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Known dwarf spheroidal satellite galaxies of the Milky Way overlaid on a Hammer-Aitoff projection of a 4-year LAT counts map (E > 1 GeV). The 15 dwarf galaxies included in the combined analysis are shown as filled circles, while additional dwarf galaxies are shown as open circles.
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The dwarf spheroidal satellite galaxies of the Milky Way are some of the most
dark-matter-dominated objects known. Due to their proximity, high dark matter
content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are
widely considered to be among the most promising targets for the indirect
detection of dark matter via gamma rays. H...
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Citations
... In the absence of an excess, robust constraints can be placed on the DM annihilation cross section 1 as a function of DM mass. In the GeV to TeV mass range, there are strong limits on DM annihilation from gamma-ray searches using Cherenkov telescopes [9][10][11][12][13][14][15][16] and the Large Area Telescope (LAT) on the Fermi Gamma-Ray Space Telescope [4,5,[17][18][19][20]. ...
We obtain bounds on dark matter annihilation using 14 years of publicly available Fermi-LAT data from a set of 54 dwarf spheroidal galaxies, using spectral information from 16 energy bins. We perform this analysis using our updated and publicly available code , which can be used to test a variety of models for dark matter particle physics and astrophysics in an accessible manner. In particular, we note that including Carina III in the analysis strengthens constraints on s -wave annihilation into two-body Standard Model final states by a factor of ∼ 3 but broadens the error on the constraint due to the large uncertainty of its J -factor. Our findings illustrate the importance of verifying if Carina III is in fact a dwarf spheroidal galaxy and measuring more precisely its J -factor. More generally, they highlight the significance of forthcoming discoveries of nearby ultrafaint dwarfs for dark matter indirect detection.
Published by the American Physical Society 2024
... The astrophysical component to the annihilation signal for velocity-independent annihiliation may be expressed through the J-factor (see, e.g., Walker et al. 2011), which for stellar tracers embedded in an NFW subhalo can be estimated from (see Equation (13) In the above equation, the integral is performed along the line of sight l over a solid angle ΔΩ, and D, R h , and σ los are the heliocentric distance, projected half-light radius, and line-ofsight velocity dispersion of UMa3/U1, respectively. The angle θ limits the solid angle over which the integral is computed, and is chosen here to match the Fermi Large Area Telescope resolution at gigaelectronvolt scales, θ = 0°.5 (Ackermann et al. 2014). The J-factor of ∼10 21 GeV 2 c −4 cm −5 computed in Equation (13) takes the measured properties of UMa3/U1 at face value. ...
The recently discovered stellar system Ursa Major III/UNIONS 1 (UMa3/U1) is the faintest known Milky Way satellite to date. With a stellar mass of 16 − 5 + 6 M ⊙ and a half-light radius of 3 ± 1 pc, it is either the darkest galaxy ever discovered or the faintest self-gravitating star cluster known to orbit the Galaxy. Its line-of-sight velocity dispersion suggests the presence of dark matter, although current measurements are inconclusive because of the unknown contribution to the dispersion of potential binary stars. We use N -body simulations to show that, if self-gravitating, the system could not survive in the Milky Way tidal field for much longer than a single orbit (roughly 0.4 Gyr), which strongly suggests that the system is stabilized by the presence of large amounts of dark matter. If UMa3/U1 formed at the center of a ∼10 ⁹ M ⊙ cuspy LCDM halo, its velocity dispersion would be predicted to be of order ∼1 km s ⁻¹ . This is roughly consistent with the current estimate, which, neglecting binaries, places σ los in the range 1–4 km s ⁻¹ . Because of its dense cusp, such a halo should be able to survive the Milky Way tidal field, keeping UMa3/U1 relatively unscathed until the present time. This implies that UMa3/U1 is plausibly the faintest and densest dwarf galaxy satellite of the Milky Way, with important implications for alternative dark matter models and for the minimum halo mass threshold for luminous galaxy formation in the LCDM cosmology. Our results call for multi-epoch high-resolution spectroscopic follow-up to confirm the dark matter content of this extraordinary system.
