-
A. Boselli,
S. Boissier,
L. Cortese,
A. Gil de Paz,
V. Buat,
J. Iglesias-Paramo,
B. F. Madore,
T. Barlow,
L. Bianchi, Y.-I. Byun, [......],
P. Morrissey,
S. Neff,
R. M. Rich,
D. Schiminovich,
M. Seibert,
O. Siegmund,
T. Small,
A. S. Szalay,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We present GALEX near-ultraviolet (2310 Å) and far-ultraviolet (1530 Å) images of the interacting galaxy NGC 4438 (Arp 120) in the center of the Virgo Cluster. These images show an extended (20 kpc) tidal tail at the northwest edge of the galaxy that was previously undetected at other wavelengths; this tail is 15-25 kpc from NGC 4438's nucleus. Except for in the nucleus, the UV morphology of NGC 4438 is totally different from the Hα + [N II] morphology, which is more similar to the X-ray emission, confirming its gas cooling origin. We study the star formation history of NGC 4438 by combining spectrophotometric data in the UV-visible-near-IR wavelength range with population synthesis and galaxy evolution models. The data are consistent with a recent (~10 Myr), instantaneous burst of star formation in the newly discovered UV northwestern tail that is significantly younger than the age of the tidal interaction with NGC 4435, dated by dynamical models at ~100 Myr ago. Recent star formation events are also present at the edge of the northern arm and in the southern tail, while totally lacking in the other regions, which are dominated by the old stellar population that was perturbed during the dynamical interaction with NGC 4435. The contribution of this recent starburst to the total galaxy stellar mass is lower than 0.1%, an extremely low value for such a violent interaction. High-velocity, off-center tidal encounters such as that observed in Arp 120 are thus not sufficient to significantly increase the star formation activity of cluster galaxies.
The Astrophysical Journal 12/2008; 623(1):L13. · 6.02 Impact Factor
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Mark Seibert,
D. Christopher Martin,
Timothy M. Heckman,
Veronique Buat,
Charles Hoopes,
T. Barlow,
L. Bianchi, Y.-I. Byun,
J. Donas,
K. Forster, [......],
B. Milliard,
P. Morrissey,
S. Neff,
R. M. Rich,
D. Schiminovich,
O. Siegmund,
T. Small,
A. S. Szalay,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We test the empirical relation between ultraviolet color and attenuation as derived for starburst galaxies with a wide assortment of galaxy types detected by the Galaxy Evolution Explorer and find that it systematically overestimates the far-ultraviolet attenuation of our sample by ~0.5 mag. Our efforts to find an additional parameter that could improve the starburst reddening relation were unsuccessful. In particular, UV - Ks colors (in nonmatching apertures) show no correlation with the offset from the starburst reddening relation, suggesting either that UV - Ks colors are a poor tracer of present to past average star formation history (the "b" parameter) or that the intrinsic dust distribution/geometry may be responsible for moving galaxies off the correlation. It is possible to reduce the systematic overestimate of AFUV by using the linear correlation derived from our sample, which simply lowers the starburst predicted values of AFUV by 0.58 mag. The scatter, however, remains large at 0.89 mag.
The Astrophysical Journal 12/2008; 619(1):L55. · 6.02 Impact Factor
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S. Arnouts,
D. Schiminovich,
O. Ilbert,
L. Tresse,
B. Milliard,
M. Treyer,
S. Bardelli,
T. Budavari,
T. K. Wyder,
E. Zucca, [......],
R. Scaramella,
M. Scodeggio,
M. Seibert,
O. Siegmund,
T. Small,
A. S. Szalay,
B. Welsh,
C. K. Xu,
G. Zamorani,
and A. Zanichelli
[show abstract]
[hide abstract]
ABSTRACT: We present the first measurement of the galaxy luminosity function (LF) at 1500 Å 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.
