A sub-Neptune planet around TOI-1695 discovered and characterized with SPIRou and TESS

TOI-1695 is a V-mag=13 M-dwarf star from the northern hemisphere at 45$\,$pc Sun, around which 3.134-day periodic transit signal super-Earth candidate was identified in TESS photometry. With depth of 1.3$\,$mmag, radius TOI-1695.01 estimated by pipeline to be 1.82$\,$R$_\oplus$ with an equilibrium temperature $\sim 620\,$K. We successfully detect reflex motion and establish it due planetary companion orbital period consistent photometric thanks year-long radial-velocity monitoring SPIRou infrared spectropolarimeter. use compare different methods reduce analyse those data. report 5.5-$\sigma$ detection signal, giving mass $5.5 \pm 1.0\,$M$_\oplus$ $2.03 0.18\,$R$_\oplus$. derive mean planet $590 90\,$K. The density this small $3.6 1.1\,$g$\,$cm$^{-3}$ similar (1.7-$\sigma$ lower) than that Earth. It leads non-negligible fraction volatiles its atmosphere $f_{H,He}=0.28^{+0.46}_{-0.23}$% or $f_\text{water}=23 12$%. TOI-1695$\,$b new sub-Neptune border valley can help test formation scenarios for super-Earth/sub-Neptune-like planets.