* Astronomy

Title: Interferometric CO(3-2) Observations toward the Central Region of NGC 1068
Authors: Mengchun Tsai (1), Chorng-Yuan Hwang (1), Satoki Matsu****a (2 and 3), Andrew J. Baker (4), Daniel Espada (5 and 6 and 2) ((1) Institute of Astronomy, National Central University, Taiwan, R.O.C., (2) Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan, R.O.C., (3) Academia Sinica Institute of Astronomy and Astrophysics, Joint ALMA Office, Las Condes, Santiago, Chile, (4) Department of Physics and Astronomy, Rutgers, the State University of New Jersey, Piscataway, NJ, (5) Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain, (6) Harvard-Smithsonian Centre for Astrophysics, Cambridge, MA)

We present CO(3-2) interferometric observations of the central region of the Seyfert 2 galaxy NGC 1068 using the Submillimeter Array, together with CO(1-0) data taken with the Owens Valley Radio Observatory Millimeter Array. Both the CO(3-2) and CO(1-0) emission lines are mainly distributed within ~5 arcsec of the nucleus and along the spiral arms, but the intensity distributions show differences; the CO(3-2) map peaks in the nucleus, while the CO(1-0) emission is mainly located along the spiral arms. The CO(3-2)/CO(1-0) ratio is about 3.1 in the nucleus, which is four times as large as the average line ratio in the spiral arms, suggesting that the molecular gas there must be affected by the radiation arising from the AGN. On the other hand, the line ratios in the spiral arms vary over a wide range from 0.24 to 2.34 with a average value around 0.75, which is similar to the line ratios of star-formation regions, indicating that the molecular gas is affected by star formation. Besides, we see a tight correlation between CO(3-2)/(1-0) ratios in the spiral arms and star formation rate surface densities derived from Spitzer 8 {\mu}m dust flux densities. We also compare the CO(3-2)/(1-0) ratio and the star formation rate at different positions within the spiral arms; both are found to decrease as the radius from the nucleus increases.

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Astronomers from the University of Georgia have discovered a startling absence of hot gas being given off by the "disk" of the spiral galaxy NGC 1068. The galaxy is younger than the Milky Way and could thus offer insights into the formation of our own galaxy.

"In many ways, NGC 1068 is a window on our past. What we've found is that the process of heating gas in this galaxy is more complex that we had expected" - Robin Shelton, leader of the research.

The researchers used the FUSE satellite to plot out the emission of ionised oxygen-6 (O VI) and see how much hot gas was in the disk of 1068.

"Oxygen-6 is a tracer of hot gas, so examining it tells us a lot about how much gas is in these galaxies" - Robin Shelton.

The research was presented this week at the 208th Annual Meeting of the American Astronomical Society in Calgary, Alberta, Canada. Also assisting in the research, which was presented in a poster session, was UGA doctoral student Shinya Miyake.

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The Seyfert galaxy NGC 1068 (M-77) is located about 60 million light years away in the constellation Cetus, making it the closest and best-studied example of an active galactic nucleus (AGN). An AGN emits copious amounts of energy from its nucleus, from very energetic x-rays to long wavelength radio waves. In addition to the intense radiation field, the nucleus of NGC 1068 contains a large amount of highly ionised and fast moving gas. In fact, some of the gas has been measured moving at up to several thousand kilometres per second.
The accepted view is that the high-energy photons and high speed of the gases are generated in the vicinity of a massive black hole at the very centre of the galaxy which is thought to have a mass of several million times that of the Sun. Studying the properties of gas and hot dust in such environment is a powerful approach to understanding the nature and evolution of massive black holes.


Position(2000): RA: 02h 42m 40.2s Dec: -00°00'48"

Two upcoming papers based on optical and mid-infrared data from the Gemini North telescope focus on the dynamic core of the magnitude 9.6 spiral galaxy NGC 1068. Described here are summaries of these papers.

Mid-infrared View of the Environment Surrounding NGC 1068’s Central Black Hole

Rachel Mason (Cerro Tololo Inter-American Observatory, NOAO) and her United States/Gemini staff team used MICHELLE, the mid-infrared imager and spectrometer at the 8-meter Gemini North telescope, to obtain deep 10 micron spectra of the nucleus and central ionisation cones of NGC 1068. The superb spatial resolution of the MICHELLE spectra, ~0.4 arcseconds or 30 parsecs at NGC 1068, let the team investigate the close environment of the central back hole on much finer scales than previous work. This allowed Mason et al. to discover that the mid-infrared emission from NGC 1068 originates in two distinct components:

1. Emission from the central region (within a diameter of 0.4 arcseconds) is dominated by the infrared-bright obscuring torus. This region is unresolved in the Gemini data, which is consistent with the compact (~3 parsec) size determined by mid-infrared interferometry.

2. At larger scales, the mid-infrared flux is dominated by diffuse emission from the AGN-heated dust within the ionisation cones. Since the areas within the ionisation cones are relatively devoid of material, they have a direct line of sight to the black hole itself. This means that the radiation emitted by the black hole can directly heat the dust present along the inner walls of the cones. The dust absorbs the high-energy photons from the central engine and then re-radiates them in the mid-infrared.

The most striking aspect of the mid-infrared data is the variation in the shape of the spectra (slope of the continuum and strength of the silicate feature and fine structure line fluxes) over small distances. There is significant structure in the dust in the circumnuclear regions even on subarcsecond scales. The 9.7-micron silicate feature appears to be present in the cone.

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Optical probing of the jet of gas and of stellar velocities

Joris Gerssen (University of Durham) and his United Kingdom/Gemini staff team used the GMOS-North integral field unit (IFU) to map the velocities of the ionised gas and stars in the central region of NGC 1068 at optical wavelengths. The resulting datacube is rich in complex features, particularly in the morphology of the (O III) doublet and the H-beta line. To interpret the observed structure in the lines the authors constructed an atlas of velocity components by Gaussian fitting of each line.


The top panels (each covering an area of 10.3 x 7.3 arcseconds) show a series of one-Angstrom wide wavelength slices through the data across the (OIII) 500.7-nanometer line of doubly ionised oxygen. Across this line the central morphology of NGC 1068 develops various subcomponents corresponding to different velocities. Lower panels show a similar “movie” across the H-beta 486.1 nanometer line of hydrogen.

The atlas contains many features that cannot be readily associated with physical structures in the nucleus; however, some components are likely associated with the expected biconic outflow. Both the H-beta 468.1 nanometer line of hydrogen and the (OIII) 500.7 nanometer line of ionised oxygen are very broad, indicative of velocities between 1000 to 2000 kilometres per second. Centroids of the radial velocity of the gas range from –1000 to 0 kilometres per second over the spatial extent of the jet . Both the gas and stellar data present a very rich and complex morphology. Indeed, a third set of distinct features found in the datacube are suggestive of distinct high-velocity gas flows and a large disk-like structure.


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Additionally the stellar kinematics of the nuclear region were mapped through the detection of the Mg b absorption line feature in the GMOS spectra. The resulting position angle and kinematic axis in the GMOS velocity map is consistent with previously published data on the motions of carbon monoxide in the same region.

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