Transcript Large-Scale Velocity Fields

Large-Scale Flows: A historical overview
Manolis Plionis
Bernard’s 60 birthday,
Valencia, 2006
Large-Scale Flows
The 60’s
Stewart & Sciama (Nat., 216, 748) in 1967 predicted the dipole anisotropy of the
CMB due to motion of Sun with respect to cosmic rest frame and attempt for the
first time to estimate this motion with respect to galaxy distribution (that of the
Local Supercluster).
Conklin 1969, Nat., 222, 971, measured for the
first time the CMB dipole anisotropy which
provided a LG velocity of 590 km/sec towards
l=282o, b=18o, very close to today’s value !
Large-Scale Flows
de Vaucouleurs & Peters in 1968 attempt for the first time a very systematic
study of the motion of the Sun with respect to the galaxy distribution (Nat, 220,
868) and its effect on the estimates of the Hubble constant.
Wolfe in 1969 (ApJ, 156, 803) attempts to connect an inhomogeneity in the
distribution of high-z QSO’s with the anisotropy in the CMB.
Large-Scale Flows
The 70’s
In the ’70s Rubin & Ford and Tammann, Sandage & Yahil, as well as Peebles start
investigating deviations from Hubble flow and the Local Group motion with
respect to the galaxy distribution.
However, Fall & Jones 1976
argue against the Rubin-Ford
effect:
Detection of Virgo-centric infall by Peebles (1976) and of flows (VLG ~ 450 km/sec,
within 3500<cz<6500 km/sec using 96 Sc galaxies) by Rubin et al. (1976)
Large-Scale Velocity Fields
From continuity, Euler’s and Poisson equations, in comoving coordinates and
after linearizing, we have that:
velocity and acceleration:
Ho
v( x) 
4
v   and the relation between
v=βg
 
 3
x  x
 | x  x |3  ( x )d x
  m 0.6 / b
First attempts to derive Cosmological Density Parameter:
•Peebles (1976) find that Virgo-centric infall of LG is consistent with both open
and flat Cosmological models.
•Tammann, Yahil, Sandage (1979), from motion of LG relative to Virgo Cluster
using RSA catalog derived: vVirgo~60 km/sec, <M>/<L>=1900 qo.
•Yahil, Sandage & Tammann (1980), calculated acceleration of LG due to Virgo
which induces a vLG~3700 qo, from which the derived qo<<0.5.
•Clutton-Brock & Peebles (1981), found that the Rubin-Ford flow was consistent
with Ωm~1 for the observed level of density (galaxy-number) fluctuations.
•Davis & Huchra (1982) found from estimating the LG acceleration that
0.3<Ωm<0.5
Large-Scale Velocity Fields
The 80’s : Velocity field studies get a strong kick…
Contradicting results:
 Aaronson et al. (1986) from IR TF 4000<cz<11000 km/sec no bulk flow,
 Collins, Joseph, Robertson (1986) using Rubin-Ford Sc’s <cz>~5000 km/sec 
find streaming motion of ~1000 km/sec and
 Lilje, Yahil, Jones (1986) find shear in the LSC pointing towards HydraCentaurus (l~308, b~13), while the bulk velocity of LSC is ~500 km/sec towards
l~288, b~-9.
 Dressler et al. (1987) and Lynden-Bell et al. (1988) [8 Samurai]: Large streaming
motion with ~520 km/sec towards a hidden supercluster with M~5 x 1016 Mo (l~307,
b~9).
“The Great Attractor” Saga begins…..
Searching for the GA
Is the GA really a Great Wall ?
Voyage to the GA
Is the Cosmic Drift a Cosmic Myth?
The Core of the GA
Behind the GA
Bulk flows, Shear and the GA
Goodbye GA
Large-Scale Velocity Fields
End ’80s: “The Great Attractor” Saga continues…..
Attempts to verify or refute the GA model provide contradicting results:
 Lucey & Carter (1988) do not support GA
 Staveley-Smith & Davies (1989) point in Hydra-Centaurus as the GA.
