Journal Article

When galaxies collide: understanding the broad absorption-line radio galaxy 4C +72.26

D. J. B. Smith, C. Simpson, A. M. Swinbank, S. Rawlings and M. J. Jarvis

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 404, issue 3, pages 1089-1099
Published in print May 2010 | ISSN: 0035-8711
Published online May 2010 | e-ISSN: 1365-2966 | DOI:
When galaxies collide: understanding the broad absorption-line radio galaxy 4C +72.26

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We present a range of new observations of the ‘broad absorption-line radio galaxy’ 4C +72.26 (z≈ 3.5), including sensitive rest-frame ultraviolet integral field spectroscopy using the Gemini/GMOS-N instrument and Subaru/CISCO K-band imaging and spectroscopy. We show that 4C +72.26 is a system of two vigorously star-forming galaxies superimposed along the line of sight separated by ∼1300 ± 200 km s−1 in velocity, with each demonstrating spectroscopically resolved absorption lines. The most active star-forming galaxy also hosts the accreting supermassive black hole which powers the extended radio source. We conclude that the star formation is unlikely to have been induced by a shock caused by the passage of the radio jet, and instead propose that a collision is a more probable trigger for the star formation. Despite the massive starburst, the ultraviolet-mid-infrared spectral energy distribution suggests that the pre-existing stellar population comprises ∼1012 M of stellar mass, with the current burst only contributing a further ∼2 per cent, suggesting that 4C +72.26 has already assembled most of its final stellar mass.

Keywords: galaxies: haloes; galaxies: high-redshift; galaxies: individual: 4C +72.26; quasars: emission lines; galaxies: starburst

Journal Article.  8358 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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