We present the first measurement of the cross-correlation between anisotropic birefringence and galaxy number counts, utilizing polarization data from Planck NPIPE and the Quaia quasar catalog. By employing a QML/pseudo-$C_\ell$ combined estimator, we compute the angular power spectrum up to $\ell=191$ from birefringence and clustering maps at $N_{ \rm side}=64$. Our analysis indicates that the observed spectrum is well consistent with the null-hypothesis, with a probability to exceed of 37% and an estimated scale-invariant amplitude of $A^{ \mathcal{ D}_\ell}=(2.22\pm2.09)\times10^{ -4}\,\text{ deg}$, at the 68% confidence level. Finally, we derive constraints on the axion-parameters within an early dark energy model of birefringence. Our findings reveal an unprecedented upper bound on the axion-photon coupling down to $g_{ \phi\gamma}=10^{ -15}\,\text{ GeV}^{ -1}$ for masses around $10^{ -32}\,\text{ eV}$ and high initial misalignment angles. This result opens a previously unexplored window in parameter space, providing the first constraint in this ultra-light mass regime.
Categories: astro-ph.CO hep-ph