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Star formation and molecular gas in (U)LIRGs

Star formation and molecular gas in (U)LIRGs. Sant Cugat April 17, 2012. Credits. Kate Isaak (ESTEC) Padelis Papadopoulos (MPI für Radioastronomie) Marco Spaans (Kapteyn Astronomical Institute) Eduardo González-Alfonso (Henares) Rowin Meijerink (Leiden Observatory)

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Star formation and molecular gas in (U)LIRGs

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  1. Star formation and molecular gas in (U)LIRGs SantCugat April 17, 2012

  2. Credits Kate Isaak (ESTEC) Padelis Papadopoulos (MPI für Radioastronomie) Marco Spaans (Kapteyn Astronomical Institute) Eduardo González-Alfonso (Henares) Rowin Meijerink (Leiden Observatory) Edo Loenen (Leiden Observatory) Alicia Berciano Alba (Leiden Observatory/ASTRON) Axel Weiß (MPI für Radioastronomie) + the HerCULES team Molecular gas in (U)LIRGs

  3. LIR/LCO  SFR/MH2  SFE (Gao & Solomon 2001) LIR SFR Conditions in ULIRGs • Starbursts cannot • be simply scaled up. • More intense starbursts are also more efficient with their fuel. Molecular gas in (U)LIRGs

  4. (U)LIRGs from low to high z • LIRGs dominate cosmic star formation at high redshift (Magnelliet al. 2011) Molecular gas in (U)LIRGs

  5. ISM in luminous high-z galaxies (Danielson et al. 2010) (Weiß et al. 2007) • Even in ALMA era, limited spatial resolution on high-z galaxies. • For unresolved galaxies, multi-line spectroscopy will be a key diagnostic Molecular gas in (U)LIRGs

  6. Outline • CO as a probe of the energy source un (U)LIRGs • H2O emission in (U)LIRGs • The X-factorin (U)LIRGs Molecular gas in (U)LIRGs

  7. HerCULES Herschel Comprehensive (U)LIRG Emission Survey Open Time Key Program on the Herschel satellite Molecular gas in (U)LIRGs

  8. Who is HerCULES? Jesus Martín-Pintado (Madrid) Joe Mazzarella (IPAC) Rowin Meijerink (Leiden) David Naylor (Lethbridge) Padelis Papadopoulos (Bonn) Dave Sanders (U Hawaii) Giorgio Savini (Cardiff/UCL) Howard Smith (CfA) Marco Spaans(Groningen) Luigi Spinoglio (Rome) Gordon Stacey (Cornell) Sylvain Veilleux (U Maryland) Cat Vlahakis (Leiden/Santiago) Fabian Walter (MPIA) Axel Weiß(MPIfR) Martina Wiedner (Paris) ManolisXilouris (Athens) Paul van derWerf (Leiden; PI) Susanne Aalto (Onsala) Lee Armus (Spitzer SC) VassilisCharmandaris (Crete) KalliopiDasyra (CEA) Aaron Evans (Charlottesville) Jackie Fischer (NRL) Yu Gao (Purple Mountain) Eduardo González-Alfonso (Henares) Thomas Greve (Copenhagen) Rolf Güsten (MPIfR) Andy Harris (U Maryland) Chris Henkel (MPIfR) Kate Isaak(ESA) Frank Israel (Leiden) Carsten Kramer (IRAM) Edo Loenen (Leiden) Steve Lord (NASA Herschel SC) Molecular gas in (U)LIRGs

  9. HerCULES in a nutshell • HerCULES has uniformly and statistically measured the neutral gas cooling lines in a flux-limited sample of 29 (U)LIRGs. • Sample: • all IRAS RBGS ULIRGs with S60 > 12.19 Jy (6 sources) • all IRAS RBGS LIRGs with S60 > 16.8 Jy (23 sources) • Observations: • SPIRE/FTS full high-resolution scans: 200 to 670 m at R ≈ 600, covering CO 4—3 to 13—12 and [CI] + any other bright lines • PACS line scans of [CII] and both [OI] lines • All targets observed to same (expected) S/N • Extended sources observed at several positions Molecular gas in (U)LIRGs

  10. HerCULES sample Molecular gas in (U)LIRGs

  11. Warning: may contain... • quiescent molecular (and atomic) gas • star-forming molecular gas (PDRs) • AGN (X-ray) excited gas (XDRs) • cosmic ray heated gas • shocks • mechanically (dissipation of turbulence) heated gas • warm very obcured gas (hot cores) Molecular gas in (U)LIRGs

