Radhakrishnan Srinivasan, Tae-hyeon Shin, Anja von der Linden, Ricardo Herbonnet, Matthias Klein, Tamas N. Varga, Antonio Frigo, Lindsey E. Bleem, Hao-Yi Wu, Zhuowen Zhang, Benjamin Levine, Alex Alarcon, Alexandra Amon, Matthew B. Bayliss, Keith Bechtol, Matthew Becker, Gary Bernstein, Sebastian Bocquet, Andresa Campos, Aurelio Carnero Rosell, Matias Carrasco Kind, Chihway Chang, Rebecca Chen, Ami Choi, Juan De Vicente, Joseph DeRose, Scott Dodelson, Cyrille Doux, Alex Drlica-Wagner, Jack Elvin-Poole, Spencer Everett, Agnès Ferté, Marco Gatti, Raven Gassis, Michael D. Gladders, Sebastian Grandis, Daniel Gruen, Robert Gruendl, Ian Harrison, Mike Jarvis, Niall MacCrann, Jamie McCullough, Michael A. McDonald, Justin Myles, Andres Navarro Alsina, Shivam Pandey, Judit Prat, Marco Raveri, Christian L. Reichardt, Richard Rollins, Eli Rykoff, Carles Sanchez, Arnab Sarkar, Lucas F. Secco, Ignacio Sevilla, Erin Sheldon, Taweewat Somboonpanyakul, Brian Stalder, Anthony A. Stark, Michael A. Troxel, Isaac Tutusaus, Brian Yanny, Boyan Yin, Michel Aguena, Sahar Allam, Felipe Andrade-Oliveira, David Bacon, Jonathan Blazek, David Brooks, David Burke, Ryan Camilleri, Jorge Carretero, Matteo Costanzi, Luiz da Costa, Maria Elidaiana da Silva Pereira, Shantanu Desai, H. Thomas Diehl, Juan Garcia-Bellido, Gaston Gutierrez, Samuel Hinton, Devon L. Hollowood, Sujeong Lee, Jennifer Marshall, Juan Mena-Fernández, Felipe Menanteau, Ramon Miquel, Andrés Plazas Malagón, Ricardo Ogando, Kathy Romer, Aaron Roodman, Eusebio Sanchez, David Sanchez Cid, Eric Suchyta, Molly Swanson, Noah Weaverdyck, Jochen Weller

The orientation of triaxial galaxy clusters with respect to the line-of-sight is expected to be one of the prime sources of scatter and potential bias in optical observables (e.g., richness and weak-lensing signal) of galaxy clusters. In this work, we use the observed shape of the central Brightest Cluster Galaxy (BCG) as proxy for the orientation along the line-of-sight for clusters selected via the Sunyaev-Zel'dovich (SZ) effect from the South Pole Telescope (SPT) and Atacama Cosmology Telescope (ACT) surveys, matched to optically selected clusters from the Dark Energy Survey Year 3 (DES). We construct two samples of clusters that are designed to be identical in SZ mass estimate and redshift but with the roundest vs. the most elliptical BCGs, which we expect to correspond to BCGs (and clusters) with major axes aligned along the line-of-sight vs. in the plane of the sky, respectively. We find that the optical richness of round-BCG clusters is $\sim 10$\% larger than that of elliptical-BCG clusters, in agreement with the expectation from projection effects and presenting the first such detection in data. The density profiles, however, are not in agreement with the expectation from projection effects: the 1-halo term (below $6~h^{-1}\rm{Mpc}$) of both the weak-lensing and galaxy density profiles are the same for the subsamples, contrary to previous studies based on X-ray selected clusters. In the 2-halo regime (above $6~h^{-1}\rm{Mpc}$), we find a significant excess of the elliptical-BCG cluster profiles compared to the round-BCG cluster profiles, which is the opposite of the expectation from numerical simulations. We hypothesize that the intrinsic shape of the BCG reflects not just the orientation angle, but also intrinsic properties of the cluster which can affect both the SZ signal and the amplitude of the 2-halo term.