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Probing the Universe with QSO Absorption Lines

Probing the Universe with QSO Absorption Lines. David Turnshek University of Pittsburgh. Outline: QSO Absorption Line Overview Investigating the Neutral Gas Component Future Work with SDSS Data Collaborators: Sandhya Rao Daniel Nestor Brice Menard Eric Monier Michele Belfort-Mihalyi

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Probing the Universe with QSO Absorption Lines

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  1. Probing the Universe with QSO Absorption Lines David Turnshek University of Pittsburgh

  2. Outline: • QSO Absorption Line Overview • Investigating the Neutral Gas Component • Future Work with SDSS Data • Collaborators: • Sandhya Rao • Daniel Nestor • Brice Menard • Eric Monier • Michele Belfort-Mihalyi • Andrew Hopkins • Lorenzo Rimoldini • Ravi Sheth • Daniel Vanden Berk • Stefano Zibetti • Anna Quider • + new SDSS collaborators …

  3. Quasar Absorption Lines: Probing the Gas in the Universe Courtesy John Webb Quasar spectroscopy offers the opportunity to study foreground gas.

  4. Motivation • galaxy formation  conversion of gas into stars • probe to large redshift (look back time) without luminosity bias • use QSO absorption lines to study: • dark matter • extragalactic UV ionizing background • structure formation • physical properties of gas/dust • e.g., gas-phase metallicity, ionization, density, temperature, distribution and extent, Wgas

  5. QSO Absorption-Line Jargon • Intrinsic QSO Absorbers (e.g. BALs)  tomorrow • Lya (l1216) forest: • weak systems trace the dark matter • z>1.65 (optical spectroscopy), z>2.2 (SDSS) • Metal-Line Systems: • OIV – samples high ionizations • CIV – samples moderate ionizations • MgII - samples a large range in HI column density • Lya forest • Lyman Limit • Damped Lya (DLA) • DLAs (bulk of neutral gas component!)

  6. Some QSO Absorption Line Studies • Lya forest: • ground-based +HST (Weymann et al) • Keck/VLT Hi-Res  1.5<z<4, 90% of baryons in forest • SDSS (Bernardi et al)  near z=3, signature of HeII reionization (temp, opt depth) • SDSS (McDonald, Seljak et al)  clustering, power spectrum, cosmological parameters, neutrino mass • Metal-Line Systems: • ground-based CIV + MgII Surveys (Sargent et al; Churchill et al) • HST OVI Surveys – warm-hot IGM (Tripp et al)

  7. Weymann et al. (1998):

  8. Steidel, Sargent, Boksenberg (1988):

  9. courtesy Chris Churchill:

  10. QSO Absorption-Line Jargon • Intrinsic QSO Absorbers (e.g. BALs)  tomorrow • Lya (l1216) forest: • weak systems trace the dark matter • z>1.65 (optical spectroscopy), z>2.2 (SDSS) • Metal-Line Systems: • OVI – samples high ionizations • CIV – samples moderate ionizations • MgII - samples a large range in HI column density • Lya forest • Lyman Limit • Damped Lya (DLA) • DLAs (bulk of neutral gas component!)

  11. Damped Lyman Alpha lines: NHI> 2 x 1020 atoms cm-2 • DLA systems are very rare. • Yet, they contain about 95% of the • neutral gas mass in the universe. • They are important because • galaxy formation and evolution • involves the collapse of neutral gas • that eventually forms stars. • by tracking DLA systems back in • time (redshift), we can study galaxy • formation and evolution. Kim et al. 2002 f is the frequency distribution of HI column densities.

