Nearby Galaxy Studies with the SMA

Extragalactic Astrochemistry

The large instantaneous bandwidth provided by the SMA is key for the study of the chemical composition of both nearby and distant galaxies. The SMA allows for observations of multiple transitions simultaneously such as the CO J = 3-2 and HCO+ J = 4-3 or the HCN and HCO+ J = 3-2. This is indeed a key feature as the ratio between the species CO, HCN and HCO+ are claimed to be good tracers of the leading power source in the heavily obscured galactic nuclei (Active Galactic Nucleus vs. Starburst). Thus, the ratio of these species have been measured and spatially resolved with the SMA, providing important information to test the chemical models (Krips et al., in prep.).

The chemistry in distant galaxies was started with the 1.3 mm line survey carried out with the SMA towards the UltraLuminous Infrared Galaxy prototype Arp 220 at a distance of ~80 Mpc. This is the first interferometric unbiased line survey towards an external galaxy. This project was possible thanks to the wide band receivers at the SMA and to the size of the synthesized beam perfectly matching the compact emission of this galaxy. The confusion limited survey from 202 to 242 GHz has lead to the identification of more than 40 molecular transitions of 18 different species, some of them never detected before towards this galaxy. The survey revealed the presence of a high excitation molecular component that is not detected in nearby starbursts. This galaxy is likely to become prototype of the chemistry of galaxies in the early universe (Martin et al., in prep).

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Figure 3: Composite of the 1.3 mm frequency scan carried out with the SMA between 202 and 242 GHz. The CO J=2-1 emission line dominates the spectral range and is shown in a separate box in the upper right hand side, where the velocity scale refers to the rest frequency of this transition. The calculated continuum level is represented by a continuous line. Molecular emission contributes ~28% to the overall 40 GHz measured flux (Martin et al. in prep.).

Southern Galaxies

The location of the SMA near the equator allows access to southern parts of the sky unattainable by existing millimeter-wave interferometers. Espada et al. (2009) have imaged with unprecedented resolution (6 x 2 arcsec, 100 x 30 pc) the molecular gas along the dust lane of the closest radio galaxy, Centaurus A, as traced by the CO J = 2-1 line. They resolve a large amount of molecular gas in the circumnuclear regions (r < 200 pc) in the form of a disk/torus just perpendicular to the X-ray/radio jet, which provides a direct 3D link between the active nucleus and the molecular gas. In addition, a more extended component in molecular gas is seen to be coextensive with the parallelogram structure previously observed in dust emission (Spitzer/IRAC, Quillen et al. 2006), well reproduced, in principle, by a highly inclined warped disk. However, a possible contribution of a weak bi-symmetric potential may be present, since the distribution and kinematic maps substantially deviate with respect to the warped disk model.

A legacy program called B0DEGA (Below 0 DEgree GAlaxies; Espada et al., in prep) has been carried out since 2008. This project observes the CO J = 2-1 line of ~100 IR-bright galaxies in the southern hemisphere. The lack of mm/submm interferometers in the southern hemisphere has resulted in a large sample galaxies with no previous CO interferometric observations. With the SMA able to reach declinations of less than -50 degrees, this project was conceived as a pathfinder experiment to determine detailed morphology and kinematics of these galaxies, making up for the lack of facilities south of the equator. The data from this project will give statistical significance about what are the general properties of molecular gas in galaxies. This is especially relevant since the most interesting sources could be potential candidates for future ALMA observations. A total of 35 galaxies have been successfully imaged already, and the data is currently being analyzed (Espada et al., in prep). The molecular gas in these galaxies possesses different morphologies, including asymmetries, rings and nuclear arms. Almost every galaxy in the sample possesses a circumnuclear disk in the inner 500 pc. In addition, we observe gradients of 12CO/13CO emission with radius, which is telling information about the physical conditions of the molecular gas and its possible origin.

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Figure 4: CO(2-1) distribution of 30 galaxies in the B0DEGA subsample. The field of view of each image is 66", slightly larger than the 52" HPBW of the SMA at 230 GHz. The horizontal segment on the lower left of each plot represents a 1kpc linear scale (Espada et al. in prep.).


S. Aalto, D. Wilner, M. Spaans, M. C. Wiedner, K. Sakamoto, J. H. Black, M. Caldas, High-resolution HNC 3-2 SMA observations of Arp220, 2009, A&A, 493, 481

D. Espada, S. Martin, P.-Y. Hsieh, P.T.P. Ho, S. Matsushita, L. Verdes-Montenegro, J. Sabater, S. Verley, M. Krips, V. Espigares, Molecular gas properties of galaxies: The SMA CO(2-1)B0DEGA legacy project, arXiv:1010.3428v1

M. Krips, S. Martin, R. Neri, S. Garcia-Burillo, F. Combes, G. Petitpas, A. Fuente, A. Usero, Feedback of AGN and SB Activity: Gas Chemistry and Excitation Conditions in the Centers of Nearby Active Galaxies, 2009, ASPC, 408, 142K

S. Martin, M. Krips, J. Martin-Pintado, S. Aalto, J.-H. Zhao, A.B. Peck, G.R. Petitpas, R. Monje, T.R. Greve, T. An, The Submillimeter Array 1.3 mm line survey of Arp 220, 2010, accepted to A&A

S. Matsushita, D. Iono, G. R. Petitpas, R. C.-Y. Chou, M. A. Gurwell, T. R. Hunter, J. Lim, S. Muller, A. B. Peck, K. Sakamoto, S. Sawada-Satoh, M. C. Wiedner, D. J. Wilner, C. D. Wilson, SMA CO(J=6-5) and 435 micron interferometric imaging of the nuclear region of Arp 220, 2009, ApJ, 693, 56

A. Quillen, M. Brookes, J. Keene, D. Stern, C. Lawrence, M. Werner, Spitzer Observations of the Dusty Warped disk of Centaurus A, 2006, ApJ, 645, 1092

K. Sakamoto, J. Wang, M. C. Wiedner, Z. Wang, A. B. Peck, Q. Zhang, G. R. Petitpas, P. T. P. Ho, D. J. Wilner, SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity, 2008, ApJ, 684, 957

K. Sakamoto, S. Aalto, D. J. Wilner, J. H. Black, J. E. Conway, F. Costagliola, A. B. Peck, M. Spaans, J. Wang, M. C. Wiedner, P-Cygni Profiles of Molecular Lines toward Arp 220 Nuclei, ApJ, 700, L104

C. D. Wilson, G. R. Petitpas, D. Iono, A. J. Baker, A. B. Peck, M. Krips, B. Warren, J. Golding, A. Atkinson, L. Armus, T. J. Cox, P. Ho, M. Juvela, S. Matsushita, J. C Mihos, Y. Pihlstrom, M. S. Yun, Luminous Infrared Galaxies with the Submillimeter Array: I. Survey Overview and the Central Gas to Dust Ratio, 2008, ApJS, 178, 189

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SMA Research: Nearby Galaxies

SMA Research