An obscured narrow-line Seyfert 1 galaxy candidate, Mrk 1388 with nonthermal jets

Abstract

Mrk 1388 has an unusual Seyfert nucleus that shows narrow emission-line components without broad emission-line ones, but shows a strong featureless continuum and strong iron-forbidden, high-ionization emission lines. The apparent coexistence of type-1/2 characteristics is potentially attributed to a heavily obscured broad-line region or to an intermediate-mass black hole with a broad-line component that is intrinsically narrower than those of typical narrow-line Seyfert 1 (NLS1) galaxies. Our observation carried out by using very-long-baseline interferometry (VLBI) reveals high-brightness radio emission in nonthermal jets emerging from an active galactic nucleus (AGN) with a significant radio luminosity. Furthermore, we investigate the radial profile of the host galaxy using a Hubble Space Telescope (HST) image, which shows a Sérsic index suggestive of a pseudobulge. Using the VLBI and HST results which essentially are not affected by dust extinction, we apply the three individual methods to an estimate of the black hole mass and obtain three similar ones: (0.76-5.4) × 10⁶ M_⊙, 1.5 × 10⁶ M_⊙, and 4.1 × 10⁶ M_⊙. These masses are within a range that is fitted with typical NLS1 galaxies rather than with intermediate-mass black holes. Based on the estimated masses, a full width at half maximum FWHM(Hβ) of approximately 1200-1700 km s^-1 should have been seen. The scenario in a heavily absorbed NLS1 nucleus can explain the peculiarities previously observed.