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Molecular tracers in the Galaxy (and beyond…)

Molecular tracers in the Galaxy (and beyond…). Willem Baan 1 & Edo Loenen 1,2 1 ASTRON, 2 Kapteyn Astronomical Institute. Galactic Molecular Survey (in progress) ‏.

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Molecular tracers in the Galaxy (and beyond…)

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  1. Molecular tracers in the Galaxy (and beyond…) Willem Baan1 & Edo Loenen1,2 1ASTRON, 2Kapteyn Astronomical Institute

  2. Galactic Molecular Survey (in progress)‏ • Objectives: (1) to understand physical and chemical conditions of molecular gas by using multiple-molecule multiple-line analysis (2) integrate with physical/chemistry modeling (see Meijerink etal ‘05,’06,’07)(3) bootstrap => Galactic properties => nearby extragalactic => distant galaxies • First Onsala narrow-band sample (ongoing analysis)‏ • 32 CS-selected HII regions along Galactic plane • HCN, HNC, HCO+, 13CO, C18O, HNCO, N2H+, CN, CS • First Mopra broad-band sample (being reduced)‏ • 7 cores in CMZ, 28 in G333.3, 15 HII regions • 4 broadband windows covering 84 - 116 GHz

  3. Preliminary results (Onsala Data)‏ • data shows global trends in line ratios • strong similarity with extra- galactic sources • ratios can be explained using extensive physics/chemistry modeling • diagnostics of excitation/heating conditions • very low HNC/HCNratios (so far) unexplained • Enhanced cosmic ray flux? Hot Core chemistry? Extra-Galactic Galactic

  4. Preliminary results (Onsala Data)‏ • HNC/HCN line ratio changes as function of distance to Galactic Center! • Large scale change of physical environment along the Milky Way • Cosmic Ray flux is possible cause • many more molecules to analyze: just the tip of the iceberg!

  5. ExtraGalactic: Density Evolution (ongoing)‏ • Large database (nearby & active galaxies) (Baan etal 2008)‏ • low density gas: CO(1-0) & CO(2-1)‏ • high density gas: HCN(1-0), HNC(1-0), HCO+(1-0), CN(1-0), CN(2-1), CS(3-2)‏ • Comparison with physics/chemistry modeling (Loenen etal 2008)‏ • Large differentiation in line ratios: • HD vs LD tracers => evolution & depletion • HD tracers => chemistry effects • Evidence for chemical evolution of galaxies during FIR/starburst • Higher HCO+/HCN at lower LFIR indicates evolution (Baan etal 2008)‏ (filled symbols are ULIRGs/OH MM)‏ decreasing LFIR

  6. ExtraGalactic: Chemistry • physics/chemistry modeling results show distinct excitation regimes => color tracks in diagnostic diagrams (Loenen et al ‘08, ‘09)‏ • differentiation in HD line ratios due to density and nature of heating source: • HCO+/HCN and HCO+/HNC ratios sensitive to density • HNC/HCN ratio sensitive to heating source: • >1: X-rays (XDRs)‏ • 0.5 – 1: UV (young PDRs)‏ • < 0.5: UV + added mechanical heating (SNe, older PDRs)‏ density low high low

  7. Our wishes for aMopra Milky Way Survey • Broad-band 84-92 GHz to include: • 29SiO, 30SiO, HC18O+, SiO, NH2D, H13CN, HCO, H13CO+ , HC17O+, HN13C, HNCO, CH3OH, HCN, H15NC, HCN, HCO+, HOC+, HNC, … • combined with 108-116 GHz for CN lines, CO, 13CO, and C18O • To include weaker lines => longer integration times: • Survey on selected sources instead of OTF to investigate chemical changes between different regions? • mapping of interesting region (Galactic Center?, strip along/through Galactic Plane?)‏ • On-the-fly mapping not sufficient • There must be sufficient line information to do new physics !!

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