BH masses in NLS1: the role of the broad-line region geometry

Abstract

Narrow Line Seyfert 1 galaxies (NLS1) are generally believed to host "under-massive" black holes with respect to the predictions from the host galaxy -- black hole mass scale relations. Black hole masses in NLS1 are estimated from the continuum luminosity and the width of broad emission lines. Here we show that the "mass deficit" can be canceled out if we assume that the broad line region (BLR) in type-1 AGN has a flat geometry, which is seen face-on in NLS1. The detection of relativistic jets aligned along the line of sight in a number of NLS1 supports this picture. Moreover, a flat geometry of the BLR is also suggested by a general trend of the mass deficit as a function of the line width observed in other type-1 AGN, from quasars to BL Lac objects, and is consistent with a simple extension of the Unified Model of AGN to the BLR geometry.