Magnification by Galaxy Group Dark Matter Halos

TL;DR

This paper reports the first detection of gravitational lensing magnification by galaxy groups using X-ray selected groups and high-redshift galaxies, demonstrating the potential of magnification measurements to complement shear in weak-lensing studies.

Contribution

It introduces a novel detection of magnification by galaxy groups, employing an optimized cross-correlation technique and modeling the mass distribution with composite-halo profiles, aligning with weak-lensing shear results.

Findings

Detected magnification at 4.9 sigma significance.

Best-fit mass profiles are consistent with shear-based measurements.

Highlights the importance of including magnification in future weak-lensing analyses.

Abstract

We report on the detection of gravitational lensing magnification by a population of galaxy groups, at a significance level of 4.9 sigma. Using X-ray selected groups in the COSMOS 1.64 deg^2 field, and high-redshift Lyman break galaxies as sources, we measure a lensing-induced angular cross-correlation between the samples. After satisfying consistency checks that demonstrate we have indeed detected a magnification signal, and are not suffering from contamination by physical overlap of samples, we proceed to implement an optimally weighted cross-correlation function to further boost the signal to noise of the measurement. Interpreting this optimally weighted measurement allows us to study properties of the lensing groups. We model the full distribution of group masses using a composite-halo approach, considering both the singular isothermal sphere and Navarro-Frenk-White profiles, and find our best fit values to be consistent with those recovered using the weak-lensing shear technique. We argue that future weak-lensing studies will need to incorporate magnification along with shear, both to reduce residual systematics and to make full use of all available source information, in an effort to maximize scientific yield of the observations.