blog

Joan Najita (NOIRLab)

30 May 2024

This past weekend, Kitt Peak National Observatory (KPNO) hosted an Open Night for members of the Tohono O’odham Nation. KPNO, where the DESI project is underway, is located atop I’oligam Du’ag (Manzanita Shrub Mountain) in the Tohono O’odham homeland. KPNO Open Nights celebrate the relationship between the Nation and the Kitt Peak astronomy community and express the community’s appreciation for the privilege of carrying out research at a site that is of deep historical and cultural significance to the Nation.

For the 25 May 2024 event, KPNO opened its doors, welcoming 600 Tohono O’odham community members to the observatory. Tribal members of all ages joined in a wide variety of activities, including solar and night-time telescope viewing, Waila music, hands-on activities, and observatory tours.

Visitors to the 4m Mayall Telescope were greeted by volunteers — including DESI collaboration members Dick Joyce, Luke Tyas, Chris Brownewell, Bob Stupak, Yuanyuan Zhang, and Joan Najita — who described the DESI project, its amazing technology and goals, and how the observations are carried out. Elsewhere on the mountain, DESI collaboration member and Mid-Scale Observatories Director Lori Allen greeted visitors as they arrived and helped them view highlights of the night sky through a small telescope.

BaoBan, DESI’s ambassador for Education and Public Outreach, made several guest appearances. A coyote from the wilds of Arizona, BaoBan appeared on DESI-themed souvenir postcards created for the event and in the inaugural KPNO Newsletter for the Tohono O’odham Nation, both of which were distributed to visitors. BaoBan has previously appeared at the Tohono O’odham Rodeo, in comic strips, and other DESI-related public engagement activities.

The 25 May Open Night was long anticipated, with the recent coronavirus pandemic and Contreras fire of 2022 having disrupted the usual 2-3 year cadence of these events. With the mountain now reopened and normal observatory operations resumed, the Kitt Peak astronomy community was eager to restart the series. More than 70 volunteers from NOIRLab and Kitt Peak facilities worked together with local Tucson community organizations in hosting the event.

For Bob Stupak, NOIRLab Electronics Technician and DESI collaboration member, welcoming visitors at the Mayall was “a great time,” an opportunity to share the excitement of DESI with the community, resulting in smiles all around. He noted, “I was working at the top of the visitor’s elevator and everyone leaving the building seemed to have been really impressed.”

Further details about the event are available in a NOIRLab press release.

Joan Najita (NOIRLab) and Luke Tyas (LBL)

Science communicators across the internet are discussing DESI’s Year 1 results and their implications for the fate of the Universe. Here are some of the highlights.

World Science Festival: Is Dark Energy Decaying? 

Brian Greene sits down with Michael Levi (LBL) to discuss DESI’s revolutionary observations that may upend our understanding of the cosmos. In an hour-long conversation that takes us from the discovery of dark energy to the birth of the DESI project and on to its Year 1 Key Project results, Greene and Levi highlight the cutting-edge nature of the story. That is, we’re finding an intriguing hint that dark energy is weakening (i.e., becoming “less pushy” over time), and but we’re not completely sure. Commenting on the uncertainty, and how we’ll know more soon, “This is why I love doing physics,” says Levi, “It’s detective novel that you get to read and discover, and it was written by the Universe!” As for the bigger picture meaning of the results, should they hold up, the weakening accelerated expansion of the universe seems reminiscent of the end of the inflationary expansion phase that marked the birth of the Universe. Levi finds it “appealing that we may be living in an epoch that ties back to the beginning of time.”

PBS Nova: New Map of the Universe Hints that Dark Energy May Be Evolving

This 3-minute video, which includes commentary from David Kaiser (MIT) and Priya Natarajan (Yale), describes how the DESI results could “fundamentally change what we know about the Universe and how it may come to an end.” Kaiser says the new DESI map of the Universe is more than a simple accounting where stuff is at any given moment. It also captures the Universe’s dynamics, creating something more like a movie that shows how fast space was stretching at different times over the Universe’s history. Natarajan emphasizes the possible cosmological implications of the results, noting that “If dark energy was a constant, the fate of the Universe would be grim.” Instead The DESI results appear to “open the door to the possibility of changing dark energy models”, which for Natarajan, “means that we have more exciting (possible) fates that await us.”

NPR: This week in science: Pompeiian frescoes, dark energy and the largest marine reptile  — NPR’s Mary Louise Kelly talks with Emily Kwong and Rachel Carson of Short Wave about how dark energy may be changing, with commentary from Priya Natarajan (Yale).

Dr Becky: Does the expansion rate of the Universe CHANGE over time?! DESI 1 year results — In this 12-minute video, astrophysicist Dr Becky Smethurst (Oxford) explains Baryon Acoustic Oscillations in words normal people can understand and walks the listener through the main plots and results from the Year 1 Key Project papers and press release.

Anton Petrov: Strange Expansion of the Universe Results from the Most Accurate Map — With a phenomenal 268,000 views as of this writing, this 12-minute video from scientist and educator Anton Petrov describes the use of Baryonic Acoustic Oscillations as a cosmological standard ruler and the implications of the DESI results for our understanding of what the universe “was doing billions of years ago, what it’s going to be doing in the future, and how all of this ends.”

AM24:First Year Results from the Dark Energy Spectroscopic Instrument (DESI) — Three talks by DESI scientists at the April 2024 meeting of the American Physical Society unveil DESI’s cutting-edge results. First, Hee-Jong Seo (Ohio University) presents the BAO results from galaxies and quasars at z < 2. Next, Julien Guy (Berkeley Lab) presents BAO results from the Lyman-alpha forest at z > 2. Finally, Mustapha Ishak (UT Dallas) presents the cosmology implications of the measurements.

Joan Najita (NOIRLab)

The original discovery, in 1998, that the expansion of the Universe is accelerating rather than slowing with time, could be understood as evidence that the vacuum of space possesses a tiny amount of energy of its own, i.e., a “dark energy.” That idea found an echo in an earlier proposal from Einstein of a “cosmological constant,” a concept that has been at the heart of our standard model of the Universe for the past two decades.

The model has been popular. In finding explanations for how the world and the Universe works, physicists sometimes use aesthetics as a guide and are drawn to explanations that have a simplicity or elegance, often of a mathematical kind. The standard model fits the bill. Explaining the attractiveness of the standard model and the role of the cosmological constant, Licia Verde told Quanta magazine: “It’s simple. It’s one number. It has some story you can attach to it. That’s why it’s believed to be constant.”

The new DESI results shake that foundation.

If dark energy isn’t a strict constant, who knows how it evolves. That uncertainty, and the potential unshackling from a cosmological constant, opens a richer set of potential futures for us. If dark energy continues to significantly weaken with time, it may become not only “less pushy,” but perhaps even “sucky,” causing the Universe to contract rather than expand. On the other hand, it may also grow stronger with time or possibly just fade away.

Commenting on these options, Durham University Professor Carlos Frenk told the Guardian that if DESI’s hints are right, our earlier understanding “goes out the window and essentially we have to start from scratch, and that means revising our understanding of basic physics, our understanding of the big bang itself, and our understanding of the long-range forecast for the Universe.”

The news may be soothing to some of us, at a human level.

In covering the DESI results, NPR characterized our current model of the Universe as painting a bleak picture of the future, i.e., that if dark energy is constant, it “will continue to push everything in the Universe apart. So much so that one day other galaxies won’t be visible from Earth. Even the stars in our own galaxy will die out, leaving behind a cold dark nothing…” Pretty depressing. But Priya Natarajan told NPR that the possibility of a changing dark energy opens the way to a happier ending: “Our fate may not be as lonely and desolate and grim as we imagine.”

