ScienceProblem:DynamicsofAGNandStarburstNuclei

PrimaryActor

Astronomer

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ScienceGoal

To establish the dynamics and environmental conditions in the inner regions of active galaxies containing compact starbursts and/or AGN.

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DataSets

High resolution (spatial and spectral) radio and optical data (e.g. HST, radio interferometry including VLBI.

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ProblemDescription:

Galaxies containing Seyfert nuclei or other evidence of activity might contain a black hole being fed via one or more discs and possibly bars. However in some objects there is evidence for compact starburst regions but not necessarily a black hole. Many such galaxies are (U)LIRGS showing signs of a past or present merger. Optical lines, HI absorption and maser emission trace the velocities of ionised, atomic and molecular material respectively, at distances from <1 to a few 100 pc. Combining 21cm radio data sets from different instruments reveals details of the HI distribution that cannot be seen at any single resolution. It is necessary to measure the rotation curve(s) over as large a region as possible to distinguish between Keplerian and solid body rotation and get a clear picture of the mass distribution as well as the overall mass density and thus potentially establish the presence of a black hole.

Such observations must be related to the structure of the galaxy and any companions on scales up to many tens of kpc - for example using HI emission to find the recessional velocity of the centre of mass of the whole galaxy. Additional observations (e.g. x-ray column absorption, IR imaging etc.) are also important.

To date, some intriguing patterns of extra-galactic bright maser behaviour have been discovered but are not fully understood:

OH masers are almost always associated with (U)LIRGS showing signs of mergers, usually Seyfert 2s but occasionally Seyfert 1s. Both mainline frequencies are found together in 10 - 100 pc-scale regions, probably rotating discs, which could contain either or both starbursts and massive black holes. Diffuse 1665 MHz (and occasionally other OH lines) is sometimes seen, possibly associated with non-nuclear starbursts.

H2O masers are only found in Seyfert 2 or LINER galaxies. In a few cases Keplerian rotation demonstrates the presence of a massive black hole. In other cases they are very variable and hard to interpret, and possibly associated with material shocked by the passage of a jet.

OH and H2O emission is never found in the same galaxy. Only one OH megamaser galaxy has a small jet.

If these and other characteristics can be used to establish the conditions for maser amplification this will give additional information about the temperature, velocity profiles, clumping scales and other properties of inner molecular regions of active galaxies.

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CurrentSolution:

Individual objects are studied in great detail but with a limited range of instruments, and sometimes archive data can be located and combined. Difficulties include different velocity conventions (even though most objects are at z<0.1), scaling column density measurements based on different assumptions, and interpreting data taking at different, large resolutions. It is even harder to compile complete samples from observations made at different times with different sensitivities and to ascertain if non-detection of high velocity emission is due to the absence of emission or to instrumental limitations. Much of the literature looks at one or two aspects of the galaxy in isolation and produces contradictory models, probably because there is actually too much data on many objects (optical lines, x-ray, relationships with nearby galaxies...), in incompatible formats.

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VOSolution:

The ability to search for information around a position and adjust the results to standard conventions will save much time (ie remote use of the appropriate software and details of instrumental characteristics). The user could compare e.g. IR colours and OH maser intensity and type of emission, with larger-scale morphology or with x-ray data; AG can be used to filter only those properties which do show some significant relationship.

Kinematics from optical and radio lines could be compared without having to be an expert in the various complicated data reduction methods. The constraints on enclosed mass density in the galactic centres could be readily expressed in terms of the parameter space of various phenomena - globular cluster density, super starburst density, black hole density...

Maser theorists could predict correlations to test against the most readily available observables, which could be used to search for new maser galaxies.

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KeyReferences:

Baan, Willem A., Salzer, John J., & Lewinter, Robin D. 1998, The Astrophysical Journal, Volume 509, Issue 2, pp. 633-645. Optical Classification of Megamaser Galaxies

Braatz, J. A., Wilson, A. S., & Henkel, C. 1997, Astrophysical Journal Supplement v.110, p.321 A Survey for H 2O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

Pihlström, Y. M., Conway, J. E., Booth, R. S., Diamond, P. J., & Polatidis, A. G. 2001, Astronomy and Astrophysics, v.377, p.413-424 (2001) EVN and MERLIN observations of . A starburst continuum and an OH maser ring

Wills, K. A., Das, M., Pedlar, A., Muxlow, T. W. B., & Robinson, T. G. 2000, Monthly Notices of the Royal Astronomical Society, Volume 316, Issue 1, pp. 33-48. Modelling the bar in the centre of the starburst galaxy M82

Gallimore, J. F., Baum, S. A., O'Dea, C. P., Pedlar, A., & Brinks, E. 1999, The Astrophysical Journal, Volume 524, Issue 2, pp. 684-706. Neutral Hydrogen (21 Centimeter) Absorption in Seyfert Galaxies: Evidence for Free-Free Absorption and Subkiloparsec Gaseous Disks

Beswick, R. J., Pedlar, A., & Holloway, A. J. 2002, Monthly Notices of the Royal Astronomical Society, Volume 329, Issue 3, pp. 620-628. A radio study of neutral gas and dust in the radio galaxy 3C 293

Carilli, C. L. & Taylor, G. B. 2000, The Astrophysical Journal, Volume 532, Issue 2, pp. L95-L99. The Extreme Compact Starburst in Markarian 273

Yates, J. A., Richards, A. M. S., Wright, M. M., Collett, J. L., Gray, M. D., Field, D., & Cohen, R. J. 2000, Monthly Notices of the Royal Astronomical Society, Volume 317, Issue 1, pp. 28-36. Resolved OH megamaser emission in the nuclear region of the ultraluminous infrared galaxy Markarian 273

Kartje, John F., Königl, Arieh, & Elitzur, Moshe 1999, The Astrophysical Journal, Volume 513, Issue 1, pp. 180-196. Megamaser Disks in Active Galactic Nuclei

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GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Science Problems Forum. For other ScienceProblems, refer to the ScienceProblemList.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

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In terms of technical challenges this is a subset of the VO.DeepFieldSurveys case.

-- NicholasWalton - 17 Apr 2002

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-- AnitaRichards - 06 Feb 2002