33 research outputs found
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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Properties of Submillimeter Galaxies in a Semi-analytic Model using the "Count Matching" Approach: Application to the ECDF-S
We present a new technique for modeling submillimeter galaxies (SMGs): the
"Count Matching" approach. Using lightcones drawn from a semi-analytic model of
galaxy formation, we choose physical galaxy properties given by the model as
proxies for their submillimeter luminosities, assuming a monotonic
relationship. As recent interferometric observations of the Extended Chandra
Deep Field South show that the brightest sources detected by single-dish
telescopes are comprised by emission from multiple fainter sources, we assign
the submillimeter fluxes so that the combined LABOCA plus bright-end ALMA
observed number counts for this field are reproduced. After turning the model
catalogs given by the proxies into submillimeter maps, we perform a source
extraction to include the effects of the observational process on the recovered
counts and galaxy properties. We find that for all proxies, there are lines of
sight giving counts consistent with those derived from LABOCA observations,
even for input sources with randomized positions in the simulated map.
Comparing the recovered redshift, stellar mass and host halo mass distributions
for model SMGs with observational data, we find that the best among the
proposed proxies is that in which the submillimeter luminosity increases
monotonically with the product between dust mass and SFR. This proxy naturally
reproduces a positive trend between SFR and bolometric IR luminosity. The
majority of components of blended sources are spatially unassociated.Comment: 21 pages, 20 figures, 5 tables. Accepted for publication in MNRA
The SFR-M <sub>∗</sub> Correlation Extends to Low Mass at High Redshift
To achieve a fuller understanding of galaxy evolution, SED fitting can be
used to recover quantities beyond stellar masses (M) and star formation
rates (SFRs). We use Star Formation Histories (SFHs) reconstructed via the
Dense Basis method of Iyer \& Gawiser (2017) for a sample of galaxies
at in the CANDELS GOODS-S field to study the nature and evolution of
the SFR-M correlation. The reconstructed SFHs represent trajectories in
SFR-M space, enabling us to study galaxies at epochs earlier than observed
by propagating them backwards in time along these trajectories. We study the
SFR-M correlation at using both direct fits to galaxies
observed at those epochs and SFR-M trajectories of galaxies observed at
lower redshifts. The SFR-M correlations obtained using the two approaches
are found to be consistent with each other through a KS test. Validation tests
using SFHs from semi-analytic models and cosmological hydrodynamical
simulations confirm the sensitivity of the method to changes in the slope,
normalization and shape of the SFR-M correlation. This technique allows us
to further probe the low-mass regime of the correlation at high-z by
dex and over an effective volume of larger than possible with
just direct fits. We find that the SFR-M correlation is consistent with
being linear down to M at . The evolution of the
correlation is well described by , where is the age of the universe in Gyr.Comment: 22 pages, 10 figures. Accepted for publication in Ap
New Limits on Sterile Neutrinos from Suzaku Observations of the Ursa Minor Dwarf Spheroidal Galaxy
We present results of our search for X-ray line emission associated with the
radiative decay of the sterile neutrino, a well-motivated dark matter
candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal
galaxy. These data represent the first deep observation of one of these extreme
mass-to-light systems and the first dedicated dark matter search using an X-ray
telescope. No such emission line is positively detected, and we place new
constraints on the combination of the sterile neutrino mass and the
active-sterile neutrino oscillation mixing angle. Line flux upper limits are
derived using a maximum-likelihood-based approach that, along with the lack of
intrinsic X-ray emission, enables us to minimize systematics and account for
those that remain. The limits we derive match or approach the best previous
results over the entire 1--20 keV mass range from a single Suzaku observation.
These are used to place constraints on the existence of sterile neutrinos with
given parameters in the general case and in the case where they are assumed to
constitute all of the dark matter. The range allowed implies that sterile
neutrinos remain a viable candidate to make up some -- or all -- of the dark
matter and also explain pulsar kicks and various other astrophysical phenomena.Comment: revised to closely match version to be published in ApJ v. 69
The UV Continuum of z > 1 Star-forming Galaxies in the Hubble Ultraviolet Ultradeep Field
We estimate the UV continuum slope, β, for 923 galaxies in the range 1 = – 1.382(– 1.830) ± 0.002 (random) ± 0.1 (systematic). We find comparable scatter in β (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of β with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, dβ/dM = –0.11 ± 0.01, and no evolution in dβ/dM with redshift. A modest increase in dust reddening with redshift and luminosity, ΔE(B – V) ~ 0.1, and a comparable increase in the dispersion of dust reddening at z 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, dβ/dz = –0.09 ± 0.01 for low luminosity (0.05 L^(*)_(z=3), and dβ/dz = –0.06 ± 0.01 for medium luminosity (0.25 $L^(*)_(z=3) galaxies
UVUDF: Ultraviolet Imaging of the Hubble Ultradeep Field with Wide-field Camera 3
We present an overview of a 90-orbit Hubble Space Telescope treasury program
to obtain near ultraviolet imaging of the Hubble Ultra Deep Field using the
Wide Field Camera 3 UVIS detector with the F225W, F275W, and F336W filters.
