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We describe HST imaging of recent star formation complexes located in the extended UV disk (XUV-disk) component of NGC 5236 (M 83), NGC 5055 (M 63), and NGC 2090. Photometry in four FUV-visible bands permits us to constrain the type of resolved stars and effective age of clusters, in addition to extinction. The preliminary results given herein focus on CMD analysis and clustering properties in this unique star-forming environment.

We present the Galaxy Evolution Exlorer (GALEX) near-ultraviolet (2310 angstrom) and far-ultraviolet ( 1530 angstrom) galaxy luminosity functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3 <= M-AB <= -13.3. The luminosity functions are consistent with previous (similar to 2 mag shallower) estimates based on the FOCA and FAUST experiments, but they display a steeper faint-end slope than the GALEX luminosity function for local field galaxies. Using spectrophotometric optical data, we select star-forming systems from quiescent galaxies and study their separate contributions to the cluster luminosity function. We find that the UV luminosity function of cluster star-forming galaxies is consistent with the field. The difference between the cluster and field luminosity functions is entirely due to the contribution at low luminosities (M-AB > -16 mag) of non - star-forming, early-type galaxies that are significantly overdense in clusters.

The NASA Galaxy Evolution Explorer (GALEX) satellite has obtained simultaneous near and far ultraviolet light curves of the ROTSE-I Catalog RR Lyrae ab-type variable star J143753.84+345924.8. A series of 38 GALEX Deep Imaging Survey observations well distributed in phase within the star's 0.56432d period shows an AB=4.9mag variation in the far UV (1350-1750A) band and an AB=1.8mag variation in the near UV (1750-2750A) band, compared with only a 0.8mag variation in the broad, unfiltered ROTSE-I (4500-10000A) band. These GALEX UV observations are the first to reveal a large RR Lyrae amplitude variation at wavelengths below 1800A. We compare the GALEX and ROTSE-I observations to predictions made by recent Kurucz stellar atmosphere models. We use published physical parameters for the comparable period (0.57433d), well-observed RR Lyrae star WY Antliae to compute predicted FUV, NUV, and ROTSE-I light curves for J143753.84+345924.8. The observed light curves agree with the Kurucz predictions for [Fe/H]=-1.25 to within AB=0.2mag in the GALEX NUV and ROTSE-I bands, and within 0.5mag in the FUV. At all metallicities between solar and one hundredth solar, the Kurucz models predict 6-8mag of variation at wavelengths between 1000-1700A. Other variable stars with similar temperature variations, such as Cepheids, should also have large-amplitude FUV light curves, observable during the ongoing GALEX imaging surveys., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http:/www.galex.caltech.edu/PUBLICATIONS after November 22, 2004

We have imaged the nearby galaxy merger Arp 299 at arcsecond and milliarcsecond resolution, using both the Very Large Array and the Very Long Baseline Array. The large-scale radio emission from the merger contains 5 bright, compact radio sources embedded in diffuse emission, with diameters less than 200 pc. Supernova rates of 0.1 to 1 per year are required to produce the VLA-detected radio emission in these sources. Two of the compact VLA radio sources, designated Source A and Source D, also have been detected and imaged at milliarcsecond scales. Source A, which is associated with the nucleus of one of the merging galaxies, contains five milliarcsecond-scale sources, each with a radio power between 100 and 1000 times that of the Galactic supernova remnant Cassiopeia A. Four of these have flat or inverted spectra and appear to be young supernovae. Three of the VLBI-scale sources are located within 10 pc (projected) of one another, and two are separated by less than 3 pc, indicating that they all may be within the same super starcluster or complex of such clusters. The brightest VLBI-scale source, A0, has an extremely inverted pectrum, with alpha larger than +2 at gigahertz frequencies. It seems to be the youngest supernova, which has not yet broken out of its circumstellar shell. The milliarcsecond radio sources within Source A appear to constitute a upernova factory, confirming the presence of an extreme starburst that peaked at least a few million years ago., Comment: Accepted for the Astrophysical Journal, 22 pages, 10 figures

