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[show abstract]
[hide abstract]
ABSTRACT: We assess the metal content of the cool (10^4 K) circumgalactic medium (CGM)
about galaxies at z<1 using an H I-selected sample of 28 Lyman limit systems
(LLS, defined here as absorbers with 16.2<log N(H I)<18.5) observed in
absorption against background QSOs by the Cosmic Origins Spectrograph on-board
the Hubble Space Telescope. The N(H I) selection avoids metallicity biases
inherent in many previous studies of the low-redshift CGM. We compare the
column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to
N(H I) in the strongest H I component of each absorber. We find that the
metallicity distribution of the LLS (and hence the cool CGM) is bimodal with
metal-poor and metal-rich branches peaking at [X/H]=-1.6 and -0.3 (or about
2.5% and 50% solar metallicities). The cool CGM probed by these LLS is
predominantly ionized. The metal-rich branch of the population likely traces
winds, recycled outflows, and tidally stripped gas; the metal-poor branch has
properties consistent with cold accretion streams thought to be a major source
of fresh gas for star forming galaxies. Both branches have a nearly equal
number of absorbers. Our results thus demonstrate there is a significant mass
of previously-undiscovered cold metal-poor gas and confirm the presence of
metal enriched gas in the CGM of z<1 galaxies.
02/2013;
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D. A. Perley,
A. J. Levan,
N. R. Tanvir,
S. B. Cenko,
J. S. Bloom,
J. Hjorth,
T. Kruehler,
A. V. Filippenko,
A. Fruchter,
J. P. U. Fynbo,
P. Jakobsson,
J. Kalirai,
B. Milvang-Jensen,
A. N. Morgan, J. X. Prochaska,
J. M. Silverman
[show abstract]
[hide abstract]
ABSTRACT: We present observations and analysis of the host galaxies of 23 heavily
dust-obscured gamma-ray bursts (GRBs) observed by the Swift satellite between
the years 2005-2009, a sample representing all GRBs during this period with an
unambiguous host-frame extinction of at least A_V>1 mag. Deep observations with
Keck, Gemini, VLT, HST, and Spitzer successfully detect the host galaxies and
establish redshifts for all 23 events, enabling us to provide measurements of
the host stellar masses, star-formation rates (SFRs), and mean extinctions.
Compared to the hosts of unobscured GRBs at similar redshifts, we find that the
hosts of dust-obscured GRBs are (on average) more massive by about an order of
magnitude and are also significantly more rapidly star-forming and more
dust-obscured. However, while the inclusion of this population of dust-obscured
hosts shows that GRBs populate all types of star-forming galaxies including the
most massive, luminous systems at z~2, at redshifts below z<1.5 the overall GRB
population continues to show a highly significant aversion away from massive
galaxies and a corresponding preference for low-mass systems relative to would
be expected given a purely SFR-selected galaxy sample. This supports the notion
that the GRB rate is strongly dependent on metallicity, and may suggest that
the most massive galaxies in the universe underwent an significant transition
in their chemical properties approximately 9 Gyr ago. We also conclude that,
based on the absence of unobscured GRBs in massive galaxies and the absence of
obscured GRBs in low-mass galaxies, the dust distributions of both the
lowest-mass and the highest-mass galaxies are relatively homogeneous, while
intermediate-mass galaxies (~10^9 M_sun) have much more diverse internal dust
properties.
