5,219 research outputs found
COBE Constraints on a Local group X-ray Halo
We investigate the effect of a putative X-ray emitting halo surrounding the
Local Group of galaxies, and specifically the possible temperature anisotropies
induced in the COBE-DMR four-year sky maps by an associated Sunyaev-Zel'dovich
effect. By fitting the isothermal spherical halo model proposed by Suto et.al.
(1996) to the coadded four-year COBE-DMR 53 and 90 GHz sky maps in Galactic
coordinates, we find no significant evidence of a contribution. We therefore
reject the claim that such a halo can affect the estimation of the primordial
spectral index and amplitude of density perturbations as inferred from the DMR
data. We find that correlation with the DMR data imposes constraints on the
plausible contribution of such an X-ray emitting halo to a distortion in the
CMB spectrum (as specified by the Compton-y parameter), up to a value for R --
the ratio of the core radius of the isothermal halo gas distribution to the
distance to the Local Group centroid -- of 0.68. For larger values of R, the
recent cosmological upper limit derived by COBE-FIRAS provides stronger
constraints on the model parameters. Over the entire parameter space for R, we
find an upper limit to the inferred sky-RMS anisotropy signal of 14 microKelvin
(95% c.l.), a negligible amount relative to the 35 microKelvin signal observed
in the COBE-DMR data.Comment: 4 pages, 3 figures; accepted for publication in MNRAS pink page
Evidence for non-Gaussianity in the CMB
In a recent Letter we have shown how COBE-DMR maps may be used to disprove
Gaussianity at a high confidence level. In this report we digress on a few
issues closely related to this Letter. We present the general formalism for
surveying non-Gaussianity employed. We present a few more tests for
systematics. We wonder about the theoretical implications of our result.Comment: Proceedings of the Planck meeting, Santender 9
The 4 Year COBE DMR data is non-Gaussian
I review our recent claim that there is evidence of non-Gaussianity in the 4
Year COBE DMR data. I describe the statistic we apply, the result we obtain and
make a detailed list of the systematics we have analysed. I finish with a
qualitative understanding of what it might be and its implications.Comment: Proceedings of Rome 3K conference, 5 pages, 3 figure
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