DESI DR2: Survey Overview and Cosmological Constraints from the Baryon Acoustic Oscillations

Arnaud de Mattia

CEA Paris-Saclay, Irfu

Nice, March 25th

Thanks to our sponsors and

72 Participating Institutions!

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: a stage IV survey

Schlegel+22, arXiv:2209.03585

10 years = $10 \times $

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

86 cm

Focal plane: 5000 robotic positioners

Exposure time (dark): 1000 s

Configuration of the focal plane
CCD readout
Go to next pointing

140 s

0.1 mm

Focal plane: 5000 robotic positioners

positioning within $5\, \mu\mathrm{m}$ RMS

Spectroscopic pipeline

wavelength

fiber number

$z = 2.1$ QSO

$z = 0.9$ ELG

Ly$\alpha$

CIV

CIII

[OII] doublet at $3727 \AA$ up to $z = 1.6$

[OII]

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

DESI data release 1 (DR1)

Observations from May 14th 2021 to June 12th 2022

approved

construction started

first light

survey started

DR1 sample

DR1 results

DR2 sample

DR3 sample

DR2 results

2015

>15 million galaxy and QSO redshifts
6 million used for cosmology
Cosmology results: April 2024
Data release: April 2025

DESI data release 2 (DR2)

Observations from May 14th 2021 to April 9th 2024

approved

construction started

first light

survey started

DR1 sample

DR1 results

DR2 sample

DR3 sample

DR2 results

2015

>30 million galaxy and QSO redshifts
14 million used for cosmology
Cosmology results: April 2025 (BAO), other analyses in a few months

DR3... Finished! (ahead of schedule)

footprint: 14k $\mathrm{deg}^2$
4 5 bright time passes
7 dark time passes

approved

construction started

first light

survey started

DR1 sample

DR2 sample

DR3 sample

DR2 results

2015

40 million extragalactic redshifts in 5 years

DR3... and beyond (DR5)!

17k $\mathrm{deg}^2$

footprint: 14k $\mathrm{deg}^2$
5 bright time passes
7 dark time passes

40 million extragalactic redshifts in 5 years

new LRG (Luminous Red Galaxy) targets: +50% density
higher completeness: +20% ELG (Emission Line Galaxy) density

DESI DR1-5 galaxy samples

8 years

$\sim 60$ M extragalactic redshifts over 17k $\mathrm{deg}^2$

DESI data release 2 (DR2)

30M galaxy and QSO redshifts in 3 years of operation
14M used in the DR2 analysis (6M in DR1)
Including 820,000 Ly$\alpha$ QSO at $z > 2.09$ (420,000 in DR1)
$> 2\times$ increase in number of tracers

higher completeness (deeper)

extended mag cut

Release of DESI DR2 (BAO) results

March 19th 2025

First batch of DESI DR2 cosmological analyses: https://data.desi.lbl.gov/doc/papers /dr2

• DESI Collaboration et al. (2025), DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest
• DESI Collaboration et al. (2025), DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints

Companion supporting papers:

Lodha et al. (2025), Extended Dark Energy analysis

Elbers et al. (2025), Constraints on Neutrino Physics

Andrade et al. (2025), Validation of the DESI DR2 BAO mesurements

Casas et al. (2025), Validation of the DESI DR2 Lyα BAO analysis using synthetic datasets

Brodzeller et al. (2025), Construction of the Damped Lyα Absorber Catalog for DESI DR2 Lyα BAO

DR1 public!

Baryon Acoustic Oscillations

Sound waves in primordial plasma

At recombination ($z \simeq 1100$)

plasma changes to optically thin
baryons decouple from photons
sound wave stalls after travelling $r_\mathrm{d}$

Sound horizon scale at the drag epoch

$r_\mathrm{d} \simeq 150\; \mathrm{Mpc}$

standard ruler

Baryon Acoustic Oscillations

CMB ($z \simeq 1100$)

Sound waves in primordial plasma

At recombination ($z \simeq 1100$)

plasma changes to optically thin
baryons decouple from photons
sound wave stalls after travelling $r_\mathrm{d}$

Sound horizon scale at the drag epoch

$r_\mathrm{d} \simeq 150\; \mathrm{Mpc}$

standard ruler

CMB ($z \simeq 1100$)

