arXiv subjects

Man Ho Chan

Publications and source records attributed to Man Ho Chan.

At least 55 records · Page 3Linked to original sources

arXiv2021

The evaporating primordial black hole fraction in cool-core galaxy clusters

Recent studies of gamma-ray, cosmic-ray and radio data put stringent constraints on the fraction of primordial black holes (PBHs) in our universe. In this article, we propose a new indirect method in using the X-ray luminosity data of cool-core clusters to constrain the evaporating PBH fraction for the monochromatic, log-normal and power-law mass distributions. The present results show that the amount of evaporating PBHs only constitutes a minor component of dark matter for a large parameter space. The constraints are consistent with and close to that obtained from other cosmic-ray and multi-wavelength observations.

astro-ph.HE↗

arXiv2021

Analysing the radio flux density profile of the M31 galaxy: a possible dark matter interpretation

Some recent studies have examined the gamma-ray flux profile of our Galaxy to determine the signal of dark matter annihilation. However, the results are controversial and no confirmation is obtained. In this article, we study the radio flux density profile of the M31 galaxy and show that it could manifest a possible signal of dark matter annihilation. By comparing the likelihoods between the archival observed radio flux density profile data and the predicted radio flux density profile contributed by dark matter and stellar emission, we can constrain the relevant dark matter parameters. Specifically, for the thermal annihilation cross section via the $b\bar{b}$ channel, the best-fit value of dark matter mass is $\sim 30$ GeV, which is consistent with the results of many recent studies. We expect that this method would become another useful way to constrain dark matter, which is complementary to the traditional radio analyses and the other indirect detections.

astro-ph.HE↗

arXiv2020

Constraining annihilating dark matter mass by the radio continuum spectral data of NGC4214 galaxy

Recent gamma-ray and radio observations provide stringent constraints for annihilating dark matter. The current $2σ$ 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 $5σ$ lower limits of thermal relic annihilating dark matter mass obtained are 300 GeV, 220 GeV, 220 GeV, 500 GeV and 600 GeV for $e^+e^-$, $μ^+μ^-$, $τ^+τ^-$, $W^+W^-$ and $b\bar{b}$ channels respectively. These limits challenge the dark matter interpretation of the gamma-ray, positron and antiproton excess in our Milky Way.

astro-ph.HE↗

arXiv2020

A possible radio signal of annihilating dark matter in the Abell 4038 cluster

In the past decade, some telescopes (e.g. Fermi-LAT, AMS and DAMPE) were launched to detect the signals of annihilating dark matter in our Galaxy. Although some excess of gamma rays, anti-protons and electrons/positrons have been reported and claimed as dark matter signals, the uncertainties of Galactic pulsars' contributions are still too large to confirm the claims. In this letter, we report a possible radio signal of annihilating dark matter manifested in the archival radio continuum spectral data of the Abell 4038 cluster. By assuming the thermal annihilation cross section and comparing the dark matter annihilation model with the null hypothesis (cosmic ray emission without dark matter annihilation), we get very large Test Statistic values TS $>45$ for four popular annihilation channels, which correspond to more than $6.5 σ$ statistical preference. This provides a very strong evidence for the existence of annihilating dark matter. In particular, our results also support the recent claims of dark matter mass $m \approx 30-50$ GeV annihilating via the $b\bar{b}$ quark channel with the thermal annihilation cross section.

astro-ph.HE↗

arXiv2020

Constraining Primordial Black Hole Fraction at the Galactic Centre using radio observational data

Recent gamma-ray and cosmic-ray observations have put strong constraints on the amount of primordial black holes (PBHs) in our universe. In this article, we use the archival radio data of the inner Galactic Centre to constrain the PBH to dark matter ratio for three different PBH mass distributions including monochromatic, log-normal and power-law. We show that the amount of PBHs only constitutes a very minor component of dark matter at the Galactic Centre for a large parameter space.

astro-ph.HE↗

arXiv2020

Constraining annihilating dark matter mass by the radio continuum spectral data of a high-redshift galaxy cluster

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 ($e^+e^-$, $μ^+μ^-$ and $τ^+τ^-$) can give very good fits to the radio continuum spectrum of the A697 cluster.

astro-ph.HE↗

arXiv2020

Constraining the spin-independent elastic scattering cross section of dark matter using the Moon as a detection target and the background neutrino data

Our Moon is a natural giant direct-detection target for constraining dark matter. By considering the dark matter capture rate of the Moon, we obtain some constraints of the spin-independent elastic scattering cross section of dark matter particles on nucleons $σ_p^{\rm SI}$ using the background neutrino data. The upper limits of $σ_p^{\rm SI}$ can be constrained to $\sim 10^{-38}-10^{-36}$ cm$^2$ for certain `resonance dark matter mass' ranges. These stringent astrophysical constraints are complementary to the constraints obtained by the direct-detection experiments.

astro-ph.HE↗

arXiv2020

The decaying and scattering properties of the $d^*$(2380) hexaquark Bose Einstein Condensate dark matter

