Dipolar modulation in the size of galaxies: The effect of Doppler magnification

Understand

Objects falling into an overdensity appear larger on its near side and smaller on its far side than other objects at the same redshift.

• This produces a dipolar pattern of magnification, primarily as a consequence of the Doppler effect.
• At low redshift this Doppler magnification completely dominates the usual integrated gravitational lensing contribution to the lensing magnification.
• We show that one can optimally observe this pattern by extracting the dipole in the cross-correlation of number counts and galaxy sizes.