111 research outputs found
Spitzer UltRa Faint SUrvey Program (SURFS UP). II. IRAC-Detected Lyman-Break Galaxies at 6 < z < 10 Behind Strong-Lensing Clusters
We study the stellar population properties of the IRAC-detected galaxy candidates from the Spitzer UltRa Faint SUrvey Program
(SURFS UP). Using the Lyman Break selection technique, we find a total of 16
new galaxy candidates at with in at
least one of the IRAC m and m bands. According to the best mass
models available for the surveyed galaxy clusters, these IRAC-detected galaxy
candidates are magnified by factors of --. We find that the
IRAC-detected sample is likely not a homogeneous
galaxy population: some are relatively massive (stellar mass as high as ) and evolved (age Myr) galaxies, while
others are less massive () and very
young ( Myr) galaxies with strong nebular emission lines that boost
their rest-frame optical fluxes. We identify two Ly emitters in our
sample from the Keck DEIMOS spectra, one at (in
RXJ1347) and one at (in MACS0454). We show that IRAC
color, when combined with photometric redshift, can be used to
identify galaxies likely with strong nebular emission lines within certain
redshift windows.Comment: ApJ in pres
On The Detection Of Ionizing Radiation Arising From Star-Forming Galaxies At Redshift z ~ 3-4 : Looking For Analogs Of "Stellar Reionizers"
We use the spatially-resolved, multi-band photometry in the GOODS South field
acquired by the CANDELS project to constrain the nature of candidate Lyman
continuum (LyC) emitters at redshift z~3.7 identified using ultra-deep imaging
below the Lyman limit (1-sigma limit of ~30 AB in a 2" diameter aperture). In
18 candidates, out of a sample of 19 with flux detected at >3-sigma level, the
light centroid of the candidate LyC emission is offset from that of the LBG by
up to 1.5". We fit the SED of the LyC candidates to spectral population
synthesis models to measure photometric redshifts and the stellar population
parameters. We also discuss the differences in the UV colors between the LBG
and the LyC candidates, and how to estimate the escape fraction of ionizing
radiation (f_esc) in cases, like in most of our galaxies, where the LyC
emission is spatially offset from the host galaxy. In all but one case we
conclude that the candidate LyC emission is most likely due to lower redshift
interlopers. Based on these findings, we argue that the majority of similar
measurements reported in the literature need further investigation before it
can be firmly concluded that LyC emission is detected. Our only surviving LyC
candidate is a LBG at z=3.795, which shows the bluest (B-V) color among LBGs at
similar redshift, a stellar mass of M~2 x 10^9 Msun, weak interstellar
absorption lines and a flat UV spectral slope with no Lya in emission. We
estimate its f_esc to be in the range 25%-100%, depending on the dust and
intergalactic attenuation.Comment: Submitted to The Astrophysical Journal, 20 pages, 8 figures, 1 tabl
Hubble Frontier Field Photometric Catalogues of Abell 370 and RXC J2248.7-4431: Multiwavelength photometry, photometric redshifts, and stellar properties
This paper presents multiwavelength photometric catalogues of the last two
Hubble Frontier Fields (HFF), the massive galaxy clusters Abell 370 and RXC
J2248.7-4431. The photometry ranges from imaging performed on the Hubble Space
Telescope (HST) to ground based Very Large Telescope (VLT) and Spitzer/IRAC, in
collaboration with the ASTRODEEP team, and using the ASTRODEEP pipeline. While
the main purpose of this paper is to release the catalogues, we also perform,
as a proof of concept, a brief analysis of z > 6 objects selected using
drop-out method, as well as spectroscopically confirmed sources and multiple
images in both clusters. While dropout methods yield a sample of high-z
galaxies, the addition of longer wavelength data reveals that as expected the
samples have substantial contamination at the ~30-45% level by dusty galaxies
at lower redshifts. Furthermore, we show that spectroscopic redshifts are still
required to unambiguously determine redshifts of multiply imaged systems.