LSS

Baryon Acoustic Oscillations

BAO measurements

distribution of galaxies (cartoonish)

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

transverse comoving distance

sound horizon $r_\mathrm{d}$

angle on the sky (transverse to the line-of-sight): $\theta_\mathrm{BAO} = \orange{r_\mathrm{d}}/\green{D_\mathrm{M}(z)}$
$\Delta z$ (along the line-of-sight): $ \Delta z_\mathrm{BAO} = r_\mathrm{d} / D_\mathrm{H}(z) = \green{H(z)} \orange{r_\mathrm{d}} / c $

BAO measurements

distribution of galaxies (cartoonish)

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

Hubble distance $c/H(z)$

sound horizon $r_\mathrm{d}$

angle on the sky (transverse to the line-of-sight): $\theta_\mathrm{BAO} = \orange{r_\mathrm{d}}/\green{D_\mathrm{M}(z)}$
$\Delta z$ (along the line-of-sight): $ \Delta z_\mathrm{BAO} = r_\mathrm{d} / D_\mathrm{H}(z) = \green{H(z)} \orange{r_\mathrm{d}} / c $

BAO measurements

angle on the sky (transverse to the line-of-sight): $\theta_\mathrm{BAO} = \orange{r_\mathrm{d}}/\green{D_\mathrm{M}(z)}$
$\Delta z$ (along the line-of-sight): $ \Delta z_\mathrm{BAO} = r_\mathrm{d} / D_\mathrm{H}(z) = \green{H(z)} \orange{r_\mathrm{d}} / c $
at multiple redshifts $z$

Probes the expansion history ($\green{D_\mathrm{M}, D_H}$), hence the energy content (e.g. dark energy)

Absolute size at $z = 0$: $H_0 \orange{r_\mathrm{d}}$

z_1

z_2

z_3

BAO measurements

correlation function

BAO peak

line of sight

monopole

BAO measurements

correlation function

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

BAO peak

line of sight

monopole

isotropic

comoving transverse distance

Hubble distance $c/H(z)$

sound horizon (standard ruler)

BAO measurements

isotropic

anisotropic

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

BAO peak

line of sight

monopole

quadrupole

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

parameters used in cosmological inference

low S/N

BAO detection: $14.7\sigma$

0.1 < z < 0.4

0.4 < z < 0.6

0.6 < z < 0.8

0.8 < z < 1.1

1.1 < z < 1.6

Eisenstein+05

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

Correlation functions

Ly$\alpha$ forest auto-correlation

$\langle \delta_F(\mathbf{x}) \delta_F(\mathbf{x + s}) \rangle$

Ly$\alpha$ forest - QSO cross-correlation

$\langle \delta_F(\mathbf{x}) Q(\mathbf{x + s}) \rangle$

BAO measurements

BAO is a very robust probe (theory and observations)!

Subdominant systematics: $\sigma_\mathrm{stat+syst} < 1.1 \sigma_\mathrm{stat}$

DESI DR2 BAO

DESI DR2 BAO measurements

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

\propto (H_0 r_\mathrm{d})^{-1} \qquad \text{(low z)}

DESI DR2 BAO

DESI DR2 BAO measurements

\propto D_{\mathrm{M}}(z) / D_\mathrm{H}(z) = f(\Omega_\mathrm{m})

DESI DR2 BAO

DESI DR2 BAO measurements

DESI DR2 BAO

DESI DR2 BAO measurements

DESI DR2 BAO

DESI DR2 BAO measurements

DESI DR2 BAO

DESI DR2 BAO measurements

DESI DR2 BAO

DESI DR2 BAO measurements

Consistent with each other,

and complementary

\underbrace{\begin{align*} \Omega_\mathrm{m} &= 0.2975 \pm 0.0086 & \mathbf{(3.0\%)} \\ H_{0} r_\mathrm{d} &= (101.54 \pm 0.73) \, [100 \, \mathrm{km} \, \mathrm{s}^{-1}] & \mathbf{(0.7\%)} \end{align*}}_{\textstyle \text{\color{black}{DESI}}}

