We introduce a new quantity, the mass flux density of galaxies evolving from the blue sequence to the red sequence. We propose a simple technique for constraining this mass flux using the ...volume-corrected number density in the extinction-corrected UV-optical color-magnitude distribution, the stellar age indexes H delta sub(A) and unk(4000), and a simple prescription for spectral evolution using a quenched star formation history. We exploit the excellent separation of red and blue sequences in the NUV - r band Hess function. The final value we measure, rho T = 0.033 m unk yr super(-1) Mpc super(-3), is strictly speaking an upper limit due to the possible contributions of bursting, composite, and extincted galaxies. However, it compares favorably with estimates of the average mass flux that we make based on the red luminosity function evolution derived from the DEEP2 and COMBO-17 surveys, rho R - +0034 M unk yr super(-1) Mpc super(-3). We find that the blue sequence mass has remained roughly constant since z = 1 ( rho B unk 0.01 M unk yr super(-1) Mpc super(-3), but the average on-going star formation of rho SF unk 0.037 M unk yr super(-1) Mpc super(-3) over 0 < z < 1 is balanced by mass flux off the blue sequence. We explore the nature of the galaxies in the transition zone with particular attention to the frequency and impact of active galactic nuclei (AGNs). The AGN fraction peaks in the transition zone. We find circumstantial, albeit weak evidence that the quench rates are higher in higher luminosity AGNs.
The Calibration and Data Products of GALEX Morrissey, Patrick; Conrow, Tim; Barlow, Tom A ...
The Astrophysical journal. Supplement series,
12/2007, Letnik:
173, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We describe the calibration status and data products pertaining to the GR2 and GR3 data releases of the Galaxy Evolution Explorer (GALEX). These releases have identical pipeline calibrations that are ...significantly improved over the GR1 data release. GALEX continues to survey the sky in the far-ultraviolet (FUV, similar to 154 nm) and near-ultraviolet (NUV, similar to 232 nm) bands, providing simultaneous imaging with a pair of photon-counting, microchannel plate, delay line readout detectors. These 1.25 degree field of view detectors are well suited to ultraviolet observations because of their excellent red rejection and negligible background. A dithered mode of observing and photon list output pose complex requirements on the data processing pipeline, entangling detector calibrations, and aspect reconstruction algorithms. Recent improvements have achieved photometric repeatability of 0.05 and 0.03 m sub(AB) in the FUV and NUV, respectively. We have detected a long-term drift of order 1% FUV and 6% NUV over the mission. Astrometric precision is of order 0.5" rms in both bands. In this paper we provide the GALEX user with a broad overview of the calibration issues likely to be confronted in the current release. Improvements are likely as the GALEX mission continues into an extended phase with a healthy instrument, no consumables, and increased opportunities for guest investigations.
We have analyzed the bivariate distribution of galaxies as a function of ultraviolet-optical colors and absolute magnitudes in the local universe. The sample consists of galaxies with redshifts and ...optical photometry from the Sloan Digital Sky Survey (SDSS) main galaxy sample matched with detections in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands in the Medium Imaging Survey being carried out by the Galaxy Evolution Explorer (GALEX) satellite. In the (NUV - r) sub(0.1) versus M sub(r.01) galaxy color-magnitude diagram, the galaxies separate into two well-defined blue and red sequences. The (NUV - r) sub(0.1) color distribution at each M sub(r.0.1) is not well fit by the sum of two Gaussians due to an excess of galaxies in between the two sequences. The peaks of both sequences become redder with increasing luminosity, with a distinct blue peak visible up to M sub(r.0.1) similar to -23. The r sub(0.1) -band luminosity functions vary systematically with color, with the faint-end slope and characteristic luminosity gradually increasing with color. After correcting for attenuation due to dust, we find that approximately one-quarter of the color variation along the blue sequence is due to dust, with the remainder due to star formation history and metallicity. Finally, we present the distribution of galaxies as a function of specific star formation rate and stellar mass. The specific star formation rates imply that galaxies along the blue sequence progress from low-mass galaxies with star formation rates that increase somewhat with time to more massive galaxies with a more or less constant star formation rate. Above a stellar mass of similar to 10 super(10.5) M unk, galaxies with low ratios of current to past averaged star formation rate begin to dominate.
The GALEX Ultraviolet Atlas of Nearby Galaxies Gil de Paz, Armando; Boissier, Samuel; Madore, Barry F ...
