1. Molecules in Starbursts and Active Galactic Nuclei Amiel Sternberg School of Physics & Astronomy Tel Aviv University NGC 1068

2. Neutral interstellar hydrogen clouds where 6-13.6 eV far-ultraviolet (FUV) radiation dominates the chemistry and gas heating. FUV photon penetration limited by dust absorption. Heating by photo-electric emission of electrons from dust grains. Chemistry driven by FUV ionization. Photon-Dominated Regions (PDRs) X-ray Dominated Regions (XDRs) Neutral hydrogen clouds where (keV) X-rays dominate the chemistry and gas heating. X-ray penetration limited by photoionization of the “ heavy elements ”. (Greater photon penetration lengths than in PDRs). Heating by X-ray photoionization of H and H 2. (More efficient gas heating than in PDRs). Chemistry driven by X-ray ionization. Seyfert-2 Galaxy NGC 1068 Orion Bar PAH CO H2H2

3. Broadly defined, PDRs include: (8000  K) (100  K) Diffuse “ warm neutral medium ” (WNM) and “ cold neutral medium ” (CNM). Translucent clouds: moderate optical extinction (A V < 5), low gas densities, n H < 1000 cm -3 weak FUV fields. Dense molecular clouds: high extinction (A V ~ 10), n H > 1000 cm -3 intense FUV fields near massive and hot “ OB-type ” stars. ~90% of the Galactic molecular ISM may be “ photon-dominated ”. Photon-Dominated Regions:

4. PDRs: Basic Structure: 1-D steady-state model, escape probability method. FUV 6-13.6 eV ( “ non-ionizing ” ) 100  to 2000  K 10  to 100  K Grain surface formation, H 2 self-shielding. Controlling parameters: 1) cloud density, pressure 2) FUV intensity 3) grain scattering properties 4) H 2 formation rate coefficient 5) geometry/clumpiness 6) gas phase abundances 7) magnetic field.

5. Starburst Galaxy M82 (optical) distance = 3.3 Mpc vib rot H 2 infrared/submillimeter/millimeter spectroscopy (e.g. Genzel & Cesarsky 2000) PDR emission lines Dense PDRs: Dense PDRs exposed to intense FUV fields in star-forming molecular clouds are important as sources of luminous atomic fine-structure and molecular line (cooling) radiation, and far-IR thermal dust continuum emission. Line to continuum ratio typically 0.1 – 1%. Far-infrared dust continuum is reradiated ultraviolet stellar radiation.

6. Far-Ultraviolet (FUV) Radiation Field (6 - 13.6 eV 912 - 2070 Å ): Empirically based for solar neighborhood. Habing 1968 BAN 19, 421; Draine 1978 ApJS 36, 595 photon energy (eV) F(E) (Photons cm -2 s -1 ster -1 eV -1 ) interstellar FUV field Produced by massive and hot 3-120 M  “ OB type ” stars, in associations and clusters. Parravano, Hollenbach & McKee 2003 ApJ 584, 797 G 0  1

7. Radiation Fields of Evolving OB Clusters: Sternberg, Hoffmann & Pauldrach 2003, ApJ, 599, 1333 FUV EUV Intensity and spectral shape of FUV field depend on cluster mass and age. G 0 >> 1

8. Heating Mechanisms: FUV photoelectric heating, beginning with Spitzer 1948 ApJ 107, 6 FUV-pumping of H 2 in dense PDRs. Sternberg & Dalgarno 1989 ApJ 338, 197 Leads to high gas temperatures T > 1000  K in the H/H 2 layers.

9. CII 157.7  m Fine-Structure Line Cooling: Expected theoretically - e.g. Dalgarno & McCray 1972 ARAA 10, 375 First far-IR (Lear jet) detections were in in NGC 2024 and Orion. Russell et al. 1980 ApJ 240, L99 Since then, widely detected with far-infrared spectrometers, KAO, ISO... … and most recently in the millimeter- waves, in a high redshift quasar. Maiolino et al. 2005 AA 440 L51 Tielens & Hollenbach 1985 ApJ 291, 722 CNM WNM Wolfire et al. 2003 dense PDRs T (  K) CII 157.7  m (erg s -1 particle -1 )

10. Accounting for: [CII] 157.7  m [OI] 63.2  m & 145.6  m [CI] 609.2  m & 229.9  m and other “ low-ionization ” fine-structure emission lines observed in star-forming molecular clouds. Line strengths ~ 0.1 - 1% of far-IR dust continuum. FUV (6-13.6 eV) heating via photoelectric emission from dust grains: mean photon energy = 10 eV typical grain work function = 6 eV (for neutral grains). photoelectric yield = 0.1 Thus, heating efficiency = (4/10) x 0.1 = 0.04 (smaller for positively charged grains). Fine-Structure Emission Lines in Star-Forming Molecular Clouds:

