Eiichiro Komatsu (Univ. of Texas, Austin) Astrophysics Seminar@UCSB May 23, 2007

1. Probing the High-zUniverse with GalaxyCounts from UltraDeepSurveys and the CosmicNearInfraredBackground Eiichiro Komatsu (Univ. of Texas, Austin) Astrophysics Seminar@UCSB May 23, 2007 • References • Elizabeth Fernandez & EK, ApJ, 646, 703 (2006) • Elizabeth Fernandez & EK, to be submitted

2. What Do I Mean By “High-z”? • I mean z>6. • An interesting epoch in the cosmic history: reionization of the universe • Direct detections of galaxies at z>6 are now possible. • eg., Ly emitter at z=6.96 discovered in the Subaru Deep Field (Iye et al. 2006)

3. Going Further… • JWST will peer deeper into the high-z universe…after 2013. • Can we do anything interesting now, and help define science goals of JWST better? • Two topics in this talk along this direction: • The Cosmic Near Infrared Background • Lyemitters at z>6 • One more topic if time permits: • 21-cm fluctuations vs the Cosmic Microwave Background (Alvarez, EK, Dore & Shapiro 2006)

4. Why Study Cosmic Near Infrared Background? (1-4um) • New window into 7<z<30 (e.g., Redshifted Ly) • Can we detect photons from early generation stars and their nebulae? What can we learn from these photons? • The presence of the signal is guaranteed, but the amplitude of the signal is not known. • Measurement of these photons is challenging because of contaminations due to: • Zodiacal light, and • Galaxies at z<6.

5. Near Infrared Background: Current Data vs Challenges Observed NIRB • Extra-galactic infrared background in J and K bands above “zodiacal light” ~ 70 nW/m2/sr • These Measurements have been challenged. • Upper limits from blazar spectra: <14 nW/m2/sr (Aharonian et al. 2006) • Incomplete subtraction of Zodiacal light? ~15 nW/m2/sr (Wright 2001); <6 nW/m2/sr (Thompson et al. 2006) • Let’s be open-minded. • Clearly, we need better data! • Better data will come from a rocket experiment, CIBER (Bock et al), in 2008. Excess? Galaxy Contribution at z<6 Matsumoto et al. (2005)

6. Previous Study: Metal-free Stars, or Mini-quasars? • First stars? • Very massive (~1000 Msun), metal-free (Z=0) stars can explain the excess signal. • Santos, Bromm & Kamionkowski (2002); Salvaterra & Ferrara (2003) • Mini quasars? • Cooray & Yoshida (2004) studied the contribution from mini-quasars. • Madau & Silk (2005) showed that it would over-produce soft X-ray background.

7. Our Prediction: Fernandez & Komatsu (2006) • We don’t need metal-free stars! • Don’t be too quick to jump into conclusion that metal-free, first stars have been seen in the NIRB. (Kashlinsky et al. 2005, 2007) • We don’t need them (yet) to explain the data. • Stars with metals (eg, Z=1/50 solar) can produce nearly the same amount of excess light per star formation rate. • This is not a negative result, but is actually a good news for NIRB: we don’t really expect a lot of metal-free stars to be around at z~7-10. • Why? A simple energy conservation.

8. Simple, but Robust, Calculation What we measure Simple argument: Luminosity per volume = (Stellar mass energy) x(Radiation efficiency) /(Time during which radiation is emitted) Can be calculated Unknown “Radiation Efficiency” IMF (Salpeter, Larson, Top-heavy)

9. Stellar data from Schaller et al. (1992); Schaerer (2002)

10. Sample Initial Mass Functions of Stars Salpeter: ) ( Larson: Top-heavy:

11. Rest-frame Spectrum of <>

12. NIRB Spectrum per SFR

13. The “Madau Plot” at z>7 You don’t have to take this seriously for now. We need better measurements!

14. How About Metal Production? • Is the inferred stat formation rate at z>7 consistent with the metal abundance in the universe? • Did these early stars that are responsible for the near infrared background over-enrich the metals in the universe too early?

