DESI 2024: Survey overview and first cosmological results

Arnaud de Mattia - CEA Saclay

Paris, October 29th

- survey

- BAO results

- Full Shape is coming

DESI 3D Map

Physics program
- Galaxy and quasar clustering
- Lyman-alpha forest
- Clusters and cross-correlations
- Galaxy and quasar physics
- Milky Way Survey
- Transients and low-z

DESI 3D Map

Physics program
- Galaxy and quasar clustering
- Lyman-alpha forest
- Clusters and cross-correlations
- Galaxy and quasar physics
- Milky Way Survey
- Transients and low-z

DESI Y5 galaxy samples

Bright Galaxies: 14M (SDSS: 600k)

0 < z < 0.4

LRG: 8M (SDSS: 1M)

0.4 < z < 0.8

ELG: 16M (SDSS: 200k)

0.6 < z < 1.6

QSO: 3M (SDSS: 500k)

Lya $1.8 < z$

Tracers $0.8 < z < 2.1$

Y5 $\sim 40$M galaxy redshifts!

$z = 0.4$

$z = 0.8$

$z = 0$

$z = 1.6$

$z = 2.0$

$z = 3.0$

DESI: a stage IV survey

Schlegel et al. 2022, arXiv:2209.03585

10 years = $10 \times $

Thanks to our sponsors and

72 Participating Institutions!

Thanks to our sponsors and

72 Participating Institutions!

900 researchers

From images to redshifts

imaging surveys (2014 - 2019) + WISE (IR)

target selection

spectroscopic observations

spectra and redshift measurements

From images to redshifts

imaging surveys (2014 - 2019) + WISE (IR)

target selection

spectroscopic observations

spectra and redshift measurements

Mayall Telescope

focal plane 5000 fibers

wide-field corrector

6 lenses, FoV $\sim 8~\mathrm{deg}^{2}$

Kitt Peak, AZ

4 m mirror

Mayall Telescope

focal plane 5000 fibers

fiber view camera

ten 3-channel spectrographs

49 m, 10-cable fiber run

Kitt Peak, AZ

Focal plane: 5000 robotic positioners

Exposure time (dark): 1000 s

Configuration of the focal plane
CCD readout
Go to next pointing

140 s

Spectroscopic pipeline

wavelength

fiber number

$z = 2.1$ QSO

$z = 0.9$ ELG

Ly$\alpha$

CIV

CIII

[OII] doublet at $2727 \AA$ up to $z = 1.6$

[OII]

Ly$\alpha$ at $1216 \AA$ down to $z = 2.0$

Release of DESI DR1 (BAO) results

April 4th 2024

First batch of DESI Y1 cosmological analyses
data.desi.lbl.gov/doc/papers/

• DESI 2024 I: First year data release
• DESI 2024 II: DR1 catalogs
• DESI 2024 III: BAO from Galaxies and Quasars
• DESI 2024 IV: BAO from the Lyman-Forest
• DESI 2024 V: RSD from Galaxies and Quasars
• DESI 2024 VI: Cosmological constraints from BAO measurements
• DESI 2024 VII: Cosmological constraints from RSD measurements

Release of DESI DR1 (BAO) results

April 4th 2024

First batch of DESI Y1 cosmological analyses
data.desi.lbl.gov/doc/papers/

• DESI 2024 I: First year data release
• DESI 2024 II: DR1 catalogs
• DESI 2024 III: BAO from Galaxies and Quasars
• DESI 2024 IV: BAO from the Lyman-Forest
• DESI 2024 V: RSD from Galaxies and Quasars
• DESI 2024 VI: Cosmological constraints from BAO measurements
• DESI 2024 VII: Cosmological constraints from RSD measurements

Y1KP4 leads

Hee-Jong Seo

Nikhil Padmanabhan

Baryon acoustic oscillations

Sound waves in primordial plasma

At recombination ($z \sim 1100$)

plasma changes to optically thin
baryons decouple from photons
sound wave stalls

Baryon acoustic oscillations

Sound waves in primordial plasma

At recombination ($z \sim 1100$)

plasma changes to optically thin
baryons decouple from photons
sound wave stalls

spherical shell in the distribution of galaxies, of radius the distance that sound waves travelled

= sound horizon scale at the drag epoch $ r_\mathrm{d} \sim 150 \; \mathrm{Mpc} \sim 100 \; \mathrm{Mpc}/h $

Baryon acoustic oscillations

Sound waves in primordial plasma

At recombination ($z \sim 1100$)

plasma changes to optically thin
baryons decouple from photons
sound wave stalls

spherical shell in the distribution of galaxies, of radius the distance that sound waves travelled