Our understanding of exactly what the future holds depends on what we learn about whether and how dark energy is evolving. We should know more soon. The reported results are based on just the first year of data from the DESI survey, which is designed to extend over 5 years. So stay tuned!

Read other news reports on the recent DESI results here.

In this blogpost we introduce another batch of supporting papers released yesterday on April 11, just one week after releasing our cosmological results using BAO from galaxies and quasars and the Lyman-alpha forest. 

Yesterday’s papers do not exhibit new results, but represent major stepping stones towards the cosmology results from the RSD (aka Full Shape) analysis we plan to release soon. They fall into the two categories: 

• DESI 2024 II: Sample definitions, characteristics, and two-point clustering statistics.
• DESI 2024 V: Analysis of the full-shape of two-point clustering statistics from galaxies and quasars

DESI 2024 II: Sample definitions, characteristics, and two-point clustering statistics.

These papers describe the methods by which we ensure that all results properly take into account systematic effects, including: incomplete galaxy sampling, human biases, and imaging systematics. For a general overview of how DESI selects its targets, see this blog post, and for more information about survey validation see this blog post.

Most papers attributed to this category are yet to come out. But one of them, the paper presenting the DESI Blinding strategy, was already released yesterday, given its synergy with the BAO papers released a week ago, and with the Full Shape papers also released yesterday. It represents a major stepping stone validating the DESI 2024 Blinding strategy for the BAO and RSD (Full Shape) analysis.

Validating the Galaxy and Quasar catalog-level Blinding Scheme for the DESI 2024 analysis

Corresponding Author: Uendert Andrade

Arxiv: https://arxiv.org/abs/2404.07282 

Summary:

Short: This paper introduces the blinding strategy ensuring a data analysis without confirmation bias, validating it using mock catalogs and blinded data. 

Long: This paper introduces the galaxy and quasar BAO and RSD blinding scheme, where galaxy redshifts are displaced in two ways, such that overall they mimic i) a dark energy expansion history different than in the fiducial model with cosmological constant and 2) a different growth of structure history corresponding to a different law of gravity. Additionally, galaxy weights are applied to mimic the effect of primordial non-Gaussianity. BAO fits and full-shape fits (ShapeFit) are applied to one realization of Abacus mocks that was blinded according to 16 different varying dark energy and primordial non-Gaussianity scenarios. Additionally, the blinding scheme was applied to the blinded data and validated on that “double-blinded” catalog using BAO fits. 

This figure shows for one particular case the fitted isotropic and anisotropic BAO dilation parameters scaled to the expectation obtained from 8 different blindingalues of (w0, wa) and either positive (fnl=20) or negative (fnl=-20) primordial non-Gaussianity. Deviations from 1 are observed only for very extreme pairs of blinding values.

DESI 2024 V: Analysis of the full-shape of two-point clustering statistics from galaxies and quasars

This set of papers document various clustering statistics, modeling, and systematic analysis of DESI’s Year one galaxy and quasar samples. While there is yet more to come out, yesterday’s set of papers focus on the comparison between different Perturbation Theory models (based on Effective Field Theory (EFT)) and codes to the AbacusSummit LRG, ELG and QSO mocks. Overall, they find very good agreement among the different pipelines, corresponding to the Lagrangian and Eulerian Perturbation Theory (LPT and EPT) implementations within Velocileptors, as well as the EFT implementations of PyBird and FOLPSv, where the latter also features an improved model of the impact of massive neutrinos on structure formation.

Furthermore, the papers find excellent agreement between two very different approaches that are used nowadays to infer cosmological information from the full-shape of 2-point clustering statistics: 

1. Template fits: Here, templates of the two-point statistics at a fixed fiducial cosmology are used to extract physical information from the data, the so-called ‘compressed parameters’ such as the isotropic and anisotropic dilation scales, the growth rate, and the scale-dependence, or shape. The latter is a rather new observable proposed in the ‘ShapeFit’ method, which represents the state-of-the-art method when it comes to template fits. Cosmological parameters are obtained by fitting cosmological models to these compressed parameters measured in each redshift bin. This is very similar to the philosophy behind the BAO analysis, where the (compressed) BAO scaling parameters are measured first in each redshift bin and cosmological parameters are obtained in a second step. 
2. Full modeling fits: Here, the step of measuring compressed parameters is avoided. Instead, the 2-point statistics of all redshift bins are directly fitted according to the cosmological model. This is similar to the philosophy behind the analysis of cosmic microwave background (CMB) or weak lensing, where the 2-point statistics are also fitted directly, without an additional compression step in between.

Both these approaches have advantages and disadvantages. Template fits are designed to extract only the most robust information and allows for a modular interpretation. For example, they allow us to decouple the information on expansion history, growth history, and shape in an effective way. On the other hand, the extra compression step within the template fit method can erase some of the cosmological information within 2-point statistics. Direct fits allow us to squeeze all of the cosmological information out of the data. At the same time, their results are, by nature, model-dependent, and they do not provide the same means of performing diagnostic tests such as template fits.

For the DESI 2024 Full Shape analysis, we therefore plan to explore both approaches, and yesterday’s papers lay out the pathway of how to carry out both types of analysis in a robust way.

A comparison of effective field theory models of redshift space galaxy power spectra for DESI 2024 and future surveys

Corresponding Authors: Mark Maus, Yan Lai, Hernan E. Noriega and Sadi Ramirez-Solano

arXiv: https://arxiv.org/abs/2404.07272 

Summary:

Short: This paper models the redshift-space galaxy power spectrum into the quasi-linear regime with several different EFT models, compares the different models to each other, and tests each using the AbacusSummit simulations.

Long: This paper demonstrates the level of consistency between the different effective field theory models used for fitting galaxy power spectra in redshift space. We show, by fitting to Abacus cubic mocks, that velocileptors (Lagrangian and Eulerian PT versions), PyBird, and FOLPSv give consistent constraints in LCDM and ShapeFit parameters with differences in means of <0.1sigma. We also fit to noiseless theoretical data vectors created by each model while varying scale cuts, and show that for kmax=0.18 h/Mpc the systematic errors are far below the statistical errors for all parameters at precisions corresponding to 8 (Gpc/h)3 volumes.

An analysis of parameter compression and full-modeling techniques with Velocileptors for DESI 2024 and beyond

Corresponding author: Mark Maus 

arXiv: https://arxiv.org/abs/2404.07312 

Summary:

Short: This paper includes validation testing of various features of the analysis using the Velocileptors pipeline in combination with AbacusSummit mocks. Studies the dependence of the results on parameter compression, scale cuts, joint fitting, beyond-Lambda CDM modeling, inclusion of external data, and more.

Long: We present systematics tests and comparisons of three different modeling methods (Full-modeling, ShapeFit, and standard template) within velocileptors for modeling the galaxy power spectrum in redshift space using a Lagrangian effective field theory framework. We fit Abacus N-body simulations created to mimic the LRG, ELG, and QSO tracers that DESI targets, and show that ShapeFit and Full-modeling have consistent constraints and similar constraining power on LCDM models. We demonstrate the behavior of the three modeling methods for a variety of fitting settings with/without including BAO information in order to describe optimal fitting settings for velocileptors for DESI Y1 analyses and beyond.

We demonstrate constraints on the LRG mock data for the three modeling methods in the right panel of Fig. 3, also shown here:

Comparing Compressed and Full-modeling Analyses with FOLPS: Implications for DESI 2024 and beyond

Corresponding author: Hernan E. Noriega

arXiv: https://arxiv.org/abs/2404.07269 

Summary: 

Short: This paper explores potential sources of systematic error in the full-shape analysis and compression techniques, using the AbacusSummit mocks.