01/2013;
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A. Cucchiara, J. X. Prochaska,
G. Zhu,
B. Ménard,
J. P. U. Fynbo,
D. B. Fox,
H. -W. Chen,
K. L. Cooksey,
S. B. Cenko,
D. Perley,
J. S. Bloom,
E. Berger,
N. R. Tanvir,
V. D'Elia,
S. Vergani,
S. Lopez,
R. Chornock,
Thomas deJaeger
[show abstract]
[hide abstract]
ABSTRACT: In 2006, Prochter et al. reported a statistically significant enhancement of
very strong Mg II absorption systems intervening the sightlines to gamma-ray
bursts (GRBs) relative to the in- cidence of such absorption along quasar
sightlines. This counterintuitive result, has inspired a diverse set of
astrophysical explanations (e.g. dust, gravitational lensing) but none of these
has obviously resolved the puzzle. Using the largest set of GRB afterglow
spectra available, we reexamine the purported enhancement. In an independent
sample of GRB spectra with a survey path 3 times larger than Prochter et al.,
we measure the incidence per unit redshift of $\geq 1$\AA rest-frame equivalent
width Mg II absorbers at $z \approx 1$ to be l(z)= 0.18 $\pm$ 0.06. This is
fully consistent with current estimates for the incidence of such absorbers
along quasar sightlines. Therefore, we do not confirm the original enhancement
and suggest those results suffered from a statistical fluke. Signatures of the
original result do remain in our full sample (l(z) shows an $\approx 1.5$
enhancement over l(z)QSO), but the statistical significance now lies at
$\approx 90%$ c.l. Restricting our analysis to the subset of high-resolution
spectra of GRB afterglows (which overlaps substantially with Prochter et al.),
we still reproduce a statistically significant enhancement of Mg II absorption.
The reason for this excess, if real, is still unclear since there is no
connection between the rapid afterglow follow-up process with echelle (or
echellette) spectrographs and the detectability of strong Mg II doublets. Only
a larger sample of such high-resolution data will shed some light on this
matter.
11/2012;
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A. Cucchiara,
S. B. Cenko,
J. S. Bloom,
A. Melandri,
A. Morgan,
S. Kobayashi,
R. J. Smith,
D. A. Perley,
W. Li,
J. L. Hora, [......],
B. Cobb,
G. Worseck,
C. G. Mundell,
I. A. Steele,
A. V. Filippenko,
M. Fumagalli,
C. R. Klein,
A. Stephens,
A. Bluck,
and R. Mason
[show abstract]
[hide abstract]
ABSTRACT: Understanding the origin and diversity of emission processes responsible for gamma-ray bursts (GRBs) remains a pressing challenge. While prompt and contemporaneous panchromatic observations have the potential to test predictions of the internal-external shock model, extensive multiband imaging has been conducted for only a few GRBs. We present rich, early-time, multiband data sets for two Swift events, GRB 110205A and GRB 110213A. The former shows optical emission since the early stages of the prompt phase, followed by the steep rising in flux up to ~1000 s after the burst (t –α with α = –6.13 ± 0.75). We discuss this feature in the context of the reverse-shock scenario and interpret the following single power-law decay as being forward-shock dominated. Polarization measurements, obtained with the RINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the nature of the emitting ejecta. The latter event, instead, displays a very peculiar optical to near-infrared light curve, with two achromatic peaks. In this case, while the first peak is probably due to the onset of the afterglow, we interpret the second peak to be produced by newly injected material, signifying a late-time activity of the central engine.
The Astrophysical Journal 12/2011; 743(2):154. · 6.02 Impact Factor
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J Tumlinson,
C Thom,
J K Werk, J X Prochaska,
T M Tripp,
D H Weinberg,
M S Peeples,
J M O'Meara,
B D Oppenheimer,
J D Meiring,
N S Katz,
R Davé,
A B Ford,
K R Sembach
[show abstract]
[hide abstract]
ABSTRACT: The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150-kiloparsec) halos of ionized oxygen surrounding star-forming galaxies; we found much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. Our data indicate that it is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution.
Science 11/2011; 334(6058):948-52. · 31.20 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present Cosmic Origins Spectrograph (COS) measurements of metal abundances
in eight 0.083<z<0.321 damped Lyman-\alpha (DLA) and sub-damped Ly-\alpha\
absorption systems serendipitously discovered in the COS-Halos survey. We find
that these systems show a large range in metallicities, with -1.10<[Z/H]<0.31,
similar to the spread found at higher redshifts. These low-redshift systems on
average have subsolar metallicities, but do show a rise in metallicity over
cosmic time when compared to higher-redshift systems. We find the average
sub-DLA metallicity is higher than the average DLA metallicity at all
redshifts. Nitrogen is underabundant with respect to \alpha-group elements in
all but perhaps one of the absorbers. In some cases, [N/\alpha] is
significantly below the lowest nitrogen measurements in nearby galaxies.
