Galaxy Alignments with Surrounding Structure in the Sloan Digital Sky Survey

Using data from the Sloan Digital Sky Survey Legacy Survey, we study the alignment of luminous galaxies with spectroscopic data with the surrounding larger-scale structure as defined by galaxies with only photometric data. We find that galaxies from the red sequence have a statistically significant tendency for their apparent long axes to align parallel to the projected surrounding structure. Red galaxies more luminous than the median of our sample (M ( r ) < -21.78) have a mean alignment angle phi < 45 degrees, indicating preferred parallel alignment, at a significance level >4.5 sigma on projected scales 0.1 Mpc < r ( p ) <= 7.5 Mpc. Fainter red galaxies have phi < 45 degrees at a significance level >4.3 sigma at scales 1 Mpc < r ( p ) < 3 Mpc. At a projected scale r ( p ) = 3.0 Mpc, the mean alignment angle decreases steadily with increasing luminosity for red galaxies with M ( r ) less than or similar to -22.5, reaching phi = 40.degrees 49 +/- 0.degrees 56 for the most luminous 1% (M ( r ) similar to -23.57). Galaxies from the blue sequence show no statistically significant tendency for their axes to align with larger-scale structure, regardless of galaxy luminosity. Galaxies in higher-density regions do not show a statistically significant difference in the mean alignment angle from galaxies in lower-density regions; this holds true for the faint blue, luminous blue, faint red, and luminous red subsets.