Session Z08: Dark Energy Spectroscopic Instrument (DESI)-On Sky

Live

The Lyman alpha forest measured from the spectra of high-redshift quasars observed with DESI will provide a wealth of information for cosmology. It will allow us to unveil the expansion history with great precision by measuring the BAO scale at redshift above 2, through the measurement of the forest absorptions auto-correlation and cross-correlations with quasars. Furthermore, it will provide information on scales of about tens of Mpc, allowing to set strong constraints to massive neutrinos and dark matter with small scale suppression, such as warm and scalar field dark matter. In this talk I will give an overview of the Lyman alpha data quality from DESI Survey Validation and show preliminary results that support it fulfils our science requirements.   

Live

The Dark Energy Spectroscopic Instrument (DESI) comprises a focal plane with 5000 robotically actuated fibers feeding 10 spectrographs installed in a thermally controlled room. Each spectrograph is composed of 3 optical arms optimized to cover the wavelength range accessible from the ground with CCDs, from 360 to 980nm, with a spectral resolution from 2000 to 5000 allowing to resolve the [O II] doublet of faint emission line galaxies. The goal of the DESI survey is to acquire the spectra and measure the redshifts of 35 million galaxies and quasars. We present here an overview of the spectroscopic pipeline and its performances, in terms of wavelength and spectrophotometric calibration, sky background subtraction, redshift completeness and purity.   

Live

The DESI Survey will rely on multiple strategies to select targets for observation. The DESI Bright Galaxy Sample will focus on roughly ten million objects at the lowest redshifts ($z<0.4$). Roughly 8 million Luminous Red Galaxy targets will efficiently trace the large-scale structure of the Universe over the redshift range $0.4 [Preview Abstract]

Live

The recently commissioned Dark Energy Spectroscopic Instrument (DESI) is a fiber-fed spectroscopic instrument installed on the 4-meter Mayall telescope at Kitt Peak National Observatory (KPNO). It is now embarking on an ambitious survey to explore the nature of dark energy with spectroscopic observations of 35 million galaxies and quasars in just five years using the Baryon Acoustic Oscillation method to measure distances from the nearby universe out to redshift z = 3.5, and Redshift Space Distortions to measure the growth of structure and probe potential modifications to general relativity. In this talk we describe the significant instrumentation development for the 4-m Mayall telescope at Kitt Peak National Observatory that enables the DESI survey.    

Live

LCDM cosmological models with Early Dark Energy (EDE) have been proposed to resolve tensions between the Hubble constant measured locally and H0 deduced from Planck cosmic microwave background (CMB) and other early universe measurements plus LCDM. EDE models do this by adding a scalar field that temporarily adds dark energy equal to about 10{\%} of the cosmological energy density at the end of the radiation-dominated era. I will compare linear and nonlinear predictions of a Planck-normalized LCDM model including EDE giving H0 $=$ 72.8 km/s/Mpc with those of standard Planck LCDM with H0 $=$ 67.8 km/s/Mpc both for power spectra of fluctuations and halo mass functions at low redshifts. I will also show predicted galaxy abundances and clustering of Luminous Red Galaxies that will soon be tested by DESI observations from baryonic acoustic oscillations (BAOs) and correlation functions that differ by about 2{\%} between the models - an effect that is not washed out by nonlinearities. Both standard LCDM and the EDE model presented here agree well with presently available acoustic-scale observations, but DESI measurements will provide stringent new tests.   

Live

The success of the Dark Energy Spectroscopic Instrument (DESI) depends on its ability to collect photons from distant sources in its spectrographs. The efficiency of photon collection has many contributions: the telescope collecting area, the throughput of the fibers, optical system, and camera, the positioning of the fibers on target, the point spread function in the focal plane, and the accuracy of fiber positioning. Fiber dithering allows the contributions to the total system throughput from fiber positioning accuracy and the point spread function to be separated from other sources of light loss. We show that DESI positions fibers with an accuracy of 11 microns (0.16 arcseconds) and delivers a total throughput within 80\% of expectations, with improvements possible as DESI completes commissioning. This performance will enable DESI to meet its goal of measuring redshifts for $>$30 million galaxies to measure the history of the expansion of the universe and the growth of structure.   

Live

The Dark Energy Spectroscopic Instrument (DESI) aims to optimize its observing strategy by mitigating the effects of observational systematics using a dynamical exposure time calculator (ETC). Using a simulated large scale structure catalog comprised of luminous red galaxies, emission line galaxies, and quasars, we examine the effectiveness of the ETC by analyzing the impact of observational systematics on redshift efficiency and how this ultimately propagates to galaxy clustering measurements.   

Live

Cross-correlations between the lensing of the cosmic microwave background (CMB) and other tracers of large-scale structure provide a unique way to reconstruct the growth of dark matter, break degeneracies between cosmology and galaxy physics, and test theories of modified gravity. We report a high S/N detection of the cross-correlation between DESI luminous red galaxies and CMB lensing maps reconstructed with the Planck satellite, discuss the implications and expectations for the future.   

Live

The Dark Energy Spectroscopic Instrument (DESI) will observe millions of galaxies and quasars, including 8 million luminous red galaxies (LRGs) in the redshift range of $0.3 < z < 1.0$. With higher redshifts and higher density than the earlier LRG samples from SDSS, the DESI LRGs will enable precise measurements of the expansion history of the Universe and the growth of structure. In this talk, I will give an overview of the science that has been and will be done with the DESI LRG sample. I will describe new clustering measurements made using the LRG target sample based purely on imaging data, including studies of the galaxy-dark matter connection and determination of the baryon acoustic oscillation scale at $z \sim 0.9$. I will also discuss the new science opportunities that will be enabled by spectroscopic redshifts from DESI.