Long: This work validates the robustness of the theoretical modelling of FOLPS, which properly takes into account the presence of massive neutrinos. The study finds that potential modelling errors are fully sub-dominant for DESI’s statistical precision. The research also compares Full-Modeling and ShapeFit fitting approaches, demonstrating their agreement. Overall, this work paves the way for a robust analysis of the DESI power spectrum.

A comparison between Shapefit compression and Full-Modelling method with PyBird for DESI 2024 and beyond

Corresponding author: Yan Lai

arXiv: https://arxiv.org/abs/2404.07283 

Summary: 

Short: This paper shows that the Shapefit compression matches cosmological constraints using traditional full-shape analysis for ΛCDM, wCDM, and oCDM models.

Long: In this paper, we compare the constraints of cosmological parameters from Shapefit and Full-Modelling with PyBird. We do this with the DESI cubic box mocks for Luminous Red galaxies (LRG), Emission Line Galaxies (ELG), and Quasi Steller Object (QSO) for the LCDM, wCDM, and oCDM models. We found for all three cosmological models tested, the constraints from Shapefit and Full-Shape are consistent with each other. Furthermore, the constraints from both methodologies agree with the underlying cosmology.

Full Modeling and Parameter Compression Methods in configuration space for DESI 2024 and beyond

Corresponding author: Sadi Ramirez-Solano

arXiv: https://arxiv.org/abs/2404.07268
Summary: 

Short: This paper includes similar studies as the other projects in this group, but for configuration space

Long: This work conducts a thorough comparison of various methodologies for modeling the full shape of the two-point statistics in configuration space. We investigate the performance of both direct fits (Full-Modeling) and the parameter compression approaches (ShapeFit and Standard) with CLPT-EFT. Our pipeline recovers unbiased cosmological parameter values for a 1-year DESI volume. We also present the comparisons of the configuration space version of different EFT models.

 

On April 4, DESI released a set of papers marking our first release of year one (Y1) results. This page contains summaries of our main results and a guide to the publications. The papers will be available on arXiv at 5pm PST on April 4, and until then are available here.

Helpful links

• A press release containing a high-level overview of our main results: https://newscenter.lbl.gov/2024/04/04/desi-first-results-make-most-precise-measurement-of-expanding-universe/ 
• A brief announcement on our webpage: https://www.desi.lbl.gov/2024/04/04/first-cosmology-results-from-desi-most-precise-measurement-of-the-expanding-universe/ 
• A list of current papers: https://data.desi.lbl.gov/doc/papers/ 
• For more background on DESI’s science, see our public webpages.
• DESI’s Y1 data is not yet public, but you can find our early data release and any updates on this site: https://data.desi.lbl.gov/doc/releases/

The Y1 results fall into seven main categories, three of these (highlighted in blue) are released on April 4:, BAO measurements with galaxies and quasars (DESI 2024 III), BAO with the Lyman-alpha forest  (DESI 2024 IV), and cosmological inference from BAOs (DESI 2024 VI). This figure displays the publication organization with the results released on April 4 highlighted in blue, and summaries of each can be found below.

 

 

 

 

 

 

 

 

 

 

 

April 4 Paper Summaries

BAO Measurements from Galaxies and Quasars

Baryon Acoustic Oscillations (BAO) are a powerful tool to measure cosmic expansion through the “standard rulers” created by expanding overdensities from the early universe. Using galaxies as tracers of these overdensities, this set of papers describe DESI’s galaxy BAO measurements. This is the largest dataset ever used to measure BAO, by both number of galaxies and volume. They are the most precise measurements of their kind, at 0.52%.

DESI 2024 III: Baryon Acoustic Oscillations from Galaxies and Quasars

Arxiv: 2404.03000

Summary: This is an overview of the main DESI Year-1 BAO results from galaxies and quasars.

Baryon Acoustic Oscillation Theory and Modelling Systematics for the DESI 2024 results (submitted in Feb 2024)

Corresponding author: Shi-Fan Chen

Arxiv:  2402.14070 

Summary: Baryon acoustic oscillations are one of the best standard rulers there are. In this paper the authors work out just how robust they are, and how to best fit and extract the signal from DESI data.

 

Optimal reconstruction of baryon acoustic oscillations for DESI 2024

Corresponding authors: Enrique Paillas, Zhejie Ding, Xinyi Chen

Arxiv: 2404.03005

Summary: This paper investigates different reconstruction settings to optimize BAO detection. Reconstruction is a sophisticated technique enabling a more precise (lower statistical error) and more accurate (lower systematic error) BAO measurement. When considering the galaxy distribution, unfortunately the pristine BAO signal is slightly erased and contaminated by the galaxies’ velocity originating from their mutual gravitational interaction. Luckily, from the observed galaxy density we can calculate the gravitational potential at each galaxy and hence estimate their velocities. Using that estimate, we can displace each galaxy to its initial position and hence “reconstruct” the initial galaxy field exhibiting the original, pristine BAO signal. This work shows on Abacus mock catalogs that after applying reconstruction (post-recon) the BAO peak in the two-point correlation function is enhanced (see figure) and slightly shifted (not visible by eye in this figure) towards the location predicted by the cosmological model. 

For non-cosmologists: the two-point correlation function is basically a histogram of the number of galaxy pairs that are separated by a distance “s”. It hence describes the excess probability of finding two galaxies separated by “s”.

Semi-analytical covariance matrices for two-point correlation function for DESI 2024 data

Corresponding author: Michael Rashkovetskyi

Arxiv: 2404.03007

Summary: This work improves and validates an efficient method for generating covariance matrices for clustering analyses using the correlation functions. In particular, the authors report a close agreement in projected errorbars for BAO scale parameters between the mock-based (more standard) and semi-analytical (faster) covariance matrices, as shown in the right figure.

HOD-Dependent Systematics for Luminous Red Galaxies in the DESI 2024 BAO Analysis

Corresponding author: Juan Mena-Fernández

Arxiv: 2404.03008

Summary: This paper investigates how the halo occupation distribution (HOD) modeling might affect the measurement of the BAO distance scale in the DESI Y1 analysis. This is done for LRGs, using several sets of Abacus simulations (that rely on dark matter only) with different HOD models (that populate dark matter halos with galaxies) in order to estimate the amplitude of the so-called HOD systematics. This work finds that the BAO measurements are robust enough against these kinds of systematics for the DESI 2024 analysis, and provides the estimated error budget.

HOD-Dependent Systematics for Emission Line Galaxies in the DESI 2024 BAO analysis 

Corresponding author: Cristhian Garcia-Qunitero

Arxiv: 2404.03009

Summary: This paper consists of a series of tests to assess the robustness of the BAO analysis against HOD-dependence in the ELG tracer, and compare the differences found with the forecasted error with one year of DESI data.

We found that our BAO fits are robust enough against this systematics for DESI 2024 results and provide the error budget for this particular systematics.

 

BAO with the Lyman-alpha forest

The Lyman-alpha forest refers to absorption lines in the light of distant quasars, which reveal the distribution of gas along the line of sight. This allows DESI to extend our BAO analysis beyond the galaxy tracers and measure the most ancient BAO signatures, up to when the Universe was just ⅕ its current age. DESI’s Y1 results provide measurements of the isotropic BAO scale at 1.1% precision, the most precise measurement in the redshift ranges of 2 < z < 4.

 

DESI 2024 IV: Baryon Acoustic Oscillations from the Lyman Alpha Forest

Arxiv: 2404.03001

Summary: This is the main paper for BAO with the Lyman Alpha Forest, presenting the Lyman Alpha forest BAO measurement from over 420,000 spectra and their correlation with >700,000 quasars at an effective redshift of z=2.33.