= sound horizon scale at the drag epoch $ r_\mathrm{d} \sim 150 \; \mathrm{Mpc} \sim 100 \; \mathrm{Mpc}/h $

standard ruler

transverse to the line-of-sight: $D_\mathrm{M}(z) / r_\mathrm{d}$

\theta_\mathrm{BAO} = r_\mathrm{d} / D_\mathrm{M}(z)

BAO measurements

transverse comoving distance

sound horizon $r_d$

transverse to the line-of-sight: $D_\mathrm{M}(z) / r_\mathrm{d}$
along the line-of-sight: $D_\mathrm{H}(z) / r_\mathrm{d} = c / (H(z) r_\mathrm{d}) $

BAO measurements

\Delta z_\mathrm{BAO} = r_\mathrm{d} / D_\mathrm{H}(z)

Hubble distance

sound horizon $r_d$

transverse to the line-of-sight: $D_\mathrm{M}(z) / r_\mathrm{d}$
along the line-of-sight: $D_\mathrm{H}(z) / r_\mathrm{d} = c / (H(z) r_\mathrm{d}) $

At multiple redshifts $z$

BAO measurements

z_1

z_2

z_3

Probes the expansion history, hence the energy content

Absolute size at $z = 0$: $H_0 r_d$

Correlation functions

Excess probability to find 2 galaxies separated by a separation s

Correlation functions

BAO peak

Power spectra

BAO wiggles

Some fits: configuration space

isotropic measurement

anisotropic measurement

\propto (D_{\mathrm{M}}^{2}(z) D_\mathrm{H}(z))^{1/3} / r_\mathrm{d}

\propto D_{\mathrm{M}}(z) / D_\mathrm{H}(z)

Non-linear evolution

Non-linear structure growth and peculiar velocities blur and shrink (slightly) the ruler

Eisenstein et al. 2008, Padmanabhan et al. 2012

Density field reconstruction

Estimates Zeldovich displacements from observed field and moves galaxies back: refurbishes the ruler (improves precision and accuracy)

reconstruction

Density field reconstruction

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)

5.7 million unique redshifts

Effective volume $V_\mathrm{eff} = 18 \; \mathrm{Gpc}^{3}$

$3 \times $ bigger than SDSS!

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)
Blind analysis to mitigate observer / confirmation biases (catalog-level blinding)

(\mathrm{R.A.}, \mathrm{Dec.}, z) \Longrightarrow (x, y, z) \Longrightarrow (\mathrm{R.A.}^\prime, \mathrm{Dec.}^\prime, z^\prime)

fiducial cosmology

blinded cosmology ($\Omega_\mathrm{m}, w_0, w_a$)

(random & unknown)

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)
Blind analysis to mitigate observer / confirmation biases (catalog-level blinding)

(\mathrm{R.A.}, \mathrm{Dec.}, z) \Longrightarrow (x, y, z) \Longrightarrow (\mathrm{R.A.}^\prime, \mathrm{Dec.}^\prime, z^\prime)

fiducial cosmology

blinded cosmology ($\Omega_\mathrm{m}, w_0, w_a$)

(random & unknown)

+ RSD blinding: change reconstructed peculiar velocities

+ $f_\mathrm{NL}^\mathrm{loc}$ blinding: add clustering-dependent signal on large scales with weights

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)
Blind analysis to mitigate observer / confirmation biases (catalog-level blinding)
Theory developments in BAO fitting code

P_\mathrm{gg}(k, \mu) = \mathcal{B}(k, \mu) P_\mathrm{nw}(k) + \mathcal{C}(k, \mu) P_\mathrm{w}(k) + \orange{\mathcal{D}(k, \mu)}

Chen, Howlett et al. 2024, arXiv:2402.14070

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)
Blind analysis to mitigate observer / confirmation biases (catalog-level blinding)
Theory developments in BAO fitting code
New and improved reconstruction methods
New combined tracer method used for overlapping galaxy samples (LRG and ELG in $0.8 < z < 1.1$)

DESI Y1 BAO analysis

Biggest ever spectroscopic BAO dataset ($N_\mathrm{tracer}$ and $V$)
Blind analysis to mitigate observer / confirmation biases (catalog-level blinding)
Theory developments in BAO fitting code
New and improved reconstruction methods
New combined tracer method used for overlapping galaxy samples (LRG and ELG in $0.8 < z < 1.1$)
Unified BAO pipeline applied to all (discrete) tracer / redshift bins consistently

