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Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N
Univ Paris Diderot, Lab AIM Paris Saclay, CEA IRFU SAp, F-91191 Gif Sur Yvette, France..
Univ Paris Diderot, Lab AIM Paris Saclay, CEA IRFU SAp, F-91191 Gif Sur Yvette, France..
Leibniz Inst Astrophys, Sternwarte 16, D-14482 Potsdam, Germany..
Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA, England.;Univ Antofagasta, Unidad Astron, Fac Ciencias Basicas, Avda U Antofagasta 02800, Antofagasta, Chile..
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 585, A79Article in journal (Refereed) PublishedText
Abstract [en]

Context. We present Integral Field Unit (IFU) observations with MUSE and deep imaging with FORS of a dwarf galaxy recently formed within the giant collisional HI ring surrounding NGC 5291. This Tidal Dwarf Galaxy (TDG) -like object has the characteristics of typical z = 1-2 gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy interstellar medium, the absence of an old stellar population, and a moderate metallicity and star formation efficiency. Aims. The MUSE spectra allow us to determine the physical conditions within the various complex substructures revealed by the deep optical images and to scrutinize the ionization processes at play in this specific medium at unprecedented spatial resolution. Methods. Starburst age, extinction, and metallicity maps of the TDG and the surrounding regions were determined using the strong emission lines H beta, [OIII], [OI], [NII], H alpha, and [SII] combined with empirical diagnostics. Different ionization mechanisms were distinguished using BPT-like diagrams and shock plus photoionization models. Results. In general, the physical conditions within the star-forming regions are homogeneous, in particular with a uniform half-solar oxygen abundance. On small scales, the derived extinction map shows narrow dust lanes. Regions with atypically strong [OI] emission line immediately surround the TDG. The [OI]/H alpha ratio cannot be easily accounted for by the photoionization by young stars or shock models. At greater distances from the main star-foming clumps, a faint diffuse blue continuum emission is observed, both with the deep FORS images and the MUSE data. It does not have a clear counterpart in the UV regime probed by GALEX. A stacked spectrum towards this region does not exhibit any emission line, excluding faint levels of star formation, or stellar absorption lines that might have revealed the presence of old stars. Several hypotheses are discussed for the origin of these intriguing features.

Place, publisher, year, edition, pages
2016. Vol. 585, A79
Keyword [en]
HII regions, galaxies: dwarf, galaxies: ISM, galaxies: individual: NGC 5291N, galaxies: starburst, galaxies: interactions
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-282003DOI: 10.1051/0004-6361/201527141ISI: 000369710300086OAI: oai:DiVA.org:uu-282003DiVA: diva2:916166
Swedish Research Council, 2011-5349
Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2016-04-01Bibliographically approved

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Zackrisson, Erik
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