* Astronomy

Title: Multi-molecule ALMA observations towards the Seyfert 1 galaxy NGC 1097
Author: S.Martin, K. Kohno, T. Izumi, M. Krips, D. S. Meier, R. Aladro, S. Matsushíta, S. Takano, J. L. Turner, D. Espada, T. Nakajima, Y. Terashima, K. Fathi, P.-Y. Hsieh, M. Imanishi, A. Lundgren, N. Nakai, E. Schinnerer, K. Sheth, T. Wiklind

The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory to explore the molecular chemistry in the presence and surroundings of an active galactic nucleus. Exploring the distribution of different molecular species allows us to understand the physical processes affecting the ISM both in the AGN vicinity as well as in the outer star forming molecular ring. We carried out 3 mm ALMA observations of HCN, HCO+, CCH, CS, HNCO, SiO, HC3N, and SO as well as the 13C isotopologues. All species were imaged over the central 2 kpc (~30") of the galaxy at a resolution of ~2.2"x1.5 (150 pc x 100 pc). HCO+ and CS appear to be slightly enhanced in the star forming ring. CCH, showing the largest variations across NGC 1097, is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO and HC3N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO+ and HCN/CS differences observed between AGN dominated and starburst galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally we claim the lower HCN/CS to be a combination of a small under-abundance of CS in AGNs together with excitation effects, where a high dense gas component (~10^6 cm^-3) may be more prominent in SB galaxies. However the most promising are the differences found among the dense gas tracers which, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well shielded gas in the disk, surrounding the dense material moderately exposed to X-ray radiation traced by HC3N. Finally SiO might be the innermost molecule in the disk structure.

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Title: Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 1097
Authors: Lien-Hsuan Lin, Hsiang-Hsu Wang, Pei-Ying Hsieh, Ronald E. Taam, Chao-Chin Yang, David C. C. Yen

NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable which is consistent with the observation in Hsieh et al. (2011). Our simulations show that the gas inflow rate is 0.17 solar masses yr^{-1} into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk.

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Hubble Eyes a Wanderer Dancing the Dance of Stars and Space

The NASA/ESA Hubble Space Telescope provides us this week with a spectacular image of the bright star-forming ring that surrounds the heart of the barred spiral galaxy NGC 1097. In this image, the larger-scale structure of the galaxy is barely visible: its comparatively dim spiral arms, which surround its heart in a loose embrace, reach out beyond the edges of this frame.
This face-on galaxy, lying 45 million light-years away from Earth in the southern constellation of Fornax (The Furnace), is particularly attractive for astronomers. NGC 1097 is a Seyfert galaxy. Lurking at the very center of the galaxy, a supermassive black hole 100 million times the mass of our sun is gradually sucking in the matter around it. The area immediately around the black hole shines powerfully with radiation coming from the material falling in.
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Title: A Study of Heating and Cooling of the ISM in NGC 1097 with Herschel-PACS and Spitzer-IRS
Authors: P. Beirao, L. Armus, G. Helou, P. N. Appleton, J.-D. T. Smith, K. V. Croxall, E. J. Murphy, D. A. Dale, B. T. Draine, M. G. Wolfire, K. M. Sandstrom, G. Aniano, A. D. Bolatto, B. Groves, B. R. Brandl, E. Schinnerer, A. F. Crocker, J. L. Hinz, H.-W. Rix, R. C. Kennicutt, D. Calzetti, A. Gil de Paz, G. Dumas, M. Galametz, K. D. Gordon, C.-N. Hao, B. Johnson, J. Koda, O. Krause, T. van der Laan, A. K. Leroy, Y. Li, S. E. Meidt, J. D. Meyer, N. Rahman, H. Roussel, M. Sauvage, S. Srinivasan, L. Vigroux, F. Walter, B. E. Warren

NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar and an active nucleus. We present a detailed study of the spatial variation of the far infrared (FIR) [CII]158um and [OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a larger fraction of ionised PAHs, but no clear correlation with [CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in the Enuc S. SED modelling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high intensity photodissociation regions (PDRs), in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the the H2 emission in the starburst ring could come from warm regions in the diffuse ISM that are heated by turbulent dissipation or shocks.

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