Friday, July 24, 2009

Interesting Astrophysics: Jul 14 to 24

This edition of Interesting Astrophysics is graced by not one, not two, but five papers on galactic winds. Matsubayashi et al present Fabry-Perot observations of the NGC 253's wind, while both Westmoquette et al and Veilleux et al present observations of M82's wind. Two papers consider theoretical models, specifically numerical simulations, of winds: Cooper et al simulate individual cloud(s) in a superwind at very high resolution, while Kapferer et al simulate clusters of galaxies including a semi-analytical prescription for mixed mode thermal/CR-driven winds.

Finally there is a very extensive discussion of Fermi's Paradox by Cirkovic, which is well worth a read by anyone interested in astrobiology, while Selvelli and Molaro discuss the nature of the telescopes in the paintings of Brueghel the Elder.


Galaxies and Starbursts

Galactic Wind in the Nearby Starburst Galaxy NGC 253 Observed with the Kyoto3DII Fabry-Perot Mode
K. Matsubayashi, H. Sugai, T. Hattori, A. Kawai, S. Ozaki, G. Kosugi, T. Ishigaki, A. Shimono, arXiv:0907.2012 [ps, pdf, other]
Comments: 22 pages, 5 figures, 1 table, accepted for publication in ApJ

The Optical Structure of the Starburst Galaxy M82. II. Nebular Properties of the Disk and Inner-Wind
M. S. Westmoquette, J. S. Gallagher, L. J. Smith, G. Trancho, N. Bastian, I. S. Konstantopoulos, arXiv:0907.3162 [ps, pdf, other]
Comments: 27 pages, 18 figures (13 in colour), accepted for publication in ApJ

WARM MOLECULAR HYDROGEN IN THE GALACTIC WIND OF M82
Sylvain Veilleux, David S. N. Rupke, and Rob Swaters, 2009, ApJ, 700, L149
PDF (1.23 MB) | HTML

Mass Loss From Planetary Nebulae in Elliptical Galaxies
Joel N. Bregman, Joel R. Parriott, arXiv:0907.3489 [ps, pdf, other]
Comments: 34 pages with 20 figures. Higher quality figures are in the ApJ version
Journal-ref: ApJ, 699, 2009, 923-932

Radio monitoring of NGC 7469: Late time radio evolution of SN 2000ft and the circumnuclear starburst in NGC 7469
M.A. Perez-Torres, A. Alberdi, L. Colina, J.M. Torrelles, N. Panagia, A. Wilson, E. Kankare, S. Mattila, arXiv:0907.2644 [ps, pdf, other]
Comments: 10 pages, 5 figures, accepted for publication in MNRAS

Integral field optical spectroscopy of a representative sample of ULIRGs: I. The Data
M. Garcia-Marin, L. Colina, S. Arribas, A. Monreal-Ibero, arXiv:0907.2408 [pdf, other]
Comments: To appear in A&A. Paper with higher quality images can be found at this http URL

Integral field optical spectroscopy of a representative sample of ULIRGs: II. Two-dimensional kpc-scale extinction structure
M. Garcia-Marin, L. Colina, S. Arribas, arXiv:0907.2218 [ps, pdf, other]
Comments: To appear in A&A

Starburst-Driven Galactic Winds: Filament Formation and Emission Processes
J. L. Cooper, G. V. Bicknell, R. S. Sutherland, J. Bland-Hawthorn
Comments: Accepted to ApJ, 39 pages, 21 figures, movie file can obtained at this http URL

From their abstract, with my comments in square brackets: "The degree of fragmentation is highly dependent on the resolution of the simulation, with the number of cloudlets formed increasing as the Kelvin-Helmholtz instability is better resolved [1]. Nevertheless, there is a clear qualitative trend, with the filamentary structure still persistent at high resolution. We confirm the mechanism behind the formation of the H-alpha emitting filaments found in our global simulations of a starburst-driven wind. Based on our resolution study, we conclude that bow shocks around accelerated gas clouds, and their interaction, are the main source of the soft X-ray emission observed in these galactic-scale winds [2]."

[1] This is actually a very worrying result, and indeed is one of the primary reasons I have not pushed forward to publish our our high resolution 2-D and 3-D simulations but have instead switched to analytical theory. The characteristic size of H-alpha cloudlets in reality cannot be arbitrarily small (and if it were, there would be adverse dynamical consequences), so increasing fragmentation in the numerical simulations suggests that the results are being driven by numerics and not physics. There are reason to worry about instabilities, structure formation and mixing processes within even apparently converged grid-based simulations (as demonstrated by e.g. the Santa Barbara Cluster Comparison Project; Frenk et al 1999).

