# Presentation: 090146

## Kyungjin Ahn

-  (+: The Inhomogeneous Background of H2 Dissociating Radiation During Cosmic Reionization)

- The University of Texas at Austin
- First Stars III
- Santa Fe
- July 2007

## Does Radiative Feedback by the First Stars Promote or Prevent Second Generation Star Formation?

-                                                           w/ P. R. Shapiro (Texas)

## Radiative Feedback effects on the First Star Formation

- First stars form inside minihalos (<~108 M)
- Forms by H2 cooling
- one star per one minihalo
- subject to radiative and dynamical feedback effects
- Prerequisite for determining star formation rate inside minihalos: study of feedback
- Feedback Effects (positive vs. negative for further star formation)
- Negative – star formation quenched
- H**2** is fragile: dissociation by Lyman-Werner band photons (Haiman, Abel, Rees 2000; Machacek, Bryan, Abel 2001; Yoshida, Abel, Hernquist, Sugiyama 2003; Bryan, Mesinger, Haiman 2006; O’shea, Norman 2007)
- Positive – star formation promoted
- Hard photons partially ionize IGM to create H**2** (Haiman, Rees, Loeb 1996; Ricotti, Gnedin, Shull 2002)

## Feedback Effects of the First Stars onto Nearby Collapsed Objects (study by 3-D simulations)
O'shea, Abel, Whalen & Norman (2005)
Assume full ionization of nearby halos of M~5*105 M
Quick formation of H2
Inner core collapses; Outer region evaporates
Alvarez, Bromm, Shapiro (2005)
Track I-front propagation through nearby halos of M~5*105 M using I-front jump condition
I-front slows down and being trapped.
I-front fails to reach the center: Center remains neutral
Neutral center: probably no further formation of H2 after source dies at the center?
Negative feedback then?? (no hydro, no H2 treated)

- O'shea, Abel, Whalen & Norman (2005)
- Assume full ionization of nearby halos of M~5*10**5** M
- Quick formation of H**2**
- Inner core collapses; Outer region evaporates
- Alvarez, Bromm, Shapiro (2005)
- Track I-front propagation through nearby halos of M~5*10**5** M** **using I-front jump condition
- I-front slows down and being trapped.
- I-front fails to reach the center: Center remains neutral
- Neutral center: probably no further formation of H**2** after source dies at the center?
- Negative feedback then?? (no hydro, no H2 treated)

- _Radiative Feedback effects on the First Star Formation_

## Nearby minihalo core doesn’t get photoionized 

- Alvarez, Bromm, Shapiro (2005)

- Volume visualization at z = 20 of neutral density field (blue – low density, red – high density) and I-front (translucent white surface). Top row panels show a cubic volume ∼ 13.6 kpc (proper) across, middle row ∼ 6.8 kpc, and bottom row ∼ 3.4 kpc. Left column is at the initial time, middle column shows simulation at t∗ = 3 Myr for the run with stellar mass M∗ = 80M⊙, and the right column shows simulation at t∗ = 2.2 Myr for the run with stellar mass M∗ = 200M⊙. The empty black region in the lower panels of middle and right columns indicates fully ionized gas around the source, and is fully revealed as the volume visualized shrinks to exclude the I-front that obscures this region in the larger volumes above.

## Radiative + Dynamical Feedback Effects of the First Stars onto Nearby Minihalos (study by 1-D simulation)
Use 1-D radiation, hydrodynamics code
Full treatment of primordial chemistry, radiative transfer, cooling/heating, hydrodynamics
1-D spherical geometry
High resolution possible
Analysis relatively easier than 3-D
Irradiate target halos with a Pop III starlight
Is I-front trapped?
What happens to the center?
Any H2 formation/dissociation interesting?
Is it positive or negative feedback effect? 

- Use 1-D radiation, hydrodynamics code
- Full treatment of primordial chemistry, radiative transfer, cooling/heating, hydrodynamics
- 1-D spherical geometry
- High resolution possible
- Analysis relatively easier than 3-D
- Irradiate target halos with a Pop III starlight
- Is I-front trapped?
- What happens to the center?
- Any H**2** formation/dissociation interesting?
- Is it positive or negative feedback effect?

