The DESI Experiment Part I: Science,Targeting, and Survey Design

 

Authors: DESI collaboration
Journal: ArXiv
Year: 2016
Download: ADS | arXiv

 


Abstract

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to even higher redshift, DESI will target bright [O II] emission line galaxies up to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying dark matter distribution and, at higher redshifts ($ 2.1 < z < 3.5$), for the Ly-$\alpha$ forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen. When moonlight prevents efficient observations of the faint targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.

 

 

The DESI Experiment Part II: Instrument Design

 

Authors: DESI collaboration
Journal: ArXiv
Year: 2016
Download: ADS | arXiv

 


Abstract

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution

R=λ/ΔλR= λ/Δλ

between 2000 and 5500, depending on wavelength. The DESI instrument will be used to conduct a five-year survey designed to cover 14,000 deg

2^2

. This powerful instrument will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak, Arizona, along with a new optical corrector, which will provide a three-degree diameter field of view. The DESI collaboration will also deliver a spectroscopic pipeline and data management system to reduce and archive all data for eventual public use.

 

 

CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment

Authors: T. Schrabback et al.
Journal: MNRAS
Year: 2015
Download: ADS | arXiv


Abstract

We present weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment. Using data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), we measure the weighted-average ratio of the aligned projected ellipticity components of galaxy matter haloes and their embedded galaxies,

fhf_\mathrm{h}

, split by galaxy type. We then compare our observations to measurements taken from the Millennium Simulation, assuming different models of galaxy-halo misalignment. Using the Millennium Simulation we verify that the statistical estimator used removes contamination from cosmic shear. We also detect an additional signal in the simulation, which we interpret as the impact of intrinsic shape-shear alignments between the lenses and their large-scale structure environment. These alignments are likely to have caused some of the previous observational constraints on

fhf_\mathrm{h}

to be biased high. From CFHTLenS we find

fh=0.04±0.25f_\mathrm{h}=-0.04 \pm 0.25

for early-type galaxies, which is consistent with current models for the galaxy-halo misalignment predicting

fh0.20f_\mathrm{h}\simeq 0.20

. For late-type galaxies we measure

fh=0.690.36+0.37f_\mathrm{h}=0.69_{-0.36}^{+0.37}

from CFHTLenS. This can be compared to the simulated results which yield

fh0.02f_\mathrm{h}\simeq 0.02

for misaligned late-type models.

The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field

Authors: J. Coupon et al.
Journal: MNRAS
Year: 2015
Download: ADS | arXiv


Abstract

We present new constraints on the relationship between galaxies and their host dark matter halos, measured from the location of the peak of the stellar-to-halo mass ratio (SHMR), up to the most massive galaxy clusters at redshift

z0.8z\sim0.8

and over a volume of nearly 0.1~Gpc

3^3

. We use a unique combination of deep observations in the CFHTLenS/VIPERS field from the near-UV to the near-IR, supplemented by

60000\sim60\,000

secure spectroscopic redshifts, analysing galaxy clustering, galaxy-galaxy lensing and the stellar mass function. We interpret our measurements within the halo occupation distribution (HOD) framework, separating the contributions from central and satellite galaxies. We find that the SHMR for the central galaxies peaks at

Mh,peak=1.90.1+0.2×1012MM_{\rm h, peak} = 1.9^{+0.2}_{-0.1}\times10^{12} M_{\odot}

with an amplitude of

0.0250.025

, which decreases to

0.001\sim0.001

for massive halos (

Mh>1014MM_{\rm h} > 10^{14} M_{\odot}

). Compared to central galaxies only, the total SHMR (including satellites) is boosted by a factor 10 in the high-mass regime (cluster-size halos), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modelling, we have compared our results with a large number of results from the literature up to

z=1z=1

: we find good general agreement, independently of the method used, within the typical stellar-mass systematic errors at low to intermediate mass (

M<1011M{M}_{\star} < 10^{11} M_{\odot}

) and the statistical errors above. We have also compared our SHMR results to semi-analytic simulations and found that the SHMR is tilted compared to our measurements in such a way that they over- (under-) predict star formation efficiency in central (satellite) galaxies.