The Astrophysical Journal 12/2008; 619(1):L43. · 6.02 Impact Factor
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V. Buat,
J. Iglesias-Páramo,
M. Seibert,
D. Burgarella,
S. Charlot,
D. C. Martin,
C. K. Xu,
T. M. Heckman,
S. Boissier,
A. Boselli, [......],
B. Milliard,
P. Morissey,
S. Neff,
M. Rich,
D. Schiminovitch,
O. Siegmund,
T. Small,
A. S. Szalay,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We compare the dust attenuation properties of two samples of galaxies purely selected in the Galaxy Evolution Explorer (GALEX) near-ultraviolet band (NUV; 1750-2750 Å, λmean = 2310 Å) and in the far-infrared (FIR) at 60 μm. These samples are built using the GALEX and IRAS sky surveys over ~600 deg2. The NUV-selected sample contains 95 galaxies detected down to NUV = 16 mag (AB system). Eighty-three galaxies in this sample are spiral or irregular, and only two of them are not detected at 60 μm. The FIR-selected sample is built from the IRAS PSCz survey, which is complete down to 0.6 Jy. Among the 163 sources, we select 118 star-forming galaxies that are well measured by IRAS; all but one are detected in NUV, and 14 galaxies are not detected in the far-ultraviolet band (FUV; 1350-1750 Å, λmean = 1530 Å). 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 two-thirds of the FIR-selected sample exhibit a lower dust attenuation than expected from the tight relation found previously for starburst galaxies between dust attenuation and the slope of the ultraviolet continuum. The situation is reversed for the remaining third of the FIR-selected galaxies: their extinction is higher than that deduced from their FUV - NUV color and the relation for starbursts.
The Astrophysical Journal 12/2008; 619(1):L51. · 6.02 Impact Factor
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L. Cortese,
A. Boselli,
G. Gavazzi,
J. Iglesias-Paramo,
B. F. Madore,
T. Barlow,
L. Bianchi, Y.-I. Byun,
J. Donas,
K. Forster, [......],
P. Morrissey,
S. Neff,
R. M. Rich,
D. Schiminovich,
O. Siegmund,
T. Small,
A. S. Szalay,
M. A. Treyer,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We present the Galaxy Evolution Exlorer (GALEX) near-ultraviolet (2310 Å) and far-ultraviolet (1530 Å) galaxy luminosity functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3 ≤ MAB ≤ -13.3. The luminosity functions are consistent with previous (~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 (MAB > -16 mag) of non-star-forming, early-type galaxies that are significantly overdense in clusters.
The Astrophysical Journal 12/2008; 623(1):L17. · 6.02 Impact Factor
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S. G. Neff,
D. A. Thilker,
M. Seibert,
A. Gil de Paz,
L. Bianchi,
D. Schiminovich,
D. C. Martin,
B. F. Madore,
R. M. Rich,
T. A. Barlow, [......],
P. N. Jelinsky,
Y.-W. Lee,
R. F. Malina,
B. Milliard,
P. Morrissey,
O. H. W. Siegmund,
T. Small,
A. S. Szalay,
B. Y. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: New Galaxy Evolution Explorer (GALEX) observations have detected significant far-UV (FUV; 1530 Å) and near-UV (NUV; 2310 Å) emission from stellar substructures within the tidal tails of four ongoing galaxy mergers. The UV-bright regions are optically faint and are coincident with H I density enhancements. FUV emission is detected at any location where the H I surface density exceeds ~2 M☉ pc-2, and it is often detected in the absence of visible wavelength emission. UV luminosities of the brighter regions of the tidal tails imply masses of 106 to ~109 M☉ in young stars in the tails, and H I luminosities imply similar H I masses. UV-optical colors of the tidal tails indicate stellar populations as young as a few megayears, and in all cases ages under 400 Myr. 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.
The Astrophysical Journal 12/2008; 619(1):L91. · 6.02 Impact Factor
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D. Schiminovich,
O. Ilbert,
S. Arnouts,
B. Milliard,
L. Tresse,
O. Le Fèvre,
M. Treyer,
T. K. Wyder,
T. Budavári,
E. Zucca, [......],
R. Scaramella,
M. Scodeggio,
M. Seibert,
O. Siegmund,
T. Small,
A. S. Szalay,
G. Vettolani,
B. Welsh,
C. K. Xu,
and A. Zanichelli
[show abstract]
[hide abstract]
ABSTRACT: In a companion Letter (Arnouts et al.) we present new measurements of the galaxy luminosity function at 1500 Å out to z ~ 1 using Galaxy Evolution Explorer VIMOS-VLT Deep Survey observations (1039 galaxies with NUV ≤ 24.5 and z > 0.2) and at higher z using existing data sets. In this Letter we use the same sample to study evolution of the FUV luminosity density ρ1500. 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 (UVLGs) is undergoing dramatic evolution (30 times) between 0 < z < 1. UVLGs are responsible for a significant fraction (>25%) of the total far-ultraviolet 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 in the rest ultraviolet and Hα given the still significant uncertainties in the attenuation correction.
