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Astrochemistry of the dense and warm interstellar medium

The IR-mm spectrum of a starburst galaxy. School of Physics and Astronomy FACULTY OF MATHEMATICS & PHYSICAL SCIENCES. Astrochemistry of the dense and warm interstellar medium. Hubble. Paola Caselli. Spitzer. Herschel. Outline. Photodissociation regions The [CII]158 m line

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Astrochemistry of the dense and warm interstellar medium

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

  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 AV < ~5 mag and FUV radiation still plays an important role. PDRs are the origin of much of the IR radiation from the ISM. IRAS view

  4. PDRs: The Orion Bar Go ~ 105 and nH ~ 105 cm-3 Tielens & Hollenbach 1985 Drop in photoelectric heating efficiency Tielens & Hollenbach 1985 See also: Bayet, Viti et al. 2009, 2011; Meijerink & Spaans 2005; Meijerink et al. 2007

  5. PDRs: The Orion Bar Tielens & Hollenbach 1985

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

  7. Photodissociation Regions (PDRs) Oxygen chemistry O2 O Sternberg & Dalgarno 1995 OH OH+ H2O+ H2O H3O+

  8. Photodissociation Regions (PDRs) Nitrogen chemistry N2H+ N2 Sternberg & Dalgarno 1995 H3+ HCN NH3 see also Viti et al. 2011

  9. Detection of hydrates toward the high mass YSO W3 IRS 5 (Benz et al. 2010): OH+ and H2O+ are new molecules ! H2O+/H2O from 0.01 to > 1 (Wyrowski et al. 2010)

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

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

  12. Maiolino+05,09 Iono+06 [CII] high-z low-z Observations of [CII] at low and high-z The 2P3/22P1/2 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. Evidence for enhanced emission at high redshift, probably due to lower metallicities.

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

  14. The importance of dust grains H + H  H2 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)

  15. The importance of dust grains REACTANTS: MAINLY MOBILEATOMS AND RADICALS A + B AB association H + H H2 H + X XH (X = O, C, N, CO, etc.) Accretion WHICH CONVERTS O  OH  H2O C CH  CH2  CH3  CH4 N  NH  NH2  NH3 CO  HCO  H2CO  H3CO  CH3OH 10/[Tk1/2 n(H2)] days Diffusion+Reaction tqt(H)10-5-10-3 s RE: Watson & Salpeter 1972; Allen & Robinson 1977; Pickes & Williams 1977; d’Hendecourt et al. 1985; Hasegawa et al. 1992; Caselli et al. 1993..

  16. SO HCN HCO+ CH3OH CH3CH2CN HCOOCH3 The importance of dust grains 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) See also Gonzalez-Alfonso et al. (2010, 2011)

  17. The importance of dust grains G0 variations Grain size variations Hollenbach et al. 2009

  18. 10-1 0.1 0.01 10-2 10-3 10-4 10-5 10-6 D/H (Cazaux, Caselli & Spaans 2011) Tdust = 17 K HDO/H2O 15 K Turbulent solar nebula model 12 K 103 104 105 10-1 0.1 0.01 10-2 HDCO/H2CO 10-3 D2CO/H2CO Earth 10-4 ⊕ 10-5 10-6 Ehrenfreund et al. 2002 time

  19. [CII] Summary PDRs are the origin of much of the IR radiation from the ISM. Rich chemistry (low & high T). The [CII]158m is the brightest emission line in the spectrum of galaxies. Good tracer of the “dark” molecular mass. ALMA (z10!). Dust: efficient formation of molecules (e.g. H2O) on grain surfaces. Main cause of freeze-out & chemical differentiation.

  20. Observations of [CII] at high-z At z>7 galaxies could be identified through the detection of high order CO lines, Jupper>7... are these transitions excited? 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)  z

  21. ALMA Courtesy of A. Wotten 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.

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