High-resolution MEGARA Integral-field Unit 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, which are 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 Sloan Digital Sky Survey i-band data to investigate the formation of its disky (bulge) component, which makes up similar to 30% of the total galaxy light. With a Sersic index n similar to 1.80 +/- 0.24, a half-light radius R-e similar to 1.70 +/- 0.43 kpc, and stellar mass M-* similar to (4.34 +/- 1.70) x 10(10) M-circle dot, this bulge dominates the galaxy light distribution in the inner R similar to 15 '' (similar to 4.7 kpc). Measuring the spins (lambda) and ellipticities (epsilon) enclosed within nine different circular apertures with radii R <= R-e, we show that the bulge, which exhibits a spin track of 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 be driving gas and stars out of the disk into the inner regions of the galaxy, building up the massive pseudo-bulge.