  12. PDRs vs. XDRs Four differences: • X-rays penetrate much larger column densities than UV photons • Gas heating efficiency in XDRs is ≈10—50%, compared to <3% in PDRs • Dust heating much more efficient in PDRs than in XDRs • High ionization levels in XDRs drive ion-molecule chemistry over large column density Molecular gas in (U)LIRGs

  13. PDRs vs. XDRs: CO lines • XDRs produce larger column densities of warmer gas • Identical incident energy densities give very different CO spectra • Very high J CO lines are excellent XDR tracers • Need good coverage of CO ladder (Spaans & Meijerink 2008) Molecular gas in (U)LIRGs

  14. Mrk231 • At z=0.042, one of the closest QSOs (DL=192 Mpc) • With LIR = 41012 L , the most luminous ULIRG in the IRAS Revised bright Galaxy Sample • “Warm” infrared colours • Star-forming disk (~500 pc radius) + absorbed X-ray nucleus • Face-on molecular disk, MH2 ~ 5109 M HST/ACS (Evans et al., 2008) Molecular gas in (U)LIRGs

  15. Mrk231SPIREFTS (Van der Werf et al., 2010) Molecular gas in (U)LIRGs

  16. CO excitation 2 PDRs + XDR 6.4:1:4.0 n=104.2, FX=28* n=103.5, G0=102.0 n=105.0, G0=103.5 * 28 erg cm-2 s-1 G0=104.2 Molecular gas in (U)LIRGs

  17. CO excitation 3 PDRs6.4:1:0.03 n=106.5, G0=105.0 n=103.5, G0=102.0 n=105.0, G0=103.5 Molecular gas in (U)LIRGs

  18. High-J lines: PDR or XDR? • High-J CO lines can also be produced by PDR with n=106.5 cm—3 and G0=105, containinghalf the molecular gas mass. • Does this work? • G0=105 only out to 0.3 pc from O5 star; then we must havehalf of the molecular gas and dust in 0.7% of volume. • With G0=105,50% of the dust mass would be at 170K, which is ruled out by the Spectral Energy Distribution • [OH+] and [H2O+] > 10—9 in dense gas requires efficient and penetrative source of ionization;PDR abundances factor 100—1000 lower Only XDR model works! Molecular gas in (U)LIRGs

  19. High-J CO lines and AGNs Highly excited CO ladders are found in all high luminosity/compact sources with an energetically dominant AGN (and only in those sources). Molecular gas in (U)LIRGs

  20. Outline • CO as a probe of the energy source in (U)LIRGs • H2O emission in (U)LIRGs • The X-factorin (U)LIRGs Molecular gas in (U)LIRGs

  21. Water in molecular clouds • H2O ice abundant in molecular clouds • Can be released into the gas phase by UV photons, X-rays, cosmic rays, shocks,... • Can be formed directly in the gas phase in warm molecular gas • Abundant, many strong transitions  expected to be major coolant of warm, dense molecular gas Herschel image of (part of) the Rosetta Molecular Cloud Molecular gas in (U)LIRGs

  22. Low-z H2O: M82 vs. Mrk231 M82 Mrk231 • At z=0.042, one of the closest QSOs (DL=192 Mpc) • With LIR = 41012 L , the most luminous ULIRG in the IRAS Revised bright Galaxy Sample • At D = 3.9 Mpc, one of the closest starburst galaxies • With LIR = 31010 L , a very moderate starburst Molecular gas in (U)LIRGs

  23. H2O lines in M82 (Weiß et al., 2010) (Panuzzo et al., 2010) • Faint lines, complex profiles • Only lines of low excitation Molecular gas in (U)LIRGs

  24. Mrk231:strong H2O lines, high excitation (Van der Werf et al., González-Alfonso et al., 2010) Molecular gas in (U)LIRGs

  25. H2O lines in Mrk231 • Low lines: pumping by cool component + some collisional excitation • High lines: pumping by warm component • Radiative pumping dominates and reveals an infrared-opaque (100m ~ 1) disk. (González-Alfonso et al., 2010) Molecular gas in (U)LIRGs

  26. High-z connection: H2O at z=3.9 Van der Werf et al., 2011 • Line ratios similar to Mrk231 • FIR pumping dominates, implies 100 m-opaque disk • Radiation pressure dominates, Eddington-limited Molecular gas in (U)LIRGs

  27. H2O in HerCULES red = wet Molecular gas in (U)LIRGs

  28. Lessons from H2O (1 + 2 + 3 + 4) 2) Radiatively H2O lines reveal extended infrared-opaque circumnuclear gas disks. 3) Extinction and radiative pumping of highest CO lines. 1) In spite of high luminosities, H2O lines are unimportant for cooling the warm molecular gas. 4) Detection of H2O lines implies high FIR radiation field, but not the presence of an AGN. Molecular gas in (U)LIRGs

