Abstracts for Accepted Cycle 2 Programs
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We propose to make a complete survey in the FUV and NUV bands at a depth of the MIS (1.5ksec/pointing) of the central 120 sq.deg. of the Virgo cluster region. Combined with fields already available, 82 new pointing are required to complete this project. The data will be used to make the first, complete study of the UV properties of galaxies inhabiting a rich cluster down to the dwarf population, including both star forming and quiescent objects, from the cluster core to the periphery. The data will be combined with our 2-D chemo-spectrophotometric models of galaxy evolution and with data that our team is gathering or has already obtained in other bands (optical: NGVS; infrared: HeViCS; HI: ALFALFA) to make a complete and exhaustive study of the effects of the environment on the evolution of galaxies in high density regions.
Two cataclysmic variables containing pulsating white dwarfs underwent rare outbursts in 2007 (GW Lib and V455 And). As we know outbursts heat the white dwarfs by more than 10,000K and they gradually cool to their quiescent temperatures over the course of about 3 years, these two objects present the first unique opportunity to follow the pulsation spectrum of a white dwarf as it cools on much more rapid timescales than evolutionary ones for single white dwarfs. As these 2 objects cool, they should re-enter their instability strips and we can witness changes in the driving mechanism and detect modes that are excited by the T changes. Our 2008 ground-based data on GW Lib showed an intermittent new pulsation at a longer period than at quiescence. The data in 2010 will be the critical 3rd year and will be combined with our DOT and Cycle 4,5 GI observations to determine the long term cooling of GW Lib. Similar information will be obtained for V455 And. The higher pulse amplitude in UV vs optical and the time-tag mode means that GALEX can provide optimum data over the optical. Data on both systems will provide an important contrast in how the white dwarfs react to an outburst, as GW Lib at quiescence has a hot white dwarf far outside the normal instability strip for non-accreting white dwarfs, while V455 And is cool and inside this strip.
H-alpha nebular emission and the non-ionizing UV continuum flux trace star formation over different timescales, and we propose to exploit this difference to constrain the recent star formation histories of galaxies at z=0.8. At these redshifts the overall star formation activity in massive galaxies is nearly an order of magnitude higher than it is today, yet the causes for this increased activity are not well understood. Are such high SFRs "normal" at these redshifts, or is it the consequence of many galaxies experiencing bursts, for example, due to more frequent mergers and interactions? We directly answer this question by determining the primary mode of star formation of galaxies at z=0.8 and comparing with local measurements. H alpha fluxes, typically rare at these redshifts, will be provided by our near-IR narrow-band imaging survey in the Subaru-XMM/Newton Deep Survey (SXDS) field. To obtain similar rest-frame FUV detection rates and flux ratio errors that will allow us to distinguish different SF histories, we require 50 ks of new GALEX imaging, which will nearly triple the depth of the currently available GALEX NUV data in this field. SXDS, like COSMOS and EGS, is a primary extragalactic deep field with a rich multiwavelength dataset (including UKIDSS near-IR Ultra Deep Survey field), yet has only 15% of their GALEX depth. In addition to facilitating our project, the new data will help reduce this discrepancy and have lasting legacy value. PSF-extracted catalogs of this field based on archival plus new observations will be provided to the public soon after the data were received.
