We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Lyα absorption in the spectra of these quasars evolves strongly with redshift. To z ∼ 5.7, the Lyα absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z = 6.28), the average transmitted flux is 0.0038 ± 0.0026 times that of the continuum level over 8450 Å < λ < 8710 Å (5.95 < zabs < 6.16), consistent with zero flux. Thus the flux level drops by a factor of greater than 150 and is consistent with zero flux in the Lyα forest region immediately blueward of the Lyα emission line, compared with a drop by a factor of ∼10 at zabs ∼ 5.3. A similar break is seen at Lyβ; because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, τeff > 20, on the optical depth to Lyα absorption at z = 6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Lyα forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z ∼ 5 to 6, and the universe is approaching the reionization epoch at z ∼ 6.
Early data taken during commissioning of the Sloan Digital Sky Survey (SDSS) have resulted in the discovery of a very cool white dwarf. It appears to have stronger collision-induced absorption from molecular hydrogen than any other known white dwarf, suggesting it has a cooler temperature than any other. While its distance is presently unknown, it has a surprisingly small proper motion, making it unlikely to be a halo star. An analysis of white dwarf cooling times suggests that this object may be a low-mass star with a helium core. The SDSS imaging and spectroscopy also recovered LHS 3250, the coolest previously known white dwarf, indicating that the SDSS will be an effective tool for identifying these extreme objects.
The Sloan Digital Sky Survey (SDSS) automatically targeted as a quasar candidate the recently discovered, gravitationally lensed, extremely reddened z = 2.2 quasar PMN 0134-0931. The SDSS spectrum exhibits Ca II absorption at z = 0.76451, which we identify as the redshift of a lensing galaxy. Hubble Space Telescope imaging shows that components C, D, and E of the system are significantly redder than components A or B and detects faint galaxy emission between D and A+B. The redshift of the dust responsible for the reddening remains unconstrained with current data. However, we outline a model wherein lensing and differential reddening by a z = 0.76451 galaxy pair can entirely explain this system.
We present new VLT spectroscopic observations of the most distant quasar known, SDSS J1030+0524 at z = 6.28, which was recently discovered by the Sloan Digital Sky Survey. We confirm the presence of a complete Gunn-Peterson trough caused by neutral hydrogen in the intergalactic medium. There is no detectable flux over the wavelength range from 8450 to 8710 Å. We set a stronger limit on the drop of the flux level blueward of the Lyα line: a factor of more than 200. Below 8450 Å the spectrum shows a rise in flux, with a large fraction (>60%) of the total emission produced by a few narrow features of transmitted flux. We discuss the proximity effect around this quasar, with the presence of transmitted flux with many absorption features in a region of about 23 h-1 comoving Mpc. If we assume that the surrounding medium is completely neutral, the size of this region would imply a quasar lifetime of ∼1.3 × 107 yr. We also present near-IR spectroscopy of both SDSS J1030+0524 and SDSS J1306+05, the second most distant quasar known, at redshift 6.0. We combine measurements of the C IV line and limits on the He II emission from the near-IR spectra with the N V line measurements from the optical spectra to derive the metal abundances of these early quasar environments. The results are indistinguishable from those of lower redshift quasars and indicate little or no evolution in the metal abundances from z ∼ 6 to 2. The line ratios suggest supersolar metallicities, implying that the first stars around the quasars must have formed at least a few hundreds of megayears prior to the observation, i.e., at redshifts higher than 8.
We present Sloan Digital Sky Survey (SDSS) photometry and spectroscopy in the fields of 27 gamma‐ray bursts observed by Swift, including bursts localized by Swift, HETE‐2, and INTEGRAL, after 2004 December. After this bulk release, we plan to provide individual releases of similar data shortly after the localization of future bursts falling in the SDSS survey area. These data provide a solid basis for the astrometric and photometric calibration of follow‐up afterglow searches and monitoring. Furthermore, the images provided with this release will allow observers to find transient objects up to a magnitude fainter than is possible with Digitized Sky Survey images.
