The University of Southampton
University of Southampton Institutional Repository

Embedded AGN and star formation in the central 80 pc of IC 3639

Fernandez-Ontiveros, J.A., Tristram, K.R.W., Hönig, S., Gandhi, P. and Weigelt, G. (2017) Embedded AGN and star formation in the central 80 pc of IC 3639. Astronomy & Astrophysics.

Record type: Article

Abstract

[Abridged] Methods: We use interferometric observations in the $N$-band with VLTI/MIDI to resolve the mid-IR nucleus of IC 3639. The origin of the nuclear infrared emission is determined from: 1) the comparison of the correlated fluxes from VLTI/MIDI with the fluxes measured at subarcsec resolution (VLT/VISIR, VLT/ISAAC); 2) diagnostics based on IR fine-structure line ratios, the IR continuum emission, IR bands produced by polycyclic aromatic hydrocarbons (PAH) and silicates; and 3) the high-angular resolution spectral energy distribution.

Results: The unresolved flux of IC 3639 is $90 \pm 20\, \rm{mJy}$ at $10.5\, \rm{\mu m}$, measured with three different baselines in VLTI (UT1-UT2, UT3-UT4, and UT2-UT3; $46$-$58\, \rm{m}$), making this the faintest measurement so far achieved with mid-IR interferometry. The correlated flux is a factor of $3$-$4$ times fainter than the VLT/VISIR total flux measurement. The observations suggest that most of the mid-IR emission has its origin on spatial scales between $10$ and $80\, \rm{pc}$ ($40$-$340\, \rm{mas}$). A composite scenario where the star formation component dominates over the AGN is favoured by the diagnostics based on ratios of IR fine-structure emission lines, the shape of the IR continuum, and the PAH and silicate bands.

Conclusions: A composite AGN-starburst scenario is able to explain both the mid-IR brightness distribution and the IR spectral properties observed in the nucleus of IC 3639. The nuclear starburst would dominate the mid-IR emission and the ionisation of low-excitation lines (e.g. [NeII]$_{12.8 \rm{\mu m}}$) with a net contribution of $\sim 70\%$. The AGN accounts for the remaining $\sim 30\%$ of the mid-IR flux, ascribed to the unresolved component in the MIDI observations, and the ionisation of high-excitation lines (e.g. [NeV]$_{14.3 \rm{\mu m}}$ and [OIV]$_{25.9 \rm{\mu m}}$).

Text
1711.01268 - Accepted Manuscript

Accepted/In Press date: 3 November 2017
e-pub ahead of print date: 13 November 2017

Identifiers

Local EPrints ID: 415587
URI: http://eprints.soton.ac.uk/id/eprint/415587
ISSN: 0004-6361
PURE UUID: 5b114313-bec8-4ba4-b7d0-1d2990a5d2c2
ORCID for P. Gandhi: orcid.org/0000-0003-3105-2615

Catalogue record

Date deposited: 15 Nov 2017 17:30

Contributors

Author: J.A. Fernandez-Ontiveros
Author: K.R.W. Tristram
Author: S. Hönig
Author: P. Gandhi
Author: G. Weigelt