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P. A. Price, A. Songaila,
L. L. Cowie,
J. Bell Burnell,
E. Berger,
A. Cucchiara,
D. B. Fox,
I. Hook,
S. R. Kulkarni,
B. Penprase,
K. C. Roth,
and B. Schmidt
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ABSTRACT: We describe the properties of the host galaxy of the gamma-ray burst GRB 060510B based on a spectrum of the burst afterglow obtained with the Gemini North 8 m telescope. The galaxy lies at a redshift of z = 4.941, making it the fourth highest spectroscopically identified burst host. However, it is the second highest redshift galaxy for which the quality of the spectrum permits a detailed metallicity analysis. The neutral hydrogen column density has a logarithmic value of 21.0-21.2 cm-2, and the weak metal lines of Ni, S, and Fe show that the metallicity is in excess of a tenth of solar, which is far above the metallicities in damped Lyα absorbers at high redshift. The tightest constraint is from the Fe lines, which place [Fe/H] in excess of -0.8. We argue that the results suggest that metallicity bias could be a serious obstacle to inferring star formation from the GRB population, and we consider how future higher quality measurements could be used to resolve this issue.
The Astrophysical Journal 12/2008; 663(2):L57. · 6.02 Impact Factor
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ABSTRACT: The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE2347-4342, Q1157+3143, and HS1700+6416 in the redshift interval 1.8 < z < 2.9. The systems are analyzed by means of the Monte Carlo Inversion method completed with the spectral shape recovering procedure. The UVB spectral shape fluctuates at 2.4 < z < 2.9 mostly due to radiative transfer processes in the clumpy IGM. At z < 1.8, the IGM becomes almost transparent both in the HI and HeII Lyman continua and the variability of the spectral shape comes from diversity of spectral indices describing the QSO/AGN intrinsic radiation. At z > 2.4, the recovered spectral shapes show intensity depression between 3 and 4 Ryd due to HeII Ly-alpha absorption in the IGM clouds (line blanketing) and continuous medium (true Gunn-Petersen effect). The mean HeII Ly-alpha opacity estimated from the depth of this depression corresponds within 1-2sigma to the values directly measured from the HI/HeII Ly-alpha forest towards the quasars studied. The observed scatter in eta = N(HeII)/N(HI) and anti-correlation between N(HI) and eta can be explained by the combined action of variable spectral softness and differences in the mean gas density between the absorbing clouds. Neither of the recovered spectral shapes show features which can be attributed to the putative input of radiation from soft sources like starburst galaxies. Comment: 20 pages, 20 figures. Accepted for publication in A&A
10/2006;
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ABSTRACT: In preparation of a study of the HeII/HI ratio towards the bright QSO HS1700+6416, we predict the metal line content of the far-UV spectral range by modelling 18 metal absorption line systems with redshifts 0.2<z<2.6 identified in the spectrum of this quasar. For that purpose, we investigate the spectral energy distribution of the metagalactic ionizing radiation field. Simple photoionization models based on 8 different shapes of the ionizing background are tested for each system. The adopted energy distributions comprise the Haardt & Madau (2001, HM) model of metagalactic UV background as well as typical spectra of AGN and starburst galaxies. The models are evaluated and the favoured one is estimated. We find that the majority of the considered systems is best reproduced with a HM-like ionizing radiation, where the HeII break, formally located at 4 Ryd, is shifted to lower energies (~3 Ryd), probably due to the opacity of the higher HeII Lyman series lines. The remaining systems can be reasonably described with models based on the unmodified HM background or the spectra of AGN or starburst galaxies. This finding supports the idea that the UV background is spatially variable due to both IGM opacity variations and to local sources. In comparison to an unmodified HM background, the resulting ionizing spectrum leads to carbon abundances lower by ~0.5 dex. Furthermore, if the ionizing radiation field as determined from metal line systems was typical for the IGM, the expected HeII/HI ratio would be 150 to 190. Comment: 25 pages, 8 figures and 17 figures online material, accepted for publication in A&A
05/2006;
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C. Fechner,
D. Reimers,
G. A. Kriss,
R. Baade,
W. P. Blair,
M. L. Giroux,
R. F. Green,
H. W. Moos,
D. C. Morton,
J. E. Scott,
J. M. Shull,
R. Simcoe, A. Songaila,
W Zheng
