Evidence for a Galactic gamma-ray halo

Dixon, David; Hartmann, D.; Kolaczyk, Eric D.; Samimi, J.; Diehl, R.; Kanbach, G.; Mayer‐Hasselwander, H. A.; Strong, A. W.

doi:10.1016/s1384-1076(98)00024-4

Cited by 82 publications

(74 citation statements)

References 24 publications

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“…Atomic gas (often identified as HVCs) is observed in the radio band (particularly at 21 cm) and through absorption lines towards field stars and quasars. The hot gas may be detected in X-rays, while searches for cold gas clouds in galactic halos are more problematic as are searches for them by the presence of a gamma-ray halo (Dixon et al 1998;De Paolis et al 1999), stellar scintillations (Moniez 2003;Habibi et al 2010), obscuration events towards the LMC (Drake & Cook 2003), ortho-H 2 D + line at 372 GHz (Ceccarelli & Dominik 2006), and extreme scattering events in quasar radioflux variations (Walker & Wardle 1998) have given no clear indication of their presence.…”

Section: Discussionmentioning

confidence: 99%

Possible detection of the M 31 rotation in WMAP data

Paolis

Gurzadyan

Ingrosso

et al. 2011

A&A

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Data on the cosmic microwave background (CMB) radiation by the Wilkinson Microwave Anisotropy Probe (WMAP) had a profound impact on the understanding of a variety of physical processes in the early phases of the Universe and on the estimation of the cosmological parameters. Here, the 7-year WMAP data are used to trace the disk and the halo of the nearby giant spiral galaxy M 31. We analyzed the temperature excess in three WMAP bands (W, V, and Q) by dividing the region of the sky around M 31 into several concentric circular areas. An asymmetry in the mean microwave temperature in the M 31 disk along the direction of the M 31 rotation is observed with a temperature contrast up to 130 μK/pixel. We also find a temperature asymmetry in the M 31 halo, which is much weaker than for the disk, up to a galactocentric distance of about 10 • ( 120 kpc) with a peak temperature contrast of about 40 μK/pixel. We studied the robustness of these possible detections by considering 500 random control fields in the real WMAP maps and simulating 500 sky maps from the best-fitted cosmological parameters. By comparing the obtained temperature contrast profiles with the real ones towards the M 31 galaxy, we find that the temperature asymmetry in the M 31 disk is fairly robust, while the effect in the halo is weaker. Although the confidence level of the signal is not high, if estimated purely statistically, which could be expected due to the weakness of the effect, the geometrical structure of the temperature asymmetry points towards a definite effect modulated by the rotation of the M 31 halo. This result might open a new way to probe these relatively less studied galactic objects using high-accuracy CMB measurements, such as those with the Planck satellite or planned balloon-based experiments, which could prove or disprove our conclusions.

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Section: Discussionmentioning

confidence: 99%

Possible detection of the M 31 rotation in WMAP data

Paolis

Gurzadyan

Ingrosso

et al. 2011

A&A

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“…photons cm −2 s −1 sr −1 above 1 GeV is claimed even after correction for the expected background of cosmic rays and the diffuse extragalactic emission [58]. These residual intensities although marginal have rather interesting implications for the halo density profile.…”

Section: A Flux From the Galactic Halomentioning

confidence: 91%

“…These residual intensities although marginal have rather interesting implications for the halo density profile. We computed the expected intensity, averaged over cells of 0.5 o × 0.5 o as considered in [58], in the direction b = 90 o . Table 3 gives the expected intensity as a function of the neutralino mass for the α-profile (with a central cusp) and the Plummer profile (with a central core).…”

Section: A Flux From the Galactic Halomentioning

confidence: 99%

Indirect search for dark matter: Prospects for GLAST

2004

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Possible indirect detection of neutralino, through its γ-ray annihilation product, by the forthcoming GLAST satellite from our galactic halo, M31, M87 and the dwarf galaxies Draco and Sagittarius is studied. γ-ray fluxes are evaluated for two representative energy thresholds, 0.1 GeV and 1.0 GeV, at which the spatial resolution of GLAST varies considerably. Apart from dwarfs, which are described either by a modified Plummer profile or by a tidally-truncated King profile, fluxes are compared for halos with central cusps and cores. It is demonstrated that substructures, irrespective of their profiles, enhance the γ-ray emission only marginally. The expected γ-ray intensity above 1 GeV at high galactic latitudes is consistent with the residual emission derived from EGRET data if the density profile has a central core and mχ ≤ 50 GeV, whereas for a central cusp only a substantial enhancement would explain the observations. From M31, the flux can be detected above 0.1 GeV and 1.0 GeV by GLAST only if mχ ≤ 300 GeV and if the density profile has a central cusp, case in which a significant boost in the γ-ray emission is produced by the central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the fluxes are always below the sensitivity limit of GLAST.

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“…As a result of this freedom in modelling, the γ-ray data must be regarded as inconclusive at present. However, we note that Dixon et al (1998) discovered an unmodelled Galactic 'halo' component in the γ-ray background, and the simplest explanation for this is that it is due to unseen (cold, dense) gas.…”

Section: Non-thermal Emissionmentioning

confidence: 82%

The Cloudy Universe

Walker

Wardle

1999

Publ. – Astron. Soc. Aust

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Abstract:Modelling of extreme scattering events suggests that the Galaxy's dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture-thermal/non-thermal emission, extinction and lensing-are problematic. The theoretical situation is less comfortable, but still satisfactory. Galactic clouds can survive in their current condition for billions of years, but we do not have a firm description for either their origin or their evolution to the present epoch. We hypothesise that the proto-clouds formed during the quark-hadron phase transition, thereby introducing the inhomogeneity necessary for compatibility with light element nucleosynthesis in a purely baryonic universe. We outline the prospects for directly detecting the inferred cloud population. The most promising signatures are cosmic-ray-induced Hα emission from clouds in the solar neighbourhood, optical and X-ray flashes arising from cloud-cloud collisions, ultraviolet extinction, and three varieties of lensing phenomena.

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Evidence for a Galactic gamma-ray halo

Cited by 82 publications

References 24 publications

Possible detection of the M 31 rotation in WMAP data

Possible detection of the M 31 rotation in WMAP data

Indirect search for dark matter: Prospects for GLAST

The Cloudy Universe

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