Surveying the Universe in 4D: Beating Cosmic Variance with Wide-Field Slitless Spectroscopy from HST, JWST, Euclid, Roman, and Beyond

Massively multiplexed spectroscopy is revolutionizing our understanding of the universe by enabling efficient, statistically robust surveys across large cosmic volumes. By capturing spectra for thousands of sources simultaneously, it enables us to map large-scale structures, trace galaxy growth in statistically significant samples, and quantify the physical processes driving galaxy evolution as a function of environment. Wide survey areas are also essential to mitigate cosmic variance and place rare or extreme populations within the broader context of the evolving web of matter and dark energy.

Wide-Field Slitless Spectroscopy (WFSS) is critical to this effort by mitigating the selection biases inherent in targeted spectroscopic surveys. Deep, unbiased emission-line samples from HST/ACS and WFC3 grism programs have demonstrated the power of this approach in both blank and cluster fields. JWST’s NIRISS, NIRCam, and MIRI now extend WFSS to fainter fluxes and higher redshifts, enabling integrated and spatially-resolved rest-frame optical spectroscopy into the epoch of reionization. Euclid and Roman WFSS further scale these capabilities to thousands of square degrees, delivering homogeneously selected samples for statistical studies of galaxy evolution, structure formation, and cosmology — without target preselection.

Given the rapid expansion of WFSS modes and the growing volume of legacy data products, there is a pressing need to increase community awareness of both the science cases and the available analysis tools. This workshop will address key science questions related to galaxy evolution, large-scale structure assembly, and time-domain spectroscopy, as well as practical challenges in WFSS calibration and analysis. We aim to bring together experts from HST, JWST, Euclid, Roman, and beyond (e.g., CASTOR), and we strongly encourage participation from researchers at all levels of experience. The program will include science talks, hands-on technical tutorials, and discussion sessions. We invite submissions for talks, posters, and tutorials. A white paper summarizing strategies, lessons learned, and future directions will be produced following the meeting.