Revisiting narrow-line Seyfert 1 galaxies and their place in the Universe (NLS1-2018), 9-13 April 2018, Padova Botanical Garden, Italy
Although more than 30 years have passed since their discovery, narrow-line Seyfert 1 galaxies (NLS1s) still present challenges for unified models of active galactic nuclei (AGN). Sources of electromagnetic emission at all frequencies, their physical properties and role in galaxy evolution remain poorly understood. The aim of this workshop is to present and to discuss developments in the field over the seven years since the most recent NLS1 conference (Milano 2011). The main topics of the workshop will include the multiwavelength properties of these objects from radio wavelengths to gamma rays, their role in AGN evolution, their relationship to other classes of AGN, and their place in the framework of AGN unified models. The workshop will be held at the Orto Botanico di Padova (Italy), the world's oldest academic botanical garden. During the event, a one-hour session will be devoted to the topic of gender balance in astrophysics. This session will be dedicated to Lucrezia Cornaro of the University of Padova, the first woman in the world to obtain a Ph.D. degree. We will commemorate the 340th anniversary of this event.
Two major challenges to unification schemes for active galactic nuclei (AGN) activity are the existence of Narrow-Line Seyfert 1s (NLS1s) and the existence of changing-look (CL) AGNs. AGNs can drastically change their spectral appearance in the optical (changing their Seyfert type) and/or in the X-ray region. We illustrate the CL phenomenon with our multi-wavelength monitoring of the typical CL AGN NGC 2617 and discuss its properties compared with NLS1s. There are few examples of CL NLS1s and the changes are mostly only in the X-ray region. So far only a few NLS1s have been found to have strong changes in the optical emission lines. It has been proposed that some of these could be cases of a tidal-disruption events (TDE) or supernova events. If NLS1s are seen face-on and BLRs have a flat geometry then we have to see CL cases only if the orientation of the BLR changes as a result of a TDE or a close encounter of a star without a TDE.If NLS1s include both high Eddington rate accretion and low-inclination AGNs then a significant fraction of NLS1s could be obscured and would not be identified as NLS1s. CL cases might happen more in such objects if dust sublimation occurs following a strong increase in the optical luminosity.