The Astrophysical journal. Supplement series,
12/2007, Letnik:
173, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its ...far-ultraviolet (FUV; unk = 1516 AA) and near-ultraviolet (NUV; unk = 2207 AA) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate SFR) of galaxies in the local universe. From the surface brightness profiles obtained we have computed asymptotic magnitudes, colors, and luminosities, along with the concentration indices C31 and C42. We have also morphologically classified the UV surface brightness profiles according to their shape. 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 subtypes. Elliptical galaxies with brighter K-band luminosities (i.e., more massive) are redder in (NUV - K) color but bluer In (FUV - NUV) (a color sensitive to the presence of a strong UV upturn) 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 (or, equivalently, the slope of the UV spectrum, beta ) 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.
We have derived the bivariate luminosity function for the far ultraviolet (1530Angstroms) and far infrared (60 microns). We used matched GALEX and IRAS data, and redshifts from NED and PSC-z. We have ...derived a total star formation luminosity function phi(L_{tot}), with L_{tot} = L_{FUV}+L_{FIR}. Using these, we determined the cosmic ``star formation rate\'\' function and density for the local universe. The total SFR function is fit very well by a log-normal distribution over five decades of luminosity. We find that the bivariate luminosity function phi(L_{FUV},L_{FIR}) shows a bimodal behavior, with L_{FIR} tracking L_{FUV} for L_{TOT}< 10^10 L_sun, and L_{FUV} saturating at 10^10 L_sun, while L_{TOT} L_{FIR} for higher luminosities. We also calculate the SFR density and compare it to other measurements.
We have initiated a search for extended ultraviolet disk (XUV-disk) galaxies in the local universe. Here we compare GALEX UV and visible-NIR images of 189 nearby (D < 40 Mpc) S0-Sm galaxies Included ...in the GALEX Atlas of Nearby Galaxies and present the first catalog of XUV-disk galaxies. We find that XUV-disk galaxies are surprisingly common but have varied relative (UV/optical) extent and morphology. Type 1 objects ( unk 20% incidence) have structured, UV-bright/optically faint emission features in the outer disk, beyond the traditional star formation threshold. Type 2 XUV-disk galaxies ( similar to 10% incidence) exhibit an exceptionally large, UV-bright/optically low surface brightness (LSB) zone having blue UV-K sub(S) outside the effective extent of the inner, older stellar population, but not reaching extreme galactocentric distance. If the activity occurring in XUV-disks is episodic, a higher fraction of present-day spirals could be influenced by such outer disk star formation. Type 1 disks are associated with spirals of all types, whereas Type 2 XUV-disks are predominantly found In late-type spirals. Type 2 XUV-disks are forming stars quickly enough to double their (currently low) stellar mass in the next Gyr (assuming a constant star formation rate). XUV-disk galaxies of both types are systematically more gas-rich than the general galaxy population. Minor external perturbation may stimulate XUV-disk incidence, at least for Type 1 objects. XUV-disks are the most actively evolving galaxies growing via inside-out disk formation in the current epoch, and may constitute a segment of the galaxy population experiencing significant, continued gas accretion from the intergalactic medium or neighboring objects.
The Local Hosts of Type Ia Supernovae Neill, James D; Sullivan, Mark; Howell, D. Andrew ...
The Astrophysical journal,
12/2009, Letnik:
707, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We use multi-wavelength, matched aperture, integrated photometry from the Galaxy Evolution Explorer (GALEX), the Sloan Digital Sky Survey, and the RC3 to estimate the physical properties of 166 ...nearby galaxies hosting 168 well-observed Type Ia supernovae (SNe Ia). The ultraviolet (UV) imaging of local SN Ia hosts from GALEX allows a direct comparison with higher-redshift hosts measured at optical wavelengths that correspond to the rest-frame UV. Our data corroborate well-known features that have been seen in other SN Ia samples. Specifically, hosts with active star formation produce brighter and slower SNe Ia on average, and hosts with luminosity-weighted ages older than 1 Gyr produce on average more faint, fast, and fewer bright, slow SNe Ia than younger hosts. New results include that in our sample, the faintest and fastest SNe Ia occur only in galaxies exceeding a stellar mass threshold of ~1010 M, leading us to conclude that their progenitors must arise in populations that are older and/or more metal rich than the general SN Ia population. A low host extinction subsample hints at a residual trend in peak luminosity with host age, after correcting for light-curve shape, giving the appearance that older hosts produce less-extincted SNe Ia on average. This has implications for cosmological fitting of SNe Ia, and suggests that host age could be useful as a parameter in the fitting. Converting host mass to metallicity and computing 56Ni mass from the supernova light curves, we find that our local sample is consistent with a model that predicts a shallow trend between stellar metallicity and the 56Ni mass that powers the explosion, but we cannot rule out the absence of a trend. We measure a correlation between 56Ni mass and host age in the local universe that is shallower and not as significant as that seen at higher redshifts. The details of the age-56Ni mass correlations at low and higher redshift imply a luminosity-weighted age threshold of ~3 Gyr for SN Ia hosts, above which they are less likely to produce SNe Ia with 56Ni masses above ~0.5 M.