Tests of systematic errors

Considered many possible sources of systematic errors using simulations and data:

observational effects (imaging systematics, fiber collisions)
BAO reconstruction (2 algorithms compared)
covariance matrix construction
incomplete theory modelling
choice of fiducial cosmology
galaxy-halo (HOD) model uncertainties

no systematics detected

systematics << statistics

Max effect: $\sigma_\mathrm{stat. + syst.} < 1.05 \sigma_\mathrm{stat.}$

Release of DESI Y1 (BAO) results

April 4th 2024

First batch of DESI Y1 cosmological analyses
https://data.desi.lbl.gov/doc/papers/

• DESI 2024 I: First year data release
• DESI 2024 II: DR1 catalogs
• DESI 2024 III: BAO from Galaxies and Quasars
• DESI 2024 IV: BAO from the Lyman-Forest
• DESI 2024 V: RSD from Galaxies and Quasars
• DESI 2024 VI: Cosmological constraints from BAO measurements
• DESI 2024 VII: Cosmological constraints from RSD measurements

Y1KP6 leads

Alma Gonzalez

Julien Guy

Andreu Font-Ribera

Ly$\alpha$ forest

Absorption in QSO spectra by neutral hydrogen in the intergalactic medium: $\lambda_\mathrm{abs} = (1 + z_\mathrm{HI}) \times 1215.17 \; \AA $

Transmitted flux fraction $F = e^{-\tau}$ probes the fluctuation in neutral hydrogen density, $\tau \propto n_\mathrm{HI} $

credit: Andrew Pontzen

Ly$\alpha$ correlation functions in DESI Y1

Ly$\alpha$ - Ly$\alpha$

Ly$\alpha$ - QSO

QSO

HI cloud

QSO

DESI Y1 Ly$\alpha$ BAO analysis

Biggest ever Ly$\alpha$ dataset ($N_\mathrm{tracer}$)

>420,000 Ly$\alpha$ QSO at z > 2.1

$2 \times $ more than SDSS!

DESI Y1 Ly$\alpha$ BAO analysis

Biggest ever Ly$\alpha$ dataset ($N_\mathrm{tracer}$)
First blind analysis to mitigate observer / confirmation biases (correlation function-level blinding)

DESI Y1 Ly$\alpha$ BAO analysis

Biggest ever Ly$\alpha$ dataset ($N_\mathrm{tracer}$)
First blind analysis to mitigate observer / confirmation biases (correlation function-level blinding)
Modelling of the correlation function: cosmological signal, and many contaminants!

DESI Y1 Ly$\alpha$ BAO analysis

Biggest ever Ly$\alpha$ dataset ($N_\mathrm{tracer}$)
First blind analysis to mitigate observer / confirmation biases (correlation function-level blinding)
Modelling of the correlation function: cosmological signal, and many contaminants!
Very stable results, systematic uncertainty neglected

Release of DESI Y1 (BAO) results

April 4th 2024

First batch of DESI DR1 cosmological analyses
https://data.desi.lbl.gov/doc/papers/

• DESI 2024 I: First year data release
• DESI 2024 II: DR1 catalogs
• DESI 2024 III: BAO from Galaxies and Quasars
• DESI 2024 IV: BAO from the Lyman-Forest
• DESI 2024 V: RSD from Galaxies and Quasars
• DESI 2024 VI: Cosmological constraints from BAO measurements
• DESI 2024 VII: Cosmological constraints from RSD measurements

Y1KP7 leads

Eva-Maria Mueller

Dragan Huterer

transverse to the line-of-sight: $D_\mathrm{M}(z) / r_\mathrm{d}$
along the line-of-sight: $D_\mathrm{H}(z) / r_\mathrm{d} = c / (H(z) r_\mathrm{d}) $
low S/N, isotropic average: $ D_\mathrm{V}(z) / r_\mathrm{d} = (z D_{\mathrm{M}}^{2}(z) D_\mathrm{H}(z))^{1/3} / r_\mathrm{d}$

BAO measurements

BAO measures ratios of distances over the sound horizon scale at the drag epoch ["standard ruler"] $r_\mathrm{d}$

Let's factor out the $h$ terms:

$\color{blue}{[D_\mathrm{M}(z) h] (\Omega_\mathrm{m}, f_\mathrm{DE}, \Omega_\mathrm{K}, ...)} \color{black}{/} \color{orange}{[r_\mathrm{d}(\Omega_\mathrm{m} h^{2}, \Omega_\mathrm{b} h^{2}) h]} $
$ \color{blue}{[D_\mathrm{H}(z) h] (\Omega_\mathrm{m}, f_\mathrm{DE}, \Omega_\mathrm{K}, ...)} \color{black}{/} \color{orange}{[r_\mathrm{d}(\Omega_\mathrm{m} h^{2}, \Omega_\mathrm{b} h^{2}) h]} $

