منابع مشابه
Variable 21 cm absorption at z = 0 . 3127
We report multi-epoch GMRT HI observations of the z = 0.3127 damped absorber towards the quasar PKS 1127-145 , which reveal variability in both the absorption profile and the flux of the background source, over a timescale of a few days. The observed variations cannot be explained by simple inter-stellar scintillation (ISS) models where there are only one or two scintillating components and all...
متن کاملHI 21 cm absorption at z ∼ 2 . 347 towards PKS B 0438 − 436
We report the detection of redshifted HI 21cm absorption in the z ∼ 2.347 damped Lymanα absorber (DLA) towards PKS B0438−436, with the Green Bank Telescope. This is the second-highest redshift at which 21cm absorption has been detected in a DLA. The absorption extends over ∼ 60 km s and has two distinct components, at z = 2.347477(12) and z = 2.347869(20). A similar velocity structure is seen i...
متن کاملThe 21 cm Forest: Radio Absorption Spectra as Probes of Minihalos Before Reionization
We study the absorption along lines of sight toward high-z radio sources caused by the 21 cm transition of neutral hydrogen in the intergalactic medium (IGM) before reionization. Using semi-analytic methods, we compute the number density of observable features caused by both “minihalos” (bound objects that are unable to cool efficiently because of their small virial temperatures) and protogalac...
متن کاملH I 21 - cm absorption and unified schemes of active galactic nuclei
In a recent study of z > ∼ 0.1 active galactic nuclei (AGN), we found that 21-cm absorption has never been detected in objects in which the ultra-violet luminosity exceeds LUV ∼ 10 W Hz. In this paper, we further explore the implications that this has for the currently popular consensus that it is the orientation of the circumnuclear obscuring torus, invoked by unified schemes of AGN, which det...
متن کاملLimits on variations in fundamental constants from 21-cm and ultraviolet Quasar absorption lines.
Quasar absorption spectra at 21-cm and UV rest wavelengths are used to estimate the time variation of x [triple-bond] alpha(2)g(p)mu, where alpha is the fine structure constant, g(p) the proton g factor, and m(e)/m(p) [triple-bond] mu the electron/proton mass ratio. Over a redshift range 0.24 < or = zeta(abs) < or = 2.04, (Deltax/x)(weighted)(total) = (1.17 +/- 1.01) x 10(-5). A linear fit give...
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ژورنال
عنوان ژورنال: Symposium - International Astronomical Union
سال: 1957
ISSN: 0074-1809
DOI: 10.1017/s0074180900048889