Probing the Dust Obscuration in Seyfert Galaxies using Infrared Spectroscopy. II. Implication for the Unification of Seyfert Galaxies

Abstract

We report near-IR spectroscopic observations of 11 Seyfert galaxies (six Seyfert 1s, one Seyfert 1.9, and four Seyfert 2s) and additional galaxies (four LINERs, two H ii, and one type 2 transition) for comparison, obtained using the Gemini twin-channel near-IR camera on the Shane 3 m telescope at Lick Observatory. With the unique design of the Gemini camera, full J and K spectra were taken simultaneously through the same slit. This produced accurate line ratios of hydrogen recombination lines over a large wavelength baseline. For the Seyfert 1s ( 1.5), the line ratios of Pa /Br are not only comparable in both broad-and narrow-line regions but also consistent with case B recombination, indicating little or no reddening in both narrow-and broad-line regions. Seyfert 2 (>1.5) galaxies, however, show substantial reddening toward the narrow-line regions. We compare optical reddening data from the literature and find significant support for the dichotomy between Seyfert 1s and Seyfert 2s, at least in lowluminosity objects. Two different scenarios are explored to explain the observed difference in reddening: a difference in reddening due to an extended dusty torus under active galactic nucleus unification, and a difference due to a different grain size distribution between the two Seyfert types. We also discuss a similar potential difference found in the strength of the 9.7 m silicate line, along with a possible correlation between the narrow-line reddening and the strength of the silicate absorption line. We also analyzed CO band head absorption features longward of 2.3 m to look for nonstellar contamination and evidence of recent star formation activity. The CO band head in Seyfert 1s shows heavy contamination from nonstellar radiation, which is correlated with an H À K nuclear color excess. We confirm that the CO spectroscopic indices in both Seyfert types do not show evidence of recent star formation. Taking the nonstellar contamination into account, there is little evidence from the CO index for a difference in star formation rates in the nuclei of Seyfert 1s and Seyfert 2s in our low-luminosity sample.

Size and properties of the narrow-line region in Seyfert-1 galaxies from spatially-resolved optical spectroscopy

“…When excluding NGC 526a, which can be considered as a galaxy of transient Seyfert-type 1.9, the average reddening value for four Seyfert-1 galaxies is indeed the same as that for Sy2s: E B−V 4 Sy1s ∼ 0.41 ± 0.03 mag. Our results differ from those of Rhee & Larkin (2005), who concluded that Sy 1s have much lower (or zero) reddening than Sy 2s, based on near-IR line ratios. They speculate that the difference could be caused either by a large-scale (>100 pc) torus or by an intrinsically different grain size distributions in Sy 1s and 2s.…”

Is IRAS 01072+4954 a True-Seyfert 2?

“…The measured A V is consistent with the median value A V = 1.64 mag of 27 Sy2 galaxies from the database of Ho et al (1997a), as pointed out by Rhee & Larkin (2005). In contrast, the median extinction of the 9 Sy1 sources of the same sample was <0.03 mag.…”

The Hunt for Intermediate-mass Black Holes in the JWST Era

“…The highest ratios in each plot is normalized to one. 2000); Rhee & Larkin (2005) ionize the gas and affect the observed emission line spec- trum (Allen et al 2008;Kewley et al 2013). The presence of blue-shifted line profiles in many CLs is indeed consistent with the presence of outflows (e.g., Marconi et al 1996;Mazzalay & Rodríguez-Ardila 2007;Rodríguez-Ardila et al 2006Müller-Sánchez et al 2011).…”