Ultraviolet imaging with the Galaxy Evolution Explorer (GALEX) has revealed an extensive sample of UV-bright stellar complexes in the extreme outer disk of M83, extending to about four times the radius where the majority of HII regions are detected (R_HII = 5.1' or 6.6 kpc). These sources are typically associated with large-scale filamentary HI structures in the warped outer disk of M83, and are distributed beyond the galactocentric radii at which molecular ISM has yet been detected. We present measured properties of these stellar complexes, including FUV and NUV magnitudes and local gas surface density. Only a subset of the outer disk UV sources have corresponding HII regions detected in H-alpha imaging, consistent with a sample of mixed age in which some sources are a few Myr old and others are much more evolved (~ 10^8 yr)., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

M32, the compact elliptical-galaxy companion to the Andromeda spiral galaxy has been imaged by the Galaxy Evolution Explorer (GALEX) in two ultraviolet bands, centered at ~1500 (FUV) and 2300 Angstroms (NUV). The imaging data have been carefully decomposed so as to properly account for the complicated background contamination from the disk of M31. We have derived the surface brightness and color profiles finding a slightly positive color gradient of Delta(FUV-B)/Delta log(r)=+0.15+/-0.03 within one effective radius. Earlier data from the Ultraviolet Imaging Telescope suggested that M32 had an extremely large (negative) FUV-optical color gradient (Delta(FUV-B)/Delta log(r)<-2), inverted with respect to the majority of gradients seen in giant elliptical galaxies. Our new results show that, despite of its very low UV-upturn, M32 has similar UV properties to those observed in luminous elliptical galaxies., Comment: 5 pages, 3 figures. This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

The total ultraviolet (UV) flux (from 1412 to 2718 AA) of M 101 is compared on a pixel-to-pixel basis with the total far-infrared (FIR) flux (from 60 to 170 micron), using the maps of the galaxy taken by GALEX in the near-UV and far-UV and by ISOPHOT at 60, 100 and 170 micron. The main result of this investigation is the discovery of a tight dependence of the FIR/UV ratio on radius, with values monotonically decreasing from around 4 in the nuclear region to nearly zero towards the edge of the optical disk. Although the tightness of this dependence is in part attributable to resolution effects, the result is consistent with the presence of a large-scale distribution of diffuse dust having a face-on optical depth which decreases with radius and which dominates over the more localized variations in opacity between the arm and interarm regions. We also find a trend for the FIR/UV ratio to take on higher values in the regions of diffuse interarm emission than in the spiral-arm regions, at a given radius. This is interpreted quantitatively in terms of the escape probability of UV photons from spiral arms and their subsequent scattering in the interarm regions, and in terms of the larger relative contribution of optical photons to the heating of the dust in the interarm regions., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) ApJ Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after Nov. 22, 2004. For version with full resolution images go to: http://edoc.mpg.de/204700.0

