Rupert Croft. QuickTime and a decompressor are needed to see this picture.

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1 Rupert Croft QuickTime and a decompressor are needed to see this picture.

2 yesterday: Plan for lecture 1: History : -the first quasar spectra -first theoretical models (all wrong) -CDM cosmology meets the Lya forest The Lya forest in simulations The Lya forest as cosmological tool: Conclusions -the matter power spectrum -constraints on neutrino mass -baryon oscillations

3 Plan for lecture 2: The Lya forest- beyond the power spectrum Recap : - The physics of the Lya forest Searching for the ionized baryons: CMB-Lya cross correlations Measuring quasar and galaxy halo masses from the Lya forest around them. The Lya forest and the cosmic radiation field Searching the forest for light echoes from dead quasars The future of Lya forest studies

4 quasar hydrogen atoms spectrum Absorption lines

5 Energy levels of a Hydrogen atom

6 The stars in a simulated universe

7 The baryons in a simulated universe

8 absorption level in quasar spectra tells you how much neutral hydrogen there is along the line of sight

9 or more simply, Density of matter τ [ ρ ( r)] J ( r) ~ 1.6 remember that F=e -τ (observable quantity) also Ionizing radiation intensity Analyses assume that J(r) is a constant (does not fluctuate spatially), so that measuring properties of F will give us properties of ρ (such as P(k)) later We assume this for now - we will drop this assumption tomorrow

10 Intergalactic space is where most of the baryons are predicted to be Actually most of the atoms have been ionized: γ e - H p Only 1 atom in a million remains neutral because of photoionization (there are lots of high energy photons out there) With the Lya forest, we can detect the one hydrogen atom in a million that is neutral What about the ionized hydrogen?

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12 Sunyaev-Zeldovich Effect (see Arthur Kosowsky s lectures) QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. Compton scattering of CMB photons to higher energies causes deficit (or temperature decrement) seen by an observer QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. (thermal SZ) Measures electron density (and temperature) along line of sight.

13 But even detecting huge dense galaxy clusters is difficult using SZ how can we detect very diffuse gas in the intergalactic medium? Answer- we cross correlate the Lyman alpha forest with the SZ from the CMB -we use the neutral hydrogen (from the Lya) to tell us where to look for the ionized hydrogen

14 mean level of absorption This mean level for each spectrum tells us how much neutral hydrogen is along the sightline to the quasar We write the mean absorption as an effective optical depth: τ eff = -log e <F>

15 Simulated SZ maps and Lyman alpha spectra thermal SZ 1 degree kinetic SZ

16 more simulated maps TSZ map KSZ map τ eff map to make an actual map like this we would need a grid of background quasars CMB CMB Lya

17 The CMB SZ decrement is higher for higher Lya optical depths. histogram of Lya optical depths for many simulated spectra We can look at the contribution from different redshifts (here we show z=2,3,4) We are seeing the same gas in the CMB and Lya, just the ionized (CMB) and neutral (Lya) parts.

18 Observational test cross-correlation With 3000 SDSS quasars (DR3) and WMAP (yr 1) data we can limit the density of ionized baryons at z=3 to Ω (ionized) b <0.8 (RC, Banday and Hernquist 2006) at the 2 σ level

19 Ω doesn t sound very impressive (ionized) b <0.8 (can just rule out a universe closed by ionized baryons) BUT there are two reasons why doing this is interesting (1) With this method, we are looking for a direct detection of Ω b (in the CMB maps) - every other method is indirect - no one has ever seen the majority of baryons (and at z=3, 95% are in the intergalactic medium, and even at z=0, >50% are) (2) Future experiments can tighten the limits dramatically and lead to an actual detection. The measurement can be competitive with indirect methods. We need lower noise and more quasar spectra. QuickTime and a decompressor are needed to see this picture. e.g. ACT quasars

20 QuickTime and a decompressor are needed to see this picture. Looking at the dark matter density around foreground galaxies or quasars using the Lya forest QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture.