We propose to extend our analysis of the mid-IR through optical properties of type 1 SDSS quasars into the UV regime as probed by GALEX. We have previously built multi-wavelength SEDs for 259 quasars with both Sloan Digital Sky Survey (SDSS) and Spitzer photometry, supplemented by GALEX data where available (Richards et al. 2006). Since that time the SDSS+Spitzer sample has grown to over 400 spectroscopically confirmed SDSS quasars at the same time that the GALEX coverage and depth has improved in these same regions. Our group has also identified thousands of photometrically selected quasars (both type 1 and type2) in the proposed fields. We will further extend our analysis to the deepest imaging from the SDSS (on "Stripe 82") where we have been awarded warm Spitzer time to observe over 300 z>2.2 quasars. GALEX data fills crucial gaps in our SED analyses, acting essentially as the 6th and 7th broadband SDSS filters and allowing direct comparisons of the rest-frame UV between high- and low-redshift quasars. Current investigations that rely on estimated masses and accretion rates for quasars do so using tenuous extrapolations from monochromatic to bolometric luminosities. These bolometric corrections can be improved by having better sampling of the true SEDs of quasars. For low-redshift quasars, GALEX can be used to determine the amount/type of dust intrinsic to quasars and thus the intrinsic spectral index. For higher redshift quasars, we can statistically correct for Lyman-alpha forest absorption to unveil the true SED of quasars near where the quasar SED "turns over"; this information is crucial for models of accretion disk winds. Finally, analysis of the UV properties of z~3 quasars being targeted by the Baryon Oscillation Spectroscopic Survey (as part of SDSS-III) will enable more efficient rejection of interlopers among BOSS quasar targets
The Herschel Reference Survey (HRS) is a Herschel Guaranteed Time Key Program focused on the study of the dust properties of galaxies in the nearby universe. It represents the first survey sensitive to all the dust in galaxies of all Hubble types, covering a volume limited (15<D<25 Mpc) complete sample of 323 galaxies extracted from 2MASS. Here we propose to obtain FUV and NUV images at MIS depths for those galaxies which are not included in the planned GALEX observations. We will combine GALEX-UV data with Herschel, HI, CO, Halpha, optical and near-infrared observations to investigate the interplay between UV interstellar radiation field, dust, atomic and molecular hydrogen in the star formation cycle, to study the properties of the ISM in UV disks, to unravel the origin of UV emission and dust in elliptical galaxies, to shed light on the effects of the environment on dust and star formation and to determine the UV to sub-millimeter spectral energy distributions of galaxies along the Hubble sequence. Given the completeness and selection criteria of the HRS, a full UV coverage will provide a Legacy set of observations for the astronomical community, well beyond the synergy with Herschel.
We propose to obtain 1.5 ksec GALEX observations of a sample of massive gas-rich but underluminous galaxies, detected in the HI line by the currently ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey. Based on SDSS colors and a standard IMF, their HI to stellar mass ratio is larger than one, i.e., they are underluminous and most are blue fast rotators; few host AGNs. Residing in such large gas reservoirs, these galaxies may be in a critical stage of assembling themselves. GALEX FUV/NUV images will allow us to constrain the spatial extents and current rates of star formation as we ask why and how these particular galaxies have managed to maintain massive HI disks without forming massive stellar ones
We propose GALEX grism spectroscopy of a selected sample of Planetary Nebulae, with diameter larger than one arcminute. Targets have been selected from previous imaging in the GALEX archive, and show a prominent nebular shell in FUV and NUV broad-band images. We expect the grism data to produce a series of 2D images in the UV nebular emission lines, which we will extract and analyze together with optical data, to derive physical parameters, including carbon abundances. The results will be relevant to understand the late evolutionary phases of intermediate mass stars, and the yield of chemical elements, which drives the evolution of the interstellar medium. The resulting custom-extracted data will be made publicly available.
Large spectroscopic surveys conclude that environmental influences on galaxies properties are effective well outside cluster cores, at local galaxy densities more typical of the group environments. Hierarchical evolutionary scenarios suggest that accretion/merging episodes re-process group galaxies transforming them from field (i.e. spiral) to cluster-like (i.e. early-type) objects. This transformation drives groups from an "active" (i.e. star forming) phase to a "passive" one, more typical of dense environments. We propose to use GALEX to investigate this transition on six well selected loose groups containing an increasing fraction of early-type galaxies. GALEX will provide the crucial elements to determine a luminosity weighted dynamical analysis and the far UV part of the spectral energy distribution which will allow us to decipher the star formation history of the early-type galaxies, likely the debris of the group evolution during the ages.
We propose to image the z=0.055 cluster Abell 85 and its filament with GALEX. Our team discovered the filament initially using X-ray observations. Recently, in order to study the dynamical and star formation properties, we have further supplemented our dataset with more than 500 new spectra covering cluster galaxies down to r'=21. The proposed GALEX observations will allow a homogeneous coverage of both the filament and cluster down to a FUV magnitude of 25.2, detecting galaxies with bursts of star formation down to the mass of irregular dwarfs. We will measure UV extinction corrected star formation rates in galaxies belonging both to the cluster and the filament - estimates which are crucial in the understanding of galaxy evolution in and around clusters. Additionally, the data will be essential in analyzing the spectral energy distribution of the galaxy samples. In particular, we will be able to separate type-1 AGN from star-formation dominated galaxies.
