The redshift and broad-band spectral energy distribution of NRAO 150^*

¹ Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea, s/n, 38200, La Laguna, Tenerife, Spain e-mail: jap@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³ Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
⁴ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
⁵ Department of Physics & Astronomy, University of Shefield, UK
⁶ Isaac Newton Group of Telescopes, La Palma, Spain

Received: 23 December 2009
Accepted: 9 March 2010

Abstract

Context. NRAO 150 is one of the brightest radio and mm AGN sources in the northern sky, and is an interesting source to study extreme relativistic jet phenomena. However, its cosmological distance has not yet been calibrated, because of its optical faintness due to strong Galactic extinction.

Aims. We measure the redshift of NRAO 150, to enable us to perform quantitative studies of the source.

Methods. We conducted spectroscopic and photometric observations of the source in both the near-IR and the optical.

Results. All these observations were successful in detecting the source. The near-IR spectroscopic observations exhibit strong Hα and Hβ emission lines from which the cosmological redshift of NRAO 150 (z = 1.517 ± 0.002) is determined for the first time. We classify the source as a flat-spectrum radio-loud quasar, for which we estimate a high supermassive black-hole mass ~5× 10⁹ . After extinction correction, the new near-IR and optical data show a high-luminosity continuum-emission excess in the optical (peaking in the rest frame at ~2000 Å) that we attribute to thermal emission from the accretion disk for which we estimate a high accretion rate of ~30% the Eddington limit.

Conclusions. Comparison of the source properties and its broad-band spectral-energy distribution with those of Fermi blazars allows us to predict that NRAO 150 is among the most powerful of blazars, and hence a high luminosity – although not yet detected – γ-ray emitter.