15. Theoretical data for Z=1/50 solar from Portinari et al. (1998) White dwarf or neutron star Weak SN Black hole by fallback Direct collapse to black hole Type II SN Pulsational Pair Instability SN Pair Instability SN

16. Metal Production (Z=1/50 solar) The metal density now is 1.2 * 108 M8 Mpc-3 -> The upper limit from the near infrared background for a larson IMF is excluded, but most of the parameter space survives the metallicity constraint.

17. A Comment on Madau & Silk (2005) • They claim that the stellar mass density required to explain the excess near infrared background is at least 2% of the baryon density in the universe. • “this is energetically and astrophysically daunting” (Madau & Silk 2005) • It would be “daunting” if, and only if, these baryons had remained locked up in the stars and their remnants; however, • Baryons should be recycled!! If all the baryons were recycled (other extreme case), 2% should be divided by the number of generations of star formation, which is of order 10. So, the actual number should be somewhere between 2% and ~0.1%, which is not daunting at all.

18. “Smoking-gun”: Anisotropy • Press-release from Kashlinsky et al.: • Detection of significant anisotropy in the Spitzer IRAC data • They claim that the detected anisotropy originates from the first stars. • Their claim has been challenged by Cooray et al. • We need better data from CIBER, which is designed to measure anisotropy over 2 deg2 • The Spitzer image (left) is over 12’x6’.

19. The Future is in Anisotropy • Previous model (Kashlinsky et al. 2005; Cooray et al. 2006) ignored ionized bubbles. • May not be accurate enough to interpret the data from CIBER. • We will use the reionization simulation (Iliev et al. 2006) to make simulated maps of the NIRB anisotropy: coming soon!

20. One candidate: Lyman-alpha emitting galaxies at z>7. What do we learn about them from the existing Lyman-alpha Emitter (LAE) searches? Subaru Deep Field 34 LAEs at z=5.7 (Shimasaku et al. 2006) 17 LAEs at z=6.5 (Taniguchi et al. 2005; Kashikawa et al. 2006) 1 LAE at z=7 (Iye et al. 2006) LALA Survey 1 LAE at z=6.5 (Rhoads et al. 2004) ISAAC/VLT No detection at z=8.8 (Willis et al. 2006; Cuby et al. 2007) What Are the Sources of the Near Infrared Background?

21. Simply count the number of halos above a certain mass = Cumulative Mass Function Mass is related to luminosity by a “mass-to-light ratio” = M/L (M is the total mass.) We just stretch the cumulative mass function horizontally by rescaling the mass with M/L. One parameter fit! Very Simple Model of Luminosity Function

22. Cumulative Mass Function (Sheth-Tormen Mass Function) If we stretch the horizontal axis by M/L, then we get…

23. Luminosity Function of LAEs (1): SDF at z=5.7 M/Lband=95-120

24. Luminosity Function of LAEs (2): SDF at z=6.5 M/Lband=85-100

25. Luminosity Function of LAEs (3): SDF at z=7 (from 1 LAE) M/Lband~100

26. Luminosity Function of LAEs (4):VLT/ISAAC at z=8.8 (no detection) M/Lband>7

27. Mass-to-“observed light” Ratio to Mass-to-“bolometric light” Ratio • The luminosity of LAEs estimated from a given survey is not the actual luminosity of the source. • It’s a luminosity integrated over instrument’s bandwidth. • It’s a luminosity after absorption and extinction. • Conversion:

28. Getting Lbol/Lband From Model Spectrum • A sample spectrum for a galaxy of Z=1/50 solar with a Salpeter IMF. The intrinsic equivalent width of Lyman-alpha = 483 angstroms.

30. Lower metallicity -> Larger Lyman-alpha We don’t lose much light -> less correction necessary. Hence, larger Lband/Lbol. Very insensitive to the IMF Lband/Lbol: How Much Light Are We Losing?