We propose to observe the nearby stellar jet system of the symbiotic R Aqr. Recent work with Chandra and FUSE have shown that the jets are moving outward with a bulk velocity of up to 600 km/s, with new jets being formed on timescales of years or less. FUSE data have allowed us to develop a new model for these jets that successfully reproduces the O VI profiles, based on a hybrid radiative/non-radiative bow shock. Shock velocities of about 200-300 km/s are indicated. GALEX imagery and spectroscopy will provide fluxes for shock diagnostic lines such as C IV and He II to compare to this model and will help us understand the conditions in the 10^4 K gas behind the bow shock, the dominant temperature regime of the jet. We expect the GALEX data to tightly constrain the physical characteristics of the jets and thus their origins and formation mechanisms.
The rate of star formation (SFR) is a fundamental parameter shaping the evolution of a galaxy. In the extreme environments of starburst galaxies, the elevated levels of star formation can have a dramatic impact on the chemical composition and dynamics of the galaxy, on the future star formation within the galaxy, and potentially drive enriched material into the intergalactic medium surrounding the galaxy. While starbursts are a very important phenomenon with many aspects still not well understood, there has been no GALEX survey dedicated to the study of the nearest starburst galaxies. Starburst dwarf galaxies are ultimately an ultraviolet (UV) phenomenon due to their low dust content and as such warrant a legacy project of deep observations with GALEX that will produce a homogeneous archive. We propose a comprehensive comparison of the SFRs and spatial structure in twenty nearby, spatially resolved starburst galaxies derived from new and existing GALEX observations. Our sample of nearby starbursts is composed of galaxies for which we have reconstructed star formation histories (SFHs) from resolved stars using archival Hubble Space Telescope (HST) observations. The spatial structure, the SFRs, and the temporally resolved SFHs will allow us to understand the true nature of starbursts in dwarf galaxies for the first time. We will be able to determine how the bursts propagate within a galaxy, whether they are causally connected or of a more stochastic nature, and if starbursts are indeed ``self-quenching". Further, we will be able to probe the timescales of star formation responsible for the UV emission while considering the spatial migration of a starburst. Finally, the UV data will be coupled with Spitzer 24 micron and HST data sets to populate a new public archive of multi-wavelength observations of great use to a large community of researchers. Our proposed work will build our understanding of how galaxies change over time, one of NASA's strategic goals.
Giant LSB disk galaxies may be analogues of the extended UV-disk (XUV-disk) galaxy population operating on an extreme scale. Delayed formation of anomalously large, faint disks around otherwise typical galaxies could occur via stochastic accretion of gas from a merger. Observations with GALEX now suggest that accretion-driven outer structure formation is more common than thought. We propose to deeply observe three E / S0 galaxies hosting giant LSB HI disks in order to study their star formation history (with corollary visible imaging) and estimate the star formation efficiency in the tenuous outer gas disk. Our target galaxies were selected to represent a sequence in the degree to which the giant LSB component has already evolved, and should provide insight as to how the disk forming process occurs.
We propose an archival study of UV (GALEX) and IR (Spitzer) galaxy substructure to quantify (for the first time) the complex relation between un-obscured and embedded SF complexes in a large, representative galaxy sample. We will utilize a sample of 162 nearby galaxies that have GALEX imaging with significant FUV exposure (>500 sec), as well as Spitzer 24-micron and 3.6-micron data. Analysis of the panchromatic imaging will be accomplished using a special-purpose code designed for multi-wavelength, multi-scale, adaptive photometry capable of decomposing crowded galactic disks into discrete substructures and diffuse emission. Our science goals include assessing the demographics of complexes detected in UV/IR bands, refining the attenuation-luminosity relation for individual SF regions, and probing the heating mechanism of diffuse dust that occupies the interstellar medium. Data products (e.g. deconvolved imaging, substructure catalogs, diffuse emission maps) resulting from our analysis will be made public.
