Entering the Era of Dark Matter Astronomy? Near to Long-Term Forecasts in X-Ray and Gamma-Ray Bands

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.