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ABSTRACT: We present the far-UV spectrum of the quasar HS1700+6416 taken with FUSE. This QSO provides the second line of sight with the HeII absorption resolved into a Ly alpha forest structure. Since HS1700+6416 is slightly less redshifted (z=2.72) than HE2347-4342, we only probe the post-reionization phase of HeII, seen in the evolution of the HeII opacity, which is consistent with a simple power law. The HeII/HI ratio eta is estimated using a line profile-fitting procedure and an apparent optical depth approach, respectively. The expected metal line absorption in the far-UV is taken into account as well as molecular absorption of galactic H_2. About 27% of the eta values are affected by metal line absorption. In order to investigate the applicability of the analysis methods, we create simple artificial spectra based on the statistical properties of the HI Ly alpha forest. The analysis of the artificial data demonstrates that the apparent optical depth method as well as the line profile-fitting procedure lead to confident results for restricted data samples only (12.0 < log N(HI) < 13.0). The reasons are saturation in the case of the apparent optical depth and thermal line widths in the case of the profile fits. Furthermore, applying the methods to the unrestricted data set may mimic a correlation between eta and the strength of the HI absorption. For the restricted data samples a scatter of 10 - 15% in eta would be expected even if the underlying value is constant. The observed scatter is significantly larger than expected, indicating that the intergalactic radiation background is indeed fluctuating. In the redshift range 2.58 < z < 2.72, where the data quality is best, we find eta ~ 100, suggesting a contribution of soft sources like galaxies to the UV background. Comment: 18 pages, 14 figures, accepted for publication in A&A
05/2006;
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ABSTRACT: We report near simultaneous multi-color (RIYJHK) observations made with the MAGNUM 2m telescope of the gamma ray burst GRB 050904 detected by the SWIFT satellite. The spectral energy distribution shows a very large break between the I and J bands. Using intergalactic transmissions measured from high redshift quasars we show that the observations place a 95% confidence lower limit of z=6.18 on the object, consistent with a later measured spectroscopic redshift of 6.29 obtained by Kawai et al. (2005) with the Subaru telescope. We show that the break strength in the R and I bands is consistent with that measured in the quasars. Finally we consider the implications for the star formation history at high redshift. Comment: Accepted for publication in the Astrophysical Journal. Expanded introduction and discussion
09/2005;
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ABSTRACT: We present FUSE observations of the HeII Lyman alpha forest in the redshift range 2.3 < z < 2.7 towards HS1700+6416. Between October 2002 and February 2003, the brightness of the QSO increased by a factor 2. Therefore, with an exposure time of 203 ks during orbital night, the quality of the resulting spectrum is comparable to the HE2347-4342 data. This second line of sight with a resolved HeII Lyman alpha forest reveals a similar variation of several orders of magnitude of the column density ratio eta = N(HeII)/N(HI) and confirms the results of previous studies. The well-known metal line spectrum of HS1700+6416 permits to examine the influence of metal line absorption on the HeII column densities.
11/2004;
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ABSTRACT: We report the results of an extensive spectroscopic survey of galaxies in the roughly 160 square arcminute ACS-GOODS region surrounding the HDF-N. We have identified 787 galaxies or stars with z'<24, R<24.5, or B<25 lying in the region. The spectra were obtained with either the DEIMOS or LRIS spectrographs on the Keck 10m telescopes. The results are compared with photometric redshift estimates and with redshifts from the literature, as well as with the redshifts of a parallel effort led by a group at Keck. Our sample, when combined with the literature data, provides identifications for 1180 sources. We use our results to determine the redshift distributions with magnitude, to analyze the rest-frame color distributions with redshift and spectral type, and to investigate the dependence of the X-ray galaxy properties on the local galaxy density in the redshift interval z=0-1.5. We find the rather surprising result that the galaxy X-ray properties are not strongly dependent on the local galaxy density for galaxies in the same luminosity range. Comment: Submitted to the Astronomical Journal
01/2004;
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11/2003; 24:499-535.
