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Register a new userRuling out $sim 100-300$ GeV thermal relic annihilating dark matter by radio observation of the Andromeda galaxy
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In the past few years, some studies claimed that annihilating dark matter with mass $sim 10-100$ GeV can explain the GeV gamma-ray excess in our Galaxy. However, recent analyses of the Fermi-LAT and radio observational data rule out the possibility of the thermal relic annihilating dark matter with mass $m le 100$ GeV for some popular annihilation channels. By using the new observed radio data of the Andromeda galaxy, we rule out the existence of $sim 100-300$ GeV thermal relic annihilating dark matter for ten annihilation channels. The lower limits of annihilating dark matter mass are improved to larger than 330 GeV for the most conservative case, which is a few times larger than the current best constraints. Moreover, these limits strongly disfavor the benchmark model of weakly interacting massive particle (WIMP) produced through the thermal freeze-out mechanism.
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Recent gamma-ray and radio observations provide stringent constraints for annihilating dark matter. The current $2sigma$ lower limits of dark matter mass can be constrained to $sim 100$ GeV for thermal relic annihilation cross section. In this article, we use the radio continuum spectral data of a nearby galaxy NGC4214 and differentiate the thermal contribution, dark matter annihilation contribution and cosmic-ray contribution. We can get more stringent constraints of dark matter mass and annihilation cross sections. The $5sigma$ lower limits of thermal relic annihilating dark matter mass obtained are 300 GeV, 220 GeV, 220 GeV, 500 GeV and 600 GeV for $e^+e^-$, $mu^+mu^-$, $tau^+tau^-$, $W^+W^-$ and $bbar{b}$ channels respectively. These limits challenge the dark matter interpretation of the gamma-ray, positron and antiproton excess in our Milky Way.
In their recent paper, Chan and Lee discuss an interesting possibility: radio continuum emission from a dwarf irregular galaxy may be used to constrain upper limits on the cross section of annihilating dark matter. They claim that the contributions from nonthermal and thermal emission can be estimated with such accuracy that one can place new upper limits on the annihilation cross section. We argue that the observations presented can be explained entirely with a standard spectrum and no contribution from dark matter. As a result, the estimated upper limits of Chan and Lee are atleast by a factor of 100 too low.
In the past decade, the properties of annihilating dark matter models were examined by various kinds of data, including the data of gamma rays, radio waves, X-ray, positrons, electrons, antiprotons and neutrinos. In particular, most of the studies focus on the data of our Galaxy, nearby galaxies (e.g. M31 galaxy) or nearby galaxy clusters (e.g. Fornax cluster). In this article, we examine the archival radio continuum spectral data of a relatively high-redshift galaxy cluster (A697 cluster) to constrain the properties of annihilating dark matter. We find that leptophilic annihilation channels ($e^+e^-$, $mu^+mu^-$ and $tau^+tau^-$) can give very good fits to the radio continuum spectrum of the A697 cluster.
Large-scale faint structure detected by the recent observations in the halo of the Andromeda galaxy (M31) provides an attractive window to explore the structure of outer cold dark matter (CDM) halo in M31. Using an N-body simulation of the interaction between an accreting satellite galaxy and M31, we investigate the mass density profile of the CDM halo. We find the sufficient condition of the outer density profile of CDM halo in M31 to reproduce the Andromeda giant stream and the shells at the east and west sides of M31. The result indicates that the density profile of the outer dark matter halo of M31 is a steeper than the prediction of the theory of the structure formation based on the CDM model.
Weakly interacting cold dark matter (CDM) particles, which are otherwise extremely successful in explaining various cosmological observations, exhibit a number of problems on small scales. One possible way of solving these problems is to invoke (so-called) warm dark matter (WDM) particles with masses $m_x sim$ keV. Since the formation of structure is delayed in such WDM models, it is natural to expect that they can be constrained using observations related to the first stars, e.g., the 21 cm signal from cosmic dawn. In this work, we use a detailed galaxy formation model, Delphi, to calculate the 21 cm signal at high-redshifts and compare this to the recent EDGES observations. We find that while CDM and 5 keV WDM models can obtain a 21 cm signal within the observed redshift range, reproducing the amplitude of the observations requires the introduction of an excess radio background. On the other hand, WDM models with $m_x leq 3$ keV can be ruled out since they are unable to match either the redshift range or the amplitude of the EDGES signal, irrespective of the parameters used. Comparable to values obtained from the low-redshift Lyman Alpha forest, our results extend constraints on the WDM particle to an era inaccessible by any other means; additional forthcoming 21 cm data from the era of cosmic dawn will be crucial in refining such constraints.
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