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Spitzer 24 um image: l ~ 358 - 359

Spitzer 24 um image: l ~ 358 - 359. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C. 24  m. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C. 70  m. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C. 160  m.

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Spitzer 24 um image: l ~ 358 - 359

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  1. Spitzer 24 um image: l ~ 358 - 359

  2. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 24 m

  3. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 70 m

  4. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 160 m

  5. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 250 m

  6. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 350 m

  7. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 500 m

  8. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 1100 m

  9. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 20 cm

  10. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 24 m

  11. Bania’s Clump 2 l = 1.3 Sgr B2 / B1 Sgr A Sgr C 70 m

  12. 24 m 350 m 2/3 gas, dust: + longitudes 2/3 24 m sources: - longitudes

  13. Galactic Center: 8 m Sgr B2 Sgr A (CND)

  14. Galactic Center Bubble: 24m

  15. 8 m70 m350 m

  16. Galactic Center: 20 cm

  17. Tdust(Rome algorithm)

  18. N(H2) from dust (Cara Battersby)

  19. Galactic Center Bubble => Sofue-Handa Lobe => Fermi-LAT Bubble ? Finkbeiner et al. (2010) Sofue- Handa Lobe … or Sco-Cen superbubble 150 pc from Sun? 3.5 cm (GBT) 2 deg. Law et al. (2008)

  20. Sgr A & Circum Nuclear Ring (CNR): 70 um, 160 um, 350 um (SHARC/CSO) Black Hole HCN (1-0) + P 50 km/s cloud20 km/s cloud Feeding star formation in the CNR? Sgr A cluster L-band: (Viehmann 06)

  21. Summary & Review: Collisional Processes & cross-sections: neutral-neutral:  = constant Rate = nV ~ T1/2 charge-neutral:  = c V-1 Rate = indep of T charge-charge:  = c V-4 Rate = nV ~ T-1/2 Overview of Heating & Cooling processes Radiative decay rates: A, B coefficients Molecular transitions Electronic, vibrational, rotational, etc. CO, high-dipole moment molecules in the sub-mm to cm Dust emission, absorption Excitation and and radiative transfer Next: Heating <=> cooling (see Dalgarno & McCray 1972, ARAA, 10, 375) n, T & the two and three-phase ISM models

  22. Total ISM Pressure High  Magnetic P low  Stable Cold phase Forbidden: T ~ 270 - 6000 0.8 - 7 cm-3 Stable Warm phase Two-Phase ISM model: Field, Goldsmith, Habing 1969, ApJL, 155, L149 Cox, D. P. 2005, ARA&A, 43, 337 Warm Phase: hot X-ray bubbles (HIM), HII (ELD HII + HII regions) Cold Phase: warm (T > 103) HI, cold HI (T < 103) , Molecular clouds • Balance between • (Heating) & Cooling => T(n) P / k = n * T(n)

  23. Total cooling rate: H becomes ionized Recombinations: H+ => HI UV line of metals X-ray emission: Metal lines, f-f Fine structure cooling” OIII, C+, NII, OI, … Depends on Fractional ionization ne/nH

  24. Heating • Ionizing: E > 13.6 eV FUV : HII regions • Soft UV: E < 13.6 eV EUV : HI regions, PDR, • cloud surfaces; AV < few mag. • Photoelectric effect HI • H2 destruction followed by re-formation on grains HI • Visual and IR photons (AV ~ 1 - 10 mag.) H2 • In dense gas (n > 105 cm-3) warm grains near luminous sources • heat the gas. • X-rays (AV > few mag.) H2 • MHD effects (magnetic reconnection) HI,H2 • Compression (shocks etc.) HII regions,HI,H2 • Cosmic rays H2

  25. Heating • Ionizing UV (“extreme” UV or EUV): E > 13.6 eV • EUV (HII regions) • does not penetrate neutral HI or H2 • Soft UV (“far” UV or FUV): 6 eV < E < 13.6 eV • FUV (HI regions, PDRs cloud surfaces) • penetrates to AV ~ few • Cosmic-rays • > MeV protons. Penetrate to AV ~ 10 to 100 • X-rays • Penetrates to AV > 10, low flux • produced by SN, SNR, young stars (Lx ~ 10-4 Lo) • MHD effects • B-reconnection, ambipolar diffusion (ion-neutral Drift) • Compression by shock waves • External sources: SNR, supershells, ionization fronts • Internal sources. Decay of turbulence, outflows

  26. Interstellar Radiation fields

  27. Free-free radiation from ionized H

  28. Cosmic Ray flux & Ionization Rates

  29. Heating • (Dalgarno & McCray 1972, ARA&A 10,375) • Impacts of FUV revisited: • H2 dissociation => reformation on grains • E(H2)binding ~ 4.5 eV • A fraction of the release energy is kinetic E of • ejected H2. • E(KE) ~ 4.5eV - (H2) •  = grain surface “work function”~ 0.5 to 2 eV • Photo-electric effect on grains • Epe = h - (f + V) • f = grain photoelectric “work function” ~ 6 eV • V= electrostatic potential of grain • nPE = 10-24nG/Go (erg s-1 cm-3) e= 0.05 , heating efficiency • Go = 1.6 x 10-3 (erg s-1 cm-2 ) :FUV “Habing field” • - Grain charging limits PE heating! • (deJong 1977, A&A, 55, 137)

