* Astronomy

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RE: NGC1097

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NASA's Spitzer Space Telescope has imaged a wild creature of the dark - a coiled galaxy with an eye-like object at its center.
The galaxy, called NGC 1097, is located 50 million light-years away. It is spiral-shaped like our Milky Way, with long, spindly arms of stars. The "eye" at the center of the galaxy is actually a monstrous black hole surrounded by a ring of stars. In this colour-coded infrared view from Spitzer, the area around the invisible black hole is blue and the ring of stars, white.
The black hole is huge, about 100 million times the mass of our sun, and is feeding off gas and dust along with the occasional unlucky star. Our Milky Way's central black hole is tame by comparison, with a mass of a few million suns.

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Position (2000): RA 02h 46m 19.00s, Dec -30° 16' 29.00"

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How does matter spiral its way to the centre of a galaxy and into the mouth of a supermassive black hole?

A new study provides the best glimpse yet at the death spiral of material as it descends into the core of a galaxy hosting a large black hole. The study predicts that, barring obstructions, the galactic debris will take about 200,000 years to make a one-way trip through the inner regions of the galaxy and into oblivion.

An international team of scientists led by Kambiz Fathi at Rochester Institute of Technology, together with astronomers in Brazil, Italy, and Chile, measured the internal motions of gas surrounding the nucleus of the active galaxy NGC1097. Using sophisticated spectroscopic techniques with the Gemini South Telescope in Chile, the team measured the spiral motions of gas streaming inside the nuclear ring. Using sophisticated spectroscopic techniques with the Gemini South Telescope in Chile, the team measured the motion of matter streaming from the galaxy's spiral arms to the heart of the galaxy.
The observations zoomed in 10 times closer to the supermassive black hole than ever before, to see clouds of material within 10 light-years of the galactic core. Previous observations of this type of environment have detected gas clouds located between 100 and 1,000 light-years from the galaxy’s nucleus.

Fathi presented the team’s results at the 207th meeting of the American Astronomical Society January 9 , 2006, in Washington, D.C, US.

"It is the first time anyone has been able to follow gas this close to the supermassive black hole in the centre of another galaxy. The work of our team confirms the main theories that have never been observationally confirmed at this level. We have been able to show that it is possible to measure these velocities down to these scales" - Kambiz Fathi, postdoctoral scholar at RIT

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Position(2000): RA 02h 46m 18.9s Dec -30° 16' 21"
NGC1097 is a medium sized bared galaxy in centre of Fornax with a diameter of 10 arc minutes and a brightness of 10th magnitude. The bar is stretched in NW to SE, and very indistinct two arms are coiled up from tips of the bar structure.

Modelling the galaxy’s spectra revealed the dynamic shifts in the gas and showed the spiral arms pulling gas from about a thousand light-years out from the centre to the nucleus at 52 kilometres per second. Previous imaging by the Hubble Space Telescope and the European Southern Observatory Very Large Telescope has shown structure inside the central ring of NGC1097. The Gemini data complement this with a velocity map of the gas inside the ring.

"When we extrapolate our last data points, about 30 light-years from the black hole, this is where we find that it would take about 200,000 years for the gas to travel the last leg of its one-way journey to the supermassive black hole" - Kambiz Fathi.

The team measured the streaming motions toward the black hole by using two-dimensional spectroscopy to capture spectral data at several thousand points surrounding the nucleus of the galaxy.

"The resolution of this data is unprecedented when you look at how we were able to isolate so many different points around the nucleus of this galaxy and acquire a spectrum for each point at once. This paints an incredibly detailed picture of the region around the black hole and gives us a new glimpse at something we could only imagine before" - Thaisa Storchi Bergmann, Instituto de Fisica in Brazil.

The technology that allows these types of observations is called integral field spectroscopy. It takes light from many different parts of the telescope’s field simultaneously and splits the light from each region into a rainbow or spectrum of light.

"This allows astronomers to do in 30 minutes what would have taken four nights a decade ago" - Kambiz Fathi.