The Astrophysical Journal 12/2008; 619(1):L47. · 6.02 Impact Factor
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S. K. Yi,
S.-J. Yoon,
S. Kaviraj,
J.-M. Deharveng,
R. M. Rich,
S. Salim,
A. Boselli,
Y.-W. Lee,
C. H. Ree,
Y.-J. Sohn, [......],
D. Schiminovich,
O. Siegmund,
T. Small,
A. S. Szalay,
M. J. Jee,
S.-W. Kim,
T. Barlow,
K. Forster,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: 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 Astrophysical Journal 12/2008; 619(1):L111. · 6.02 Impact Factor
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J. Iglesias-Páramo,
V. Buat,
T. T. Takeuchi,
K. Xu,
S. Boissier,
A. Boselli,
D. Burgarella,
B. F. Madore,
A. Gil de Paz,
L. Bianchi, [......],
P. F. Morrissey,
S. G. Neff,
R. M. Rich,
D. Schiminovich,
M. Seibert,
O. H. W. Siegmund,
T. Small,
A. S. Szalay,
B. Y. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: This work presents the main ultraviolet (UV) and far-infrared (FIR) properties of two samples of nearby galaxies selected from the GALEX (λ = 2315 Å, hereafter NUV) and IRAS (λ = 60 μm) surveys, respectively. They are built in order to obtain detection at both wavelengths for most of the galaxies. Star formation rate (SFR) estimators based on the UV and FIR emissions are compared. Systematic differences are found between the SFR estimators for individual galaxies based on the NUV fluxes corrected for dust attenuation and on the total IR luminosity. A combined estimator based on NUV and IR luminosities seems to be the best proxy over the whole range of values of SFR. Although both samples present similar average values of the birthrate parameter b, their star-formation-related properties are substantially different: NUV-selected galaxies tend to show larger values of b for lower masses, SFRs, and dust attenuation, supporting previous scenarios of star formation history (SFH). Conversely, about 20% of the FIR-selected galaxies show high values of b, SFR, and NUV attenuation. These galaxies, most of them being LIRGs and ULIRGs, break down the downsizing picture of SFH; however, their relative contribution per unit volume is small in the local universe. Finally, the cosmic SFR density of the local universe is estimated in a consistent way from the NUV and IR luminosities.
The Astrophysical Journal Supplement Series 12/2008; 164(1):38. · 13.46 Impact Factor
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Mark Seibert,
Tamás Budavári,
Jaehyon Rhee,
Soo-Chang Rey,
David Schiminovich,
Samir Salim,
D. Christopher Martin,
Alex S. Szalay,
Karl Forster,
R. Michael Rich, [......],
Y.-W. Lee,
B. F. Madore,
R. Malina,
B. Milliard,
P. Morrissey,
S. Neff,
O. Siegmund,
T. Small,
B. Welsh,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We have matched 358,046 objects in 143 deg2 of overlap between the Galaxy Evolution Explorer (GALEX) and the Sloan Digital Sky Survey (SDSS). This Letter provides matching statistics at Medium Imaging Survey and All-sky Imaging Survey depths for SDSS-classified stars and galaxies as well as spectroscopic star, galaxy, and QSO subsamples. Distributions of magnitudes, redshifts, and colors are provided. Near-ultraviolet (NUV)-based color-color diagrams reveal (1) the segregation of main-sequence, horizontal-branch, subdwarf, white dwarf, M dwarf, and M dwarf-white dwarf binary stellar populations, (2) a bimodal distribution of galaxies, and (3) the higher signal quality of the GALEX NUV compared to the SDSS u band.