 Dressler & Faber (1990) confirm GA (outflow of Hydra-Centaurus)
 Willick (1990) find strong flow of PP galaxies towards the LG (-450 km/sec)
 Huge numbers of publications appear estimating velocity fields using TF, FJ,
Dn-σ relations, etc (……)
Theoretical modelling intense: Vittorio, Juszkiewicz, Davis 1986; Bertschinger &
Juszkiewicz 1988; Bertschinger & Dekel 1989; Juszkiewicz & Yahil 1989;
Juszkiewicz, Vittorio & Wyse 1990, Kaiser 1991; etc etc
IRAS whole sky survey
Large-Scale Dipole (Acceleration field)
mid ’80s and early ’90s…..
DIPOLES: First whole sky dipole studies appear to support that the LG motion
with respect to the CMB is determined by joint gravitational influence of
matter fluctuations within ~4000 – 5000 km/sec !
IRAS flux-weighted dipole (Yahil, Walker & Rowan-Robinson (1986), Meiksin &
Davis 1986, Harmon, Lahav & Meurs 1987; Villumsen & Strauss 1987) or using
redshift samples (1.94Jy, QDOT-0.6Jy, 1.2Jy):, Strauss & Davis 1988; RowanRobinson et al. 1990 [2100 z’s], Strauss et al. 1992 [5300 gals]).
Simultaneously, optical whole-sky galaxy catalogues have been constructed
(ESO,UGC,MCG, zCAT) and their dipole analysed: Lahav 1987, Lahav, LyndenBell & Rowan-Robinson 1988; Lynden-Bell, Lahav & Burstein 1988, Pellegrini &
da Costa 1990; Hudson 1993.
Main Results:
1. Galaxy & CMB dipole misalignment angles < 20o.
2. Galaxy dipole seems to converge at ~5000 km/sec
3. βg~ 0.4-0.7  consistent with Ωm~1
Large-Scale Dipole
We are still in the end of the ’80s and early ’90s….. and there are some
indications for much deeper contributions to the LG acceleration (depths
~15000 – 18000 km/sec)
Melnick & Moles (1987) identify a huge concentration of galaxies in Shapley
and discuss possible influence on LG motion
Plionis (1988) find Lick dipole aligned (within ~35 deg. with CMB) that could
only be produced by mass fluctuations on depths comparable to ~D* (200 Mpc)
Scaramella et al. (1989) discuss the possibility for the Shapley concentration
to be a major contributor to the LG motion.
Plionis & Valdarnini (1991), Scaramella, Vettolani & Zamorani (1991) analyse
Abell cluster dipole and find significant contributions from ~16000 km/sec to LG
motion!
Main Results:
1. Cluster & CMB dipole misalignment angles < 20o.
2. Cluster dipole has significant contributions from
~16000 km/sec
3. βc~ 0.2 (±0.1)  consistent with Ωm~1
Large-Scale Dipole
Analyses of the QDOT and PSCz dipoles also indicate deeper contributions
(eg. Rowan-Robinson et al. 1999; Schmoldt et al. 1999; Branchini et al. 1999;
Basilakos & Plionis 1997, 2006) while recent whole sky X-ray cluster samples
verify previous cluster results: Plionis & Kolokotronis 1998; Kocevski, Mullis
& Ebeling 2004; Kocevski & Ebeling 2006
However, 2MASS dipole also
verified previous (optical)
galaxy results of shallow
convergence (Erdogdu et al.
2006). However N(z) is
dominated by lower-z’s with
respect to PSCz.
ISSUE No 1: There seems to be
a dichotomy
between Galaxy and Cluster results:
Although both are aligned with CMB there is a difference in
the dipole amplitude build-up, while if linear biasing was
valid, on the corresponding scales, there should have been a
constant difference in their respective dipole amplitudes.
Large-Scale Velocity Fields
The 90’s : Major development  POTENT
Bertschinger & Dekel (1989; 1990 ….)
Basic idea: In the linear regime we can assume that the velocity field is irrotational, i.e., the
peculiar velocities can be considered as resulting from a potential field:
v = -
Then the Potential field can be
recovered from the peculiar
velocity along the line of sight.
