Speaker
Description
Constraining the clustering of high-redshift Lyman-break Galaxies (LBGs) and their cross-correlation with CMB lensing will provide a cosmological probe that is highly complementary with LSST's usual "low-redshift" 3x2pt analysis. To maximize the potential of this measurement, we must understand how photometric redshift uncertainties of LBGs affect cosmological inference. While LSST has stringent calibration requirements at low redshift, the precision needed for high-redshift LBG samples remains uncertain.
I will present the first systematic forecast of photometric redshift requirements for LBG-CMB lensing analyses. Using Fisher forecasts, we determine the constraining power of LBGs on $\Omega_M$, $S_8$, $w_0$-$w_a$, and $\Sigma m_{\nu}$, considering an isolated LBG analysis and a joint analysis with "low-redshift" 3x2pt data. We model key sources of redshift uncertainty by modifying the mean redshift and redshift variance of the LBG population, and varying the low-redshift interloper contamination, while propagating the effects into cosmological parameter inference.
We find that photometric redshift requirements for high-redshift LBGs are significantly less stringent than those for low-redshift galaxy samples, largely due to the slow redshift evolution of the CMB lensing kernel at high redshifts. As a result, LBGxCMB lensing measurements remain robust even in the presence of realistic photometric redshift uncertainties. These results establish LBGs as a powerful cosmological probe for LSST, with requirements that can be met using near-future datasets. I will outline a practical path to achieving these calibration requirements using Rubin, Roman, and medium-band data, and cross-correlating with low-redshift DESI spectroscopic tracers to empirically remove low-redshift contamination.