Why do we see Narrow Line Seyfert 1 (NLS1) galaxies, with permitted lines only slightly broader than forbidden lines?
Originally, there were two theories on this: one, that NLS1 might be Seyfert 1 objects but just viewed closer to the spin axis or perhaps have obscured BLRs, or two, that NLS1 galaxies have intrinsically lower mass black holes (10^6 to 10^7 solar masses), which must therefore accrete at near-Eddington or super-Eddington rates to maintain an AGN-like luminosity (Boller et al., 1996). Mathur (2001) proposed, in line with this, that NLS1s are just young S1s. The idea that the BLR is seen nearly face-on or obscured seems to have been discredited with the lack of any polarization signatures, so most researchers seem convinced that NLS1s are S1s with smaller black holes. (Recent research on this: Botte et al.
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