SGAS: Sloan Giant Arcs Survey 

I am leading the SL modeling of cluster lenses in SGAS.

Our group has discovered hundreds of cluster- and group-size gravitational lenses, in a thorough and statistically-meaningful survey. Some of these are homes for truly spectacular arcs. We aim to study the population of SL clusters via mass measurements using proxies in different wavelengths (from Xray through the SZ effect); measure their mass distribution and abundance for cosmological studies; and analyze background galaxies that have been magnified by these clusters, providing the opportunity to study them in an unprecedented detail. 

Several daughter projects originated from SGAS and/or SGAS collaborators, including many of the ones listed below: MEGASAURA, LEGGOS, COOL-LAMPS, WSLQS.

Core collaborators: Mike Gladders (PI, UChicago), Hakon Dahle (Oslo), Jane Rigby (Goddard), Matt Bayliss (Cincinnati), Michael Florian (Arizona), Gourav Khullar (U. Washington), Emil Rivera Thorsen (Sweden), Kate Napier (Vera Rubin Observatory)

SGAS-HST:

"Resolving the Star Formation in Distant Galaxies"; PI:Gladders; 107 orbit program in Cycle 20, to image 37 lensing clusters from SGAS.

Strong Lens Models for 37 Clusters of Galaxies from the SDSS Giant Arcs Survey; Sharon et al. (2020)

LEGGOS

Galaxies Under Construction: Resolved Scaling Relations and Stellar Mass Assembly as Revealed by Lensed Star-Forming Clumps at Cosmic Noon:  a Cycle-2 JWST survey of clump demographics in 8 lensed galaxies (6 new targets and 2 archival), covering over 100 clumps down to at least the 50pc scale, to directly address questions such as: How are galaxies assembled? How do clumpy structures form? How do bulges form? How do galaxy-wide scaling relations like the fundamental metallicity relation come to be? Did clumps ionize the universe? (PIs: Michael Florian, Gourav Khullar; Matt Bayliss)

SLICE -- JWST Cluster SLICE - Strong LensIng and Cluster Evolution

The JWST Survey SLICE has already imaged >100 massive galaxy clusters with two very wide NIRCam bands (F150W2+F322W2). The selected sample tracks 8 Gyrs of cluster formation history from z=1.9 to z=0.2, exploring two key fundamental properties of their

evolution: (A) How infalling cluster galaxies build-up the stellar content of 1) the bright central galaxy, 2) the intra-cluster light and 3) the large

population of globular clusters. (B) How dark matter distributes over the cluster, and gets tidally stripped from sub-halos to feed the main cluster's

potential. The requested data will more than double the total number of JWST observed strong lensing sightlines in just a year, enabling a variety of galaxy evolution studies with lensed systems.

PI: Guillaume Mahler

Papers: Cerny et al. (2025)

SPT Clusters

The South Pole Telescope discovered hundreds of clusters, identifying them by their Sunyaev Zel'dovich imprint on the cosmic microwave background radiation. Our group at Michigan participates in the strong lensing analysis of the sample of these clusters that were identified as strong lenses. We sue Michigan Magellan time to measure the spectroscopic redshifts of background sources, and prepare for 

SPT-SNAP

Cycle 25 HST/SNAP program to observe hundreds of SPT clusters. We expect about 70 lensing clusters to be observed in 2017-2019. The observations will enable multiple lines of research; At the University of Michigan, we will investigate the lensing properties of these clusters, map the mass distribution in the clusters' cores, and inform the mass-concentration relation as a function of redshift and cluster mass. 

MEGASAURA

The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MEGaSaURA, PI: Rigby) is a high-resolution spectroscopy survey of lensed, highly magnified,  galaxies, using the MagE spectrograph on Magellan.  Most of the targeted fields are from SGAS, with a few other known lenses from other surveys. Our team at Michigan is supporting this program with lensing analysis and observations.

RELICS

The Reionization Lensing Clusters Survey is a Hubble Space Telescope Treasury program (PI Coe) and Spitzer Space Telescope GO program (PI Bradač). RELICS uses clusters as cosmic telescopes to find high-redshift galaxies, and measure the luminosity functions of galaxies at cosmic dawn. 

Public site  | Internal site 

RELICS

Hubble Frontier Fields

Our research group was chosen as one of five teams to provide the community with detailed lensing magnification maps of the six Frontier Fields clusters. These public lensing magnification maps will enable the use of the Frontier Fields clusters as powerful cosmic telescopes. Frontier Fields @STScI  has links to our lens models outputs. 

Internal website

Johnson, Sharon, Bayliss, Gladders, Coe & Ebeling (2014)

BUFFALO

Beyond Ultra-deep Frontier Fields And Legacy Observations (BUFFALO) is an astronomical survey built around the six Hubble Space Telescope (HST) Frontier Fields clusters designed to learn about early galactic assembly and clustering and prepare targets for observations with the James Webb Space Telescope.  BUFFALO will place significant new constraints on how and when the most massive and luminous galaxies in the universe formed and how early galaxy formation is linked to dark matter assembly. The same data will also probe the temperature and cross section of dark matter in the massive Frontier Fields galaxy clusters, and tell us how the dark matter, cluster gas, and dynamics of the clusters influence the galaxies in and around them. These important studies are possible because the Spitzer Space Telescope, Chandra X-ray Observatory, and ground based telescopes have already invested heavily in deep observations around the Frontier Fields, so that the addition of HST observations can yield significant new results. Our international team of nearly 100 astronomers from 13 countries includes experts in theory, simulation, and observations of early galactic evolution, gravitational lensing, and supernovae.

RCS2 0327

A giant arc at z~1.7,one of the brightest known at this high redshift, was discovered as part of RCS. Since its discovery it has been the subject of detailed study by our group, including multi-band photometry and spatially-resolved spectra. We think of it as the prototype for many subsequent studies because it is such a rich dataset and magnificent lens. 

RCS2 0327 publications

New model of RCS0327 in Cerny et al (2025) -- SLICE

Multiply imaged galaxies

behind the cluster and lensed quasar

SDSS J1004+4112

WOOTS - Wise Observatory Optical Transient Search 

The Wise Observatory Optical Transient Search was led by Avishay Gal-Yam, using the 1-m telescope at the Wise observatory in the Israeli Negev desert. Gal-Yam discovered and followed up a sample of SNe in low-z galaxy clusters, which I used to measure the SN rates at low redshift. 

• Rates paper: Supernovae in Low-Redshift Galaxy Clusters: the Type-Ia Supernova Rate, Sharon et al. (2007) 

• WOOTS SNe paper: Gal-Yam et al. (2008)