Dark Matter and Galaxy Cross-Correlations with the Cherenkov Telescope Array Observatory

Abstract

The Cherenkov Telescope Array Observatory (CTAO) will be a ground-based Cherenkov telescope performing wide-sky surveys, ideal for anisotropy studies such as cross-correlations with tracers of the cosmic large-scale structure. Cross-correlations can shed light on high-energy $γ$-ray sources and potentially reveal exotic signals from particle dark matter. In this work, we investigate CTAO sensitivity to cross-correlation signals between $γ$-ray emission and galaxy distributions. We find that by using dense, low-redshift catalogs like 2MASS, and for integration times around 50 hours, this technique achieves sensitivities to both annihilating and decaying dark matter signals that are competitive with those from dwarf galaxy and cluster analyses.

Figures (28)

• Figure 1: Pointing directions for the region of the sky planned to be covered by the extragalactic survey. The pointing directions are shown using a HEALPix pixelization with NSIDE = 16.
• Figure 2: Overlapping areas of different pointings. Top: A zoomed-in scheme of the pointing strategy shown in \ref{['fig:pnts']} (red), together with the overlapping fields of view of individual pointings (turquoise). Bottom: Simulated exposure map showing variations relative to the average exposure, highlighting the anisotropic pattern created by overlapping pointing regions.
• Figure 3: Strategy for assigning Instrument Response Functions (IRFs) across the extragalactic survey region as a function of zenith angle. In the left panel, the color scale shows, for each sky position, the zenith angle as measured in the observatory reference frame during observation (the values of the zenith angles and their color coding are reported on the vertical bar on the left). Since the IRFs are derived in three zenith angle bins (indicated by the color bar on the side of the right panel), the right panel shows which IRF is assigned to each region of the sky. The three IRFs shown here refer to 5 hrs of observation and to zenith angles below 30 deg (dark blue), between 30 and 50 deg (light blue) and above 60 deg (green).
• Figure 4: The $\gamma$-ray window functions, normalized to the mean $\gamma$-ray intensity and divided by the Hubble parameter, as a function of redshift. Blue solid and dashed lines show HSP and LISP astrophysical sources for 3 hours of observation, respectively. Red and green lines correspond to DM annihilation into $b\bar{b}$, $\langle \sigma v \rangle = 3 \times 10^{-26}$cm$^{-3}$s$^{-1}$ for DM masses of 1 TeV (red) and 30 TeV (green). Upper panel: $E_\gamma = 50$ GeV; lower panel: $E_\gamma = 1$ TeV (only 30 TeV DM case shown).
• Figure 5: Left: Predicted upper bounds on the dark matter cross-section $\langle \sigma v \rangle$, for annihilation into $b\bar{b}$, based on 3-hour and 50-hour of observations. The curves represent the bounds from $\gamma$-ray auto-correlation (dot-dashed) and cross-correlation with the 2MASS galaxy catalog (solid). Right: Same as the left panel, but for the lower bound on the DM particle lifetime $\tau$.