Galaxy Alignment with Surrounding Large-Scale Structure
Abstract
Galaxy alignments can shed light on the intrinsic properties of the cosmic structure and help make the weak gravitational lensing measurements better by reducing the contamination in weak lensing due to intrinsic alignments. From tidal torque theory, one can expect alignment of the long axis of a target galaxy's image with that of its surrounding galaxy distribution due to gravitational interactions between a galaxy and its surrounding structure. Using a sample of ~400,000 low redshift (0.02 < z < 0.25) spectroscopic galaxies from the Sloan Legacy Survey, we study alignment of these targets with their surrounding galaxy distributions. We define the alignment angle, ranging from 0° to 90°, as the angle between long axes of target galaxy image and its surrounding galaxy distribution shape. We further focus on how the alignment depends on the properties of target galaxies: color, luminosity, offset between center of the surrounding galaxy distribution and target galaxy, radius of the surrounding distribution, and the number of surrounding galaxies. It is evident that the luminous red galaxies show the highest parallel alignment (at a 6σ significance level) on average with their surrounding environment. However, there is no significant correlation between the alignment angle and the number of surrounding galaxies or the offset between center of the surrounding galaxy distribution and target galaxy. When looking at alignment of a luminous red target galaxy with its surrounding structure out to a projected distance rp, the alignment is greatest (at only 2σ significance level) for rp ~ 7 Mpc. To further investigate this dependence of alignment on the surrounding radius, we look at alignment of position angle of the target galaxy, inner surrounding structure, and outer surrounding structure, making a division at 15 Mpc. In general, this study shows that luminous red galaxies at low redshifts tend to align parallel with their surrounding structure within projected distance rp = 30 Mpc, with the strongest alignment signal at rp ~ 7 Mpc. By comparison, the faint red, luminous blue, or faint blue galaxies don't show a significant alignment with their surrounding structure.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23527907D