87 research outputs found
Quasar Host Environments: The view from Planck
We measure the far-infrared emission of the general quasar (QSO) population
using Planck observations of the Baryon Oscillation Spectroscopic Survey QSO
sample. By applying multi-component matched multi-filters to the seven highest
Planck frequencies, we extract the amplitudes of dust, synchrotron and thermal
Sunyaev-Zeldovich (SZ) signals for nearly 300,000 QSOs over the redshift range
. We bin these individually low signal-to-noise measurements to obtain
the mean emission properties of the QSO population as a function of redshift.
The emission is dominated by dust at all redshifts, with a peak at ,
the same location as the peak in the general cosmic star formation rate.
Restricting analysis to radio-loud QSOs, we find synchrotron emission with a
monochromatic luminosity at (rest-frame) rising from
to between
and 3. The radio-quiet subsample does not show any synchrotron emission,
but we detect thermal SZ between and 4; no significant SZ emission is
seen at lower redshifts. Depending on the supposed mass for the halos hosting
the QSOs, this may or may not leave room for heating of the halo gas by
feedback from the QSO.Comment: 14 pages, 11 figures, accepted by A&
Sky reconstruction from transit visibilities: PAON-4 and Tianlai Dish Array
The spherical harmonics -mode decomposition is a powerful sky map
reconstruction method suitable for radio interferometers operating in transit
mode. It can be applied to various configurations, including dish arrays and
cylinders. We describe the computation of the instrument response function, the
point spread function (PSF), transfer function, the noise covariance matrix and
noise power spectrum. The analysis in this paper is focused on dish arrays
operating in transit mode. We show that arrays with regular spacing have more
pronounced side lobes as well as structures in their noise power spectrum,
compared to arrays with irregular spacing, specially in the north-south
direction. A good knowledge of the noise power spectrum
is essential for intensity mapping experiments as
non uniform is a potential problem for the
measurement of the HI power spectrum. Different configurations have been
studied to optimise the PAON-4 and Tianlai dish array layouts. We present their
expected performance and their sensitivities to the 21-cm emission of the Milky
Way and local extragalactic HI clumpsComment: 20 pages, 18 figures - Submitted to MNRAS ( the appendix A,B are not
included in the accepted version
Sky reconstruction for the Tianlai cylinder array
In this paper, we apply our sky map reconstruction method for transit type
interferometers to the Tianlai cylinder array. The method is based on the
spherical harmonic decomposition, and can be applied to cylindrical array as
well as dish arrays and we can compute the instrument response, synthesised
beam, transfer function and the noise power spectrum. We consider cylinder
arrays with feed spacing larger than half wavelength, and as expected, we find
that the arrays with regular spacing have grating lobes which produce spurious
images in the reconstructed maps. We show that this problem can be overcome,
using arrays with different feed spacing on each cylinder. We present the
reconstructed maps, and study the performance in terms of noise power spectrum,
transfer function and beams for both regular and irregular feed spacing
configurations.Comment: 15 pages, 12 figures, accepted by RA
2-point statistics covariance with fewer mocks
We present an approach for accurate estimation of the covariance of 2-point
correlation functions that requires fewer mocks than the standard mock-based
covariance. This can be achieved by dividing a set of mocks into jackknife
regions and fitting the correction term first introduced in Mohammad & Percival
(2022), such that the mean of the jackknife covariances corresponds to the one
from the mocks. This extends the model beyond the shot-noise limited regime,
allowing it to be used for denser samples of galaxies. We test the performance
of our fitted jackknife approach, both in terms of accuracy and precision,
using lognormal mocks with varying densities and approximate EZmocks mimicking
the DESI LRG and ELG samples in the redshift range of z = [0.8, 1.2].
We find that the Mohammad-Percival correction produces a bias in the 2-point
correlation function covariance matrix that grows with number density and that
our fitted jackknife approach does not. We also study the effect of the
covariance on the uncertainty of cosmological parameters by performing a
full-shape analysis. We find that our fitted jackknife approach based on 25
mocks is able to recover unbiased and as precise cosmological parameters as the
ones obtained from a covariance matrix based on 1000 or 1500 mocks, while the
Mohammad-Percival correction produces uncertainties that are twice as large.
