The nature of the HE0450-2958 system

Abstract

Magain et al. argued that the host galaxy of the quasar in HE0450−2958 is substantially underluminous given the quasar brightness. Using kinematical information from the spectra of the quasar and the companion galaxy, an ultraluminous infrared galaxy, we test the hypothesis that the black hole powering the quasar was ejected from the companion galaxy during a merger. We argue that the ejection model is unlikely, since the kick velocity required to remove the black hole from the galaxy is ≳500 km s−1, inconsistent with the presence of narrow emission‐line gas at the same redshift as the quasar nucleus. We also show that the quasar in HE0450−2958 has the spectral characteristics of a narrow‐line Seyfert 1 galaxy and calculate a mass for its black hole that is roughly an order of magnitude smaller than that estimated by Magain et al. The predicted luminosity of the host galaxy is then consistent with the upper limits inferred by those authors.

The Host Galaxy of the Quasar HE 0450−2958

“…This perception appears to be driven by the association of the HE 0450À2958 system with an infraredbright source, with the implicit assumption that most of the infrared emission arises from stellar heating intrinsic to the companion galaxy, by the fact that the companion has a young stellar population (Canalizo & Stockton 2001;M05;Merritt et al 2006), and the suggestion, based on its apparently large Balmer decrement, that the companion appears to be highly extincted (M05).…”

“…See text for details. The dashed lines and stippled region represent the bulge luminosity (and its 1 standard deviation) for M ¼ 9 ; 10 7 M ( Merritt et al 2006) predicted from the M -L bul relation of Marconi & Hunt (2003). The relation of McLure & Dunlop (2002) would predict a bulge luminosity larger by 0.7 mag.…”

“…This value, however, is about a factor of 10 too large. Merritt et al (2006) showed that HE 0450À2958 shares many of the properties of narrow-line Seyfert 1 galaxies, which are thought to be relatively low mass black holes radiating near or perhaps even greater than their Eddington limit (e.g., Collin & Kawaguchi 2004). From an analysis of the optical spectra taken by M05, Merritt et al obtained a new estimate of the black hole mass using the virial method (e.g., Kaspi et al 2000), as presented by Greene & Ho (2005b).…”

“…In the recent literature (e.g., M05; Haehnelt et al 2006;Hoffman & Loeb 2006;Merritt et al 2006), the companion is often referred to as an ultraluminous infrared galaxy (ULIRG), which is a highly obscured system experiencing a high level of ongoing star formation. This perception appears to be driven by the association of the HE 0450À2958 system with an infraredbright source, with the implicit assumption that most of the infrared emission arises from stellar heating intrinsic to the companion galaxy, by the fact that the companion has a young stellar population (Canalizo & Stockton 2001;M05;Merritt et al 2006), and the suggestion, based on its apparently large Balmer decrement, that the companion appears to be highly extincted (M05).…”

Electromagnetic Signatures of Recoiling Black Holes

“…where v k is the kick velocity (Merritt et al 2006). This region is on the order of the size of the broad-line region (BLR) of AGN (Peterson 2007), which will therefore typically remain bound to the SMBH while the bulk of the host galaxy's narrow-line region (NLR) will remain behind.…”