 

The Lyman-α forest catalog from the Dark Energy Spectroscopic Instrument Early Data Release (published in December 2023)

Corresponding author: César Ramírez-Pérez

Article: https://academic.oup.com/mnras/article/528/4/6666/7462317?login=false 

Summary: This publication presents and validates the Lyman-alpha forest fluctuations in the first DESI data release. To accomplish this measurement, the continua of DESI quasars were fitted not only in the Lyman-alpha forest region but also in featureless regions to the right of the Lyman-alpha emission line, which were used for calibration.

The image displays the observed flux (black) of a high-SNR DESI quasar. The different coloured lines show the expected flux for each of the regions (quasar continuum corrected by the mean absorption), for the Lyman-alpha forest region and the SIV, CIV and CIII calibration regions.

 

3D Correlations in the Lyman-α Forest from Early DESI Data (published in November 2023)

Corresponding author: Calum Gordon

Article: https://iopscience.iop.org/article/10.1088/1475-7516/2023/11/045

Summary: This is the first analysis of 3D Lyman-a correlations in early DESI data. The BAO peak is strongly detected, and the results are in good agreement with previous analyses of Lyman-a forest correlations from eBOSS. The figure here shows the measured auto-correlation in bins of mu = r_parallel / r, including eBOSS and DESI early data, and the best-fitting model.

Synthetic spectra for Lyman-α forest analysis in the Dark Energy Spectroscopic Instrument (submitted in January 2024)

Corresponding author: Hiram K. Herrera-Alcantar

Arxiv: 2401.00303

Summary: This paper presents the methodology followed to produce synthetic DESI Lyman-𝛼 datasets. We include all the steps from the raw transmitted flux generation to the addition of a continuum and instrumental noise to spectra. We perform a qualitative comparison of the results of DESI EDR+M2 simulated and observed data. And present a Forecast of the full DESI survey constraining power (show in figure).

 

Impact of Systematic Redshift Errors on the Cross-correlation of the Lyman-α Forest with Quasars at Small Scales Using DESI Early Data (submitted in February 2024)

Corresponding author: Abby Bault

arxiv: 2402.18009

Summary: 

This publication presents a measurement of the systematic redshift errors from the DESI EDR+M2 quasar sample. We find evidence for a redshift-dependent bias causing redshifts to be underestimated with increasing redshift. This bias stems from the templates used for redshift estimation in the EDR+M2 sample. After deriving new templates for the DESI Year 1 quasar sample we repeat our analysis and no longer find evidence of a bias.

The image shows the measured redshift errors for the EDR+M2 and Year 1 samples when the catalog is cut into four redshift bins. For the EDR+M2 data (light blue triangles) there is a clear trend where the measured errors increase with increasing redshift. For the Year 1 data (dark blue circles) this bias is no longer present. The measured error for the full Year 1 catalog, shown in the light red region, also shows that the bias has been mitigated.

 

 

Characterization of contaminants in the Lyman-alpha forest auto-correlation with DESI

Corresponding authors: Julien Guy, Satya Gontcho A Gontcho

Arxiv: 2404.03003

Summary: This paper studies the signal introduced by the instrumental processing of the data that contaminates the signal detected from the Lyman Alpha Forest (neutral hydrogen clouds). In addition, it also studies the signal introduced by clouds of other chemical species (not neutral hydrogen) that contaminates the Lyman Alpha Forest signal. The conclusion of this paper is a thorough characterization of the instrumental and astrophysical contaminants of the Lyman Alpha Forest signal.

 

Validation of the DESI 2024 Lyα forest BAO analysis using synthetic dataset

Corresponding author: Andrei Cuceu

Arxiv: 2404.03004

Summary: This paper documents the creation of mocks for the Lyman-alpha BAO validation, validation of the pipeline using those mocks.

 

Broad Absorption Line Quasars in the Dark Energy Spectroscopic Instrument Early Data Release (submitted in September 2023)

Corresponding authors: Simon Filbert, Paul Martini

arxiv: 2309.03434

Summary: Broad absorption line (BAL) quasars can have significant absorption troughs near or coincident with the locations of some of the most prominent emission lines in quasar spectra. This paper presents a study of the impact of these features on how accurately we can measure the recession velocity (or redshift) of BAL quasars and presents strategies to mitigate their impact. The figure shows the differences in the redshift before and after mitigating the impact of the BAL features for various types of BALs.

Cosmological Inference 

This final paper interprets the analysis documented above. DESI’s Year one BAO measurements constrain the density of matter in the universe, Ωm,  and the rate of expansion of the universe, H, relative to the sound horizon, r_d. These measurements reveal the growth rate of the universe over time, and, consequently, the impact of dark energy.

 

DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations

Arxiv: 2404.03002

Summary: This paper analyzes the BAO measurements from all tracers, which are complementary to each other. The results are consistent with SDSS and CMB measurements. DESI’s measurements are compatible with the standard cosmological model, LCDM, but slightly prefer a model of dark energy which evolves with time.

Joan Najita (NOIRLab)

12 February 2024 was a spectacular night for DESI: it broke its own record and acquired nearly 200,000 redshifts in a single night. The figure is remarkable, especially in the context of history.

Forty years ago, the first and second CfA redshift surveys acquired spectra of 2200 and 15,000 galaxies respectively, giving us the first glimpses of the large scale structure of galaxies. Rather than being distributed randomly, galaxies were found to cluster in a froth-like structure, arranged on bubble-like surfaces surrounding large volumes mostly devoid of galaxies. In these pioneering surveys, redshifts were painstakingly acquired one at a time. As a result, the first CfA redshift survey took 5 years to acquire its 2200 redshifts (1977-1982). In comparison, on 12 February DESI acquired 100 times that number in a single night.

Rather than taking spectra of galaxies one at a time, DESI can acquire 5000 spectra at once through its 5000 robotically positioned fibers. Tiny robots center each fiber on an object (galaxy, quasar, or star). After an exposure is done, the fibers are quickly repositioned, within 1-2 minutes, and DESI is ready to acquire spectra of another 5000 objects. On 12 February, the seeing at the Mayall Telescope was very good (0.65 arcseconds) and DESI was able to go through the setup process more than 40 times. (The gory details: DESI observed 41 dark tiles, 4 bright tiles, and 2 backup tiles that night.)

Joan Najita (NOIRLab)

16 February 2024

BaoBan, DESI’s ambassador for Education and Public Outreach, made a recent appearance at the 85th Annual Tohono O’odham Nation Rodeo and Parade, featuring prominently in the parade entry from Kitt Peak National Observatory (KPNO). A coyote from the wilds of Arizona, BaoBan has previously appeared in comic strips and other DESI-related public engagement activities. The DESI project is being carried out at KPNO, which is located atop I’oligam Du’ag, in the homeland of the Tohono O’odham Nation.

The story behind creating and naming our favorite coyote.

Samuel Brieden, The University of Edinburgh

May 12, 2023

Welcome our new DESI ambassador for Education and Public Outreach (EPO), BaoBan! You might have met him already, when he was presenting our powerful focal plane (see a virtual tour through it here) or wishing a happy new year. From now on, BaoBan is assisting us with science communications, as long as he is in the mood. Although BaoBan is very attracted to the Mayall telescope, he shows up at Kitt Peak quite rarely because, like other wild coyotes, BaoBan spends most of his time hunting in the Arizona mountains. But whenever we are lucky enough to be honored with his visit, an aura of ancient wisdom about life and the night sky surrounding him sparks new insights and creative ideas. It’s a bit magical!

