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Star Formation in Damped Lyman alpha Systems

Star Formation in Damped Lyman alpha Systems. Art Wolfe Collaborators: J.X. Prochaska, J. C. Howk, E.Gawiser, and K. Nagamine. DLAS are. Definition of DLA: N(HI) > 2*10 20 cm -2 Distinguishing characteristic of DLAs : Gas is Neutral. DLAS are. Definition: N(HI) > 2*10 20 cm -2

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Star Formation in Damped Lyman alpha Systems

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  1. Star Formation in Damped Lyman alpha Systems Art Wolfe Collaborators: J.X. Prochaska, J. C. Howk, E.Gawiser, and K. Nagamine

  2. DLAS are • Definition of DLA: N(HI) > 2*1020 cm-2 • Distinguishing characteristic of DLAs : Gas is Neutral

  3. DLAS are • Definition: N(HI) > 2*1020 cm-2 • Distinguishing characteristic of DLAs : Gas is Neutral How are DLAs heated?

  4. Relevance of DLAs for Star Formation • DLAs Dominate the Neutral Gas Content of the Universe at z=[0,5] • Gas Content of DLAs at z=[3,4] Accounts for current visible Mass • DLAs Serve as Important Neutral Gas Reservoirs for Star Formation

  5. DLAs Dominate the Neutral Gas Content of the Universe at z=[0,5] • Gas Content of DLAs at z=[3,4] Accounts for current visible Mass • DLAs Serve as Important Neutral Gas Reservoirs for Star Formation Prochaska, Herbert-Fort, & Wolfe ‘05

  6. DLAs Dominate the Neutral Gas Content of the Universe at z=[0,5] • Gas Content of DLAs at z=[3,4] Accounts for current visible Mass • DLAs Serve as Important Neutral Gas Reservoirs for Star Formation Current Visible Matter Neutral Gas at High z

  7. Evidence for Star Formation in DLAs? • Direct Detection of Starlight • Increase of Metallicity with time • Evidence for Feedback between Stars and Absorbing Gas

  8. SFRs Inferred from DLA Emission

  9. Comparison between DLA and LBG SFRs • LBG SFRs between 3 and 100 solar masses per year A few DLAs located at either end of LBG distribution • What is SFR Distribution For a fair sample of DLAs?

  10. CII* Technique for Measuring SFRs in DLAs

  11. Outline • Heating and Cooling of DLAs • Inferring SFRs per unit Area from CII* Absorption • Global Constraints SFRs per unit Comoving Volumne Background Radiation • Relationship Between DLAs and LBGs

  12. Grain Photoeletric Heating of Neutral Gas in DLAS H II Region FUV Photon Grain Ionizing Photon Electron

  13. Thermal Balance in DLAs

  14. Obtaining Cooling Rates from CII* Absorption • [C II] 158 micron transition dominates cooling of neutral gas in Galaxy ISM • Spontaneous emission rate per atom lc=nL[CII] obtained from strength of 1335.7 absorption and Lyman alpha absorption • Thermal equilibrium condition lc= Gpe gives heating rate per atom

  15. HIRES Velocity Profiles of Metal-Rich DLA • Multi-component structure of absorbing gas • Velocity Structure of CII* and Resonance lines are similar • Strength of CII* Absorption gives heating rate of the neutral gas

  16. [C II] 158 micron Emission rates vs N(H I) • Median lc=10-26.6 ergs s-1 H-1 for positive Detections • Upper limits tend to have low N(H I) • DLA lc values about 30 times lower than for Galaxy: explained by lower dust content and similar SFRs per unit area

  17. [C II] 158 micron Emission rates vs N(H I) Critical Emission Rate

  18. Are DLAs Heated by Background Radiation Alone?

  19. Thermal Equilibria: lc versus density

  20. DLAs with Detected N(CII*) lcversus n diagrams

  21. Thermal Equilibria with local FUV Radiation Included

  22. Thermal Equilibria with local FUV Radiation Included

  23. Two-Phase Models of DLAs with Positive Detections • “CNM Model” WNM CNM • “WNM Model” WNM

  24. DLAs with Upper Limits On N(CII*): lc versus n diagrams

  25. WNM Phase Model for DLAs with Upper Limits WNM

  26. DLAs with lc > 10-27.1 CII* Forms in CNM Phase: moderate SFR/Area CII* Forms in WNM Phase: high SFR/Area DLAs with lc < 10-27.1 CII* Forms in WNM Phase: Background Heating Alone CII* Forms in WNM Phase: moderate SFR/Area Multi-phase Models and SFRs