21 Baryonic mass ~10^9 M_sun Baryonic mass ~10^11 M_sun A small slice around 4 different simulated galaxies

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23 We find an profile of absorption around quasars The depth of the profile depends on the dark matter mass profile and hence the halo mass of the object -> we can constrain the dark matter halo mass of quasars

24 Same thing measured for z=3 Lyman break galaxies: There is less absorption - lower halo masses

25 we find mean host halo mass of bright SDSS quasars at z=3 ~5x10 12 solar masses (error bars a factor of 2) halo mass of Lyman Break Galaxies ~20 times less (Kim and RC, 2007)

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27 The model of the IGM can reproduce many observations. However, it ignores the possible effect of the discrete nature of photoionizing sources (the radiation field is not uniform.) The photoionizing radiation may be provided by quasars

28 Spatial structure in the density field is only half the story τ [ ρ ( r)] J ( r) 1.6 The ionizing radiation intensity may fluctuate spatially:

29 The UV radiation field J(r) is generated by 3 different main sources: (1) hot young stars in galaxies (2) recombination radiation from the Lyman alpha forest itself (3) quasars In order for there to be fluctuations due to sources, each point in space must be able to see only a few sources. The mean free path of ionizing photons is >100 Mpc at z=3, so only quasars will cause substantial fluctuations.

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31 The proximity effect in 2008 line of sight foreground quasar-pixel measurements from SDSS, Fang, RC and Hernquist, in prep

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33 line of sight foreground quasar-pixel The foreground effect is not seen -this is a puzzle Before we seek an explanation let s look at modelling of the radiation field

34 Radiative transfer simulations: -couple RT with cosmological hydrodynamic simulation -we raytrace the paths of photons from sources through the cosmic gas.

35 State of the Universe 100 million years after the turn on of a quasar with lifetime 10 million years.

36 t q =10 7 yrs

37 t q =10 8 yrs

38 Two other effects: 1) Lightcone: - we see different parts of the Universe at different times. QuickTime and a decompressor are needed to see this picture. QuickTime and a decompressor are needed to see this picture. (no edge) QuickTime and a decompressor are needed to see this picture.

39 quasar lifetime 100 million yrs quasar lifetime 10 million yrs quasar lifetime 10 million yrs

40 t q =10 7 yrs

41 t q =10 8 yrs

42 2) Beaming We expect that the ionizing radiation from quasars might be output in a cone. -opening angle ~90 degrees In this case, there are many more quasars than those we see, depending on the opening angle.

43 t q =10 8 yrs

44 Two random sightlines, showing radiation field, density field and Lyman alpha spectra:

45 What is the effect of the inhomogeneous radiation field on the Lyman-alpha power spectrum P(k)? It suppresses the clustering (large overdensities have more radiation): relative fractional difference in P(k) Effect is small ~10% in the flux P(k) -but must be taken into account to do cosmology - i.e. measure dark matter P(k) current measurements (e.g. SDSS) do this.

46 We expect to see a reduction in absorption because of the extra photoionizing radiation close to quasars BUT we don t see it in the observations What could be causing this?

47 Perhaps the quasar radiation is highly beamed -so we only see the effect along the sightline to use and not transverse to it. Or else perhaps the quasar lifetime is relatively short - the radiation doesn t have time to cross over to other sightlines. quasar lifetime 10 million yrs but we could see transverse effect from dead quasars: quasar lifetime 10 million yrs

48 Detecting dead quasars with quasar light echos (Visbal & RC 2008) simulation density field light echo simulated lya spectra

49 We can detect dead quasars using observational data -significance will depend on luminosity

50 Quasars as standard candles QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. We have observed many more high-z quasars than supernovae - would be good to use them to measure dark energy

51 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. ionized intergalactic gas close to quasar radius of ionized region -> luminosity of quasar observed quasar flux Distance to quasar

52 Test of recovering quasar luminosity from simulated lyman alpha spectra Get ~100% statistical error in distance to quasar per spectrum. input luminosity Kim and RC (in prep) Need to marginalize over quasar host mass - systematic errors.

53 The idea is to replace the ~100 z=1 supernovae with ~ z=2-4 quasars from BOSS QuickTime and a decompressor are needed to see this picture. -> 0.25% statistical error in distance to z=3

54 Crazy things you can do with a 42m optical telescope. ELT QuickTime and a decompressor are needed to see this picture. 42m

55 Can we measure the deceleration (or accel) of cosmic objects in real time? -would be a very direct way to measure dark energy -paper by Loeb (1999) we need many objects to observe and a very stable spectrograph the Lya forest is perfect for this

56 Cristiani et al (2008)

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58 Conclusions for part II The Lyman alpha forest is a very rich resource for cosmology. We are just scratching the surface of what can be done with it. In this talk we have seen how we can use it to -directly detect the majority of baryons in the Universe - measure the dark matter mass in galaxies and quasars -detect long dead quasars -make a standard candle from quasars -even perhaps directly detect the deceleration of the Universe. Upcoming surveys will increase the current datasets by a factor of 100