Where is the fuzz? Undetected Lyman alpha nebulae around QSOs at z~2.3

Abstract

We observed a small sample of 5 radio-quiet QSOs with integral field spectroscopy to search for possible extended emission in the Ly\(\alpha\) line. We subtracted the QSO point sources using a simple PSF self-calibration technique that takes advantage of the simultaneous availability of spatial and spectral information. In 4 of the 5 objects we find no significant traces of extended Ly\(\alpha\) emission beyond the contribution of the QSO nuclei itself, while in UM 247 there is evidence for a weak and spatially quite compact excess in the Ly\(\alpha\) line at several kpc outside the nucleus. For all objects in our sample we estimated detection limits for extended, smoothly distributed Ly\(\alpha\) emission by adding fake nebulosities into the datacubes and trying to recover them after PSF subtraction. Our observations are consistent with other studies showing that giant Ly\(\alpha\) nebulae such as those found recently around some quasars are very rare. Ly\(\alpha\) fuzz around typical radio-quiet QSOs is fainter, less extended and is therefore much harder to detect. The faintness of these structures is consistent with the idea that radio-quiet QSOs typically reside in dark matter haloes of modest masses.