The Southern Hemisphere Narrow-Line Seyfert 1 Infrared Survey

TL;DR

This study conducts a near-infrared spectroscopic survey of southern hemisphere narrow-line Seyfert 1 galaxies, analyzing their broad-line region kinematics and black hole mass estimates using hydrogen emission lines.

Contribution

It provides the first detailed near-infrared spectroscopic analysis of southern NLS1 galaxies, comparing line profile fits and refining black hole mass estimates with new insights into BLR structure.

Findings

Lorentzian fits are preferred over Gaussian for line profiles.

Black hole mass estimates are consistent between Paα and Hβ lines.

Dust absorption affects line radiation, influencing mass measurements.

Abstract

We present a near-infrared spectroscopic survey of narrow-line Seyfert 1 galaxies in the southern hemisphere (using the SOFI instrument on the ESO-NTT telescope), sampled from optical surveys. We examine the kinematics of the broad-line region, probed by the emission line width of hydrogen (Pa$\alpha$ and H$\beta$). We observed 57 objects, of which we could firmly measure Pa$\alpha$ in 49 cases. We find that a single Lorentzian fit (preferred on theoretical grounds) is preferred over multi-component Gaussian fits to the line profiles; a lack of narrow-line region emission, overwhelmed by the pole-on view of the broad line region (BLR) light, supports this. We recompute the catalog black hole (BH) mass estimates, using the values of FWHM and luminosity of H$\beta$, both from catalog values and re-fitted Lorentzian values. We find a relationship slope greater than unity compared to the catalog values. We ascribe this to contamination by galactic light or difficulties with line flux measurements. However, the comparison of masses computed by the fitted Lorentzian and Gaussian measurements show a slope close to unity. Comparing the BH masses estimated from both Pa$\alpha$ and H$\beta$, the line widths and fluxes shows deviations from expected; in general, however, the computed BH masses are comparable. We posit a scenario where an intermixture of dusty and dust-free clouds (or alternately a structured atmosphere) differentially absorbs the line radiation of the BLR, due to dust absorption and hydrogen bound-free absorption.