# Presentation: 673876

## Feedback Effects on Population III Star Formation

- Greg Bryan
- (Columbia University)

- Ian McGreer (Columbia)
- Andrei Mesinger (Yale), Zoltan Haiman (Columbia)

**Notes:**
Talk given October 12, 2005

## Feedback from the first stars

- Ionizing radiation from the first stars:
- Positive?  (more stars, leading to runaway)
- Ionization  free e-  more H2  more cooling
- HD cooling (T cools to TCMB  fragmentation?)
- Negative? (fewer stars, self-suppression)
- Ionization  heating  higher entropy gas
- H2 Photo-dissociating flux (11.2-13.6 eV)
- Can suppresses or delay new “first” star formation
- Supernovae
- Metal enrichment
- Blast wave

## Outline

- Impact of Fossil HII regions on future Population III star formation
- Impact of HD cooling
- Primordial halos
- Halos with enhanced e- fraction (e.g. ionized)

## Outline

- Impact of Fossil HII regions on future  Population III star formation
- Impact of HD cooling
- Primordial halos
- Halos with enhanced e- fraction (e.g. ionized)

## Global UV Feedback: Entropy Floor from Fossil HII Regions

**Fossil HII Regions:**

** **First star creates ~ few kpc
-   ionized bubble
-  Star dies after ~106 yrs
-   and HII region recombines
-  Fossil HII region recombines and
-   cools
-  Residual T~300 K implies excess
-   entropy
-  Entropy Inhibits contraction, H2
-   formation

- HII region
-  (ionized)

- Fossil HII region
- (enhanced entropy)

## Simulating the Impact of Relic HII Regions

** ****AMR Simulations with Enzo ****(Mesinger, Bryan & Haiman 2006)**
**      **- (1 *h**-1* Mpc)3 comoving, 1283 root grid, run from z=99 to z=15
-       - re-simulate inner (0.25 *h**-1* Mpc)3
-          - 10 levels of refinement - 0.02 *h**-1* pc (absolute) resolution at z=20
-       - biased (2) region, yields hundreds of DM halos (10**5**M****<M<10**7**M******)**
** ****Examine Effects of Transient Photoheating: 4 runs**
**      **- J(UV) = 0    (control run)
-       - Flash ionization at z = 25  (c.f. O’Shea et al. 2006)
-       - J(UV) = 0.08 at z = 25 for 3107 years (uniform, optically thin)
-       - J(UV) = 0.8   at z = 25 for 3107 years (uniform, optically thin)
** ****Examine Effect of adding LW background**
**       **- 10**-3 **< J(LW) < 10**-1      **added to J(UV)=0.8 run

## Simulating the Impact of Relic HII Regions

-  Ionization occurs at z = 25 due to (unmodeled) nearby star
-  Flux is the same everywhere
-  Density field relatively unevolved
-  Examine impact at z = 18

- Density distribution
- (at z = 25) of gas which ends up in 105 and 106 M****** **halos at    z = 18

## The impact of a Fossil HII region on the first stars

- The impact of a Fossil HII region on the first stars

- No ionizing flux

- With ionizing flux
- (J21 = 0.8 for 3 Myr at z=25)

- 12 kpc

- Log density at z = 18

## Gas Fractions at z = 18

- No UV

- Flash

- J=0.08

- J=0.8

- total gas
- fraction

- cooled gas
- fraction

## Gas Fractions at z = 18

- No UV

- Flash

- J=0.08

- J=0.8

- total gas
- fraction

- cooled gas
- fraction

## Gas Fractions at z = 18

- No UV

- Flash

- J=0.08

- J=0.8

**+ve**

- total gas
- fraction

- cooled gas
- fraction

## Gas Fractions at z = 18

- No UV

- Flash

- J=0.08

- J=0.8

**+ve**

**?**

- total gas
- fraction

- cooled gas
- fraction

## Gas Fractions at z = 18

- No UV

- Flash

- J=0.08

- J=0.8

**+ve**

**-ve**

**?**

- total gas
- fraction

- cooled gas
- fraction

## Impact of Ionizing Flux on Number and Mass of Halos that can cool

- Mass of cooled gas

- Number of
- Halos that
- Can cool

## Why is the effect small?Ionization of a low-density halo

- Mesinger, Bryan & Haiman (2006)

## Interpretation: Delayed Cooling

**      **
-                           t = tcool ∝ T / ngas xH2
-  Works on halo-by-halo basis - near cancelation
**      **
-                           T:     varies little (initial Compton cooling)
-                           ngas:  depressed by factor of ~ 20
-                           xH2:  increased  by factor of ~ 10
-                        net delay:  factor of ~2
-  Statistics for the population as a whole?

## Positive and Negative feedback nearly cancel

## Lyman-Werner Simulation Results 

- redshift

-  Entropy floor reduces critical J(LW) from 0.01 to 0.001
-  for J(LW) ≳0.01 strong suppression persists beyond 100 Myr

## Outline

- Impact of Fossil HII regions on future Pop III star formation
- Impact of HD cooling
- Primordial halos
- Halos with enhanced e- fraction (e.g. ionized)

## HD Cooling in Primordial Halos

- HD Cooling
-  HD dominates H2 cooling
-    below ~200 K
-  Can cool down to TCMB
-     (Johnson & Bromm 2006)
-  Critical density n~105 cm-3

- Lipovka et al 2005

- The Simulation
-  L = (0.7 Mpc)3 box,
-   10243 effective initial resolution
-  final resolution: 46 AU
-  multiple halos

- HD cooling curve

- See poster by
- Ian McGreer

## I. HD cooling in Primordial Halos

- McGreer & Bryan (2007)

- H2 only

- H2 + HD

- M = 1.1 x 106 M****

- M = 0.6 x 106 M****

- H2 only

- H2 + HD

## I. HD cooling in Primordial Halos

- McGreer & Bryan (2007)

- H2 only

- H2 + HD

- M = 1.1 x 106 M****

- M = 0.6 x 106 M****

## The Role of HD cooling in primordial stars

-  HD dominates over H2
-    for T < 300 K
-  HD borderline, but if
-    important it cools strongly
-  critical fraction
-    X(HD)/X(H2) ~ 0.001

- Low mass halo

- High mass halo

## II. HD cooling in ionized halos

- H2 only

- H2 + HD

- CMB
- Temperature

- Same as before, but now we flash ionize halo at z = 20

## HD cooling reduces stellar massbut only by a factor of a few

- H2 only

- H2 + HD

- Shu Accretion
- Time (GM/cs3)

- Primordial
- halos

- Ionized
- halos

-        H2 + HD
- (low mass halo)

## Conclusions

- Fossil HII regions can create entropy floor
- Mild suppression if flux is strong enough (J21 > 0.1)
- Halos more susceptible to LW photo-dissociation
- HD cooling _can_ play a role in low-mass primoridal halos (Ripamonti et al 2007)
- HD cooling is important in ionized halos
- Reduces minimum temperature to TCMB
- Mild decrease in accreted stellar mass          (~100 M****  ~30 M****)