... Astrophysical, that is, indirect searches for TeV-scale DM has been ★ E-mail: laura.eisenberger@stud-mail.uni-wuerzburg.de † E-mail: thomas.siegert@uni-wuerzburg.de performed in several studies including Fermi/LAT (e.g., Ackermann et al. 2014Ackermann et al. , 2017, MAGIC (e.g. MAGIC Collaboration 2016), or HESS (e.g., Abdalla et al. 2022) for electromagnetic signals, and PAMELA (e.g., Adriani et al. 2013) or AMS-02 (e.g., Aguilar et al. 2013) for cosmic-ray excesses at Earth. ...
The indirect search for dark matter is typically restricted to individual photon bands and instruments. In the context of multiwavelength observations, finding a weak signal in large fore- and backgrounds at only one wavelength band is hampered by systematic uncertainties dominating the signal strength. Dark matter particle annihilation is producing Standard Model particles of which the prompt photon emission is searched for in many studies. However, also the secondary emission of charged particles from dark matter annihilation in the TeV range results in comparable or even stronger fluxes in the GHz–GeV range. In this study, we calculate the prompt and secondary emission of a scotogenic WIMP with a mass of 1 TeV in 27 dwarf galaxies of the Milky Way. For the secondary emission, we include Inverse Compton scattering, bremsstrahlung, and synchrotron radiation, which results in a ‘triple hump’ structure characteristic for only dark matter and no other astrophysical source. In order to determine the best candidates for multi-instrument analyses, we estimate the diffuse emission component of the Milky Way itself, including its own dark matter halo from the same scotogenic WIMP model. We find signal-to-background ratios of individual sources on the order of 10−3–10−2 across X- to γ-rays assuming J-factors for the cold dark matter distribution inferred from observations and no additional boosting due to small-scale clumping. We argue that a joint multi-wavelength analysis of all nearby galaxies as well as the extension towards the Cosmic Gamma-ray Background is required to disentangle possible dark matter signals from astrophysical back- and foregrounds.
... Because independent, direct evidence for NBDM remains unavailable [32,33], this popular explanation for RC continues to be questioned. For example, many researchers since the 1980s have attempted to explain RC by altering Newton's gravitational constant Figure 2. Least-squares fit to the HI mass and luminosity for various galaxies used by Salucci and Persic [5] to determine the baryonic inventory. ...
... Because independent, direct evidence for NBDM remains unavailable [32,33], this popular explanation for RC continues to be questioned. For example, many researchers since the 1980s have attempted to explain RC by altering Newton's gravitational constant (G), an approach initiated by Milgrom [34,35]. ...
... The consequence is a popular multicomponent fitting approach that neither addresses baryons stored in galactic atmospheres (CGM) nor accounts for the vast volumes of space (IGM) with very low density (Sections 2 and 5.2), and that does not actually need baryonic matter to fit RC data (Section 1.1.1). Moreover, no direct evidence exists for NBDM, despite decades of searching for observational confirmation, as well as independent attempts to find supportive data from high-energy physics experiments [32,33]. ...
Available inventories of baryonic mass in the universe are based largely on galactic data and empirical calculations made >20 years ago. Values falling below cosmological estimates underlie proposals that certain rarified gassy regions could have extremely high T, which motivated absorption measurements and hydrodynamic models. Yet, the shortfall remains. We inventory the total baryonic mass, focusing on gravitational interactions and updated measurements. A recent analytical inverse method for analyzing galactic rotation curves quantified how baryon mass and associated volumetric density (ρ) depend on distance (r) from galactic centers. The model is based on the dynamical consequences of the observed oblate shape of galaxies and the Virial Theorem. The parameter-free solution provides ρ(r) ∝ 1/r2 which describes star-rich galactic interiors, gas-rich outer discoids, circumgalactic media, and gradation into intergalactic media. Independent observational determinations of baryonic ρ validate that our 1/r2 result describes baryons alone. This solution shows that total baryonic mass associated with any galaxy is 2.4 to 40 times detectable luminosity, depending on galaxy size and spacing. Luminosity data within 50 Mpc show that Andromeda equivalents separated by ~1 Mpc represent the local universe. Combining the above yields (6 ± 2) × 10−25 kg m−3 for the present-day universe. Three other approaches support this high density: (1) evaluating trends and luminosity data near 1000 Mpc; (2) using a recent estimate for the number of galaxies in the universe; (3) calculating an energy balance. We discuss uncertainties in the critical density. Implications of large baryonic ρ are briefly discussed.
