New bounds on Axion-Like Particles in the Ultraviolet from Legacy Data

We use legacy data from the Hubble Space Telescope (HST) and the International Ultraviolet Explorer (IUE) to search for a spectral line from the spontaneous decay of axion-like particle (ALP) dark matter. The HST data consist of blank sky observations taken with the Faint Object Spectrograph in the 165–240~nm wavelength range, while the IUE data consist of observations of the Virgo Cluster obtained with the long- and short-wavelength spectrographs, covering 195–325~nm and 123–200~nm, respectively. We set a 95% C.L. upper limit on the ALP–photon coupling $g_{a\gamma }\lesssim {10}^{-11}{\mathrm{G}\mathrm{e}\mathrm{V}}^{-1}$ across the whole probed ALP mass range. Notably, we rule out values of $g_{a\gamma }$ above $2.3\times {10}^{-12}{\mathrm{G}\mathrm{e}\mathrm{V}}^{-1}$ for ALP masses between 12.4 and 14.5,eV, improving upon previous limits by a factor of seven.