Gas Accretion and Star-Formation Rates with IFUs and Background Quasars
  Star-forming galaxies (SFGs) are forming stars at a regular pace, forming the
so-called main sequence (MS). However, all studies of their gas content show
that their gas reservoir ought to be depleted in 0.5-2 Gyr. Thus, SFGs are
thought to be fed by the continuous accretion of intergalactic gas in order to
sustain their star-formation activity. However, direct observational evidence
for this accretion phenomenon has been elusive. Theoretically, the accreted gas
coming from the intergalactic medium is expected to orbit about the halo,
delivering not just fuel for star-formation but also angular momentum to the
galaxy. This accreting material is thus expected to form a gaseous structure
that should be co-rotating with the host once at $r<0.3\;R_{\rm vir}$ or
$r<10-30$ kpc. Because of the rough alignment between the star-forming disk and
this extended gaseous structure, the accreting material can be most easily
detected with the combination of background quasars and integral field units
(IFUs). In this chapter, accretion studies using this technique are reviewed.
