Probing the Universe with QSO Absorption Lines

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

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

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QSO Absorption-Line Jargon

• Intrinsic QSO Absorbers (e.g. BALs) ? tomorrow
• Lya (l1216) forest
• weak systems trace the dark matter
• zgt1.65 (optical spectroscopy), zgt2.2 (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!)

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Some QSO Absorption Line Studies

• Lya forest
• ground-based HST (Weymann et al)
• Keck/VLT Hi-Res ? 1.5ltzlt4, 90 of baryons in
  forest
• SDSS (Bernardi et al) ? near z3, 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)

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Weymann et al. (1998)
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Steidel, Sargent, Boksenberg (1988)
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courtesy Chris Churchill
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QSO Absorption-Line Jargon

• Intrinsic QSO Absorbers (e.g. BALs) ? tomorrow
• Lya (l1216) forest
• weak systems trace the dark matter
• zgt1.65 (optical spectroscopy), zgt2.2 (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!)

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Damped Lyman Alpha lines NHI gt 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.
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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
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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 z0)
• found WHI(hi-z) approximately equals W(z0)
• redshifts too high to search for galaxy light in
  the optical (cosmological dimming)

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Courtesy John Webb
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H I 21 cm Maps of Some Nearby Galaxies
VLA and WSRT maps courtesy John Hibbard, NRAO
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H I 21 cm Maps of Some Nearby Galaxies
VLA and WSRT maps courtesy John Hibbard, NRAO
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H I 21 cm Maps of Some Nearby Galaxies
VLA and WSRT maps courtesy John Hibbard, NRAO
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Optical Images of Stars in M51
Courtesy NOAO
Deep exposure
Short exposure
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How to Probe to Low-z?

• Problem need scarce HST UV spectroscopy time to
  search at zlt1.65
• zlt1.65 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.

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How to Probe to Low-z?

• Solution use low-z (zgt0.13) MgIIll2796,2802 AL
  systems as tracers for DLAs and measure NHI with
  HST ? Rao, Turnshek, Briggs (1995)
• Rao, Turnshek (2000)
• Rao, Turnshek, Nestor (2004)

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SDSS Spectrum of MgII Absorption

• z0.741 MgII absorption system (REW2796
  2.95Angstroms)

Right Strong MgII doublet and weaker MgI
line. Left Two Strong FeII lines and
three weaker MnII lines.
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Optical MgII AL Surveys

• z 0.37?2.27 SDSS spectroscopy of 3700 QSO
  sightlines (Nestor, Turnshek, Rao 2004)
• gt1300 MgII systems
• REW gt 0.3 Angstrom
• z 0.14?0.96 MMT spectroscopy of 400 QSO
  sightlines (Nestor, Turnshek, Rao 2005)
• 141 MgII systems
• REW gt 0.1 Angstrom

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Interpretation of Absorption Rest Equivalent
Width (REW)

• Due to curve-of-growth saturation effects, MgII
  REWs mostly measure kinematic spread.
• REW1 Angstrom black absorption ? gt 107 km/s.

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How to Probe to Low-z?

• Solution use low-z (zgt0.13) 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

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SDSS Redshift-REW Sightline Coverage

• Small REWs require high S/N for detection
• Large REWs can be detected in most spectra

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MgII REW DistN 0.1?5 Angstroms

• Left SDSS and MMT Surveys
• Right SDSS Survey alone

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MgII REW DistN 0.1?1.5 Angstroms

• Shows details of smaller REWs
• Evidence for two Populations?