Supernova (SN) explosions play a pivotal role in triggering, driving, and (later on) inhibiting further star formation in galaxies. In fact, the combination of new observations and refined modelling shows that the little-understood and poorly constrained contribution of SNe to galaxy evolution processes (often hidden under the generic name of ``feedback'') is probably the weakest link in our understanding of structure formation in the Universe. Setting observational limits on the rate, environments, and energy output of high-redshift SNe is therefore one of the main science drivers of recent Hubble Space Telescope (HST) legacy programs, as well as of future missions like the James Webb Space Telescope (JWST). However, observations of high-redshift SNe in the optical (by HST), or in the near-IR (by JWST), actually sample the rest-frame UV of these objects. Thus, proper interpretation of these observations requires knowledge about the UV properties of SNe. Such UV data are also powerful probes of the SN environment, progenitor structure and explosion mechanism. Unfortunately, UV spectroscopy of local SNe of all types, which can only be obtained from space, is scarce. Previous efforts using HST and IUE were focussed on a single SN sub-type, SNe Ia (~10 objects observed), while data for SN of all other types (core-collapse events) is almost non-existent. To remedy this situation, we have undertaken target-of-opportunity GALEX spectroscopic observations of nearby, bright, core-collapse SN in cycles 1-5, and so far observed 6 events. Following the successful implementation of our program, we request here similar spectroscopic observations for additional SNe. The accumulated GALEX data on non-Ia events, combined with the results from past efforts using HST and IUE, is leading toward a full characterization of the UV spectral evolution of SNe of all types.
We propose to cross-correlate the largest optical spectroscopic sample of low-mass stars with the GALEX database. With a catalog of almost 50,000 M and L dwarfs, we anticipate creating a matched catalog of a few thousand UV active low-mass stars, the largest sample ever assembled. Using these data we will investigate how the optical magnetic activity emission (namely H-alpha) correlates with the GALEX NUV and FUV emission, and calculate the statistical properties of UV active M and L dwarfs. Previous studies suggest that a significant fraction of the UV active M dwarfs might be in tight binaries with white dwarfs or other low-mass stars. We therefore will also use this sample to help understand how binarity plays a role in the magnetic activity of M and L dwarfs. This study will put important constraints on models of the magnetic field generation in low-mass dwarfs and is a vital step towards discovering how magnetic activity affects the habitability and atmosphere retention of attending planets.
Over the past few years, our group has established that HD 179949 (as well as other hot-Jupiter host stars) exhibits observable signatures of magnetospheric Star-Planet Interactions (SPI), an indirect probe of extrasolar planetary magnetic fields. Understanding this phenomenon in detail requires a collaborative effort to analyze its effect at a range of stellar atmospheric heights, and thus wavelengths. We have monitored the planet-induced chromospheric emission in optical spectra over several years. Coronal activity modulated by the planet will be searched for with the XMM-Newton X-ray Observatory in the Fall of 2009. The missing links between these optical and X-ray diagnostics of SPI are the powerful UV probes of the upper chromosphere and transition region (TR), uniquely available now with GALEX imaging. We propose to look for variable stellar activity in both the FUV and NUV bandpasses due to magnetic interaction between the star and the planet, which will be phased with the planet's orbit (3.1 d). We need to disentangle the the planet's signature with variability due to the star's rotation (10 d). We thus request 15 observations over 15 days to fully sample both periods. We will also propose for contemporaneous optical spectropolarimety with ESPaDOnS at the CFHT in order to map the stellar magnetic field and monitor the lower chromosphere. With both GALEX and CFHT collecting data of HD 179949 (near-)simultaneously, we will be able to (1) map the energy distribution of magnetic SPI as a function stellar atmospheric height, from the lower chromosphere (H-alpha Ca II) and upper chromosphere and TR (NUV & FUV), (2) map the 3-D magnetic structure of the coronal environment in which the planet is orbiting, and (3) determine the total energy budget needed to constrain the proposed SPI mechanisms.
We propose to image the denser regions of the high velocity cloud Complex GCP, commonly known as the Smith Cloud, to find signs of recent star formation. Recent studies of XUV disks and galaxy groups suggest that stars can form in regions beyond the classic star formation threshold, and the Smith Cloud may be a new potential candidate. Specific targets include the denser core of the Smith Cloud and finer structure in its diffuse tail, these being the most likely regions of star formation. GALEX's large field of view and high sensitivity are ideal for this project, considering the Smith Cloud subtends several degrees on the sky and any UV emission is likely to be very faint. Detection of recent (<100 Myr) star formation activity would not only impact current size and distance estimates of HVCs, but also suggest the presence of significant amounts of dark matter, providing insight into the possible origins of HVCs.