Recently, a study has shown that the Bose Einstein Condensates formed by the $d^*$(2380) hexaquarks ($d^*$(2380)-BECs) can be thermally produced in the early universe and they are stable enough to be a competitive candidate of dark matter. Searching for the decaying signature of $d^*$(2380)-BECs is a possible way to verify this dark matter model. In this article, we discuss the scattering and decaying properties of the $d^*$(2380)-BECs and we show that the decay rate of the $d^*$(2380)-BECs is correlated with the TeV cosmic-ray flux. The predicted average decay rate in our Galaxy is several orders of magnitude larger than the current observed upper limit. Therefore, it would be very difficult for us to search for the decaying signature of the $d^*$(2380)-BEC dark matter model. Nevertheless, the size of the $d^*$(2380)-BECs may be large enough to have self-interaction so that we can possibly detect them in the future.

astro-ph.HE↗

arXiv2020

A tight correlation between the enclosed gravitational mass and hot gas mass in galaxy clusters at intermediate radii

Many studies point out that there exists some tight correlations between dark matter and baryonic matter at different radii in galaxies. However, similar tight correlations can only be found in galaxy clusters for large radii. Here we report extremely tight correlations between the gravitational mass $M_{\rm grav}$ and hot gas mass $M_{\rm gas}$ in galaxy clusters at the hot gas core radius $r_c$ and at $2r_c$ (i.e. $M_{\rm grav}(r_c)$ vs $M_{\rm gas}(r_c)$ and $M_{\rm grav}(2r_c)$ vs $M_{\rm gas}(2r_c)$). By using the X-ray data of 64 large galaxy clusters with different sizes and masses, we find that the correlations can be described by a single relation $\log(M_{\rm grav}/M_{\odot})=(0.74 \pm 0.02) \log(M_{\rm gas}/M_{\odot})+(4.47 \pm 0.23)$ for a wide range of hot gas mass ($10^{11}M_{\odot}-10^{14}M_{\odot}$). The corresponding correlation coefficient and scatter are 0.97 and 0.10 dex respectively. This would be the first tight correlation with very small scatter between the enclosed gravitational mass and hot gas mass for galaxy clusters within intermediate radii ($\sim 100-1000$ kpc) and it provides a new kind of observational evidence to support the universality of correlation between dark matter and baryons.

astro-ph.CO↗

arXiv2020

The radial acceleration relation in galaxy clusters

Recently, the discovery of the radial acceleration relation (RAR) in galaxies has been regarded as an indirect support of alternative theories of gravity such as Modified Newtonian Dynamics (MOND) and modified gravity. This relation indicates a tight correlation between dynamical mass and baryonic mass in galaxies with different sizes and morphology. However, if the RAR relation is scale-independent and could be explained by alternative theories of gravity, this relation should be universal and true for galaxy clusters as well. In this article, by using the x-ray data of a sample of galaxy clusters, we investigate if there exists any tight correlation between dynamical mass and baryonic mass in galaxy clusters, assuming hot gas mass distribution almost representing baryonic distribution and that the galaxy clusters are virialized. We show that the resulting RAR of 52 non-cool-core galaxy clusters scatters in a large parameter space, possibly due to our simplifying assumptions and unclear matter content in galaxy clusters. This might indicate that the RAR is unlikely to be universal and scale-independent.

astro-ph.GA↗

arXiv2019

Fitting dark matter mass with the radio continuum spectral data of the Ophiuchus cluster

Recent gamma-ray and anti-proton analyses suggest that dark matter with mass $m=48-67$ GeV annihilating via $b\bar{b}$ channel can explain the Galactic center GeV gamma-ray excess and the anti-proton excess as measured by AMS-02 simultaneously. In this article, by differentiating the contributions of dark matter annihilation and normal diffuse cosmic rays, we show that dark matter with mass $m=40-50$ GeV annihilating via $b\bar{b}$ channel with the thermal relic annihilation cross section can best explain the radio continuum spectrum of the central radio halo of the Ophiuchus cluster. This mass range, annihilation cross section, and the annihilation channel is completely consistent with the dark matter interpretations of the GeV gamma-ray excess and the anti-proton excess.

astro-ph.HE↗

arXiv2019

Origin of the DAMPE 1.4 TeV peak

Recent accurate measurements of cosmic ray electron flux by the Dark Matter Particle Explorer (DAMPE) reveal a sharp peak structure near 1.4 TeV, which is difficult to explain by standard astrophysical processes. In this letter, we propose a simple model that the enhanced dark matter annihilation via the $e^+e^-$ channel and with the thermal relic annihilation cross section around the current nearest black hole (A0620-00) can satisfactorily account for the sharp peak structure. The predicted dark matter mass is $\sim 1.5-3$ TeV.

