Abstract
Forty years after the discovery of Narrow-Line Seyfert 1 Galaxies (NLS1s), and 20 years since the discovery of the remarkable ultrasoft soft X-ray emissions of NLS1s, strategic publications improved the understanding of the Seyfert phenomenon more generally. New theoretical models emerged from the observations and stimulated the discussions on the innermost regions of AGN. NLS1s are an amazing class of AGN for X-ray, optical and multiwavelength science.
Highlights
Type 1 AGN are divided into Broad Line Seyfert 1 Galaxies (BLS1s) and Narrow-Line Seyfert 1 Galaxies (NLS1s)
The FWHM values of BLS1s are much higher than the velocity dispersions found from the rotation curves of normal galaxies, which reach only a few 100 km s−1
In 1970, Fritz Zwicky (∗14.2.1898, Bulgaria,+ 8.2.1974, Pasadena, Califormia, USA) made the fundamental discovery that type 1 AGN exhibit FWHM of the optical permitted lines much less than that what was observed in BLS1s, with FWHM values down to 500 km s−1 (Zwicky 1970). These objects were sometimes misclassified with normal galaxies, the presence of very strong Fe II multiplet emission definitely revealed the type 1 AGN nature of these sources, as Fe II multiplet emission is only occurring in high density regions with densities larger than 109 cm−3
Summary
Type 1 AGN are divided into Broad Line Seyfert 1 Galaxies (BLS1s) and Narrow-Line Seyfert 1 Galaxies (NLS1s). In 1970, Fritz Zwicky (∗14.2.1898, Bulgaria,+ 8.2.1974, Pasadena, Califormia, USA) made the fundamental discovery that type 1 AGN exhibit FWHM of the optical permitted lines much less than that what was observed in BLS1s, with FWHM values down to 500 km s−1 (Zwicky 1970) These objects were sometimes misclassified with normal galaxies, the presence of very strong Fe II multiplet emission definitely revealed the type 1 AGN nature of these sources, as Fe II multiplet emission is only occurring in high density regions with densities larger than 109 cm−3. Such densities are only present in the BLR clouds or the accretions disc in AGNs. 1978, Davidson and Kinman Davidson and Kinman (1978) investigated the optical spectrum of Mrk 359. They pointed out that the object has unusually narrow permitted optical lines and that ’this object merits further observations‘
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