Timescales of merger, starburst and AGN activity in radio galaxy B2 0648+27

B. H.C. Emonts, R. Morganti, C. N. Tadhunter, J. Holt, T. A. Oosterloo, J. M. Van Der Hulst, K. A. Wills

Research output: Contribution to journalArticleAcademicpeer-review

49 Citations (Scopus)


We use neutral hydrogen (H I) and optical spectroscopic observations to compare the timescales of a merger event, starburst episode and radio-AGN activity in the radio galaxy B2 0648+27. We detect a large ring-like structure of H I in emission around the early-type host galaxy of B2 0648+27 (MH I = 8.5 × 109 M⊙, diameter = 190 kpc). We interpret this as the result of a major merger that occurred ≳ 1.5 Gyr ago. From modelling optical long-slit spectra we find that a young stellar population of 0.3 Gyr, indicative of a past starburst event, dominates the stellar light throughout the galaxy. The off-set in time between the merger event and the starburst activity in B2 0648+27 suggests that the starburst was triggered in an advanced stage of the merger, which can be explained if the gas-rich progenitor galaxies contained a bulge. Although the exact age of the radio source remains uncertain, there appears to be a significant time-delay between the merger/starburst event and the current episode of radio-AGN activity. We also observe an outflow of emission-line gas in this system, which is likely related to superwinds driven by the stars that formed during the starburst event. We argue that the radio galaxy B2 0648+27 is a link in the evolutionary sequence between Ultra-Luminous Infrared Galaxies (ULIRGs) and genuine early-type galaxies.
Original languageEnglish
Pages (from-to)125-135
Number of pages11
JournalAstronomy & Astrophysics
Issue number1
Publication statusPublished - Jul 2006


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