudio de Especies Invasivas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Leponce, M.. Royal Belgian Institute of Natural Sciences. Aquatic and Terrestrial Ecology unit; BélgicaFil: Achury, R.. University of Illinois at Urbana; Estados UnidosFil: Suarez, A. V.. University of Illinois at Urbana; Estados UnidosFil: Silva, R. R.. Museu Paraense Emílio Goeldi; BrasilFil: Paris, Carolina Ivon. Universidad de Buenos Aires; Argentin

Estudo da regeneração florestal de uma área de caíva com extração de erva-mate e pastejo animal no Planalto Norte Catarinense.

Caívas são remanescentes de florestas nativas com diferentes níveis de adensamento florestal, cujos estratos herbáceos são compostos por pastagens nativas, extensivamente pastejadas. Essas áreas de caívas, ainda que em diferentes estágios sucessionais, são importantes referências ambientais para diversas espécies da fauna e da flora local e ocupam, aproximadamente 13% da área do Planalto Norte Catarinense. Por serem áreas antropizadas, sua manutenção depende, em grande parte, do potencial de regeneração das espécies florestais presentes. Este trabalho teve por objetivo realizar o levantamento fitossociológico da regeneração de uma caíva, com área total de 10 ha, que vem sendo utilizada para extração de erva-mate nativa e pastejo animal há mais de 60 anos. O levantamento foi realizado em novembro e dezembro de 2010, em uma área experimental de 4.320 m2 demarcada dentro da caíva, onde foram alocadas 27 parcelas amostrais de 144m² cada. Todos os indivíduos arbustivos inferiores a 50 cm de altura, presentes nas parcelas, foram medidos e identificados. A identificação taxonômica foi realizada em campo com o apoio de um mateiro com experiência. A ordenação das famílias e gêneros foi baseada no APG III e a nomenclatura das espécies foi verificada nos arquivos on-line de Missouri Botanical Garden. Para análise fitossociológica foram realizadas as análises de frequência e dominância, absoluta e relativa. As plântulas foram agrupadas por altura, nos níveis de 0-10; 11-20; 21-40 e >41 cm. Na ordenação por altura, a maior concentração de plântulas ocorreu no extrato de 21-40 cm, sendo que foram encontradas 52% das plântulas neste extrato. Dentre as 1.641 plântulas amostradas foram identificadas 31 espécies, 19 famílias e 29 gêneros botânicos. Das espécies com maior densidade destacaram-se Zanthoxylum sp. (mamica de cadela), Allophylus edulis (vacum), Myrcia sp. (guamirim), Ilex microdonta Reissek (congonha), Mosiera prismatica (cerninho). Com relação à freqüência, as espécies que mais se destacaram foram: Zanthoxylum sp. (mamica de cadela), Allophylus edulis (vacum), Myrcia sp. (guamirim), Ilex microdonta Reissek (congonha), Ocotea sp. (canela). A quantidade e diversidade de espécies das plântulas levantadas na área amostral indicam que o processo de regeneração das áreas de caíva é intenso e atende a demanda para manutenção das características das caívas da região

Ferromagnetism in a hard-core boson model

The problem of ferromagnetism -- associated with a ground state with maximal total spin -- is discussed in the framework of a hard-core model, which forbids the occupancy at each site with more than one particle. It is shown that the emergence of ferromagnetism on finite square lattices crucially depends on the statistics of the particles. Fermions (electrons) lead to the well-known instabilities for finite hole densities, whereas for bosons (with spin) ferromagnetism appears to be stable for all hole densities.Comment: 8 pages, 7 figures, RevTex