316 research outputs found
Anti-Black racism workshop during the Vera C. Rubin Observatory virtual 2021 Project and Community Workshop
Systemic racism is a ubiquitous theme in societies worldwide and plays a
central role in shaping our economic, social, and academic institutions. The
Vera C. Rubin Observatory is a major US ground-based facility based in Chile
with international participation. The Observatory is an example of excellence
and will deliver the largest survey of the sky ever attempted. Rubin's full
scientific and social potential can not be attained without addressing systemic
racism and associated barriers to equity, diversity, and inclusion (EDI).
During Rubin's 2021 virtual Project and Community Workshop (PCW), the annual
Rubin community-based meeting, an anti-Black racism workshop took place,
facilitated by 'The BIPOC Project' organization. About 60 members from
different parts of the Rubin ecosystem participated. We describe the
motivation, organization, challenges, outcomes, and near- and long-term goals
of this workshop.Comment: Contribution to appear in 'An Astronomical Inclusion Revolution:
Advancing Diversity, Equity, and Inclusion in Professional Astronomy and
Astrophysics', to be published by IOP ebook
A General Framework for Removing Point Spread Function Additive Systematics in Cosmological Weak Lensing Analysis
Cosmological weak lensing measurements rely on a precise measurement of the
shear two-point correlation function (2PCF) along with a deep understanding of
systematics that affect it. In this work, we demonstrate a general framework
for describing the impact of PSF systematics on the cosmic shear 2PCF, and
mitigating its impact on cosmological analysis. Our framework can describe
leakage and modeling error from all spin-2 quantities contributed by the PSF
second and higher moments, rather than just the second moments. We interpret
null tests using the HSC Year 3 (Y3) catalogs with this formalism, and find
that leakage from the spin-2 combination of PSF fourth moments is the leading
contributor to additive shear systematics, with total contamination that is an
order of magnitude higher than that contributed by PSF second moments alone. We
conducted a mock cosmic shear analysis for HSC Y3, and find that, if
uncorrected, PSF systematics can bias the cosmological parameters
and by 0.3. The traditional second moment-based model can
only correct for a 0.1 bias, leaving the contamination largely
uncorrected. We conclude it is necessary to model both PSF second and fourth
moment contamination for HSC Y3 cosmic shear analysis. We also reanalyze the
HSC Y1 cosmic shear analysis with our updated systematics model, and identify a
0.07 bias on when using the more restricted second moment
model from the original analysis. We demonstrate how to self-consistently use
the method in both real space and Fourier space, assess shear systematics in
tomographic bins, and test for PSF model overfitting.Comment: 29 pages, 25 figures, submitted to MNRAS. Comments welcome
Photometry, Centroid and Point-Spread Function Measurements in the LSST Camera Focal Plane Using Artificial Stars
The Vera C. Rubin Observatory's LSST Camera pixel response has been
characterized using laboratory measurements with a grid of artificial stars. We
quantify the contributions to photometry, centroid, point-spread function size,
and shape measurement errors due to small anomalies in the LSSTCam CCDs. The
main sources of those anomalies are quantum efficiency variations and pixel
area variations induced by the amplifier segmentation boundaries and
"tree-rings" -- circular variations in silicon doping concentration. We studied
the effects using artificial stars projected on the sensors and find that the
resulting measurement uncertainties pass the ten-year LSST survey science
requirements. In addition, we verify that the tree-ring effects can be
corrected using flat-field images if needed, because the astronomic shifts and
shape measurement errors they induce correlate well with the flat-field signal.
