Detection of the effect of cosmological large- scale structure on the orientation of galaxies Ignacio Trujillo, Conrado Carretero & Santiago G. Patiri 2006, ApJ, 640, L111

A theoretical motivation The Tidal Torque Theory (TTT): Spin of spiral galaxies is generated by tidal torques operating on the primordial material destined to form a galaxy (Peebles 1969; White 1984) Millennium gas project Pearce et al. (2006)

A theoretical motivation: stability of the large-scale structure with cosmic time The TTT prediction: There must be local correlations between the galaxy rotation axes and the surrounding matter field

A theoretical motivation The TTT prediction: Lee (2004) provides an analytical description of the effect s n  s n   deg  P (cos  ) C=0 C=0.3 C=0.5 C=0.7 C=1 Lee (2004)

Detection problems (1) Estimating spin vector : galaxy orientation is degenerated ς: Inclination is estimated from the semi-minor to semi-major axis b/a ς=±arcsin(b/a) Solution: select Edge-on (i.e. ς ≤12 ° ) or Face-on (i.e. ς ≥78 ° )

Detection problems (1) Estimating spin vector : galaxy orientation is degenerated ς: Inclination is estimated from the semi-minor to semi-major axis b/a ς=±arcsin(b/a) Solution: select Edge-on (i.e. ς ≤12 ° ) or Face-on (i.e. ς ≥78 ° )

Detection problems (2) Cosmic planes are not measured in real space but in redshift space: cz=H 0 d+v 0 => Redshift distortion => Finger of God (FOG) Uncertainty in position of individual galaxies is: ±4.2 h -1 Mpc Characterization of planes is degenerated

Void based method: a new approach Search for orientation in the shells of big (>10 h -1 Mpc) voids Advantages: -They are not spurious structures - Uncertainty in centre position: ±2.5 h -1 Mpc - r: the vector joining the centre of the void to the centre of the galaxy is a good approximation of the vector n that describes the matter distribution Disadvantages: - Large voids are scarce © The Virgo Proyect

Void based method: estimating θ 1) Searching voids: (x,y,z,r) void HB Void Finder (Patiri et al. 2006) 2) Selecting galaxies in the shell 3) Selecting edge-on/face-on (spin) 4)

SDSS DR square degrees 5.5x10 5 galaxies b J = 18.8 mag (90%) Surveys used: 2dFGRS and SDSS DR square degrees 2.2x10 5 galaxies b J = 19 mag (90% ) 2dFGRS Maximizing the volume and number of galaxies imply estimate voids using all galaxies brighter than: M b J = log(h) z<0.14 (2dFGRS) z<0.13 (SDSS)

Our sample Voids (>10 h -1 Mpc) + shells (4 h -1 Mpc) within the survey: 149 (2dFGRS) 321 (SDSS DR3) Voids which contain at least one edge-on/face-on spiral in their shells: 49 (2dFGRS) 129 (SDSS) Final number of galaxies: 60 (edge-on; 2dFGRS) 118 (edge-on; SDSS) 23 (face-on; SDSS) Total: 201

Results Statistical Tests for the combined sample (rejection of null hypothesis): Kolmogorov-Smirnov: 99.6% Χ 2 -test: 99.8% Deviation of sin(θ): 99.7% Best strength correlation parameter c: True value (without redshift distortion) must be higher!!!

Summary 1. First statistical significant observation of alignments between disk galaxy orientation and large scale structure 2. Confirmation of one of the main prediction of the Tidal Torque Theory 3. Estimation of the strength correlation parameter c 4. Potential explanation of the Holmberg Effect