High-resolution Spectropolarimetric Observations of the Optical Filaments surrounding NGC 1275 with ESPaDOnS

Abstract We analyze archival high-spectral-resolution ESPaDOnS spectropolarimetric observations ( R = λ /Δ λ = 68000) of three targeted locations within the filamentary nebula surrounding NGC 1275. We present here the analysis of the main filaments' emission lines, namely, [N ii ] λ 6584, H α , and [N ii ] λ 6548, across our three pointings displaying clear detectable emission, with one also showing an additional [S ii ] λ 6716 and [S ii ] λ 6731 emission line doublet. Using a Markov Chain Monte Carlo (MCMC) algorithm and thanks to the exceptionally high spectral resolution of the observations, we resolve for the first time each of the emission lines within one of the pointings into a set of three emission components with a remarkable velocity dispersion contrast ( σ 1 ∼ 25 km s −1 , σ 2 ∼ 90 km s −1 , and σ 3 ∼ 208 km s −1 ). We also perform flux ratios of the three detected emission components, which reveal differences in electron density and ionization sources. Consequently, the ESPaDOnS observations appear to reveal for the first time the overlap of an outer quiescent filament and a central turbulent filament likely affected by the active galactic nucleus (AGN) activity at a distance of ∼6 . ″ 8 (∼2.5 kpc) from the central brightest cluster galaxy (BCG). Finally, ESPaDOnS polarimetric data of one of the pointing allow us to confirm an average linear polarization degree of ∼0.15%–0.14% and an angle of polarization of 5 . ° 3 ± 25 . ° 7 for the optical emission of the filaments, as well as polarization dips associated with the H α emission line and its multiple emission components. We interpret these features and measurements as tentative polarization due to dust scattering.