How to cheat with maps. perfectly sensible, honest version

Transcription

1 How to cheat with maps watch out for weasel maps : logarithmic (favors solar system) conformal (blows up BB singularity into something significant, popular with CMB types) comoving (makes the local universe look bad, anti-sdss, pro-high z galaxies) linear (unneccessary emphasis on what occupies most of the volume, most of the time) CMB perfectly sensible, honest version Lyalpha forest lensing galaxies

2 The Gaseous Cosmic Web From the Lyman alpha forest to Galaxies and back

3 The Cosmic Web Web of filaments and sheets formed by gravitational instability main reservoir of baryons at z > 2 dumping ground for metals and photons detailed archaeological record here How is the gas distributed spatially? How does it move? How does it evolve (ionisation, abundances)? what are the dominant physical processes shaping it? (e.g., gravity, galactic outflows?)

4 Intergalactic Medium = Gaseous Cosmic Web = Ly α Forest HI & He gas near mean density filamentary structure ~ 1-2 Mpc ~photoionization temperatures 10 4 K good tracer of mildly non-linear dark matter optical depth differs from DM on sub Mpc scales: thermal pressure ( Jeans ), thermal broadening (line width), peculiar velocities

5 The Lyman alpha forest Map I: a one-dimensional smoothed map of the neutral gas density

6 The Lyman alpha forest: one dimensional smoothed map of the neutral gas density absorbed flux : F (z) =e τ(z) optical depth : τ(z) =σ c H 0 neutral H density : n HI H(z s v pec (s),b(s))ds temperature τ(z) n HI (Ω bh 2 ) 2 hγ(z) T 0.76 ( ρ <ρ> photoionization rate (gas) density ) 2

7 overall normalization τ(z) n HI (Ω bh 2 ) 2 hγ(z) T 0.76 ( ρ <ρ> ) 2 scale τ until P (e τ )d(e τ ) from simulation fits data Ω b τ 0 1) assume measure evolution of ionizing flux 2) estimate ionizing flux (e.g, from QSOs) measure Ω b

8 Ω b and the evolution of the ionizing flux most baryons in the IGM! ionization rate varies slowly (slower than QSOs toward higher z) Rauch et al 1997; Bolton et al 2005

9 The Lyman alpha forest Map II: a one-dimensional map of the dark matter density

10 Assumption : baryons trace DM above filtering scale map II: from neutral gas density to dark matter density temperature (gas) density neutral H density : n HI T 0.76 ρ 2 Γ photoionization rate T ρ γ 1 Hui & Gnedin 1997 e.g., Ricotti, Gnedin & Shull 2000; T K, 1.0 < γ < 1.5 McDonald et al 2001 fluctuating density field : τ(z) =A ( ρ(v) ρ ) γ

11 map II: from neutral gas density to dark matter density F (z) =exp[ τ] =exp[a ( ρ(v) ρ ) γ] 3-D dark matter power spectrum from 1-D flux power spectrum or from optical depth rank order map onto initial Gaussian field, then resimulate Ly alpha forest from that powerspectrum; Croft et al 1998 Inversion of flux to get optical depth ; Pichon et al 2001; Nusser & Haehnelt 2002 other efforts: Zaroubi et al 2006; Mcdonald et al 2005, Viel et al 2006; Seljak et al 2006

12 Matter Power Spectrum from the Lyman alpha Forest IGM smoothed by: - thermal pressure - thermal motion - pec. velocities spurious structure from: - continuum errors - unidentified metal lines - noise - equation of state (?) -fluctuating rad. field (?) - galactic winds (?) Tegmark & Zaldarriaga 2002

13 Cosmological Constraints σ n s =0.97 Ω m =0.25 LesGourgues et al 2007

14 The Lyman alpha forest Map III: temperature and ionization of the IGM with cosmic time

15 Strong evolution of the optical depth with time r e d s h i f t Xiaohui Fan et al study of the SDSS QSOs

16 The Lyman alpha forest: map III: temperature and ionization with cosmic time cosmic expansion optical depth : τ(z) (1 + z)6 H(z) T (z) 0.76 Γ(z) (re)ionization Temperature: at late times: adiabatic cooling and photoionization; (compressional heating, shocks) at early times: compton cooling, initial conditions of reionization (UV spectra, intensity, topology of sources, density field, galactic winds)

17 T [K] temperature and density as functions of time overdensities different initial temperatures underdensities Miralda-Escude & Rees 1994 log(1+z) different initial temperatures converge with time complex history for overdense regions