Systems for which depletion patterns can be studied show little, if any,
depletion, which is characteristic of Milky Way halo-type gas. We also identify
affiliated galaxies for 3 of the sub-DLAs using spectra obtained from
Keck/LRIS. None of these sub-DLAs arise in the stellar disks of luminous
galaxies; instead, these absorbers may exist in galaxy halos at impact
parameters ranging from 38 to 92 kpc. Multiple galaxies are present near two of
the sub-DLAs, and galaxy interactions may play a role in the dispersal of the
gas. Many of these low-redshift absorbers exhibit simple kinematics, but one
sub-DLA has a complicated mix of at least 13 components spread over 150 km/s.
We find three galaxies near this sub-DLA, which also suggests that galaxy
interactions roil the gas. This study reinforces the view that DLAs have a
variety of origins, and low-redshift studies are crucial for understanding
absorber-galaxy connections.
10/2011;
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C. S. Froning,
A. G. Cantrell,
T. J. Maccarone,
K. France,
J. Khargharia,
L. M. Wintr,
E. L. Robinson,
R. I. Hynes,
J. W. Broderick,
S. Markoff,
M. A. P. Torres,
M. Garcia,
C. D. Bailyn, J. X. Prochaska,
J. Werk,
C. Thom,
S. Beland,
C. W. Danforth,
B. Keeney,
J. C. Green
[show abstract]
[hide abstract]
ABSTRACT: [Abridged.] We present multiwavelength observations of the black hole binary
system, A0620-00. Using the Cosmic Origins Spectrograph on the Hubble Space
Telescope, we have obtained the first FUV spectrum of A0620-00. The observed
spectrum is flat in the FUV and very faint (with continuum fluxes \simeq 1e -
17 ergs/cm^2/s/A). We compiled the dereddened, broadband spectral energy
distribution of A0620-00 and compared it to previous SEDs as well as
theoretical models. The SEDs show that the source varies at all wavelengths for
which we have multiple samples. Contrary to previous observations, the
optical-UV spectrum does not continue to drop to shorter wavelengths, but
instead shows a recovery and an increasingly blue spectrum in the FUV. We
created an optical-UV spectrum of A0620-00 with the donor star contribution
removed. The non-stellar spectrum peaks at \simeq3000 {\deg}A. The peak can be
fit with a T=10,000 K blackbody with a small emitting area, probably
originating in the hot spot where the accretion stream impacts the outer disk.
However, one or more components in addition to the blackbody are needed to fit
the FUV upturn and the red optical fluxes in the optical-UV spectrum. By
comparing the mass accretion rate determined from the hot spot luminosity to
the mean accretion rate inferred from the outburst history, we find that the
latter is an order of magnitude smaller than the former, indicating that
\sim90% of the accreted mass must be lost from the system if the predictions of
the disk instability model and the estimated interoutburst interval are
correct. The mass accretion rate at the hot spot is 10^5 the accretion rate at
the black hole inferred from the X-ray luminosity. To reconcile these requires
that outflows carry away virtually all of the accreted mass, a very low rate of
mass transfer from the outer cold disk into the inner hot region, and/or
radiatively inefficient accretion.