  27. DLAs with lc > 10-27.1 CII* Forms in CNM Phase: moderate SFR/ H I Area CII* Forms in WNM Phase: high SFR/ H I Area DLAs with lc < 10-27.1 CII* Forms in WNM Phase: Background Heating Alone CII* Forms in WNM Phase: moderate SFR/ H I Area Multi-phase Models and SFRs

  28. Giavalisco etal ‘04 Observed SFR or Luminosity per unit Comoving volume De-reddened

  29. Global Constraints

  30. Consequences of LBG Constraints DLAs with lc >10-27.1 ergs s-1 H-1 • Most DLA models predict rnDLA >> rnLBG: high JnCII* • This rules out models with inefficient heating -All models where CII* absorption occurs in WNM -Models where CII* absorption occurs in CNM gas heated by FUV radiation incident on large grains • Even with efficient heating, rnDLA =rnLBG • Strong overlap between DLAs and LBGs

  31. DLAs

  32. LBGs in DLAs with lc > 10-27.1 ergs s-1 H-1 DLA LBG Dust

  33. DLA Gas May Replenish LBG Star Formation Activity • LBG Star Formation Rate Requires “Fuel” • DLA Gas would sustain SFRs for ~ 2 Gyr. • Replenishment from IGM may be required

  34. Supporting Evidence for this Scenario • Detection of DLA absorption in an LBG 2. Evidence for DLA-LBG cross correlation 3. Evidence for Grain photoelelctric heating 4. Independent Evidence for CNM Gas

  35. An LBG Galaxy Associated with a DLA (Moller etal ‘02) • SFR=25 to 50 Myr-1

  36. An LBG Galaxy Associated with a DLA (Moller etal ‘02) [O III] Emission Lya Emission 8.4 kpc

  37. Preliminary DLA-LBG Cross-Correlation Function (Cooke etal 2005) LBG-DLA: r=4.25,s=1.11 g=2.04,s=0.44 Mpc LBG-LBG: r=3.96,s=0.29 g=1.55,s=0.15 Mpc

  38. Nature of DLAs with lc < 10-27.1 ergs s-1 H- 1

  39. Low CII* Absorption

  40. Implications • Local Source of Heat Input Required for the 40% of DLAs with lc > 10-27.1 ergs s-1 H-1 • These DLAs likely heated by attenuated FUV radiation emitted by embedded LBG. • In these DLAs, gas producing CII* absorption is CNM. • Background Radiation heats the 60% of DLAs with lc < 10-27.1 ergs s-1 H-1. Gas is WNM. • LBGs may be in subset of DLAs in which starburst activity occurs. DLA gas may fuel star formation

  41. DLA Age-Metallicity Relationship • Sub-solar metals at all z • Statistically Significant evidence for increase of metals with time • Most DLAs detected at epochs prior to formation of Milky Way Disk • Mixed Evidence for star formation

  42. Incidence of DLAs per unit Absorption Distance

  43. Equivalence Between Bulge & Uniform Disk Scenarios • Disk Scenario Source Field • Bulge Scenario Field Source • Mean Intensities: JnB=JnD if Ln/AH I the same • Comoving Luminosity Densities, rnB=rnD

  44. Bolometric Backgrounds at z=0 due to Sources at z > zmin

  45. Multi-phase Diagram for Typical DLA

  46. Evidence Against WNM gas in a DLA • SiII* Absorption sensitive to warm gas • Absence of SiII* Absorption implies T < 800 K for CII* Gas

  47. Evidence for Grain Photoelectric Heating • Statistically significant correlation between lc and dust-to-gas ratio • Solid curves are lines of constant Jn • Upper limits are at low Low dust-to-gas ratios

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