... The most extreme known cases are the large number of low-luminosity early-type galaxies (ETGs) that surround the Milky Way, which exhibit optical mass-to-light ratios of up to some 10 3 or even 10 4 in Solar units, if they are assumed to be in virial equilibrium (e.g. Mateo 1998 ;Strigari et al. 2008 ;Wolf et al. 2010 ;Ackermann et al. 2014 ). E-mail: joerg@sirrah.troja.mff.cuni.cz ...
... Man y authors hav e tried to solv e this issue before by adding non-baryonic dark matter to the ETGs. For lowluminosity ETGs, corresponding mainly to low radial accelerations, this has been done for e.g. by Strigari et al. ( 2008 ), Wolf et al. ( 2010 ), and Ackermann et al. ( 2014 ). For high-luminosity ETGs, corresponding mainly to high radial accelerations, this has been done for instance MNRAS 526, 2301-2322 (2023) by Cappellari et al. ( 2006 ), Bolton et al. ( 2008 ), andTortora et al. ( 2009 ). ...
The observed radial accelerations of 462 Early-type galaxies (ETGs) at their half-mass radii are discussed. They are compared to the baryonic masses of the same galaxies, which are derived from theoretical expectations for their stellar populations and cover a range from ≈104 M⊙ to ≈1011 M⊙. Both quantities are plotted against each other, and it is tested whether they lie (within errors) along theoretical radial acceleration relations (RARs). We choose the Newtonian RAR and two Milgromian, or MONDian RARs. At low radial accelerations (corresponding to low masses), the Newtonian RAR fails without non-baryonic dark matter, but the two MONDian ones may work, provided moderate out-of-equilibrium dynamics in some of the low-mass ETGs. However all three RARs fail at high accelerations (corresponding to high masses) if all ETGs have formed their stellar populations with the canonical stellar initial mass function (IMF). A much better agreement with the observations can however be accomplished, if the theory of the integrated galaxy-wide stellar initial mass functions (IGIMFs) is used instead. This is because the IGIMF-theory predicts the formation of an overabundance of stellar remnants during the lifetime of the massive ETGs. Thus their baryonic masses today are higher than they would be if the ETGs had formed with a canonical IMF. Also the masses of the stellar-mass black holes should be rather high, which would mean that most of them probably formed when the massive ETGs were not as metal-enriched as they are today. The IGIMF-approach confirms downsizing.
... Although there have been similar searches within the dwarf's main body (Ramsay & Wu 2006b ), the number of X-ray sources observed in that region has been consistent with the expected number of background sources. Gamma-ray studies have also been conducted in the Sgr region, although typically as one of several stacked sources in searches for DM annihilation products (Viana et al. 2012 ;Abramowski et al. 2014 ;Ackermann et al. 2014 ;Hooper & Linden 2015 ). Since Sgr has no detected H I gas associated with its central core (Grcevich & Putman 2009 ), the only sources of 100 MeV gamma-ray emission (other than DM) would be millisecond pulsars (MSPs). ...
We use Fermi-LAT data to analyze the faint gamma-ray source located at the center of the Sagittarius (Sgr) dwarf spheroidal galaxy. In the 4FGL-DR3 catalog, this source is associated with the globular cluster, M54. We investigate the spectral energy distribution and spatial extension of this source, with the goal of testing two hypotheses: (1) the emission is due to millisecond pulsars within M54, or (2) the emission is due to annihilating dark matter from the Sgr halo. For the pulsar interpretation, we consider a two-component model which describes both the lower-energy magnetospheric emission and possible high-energy emission arising from inverse Compton scattering. We find that this source has a point-like morphology at low energies, consistent with magnetospheric emission, and find no evidence for a higher-energy component. For the dark matter interpretation, we find the signal favors a dark matter mass of mχ = 29.6 ± 5.8 GeV and an annihilation cross section of σv = (2.1 ± 0.59) × 10−26 cm3 s−1 for the $b \bar{b}$ channel (or mχ = 8.3 ± 3.8 GeV and σv = (0.90 ± 0.25) × 10−26 cm3 s−1 for the τ+τ− channel), when adopting a J-factor of J = 1019.6 GeV2 cm−5. This parameter space is consistent with gamma-ray constraints from other dwarf galaxies and with dark matter interpretations of the Galactic Center Gamma-Ray Excess.
