[CII] Emission from PDRs and Jet-related Shocks in the Nearby Seyfert Galaxy NGC 4258 with SOFIA
Event date
Phil Appleton/Dario Fadda
IPAC/SOFIA Science Center
Event Type

We present the [CII] 157.7μm map of the NGC 4258 (M106) galaxy obtained with the Far Infrared Field-Imaging Line Spectrometer (FIFI-LS) spectrometer onboard SOFIA. M106 contains an active nucleus classified as type 1.9 Seyfert with a warped inner rotating disk of water-vapor masers which allowed for the first high accuracy measurements of the mass of a supermassive black hole in any galaxy.

A relativistic jet is thought to be responsible for anomalous radio-continuum spiral arms, which appear several kiloparsecs from the center, and extend outwards through the outer disk. These arms do not correlate with the galaxy's underlying stellar spiral structure, and their presence suggest that in the past, the jet has strongly interacted with the galaxy's outer disk, exciting synchrotron radiation. Since that time, a new burst of activity seems to have occurred, creating a compact jet at the core of the galaxy, and two radio hotspots further out associated with optical "bow-shocks." The position angle of this new "active" jet is different from that needed to excite the outer radio arms, presumably because the jet has precessed, perhaps as a result of precession of the axis of the inner warped accretion disk.

Our observations reveal three main sources of [CII] emission: two associated with large regions of gas at the ends of the active jet, and a third minor axis filament associated with linear clumps of star formation and dust seen in Hubble Space Telescope images offset from the nucleus. We combine the SOFIA observations with previous Spitzer mid-IR, Chandra X-ray and Very Large Array radio observations to explore the nature of the detected [CII] emission. In regions along the northern active jet, we see a significant deficiency in the [CII]/FIR ratio, and higher ratios near the ends of the jet. This implies that the jet has changed the conditions of the gas along its length. In several places near the jet, the [CII] emission shows very broad lines, suggestive of enhanced turbulence. Additionally, the minor-axis filament we discovered may represent gas in-falling towards the nucleus perpendicular to the jet. The results provide clues about how radio jets in active galaxies can influence the star formation properties of their host galaxies.