The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569

We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster

The passage of the Farallon-Aluk spreading ridge along the Andean margin

Plate reconstructions show that the Farallon-Aluk mid-ocean ridge interacted with the Andean marginat 30°S by ~80 Ma and then moved southwards. This process influenced the marginproducing contrasts in the magmatic evolution. At 35º30?S, the Late Cretaceous-Paleocene LosAngeles Unit (67 Ma; Fennell et al., in press), developed with a tholeiitic to alkalinesignature, and Sr-Nd isotopic trends similar to OIB magmatism (Iannelli et al., 2018). The coevalPlan de Los Yeuques Formation (34º30?S, Muñoz et al., 2018) and Naunauco Group (37-38ºS,Zamora Valcarce et al., 2006) show calc-alkaline signatures with arc-like trends. By Eocenetimes the Farallon-Aluk ridge reached the 42°S. Its influence is seen when comparing arc-likePVNM (37-38°S; Llambías and Rapela 1989) with the alkaline-like Pilcaniyeu Belt (40-42°S;Aragón et al. 2011). The segmented configuration of this spreading ridge would have favored thedevelopment of diachronic slab windows and the upwelling of more enriched mantle. This couldexplain the geochemical signatures and distribution of magmatism. A recent methodologycombining plate reconstructions and seismic tomography supports the past existence of thisprocess.Fil: Iannelli, Sofía B.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Litvak, Vanesa D.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Gianni, Guido Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Fernández Paz, Lucía. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina8th International Symposium on Andean GeodynamicsQuitoEcuadorInstituto GeofísicoEscuela Politécnica NacionalFrench Institut de Recherche pour le Développemen

A GALEX Ultraviolet Imaging Survey of Galaxies in the Local Volume

We present results from a GALEX ultraviolet (UV) survey of a complete sample of 390 galaxies within ~11 Mpc of the Milky Way. The UV data are a key component of the composite Local Volume Legacy (LVL), an ultraviolet-to-infrared imaging program designed to provide an inventory of dust and star formation in nearby spiral and irregular galaxies. The ensemble dataset is an especially valuable resource for studying star formation in dwarf galaxies, which comprise over 80% of the sample. We describe the GALEX survey programs which obtained the data and provide a catalog of far-UV (~1500 Angstroms) and near-UV (~2200 Angstroms) integrated photometry. General UV properties of the sample are briefly discussed. We compute two measures of the global star formation efficiency, the SFR per unit HI gas mass and the SFR per unit stellar mass, to illustrate the significant differences that can arise in our understanding of dwarf galaxies when the FUV is used to measure the SFR instead of H-alpha. We find that dwarf galaxies may not be as drastically inefficient in coverting gas into stars as suggested by prior H-alpha studies. In this context, we also examine the UV properties of late-type dwarf galaxies that appear to be devoid of star formation because they were not detected in previous H-alpha narrowband observations. Nearly all such galaxies in our sample are detected in the FUV, and have FUV SFRs that fall below the limit where the H-alpha flux is robust to Poisson fluctuations in the formation of massive stars. The UV colors and star formation efficiencies of H-alpha-undetected, UV-bright dwarf irregulars appear to be relatively unremarkable with respect to those exhibited by the general population of star-forming galaxies.Comment: submitted to ApJS, revised per referee's comments; accepted Oct. 30 w/o further revision; 37 pages; figure 6 omitted due to size; figure available from http://users.obs.carnegiescience.edu/jlee/paper

The GALEX Ultraviolet Atlas of Nearby Galaxies

We present images, integrated photometry, surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the GALEX satellite in its far-ultraviolet (FUV; 1516A) and near-ultraviolet (NUV; 2267A) bands. (...) This data set has been complemented with archival optical, near-infrared, and far-infrared fluxes and colors. We find that the integrated (FUV-K) color provides robust discrimination between elliptical and spiral/irregular galaxies and also among spiral galaxies of different sub-types. Elliptical galaxies with brighter K-band luminosities (i.e. more massive) are redder in (NUV-K) color but bluer in (FUV-NUV) than less massive ellipticals. In the case of the spiral/irregular galaxies our analysis shows the presence of a relatively tight correlation between the (FUV-NUV) color and the total infrared-to-UV ratio. The correlation found between (FUV-NUV) color and K-band luminosity (with lower luminosity objects being bluer than more luminous ones) can be explained as due to an increase in the dust content with galaxy luminosity. The images in this Atlas along with the profiles and integrated properties are publicly available through a dedicated web page at http://nedwww.ipac.caltech.edu/level5/GALEX_Atlas/Comment: 181 pages, 10 figures, accepted for publication in ApJS (abstract abridged

