Near- to mid-infrared imaging and spectroscopy of two buried AGNs of the nearby merging galaxy NGC 6240 with Subaru/IRCS+AO and GTC/CanariCam

Abstract

We report near-infrared K', L', and M' band imaging observations of the nearby merging galaxy NGC 6240 with the Infrared Camera and Spectrograph on the Subaru telescope. The observations were performed with the assistance of the Subaru Adaptive Optics System, and the achieved spatial resolutions were around 0.10-0.20 ′′ . We also obtained new mid-infrared imaging in the Si-2 filter band (8.7 µm) and N-band (7.5-13 µm) spectroscopy of this galaxy with the CanariCam on the Gran Telescopio Canarias with a spatial resolution of 0.4-0.5 ′′ . In the K' band image the two nuclei of the galaxy each show a double-peak suggesting the complex geometry of the source, while the L', M', and Si-2 band images show single compact structures in each of the two nuclei. Assuming 1 that the center core observed at wavelengths longer than 3.8 µm is associated with dust heated by the buried AGN, we re-evaluated the spectral energy distributions (SEDs) of the southern nucleus from 2 to 30 µm with the additional literature values, and performed the SED+spectroscopy fitting using the clumpy torus models of Nenkova et al. (2008) and a Bayesian fitting approach. The model fit suggests that the high covering factor torus emission in the southern nucleus is also obscured by foreground dust in the host galaxy. The estimated AGN bolometric luminosity of the southern nucleus, L bol (AGN) ∼ 1 × 10 45 erg·s −1 , accounts for approximately 40% of the whole luminosity of the system.

A deep look at the nuclear region of UGC 5101 through high angular resolution mid-IR data with GTC/CanariCam

“…All these values are also consistent with the parameters, including the high covering factors, derived in other LIRGs and ULIRGs hosting deeply embedded AGN, e.g. Arp 299A (Alonso-Herrero et al 2013), NGC 6240 (Mori et al 2014), and Mrk 1066 (Ramos Almeida et al 2014b).…”

“…The high value of the foreground extinction is similar to results for other deeply embedded AGN in local LIRGs and ULIRGs (see e.g. Alonso-Herrero et al 2013 andMori et al 2014). However, the observed unresolved near-IR emission of UGC 5101 is well above the fitted CLUMPY models.…”

“…screen might not be the appropriate model for active nuclei with very deep silicate features (e.g. Mori et al 2014;Merlo et al 2014) and spherically symmetric smooth models may be more appropriate for deeply embedded objects (see Levenson et al 2007;Alonso-Herrero et al 2013).…”

Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR

“…Nevertheless the NuSTAR, BeppoSAX PDS, and Swift BAT hard X-ray variability would imply that the northern nucleus should be as bright as, or brighter than the southern nucleus in some periods. This is difficult to reconcile with the evidence that over the last ∼15 yr all the data suggest that the southern nucleus has been brighter than the northern as indicated by the Chandra data (Komossa et al 2003;Shu et al 2011;Wang et al 2014) and 3−5 μm luminosity (see, e.g., Mori et al 2014;Risaliti et al 2006). Therefore, the most plausible hypothesis is that the hard X-ray variability is mainly due to variations of the transmitted component of the southern nucleus.…”

“…The observed 0.1−10 keV luminosities of the two nuclei are 1.9 × 10 42 erg s −1 and 0.7 × 10 42 erg s −1 (Komossa et al 2003). The southern nucleus is also brighter based on 3−5 μm luminosity (see, e.g., Mori et al 2014;Risaliti et al 2006).…”