Finally, the now publicly available ASTRODEEP catalogues were combined for all
HFFs and used to explore stellar properties of a large sample of 20,000
galaxies across a large photometric redshift range. The powerful magnification
provided by the HFF clusters allows us an exploration of the properties of
galaxies with intrinsic stellar masses as low as
and intrinsic star formation rates \mbox{SFRs}\sim 0.1\mbox{-}1M_\odot/\mbox
yr at z > 6.Comment: Replaced to match the accepted versio
Recommended from our members
From California’s Extreme Drought to Major Flooding: Evaluating and Synthesizing Experimental Seasonal and Subseasonal Forecasts of Landfalling Atmospheric Rivers and Extreme Precipitation during Winter 2022/23
California experienced a historic run of nine consecutive landfalling atmospheric rivers (ARs) in three weeks’ time during winter 2022/23. Following three years of drought from 2020 to 2022, intense landfalling ARs across California in December 2022–January 2023 were responsible for bringing reservoirs back to historical averages and producing damaging floods and debris flows. In recent years, the Center for Western Weather and Water Extremes and collaborating institutions have developed and routinely provided to end users peer-reviewed experimental seasonal (1–6 month lead time) and subseasonal (2–6 week lead time) prediction tools for western U.S. ARs, circulation regimes, and precipitation. Here, we evaluate the performance of experimental seasonal precipitation forecasts for winter 2022/23, along with experimental subseasonal AR activity and circulation forecasts during the December 2022 regime shift from dry conditions to persistent troughing and record AR-driven wetness over the western United States. Experimental seasonal precipitation forecasts were too dry across Southern California (likely due to their overreliance on La Niña), and the observed above-normal precipitation across Northern and Central California was underpredicted. However, experimental subseasonal forecasts skillfully captured the regime shift from dry to wet conditions in late December 2022 at 2–3 week lead time. During this time, an active MJO shift from phases 4 and 5 to 6 and 7 occurred, which historically tilts the odds toward increased AR activity over California. New experimental seasonal and subseasonal synthesis forecast products, designed to aggregate information across institutions and methods, are introduced in the context of this historic winter to provide situational awareness guidance to western U.S. water managers
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
This paper describes the Hubble Space Telescope imaging data products and
data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). This survey is designed to document the evolution of
galaxies and black holes at , and to study Type Ia SNe beyond
. Five premier multi-wavelength sky regions are selected, each with
extensive multiwavelength observations. The primary CANDELS data consist of
imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and
UVIS channel, along with the Advanced Camera for Surveys (ACS). The
CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and
GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a
total of \sim800 square arcminutes across GOODS and three additional fields
(EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as
motivated by the scientific goals and present a detailed description of the
data reduction procedures and products from the survey. Our data reduction
methods utilize the most up to date calibration files and image combination
procedures. We have paid special attention to correcting a range of
instrumental effects, including CTE degradation for ACS, removal of electronic
bias-striping present in ACS data after SM4, and persistence effects and other
artifacts in WFC3/IR. For each field, we release mosaics for individual epochs
and eventual mosaics containing data from all epochs combined, to facilitate
photometric variability studies and the deepest possible photometry. A more
detailed overview of the science goals and observational design of the survey
are presented in a companion paper.Comment: 39 pages, 25 figure
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
is designed to document the first third of galactic evolution, over the
approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies
using three separate cameras on the Hubble Space Telescope, from the
mid-ultraviolet to the near-infrared, and will find and measure Type Ia
supernovae at z>1.5 to test their accuracy as standardizable candles for
cosmology. Five premier multi-wavelength sky regions are selected, each with
extensive ancillary data. The use of five widely separated fields mitigates
cosmic variance and yields statistically robust and complete samples of
galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the
knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8.
