Nonlinear electrodynamics and the surface redshift of pulsars

Currently is argued that the best method of determining the neutron star (NS) fundamental properties is by measuring the {\it gravitational redshift} ($z$) of spectral lines produced in the star photosphere. Measurement of $z$ at the star surface provides a unique insight on the NS mass-to-radius relation and thus on its equation of state (EoS), which reflects the physics of the strong interaction between particles making up the star. Evidence for such a measurement has been provided quite recently by Cottam, Paerels & Mendez (2002), and also by Sanwal et {\it al.} (2002). Here we argue that although the quoted observations are undisputed for canonical pulsars, they could be misidentified if the NS is endowed with a super strong $B$ as in the so-called magnetars (Duncan & Thompson 1992) and strange quark magnetars (Zhang 2002), as in the spectral line discovered by Ibrahim et {\it al.} (2002;2003). The source of this new "confusion" redshift is related to nonlinear electrodynamics (NLEDs) effects.Comment: 5 pages, emulateapj.sty, accepted for publication in Astrophysical Journa

Rickettsioses in Latin America, Caribbean, Spain and Portugal

Data on genus and infectious by Rickettsia were retrospectively compiled from the critical review literature regarding all countries in Latin America, Caribbean islands, Portugal and Spain. We considered all Rickettsia records reported for human and/or animal hosts, and/or invertebrate hosts considered being the vector. In a few cases, when no direct detection of a given Rickettsia group or species was available for a given country, the serologic method was considered. A total of 13 Rickettsia species have been recorded in Latin America and the Caribbean. The species with the largest number of country confirmed records were Rickettsia felis (9 countries), R. prowazekii (7 countries), R. typhi (6 countries), R. rickettsii (6 countries), R. amblyommii (5 countries), and R. parkeri (4 countries). The rickettsial records for the Caribbean islands (West Indies) were grouped in only one geographical area. Both R. bellii, R. akari, and Candidatus ‘R. andeane’ have been recorded in only 2 countries each, whereas R. massiliae, R. rhipicephali, R.monteiroi, and R. africae have each been recorded in a single country (in this case, R. africae has been recorded in nine Caribbean Islands). For El Salvador, Honduras, and Nicaragua, no specific Rickettsia has been reported so far, but there have been serological evidence of human or/and animal infection. The following countries remain without any rickettsial records: Belize, Venezuela, Guyana, Surinam, and Paraguay. In addition, except for a few islands, many Caribbean islands remain without records. A total of 12 Rickettsia species have been reported in Spain and Portugal: R. conorii, R. helvetica, R. monacensis, R. felis, R. slovaca, R. raoultii, R. sibirica, R. aeschlimannii, R. rioja, R. massiliae, R. typhi, and R. prowazekii. Amongst these Rickettsia species reported in Spain and Portugal, only R. prowazekii, R. typhi, R. felis, and R. massiliae have also been reported in Latin America. This study summarizes the current state of art on the rickettsial distribution in Latin America, Caribbean, Spain and Portugal. The data obtained allow a better understanding on rickettsial epidemiology and distribution of vector ecology.Reportes del genero Rickettsia y sus asociadas infecciones fueron compilados en una revisión crítica retrospectiva de la literatura científica de los países de Latinoamérica, el Caribe, Portugal y España. Se consideraron todos los reportes para huéspedes humanos y/o animales y también para huéspedes invertebrados los cuales fueron considerados como vectores asociados con Rickettsia. En algunos casos, cuando no existió detección directa a un determinado grupo de rickettsias o especies no disponible en un país, se tuvo en cuenta la detección indirecta por serología. Un total de 13 especies de Rickettsia han sido reportadas en Latinoamérica y el Caribe. Las especies más encontradas en los países fueron: Rickettsia felis (9 países), R. prowazekii (7 países), R. typhi (6 países), R. rickettsii (6 países), R. amblyommii (5 países) y R. parkeri (4 países). Los datos de las islas del Caribe (antillas menores o Indias occidentales), fueron agrupados en una sola área geográfica como un solo país. Ambas R. bellii, R. akari y Candidatus ‘R. andeane’ fueron reportadas en solo 2 países, mientras que R. massiliae, R. rhipicephali, R.monteiroi, y R. africae fueron informadas en un solo país. En este caso R. africae fue reportada en 9 islas de las Antillas menores. Para El Salvador, Honduras y Nicaragua, hasta ahora no se han reportado especies de Rickettsia, pero si evidencia serológica de infección humana y/o animal. Sin reportes de infección por Rickettsia permanecen: Belice, Venezuela, Guayana, Surinam y Paraguay. Además, a excepción de algunas islas del Caribe, muchas de ellas permanecen sin reportes. Un total de 12 especies de Rickettsia han sido documentadas en España y Portugal: R. conorii, R. helvetica, R. monacensis, R. felis, R. slovaca, R. raoultii, R. sibirica, R. aeschlimannii, R. rioja, R. massiliae, R. typhi y R. prowazekii. Entre estas, solamente R. prowazekii, R. typhi, R. felis y R. massiliae han sido documentados en Latinoamérica, España y Portugal. Los datos de este estudio permiten entender mejor la epidemiología de las rickettsias en Latinoamérica, Caribe, España y Portugal, y la distribución de los vectores