  12. The Lyman-Alpha Absorption Line of Neutral Hydrogen HI Lya (l1216) The shape of an absorption line depends on the column density of the gas, N, and the thermal velocity of the gas, b. The curve of growth 1 cm2 N = number of atoms per cm2 along the line of sight b = 2 vrms “Damped Lya”””

  13. 20 Years of Searching for DLAs • interested in selecting galaxies by gas cross-section (e.g., sightline through MWG  DLA) • Wolfe, Turnshek, Smith, Cohen (1986) probed redshifts z = 1.7  3.3 from the ground • found excess in gas cross-sections times number of absorbers (compared to expectations at z=0) • found WHI(hi-z) approximately equals W*(z=0) • redshifts too high to search for galaxy light in the optical (cosmological dimming)

  14. Courtesy John Webb

  15. H I 21 cm Maps of Some Nearby Galaxies: VLA and WSRT maps courtesy John Hibbard, NRAO

  16. H I 21 cm Maps of Some Nearby Galaxies: VLA and WSRT maps courtesy John Hibbard, NRAO

  17. H I 21 cm Maps of Some Nearby Galaxies: VLA and WSRT maps courtesy John Hibbard, NRAO

  18. Optical Images of Stars in M51: Courtesy NOAO Deep exposure Short exposure

  19. How to Probe to Low-z? • Problem: need scarce HST UV spectroscopy time to search at z<1.65 • z<1.65 covers 70% of the age of the Universe! • Problem: DLAs are rare (0.2 per unit z at hi-z, and more rare at low-z) • HST QSO AL Key Project found only one DLA during its 4 Cycles of HST observation.

  20. How to Probe to Low-z? • Solution: use low-z (z>0.13) MgIIll2796,2802 AL systems as tracers for DLAs and measure NHI with HST Rao, Turnshek, Briggs (1995) • Rao, Turnshek (2000) • Rao, Turnshek, Nestor (2004)

  21. SDSS Spectrum of MgII Absorption • z=0.741 MgII absorption system (REW2796 = 2.95Angstroms) Right: Strong MgII doublet and weaker MgI line. Left: Two Strong FeII lines and three weaker MnII lines.

  22. Optical MgII AL Surveys • z = 0.372.27: SDSS spectroscopy of 3700 QSO sightlines (Nestor, Turnshek, Rao 2004) • >1300 MgII systems • REW > 0.3 Angstrom • z = 0.140.96: MMT spectroscopy of 400 QSO sightlines (Nestor, Turnshek, Rao 2005) • 141 MgII systems • REW > 0.1 Angstrom

  23. Interpretation of Absorption Rest Equivalent Width (REW) • Due to “curve-of-growth” saturation effects, MgII REWs mostly measure kinematic spread. • REW=1 Angstrom black absorption  > 107 km/s.

  24. How to Probe to Low-z? • Solution: use low-z (z>0.13) MgIIll2796,2802 AL systems as tracers for DLAs and measure NHI with HST  Rao, Turnshek, Briggs (1995) • Rao, Turnshek (2000) • Rao, Turnshek, Nestor (2004) • Infer DLA statistics from MgII statistics

  25. SDSS Redshift-REW Sightline Coverage • Small REWs require high S/N for detection • Large REWs can be detected in most spectra

  26. MgII REW DistN: 0.15 Angstroms • Left: SDSS and MMT Surveys • Right: SDSS Survey alone

  27. MgII REW DistN: 0.11.5 Angstroms • Shows details of smaller REWs • Evidence for two Populations?

  28. Evolution of MgII REWs: z=0.42.2 • Dashed: no-evolution curves • Stronger systems may evolve away faster

  29. MgII Effective Absorbing Cross-Sections • The incidence, dn/dz, depends on the product of galaxy cross-section times comoving galaxy number density • Right: constant comoving number density

  30. How to Probe to Low-z?[Aim: study the neutral gas component] • Solution: use low-z (z>0.13) MgIIll2796,2802 AL systems as tracers for DLAs and measure NHI with HST  Rao, Turnshek, Briggs (1995) • Rao, Turnshek (2000) • Rao, Turnshek, Nestor (2004) • Infer DLA statistics from MgII statistics • HST DLA Surveys in Cycles 6, 9, 11 • 198 MgII systems studied  41 DLAs identified