09/2011;
-
A. Cucchiara,
S. B. Cenko,
J. S. Bloom,
A. Melandri,
A. Morgan,
S Kobayashi,
R. J. Smith,
D. A. Perley,
W Li,
J. L. Hora, [......],
B. Cobb,
G. Worseck,
C. G. Mundell,
I. A. Steele,
A. V. Filippenko,
M. Fumagalli,
C. R. Klein,
A. Stephens,
A. Bluck,
R. Mason
[show abstract]
[hide abstract]
ABSTRACT: Understanding the origin and diversity of emission processes responsible for
Gamma-ray Bursts (GRBs) remains a pressing challenge. While prompt and
contemporaneous panchromatic observations have the potential to test
predictions of the internal-external shock model, extensive multiband imaging
has been conducted for only a few GRBs. We present rich, early-time, multiband
datasets for two \swift\ events, GRB 110205A and GRB 110213A. The former shows
optical emission since the early stages of the prompt phase, followed by the
steep rising in flux up to ~1000s after the burst ($t^{-\alpha}$ with
$\alpha=-6.13 \pm 0.75$). We discuss this feature in the context of the
reverse-shock scenario and interpret the following single power-law decay as
being forward-shock dominated. Polarization measurements, obtained with the
RINGO2 instrument mounted on the Liverpool Telescope, also provide hints on the
nature of the emitting ejecta. The latter event, instead, displays a very
peculiar optical to near-infrared lightcurve, with two achromatic peaks. In
this case, while the first peak is probably due to the onset of the afterglow,
we interpret the second peak to be produced by newly injected material,
signifying a late-time activity of the central engine.
07/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present observations of H I and O VI absorption systems proximate to a galaxy at z gal = 0.3529. The absorption was detected serendipitously in Cosmic Origins Spectrograph observations of the low-z QSO J 0943 + 0531 (z qso = 0.564). The data show two separate clouds along the sightline at an impact parameter of 95 kpc from the galaxy. The first is likely low-metallicity gas falling onto the galaxy. This assessment is based on the high velocity offset of the cloud from the galaxy (Δv = 365 km s–1) and the weak metal line absorption, combined with photoionization modeling. The second cloud, with only a modest velocity separation from the galaxy (Δv = 85 km s–1), exhibits very strong O VI absorption qualitatively similar to O VI absorption seen in the Milky Way halo. Collisional ionization equilibrium models are ruled out by the metal line column density ratios. Photoionization modeling implies a length scale for the O VI cloud of ~0.1-1.2 Mpc, which indicates the absorbing gas most likely resides within the local filamentary structure. This system emphasizes that kinematic association alone is not sufficient to establish a physical connection to galaxies, even at small impact parameters and velocity separations. Observations such as these, connecting galaxies with their gaseous environments, are becoming increasingly important for understanding of galaxy evolution and provide constraints for cosmological simulations.
The Astrophysical Journal 06/2011; 736(1):1. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present observations of HI and OVI absorption systems proximate to a
galaxy at z_gal = 0.3529. The absorption was detected serendipitously in Cosmic
Origins Spectrograph observations of the low-z QSO J0943+0531 (z_qso = 0.564).
The data show two separate clouds along the sightline at an impact parameter of
95kpc from the galaxy. The first is likely low-metallicity gas falling onto the
galaxy. This assessment is based on the high velocity offset of the cloud from
the galaxy (delta_v = 365kms) and the weak metal line absorption, combined with
photoionization modeling. The second cloud, with only a modest velocity
separation from the galaxy (delta_v = 85kms), exhibits very strong OVI
absorption qualitatively similar to OVI absorption seen in the Milky Way halo.
Collisional ionization equilibrium models are ruled out by the metal line
column density ratios. Photoionization modeling implies a length-scale for the
OVI cloud of ~0.1-1.2Mpc, which indicates the absorbing gas most likely resides
within the local filamentary structure. This system emphasizes that kinematic
association alone is not sufficient to establish a physical connection to
galaxies, even at small impact parameters and velocity separations.
Observations such as these, connecting galaxies with their gaseous
environments, are becoming increasingly important for understanding galaxy
evolution and provide constraints for cosmological simulations.