18 Density-Temperature relation of the IGM Haehnelt, Steinmetz & Rauch 1996 thermal photoionization equilibrium Shock heating high density, thermal photo. equil. underdensities Equation of State : Adiabatic cooling and photoheating produce tight temperature density correlation (for low densities) Hui & Gnedin 1997

19 Actual measurements difficult. IGM Temperature from Line Profile Fitting: To get the temperature, need to disentangle thermal and non-thermal (Hubble expansion, turbulent) broadening: Two approaches: width of Lya forest lines from Voigt profile; model IGM with CDM based hydro-simulations or: Profile fit simultaneously two ions with different mass: HI, HeII. Need optical & far-uv high resolution data ( tough) - observed line widths broader than expected (gas hotter? Why?) - real data may show rise in temperature below z~ 3.2 (HeII reionization injects heat?) Schaye et al 2000, Ricotti et al 2000, Meiksin et al 2001, Theuns et al 2002, Faucher- Giguere et al 2007; but see McDonald et al 2002

20 Problem with the equation of state? Cosmological hydro-simulations over-predict HI absorption in voids, if they assume an isothermal or positive equation of state, a homogeneous ionizing radiation field Becker, Rauch & Sargent 2007 simulation optical depths z = observed distribution of optical depths τp (τ)

21 idea: combine simulation-based density distribution with a more general temperature-density relation: τ T 0.7 Γ 1 ρ 2 ρ 2 0.7(γ 1) measurement: < γ >= 0.5 γ =1 γ =0.5 T (ρ) ρ 0.5 inverse temperature-density relation! George Becker et al 2007

22 conceivable origins of inversion of equations of state radiative transfer hardens spectrum when passing from QSO into voids; voids get hotter than high density regions high density regions reionize earlier and cool faster than voids Bolton, Meiksin & White 2004 Furlanetto & Oh 2007 HeII reionization (probably as late as z~ 3-3.5) resets the clock Interesting consequences: - smaller density temperature slope means lower normalization for DM power spectrum and better agreement with WMAP. σ 8 - Becker et al optical depth distribution at odds with late (z~6) reionization.

23 complicated, non-monotonic equations of state inversion of n-t relation dependence on n-t relation on mean overdensity interplay of various cooling time scales z=5 z=3 14 < R < 24 Mpc inner 14 Mpc homogeneous radiation field Bolton, Meiksin & White 2004

24 Radiative transfer is a vital ingredient in future simulations of the IGM, even long after reionization

25 The Lyman alpha forest Map IV: The velocity field in the IGM

26 The Velocity Field of the IGM e.g., probe bulk motion and turbulence measuring differential velocities in adjacent lines of sight: grav. lens Lensed QSO observer IGM Velocity and column density differences as a function of spatial scale, density

27 Hubble expansion, peculiar motions and finite sizes cause decoherence between LoS sep ~ 0.22 kpc sep ~ 60 kpc sep ~ 260 kpc

28 How does the Cosmic Web Move? Measure velocity difference between absorbers in adjacent lines of sight : Sources of Motion: Hubble expansion, gravitational collapse, galactic winds?

29 Stretching of Filaments LCDM Simulation: Solid hist.: Lyalpha forest selected Dotted hist.: random regions Text z ~ 3.8 Distribution broadens with time Mean dips below 1 by z ~ 2: grav. collapse Median always above 1.0: Super-Hubble Random regions expand faster and faster z ~ 2 Rauch et al 2005

30 Comparison betw. Observed Velocity Differences (solid hist.) and the IGM in a LCDM Simulation (dotted hist.) z ~ 3.6 sep. 260 kpc Text General paradigm for IGM correct! No evidence for departure due to winds

31 No structure (density or velocity) on very small (< kpc) scales, much smaller than Jeans scale. Why don t we see winds?

32 Claimed evidence for high redshift superwinds: Lyman break galaxies appear to have outflows with several 100 km/s, similar to present day superwinds (Pettini et al 2000,2001) A lack of neutral hydrogen within 0.5 comoving Mpc from those objects may correspond to wind-blown cavities (Adelberger et al 2003; 2005)

33 degree of disturbances among two lines of sight tells us about filling factor of winds two lines of sight

34 degree of disturbances among two lines of sight tells us about filling factor of winds

35 degree of disturbances among two lines of sight tells us about filling factor of winds

36 No evidence for any disturbance in closely spaced lines of sight! z=2.7, sep ~ 0.22 kpc

37 SPH-Simulation of galactic feedback from z =2.4 Lyman break galaxies Energy E = erg (Kawata & Rauch 2007) Hot, metal enriched gas photoionized, metal poor filaments Super-Winds don t affect Lya forest: -small volume filling factor (a few percent) -hot winds break out into the voids, can t push filaments -cavities around some galaxies caused by hot accretion

