Expansion and Collapse in the Cosmic Web

Expansion and Collapse in the Cosmic Web

Rauch (OCIW), Becker (CIT), Viel (IoA),Sargent (CIT), Smette (ESO),Simcoe (MIT),

Barlow (CIT)

(based on QSO absorption line data from Keck ESI and ESO UVES )(based on QSO absorption line data from Keck ESI and ESO UVES )

How does the Cosmic Web move?

Detailed record of kinematics in here

Cen et al 1994 Cen et al 1994

Keck HIRESKeck HIRES

Web of filaments and sheets formed by gravitational instability

How does it get there ?

Does feedback mess it all up ?

Sources of Sources of SystematicSystematic Motion in the IGM Motion in the IGM

• Hubble expansion: does the cosmic web follow Hubble flow ?

• Gravitational collapse: can we see it ? How does it happen ?

• Galactic feedback (e.g., outflows): all-important or negligible ?

• Hubble expansion: does the cosmic web follow Hubble flow ?

• Gravitational collapse: can we see it ? How does it happen ?

• Galactic feedback (e.g., outflows): all-important or negligible ?

Study the earliest stages of galaxy formation when Study the earliest stages of galaxy formation when moderate overdensities break away from the Hubble flowmoderate overdensities break away from the Hubble flow

Demonstrate what the standard paradigm of Lyalpha forest actually Demonstrate what the standard paradigm of Lyalpha forest actually predicts about its motions, and check whether it is correctpredicts about its motions, and check whether it is correct

Kinematics of the IGM

Probe bulk motion and turbulence with multiple lines of sight:

Lensed QSO

IGM

observer

grav. lens

Velocity and column density differences as a function of spatial scale, density

Reconstruct some properties of 3-D velocity field Reconstruct some properties of 3-D velocity field

Measure velocity differences for individual absorption lines, Measure velocity differences for individual absorption lines, seen in both lines of sight to QSO pair or lensed QSOseen in both lines of sight to QSO pair or lensed QSO

from the 1-D velocity shear to the 3-D expansion velocitiesfrom the 1-D velocity shear to the 3-D expansion velocities

QSO images

Expanding gaseous sheets, filaments

Becker et al 2004Becker et al 2004

Decoherence in the IGMDecoherence in the IGM

sep ~ 0.22 kpcsep ~ 0.22 kpc

sep ~ 260 kpcsep ~ 260 kpc

sep ~ 60 kpcsep ~ 60 kpc

Smette et al 2005Smette et al 2005

Meaasuring velocity shiftsMeaasuring velocity shifts

• Select regions with common absorption systems Select regions with common absorption systems in both images with a cursorin both images with a cursor

• Compute flux-weighted velocity centroidsCompute flux-weighted velocity centroids

Large Scale Velocity Shear in the IGMLarge Scale Velocity Shear in the IGM

Differences between the velocities of the same absorber in two lines Differences between the velocities of the same absorber in two lines of sight separated by S:of sight separated by S:

• On On kpc scaleskpc scales, velocity shear consistent with , velocity shear consistent with zerozero..

• On On large scales (250 kpc)large scales (250 kpc) , , a significant velocity a significant velocity shear (~ 30km/s RMS) shear (~ 30km/s RMS) is visible. is visible.

• Its distribution can be reproduced assuming the Its distribution can be reproduced assuming the clouds are randomly orientated, freely expanding clouds are randomly orientated, freely expanding slabs. slabs.

kpcS 1.1

kpcS 250

Observed velocity shear

Z=2.1, sep=1 kpc

Z=2.0, sep=60 kpc

Z=3.6, sep=260 kpc

Try a model of expanding pancakes

Constant radius (D’Odorico et al 1998), homologous expansion

Random orientation, cross section weighted; perform ML fit

(cf. Haehnelt 1996, Charlton et al 1995,1997)

Hubbleexp

A

A

v/v r ratio Hubble

angle azimuthal

tilt

D distance diam. Ang.

H(z)constant Hubble

)sin()tan()(D H(z)v

zr

N.B.: velocity shear independent of Hubble constant

Velocity shear modelsVelocity shear models

Adopting a coherence length ~500 physical kpc (e.g., D’Odorico etal 1998), Adopting a coherence length ~500 physical kpc (e.g., D’Odorico etal 1998),

expansion velocity at z~2 is about 80 % of Hubble flowexpansion velocity at z~2 is about 80 % of Hubble flow..

Not clear whether one should expect to find clouds to follow Hubble flow Not clear whether one should expect to find clouds to follow Hubble flow exactly (column density limited sample, crude modelling, observational errors) exactly (column density limited sample, crude modelling, observational errors)

)3(2.08.0 v/v Hubbleexp r

Define “Hubble ratio”:

Is this really a measurement ?

Need to have more realistic model to check predictions of gravitational structure formation.

Run artifical LoS pairs through cosmologicalHydro-simulation (Viel, Haehnelt and Springel 2004)

1. Quantify observational selection effects 2. See which 3-D distribution of velocities produces the

observed 1-D shear (look up density, peculiar velocity field)3. Check how the cosmic web expands in theory

From LoS velocity shear to radial expansion velocityFrom LoS velocity shear to radial expansion velocityin cosmological hydro-simulationsin cosmological hydro-simulations

1. Identify absorption lines in both LoS in velocity space

2. Calculate the spatial centroid of the absorbing gas along the LoS

3. Measure velocity of expansion along line connecting the centroids

4. Compare with velocity shear along the LoS

comparison between observed velocity shear (solid hist.) comparison between observed velocity shear (solid hist.) and the IGM in the LCDM simulation (dotted hist.)and the IGM in the LCDM simulation (dotted hist.)

km/s9.14 2)z obs;(v rms

z ~ 2 z ~ 3.6

km/s6.30 3.6)z sim;(v rms

km/s0.30 3.6)z obs;(v rms

km/s6.16 2)z sim;(v rms

General paradigm for IGM correct ?