31. (M/Lbol)/esc is remarkably stable from z=5.7 to 7! No detection of sources at z=8.8 is consistent with the expectation. We see no evidence for the evolution of (M/Lbol)/esc from z=5.7 to 8.8. Main Result: Inferred (M/Lbol)/esc

32. LAEs are normal galaxies, if: M/Lbol~10, if a good fraction of Lyman-alpha photons survived, esc~0.5. The predicted EW is consistent with observation, EW~50-300 angstroms, if the metallicity is “normal”: Z=1/50-1 solar. LAEs are starbursts, if: M/Lbol~1, if esc~0.05-0.1. The predicted EW is consistent with observation, if the metallicity is low: Z=0-1/50 solar. No evidence for the end of reionization! No evidence for the evolution of esc, unless esc goes down and M/Lbol goes up by the same amount to keep (M/Lbol)/esc constant. What Do Our Results Imply?

33. You can make it more complex. • Why not stretching it vertically as well? • “Duty cycle”, . (Haiman & Spaans 1999; Dijkstra, Wyithe & Haiman 2006). • In our model,  • Why assuming a deterministic L-M relation? • P(L|M): Probability for a halo of mass M to host a galaxy of luminosity, L. (e.g., Cooray & Milosavljevic 2005) • In our model, P(L|M)=delta[M-(M/L)L]. • The data are not good enough to constrain more parameters necessary to characterize these properties. • Our simpler model does yield reasonable results.

34. A Comment on Salvaterra&Ferrara (2006) • They claim that the excess near infrared background cannot originate from high-z galaxies, because such galaxies are not seen in high-z galaxy surveys. • They show that the excess NIRB requires hundreds of galaxies to be detected in e.g., VLT/ISAAC field, where none was found. • Their model galaxy is extremely bright: M/L~0.001. • But, we don’t need such a population! • NIRB measures the TOTAL energy. • Galaxies can release the same amount of energy by • an intense starbust for a few million years (M/L~0.001), • a moderate burst for a few hundred million years (M/L~0.1-1), or • a normal star formation (M/L~10). • SF(2006) ruled out only the first possibility.

35. Reionization & CMB - 21cm correlationAlvarez, Komatsu, Dore & Shapiro 2006, ApJ, 647, 840 21-cm maps result from line-emission Doppler is a projected effect on CMB • Doppler effect comes from peculiar velocity along l.o.s. • 21-cm fluctuations due to density and ionized fraction • We focus on degree angular scales

36. 21cm x CMB Doppler • 21cm lines • Produced by neutral hydrogen during reionization • As reionization proceeds, 21cm slowly dissappears – morphology of reionization imprinted on 21cm anisotropy • Because it is line emission, redshift frequency • CMB Doppler effect • Free electrons during reionization scatter CMB photons • Electrons moving towards us  blueshift  hot spot • Electrons moving away from us  redshift  cold spot • Doppler effect is example of “secondary anisotropy” in CMB • Both effects are sensitive to reionization • The cross-correlation is cleaner! • In analogy to TE correlation of CMB, their cross correlation is more immune to systematics because errors are uncorrelated between the two observations

37. The Effect is Easy to Understand • Reionization  positive correlation • Recombination  negative correlation

38. Probing Reionization History • Cross-correlation peaks when ionized fraction about a half • Sign and amplitude of correlation constrains derivative of ionized fraction • Typical signal amplitude ~500 (K)2 • Above expected error from Square Kilometer Array for ~1 year of observation ~135 (K)2

39. Our Prediction for SKA • The SKA data should be correlated with CMB, and WMAP data are good enough! • It is even plausible that the first convincing evidence for 21-cm from reionization would come from the cross-correlation signal. • Systematic errors, foregrounds, or unaccounted noise won’t produce the cross-correlation, but will produce spurious signal in the auto-correlation.

40. Summary • There are various observational windows to the universe at z>7 before JWST. • Near infrared background • Lyman-alpha emitters • The current data of LAEs do not show evidence for the end of reionization up to z~7. • On-going follow-up, deeper surveys with Subaru at z=7 and VLT at z=8.8 are going to be very interesting! • The excess near infrared background is likely caused by stars with metals. • We don’t need metal-free stars, which is a good news. • Future lies in anisotropy: a better prediction is required for the data from CIBER (launch in 2008) • More ambitious future with 21-cm • The 21-cm data should be correlated with CMB for a conclusive detection of the cosmic signal.