-
S. Gezari,
D. C. Martin, K. Forster,
J. D. Neill,
M. Huber,
T. Heckman,
L. Bianchi,
P. Morrissey,
S. G. Neff,
M. Seibert,
D. Schiminovich,
T. K. Wyder,
W. S. Burgett,
K. C. Chambers,
N. Kaiser,
E. A. Magnier,
P. A. Price,
J. L. Tonry
[show abstract]
[hide abstract]
ABSTRACT: We present the selection and classification of over a thousand ultraviolet
(UV) variable sources discovered in ~ 40 deg^2 of GALEX Time Domain Survey
(TDS) NUV images observed with a cadence of 2 days and a baseline of
observations of ~ 3 years. The GALEX TDS fields were designed to be in spatial
and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which
provides deep optical imaging and simultaneous optical transient detections via
image differencing. We characterize the GALEX photometric errors empirically as
a function of mean magnitude, and select sources that vary at the 5\sigma level
in at least one epoch. We measure the statistical properties of the UV
variability, including the structure function on timescales of days and years.
We report classifications for the GALEX TDS sample using a combination of
optical host colors and morphology, UV light curve characteristics, and matches
to archival X-ray, and spectroscopy catalogs. We classify 62% of the sources as
active galaxies (358 quasars and 305 active galactic nuclei), and 10% as
variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2
cataclysmic variables). The remaining unclassified sources include UV-bright
extragalactic transients, two of which have been spectroscopically confirmed to
be a young core-collapse supernova and a flare from the tidal disruption of a
star by dormant supermassive black hole. We calculate a surface density for
variable sources in the UV with NUV < 23 mag and |\Delta m| > 0.2 mag of ~ 8.0,
7.7, and 1.8 deg^-2 for quasars, AGNs, and RR Lyrae stars, respectively. We
also calculate a surface density rate in the UV for transient sources, using
the effective survey time at the cadence appropriate to each class, of ~ 15 and
52 deg^-2 yr^-1 for M dwarfs and extragalactic transients, respectively.
(Abridged.)
02/2013;
-
S Gezari,
R Chornock,
A Rest,
M E Huber, K Forster,
E Berger,
P J Challis,
J D Neill,
D C Martin,
T Heckman, [......],
W M Wood-Vasey,
W S Burgett,
K C Chambers,
T Grav,
J N Heasley,
N Kaiser,
R-P Kudritzki,
E A Magnier,
J S Morgan,
P A Price
[show abstract]
[hide abstract]
ABSTRACT: The flare of radiation from the tidal disruption and accretion of a star can be used as a marker for supermassive black holes that otherwise lie dormant and undetected in the centres of distant galaxies. Previous candidate flares have had declining light curves in good agreement with expectations, but with poor constraints on the time of disruption and the type of star disrupted, because the rising emission was not observed. Recently, two 'relativistic' candidate tidal disruption events were discovered, each of whose extreme X-ray luminosity and synchrotron radio emission were interpreted as the onset of emission from a relativistic jet. Here we report a luminous ultraviolet-optical flare from the nuclear region of an inactive galaxy at a redshift of 0.1696. The observed continuum is cooler than expected for a simple accreting debris disk, but the well-sampled rise and decay of the light curve follow the predicted mass accretion rate and can be modelled to determine the time of disruption to an accuracy of two days. The black hole has a mass of about two million solar masses, modulo a factor dependent on the mass and radius of the star disrupted. On the basis of the spectroscopic signature of ionized helium from the unbound debris, we determine that the disrupted star was a helium-rich stellar core.