This survey is designed to: (i) Investigate the episode of peak star formation
activity in galaxies at 1<z<2.5; (ii) Probe the evolution of massive galaxies
by resolving sub-galactic units (clumps); (iii) Examine the escape fraction of
ionizing radiation from galaxies at z~2-3; (iv) Greatly improve the reliability
of photometric redshift estimates; and (v) Measure the star formation rate
efficiency of neutral atomic-dominated hydrogen gas at z~1-3. In this overview
paper, we describe the survey details and data reduction challenges, including
both the necessity of specialized calibrations and the effects of charge
transfer inefficiency. We provide a stark demonstration of the effects of
charge transfer inefficiency on resultant data products, which when
uncorrected, result in uncertain photometry, elongation of morphology in the
readout direction, and loss of faint sources far from the readout. We agree
with the STScI recommendation that future UVIS observations that require very
sensitive measurements use the instrument's capability to add background light
through a "post-flash". Preliminary results on number counts of UV-selected
galaxies and morphology of galaxies at z~1 are presented. We find that the
number density of UV dropouts at redshifts 1.7, 2.1, and 2.7 is largely
consistent with the number predicted by published luminosity functions. We also
confirm that the image mosaics have sufficient sensitivity and resolution to
support the analysis of the evolution of star-forming clumps, reaching 28-29th
magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on
filter and observing epoch.Comment: Accepted A
The relationship between star formation activity and galaxy structural properties in CANDELS and a semi-analytic model
We study the correlation of galaxy structural properties with their location
relative to the SFR-M* correlation, also known as the star formation "main
sequence" (SFMS), in the CANDELS and GAMA surveys and in a semi-analytic model
(SAM) of galaxy formation. We first study the distribution of median Sersic
index, effective radius, star formation rate (SFR) density and stellar mass
density in the SFR-M* plane. We then define a redshift dependent main sequence
and examine the medians of these quantities as a function of distance from this
main sequence, both above (higher SFRs) and below (lower SFRs). Finally, we
examine the distributions of distance from the main sequence in bins of these
quantities. We find strong correlations between all of these galaxy structural
properties and the distance from the SFMS, such that as we move from galaxies
above the SFMS to those below it, we see a nearly monotonic trend towards
higher median Sersic index, smaller radius, lower SFR density, and higher
stellar density. In the semi-analytic model, bulge growth is driven by mergers
and disk instabilities, and is accompanied by the growth of a supermassive
black hole which can regulate or quench star formation via Active Galactic
Nucleus (AGN) feedback. We find that our model qualitatively reproduces the
trends described above, supporting a picture in which black holes and bulges
co-evolve, and AGN feedback plays a critical role in moving galaxies off of the
SFMS.Comment: 25 pages, 17 figures. Accepted for publication in MNRA
A spatially resolved analysis of star-formation burstiness by comparing UV and H in galaxies at z1 with UVCANDELS
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep
Extragalactic Legacy Survey Fields (UVCANDELS) program provides HST/UVIS F275W
imaging for four CANDELS fields. We combine this UV imaging with existing
HST/near-IR grism spectroscopy from 3D-HST+AGHAST to directly compare the
resolved rest-frame UV and H emission for a sample of 979 galaxies at
spanning a range in stellar mass of . Since
both rest-UV and H are sensitive to on-going star-formation but over
different timescales, their resolved comparison allows us to infer the
burstiness in star-formation as a function of galaxy structural parameters. We
generate homogenized maps of rest-UV and H emission for all galaxies in
our sample and stack them to compute the average UV-to-H luminosity
ratio as a function of galactocentric radius. We find that galaxies below
stellar mass of , at all radii, have a UV-to-H
ratio higher than the equilibrium value expected from constant star-formation,
indicating a significant contribution from bursty star-formation. Even for
galaxies with stellar mass , the UV-to-H ratio
is elevated towards in their outskirts (), suggesting that
bursty star-formation is likely prevalent in the outskirts of even the most
massive galaxies but is likely over-shadowed by their brighter cores.
Furthermore, we present the UV-to-H ratio as a function of galaxy
surface brightness, a proxy for stellar mass surface density, and find that
regions below are consistent with bursty
star-formation, regardless of their galaxy stellar mass, potentially suggesting
that local star-formation is independent of global galaxy properties at the
smallest scales.Comment: 19 pages, 8 figures; submitted to Ap