11. FUV intensity G 0 line intensity (erg cm -2 s -1 sr -1 ) [CII] 157.7  m [OI] 63.2  m Fine-Structure Line Emissions from PDRs: Hollenbach & Tielens 1997 ARAA, 35, 179 Hollenbach & Tielens 1999 Rev. Mod. Phys., 71, 173 0.05 x far-IR

12. Neutral Atomic Carbon: S + C +  S + + C C + + e  C + photon “ radical region ”

13. Polycyclic Aromatic Hydrocarbons (PAHs): Reflection Nebula NGC 7023 (optical) Herbig B3Ve star Optical  “internal conversion”  IR Draine 2002 Cesarsky et al. 1996 AA 315 L305 Infrared Space Observatory

14. PAHs in PDRs: Bakes & Tielens 1998 ApJ 499, 258 PAH + PAHPAH - dashed – without PAHs solid – with PAHs (2 x 10 -7 ) mutual neutralization C + + PAH -  C + PAH competes with or dominates radiative recombination C + + e  C + photon Lepp & Dalgarno 1988 ApJ 335, 769 Similarly, “ grain-assisted recombination ” may become important for fractional ionizations x e < 10 -3. Draine & Sutin 1987 ApJ 320, 803 Weingartner & Draine 2001 ApJ 563, 842

15. Molecular Diagnostics: CN / HCN in NGC 7023 (Reflection Nebula): Reflection Nebula NGC 7023 (optical)

16. Molecular Diagnostics: CN / HCN in NGC 7023 (Reflection Nebula): At interface: G 0 = 2.4 x 10 3 n = 1.0 x 10 4 cm -3 Plateau de Bure & 30m illuminating star (Herbig B3Ve) Fuente et al. 1993 AA 276, 473 2003 AA 899, 913 Molecular Peak CN / HCN small PDR Peak CN / HCN large Distance from star (arcseconds)

17. Free Carbon and CN / HCN: Boger & Sternberg 2005 ApJ 632, 302 G 0 = 10 3 n = 10 4 cm -3

18. Free Carbon and CN / HCN: Boger & Sternberg 2005 ApJ 632 302 G 0 = 10 3 n = 10 4 cm -3

19. CN / HCN in the “ Radical Region ” : CN peak forms where the C + density is still high, but where the CN photodissociation rate is attenuated.

20. XDR highly ionized region H H/H 2  0.01 H 2 x e  10 -2 – 10 -1 x e  10 -3 – 10 -2 x e < 10 -3 High H Xray / n ……………………..…… Low H Xray / n keV X-rays H Xray = X-ray photon energy deposition rate n = gas density X-ray Dominated Regions (XDRs): Maloney, Hollenbach & Tielens 1996 Sternberg, Yan & Dalgarno 1996 Yan & Dalgarno 1997 Meijerink & Spaans 2005 T ~ 10 4 K T ~ 2000 K T < 200 K C +, C C, C + CO, C, C + O O O, OH, O 2, H 2 O large penetration depth

21. ionization excitation Coulomb scattering X-ray Photon Energy Secondary Electron Energy Deposition: H 2 + Xray  H 2 + + e* e* + H 2  H 2 + + e + e* H 2 + + H 2  H 3 + + H H 3 + + e  H 2 + H So almost all of the ionization energy (15.4 eV) is available for gas heating. Glassgold & Langer 1974 ApJ 186, 159 Energy lost to e* per ion-pair produced = 37.7 eV Dalgarno, Yan & Liu 1999 ApJS, 125 237 So, for a molecular XDR, the X-ray heating efficiency  15.4 / 37.7 = 0.4 … much higher than in PDRs. UV decay: photo- dissociation and dust heating,  far-IR “ fast electron ”

22. n = 10 3 cm -3 Fine-Structure Line Emissions from XDRs: far-IR continuum Maloney, Hollenbach & Tielens 1996 ApJ 466, 571

23. Extragalactic PDRs and XDRs

24. “ The Antennae ” NGC 4038/4039 Interacting Galaxies Hubble Space Telescope (optical) Infrared Space Observatory (10  m) Keck

25. FUV-Pumped Molecular Hydrogen in the Antennae: Mid-IR Cluster Gilbert et al. 2000 ApJ 533, L57 H 2 vibrational emission lines

26. FUV Pumping and Photodissociation of Molecular Hydrogen: Near IR FUV Pumping Dissociation Effective Potential Energy v=0 1 2 3 Internuclear Separation Energy Black & Dalgarno 1976 Black & van Dishoeck 1987 Sternberg 1988 Sternberg & Dalgarno 1989 Draine & Bertoldi 1996 Sternberg & Neufeld 1999 Shaw et al. 2005 CLOUDY

27. NGC 4038/4039 interacting galaxies CII emission from NGC 4038/4039 Nikola et al. 1998 ApJ 504, 749 Dense PDRs dominate: G 0 = 500 n H = 10 5 cm -3 (CNM a small fraction.)

