Simulating HI 21-cm Signal from EoR and Cosmic Dawn. Kanan K. Datta Presidency University, Kolkata

Transcription

1 Simulating HI 21-cm Signal from EoR and Cosmic Dawn Kanan K. Datta Presidency University, Kolkata

2 Plan of the talk Why simulations?! Dynamic ranges of simulations! Basic flowchart for simulation! Various techniques! Numerical, Semi-numerical, 1D radiative transfer (Raghunath Ghara s talk), Comparison! Applications! (i) RSD,! (ii) Light Cone effect! (iii) QSO HII regions (follow Suman Majumdar s talk)! Effect of X-sources, and Ly-alpha photons (Raghunath Ghara s talk)! Future outlook

3 Why Simulations? Understanding the HI 21-cm signal! Effect of sources, feedbacks, recombinations! Effect of different line of sight effects such as RSD, LC, AP! Crucial for array design, develop detection strategies! Information extraction

4 Simulation sizes and Dynamic range Simulation of ~Gpc size (for 5 degree FoV experiment)!!!!! Need to resolve 10^8 solar mass DM halos (sub Mpc scale) which produce photons!! This requires huge dynamic range and extremely high computational cost.

5 HI 21 cm signal

6 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs)

7 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs) Find DM halo! (density peaks)

8 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs) Find DM halo! (density peaks) Assign luminosity! and illuminate them

9 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs) Find DM halo! (density peaks) Assign luminosity! and illuminate them

10 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs) Find DM halo! (density peaks) Assign luminosity! and illuminate them Numerical! Semi-numerical! 1D RT

11 Flowchart: Reionization Simulations Dark Matter distribution! (During reionization epoch! ~0.4-1 Billion yrs) Find DM halo! (density peaks) Assign luminosity! and illuminate them Multiply Simulated 21 cm Signal

12 Numerical Simulations C2-RAY: (Conservative-Causal Ray Tracing) (Mellema et al 2006) Ionization equation Solution where,

13 Numerical Simulations C2-RAY: (Conservative-Causal Ray Tracing) (Mellema et al 2006) Numerically Test for convergence Advance to the next cell Simulation size ~607 Mpc 165 billion DM particle took 10 months to run, total 8 million (3.3 GHz) core-hours!!! used 32 to 40,032 cores simultaneously.

14 Numerical Simulations C2-Ray -Flowchart Mellema et al 2006

15 Semi-Numerical Simulations Ionization condition Reionizing! Sources ~10s of core-hours Zahn et al 2007, Choudhury et al 2009, Majumdar et al 2011

16 Semi-Numerical Simulations Ionization condition Reionizing! Sources Zahn et al 2007, Choudhury et al 2009, Majumdar et al 2011

17 Semi-Numerical Simulations Ionization condition Reionizing! Sources Zahn et al 2007, Santos (2008), Choudhury et al 2009, Majumdar et al 2011

18 Semi-numerical simulation without DM halo Collapse fraction Dark matter distribution Ionization condition Mesinger et al 2007, Majumdar et al 2014, Ghara et al 2014

19 Comparison between different techniques Majumdar, Mellema, Datta, Jensen, Choudhury, Bharadwaj, Friedrich, MNRAS, 2015 C2-Ray Sem-Num 1 Sem-Num 2 (CPS) Movie credit: Suman Majumdar

20 Comparison between different techniques Majumdar, Mellema, Datta, Jensen, Choudhury, Bharadwaj, Friedrich, MNRAS, 2015 C2-Ray Sem-Num 1 Sem-Num 2 (CPS) Movie credit: Suman Majumdar

21 1D-Radiative Transfer Code

22 Applications Light Cone Effect A volume (3D) will be observed y-axis!! x-axis z1 z2 Simulations provides boxes at a fixed redshift.! Observations provide a volume which spread over a redshift range!! Near side and far side of an observed 3D volume represent different stages of reionization.!! The statistics of HI fluctuations evolve over the LOS.!! Datta et al, 2012, MNRAS

23 Applications Light Cone Effect!!! Simulations provides boxes at a fixed redshift.! Observations provide a volume which spread over a redshift range! Near side and far side of an observed 3D volume represent different stages of reionization.!! The statistics of HI fluctuations evolve over the LOS.!! Datta et al, 2012, MNRAS

24 Applications Light Cone Effect on HI power spectrum LC effect is most dramatic at neutral fraction 0.8 and 0.2! The effect is stronger at large scales ( 100 cmpc)! A factor of 5 enhancement in the power spectrum!!!! Datta, Jensen, Majumdar et al, MNRAS 2014

25 Applications Light Cone Effect on HI power spectrum Light Cone Effect if much more dramatic during Cosmic Dawn (when Ts<~Tcmb) (follow Raghunath Ghara s talk) LC effect is most dramatic at neutral fraction 0.8 and 0.2! The effect is stronger at large scales ( 100 cmpc)! A factor of 5 enhancement in the power spectrum!!!! Datta, Jensen, Majumdar et al, MNRAS 2014

26 Applications Redshift Space Distortion (Peculiar Velocity) DM Density In Real Space

27 Applications Redshift Space Distortion (Peculiar Velocity) DM Density In Redshift Space Fluctuations in density get enhanced Angular averaged power spectrum is enhanced by a factor of 1.87 (Keiser 1987)

28 Applications Redshift Space Distortion (Peculiar Velocity) Ionized DM Density In Redshift Space Fluctuations in density get enhanced Angular averaged power spectrum is enhanced by a factor of 1.87 (Keiser 1987)

29 Applications Redshift Space Distortion (Peculiar Velocity) no 21-cm signal DM Density In Redshift Space Fluctuations in density get enhanced Angular averaged power spectrum is enhanced by a factor of 1.87 (Keiser 1987)

30 RSD effect on HI power spectrum A factor of 3-4 enhancement in the power spectrum at large scale in the early stages of EoR Jensen, H; Datta, K. K., & LOFAR EoR Group, MNRAS,2013

31 Anisotropies in the Power spectrum -I Astrophysics (QSOs, Stars) DM power spectrum! (probe early Universe,! Cosmology) Can be used to measure cosmological parameters, dark energy

32 Anisotropies in the Power spectrum Detection with LOFAR Jensen, H; Datta, K. K., & LOFAR EoR Group, MNRAS,2013

33 Anisotropies in the Power spectrum -II What happens to the quadrupole moment under different reionization models? when Line T S of >> Sight T CMB o Kaiser, N., 1987, MNRAS, 227, 1 (Galaxy Redshift Surveys) o Hamilton, A. J. S., 1992, APJL, 385, L5 o Majumdar, Bhardwaj & Choudhury, 2013, MNRAS, 434, 3 o Majumdar, Mellema, Datta et al., 2014, MNRAS, 443, 4 (EoR 21-cm signal)

34 Different Reionization Scenarios x HI =0.5 Fiducial Clumping UIB Dom LoS SXR Dom UV+SXR+UIB PL 2 mk Mpc Majumdar, Jensen, Mellema et al., 2015, in prep.

35 Evolution of the Quadrupole Moment Majumdar, Jensen, Mellema et al., 2015, in prep.

36 Summary Simulations are import in order to understand HI 21-cm signal, study various effects, design detection strategies, extract information. Challenge is to simulate large scale (~Gpc) simulations which have less computational requirements but accurate enough. These should be used explore large parameter space. Semi numerical techniques are economic and produce reasonably good results Light cone effect and the peculiar velocity effects change the power spectrum significantly and should be considered while modeling the power spectrum.

37 Reionization models Majumdar et al (in Prep) Movie credit: Suman Majumdar (Stockholm University)