[2] Good! - that's what I've been saying for years (for very similar reasons and with similar or greater levels of quantitative justification, dare I say it).

I really would have liked to see some quantitative justification for the claims regarding both the X-ray emission and whether the H-alpha cloud complexes/filaments are really luminous enough to reproduce real winds.

The classic problem with simulating winds is that is it trivial to produce things that qualitatively reproduce wind-like structures, and adding resolution always generates more structure which makes the simulation superficially look more like real (complex, multiphase, messy) superwinds. But those same simulations can be orders of magnitude off in terms of quantitatively matching real winds. Even when you can get the models to match one particular observational parameter well quantitatively (e.g. the cloud OVI/X-ray flux ratio; Marcolini et al 2005) you often find some other observable parameter has values that tell you your beautiful simulation can't be a truly realistic model of reality (e.g. you cloud lifetime is ~1 Myr when real cloud lifetimes must be ~10 Myr, or the OVI column density through the cloud is one hundredth of the observed total line of sight OVI column density, meaning that your model implies you'd need ~100 clouds along every line of sight through a superwind).

Overall, its nice work but the very limited time scales (~ 1 Myr), the numerical issues I mentioned above, and lack of quantification in terms of luminosities make its claims seem no more strongly justified than preceding work.


Metal enrichment of the intra-cluster medium by thermally and cosmic-ray driven galactic winds
W. Kapferer, T. Kronberger, D. Breitschwerdt, S. Schindler, E. van Kampen, S. Kimeswenger, W. Domainko, M. Mair, M. Ruffert, arXiv:0907.3800 [ps, pdf, other]
Comments: 9 pages, 6 figures, accepted by A&A

Assumes that the terminal velocity of the (effectively single phase) wind is equal to the galactic escape velocity. Its a common assumption, and may have some semi-empirical justification for the entrained cool gas (T<105 K) in starburst-driven winds, but this assumption lacks theoretical and observational justification for the hot gas (admittedly, and notably, all the observational data is on winds from starburst galaxies, which are almost certainly predominantly thermally-driven). And in thermal or even mixed-mode thermal+CR winds its the hot gas that is involved in driving the wind and holds the metals.

Numerical simulations of hot halo gas in galaxy mergers
Manodeep Sinha, Kelly Holley-Bockelmann, 2009, MNRAS, 397, 190
Full Text: HTML, PDF (Size: 46324K)

Less than 10 percent of star formation in z=0.6 massive galaxies is triggered by major interactions

Aday R. Robaina, et al, arXiv:0907.3728 [ps, pdf, other]
Comments: Submitted to ApJ. 41 pages, 11 figures


Black Holes and AGN

Optical--to--X-ray emission in low-absorption AGN: Results from the Swift-BAT 9 month catalogue
R. V. Vasudevan, R. F. Mushotzky, L. M. Winter, A. C. Fabian, arXiv:0907.2272 [ps, pdf, other]
Comments: 25 pages, 22 figures, 4 tables, accepted for publication in MNRAS

AGN with strong forbidden high-ionization lines selected from the Sloan Digital Sky Survey
Jonathan M. Gelbord, James R. Mullaney, Martin J. Ward, 2009, MNRAS, 397, 172
Full Text: HTML, PDF (Size: 2513K)

Black Holes in the Galaxy
Josep M. Paredes, arXiv:0907.3602 [ps, pdf, other]
Comments: Notes to a series of five Lectures given in the First La Plata International School on Astronomy and Geophysics: Compact Objects and their emission, La Plata Observatory, 10-14 March 2008, Argentina, 32 pages, 12 figures, 1 table, editors G.E. Romero and P. Benaglia; ISBN 978-987-24948-0-3


Other

On the telescopes in the paintings of J. Brueghel the Elder
Pierluigi Selvelli, Paolo Molaro, arXiv:0907.3745 [ps, pdf, other]
Comments: 5 pages, 3 figures. Proceedings of 400 years of Astronomical telescopes Conference at ESA/ESTEC in Noordwijk. Brandl, Bernhard R.; Stuik, Remko; Katgert-Merkeli, J.K. (Jet) (Eds.)

Fermi's Paradox - The Last Challenge for Copernicanism?
Milan M. Cirkovic, arXiv:0907.3432 [ps, pdf, other]
Comments: 39 pages, 3 figures, slightly expanded in comparison to the journal version
Journal-ref: Serbian Astronomical Journal, vol. 178, pp. 1-20 (2009)

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