UV properties of early-type galaxies in the Virgo cluster

We study the UV properties of a volume limited sample of early-type galaxies in the Virgo cluster combining new GALEX far- (1530 A) and near-ultraviolet (2310 A) data with spectro-photometric data available at other wavelengths. The sample includes 264 ellipticals, lenticulars and dwarfs spanning a large range in luminosity (M(B)<-15). While the NUV to optical or near-IR color magnitude relations (CMR) are similar to those observed at optical wavelengths, with a monotonic reddening of the color index with increasing luminosity, the (FUV-V) and (FUV-H) CMRs show a discontinuity between massive and dwarf objects. An even more pronounced dichotomy is observed in the (FUV-NUV) CMR. For ellipticals the (FUV-NUV) color becomes bluer with increasing luminosity and with increasing reddening of the optical or near-IR color indices. For the dwarfs the opposite trend is observed. These observational evidences are consistent with the idea that the UV emission is dominated by hot, evolved stars in giant systems, while in dwarf ellipticals residual star formation activity is more common.Comment: 5 pages, 2 figures, 1 table. Accepted for publication in Astrophysical Journal Letter

Radial distribution of stars, gas and dust in SINGS galaxies. I. Surface photometry and morphology

We present ultraviolet through far-infrared surface brightness profiles for the 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). The imagery used to measure the profiles includes GALEX UV data, optical images from KPNO, CTIO and SDSS, near-IR data from 2MASS, and mid- and far-infrared images from Spitzer. Along with the radial profiles, we also provide multi-wavelength asymptotic magnitudes and several non-parametric indicators of galaxy morphology: the concentration index (C_42), the asymmetry (A), the Gini coefficient (G) and the normalized second-order moment of the brightest 20% of the galaxy's flux (M_20). Our radial profiles show a wide range of morphologies and multiple components (bulges, exponential disks, inner and outer disk truncations, etc.) that vary not only from galaxy to galaxy but also with wavelength for a given object. In the optical and near-IR, the SINGS galaxies occupy the same regions in the C_42-A-G-M_20 parameter space as other normal galaxies in previous studies. However, they appear much less centrally concentrated, more asymmetric and with larger values of G when viewed in the UV (due to star-forming clumps scattered across the disk) and in the mid-IR (due to the emission of Polycyclic Aromatic Hydrocarbons at 8.0 microns and very hot dust at 24 microns).Comment: 66 pages in preprint format, 14 figures, published in ApJ. The definitive publisher authenticated version is available online at http://dx.doi.org/10.1088/0004-637X/703/2/156

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

An Ultraviolet-to-Radio Broadband Spectral Atlas of Nearby Galaxies

The ultraviolet-to-radio continuum spectral energy distributions are presented for all 75 galaxies in the Spitzer Infrared Nearby Galaxies Survey (SINGS). A principal component analysis of the sample shows that most of the sample's spectral variations stem from two underlying components, one representative of a galaxy with a low infrared-to-ultraviolet ratio and one representative of a galaxy with a high infrared-to-ultraviolet ratio. The influence of several parameters on the infrared-to-ultraviolet ratio is studied (e.g., optical morphology, disk inclination, far-infrared color, ultraviolet spectral slope, and star formation history). Consistent with our understanding of normal star-forming galaxies, the SINGS sample of galaxies in comparison to more actively star-forming galaxies exhibits a larger dispersion in the infrared-to-ultraviolet versus ultraviolet spectral slope correlation. Early type galaxies, exhibiting low star formation rates and high optical surface brightnesses, have the most discrepant infrared-to-ultraviolet correlation. These results suggest that the star formation history may be the dominant regulator of the broadband spectral variations between galaxies. Finally, a new discovery shows that the 24 micron morphology can be a useful tool for parametrizing the global dust temperature and ultraviolet extinction in nearby galaxies. The dust emission in dwarf/irregular galaxies is clumpy and warm accompanied by low ultraviolet extinction, while in spiral galaxies there is typically a much larger diffuse component of cooler dust and average ultraviolet extinction. For galaxies with nuclear 24 micron emission, the dust temperature and ultraviolet extinction are relatively high compared to disk galaxies.Comment: Accepted for publication in the Astrophysical Journal; Fixed radio flux density units (mJy