This article is a chronology of our common history with BaoBan. From the story of his ancestors, to how he was brought to life and given a name, and finally his meaning to us, to our roots as a scientific collaboration, and to our environment.

The Tohono O’odham Nation

DESI resides in the Mayall telescope at Kitt Peak National Observatory (KPNO), which sits atop I’oligam Du’ag (audio below) in the homeland of the Tohono O’odham (audio below) Nation (TON). Since time immemorial the Tohono O’odham (TO), meaning “desert people”, have lived in the Sonoran desert and preserved their rich culture. The nation is governed by the TON Tribal Government, organized into 11 districts. You can learn more about the history and culture of the TON here. We are deeply grateful for their permission to undertake observations of the night sky within the TON homeland at KPNO, and we cannot emphasize enough that the success of our scientific mission would not be possible without the TON’s generosity.

Pronunciation of “I’oligam Du’ag”

Pronunciation of “Tohono O’odham”

The DESI logo

It is this relation to the TON that must have inspired Berkeley Lab engineer (and artist!) Robin Lafever when he created the DESI logo in 2013, and in particular the detail in the lower right corner: the profile of a howling coyote. In fact, the coyote plays an important role in the TO mythology. Robin had seven different names for the coyote in mind, his favorite being “Bao Wao Wao”. “Bao” is reminiscent of baryon acoustic oscillations (BAO), the primary cosmological observable DESI is measuring to infer the expansion history of the universe, and “Wao” represents the coyote’s howl.

A new coyote is born

The DESI logo inspired Claire Lamman, PhD student at Harvard University and member of the DESI EPO committee, to transform Robin’s profile-view creation into a fully-fledged comic figure.  As you can see in her comic strips, at first the coyote seems nice and harmless, but the sheer power of the Dark Energy Spectroscopic Instrument occasionally evokes his dark side. All Claire’s comic strips can be found here.

Amazed by his strong character, the EPO committee considered how to introduce Claire’s extraordinary art to the public. There was only one thing missing for Claire’s comic figure to become even more successful than Looney Tunes legend Wile E. Coyote: a proper name!

Setting up a poll

Several candidates emerged from our initial brainstorming, playing either on the location of the telescope (Coyote-Kitt, Maya), on the pursued science (Cosmo-Coyote, Bao), or simply on the survey name itself (Desiree). This was so much fun that we decided to poll the entire collaboration for suggestions. Other names received were Can-do Canis, Desita, and the name of the original coyote in Robin’s DESI logo: Bao Wao Wao. Around 60 collaboration members voted in just one day, and the majority decided to conduct a naming contest within the Tohono O’odham school district (see the compilation of Slack messages below).

Back to the roots

We first consulted Jacelle Erin Ramon-Sauberan, PhD Candidate at the University of Arizona, faculty at Tohono O’odham Community College, and information specialist for AURA/NOIRLab, and worked closely with KPNO. Jacelle put us in contact with the TON Youth Council  (TONYC). The TONYC consists of four representatives from each of the 11 districts, and their mission is to enhance the cultural awareness and self-esteem of TON youth within modern times by organizing social events. The Council holds monthly meetings, which are open to the public. Francine Senechal, the TONYC Manager, kindly invited us to present the coyote naming contest at a Council meeting.

At the same time we decided to reach out to the TON, two collaboration members independently raised the idea that the name include “Ban”, the word for “coyote” in the TO language. It was suggested that we connect “Ban” with the TO word “Ba:”, meaning “Where”, such that the combination “Ba:Ban” is extendable to “Where is coyote looking?” This would allude to the mysteries of dark energy DESI is trying to unravel, and sparked the obvious idea of “BaoBan”, combining “Ba:Ban” with the previous suggestions that include “Bao”.

The day of the TONYC meeting arrived, and fortunately it was held virtually so I could attend from Barcelona. After introducing DESI and the science we pursue with it, I talked about our plan to find a name for the DESI coyote. I provided a list of all the suggestions we had collected so far, as well as their variants, meanings, pronunciations, etc., and asked them to vote for the name they found most suitable. The TONYC members were interested and very keen to help. They agreed to bring the list of names into the local youth communities of the district each of them represents, engage their members to discuss the different options, and choose their favorite name.

The final decision

After thoroughly considering all names, discussing them within each district, and exchanging their ideas at a meeting, the TONYC voted, and Francine communicated the official result:

1. BaoBan
2. Cosmo Coyote

What a great choice! Within the EPO committee we immediately fell in love with the name BaoBan, as it nicely combined all the different ideas the collaboration had in mind throughout the process. “Ban” as the TO word for coyote, reminding us of the roots of where the DESI telescope is built, and “Bao” as both the sound the coyote makes, and a clear reference to DESI’s primary science goal: measuring BAO from galaxy maps. These ideas culminated in another new comic strip by Claire (below), which celebrates that together with the TONYC we found such a beautiful name for our DESI ambassador! And there is even more to the story…

An alternative meaning

Not only did the TONYC vote for the name, they also put me in contact with TO language experts Leslie Luna and Ronald Geronimo from the TO Community College, with whom I discussed the prospect of connecting “BaoBan” to the meaning behind the similar suggestion “Ba: Ban”, where “Ba:” = “Where?” as mentioned before. As it turns out, the TO expression “Ba: ‘o …” actually means “Where is …”, but this does not imply that “Ba: ‘o Ban” would mean “Where is coyote”, because “‘o” is an auxiliary verb that must be accompanied by a full verb. However, we can extend the expression to “Ba: ‘o ñia g Ban” (audio below), which literally means “Where is coyote looking?” and argue that “BaoBan” (audio below) is just the short form of that longer name. In this way, the name BaoBan also serves as a symbol that we and the TON may work together to explore new discoveries in our beautiful sky.

Pronunciation of “Ba: ‘o ñia g Ban”

Pronunciation of “BaoBan”

Final remarks

Throughout this process it has been amazing to see how an enjoyable drawing and a simple idea (finding a name for that drawing) can lead to something big, both engaging the collaboration and establishing a new link between DESI scientists and the TO community.

BaoBan symbolizes how the enormous scientific effort by ~70 member institutions with over 700 active collaboration members from all over the world is deeply connected with the TO, who share part of their homeland to discover the mysteries of our universe. BaoBan reminds us that the night sky is the same for everyone, independent of national or cultural identity. Furthermore, BaoBan reminds us to always respect our roots and our environment, and to never forget that the deeper our maps of the cosmos become, the deeper the relationships we will foster among different cultures and people.

It is no coincidence that Robin Lafever began this processes at the very moment his pencil touched paper to create the DESI logo. Robin was known as a man with a wonderfully warm and engaging personality, who delighted everyone around him with his creativity. Almost two years after his passing he would surely be flattered that people enjoy his creation enough that they continue to develop it, from Bao Wao Wao to BaoBan.

Acknowledgements

I would like to express deep thanks to all the wonderful DESI collaborators involved in this journey, those who participated in the poll and brought in their naming suggestions, and especially Claire Lamman, Angela Berti, Biprateep Dey, Parker Fagrelius, and everyone from the DESI EPO committee. Special thanks also to Daniel Eisenstein, Dustin Lang, Eric Linder, David Sprayberry, Lori Allen, Arjun Dey, Nathalie Palanque-Delabroullie, Kyle Dawson, and Michael Levi. Finally, I am indebted to Jacelle Erin Ramon-Sauberan, Francine Senechal, Leslie Luna, and Ronald Geronimo for all their effort and kindness giving me insight into their fascinating culture.

