Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
권호 표지
DOI QR코드

DOI QR Code

TURBULENCE IN THE OUTSKIRTS OF THE MILKY WAY

  • Sanchez-Salcedo, F.J. (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria) ;
  • Santillan, A. (Computo Aplicado-DGSCA, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria) ;
  • Franco, Jose (Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ciudad Universitaria)
  • Published : 2007.12.31
Download PDF
⟨ Previous Next ⟩

Abstract

In external galaxies, the velocity dispersion of the atomic hydrogen gas shows a remarkably flat distribution with the galactocentric radius. This has been a long-standing puzzle because if the gas velocity dispersion is due to turbulence caused by supernova explosions, it should decline with radius. After a discussion on the role of spiral arms and ram pressure in driving interstellar turbulence in the outer parts of galactic disks, we argue that the constant bombardment by tiny high-velocity halo clouds can be a significant source of random motions in the outer disk gas. Recent observations of the flaring of H I in the Galaxy are difficult to explain if the dark halo is nearly spherical as the survival of the streams of tidal debris of Sagittarius dwarf spheroidal galaxy suggests. The radial enhancement of the gas velocity dispersion (at R > 25 kpc) due to accretion of cloudy gas might naturally explain the observed flaring in the Milky Way. Other motivations and implications of this scenario have been highlighted.

