Stellar populations with MEGARA: the inner regions of NGC 7025
  Context. We aim to determine the capabilities of the MEGARA@GTC instrument
integral-field unit to study stellar populations and exploit its combination of
high spectral (R \sim 6,000, 12,000 and 20,000) and spatial (0.62") resolutions
within its 12.5"x11.3" field of view. Aims. We pursue to establish a systematic
method through which we can determine the properties of the stellar populations
in the observations made with MEGARA, more specifically within the MEGADES
legacy project and, for this paper, those of the stellar populations of NGC
7025. Methods. We use MEGARA observations of galaxy NGC 7025. We apply
different approaches to estimate the properties of the stellar populations with
the highest possible certainty. Numerous tests were also performed to check the
reliability of the study. Results. All the studies we conduct (both full
spectral fitting and absorption line indices) on the stellar populations of NGC
7025 indicate that the stars that form its bulge have supersolar metallicity
and considerably old ages (\sim 10 Gyr), in general. We determined that the
bulge of NGC 7025 has a mild negative mass-weighted age gradient using three
different combinations of MEGARA spectral setups. Regarding its more detailed
star formation history, our results indicate that, besides a rather constant
star formation at early epochs, a peak in formation history of the stars in the
bulge is also found 3.5-4.5 Gyr ago, partly explaining the mass-weighted age
gradients measured. Conclusions. The scenario presented in NGC 7025 is that of
an isolated galaxy under secular evolution that about 3.5-4.5 Gyr ago likely
experimented a minor merger (mass ratio 1/10) that induced an increase in star
formation and also perturbed the morphology of its outer disc. We report on
different lessons learned for the ongoing exploitation of the MEGADES survey
with GTC.