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

We have used the GALEX UV photometric data to construct a first near-ultraviolet (NUV) color-magnitude relation (CMR) for the galaxies pre-classified as early-type by SDSS studies. The NUV CMR is a powerful tool for tracking the recent star formation history in early-type galaxies, owing to its high sensitivity to the presence of young stellar populations. Our NUV CMR for UV-weak galaxies shows a well-defined slope and thus will be useful for interpreting the restframe NUV data of distant galaxies and studying their star formation history. Compared to optical CMRs, the NUV CMR shows a substantially larger scatter, which we interpret as evidence of recent star formation activities. Roughly 15% of the recent epoch (z < 0.13) bright (M[r] < -22) early-type galaxies show a sign of recent (< 1Gyr) star formation at the 1-2% level (lower limit) in mass compared to the total stellar mass. This implies that low level residual star formation was common during the last few billion years even in bright early-type galaxies., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We present measurements of the FUV (1530A) and NUV (2310A) galaxy luminosity functions (LF) at low redshift (z<0.2) from GALEX observations matched to the 2dF Galaxy Redshift Survey. We split our FUV and NUV samples into two UV-bj color bins and two redshift bins. As observed at optical wavelengths, the local LF of the bluest galaxies tend to have steeper faint end slopes and fainter characteristic magnitudes M* than the reddest subsamples. We find evidence for color dependent evolution at very low redshift in both bands, with bright blue galaxies becoming dominant in the highest redshift bin. The evolution of the total LF is consistent with an 0.3 magnitude brightening between z=0 and 0.13, in agreement with the first analysis of deeper GALEX fields probing adjacent and higher redshifts., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at : http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We present measurements of the UV galaxy luminosity function and the evolution of luminosity density from GALEX observations matched to the Sloan Digital Sky Survey (SDSS). We analyze galaxies in the Medium Imaging Survey overlapping the SDSS DR1 with a total coverage of 44 deg^2. Using the combined GALEX+SDSS photometry, we compute photometric redshifts and study the LF in three redshift shells between z=0.07 and 0.25. The Schechter function fits indicate that the faint-end slope alpha is consistent with -1.1 at all redshifts but the characteristic UV luminosity M* brightens by 0.2 mag from z=0.07 to 0.25. In the lowest redshift bin, early and late type galaxies are studied separately and we confirm that red galaxies tend to be brighter and have a shallower slope alpha than blue ones. The derived luminosity densities are consistent with other GALEX results based on a local spectroscopic sample from 2dF and the evolution follows the trend reported by deeper studies., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We present Galaxy Evolution Explorer (GALEX) images of the prototypical edge-on starburst galaxies M82 and NGC253. Our initial analysis is restricted to the complex of ultraviolet (UV) filaments in the starburst-driven outflows in the galaxy halos. The UV luminosities in the halo are too high to be provided by shock-heated or photoionized gas except perhaps in the brightest filaments in M82, suggesting that most of the UV light is the stellar continuum of the starburst scattered into our line of sight by dust in the outflow. This interpretation agrees with previous results from optical imaging polarimetry in M82. The morphology of the UV filaments in both galaxies shows a high degree of spatial correlation with H-alpha and X-ray emission. This indicates that these outflows contain cold gas and dust, some of which may be vented into the intergalactic medium (IGM). UV light is seen in the ``H-alpha cap'' 11 kpc North of M82. If this cap is a result of the wind fluid running into a pre-existing gas cloud, the gas cloud contains dust and is not primordial in nature but was probably stripped from M82 or M81. If starburst winds efficiently expel dust into the IGM, this could have significant consequences for the observation of cosmologically distant objects., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We derive a variety of physical parameters including star formation rates (SFRs), dust attenuation and burst mass fractions for 6472 galaxies observed by the Galaxy Evolution Explorer (GALEX) and present in the SDSS DR1 main spectroscopic sample. Parameters are estimated in a statistical way by comparing each observed broad-band SED (two GALEX and five SDSS bands) with an extensive library of model galaxy SEDs, which cover a wide range of star formation histories and include stochastic starbursts. We compare the constraints derived using SDSS bands only with those derived using the combination of SDSS and GALEX photometry. We find that the addition of the GALEX bands leads to significant improvement in the estimation of both the dust optical depth and the star formation rate over timescales of 100 Myr to 1 Gyr in a galaxy. We are sensitive to SFRs as low as 10^{-3} M_sun/yr, and we find that low levels of star formation (SF) are mostly associated with early-type, red galaxies. The least massive galaxies have ratios of current to past-averaged SF rates (b-parameter) consistent with constant SF over a Hubble time. For late-type galaxies, this ratio on average decreases with mass. We find that b correlates tightly with NUV-r color, implying that the SF history of a galaxy can be constrained on the basis of the NUV-r color alone. The fraction of galaxies that have undergone a significant starburst episode within the last 1 Gyr steeply declines with mass-from ~20% for galaxies with ~10^8 M_sun to ~5% for ~10^11 M_sun galaxies., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) ApJ Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS after Nov 22, 2004

