A mid-infrared view of the inner parsecs of the Seyfert galaxy Mrk 1066 using CanariCam/GTC

Abstract

We present mid-infrared (MIR) imaging and spectroscopic data of the Seyfert 2 galaxy Mrk 1066 obtained with CanariCam (CC) on the 10.4 m Gran Telescopio CANARIAS (GTC). The galaxy was observed in imaging mode with an angular resolution of 0.24 ′′ (54 pc) in the Si-2 filter (8.7 µm). The image reveals a series of star-forming knots within the central ∼400 pc, after subtracting the dominant active galactic nucleus (AGN) component. We also subtracted this AGN unresolved component from the 8-13 µm spectra of the knots and the nucleus, and measured equivalent widths (EWs) of the 11.3 µm Polycyclic Aromatic Hydrocarbon (PAH) feature which are typical of pure starburst galaxies. This EW is larger in the nucleus than in the knots, confirming that, at least in the case of Mrk 1066, the AGN dilutes, rather than destroys, the molecules responsible for the 11.3 µm PAH emission. By comparing the nuclear GTC/CC spectrum with the Spitzer /IRS spectrum of the galaxy, we find that the AGN component that dominates the continuum emission at λ <15 µm on scales of ∼60 pc (90-100%) decreases to 35-50% when the emission of the central ∼830 pc is considered. On the other hand, the AGN contribution dominates the 15-25 µm emission (75%) on the scales probed by Spitzer /IRS. We reproduced the nuclear infrared emission of the galaxy with clumpy torus models, and derived a torus gas mass of 2×10 5 M ⊙ , contained in a clumpy structure of ∼2 pc radius and with a column density compatible with Mrk 1066 being a Compton-thick candidate, in agreement with X-ray observations. We find a good match between the MIR morphology of Mrk 1066 and the extended Paβ, Brγ and [O III]λ5007 emission. This coincidence implies that the 8.7 µm emission is probing star formation, dust in the narrow-line region, and the oval structure previously detected in the near-infrared. On the other hand, the Chandra soft X-ray morphology does not match any of the previous, contrary to what it is generally assumed for Seyfert galaxies. A thermal origin for the soft X-ray emission, rather than AGN photoionization, is suggested by the different data analyzed here.

Self-consistent two-phase AGN torus models

“…It is now recognized that smooth and clumpy torus models (Feltre et al 2012) can reproduce the whole range of features that are observed using Spitzer spectroscopy (Siebenmorgen et al 2005;Hao et al 2005;Spoon et al 2007;Schweitzer et al 2008;Mendoza-Castrejón et al 2015;Hatziminaoglou et al 2015) as well as high spatial resolution ground-based data Alonso-Herrero et al 2011;González-Martín et al 2013;Esquej et al 2014;Ramos Almeida et al 2014a). Another challenge for these models is trying to explain the spatial extent of the mid-IR emission which also looked puzzling initially.…”

“…At ∼20 pc resolution Ruschel-Dutra et al (2014) detected the silicate feature at 9.7 µm in absorption for the Seyfert 2 NGC 1386, and in emission for the Seyfert 1 NGC 7213 with a peak wavelength beyond 10.5 µm. Ramos Almeida et al (2014a) compared the nuclear mid-IR spectrum with the Spitzer spectrum and find that the AGN in Mrk1066 dominates the continuum emission at λ < 15 µm on scales of ∼60 pc (90−100%), whereas this contribution decreases to below 50% when the emission of the central ∼830 pc is considered.…”

The nuclear and extended mid-infrared emission of Seyfert galaxies

“…Prominent features in the MIR spectrum of AGN are the 9.7 µm silicate feature, and the Polycyclic Aromatic Hydrocarbon (PAH) emission bands, although the latter can be diluted by the bright AGN continuum (see e.g. Esquej et al 2014;Alonso-Herrero et al 2014;Ramos Almeida et al 2014;García-Bernete et al 2015). The PAH features are often used as indicators of the star formation rate (SFR) of galaxies (see e.g.…”

The nuclear and integrated far-infrared emission of nearby Seyfert galaxies

“…The only discrepant galaxy is the Seyfert 2 galaxy Mrk 1066, which has a high total fν (70 µm)/fν (160 µm) flux ratio, but also a high value of the EW of the PAHs. AlonsoHerrero et al (2014) and Ramos Almeida et al (2014) have shown, based on high angular resolution (0.3arcsec) MIR spectroscopy, that this galaxy has a strong nuclear starburst including the central ∼ 60 pc region. This would explain the elevated FIR colours of this galaxy.…”

“…This probably suggests that the elevated fν (70 µm)/fν (160 µm) flux ratios are due to strong star formation rather than AGN dominated fluxes at 70 µm (see Ramos Almeida et al 2014, for a detailed discussion of Mrk 1066).…”