New tool created by ASU researchers turns astronomers into cosmic 'sleuths'

Scientists at Arizona State University’s Beus Center for Cosmic Foundations and School of Earth and Space Exploration are creating a new analysis tool to help unlock one of the richest but least-used types of data from NASA’s James Webb Space Telescope (JWST).

Vince Estrada-Carpenter, an assistant research scientist at the School of Earth and Space Exploration (SESE), leads the research with SESE’s Seth Cohen, Nicholas Foo, Allison Noble and Rogier Windhorst, along with Jeremy Favaro and Marcin Sawicki from Saint Mary's University and Casey Papovich from Texas A&M University, to work with data known as Wide Field Slitless Spectroscopy (WFSS), from the JWST's NIRISS and NIRCam instruments.

Unlike traditional spectroscopy, slitless spectroscopy disperses the spectra of every object in the telescope's field of view at once, resulting in thousands of spatially resolved spectra per pointing. While this makes it incredibly efficient, it also means that thousands of overlapping spectra are projected onto a single image. Separating these blended signals and reconstructing the true spectra of individual galaxies is computationally challenging, requiring sophisticated modeling. These spectra also suffer from a unique problem called self-contamination, where light from different parts of a large galaxy overlaps with itself, making it difficult to separate the galaxy's true signal.

Despite its potential, WFSS data has long been notoriously difficult to process and analyze, so much of it remains underexplored.

Estrada-Carpenter has worked with this kind of data, called slitless or "grism" spectroscopy, for 10 years. Using his experience, he created Sleuth, a new analysis code that addresses many of the problems with current tools. Sleuth can produce detailed maps of emission lines in galaxies, showing where stars are forming, producing chemicals and how galaxies change over time.

"The Sleuth database will be the largest of its kind, presenting this complex data in a more accessible and user-friendly form," Estrada-Carpenter said.

As part of JWST's fifth year of science operations (Cycle 5), the team was awarded a Legacy Archival Research program to use Sleuth to analyze all publicly available WFSS data from NIRISS and NIRCam. The project will create a large, consistent set of emission-line maps and one-dimensional spectra for anyone to use.

"There is a treasure trove of information about galaxies already collected by JWST but not being fully utilized. Sleuth will unlock much of that treasury, giving astronomers a new window into how galaxies form and evolve across cosmic time,” Sawicki said.

The archive will process observations from more than 300 hours of JWST WFSS, producing spatially resolved measurements for tens of thousands of galaxies, making it the largest uniformly processed WFSS dataset ever released.

"This large sample of high-redshift, spatially resolved data will enable discoveries about how galaxies grow, evolve and eventually quench their star formation," Estrada-Carpenter said.

By turning this data into an easy-to-use format, the project should make it much easier for other researchers to study how galaxies form and change using JWST’s most detailed and challenging spectroscopic data.

The archival program should help make the released data products easier for the wider astronomy community to use. Sleuth is already enabling a diverse range of science, from nearby brown dwarfs and galaxy-galaxy gravitational lenses to the formation and evolution of galaxies in the early universe.