Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?

¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: mmezcua@iac.es
² Instituto de Astrofísica de Canarias, vía Láctea S/N, 38200 La Laguna, Tenerife, Spain
³ Dept. Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁴ Instituto Nacional de Astrofísica, Óptica y Electrónica, Apdo. Postal 51, 72000 Puebla, México
⁵ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland

Received: 18 July 2011
Accepted: 20 June 2012

Abstract

We present new spectroscopic identifications of 12 X-shaped radio galaxies and use the spectral data to derive starburst histories and masses of the nuclear supermassive black holes in these galaxies. The observations were done with the 2.1-m telescope of the Observatorio Astronómico Nacional at San Pedro Mártir, México. The new spectroscopic results extend the sample of X-shaped radio galaxies studied with optical spectroscopy. We show that the combined sample of the X-shaped radio galaxies has statistically higher black-hole masses and older episodes of star formation than a control sample of canonical double-lobed radio sources with similar redshifts and luminosities. The data reveal enhanced star-formation activity in the X-shaped sample on the timescales expected in galactic mergers. We discuss the results obtained in the framework of the merger scenario.