On the Intrinsic Alignments of the Late-Type Spiral Galaxies from the Sloan Digital Sky Survey Data Release 7

TL;DR

This study detects significant intrinsic alignments of late-type spiral galaxies using SDSS DR7 data, revealing their spin correlations and dependence on local density, consistent with tidal torque theory.

Contribution

It provides the first robust observational detection of intrinsic galaxy spin alignments and compares these with tidal torque theory predictions, highlighting stronger alignments than dark halos.

Findings

Significant intrinsic spin correlations at ~1-2 Mpc/h scales.

Spin correlations are stronger in dense environments.

Observed alignments follow quadratic scaling with density correlation.

Abstract

A robust detection of the tidally induced intrinsic alignments of the late-type spiral galaxies with high statistical significance is reported. From the spectroscopic galaxy sample of SDSS DR7 compiled by Huertas-Company et al. which lists each galaxy's probabilities of being in five Hubble types, P(E),P(Ell), P(S0),P(Sab), P(Scd), we select the nearby large late-type spiral galaxies which have redshifts of 0<=z<=0.02, probabilities of P(Scd)>=0.5 and angular sizes of D>=7.92 arcsec. The spin axes of the selected nearby large late-type spiral galaxies are determined up to the two-fold ambiguity with the help of the circular thin-disk approximation and their spatial correlations are measured as a function of the separation distance r. A clear signal of the intrinsic correlation as high as 3.4 sigma and 2.4 sigma is found at the separation distance of r~1Mpc/h and r~2Mpc/h, respectively. The comparison of this observational results with the analytic model based on the tidal torque theory reveals that the spin correlation function for the late-type spiral galaxies follow the quadratic scaling of the linear density correlation and that the intrinsic correlations of the galaxy spin axes are stronger than that of the underlying dark halos. We investigate a local density dependence of the galaxy spin correlations and found that the correlations are stronger for the galaxies located in dense regions having more than 10 neighbors within 2Mpc/h. We also attempt to measure a luminosity dependence of the galaxy spin correlations, but find that it is impossible with our magnitude-split samples to disentangle a luminosity from a redshift dependence. We provide the physical explanations for these observational results and also discuss the effects of possible residual systematics on the results.