Intermediate-age stars as origin of the low-velocity dispersion nuclear ring in Mrk 1066

Abstract

We report the first two-dimensional stellar population synthesis in the near-infrared of the nuclear region of an active galaxy, namely, Mrk 1066. We have used integral field spectroscopy with adaptative optics at the Gemini North Telescope to map the age distribution of the stellar population in the inner 300 pc at a spatial resolution of 35 pc. An old stellar population component (age >~ Gyr) is dominant within the inner ≈160 pc, which we attribute to the galaxy bulge. Beyond this region, up to the borders of the observation field (∼300 pc), intermediate-age components (0.3–0.7 Gyr) dominate. We find a spatial correlation between this intermediate-age component and a partial ring of low stellar velocity dispersions (σ∗). Low-σ∗ nuclear rings have been observed in other active galaxies and our result for Mrk 1066 suggests that they are formed by intermediate-age stars. This age is consistent with an origin for the low-σ∗ rings in a past event which triggered an inflow of gas and formed stars which still keep the colder kinematics (as compared to that of the bulge) of the gas from which they have formed. At the nucleus proper we detect, in addition, two unresolved components: a compact infrared source, consistent with an origin in hot dust with mass ≈1.9 × 10-² Mʘ , and a blue featureless power-law continuum, which contributes with only ≈15% of the flux at 2.12 μm.