THRILS -- The High-(Redshift+Ionization) Line Search: Program Description & Redshift Catalog

Taylor A. Hutchison, Rebecca L. Larson, Pablo Arrabal Haro, Erini Lambrides, Katherine Chworowsky, Gourav Khullar, Kelcey Davis, Steven L. Finkelstein, Jane R. Rigby, Guillermo Barro, Nikko J. Cleri, Dale Kocevski, Jacqueline Antwi-Danso, Mic Bagley, Danielle A. Berg, Volker Bromm, Oscar Chavez Ortiz, John Chisholm, Sadie C. Coffin, M. C. Cooper, Olivia Cooper, Isa G. Cox, Mark Dickinson, Harry Ferguson, Maximilien Franco, Jonathan P. Gardner, Ananya Ganapathy, Norman Grogin, Michaela Hirschmann, Marc Huertas-Company, Intae Jung, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Ray A. Lucas, Elizabeth McGrath, Alexa M. Morales, Grace M. Olivier, Casey Papovich, Pablo G. Perez-Gonzalez, Nor Pirzkal, Rachel S. Somerville, Anthony J. Taylor, Jonathan R. Trump, Brittany Vanderhoof, Benjamin Weiner, Brian Welch, L. Y. Aaron Yung, Jorge A. Zavala, the THRILS collaboration

First listed 2025-12-14 | Last updated 2025-12-14

Abstract

To date, many spectroscopic confirmations of z>7 galaxies have been obtained using JWST/NIRSpec prism observations, with most of their physical properties inferred from these observations and corresponding imaging. What is needed are higher-resolution spectra at deeper depths to study these sources in detail. We present The High-(Redshift+Ionization) Line Search (THRILS) program: deep (>8 hr) observations in two pointings of JWST/NIRSpec G395M spectroscopy to 1) probe high ionization spectral features in z>8 galaxies that are indicative of top-heavy initial mass functions or growing massive black holes, 2) search for accreting supermassive black holes in typical galaxies at z~4-9 through broad Balmer line emission, and 3) probe the stellar-mass growth histories of massive galaxies. We include spectroscopic redshift measurements for 89 sources from the THRILS data, as well as a detection threshold for the full and half depth integration times of the program.

Short digest

THRILS delivers deep (>8 hr) JWST/NIRSpec G395M spectroscopy in two CEERS pointings to target high-ionization features at z>8 and to search for accreting SMBHs at z~4–9 via broad Balmer emission. The program provides 89 spectroscopic redshifts plus detection thresholds for full (30 ks) and half (15 ks) depths, clarifying what is reachable for typical, non-EELG sources. A case study (THRILS-19512) demonstrates the payoff of depth, revealing faint lines such as He I 3890 and H 4103 that were missed in shallower prism data—key for testing top-heavy IMFs and early black-hole growth. A spec–phot redshift comparison across the sample documents measurement confidence and target-selection fidelity.

Key figures to inspect

• Fig. 1 (footprints on CEERS): Check how the two NIRSpec pointings land within the CEERS/NIRCam mosaic and the DDT-2750 parallels to understand which legacy imaging supports the spectra and potential ancillary constraints.
• Fig. 2 (z_spec vs z_phot): Inspect the distribution and residuals, with confidence grades and HST-only photo-z flags, to gauge selection reliability and where photometric redshifts deviated.
• Fig. 3 (depth vs detectability): Use F444W magnitude–redshift plots for primary vs filler targets to see which sources fell below the NIRSpec detection threshold, and how depth (30 ks vs 15 ks) impacts non-EELG detectability and planning.
• Fig. 4 (THRILS-19512 spectrum): Compare the 52.1 min CEERS spectrum to the 8.85 hr THRILS extraction to see newly secured weak features (He I 3890, H 4103) and the medium-resolution gains enabling high-ionization and Balmer diagnostics relevant to SMBH/IMF tests.