1. School of Physics and Astronomy FACULTY OF MATHEMATICS & PHYSICAL SCIENCES The IR-mm spectrum of a starburst galaxy Paola Caselli Astrochemistry of the dense and warm interstellar medium SpitzerHerschel Hubble

2. Outline Photodissociation regions The [CII]158  m line The importance of dust grains D/H

3. Photodissociation Regions (PDRs) A PDR is a region where FUV (6 eV < h < 13.6 eV) radiation dominates the heating and/or some important aspects of the chemistry. Most molecular clouds in our Galaxy have A V < ~5 mag and FUV radiation still plays an important role. IRAS view PDRs are the origin of much of the IR radiation from the ISM.

4. PDRs: The Orion Bar Tielens & Hollenbach 1985 See also: Bayet, Viti et al. 2009, 2011; Meijerink & Spaans 2005; Meijerink et al. 2007 Drop in photoelectric heating efficiency G o ~ 10 5 and n H ~ 10 5 cm -3 Tielens & Hollenbach 1985

5. PDRs: The Orion Bar

6. Photodissociation Regions (PDRs) Carbon chemistry Sternberg & Dalgarno 1995 HCO + CO C+C+ C

7. Photodissociation Regions (PDRs) Oxygen chemistry Sternberg & Dalgarno 1995 OH + H2OH2O O H2O+H2O+ H3O+H3O+ OH O2O2

8. Photodissociation Regions (PDRs) Sternberg & Dalgarno 1995 Nitrogen chemistry N2N2 HCN NH 3 N2H+N2H+ H3+H3+ see also Viti et al. 2011

9. Detection of hydrates toward the high mass YSO W3 IRS 5 (Benz et al. 2010): OH + and H 2 O + are new molecules ! H 2 O + /H 2 O from 0.01 to > 1 (Wyrowski et al. 2010)

10. Photodissociation Regions (PDRs) Kaufman et al. 1999 The PDR surface temperature typically increases with G o. The effect of lowering the dust abundance is to increase the physical extent of a PDR model.

11. Photodissociation Regions (PDRs) Wolfire et al. 2010 See also Poster 14-Heiner, 24-Bisbas The “dark” molecular mass: fraction ~30% (for ~ 8) insensitive to: UV field, internal density distribution, mass of the molecular cloud increases with decreasing

12. Observations of [CII] at low and high-z Evidence for enhanced emission at high redshift, probably due to lower metallicities. [CII] The 2 P 3/2  2 P 1/2 fine-structure line of C + at 157.8  m is generally the brightest emission line in the spectrum of galaxies, accounting as much as ~0.1-1% of their total luminosity. high-z low-z Maiolino+05,09 Iono+06

13. L [CII] /L FIR L CO(1-0) /L FIR De Breuck et al. 2011 The z=4.76 sub-millimeter galaxy: LESS J033229 ALMA data coming up !!

14. H + H  H 2 on the surface of dust grains (Gould & Salpeter 1963; Hollenbach & Salpeter 1970; Jura 1974; Pirronello et al. 1999; Cazaux & Tielens 2002; Habart et al. 2003; Bergin et al. 2004; Cuppen & Herbst 2005; Cazaux & Spaans 2009) The importance of dust grains

15. REACTANTS: MAINLY MOBILE ATOMS AND RADICALS A + B  AB association H + H  H 2 H + X  XH (X = O, C, N, CO, etc.) WHICH CONVERTS O  OH  H 2 O C  CH  CH 2  CH 3  CH 4 N  NH  NH 2  NH 3 CO  HCO  H 2 CO  H 3 CO  CH 3 OH RE: Watson & Salpeter 1972; Allen & Robinson 1977; Pickes & Williams 1977; d’Hendecourt et al. 1985; Hasegawa et al. 1992; Caselli et al. 1993.. Accretion Diffusion+Reaction  10/[T k 1/2 n(H 2 )] days t qt (H)  10 -5 -10 -3 s The importance of dust grains

16. Complex organic molecules in hot cores and hot corinos ( e.g. Wright et al. 1996; Cazaux et al. 2003; Bottinelli et al. 2004,2008; Kuan et al. 2004 ) HCN HCO + HCOOCH 3 CH 3 OHCH 3 CH 2 CN SO The importance of dust grains See also Gonzalez-Alfonso et al. (2010, 2011)

17. G 0 variationsGrain size variations The importance of dust grains Hollenbach et al. 2009

18. Ehrenfreund et al. 2002 Turbulent solar nebula model ⊕ Earth D/H (Cazaux, Caselli & Spaans 2011) T dust = 17 K 15 K 12 K HDO/H 2 O 0.1 0.01 10 -3 10 -2 10 -1 10 -4 10 -5 10 -6 0.1 0.01 10 -3 10 -2 10 -1 10 -4 10 -5 10 -6 HDCO/H 2 CO D 2 CO/H 2 CO time 10 3 10 4 10 5

19. Summary The [CII]158  m is the brightest emission line in the spectrum of galaxies. Good tracer of the “dark” molecular mass. ALMA (z  10!). PDRs are the origin of much of the IR radiation from the ISM. Rich chemistry (low & high T). [CII] Dust: efficient formation of molecules (e.g. H 2 O) on grain surfaces. Main cause of freeze-out & chemical differentiation.

20. At z>7 galaxies could be identified through the detection of high order CO lines, J upper >7... are these transitions excited? z at high J rapid drop of intensity... bad news for ALMA: difficult to use CO at z>7, unusable at z>10 (Weiss et al. 2005) Observations of [CII] at high-z

21. Courtesy of A. Wotten ALMA Simulated ALMA spectrum (24 h integration) of a quasar with the same redshift (z=6.4) and luminosity of the QSO J1148+5251, one of the most distant currently known.