Nature 01/2012; 485(7397):217-20. · 36.28 Impact Factor
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L. Chomiuk,
R. Chornock,
A. M. Soderberg,
E. Berger,
R. A. Chevalier,
R. J. Foley,
M. E. Huber,
G. Narayan,
A. Rest,
S. Gezari, [......],
N. Kaiser,
R. P. Kudritzki,
E. A. Magnier,
D C Martin,
J. S. Morgan,
J. D. Neill,
P. A. Price,
K. C. Roth,
N. E. Sanders,
R. J. Wainscoat
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of two ultra-luminous supernovae (SNe) at z ~ 0.9
with the Pan-STARRS1 Medium-Deep Survey. These SNe, PS1-10ky and PS1-10awh, are
amongst the most luminous SNe ever discovered, comparable to the unusual
transients SN 2005ap and SCP 06F6. Like SN 2005ap and SCP 06F6, they show
characteristic high luminosities (M_bol ~ -22.5 mag), blue spectra with a few
broad absorption lines, and no evidence for H or He. We have constructed a full
multi-color light curve sensitive to the peak of the spectral energy
distribution in the rest-frame ultraviolet, and we have obtained time-series
spectroscopy for these SNe. Given the similarities between the SNe, we combine
their light curves to estimate a total radiated energy over the course of
explosion of (0.9-1.4) x 10^51 erg. We find photospheric velocities of
12,000-19,000 km/s with no evidence for deceleration measured across ~3
rest-frame weeks around light-curve peak, consistent with the expansion of an
optically-thick massive shell of material. We show that, consistent with
findings for other ultra-luminous SNe in this class, radioactive decay is not
sufficient to power PS1-10ky, and we discuss two plausible origins for these
events: the initial spin-down of a newborn magnetar in a core-collapse SN, or
SN shock breakout from the dense circumstellar wind surrounding a Wolf-Rayet
star.
07/2011;
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S. Gezari,
A. Rest,
M. E. Huber,
G. Narayan, K. Forster,
J. D. Neill,
D. C. Martin,
S. Valenti,
S. J. Smartt,
R. Chornock, [......],
J. S. Morgan,
P. M. Onaka,
P. A. Price,
P. H. Rhoads,
W. A. Siegmund,
C. W. Stubbs,
J. L. Tonry,
R. J. Wainscoat,
M. F. Waterson,
and C. G. Wynn-Williams
[show abstract]
[hide abstract]
ABSTRACT: We present the early UV and optical light curve of Type IIP supernova (SN) 2010aq at z = 0.0862, and compare it to analytical models for thermal emission following SN shock breakout in a red supergiant star. SN 2010aq was discovered in joint monitoring between the Galaxy Evolution Explorer (GALEX) Time Domain Survey (TDS) in the NUV and the Pan-STARRS1 Medium Deep Survey (PS1 MDS) in the g, r, i, and z bands. The GALEX and Pan-STARRS1 observations detect the SN less than 1 day after the shock breakout, measure a diluted blackbody temperature of 31, 000 ± 6000 K 1 day later, and follow the rise in the UV/optical light curve over the next 2 days caused by the expansion and cooling of the SN ejecta. The high signal-to-noise ratio of the simultaneous UV and optical photometry allows us to fit for a progenitor star radius of 700 ± 200R ☉, the size of a red supergiant star. An excess in UV emission two weeks after shock breakout compared with SNe well fitted by model atmosphere-code synthetic spectra with solar metallicity is best explained by suppressed line blanketing due to a lower metallicity progenitor star in SN 2010aq. Continued monitoring of PS1 MDS fields by the GALEX TDS will increase the sample of early UV detections of Type II SNe by an order of magnitude and probe the diversity of SN progenitor star properties.
