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.
Abstract
The Dark Energy Spectroscopic Instrument (DESI) is carrying out a five-year survey that aims to measure the redshifts of tens of millions of galaxies and quasars, including 8 million ...luminous red galaxies (LRGs) in the redshift range 0.4 <
z
≲ 1.0. Here we present the selection of the DESI LRG sample and assess its spectroscopic performance using data from Survey Validation (SV) and the first two months of the Main Survey. The DESI LRG sample, selected using
g
,
r
,
z
, and
W
1 photometry from the DESI Legacy Imaging Surveys, is highly robust against imaging systematics. The sample has a target density of 605 deg
−2
and a comoving number density of 5 × 10
−4
h
3
Mpc
−3
in 0.4 <
z
< 0.8; this is a significantly higher density than previous LRG surveys (such as SDSS, BOSS, and eBOSS) while also extending to
z
∼ 1. After applying a bright star veto mask developed for the sample, 98.9% of the observed LRG targets yield confident redshifts (with a catastrophic failure rate of 0.2% in the confident redshifts), and only 0.5% of the LRG targets are stellar contamination. The LRG redshift efficiency varies with source brightness and effective exposure time, and we present a simple model that accurately characterizes this dependence. In the appendices, we describe the extended LRG samples observed during SV.
Abstract
The Dark Energy Spectroscopic Instrument (DESI) will precisely constrain cosmic expansion and the growth of structure by collecting ∼40 million extragalactic redshifts across ∼80% of cosmic ...history and one-third of the sky. The Emission Line galaxy (ELG) sample, which will comprise about one-third of all DESI tracers, will be used to probe the universe over the 0.6 <
z
< 1.6 range, including the 1.1 <
z
< 1.6 range, which is expected to provide the tightest constraints. We present the target selection for the DESI Survey Validation (SV) and Main Survey ELG samples, which relies on the imaging of the Legacy Surveys. The Main ELG selection consists of a
g
-band magnitude cut and a (
g
−
r
) versus (
r
−
z
) color box, while the SV selection explores extensions of the Main selection boundaries. The Main ELG sample is composed of two disjoint subsamples, which have target densities of about 1940 deg
−2
and 460 deg
−2
, respectively. We first characterize their photometric properties and density variations across the footprint. We then analyze the DESI spectroscopic data that have been obtained from 2020 December to 2021 December in the SV and Main Survey. We establish a preliminary criterion for selecting reliable redshifts, based on the O
ii
flux measurement, and assess its performance. Using this criterion, we are able to present the spectroscopic efficiency of the Main ELG selection, along with its redshift distribution. We thus demonstrate that the Main selection 1940 deg
−2
subsample alone should provide 400 deg
−2
and 460 deg
−2
reliable redshifts in the 0.6 <
z
< 1.1 and the 1.1 <
z
< 1.6 ranges, respectively.
ABSTRACT We present extensive optical (UBV RI, , and open CCD) and near-infrared (ZY JH) photometry for the very nearby Type IIP SN 2013ej extending from +1 to +461 days after shock breakout, ...estimated to be MJD 56496.9 0.3. Substantial time series ultraviolet and optical spectroscopy obtained from +8 to +135 days are also presented. Considering well-observed SNe IIP from the literature, we derive UBV RIJHK bolometric calibrations from UBV RI and unfiltered measurements that potentially reach 2% precision with a B − V color-dependent correction. We observe moderately strong Si ii as early as +8 days. The photospheric velocity ( ) is determined by modeling the spectra in the vicinity of Fe ii whenever observed, and interpolating at photometric epochs based on a semianalytic method. This gives km s−1 at +50 days. We also observe spectral homogeneity of ultraviolet spectra at +10-12 days for SNe IIP, while variations are evident a week after explosion. Using the expanding photosphere method, from combined analysis of SN 2013ej and SN 2002ap, we estimate the distance to the host galaxy to be Mpc, consistent with distance estimates from other methods. Photometric and spectroscopic analysis during the plateau phase, which we estimated to be 94 7 days long, yields an explosion energy of erg, a final pre-explosion progenitor mass of 15.2 4.2 and a radius of 250 70 . We observe a broken exponential profile beyond +120 days, with a break point at +183 16 days. Measurements beyond this break time yield a 56Ni mass of 0.013 0.001 M .
