1. Probing Reionization with Lyman Alpha Emitters Pratika Dayal
SISSA / International School for Advanced Studies
Collaborators : Stefano Borgani, Andrea Ferrara, Simona Gallerani, Hiroyuki Hirashita, Ruben Salvaterra, Alex Saro, Luca Tornatore…
MNRAS, 2008, 389, 1683
arXiv:
arXiv:
arXiv:
19th August, 2009
Albanova Center

2. OUTLINE A brief introduction to Reionization (a) the theoretical model
(b) the scenarios
Linking LAEs and reionization
(a) What are they?
(b) Why are they important?
(c) How can they be used to constrain reionization?
(d) What do we know of their nature?
(e) How much do they contribute to reionization?
Summary

3. Reionization at a glance
Barkana & Loeb, 2007
QSOs
WMAP 5

4. Building a consistent reionization model
Choudhury & Ferrara 2006
Vol averaged
fraction of HI
Electron sc.
Optical depth
Evolution of LL
systems with z
SFR density
GP Ly optical
depth
GP Ly optical
No. counts of
High-z sources
Temperature
Hi photo-
Ionization rate

5. The possible Reionization scenarios
Early Reionization Model - reionization ends at z ~ 7.
Late Reionization Model - reionization ends at z ~ 6.
Filling factor of HI Fraction of HI
Gallerani et al. 2008

6. The focus of the talk - LAEs and Reionization
Q1: What are LAEs?
Q2: Why are they important ?
Q3: How can they be used to probe reionization ?
Q4: What is the nature of LAEs?
Q5: How much do they contribute to reionization ?

7. What are LAEs ? Galaxies with an observable Lya line.
Observed EW > 20 A
Lya line very strong and narrow
Sharp cut-off blueward of the Lya line
Kashikawa et al. 2006

8. Why are LAEs important ?
Highest redshift galaxies with good statistics.
Since Ly sensitive to HI, excellent probes of ionization state of the IGM.
Relative damping of Ly and UV used to constrain dust amounts/distribution.
Deficit due to mass fn. evolution or reionization?
Inc. dust/ dec. SFR at z=5.7
Cumulative Ly LF UV LF
Kashikawa et al. 2006

9. The LAE model : SPH+semi-analytics
Cosmological SPH simulations
75/h cMpc
For each galaxy, obtain (a) SFR, (b) age, (c) metallicity.
The LAE model : SPH+semi-analytics
Use intrinsic properties of each galaxy to obtain spectra.
Clustered galaxies
Build a Stromgren Sphere around each galaxy and include photoionization boost due to clustered galaxies.
Transmission through IGM
Use the value of HI at each point along the LOS to calculate the transmission for the ERM.
Spectra from SB99+lum from cooling of collisionally excited HI

10. The Lya Luminosity Function
Clustering effects negligible for a highly ionized IGM,
Dayal et al. arXiv:
Including clustering
Excluding clustering
Including/ Excluding clustering
Clustering effects important for a highly ionized IGM,
Only about 30% of the Ly photons must escape the galaxy, undamped by dust

11. The UV Luminosity Function
22% of UV photons escape the galaxy undamped by dust
E(B-V) = 0.15
37% of UV photons escape the galaxy undamped by dust
E(B-V) ~ 0.1
Dust distribution / inhomogeneity evolving with redshift.
Dayal et al. arXiv:

12. Clustering Results Boost imparted by clustering <2
Dayal et al. arXiv:
Boost imparted by clustering <2
Boost imparted by clustering ~ 58
UVB photoionization rate evolves 3 orders of magnitude between z=7.6 and 6.6.
Contribution from clustered galaxies dominates transmission for a highly neutral IGM.

13. Validating the model with observed SEDs
Dayal et al. arXiv: , SEDs from Lai et al., 2007
Choose galaxies matching most closely in observed Ly luminosity and attenuate the spectra of the galaxy with E(B-V)=0.15.
Predict intrinsic properties of these LAEs :

14. The Nature of LAEs - I
Dayal et al. arXiv:
Halo mass
Age
Stellar metallicity
Halo mass range narrows with increasing z due to mass function Evolution.
LAEs have ages between Myr.
Stellar metallicity between 2-55% of the solar value.

15. The Nature of LAEs- II
Dayal et al. arXiv:
Star Formation rate
SFR efficiency suppressed in low mass halos due to mechanical feedback.
z = 5.7
z = 6.6
z = 7.6 *
For bulk of galaxies, I is less than 1, i.e. average SFR was higher in the past.

16. The Nature of LAEs - Dust
Dust mass
Escape fraction of Ly photons
Since SNII are primary dust factories, dust mass increases with SFR (halo mass).
z = 5.7
z = 6.6
Escape fraction of Ly photons decreases by an order of magnitude from ~ 1 due to increasing dust.
Dayal et al. arXiv:

17. A new window on LAEs - Sub-millimeter with ALMA
353 GHz
220 GHz
100 GHz
0.02 mJy
0.05 mJy
0.12 mJy
Dayal et al. arXiv:
UV photons ( A) absorbed are re-emitted in the Far Infra red (FIR) in the rest frame of the galaxy (submm in observer frame).
About 3% of LAEs visible with a 5 1 hour integration limit in 353 GHz band.
If observations do not match, exotic scenarios need to be considered: top heavy IMF, popIII stars, ages <10 Myr ?

18. LAEs are PASSIVE REIONIZATION TRACERS !
How much do LAEs contribute to reionization
LAEs contribute about 1% of the ionizing photons budget at z ~ 6.6.
LAEs are PASSIVE REIONIZATION TRACERS !

19. SUMMARY
We use cosmological SPH simulations coupled with a Ly/continuum production/ transmission model to use LAEs to probe reionization.
The ERM reproduces the observations well; the LRM can not still be completely ruled out.
Escape fractions of Ly, continuum photons are (0.3,0.3), (0.22,0.37) at z=(5.7,6.6).
The dust inhomogeneity / clumping is evolving with redshift.
Ly escape fractions decrease with increasing halo mass (SFR), going from ~1-0.1 for halo mass between 10^9 and 10^11.2 solar masses.
LAEs can be detected with ALMA for a 5 1 hour integration.
LAEs are ‘Passive Reionization Tracers’.

21. Fraction of ionizing power from halo mass > M
LAEs