05/2011;
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C. Guidorzi,
S Kobayashi,
D. A. Perley,
G. Vianello,
J. S. Bloom,
P Chandra,
D. A. Kann,
W Li,
C. G. Mundell,
A. Pozanenko, [......],
E. Klunko,
A. Melandri,
S. Mereghetti,
A. N. Morgan,
P. T. O'Brien,
V. Rumyantsev,
R. J. Smith,
I. A. Steele,
N. R. Tanvir,
A. Volnova
[show abstract]
[hide abstract]
ABSTRACT: We report the detection of a faint optical flash by the 2-m Faulkes Telescope
North simultaneously with the second of two prompt gamma-ray pulses in INTEGRAL
gamma-ray burst (GRB) 080603A, beginning at t_rest = 37 s after the onset of
the GRB. This optical flash appears to be distinct from the subsequent emerging
afterglow emission, for which we present comprehensive broadband radio to X-ray
light curves to 13 days post-burst and rigorously test the standard fireball
model. The intrinsic extinction toward GRB 080603A is high (A_V,z = 0.8 mag),
and the well-sampled X-ray-to-near-infrared spectral energy distribution is
interesting in requiring an LMC2 extinction profile, in contrast to the
majority of GRBs. Comparison of the gamma-ray and extinction-corrected optical
flux densities of the flash rules out an inverse-Compton origin for the prompt
gamma-rays; instead, we suggest that the optical flash could originate from the
inhomogeneity of the relativistic flow. In this scenario, a large velocity
irregularity in the flow produces the prompt gamma-rays, followed by a milder
internal shock at a larger radius that would cause the optical flash. Flat
gamma-ray spectra, roughly F propto nu^-0.1, are observed in many GRBs. If the
flat spectrum extends down to the optical band in GRB 080603A, the optical
flare could be explained as the low-energy tail of the gamma-ray emission. If
this is indeed the case, it provides an important clue to understanding the
nature of the emission process in the prompt phase of GRBs and highlights the
importance of deep (R> 20 mag), rapid follow-up observations capable of
detecting faint, prompt optical emission.
05/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We report on the first Cosmic Origins Spectrograph observations of damped Lyα systems (DLAs) and sub-damped Lyα systems (sub-DLAs) discovered in a new survey of the gaseous halos of low-redshift galaxies. From observations of 37 sightlines, we have discovered three DLAs and four sub-DLAs. We measure the neutral gas density ΩH I , and redshift density d /d z, of DLA and sub-DLA systems at z < 0.35. We find d /dz = 0.25+0.24 – 0.14 and ΩH I = 1.4+1.3 – 0.7 × 10–3 for DLAs, and d /d z = 0.08+0.19 – 0.06 with ΩH I = 4.2+9.6 – 3.5 × 10–5 for sub-DLAs over a redshift path Δz = 11.9. To demonstrate the scientific potential of such systems, we present a detailed analysis of the DLA at z abs = 0.1140 in the spectrum of SDSS J1009+0713. Profile fits to the absorption lines determine log N(H I) = 20.68 ± 0.10 with a metallicity determined from the undepleted element sulfur of [S/H] = –0.62 ± 0.18. The abundance pattern of this DLA is similar to that of higher z DLAs, showing mild depletion of the refractory elements Fe and Ti with [S/Fe] = +0.24 ± 0.22 and [S/Ti] = +0.28 ± 0.15. Nitrogen is underabundant in this system with [N/H] = –1.40 ± 0.14, placing this DLA below the plateau of the [N/α] measurements in the local universe at similar metallicities. This DLA has a simple kinematic structure with only two components required to fit the profiles and a kinematic width of Δv 90 = 52 km s–1. Imaging of the QSO field with the Hubble Space Telescope/Wide Field Camera 3 reveals a spiral galaxy at very small impact parameter to the QSO and several galaxies within 10'', or 20 comoving kpc at the redshift of the DLA. Follow-up spectra with the Low Resolution Imaging Spectrometer on the Keck telescope reveal that none of the nearby galaxies are at the redshift of the DLA. The spiral galaxy is identified as the host galaxy of the QSO based on the near perfect alignment of the nucleus and disk of the galaxy as well as spectra of an H II region showing emission lines at the QSO redshift. A small feature appears 070 from the nucleus of the QSO after point-spread function subtraction, providing another candidate for the host galaxy of the DLA system. Even with these supporting data, we are unable to unambiguously identify the host galaxy of the DLA, exemplifying some of the difficulties in determining DLA hosts even at low redshift.