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G A Kriss,
J M Shull,
W Oegerle,
W Zheng,
A F Davidsen, A Songaila,
J Tumlinson,
L L Cowie,
J M Deharveng,
S D Friedman,
M L Giroux,
R F Green,
J B Hutchings,
E B Jenkins,
J W Kruk,
H W Moos,
D C Morton,
K R Sembach,
T M Tripp
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ABSTRACT: The neutral hydrogen (H I) and ionized helium (He II) absorption in the spectra of quasars are unique probes of structure in the early universe. We present Far-Ultraviolet Spectroscopic Explorer observations of the line of sight to the quasar HE2347-4342 in the 1000 to 1187 angstrom band at a resolving power of 15,000. We resolve the He II Lyman alpha (Lyalpha) absorption as a discrete forest of absorption lines in the redshift range 2.3 to 2.7. About 50 percent of these features have H I counterparts with column densities N(H I) > 10(12.3) per square centimeter that account for most of the observed opacity in He II Lyalpha. The He II to H I column density ratio ranges from 1 to >1000, with an average of approximately 80. Ratios of <100 are consistent with photoionization of the absorbing gas by a hard ionizing spectrum resulting from the integrated light of quasars, but ratios of >100 in many locations indicate additional contributions from starburst galaxies or heavily filtered quasar radiation. The presence of He II Lyalpha absorbers with no H I counterparts indicates that structure is present even in low-density regions, consistent with theoretical predictions of structure formation through gravitational instability.
Science 09/2001; 293(5532):1112-6. · 31.20 Impact Factor
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apss. 12/1999; 269:201-208.
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ABSTRACT: We present the results of an HK' wide-field survey encompassing the Hubble Deep Field and its Flanking Fields. Our wide-field survey provides uniform coverage of an area 61.8 square arcmin to a depth equivalent to K=20.1 at 5-sigma. We have also imaged the Hubble Deep Field in HK', providing uniform coverage of an area 7.8 square arcmin to a depth equivalent to K=21.2 at 5-sigma. Using these data in combination with new deep UH 8K V and I imaging obtained on the CFHT, we find only a small population of objects with colors redder than an equivalent I-K=4, the color expected for an evolved elliptical at z>1. We infer that only a fraction of the local field elliptical population with M_K<-23.4 could have formed in single bursts at high redshift. Comment: 20 pages, to appear in the Jan 1999 issue of The Astronomical Journal
09/1998;
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ABSTRACT: Models for the composition of the diffuse intergalactic medium predict that low-density intergalactic gas at high redshift should be very poor in heavy elements. This is because locations of early star formation (and thus of heavy-element synthesis) and of gas delivery from such stars are located preferentially within higher-density regions of the intergalactic gas. Here we present a method for analysing carbon and oxygen absorption lines in quasar spectra that allows us to probe the heavy-element abundances at a redshift of three within low-density regions of intergalactic gas. We find that the ratio of triply ionized carbon to neutral hydrogen is roughly constant over a wide range of densities, and that, even as the density approaches zero, the ratio remains high. This unexpected enrichment of low-density gas in heavy elements suggests that early generations of small galaxies might be much more efficient at ejecting heavy elements into the intergalactic medium than has previously been thought.
Nature 08/1998; 394(6688):44-6. · 36.28 Impact Factor
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ABSTRACT: Using the Keck 10 m telescope data with the HIRES spectrograph, we analyzed the evolution of Lymanff forest clouds at z ? 2 down to the HI column density 10 12:8 cm Gamma2 . The number density per unit column density does not change with redshifts at lower HI cloumn density (N HI ! 10 14 cm Gamma2 ), while the forest clouds at higher column density disappear rapidly. The cutoff b value, the thermal temperature indicator, increases as redshift decreases. The correlation strength seems to be stronger as redshift decreases. Key Words : astronomy, astrophysics I. INTRODUCTION Lyff forest clouds refer to numerous narrow absorption lines in the spectra of high redshift QSOs, which are produced by intervening neutral hydrogen clouds (N HI ! 10 17 cm Gamma2 ) along the lines of sight towards QSOs. Although the true origin of Lyff forest clouds is still uncertain, they are the only normal materials observable up to z ¸ 5. This advantage provides us to study the structure of mat...
