Optical and NIR spectroscopy of Mrk1210: constraints and physical conditions of the active nucleus

Abstract

Near-infrared and optical spectroscopy of the nuclear and extended emission region of the Seyfert2 galaxy Mrk1210 is presented. This galaxy is outstanding because it displays signatures of recent circumnuclear star formation and a high-level of X-ray activity, in addition to the classical spectral characteristics typical of an AGN. The NIR nuclear spectrum, which covers the interval 0.8-2.4 microns, is dominated by HI and HeI recombination lines as well a [SII], [SIII] and [Fe II] forbidden lines. Coronal lines of [SVIII], [SIX], [SiVI], [SiX], and [CaVIII] in addition to molecular H_2 lines are also detected. An estimate of the contribution of the stellar population to the continuum is made by means of the ^{12}CO(6-3) 1.618 microns overtone bandhead. It was found that 83% of the H-band continuum is of stellar origin. It improves previous estimates, which claimed that at least 50% of the observed continuum was attributed to the AGN. The analysis of the emission line profiles, both allowed and forbidden, shows a narrower line on top of a broad blue-shifted component. The latter seems to be associated to a nuclear outflow. This result does not required the presence of a hidden BLR claimed to be present in previous NIR observations of this object. Internal extinction, calculated by means of several indicators including [FeII] flux ratios not previously used before in AGNs, reveals a dusty AGN, while the extended regions are little or not affected by dust. Density and temperature for the NLR are calculated using optical and NIR lines diagnostic ratios. The results show temperatures from 10000K up to 40000K and densities between 10^3-10^5 cm^{-3}. The larger temperatures points out that shocks must contribute to the line emission.