astro-ph.HE↗

arXiv2019

A universal constant for dark matter-baryon interplay

Recent studies point out that there exists some rough scaling relations for dark matter and some tight connections between dark matter and baryons. However, most of the relations and tight connections can only be found in galaxies, but not in galaxy clusters. In this article, we consider a new expression that can characterize the properties of dark matter-baryon interplay for both galactic and galaxy cluster scales. By using the archival observational data of galaxies and galaxy clusters, we show that the value $K=\bar{n}_D \bar{n}_Br_oV/v^4$ is almost a constant and scale independent within the optical radius $r_o$, where $\bar{n}_D$ is the average dark matter number density, $\bar{n}_B$ is the average baryon number density, $v$ is the characteristic velocity and $V$ is the interacting volume. This would be the first universal relation between dark matter and baryons on both galactic and galaxy cluster scales. We anticipate this result to be a starting point to explain the small-scale problem and the scaling relations for dark matter in galaxies. The constant $K$ discovered may reveal some underlying global interaction between dark matter and baryons.

astro-ph.CO↗

arXiv2019

Ruling out $\sim 100-300$ GeV thermal relic annihilating dark matter by radio observation of the Andromeda galaxy

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.

astro-ph.GA↗

arXiv2018

Constraining the population of intermediate mass black holes by gamma-ray data of the Fornax cluster

Recent studies of merging black holes suggest that the cosmological mass fraction of primordial black holes (PBHs) is not completely negligible. The mass of a PBH can be as massive as an intermediate mass black hole (IMBH). In this article, we assume that dark matter particles are thermal relic particles and they can self-annihilate. The dark matter around an IMBH may have formed a density spike so that the rate of dark matter annihilation would be greatly enhanced. Using the gamma-ray data of the Fornax cluster and assuming merging events in the cluster are not important, we show that the amount of IMBHs (including PBHs) is very sub-dominant compared with the amount of baryons and dark matter. The upper limit on the IMBH-to-baryon ratio is $\sim 7\times 10^{-4}$ for $m_{\rm DM} \le 10$ TeV.

astro-ph.HE↗

arXiv2018

Constraining dark matter by the 511 keV line

In the past few decades, observations indicated that an unexplained high production rate of positrons (the strong 511 keV line) exists in the Milky Way center. By using the fact that a large amount of high density gas used to exist near the Milky Way center million years ago, we model the rate of positrons produced due to dark matter annihilation. We consider the effect of adiabatic contraction of dark matter density due to the supermassive black hole at the Milky Way center and perform a detailed calculation to constrain the possible annihilation channel and dark matter mass range. We find that only three annihilation channels ($μ^+μ^-$, $4e$ and $4 μ$) can provide the required positron production rate and satisfy the stringent constraint of gamma-ray observations. In particular, the constrained mass range for the $μ^+μ^-$ channel is $m \approx 80-100$ GeV, which is close to the mass range obtained for the dark matter interpretation of the GeV gamma-ray and positron excess. In other words, the proposed scenario can simultaneously provide the required positron production rate to explain the 511 keV emission, the positron excess and the GeV gamma-ray excess in our Milky Way, and it is compatible with the density spike due to adiabatic growth model of the supermassive black hole.

astro-ph.HE↗

arXiv2018

Slowly rotating Bose Einstein Condensate galactic dark matter halos, and their rotation curves

If dark matter is composed of massive bosons, a Bose-Einstein Condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a condensate, characterized by a strong self-interaction. We consider the effects of rotation on the Bose-Einstein Condensate dark matter halos, and we investigate how rotation might influence their astrophysical properties. In order to describe the condensate we use the Gross-Pitaevskii equation, and the Thomas-Fermi approximation, which predicts a polytropic equation of state with polytropic index $n=1$. By assuming a rigid body rotation for the halo, with the use of the hydrodynamic representation of the Gross-Pitaevskii equation we obtain the basic equation describing the density distribution of the rotating condensate. We obtain the general solutions for the condensed dark matter density, and we derive the general representations for the mass distribution, boundary (radius), potential energy, velocity dispersion, tangential velocity and for the logarithmic density and velocity slopes, respectively. Explicit expressions for the radius, mass, and tangential velocity are obtained in the first order of approximation, under the assumption of slow rotation. In order to compare our results with the observations we fit the theoretical expressions of the tangential velocity of massive test particles moving in rotating Bose-Einstein Condensate dark halos with the data of 12 dwarf galaxies, and the Milky Way, respectively.

gr-qc↗

arXiv2018

Testing the Cubic Galileon Gravity model by the Milky Way rotation curve and SPARC data

Recently, the Cubic Galileon Gravity (CGG) model has been suggested as an alternative gravity theory to General Relativity. The model consists of an extra field potential term which can serve as the `fifth-force'. In this article, we examine the possibility whether this extra force term can explain the missing mass problem in galaxies without the help of dark matter. By using the Milky Way rotation curve and the Spitzer Photomery & Accurate Rotation Curves (SPARC) data, we show that this CGG model can satisfactorily explain the shapes of these rotation curves without dark matter. The CGG model can be regarded as a new alternative theory to challenge the existing dark matter paradigm.

astro-ph.GA↗