We present ultraviolet photometry for globular clusters (GCs) in M31 from 15 square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect 200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750 Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses, respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV, to an approximate limiting V magnitude of 19. Out of six clusters with [Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore, we find no candidate metal-rich clusters with significant FUV flux, because of the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC 6441, which are metal-rich Galactic GCs with hot HB stars. We show that our GALEX photometry follows the general color trends established in previous UV studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in the UV and with population synthesis models, we suggest that the age range of M31 and Galactic halo GCs are similar., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We use the far-UV (FUV) and near-UV (NUV) images of M83 obtained by GALEX to compute the radial profile of the UV spectral slope in the star forming disk. We briefly present a model of its chemical evolution which allows us to obtain realistic intrinsic properties of the stellar populations. Using corollary data, we also compute the profiles of H-alpha/H-beta and of the total IR (TIR) to FUV ratio. Both data and model are used to estimate and compare the extinction gradients at the FUV wavelength obtained from these various indicators. We discuss the implications for the determination of the star formation rate., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004. A high resolution version of figure 1 is available at http://www.ociw.edu/~boissier/M83/fig1.ps

New GALEX observations have detected significant FUV (1530 Angstroms) and NUV (2310 Angstroms) emission from stellar substructures within the tidal tails of four ongoing galaxy mergers. The UV-bright regions are optically faint and are coincident with HI density enhancements. FUV emission is detected at any location where the HI surface density exceeds ~2 M_sun pc^{-2}, and is often detected in the absence of visible wavelength emission. UV luminosities of the brighter regions of the tidal tails imply masses of 10^6 M_sun to ~10^9 M_sun in young stars in the tails, and HI luminosities imply similar HI masses. UV-optical colors of the tidal tails indicate stellar populations as young as a few Myr, and in all cases ages < 400Myr. Most of the young stars in the tails formed in single bursts rather than resulting from continuous star formation, and they formed *in situ* as the tails evolved. Star formation appears to be older near the parent galaxies and younger at increasing distances from the parent galaxy. This could be because the star formation occurs progressively along the tails, or because the star formation has been inhibited near the galaxy/tail interface. The youngest stellar concentrations, usually near the ends of long tidal tails, have masses comparable to confirmed tidal dwarf galaxies and may be newly forming galaxies undergoing their first burst of star formation., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

In order to investigate the origin of the far-UV (FUV) flux from the early-type galaxies, Galaxy Evolution Explorer (GALEX) is collecting the UV data for the elliptical-rich clusters at moderate redshifts (z < 0.2) where the dominant FUV source is predicted to be hot horizontal-branch (HB) stars and their post-HB progeny. Here we present our first result for the early-type galaxies in Abell 2670 at z = 0.076. Compared to NGC 1399, a nearby giant elliptical galaxy in the Fornax cluster, it appears that the rest-frame FUV - V color of the giant ellipticals gets redder by ~ 0.7 mag at the distance of Abell 2670 (z = 0.076; look-back time ~ 1.0 Gyr). Although a detailed comparison with the models is postponed until more cluster data are accumulated, it is interesting to note that this value is consistent with the variation predicted by the population synthesis models where the mean temperature of HB stars declines rapidly with increasing look-back time., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS

