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Register a new userSearching for Light in the Darkness: Bounds on ALP Dark Matter with the optical MUSE-Faint survey
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We use MUSE spectroscopic observations of the dwarf spheroidal galaxy Leo T between 470 and 935 nm to search for radiative decays of axion like particles (ALPs). Under the assumption that ALPs constitute the dark matter component of the Leo T halo, we derive bounds on the effective ALP-two-photon coupling. We improve existing limits by more than one order of magnitude in the ALP mass range 2.7-5.3 eV.
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Fuzzy dark matter (FDM) is an attractive dark matter candidate motivated by small scale problems in astrophysics and with a rich phenomenology on those scales. We scrutinize the FDM model, more specifically the mass of the FDM particle, through a dynamical analysis for the Galactic ultra-faint dwarf (UFD) galaxies. We use a sample of 18 UFDs to place the strongest constraints to date on the mass of the FDM particle, updating on previous bounds using a subset of the sample used here. We find that most of the sample UFDs prefer a FDM particle mass heavier than $10^{-21}mathrm{eV}$. In particular, Segue 1 provides the strongest constraint, with $m_psi=1.1^{+8.3}_{-0.7}times10^{-19}mathrm{eV}$. The constraints found here are the first that are compatible with various other independent cosmological and astrophysical bounds found in the literature, in particular with the latest bounds using the Lyman-$alpha$ forest. We also find that the constraints obtained in this work are not compatible with the bounds from luminous dwarf galaxies, as already pointed out in the previous work using UFDs. This could indicate that although a viable dark matter model, it might be challenging for the FDM model to solve the small scale problems.
Aims. We use stellar line-of-sight velocities to constrain the dark matter-density profile of Eridanus 2, an ultra-faint dwarf galaxy ($M_mathrm{V} = -7.1$, $M_* approx 9 times 10^4,M_odot$). We furthermore derive constraints on fundamental properties of self-interacting and fuzzy dark matter scenarios. Methods. We present new observations of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with MUSE on the Very Large Telescope, and determine line-of-sight velocities for stars inside the half-light radius. Combined with literature data, we have 92 stellar tracers out to twice the half-light radius. We constrain models of cold dark matter, self-interacting dark matter, and fuzzy dark matter with these tracers, using CJAM and pyGravSphere for the dynamical analysis. Results. We find substantial evidence for cold dark matter over self-interacting dark matter and weak evidence for fuzzy dark matter over cold dark matter. We find a virial mass $M_{200} sim 10^8,M_odot$ and astrophysical factors $J(alpha_mathrm{c}^J) sim 10^{11},M_odot^2,mathrm{kpc}^{-5}$ and $D(alpha_mathrm{c}^D) sim 10^2$-$10^{2.5},M_odot,mathrm{kpc}^{-2}$. We do not resolve a core ($r_mathrm{c} < 47,mathrm{pc}$, 68-% level) or soliton ($r_mathrm{sol} < 7.2,mathrm{pc}$, 68-% level). These limits are equivalent to an effective self-interaction coefficient $fGamma < 2.2 times 10^{-29},mathrm{cm}^3,mathrm{s}^{-1},mathrm{eV}^{-1},c^2$ and a fuzzy-dark-matter particle mass $m_mathrm{a} > 4.0 times 10^{-20},mathrm{eV},c^{-2}$. The constraint on self-interaction is complementary to those from gamma-ray searches. The constraint on fuzzy-dark-matter particle mass is inconsistent with those obtained for larger dwarf galaxies, suggesting that the flattened density profiles of those galaxies are not caused by fuzzy dark matter. (Abridged)
Analytic arguments and numerical simulations show that bosonic ultra-light dark matter (ULDM) would form cored density distributions (`solitons) at the center of galaxies. ULDM solitons offer a promising way to exclude or detect ULDM by looking for a distinctive feature in the central region of galactic rotation curves. Baryonic contributions to the gravitational potential pose an obstacle to such analyses, being (i) dynamically important in the inner galaxy and (ii) highly non-spherical in rotation-supported galaxies, resulting in non-spherical solitons. We present an algorithm for finding the ground state soliton solution in the presence of stationary non-spherical background baryonic mass distribution. We quantify the impact of baryons on the predicted ULDM soliton in the Milky Way and in low surface-brightness galaxies from the SPARC database.
We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors.
Non-relativistic QCD axions or axion-like particles are among the most popular candidates for cold Dark Matter (DM) in the universe. We proposed to detect axion-like DM, using linearly polarized pulsar light as a probe. Because of birefringence effect potentially caused by an oscillating galactic axion DM background, when pulsar light travels across the galaxy, its linear polarization angle may vary with time. With a soliton+NFW galactic DM density profile, we show that this strategy can potentially probe an axion-photon coupling as small as $sim 10^{-13}$ GeV$^{-1}$ for axion mass $m_a sim 10^{-22}-10^{-20}$ eV, given the current measurement accuracy. An exclusion limit stronger than CAST ($ sim 10^{-10}$ GeV$^{-1}$) and SN1987A ($ sim 10^{-11}$ GeV$^{-1}$) could be extended up to $m_a sim 10^{-18}$ eV and $sim 10^{-19}$ eV, respectively.
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