Patrick Jelinsky

The Galaxy Evolution Explorer: A Space ultraviolet survey mission

We give an overview of the Galaxy Evolution Explorer (GALEX), a NASA Explorer Mission launched on 2003 April 28. GALEX is performing the first space UV sky survey, including imaging and grism surveys in two bands (1350-1750 and 1750-2750 ?). The surveys include an all-sky imaging survey (mAB 20.5), a medium imaging survey of 1000 deg2 (mAB 23), a deep imaging survey of 100 deg2 (mAB 25), and a nearby galaxy survey. Spectroscopic (slitless) grism surveys (R = 100-200) are underway with various depths and sky coverage. Many targets overlap existing or planned surveys in other bands. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the relationship of the UV and global star formation rate in local galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the redshift range 0 < z < 2 and probe the physical drivers of star formation in galaxies. The GALEX mission includes a guest investigator program, supporting the wide variety of programs made possible by the first UV sky survey.

Wedge-and-strip anodes for centroid-finding position-sensitive photon and particle detectors

We discuss new anode geometries, employing position‐dependent charge partitioning, which can be used with microchannel plates, planar proportional counters, and mesh dynode electron multipliers to obtain a two‐dimensional position signal from each detected photon or particle. Only three or four anode electrodes and signal paths are required, yet images comprised of a number of detected events have little geometric distortion and the resolution is not limited by thermal noise inherent in resistive sheet anodes. We present an analysis of the geometrical image nonlinearity in the relationship between event centroid location and the charge partition ratios. Fabrication and testing of two wedge‐and‐strip anode systems are discussed. Images obtained with EUV radiation and microchannel plates that verify the predicted performance of this readout system are shown. We emphasize that the spatial resolution of the wedge‐and‐strip anode is in no way limited by the coarseness of the anode conductor pattern. The resolu...

Galaxy evolution explorer ultraviolet color-magnitude relations and evidence of recent star formation in early-type galaxies

We have used the Galaxy Evolution Explorer UV photometric data to construct a first near-UV (NUV) color-magnitude relation (CMR) for the galaxies preclassified as early-type by Sloan Digital Sky Survey 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 rest-frame 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 (1 Gyr) 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.

The GALEX-VVDS measurement of the evolution of the far-ultraviolet luminosity density and the cosmic star formation rate

In a companion paper (Arnouts et al. 2004) we presented new measurements of the galaxy luminosity function at 1500 Angstroms out to z~1 using GALEX-VVDS observations (1039 galaxies with NUV 0.2) and at higher z using existing data sets. In this paper we use the same sample to study evolution of the FUV luminosity density. We detect evolution consistent with a (1+z)^{2.5+/-0.7} rise to z~1 and (1+z)^{0.5+/-0.4} for z>1. The luminosity density from the most UV-luminous galaxies (UVLG) is undergoing dramatic evolution (x30) between 025%) of the total FUV luminosity density at z<1. We measure dust attenuation and star formation rates of our sample galaxies and determine the star formation rate density as a function of redshift, both uncorrected and corrected for dust. We find good agreement with other measures of the SFR density in the rest ultraviolet and Halpha given the still significant uncertainties in the attenuation correction.

THE ON-ORBIT PERFORMANCE OF THE GALAXY EVOLUTION EXPLORER

We report the first years 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 125 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.

Recent Star Formation in the Extreme Outer Disk of M83

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 4 times the radius at which the majority of H II regions are detected (R = 51, or 6.6 kpc). These sources are typically associated with large-scale filamentary H I structures in the warped outer disk of M83 and are distributed beyond the galactocentric radii at which molecular interstellar medium has yet been detected. We present measured properties of these stellar complexes, including far-UV and near-UV magnitudes and local gas surface density. Only a subset of the outer-disk UV sources have corresponding H II regions detected in Hα imaging, consistent with a sample of mixed age in which some sources are a few megayears old and others are much more evolved (~108 yr).