04/1997;
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ABSTRACT: Intergalactic gas clouds at high redshifts have element abundances that are close to primordial. The ratio of deuterium to hydrogen (D/H) within such clouds-which is determined from absorption lines in the spectra of more distant quasars that lie along the same line of sight-provides the best estimate of the density of baryons (omegaB) in the Universe. Previous estimates of D/H in the early Universe have yielded values that differ by about an order of magnitude, with the lower values implying a high density of baryons that may be difficult to reconcile with both estimates of the primordial abundances of other light elements (especially 4He) and the known number of light neutrinos. The accuracy of such D/H determinations is heavily dependent on the inferred column density of neutral hydrogen in the absorbing clouds. Here we report an independent measurement of the neutral hydrogen column density in the cloud towards the quasar Q1937 - 1009, for which one of the low D/H values was derived. Our measurement requires a substantial revision to the D/H value reported previously; we obtain a lower limit of D/H > 4 x 10(-5) for this cloud, which implies omegaB < 0.016 for a Hubble constant of 100 km s(-1) Mpc(-1). This reduced upper limit for the baryon density relieves any conflict with standard Big Bang nucleosynthesis.
Nature 01/1997; 385(6612):137-9. · 36.28 Impact Factor
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ABSTRACT: We present the results of a wide-field K-selected galaxy survey with complementary optical I- and B-band imaging in six fields with a total coverage of 9.8 square degrees. This survey establishes the bright-end K-band galaxy number counts in the magnitude range 13<K<16 with high precision. We find that our bright-end counts have a significantly steeper slope than the prediction of a no-evolution model, which cannot be accounted for by known observational or theoretical error. We also argue against the likelihood of sufficient evolution at such low redshifts to account for this effect, we describe an alternative picture in which there is a local deficiency of galaxies by a factor of 2 on scale sizes of around 300 Mpc. Taken at face value, this would imply that local measurements of \Omega_0 underestimate the true value of the cosmological mass density by this factor and that local measurements of $H_0$ could be high by as much as 33%. Comment: 24 pages Latex + 8 PostScript figures, to appear in Astrophysical Journal(02/97)
10/1996;
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ABSTRACT: Angular and spatial correlations are measured for K-band--selected galaxies, 248 having redshifts, 54 with z>1, in two patches of combined area 27 arcmin^2. The angular correlation for K<=21.5 mag is (theta/1.4+/-0.19 arcsec e^{+/-0.1})^{-0.8}. From the redshift sample we find that the real-space correlation, calculated with q_0=0.1, of M_K<=-23.5 mag galaxies (k-corrected) is \xi(r) = (r/2.9e^{+/-0.12}1/h Mpc)^{-1.8} at a mean z= 0.34, (r/2.0e^{+/-0.15}1/h Mpc)^{-1.8} at z= 0.62, (r/1.4e^{+/-0.15}1/h Mpc)^{-1.8} at z= 0.97, and (r/1.0e^{+/-0.2}1/h Mpc)^{-1.8} at z= 1.39, the last being a formal upper limit for a blue-biased sample. In general, these are more correlated than optically selected samples in the same redshift ranges. Over the interval 0.3<= z<=0.9 galaxies with red rest-frame colors, (U-K)_0>2 AB mag, have \xi(r)=(r/2.4e^{+/-0.14}1/h Mpc)^{-1.8} whereas bluer galaxies, which have a mean B of 23.7 mag and mean [OII] equivalent width W_{eq} = 41=\AA, are very weakly correlated, with \xi(r)=(r/0.9e^{+/-0.22}1/h Mpc)^{-1.8}. For our measured growth rate of clustering, this blue population, if non-merging, can grow only into a low-redshift population less luminous than 0.4L_\ast. The cross-correlation of low- and high-luminosity galaxies at z=0.6 appears to have an excess in the correlation amplitude within 100/h kpc. The slow redshift evolution is consistent with these galaxies tracing the mass clustering in low density, Omega= 0.2, relatively unbiased, sigma_8=0.8, universe, but cannot yet exclude other possibilities. Comment: to be published in the Aug 1 ApJ, 20 pages as a uuencoded postscript file Postscript with all figures is available at http://manaslu.astro.utoronto.ca/~carlberg/papers
05/1996;
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ABSTRACT: KNOWLEDGE of the physical state of the relatively uniform component of the
intergalactic medium (the 'substrate') is critical to understanding the
propagation of ionizing radiation and dynamical energy through intergalactic
space, and for establishing the boundary conditions for the formation of the
intergalactic gas clouds and galaxies that are assumed to have condensed from
it. Uniformly distributed hydrogen, and, even more so, He+ will
produce characteristic smooth absorption in the spectra of high-redshift
quasars14, but at low spectral resolution it is difficult to
distinguish such an absorption trough from the cumulative effect of absorption
by the Lyman-α 'forest' of clouds. We report the detection of a
population of weak 'forest' clouds with column density down to 2 x
1012 cm−2, and show that absorption in these
clouds can account for a recent measurement1 of strong
He+ absorption without necessarily having to invoke a diffuse
intergalactic medium.
