ORCID Profile
0000-0002-3033-7312
Current Organisation
Institut de Física d'Altes Energies
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Publisher: Oxford University Press (OUP)
Date: 29-07-2022
Abstract: Using synthetic Lyman-α forests from the Dark Energy Spectroscopic Instrument (DESI) survey, we present a study of the impact of errors in the estimation of quasar redshift on the Lyman-α correlation functions. Estimates of quasar redshift have large uncertainties of a few hundred km s−1 due to the broadness of the emission lines and the intrinsic shifts from other emission lines. We inject Gaussian random redshift errors into the mock quasar catalogues, and measure the auto-correlation and the Lyman-α-quasar cross-correlation functions. We find a smearing of the BAO feature in the radial direction, but changes in the peak position are negligible. However, we see a significant unphysical correlation for small separations transverse to the line of sight which increases with the litude of the redshift errors. We interpret this contamination as a result of the broadening of emission lines in the measured mean continuum, caused by quasar redshift errors, combined with the unrealistically strong clustering of the simulated quasars on small scales.
Publisher: American Astronomical Society
Date: 02-2023
Abstract: We present Dark Energy Spectroscopic Instrument (DESI) observations of the inner halo of M31, which reveal the kinematics of a recent merger—a galactic immigration event—in exquisite detail. Of the 11,416 sources studied in 3.75 hr of on-sky exposure time, 7438 are M31 sources with well-measured radial velocities. The observations reveal intricate coherent kinematic structure in the positions and velocities of in idual stars: streams, wedges, and chevrons. While hints of coherent structures have been previously detected in M31, this is the first time they have been seen with such detail and clarity in a galaxy beyond the Milky Way. We find clear kinematic evidence for shell structures in the Giant Stellar Stream, the Northeast Shelf, and Western Shelf regions. The kinematics are remarkably similar to the predictions of dynamical models constructed to explain the spatial morphology of the inner halo. The results are consistent with the interpretation that much of the substructure in the inner halo of M31 is produced by a single galactic immigration event 1–2 Gyr ago. Significant numbers of metal-rich stars ([Fe/H] − 0.5) are present in all of the detected substructures, suggesting that the immigrating galaxy had an extended star formation history. We also investigate the ability of the shells and Giant Stellar Stream to constrain the gravitational potential of M31, and estimate the mass within a projected radius of 125 kpc to be log 10 M NFW ( 125 kpc ) / M ⊙ = 11.80 − 0.10 + 0.12 . The results herald a new era in our ability to study stars on a galactic scale and the immigration histories of galaxies.
Publisher: American Astronomical Society
Date: 03-03-2023
Abstract: We describe the spectroscopic data processing pipeline of the Dark Energy Spectroscopic Instrument (DESI), which is conducting a redshift survey of about 40 million galaxies and quasars using a purpose-built instrument on the 4 m Mayall Telescope at Kitt Peak National Observatory. The main goal of DESI is to measure with unprecedented precision the expansion history of the universe with the baryon acoustic oscillation technique and the growth rate of structure with redshift space distortions. Ten spectrographs with three cameras each disperse the light from 5000 fibers onto 30 CCDs, covering the near-UV to near-infrared (3600–9800 Å) with a spectral resolution ranging from 2000 to 5000. The DESI data pipeline generates wavelength- and flux-calibrated spectra of all the targets, along with spectroscopic classifications and redshift measurements. Fully processed data from each night are typically available to the DESI collaboration the following morning. We give details about the pipeline’s algorithms, and provide performance results on the stability of the optics, the quality of the sky background subtraction, and the precision and accuracy of the instrumental calibration. This pipeline has been used to process the DESI Survey Validation data set, and has exceeded the project’s requirements for redshift performance, with high efficiency and a purity greater than 99% for all target classes.
Publisher: IOP Publishing
Date: 05-2014
DOI: 10.1088/1475-7516/2014/05/027
Abstract: We measure the large-scale cross-correlation of quasars with the Lyα forest absorption, using over 164,000 quasars from Data Release 11 of the SDSS-III Baryon Oscillation Spectroscopic Survey. We extend the previous study of roughly 60,000 quasars from Data Release 9 to larger separations, allowing a measurement of the Baryonic Acoustic Oscillation (BAO) scale along the line of sight c /( H ( z = 2.36) r s ) = 9.0±0.3 and across the line of sight D A ( z = 2.36)/ r s = 10.8±0.4, consistent with CMB and other BAO data. Using the best fit value of the sound horizon from Planck data ( r s = 147.49 Mpc), we can translate these results to a measurement of the Hubble parameter of H ( z = 2.36) = 226±8 km s −1 Mpc −1 and of the angular diameter distance of D A ( z = 2.36) = 1590±60 Mpc. The measured cross-correlation function and an update of the code to fit the BAO scale (baofit) are made publicly available.
