Stellar envelopes as sources of broad line region emission: New possibilities allowed

Abstract

Abstract. In Active Galactic Nuclei (AGNs) the presence of a star cluster around the central black hole can have several effects on the dynamics and the emission of the global system. In this paper we analyze the interaction of stellar atmospheres with a wind outflowing from the central region of the AGN nucleus. Even a small mass loss from stars, as well as possible star collisions, can give a non-negligible contribution in feeding matter into the AGN nuclear wind. Moreover, stellar mass loss can produce envelopes surrounding stars that turn out to be suitable for reproducing the observed emission from the Broad Line Region (BLR). In this framework, the envelope can be confined by the bow shock arising from the interaction between the expanding stellar atmosphere and the AGN nuclear wind.

Is the Broad‐Line Region Clumped or Smooth? Constraints from the Hα Profile in NGC 4395, the Least Luminous Seyfert 1 Galaxy

“…Alternative suggestions for the origin of BLR clouds include gas streams produced by tidally disrupted stars (Hills 1975;Roos 1992), or by star-disk collisions (Zurek et al 1994;Vilkoviskij & Czerny 2002), or clumps in a gravitationally unstable outer disk (Collin & Huré 2001). Other scenarios invoke density inhomogeneities produced by wind interaction with nearby obstacles (Perry & Dyson 1985), such as stellar atmospheres (Torricelli-Ciamponi & Pietrini 2002), supernova remnants (Pittard et al 2003), or the the accretion-disk surface (Cassidy & Raine 1996). Alternatively, it was suggested that the clouds are density enhancements produced by shocks in an accreting gas (Fromerth & Melia 2001).…”

The formation of broad emission line regions in supernova-QSO wind interactions

“…They include: i) magnetic acceleration of clouds off accretion discs (Emmering et al 1992); ii) the interaction of an outflowing wind with the surface of an accretion disc (Cassidy & Raine 1996); iii) interaction of stars with accretion discs (Zurek et al 1994); iv) tidal disruption of stars in the gravitational field of the BH (Roos 1992); v) interaction of an AGN wind with supernovae and star clusters (Perry & Dyson 1985;Williams & Perry 1994); vi) emission from accretion shocks (Fromerth & Melia 2001); vii) ionized stellar envelopes (e.g. Torricelli-Ciamponi & Pietrini 2002). Many other models have been shown to possess serious difficulties (see references in Pittard et al 2001): in particular, any model must overcome the 'confinement problem', and/or continually generate clouds.…”