310 research outputs found
Testing LSST dither strategies for Survey Uniformity and Large-Scale Structure Systematics
The Large Synoptic Survey Telescope (LSST) will survey the southern sky from 2022{2032 with unprecedented detail. Since the observing strategy can lead to artifacts in the data, we investigate the eects of telescope-pointing osets (called dithers) on the r-band coadded 5 depth yielded after the 10-year survey. We analyze this survey depth for several geometric patterns of dithers (e.g.,random, hexagonal lattice, spiral) with amplitude as large as the radius of the LSST eld-of-view, implemented on dierent timescales (per season, per night, per visit). Our results illustrate that per night and per visit dither assignments are more eective than per season. Also, we find that some dither geometries (e.g., hexagonal lattice) are particularly sensitive to the timescale on whichthe dithers are implemented, while others like random dithers perform well on all timescales. We then model the propagation of depth variations to articial uctuations in galaxy counts, which are a systematic for large-scale structure studies. We calculate the bias in galaxy counts caused by the observing strategy, accounting for photometric calibration uncertainties, dust extinction, and magnitude cuts; uncertainties in this bias limit our ability to account for structure induced by the observing strategy. We nd that after 10 years of the LSST survey, the best dither strategies lead to uncertainties in this bias smaller than the minimum statistical floor for a galaxy catalog as deep asr<27.5. A few of these strategies bring the uncertainties close to the statistical floor for r<25.7 after only one year of survey.Fil: Awan, Humna. Rutgers University; Estados UnidosFil: Gawiser, Eric. Rutgers University; Estados UnidosFil: Kurczynski, Peter. Rutgers University; Estados UnidosFil: Lynne Jones, R.. University of Washington; Estados UnidosFil: Zhan, Hu. Chinese Academy of Sciences; República de ChinaFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; ChileFil: Muñoz Arancibia, Alejandra M.. Pontificia Universidad Católica de Chile; ChileFil: Orsi, Alvaro. Centro de Estudios de Fisica del Cosmos de Aragon; EspañaFil: Cora, Sofia Alejandra. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica la Plata; ArgentinaFil: Yoachim, Peter. University of Washington; Estados Unido
A Simultaneous Stacking and Deblending Algorithm for Astronomical Images
Stacking analysis is a means of detecting faint sources using a priori
position information to estimate an aggregate signal from individually
undetected objects. Confusion severely limits the effectiveness of stacking in
deep surveys with limited angular resolution, particularly at far infrared to
submillimeter wavelengths, and causes a bias in stacking results. Deblending
corrects measured fluxes for confusion from adjacent sources; however, we find
that standard deblending methods only reduce the bias by roughly a factor of
two while tripling the variance. We present an improved algorithm for
simultaneous stacking and deblending that greatly reduces bias in the flux
estimate with nearly minimum variance. When confusion from neighboring sources
is the dominant error, our method improves upon RMS error by at least a factor
of three and as much as an order of magnitude compared to other algorithms.
This improvement will be useful for Herschel and other telescopes working in a
source confused, low signal to noise regime.Comment: accepted to The Astronomical Journal. 18 pages, 6 figure
Improving the LSST dithering pattern and cadence for dark energy studies
The Large Synoptic Survey Telescope (LSST) will explore the entire southern
sky over 10 years starting in 2022 with unprecedented depth and time sampling
in six filters, . Artificial power on the scale of the 3.5 deg LSST
field-of-view will contaminate measurements of baryonic acoustic oscillations
(BAO), which fall at the same angular scale at redshift . Using the
HEALPix framework, we demonstrate the impact of an "un-dithered" survey, in
which of each LSST field-of-view is overlapped by neighboring
observations, generating a honeycomb pattern of strongly varying survey depth
and significant artificial power on BAO angular scales. We find that adopting
large dithers (i.e., telescope pointing offsets) of amplitude close to the LSST
field-of-view radius reduces artificial structure in the galaxy distribution by
a factor of 10. We propose an observing strategy utilizing large dithers
within the main survey and minimal dithers for the LSST Deep Drilling Fields.
We show that applying various magnitude cutoffs can further increase survey
uniformity. We find that a magnitude cut of removes significant
spurious power from the angular power spectrum with a minimal reduction in the
total number of observed galaxies over the ten-year LSST run. We also determine
the effectiveness of the observing strategy for Type Ia SNe and predict that
the main survey will contribute 100,000 Type Ia SNe. We propose a
concentrated survey where LSST observes one-third of its main survey area each
year, increasing the number of main survey Type Ia SNe by a factor of
1.5, while still enabling the successful pursuit of other science
drivers.Comment: 9 pages, 6 figures, published in SPIE proceedings; corrected typo in
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Quantifying the UV-continuum slopes of galaxies to z ˜ 10 using deep Hubble+Spitzer/IRAC observations
Measurements of the UV-continuum slopes β provide valuable information on the physical properties of galaxies forming in the early universe, probing the dust reddening, age, metal content, and even the escape fraction. While constraints on these slopes generally become more challenging at higher redshifts as the UV-continuum shifts out of the Hubble Space Telescope bands (particularly at z > 7), such a characterization actually becomes abruptly easier for galaxies in the redshift window z = 9.5-10.5 due to the Spitzer/Infrared Array Camera 3.6 μm-band probing the rest-UV continuum and the long wavelength baseline between this Spitzer band and the Hubble Hf160w band. Higher S/N constraints on β are possible at z ˜ 10 than at z = 8. Here, we take advantage of this opportunity and five recently discovered bright z = 9.5-10.5 galaxies to present the first measurements of the mean β for a multi-object sample of galaxy candidates at z ˜ 10. We find the measured βobs's of these candidates are -2.1 ± 0.3 ± 0.2 (random and systematic), only slightly bluer than the measured β's (βobs ≈ -1.7) at 3.5 < z < 7.5 for galaxies of similar luminosities. Small increases in the stellar ages, metallicities, and dust content of the galaxy population from z ˜ 10 to z ˜ 7 could easily explain the apparent evolution in β
Dust Attenuation in UV-selected Starbursts at High Redshift and their Local Counterparts: Implications for the Cosmic Star Formation Rate Density
We present a new analysis of the dust obscuration in starburst galaxies at
low and high redshift. This study is motivated by our unique sample of the most
extreme UV-selected starburst galaxies in the nearby universe (z<0.3), found to
be good analogs of high-redshift Lyman Break Galaxies (LBGs) in most of their
physical properties. We find that the dust properties of the Lyman Break
Analogs (LBAs) are consistent with the relation derived previously by Meurer et
al. (M99) that is commonly used to dust-correct star formation rate
measurements at a very wide range of redshifts. We directly compare our results
with high redshift samples (LBGs, BzK, and sub-mm galaxies at z=2-3) having IR
data either from Spitzer or Herschel. The attenuation in typical LBGs at z=2-3
and LBAs is very similar. Because LBAs are much better analogs to LBGs compared
to previous local star-forming samples, including M99, the practice of
dust-correcting the SFRs of high redshift galaxies based on the local
calibration is now placed on a much more solid ground. We illustrate the
importance of this result by showing how the locally calibrated relation
between UV measurements and extinction is used to estimate the integrated,
dust-corrected star formation rate density at z=2-6.Comment: Accepted for publication in ApJ Letters (6 pages, 4 figures, 1 table
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