| Abstract: Extended ultraviolet (XUV) emission traces inside-out disk growth through low-efficiency star formation in galaxy outskirts, but such systems have so far been almost exclusively found in the local Universe due to the need for deep UV imaging. Using AstroSat/UVIT, we report the detection of a clumpy XUV disk at $z=0.67$ in a massive, isolated spiral galaxy ($\log(M_*/M_\odot)\approx11.04$). The PSF-corrected rest-frame FUV surface brightness profile reveals a UV disk that is significantly more extended than the optical and near-infrared emission, reaching nearly twice the optical radius. The outer disk hosts a large, UV-bright, low-surface-brightness component, consistent with a Type II XUV disk. The presence of UV clumps without optical counterparts also supports a Type I classification, indicating recent, localized star formation likely driven by gravitational instabilities. Together, these features point to ongoing cold gas accretion onto the outer disk, and from the observed asymmetry in the UV light profile, we estimate a gas accretion rate of $\sim11\ M_\odot,{\rm yr}^{-1}$, providing direct evidence for active disk growth in a massive galaxy at intermediate redshift. |
