Constraining eV-scale axion-like particle dark matter: insights from the M87 Galaxy

Abstract: Axion-like particles (ALPs) can account for the observed dark matter (DM) of the Universe and if their masses are at the eV scale, they can decay into infrared, optical and ultraviolet photons with a decay lifetime larger than the age of the Universe.We analyze multi-wavelength data obtained from the central region of Messier 87 (M87) galaxy by several telescopes, such as, Swift, Astrosat, Kanata, Spitzer and International Ultraviolet Explorer in the infrared to ultraviolet frequencies ($\sim 2\times10^{14} \, {\rm Hz} - 3\times10^{15}$ Hz), to constrain the narrow emission lines indicative of the eV scale ALP DM decay. We derive constraints on the ALP coupling to two photons ($g_{a\gamma\gamma}$) for ALP mass range $2 \, {\rm eV} \lesssim m_a \lesssim 20 \, {\rm eV}$, assuming ALPs form the DM in the M87 halo. We find that our bounds on ALP-two-photon coupling can become stronger than the existing ones by an order of magnitude in the ALP mass range $8 \, {\rm eV} \lesssim m_a \lesssim 20 \, {\rm eV}$.