The Astrophysical Journal 04/2011; 732(1):35. · 6.02 Impact Factor
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S. B. Cenko,
D. A. Frail,
F. A. Harrison,
J. B. Haislip,
D. E. Reichart,
N. R. Butler,
B. E. Cobb,
A. Cucchiara,
E. Berger,
J. S. Bloom, [......],
A. V. Filippenko,
K. Glazebrook,
K. M. Ivarsen,
M. M. Kasliwal,
S. R. Kulkarni,
A. P. LaCluyze,
S. Lopez,
A. N. Morgan,
M. Pettini,
and V. R. Rana
[show abstract]
[hide abstract]
ABSTRACT: We present broadband (radio, optical, and X-ray) light curves and spectra of the afterglows of four long-duration gamma-ray bursts (GRBs; GRBs 090323, 090328, 090902B, and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite. With its wide spectral bandpass, extending to GeV energies, Fermi is sensitive to GRBs with very large isotropic energy releases (1054 erg). Although rare, these events are particularly important for testing GRB central-engine models. When combined with spectroscopic redshifts, our afterglow data for these four events are able to constrain jet collimation angles, the density structure of the circumburst medium, and both the true radiated energy release and the kinetic energy of the outflows. In agreement with our earlier work, we find that the relativistic energy budget of at least one of these events (GRB 090926A) exceeds the canonical value of 1051 erg by an order of magnitude. Such energies pose a severe challenge for models in which the GRB is powered by a magnetar or a neutrino-driven collapsar, but remain compatible with theoretical expectations for magnetohydrodynamical collapsar models (e.g., the Blandford-Znajek mechanism). Our jet opening angles (θ) are similar to those found for pre-Fermi GRBs, but the large initial Lorentz factors (Γ0) inferred from the detection of GeV photons imply θΓ0 70-90, values which are above those predicted in magnetohydrodynamic models of jet acceleration. Finally, we find that these Fermi-LAT events preferentially occur in a low-density circumburst environment, and we speculate that this might result from the lower mass-loss rates of their lower-metallicity progenitor stars. Future studies of Fermi-LAT afterglows at radio wavelengths with the order-of-magnitude improvement in sensitivity offered by the Extended Very Large Array should definitively establish the relativistic energy budgets of these events.
The Astrophysical Journal 04/2011; 732(1):29. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have serendipitously detected a strong O VI-bearing Lyman limit system at
z_abs = 0.3558 toward the QSO J1009+0713 (z_em = 0.456) in our survey of
low-redshift galaxy halos with the Hubble Space Telescope's Cosmic Origins
Spectrograph. Its rest-frame equivalent width of W_r = 835 +/- 49 mA is the
highest for an intervening absorber yet detected in any low-redshift QSO
sightline, with absorption spanning 400 km s^-1 in its rest frame. HST/WFC3
images of the galaxy field show that the absorber is associated with two
galaxies lying at 14 and 46 kpc from the QSO line of sight. The bulk of the
absorbing gas traced by H I resides in two strong, blended component groups
that possess a total logN(HI) = 18 - 18.8. The ion ratios and column densities
of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a
simple photoionization model in which diffuse, low-metallicity halo gas is
exposed to a photoionizing field from stars in the nearby galaxies that
propagates into the halo at 10% efficiency. We constrain the metallicity firmly
within the range 0.1 - 1 Zsun, and photoionization modeling indirectly
indicates a subsolar metallicity of 0.05 - 0.5 Zsun. The appearance of strong O
VI and nine Mg II components and our review of similar systems in the
literature support the "interface" picture of high-velocity O VI: the total
strength of the O VI shows a positive correlation with the number of detected
components in the low-ionization gas, however the total O VI column densities
still far exceed the values expected from interface models for the number of
detected clouds.
