Quantifying the Impact of LSST u-band Survey Strategy on Photometric Redshift Estimation and the Detection of Lyman-break Galaxies

Journal Article · Fri Dec 05 00:00:00 EST 2025 · The Astrophysical Journal. Supplement Series

DOI:https://doi.org/10.3847/1538-4365/ae14f0· OSTI ID:3015209

Crenshaw, John Franklin ^[1]; Leistedt, Boris ^[2]; Graham, Melissa Lynn ^[1]; Payerne, Constantin ^[3]; Connolly, Andrew J. ^[1]; Gawiser, Eric ^[4]; Karim, Tanveer ^[5]; Malz, Alex I. ^[6]; Newman, Jeffrey A. ^[7]; Ricci, Marina ^[8]

---

1. University of Washington, Seattle, WA (United States)
2. Imperial College London (United Kingdom)
3. Université Paris-Saclay, Gif-sur-Yvette (France)
4. Rutgers, the State University of New Jersey, Piscataway, NJ (United States)
5. University of Toronto, ON (Canada)
6. Carnegie Mellon University, Pittsburgh, PA (United States)
7. University of Pittsburgh, PA (United States)
8. Université Paris Cité (France)

The Vera C. Rubin Observatory will conduct the Legacy Survey of Space and Time (LSST), promising to discover billions of galaxies out to redshift 7, using six photometric bands (ugrizy) spanning the near-ultraviolet to the near-infrared. The exact number of and quality of information about these galaxies will depend on survey depth in these six bands, which in turn depends on the LSST survey strategy, i.e., how often and how long to expose in each band. u-band depth is especially important for photometric redshift (photo-z) estimation and for detection of high-redshift Lyman-break galaxies (LBGs). In this paper, we use a simulated galaxy catalog and an analytic model for the LBG population to study how recent updates and proposed changes to Rubin’s u-band throughput and LSST survey strategy impact photo-z accuracy and LBG detection. We find that proposed variations in u-band strategy have a small impact on photo-z accuracy for z < 1.5 galaxies, but the outlier fraction, scatter, and bias for higher-redshift galaxies vary by up to 50%, depending on the survey strategy considered. The number of u-band dropout LBGs at z ∼ 3 is also highly sensitive to the u-band depth, varying by up to 500%, while the number of griz-band dropouts is only modestly affected. Under the new u-band strategy recommended by the Rubin Survey Cadence Optimization Committee, we predict u-band dropout number densities of 110 deg⁻² (3200 deg⁻²) in year 1 (10) of LSST. We discuss the implications of these results for LSST cosmology.

• Research Organization: Stanford University, CA (United States); Univ. of Washington, Seattle, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); USDOE Office of Science (SC), High Energy Physics (HEP)
• Contributing Organization: The LSST Dark Energy Science Collaboration
• Grant/Contract Number: AC02-05CH11231; AC02-76SF00515; SC0010008; SC0011665; SC0022083
• OSTI ID: 3015209
• Alternate ID(s): OSTI ID: 3011773
• Report Number(s): DOEPRB22083
• Journal Information: The Astrophysical Journal. Supplement Series, Journal Name: The Astrophysical Journal. Supplement Series Journal Issue: 2 Vol. 281; ISSN 1538-4365; ISSN 0067-0049
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
High-redshift galaxies
Large-scale structure of the universe
Lyman-break galaxies
Observational cosmology
high-redshift galaxies
large-scale structure of the universe
observational cosmology