- _What is the aftermath of Pop III starlight I-front trapping by minihalos ?_

## Does Radiative Feedback by the First Stars Promote or Prevent 2nd Generation Star Formation ?

-  A range of distances considered between the source and the target minihalos for different minihalo masses and also the evolutionary stages of the target minihalo when radiation arrives.
-  Proper distances:   D = 50, 180, 360, 540, 1000 pc
-  Ionizing Photon Fluxes:  F0 = Nph,50 / r2kpc = 600, 46, 11, 5, 1.5 [i.e. Nph,50 (120 solar mass Pop III star) = 1.5]
-  Minihalo masses:   M / (105 solar mass) = 0.25, 0.5, 1, 2, 4, 5.5, 8
-  Initial evolutionary stages:  Phase I (unevolved) or
-                                            Phase II (evolved)

- KA & Shapiro (2007, MNRAS 375, 881)

- _Does Radiative Feedback by the First Stars Promote or Prevent 2__nd__ Generation Star Formation ?_

## Rule of Thumbs

- H atomic cooling : down to ~10000K
- collisional ionization : at > ~10000K
- photo-ionization front : thickness ~ mean free path of ionizing photons
- R-type ionization front: I-front moves supersonically into neutral region; gas doesn’t respond dynamically
- D-type ionization front: I-front moves subsonically into neutral region; gas responds, shock-front develops
- Primary H**2** formation mechanism (with electron!)
- H + e  H**-** + ****H- + H  H**2** + e
- H**2** cooling : down to ~100K at H**2**/H >~ 10**-4**
- Low temperature, T <~ 1000K, required to have H**2**/H >~ 10**-4** to be safe from collisional dissociation
- H**2** self-shielding effective at N(H**2**)>~10**14** cm**-2** in *static*.

## Does Radiative Feedback by the First Stars Promote or Prevent Second Generation Star Formation ?

-  Initial conditions for target minihalos:
-  nonsingular Truncated Isothermal Spheres (TIS) (dark matter + baryons)     (Shapiro, Iliev, & Raga 1999; Iliev & Shapiro 2001)
-   **Phase I** (no evolution)  mean IGM chemical abundances @ z = 20   H2 ~ 10-6 ,  e- ~ 10-4  ,  Tcore = Tvirial
-         OR
-   **Phase II** (evolved from Phase I for a few million years << tHubble)
-             H2 ↑  as  e- ↓ in core  H2 ~ 10-4 to 10-3,  e-  ~ 10-5
-             H2  radiative cooling to Tcore ~ 100 K causes core to
-                compress by factor ~ 1 to 20,  higher for higher M

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

- target halo @  M=2e5 Msun

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- target halo @  M=2e5 Msun
- With no radiation: tcoll=31 Myrs

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- target halo @  M=2e5 Msun
- With no radiation: tcoll=31 Myrs
- With radiation:
-  Flux F0=46.3 (D=180 pc)
-  tcoll=2.3 Myrs
** ****expedited collapse**** with help of shock-induced molecule formation(SIMF)**
** ****second star forms** **before the first star dies!**

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

## Slide 13

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

- target halo @  M=1e5 Msun

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

- target halo @  M=1e5 Msun
- With no radiation : tcoll=89 Myrs

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- target halo @  M=1e5 Msun
- With no radiation : tcoll=89 Myrs
- With radiation:
- Flux F0=46.3 (D=180 pc)
- tcoll=129 Myrs
**delayed collapse**** (SIMF doesn’t help: small halos are more fragile against dynamical disturbance)**
**second star forms after the first star dies,**** ****but still within a Hubble time**

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback

## Slide 17

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (no H2 self-shielding)

- target halo @  M=5.5e5 Msun located at D=50 pc

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (no H2 self-shielding)

-  2nd star forms in the merging halo after the first star dies (Abel, Wise & Bryan 2006)

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (no H2 self-shielding)

- target halo @  M=5.5e5 Msun
- With no radiation : tcoll=11 Myrs

## target halo @  M=5.5e5 Msun

- target halo @  M=5.5e5 Msun
- With no radiation : tcoll=11 Myrs
- With radiation
- Flux F0=600 (D=50 pc)
- tcoll=47 Myrs
**delayed collapse****, even with SIMF**
**second star forms** **after the first star ****dies**

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (no H2 self-shielding)

## Slide 22

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (including H2 self-shielding)

- target halo @  M=5.5e5 Msun

## 120 solar mass Pop III star irradiates nearby minihalos at z=20: 

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (including H2 self-shielding)

- target halo @  M=5.5e5 Msun
- With no radiation: tcoll=11 Myrs

## target halo @  M=5.5e5 Msun

- target halo @  M=5.5e5 Msun
- With no radiation: tcoll=11 Myrs
- With radiation:
- Flux F0=600 (D=50 pc)
- tcoll=1.1 Myrs
**expedited collapse**** with help of SIMF**
**second star forms** **before the first star dies!**

