cosmic variance of small-scale structure formation: …afialkov/talk_ahn.pdf · cosmic variance of...
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Cosmic Variance of Small-Scale Structure
Formation: Large-Scale Density and CDM-Baryon
Drift Velocity Environment
Based on collaboration with:
Paul Shapiro (Texas), Ilian Iliev (Sussex), Garrelt Mellema
(Stockholm), Jun Koda (Studi Roma Tre), Yi Mao (Tsinghua), Ue-Li
Pen (CITA);
Britton Smith (UC San Diego), Mike Norman (UC San Diego)
Kyungjin Ahn (Chosun U, Korea)
Aspen Winter Conference
Feb 2018
Outline- Motivation
- Previous work: cosmic reionizaiton with minihalo
stars and massive-halo stars
- Recent work: CDM-baryon streaming velocity +
Density environment affecting halo & star formation
- In progress, along this line
- BCCOMICS (initial condition generator)
- BCCOMICS+enzo cosmic variance of halo
formation, star formation, etc.
- Summary/prospect
• Large-box simulation preferred– The larger, the better in statistics (Barkana & Loeb )
– >~100 Mpc to see bubbles with ~20 Mpc or larger
• Resolution limited– Cannot resolve minihalos
– Cannot use minihalo stars
– Losing photon budget
• Need subgrid treatment– Then can cover all stars
Motivation
What’s new?• Populating grid with
minihalos (first stars!)– small-box (6.3/h Mpc)
simulation resolving minihalos– correlation between density &
minihalo population (nonlinear bias: KA+ in preparation)
– put one Pop III star per minihalo
• Considering photo-dissociation of coolant– calculate transfer of Lyman-
Werner Background (KA, Shapiro, Iliev, Mellema, Pen 2009)
– remove first star from minihalos, if LW intensity over-critical
• Retarded-time Green’s function calculation (KA 2015, JKAS)
• Self-regulated first star formation epoch as expected by us? (Miranda, Lidz, Heinrich, Hu 2017)
Some hint of early first star formation from Planck
• baryon moving against dark matter – velocity offset @ recombination – ~ km/s velocity offset @ z~20
(Tseliakhovich & Hirata 2010)
• baryon formation offset– velocity offset formation offset
(O’Leary & McQuinn 2012)– Jeans mass up Delayed star
formation (Maio, Koopmans, Ciardi 2011; Greif, White, Klessen, Springel2011; Stacy, Bromm, Loeb 2011)
– heating 21cm signal of streaming-velocity (McQuinn & O’Leary 2012)
– Variation of baryon/CDM fraction (Fialkov, Barkana, Tseliakhovich, Hirata 2012)
Baryon bulk motion w.r.t. CDM
Equations that are integrated←Tseliakhovich & Hirata 2010 (streaming velocity but without density environment)
KA 2016 (streaming velocity with density environment)
↓
BCCOMICS: Baryon-Cold dark
matter COsMological Initial
Condition generator for Small-scale
structures(by KA, soon to be released)
Flow Chart
run CAMB:TF output @ z=zi=1000
Radom seed and FFT
Δc Θc
Δb Θb
ΔT Vc-Vb
δc θc
δb θb
δT
which patch?
Δc Θc
Δb Θb
ΔT Vc-Vb
Time-integrate to zf
TF output @ zf
(e.g. zf =200)
Radom seed and FFT
δb θb δT
Lagrangianperturbation
xc vc
(xb vb)
• CICsASS (O’Leary & McQuinn 2012)– Cosmological Initial Conditions for AMR and SPH
Simulations
– Based on Tseliakhovich & Hirata 2010 (streaming velocity variation)
• BCCOMICS (for overdense patch)– Baryon-Cold dark matter COsMological Initial Condition
generator for Small-scale structures
– Based on KA 2016 (streaming velocity, density, velocity divergence, temperature)
• Bad practice – not using these IC generators– Sudden turn-on of streaming velocity very common, but this
is starting from wrong IC (e.g. O’Leary & McQuinn)
– Zero streaming velocity is too rare!
CICsASS vs BCCOMICS
• No need to change cosmological parameters– May use CICsASS
– For more variants (e.g. non-zero temperature overdensity), should use BCCOMICS
Mean-density cases
• So far, BCCOMICS is the only tool– Non-zero overdensity, non-zero temperature overdensity,
non-zero streaming velocity
• In practice, take the overdense patch as a separate universe with non-zero curvature– “local”: what’s observed in the patch
– Local H different: 𝐻𝑙𝑜𝑐𝑎𝑙 = 𝐻 − ሶ∆/3(1 + ∆)
– Local ρcrit different, local Ω different
– Local scale factor different
– Simulating structure formation inside a peak or a void (e.g. Goldberg & Vogeley 2004)
Non-zero overdensity cases
• Warning: overdense cases are wrong, they should have more halos than the mean-density patches.– Will find bugs and correct.
Halo mass function ((too) preliminary)
• Star formation rate
• Baryon/DM ratio inside halos
• Spatial modulation of IGM heating– relevant to high-z 21cm cosmology (McQuinn & O’Leary
2012)
• Finding rare, bright objects– Can help pencil-beam observations to find targets
– Can help push source-finding observations to go to higher-than-usual redshifts
Other useful analysis
• Minihalo stars (Pop III mostly) in reionization– Density bias
• Minihalos in general (high-z astrophysics)– Streaming velocity bias (Tseliakhovich & Hirata 2010)
– Streaming velocity bias, density bias, temperature bias (KA 2016)
– Use BCCOMICS; I am
• High-z 21cm cosmology– Streaming velocity bias, density bias, temperature bias
• Local patch simulation scheme– Useful for larger-scale structure too
– Useful for rare-object hunters
Summary (cosmic variance of structure formation)