The velocity shear distributions identical

between observations and simulations,

whatever is causing it appears to be

present in both Nature and theory.

N.B.: no feedback …

How does the Cosmic Web move ?

Look at the distribution of expansion velocities,

as functions of z , transverse separation, and column density

Frequency distributions of Hubble ratiosFrequency distributions of Hubble ratiosat different redshifts, from the simulationat different redshifts, from the simulation

z ~ 3.8

Solid hist.: Lyalpha forest selected

z ~ 3.4

z ~ 2

Dotted hist.: random regions

• Distribution broadens with time

• <r> dips below 1 by z ~ 2: grav. collapse

• median always above 1.0: “Super-Hubble”

• random regions expand faster and faster

Are the observations consistent with extragalactic feedback ?

Cosmological pop. of z~ 3 superwinds from Lybreak galaxies• Wind velocities 300-600 km/s• reduced HI in large bubbles (r~ 125 kpc)• Large escape fraction for ionizing radiation (ISM cracked by winds)• largely responsible for in situ (CIV) metal pollution(Pettini et al 2000, 2001; Steidel, Pettini, Adelberger 2001;Adelberger et al 2003)

Strong MgII / OVI absorbers may be partly superwinds

(Bond et al 2001a,b; Simcoe et al 2002).

Claims by the superwind lobby:

Lyalpha clouds produced / disturbed / destroyed by such winds

Velocity shear distribution from expanding bubbles consistent with observations at z~2:

To match the observed shear, bubbles cannot expand faster than with 45-85 km/s.

Superwinds ? Limp winds !

Consistent with observed velocity shear (16.6km/s RMS))

Are limp winds out there everywhere ?

Possibly, Theory suggests entrainment, infall, higher density ambient medium slow

down winds considerably to values as we have seen them; (e.g., Madau, Ferrara & Rees 2001; Furlanetto & Loeb 2003; Fujita et al 2004)

But Unlikely. Distribution of velocity shear (shape, width, at different z,spatial scale)

already explained by standard LCDM w/o feedback (see this paper) Lyalpha forest density field on kpc scales undisturbed (Rauch et al 2001)

Rate of incidence of strong OVI absorbers (most likely to be identified with

winds) is very small (< 3% filling factor in Lya forest) (based on Simcoe et al 2002)

N.B.: we test for galaxies blowing winds at the epoch of observation. At some early stage, every galaxy could have had a wind, as

long as its effects are gone by now.

Cosmic Seismometry:observe relative disturbance of two LoS by

passing winds

Rauch et al 2001b

Why don’t we see extragalactic superwinds in the general z~3 Lyalpha forest ?

• Small filling factor in the Lya forest, just very rare

• highly collimated, hot gas blow out into voids (large filling factor by volume possible; hard to verify)

• Superwinds don’t get out

• Superwinds don’t exist

gas phases in a hypothetical large scale filamentgas phases in a hypothetical large scale filament

100 kpc100 kpc

Are z~3 LBG superwinds necessary ?

• Pollution of universe with metals must at least startmuch earlier (Songaila 2001; Pettini et 2003)

• Metals get out more easily with dwarf winds than from massive galaxies(Martin 1998; Scannapieco et al 2002; Fujita et al 2004)

• Actual metal enrichment mostly done by dwarfs (Tremonti et al 2004)

• CIV too widespread to be expelled by individual winds (Scannapieco et al 2005)

• Sizes of Adelberger et al bubbles based on small statistics

• Large escape fraction (Steidel et al 2001) not confirmed by others

• Many galaxies at z<3 surrounded by shocked gas and hot halos heated by gravitational compression, not unlike wind bubbles.

Kinematics of the Cosmic WebKinematics of the Cosmic Web

• Distribution of velocity shear gives first glimpse of LSS velocity field Distribution of velocity shear gives first glimpse of LSS velocity field in the low density IGMin the low density IGM

• Velocity shear (over 1 - 260 kpc) consistent with a LCDM universe Velocity shear (over 1 - 260 kpc) consistent with a LCDM universe without extragalactic feedbackwithout extragalactic feedback

• Simulations show: overdense regions in the cosmic web selected Simulations show: overdense regions in the cosmic web selected by Lya absorption expand mostly with “super-Hubble velocities by Lya absorption expand mostly with “super-Hubble velocities (draining of filaments)(draining of filaments)

• Some clouds seen in states of comoving, proper contraction.Some clouds seen in states of comoving, proper contraction.

• Random regions expand fasterRandom regions expand faster

• Little structure on very small (< kpc) scales. May be seeing gas Little structure on very small (< kpc) scales. May be seeing gas “circling the drain” in a few instances“circling the drain” in a few instances

• Do not find compelling evidence for extragalactic “super”winds; Do not find compelling evidence for extragalactic “super”winds; “limp” winds may be ok, but unnecessary to explain observations.“limp” winds may be ok, but unnecessary to explain observations.

CIV absorption from the filamentary LSS structure

SPH modelling of pre-enriched gas SPH modelling of pre-enriched gas undergoing gravitational collapse undergoing gravitational collapse reproduces all know properties of CIV reproduces all know properties of CIV systems systems

(except clustering – box too small)(except clustering – box too small)

Distribution of CIV line widthsDistribution of CIV line widths(thermal + turbulent) (thermal + turbulent)

Rauch, Haehnelt & Steinmetz 1997Rauch, Haehnelt & Steinmetz 1997