Abstract We present cosmological analysis of 12 nearby ( z < 0.06) Type IIP supernovae (SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise photometry, we present a new ...image-differencing technique that is implemented for the first time on the ROTSE SN photometry pipeline. With this method, we find up to a 20% increase in the detection efficiency and significant reduction in residual rms scatter of the SN lightcurves when compared to the previous pipeline performance. We use the published optical spectra and broadband photometry of well-studied SNe IIP to establish temporal models for ejecta velocity and photospheric temperature evolution for our SNe IIP population. This study yields measurements that are competitive with other methods even when the data are limited to a single epoch during the photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and optical spectra, we apply these models to the respective photometric epochs for each SN in the ROTSE IIP sample. This facilitates the use of the Expanding Photosphere Method (EPM) to obtain distance estimates to their respective host galaxies. We then perform cosmological parameter fitting using these EPM distances, from which we measure the Hubble constant to be 72.9 − 4.3 + 5.7 km s − 1 Mpc − 1 , which is consistent with the standard ΛCDM model values derived using other independent techniques.
ABSTRACT
Combining different observational probes, such as galaxy clustering and weak lensing, is a promising technique for unveiling the physics of the Universe with upcoming dark energy ...experiments. The galaxy redshift sample from the Dark Energy Spectroscopic Instrument (DESI) will have a significant overlap with major ongoing imaging surveys specifically designed for weak lensing measurements: the Kilo-Degree Survey (KiDS), the Dark Energy Survey (DES), and the Hyper Suprime-Cam (HSC) survey. In this work, we analyse simulated redshift and lensing catalogues to establish a new strategy for combining high-quality cosmological imaging and spectroscopic data, in view of the first-year data assembly analysis of DESI. In a test case fitting for a reduced parameter set, we employ an optimal data compression scheme able to identify those aspects of the data that are most sensitive to cosmological information and amplify them with respect to other aspects of the data. We find this optimal compression approach is able to preserve all the information related to the growth of structures.
ABSTRACT
We present and validate the catalogue of Lyman-α forest fluctuations for 3D analyses using the Early Data Release (EDR) from the Dark Energy Spectroscopic Instrument (DESI) survey. We used ...88 511 quasars collected from DESI Survey Validation (SV) data and the first two months of the main survey (M2). We present several improvements to the method used to extract the Lyman-α absorption fluctuations performed in previous analyses from the Sloan Digital Sky Survey (SDSS). In particular, we modify the weighting scheme and show that it can improve the precision of the correlation function measurement by more than 20 per cent. This catalogue can be downloaded from https://data.desi.lbl.gov/public/edr/vac/edr/lya/fuji/v0.3, and it will be used in the near future for the first DESI measurements of the 3D correlations in the Lyman-α forest.
Although antiretroviral therapy has limited efficiency, patients should take multiple drugs in combination in prescribed time for lifelong and they should also require specific food and fluid ...restriction. Due to these and other factors patients may discontinue their medication and therefore face significant challenges in adherence.
To assess factors associated with non-adherence among people living with HIV receiving the antiretroviral therapy.
Between July 2011 to January 2012, a cross sectional survey was conducted among patients visiting HIV/AIDS unit, Tribhuvan University Teaching Hospital for therapy. After taking informed consent, a pre-structured questionnaire was filled up and data were entered into SPSS 11.5 system and analyzed.
Of the 100 studied subjects, 61 (61.0%) were male and 39 (39%) were female. Adherence was found to be 79%. The major barrier to adherence was reported to be simply forgetfulness (33.3% of those non adherents). Non adherence was significantly associated with types of family (X² value, 7.11), smoking (X² value, 5.44) and alcoholic habit (X² value, 5.69) but not with gender (X² value, 2.57). Besides this, poor economic status, and attendance to religious ceremony were reported to be major obstacles to adherence.
Adherence at this center was found to be only satisfactory. Forgetfulness was reported to be the major cause of non adherence. Persons living in joint family and those with alcoholic and /or smoking habit were more likely to miss the pills. It can be recommended that effective counseling, moral/financial support for HIV/AIDS patients may increase their adherence.
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