  31. Some Representative HST DLA Data

  32. HST DLA Data: Detection of Double DLA zabs=0.945, 1.031 N(HI)=1.45E21, 2.60E21 atoms cm-2 [Zn/H]=26.5%, 4.7% solar Turnshek et al. 2004

  33. MgII-FeII-DLA Selection Filled circles  DLAs with NHI > 2 x 1020 atoms cm-2 Left: MgII REW versus FeII REW Right: NHI versus MgII REW

  34. Evolution of Incidence of DLAs • solid curve: no-evolution • incidence is product of absorber cross-section times absorber number density

  35. Evolution of HI Cosmological Mass Density from DLAs • HI gas mass approximately constant from z=0.54.5, but is 3x lower at z=0.

  36. Identification of MgII Absorbing Galaxies Quasar 3C336 Sightline Hubble Space Telescope image of a field with several quasar absorption line system galaxies identified. A galaxy at the DLA redshift (z=0.656) is not visible. Courtesy Chuck Steidel

  37. Identification of DLA Absorbing Galaxies Infrared K-band image of the Q0738+313 sightline with DLAs at z = 0.091 and z = 0.221. IDs put the galaxies at 0.08 and 0.1L*, respectively. Turnshek et al. 2001

  38. Identification of DLA Absorbing Galaxies Infrared K-band image of the SDSS QSO 1727+5302 sightline with DLAs at z = 0.945 and z = 1.031. IDs for G1 and G2 are, conservatively, 0.06 and 0.15 L*. Turnshek et al. 2004

  39. Some Results on DLA Galaxy IDs ?

  40. Evolution of Neutral Gas Metal Abundance • Beginning to measure abundances at lower-z, seeing evidence for evolution. Rao et al. 2004

  41. Theory • Prochaska & Wolfe (1997) proposed that leading edge asymmetry in hi-z absorption profiles were signatures of thick rotating HI disks. Keck HIRES

  42. Theory • Haehnelt, Steinmetz, Rauch (1998) found that merging fragments could also account for profiles.

  43. Theory • Luminous disks as favored by Prochaska & Wolfe (1997) ?  e.g., Eggen, Lynden-Bell, Sandage (1962) scenario of monolithic disk collapse. • Merging fragments as favored by Haehnelt, Steinmetz, Rauch (1998) ?  e.g., merging hierarchy of CDM halos (White & Rees 1978). • Great variety  seems to rule possibility that DLAs are exclusively large disks.

  44. Theory • Pei, Fall, Hauser (1999): W* WHI Wbary_gal Wbary_flow Right: Models of Cosmic SF Left: Corresponding Predictions

  45. Cosmic Star Formation and DLAs • Hopkins: DLAs filled black circles

  46. Progress on MgIIs and DLAs with SDSS • SDSS continues to offer a wealth of knew information • Summer 2004: have recently-generated catalog of 20,000 MgII Absorbers (about 40% of eventual total) • Preliminary work in many areas …

  47. Current SDSS MgII Plans • 1. Statistical Properties of MgII Absorbers • must improve statistics at higher REW • Only have analyzed 243 MgII systems with kinematically extreme absorption (REW > 2 Angstroms).  Potentially: ~9000

  48. Current SDSS MgII Plans • 2. Neutral Gas-Phase Element Abundances + Dust • use HST NHI measurements and SDSS composites

  49. Neutral Gas-Phase Element Abundances + Dust Turnshek, Nestor, et al 3700+ composite: • NHI ~ constant for saturated MgII REWs! • find increasing metallicity with increasing kinematic spread Unsaturated ZnIIl2026 CrIIl2062

  50. Current SDSS MgII Plans Observed Frame: amplification/reddening (Menard, Nestor, Turnshek 2004) • 3. Gravitational Amplification of Bkgd QSOs Top 2 rows, fake data Bottom row, real data

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