BAO measurements at different $z$ constrain:

energy content $ \color{blue}{(\Omega_\mathrm{m}, f_\mathrm{DE}, ...)} $
constant-over-$z$ product $\color{orange}{r_\mathrm{d} h}$ i.e. $\color{orange}{H_{0} r_\mathrm{d}}$

These quantities directly relate to base cosmological parameters

BAO measurements

$h = H_{0} / [100\; \mathrm{km}/\mathrm{s} / \mathrm{Mpc}]$

$\Omega_\mathrm{m}$ fractional energy density of matter

$f_\mathrm{DE}$ dark energy

$\Omega_\mathrm{K}$ curvature

$\Omega_{b}$ baryons

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

DESI Y1 BAO

DESI BAO measurements

Consistent with each other,

and complementary

\underbrace{\begin{align*} \Omega_\mathrm{m} &= 0.295 \pm 0.015 & \mathbf{(5.1\%)} \\ H_{0} r_\mathrm{d} &= (101.8 \pm 1.3) \, [100 \, \mathrm{km} \, \mathrm{s}^{-1}] & \mathbf{(1.3\%)} \end{align*}}_{\textstyle \text{\color{black}{DESI}}}

Consistency with other probes

DESI Y1 BAO consistent with:

Consistency with other probes

DESI Y1 BAO consistent with:

SDSS eBOSS Collaboration, 2020

Consistency with other probes

DESI Y1 BAO consistent with:

SDSS eBOSS Collaboration, 2020
primary CMB: Planck Collaboration, 2018 and CMB lensing: Planck PR4 + ACT DR6 lensing ACT Collaboratio n, 2023, Carron, Mirmelstein, Lewis, 2022

Consistency with other probes

DESI Y1 BAO consistent with:

SDSS eBOSS Collaboration, 2020
primary CMB: Planck Collaboration, 2018 and CMB lensing: Planck PR4 + ACT DR6 lensing ACT Collaboratio n, 2023, Carron, Mirmelstein, Lewis, 2022

\underbrace{ \Omega_\mathrm{m} = 0.3069 \pm 0.0050 \; \mathbf{(1.6\%)} }_{\textstyle \text{\green{DESI + CMB}}}

BAO constrains $ r_\mathrm{d}(\blue{\Omega_\mathrm{m}} h^{2}, \orange{\Omega_\mathrm{b} h^{2}}) h $
$ \blue{\Omega_\mathrm{m}} $ constrained by BAO at different $z$
$\orange{\Omega_\mathrm{b}h^2}$ can be constrained by light element abundance from Big Bang Nucleosynthesis (BBN): Schöneberg et al., 2024

$\implies$ constraints on $h$ i.e. $H_0 = 100 h \; \mathrm{km} / \mathrm{s} / \mathrm{Mpc}$

Hubble constant

\underbrace{ H_0 = (68.53 \pm 0.80) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

Hubble constant

\underbrace{ H_0 = (68.52 \pm 0.62) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \theta_\ast + \text{BBN}}}

$\theta_\ast$ CMB angular acoustic scale

Consistency with SDSS

\underbrace{ H_0 = (68.53 \pm 0.80) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

Hubble constant

\underbrace{ H_0 = (68.52 \pm 0.62) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \theta_\ast + \text{BBN}}}

Consistency with SDSS
In agreement with CMB

\underbrace{ H_0 = (68.53 \pm 0.80) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

Hubble constant

\underbrace{ H_0 = (68.52 \pm 0.62) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \theta_\ast + \text{BBN}}}

Consistency with SDSS
In agreement with CMB
In $3.7 \sigma$ tension with SH0ES

\underbrace{ H_0 = (68.53 \pm 0.80) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

Hubble constant

\underbrace{ H_0 = (68.52 \pm 0.62) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \theta_\ast + \text{BBN}}}

DESI + CMB measurements favor a flat Universe

\Omega_\mathrm{K} = 0.0024 \pm 0.0016 \; \green{(\text{DESI} + \text{CMB})}

Spatial curvature

Dark Energy Equation of State

Dark Energy fluid, pressure $p$, density $\rho$

Equation of State parameter $w = p / \rho$

Linked to the evolution of Dark Energy $w(z) = -1 + \frac{1}{3}\frac{d \ln f_\mathrm{DE}(z)}{d \ln (1 + z)}$