The Astrophysical Journal 12/2008; 619(1):L23. · 6.02 Impact Factor
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A. Boselli,
S. Boissier,
L. Cortese,
A. Gil de Paz,
V. Buat,
J. Iglesias-Paramo,
B. F. Madore,
T. Barlow,
L Bianchi, Y. -I. Byun, [......],
P. Morrissey,
S. Neff,
R. M. Rich,
D. Schiminovich,
M. Seibert,
O. Siegmund,
T. Small,
A. S. Szalay,
B. Welsh,
T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We present GALEX NUV (2310 A) and FUV (1530 A) images of the interacting galaxy NGC 4438 (Arp 120) in the center of the Virgo cluster. These images show an extended (20 kpc) tidal tail at the north-west edge of the galaxy previously undetected at other wavelengths, at 15-25 kpc from its nucleus. Except in the nucleus, the UV morphology of NGC 4438 is totally different from the Halpha+[NII] one, more similar to the X-ray emission, confirming its gas cooling origin. We study the star formation history of NGC 4438 combining spectro-photometric data in the UV-visible-near-IR wavelength range with population synthesis and galaxy evolution models. The data are consistent with a recent (~ 10 Myr), instantaneous burst of star formation in the newly discovered UV north-western tail which is significantly younger than the age of the tidal interaction with NGC 4435, dated by dynamical models at ~ 100 Myr ago. Recent star formation events are also present at the edge of the northern arm and in the southern tail, while totally lacking in the other regions, which are dominated by the old stellar population perturbed during the dynamical interaction with NGC 4435. The contribution of this recent starburst to the total galaxy stellar mass is lower than 0.1%, an extremely low value for such a violent interaction. High-velocity, off-center tidal encounters such as that observed in Arp 120 are thus not sufficient to significantly increase the star formation activity of cluster galaxies. Comment: 7 pages, 3 figures, accepted for publication in Astrophysical Journal Letters. High resolution version of Fig. 3 is available at http://www.ociw.edu/~boissier/f3.ps
02/2005;
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L. Cortese,
A. Boselli,
G. Gavazzi,
J. Iglesias-Paramo,
B. F. Madore,
T. Barlow,
L Bianchi, Y. -I. Byun,
J. Donas,
K. Forster, [......],
P. Morrissey,
S. Neff,
R. M. Rich,
D. Schiminovich,
O. Siegmund,
T. Small,
A. S. Szalay,
M. A. Treyer,
B. Welsh,
T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We present the GALEX NUV (2310 A) and FUV (1530 A) 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 (~ 2 mag shallower) estimates based on the FOCA and FAUST experiments, but display a steeper faint-end slope than the GALEX luminosity function for local field galaxies. Using spectro-photometric optical data we select out 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 LF is entirely due to the contribution at low luminosities (M_AB >-16 mag) of non star-forming, early-type galaxies that are significantly over dense in clusters. Comment: 4 pages, 4 figures, 1 table. Accepted for publication in Astrophysical Journal Letters
02/2005;
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C ~K Xu,
J Donas,
S Arnouts,
T ~K Wyder,
M Seibert,
J Iglesias-Páramo,
J Blaizot,
T Small,
B Milliard,
D Schiminovich, [......],
P ~N Jelinsky,
Y -W Lee,
B ~F Madore,
R ~F Malina,
P Morrissey,
S ~G Neff,
R ~M Rich,
O ~H ~W Siegmund,
A ~S Szalay,
B ~Y Welsh
apjl. 01/2005; 619:L11-L14.
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C ~K Xu,
J Donas,
S Arnouts,
T ~K Wyder,
M Seibert,
J Iglesias-Páramo,
J Blaizot,
T Small,
B Milliard,
D Schiminovich, [......],
P ~N Jelinsky,
Y -W Lee,
B ~F Madore,
R ~F Malina,
P Morrissey,
S ~G Neff,
R ~M Rich,
O ~H ~W Siegmund,
A ~S Szalay,
B ~Y Welsh
apjl. 01/2005; 619:L11-L14.
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C ~K Xu,
J Donas,
S Arnouts,
T ~K Wyder,
M Seibert,
J Iglesias-Páramo,
J Blaizot,
T Small,
B Milliard,
D Schiminovich, [......],
P ~N Jelinsky,
Y -W Lee,
B ~F Madore,
R ~F Malina,
P Morrissey,
S ~G Neff,
R ~M Rich,
O ~H ~W Siegmund,
A ~S Szalay,
B ~Y Welsh
apjl. 01/2005; 619:L11-L14.