NGC1097 is located about 47 million light-years away in the southern constellation Fornax.
This work used data from the Gemini Observatory’s Multi-Object Spectrograph integral field unit and the Hubble Space Telescope’s high resolution Advanced Camera for Surveys.
Project collaborators include Thaisa Storchi-Bergmann, UFRGS, Brazil; David Axon and Andrew Robinson, RIT, USA; Alessandro Capetti, INAF-Turin, Italy, Alessandro Marconi, INAF-Florence, Italy; Rogemar Riffel, UFRGS, Brazil, and Claudia Winge, Gemini Observatory, Chile.
The results of this study will appear in an upcoming issue of The Astrophysical Journal Letters.

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Near-infrared images of the active galaxy NGC 1097, obtained with the NACO adaptive optics instrument on ESO's Very Large Telescope, disclose with unprecedented detail a complex central network of filamentary structure spiralling down to the centre of the galaxy. These observations provide astronomers with new insights on how super-massive black holes lurking inside galaxies get fed.

"This is possibly the first time that a detailed view of the channelling process of matter, from the main part of the galaxy down to the very end in the nucleus is released" - Almudena Prieto (Max-Planck Institute, Heidelberg, Germany), lead author of the paper describing these results.

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Credit ESO

Located at a distance of about 45 million light-years in the southern constellation Fornax (the Furnace), NGC 1097 is a relatively bright, barred spiral galaxy seen face-on. At magnitude 9.5, and thus just 25 times fainter than the faintest object that can be seen with the unaided eye, it appears in small telescopes as a bright, circular disc.
NGC 1097 is a very moderate example of an Active Galactic Nucleus (AGN), whose emission is thought to arise from matter (gas and stars) falling into oblivion in a central black hole. However, NGC 1097 possesses a comparatively faint nucleus only, and the black hole in its centre must be on a very strict "diet": only a small amount of gas and stars is apparently being swallowed by the black hole at any given moment.

Astronomers have been trying to understand for a long time how the matter is "gulped" down towards the black hole. Watching directly the feeding process requires very high spatial resolution at the centre of galaxies. This can be achieved by means of interferometry as was done with the VLTI MIDI instrument on the central parts of another AGN, NGC 1068, or with adaptive optics.
Thus, astronomers obtained images of NGC 1097 with the adaptive optics NACO instrument attached to Yepun, the fourth Unit Telescope of ESO's VLT. These new images probe with unprecedented detail the presence and extent of material in the very proximity of the nucleus. The resolution achieved with the images is about 0.15 arcsecond, corresponding to about 30 light-years across. For comparison, this is only 8 times the distance between the Sun and its nearest star, Proxima Centauri.

NGC 1097 has a very strong bar and a prominent star-forming ring inside it. Interior to the ring, a secondary bar crosses the nucleus almost perpendicular to the primary bar. The newly released NACO near-infrared images show in addition more than 300 star-forming regions, a factor four larger than previously known from Hubble Space Telescope images.
These "HII regions" can be seen as white spots in the photo. At the centre of the ring, a moderate active nucleus is located. Details from the nucleus and its immediate surroundings are however outshone by the overwhelming stellar light of the galaxy seen as the bright diffuse emission all over the image.
The astronomers therefore applied a masking technique that allowed them to suppress the stellar light. This unveils a bright nucleus at the centre, but mostly a complex central network of filamentary structures spiralling down to the centre.

"Our analysis of the VLT/NACO images of NGC 1097 shows that these filaments end up at the very centre of the galaxy", - Juha Reunanen, co-author, ESO.

"This network closely resembles those seen in computer models. The nuclear filaments revealed in the NACO images are the tracers of cold dust and gas being channelled towards the centre to eventually ignite the AGN." - Witold Maciejewski, co-worker, University of Oxford, UK.

The astronomers also note that the curling of the spiral pattern in the innermost 300 light-years seem indeed to confirm the presence of a super-massive black hole in the centre of NGC 1097. Such a black hole in the centre of a galaxy causes the nuclear spiral to wind up as it approaches the centre, while in its absence the spiral would be unwinding as it moves closer to the centre.

An image of NGC 1097 and its small companion, NGC 1097A, was taken in December 2004, in the presence of Chilean President Lagos with the VIMOS instrument on ESO's Very Large Telescope (VLT).

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