Dynamical analysis of massive galaxy clusters

Observational astronomy

Dynamical analysis of massive galaxy clusters

Project goal

We use spectroscopy data from Gemini/GMOS to investigate the dynamics of a massive galaxy cluster, G165. We also use measured spectroscopic redshifts to constrain gravitational lens models.


Brenda Frye and Massimo Pascale.


We present Hubble Space Telescope WFC3-IR imaging in the fields of six apparently bright dusty star-forming galaxies (DSFGs) at z = 2-4 identified by their rest-frame far-infrared colors using the Planck and Herschel space facilities. We detect near-infrared counterparts for all six submillimeter sources, allowing us to undertake strong-lensing analyses. One field in particular stands out for its prominent giant arcs, PLCK G165.7+67.0 (G165). After combining the color and morphological information, we identify 11 sets of image multiplicities in this one field. We construct a strong-lensing model constrained by this lensing evidence, which uncovers a bimodal spatial mass distribution, and from which we measure a mass of (2.6 ± 0.11) × 1014 solar masses within ~250 kpc. The bright (S350 ≈ 750 mJy) DSFG appears as two images: a giant arc with a spatial extent of 4.5’’ that is merging with the critical curve, and a lower-magnification counterimage that is detected in our new longer-wavelength ground- and space-based imaging data. Using our ground-based spectroscopy, we calculate a dynamical mass of 1.3-0.70+0.04 × 1015 solar masses to the same fixed radius, although this value may be inflated relative to the true value if the velocity distribution is enhanced in the line-of-sight direction. We suggest that the bimodal mass taken in combination with the weak X-ray flux and low SZ decrement may be explained as a pre-merger for which the intracluster gas is diluted along the line of sight, while the integrated surface mass density is supercritical to strong-lensing effects. Keywords: gravitational lensing: stronggalaxies: fundamental parametersgalaxies: cluster: generalgalaxies: high redshiftsubmillimeter: galaxies


M. Pascale, B. L. Frye, L. Dai, N. Foo, Y. Qin, R. Leimbach, A. M. Bauer, E. Merlin, D. Coe, J. Diego, H. Yan, A. Zitrin, S. H. Cohen, C. Conselice, H. Dole, K. Harrington, R. A. Jansen, P. Kamienski, R. A. Windhorst, M. Yun. Possible ongoing merger discovered by photometry and spectroscopy in the field of the galaxy cluster PLCK G165.7+67.0. The Astrophysical Journal, 932(85), 2022. https://doi.org/10.3847/1538-4357/ac6ce9

B. L. Frye, M. Pascale, Y. Qin, A. Zitrin, J. Diego, G. Walth, H. Yan, C. J. Conselice, M. Alpaslan, A. Bauer, L. Busoni, D. Coe, S. H. Cohen, M. Dole, M. Donahue, I. Georgiev, R. A. Jansen, M. Limousin, R. Livermore, D. Norman, S. Rabien, R. A. Windhorst. PLCK G165.7+67.0: Analysis of a massive lensing cluster in a Hubble Space Telescope census of sub-millimeter giant arcs selected using Planck/Hershel. The Astrophysical Journal, 871(51), 2019. https://doi.org/10.3847/1538-4357/aaeff7