The X-ray to [Ne V]3426 flux ratio: discovering heavily obscured AGN in the distant Universe R. Gilli, C. Vignali, M. Mignoli, K. Iwasawa, A. Comastri and G. Zamorani A&A, 519 (2010) A92 Published online: 17 September 2010 DOI: 10.1051/0004-6361/201014039