NGC 1097 Galaxy Jets: They Aren’t Just For Breakfast Anymore

by Tammy Plotner on March 31, 2010

Some 45 million light years away in the direction of the constellation of Fornax, a supermassive black hole is consuming its breakfast… and it doesn’t want just toast and tea. It has a hungry belly and the energetic area surrounding the central black hole is super-heated through its interaction with dust, gas, and other matter. Oh, dear. What can that matter be? Try a smaller galaxy that dared to get too close…

NGC1097 belongs a special class of galaxies called Seyfert – those that produce a specific type of spectrum and are thought to contain active galactic nuclei with super massive black holes. What makes this galaxy even more interesting is the very faint optical “jets” that may be the remnants of a smaller galaxy interaction many years ago.

Like a lingering smear of marmalade or a trail of toast crumbs, these optical jets leave visual and photographic clues as to their origin. In a deep search for neutral hydrogen gas associated with the faint optical “jets” of NGC 1097, researchers using the Very Large Array detected an H I source coincident with a small edge-on spiral or irregular galaxy (NGC 1097B) 12′ southwest of NGC 1097, situated between two jets. In addition, two other sources are noted – but not associated with the optical jets themselves. Click here for full size color image.

Could it be bacon?

According to James Higdon and John Wallin; “The jets’ radio-X-ray spectral energy distribution is most consistent with starlight. However, from their morphology, optical/near-infrared colors, and lack of H I, we argue that the jets are not tidal tails drawn out of NGC 1097’s disk or stars stripped from the elliptical companion NGC 1097A. We also reject in situ star formation in ancient radio jets as this requires essentially 100% conversion of gas into stars on large scales. Instead, we conclude that the jets represent the captured remains of a disrupted dwarf galaxy that passed through the inner few kiloparsecs of NGC 1097’s disk.

We present N-body simulations of such an encounter that reproduce the essential features of NGC 1097’s jets: A long and narrow “X”-shaped morphology centered near the spiral’s nucleus, right-angle bends, and no discernible dwarf galaxy remnant. A series of jetlike distributions are formed, with the earliest appearing ~1.4 Gyr after impact. Well-defined X shapes form only when the more massive galaxy has a strong disk component. Ram-pressure stripping of the dwarf’s interstellar medium would be expected to occur while passing through NGC 1097’s disk, accounting for the jets’ lack of H I and H II. The remnants’ (B-V) color would still agree with observations even after ~3 Gyr of passive evolution, provided the cannibalized dwarf was low-metallicity and dominated by young stars at impact.”

Bu that’s not all that’s on the table…

“The nucleus of the nearby galaxy NGC 1097 is known to host a young, compact (r < 9 pc) nuclear star cluster, as well as a low-luminosity active galactic nucleus (AGN). It has been suggested both that the nuclear stellar cluster is associated with a dusty torus and that low-luminosity AGNs like NGC 1097 do not have the torus predicted by the unified model of AGNs. To investigate these contradictory possibilities we have acquired Gemini/T-ReCS 11.7 and 18.3 ?m images of the central few hundred parsecs of this galaxy at <45 pc angular resolution, in which the nucleus and spectacular, kiloparsec-scale star-forming ring are detected in both bands." says R.E. Mason (et al). "The small-scale mid-IR luminosity implies thermal emission from warm dust close to the central engine. Fitting of torus models shows that the observed mid-IR emission cannot be accounted for by dust heated by the central engine. Rather, the principal source heating the dust in this object is the nuclear star cluster itself, suggesting that the detected dust is not the torus of AGN unified schemes (although it is also possible that the dusty starburst itself could provide the obscuration invoked by the unified model). Comparison of Spitzer IRS and Gemini GNIRS spectra shows that, although PAH bands are strong in the immediate circumnuclear region of the galaxy, PAH emission is weak or absent in the central 19 pc. The lack of PAH emission can probably be explained largely by destruction/ionization of PAH molecules by hard photons from the nuclear star cluster. If NGC 1097 is typical, PAH emission bands may not be a useful tool with which to find very compact nuclear starbursts even in low-luminosity AGNs."

And starbursts as recently as 5 years ago from this early rising Seyfert are definitely on the menu...

"We report evidence of a recent burst of star formation located within 9 pc of the active nucleus of NGC 1097. The observational signatures of the starburst include UV absorption lines and continuum emission from young stars observed in a small-aperture Hubble Space Telescope spectrum." says T. Storchi-Bergmann (et al). "The importance of this finding is twofold: (1) the proximity of the starburst to the active nucleus and thus its possible association with it, and (2) its obscuration by and apparent association with a dusty absorbing medium, while the broad emission lines appear unobscured, suggesting that the starburst could be embedded in a circumnuclear torus as predicted in the unified model of active galactic nuclei."

Can I have eggs with that?

Many thanks to NorthernGalactic member, Ken Crawford for his exclusive images. Be sure to check out Ken’s webpages at Imaging Deep Sky.

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

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