The survey covers approximately 800 arcmin^2 and is divided into two parts. The
CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125
arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and
three additional fields (EGS, COSMOS, and UDS) and covers the full area to a
5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble
Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach
that has proven efficient for extragalactic surveys. Data from the survey are
nonproprietary and are useful for a wide variety of science investigations. In
this paper, we describe the basic motivations for the survey, the CANDELS team
science goals and the resulting observational requirements, the field selection
and geometry, and the observing design. The Hubble data processing and products
are described in a companion paper.Comment: Submitted to Astrophysical Journal Supplement Series; Revised
version, subsequent to referee repor
Polarized blazar X-rays imply particle acceleration in shocks
Most of the light from blazars, active galactic nuclei with jets of magnetized plasma that point nearly along the line of sight, is produced by high-energy particles, up to around 1 TeV. Although the jets are known to be ultimately powered by a supermassive black hole, how the particles are accelerated to such high energies has been an unanswered question. The process must be related to the magnetic field, which can be probed by observations of the polarization of light from the jets. Measurements of the radio to optical polarization—the only range available until now—probe extended regions of the jet containing particles that left the acceleration site days to years earlier1,2,3, and hence do not directly explore the acceleration mechanism, as could X-ray measurements. Here we report the detection of X-ray polarization from the blazar Markarian 501 (Mrk 501). We measure an X-ray linear polarization degree ΠX of around 10%, which is a factor of around 2 higher than the value at optical wavelengths, with a polarization angle parallel to the radio jet. This points to a shock front as the source of particle acceleration and also implies that the plasma becomes increasingly turbulent with distance from the shock
Magnetic Field Properties inside the Jet of Mrk 421: Multiwavelength Polarimetry Including the Imaging X-ray Polarimetry Explorer
We conducted a polarimetry campaign from radio to X-ray wavelengths of the
high-synchrotron-peak (HSP) blazar Mrk 421, including Imaging X-ray Polarimetry
Explorer (IXPE) measurements on 2022 December 6-8. We detected X-ray
polarization of Mrk 421 with a degree of =141 and an
electric-vector position angle =1073 in the 2-8
keV band. From the time variability analysis, we find a significant episodic
variation in . During 7 months from the first IXPE pointing of
Mrk 421 in 2022 May, varied across the range of 0 to
180, while maintained similar values within
10-15. Furthermore, a swing in in 2022 June was
accompanied by simultaneous spectral variations. The results of the
multiwavelength polarimetry show that the X-ray polarization degree was
generally 2-3 times greater than that at longer wavelengths, while the
polarization angle fluctuated. Additionally, based on radio, infrared, and
optical polarimetry, we find that rotation of occurred in the opposite
direction with respect to the rotation of over longer timescales
at similar epochs. The polarization behavior observed across multiple
wavelengths is consistent with previous IXPE findings for HSP blazars. This
result favors the energy-stratified shock model developed to explain variable
emission in relativistic jets. The accompanying spectral variation during the
rotation can be explained by a fluctuation in the physical
conditions, e.g., in the energy distribution of relativistic electrons. The
opposite rotation direction of between the X-ray and longer-wavelength
polarization accentuates the conclusion that the X-ray emitting region is
spatially separated from that at longer wavelengths.Comment: 17 pages, 13 figures, 4 tables; Accepted for publication in A&
Discovery of X-ray polarization angle rotation in active galaxy Mrk 421
The magnetic field conditions in astrophysical relativistic jets can be
probed by multiwavelength polarimetry, which has been recently extended to
X-rays. For example, one can track how the magnetic field changes in the flow
of the radiating particles by observing rotations of the electric vector
position angle . Here we report the discovery of a
rotation in the X-ray band in the blazar Mrk 421 at an average flux state.
Across the 5 days of Imaging X-ray Polarimetry Explorer (IXPE) observations of
4-6 and 7-9 June 2022, rotated in total by .
Over the two respective date ranges, we find constant, within uncertainties,
rotation rates ( and ) and polarization
degrees (). Simulations of a random walk of the
polarization vector indicate that it is unlikely that such rotation(s) are
produced by a stochastic process. The X-ray emitting site does not completely
overlap the radio/infrared/optical emission sites, as no similar rotation of
was observed in quasi-simultaneous data at longer wavelengths. We
propose that the observed rotation was caused by a helical magnetic structure
in the jet, illuminated in the X-rays by a localized shock propagating along
this helix. The optically emitting region likely lies in a sheath surrounding
an inner spine where the X-ray radiation is released
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