MUSE discovers perpendicular arcs in the inner filament of Centaurus A

Abstract

Context. Evidence of active galactic nuclei (AGN) interaction with the intergalactic medium is observed in some galaxies and many cool core clusters. Radio jets are suspected to dig large cavities into the surrounding gas. In most cases, very large optical filaments (several kpc) are also seen all around the central galaxy. The origin of these filaments is still not understood. Star-forming regions are sometimes observed inside the filaments and are interpreted as evidence of positive feedback (AGN-triggered star formation). Aims. Centaurus A is a very nearby galaxy with huge optical filaments aligned with the AGN radio-jet direction. Here, we searched for line ratio variations along the filaments, kinematic evidence of shock-broadend line widths, and large-scale dynamical structures. Methods. We observed a 1 × 1 region around the so-called inner filament of . MUSE shows that the filaments are made of clumpy structures inside a more diffuse medium aligned with the radio-jet axis. We find evidence of shocked shells surrounding the star-forming clumps from the line profiles, suggesting that the star formation is induced by shocks. The clump line ratios are best explained by a composite of shocks and star formation illuminated by a radiation cone from the AGN. (ii) We also report a previously undetected large arc-like structure: three streams running perpendicular to the main filament; they are kinematically, morphologically, and excitationally distinct. The clear difference in the excitation of the arcs and clumps suggests that the arcs are very likely located outside of the radiation cone and match the position of the filament only in projection. The three arcs are thus most consistent with neutral material swept along by a backflow of the jet plasma from the AGN outburst that is ionised through a difuse radiation field with a low-ionisation parameter that continues to excite gas away from the radiation cone.

The outer filament of Centaurus A as seen by MUSE

“…It is worth noting that we find similarities with the results recently obtained (also using MUSE) for the inner filament of Cen A (Hamer et al 2015). Indeed, both the inner and the outer filaments contain a well-defined linear knotty plus a more diffuse structure that show different kinematics and line ratios.…”

“…Furthermore, they can place important constraints on the main parameters of the models used to simulate these interactions. Signatures of jet-ISM interactions have also been found in the nearby AGN Centaurus A (Cen A, see Rejkuba et al 2002;Oosterloo & Morganti 2005;Hamer et al 2015;Santoro et al 2015). This led us to choose this galaxy as a target for a detailed study of the jet-ISM interaction phenomenon.…”

The rise and fall of star formation in z ∼ 0.2 merging galaxy clusters

“…Werner et al (2010) found Hα filaments in the immediate downstream area from the jet-termination shock front in M87. Crockett et al (2012) and Hamer et al (2014) found evidence for shock-induced shells around star-forming clumps. The locations of these shells along the optical filaments connecting the two radio jets in the Centaurus A galaxy is consistent with material being swept along the back flow of the jet and ionised through shocks.…”

Star formation efficiency along the radio jet in Centaurus A

“…Optical observations have been carried on both the inner and outer filaments with MUSE on the VLT during the science verification period on 25 June 2014 (Hamer et al 2015 for the inner filament, Santoro et al 2015b for the outer filament). Hamer et al (2015) made three pointings with a 3 dither and 90…”