High-resolution MEGARA IFU spectroscopy and structural analysis of a
  fast-rotating, disky bulge in NGC 7025
  Disky bulges in spiral galaxies are commonly thought to form out of disk
materials (mainly) via bar driven secular processes, they are structurally and
dynamically distinct from `classical bulges' built in violent merger events. We
use high-resolution GTC/MEGARA integral-field unit spectroscopic observations
of the Sa galaxy NGC 7025, obtained during the MEGARA commissioning run,
together with detailed 1D and 2D decompositions of this galaxy's SDSS $i$-band
data to investigate the formation of its disky (bulge) component which makes up
$\sim 30\%$ of the total galaxy light. With a S\'ersic index $n \sim 1.80 \pm
0.24$, half-light radius $R_{\rm e} \sim 1.70 \pm 0.43$ kpc and stellar mass
$M_{*} \sim (4.34 \pm 1.70) \times10^{10} M_{\odot}$, this bulge dominates the
galaxy light distribution in the inner $R \sim 15"$ ($\sim 4.7$ kpc). Measuring
the spins ($\lambda$) and ellipticities ($\epsilon$) enclosed within nine
different circular apertures with radii $R \le R_{\rm e}$, we show that the
bulge, which exhibits a spin track of an outwardly rising $\lambda$ and
$\epsilon$, is a fast rotator for all the apertures considered. Our findings
suggest that this inner disky component is a pseudo-bulge, consistent with the
stellar and dust spiral patterns seen in the galaxy down to the innermost
regions but in contrast to the classical bulge interpretation favored in the
past. We propose that a secular process involving the tightly wound stellar
spiral arms of NGC 7025 may drive gas and stars out of the disk into the inner
regions of the galaxy, building up the massive pseudo-bulge.
