957 research outputs found
Particle decay in the early universe: predictions for 21 cm
The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark
matter particles on the emission and absorption characteristics of neutral
hydrogen in 21 cm at redshifts is considered. In presence of UHECRs
21 cm can be seen in absorption with the brightness temperature
mK in the range . Decayng particles can stimulate a 21 cm signal in
emission with mK at , and mK at . Characteristics of the fluctuations of the brightness temperature, in
particular, its power spectrum are also calculated. The maps of the power
spectrum of the brightness temperature on the plane {\it wavenumber-redshift}
are shown to be sensitive to the parameters of UHECRs and decaying dark matter.
Observational possibilities to detect manifestations of UHECRs and/or decaying
particles in 21 cm with the future radio telescopes (LOFAR, 21CMA and SKA), and
to distinguish contributions from them are briefly discussed.Comment: 10 pages, 9 figures, accepted in MNRA
Joint deprojection of Sunyaev-Zeldovich and X-ray images of galaxy clusters
We present two non-parametric deprojection methods aimed at recovering the
three-dimensional density and temperature profiles of galaxy clusters from
spatially resolved thermal Sunyaev-Zeldovich (tSZ) and X-ray surface brightness
maps, thus avoiding the use of X-ray spectroscopic data. In both methods,
clusters are assumed to be spherically symmetric and modeled with an onion-skin
structure. The first method follows a direct geometrical approach. The second
method is based on the maximization of a single joint (tSZ and X-ray)
likelihood function, which allows one to fit simultaneously the two signals by
following a Monte Carlo Markov Chain approach. These techniques are tested
against a set of cosmological simulations of clusters, with and without
instrumental noise. We project each cluster along the three orthogonal
directions defined by the principal axes of the momentum of inertia tensor.
This enables us to check any bias in the deprojection associated to the cluster
elongation along the line of sight. After averaging over all the three
projection directions, we find an overall good reconstruction, with a small
(<~10 per cent) overestimate of the gas density profile. This turns into a
comparable overestimate of the gas mass within the virial radius, which we
ascribe to the presence of residual gas clumping. Apart from this small bias
the reconstruction has an intrinsic scatter of about 5 per cent, which is
dominated by gas clumpiness. Cluster elongation along the line of sight biases
the deprojected temperature profile upwards at r<~0.2r_vir and downwards at
larger radii. A comparable bias is also found in the deprojected temperature
profile. Overall, this turns into a systematic underestimate of the gas mass,
up to 10 percent. (Abridged)Comment: 17 pages, 15 figures, accepted by MNRA
Cluster Morphologies and Model-independent Y_(SZ) Estimates from Bolocam Sunyaev-Zel'dovich Images
We present initial results from our ongoing program to image the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters at 143 GHz using Bolocam; five clusters and one blank field are described in this manuscript. The images have a resolution of 58 arcsec and a radius of ≃ 6-7 arcmin, which is approximately r_(500)-2r_(500) for these clusters. We effectively high-pass filter our data in order to subtract noise sourced by atmospheric fluctuations, but we are able to obtain unbiased images of the clusters by deconvolving the effects of this filter. The beam-smoothed rms is ≃ 10 μK_(CMB) in these images; with this sensitivity, we are able to detect the SZ signal to beyond r_(500) in binned radial profiles. We have fit our images to beta and Nagai models, fixing spherical symmetry or allowing for ellipticity in the plane of the sky, and we find that the best-fit parameter values are in general consistent with those obtained from other X-ray and SZ data. Our data show no clear preference for the Nagai model or the beta model due to the limited spatial dynamic range of our images. However, our data show a definitive preference for elliptical models over spherical models, quantified by an F ratio of ≃ 20 for the two models. The weighted mean ellipticity of the five clusters is ϵ = 0.27 ± 0.03, consistent with results from X-ray data. Additionally, we obtain model-independent estimates of Y_(500), the integrated SZ y-parameter over the cluster face to a radius of r_(500), with systematics-dominated uncertainties of ≃ 10%. Our Y_(500) values, which are free from the biases associated with model-derived Y_(500) values, scale with cluster mass in a way that is consistent with both self-similar predictions and expectations of a ≃ 10% intrinsic scatter
Constraints on dark matter annihilation by radio observations of M31
We used radio observations of the neighbor galaxy M31 in order to put constraints on the dark matter particle mass and annihilation cross section. Dark matter annihilation in M31 halo produces highly energetic leptons, which emit synchrotron radiation on radio frequencies in the galactic magnetic field. We predicted expected radio fluxes for the two annihilation channels: χχ→bb̅ and χχ→τ^+τ^-. We then compared them with available data on the central radio emission of M31 as observed by four radio surveys: VLSS (74 MHz), WENSS (325 MHz), NVSS (1400 MHz), and GB6 (4850 MHz). Assuming a standard Navarro-Frenk-White dark matter density profile and a conservative magnetic field distribution inside the Andromeda galaxy, we find that the thermal relic annihilation cross section or higher ⟨σv⟩≥3×10^(-26) cm^3/s are only allowed for weakly interacting massive particle masses greater than ≈100 and ≈55 GeV for annihilation into bb̅ and τ^+τ^-, respectively. Taking into account potential uncertainties in the distributions of dark matter density and the magnetic field, the mentioned weakly interacting massive particle limiting masses can be as low as 23 GeV for both channels, and as high as 280 and 130 GeV for annihilation into bb̅ and τ^+τ^-, respectively. These mass values exceed the best up-to-date known constraints from Fermi gamma observations: 40 and 19 GeV, respectively [A. Geringer-Sameth and S. M. Koushiappas, Phys. Rev. Lett. 107 241303 (2011)]. Precise measurements of the magnetic field in the relevant region and better reconstruction of the dark matter density profile of M31 will be able to reduce the uncertainties of our exclusion limits
Dark matter implications of the WMAP-Planck Haze
Gamma rays and microwave observations of the Galactic Center and surrounding
areas indicate the presence of anomalous emission, whose origin remains
ambiguous. The possibility of dark matter (DM) annihilation explaining both
signals through prompt emission at gamma-rays and secondary emission at
microwave frequencies from interactions of high-energy electrons produced in
annihilation with the Galactic magnetic fields has attracted much interest in
recent years. We investigate the DM interpretation of the Galactic Center
gamma-ray excess by searching for the associated synchrotron in the WMAP-Planck
data. Considering various magnetic field and cosmic-ray propagation models, we
predict the synchrotron emission due to DM annihilation in our Galaxy, and
compare it with the WMAP-Planck data at 23-70GHz. In addition to standard
microwave foregrounds, we separately model the microwave counterpart to the
Fermi Bubbles and the signal due to DM, and use component separation techniques
to extract the signal associated with each template from the total emission. We
confirm the presence of the Haze at the level of 7% of the total sky intensity
at 23GHz in our chosen region of interest, with a harder spectrum than the synchrotron from regular cosmic-ray electrons. The data do
not show a strong preference towards fitting the Haze by either the Bubbles or
DM emission only. Inclusion of both components provides a better fit with a DM
contribution to the Haze emission of 20% at 23GHz, however, due to significant
uncertainties in foreground modeling, we do not consider this a clear detection
of a DM signal. We set robust upper limits on the annihilation cross section by
ignoring foregrounds, and also report best-fit DM annihilation parameters
obtained from a complete template analysis. We conclude that the WMAP-Planck
data are consistent with a DM interpretation of the gamma-ray excess.Comment: 34 pages, 9 figure
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