The Astrophysical Journal Letters 08/2010; 720(1):L77. · 5.53 Impact Factor
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M. T. Botticella,
C. Trundle,
A. Pastorello,
S. Rodney,
A. Rest,
S. Gezari,
S. J. Smartt,
G. Narayan,
M. E. Huber,
J. L. Tonry, [......],
J. S. Morgan,
P. M. Onaka,
P. A. Price,
P. H. Rhoads,
W. A. Siegmund,
W. E. Sweeney,
R. J. Wainscoat,
C. Waters,
M. F. Waterson,
and C. G. Wynn-Williams
[show abstract]
[hide abstract]
ABSTRACT: We present photometric and spectroscopic observations of a luminous Type IIP Supernova (SN) 2009kf discovered by the Pan-STARRS 1 (PS1) survey and also detected by the Galaxy Evolution Explorer. The SN shows a plateau in its optical and bolometric light curves, lasting approximately 70 days in the rest frame, with an absolute magnitude of M V = –18.4 mag. The P-Cygni profiles of hydrogen indicate expansion velocities of 9000 km s-1 at 61 days after discovery which is extremely high for a Type IIP SN. SN 2009kf is also remarkably bright in the near-ultraviolet (NUV) and shows a slow evolution 10-20 days after optical discovery. The NUV and optical luminosity at these epochs can be modeled with a blackbody with a hot effective temperature (T ~ 16,000 K) and a large radius (R ~ 1 × 1015 cm). The bright bolometric and NUV luminosity, the light curve peak and plateau duration, the high velocities, and temperatures suggest that 2009kf is a Type IIP SN powered by a larger than normal explosion energy. Recently discovered high-z SNe (0.7 < z < 2.3) have been assumed to be IIn SNe, with the bright UV luminosities due to the interaction of SN ejecta with a dense circumstellar medium. UV-bright SNe similar to SN 2009kf could also account for these high-z events, and its absolute magnitude M NUV = –21.5 ± 0.5 mag suggests such SNe could be discovered out to z ~ 2.5 in the PS1 survey.
The Astrophysical Journal Letters 06/2010; 717(1):L52. · 5.53 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We report serendipitous GALEX observations of the extremely luminous
optical transient CSS100217:102913+404220 discovered by CRTS (ATEL
#2544). The object was detected on 24 April 2004 by the All Sky Imaging
Survey with FUV = 19.52 and NUV = 18.978, and on 29 January 2010 by the
Medium Imaging Survey with NUV = 17.078 (the FUV detector was
temporarily not operational). The brightening of the object by 1.9 mag
in the NUV corresponds to a transient source with NUV = 17.285 close to
the time of the optical peak.
The Astronomer's Telegram. 03/2010; 2554:1.
-
M. T. Botticella,
C. Trundle,
A. Pastorello,
S. Rodney,
A. Rest,
S. Gezari,
S. J. Smartt,
G. Narayan,
M. E. Huber,
J. L. Tonry, [......],
J. S. Morgan,
P. M. Onaka,
P. A. Price,
P. H. Rhoads,
W. A. Siegmund,
W. E. Sweeney,
R. J. Wainscoat,
C. Waters,
M. F. Waterson,
C. G. Wynn-Williams
[show abstract]
[hide abstract]
ABSTRACT: We present photometric and spectroscopic observations of a luminous type IIP Supernova 2009kf discovered by the Pan-STARRS 1 (PS1) survey and detected also by GALEX. The SN shows a plateau in its optical and bolometric light curves, lasting approximately 70 days in the rest frame, with absolute magnitude of M_V = -18.4 mag. The P-Cygni profiles of hydrogen indicate expansion velocities of 9000km/s at 61 days after discovery which is extremely high for a type IIP SN. SN 2009kf is also remarkably bright in the near-ultraviolet (NUV) and shows a slow evolution 10-20 days after optical discovery. The NUV and optical luminosity at these epochs can be modelled with a black-body with a hot effective temperature (T ~16,000 K) and a large radius (R ~1x10^{15} cm). The bright bolometric and NUV luminosity, the lightcurve peak and plateau duration, the high velocities and temperatures suggest that 2009kf is a type IIP SN powered by a larger than normal explosion energy. Recently discovered high-z SNe (0.7 < z < 2.3) have been assumed to be IIn SNe, with the bright UV luminosities due to the interaction of SN ejecta with a dense circumstellar medium (CSM). UV bright SNe similar to SN 2009kf could also account for these high-z events, and its absolute magnitude M_NUV = -21.5 +/- 0.5 mag suggests such SNe could be discovered out to z ~2.5 in the PS1 survey. Comment: Accepted for publication in APJL
01/2010;
-
T. Budavari,
S. Heinis,
A. S. Szalay,
M. Nieto-Santisteban,
J. Gupchup,
B. Shiao,
M Smith,
R. Chang,
G. Kauffmann,
P. Morrissey, [......], K. Forster,
