Quasars have historically been identified in optical surveys, which are insensitive to sources at z > 6.5. Infrared deep-sky survey data now make it possible to explore higher redshifts, with the result that a luminous quasar (ULAS J1120+0641) with a redshift z = 7.085, beyond the previous high of z = 6.44, has now been identified. Further observations of this and other distant quasars should reveal the ionization state of the Universe as it was only about 0.75 billion years after the Big Bang. The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed1 by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified2,3,4 in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 1013L⊙ and hosts a black hole with a mass of 2 × 109M⊙ (where L⊙ and M⊙ are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing5, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

A luminous quasar at a redshift of z = 7.085

http://inspirehep.net/record/1084324/files/arXiv:1201.2434.pdf

Observational probes of cosmic acceleration

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit Multi-Cycle Treasury Program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the cluster cores, a key prediction of structure formation models. The CLASH cluster sample is larger and less biased than current samples of space-based imaging studies of clusters to similar depth, as we have minimized lensing-based selection that favors systems with overly dense cores. Specifically, 20 CLASH clusters are solely X-ray selected. The X-ray-selected clusters are massive (kT > 5 keV) and, in most cases, dynamically relaxed. Five additional clusters are included for their lensing strength (θ_Ein > 35" at z_s = 2) to optimize the likelihood of finding highly magnified high-z (z > 7) galaxies. A total of 16 broadband filters, spanning the near-UV to near-IR, are employed for each 20-orbit campaign on each cluster. These data are used to measure precise (σ_z ~ 0.02(1 + z)) photometric redshifts for newly discovered arcs. Observations of each cluster are spread over eight epochs to enable a search for Type Ia supernovae at z > 1 to improve constraints on the time dependence of the dark energy equation of state and the evolution of supernovae. We present newly re-derived X-ray luminosities, temperatures, and Fe abundances for the CLASH clusters as well as a representative source list for MACS1149.6+2223 (z = 0.544).

/pdf/the-cluster-lensing-and-supernova-survey-with-hubble-an-24f8b3nrm9.pdf

The cluster lensing and supernova survey with hubble: an overview

The physics of gamma-ray bursts & relativistic jets

Understanding massive stars is essential for a variety of branches of astronomy including galaxy and star cluster evolution, nucleosynthesis and supernovae, pulsars, and black holes. It has become evident that massive star evolution is very diverse, being sensitive to metallicity, binarity, rotation, and possibly magnetic fields. Although the problem to obtain a good statistical observational database is alleviated by current large spectroscopic surveys, it remains a challenge to model these diverse paths of massive stars toward their violent end stage. I show that the main sequence stage offers the best opportunity to gauge the relevance of the various possible evolutionary scenarios. This also allows sketching the post-main-sequence evolution of massive stars, for which observations of Wolf-Rayet stars give essential clues. Recent supernova discoveries owing to the current boost in transient searches allow tentative mappings of progenitor models with supernova types, including pair-instability supernova...

Presupernova Evolution of Massive Single and Binary Stars

Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars(1), and some are bright enough that they should be observable out to redshifts of z > 20 using current technology(2-4). Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy(5). Here we report that GRB 090423 lies at a redshift of z approximate to 8.2, implying that massive stars were being produced and dying as GRBs similar to 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

/pdf/a-g-ray-burst-at-a-redshift-of-z-8-2-3jdogy0e12.pdf

A. Allan

Papers

A γ-ray burst at a redshift of z ≈ 8.2