Radio constraints on dark matter annihilation in Canes Venatici I with LOFAR†

Abstract

<jats:title>ABSTRACT</jats:title> <jats:p>Dwarf galaxies are dark matter (DM) dominated and therefore promising targets for the search for weakly interacting massive particles (WIMPs), which are well-known candidates for DM. The annihilation of WIMPs produces ultrarelativistic cosmic ray electrons and positrons that emit synchrotron radiation in the presence of magnetic fields. For typical magnetic field strengths (few μG) and $\mathcal {O}$(GeV–TeV) WIMP masses, this emission peaks at hundreds of MHz. Here, we use the non-detection of 150-MHz radio continuum emission from the dwarf spheroidal galaxy Canes Venatici I with the Low-Frequency Array to derive constraints on the annihilation cross-section of WIMPs into primary electron–positron and other fundamental particle–antiparticle pairs. Our main underlying assumption is that the transport of the cosmic rays can be described by the diffusion approximation, thus requiring a non-zero magnetic field strength with small-scale structure. In particular, by adopting magnetic field strengths of $\mathcal {O}(1\, \mu$G) and diffusion coefficients $\sim \!10^{27}~\rm cm^2\, s^{-1}$, we obtain limits that are comparable with those set by the Fermi Large Area Telescope using gamma-ray observations of this particular galaxy. Assuming s-wave annihilation and WIMPs making up 100 per cent of the DM density, our benchmark limits exclude several thermal WIMP realizations in the [2, 20]-GeV mass range. We caution, however, that our limits for the cross-section are subject to enormous uncertainties that we also quantitatively assess. In particular, variations on the propagation parameters or on the DM halo can shift our limits up by several orders of magnitude (in the pessimistic scenario).</jats:p>

Status, Challenges and Directions in Indirect Dark Matter Searches

“…Results are dependent on the galactic diffusion model used and assumed magnetic field strengths, and results are shown for three different models (blue dotted, black full and red dashed lines). Figure from [271]. See reference for details in the diffusion models used.…”

“…The author in [270] used Draco as early as 2002 to set limits on the dark matter velocity averaged self annihilation cross section from VLA observations. More recently, the LOFAR collaboration has carried out a competitive search for dark matter in the dwarf galaxy Canis Venatici [271]. The results of this technique depend on the diffusion of the charged particles once emitted and on the profile of the local magnetic field, two quantities that are not well known, so the results are ineluctably model-dependent.…”

“…However, with reasonable assumptions on the structure and magnetic field strength from a given source, this method yields competitive results to gamma-ray, cosmic-ray or neutrino dark matter searches from dwarf galaxies as illustrated in Figure 15. [271]. See reference for details in the diffusion models used.…”

Radio Constraints of Dark Matter: A Review and Some Future Perspectives

“…Since many radio telescopes and interferometers have very good sensitivity and resolution, any synchrotron signals due to dark matter annihilation from extragalactic origins could still be detected. For example, earlier studies have examined the radio signals of our galaxy and its satellite galaxies to constrain dark matter [14][15][16][17][18][19][20][21][22][23][24][25][26]. Later, radio signals from other nearby galaxies such as the M31 [27][28][29], M33 [30,31], NGC 1569 [32], and NGC 2976 [33] galaxies were also investigated in constraining dark matter.…”

Comment on “Constraining the annihilating dark matter mass by the radio continuum spectral data of the NGC4214 galaxy”

“…Searches so far have concentrated on dwarf spheroidal galaxies because they have very little star formation and thus no contaminating emission at radio frequencies. So far, these searches have not provided any detection and upper limits on the radio flux density can be converted to upper limits on the annihilation cross section for various annihilation channels [1].…”