... In this work, we show that CR antihelium produced by DM annihilation can be naturally enhanced if the DM particles annihilate into SM quarks through a mediator particle with a mass m φ ≈ 8 GeV, which is slightly above the 3 He production threshold E ( 3 He) thr ≈ 5.6 GeV. We find that compared with the direct DM annihilation scenario, the DM antihelium flux can be enhanced up to three orders of magnitude under the constraints from the AMS-02 antiproton-to-proton ratio data [36] and the Fermi-LAT dSph γ-ray observations [37,38]. We show that the AMS-02 experiment is capable of detecting the enhanced DM antihelium flux in this scenario. ...
... For DM annihilation through hadrophilic mediators, the DM annihilation cross section is subject to stringent constraints from the data of CR antiprotons and γ-rays. In this section, we derive the constraints from the AMS-02 antiproton-to-proton (p/p) ratio data [36] and the Fermi-LAT dSph γ-ray observation [37,38]. In this work, the constraints on DM annihilation cross section from CR p/p and dSph γ-rays are derived individually, and we do not attempt to combine them. ...
... The fluxes were calculated from the PASS8 analysis using the six years of Fermi-LAT data, with γ-ray energy ranging from 500 MeV to 500 GeV. In this work, we choose the 15 dSphs that have independent sky regions and J-factor uncertainties [37] to place constraints on the DM annihilation cross sections. ...
Cosmic-ray (CR) antihelium is an important probe for the indirect search of dark matter (DM) annihilation in the Galaxy. However, due to stringent constraints from the measurements of CR antiprotons and γ -rays, the flux of CR antihelium from the conventional DM direct annihilation into Standard Model final states is expected to be far below the sensitivity of the current experiments. We show that the production of antihelium can be significantly enhanced if the DM particles annihilate through light mediator particles with a mass m ϕ ≈ 8 GeV close to the antihelium production threshold. After taking into account the constraints from the AMS-02 antiproton data and the Fermi-LAT γ -ray data on the spheroidal dwarf galaxies, we find that in this scenario the CR antihelium flux can be enhanced by three orders of magnitude, which makes it within the sensitivity of the ongoing AMS-02 experiment.
... As the strength of these signals increases with dark matter density squared and decreases with the distance to target squared, the indirect detection targets with the greatest signal rate are the largest and closest conglomerations of dark matter. The highest intensity signals are therefore expected to be seen from our own Milky Way Galactic Center, but other nearby galaxiessuch as Andromeda (M31) [2,3], the Large Magellanic Cloud (LMC) [4], the Small Magellanic Cloud (SMC) [5], and local dwarf galaxies [6][7][8][9][10][11][12] -can have significant signals too. As the backgrounds and systematics for these systems differ from the Milky Way, they can be compelling targets despite the lower signal rate. ...
... As the leakage out of the masked signal region is minimal and the signal morphology depends only weakly on the choice of mass and diffusion parameters, the resulting fits can be applied to signals with other values of m χ and D 0 . The cross-section is chosen to be approximately an order of magnitude larger than the best fit value from the GCE [15][16][17][18] and existing limits from dwarf galaxies [6][7][8][9][10]. ...
... GeV and D 0 = 1 × 10 28 cm 2 /s along with the data in the search region as a function of elliptical distance from the center of the map (this choice of signal parameters is excluded at 95% confidence). 8 As can be seen, the residuals of the data with respect to the background-only model are negative for R e 4 kpc. These large negative residuals can be traced specifically to the large negative excursion in the observed flux, located around (x, y) ∼ (−2, 1) kpc and clearly visible in Figures 1 and 18(a). ...
