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 ($\lesssim 500$ ks) and Lynx ($\lesssim 100$ ks). We find that large field of view (FOV) exposures remain the most sensitive methods for detection of dark matter 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 aboard the enhanced X-ray Timing and Polarimetry (eXTP) mission will be highly sensitive to DM signals, with a prospect of $\approx\! 2\times 10^6$ events from the 3.5 keV line in a 10 ks exposure. We also investigate detailed all-sky luminosity maps for both DM annihilation and decay signals, evaluating the signal-to-noise for a DM detection, taking into account realistic X-ray and gamma-ray backgrounds, as a guideline for what could be a forthcoming era of DM astronomy.