28. High Redshift Detection of the CII 157.7  m Line: Maiolino et al. 2005 AA 440 L51 IRAM 30-meter z = 6.42 quasar J1148+5251 L FIR = 2.2 x 10 13 L  L CII = 4.4 x 10 9 L  Star-formation rate  3000 M  yr -1 L CII / L FIR = 2 x 10 -4 small! (similar deficit observed in ULIRGs) [CII] CO(6-5)

29. CII Line Deficit in Ultra-Luminous IR Galaxies (ULIRGs): ISO-LWS ULIRG sample. L IR > 10 12 L  Luhman et al. 2003 ApJ 594, 758 Possible Explanations 1)G 0 / n >> 1 cm 3 in ULIRGs inefficient photoelectric gas heating. 2)Underabundance of OB stars (unlikely). 3) Self absorption. 4) Absorption of UV photons in dusty HII regions. Requires high ionization- parameters (U   dust ). Is this consistent with nebular emission-line excitation? TBD (basic assumption: FIR is reradiated FUV energy.)

30. Starburst Galaxy M82 (optical) distance = 3.3 Mpc CN / HCN in M82 Fuente et al. 2005 ApJ 619 L155 CN/HCN ~ 5 across 650 pc star-forming disk. PDR signature.

31. XDRs and the Active Nucleus in NGC 4258: Central luminosity provided by an accreting, super- massive, black hole. X-rays. distance = 7.3 Mpc

32. NGC 4258: Water Masers Around the Supermassive Black Hole in NGC 4258: red-shifted maser spots blue-shifted maser spots In the galaxy center: A resolved Keplerian disk with orbiting water maser spots. v 2 = GM / R M = 3 x 10 7 M  ortho - H 2 O 22 GHz Energy (cm -1 ) rotational quantum number ”

33. XDR Production of H 2 O: MASING Neufeld, Maloney & Conger 1994 ApJ 436, L127

34. H 2 O Formation: OHH2OH2O e e H3O+H3O+ H2O+H2O+ OH + H3+H3+ H2H2 H2H2 O ion-molecule (cold) Herbst & Klemperer, 1973, ApJ, 185, 505 Prasad & Huntress, 1980, ApJS, 43, 1 H2H2 H2H2 neutral-neutral (warm) Neufeld & Dalgarno 1989, ApJ, 340 869 (J-shocks) Sternberg & Dalgarno 1995, ApJS, 99, 565 (PDRs) Maloney, Hollenbach & Tielens 1996, ApJ, 466, 571 (XDRs)

35. NGC 1068 (optical) Molecules in the Seyfert-2 Galaxy NGC 1068 (M77): 1 kpc distance = 15.5 Mpc

36. Molecules in the Seyfert-2 Galaxy NGC 1068: 100 pc IRAM 30m + PdB Tacconi et al. 1994, ApJ, 426, L77 Sternberg, Genzel & Tacconi 1994, ApJ, 436, L131 Helfer & Blitz 1995, ApJ, 450, 90 Usero et al. 2004, AA, 419, 897

37. XDRs in NGC 1068 ? In the nucleus, HCN/CO  10 -3 (large!) … … possible signature of enhanced ionization rate in molecular gas exposed to X-rays. Lepp & Dalgarno 1996, AA, 306, L21 Usero et al. 2004, AA, 419, 897 M gas  5 x 10 7 M  L Xray  2 x 10 11 L 

38. fractional abundance n /  -17 (cm -3 ) gas-density / ionization-rate “ high-ionization phase ” “ low-ionization phase ” Boger & Sternberg 2005 ApJ 632, 302 2006 ApJ in press High-ionization rate gives large HCN / CO … and also large CN / HCN as observed in the nucleus of NGC 1068. Usero et al. 2004 Note: C / CO is large in the high-ionization phase.

39. XDRs versus PDRs? In XDRs multiply charged atomic ions co-exist with neutral H, H 2 and He. Produced via inner-shell photoionization, & Auger decay. Multiply charged species may persist when charge-transfer neutralization is slow, e.g., C 2+ or S 2+ [S III] 33.5  m & 18.7  m fine-structure emissions as XDR diagnostics. or if react with H 2 lead to enhanced CH + or SH +.

40. A Golden Age! Space Infrared Telescope Facility (SIRTF) Stratospheric Observatory for Infrared Astronomy Atacama Large Millimeter Array (ALMA) Herschel Space Observatory (submillimeter)