We analyze the anisotropic clustering of massive galaxies from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) sample, which consists of 264,283 galaxies in the redshift range 0.43 < z < 0.7 spanning 3,275 square degrees. Both peculiar velocities and errors in the assumed redshift-distance relation ("Alcock-Paczynski effect") generate correlations between clustering amplitude and orientation with respect to the line-of-sight. Together with the sharp baryon acoustic oscillation (BAO) standard ruler, our measurements of the broadband shape of the monopole and quadrupole correlation functions simultaneously constrain the comoving angular diameter distance (2190 +/- 61 Mpc) to z=0.57, the Hubble expansion rate at z=0.57 (92.4 +/- 4.5 km/s/Mpc), and the growth rate of structure at that same redshift (d sigma8/d ln a = 0.43 +/- 0.069). Our analysis provides the best current direct determination of both DA and H in galaxy clustering data using this technique. If we further assume a LCDM expansion history, our growth constraint tightens to d sigma8/d ln a = 0.415 +/- 0.034. In combination with the cosmic microwave background, our measurements of DA, H, and growth all separately require dark energy at z > 0.57, and when combined imply \Omega_{\Lambda} = 0.74 +/- 0.016, independent of the Universe's evolution at z<0.57. In our companion paper (Samushia et al. prep), we explore further cosmological implications of these observations.
The paper 'The size distribution of galaxies in the Sloan Digital Sky Survey' was published in Mon.Not.R. Astron.Soc.343, 978-994 (2003).The value of fitting parameter b in equation ( 17) of fig.11 given in table 1 is wrong.The correct value is 2.88 × 10 -6 .However, the corresponding parameter a in equation ( 17) is unchanged, and the changed quantity makes no difference to any of our results and conclusions.
We study the recently discovered gravitational lens SDSS J1004+4112, the first quasar lensed by a cluster of galaxies. It consists of four images with a maximum separation of 1462. The system was selected from the photometric data of the Sloan Digital Sky Survey (SDSS) and has been confirmed as a lensed quasar at z = 1.734 on the basis of deep imaging and spectroscopic follow-up observations. We present color-magnitude relations for galaxies near the lens plus spectroscopy of three central cluster members, which unambiguously confirm that a cluster at z = 0.68 is responsible for the large image separation. We find a wide range of lens models consistent with the data, and despite considerable diversity they suggest four general conclusions: (1) the brightest cluster galaxy and the center of the cluster potential well appear to be offset by several kiloparsecs; (2) the cluster mass distribution must be elongated in the north-south direction, which is consistent with the observed distribution of cluster galaxies; (3) the inference of a large tidal shear (~0.2) suggests significant substructure in the cluster; and (4) enormous uncertainty in the predicted time delays between the images means that measuring the delays would greatly improve constraints on the models. We also compute the probability of such large-separation lensing in the SDSS quasar sample on the basis of the cold dark matter model. The lack of large-separation lenses in previous surveys and the discovery of one in SDSS together imply a mass fluctuation normalization σ8 = 1.0 (95% confidence) if cluster dark matter halos have an inner density profile ρ ∝ r-1.5. Shallower profiles would require higher values of σ8. Although the statistical conclusion might be somewhat dependent on the degree of the complexity of the lens potential, the discovery of SDSS J1004+4112 is consistent with the predictions of the abundance of cluster-scale halos in the cold dark matter scenario.
We analyse the large-scale clustering in Fourier space of emission line galaxies (ELG) from the Data Release 16 of the Sloan Digital Sky Survey IV extended Baryon Oscillation Spectroscopic Survey. The ELG sample contains 173,736 galaxies covering 1,170 square degrees in the redshift range $0.6 < z < 1.1$. We perform a BAO measurement from the post-reconstruction power spectrum monopole, and study redshift space distortions (RSD) in the first three even multipoles. Photometric variations yield fluctuations of both the angular and radial survey selection functions. Those are directly inferred from data, imposing integral constraints which we model consistently. The full data set has only a weak preference for a BAO feature ($1.4\sigma$). At the effective redshift $z_{\rm eff} = 0.845$ we measure $D_{\rm V}(z_{\rm eff})/r_{\rm drag} = 18.33_{-0.62}^{+0.57}$, with $D_{\rm V}$ the volume-averaged distance and $r_{\rm drag}$ the comoving sound horizon at the drag epoch. In combination with the RSD measurement, at $z_{\rm eff} = 0.85$ we find $f\sigma_8(z_{\rm eff}) = 0.289_{-0.096}^{+0.085}$, with $f$ the growth rate of structure and $\sigma_8$ the normalisation of the linear power spectrum, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 20.0_{-2.2}^{+2.4}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.17 \pm 0.99$ with $D_{\rm H}$ and $D_{\rm M}$ the Hubble and comoving angular distances, respectively. These results are in agreement with those obtained in configuration space, thus allowing a consensus measurement of $f\sigma_8(z_{\rm eff}) = 0.315 \pm 0.095$, $D_{\rm H}(z_{\rm eff})/r_{\rm drag} = 19.6_{-2.1}^{+2.2}$ and $D_{\rm M}(z_{\rm eff})/r_{\rm drag} = 19.5 \pm 1.0$. This measurement is consistent with a flat $\Lambda$CDM model with Planck parameters.