L Bianchi,
J. Donas,
P. G. Friedman,
T. M. Heckman,
Y W Lee,
B. F. Madore,
S. G. Neff,
R. M. Rich,
B. Y. Welsh
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed study of the Galaxy Evolution Explorer's photometric catalogs with special focus on the statistical properties of the All-sky and Medium Imaging Surveys. We introduce the concept of primaries to resolve the issue of multiple detections and follow a geometric approach to define clean catalogs with well-understood selection functions. We cross-identify the GALEX sources (GR2+3) with Sloan Digital Sky Survey (DR6) observations, which indirectly provides an invaluable insight about the astrometric model of the UV sources and allows us to revise the band merging strategy. We derive the formal description of the GALEX footprints as well as their intersections with the SDSS coverage along with analytic calculations of their areal coverage. The crossmatch catalogs are made available for the public. We conclude by illustrating the implementation of typical selection criteria in SQL for catalog subsets geared toward statistical analyses, e.g., correlation and luminosity function studies.
05/2009;
-
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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B. D. Johnson,
D. Schiminovich,
M. Seibert,
M. A. Treyer,
S. Charlot,
T. M. Heckman,
D. C. Martin,
S. Salim,
G. Kauffmann,
L. Bianchi, [......],
B. Milliard,
P. Morrissey,
S. G. Neff,
R. M. Rich,
A. S. Szalay, K. Forster,
T. A. Barlow,
T. Conrow,
T. Small,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: We combine data from the Sloan Digital Sky Survey (SDSS), the Galaxy Evolution Explorer (GALEX), and the Spitzer Space Telescope to create a sample of galaxies observed homogeneously from the UV to the far-IR. This sample, consisting of ~460 galaxies observed spectroscopically by the SDSS, provides us with a multiwavelength (0.15-24 μm) view of obscured and unobscured star formation in nearby (z < 0.3) galaxies with star formation rates (SFRs) ranging from 0.01 to 100 M☉ yr-1. We calculate a robust dust measure from the infrared-to-UV ratio (or infrared excess [IRX]) and explore the influence of star formation history (SFH) on the dust-UV color relation (i.e., the IRX-β relation). We find that the UV colors of galaxies are only weakly dependent on their SFH as measured by the 4000 Å break. However, we find that the contributions of dust and SFH are distinguishable when colors at widely separated wavelengths (e.g., 0.23-3.6 μm) are introduced. We show this explicitly by recasting the IRX-β relation as a more general IRX-SFH-color relation, which we examine in different projections. We also determine simple fits to this relation.
The Astrophysical Journal 12/2008; 644(2):L109. · 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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S. Kaviraj,
K. Schawinski,
J. E. G. Devriendt,
I. Ferreras,
S. Khochfar,
S.-J. Yoon,
S. K. Yi,
J.-M. Deharveng,
A. Boselli,
T. Barlow, [......],
T. Small,
T. Wyder,
L. Bianchi,
J. Donas,
T. Heckman,
Y.-W. Lee,
B. Madore,
B. Milliard,
R. M. Rich,
and A. Szalay
[show abstract]
[hide abstract]
ABSTRACT: We have studied ~2100 early-type galaxies in the SDSS DR3 which have been detected by the GALEX Medium Imaging Survey (MIS), in the redshift range 0 < z < 0.11. Combining GALEX UV photometry with corollary optical data from the SDSS, we find that, at a 95% confidence level, at least ~30% of galaxies in this sample have UV to optical colors consistent with some recent star formation within the last Gyr. In particular, galaxies with an NUV − r color less than 5.5 are very likely to have experienced such recent star formation, taking into account the possibility of a contribution to NUV flux from the UV upturn phenomenon. We find quantitative agreement between the observations and the predictions of a semianalytical ΛCDM hierarchical merger model and deduce that early-type galaxies in the redshift range 0 < z < 0.11 have ~1%-3% of their stellar mass in stars less than 1 Gyr old. The average age of this recently formed population is ~300-500 Myr. We also find that "monolithically" evolving galaxies, where recent star formation can be driven solely by recycled gas from stellar mass loss, cannot exhibit the blue colors (NUV − r < 5.5) seen in a significant fraction (~30%) of our observed sample.