Based on an exploratory survey of about 100 early-type galaxies already in the GALEX archive we have discover several new modes of star formation occurring in and around elliptical and lenticular galaxies. These galaxies are traditionally thought to have terminated most (all?) of their star formation aeons ago. In response we have built a diameter-limited sample of over 6,000 E/S0 galaxies for which there is existing GALEX data and we plan to produce the deepest co-added images possible from over 37,000 visits in the NUV and 20,000 visits in the FUV. From this set we will identify and classify the UV morphology of each object and begin to investigate the global and environmental systematics of this unanticipated phenomenon. All data will be made public through NED.
We propose a deep GALEX legacy imaging survey of 24 galaxy clusters at 0.15<z<0.3 from LoCuSS, the Local Cluster Substructure Survey. The primary goal is to study the transition from blue star-forming to red passive galaxies by identifying a complete sample of `Green Valley' galaxies down to a fixed stellar mass limit of 10^10 solar masses, far lower than in most previous studies. Due to the extraordinarily broad data set compiled as part of LoCuSS, including Spitzer and Herschel mid- to far-IR imaging, an extensive redshift survey with MMT Hectospec, deep Chandra and XMM X-ray imaging, and weak-lensing based mass maps for each cluster, deep GALEX observations would provide excellent legacy value to the community. The proposed legacy survey will tie together multiple science goals of GALEX, both in terms of the broad cross-section of clusters at a variety of dynamical states that LoCuSS has been designed to assess, as well its ability to complement other deep GALEX imaging of higher or lower redshift clusters, along with deep fields in sparser environments, and even time domain studies of AGN identified via UV variability.
As part of a comprehensive and multi-wavelength study of the impact of environment on the evolution of galaxies, we propose to use the GALEX AIS archive to measure the UV properties of galaxies in the Coma-Abell 1367 Supercluster. The primary component of our study is a new blind H~I survey of the entire supercluster which will detect over 3000 sources, at least a third of which are likely to not have been previously cataloged. The UV data requested here, combined with new H~I data, will yield a measure of the relation between gas content and recent star formation in galaxies residing across the entire supercluster. The goal of this work is to understand the relationship between star formation (via GALEX), gas content (HI), AGN activity (GALEX, SDSS, NVSS), and stellar content (SDSS, 2MASS, GALEX) as a function of environment for a large sample of galaxies throughout the Coma-Abell 1367 Supercluster.
We propose to obtain new GALEX imaging observations of 8 spiral galaxies that are part of our HALOGAS survey project. HALOGAS is an ambitious 21-cm survey with the Westerbork Synthesis Radio Telescope, supplemented with additional observations with the Very Large Array and optical data, of a sample of two dozen nearby spiral galaxies to detect and characterize the nature and origin of extra-planar and accreting cold gas. The galaxies selected span a range of star formation and Hubble types. The project has already received more than 1000 hours of WSRT time, with more than 2500 hours projected. The sample includes two dozen nearby galaxies, split between edge-on systems and moderately inclined systems. The latter group allows for detection of halogas through its kinematic signatures. Our proposed deep GALEX observations address a subsample of 8 objects selected to have low foreground extinction, for which HI data either are or will be available within the next year. Within a year, there will also be archival GALEX data of sufficient depth for another 6 of our galaxies. The proposed GALEX observations will provide the most sensitive probe of star formation in the accreting gas, outer disks, and halos of the galaxies, allowing us to study the correlation between gas accretion and outer disk star formation. In addition, for the edge-on galaxies the GALEX data will enable a study of scattered UV light in the halos to search for evidence of dust in the halo gas, which would help elucidate the origin of this material.
