Cosmic Variance of Small-Scale Structure Formation: Large-Scale Density and CDM-Baryon Drift Velocity Environment

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1 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

2 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

3 Reionization by minihalo stars and massive halo stars (KA, Iliev, Shapiro, Mellema, Koda, Mao 2012)

4 Motivation 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

5 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 photodissociation of coolant calculate transfer of Lyman- Werner Background (KA, Shapiro, Iliev, Mellema, Pen 2009) remove first star from minihalos, if LW intensity overcritical Retarded-time Green s function calculation (KA 2015, JKAS)

6 With and Without Minihalos KA, Iliev, Shapiro, Mellema, Koda, Mao 2012

7 Some hint of early first star formation from Planck Self-regulated first star formation epoch as expected by us? (Miranda, Lidz, Heinrich, Hu 2017)

8 CDM-baryon streaming velocity & density environment affecting halo and star formation (KA 2016)

9 Power recombination (from CAMB)

10 Baryon bulk motion w.r.t. CDM baryon moving against dark matter velocity recombination ~ km/s velocity 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, Springel 2011; Stacy, Bromm, Loeb 2011) heating 21cm signal of streamingvelocity (McQuinn & O Leary 2012) Variation of baryon/cdm fraction (Fialkov, Barkana, Tseliakhovich, Hirata 2012)

11 Equations that are integrated Tseliakhovich & Hirata 2010 (streaming velocity but without density environment) KA 2016 (streaming velocity with density environment)

12 Equations that are integrated Tseliakhovich & Hirata KA

13 Equations that are integrated Tseliakhovich & Hirata KA

14 What various fields look like (at z=1000)

15 What CDM overdensity and V cb look like (at z=1000)

16 BCCOMICS: Baryon-Cold dark matter COsMological Initial Condition generator for Small-scale structures (by KA, soon to be released)

17 Flow Chart run CAMB: TF z=z i =1000 Radom seed and FFT Δ c Θ c Δ b Θ b Δ T V c -V b which patch? δ c θ c δ b θ b δ T Time-integrate to z f Δ c Θ c Δ b Θ b Δ T V c -V b TF z f (e.g. z f =200) δ b θ b δ T Radom seed and FFT Lagrangian perturbation x c v c (x b v b )

18 Small-scale fields (Lbox=1.3 Mpc at z=200): CDM overdensity

19 Small-scale fields (L box =1.3 Mpc at z=200): baryon overdensity

20 CICsASS vs BCCOMICS 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!

21 BCCOMICS + Enzo (by KA, Smith, Norman, in preparation)

22 Mean-density cases No need to change cosmological parameters May use CICsASS For more variants (e.g. non-zero temperature overdensity), should use BCCOMICS

23 Non-zero overdensity 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: H local = H /3(1 ሶ + ) Local ρ crit different, local Ω different Local scale factor different Simulating structure formation inside a peak or a void (e.g. Goldberg & Vogeley 2004)

24 Halo mass function ((too) preliminary) Warning: overdense cases are wrong, they should have more halos than the mean-density patches. Will find bugs and correct.

25 Other useful analysis 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 higherthan-usual redshifts

26 Summary (cosmic variance of structure formation) 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