886 research outputs found
Variability of sub-mJy radio sources
We present 1.4 GHz VLA observations of the variability of radio sources in
the Lockman Hole region at the level of > 100 uJy on timescales of 17 months
and 19 days. These data indicate that the areal density of highly variable
sources at this level is < 0.005 arcmin^{-2}. We set an upper limit of 2% to
the fraction of 50 to 100uJy sources that are highly variable (> 50%). These
results imply a lower limit to the beaming angle for GRBs of 1deg, and give a
lower limit of 200 arcmin^2 to the area that can be safely searched for GRB
radio afterglows before confusion might become an issue.Comment: aastex 2 postscript figures. to appear in the Astrophysical Journa
Intensity Mapping of Molecular Gas During Cosmic Reionization
I present a simple calculation of the expected mean CO brightness temperature from the large-scale distribution of
galaxies during cosmic reionization. The calculation is based on the cosmic star formation rate density required
to reionize, and keep ionized, the intergalactic medium, and uses standard relationships between star formation
rate, IR luminosity, and CO luminosity derived for star-forming galaxies over a wide range in redshift. I find
that the mean CO brightness temperature resulting from the galaxies that could reionize the universe at z = 8 is
T_B ∼ 1.1(C/5)(fesc/0.1)−1μK, where fesc is the escape fraction of ionizing photons from the first galaxies and C is
the IGM clumping factor. Intensity mapping of the CO emission from the large-scale structure of the star-forming
galaxies during cosmic reionization on scales of order 102 to 103 deg^2, in combination with H i 21 cm imaging of
the neutral IGM, will provide a comprehensive study of the earliest epoch of galaxy formation
Searching for high-redshift centimeter-wave continuum, line and maser emission using the Square Kilometer Array
We discuss the detection of redshifted line and continuum emission at radio
wavelengths using a Square Kilometer Array (SKA), specifically from
low-excitation rotational molecular line transitions of CO and HCN (molecular
lines), the recombination radiation from atomic transitions in almost-ionized
hydrogen (radio recombination lines; RRLs), OH and water maser lines, as well
as from synchrotron and free-free continuum radiation and HI 21-cm line
radiation. The detection of radio lines with the SKA offers the prospect to
determine the redshifts and thus exact luminosities for some of the most
distant and optically faint star-forming galaxies and active galactic nuclei
(AGN), even those galaxies that are either deeply enshrouded in interstellar
dust or shining prior to the end of reionization. Moreover, it provides an
opportunity to study the astrophysical conditions and resolved morphologies of
the most active regions in galaxies during the most active phase of star
formation at redshift z~2. A sufficiently powerful and adaptable SKA correlator
will enable wide-field three-dimensional redshift surveys at chosen specific
high redshifts, and will allow new probes of the evolution of large-scale
structure (LSS) in the distribution of galaxies. The detection of molecular
line radiation favours pushing the operating frequencies of SKA up to at least
26 GHz, and ideally to 40 GHz, while very high redshift maser emissions
requires access to about 100 MHz. To search for LSS the widest possible
instantaneous field of view would be advantageous.Comment: 12 pages, 2 figures. To appear in "Science with the Square Kilometer
Array," eds. C. Carilli and S. Rawlings, New Astronomy Reviews (Elsevier:
Amsterdam
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