The number of mocks required to obtain an accurate estimation of the covariance
for 2-point correlation function is therefore reduced by a factor of 40-60.Comment: 13 pages, 14 figures, submitted to MNRA
The DESI Bright Galaxy Survey: Final Target Selection, Design, and Validation
Over the next 5 yr, the Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on the 4 m Mayall Telescope at Kitt Peak National Observatory to conduct the first Stage IV dark energy galaxy survey. At z 10 million galaxies spanning 14,000 deg2 . In this work, we present and validate the final BGS target selection and survey design. From the Legacy Surveys, BGS will target an r 80% fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve >95% redshift success over any observing condition. BGS meets the requirements for an extensive range of scientific applications. BGS will yield the most precise baryon acoustic oscillation and redshift-space distortion measurements at z < 0.4. It presents opportunities for new methods that require highly complete and dense samples (e.g., N-point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter
Recommended from our members
Astro2020 APC White Paper: The MegaMapper: a z > 2 spectroscopic instrument for the study of Inflation and Dark Energy
MegaMapper is a proposed ground-based experiment to measure Inflation
parameters and Dark Energy from galaxy redshifts at
A Spectroscopic Road Map for Cosmic Frontier: DESI, DESI-II, Stage-5
In this white paper, we present an experimental road map for spectroscopic
experiments beyond DESI. DESI will be a transformative cosmological survey in
the 2020s, mapping 40 million galaxies and quasars and capturing a significant
fraction of the available linear modes up to z=1.2. DESI-II will pilot
observations of galaxies both at much higher densities and extending to higher
redshifts. A Stage-5 experiment would build out those high-density and
high-redshift observations, mapping hundreds of millions of stars and galaxies
in three dimensions, to address the problems of inflation, dark energy, light
relativistic species, and dark matter. These spectroscopic data will also
complement the next generation of weak lensing, line intensity mapping and CMB
experiments and allow them to reach their full potential.Comment: Contribution to Snowmass 202
The Spectroscopic Data Processing Pipeline for the Dark Energy Spectroscopic Instrument
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 to 9800 Angstrom) 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 percent for all target classes.Comment: AJ, revised version, 55 pages, 55 figures, 4 table
The DESI survey validation : results from visual inspection of bright galaxies, luminous red galaxies, and emission line galaxies
Funding: TWL was supported by the Ministry of Science and Technology (MOST 111-2112-M-002-015-MY3), the Ministry of Education, Taiwan (MOE Yushan Young Scholar grant NTU-110VV007), National Taiwan University research grants (NTU CC-111L894806, NTU- 111L7318), and NSF grant AST-1911140. DMA acknowledges the Science Technology and Facilities Council (STFC) for support through grant code ST/T000244/1. This research is supported by the Director, Office of Science, Office of High Energy Physics of the U.S. Department of Energy under Contract No. DE–AC02–05CH11231, and by the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility under the same contract; additional support for DESI is provided by the U.S. National Science Foundation, Division of Astronomical Sciences under Contract No. AST-0950945 to the NSF’s National Optical-Infrared Astronomy Research Laboratory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technology of Mexico (CONACYT); the Ministry of Science and Innovation of Spain (MICINN), and by the DESI Member Institutions: https://www.desi.lbl.gov/ collaborating-institutions.The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies for validating the final survey design and target selections. To assist these tasks, we visually inspect (VI) DESI spectra of approximately 2,500 bright galaxies, 3,500 luminous red galaxies, and 10,000 emission line galaxies, to obtain robust redshift identifications. We then utilize the VI redshift information to characterize the performance of the DESI operation. Based on the VI catalogs, our results show that the final survey design yields samples of bright galaxies, luminous red galaxies, and emission line galaxies with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km/s for bright galaxies and emission line galaxies and approximately 40 km/s for luminous red galaxies. The average redshift accuracy is within 10 km/s for the three types of galaxies. The VI process also helps to improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Lyman 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 PDFPeer reviewe
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
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