  30. Heating • Ionization: f(H) = 13.6 eV ; f(C) = 11.6 eV ; f(O) = 13.6 eV • f(Na) = 5.1 eV ; f(K) = 4.3 eV • E = hn – f ~ 1 – 10 eV for H near an O star • ~few eV for C+ near an A or B star • Cosmic Ray ionization Rate: (E > 0.3 MeV), low E dominate • x = 1 -- 30 x 10-17s-1(in GMCs: x10 higher?) • Heating rate: nG = x E (E,x) nH ~ 1 - 30 x 10-28 n (erg s-1 cm-3) Dominates in shielded (from UV) regions: eg. Molecular clouds

  31. Heating and Cooling in the ISM: - Cooling: Recombination, collisional excitation: => photons free-free, free-bound, bound-bound transitions Continuum emission from plasma Grains (IR => mm) “grey-body” S = B(T) (/0)  Transiently heated small grains Line emission from ions, atoms, molecules Band emission from small grains (PAHs)

  32. Cooling in the ISM: • Cooling depends on phase: • GMCs: @ n < 104 cm-3: • CO (m ~ 0.1 debye), dust • @ n > 104 cm-3:`High dipole moment’ molecules • HCN, HCO+, CS, … (m > 0.2 debye) , dust • cold HI: T ~ 100 K • CII (158 mm) E = 92 K n < ncrit ~ 3,000 cm-3 • OI (63 mm) E = 228 K • ne ~ n(CII) ~ 3 x 10-4 nH (But, C can be depleted) • warm HI: T > 103 K • OI (63 mm) E = 228 K, Si II, … • Ionized: T ~ 104 K • f-f: Lff = 1.4x10-27 T 0.5 ne(n H+ + n He+ + n He++ ) erg s-1 cm-3 • b-f, b-b: lines, Lyman a, 2eV forbidden lines of [OIII], [SII], …

  33. HI 21 cm Dominant line in WNM

  34. CII 157.74m Dominant coolant in WNM

  35. Most important Coolants in warm HI clouds: Mid-IR <=> thermal IR

  36. Cooling of HI phases by various species: • Notes: • Collisional excitation • of upper upper state • Radiative decay - Characteristic T set by E of transition • Cooling rate depends on • abundance of species • times density:  [Xi * n(H)] * n(H) = Xi * n(H)2

  37. Cooling Rates: WNM (warm neutral medium) CNM (cold neutral medium)

  38. Most important Coolants in GMCs and HI clouds: FIR & sub-mm

  39. Linear Molecule: • Carbon Monoxide (CO) • Tracer of H2 • molecular clouds • - Low density gas tracer • n(H2) > 100 cm-3

  40. Total cooling rate by CO at 10 and 20 K: (GMCs) (Goldsmith & Langer 1978):

  41. Review of Molecular Transitions (rot, vib.) Molecule geometry - effects spectrum Rotational states: mm / sub-mm Linear (CO): - rotation ladder E ~ hB J(J+1) Symmetric top (NH3 = ammonia): - Complex J, K ladders Asymmetric top (H2O = water) - Nearly random forest of lines Vibrational states: near-IR / mid-IR Quasi harmonic oscillator

  42. Symmetric top: Ammonia (NH3) 22=>23 GHz (1.3 cm) inversion transitions: - Thermometer of ISM dense molecular clouds - Dense gas tracer n(H2) > 104 cm-3

  43. Ro-Vibration spectra: CO, H2, HCN, PAHs, …. - Coolant of warm ISM 100 to 10,000 K gas S => J = 2 P => J = 1 Q => J = 0 R => J = -1 O => J = -2 Ex: H2 S(1) at 2.1218 m

  44. Asymmetric top: Water (H2O) 22=>23 GHz (1.3 cm) - Coolant of ISM dens molecular clouds - 22 GHz Maser: Dense gas tracer n(H2) > 1010 cm-3

  45. Total cooling rate: H becomes ionized Recombinations: H+ => HI UV line of metals X-ray emission: Metal lines, f-f Fine structure cooling” OIII, C+, NII, OI, … Depends on Fractional ionization ne/nH

  46. Total ISM Pressure High  low  Stable Cold phase Stable Warm phase Two-Phase ISM model: Cox, D. P. 2005, ARA&A, 43, 337 Warm Phase: hot X-ray bubbles (HIM), HII (ELD HII + HII regions) Cold Phase: warm (T > 103) HI, cold HI (T < 103) , Molecular clouds • Balance between • (Heating) & Cooling => T(n) P / k = n * T(n) Magnetic P

  47. Cox, D. P. 2005, ARA&A, 43, 337

  48. Galactic Ecology: Cloud formation Powered by spiral arms ? Gravo-thermal Instability ? Super-bubbles ?

  49. Galactic Ecology:Star Formation & the Interstellar Medium

  50. A (very) useful Website: Jinhua He Yunnan Astronomical Observatory Chinese Academy of Sciences http://www.ynao.ac.cn/~jinhuahe/index.html CO and mass determination: http://www.ynao.ac.cn/~jinhuahe/know_base/astro_objects/sfr.htm#formula_co_mass

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