Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115-2124 (the Bird)

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Väisänen , P , Reunanen , J , Kotilainen , J , Mattila , S , Johansson , P H , Ramphul , R , Romero-Canizales , C & Kuncarayakti , H 2017 , ' Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115-2124 (the Bird) ' , Monthly Notices of the Royal Astronomical Society , vol. 471 , no. 2 , pp. 2059-2076 . https://doi.org/10.1093/mnras/stx1685

Title: Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115-2124 (the Bird)
Author: Väisänen, Petri; Reunanen, Juha; Kotilainen, Jari; Mattila, Seppo; Johansson, Peter H.; Ramphul, Rajin; Romero-Canizales, Cristina; Kuncarayakti, Hanindyo
Contributor: University of Helsinki, Department of Physics
Date: 2017-10
Language: eng
Number of pages: 18
Belongs to series: Monthly Notices of the Royal Astronomical Society
ISSN: 0035-8711
URI: http://hdl.handle.net/10138/224422
Abstract: We present new SINFONI near-infrared (NIR) integral field unit (IFU) spectroscopy and Southern African Large Telescope (SALT) optical long-slit spectroscopy characterizing the history of a nearby merging luminous infrared galaxy, dubbed the Bird (IRAS19115-2124). TheNIR line-ratio maps of the IFU data cubes and stellar population fitting of the SALT spectra now allow dating of the star formation (SF) over the triple system uncovered from our previous adaptive optics data. The distinct components separate clearly in line-ratio diagnostic diagrams, both thermal and non-thermal excitation is present. An off-nuclear starburst dominates the current SF of the Bird with 60-70 per cent of the total, with a 4-7 Myr age. The most massive nucleus, in contrast, is quenched with a starburst age of >40 Myr and shows hints of budding active galactic nucleus (AGN) activity. The secondary massive nucleus is at an intermediate stage. The two major components have signs of an older stellar population, consistent with a starburst triggered 1 Gyr ago in a first encounter. The simplest explanation of the history is that of a triple merger, where the strongly star-forming component has joined later. We detect multiple gas flows. The Bird offers an opportunity to witness multiple stages of galaxy evolution in the same system; triggering as well as very recent quenching of SF, and, perhaps, an early appearance of AGN activity. It also serves as a cautionary note on interpretations of observations with lower spatial resolution and/or without infrared data. At high redshift the system would look like a clumpy starburst with crucial pieces of its puzzle hidden in danger of misinterpretations.
Subject: galaxies: evolution
galaxies: individual: IRAS 19115-2124
galaxies: interactions
galaxies: nuclei
galaxies: starburst
STAR-FORMING GALAXIES
NEAR-INFRARED SPECTROSCOPY
INTEGRAL FIELD SPECTROSCOPY
SPITZER-SPACE-TELESCOPE
AFRICAN LARGE TELESCOPE
ACTIVE GALACTIC NUCLEI
DIGITAL SKY SURVEY
POPULATION SYNTHESIS
MOLECULAR-HYDROGEN
MULTIPLE MERGER
115 Astronomy, Space science
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