Analysis of shape and angular orientation parameters of velocity-dependent dark matter annihilation signals in Galactic Centers for FIRE simulations

Abstract

We use FIRE-2 zoom cosmological simulations of Milky Way size galaxy halos to characterize the shape of the J-factor emission signal on the sky. We find that, at a fixed dJ/dΩ contour,the shape is well-fit by an ellipse, with semi-major axis Rmajor and semi-minor axis Rminor measured in degrees on the sky. We use least squares fitting to fit ellipses to the J-factor emission, viewed from the solar location. The ratio of minor to major axes (Rminor/Rmajor) allows us to characterize the shape of each contour, with ratio 1.0 corresponding to circular/spherical emission. These results provide new expectations for the shape of dark matter annihilation emission signals we might expect to see if dark matter is annihilating with its own anti-particle. We find that both the shape and angular orientation of the emission signal is different than results predict from dark matter only simulations. In terms of shape, we find that the ratios of semi-minor to semi-major axis is always consistently at 0.8, revealing a consistent circular emission shape, whereas with dark matter only emission signals the range of ratios from halo to halo is broader, and often closer to 0.5, showing a much more elliptical shape in general. In terms of angular orientation, we find that the major axis of the J-factor emission signal maps for FIRE halos are consistently aligned with the galactic plane within a few degrees, meaning that excess emission out of the plane would be hard to explain with a dark matter annihilation signal. However, we also find that the expected emission signal would be consistent with Fermi-LAT measurements showing a galactic center excess in full hydrodynamical simulations with stars and gas included, while dark-matter-only simulations do not produce the expected signal.

arXiv comment10 pages, 5 figures. Published in Monthly Notices of the Royal Astronomical Society

References in corpus (32)

• Statistical Properties of X-ray Clusters: Analytic and Numerical Comparisons
• GIZMO: A New Class of Accurate, Mesh-Free Hydrodynamic Simulation Methods
• FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation
• Multi-scale initial conditions for cosmological simulations
• Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope
• A New Calculation of the Ionizing Background Spectrum and the Effects of HeII Reionization
• Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy
• The Shape of Dark Matter Halos: Dependence on Mass, Redshift, Radius, and Formation
• The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration
• Not so lumpy after all: modeling the depletion of dark matter subhalos by Milky Way-like galaxies
• A Comparison of Methods for Determining the Molecular Content of Model Galaxies
• The Local Group on FIRE: Dwarf galaxy populations across a suite of hydrodynamic simulations
• Galactic Bulge Preferred Over Dark Matter for the Galactic Center Gamma-Ray Excess
• How to Zoom: Bias, Contamination, and Lagrange Volumes in Multimass Cosmological Simulations
• Star formation histories of dwarf galaxies in the FIRE simulations: dependence on mass and Local Group environment
• What FIREs Up Star Formation: the Emergence of the Kennicutt-Schmidt Law from Feedback
• A profile in FIRE: resolving the radial distributions of satellite galaxies in the Local Group with simulations
• Synthetic Gaia surveys from the FIRE cosmological simulations of Milky Way-mass galaxies
• The Connection between Gamma-Ray Bursts and Extremely Metal-Poor Stars: Black Hole-forming Supernovae with Relativistic Jets
• The characteristics of the Galactic center excess measured with 11 years of Fermi-LAT data
• Scalar Dark Matter Models with Significant Internal Bremsstrahlung
• Strong constraints on thermal relic dark matter from Fermi-LAT observations of the Galactic Center
• On velocity-dependent dark matter annihilations in dwarf satellites
• The Effective J-Factor of the Galactic Center for Velocity-Dependent Dark Matter Annihilation
• Search for gamma-ray emission from $p$-wave dark matter annihilation in the Galactic Center
• Estimating the GeV Emission of Millisecond Pulsars in Dwarf Spheroidal Galaxies
• Amplified J-factors in the Galactic Center for velocity-dependent darkmatter annihilation in FIRE simulations
• The impact of galactic feedback on the shapes of dark-matter haloes
• p-wave Annihilating Dark Matter from a Decaying Predecessor and the Galactic Center Excess
• Velocity-dependent J-factors for annihilation radiation from cosmological simulations
• Spherical Cows in Dark Matter Indirect Detection
• Dark matter annihilation and the Galactic Centre Excess