Manolis Plionis Bernard’s 60 birthday, Valencia, 2006 Large-Scale Flows: A historical overview
The 60’s Large-Scale Flows Stewart & Sciama (Nat., 216, 748) in 1967 predictedthe 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). Conklin1969, 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 & Petersin 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. Wolfein 1969 (ApJ, 156, 803) attempts to connect an inhomogeneity in the distribution of high-z QSO’s with the anisotropy in the CMB.
The 70’s Large-Scale Flows In the ’70sRubin & 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<6500km/secusing96 Sc galaxies) by Rubin et al. (1976)
From continuity, Euler’s and Poisson equations, in comoving coordinates and after linearizing, we have that: v and the relation between velocity and acceleration:v = βg Large-Scale Velocity Fields • 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
The 80’s : Velocity field studies get a strong kick… Large-Scale Velocity Fields 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 Hydra-Centaurus (l~308, b~13), while the bulk velocity of LSC is ~500 km/sec towards l~288, b~-9. • Dressler et al. (1987) andLynden-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…..
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 Large-Scale Velocity Fields IRAS whole sky survey
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 ! Large-Scale Dipole (Acceleration field) • 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; Rowan-Robinson 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, Lynden-Bell & Rowan-Robinson 1988; Lynden-Bell, Lahav & Burstein 1988, Pellegrini & da Costa 1990; Hudson 1993. • Main Results: • Galaxy & CMB dipole misalignment angles < 20o. • Galaxy dipole seems to converge at ~5000 km/sec • βg~ 0.4-0.7 consistent with Ωm~1
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! Large-Scale Dipole • Main Results: • Cluster & CMB dipole misalignment angles < 20o. • Cluster dipole has significant contributions from ~16000 km/sec • βc~ 0.2 (±0.1) consistent with Ωm~1
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 Large-Scale Dipole 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.
The 90’s : Major development POTENT Large-Scale Velocity Fields 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
The 90’s : Reconstruction algorithms Large-Scale Velocity Fields Yahil 1988; Strauss & Davis 1988 Basic idea:In the linear regime we can use iterative procedure to recover real-space from z-space distribution of galaxies solving in closed loop: cz=Ho |r|+ [u(r)-u(0)] ·r/|r| and u(r) = βg(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
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 (0-6000 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. 2001EFAR, (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
Meanwhile in late ’90sand 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) Shellflowusing 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
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 comparisons ISSUE No 3:Is there a consistent estimation of β from different data sets and methods ?
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 build-up, while if linear biasing was valid, on the corresponding scales, there should have been a 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:There is a consistent estimation of β from different data’seta and methods ?