DESI DR2 BAO

DESI DR2 BAO measurements

DESI DR2 BAO fully consistent with DESI DR1
Improvement of $\simeq 40\%$
$2.3 \sigma$ discrepancy with primary CMB¹ + CMB lensing²
DESI BAO and CMB agree
very well on the acoustic angular
scale $\theta_\star$
Discrepancy is on $\Omega_\mathrm{m}h^2$

Consistency with other data

1. Planck PR4 CamSpec

2. Planck PR4 + ACT DR6 lensing

BAO vs CMB

Camphuis+25

SPA = SPT+Planck+ACT

$\Lambda\mathrm{CDM}$ constraints

\underbrace{ H_0 = (68.51 \pm 0.58) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

BAO constrains $\Omega_\mathrm{m}$, $h \times r_d(\Omega_\mathrm{b}h^2, \Omega_\mathrm{m}h^2)$
Calibrating BAO relative distance measurements using BBN $\Omega_\mathrm{b} h^2$

$\Lambda\mathrm{CDM}$ constraints

\underbrace{ H_0 = (68.45 \pm 0.47) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{orange}{\text{DESI} + \theta_\ast + \text{BBN}}}

BAO constrains $\Omega_\mathrm{m}$, $h \times r_d(\Omega_\mathrm{b}h^2, \Omega_\mathrm{m}h^2)$
Calibrating BAO relative distance measurements using BBN $\Omega_\mathrm{b} h^2$

\underbrace{ H_0 = (68.51 \pm 0.58) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

Adding very precise CMB acoustic angular scale

$\Lambda\mathrm{CDM}$ constraints

In $4.5\sigma$ tension with SH0ES (Breuval et al. 2024) (independently of the CMB)

\underbrace{ H_0 = (68.51 \pm 0.58) \, {\rm km\,s^{-1}\,Mpc^{-1}} }_{\textstyle \color{darkblue}{\text{DESI} + \text{BBN}}}

BAO constrains $\Omega_\mathrm{m}$, $h \times r_d(\Omega_\mathrm{b}h^2, \Omega_\mathrm{m}h^2)$
Calibrating BAO relative distance measurements using BBN $\Omega_\mathrm{b} h^2$

Dark energy fluid

(not a physical model, but a very good approximation to physical models)
No strong preference for dark energy evolution: $1.7\sigma$ from DESI data alone

Dark Energy Equation of State

$\Lambda$

p / \rho = w = w_0 + w_a (1 - a)

pressure

density

CPL

Combining DESI + CMB:

Dark Energy Equation of State

\underbrace{ w_{0} = -0.42 \pm 0.21 \qquad w_{a} = -1.75 \pm 0.58 }_{\textstyle \textcolor{orange}{\text{DESI + CMB} \; \implies \; 3.1\sigma}}

CMB early-Universe priors: $2.4\sigma$
Without CMB lensing $2.7\sigma$

$+0.5\sigma$ compared to DR1

Dark Energy Equation of State

Combining all DESI + CMB + SN

\underbrace{ w_{0} = -0.838 \pm 0.055 \qquad w_{a} = -0.62^{+0.22}_{-0.19} }_{\textstyle \textcolor{blue}{\text{DESI + CMB + Pantheon+} \; \implies \; 2.8\sigma}}

\underbrace{ w_{0} = -0.667 \pm 0.088 \qquad w_{a} = -1.09^{+0.31}_{-0.27} }_{\textstyle \color{orange}{\text{DESI + CMB + Union3} \; \implies \; 3.8\sigma}}

\underbrace{ w_{0} = -0.752 \pm 0.057 \qquad w_{a} = -0.86^{+0.23}_{-0.20} }_{\textstyle \color{green}{\text{DESI + CMB + DES-SN5YR} \; \implies \; 4.2\sigma}}

$+0.3\sigma$ compared to DR1

Original version in DESI DR2 papers (2025)

Dark Energy Equation of State

SN updates

Pantheon+ and Union3.1: new host galaxy masses (Hoyt+26)
DESY5-Dovekie: re-calibration, numerical fixes (Propovic+25)

{\textstyle \color{orange}{\text{DESI + CMB + Union3} \; \implies \; 3.8\sigma}}

{\textstyle \textcolor{blue}{\text{DESI + CMB + Pantheon+} \; \implies \; 2.8\sigma}}

{\textstyle \color{green}{\text{DESI + CMB + DES-SN5YR} \; \implies \; 4.2\sigma}}

$3.2\sigma$

$3.4\sigma$

$3.3\sigma$

Understanding tensions

doesn't fit the SN!