(r)- v(r,θ,φ) dr
Then the three components of
the velocities can be found by
differentiation:
v(r) = -(r)
From l.p.t. in comoving
coordinates we have:
δv(r) =β-1 v (r)
β~ 1.28
Large-Scale Velocity Fields
The 90’s :
Reconstruction algorithms
Yahil 1988; Strauss & Davis 1988
Basic idea: In the linear regime we can
use iterative procedure to recover realspace from z-space distribution of
galaxies solving in closed loop:
cz=Ho |r|+ [u(r)-u(0)] ·r/|r| and
u(r) = β g(r)
Peebles 1989; 1990; Shaya, Peebles,
Tully 1995
Based on least action principle:
Galaxy orbits that correspond to the
minimum of the action can be recovered by
fixing present day coordinates and requiring
the three Cartesian peculiar velocity
components to vanish at early times.
BP96
Abell/ACO cluster velocity field in
supergalactic plane (BPS 1996)
Local Group galaxy orbits
Large-Scale Velocity Fields
Meanwhile in the ’90s more observations of velocity fields with yet
contradicting results…
 Bothun et al (1992) attempt to find back-infall to GA with inconclusive results
 Mathewson, Ford & Buchhorn (1992), Mathewson & Ford (1994) analysing 1355
and 2400 spirals respectively, find no back-infall in GA but bulk flow of 600 km/sec
on scales >60 h-1 Mpc. They conclude that GA does not exist (fail to point out that
it could exist and participate in bulk flow).
 Han & Mould (1992) using TF in PP region find that local infall is as good as a
bulk flow model.
 Courteau et al. (1993) using 3000 gals find streaming motion of 360 km/sec (06000 km/sec volume) that extends beyond the GA in the direction l=273, b=0 !
 Lauer & Postman (1994) using BCG and volume ~15000 km/sec find 690 km/sec
bulk flow of whole volume but towards l=343, b=52 !!
 Wegner et al. 1996, Colless et al. 2001 EFAR, (736 ellipticals in 84 clusters to
9000 km/sec), find no bulk flow (but restricted sky coverage in 2 superclusters).
Giovanelli et al. 1997, 1998, 1999… SCI (782 spirals in 24 clusters), SC2 (522
spirals in 52 clusters out to 20000 km/sec) and SFI (1631 field galaxies ~9000
km/sec) and find very small bulk flow (100-200 km/sec).
Large-Scale Velocity Fields
Large-Scale Velocity Fields
Meanwhile in late ’90s and early 2000 more observations of
velocity fields with yet contradicting results…
 Hudson et al. (1999) SMAC … 699 early-type gals in 56 clusters (3000-14000
km/sec) find bulk-flow 630 km/sec towards l=260, b=-1 (effective radius~8000
km/sec)
 Willick (1999) LP10K survey analysing spirals and elliptical in an effective
volume of 15000 km/sec, find bulk flow of ~700 km/sec towards l=272, b=10 (in
agreement with SMAC).
 Courteau et al. (2000) Shellflow using TF of 274 Sb/Sc gals between 4500-7000
km/sec find bulk flow ~70±70 km/sec… in disagreement with SMAC & LP10K but
in agreement with SCI, SC2, SFI
 Tonry et al. (2000) using the SBF method of 300 early types within 3000 km/sec
find the local volume at rest with respect to CMB.
 Hudson (1999) using Tonry et al. (2003) 65 SNIa 6000<cz<30000 km/sec find
~610 km/sec towards l=311, b=9 (effective depth ~10000 km/sec)
 Hudson et al. (2004) analysing all data sets find bulk flow of ~230 km/sec toward
l=300, b=10… but…
Large-Scale Velocity Fields
ISSUE No 2:
There is a dichotomy
between different bulk
flow measurements !
What is going on ?
Has the L&P result been
explained ?.
Cosmological Density parameter from v-v, δ-δ and v-g comparison
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0.9
0.8
0.7
v-v
β
0.6
δ-δ
0.5
v-g
0.4
0.3
0.2
0.1
0
1
ISSUE No 3:
methods ?
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Is there a consistent estimation of β from different data sets
OPEN ISSUES
ISSUE No 1: There seems to be
a dichotomy between Galaxy and Cluster
results:
Although both are aligned with CMB there is a difference in the dipole amplitude buildwhile if linear biasing was valid, on the corresponding scales, there should have bee
constant difference in their respective dipole amplitudes.
ISSUE No 2:
There is a dichotomy between different bulk flow measurements !
Has the L&P result been explained ?.
ISSUE No 3:
methods ?
There is a consistent estimation of β from different data’seta