1. TINY-SCALE NEUTRAL STRUCTURE Tiny-Scale Atomic Structure (TSAS) –Observations, THEN and NOW –Pressure problem –Interpretive Solutions Tiny-Scale Molecular Structure (SAMS) –Observations –Interpretative aspects: “Stones”, “Clumpuscules” –The “Missing/Dark Matter”? Carl Heiles, Astronomy, UC Berkeley

2. TSAS OBSERVATIONS THEN – 1990’S

11. The single descriptive word was... UBIQUITOUS

12. TSAS OBSERVATIONS NOW – 2000’S

19. (Also: Minter, Balser, Kartalepe 2005; PSR B0329+54)

21. Today’s picture Pulsar HI absorption spectra is less rosy than yesteryear’s! It indicates that TSAS is NOT SO UBIQUITOUS! HOWEVER... VLBI still shows structure against 3 sources, one of which is both time- and space-variable! OPTICAL ABSORPTION LINES are still going strong (sensitive to ionization fraction)!

22. TSAS --- INTERPRETIVE ISSUES

23. MAX MIN PRESSURE CONSTRAINT/THERMAL EQUILIBRIUM The THERMAL P CNM > MIN (MICROphysics requirement). The Boulares/Cox Hydrostatic Limit is strict for long-lived structures MACROphysics requirement). CONCLUSION: If in equilibrium, the CNM thermal pressure must lie between MIN and Hydrostatic--a range of about 10. (from Wolfire et al 2003) Galactic Hydrostatic Equilibrium Limit

25. To avoid high TSAS pressure, we want... * Low Temperature * High Anisotropy (High G) High G means L || >> L perp :

28. IF TSAS IS DISCRETE QUASISTATIC STRUCTURES… T low, ~16 K L ┴ ~30 AU P/k ~ 4000 cm -3 K L || = G L ┴ ~ 190 AU

29. HOW ABOUT G? ARECIBO/GALFA PROVIDES NEW EVIDENCE FOR ANISOTROPY AT LARGER SCALES: * A PANCAKE (sheet) * A CIGAR (filament)

30. Knapp/Verschuur cloud: 17 K; a very thin sheet (0.03 pc).

33. GALFA data of this 150 sq deg region: Vlsr = 5 to 12 km/s Note the long, straight filaments!

37. (from Jenkins and Tripp)

38. How about possibilities other than discrete structures in pressure equilibrium? 1. Discrete structures, but highly overpressured (Tripp—stay tuned!) 2. Velocity gradients plus 21-cm line scintillation lead to apparent variations in 21-cm line opacity (Gwinn—not present at this meeting) 3. Simply the random pileup of column density/velocity along the line of sight—will produce observable fluctuations if the turbulent spectrum is flat enough (Deshpande; not present at this meeting).

39. SAMS OBSERVATIONS Heithausen discovered isolated Tiny-Scale MOLECULAR Structures. He christened them... SAMS – Small-Area Molecular Structures

44. at 100 pc, n(H2) ~ 500000 per cc; R ~ 200 AU; M ~ 100 M(Jup; V_exp ~ 0.3 km/s

45. SAMS OBSERVED PROPERTIES Intrinsic CO linewidth ~ 0.4 km/s Vel gradient ~ 1 km/s over 6000 AU N(H) ~ few x 10 19 (HI? H 2 ? X factor?) Radius ~ few hundred AU n(H) ~ few x 10 4 or more cm -3 At T ~ 10 K, BIG PRESSURE PROBLEM! Mass ~ few x 10 -4 Suns or ~ 1 Jupiter Dense clouds oscillate in Z, period 240 Myr Cloud velocities low (few km/s)

46. THEORETICAL/INTERPRETIVE ISSUES A cloud should “drop like a stone”, oscillate in Galactic z-gravity Period 240 Myr Vz,max = 2.5 km/s for Zmax = 100 pc, commensurate with observed low velocities But this “stone” picture implies a cohesive object. Self-gravity seems the only mechanism!

48. SUMMARY OF PFENNIGER/COMBES Argue that ISM is hierarchical and fractal Set minimum size by equating cooling time to free-fall time: the “CLUMPUSCULE” Clumpuscule properties are similar to observed molecular clumps!

49. ‘MISSING MATTER” – “DARK MATTER”? Pfenniger/Combes1994: Clumpuscules Walker/Wardle 1998: ISRF ionizes outside of clumpsicules and produces ESE lenses (Ionized Structure: Rickett, stay tuned!) –Ionized clumpsicule covering fraction 0.7% –1000 times more clumpuscules than stars! –Solves “missing/dark matter” problem! Gerhard/Silk 1996 also postulate small molecular clouds—cosmology only.

51. OVERALL SUMMARY—TSAS * Discrete structures in quasi-equilibriuim—favored by VLBI and my prejudice; needs Low T, High G * Discrete structures, Overpressured >> Galactic hydrostatic pressure. (Tripp) * Multiscale contributions from turbulent spectrum (Deshpande) OVERALL SUMMARY—SAMS * Discrete clumpuscules (Heithausen and Dirsch et al. data, 2002/2004) * If ESE, they are the dark matter (Pfenniger/Combes 1993; Walker/Wardle 1998)!

52. S mall I onized and N eutral S tructures (in the Diffuse ISM) [by Carl Heiles]: SINS V ital I nterstellar R egions: T iny, U nexpected, E xpanding S tructures [by Lou Hobbs]: VIRTUES