We are actively investigating the star forming properties of extended gaseous disks and HI debris in 12 nearby (v < 2500 km/s) galaxies. Archival GALEX long exposures (t > 1000s) will complement a rich, uniform data set that already features deep H-alpha images, high-resolution multi-slit optical spectra, and detailed HI synthesis maps. This particular sample is unique in that all 12 galaxies contain confirmed isolated HII regions in their outermost parts (r > 2 X r25), within tidal arms or extended gaseous disks. New results from SINGG and SUNGG (Survey for Ionization/UV in Neutral Gas Galaxies) indicate that where there are isolated HII regions, there is extended UV emission, therefore GALEX data will provide a more complete picture of the ongoing and recent star formation in these extended gaseous components. The existing HI synthesis maps will allow for measurements of gas column densities and kinematics that will help us understand the relationship between this star formation and its gaseous environment. Combined with metallicity measurements of the isolated HII regions using the GMOS spectra and Halpha observations, deep UV images will allow us to place important age and mass constraints on the stellar populations of these extended gaseous features, and examine the Halpha/UV discrepancy that may indicate a truncated IMF in the outer parts of galaxies. The GALEX UV data are essential to our understanding of the star formation that takes place in the outermost regions of galaxies. This study will increase our knowledge of how gaseous environments relate to star formation rates and stellar populations, the metal-enrichment and evolution of outer-galaxy gas, and the ways in which new stellar populations emerge in the extreme outskirts of galaxies.
We will create the GALEX Extragalactic Stars (GES) Catalog by a careful reanalysis of the photometry of point sources in GALEX images of nearby (< 10 Mpc) galaxies. The GES catalog will provide FUV and NUV magnitudes and photometry from cross-matched stars in surveys: from other surveys: Optical (Massey etal, our own HST ACS survey of galaxies for TRGB distance measurements and other archival [e.g., SDSS, CFHT, NOAO/Mosaic Imager] and upcoming data [Pan-STARRS]); X-ray (Chandra, ROSAT/HRI); IR (Spitzer & 2MASS); and earlier UV surveys (UIT), when available. These data are currently so accurate, especially in the optical, that information on the evolutionary state of the stars, as well as the extinction along the line of sight (including the R-value) can be derived. Because the galaxy's relative distances are well known, we will determine the stars' absolute magnitudes. The astrophysical goal of this proposal is to estimate individual reddening values for all selected stars as well as the physical properties of these stars: absolute magnitude, surface-gravity, metallicity, possible binarity, variability and age. We will then be able to examine numbers of rare/bright stars (e.g., supergiants, Wolf-Rayet, Ofpe/WN9, Luminous Blue Variables and Ultra Long Period Cepheids) to evaluate the rate of evolution along their evolutionary tracks to be compared with theoretical predictions. Some of these stars will be precursors to type II supernovas. And we will examine how all of this changes with type and metallicity of the galaxy. GALEX data is crucial for this project because the UV colors are uniquely sensitive to metallicity and surface gravity effects (via line-blanketing).
Supernova science is on the verge of a revolution fueled by large area time-domain surveys that will fill in significant unexplored regions of supernova (SN) parameter space. These dark corners are already revealing SNe with record-breaking luminosities that were previously missed because they appear in low-luminosity hosts. These unusual supernovae include some of the first candidates for a previously unobserved, but theoretically predicted supernova explosion mechanism: a collapse due to electron-positron pair production. They also include thermonuclear SNe that exceed the Chandrasekhar mass limit. We propose to explore the connection between these luminous supernovae and their sub-luminous hosts. Why are they rare in more massive hosts? Is the intial-mass-function different in low mass and presumably low metallicity hosts? What effect do these extreme supernovae have on the chemical evolution of their hosts? By gathering high-quality GALEX data on these hosts and combining them with corollary optical photometry and spectroscopy, we hope to constrain their star formation histories, ages, masses and metallicities. A comparison with extant galaxy samples will allow us to determine how extreme these hosts are. Mass measurements provide constraints on dynamical models of the gas within these dwarf galaxies to determine the impact of these supernovae on the chemical enrichment of the intra-galactic medium, or of subsequent merger partners.
Intracluster light (ICL) is a fossil record of hierarchical galaxy formation in clusters. Virgo's close proximity, rich interaction history, and plethora of ancillary data make it the ideal laboratory of ICL studies. Using archival GALEX images of Virgo, we have recently discovered the first UV-detected IC plume. This is the only feature of its kind and was unexpected given the old age of IC stars implied by optical ICL studies in several clusters. We request 24ks in a single GALEX pointing, centered on Virgo. This will provide a more robust detection of the new UV plume. More importantly, it will facilitate a search for additional low surface brightness UV-features, that have gone undetected. We will use the archival and new observations to determine the age and dust content of the existing plume and any new discoveries. These parameters are critical for constraining models of structure formation and the chemical enrichment of the intracluster medium. Given the significance of Virgo to the study of galaxy evolution our requested observations will have lasting archival value, complementing existing and future multi-wavelength programs.
