Issue |
A&A
Volume 690, October 2024
|
|
---|---|---|
Article Number | A155 | |
Number of page(s) | 19 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202347589 | |
Published online | 04 October 2024 |
The peculiar optical spectrum of Mrk 231
1
I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50939 Köln, Germany
2
Max-Planck Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
Received:
27
July
2023
Accepted:
26
February
2024
Markarian 231 (Mrk 231) is one of the closest and brightest ultra-luminous infrared galaxies that is considered to be in a late galaxy merger stage. The optical spectrum of Mrk 231 presents peculiar features and has been the subject of detailed studies. In this paper we study the optical long-slit spectroscopy of the central arcsecond of Mrk 231 as well as six off-nuclear spectral positions observed using the multi-object double spectrographs at the Large Binocular Telescope. Additionally, we carefully examine acquisition images taken before the spectroscopic observations. We find that both the nuclear and off-nuclear spectra of Mrk 231 exhibit broad Hα emission lines, which could be attributed to high-velocity outflows from the nucleus of Mrk 231, an extreme circumnuclear starburst, or a disturbed circumnuclear disc and broad line region associated with the merger of galaxies. The narrow Hα emission line has three components in every spectrum, which could be indicative of low-velocity outflows or a disturbed structure of the narrow-line region. The region to the south of the nucleus exhibits weak Hβ emission, and the regions to the north show no or extremely faint Hβ emission. The continuum has a stronger blue component in the south compared to the north. The central spectrum has prominent broad absorption lines at a redshift of ∼0.0262, which is distinct from the redshift of the emission line system, ∼0.0422. Broad absorption lines belonging to at least three systems are present in all of the off-nuclear spectra, but the regions to the south have their most prominent absorption lines at a redshift of ∼0.0262, and all three systems have absorption lines of similar strengths in the regions to the north. A careful examination of the acquisition images of Mrk 231 shows that there is diffuse emission in the region adjacent to the northern tail, extending in the north-east direction almost orthogonally, which might be an indication of a more complex interaction history.
Key words: Galaxy: kinematics and dynamics / galaxies: active / galaxies: evolution / galaxies: interactions / galaxies: starburst
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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