star formation in damped lyman alpha systems
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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Star Formation in Damped Lyman alpha Star Formation in Damped Lyman alpha SystemsSystems
Art Wolfe
Collaborators:
J.X. Prochaska, J. C. Howk, E.Gawiser, and K. Nagamine
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DLAS are
•Definition of DLA: N(HI) > 2*1020 cm-2
•Distinguishing characteristic of DLAs : Gas is Neutral
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DLAS are
•Definition: N(HI) > 2*1020 cm-2
•Distinguishing characteristic of DLAs : Gas is Neutral
How are DLAs heated?
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•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
Relevance of DLAs for Star FormationRelevance of DLAs for Star Formation
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•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
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•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
CurrentVisibleMatter
NeutralGas atHigh z
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Evidence for Star Formation in DLAs?
• Direct Detection of Starlight
• Increase of Metallicity with time
• Evidence for Feedback between Stars and Absorbing Gas
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SFRs Inferred from DLA EmissionSFRs Inferred from DLA Emission
DLA Redshift Method SFR (My-
1)Ref.
0458-02 2.040 Ly-alpha > 1.5 Moller etal 04
0953+47 3.407 Ly-alpha 0.8 to 7.0 Bunker etal 05
2206-19A 1.921 Cntuum. 25 to 50 Moller etal 02
1210+17 1.892 H-alpha < 5.0 Kularni etal 01
1244-34 1.859 H-alpha < 1.6 Kulkarni etal 00
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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?
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CII* Technique for Measuring SFRs in DLAs
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OutlineOutline
• 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
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FUV Photon
Ionizing PhotonGrain
Grain Photoeletric Heating of Neutral Gas in DLAS
H II Region
Electron
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Thermal Balance in DLAsThermal Balance in DLAs
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Obtaining Cooling Rates from CII* AbsorptionObtaining Cooling Rates from CII* Absorption
• [C II] 158 micron transition dominates cooling of neutral gas in Galaxy ISM
• Spontaneous emission rate per atom lc=n[CII] obtained from strength of 1335.7 absorption and Lyman alpha absorption
• Thermal equilibrium condition lc= pe gives heating rate per atom
2121)IH(*)IIC(
][ ~ Ahn NN
IIC ν 2121)IH(*)IIC(
][ ~ Ahn NN
IIC ν
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HIRES Velocity Profiles of Metal-Rich DLAHIRES 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
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[C II] 158 micron Emission rates vs N(H I)[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
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[C II] 158 micron Emission rates vs N(H I)[C II] 158 micron Emission rates vs N(H I)
Critical Emission Rate
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Are DLAs Heated by Background RadiationAlone?
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Thermal Equilibria: lThermal Equilibria: lcc versus density versus density
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DLAs with Detected N(CII*)
lc versus ndiagrams
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Thermal Equilibria with local FUV Radiation Thermal Equilibria with local FUV Radiation IncludedIncluded
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Thermal Equilibria with local FUV Radiation Thermal Equilibria with local FUV Radiation IncludedIncluded
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Two-Phase Models of DLAs with Positive DetectionsTwo-Phase Models of DLAs with Positive Detections
WNM
WNM
CNM
•“CNM Model”
•“WNM Model”
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DLAs with Upper LimitsOn N(CII*):
lc versus n diagrams
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WNM Phase Model for DLAs with Upper LimitsWNM Phase Model for DLAs with Upper Limits
WNM
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Multi-phase Models and SFRsMulti-phase Models and SFRs
DLAs with lc > 10-27.1
1. CII* Forms in CNM Phase: moderate SFR/Area
2. CII* Forms in WNM Phase: high SFR/Area
DLAs with lc < 10-27.1
1. CII* Forms in WNM Phase: Background Heating Alone
2. CII* Forms in WNM Phase: moderate SFR/Area
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Multi-phase Models and SFRsMulti-phase Models and SFRs
DLAs with lc > 10-27.1
1. CII* Forms in CNM Phase: moderate SFR/ H I Area
2. CII* Forms in WNM Phase: high SFR/ H I Area
DLAs with lc < 10-27.1
1. CII* Forms in WNM Phase: Background Heating Alone
2. CII* Forms in WNM Phase: moderate SFR/ H I Area
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SFR or Luminosity perSFR or Luminosity per unit Comoving volumeunit Comoving volume
Observed
De-reddened
Giavalisco etal ‘04
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Global ConstraintsGlobal Constraints
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Consequences of LBG ConstraintsConsequences of LBG Constraints
• Most DLA models predict νDLA >> ν
LBG: high JνCII*
• 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, νDLA =ν
LBG
• Strong overlap between DLAs and LBGs
1. DLAs with lc >10-27.1 ergs s-1 H-1
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DLAs
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LBGs in DLAs with LBGs in DLAs with llcc > > 1010-27.1-27.1 ergs s ergs s-1 -1 HH-1-1
LBG
Dust
DLA
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DLA Gas May Replenish LBG Star DLA Gas May Replenish LBG Star Formation ActivityFormation Activity
• LBG Star Formation Rate Requires “Fuel”
• DLA Gas would sustain SFRs for ~ 2 Gyr.
• Replenishment from IGM may be required
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Supporting Evidence for this ScenarioSupporting Evidence for this Scenario
1. 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
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An LBG Galaxy Associated with a DLA (Moller etal ‘02)An LBG Galaxy Associated with a DLA (Moller etal ‘02)
•SFR=25 to 50 Myr-1
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An LBG Galaxy Associated with a DLA (Moller etal ‘02)An LBG Galaxy Associated with a DLA (Moller etal ‘02)
8.4 kpc
LyEmission [O III] Emission
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Preliminary DLA-LBG Cross-Correlation FunctionPreliminary DLA-LBG Cross-Correlation Function(Cooke etal 2005)(Cooke etal 2005)
LBG-DLALBG-DLA:
r=4.25,=1.11
LBG-LBG:LBG-LBG:
r=3.96,=0.15
Mpc
Mpc
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Nature of DLAs with lNature of DLAs with lcc < 10 < 10-27.1 -27.1 ergs s ergs s-1 -1 HH- 1- 1
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Low CII* Absorption
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ImplicationsImplications• 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
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DLA Age-Metallicity RelationshipDLA 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
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Incidence of DLAs per unit Absorption Incidence of DLAs per unit Absorption DistanceDistance
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Equivalence Between Bulge & Uniform Disk ScenariosEquivalence Between Bulge & Uniform Disk Scenarios
•Disk ScenarioSource
Field
•Bulge Scenario
Source
Field
•Mean Intensities: JνB=Jν
D if LνH I the same•Comoving Luminosity Densities, ν
B=νD
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Bolometric Backgrounds at z=0 due to Bolometric Backgrounds at z=0 due to Sources at z > zSources at z > zminmin
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Multi-phase Diagram for Typical DLAMulti-phase Diagram for Typical DLA
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Evidence Against WNM gas in a DLAEvidence Against WNM gas in a DLA
• SiII* Absorption sensitive to warm gas
• Absence of SiII* Absorption implies T < 800 K for CII* Gas
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Evidence for Grain Photoelectric HeatingEvidence for Grain Photoelectric Heating
• Statistically significant correlation between lc and dust-to-gas ratio
• Solid curves are lines of constant Jν
• Upper limits are at lowLow dust-to-gas ratios