Claire Lamman, Harvard University

April 7, 2023

DESI’s planetarium show, “5000 Eyes”, was recently released to the public. It will be shown in hundreds of planetariums around the world and translated into ten languages. The support and contributions of many DESI members grew this project far beyond the little film I initially imagined. Here is how “5000 Eyes” went from the daydream of a first-year graduate student to a global production.

A couple months after delivering my final show at Fiske Planetarium, I was sitting in a session at DESI’s 2019 summer collaboration meeting. I had committed to starting graduate school at Harvard in the fall but was undecided about a research path. I was new to cosmology and just starting to learn about DESI. When a talk started to go over my head, which was often, I imagined what a planetarium show about DESI might look like.

Kitt Peak was building an outreach center and I thought it would be nice to record myself giving a short planetarium talk about DESI that could be shown at the center. A leader from our Education and Public Outreach Committee, Parker Fagrelius, encouraged me to reach out to DESI’s director, Michael Levi, and seek funding from the DESI Institutional Board. With the enthusiastic support from Parker and Michael, I formulated a proposal to create a small planetarium film. My idea was to use as much existing media as possible—such as 3D models of the Mayall telescope, footage on Kitt Peak, and DESI data, to make the best use of any resources given to the project. It received unanimous support from the Institutional Board and I found myself, a graduate student still unsure about what my thesis would be on, in charge of a full-scale production.

Fortunately, I helped Fiske make a series of short films during my time as an undergrad at CU Boulder and generally knew what went into making a planetarium film. I developed a script based on the media available and what I knew of Fiske’s software. After many iterations on the script and feedback from DESI people, we began working with Fiske to produce the movie.

There is so much to say about DESI (just check out all the blog posts below this one!), so it was not easy to decide what to include in a 20 minute movie. One idea we wanted to make sure to communicate was that advances in modern cosmology don’t magically spring from the minds of a couple scientists. It takes many people, including many young people, with a variety of backgrounds. We came up with a selection of six DESI members from four continents. The international participants all found ways to get high-quality recordings themselves! For those of us in the U.S., we were able to coordinate an in-person shoot on Kitt Peak.

Our visit to Kitt Peak was my favorite part of making the film. We had two days with the videographer from Fiske to shoot interviews and capture footage of the telescope and mountain. During this time, the Kitt Peak Staff was especially helpful and accommodating. I was even able to carry out one of my support observing shifts in person. Up until this trip, I was hesitant about representing DESI as such a new member. But observing on the mountain made me feel like I was truly part of the collaboration for the first time.

As main production ramped up, I directed the Fiske team and coordinated some additional contributions of DESI members. In particular, once I found out that David Kirkby could make a moving 3D model of the focal plane, I knew we absolutely had to include it. Who doesn’t want to fly through a forest of robots?? He put in an impressive amount of work to faithfully bring the focal plane to life and create a memorable scene.

Fiske’s team was also very excited about the film, especially once we had the go-ahead to use galaxy positions from DESI’s full year one data. This was somewhat of a technical challenge, since they were determined to render every single galaxy and, unlike DESI, did not have access to a supercomputer! The resulting fly-through is stunning. All the time I spent using DESI data in my research did not compare to soaring through the most detailed map ever made of our nearby universe in a planetarium. I am very impressed with the work of Fiske’s production team.

Because DESI is an international collaboration, it was important to make the film widely available and in multiple languages. Many DESI members have volunteered to help create translations. As of the writing of this blog, there are plans to translate the film into 10 different languages! Small planetariums all over the world are excited to have access to a free film in their local language. The film’s download site also includes an educational guide and outreach package filled with additional material that DESI people have put together. Our science will reach a large, diverse audience thanks to the work of our collaboration!

It has been exciting to see the ways that DESI members are using this film to engage with their local communities. At the premieres, it’s also been a joy to see our family members, especially kids, get a glimpse into what we work on. Looking back, it’s a bit staggering to see how much this project has grown and how many people contributed. This truly is a film about DESI, by DESI!

As of the writing of this blog, the film has been downloaded by 112 planetariums in 31 states and 24 countries.

…in Story and Science

Joan Najita, NOIRLab

April 4, 2023

One of the most spectacular things in the night sky is the Milky Way, which arches above the 4-meter Mayall Telescope in this image. The DESI survey is currently underway at the Mayall Telescope at Kitt Peak National Observatory, which is located in the Schuk Toak District of the Tohono O’odham Nation. Known as “tohmog” or “to:mog” in the language of the Tohono O’odham, the Milky Way looks like a pale band of bright specks entangled with dark clouds and glowing red wisps that shimmer like fireworks. In one Tohono O’odham story, the Milky Way was created when Coyote, the trickster, was playing in the kitchen and looking for something to eat. Hearing someone coming, he grabs a bag of flour and escapes into the sky in a great hurry. The bag tears open and flour spills out, creating the Milky Way.

There’s an echo of that story in how astronomers understand the Milky Way, just with the light and dark reversed. Here the bright white specks are not powdery flour, but stars in our galaxy. And a different kind of powdery substance, interstellar dust, creates the dark clouds, by scattering and absorbing the light from background stars. This dust isn’t the same stuff we sweep up from under our beds. Instead, it’s a kind of “soot” that forms in the atmospheres of some stars and is the stuff from which planets like Earth are made. It’s pretty valuable stuff—just like the flour that Coyote ran off with!

In this image, we can also see other interesting features. The familiar constellation of Orion the hunter is just above the Mayall Telescope to the left. And the glowing red fireworks spread across the sky are bright clouds of gas in the galaxy that are lit up by hot stars.

Recovering from the Contreras Fire

Benjamin Weaver, NOIRLab

January 24, 2023

DESI collaborators have previously reported on the Contreras Fire and how it initially affected DESI operations along with an update as personnel were able to return to Kitt Peak National Observatory (KPNO). Even as we were cleaning up KPNO and the DESI instrument in August 2022, we knew that it would possibly be several months before the Tohono O’odham Utility Authority (TOUA) could replace the infrastructure bringing electrical power and line internet (a fiber-optic link) to KPNO. In fact, line internet was not restored until December 7, 2022, almost exactly six months after the start of the fire.

The story of restoring electrical power and the generators used while restoration was in progress is definitely worth telling, and far more lengthy and detailed than the story I’d like to tell now, recovering from the missing internet connection.

The DESI Data Management team, working closely with the on-site NOIRLab personnel, developed a plan to work around the missing internet, even as DESI returned to full-night operations. It wasn’t a new plan; in fact, it was a very old plan: “Sneakernet”. The idea is that a human being (presumably wearing sneakers) can hand-carry data on physical media from one location to another, and in certain circumstances, the effective bandwidth of that transfer can be much, much higher than the bandwidth of an internet connection or other communication channel. This is actually even more true now than it was in the past, because the storage density of physical media has experienced exponential growth similar to that of Moore’s law for CPU performance. However, while Moore’s law has been showing signs of reaching fundamental physical limits, storage density trends continue to rise.

With that in mind, we purchased six 2 TB SanDisk solid-state drives (SSDs), and a few fast USB cables. There is nothing exotic about the hardware; these items would be available in many consumer electronics or department stores. Then with the 6 disks initially carried to KPNO, we would place an entire night of data (or sometimes several nights) on a SSD. One of the personnel working at KPNO would be designated to carry the SSD to Tucson at the end of the work day. Then we would pick up the disk either in person or from a drop box and copy the data to NERSC where it could be processed with the usual DESI data pipeline. Since we purchased six SSDs, that meant we always had several SSDs on standby at KPNO in case an already-transferred SSD could not be brought back from Tucson to KPNO the next day. On weekends, no one would be available to carry the SSDs, so we simply had several nights on Monday evening’s SSD.  From the point of view of the pipeline, the only difference was that an entire night (or several nights) would arrive all at once, after a delay of 1 to 3 days, instead of the normal operations procedure of one exposure at a time, almost immediately after the exposure is completed.