03/2011;
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D. A. Perley,
A. N. Morgan,
A. Updike,
F. Yuan,
C. W. Akerlof,
A. A. Miller,
J. S. Bloom,
S. B. Cenko,
W. Li,
A. V. Filippenko, [......],
N. R. Tanvir,
A. J. Levan,
N. R. Butler,
P. Christian,
D. H. Hartmann,
P. Milne,
E. S. Rykoff,
W. Rujopakarn,
J. C. Wheeler,
and G. G. Williams
[show abstract]
[hide abstract]
ABSTRACT: We present early-time optical through infrared photometry of the bright Swift gamma-ray burst (GRB) 080607, starting only 6 s following the initial trigger in the rest frame. Complemented by our previously published spectroscopy, this high-quality photometric data set allows us to solve for the extinction properties of the redshift 3.036 sightline, giving perhaps the most detailed information to date on the ultraviolet continuum absorption properties of any sightline outside our Local Group. The extinction properties are not adequately modeled by any ordinary extinction template (including the average Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud curves), partially because the 2175 Å feature (while present) is weaker by about a factor of two than when seen under similar circumstances locally. However, the spectral energy distribution is exquisitely fitted by the more general Fitzpatrick & Massa parameterization of Local-Group extinction, putting it in the same family as some peculiar Milky Way extinction curves. After correcting for this (considerable, AV = 3.3 ± 0.4 mag) extinction, GRB 080607 is revealed to have been among the most optically luminous events ever observed, comparable to the naked-eye burst GRB 080319B. Its early peak time (t rest < 6 s) indicates a high initial Lorentz factor (Γ>600), while the extreme luminosity may be explained in part by a large circumburst density. Only because of its early high luminosity could the afterglow of GRB 080607 be studied in such detail in spite of the large attenuation and great distance, making this burst an excellent prototype for the understanding of other highly obscured extragalactic objects, and of the class of "dark" GRBs in particular.
The Astronomical Journal 12/2010; 141(2):36. · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present a composite spectrum of 60 long duration gamma-ray burst (GRB)
afterglows with redshifts in the range 0.35<z<6.7 observed with low resolution
optical spectra. The composite spectrum covers the wavelength range 700-6600 A
in the rest frame and has a mean signal-to-noise ratio of 150 per 1 A pixel and
reaches a maximum of ~300 in the range 2500-3500 A. Equivalent widths are
measured from metal absorption lines from the Lya line to ~5200 A, and
associated metal and hydrogen lines are identified between the Lyman break and
Lya line. The average transmission within the Lyman forest is consistent with
that found along quasar lines of sight. We find a temporal variation in fine
structure lines when dividing the sample into bursts observed within 2 hours
from their trigger and those observed later. Other lines in the predominantly
neutral gas show variations too, but this is most likely a random effect caused
by weighting of individual strong absorption lines and which mimics a temporal
variation. Bursts characterized with high or low prompt GRB energy release
produce afterglows with similar absorption line strengths, and likewise for
bursts with bright or faint optical afterglows. Bursts defined as dark from
their optical to X-ray spectral index have stronger absorption lines relative
to the optically bright bursts. The composite spectrum has strong CaII and MgII
absorption lines as commonly found in dusty galaxies, however, we find no
evidence for dust or a significant molecular content based on the non-detection
of diffuse interstellar bands. Compared to starburst galaxy spectra, the GRB
composite has much stronger fine structure lines, while metal absorption lines
are weaker.