We propose to obtain photometric observations in both the FUV and NUV filters of the hosts of all type Ia supernovae discovered as part of the ESSENCE Survey. With this data set we plan to lower the overall systematic error budget on measuring the equation of state of the Universe, clarify the debate about the timescales and progenitor systems, and obtain accurate and reliable stellar populations and specific star formation histories with a deeper examination of the properties of the SN Host galaxies.
The Cosmic Web that permeates our universe is defined by the alignment of galaxies into filaments, clusters, and walls, as well as by the voids between them which are (mostly) empty. Void galaxies, found occupying these underdense regions, are an environmentally defined population whose isolated nature and extreme environment provides an ideal opportunity to test theories of galaxy formation and evolution. Their existence also poses a well defined observational constraint to Lambda CDM cosmological models. We propose to do UV imaging of a sample of SDSS selected void galaxies located in the deepest underdensities of nearby voids. Our galaxies were selected using the Delaunay Tesselation Field estimator, a novel, purely structural and geometric technique, to produce a sample that more uniformly represents the void galaxy population. In addition, we use a powerful new backend of the Westerbork Synthesis Radio Telescope that allows us to probe the neutral gas content in a huge volume around each targeted void galaxy, while still resolving individual galaxy kinematics and detecting faint companions in H I. We specifically aim to study the star formation history of these systems, which appear to be in a more youthful stage of their evolution than field galaxies. With this combination of UV and H I data we will address questions ranging from how galaxies get their gas, how they form stars, and what role environment plays in these processes.
The GALEX data archive now includes a substantial number of grism spectra. With over 170 tiles having been observed with the grism, we can now search hundreds of grism spectra of quasars for the absorption-line signatures of neutral gas called "damped Lyman alpha" lines (DLAs). These, the strongest of all intervening quasar absorption lines, arise in columns of HI gas that are comparable to those found in the Milky Way. Since it was first recognized that DLAs are useful tracers of the neutral gas in galaxies, quasar spectra have been methodically searched to determine the incidence and evolution of these absorbers. DLAs contain the bulk of the neutral gas mass in the Universe, therefore, tracking their evolution with time is a probe of galaxy evolution. As neutral gas gets converted to molecular clouds which then form stars, studying the observed evolution of the luminosity density of the Universe along with the neutral gas density is a powerful test of galaxy evolution models. The Lyman alpha line falls in the UV for redshifts z < 1.65, making the nearby Ly-alpha (neutral gas) Universe invisible to optical surveys. The GALEX grism survey is the only (partial) all-sky spectroscopic survey of the UV sky that can be used to sample a significant number of quasar spectra in search of low redshift DLAs. We have demonstrated the feasibility of detecting and measuring a DLA line in a GALEX grism quasar spectrum through our Cycle 3 GO program. We are now proposing to systematically search the GALEX spectroscopic archive of quasar spectra for DLAs. We will carry out both a blind survey as well as a targeted survey of DLAs corresponding to known Mg II systems selected from our SDSS samples. We expect to significantly increase the number of known DLAs at low redshift, thus improving the statistical significance of our previous results. We will also be able to investigate some debated low-redshift results.
Symbiotic stars are wide binaries in which a white dwarf (WD) accretes from the wind of a red-giant companion. One of the most striking features of these binaries is that the WD luminosity is often higher than can reasonably be produced by accretion. To generate the high luminosity, it is thought that material burns quasi-steadily, in a shell, on the surface of the WD. But the origin of this burning shell is not well understood. We propose to use a symbiotic star that contains a WD with both shell burning and a strong magnetic field --- Z Andromedae (Z And) --- to discover the origin of the burning shell in this, and by extension other, symbiotic stars. The specific goal of our proposed observations is to determine whether or not the ultraviolet (UV) flux from Z And is modulated at the 28-minute WD spin period. The presence or absence of such a modulation will indicate whether the shell burning on the surface of the WD is caused by accretion onto the WD at a high rate (if there is a strong UV modulation) or by a late-stage nova outburst (if there is no UV modulation). The answer to this question has implications for our basic understanding of symbiotic binaries and for whether symbiotics might produce a significant fraction of type Ia supernovae.