The DESI instrument resumed taking data starting with night 20220825 (August 25, 2022). The first SSD was brought to Tucson on September 2, 2022. This process continued until line internet was restored on December 7, 2022. The original data transfer system was ready to go at that point and was reactivated almost immediately after line internet was restored. Thus the last night of data transferred by sneakernet was 20221206 (December 6, 2022). In total, 16,726 exposures over 100(!) nights were hand-carried to Tucson. This amounts to 6.1 TB of data.

The bandwidth of hand-carried SSDs is impressive, but so is the bandwidth of modern USB cables. After some experimentation, we discovered that we could transfer data directly from the external SSD to NERSC via Globus Online, with bandwidth performance indistinguishable from the case where the data were first copied to a workstation, then transferred via Globus. In other words, the limiting bandwidth was the internet itself between Tucson and NERSC, not the internal systems of the receiving workstation.

While we were transferring DESI data with a very old system (but with the latest SSDs), we were also experimenting with a new one: Starlink. In fact there were at least two separate Starlink installations active at KPNO during the recovery.  One, which we’ll call the “DESI Starlink”, was a strictly limited command and control channel for use by instrument experts. The DESI Starlink was not used for any significant data transfer. The other, which we’ll call the “NOIRLab Starlink” was used for more general access to all of KPNO. We did use the NOIRLab Starlink for some data transfer, with mixed results.

At least currently, Starlink works best with a point-to-point style networking connection, optimized for individuals or residences, much like a residential cable modem. Since the uplink bandwidth is currently a factor of 10-20 times slower than the downlink bandwidth, it is less practically suited as a two-way connection between two substantially-sized networks, such as between KPNO and the Tucson base facilities. This manifested as a significant, recurring routing problem. Although bandwidth was adequate for interactive use and for the transfer of small data files, the connection was frequently not working and the routing systems had to be monitored constantly. Nevertheless, we were able to use the NOIRLab Starlink to maintain an off-site copy of the DESI operations database. This copy would have been impractical to maintain using daily SSD transfers, because the copy is a real-time mirror of a live database; it is more of a stream than a set of files. There were occasions where the database mirror fell behind due to interruptions in the Starlink connection. In these cases files created by the database were transferred manually on the SSDs and then once in Tucson the data files were manually added to the database mirror.

It was interesting and a good experience to transfer data over sneakernet. It was also a lot of work and hours. I want to give credit to a big team who all contributed to this effort: Keith Blaine, Paul Demmer, Matthew Evatt, Steve Grandi, Bob Marshall, Rod Rutland, David Sprayberry, Christopher Stone, Bob Stupak (NOIRLab), Martin Landriau (LBNL), and Klaus Honscheid (OSU). Here’s one job we hope we never have to do again!

January 18, 2023

The all-sky camera on the Mayall telescope were the DESI instrument is located provides a view of the entire sky above Kitt Peak National Observatory. This camera helps observers monitor weather conditions and visibility, and confirm when it is safe to open the dome above the telescope. While the skies above Kitt Peak are very often clear, that is not always the case, as shown below in a series of camera images from the night of September 23, 2022. The night began with clouds and rain, and for over an hour flashes of lightning lit up both the sky and the camera view. Finally, toward the end of the night the storm gave way to thin clouds that allowed some stars to peek through. The final frame shows the Milky Way stretched across a mostly clear sky before the series starts over.

Credit: Luke Tyas

The all-sky camera can also capture celestial events, like the lunar eclipse that occurred on the night of November 8, 2022. DESI Lead Observer Luke Tyas created the timelapse below of the eclipse from 108 individual images from the all-sky camera. At first the full moon shines brightly just right of center, reflecting so much light into the sky that only a few bright stars are visible. As the eclipse begins the moon dims to a red dot scarcely brighter than the brightest stars, and the Milky Way can be seen following the eclipsed moon across the sky. As it nears the western horizon the moon emerges from the Earth’s eclipsing shadow, re-illuminating the telescope domes visible on the horizon and washing out the Milky Way.

Credit: Luke Tyas

David Sprayberry, NOIRLab

August 25, 2022

After the Contreras Fire swept over part of Kitt Peak in June, July was devoted to restoring electrical power and water service to the mountaintop. We also carefully assessed every structure for safety, possible fire damage, and the extent of cleaning required. Currently electricity at the summit is provided solely by back-up generators (more on that later). Because the water system lost pressure during the power outage, it was necessary to flush it with chlorine and then fresh water from the storage tanks, and then have the water tested to ensure it meets EPA standards for safe drinking water (it passed!). Work at the telescopes during July was limited to skeleton crews going up for specific tasks to prevent further issues with sensitive scientific equipment. At the Mayall, this included restarting the building’s cooling system, changing filters in the purified dry air system that purges the focal plane enclosure, and changing filters in the HVAC system serving the spectrograph clean room (fondly known as “the Shack”). We also performed regular inspections in all the NOIRLab domes for leaks and electrical faults.

Beginning August 1, telescope staff were allowed to resume almost normal on-site work. At the Mayall we spent the first week cleaning everything we could find a way to reach inside the dome, and any other areas potentially affected by ash or smoke intrusion. The interior of the dome wasn’t particularly dirty, but we cleaned everything thoroughly anyway. We also removed the protective tarp and plastic sheeting from the primary mirror and prime focus corrector, and made a preliminary inspection of the optics, which look fine. During the second week of August we caught up on overdue preventive maintenance of the telescope and dome, and worked to provide a low-bandwidth internet connection to the Mayall.

Road Conditions

Throughout August, road and weather conditions have significantly limited the time our team can spend on-site. The fire damaged guardrails along the road, and there has been a lot of erosion from burned areas washing across the road during heavy rains. This extraordinary erosion has clogged many of the drainages that cross the road, sometimes causing impassible mudflows. Additionally, the fire damaged several drainage culverts under the road. The Arizona Department of Transportation (ADOT) is making progress on repairs, but they are hampered by frequent heavy summer “monsoon” thunderstorms since late July. Finally, erosion is worsening the normal amount of rockfall along the road during storms. Combined with this year’s strong, frequent storms, we are encountering more rocks and boulders in the road.

Road restrictions are still in place. Repair work frequently requires closing both lanes, and so that we interfere as little as possible ADOT requires us to go up and down the mountain in one convoy at the same times every morning and afternoon, weather permitting. NOIRLab is also concerned for site safety due to the possibility of road closures caused by mudflows or rockfall. Whenever rain begins or is threatening, everyone on the site ceases work, makes their work site safe, and assembles for departure in an early convoy.

Electrical Power and Internet

The fire damaged between 10 and 20 utility poles that bring electricity and fiber optic data to the summit. Our utility provider, the Tohono O’odam Utility Authority (TOUA), is working hard to replace the damaged poles, but they face a number of obstacles. Many of the poles are in very remote locations. Other lines and poles elsewhere on Tribal lands were also damaged by storms. And like everyone else TOUA is grappling with supply chain disruptions. It will be at least several weeks until power is restored, and then fiber optic lines will be replaced.

The observatory is currently powered by on-site backup generators. One serves the Mayall and adjacent University of Arizona buildings, and another serves the rest of the mountaintop. This is expensive in terms of refueling needs, and leaves the site without back-up power sources if one of the generators were to fail. We are in the process of renting additional generators and connecting them to use as primary power sources. Once this is done the permanent back-up generators can return to back-up status.