The Astrophysical Journal Supplement Series 12/2008; 173(2):619. · 13.46 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,
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. Gezari,
D. C. Martin,
B. Milliard,
S. Basa,
J. P. Halpern, K. Forster,
P. G. Friedman,
P. Morrissey,
S. G. Neff,
D. Schiminovich,
M. Seibert,
T. Small,
and T. K. Wyder
[show abstract]
[hide abstract]
ABSTRACT: A supermassive black hole in the nucleus of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces and a flare of radiation is emitted by the stream of stellar debris that plunges into the black hole. Since common active galactic nuclei have accreting black holes that can also produce flares, a convincing demonstration that a stellar tidal disruption has occurred generally begins with a "normal" galaxy that has no evidence of prior nuclear activity. Here we report a luminous UV flare from an elliptical galaxy at z = 0.37 in the Groth field of the GALEX Deep Imaging Survey that has no evidence of a Seyfert nucleus from optical spectroscopy and X-ray imaging obtained during the flare. Multiwavelength data collected at the time of the event, and for 2 years following, allow us to constrain, for the first time, the spectral energy distribution of a candidate tidal disruption flare from optical through X-rays. The luminosity and temperature of the radiation and the decay curve of the flare are in excellent agreement with theoretical predictions for the tidal disruption of a star, and provide the strongest empirical evidence for a stellar disruption event to date.
The Astrophysical Journal 12/2008; 653(1):L25. · 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
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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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S. Gezari,
S. Basa,
D. C. Martin,
G. Bazin, K. Forster,
B. Milliard,
J. P. Halpern,
P. G. Friedman,
P. Morrissey,
S. G. Neff,
D. Schiminovich,
M. Seibert,
T. Small,
and T. K. Wyder
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ABSTRACT: We present two luminous UV/optical flares from the nuclei of apparently inactive early-type galaxies at z = 0.37 and 0.33 that have the radiative properties of a flare from the tidal disruption of a star. In this paper we report the second candidate tidal disruption event discovery in the UV by the GALEX Deep Imaging Survey and present simultaneous optical light curves from the CFHTLS Deep Imaging Survey for both UV flares. The first few months of the UV/optical light curves are well fitted with the canonical t−5/3 power-law decay predicted for emission from the fallback of debris from a tidally disrupted star. Chandra ACIS X-ray observations during the flares detect soft X-ray sources with Tbb = (2–5) × 105 K or Γ > 3 and place limits on hard X-ray emission from an underlying AGN down to LX(2–10 keV) 1041 ergs s−1. Blackbody fits to the UV/optical spectral energy distributions of the flares indicate peak flare luminosities of 1044-1045 ergs s−1. The temperature, luminosity, and light curves of both flares are in excellent agreement with emission from a tidally disrupted main-sequence star onto a central black hole of several times 107 M☉. The observed detection rate of our search over ~2.9 deg2 of GALEX Deep Imaging Survey data spanning from 2003 to 2007 is consistent with tidal disruption rates calculated from dynamical models, and we use these models to make predictions for the detection rates of the next generation of optical synoptic surveys.
The Astrophysical Journal 12/2008; 676(2):944. · 6.02 Impact Factor