Publisher: American Physical Society (APS)
Date: 14-12-2015
Publisher: American Astronomical Society
Date: 02-2023
Abstract: The Dark Energy Spectroscopic Instrument (DESI) survey will measure large-scale structures using quasars as direct tracers of dark matter in the redshift range 0.9 z 2.1 and using Ly α forests in quasar spectra at z 2.1. We present several methods to select candidate quasars for DESI, using input photometric imaging in three optical bands ( g , r , z ) from the DESI Legacy Imaging Surveys and two infrared bands (W1, W2) from the Wide-field Infrared Survey Explorer. These methods were extensively tested during the Survey Validation of DESI. In this paper, we report on the results obtained with the different methods and present the selection we optimized for the DESI main survey. The final quasar target selection is based on a random forest algorithm and selects quasars in the magnitude range of 16.5 r 23. Visual selection of ultra-deep observations indicates that the main selection consists of 71% quasars, 16% galaxies, 6% stars, and 7% inconclusive spectra. Using the spectra based on this selection, we build an automated quasar catalog that achieves a fraction of true QSOs higher than 99% for a nominal effective exposure time of ∼1000 s. With a 310 deg −2 target density, the main selection allows DESI to select more than 200 deg −2 quasars (including 60 deg −2 quasars with z 2.1), exceeding the project requirements by 20%. The redshift distribution of the selected quasars is in excellent agreement with quasar luminosity function predictions.
Publisher: American Astronomical Society
Date: 04-2023
Abstract: We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4 m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes ∣ b ∣ 20°, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness s les of rare stellar types, including white dwarfs, low-mass stars within 100 pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of the Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ≃500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ≃1 km s −1 and [Fe/H] accurate to ≃0.2 dex for typical stars in our main s le. We find the stellar parameter distributions from ≈100 deg 2 of SV observations with ≳90% completeness on our main s le are in good agreement with expectations from mock catalogs and previous surveys.
Publisher: EDP Sciences
Date: 11-2013
Publisher: Oxford University Press (OUP)
Date: 20-02-2023
Abstract: We present the VST ATLAS Quasar Survey, consisting of ∼1229 000 quasar (QSO) candidates with 16 & g & 22.5 over ∼4700 deg2. The catalogue is based on VST ATLAS+NEOWISE imaging surveys and aims to reach a QSO sky density of 130 deg−2 for $z$ & 2.2 and ∼30 deg−2 for $z$ & 2.2. To guide our selection, we use X-ray/UV/optical/MIR data in the extended William Herschel Deep Field (WHDF) where we find a g & 22.5 broad-line QSO density of 269 ± 67 deg−2, roughly consistent with the expected ∼196 deg−2. We find that ∼25 per cent of our QSOs are morphologically classed as optically extended. Overall, we find that in these deep data, MIR, UV, and X-ray selections are ∼70–90 per cent complete while X-ray suffers less contamination than MIR and UV. MIR is however more sensitive than X-ray or UV to $z$ & 2.2 QSOs at g & 22.5 and the $S_X(0.5-10\\, {\\rm keV})\\gt 1\\times 10^{-14}$ ergs cm−2 s−1 limit of eROSITA. We adjust the selection criteria from our previous 2QDES pilot survey and prioritize VST ATLAS candidates that show both UV and MIR excess, also selecting candidates initially classified as extended. We test our selections using data from DESI (which will be released in DR1) and 2dF to estimate the efficiency and completeness, and we use ANNz2 to determine photometric redshifts. Applying over the ∼4700 deg2 ATLAS area gives us $\\sim 917\\,000\\, z\\lt 2.2$ QSO candidates of which 472 000 are likely to be $z$ & 2.2 QSOs, implying a sky density of ∼100 deg−2, which our WHDF analysis suggests will rise to at least 130 deg−2 when eROSITA X-ray candidates are included. At $z$ & 2.2, we find ∼310() 000 candidates, of which 169 000 are likely to be QSOs for a sky density of ∼36 deg−2.
Publisher: American Astronomical Society
Date: 04-02-2016
Publisher: American Astronomical Society
Date: 22-02-2023
Abstract: A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (≈70%) of the main-survey targets are spectroscopically confirmed as quasars, with ≈16% galaxies, ≈6% stars, and ≈8% low-quality spectra lacking reliable features. A nonnegligible fraction of the quasars are misidentified by the standard spectroscopic pipeline, but we show that the majority can be recovered using post-pipeline “afterburner” quasar-identification approaches. We combine these “afterburners” with our standard pipeline to create a modified pipeline to increase the overall quasar yield. At the depth of the main DESI survey, both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km s −1 ) of ≈99% however, the modified pipeline recovers ≈94% of the visually inspected quasars, as compared to ≈86% from the standard pipeline. We demonstrate that both pipelines achieve a median redshift precision and accuracy of ≈100 km s −1 and ≈70 km s −1 , respectively. We constructed composite spectra to investigate why some quasars are missed by the standard pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of “Seyfert galaxies”) and/or more dust reddened than the standard-pipeline quasars. We also show ex le spectra to demonstrate the overall ersity of the DESI quasar s le and provide strong-lensing candidates where two targets contribute to a single spectrum.
Publisher: American Astronomical Society
Date: 29-06-2017
Publisher: American Astronomical Society
Date: 25-03-2008
DOI: 10.1086/587961
Publisher: Oxford University Press (OUP)
Date: 03-10-2023
Publisher: American Astronomical Society
Date: 2023
Abstract: The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields s les of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s −1 for bright galaxies and ELGs and approximately 40 km s −1 for LRGs. The average redshift accuracy is within 10 km s −1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show ex les of unexpected real astronomical objects, such as Ly α emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.
Publisher: Oxford University Press (OUP)
Date: 21-07-2014
Publisher: American Astronomical Society
Date: 02-08-2018
Location: United Kingdom of Great Britain and Northern Ireland
Location: United States of America
No related grants have been discovered for Andreu Font-Ribera.