DESI Commissioning Instrument Metrology

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the methods and results for the commissioning instrument metrology program. The primary goals of this program are to calculate the transformations and further develop the systems that will place fibers within 5um RMS of the target positions. We will use the commissioning instrument metrology program to measure the absolute three axis Cartesian coordinates of the five CCDs and 22 illuminated fiducials on the commissioning instrument

The DESI Sky Continuum Monitor System

The Dark Energy Spectroscopic Instrument (DESI) is an ongoing spectroscopic survey to measure the dark energy equation of state to unprecedented precision. We describe the DESI Sky Continuum Monitor System, which tracks the night sky brightness as part of a system that dynamically adjusts the spectroscopic exposure time to produce more uniform data quality and to maximize observing efficiency. The DESI dynamic exposure time calculator (ETC) will combine sky brightness measurements from the Sky Monitor with data from the guider system to calculate the exposure time to achieve uniform signal-to-noise ratio (SNR) in the spectra under various observing conditions. The DESI design includes 20 sky fibers, and these are split between two identical Sky Monitor units to provide redundancy. Each Sky Monitor unit uses an SBIG STXL-6303e CCD camera and supports an eight-position filter wheel. Both units have been completed and delivered to the Mayall Telescope at the Kitt Peak National Observatory. Commissioning results show that the Sky Monitor delivers the required performance necessary for the ETC.Comment: 9 pages, 7 figures, 1 tabl

Discovery of a z = 0.65 post-starburst BAL quasar in the DES supernova fields

We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe II (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario

Overview of the instrumentation for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) embarked on an ambitious 5 yr survey in 2021 May to explore the nature of dark energy with spectroscopic measurements of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the baryon acoustic oscillation method to measure distances from the nearby universe to beyond redshift z > 3.5, and employ redshift space distortions to measure the growth of structure and probe potential modifications to general relativity. We describe the significant instrumentation we developed to conduct the DESI survey. This includes: a wide-field, 3.°2 diameter prime-focus corrector; a focal plane system with 5020 fiber positioners on the 0.812 m diameter, aspheric focal surface; 10 continuous, high-efficiency fiber cable bundles that connect the focal plane to the spectrographs; and 10 identical spectrographs. Each spectrograph employs a pair of dichroics to split the light into three channels that together record the light from 360–980 nm with a spectral resolution that ranges from 2000–5000. We describe the science requirements, their connection to the technical requirements, the management of the project, and interfaces between subsystems. DESI was installed at the 4 m Mayall Telescope at Kitt Peak National Observatory and has achieved all of its performance goals. Some performance highlights include an rms positioner accuracy of better than 0.″1 and a median signal-to-noise ratio of 7 of the [O ii] doublet at 8 × 10−17 erg s−1 cm−2 in 1000 s for galaxies at z = 1.4–1.6. We conclude with additional highlights from the on-sky validation and commissioning, key successes, and lessons learned

Compiled Information of Unknown ROSAT X-ray sources

Compiled information from SIMBAD and Vizier on unknown ROSAT object

UV background fluctuations and three-point correlations in the large-scale clustering of the Lyman α\alpha forest

International audienceUsing the Lyman α (Lyα) Mass Association Scheme, we make theoretical predictions for the three-dimensional three-point correlation function (3PCF) of the Lyα forest at redshift z = 2.3. We bootstrap results from the (100 h^−1 Mpc)^3 Horizon hydrodynamic simulation to a (1 h^−1 Gpc)^3N-body simulation, considering both a uniform ultraviolet background (UVB) and a fluctuating UVB sourced by quasars with a comoving n_q ≈ 10^−5h^3 Mpc^−3 placed either in massive haloes or randomly. On scales of 10–30 h^−1 Mpc, the flux 3PCF displays hierarchical scaling with the square of the two-point correlation function (2PCF), but with an unusual value of Q ≡ ζ_123/(ξ_12ξ_13 + ξ_12ξ_23 + ξ_13ξ_23) ≈ −4.5 that reflects the low bias of the Lyα forest and the anticorrelation between mass density and transmitted flux. For halo-based quasars and an ionizing photon mean free path of λ = 300 h^−1 Mpc comoving, UVB fluctuations moderately depress the 2PCF and 3PCF, with cancelling effects on Q. For λ = 100 or 50 h^−1 Mpc, UVB fluctuations substantially boost the 2PCF and 3PCF on large scales, shifting the hierarchical ratio to Q ≈ −3. We scale our simulation results to derive rough estimate of the detectability of the 3PCF in current and future observational data sets for the redshift range z = 2.1–2.6. At r = 10 and 20 h^−1 Mpc, we predict a signal-to-noise ratio (SNR) of ∼9 and ∼7, respectively, for both Baryon Oscillation Spectroscopic Survey (BOSS) and extended BOSS (eBOSS), and ∼37 and ∼25 for Dark Energy Spectroscopic Instrument (DESI). At r = 40 h^−1 Mpc the predicted SNR is lower by a factor of ∼3–5. Measuring the flux 3PCF would provide a novel test of the conventional paradigm of the Lyα forest and help separate the contributions of UVB fluctuations and density fluctuations to Lyα forest clustering, thereby solidifying its foundation as a tool of precision cosmology