38 Map the Intergalactic Medium in Emission? Lyman alpha fluorescence induced by the ionizing background Ionizing photons Image cosmic web in Lya glow: 2-d image of optically thick cosmic web! HI Cloud Lyman alpha photons tau(ll)~1 SFB erg s 1 cm 2 arcsec 2 Hogan & Weymann 1987

39 Image Lya glow: narrowband filter, longslit spectrum, or IFU expect SFB to 5 find 10~30 20 erg Lyman s 1 cm 2 arcsec 2 Limit emitters on a 7 longslit per unit redshift J. Kollmeier simulation

40 Service mode hour longslit exposure on blank field with VLT/FORS2 27 single line emitters, mostly without detectable continuum, over A. Fluxes a few ; mean redshift erg cm 2 s 1 MR et al 2008

41 windows 2 x 7.6 x 1510 km/s wide; turquoise contour corresponds to xt ergs 1 cm 2 Å 1

42 expect 30, find 27, BUT: -SB higher by at least factors 2-4 and often much more than anticipated -evidence of outflows in some Lyman alpha emission profiles optically thick regions already powered by star formation?

43 2 N z Ω IF HI Lyalpha: (2.67 < z < 3.75) =98 arcmin 2 - comoving density Mpc 3 (25 x Ly break galaxies!) M yr 1 < SF rate < 1.5 M yr 1 -SF rate density M yr 1 Mpc 3 - stellar mass within a Gyr M M - total masses > M v c > 50 km s 1 virial velocities (Mo & White 2002, Wang et al 2007)

44 Mpc -3 ] 3 log(dn(> L)/dV) [h log( L Ly! [ h 70 erg s -1 ]) Steepening of the luminosity function wrt. shallower surveys and modelling with constant Lya escape fraction : escape fraction (extinction) simply may not be constant: is dust diminishing towards fainter objects?

45 Rate of incidence dn/dz: geometric cross section for lyalpha emission and number density dn dz = i σ i dl V i dz (correct for finite sizes, slit losses) log (dn(> radius)/(dz) radius [phys. kpc]) Find: emitters: damped Lyalpha absorbers: total dn/dz = 0.23; cf. dn/dz(dlas)= 0.26 (e.g., Peroux et al 2005) Are these the long-sought host galaxies of DLAS?

46 Close correspondence between emitters and DLAS: both must be extended, optically thick gas dn/dz similar to DLAS (large HI extent, large comoving density of objects) low luminosity explains why DLAS in emission difficult to detecttext low star formation rate ( M yr 1 ) low metallicity of DLAS steep luminosity function - decreasing dust contents of DLAS SF rate density ~60 percent of CII158um heating of DLAS (Wolfe et al 2003) CDM : high number density of galaxies low mass, compact objects (but Lya may be extended due to radiative transfer) low mass and likely small size of SF region consistent with upper limits on extended SF in DLAS with Wolfe & Chen (2006). Confirms protogalactic clump model for high z QSO absorbers (MR, Haehnelt, & Steinmetz 1998, HSR 1998,2000), which are low mass, multiple objects later to merge into typical present day L* galaxies.

47 Conclusions Population of faint Ly alpha emitters with high space density, low star formation rates, and probable low masses; are we finally seeing typical high z starforming gals? likely counterpart of DLAS and optically thick QSO absorption systems (cross-section, low metallicity, SF rate, heating rate) map the bulk of the neutral hydrogen in the universe! likely progenitors of present day Milky Ways (merging, reservoirs of HI) finely sampled images of the cosmic web in Ly alpha are possible w. narrow band filters / spectrographs and 30m class telescopes

48 Super -Conclusions Observations of the Intergalactic medium are mapping the average (mean density) universe in several ways; dark matter density fluctuations (> 1 Mpc scales) temperature and ionization (with time) the velocity field on scales a few hundred pc to > Mpc metallicity as a function of density / time / proximity to galaxies finely sampled images of the cosmic web in Ly alpha emission are possible w. narrow band filters / spectrographs and 30m class telescopes or dedicated campaigns on existing ones.

49 Super -Conclusions Observations of the Intergalactic medium are mapping the average (mean density) universe in several ways; dark matter density fluctuations (> 1 Mpc scales) (moderately well understood) temperature and ionization (with time) (controversial) the velocity field on scales a few hundred pc to > Mpc (little work so far) metallicity as a function of density / time / proximity to galaxies lots of effort, still controversial, not very well understood finely sampled images of the cosmic web in Ly alpha emission are possible w. narrow band filters / spectrographs and 30m class telescopes or dedicated campaigns on existing ones. just starting, will probably be major science case for ultra-large Telescopes