The GALEX (Galaxy Evolution Explorer) Nearby Galaxies Survey is providing deep far-UV and near-UV imaging for a representative sample of galaxies in the local universe. We present early results for M51 and M101, from GALEX UV imaging and SDSS optical data in five bands. The multi-band photometry of compact stellar complexes in M101 is compared to population synthesis models, to derive ages, reddening, reddening-corrected luminosities and current/initial masses. The GALEX UV photometry provides a complete census of young compact complexes on a approximately 160pc scale. A galactocentric gradient of the far-UV - near-UV color indicates younger stellar populations towards the outer parts of the galaxy disks, the effect being more pronounced in M101 than in M51., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Full paper available from http://dolomiti.pha.jhu.edu . Links to full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We present Galaxy Evolution Explorer (GALEX) far-UV and near-UV mosaic observations covering the entirety of M31 and M33. For both targets, we measure the decline of surface brightness (in FUV and NUV) and changes in FUV--NUV color as a function of galactocentric radius. These UV radial profiles are compared to the distribution of ionized gas traced by H-alpha emission. We find that the extent of the UV emission, in both targets, is greater than the extent of the observed HII regions and diffuse ionized gas. We determine the ultraviolet diffuse fraction in M33 using our FUV observations and compare it to the H-alpha diffuse fraction obtained from wide-field narrow-band imaging. The FUV diffuse fraction appears to be remarkably constant near 0.65 over a large range in galactocentric radius, with departures to higher values in circumnuclear regions and, most notably, at the limit of the H-alpha disk. We suggest that the increase in FUV diffuse fraction at large galactocentric radii could indicate that a substantial portion of the diffuse emission beyond this point is not generated in situ but rather scattered from dust, after originating in the vicinity of the disk's outermost HII regions. Radial variation of the H-alpha diffuse fraction was also measured. We found the H-alpha diffuse fraction generally near 0.4 but rising toward the galaxy center, up to 0.6. We made no attempt to correct our diffuse fraction measurements for position-dependent extinction, so the quoted values are best interpreted as upper limits given the plausibly higher extinction for stellar clusters relative to their surroundings., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004. Individual high-resolution figures can be found at http://dolomiti.pha.jhu.edu/publgoto.html

We compare the dust attenuation properties of two samples of galaxies purely selected in the near-ultraviolet (NUV) band (1750-2750 A, lambda_m = 2310 A) and in the far-infrared (FIR) at 60micron. These samples are built using the GALEX and IRAS sky surveys over ~600 square degrees. The NUV selected sample contains 95 galaxies detected down to NUV=16mag (AB system). 83 galaxies in this sample are spirals or irregulars and only two of them are not detected at 60micron. The FIR selected sample is built from the IRAS PSCz catalog complete down to 0.6Jy. Among the 163 sources, we select 118 star forming galaxies well measured by IRAS, all but 1 are detected in NUV and 14 galaxies are not detected in the far-ultraviolet (FUV) band (1350-1750 A, lambda_m = 1530 A). The dust to ultraviolet (NUV and FUV) flux ratio is calibrated to estimate the dust attenuation at both wavelengths. The median value of the attenuation in NUV is found to be ~1 mag for the NUV selected sample versus ~2 mag for the FIR selected one. Within both samples, the dust attenuation is found to correlate with the luminosity of the galaxies. Almost all the NUV selected galaxies and 2/3 of the FIR selected sample exhibit a lower dust attenuation than that expected from the tight relation found previously for starburst galaxies between the dust attenuation and the slope of the ultraviolet continuum. The situation is inverse for one third of the FIR selected galaxies: their extinction is higher than that deduced from their FUV-NUV color and the relation valid for starbursts., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue

We use the GALEX (Galaxy Evolution Explorer) Medium Imaging Survey (MIS) and All-Sky Imaging Survey (AIS) data available in the first internal release, matched to the SDSS catalogs in the overlapping regions, to classify objects by comparing the multi-band photometry to model colors. We show an example of the advantage of such broad wavelength coverage (GALEX far-UV and near-UV, SDSS ugriz) in classifying objects and augmenting the existing samples and catalogs. From the MIS [AIS] sample over an area of 75 [92] square degrees, we select a total of 1736 [222] QSO candidates at redshift less than 2, significantly extending the number of fainter candidates, and moderately increasing the number of bright objects in the SDSS list of spectroscopically confirmed QSO. Numerous hot stellar objects are also revealed by the UV colors, as expected., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Full paper available from http://dolomiti.pha.jhu.edu . Links to the full set of papers available at http://www.galex.caltech.edu/PUBLICATIONS/ after Nov.22, 2004

We report the first year on-orbit performance results for the Galaxy Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter modified Ritchey-Chretien telescope with a 1.25 degree field of view, selectable imaging and objective grism spectroscopic modes, and an innovative optical system with a thin-film multilayer dichroic beam splitter that enables simultaneous imaging by a pair of photon counting, microchannel plate, delay line readout detectors. Initial measurements demonstrate that GALEX is performing well, meeting its requirements for resolution, efficiency, astrometry, bandpass definition and survey sensitivity., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue

