12 research outputs found
The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky
The contribution of the Unresolved Extragalactic Radio Sources to the diffuse
brightness of the sky was evaluated using the source number - flux measurements
available in literature. We first optimized the fitting function of the data
based on number counts distribution. We then computed the brightness
temperature at various frequencies from 151 MHz to 8440 MHz and derived its
spectral dependence. As expected the frequency dependence can be described by a
power law with a spectral index , in agreement with the
flux emitted by the {\it steep spectrum} sources. The contribution of {\it flat
spectrum} sources becomes relevant at frequencies above several GHz. Using the
data available in literature we improved our knowledge of the brightness of the
unresolved extragalactic radio sources. The results obtained have general
validity and they can be used to disentangle the various contributions of the
sky brightness and to evaluate the CMB temperature.Comment: Accepted for publication in the Astrophysical Journa
Deep Westerbork 1.4 GHz Imaging of the Bootes Field
We present the results from our deep (16x12 hour) Westerbork Synthesis Radio
Telescope (WSRT) observations of the approximately 7 square degree Bootes Deep
Field, centered at 14h32m05.75s, 34d16'47.5" (J2000). Our survey consists of 42
discrete pointings, with enough overlap to ensure a uniform sensitivity across
the entire field, with a limiting sensitivity of 28 microJy (1 sigma rms). The
catalog contains 3172 distinct sources, of which 316 are resolved by the
13"x27" beam. The Bootes field is part of the optical/near-infrared imaging and
spectroscopy survey effort conducted at various institutions. The combination
of these data sets, and the deep nature of the radio observations will allow
unique studies of a large range of topics including the redshift evolution of
the luminosity function of radio sources, the K-z relation and the clustering
environment of radio galaxies, the radio / far-infrared correlation for distant
starbursts, and the nature of obscured radio loud AGN.Comment: Accepted for publication in AJ, 23 pages, 17 figures. Additional
information can be obtained through anonymous ftp to
ftp://ftp.nfra.nl/pub/Boote
Sources of the Radio Background Considered
We investigate different scenarios for the origin of the extragalactic radio
background. The surface brightness of the background, as reported by the ARCADE
2 collaboration, is several times higher than that which would result from
currently observed radio sources. We consider contributions to the background
from diffuse synchrotron emission from clusters and the intergalactic medium,
previously unrecognized flux from low surface brightness regions of radio
sources, and faint point sources below the flux limit of existing surveys. By
examining radio source counts available in the literature, we conclude that
most of the radio background is produced by radio point sources that dominate
at sub microJy fluxes. We show that a truly diffuse background produced by
electrons far from galaxes is ruled out because such energetic electrons would
overproduce the obserevd X-ray/gamma-ray background through inverse Compton
scattering of the other photon fields. Unrecognized flux from low surface
brightness regions of extended radio sources, or moderate flux sources missed
entirely by radio source count surveys, cannot explain the bulk of the observed
background, but may contribute as much as 10 per cent. We consider both radio
supernovae and radio quiet quasars as candidate sources for the background, and
show that both fail to produce it at the observed level because of insufficient
number of objects and total flux, although radio quiet quasars contribute at
the level of at least a few percent. We conclude that if the radio background
is at the level reported, a majority of the total surface brightness would have
to be produced by ordinary starforming galaxies above redshift 1 characterized
by an evolving radio far-infrared correlation, which changes toward the radio
loud with redshift.Comment: 12 pages, 3 figures, 1 table; MNRAS accepted and in press,
(previously submitted ApJ but withdrawn before review
Jan Oort, astronomer : catalogue of an exhibition in Leiden University library, April 20 - May 27, 2000
ASC – Publicaties niet-programma gebonde