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High-resolution mm ...
High-resolution mm and cm study of the obscured LIRG NGC 4418 A compact obscured nucleus fed by in-falling gas?
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- Costagliola, Francesco, 1981 (författare)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Aalto, Susanne, 1964 (författare)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Sakamoto, K. (författare)
- Academia Sinica Taiwan
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- Martin, S. (författare)
- European Southern Observatory Santiago
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- Beswick, R. (författare)
- University of Manchester
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- Muller, Sebastien, 1976 (författare)
- Chalmers tekniska högskola,Chalmers University of Technology
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- Klockner, H. R. (författare)
- University Of Oxford,Max Planck Gesellschaft zur Förderung der Wissenschaften e.V. (MPG),Max Planck Society for the Advancement of Science (MPG)
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(creator_code:org_t)
- 2013-07-30
- 2013
- Engelska.
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 556
- Relaterad länk:
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http://publications.... (primary) (free)
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https://www.aanda.or...
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https://research.cha...
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https://doi.org/10.1...
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Abstract
Ämnesord
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- Context. Understanding the nature of the power-source in luminous infrared galaxies (LIRG) is difficult due to their extreme obscuration. Observations at radio and mm wavelengths can penetrate large columns of dust and gas and provide unique insights into the properties of the compact obscured nuclei of LIRGs. Aims. The aim of this study is to constrain the dynamics, structure, and feeding of the compact nucleus of NGC 4418, and to reveal the nature of the main hidden power-source: starburst or active galactic nucleus (AGN). Methods. We obtained high spatial resolution observations of NGC 4418 at 1.4 and 5 GHz with MERLIN, and at 230 and 270 GHz with the SMA in very extended configuration. We used the continuum morphology and flux density to estimate the size of the emitting region, the star formation rate, and the dust temperature. Emission lines were used to study kinematics through position-velocity diagrams. Molecular emission was studied with population diagrams and by fitting a local thermal equilibrium (LTE) synthetic spectrum. Results. We detect bright 1-mm-line emission from CO, HC3N, HNC, and (CS)-S-34 and 1.4 GHz absorption from HI. The CO 2-1 emission and HI absorption can be fit by two velocity components at 2090 and 2180 km s(-1). We detect vibrationally excited HC3N and HNC, with T-vib similar to 300 K. Molecular excitation is consistent with a layered temperature structure, with three main components at 80, 160, and 300 K. For the hot component we estimate a source size of less than 5 pc. The nuclear molecular gas surface density of 10(4) M-circle dot pc(-2) is extremely high and similar to that found in the ultra-luminous infrared galaxy (ULIRG) Arp220. Conclusions. Our observations confirm the presence of a molecular and atomic in-flow, previously suggested by Herschel observations, which is feeding the activity in the center of NGC 4418. Molecular excitation confirms the presence of a very compact, hot dusty core. If a starburst is responsible for the observed IR flux, this has to be at least as extreme as the one in the ULIRG Arp 220, with an age of 3-10 Myr and a star formation rate > 10 M-circle dot yr(-1). If an AGN is present, it must be extremely Compton-thick.
Ämnesord
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
Nyckelord
- arp 220
- galaxies: starburst
- galaxies: individual: NGC 4418
- galaxies
- interstellar-medium
- line emission
- dense gas
- molecular gas
- active galactic nuclei
- galaxies: active
- star-formation
- luminous infrared
- galaxies: ISM
- ngc-4418
- galaxies: kinematics and dynamics
- vibrationally excited hc3n
Publikations- och innehållstyp
- art (ämneskategori)
- ref (ämneskategori)
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