GALEX UV Spectroscopy and Deep Imaging of LIRGs in the ELAIS S1 field

The ELAIS S1 field was observed by GALEX in both its Wide Spectroscopic and Deep Imaging Survey modes. This field was previously observed by the Infrared Space Observatory and we made use of the catalogue of multi-wavelength data published by the ELAIS consortium to select galaxies common to the two samples. Among the 959 objects with GALEX spectroscopy, 88 are present in the ELAIS catalog and 19 are galaxies with an optical spectroscopic redshift. The distribution of redshifts covers the range $0<z<1.6$. The selected galaxies have bolometric IR luminosities $10<Log(L_{IR})<13$ (deduced from the $15 \mu m$ flux using ISOCAM) which means that we cover a wide range of galaxies from normal to Ultra Luminous IR Galaxies. The mean ($\sigma$) UV luminosity (not corrected for extinction) amounts to $Log(\lambda.L_{1530}) = 9.8 (0.6)$ L_\sun for the low-z ($z \le 0.35$) sample. The UV slope $\beta$ (assuming $f_\lambda \propto \lambda^\beta$) correlates with the GALEX FUV-NUV color if the sample is restricted to galaxies below $z < 0.1$. Taking advantage of the UV and IR data, we estimate the dust attenuation from the IR/UV ratio and compare it to the UV slope $\beta$. We find that it is not possible to uniquely estimate the dust attenuation from $\beta$ for our sample of galaxies. These galaxies are highly extinguished with a median value $A_{FUV} = 2.7 \pm 0.8$. Once the dust correction applied, the UV- and IR-based SFRs correlate. For the closest galaxy with the best quality spectrum, we see a feature consistent with being produced by a bump near 220nm in the attenuation curve.Comment: This paper has been published as part of the GALEX ApJL Special Issue (ApJ 619, L63

Extinction law variations and dust excitation in the spiral galaxy NGC 300

We investigate the origin of the strong radial gradient in the ultraviolet-to-infrared ratio in the spiral galaxy NGC 300, and emphasize the importance of local variations in the interstellar medium geometry, concluding that they cannot be neglected with respect to metallicity effects. This analysis is based upon a combination of maps from GALEX and Spitzer, and from the ground (UBVRI, Halpha and Hbeta). We select ionizing stellar clusters associated with HII regions of widely varying morphologies, and derive their fundamental parameters from population synthesis fitting of their spectral energy distributions, measured to eliminate local backgrounds accurately. From these fits, we conclude that the stellar extinction law is highly variable in the line of sight of young clusters of similar ages. In the particular model geometry that we consider most appropriate to the sampled regions, we checked that our findings are not significantly altered by the correct treatment of radiative transfer effects. The variations are systematic in nature: extinction laws of the Milky Way or LMC type are associated with compact HII regions (the compacity being quantified in two different ways), while clusters surrounded by diffuse HII regions follow extinction laws of the 30 Doradus or SMC type. The Calzetti starburst attenuation law, although most often degenerate with the 30 Doradus extinction law, overpredicts ionizing photon fluxes by large amounts. We also find that the extinction law variations are correlated with the column density of dust species emitting in the near- and mid-infrared. Finally, we briefly discuss the nebular to stellar extinction ratios, and the excitation of aromatic band carriers, invalidating their claimed association with cold dust.Comment: accepted for publication in ApJ -- figure 6 abridged her