Nevertheless, further sensor anomaly studies with on-sky data should probe
possible temporal and wavelength-dependent effects.Comment: Submitted to PAS
Design of a Skipper CCD Focal Plane for the SOAR Integral Field Spectrograph
We present the development of a Skipper Charge-Coupled Device (CCD) focal
plane prototype for the SOAR Telescope Integral Field Spectrograph (SIFS). This
mosaic focal plane consists of four 6k 1k, 15 m pixel Skipper
CCDs mounted inside a vacuum dewar. We describe the process of packaging the
CCDs so that they can be easily tested, transported, and installed in a mosaic
focal plane. We characterize the performance of m thick,
fully-depleted engineering-grade Skipper CCDs in preparation for performing
similar characterization tests on science-grade Skipper CCDs which will be
thinned to 250m and backside processed with an antireflective coating. We
achieve a single-sample readout noise of for the best
performing amplifiers and sub-electron resolution (photon counting
capabilities) with readout noise from 800
measurements of the charge in each pixel. We describe the design and
construction of the Skipper CCD focal plane and provide details about the
synchronized readout electronics system that will be implemented to
simultaneously read 16 amplifiers from the four Skipper CCDs (4-amplifiers per
detector). Finally, we outline future plans for laboratory testing,
installation, commissioning, and science verification of our Skipper CCD focal
plane
Consistent lensing and clustering in a low-S8 Universe with BOSS, DES Year 3, HSC Year 1, and KiDS-1000
We evaluate the consistency between lensing and clustering based on measurements from BOSS combined with galaxy-galaxy lensing from DES-Y3, HSC-Y1, KiDS-1000. We find good agreement between these lensing datasets. We model the observations using the Dark Emulator and fit the data at two fixed cosmologies: Planck (S 8 = 0.83), and a Lensing cosmology (S 8 = 0.76). For a joint analysis limited to large scales, we find that both cosmologies provide an acceptable fit to the data. Full utilisation of the higher signal-to-noise small-scale measurements is hindered by uncertainty in the impact of baryon feedback and assembly bias, which we account for with a reasoned theoretical error budget. We incorporate a systematic inconsistency parameter for each redshift bin, A, that decouples the lensing and clustering. With a wide range of scales, we find different results for the consistency between the two cosmologies. Limiting the analysis to the bins for which the impact of the lens sample selection is expected to be minimal, for the Lensing cosmology, the measurements are consistent with A=1; A = 0.91 ± 0.04 (A = 0.97 ± 0.06) using DES+KiDS (HSC). For the Planck case, we find a discrepancy: A = 0.79 ± 0.03 (A = 0.84 ± 0.05) using DES+KiDS (HSC). We demonstrate that a kSZ-based estimate for baryonic effects alleviates some of the discrepancy in the Planck cosmology. This analysis demonstrates the statistical power of small-scale measurements, but caution is still warranted given modelling uncertainties and foreground sample selection effects
Hyper Suprime-Cam Year 3 results: cosmology from cosmic shear power spectra
We measure weak lensing cosmic shear power spectra from the 3-year galaxy shear catalog of the Hyper Suprime-Cam (HSC) Subaru Strategic Program imaging survey. The shear catalog covers 416 deg2 of the northern sky, with a mean i-band seeing of 0.59 arcsec and an effective galaxy number density of 15 arcmin−2 within our adopted redshift range. With an i-band magnitude limit of 24.5 mag, and four tomographic redshift bins spanning 0.3≤zph≤1.5 based on photometric redshifts, we obtain a high-significance measurement of the cosmic shear power spectra, with a signal-to-noise ratio of approximately 26.4 in the multipole range 300<ℓ<1800. The accuracy of our power spectrum measurement is tested against realistic mock shear catalogs, and we use these catalogs to get a reliable measurement of the covariance of the power spectrum measurements. We use a robust blinding procedure to avoid confirmation bias, and model various uncertainties and sources of bias in our analysis, including point spread function systematics, redshift distribution uncertainties, the intrinsic alignment of galaxies and the modeling of the matter power spectrum. For a flat ΛCDM model, we find S8≡σ8(Ωm/0.3)0.5=0.776+0.032−0.033, which is in excellent agreement with the constraints from the other HSC Year 3 cosmology analyses, as well as those from a number of other cosmic shear experiments. This result implies a ∼2σ-level tension with the Planck 2018 cosmology. We study the effect that various systematic errors and modeling choices could have on this value, and find that they can shift the best-fit value of S8 by no more than ∼0.5σ, indicating that our result is robust to such systematics