Keeping the generators fueled is a challenge. Not all vendors will deliver diesel fuel to our remote site. Recently our normal supplier was unable to make our regular delivery when their truck broke down, and the Mayall generator ran out of fuel before an alternate supplier could reach the summit. Storms and road conditions further complicate the situation.

For temporary internet service DESI has obtained a Starlink system and service for the Mayall. The equipment is installed and connected to one network switch in the Mayall building, but that connection requires a standalone DNS server in the Mayall to allow normal access to the many other computers and switches in the building. DNS within NOIRLab is normally provided by one central server in Tucson, but that is obviously not an option right now, so work is underway to construct this standalone DNS system.

Optics Cleaning

We want to clean both the primary mirror and front surface of the prime focus corrector with carbon dioxide “snow”, and do a wet wash of the primary mirror. However, these operations require a relative humidity of < 50%, sustained through the day, to prevent condensation after the “snow” cleanings and promote drying after the wet wash. We haven’t seen a relative humidity reading that low since the August 1 return to the summit. DESI very much wants the optics cleaned before going back on-sky, as relative throughput measurements using the guide cameras are the first tests called for. We’re waiting for the first relatively dry day to seize an opportunity for optics cleaning.

Restarting DESI

Restart of the DESI equipment can’t really begin until some internet connectivity is restored and remote monitoring of the equipment’s health is possible. The expected order of events is to re-establish a fully-functioning network with internet connectivity; then bring the DESI computer cluster back on line; and then change filters inside the focal plane cooling system, restart focal plane cooling, and test basic focal plane and fiber view camera functions.

Once the focal plane guiders are running we can perform a simple throughput test if the optics have been cleaned and observing conditions are good. The next major phase will be restoring spectrograph operations. This involves restarting the cryostat control systems, pumping down cryostats, turning on the cryocoolers, and waiting for the CCDs to reach working temperature. The spectrograph restarts do not depend on weather conditions, but we do need a back-up electrical power supply or to know that one is on the way, so we don’t risk another unplanned warm-up were the back-up generator to fail.

We don’t yet have a firm timeline for restarting DESI, as so much depends on the weather and other things we have little or no ability to control. We’re doing the best we can, and will continue to post updates as developments warrant.

Anand Raichoor and Christophe Yeche

August 22, 2022

We are glad to announce the publication on arXiv on Friday, August 19, 2022 of eight papers from Year 1 Key Project 1 (Y1KP1). These papers describe:

• how the DESI Main Survey targets are selected, along with their photometric and main spectroscopic properties (MWS: Cooper et al. 2022, BGS: Hahn et al. 2022, LRG: Zhou et al. 2022, ELG: Raichoor et al. 2022; QSO: Chaussidon et al. 2022);
• the pipeline to process those targets for DESI observations (Myers et al. 2022);
• the building of redshift truth tables based on visual inspections (Lan et al. 2022, Alexander et al. 2022).

Targets are selected from the Legacy Survey DR9 photometric catalogs, which are derived from three optical imaging surveys in the grz-bands—primarily assembled for that exact purpose, completed with the near-infrared WISE and the Gaia data.

They summarize the long-term effort by many researchers from the DESI collaboration to design a key part of the DESI experiment. All the different algorithms were tested and optimized during the Survey Validation (SV). At the end of the first part of the SV, the team has provided a final version of the target selection for all the tracers. They were finally validated during the One-Percent Survey.

With this target selection work coming to an end, the effort is now focusing on participating in the preparation of the large-scale structure analysis of the first year of data.

A second batch of papers will be published on arXiv in the coming months, prior to the SV data release…so stay tuned!

Angela Berti, University of Utah

June 29, 2022

On Saturday, June 11 a lightning strike started a wildfire in the Arizona mountains less than ten miles from the Kitt Peak National Observatory (KPNO), where DESI observing is done with the Mayall 4-meter telescope. Besides the Mayall, Kitt Peak is home to over 20 telescopes and other buildings that support scientific observations on the mountain, including dormitories where staff sleep. All of these structures were potentially threatened by the wildfire.

By Tuesday, June 14 the wildfire (now called the Contreras Fire) had spread to thousands of acres and was less than five miles from Kitt Peak. Around noon local time KPNO safety staff and the fire Incident Commander told everyone on site to immediately prepare to evacuate the mountain. Observing would have to be put on hold. The night of June 13 would be DESI’s final look at the sky for at least several weeks. Within hours a convoy was organized and began to bring those at the summit down the mountain to safety. A skeleton crew of four remained at the summit overnight for full-time fire watch.

On Wednesday, June 15 about 15 firefighters were at KPNO clearing defensive space around observatory buildings. Eight NOIRLab staff were also allowed to return for a few hours to protect critical equipment. This included taping plastic sheets and tarps over DESI’s prime focus corrector and the Mayall telescope’s primary mirror. These sensitive components could be damaged by smoke and ash should the fire get too close.

Nearly 200 firefighters were by then battling the Contreras fire, which was now only three miles away to the south. By the evening at least seven large air tankers were dropping fire retardant near KPNO.

The fire was just two miles away by the morning of June 16. Firefighting teams dropped over 100 loads of fire retardant along the perimeter of the observatory, and local news reported that the Contreras fire was the “#1 priority to wildland fire in the entire United States” due to the value of KPNO.

By early morning on Friday, June 17, the fire swept over the Southwest Ridge section of the observatory, home to MDM Observatory (two optical telescopes), the Arizona Radio Observatory, and the NRAO Very Long Baseline Array radio dish. KPNO webcams mounted on some of the telescopes stopped returning images not long after as the fire disrupted electricity and internet service on the mountain. DESI collaborators around the world could no longer monitor instruments remotely due to the loss of connectivity.

Good news finally came around midday on June 17 as light rain began to fall in nearby Tucson, Arizona. In the afternoon word came from two employees of NOIRLab who were on the mountain assisting firefighters with KPNO’s water system that no fire had reached the Mayall telescope. By the time the Contreras fire was 100% contained it had spread to nearly 30,000 acres. The fire destroyed four “non-scientific” structures, but none of the more than 20 telescopes atop Kitt Peak were burned!

On Tuesday, June 21, the DESI collaboration gathered in Berkeley, California for its first in-person meeting since 2019 due to the covid-19 pandemic. Many collaboration members who couldn’t be there in person joined remotely, and everyone expressed their gratitude for the incredible firefighters who saved DESI and KPNO from the Contreras fire.

Claire Lamman, Harvard University

February 28, 2022

We all know the recipe for a great scientific collaboration: novel technology, topical science goals, and cool stickers.

In November 2021 we achieved the final ingredient with the launch of our official DESI Swag Shop.

The DESI shop is hosted on the third-party site Redbubble. This is a place for independent artists to sell their designs on a variety of products—everything from t-shirts to shower curtains. While not specifically designed for organizations to distribute swag, it is a convenient way to make a large selection of items easily available to individuals around the world. We set our shop settings to 0% profit margin—which means DESI makes no money and the prices are as low as possible.

In honor of the opening of our online shop, I made a special DESI-gn that highlights both the science and instrumentation parts of our collaboration. “Dark Energy” is represented by a map of large-scale structure, and “Spectroscopic Instrument” is represented by our focal plane and its 5,000 robotic positioners.

Four months later, 486 items have been purchased from our shop. The most popular are:

1. DESI Logo sticker
2. DESI Plane sticker
3. DESI Logo magnet
4. DESI Plane t-shirt
5. M31 Focal Plane sticker

Beyond stickers and t-shirts the shop also has masks, mugs, puzzles, posters, and even socks. Here’s a look at how the popularity of these items compare:

Stats like this may be helpful for conference organizers deciding what types of merch products to use. The key takeaway here: never forget the stickers!