The Young and the Dustless: Interpreting Radio Observations of UltraViolet Luminous Galaxies

Ultraviolet Luminous Galaxies (UVLGs) have been identified as intensely star-forming, nearby galaxies. A subset of these, the supercompact UVLGs, are believed to be local analogs of high redshift Lyman Break Galaxies. Here we investigate the radio continuum properties of this important population for the first time. We have observed 42 supercompact UVLGs with the VLA, all of which have extensive coverage in the UV/optical by GALEX and SDSS. Our analysis includes comparison samples of multiwavelength data from the Spitzer First Look Survey and from the SDSS-Galex matched catalogs. In addition we have Spitzer MIPS data for 24 of our galaxies and find that they fall on the radio-FIR correlation of normal star-forming galaxies. We find that our galaxies have lower radio-to-UV ratios and lower Balmer decrements than other local galaxies with similar (high) star formation rates. Optical spectra show they have lower Dn(4000) and HdeltaA indices, higher Hbeta emission-line equivalents widths, and higher [OIII]5007/Hbeta emission-line ratios than normal star forming galaxies. Comparing these results to galaxy spectral evolution models we conclude that supercompact UVLGs are distinguished from normal star forming galaxies firstly by their high specific star formation rates. Moreover, compared to other types of galaxies with similar star formation rates, they have significantly less dust attenuation. In both regards they are similar to Lyman Break Galaxies. This suggests that the process that causes star formation in the supercompact UVLGs differs from other local star forming galaxies, but may be similar to Lyman Break Galaxies.Comment: 37 pages, 13 figures, accepted and scheduled to appear in ApJS December 2007 (GALEX Special Issue

UV Star Formation Rates in the Local Universe

We measure star formation rates of ~50,000 optically-selected galaxies in the local universe (z~0.1), spanning a range from gas-rich dwarfs to massive ellipticals. We obtain dust-corrected SFRs by fitting the GALEX (UV) and SDSS (optical) photometry to a library of population synthesis models that include dust attenuation. For star-forming galaxies, our UV-based SFRs compare remarkably well with those derived from SDSS H alpha. Deviations from perfect agreement between these two methods are due to differences in the dust attenuation estimates. In contrast to H alpha, UV provides reliable SFRs for galaxies with weak or no H alpha emission, and where H alpha is contaminated with an emission from an AGN. We use full-SED SFRs to calibrate a simple prescription that uses GALEX UV magnitudes to produce good SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGN, (2) those hosting an AGN, and for (3) galaxies without H alpha emission. We find that the three have distinct star formation histories, with AGN lying intermediate between the star-forming and the quiescent galaxies. Normal star forming galaxies (without an AGN) lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. Weak AGN, while also massive, have lower SFR, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent (red sequence) galaxies via strong and weak AGN. We confirm that some galaxies with no H alpha emission show signs of SF in the UV. We derive a UV-based cosmic SFR density at z=0.1 with smaller total error than previous measurements (abridged).Comment: Accepted for publication in ApJ (Special GALEX Supplement issue - Dec 2007). v2: Typo in Eq. 2 correcte

The Diverse Properties of the Most Ultraviolet Luminous Galaxies Discovered by the Galaxy Evolution Explorer

We report on the properties of a sample of ultraviolet luminous galaxies (UVLGs) selected by matching the Galaxy Evolution Explorer (GALEX) Surveys with the Sloan Digital Sky Survey Third Data Release. Out of 25362 galaxies between 0.02x10^10 L_solar at 1530 Angstroms (observed wavelength). The properties of this population are well correlated with ultraviolet surface brightness. We find that the galaxies with low UV surface brightness are primarily large spiral systems with a mixture of old and young stellar populations, while the high surface brightness galaxies consist primarily of compact starburst systems. In terms of the behavior of surface brightness with luminosity, size with luminosity, the mass-metallicity relation, and other parameters, the compact UVLGs clearly depart from the trends established by the full sample of galaxies. The subset of compact UVLGs with the highest surface brightness (``supercompact UVLGs'') have characteristics that are remarkably similar to Lyman Break Galaxies at higher redshift. They are much more luminous than typical local ultraviolet-bright starburst galaxies and blue compact dwarf galaxies. They have metallicities that are systematically lower than normal galaxies of the same stellar mass, indicating that they are less chemically evolved. In all these respects, they are the best local analogs for Lyman Break Galaxies.Comment: Fixed error in ObjID column of Table 1. 30 pages, 12 figures. Accepted for the GALEX special issue of ApJS. Abstract abridge