Understanding tensions

doesn't fit the BAO!

Understanding tensions

$w\mathrm{CDM}$ not flexible enough to fit all 3 datasets!

w = -0.970

Understanding tensions

$w_0w_a\mathrm{CDM}$ fits all 3 datasets!

Sum of neutrino masses

Internal CMB degeneracies limiting precision on the sum of neutrino masses

Broken by BAO

Sum of neutrino masses

Internal CMB degeneracies limiting precision on the sum of neutrino masses

Broken by BAO, which favors low $\Omega_\mathrm{m}$

\sum m_\nu < 0.064 \, \mathrm{eV} \; (95\%, \text{DESI + CMB})

Sum of neutrino masses

Internal CMB degeneracies limiting precision on the sum of neutrino masses

Broken by BAO, which favors low $\Omega_\mathrm{m}$

\sum m_\nu < 0.163 \, \mathrm{eV} \; (95\%, w_0w_a\mathrm{CDM})

Limit relaxed for $w_0w_a\mathrm{CDM}$

\sum m_\nu < 0.064 \, \mathrm{eV} \; (95\%, \text{DESI + CMB})

Summary

DESI already has the most precise BAO measurements ever (40% more precise than DR1)

DESI in mild, growing, tension with CMB $(2.0 - 3.7\sigma)$ when interpreted in the ΛCDM model

Tightest upper bound on $\sum m_\nu$, increasing tension with neutrino oscillations

Evidence for time-varying Dark Energy equation of state has increased with the DR2 BAO data by $0.3\sigma$: CMB: $3.1\sigma$, SN: $3.3\sigma$. $w_0w_a\mathrm{CDM}$ fixes above tensions (not $H_0$!).

At the end of DESI (8 years)

Potential for stringent DE tests with just CMB + BAO

credit: Sesh Nadathur

DESI isn't only about BAO

In a few months: DR2 Full-Shape results (probing the growth of structure)

$S_8 = \sigma_8(\Omega_\mathrm{m} / 0.3)^{0.5}$

General Relativity

growth of structure

DR1

DESI isn't only about BAO

With DR1, Maus+25

Cross-correlation with CMB lensing

Cross-correlation with galaxy lensing

Primordial non-Gaussianity

With DR1, Chaussidon+2 4

Low-$z$ growth with peculiar velocities

With DR1, Lai+26

With DR1, Porredon+25

DESI-II (2029 - 2035)

As powerful as DESI (< % BAO precision), at $z>2$: dark energy, primordial non-Gaussianity, neutrinos
High density at $z \lesssim 1$: Dark Energy, Modified Gravity
Dark Matter: stellar streams, Andromeda

Back-up

Robustness tests

tracers / redshift bins

data vector

Robustness tests

tracers / redshift bins

BAO modelling

Robustness tests

tracers / redshift bins

imaging systematics

Robustness tests

tracers / redshift bins

data splits

Robustness tests

data vector / covariance

Robustness tests

modelling choices

Robustness tests

continuum fitting

Robustness tests

data splits

Robustness tests

Removing low-$z$ SN

"Replacing CMB": DESY3 $3\times2$pt

$3.3\sigma$

Other datasets

SDSS BAO (for comparisons only): eBOSS Collaboration, 2020
Primary CMB: CamSpec PR4, HiLLiPoP/LoLLiPoP, Planck Collaboration, 2018
CMB lensing: Planck PR4 + ACT DR6 lensing ACT Collaboratio n, 2023, Carron, Mirmelstein, Lewis, 2022
BBN: Schöneberg et al., 2024
SN: Pantheon+ Brout, Scolnic, Popovic et al., 2022, Union3 Rubin, Aldering, Betoule et al. 2023, DES-SN5YR DES Collaboration

Analysis pipeline mostly the same as DR1

Again, blind analysis to mitigate observer / confirmation biases (catalog-level blinding)

Anisotropic BAO measurements for QSO (and low-$z$ ELG)

Minor updates:

- revised min fitting range ($60 < s / [\mathrm{Mpc}/h] < 150$)

- revised systematic budget (theory, fiducial cosmology, HOD): $\sigma_\mathrm{stat+syst} < 1.09 \sigma_\mathrm{stat}$

Many more robustness tests

What's new in the BAO analysis?

