The MUSE Ultra Deep Field (MUDF). IV. A pair of X-ray weak quasars at the heart of two extended Ly nebulae

We present the results obtained from follow-up observations of the MUSE Ultra Deep Field (MUDF) at X-ray energies with XMM-Newton. The MUDF is centred on a unique field with two bright, physically associated quasars at z similar or equal to 3.23, separated by similar to 500 kpc in projection. Both quasars are embedded within extended Ly alpha nebulae (greater than or similar to 100 kpc at a surface brightness flux level of approximate to 6 x 10(-19) erg s(-1) cm(-2) arcsec(-2)), whose elongated morphology is suggestive of an extended filament connecting the quasar haloes. The new X-ray observations presented here allow us to characterize the physical properties (e.g. X-ray slope, luminosities, gas column densities) in the innermost region of the MUDF quasars. We find that both quasars are X-ray underluminous compared to objects at similar ultraviolet luminosities. Based on our X-ray spectral analysis, absorbing columns of N-H(z) greater than or similar to 10(23) cm(-2) appear unlikely therefore such a weakness is possibly intrinsic. When also including literature data, we do not observe any detectable trend between the area of the nebulae and nuclear luminosities at both the rest-frame 2 keV and 2500 angstrom. The area is also not correlated with the X-ray photon index nor with the integrated band flux in the hard band (2-10 keV). We also do not find any trend between the extended Ly alpha emission of the nebulae and the nuclear X-ray luminosity. Finally, the properties of the MUDF quasars' nebulae are consistent with the observed relation between the Ly a integrated luminosity of the nebulae and their area. Our results suggest that the quasar ionization power is not a strong driver of the morphology and size of the nebulae.