Abstract
We assess Galactic Dark Matter (DM) sensitivities to photons from annihilation and decay using the spatial and kinematic information determined by state-of-the-art simulations in the Latte suite of Feedback In Realistic Environments (FIRE-2). For kinematic information, we study the energy shift pattern of DM narrow emission lines predicted in FIRE-2 and discuss its potential as DM-signal diagnosis, showing for the first time the power of symmetric observations around $l=0^{\circ}$. We find that the exposures needed to resolve the line separation of DM to gas by XRISM at $5\sigma$ to be large, $\gtrsim 4$ Ms, while exposures are smaller for Athena ($\lesssim 50$ ks) and Lynx ($\lesssim 100$ ks). We find that large field-of-view exposures remain the most sensitive methods for detection of DM annihilation or decay by the luminosity of signals in the field of view dominating velocity information. The $\sim$4 sr view of the Galactic Center region by the Wide Field Monitor (WFM) aboard the eXTP mission will be highly sensitive to DM signals, with a prospect of $\sim 10^5$ to $10^6$ events from the 3.5 keV line in a 100 ks exposure, with the range dependent on photon acceptance in WFM's field of view. We also investigate detailed all-sky luminosity maps for both DM annihilation and decay signals - evaluating the signal-to-noise for a DM detection with realistic X-ray and gamma-ray backgrounds - as a guideline for what could be a forthcoming era of DM astronomy.
Highlights
Today we know that Dark Matter (DM) accounts for ∼ 85% of the matter amount present in our observable Universe, and constitutes ∼ 1/4 of the total inferred cosmological energy budget [1]
Future X-ray and gamma-ray missions will largely extend the capability of astronomical searches for DM via photon emission from annihilation, decay or internal structure, and potentially lead us to the era of “Dark Matter Astronomy.”
We go beyond prior studies of the luminosity profile of DM annihilation or decay by using detailed hydrodynamic simulations of our Milky Way (MW) Galaxy’s formation with a representative DM spatial and velocity distribution, via the FIRE-2 Latte simulations
Summary
Today we know that Dark Matter (DM) accounts for ∼ 85% of the matter amount present in our observable Universe, and constitutes ∼ 1/4 of the total inferred cosmological energy budget [1]. While the interpretation of these findings in terms of astrophysical emission may be still considered under debate [10, 63,64,65], as of today, the series of indications of the 3.5 keV line in the X-ray sky represent one of the most intriguing claims for uncovering the particle nature of DM [9, 66] In this regard, the recent theoretical study in Ref. Maybe most importantly, the forecast signal and signal-to-background we explore here can help guide future mission design and development These topics are what we study in this paper, with special attention to the spectroscopic DM Doppler shift (velocity spectroscopy), DM dispersion line broadening, as well as the expected DM emissivity.
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