Sasmirala Individual Information for NGC 3227

Description

NGC 3227 is a low-inclination barred spiral galaxy at a redshift of z = 0.0039 (D ~ 22.1 Mpc) interacting with NGC 3226. It hosts a circum-nuclear starburst and a well-studied variable Sy 1.5 nucleus [veron-cetty_catalogue_2010] that belongs to the nine-month BAT AGN sample. In addition, NGC 3227 possesses a complex extended NLR with [O III] emission extending to the north-east (PA~ 30^∘), which does not align with the double lobe radio emission along a PA~-10^∘ [mundell_anisotropic_1995]. Furthermore, the nuclear Hα emission extends along a PA~ 65^∘ [gonzalez_delgado_circumnuclear_1997]. The first MIR observations of NGC 3227 were carried out by [kleinmann_infrared_1970] and followed by many others using bolometers [rieke_infrared_1972, rieke_infrared_1978, lebofsky_extinction_1979, cutri_statistical_1985, devereux_infrared_1987, ward_continuum_1987, wright_recent_1988]. Apart from IRAS, also ISO observations are available [perez_garcia_mid-_1998, clavel_2.5-11_2000, domingue_multiwavelength_2003, ramos_almeida_mid-infrared_2007]. The first subarcsecond N-band imaging of the nuclear region was performed with Palomar 5 m/MIRLIN in 1999 by [gorjian_10_2004], where a compact MIR nucleus was detected. The Spitzer/IRAC and MIPS images reveal S-shaped host emission extending from the dominating compact nucleus. Our nuclear IRAC 5.8 μm flux agrees with [gallimore_infrared_2010], while the IRAC 8.0 μm flux is significantly lower but in agreement with the Spitzer/IRS LR spectrum. The latter exhibits prominent PAH features, forbidden emission lines and a red spectral slope in νF_ν-space, while the presence of silicate features is uncertain (see also [wu_spitzer/irs_2009, gallimore_infrared_2010]). The arcsecond-scale MIR emission of NGC 3227 is thus severely affected or even dominated by star formation. The nuclear region was observed with Michelle in the N’ filter in 2006 [ramos_almeida_infrared_2009], and with VISIR in four N and one Q-band filter throughout 2006, 2008 and 2010 (partly published in [honig_dusty_2010-1]). A compact MIR nucleus was detected in all images, while the deepest image (N’) shows faint elliptically extended emission along the host major axis surrounding the nucleus (PA~-10^∘; major axis diameter ~ 3.5arcsec ~ 0.4 kpc). The nucleus itself appears marginally resolved but not significantly elongated (FWHM ~ 15% larger than standard star) in all cases except the ARIII and N’ images, the latter of which was taken in substandard MIR seeing conditions judged from the standard star FWHM. Thus, we classify this object as extended and measure only the unresolved nuclear component, which is on average ~ 50% lower than the Spitzer spectrophotometry and ~ 30% lower than the VISIR LR N-band spectrum presented in [honig_dusty_2010-1]. The latter is in turn consistent with our total nuclear fluxes and exhibits on average ~ 30% lower fluxes than the IRS spectrum. The fact that the VISIR spectrum extracted from the central ~ 70 pc shows still PAH emission indicates the presence of star formation on these scales, which is consistent with the findings of [rodriguez-ardila_hidden_2003] and [davies_star-forming_2006]. In addition, the VISIR spectrum appears to show silicate 10 μm emission as expected for an unobscured AGN. Finally, possible N-band flux variations of NGC 3227 are \⪅14% in the last ~ 35 years from comparison of the historical and the recent data. This is well within the expected dispersion only due to different filters, measurement methods and the feature-rich N-band SED. Interestingly, the nucleus of NGC 3227 was not detected during MIR interferometric observations with MIDI on a short baseline. This indicates that the nuclear MIR emission is dominated by very extended structures at milliarcsecond scales [burtscher_diversity_2013].

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Images

SEDs

MIR SED. The description of the symbols in all the SED plots (where present) is the following: Grey crosses and solid lines mark the Spitzer/IRAC, MIPS and IRS data. The colour coding of the other symbols is as follows: green for COMICS, magenta for Michelle, blue for T-ReCS and red for VISIR data. Darker-coloured solid lines mark spectra of the corresponding instrument. The black filled circles mark the nuclear 12 and 18 micron continuum emission estimate from the data (where present). The ticks on the top axis mark positions of common MIR emission lines, while the light grey horizontal bars mark wavelength ranges affected by the silicate 10 and 18 micron features.