pypeit/PypeIt: Version 1.14.0

Dependency Changes Main dependency bumps: numpy>=1.22, matplotlib>=3.7, ginga>=4.1.1, qtpy>=2.0.1 Functionality/Performance Improvements and Additions Improvements to wavelength grids and masking in coadd routines. Refactored coadding routines to work with lists to support coadding data from different setups. Sensitivity function models can now be computed relative to the flat-field spectrum. Improvements in 2D coaddition Fix a bug in pypeit_setup_coadd2d for the output file name of the .coadd2d file Added possibility to specify more than one Science folder in pypeit_setup_coadd2d Now only_slits parameter in pypeit_coadd_2dspec includes the detector number (similar to slitspatnum) Added exclude_slits parameter in pypeit_coadd_2dspec to exclude specific slits Fix wrong RA and Dec for 2D coadded serendips Allow wavelength calibrations for specific slits/orders to be redone (instead of adopting the value from a processed calibration frame); see new redo_slits parameter. Instrument-specific Updates Adds/Improves support for Gemini/GNIRS (IFU), Keck/KCRM, Keck/ESI, MDM/Modspec, Keck/HIRES, JWST HIRES wavelength solution improvements galore Improvements for Keck/LRIS Generated wavelength templates for all the LRIS grism & grating Added FeAr line list Improved calibration association and frame typing Improved and added documentation Changes to metadata.py including commenting out, in the pypeit file, files that have frametype None (this prevent run_pypeit to crash) Added a function check_spectrograph() (currently only defined for LRIS), that checks (during pypeit_setup) if the selected spectrograph is the corrected one for the data used. Script Changes Added a script to convert a wavelength solution into something that can be placed in the reid archive. Store user-generated wavelength solution in pypeit cache Datamodel Changes Changed calibration frame naming as an attempt to avoid very long names for files with many calibration groups. Sequential numbers are reduced to a range; e.g., '0-1-2-3-4' becomes '0+4' and '3-5-6-10-11-12-15-18-19' becomes '3-5+6-10+12-15-18+19' Instrumental FWHM map is calculated and output in Calibrations and spec1d files. Under-the-hood Improvements Change how masking is dealt with in extraction to fix a bug in how masks were being treated for echelle data Refactored function that loads wavelength calibration line lists Bug Fixes Hotfix for GTC/OSIRIS lamp list Hotfix for Arc1D stats annotations on the QA Hotfix for metadata: correctly set config_independent_frames when multiple configurations are being setup support lists in config_independent_frames Hotfix for rebin (speed-up and conserves flux) Hotfix for skysub regions GUI that used np.bool Hotfix to stop pypeit_setup from crashing on data from lbt_luci1, lbt_luci2, magellan_fire, magellan_fire_long, p200_tspec, or vlt_sinfoni. Hotfix to set BPM for each type of calibration file. Fixed a bug in echelle coadding where the wrong coadded spectra were being used in final stacks. Fix a bug in spectrograph.select_detectors, where a list of slitspatnum could not be used

A study of quasar selection in the supernova fields of the Dark Energy Survey

We present a study of quasar selection using the supernova fields of the Dark Energy Survey (DES). We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/ probabilistic modeling with variability. In all cases, we considered only objects that appear as point sources in the DES images. We examine color selection methods based on the Wide-field Infrared Survey Explorer (WISE) mid- IR W1 - W2 color, a mixture of WISE and DES colors (g − i and i - W1), and a mixture of Vista Hemisphere Survey and DES colors (g − i and i − K ). For probabilistic quasar selection, we used XDQSO, an algorithm that employs an empirical multi-wavelength flux model of quasars to assign quasar probabilities. Our variability selection uses the multi-band χ2-probability that sources are constant in the DES Year 1 griz-band light curves. The completeness and efficiency are calculated relative to an underlying sample of point sources that are detected in the required selection bands and pass our data quality and photometric error cuts. We conduct our analyses at two magnitude limits, i85% for both i-band magnitude limits and efficiencies of >80% to the bright limit and >60% to the faint limit; however, the giW1 and giW1+variability methods give the highest quasar surface densities. The XDQSOz method and combinations of W1W2/giW1/XDQSOz with variability are among the better selection methods when both high completeness and high efficiency are desired. We also present the OzDES Quasar Catalog of 1263 spectroscopically confirmed quasars from three years of OzDES observation in the 30 deg2 of the DES supernova fields. The catalog includes quasars with redshifts up to z4 and brighter than i = 22 mag, although the catalog is not complete up to this magnitude limit