251 research outputs found
Improved Constraints on The Neutral Intergalactic Hydrogen Surrounding Quasars at Redshifts z>6
We analyze the evolution of HII regions around the seven known SDSS quasars
at z>6. The comparison between observed and model radii of the HII regions
generated by these quasars individually, suggests that the surrounding
intergalactic hydrogen is significantly neutral. When all constraints are
combined, the existing quasar sample implies a volume averaged neutral fraction
that is larger than 10% at z>6. This limited sample permits a preliminary
analysis of the correlations between the quasar parameters, the sizes of their
HII regions, and the associated constraints on the neutral hydrogen fraction.
We find no evidence in these correlations to contradict the interpretation that
the red side of the Gunn-Peterson trough corresponds to the boundary between an
HII region and a partially neutral IGM.Comment: 9 pages, 4 figures. Submitted to Ap
Star formation and the interstellar medium in z>6 UV-luminous Lyman-break galaxies
We present Atacama Large Millimeter Array (ALMA) detections of atomic carbon
line and dust continuum emission in two UV-luminous galaxies at redshift 6. The
far-infrared (FIR) luminosities of these galaxies are substantially lower than
similar starbursts at later cosmic epochs, indicating an evolution in the dust
properties with redshift, in agreement with the evolution seen in ultraviolet
(UV) attenuation by dust. The [CII] to FIR ratios are found to be higher than
at low redshift showing that [CII] should be readily detectable by ALMA within
the reionization epoch. One of the two galaxies shows a complex merger nature
with the less massive component dominating the UV emission and the more massive
component dominating the FIR line and continuum. Using the interstellar atomic
carbon line to derive the systemic redshifts we investigate the velocity of
Lyman alpha emission emerging from high-z galaxies. In contrast to previous
work, we find no evidence for decreasing Lyman alpha velocity shifts at
high-redshift. We observe an increase in velocity shifts from z2 to
z6, consistent with the effects of increased IGM absorption.Comment: 10 pages, 9 figures, submitted to ApJ, revised after referees
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Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy
Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy
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