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D. Burgarella,
V. Buat,
T. Small,
T. A. Barlow,
S. Boissier,
A. Gil de Paz,
T. M. Heckman,
B. F. Madore,
D C Martin,
R. M. Rich, [......],
Y W Lee,
R. F. Malina,
B. Milliard,
P. Morrissey,
S. G. Neff,
D. Schiminovich,
O. H. W. Siegmund,
A. S. Szalay,
B. Y. Welsh,
T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: The ELAIS S1 field was observed by GALEX in both its Wide Spectroscopic and Deep Imaging Survey modes. This field was previously observed by the Infrared Space Observatory and we made use of the catalogue of multi-wavelength data published by the ELAIS consortium to select galaxies common to the two samples. Among the 959 objects with GALEX spectroscopy, 88 are present in the ELAIS catalog and 19 are galaxies with an optical spectroscopic redshift. The distribution of redshifts covers the range $0<z<1.6$. The selected galaxies have bolometric IR luminosities $10<Log(L_{IR})<13$ (deduced from the $15 \mu m$ flux using ISOCAM) which means that we cover a wide range of galaxies from normal to Ultra Luminous IR Galaxies. The mean ($\sigma$) UV luminosity (not corrected for extinction) amounts to $Log(\lambda.L_{1530}) = 9.8 (0.6)$ $L_\sun$ for the low-z ($z \le 0.35$) sample. The UV slope $\beta$ (assuming $f_\lambda \propto \lambda^\beta$) correlates with the GALEX FUV-NUV color if the sample is restricted to galaxies below $z < 0.1$. Taking advantage of the UV and IR data, we estimate the dust attenuation from the IR/UV ratio and compare it to the UV slope $\beta$. We find that it is not possible to uniquely estimate the dust attenuation from $\beta$ for our sample of galaxies. These galaxies are highly extinguished with a median value $A_{FUV} = 2.7 \pm 0.8$. Once the dust correction applied, the UV- and IR-based SFRs correlate. For the closest galaxy with the best quality spectrum, we see a feature consistent with being produced by a bump near 220nm in the attenuation curve.
12/2004;
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Luciana Bianchi,
D. Thilker,
D. Burgarella,
P. Friedman,
C. Hoopes,
S. Boissier,
A. Gil de Paz,
T. Barlow, Y. -I. Byun,
J. Donas, [......],
B. Milliard,
P. Morrissey,
S. Neff,
M. Rich,
D. Schiminovich,
O. Siegmund,
T. Small,
A. Szalay,
B. Welsh,
T. Wyder
[show abstract]
[hide abstract]
ABSTRACT: 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
11/2004;
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S. Boissier,
A. Gil de Paz,
B. F. Madore,
A. Boselli,
V. Buat,
D. Burgarella,
P. G. Friedman,
T. A. Barlow,
L Bianchi, Y. -I. Byun, [......],
B. Milliard,
P. Morrissey,
S. G. Neff,
R. M. Rich,
D. Schiminovich,
O. H. W. Siegmund,
T. Small,
A. S. Szalay,
Barry Y. Welsh,
T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: 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
11/2004;
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S. -C. Rey,
R. M. Rich,
Y W Lee,
S. -J. Yoon,
S. K. Yi,
L Bianchi,
Y. -J. Sohn,
P. G. Friedman,
T. A. Barlow, Y. -I. Byun, [......],
B. Milliard,
P. Morrissey,
S. G. Neff,
J. Rhee,
D. Schiminovich,
O. H. W. Siegmund,
T. Small,
A. S. Szalay,
B. Y. Welsh,
T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: 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
11/2004;
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Samir Salim,
Stephane Charlot,
R. Michael Rich,
Guinevere Kauffmann,
Timothy M. Heckman,
T. A. Barlow,
L Bianchi, Y. -I. Byun,
J. Donas,
K. Forster, [......],
B. Milliard,
P. Morrissey,
S. G. Neff,
D. Schiminovich,
M. Seibert,
O. H. W. Siegmund,
T. Small,
A. S. Szalay,
B. Y. Welsh,
T. K. Wyder
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ABSTRACT: 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
11/2004;
