Issue |
A&A
Volume 414, Number 1, January IV 2004
|
|
---|---|---|
Page(s) | 7 - 16 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20031546 | |
Published online | 12 January 2004 |
Evidence for a significant Blazar contamination in CMB anisotropy maps
1
ASI Science Data Center, ASDC, Agenzia Spaziale Italiana c/o ESRIN, via G. Galilei 00044 Frascati, Italy
2
INAF - Osservatorio Astronomico di Roma via Frascati 33, 00040 Monteporzio, Italy e-mail: cola@mporzio.astro.it
Corresponding author: P. Giommi, paolo.giommi@asi.it
Received:
11
June
2003
Accepted:
29
September
2003
The analysis of the recent WMAP source catalog shows that the vast
majority of bright foreground extragalactic sources detected in CMB maps are
Blazars. In this paper we calculate the contamination of CMB anisotropy maps by
this type of flat-spectrum, strongly variable and polarized extragalactic radio
sources using up-to-date results from recent deep multi-frequency surveys. From
a careful archive search and from multi-frequency catalog cross-correlations we
found that more than 50 known Blazars (or Blazar candidates) expected to be
above the sensitivity limit of the BOOMERANG experiment are included in the
90/150 GHz BOOMERANG anisotropy maps, a factor 15 larger than
previously reported. Using a recent derivation of the Blazar radio
–
we
show that Blazars, whose counts continue to grow steeply down to faint fluxes,
can sensitively affect CMB fluctuation maps with even moderate resolution and
sensitivity. We calculate specifically that these sources induce an average sky
brightness of
, corresponding to an average temperature of
4–8 μK. Moreover, we find that the associated level of fluctuations
is of the order of
at 41 GHz and
at 94 GHz.
Taking into account both Blazar variability, causing the detection of a number
of weak sources that rise above the detector sensitivity during flares in
long-exposure satellite experiments, and the many steep-spectrum radio sources
that flatten at high frequencies, as well as the contribution of radio-galaxies,
we find that the level of residual fluctuation due to discrete extragalactic
foreground sources could be factor of ~2–3 higher than the above
estimate.
We show that the Blazar induced fluctuations contaminate the CMB spectrum at the
level of
30–90% at
and
at
, and
thus they cannot be neglected in the derivation of the primordial CMB
fluctuation spectrum. Since Blazars are bright sources because they point their
jets towards the observer, at faint fluxes a more abundant population of
less-aligned sources is likely to increase the contamination of future
high-resolution high-sensitivity CMB maps. Careful cleaning for Blazar
contamination of CMB maps is therefore necessary before firm conclusions about
weak features, like secondary high-
peaks of the CMB power spectrum or
very weak signals like CMB polarization measurements, can be achieved.
Key words: cosmology: observations / cosmic microwave background / galaxies: active
© ESO, 2004
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