Well-motivated scenarios of thermally-produced dark matter often result in a population of electrons and positrons within galaxies produced through dark matter annihilation -- often in association with high-energy gamma rays. As they diffuse through galactic magnetic fields, these $e^\pm$ produce synchrotron radio emission. The intensity and morphology of this signal depends on the properties of the interstellar medium through which the $e^\pm$ propagate. Using observations of the Andromeda Galaxy (M31) to construct a model of the gas, magnetic fields, and starlight, we set constraints on dark matter annihilation to $b\bar{b}$ using the morphology of 3.6 cm radio emission. As the emission signal at the center of M31 is very sensitive to the diffusion coefficient and dark matter profile, we base our limits on the differential flux in the region between $0.9-6.9$ kpc from the center. We exclude annihilation cross sections $\gtrsim 3 \times 10^{-25}$ cm$^3$/s in the mass range $10-500$ GeV, with a maximum sensitivity of $7\times 10^{-26}$ cm$^3$/s at $20-40$ GeV. Though these limits are weaker than those found in previous studies of M31, they are robust to variations of the diffusion coefficient.
... The right panel of Figure 8 shows the 1, 2, and 3σ contours for the SFG sample, the undetected molecular outflow sample, and the detected outflow sample. For the control sample, we show the 95% upper limit on the β parameter computed using the "delta-log-likelihood" method by finding D =-L 2 log 2.71 for each α value (see, e.g., Ackermann et al. 2014Ackermann et al. , 2015MAGIC Collaboration et al. 2016). The contours of the undetected molecular outflow sample are consistent with those of the SFG comparison sample, although the undetected molecular outflow sample has a greater best-fit α dependence. ...
Many star-forming galaxies and those hosting active galactic nuclei show evidence of massive outflows of material in a variety of phases including ionized, neutral atomic, and molecular. Molecular outflows in particular have been the focus of recent interest as they may be responsible for removing gas from the galaxy, thereby suppressing star formation. As material is ejected from the cores of galaxies, interactions of the outflowing material with the interstellar medium can accelerate cosmic rays and produce high-energy gamma rays. In this work, we search for gamma-ray emission from a sample of local galaxies known to host molecular outflows using data collected by the Fermi Large Area Telescope. We employ a stacking technique in order to search for and characterize the average gamma-ray emission properties of the sample. Gamma-ray emission is detected from the galaxies in our sample at the 4.4 σ level with a power-law photon index of Γ ≈ 2 in the 1–800 GeV energy range. The emission is found to correlate with tracers of star formation activity, namely the 8–1000 μ m infrared luminosity. We also find that the observed signal can be predominantly attributed to H ii galaxies hosting energy-driven outflows. While we do not find evidence suggesting that the outflows are accelerating charged particles directly, galaxies with molecular outflows may produce more gamma rays than galaxies without outflows. In particular, the set consisting of gamma-ray-detected galaxies with molecular outflows are nearly perfect calorimeters and may be future targets for searches of high-energy neutrinos.
... We utilize a joint-likelihood analysis to accurately include information from the likelihood functions of each source in our analysis. Such techniques have been widely adapted in searches for dim dark matter signals from dwarf spheroidal galaxies [38][39][40][41][42], and has been adapted by our group for individual studies of both SFGs [10] and mAGN [9]. ...
... To account for the uncertainty induced by systematic mismodeling, studies have utilized blank sky locations to approximate the flux uncertainties in regions where no signal is expected (see e.g. [39]. In most works, the analysis chain is run separately on the true sources and the blank sky locations, and their results are then compared to calculate the statistical significance of any excess (using a bootstrapping technique). ...
The total extragalactic γ -ray flux provides a powerful probe into the origin and evolution of the highest energy processes in our universe. An important component of this emission is the isotropic γ -ray background (IGRB), composed of sources that cannot be individually resolved by current experiments. Previous studies have determined that the IGRB can be dominated by either misaligned active galactic nuclei (mAGN) or star-forming galaxies (SFGs). However, these analyses are limited, because they have utilized binary source classifications and examined only one source class at a time. We perform the first combined joint-likelihood analysis that simultaneously correlates the γ -ray luminosity of extragalactic objects with both star-formation and mAGN activity. We find that SFGs produce 48 ⁺³³ -20 % of the total IGRB at 1 GeV and 56 ⁺⁴⁰ -23 % of the total IGRB at 10 GeV. The contribution of mAGN is more uncertain, but can also be significant. Future work to quantify the radio and infrared properties of nearby galaxies could significantly improve these constraints.