Chemical Analysis of the Brightest Star of the Cetus II Ultra-Faint Dwarf Galaxy Candidate
We present a detailed chemical abundance analysis of the brightest star in
the ultra-faint dwarf (UFD) galaxy candidate Cetus II from high-resolution
Magellan/MIKE spectra. For this star, DES J011740.53-173053, abundances or
upper limits of 18 elements from Carbon to Europium are derived. Its chemical
abundances generally follow those of other UFD galaxy stars, with a slight
enhancement of the alpha-elements (Mg, Si, and Ca) and low neutron-capture
element (Sr, Ba, Eu) abundances supporting the classification of Cetus II as a
likely UFD. The star exhibits lower Sc, Ti, and V abundances than Milky Way
(MW) halo stars with similar metallicity. This signature is consistent with
yields from a supernova (SN) originating from a star with a mass of ~11.2 solar
masses. In addition, the star has a Potassium abundance of [K/Fe] = 0.81 which
is somewhat higher than the K abundances of MW halo stars with similar
metallicity, a signature which is also present in a number of UFD galaxies. A
comparison including globular clusters (GC) and stellar stream stars suggests
that high K is a specific characteristic for some UFD galaxy stars and can thus
be used to help classify objects as UFD galaxies.Comment: 15 pages, 7 figures, 5 tables, accepted to Ap
Environmental Quenching of Low Surface Brightness Galaxies near Milky Way mass Hosts
Low Surface Brightness Galaxies (LSBGs) are excellent probes of quenching and
other environmental processes near massive galaxies. We study an extensive
sample of LSBGs near massive hosts in the local universe that are distributed
across a diverse range of environments. The LSBGs with surface-brightness
24.2 mag arcsec are drawn from the Dark Energy Survey
Year 3 catalog while the hosts with masses comparable to the Milky Way and the Large Magellanic Cloud are selected
from the z0MGS sample. We study the projected radial density profiles of LSBGs
as a function of their color and surface brightness around hosts in both the
rich Fornax-Eridanus cluster environment and the low-density field. We detect
an overdensity with respect to the background density, out to 2.5 times the
virial radius for both hosts in the cluster environment and the isolated field
galaxies. When the LSBG sample is split by color or surface brightness
, we find the LSBGs closer to their hosts are significantly
redder and brighter, like their high surface-brightness counterparts. The LSBGs
form a clear 'red sequence' in both the cluster and isolated environments that
is visible beyond the virial radius of the hosts. This suggests a
pre-processing of infalling LSBGs and a quenched backsplash population around
both host samples. However, the relative prominence of the 'blue cloud' feature
implies that pre-processing is ongoing near the isolated hosts compared to the
cluster hosts.Comment: 22 pages, 7 figure
DeepZipper: A Novel Deep-learning Architecture for Lensed Supernovae Identification
Large-scale astronomical surveys have the potential to capture data on large numbers of strongly gravitationally lensed supernovae (LSNe). To facilitate timely analysis and spectroscopic follow-up before the supernova fades, an LSN needs to be identified soon after it begins. To quickly identify LSNe in optical survey data sets, we designed ZipperNet, a multibranch deep neural network that combines convolutional layers (traditionally used for images) with long short-term memory layers (traditionally used for time series). We tested ZipperNet on the task of classifying objects from four categories—no lens, galaxy-galaxy lens, lensed Type-Ia supernova, lensed core-collapse supernova—within high-fidelity simulations of three cosmic survey data sets: the Dark Energy Survey, Rubin Observatory’s Legacy Survey of Space and Time (LSST), and a Dark Energy Spectroscopic Instrument (DESI) imaging survey. Among our results, we find that for the LSST-like data set, ZipperNet classifies LSNe with a receiver operating characteristic area under the curve of 0.97, predicts the spectroscopic type of the lensed supernovae with 79% accuracy, and demonstrates similarly high performance for LSNe 1–2 epochs after first detection. We anticipate that a model like ZipperNet, which simultaneously incorporates spatial and temporal information, can play a significant role in the rapid identification of lensed transient systems in cosmic survey experiments
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