The Ultraviolet Galaxy Luminosity Function in the Local Universe from GALEX Data

We present the results of a determination of the galaxy luminosity function at ultraviolet wavelengths at redshifts of z = 0.0-0.1 from Galaxy Evolution Explorer (GALEX) data. We determined the luminosity function in the GALEX far-UV and near-UV bands from a sample of galaxies with UV magnitudes between 17 and 20 that are drawn from a total of 56.73 deg2 of GALEX fields overlapping the bJ-selected Two-Degree Field Galaxy Redshift Survey. The resulting luminosity functions are fainter than previous UV estimates and result in total UV luminosity densities of 1025.55±0.12 and 1025.72±0.12 ergs s-1 Hz-1 Mpc-3 at 1530 and 2310 A, respectively. This corresponds to a local star formation rate density in agreement with previous estimates made with Hα-selected data for reasonable assumptions about the UV extinction.

The GALEX VIMOS-VLT Deep Survey Measurement of the Evolution of the 1500 Å Luminosity Function

We present the first measurement of the galaxy luminosity function (LF) at 1500 A in the range 0.2 ≤ z ≤ 1.2 based on Galaxy Evolution Explorer VIMOS-VLT Deep Survey observations (~1000 spectroscopic redshifts for galaxies with NUV ≤ 24.5) and at higher z using existing data sets. Our main results are summarized as follows: (1) Luminosity evolution is observed with ΔM* ~ -2.0 mag between z = 0 and z = 1 and ΔM* ~ -1.0 mag between z = 1 and z = 3. This confirms that the star formation activity was significantly higher in the past. (2) The LF slopes vary in the range -1.2 ≥ α ≥ -1.65, with a marginally significant hint of increase at higher z. (3) We split the sample in three rest-frame (B - I) intervals, providing an approximate spectral type classification: Sb-Sd, Sd-Irr, and unobscured starbursts. We find that the bluest class evolves less strongly in luminosity than the two other classes. On the other hand, their number density increases sharply with z (~15% in the local universe to ~55% at z ~ 1), while that of the reddest classes decreases.

New Constraints on the Star Formation Histories and Dust Attenuation of Galaxies in the Local Universe from GALEX

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 Sloan Digital Sky Survey Data Release 1 (SDSS DR1) main spectroscopic sample. Parameters are estimated in a statistical way by comparing each observed broadband spectral energy distribution (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 attain sensitivity to SFRs as low as 10-3 M☉ yr-1, 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 ~108 M☉ to ~5% for ~1011 M☉ galaxies.

The Properties of Ultraviolet-luminous Galaxies at the Current Epoch

We have used the first matched set of Galaxy Evolution Explorer (GALEX) and Sloan Digital Sky Survey (SDSS) data to investigate the properties of a sample of 74 nearby (z < 0.3) galaxies with far-ultraviolet luminosities greater than 2 × 1010 L☉, chosen to overlap the luminosity range of typical high-z Lyman break galaxies (LBGs). GALEX deep surveys have shown that ultraviolet-luminous galaxies (UVLGs) similar to these are the fastest evolving component of the UV galaxy population. Model fits to the combined GALEX and SDSS photometry yield typical FUV extinctions in UVLGs of 0.5-2 mag (similar to LBGs and less luminous GALEX-selected galaxies). The implied star formation rates are SFR ~ 3-30 M☉ yr-1. This overlaps the range of SFRs for LBGs. We find a strong inverse correlation between galaxy mass and FUV surface brightness, and on this basis we divide the sample into large and compact UVLGs. The large UVLGs are relatively massive (M* ~ 1011 M☉) late-type disk galaxies forming stars at a rate similar to their past average (M*/SFR ~ tHubble). They are metal rich (approximately solar), have intermediate optical-UV colors (FUV - r ~ 2-3), and about a third host a type 2 (obscured) active galactic nucleus. In contrast, the compact UVLGs have half-light radii of a few kpc or less (similar to LBGs ). They are relatively low-mass galaxies (M* ~ 1010 M☉) with typical velocity dispersions of 60-150 km s-1. They span a range in metallicity from ~0.3 to 1 times solar, have blue optical-UV colors (FUV - r ~ 0.5-2), and are forming stars at a rate sufficient to build the present galaxy in ~1-2 Gyr. In all these respects they appear similar to the LBG population. These living fossils may therefore provide an opportunity for detailed investigation of the physical processes occurring in typical star-forming galaxies in the early universe.