Halo Occupation of MgII Halo Occupation of MgII AbsorbersAbsorbers

Jeremy TinkerJeremy Tinker

Hsiao-Wen ChenHsiao-Wen Chen

University of ChicagoUniversity of Chicago

Binney & Binney &

TremaineTremaine

What are MgII Absorbers?What are MgII Absorbers?

Dark matter halo, Dark matter halo, galaxy at center, galaxy at center,

cold gas probed by cold gas probed by MgII in halo.MgII in halo. Chuck Steidel

2796, 2796, 28032803

Visualizations of Sloan DataVisualizations of Sloan Data

courtesy of Mark Subbaraocourtesy of Mark Subbarao

Visualizations of Sloan DataVisualizations of Sloan Data

courtesy of Mark Subbaraocourtesy of Mark Subbarao

What do (we think) they What do (we think) they mean?mean?

Small halo = lower Small halo = lower column density, lower column density, lower

dispersion, weaker dispersion, weaker absorber absorber

((equivalent width Wequivalent width W [A]) [A])

Big halo = lots of Big halo = lots of gas, large gas, large

dispersion, stronger dispersion, stronger absorber.absorber.

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1011M

Clustering Bias Clustering Bias of MgII Systemsof MgII Systems

• Bouche et al (2006): Bouche et al (2006): bias relative to LRGs bias relative to LRGs as a function of W: as a function of W: anti-correlationanti-correlation!!

• Distribution of impact Distribution of impact parameters: “strong parameters: “strong absorbers absorbers preferentially at low preferentially at low impact parameters.”impact parameters.”

Halo-Based ModelHalo-Based Model

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W (ρ b) = Aw ρ l2 + ρ b2

( )∫ dl

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P(W |M)dW =Cg∫€

P(W |M)dW ∝ P(ρ b |M)dρ bCCgg - covering - covering fraction x fraction x incidence.incidence.

AAWW -encompass -encompass MgII gas MgII gas fraction and fraction and density-EW density-EW relation.relation.

core-isothermal core-isothermal density profile density profile of MgII gas.of MgII gas.

Low-mass Low-mass halohalo

High-High-mass halomass halo

P(P(bb)) - PDF of - PDF of impact impact parametersparameters

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Aw = A0 M /1012

( )α A

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Cg (M) = 4 − pt.spline

ResultsResults

Mass points are estimated by Bouche et Mass points are estimated by Bouche et al from b(w). Not used in model fitting.al from b(w). Not used in model fitting.

Data Used:Data Used:--FrequencyFrequency (number per unit (number per unit distance)distance)

--BiasBias relative to relative to LRGs.LRGs.

-Model: 6 free -Model: 6 free parameters. (47 parameters. (47 data points)data points)

--AA=-0.13=-0.13

Dekel & Birnboim Dekel & Birnboim 20062006

Dekel & Birnboim 2006Dekel & Birnboim 2006

Keres et al. 2005Keres et al. 2005

Low Mass = Cold Low Mass = Cold Gas (T~10Gas (T~1044 K) K)

High Mass = Hot High Mass = Hot Gas (T>10Gas (T>1066 K) no K) no

MgIIMgIITransition mass scale: Transition mass scale: shock heating occurs shock heating occurs as an inside-out as an inside-out process.process.

Simulations predict Simulations predict that this process that this process occurs over 1-2 dex in occurs over 1-2 dex in halo mass.halo mass.

In the hot mode, some In the hot mode, some cold gas still exists.cold gas still exists.

Cold vs. Hot Halo GasCold vs. Hot Halo Gas

ResultsResults

Mass points are estimated by Bouche et Mass points are estimated by Bouche et al from b(w). Not used in model fitting.al from b(w). Not used in model fitting.

-”Shock” Model: 8 -”Shock” Model: 8 free parameters.free parameters.

-ffcoldcold = 6% = 6%

-101011.011.0 transition transition mass mass shockshock=0.8 =0.8 (transition width of (transition width of 1.25 dex in mass)1.25 dex in mass)

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Rshock = R0 +α shock log(M /1012)

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fcold → R ≤ Rshock

Impact ParametersImpact Parameters

• Points+bars are mean Points+bars are mean and dispersion for and dispersion for every ten data points.every ten data points.

• Line+shade are mean Line+shade are mean and dispersion of and dispersion of model (note: these model (note: these are model predictions).are model predictions).

• Dotted line = 99% Dotted line = 99% upper bound on P(W|upper bound on P(W|bb).).

• NB! - take these data NB! - take these data with grain of salt: with grain of salt: incomplete at low incomplete at low bb and possibly biased. and possibly biased. Use for sanity check Use for sanity check only.only.

ConclusionsConclusions

• Proof of concept: Toward Proof of concept: Toward constraining the distribution of constraining the distribution of cold gas across the halo mass cold gas across the halo mass spectrum. spectrum.

• Models without a hot-cold Models without a hot-cold transition cannot fit the data.transition cannot fit the data.