  29. Lessons from H2O (5) Radiation pressure from the strong IR radiation field: Since both 100 and Td are high,radiation pressure dominates the gas dynamics in the circumnuclear disk. 5) Conditions in the circumnuclear molecular disk are Eddington-limited. Molecular gas in (U)LIRGs

  30. Mechanical feedback • Radiation pressure can drive the observed molecular outflows (e.g., Murray et al., 2005) • Aalto et al., 2012: flow prominent in HCN  dense gas • Key process in linking ULIRGs and QSOs? • Shocks probably of minor importance in Mrk231 (Fischer et al., 2010) Molecular gas in (U)LIRGs (Feruglioet al., 2010)

  31. Possible consequences • Eddington-limited conditions account forLFIR-LHCN relation within factor 2 for standard dust/gas ratio (Andrews & Thompson 2011) • If accreting towards nuclear SMBH, can account for M*/M relation (Thompson et al., 2005) • Radiation pressure can expel nuclear fuel and produce Faber-Jackson relation (Murray et al., 2005) (Andrews & Thompson, 2011) Molecular gas in (U)LIRGs

  32. Outline • CO as a probe of the energy source in (U)LIRGs • H2O emission in (U)LIRGs • The X-factorin (U)LIRGs Molecular gas in (U)LIRGs

  33. The X-factor • Converting CO flux (luminosity) into H2 column density (mass): (MW: =4; ULIRGs: =0.8) Warning: discussions of the X-factor have been the death-blow for many conferences. (U)LIRG sample (Papadopoulos, Van der Werf, Isaak & Xilouris, astro-ph/1202.1803) Molecular gas in (U)LIRGs

  34. The X-factor and optical depth Highly turbulent motions  low optical depths ( high 12CO/13CO line ratios)  low X-factor (e.g., ULIRGs: X=0.8,Downes & Solomon 1997) NB: Tline is Tb of the line, not kinetic temperature Molecular gas in (U)LIRGs

  35. Calculating X-factors • Sample of 70 (U)LIRGs, 12CO 10, 21, 32, (43, 65) and 13CO 10, (21) lines • 2 component model: high excitation and low excitation component • X-factor explicitly calculated using non-LTE excitation model and finite optical depths Molecular gas in (U)LIRGs

  36. X-factors based on low CO lines only Assumptions: • One gas component • Based on low-J CO lines only Results: • X-factors cluster between 0.5 and 1 (cf., Downes/Solomon value of 0.8 for ULIRGs) with tail up to and exceeding Milky Way values • Subthermal excitation But: • Higher CO lines and density tracing lines reveal a substantial dense gas component (U)LIRG sample (Papadopoulos, Van der Werf, Isaak & Xilouris, astro-ph/1202.1803) Molecular gas in (U)LIRGs

  37. X-factors in a 2-component model Assumptions: • Orion-like high excitation component (probably not needed with denser coverage of CO ladder  Herschel) • Radiation pressure supported disk  LFIR/M(star forming gas) = constant (observed: LFIR/LHCN = constant; e.g., Gao & Solomon, Wu et al.) Results: • X-factors in (U)LIRGs dominated by dense, star-forming gas • X-factors have values of the order 24 (i.e., significantly higher than the Downes/Solomon value of 0.8) Molecular gas in (U)LIRGs

  38. Summary: getting at X • Derive X from 12CO 10  65 + 13CO 10 (or 21); ideally, use HCN (or HCO+ or CS) lines as well • Can be used at high z too, but 13CO is challenging • Aside: why did Downes & Solomon get it right (for the low-J lines) without 13CO? • High quality data showing turbulent velocity field • Correctly produced low optical depth • Getting the optical depth right is key Molecular gas in (U)LIRGs

  39. Summary • CO-H2 conversion factor can be derived from multi-line CO data (up to J=6) – see Papadopoulos et al., 2012ab (astro-ph/1109.4176 and 1202.1803) • Multi-line CO data (up to at least J=11) can separate star formation and AGN accretion as power sources of unresolved galaxies (vdWet al., 2010) • Luminous H2O lines trace infrared-opaque nuclear disks and reveal Eddington-limited circumnuclear conditions (vdWet al., 2011) • Strong shocks are only a minor contributor to CO excitation, barring exceptional cases (in preparation). • OH+ emission requires a high electron abundance and forms another way to reveal XDRs (in preparation). Molecular gas in (U)LIRGs

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