GALEX UV Color Relations for Nearby Early-Type Galaxies

We use GALEX/optical photometry to construct color-color relationships for early-type galaxies sorted by morphological type. We have matched objects in the GALEX GR1 public release and the first IR1.1 internal release, with the RC3 early-type galaxies having a morphological type -5.5<T<-1.5 with mean error in T<1.5, and mean error on (B-V)T<0.05. After visual inspection of each match, we are left with 130 galaxies with a reliable GALEX pipeline photometry in the far-UV and near-UV bands. This sample is divided into Ellipticals (-5.5<T<-3.5) and Lenticulars (-3.5<T<-1.5). After correction for the Galactic extinction, the color-color diagrams FUV-NUV vs. (B-V)_{Tc} are plotted for the two subsamples. We find a tight anti-correlation between the FUV-NUV and (B-V)_{Tc} colors for Ellipticals, the UV color getting bluer when the (B-V)_{Tc} get redder. This relationship very likely is an extension of the color-metallicity relationship into the GALEX NUV band. We suspect that the main source of the correlation is metal line blanketing in the NUV band. The FUV-NUV vs B-V correlation has larger scatter for lenticular galaxies; we speculate this reflects the presence of low level star formation. If the latter objects (i.e. those that are blue both in FUV-NUV and B-V) are interpreted as harboring recent star formation activity, this would be the case for a few percent (~4%) of Ellipticals and ~15% of Lenticulars; this would make about 10% of early-type galaxies with residual star formation in our full sample of 130 early-type galaxies. We also plot FUV-NUV vs. the Mg_2 index and central velocity dispersion. We find a tight anti-correlation between FUV-NUV and the Mg_2 index(...).Comment: 25 pages, 5 figures, accepted for publication in ApJS (abstract abridged), typos corrected in section 2.

Extinction Corrected Star Formation Rates Empirically Derived from Ultraviolet-Optical Colors

Using a sample of galaxies from the Sloan Digital Sky Survey spectroscopic catalog with measured star-formation rates (SFRs) and ultraviolet (UV) photometry from the GALEX Medium Imaging Survey, we derived empirical linear correlations between the SFR to UV luminosity ratio and the UV-optical colors of blue sequence galaxies. The relations provide a simple prescription to correct UV data for dust attenuation that best reconciles the SFRs derived from UV and emission line data. The method breaks down for the red sequence population as well as for very blue galaxies such as the local ``supercompact'' UV luminous galaxies and the majority of high redshift Lyman Break Galaxies which form a low attenuation sequence of their own.Comment: 20 pages, 11 figures, accepted for publication in the ApJS GALEX special issu

The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe

We measure the UV-optical color dependence of galaxy clustering in the local universe. Using the clean separation of the red and blue sequences made possible by the NUV - r color-magnitude diagram, we segregate the galaxies into red, blue and intermediate "green" classes. We explore the clustering as a function of this segregation by removing the dependence on luminosity and by excluding edge-on galaxies as a means of a non-model dependent veto of highly extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies shows strong redshift space distortion on small scales -- the "finger-of-God" effect, with green galaxies having a lower amplitude than is seen for the red sequence, and the blue sequence showing almost no distortion. On large scales, \xi (r_p, \pi) for all three samples show the effect of large-scale streaming from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected auto-correlation function w_p(r_p) for red and green galaxies fits a power-law with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma ~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the clustering of a fiducial L* galaxy, the red, green, and blue have a relative bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display an increase in convexity at ~ 1 Mpc/h, with an excess of large scale clustering. Our results suggest that the majority of blue galaxies are likely central galaxies in less massive halos, while red and green galaxies have larger satellite fractions, and preferentially reside in virialized structures. If blue sequence galaxies migrate to the red sequence via processes like mergers or quenching that take them through the green valley, such a transformation may be accompanied by a change in environment in addition to any change in luminosity and color.Comment: accepted by MNRA

Ultraviolet through Infrared Spectral Energy Distributions from 1000 SDSS Galaxies: Dust Attenuation

The meaningful comparison of models of galaxy evolution to observations is critically dependent on the accurate treatment of dust attenuation. To investigate dust absorption and emission in galaxies we have assembled a sample of ~1000 galaxies with ultraviolet (UV) through infrared (IR) photometry from GALEX, SDSS, and Spitzer and optical spectroscopy from SDSS. The ratio of IR to UV emission (IRX) is used to constrain the dust attenuation in galaxies. We use the 4000A break as a robust and useful, although coarse, indicator of star formation history (SFH). We examine the relationship between IRX and the UV spectral slope (a common attenuation indicator at high-redshift) and find little dependence of the scatter on 4000A break strength. We construct average UV through far-IR spectral energy distributions (SEDs) for different ranges of IRX, 4000A break strength, and stellar mass (M_*) to show the variation of the entire SED with these parameters. When binned simultaneously by IRX, 4000A break strength, and M_* these SEDs allow us to determine a low resolution average attenuation curve for different ranges of M_*. The attenuation curves thus derived are consistent with a lambda^{-0.7} attenuation law, and we find no significant variations with M_*. Finally, we show the relationship between IRX and the global stellar mass surface density and gas-phase-metallicity. Among star forming galaxies we find a strong correlation between IRX and stellar mass surface density, even at constant metallicity, a result that is closely linked to the well-known correlation between IRX and star-formation rate.Comment: 12 pages, 8 figures, 2 tables, appearing in the Dec 2007 GALEX special issue of ApJ Supp (29 papers