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Evolution of MgII REWs z0.4?2.2

• Dashed no-evolution curves
• Stronger systems may evolve away faster

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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

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How to Probe to Low-z?Aim study the neutral
gas component

• Solution use low-z (zgt0.13) 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

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Some Representative HST DLA Data
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HST DLA Data Detection of Double DLA
zabs0.945, 1.031 N(HI)1.45E21, 2.60E21 atoms
cm-2 Zn/H26.5, 4.7 solar
Turnshek et al. 2004
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MgII-FeII-DLA Selection
Filled circles ? DLAs with NHI gt 2 x 1020 atoms
cm-2
Left MgII REW versus FeII REW
Right NHI versus MgII REW
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Evolution of Incidence of DLAs

• solid curve no-evolution
• incidence is product of absorber cross-section
  times absorber number density

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Evolution of HI Cosmological Mass Density from
DLAs

• HI gas mass approximately constant from
  z0.5?4.5, but is 3x lower at z0.

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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
(z0.656) is not visible.
Courtesy Chuck Steidel
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Identification of DLA Absorbing Galaxies
Infrared K-band image of the Q0738313
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
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Identification of DLA Absorbing Galaxies
Infrared K-band image of the SDSS QSO 17275302
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
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Some Results on DLA Galaxy IDs
?
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Evolution of Neutral Gas Metal Abundance

• Beginning to measure abundances at lower-z,
  seeing evidence for evolution.

Rao et al. 2004
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Theory

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

Keck HIRES
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Theory

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

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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.

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Theory

• Pei, Fall, Hauser (1999)

W
WHI
Wbary_gal
Wbary_flow
Right Models of Cosmic SF
Left Corresponding Predictions
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Cosmic Star Formation and DLAs

• Hopkins DLAs? filled black circles

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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

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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 gt 2
  Angstroms).

?
Potentially 9000
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Current SDSS MgII Plans

• 2. Neutral Gas-Phase Element Abundances Dust
• use HST NHI measurements and SDSS composites

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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
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Current SDSS MgII Plans

• 3. Gravitational Amplification of Bkgd QSOs

Observed Frame amplification/reddening (Menard,
Nestor, Turnshek 2004)
Top 2 rows, fake data Bottom row, real data
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Current SDSS MgII Plans

• 3. Gravitational Amplification of Bkgd QSOs

Observed Frame amplification/reddening (Menard,
Nestor, Turnshek 2004)
real data corrected for bias
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Current SDSS MgII Plans

• 4. Mean Reddening and Extinction

mean reddening in QSO frame (van den
Berk)
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Current SDSS MgII Plans

• 5. Study of Individual Absorbing Galaxies

IRTF H-band image of double DLA sightline (z1)
(Belfort-Mihalyi)
z0.009 DLA dwarf galaxy (Schulte-Ladbeck et al
2004)
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Current SDSS MgII Plans

• 6. Mean Integrated Light of Absorbing Galaxies
• ? Can stack images!

Right Putative MgII gas cross-sections of HST
UDF galaxies (Rimoldini). For SDSS MgII
absorbers, a QSO sightline passes through each
circle. Stacking images centered on the QSO will
yield mean integrated light of absorbing
galaxies.
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E.g., Composite Light from Halos of Edge-On
Galaxies
Zibetti, White, Brinkmann (2004)
For SDSS MgII Systems Use images stacked on the
position of the QSO to measure the mean
integrated light of absorbing galaxies then
compare to non-absorbed samples of
QSOs (Zibetti)
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Current SDSS MgII Plans

• 7. Absorber Kinematics and Clustering
• e.g., 2-pt correlation function
• null results on initial (small) sample
  (Rimoldini)
• but now 20x bigger
• also, account for velocity substructure (lt 500
  km/s)
• 8. MgII Absorbers and LRGs
• Bouche, Murphy, Peroux (2004) claim positive
  cross-correlation between MgIIs-LRGs, 0.67 times
  amplitude of LRG-LRG auto-correlation (212 MgIIs,
  20,000 LRGs)
• Menard cant confirm? ? but now bigger sample

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Summary Strong MgII Absorbers

• Mostly Galaxies Selected by Gas Cross-Section
• Strong MgII Absorbers ?high-NHI DLAs
• track evolution of the HI mass in the universe
• track absorber cross-section times comoving
  density
• track cosmic neutral-gas phase metallicity dust
• explore lensing/DM
• expore environment (associated galaxies,
  clustering)