Keywords

References

  1. Beckman, J. E., et al. 2002, Generation of Warps by Accretion Flows, Ap&SS, 284, 747 https://doi.org/10.1023/A:1024044416617
  2. Becquaert, J.-F., & Combes, F. 1997, The 3D Geometry of Dark Matter Halos, A&A, 325, 41
  3. Benjamin, R. A., & Danly, L. 1997, High-Velocity Rain: The Terminal Velocity Model of Galactic Infall, ApJ, 481, 764
  4. Benjamin, R. A., & Shapiro, P. R. 1993, in The Evolution of Galaxies and Their Environment, ed. D. J. Hollenbach, H. A. Thronson, & J. M. Shull (Mottett Field, CA: NASA), 338
  5. Booth, C. M., & Theuns, T. 2007, Neutral Hydrogen in Galactic Fountains, MNRAS, 381, L89 https://doi.org/10.1111/j.1745-3933.2007.00374.x
  6. Bruns, C., Kerp, J., & Pagels A. 2001, Deep H I Observations of the Compact High-Velocity Cloud (HVC 125+41-207), A&A, 370, L26 https://doi.org/10.1051/0004-6361:20010332
  7. Bureau, M., & Carignan, C. 2002, Environment, Ram Pressure, and Shell Formation in Holmberg II, AJ, 123, 1316 https://doi.org/10.1086/338899
  8. Dib, S., Bell, E., & Burkert, A. 2006, The Supernova Rate- Velocity Dispersion Relation in the Interstellar Medium, ApJ, 638, 797 https://doi.org/10.1086/498857
  9. Elmegreen, B. G., & Hunter, D. A. 2006, Radial Profiles of Star Formation in the Far Outer Regions of Galaxy Disks, ApJ, 636, 712 https://doi.org/10.1086/498082
  10. Fellhauer, M. et al. 2006, The Origin of the Bifurcation in the Sagittarius Stream, ApJ, 651,167 https://doi.org/10.1086/507128
  11. Ferguson, A. M. N., Wyse, R. F. G., Gallagher, J. S., & Hunter, D. A. 1998, Discovery of Recent Star Formation in the Extreme Outer Regions of Disk Galaxies ApJ, 506, L19 https://doi.org/10.1086/306229
  12. Garmire, G. P. et al. 1992, The Soft X-Ray Diffuse Background Observed with the HEAO 1 Low-Energy Detectors, ApJ, 399, 694
  13. Gibson, B. K. et al. 2001, High- Velocity Cloud Complex C: Galactic Fuel or Galactic Waste?, AJ, 122, 3280
  14. Gomez, G. C., & Cox, D. P. 2002, Three-dimensional Magnetohydrodynamic Modeling of the Gaseous Structure of the Galaxy: Setup and Initial Results, ApJ, 580, 235
  15. Henderson, A. P., Jackson, P. D., & Kerr, F. J. 1982, The Distribution of Neutral Atomic Hydrogen in our Galaxy beyond the Solar Circle, ApJ, 263, 116 https://doi.org/10.1086/160486
  16. Kalberla, P. M. W., Burton, W. B., Hartmann, Dap, Arnal, E. M., Bajaja, E., Morras, R., & Poppel, W. G. L. 2005, The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI. Final Data Release of the Combined LDS and IAR Surveys with Improved StrayRadiation Corrections, A&A, 440, 775 https://doi.org/10.1051/0004-6361:20041864
  17. Kalberla, P. M. W., Dedes, L., Kerp, J., & Haud, U. 2007, Dark Matter in the Milky Way. II. The HI Gas Distribution as a Tracer of the Gravitational Potential, A&A, 469, 511 https://doi.org/10.1051/0004-6361:20066362
  18. Kim, C.-G., Kim, W.-T., & Ostriker, E. C. 2006, Interstellar Turbulence Driving by Galactic Spiral Shocks, ApJ, 649, L13 https://doi.org/10.1086/508160
  19. Levine, E. S., Blitz, L., & Heiles, C. 2006a, The Vertical Structure of the Outer Milky Way H I Disk, ApJ, 643, 881 https://doi.org/10.1086/503091
  20. Levine, E. S., Blitz, L., & Heiles, C. 2006b, The Spiral Structure of the Outer Milky Way in Hydrogen, Science, 312, 1773 https://doi.org/10.1126/science.1128455
  21. Mac Low, M.-M., & Klessen, R. S. 2004, Control of Star Formation by Supersonic Turbulence, Reviews of Modern Physics, 76, 125 https://doi.org/10.1103/RevModPhys.76.125
  22. Maller, A. H., & Bullock, J. S. 2004, Multiphase Galaxy Formation: High-Velocity Clouds and the Missing Baryon Problem, MNRAS, 355, 694 https://doi.org/10.1111/j.1365-2966.2004.08349.x
  23. Maloney, P. R., & Putman, M. E. 2003, Are Compact High- Velocity Clouds Extragalactic Objects?, ApJ, 589, 270 https://doi.org/10.1086/374547
  24. Martos, M. A., & Cox, D. P. 1998, Magnetohydrodynamic Modeling of a Galactic Spiral Arm as a Combination Shock and Hydraulic Jump, ApJ, 509, 703 https://doi.org/10.1086/306514
  25. McConnachie, A. W., Venn, K. A., Irwin, M. J., Young, L. M., & Geehan, J. J. 2007, Ram Pressure Stripping of an Isolated Local Group Dwarf Galaxy: Evidence for an Intragroup Medium, ApJ, 671, L33 https://doi.org/10.1086/524887
  26. Narayan, C. A., Saha, K., & Jog, C. J. 2005, Constraints on the Halo Density Profile Using H I Flaring in the Outer Galaxy, A&A, 440, 523 https://doi.org/10.1051/0004-6361:20041055
  27. Olling, R. P. 1995, On the Usage of Flaring Gas Layers to Determine the Shape of Dark Matter Halos, AJ, 110, 591 https://doi.org/10.1086/117545
  28. Olling, R. P. 1996, The Highly Flattened Dark Matter Halo of NGC 4244, AJ, 112, 481 https://doi.org/10.1086/118029
  29. Olling, R. P., & Merrifield, M. R. 2000, Two Measures of the Shape of the Dark Halo of the Milky Way, MNRAS, 311, 361 https://doi.org/10.1046/j.1365-8711.2000.03053.x
  30. Oort J. H., 1970, The Formation of Galaxies and the Origin of the High-Velocity Hydrogen, A&A, 7, 381
  31. Petrie, A. O., & Rupen, M. P. 2007, H I Velocity Dispersion in NGC 1058, AJ, 134, 1952 https://doi.org/10.1086/518558
  32. Pisano, D. J. et al. 2004, Where Are the High-Velocity Clouds in Local Group Analogs?, ApJ, 610, L17 https://doi.org/10.1086/423239
  33. Pisano, D. J., Barnes, D. G., Gibson, B. K., Staveley-Smith, L., Freeman, K. C., & Kilborn, V. A., 2007, An H I Survey of Six Local Group Analogs. I. Survey Description and the Search for High-Velocity Clouds, ApJ, 662, 959 https://doi.org/10.1086/517986
  34. Putman, M. E. 2006, Potential Condensed Fuel for the Milky Way, ApJ, 645, 1164 https://doi.org/10.1086/504509
  35. Sanchez-Salcedo, F. J. 2004, Are Galactic Warps Induced by Intergalactic Flows?, JKAS, 37, 205
  36. Sanchez-Salcedo, F. J. 2006, On the Origin of Warps and the Role of the Intergalactic Medium, MNRAS, 365, 555 https://doi.org/10.1111/j.1365-2966.2005.09736.x
  37. Sanchez-Salcedo, F. J., Santillan, A., & Franco, J. 2007, Cloudy Intergalactic Accretion Flows in the Outer Discs of Galaxies, New Astronomy Reviews, 51, 104 https://doi.org/10.1016/j.newar.2006.10.011
  38. Santillan, A., Sanchez-Salcedo, F. J., & Franco, J. 2007, Exploring Cloudy Gas Accretion as a Source of Interstellar Turbulence in the Outskirts of Disks, ApJ, 662. L19 https://doi.org/10.1086/519247
  39. Schaye, J. 2004, Star Formation Thresholds and Galaxy Edges: Why and Where, ApJ, 609, 667 https://doi.org/10.1086/421232
  40. Shapiro P. R., & Field G. B., 1976, Consequences of a New Hot Component of the Interstellar Medium, ApJ, 205, 762 https://doi.org/10.1086/154332
  41. Soukup, J. E., & Yuan, C. 1981, Vertical Extensions of Galactic Spiral Arms, ApJ, 246, 376 https://doi.org/10.1086/158935
  42. Tubbs, A. D. 1980, Galactic spiral shocks - Vertical Structure, Thermal Phase Effects, and Self-Gravity, ApJ, 239, 882
  43. Westmeier, T. et al., 2007, The Relics of Galaxy Evolution: High-Velocity Clouds around the Andromeda Galaxy, New Astron. Rev., 51, 108 https://doi.org/10.1016/j.newar.2006.11.002
  44. White, S. D. M., & Frenk, C. S. 1991, Galaxy Formation through Hierarchical Clustering, ApJ, 379, 52 https://doi.org/10.1086/170483
  45. White, S. D. M., & Rees, M. J. 1978, Core Condensation in Heavy Halos - A Two-Stage Theory for Galaxy Formation and Clustering, MNRAS, 183, 341

Cited by

  1. Turbulence in the interstellar medium vol.21, pp.3, 2014, https://doi.org/10.5194/npg-21-587-2014