Carbon-atmosphere (spectral type DQ) white dwarfs are a recently-recognized class of star that may be the final remnant of the most massive stars to form white dwarfs. We have discovered that a subset of these white dwarfs are variable. We suspect that these "DQVs" are typical pulsating white dwarfs, and therefore would be excellent asteroseismological probes of the dividing line between white dwarfs and supernovae. Yet the optical variations of DQVs are odd, and leave open the possibility that we are not seeing pulsations, but perhaps are seeing a new and potentially interesting type of cataclysmic variable. We propose to obtain long time-series GALEX imaging of two DQVs. Our primary goals are to compare the UV and optical properties of the light curves in order to differentiate between the pulsational interpretation of the light variations and the interacting binary interpretation. If the variations are found to be due to standard white dwarf pulsations, then the full arsenal of white dwarf asteroseismology can be brought to bear on these interesting but mysterious stars.
Red spheroids contain the majority of stars in the local universe, but it was not always so. Many mechanisms have been suggested for the metamorphosis of star-forming disks into quiescent bulges and multiple avenues are likely. Each of these paths yield different predictions for the star-formation patterns and morphologies of fading green galaxies. We propose to select nearby green galaxies from the GALEX archive, and use their UV-optical color maps and optical morphologies to constrain their merger and spatially resolved star-formation histories. This archival analysis will determine the the evolutionary paths taken by transitional galaxies.
Lyman continuum (LyC) photons produced in massive starbursts may have played a dominant role in the reionization of the Universe. However, their contribution to the background depends upon the fraction of ionizing radiation that escapes from galaxies below the Lyman Limit. Despite tremendous effort, only a handful of detections have been made at z~3, which points to the escape fraction (fesc,rel) being close to zero in most starburst galaxies with a small percentage (10-20%) having large escape fractions (fesc,rel>50%). Although a few Lyman Break Galaxies (LBG) at z~3 have revealed escaping LyC, the mechanism by which some starburst galaxies have large escape fractions and others do not is not understood. We have recently discovered the first direct detection of escaping LyC in a starburst galaxy at z<3. This z~1 galaxy has a close companion, and is undergoing a merger which points to dynamical effects as the mechanism for LyC escape. Galaxy mergers offer an intriguing, logical step towards an explanation of the increased escape fraction of some galaxies. Mergers can be responsible for multiple processes, e.g. starbursts, outflowing winds, and tidal features, that can increase both the production rate of ionizing photons, and the chance these photons, can escape the galaxy. We propose to measure the fraction of LyC radiation escaping from galaxy mergers at z~1 by stacking >600 galaxy positions in deep archival GALEX data over numerous fields (GOODS-N, Extended Groth Strip and COSMOS). Since the escape probability is likely to be line-of-sight dependent in a merger, it is necessary to stack a large number of known mergers to produce a detectable signal. The high observing cost of obtaining HST spectra shows the tremendous value of exploiting the existing GALEX archive to explore this hypothesis.
We propose FUV and NUV GALEX observations of two Algol-type interacting binaries (UZ Lyr and BR Cyg) located in the field of view of the Kepler spacecraft in order to obtain their UV light curves for a study of the physics of mass transfer in the systems. Both binaries are direct-impact systems where the gas stream from the mass loser impacts the photosphere of the mass gainer at a steep angle. Based upon FUSE spectroscopy of a similar system U Cep, we expect to find evidence for an accretion hot spot centered on the impact site. Since the temperature in the hot spot is 2-3 times that of the late B-type mass gainer's photosphere, its presence is seen more prominently in the FUV. The proposed GALEX observations will be taken with a cadence of 300 s during the target's visibility and cover one orbital period (1.89 d and 1.33 d). The GALEX photometry will be combined with ground-based and Kepler photometry to determine the temperature and azimuthal location of the hot spot and the systemic parameters for the binaries. We will look for evidence of flaring activity at the impact site that would show more prominently in the UV. The GALEX observations will support Kepler observations of these systems that will be carried through by D. Gies (co-I on this proposal). Since the GALEX field-of-view is 1.2 degrees, as a bonus we will also obtain information on short-term and flare activity on many other stars in the Kepler field that might lead to a targeted Kepler proposal in future GO cycles.