- 120 solar mass Pop III star irradiates nearby minihalos at z=20:
-            1D, rad-hydro simulations of radiative feedback
- (including H2 self-shielding)

## Slide 26

## Mixture of positive and negative effects

- expedited                                           delayed

## Mixture of positive and negative effects

- reversed                                           unaffected

## Radial Profiles at collapse

## Radial Profiles at collapse

## Conclusion (Radiative Feedback by a single Pop III star)

- I-front slows down, finally gets trapped.
- Shock-front is driven, with T~1000 - 10000 K
- Heat and momentum delivered              (_negative-strong_)
- H2 formation promoted in shock-heated gas: shock heats the gas above T~1000K                                   (_positive -mild_)
- Sometimes shock-front accelerates up to >~ 10000K  heated enough to lead to collisional ionization  electron, H**2** formation: Basically identical to Shapiro & Kang 1987, evolution of shock-ionized gas                                          (_positive-strong_)
- Precursor H**2** shell formation
- Long mean-free-path of ionizing photons -> Partial ionization -> H- formation -> H**2** formation
- Shielding                                             (_positive-weak_)
- Matter Infall
- ram pressure to keep core bound           (_positive-mild_)
- Net result is, roughly, neutral!! (Also see Susa & Umemura 2006; Johnson, Greif, Bromm 2007, Whalen’s talk (to be submitted))

## The Inhomogeneous Background of H2 Dissociating Radiation During Cosmic Reionization

-  (In Preparation)

-                                                          w/ P. R. Shapiro (Texas)
-                                                               I. T. Iliev (CITA)
-                                                               G. Mellema (Stockholm)
-                                                               U.-L. Pen (CITA)

- Also take a look at the poster..

## Motivation

- mostly negative feedback
- One needs to calculate UV background, especially in the H2 Lyman-Werner (LW) band (dissociating H2)
- Usually done with parameterized J21
- Self-consistent calculations are from uniformly distributed sources (Haiman, Abel, Rees 2000), or box too small to account for source-clustering (Ricotti, Gnedin, Shull 2001; Yoshida, Abel, Hernquist, Sugiyama 2003)
- LW band photons contributed by stars in minihalos (Tvir<~104K) AND stars in atomic cooling halos (Tvir>~104K), which are responsible for reionizing the Universe
- At least, atomic cooling halos are highly clustered (e.g. Iliev et al. 2006, 2007) with mean separation of clusters about a few - ~10 comoving Mpc
- Can we calculate inhomogeneous LW background?

- _Motivation_

## Picket-Fence Modulation

- Sawtooth-modulation (Haiman, Abel, Rees 2000)
- Based upon uniformly distributed sources
- Different horizon for different Lyman resonance lines

- _Picket-Fence Modulation_

## Picket-Fence Modulation

- One single source is observed as a picket-fence in spectrum: Can effectively follow attenuation by multi-frequency phenomenon by pre-calculated modulation factor -> Huge alleviation computationally.

- _Picket-Fence Modulation_

## Retarded time emissivity

- Horizon for LW background is large (~100 comoving Mpc)
- Construct spacetime diagram and draw past line cone at a given space-time to account for LW

- _Retarded time emissivity_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## H2 Dissociating Background during EOR

- _H__2__ Dissociating Background during EOR_

## Degree of Fluctuation in LW Background

- _Degree of Fluctuation in LW Background_

## Where to look at for most pristine Pop III star forming regions?

- _Where to look at for most pristine Pop III star forming regions?_

- Inhomogeneous Radiative Feedback!!
- Highly clustered ionizing sources
- Degeneracy broken for different source properties
- escape fraction of ionizing radiation
- dissociating/ionizing photon # ratio
- Contribution to NIR background fluctuation -> Need to understand inhomogeneous feedback.

## Conclusion

- _Conclusion_

- Picket-fence modulation of LW background photons
- Ease of LW background calculaiton
- Fluctuation in LW background comes from source clustering, at a scale of ~10 comoving Mpc
- Will be “safe spots” to form the most pristine Pop III stars in minihalos
- Understanding radiative feedback on Pop III star formation in minihalos is crucial
- Stay tuned
- Various reionization scenarios
- Power spectrum of NIR (or else) fluctuation
- Mock data for JWST target field