BAO reconstruction

Non-linear structure growth and peculiar velocities smear (and slightly displace) the BAO peak
Reconstruction: estimate Zeldovich displacements from observed field and move galaxies back $\rightarrow$ refurbishes the ruler (improves precision and accuracy)

Analysis pipeline mostly the same as DR1

Again, blind analysis to mitigate observer / confirmation biases (data vector-level blinding)

Improved modelling of metals and continuum-fitting distortions

What's new in the Ly$\alpha$ analysis?

Analysis pipeline mostly the same as DR1

Again, blind analysis to mitigate observer / confirmation biases (data vector-level blinding)

Improved modelling of metals and continuum-fitting distortions

New catalog of Damped Lyman-$\alpha$ systems (masked)

Improved mocks and associated studies

Revised fitting range and priors on nuisance parameters

Include a small (0.3%) theory systematic uncertainty for non-linear BAO shift, $\sigma_\mathrm{stat+syst} < 1.06 \sigma_\mathrm{stat}$

What's new in the Ly$\alpha$ analysis?

Robustness tests

Robust to various Planck likelihoods:

- CamSpec (baseline)

- Plik (PR3)

- LiLLiPoP-LolliPoP (PR4)

$\Lambda\mathrm{CDM}$ constraints

DESI $\Omega_\mathrm{m}$ lower than the CMB ($1.8\sigma$)
DESI $\Omega_\mathrm{m}$ lower than SN:
- Pantheon+: $1.7\sigma$
- Union3: $2.1\sigma$
- DESY5: $2.9\sigma$

Understanding tensions

DESI data release 2 (DR2)

	asgn. comp. DR1	# good z DR1	asgn. comp. DR2	z. comp DR2	# of good z DR2
BGS	64%	0.3M	76%	99%	1.2M
LRG	69%	2.1M	83%	99%	4.5M
ELG	35%	2.4M	54%	74%	6.5M
QSO	87%	1.2M	94%	68%	2M

more observations

Ly$\alpha$ forest

Pre/post DESI

DESI vs BOSS/eBOSS

LRG2 (worst case)

$2.8\sigma \, (\mathrm{DR1}) \Rightarrow 2.3\sigma \, (\mathrm{DR2})$

Binned dark energy

Binned reconstruction of $w(z)$
without assuming a functional form for the EoS
$\simeq 4\sigma$ preference for $w > -1$ in the first redshift bin
Consistent with $w_0, w_a$ parameterization

Dark energy

DE parameters

q(z)\equiv{-\frac{\ddot{a}a}{\dot{a}^2}}=\frac{d\ln H}{d\ln(1+z)}-1

Om(z)\equiv\frac{h^2(z)-1}{(1+z)^3-1}

f_{\rm DE}(z) \equiv \frac{\rho_\mathrm{DE}(z)}{\rho_\mathrm{DE,0}}

DR2 footprint

Full Shape measurements

clustering

We fit the "full shape" (FS) of the galaxy power spectrum multipoles

Full Shape measurements

RSD

observed redshift = Hubble flow and peculiar velocities (RSD = "redshift space distortions")

v_\mathrm{pec} \propto f\sigma_8

shape

($ \Omega_\mathrm{cdm} h^2, \Omega_\mathrm{b} h^2, n_\mathrm{s}, \sum m_\nu $)

growth of structure $f\sigma_8$ sensitive to the theory of gravity and dark energy

We fit the "full shape" (FS) of the galaxy power spectrum multipoles

DR1 Full Shape + BAO

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

\underbrace{\begin{align*} \Omega_\mathrm{m} &= 0.2962\pm 0.0095 & \mathbf{(3.2\%)} \\ \sigma_8 &= 0.842\pm 0.034 & \mathbf{(4.0\%)} \\ H_0 &= (68.56\pm 0.75) \, {\rm km\,s^{-1}\,Mpc^{-1}} & \mathbf{(1.1\%)} \end{align*}}_{\textstyle \text{DESI + BBN + $n_{s10}$}}