We present ultraviolet photometry for a sample of morphologically early-type galaxies selected by matching the Sloan Digital Sky Survey Data Release 1 with the GALEX Medium and All-sky Imaging Surveys. We obtain a working sample of 1032 early-type galaxies with GALEX FUV detections, SDSS spectroscopy, and $z<0.2$. Using the SDSS spectra to identify galaxies with even weak star formation or evidence of AGN, and further removing galaxies with any evidence of non early-type morphology, we derive a final sample of 172 red quiescent early-type galaxies. We find that the $FUV-r$ color has a full range of 5 mag. Plotting against the $FUV-r$ color the metallicity sensitive Lick $\rm Mg_2$ and D4000 indices, and the stellar velocity dispersion, we find no correlation between our measurement of UV rising flux, and any parameter sensitive to metallicity., Comment: This paper will be published as part of the Galaxy Evolution Explorer (GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after November 22, 2004

We present new 6, 3.6, and 2 cm VLA radio observations of the nearby merger system NGC 3256, with resolutions of ~100 pc, which reveal compact radio sources embedded in more diffuse emission at all three wavelengths. The two radio nuclei are partially resolved, but the two dominant compact sources that remain coincide with the two most powerful compact Ultraluminous X-ray sources (ULXs) recently reported by Lira et al. The radio/X-ray ratios for these two sources are too high by factors of >100-1000 to be normal X-ray binaries. However, their radio and X-ray powers and ratios are consistent with low-luminosity active galactic nuclei (LLAGNs), and optical emission lines suggest the presence of a nuclear disk around the northern nucleus. If the two nuclear ULXs are LLAGNs, their associated black holes are separated by only \~1kpc, about 6 times closer to one another than those found recently in the merger galaxy NGC 6240. A third ULX on the outskirts of the merger is also a radio source, and probably is a collection of supernova remnants. The remaining ULXs are not coincident with any source of compact radio emission, and are consistent with expectations for beamed X-ray binaries or intermediate-mass black holes., Comment: Accepted for ApJ (10 pages, 5 figures)

We report the results of the analysis of the extended soft emission discovered in the Chandra ACIS pointing at the merging system NGC 4038/39 (the Antennae). We present a `multi-color' X-ray image that suggests both extensive absorption by the dust in this system, peaking in the contact region, as well as variations in the temperature of different emitting regions of the hot interstellar medium (ISM). Spectral fits to multi-component thermal emission models confirm this picture and give a first evaluation of the parameters of the hot plasma. We compare the diffuse X-ray emission with radio continuum (6cm), HI, CO, and H$\alpha$ images to take a first look at the multi-phase ISM of the Antennae galaxies. We find that the hot (X-ray) and cold (CO) gas have comparable thermal pressures in the two nuclear regions. We also conclude that the displacement between the peak of the diffuse X-ray emission in the north of the galaxy system, towards the inner regions of the northern spiral arm (as defined by H$\alpha$, radio continuum and HI), could result from ram pressure of infalling HI clouds., Comment: Accepted by ApJ

We report on deep imaging in 2 filters with the PC2 camera of HST, of five QSOs at redshift ~2, with a range of optical and radio luminosity. The observations included a suite of PSF observations which were used to construct new PSF models, described elsewhere by Dumont et al. The new PSF models were used to remove the QSO nucleus from the images. We find that the host galaxies have resolved flux of order 10% of the QSO nuclei, and are generally luminous and blue, indicating active star-formation. While most have clearly irregular morphologies, the bulk of the flux can be modelled approximately by an r**1/4 law. However, all host galaxies also have an additional approximately exponential luminosity profile beyond a radius about 0.8 arcsec, as also seen in ground-based data with larger telescopes. The QSOs all have a number of nearby faint blue companions which may be young galaxies at the QSO redshift. We discuss implications for evolution of the host galaxies, their spheroidal populations, and central black holes., Comment: 18 pages including 2 tables; to appear in AJ