Cosmological Advances: Peculiar Velocities and Hubble Constant

Recent advancements in cosmological studies have shed light on peculiar velocities and their implications for the Hubble constant, a critical measurement in understanding the universe's expansion. The Dark Energy Spectroscopic Instrument, or DESI, has released its first data set, known as the DESI DR1 Peculiar Velocity Survey. This survey has provided the largest set of peculiar velocity measurements in the local universe, specifically for early-type galaxies, with data from 98,292 unique galaxies measured to a precision of 26% random error. According to a study published on ArXiv, these peculiar velocities allow for improved understanding of dark energy at low redshifts, significantly impacting the measurement of the Hubble constant, H0.

The DESI DR1 has also offered a calibration of the zero-point for the Fundamental Plane and Tully-Fisher relations, which are essential for measuring H0. This analysis resulted in a baseline measurement of H0 at 73.7 km/s/Mpc, with a statistical uncertainty of 0.06 and a systematic uncertainty of 1.1. The calibration utilized a group catalog to enhance the number of available calibrator galaxies and explored other calibrators beyond the traditional methods. Future data releases are anticipated to refine this measurement further, aiming for a percent-level accuracy using Cepheid variables and the tip of the red giant branch as direct calibrators.

Additionally, the TDCOSMO collaboration has contributed to the ongoing discourse surrounding H0 through time-delay cosmography, which leverages strongly lensed quasars to measure the universe's expansion rate independently. Their latest results, particularly from the doubly lensed quasar HE1104-1805, yielded a measurement of H0 at 64.2 km/s/Mpc, which, while lower than DESI's findings, aligns with the precision achieved in studies of quadruply lensed quasars. This divergence in measurements highlights the ongoing debate regarding the exact value of the Hubble constant.

Moreover, a study utilizing the galaxy power spectrum from the DESI Bright Galaxy Survey and the Peculiar Velocity Survey has measured the growth rate of large-scale structures, expressed as fσ8, yielding a result of 0.450 at an effective redshift of 0.07. This measurement is consistent with predictions from the Lambda Cold Dark Matter model and General Relativity, further solidifying the connection between peculiar velocities and cosmological parameters. The enhancement of peculiar velocity data through the DESI survey not only enriches our understanding of cosmic expansion but also fosters discussions about dark energy and the universe's fate, making these advancements vital for the field of cosmology.