11/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We report on a variable high-velocity narrow absorption line outflow in the redshift 2.3 quasar J2123-0050. Five distinct outflow systems are detected with velocity shifts from -9710 to -14,050 km/s and CIV 1548,1551 line widths of FWHM = 62-164 km/s. These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc. The most likely location is ~5 pc from the quasar. The coordinated line variations in <0.63 yr (rest) are best explained by global changes in the outflow ionization caused by changes in the quasar's ionizing flux. The absence of strong X-ray absorption shows that radiative shielding is not needed to maintain the moderate ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. The kinetic energy yield of this flow is at least two orders of magnitude too low to be important for feedback to the host galaxy's evolution. Comment: 20 pages. In press with MNRAS
08/2010;
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Daniel A. Perley,
J. S. Bloom,
C. R. Klein,
S. Covino,
T. Minezaki,
P. Woźniak,
W. T. Vestrand,
G. G. Williams,
P. Milne,
N. R. Butler, [......],
L. Cowie,
P. Ferrero,
J. Greiner,
D. H. Hartmann,
Y. Kakazu,
A. Küpcü Yoldaş,
A. N. Morgan,
P. A. Price, J. X. Prochaska,
Y. Yoshii
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ABSTRACT: We present observations and analysis of the broad-band afterglow of Swift GRB 071025. Using optical and infrared (RIYJHK) photometry, we derive a photometric redshift of 4.4 < z < 5.2; at this redshift our simultaneous multicolour observations begin at ∼30 s after the gamma-ray burst trigger in the host frame, during the initial rising phase of the afterglow. We associate the light-curve peak at ∼580 s in the observer frame with the formation of the forward shock, giving an estimate of the initial Lorentz factor Γ0∼ 200. The red spectral energy distribution (even in regions not affected by the Lyman α break) provides secure evidence of a large dust column. However, the inferred extinction curve shows a prominent flat component between 2000 and 3000 Å in the rest frame, inconsistent with any locally observed template but well fitted by models of dust formed by supernovae. Time-dependent fits to the extinction profile reveal no evidence of dust destruction and limit the decrease in the extinction column to ΔA3000 < 0.54 mag after t= 50 s in the rest frame. Together with studies of high-z quasars, our observations suggest a transition in dust properties in the early Universe, possibly associated with a transition between supernova-dominated and asymptotic giant branch-dominated modes of dust production.
Monthly Notices of the Royal Astronomical Society 08/2010; 406(4):2473 - 2487. · 4.90 Impact Factor
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A Farah,
E Barojas,
N ~R Butler,
J ~S Bloom,
L Georgiev,
J González,
C Klein,
A Kutyrev,
W Lee,
H Moseley, J ~X Prochaska,
E Ramirez-Ruiz,
M Richer,
A Watson
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 07/2010
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J. Tumlinson,
A. L. Malec,
R. F. Carswell,
M. T. Murphy,
R. Buning,
N. Milutinovic,
S. L. Ellison, J. X. Prochaska,
R. A. Jorgenson,
W Ubachs,
A. M. Wolfe
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ABSTRACT: We report two detections of deuterated molecular hydrogen (HD) in QSO absorption-line systems at $z > 2$. Toward J2123-0500, we find $N$(HD) $= 13.84 \pm 0.2$ for a sub-DLA with metallicity $\simeq 0.5Z_{\odot}$ and $N$(H$_2$) = $17.64 \pm 0.15$ at $z = 2.0594$. Toward FJ0812+32, we find $N$(HD) $= 15.38 \pm 0.3$ for a solar-metallicity DLA with $N$(H$_2$) = $19.88 \pm 0.2$ at $z = 2.6265$. These systems have ratios of HD to H$_2$ above that observed in dense clouds within the Milky Way disk and apparently consistent with a simple conversion from the cosmological ratio of D/H. These ratios are not readily explained by any available model of HD chemistry and there are no obvious trends with metallicity or molecular content. Taken together, these two systems and the two published $z > 2$ HD-bearing DLAs indicate that HD is either less effectively dissociated or more efficiently produced in high-redshift interstellar gas, even at low molecular fraction and/or solar metallicity. It is puzzling that such diverse systems should show such consistent HD/H$_2$ ratios. Without clear knowledge of all the aspects of HD chemistry that may help determine the ratio HD/H$_2$, we conclude that these systems are potentially more revealing of gas chemistry than of D/H itself and that it is premature to use such systems to constrain D/H at high-redshift. Comment: accepted for publication in ApJ Letters, 5 pages emulate ApJ text
06/2010;