$\omega_\mathrm{b}$: BBN, $n_\mathrm{s} \sim \mathcal{G}(0.9649, 0.042^2)$

DR1 Full Shape + BAO

$S_8$ constraints

Consistency with SDSS
In agreement with CMB
Weak lensing prefers lower $S_8$, but still consistent

\underbrace{ S_8 = 0.836 \pm 0.035 }_{\textstyle \text{\color{blue}{DESI + BBN + $n_{s10}$}}}

$S_8 = \sigma_8 (\Omega_\mathrm{m} / 0.3)^{0.5}$ best constrained by weak lensing surveys

Modified gravity constraints

Perturbed FLRW metric

$ds^2=a(\tau)^2[-(1+2\orange{\Psi})d\tau^2+(1-2\orange{\Phi})\delta_{ij}dx^i dx^j]$

At late times:

(mass) $k^2\orange{\Psi} = -4\pi G a^2 \green{\mu(a,k)} \blue{\sum_i\rho_i\Delta_i}$

(light) $k^2(\orange{\Phi} + \orange{\Psi})=-8\pi G a^2 \green{\Sigma(a,k)} \blue{\sum_i\rho_i\Delta_i}$

gravitational potentials

density perturbations

\mu(a) = 1 + \frac{\Omega_\Lambda(a)}{\Omega_\Lambda} \green{\mu_0}

\Sigma(a) = 1 + \frac{\Omega_\Lambda(a)}{\Omega_\Lambda} \green{\Sigma_0}

Modified gravity constraints

$\Sigma_0$ constrained by

- CMB (ISW and lensing)

- galaxy lensing

\underbrace{\begin{align*} \mu_0 &= 0.04\pm 0.22 \\ \Sigma_0 &= 0.045\pm 0.046 \end{align*}}_{\textstyle \text{\color{purple}{DESI + CMB-nl + DESY3 ($3\times 2$-pt)}}}

\underbrace{ \mu_0 = 0.11^{+0.45}_{-0.54} }_{\textstyle \text{\color{blue}{DESI + BBN + $n_{\mathrm{s}10}$}}}

compared to CMB-nl + DESY3 (3x2pt) only: $\sigma(\mu_0) / 2.5$, $\sigma(\Sigma_0) / 2$

DESI DR2: Survey Overview and Cosmological Constraints from the Baryon Acoustic Oscillations

DESI 3D Map

DESI 3D Map

DESI: a stage IV survey

From images to redshifts

Mayall Telescope

Mayall Telescope

Focal plane: 5000 robotic positioners

Focal plane: 5000 robotic positioners

Spectroscopic pipeline

DESI data release 1 (DR1)

DESI data release 2 (DR2)

DR3... Finished! (ahead of schedule)

DR3... and beyond (DR5)!

DESI DR1-5 galaxy samples

DESI data release 2 (DR2)

Release of DESI DR2 (BAO) results

Baryon Acoustic Oscillations

Baryon Acoustic Oscillations

Baryon Acoustic Oscillations

BAO measurements

BAO measurements

BAO measurements

BAO measurements

BAO measurements

BAO measurements

Ly\(\alpha\) forest

Ly\(\alpha\) forest

Correlation functions

BAO measurements

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

DESI DR2 BAO

Consistency with other data

BAO vs CMB

\(\Lambda\mathrm{CDM}\) constraints

\(\Lambda\mathrm{CDM}\) constraints

\(\Lambda\mathrm{CDM}\) constraints

Dark Energy Equation of State

Dark Energy Equation of State

Dark Energy Equation of State

Dark Energy Equation of State

Understanding tensions

Understanding tensions

Understanding tensions

Understanding tensions

Understanding tensions

Sum of neutrino masses

Sum of neutrino masses

Sum of neutrino masses

Summary

At the end of DESI (8 years)

DESI isn't only about BAO

DESI isn't only about BAO

DESI-II (2029 - 2035)

Back-up

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Robustness tests

Other datasets

What's new in the BAO analysis?

BAO reconstruction

What's new in the Ly\(\alpha\) analysis?

What's new in the Ly\(\alpha\) analysis?

Robustness tests

\(\Lambda\mathrm{CDM}\) constraints

Understanding tensions

DESI data release 2 (DR2)

Ly\(\alpha\) forest