The Extreme Hosts of Extreme Supernovae Neill, James D; Sullivan, Mark; Gal-Yam, Avishay ...
The Astrophysical journal,
01/2011, Letnik:
727, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We use GALEX ultraviolet (UV) and optical integrated photometry of the hosts of 17 luminous supernovae (LSNe, having peak MV < --21) and compare them to a sample of 2,000 galaxies from a cross-match ...between the SDSS DR4 spectral catalog and GALEX interim release 1.1. We place the LSN hosts on the galaxy NUV -- r versus Mr color-magnitude diagram (CMD) with the larger sample to illustrate how extreme they are. The LSN hosts appear to favor low-density regions of the galaxy CMD falling on the blue edge of the blue cloud toward the low-luminosity end. From the UV-optical photometry, we estimate the star formation history of the LSN hosts. The hosts have moderately low star formation rates (SFRs) and low stellar masses (M *) resulting in high specific star formation rates (sSFR). Compared with the larger sample, the LSN hosts occupy low-density regions of a diagram plotting sSFR versus M * in the area having higher sSFR and lower M *. This preference for low M *, high sSFR hosts implies that the LSNe are produced by an effect having to do with their local environment. The correlation of mass with metallicity suggests that perhaps wind-driven mass loss is the factor that prevents LSNe from arising in higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe (>100 M ), by appearing in low-SFR hosts, are potential tests for theories of the initial mass function that limit the maximum mass of a star based on the SFR.
We investigate the nature of the star formation law at low gas surface densities using a sample of 19 low surface brightness (LSB) galaxies with existing H I maps in the literature, UV imaging from ...the Galaxy Evolution Explorer satellite, and optical images from the Sloan Digital Sky Survey. All of the LSB galaxies have (NUV - r) colors similar to those for higher surface brightness star-forming galaxies of similar luminosity indicating that their average star formation histories are not very different. Based upon four LSB galaxies with both UV and far-infrared (FIR) data, we find FIR/UV ratios significantly less than 1, implying low amounts of internal UV extinction in LSB galaxies. We use the UV images and H I maps to measure the star formation rate (SFR) and hydrogen gas surface density within the same region for all the galaxies. The LSB galaxy star formation rate surface densities lie below the extrapolation of the power law fit to the SFR surface density as a function of the total gas density for higher surface brightness galaxies. Although there is more scatter, the LSB galaxies also lie below a second version of the star formation law in which the SFR surface density is correlated with the gas density divided by the orbital time in the disk. The downturn seen in both star formation laws is consistent with theoretical models that predict lower star formation efficiencies in LSB galaxies due to the declining molecular fraction with decreasing density.
For a sample of 43 nearby, late-type galaxies, we have investigated the radial variation of both the current star formation rate and the dust-induced UV light attenuation. To do this we have ...cross-correlated IRAS images and GALEX observations for each of these galaxies and compiled observations of the gas (CO and H I) and metal-abundance gradients found in the literature. We find that attenuation correlates with metallicity. We then use the UV profiles, corrected for attenuation, to study several variants of the Schmidt law and conclude that our results are compatible with a simple law similar to the one of Kennicutt extending smoothly to lower surface densities, but with considerable scatter. We do not detect an abrupt break in the UV light at the threshold radius derived from H alpha data (at which the H alpha profile shows a break and beyond which only a few H II regions are usually found). We interpret the H alpha sudden break not as a change in the star formation regime (as often suggested), but as the vanishingly small number of ionizing stars corresponding to low levels of star formation.
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