  Theoretical studies predict the presence of thermal inversions in the
atmosphere of highly irradiated gas giant planets. Recent observations have
identified these inversion layers. However, the role of different chemical
species in their formation remains unclear. We search for the signature of the
thermal inversion agents TiO and Fe in the dayside emission spectrum of the
ultra-hot Jupiter WASP-33b. The spectra were obtained with CARMENES and
HARPS-N, covering different wavelength ranges. Telluric and stellar absorption
lines were removed with SYSREM. We cross-correlated the residual spectra with
model spectra to retrieve the signals from the planetary atmosphere. We find
evidence for TiO at a significance of 4.9$\mathrm{\sigma}$ with CARMENES. The
strength of the TiO signal drops close to the secondary eclipse. No TiO signal
is found with HARPS-N. An injection-recovery test suggests that the TiO signal
is below the detection level at the wavelengths covered by HARPS-N. The
emission signature of Fe is detected with both instruments at significance
levels of 5.7$\mathrm{\sigma}$ and 4.5$\mathrm{\sigma}$, respectively. By
combining all observations, we obtain a significance level of
7.3$\mathrm{\sigma}$ for Fe. We find the TiO signal at $K_\mathrm{p}$ =
$248.0_{-2.5}^{+2.0}$ km s$^{-1}$, which is in disagreement with the Fe
detection at $K_\mathrm{p}$ = $225.0_{-3.5}^{+4.0}$ km s$^{-1}$. The
$K_\mathrm{p}$ value for Fe is in agreement with prior investigations. The
model spectra require different temperature profiles for TiO and Fe to match
the observations. We observe a broader line profile for Fe than for TiO. Our
results confirm the existence of a temperature inversion layer in the planetary
atmosphere. The observed $K_\mathrm{p}$ offset and different strengths of
broadening in the line profiles suggest the existence of a TiO-depleted hot
spot in the planetary atmosphere.
