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2005MNRAS.356..515J - Mon. Not. R. Astron. Soc., 356, 515-523 (2005/January-2)
MRC B1221-423: a compact steep-spectrum radio source in a merging galaxy.
JOHNSTON H.M., HUNSTEAD R.W., COTTER G. and SADLER E.M.
Abstract (from CDS):
The pixels separate cleanly in colour-magnitude diagrams, with pixels of different colours occupying distinct regions of the host galaxy and its companion. Fitting stellar population models to these colours, we have estimated the age of each population. We find three distinct groups of ages: an old population (τ∼ 15 Gyr) in the outskirts of the host galaxy; an intermediate-age population (τ∼ 300 Myr) around the nucleus and tidal tail, and a young population (τ≲ 10 Myr) in the nucleus and blue knots.
The spectrum of the nucleus shows numerous strong emission lines, including [Oi]λ6300, [O]λ3727, [Sii]λλ6716, 6731, Hα and [Nii]λλ6548, 6583, characteristic of a low-ionization nuclear emission-line region (LINER) spectrum. The companion galaxy shows much narrower emission lines with very different line ratios, characteristic of a starburst galaxy.
We have evidence for three distinct episodes of star formation in B1221-423. The correlation of age with position suggests the two most recent episodes were triggered by tidal interactions with the companion galaxy. The evidence points to the active galactic nucleus (AGN) in the centre of B1221-423 having been caught in the act of ignition. However, none of the components we have identified is as young as the radio source, implying that the delay between the interaction and the triggering of the AGN is at least 3x108 yr.
Abstract Copyright: 2004 RAS
Journal keyword(s): galaxies: active - galaxies: interactions - galaxies: stellar content
CDS comments: P. 516: PG 0942 = PG 0942-029, SJ 9154 = [PMK98] 9154.
Simbad objects: 8
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