05/1995; 375(6527):124-126.
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ABSTRACT: We present the results of a very deep K-band survey with a 5 sigma total galaxy magnitude limit of K = 21.9 in the deepest field. A 5 sigma K-band-selected sample of 123 galaxies is presented, together with their optical colors. Only three galaxies in this sample are not detected at the 1 sigma level in Kron-Cousins I band. At K less than or = 20 the reddest (I-K) color is 5.1 +/- 0.4, and 15 of the 123 objects in the deep field sample have (I-K) greater than 4. In the blue, the galaxies show a rapid blueward trend at magnitudes beyond K = 19, dropping from a median (B-K) = 6 at K = 18 to a median (B-K) of only 4.2 at K = 21.5. The surface density of (I-K) greater than 4 objects is interpreted to imply either that there is a significant evolution toward later types in the colors of the normal galaxy population beyond z = 11 or that galaxies have faded by that redshift.
11/1994;
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ABSTRACT: We present spectra and multicolor (B, I, K) data for near-infrared (K) selected spatially complete magnitude limited (K is less than 20) galaxy samples from the Hawaii Survey. The redshift indentification of the sample of 298 galaxies is substantially complete to a B magnitude of 26 and an I magnitude of 22.5, and identification of observed galaxies ranges from nearly 100% completeness at K is less than 18 to approximately 70% completeness at K = 19-20. We note that many of the unidentified objects appear to be red (I-K) objects which are flat in the optical and spectroscopically featureless. Strengths of spectral-line features and breaks are tabulated for the 262 galaxies with reasonably secure redshifts. The measured redshifts may nearly all fall at z is less than or approximately 1, with the exception of a compact absorption-line object at z = 2.35. At K is less than or equal to 18, the redshift distribution is well fitted by a model with no luminosity evolution, implying that from the K-band Hubble diagram, the Hubble constant can vary at most by 10% over the redshift range from z approximately 0.025 to 0.25, and that positive luminosity evolution at any significant level between z = 0 and z = 1 is ruled out. However, the evolution of both the emission-line strengths and the 4000 A break indicates that galaxies were undergoing significantly more star formation at z = 1 than at the present time.
11/1994;
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ABSTRACT: During the course of the Hawaii K-band (2.1 micrometer) survey we have detected a compact object, Hawaii 167, lying at a redshift of 2.33, in which are seen both low- and high-ionization absorption lines. In the near-infrared we see broad H alpha emission at a redshift of 2.35 but do not detect the other Balmer lines, (O II) lambda 3727, or (O III) lambda 5007. The absence of strong Mg II or C IV emission in the rest ultraviolet suggests that, at these wavelengths, we may be seeing a poststarburst galaxy rather than a quasar. Indeed, this class of object may be common enough to represent a major episode of galaxy formation, possibly the formation of the spheroids. However, Q0059-2735, the most extreme member of the class of Mg II absorbing broad absorption line quasars, is very similar to the present object, and there may be an evolutionary sequence or some other close connection between Hawaii 167 and the broad absorption line quasars.
10/1994;
