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 $z = 10-50$ is considered. In presence of UHECRs 21 cm can be seen in absorption with the brightness temperature $T_b=-(5-10)$ mK in the range $z=10-30$. Decayng particles can stimulate a 21 cm signal in emission with $T_b\sim 50-60$ mK at $z =50$, and $T_b \simeq 10$ mK at $z \sim 20$. 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

Optical Cluster-Finding with An Adaptive Matched-Filter Technique: Algorithm and Comparison with Simulations

We present a modified adaptive matched filter algorithm designed to identify clusters of galaxies in wide-field imaging surveys such as the Sloan Digital Sky Survey. The cluster-finding technique is fully adaptive to imaging surveys with spectroscopic coverage, multicolor photometric redshifts, no redshift information at all, and any combination of these within one survey. It works with high efficiency in multi-band imaging surveys where photometric redshifts can be estimated with well-understood error distributions. Tests of the algorithm on realistic mock SDSS catalogs suggest that the detected sample is ~85% complete and over 90% pure for clusters with masses above 1.0*10^{14} h^{-1} M_solar and redshifts up to z=0.45. The errors of estimated cluster redshifts from maximum likelihood method are shown to be small (typically less that 0.01) over the whole redshift range with photometric redshift errors typical of those found in the Sloan survey. Inside the spherical radius corresponding to a galaxy overdensity of Delta=200, we find the derived cluster richness Lambda_{200} a roughly linear indicator of its virial mass M_{200}, which well recovers the relation between total luminosity and cluster mass of the input simulation.Comment: Accepted to ApJ. 13 pages, 9 figure