94 research outputs found
Turing Patterns and Biological Explanation
Turing patterns are a class of minimal mathematical models that have been used to discover and conceptualize certain abstract features of early biological development. This paper examines a range of these minimal models in order to articulate and elaborate a philosophical analysis of their epistemic uses. It is argued that minimal mathematical models aid in structuring the epistemic practices of biology by providing precise descriptions of the quantitative relations between various features of the complex systems, generating novel predictions that can be compared with experimental data, promoting theory exploration, and acting as constitutive parts of empirically adequate explanations of naturally occurring phenomena, such as biological pattern formation. Focusing on the roles that minimal model explanations play in science motivates the adoption of a broader diachronic view of scientific explanation
EPOCHS VII: Discovery of high redshift () AGN candidates in JWST ERO and PEARLS data
We present an analysis of a sample of robust high redshift galaxies selected
photometrically from the `blank' fields of the Prime Extragalactic Areas for
Reionization Science (PEARLS) survey and Early Release Observations (ERO) data
of the James Webb Space Telescope (JWST) with the aim of selecting candidate
high redshift active galactic nuclei (AGN). Sources were identified from the
parent sample using a threefold selection procedure, which includes spectral
energy distribution (SED) fitting to identify sources that are best fitted by
AGN SED templates, a further selection based on the relative performance of AGN
and non-AGN models, and finally morphological fitting to identify compact
sources of emission, resulting in a purity-oriented procedure. Using this
procedure, we identify a sample of nine AGN candidates at , from
which we constrain their physical properties as well as measure a lower bound
on the AGN fraction in this redshift range of \%. As this is an
extreme lower limit due to our focus on purity and our SEDs being calibrated
for unobscured Type 1 AGN, this demonstrates that AGN are perhaps quite common
at this early epoch. The rest-frame UV colors of our candidate objects suggest
that these systems are potentially candidate obese black hole galaxies (OBG),
or AGN with very little galaxy component. We also investigate emission from our
sample sources from fields overlapping with Chandra and VLA surveys, allowing
us to place X-ray and 3 GHz radio detection limits on our candidates. Of note
is a candidate source exhibiting an abrupt morphological shift in
the reddest band as compared to the bluer bands, indicating a potential merger
or an unusually strong outflow.Comment: Submitted to MNRAS, 12 pages, 11 figures, typos correcte
Magellanic System Stars Identified in the SMACS J0723.3-7327 JWST ERO Images
We identify 68 distant stars in JWST/NIRCam ERO images of the field of galaxy
cluster SMACS J0723.3-7327 (SMACS 0723). Given the relatively small
() angular separation between SMACS 0723 and the Large
Magellanic Cloud, it is likely that these stars are associated with the LMC
outskirts or Leading Arm. This is further bolstered by a spectral energy
distribution analysis, which suggests an excess of stars at a physical distance
of kpc, consistent with being associated with or located behind the
Magellanic system. In particular, we find that the overall surface density of
stars brighter than 27.0 mag in the field of SMACS 0723 is 2.3 times that
of stars in a blank field with similar galactic latitude (the North Ecliptic
Pole Time Domain Field), and that the density of stars in the SMACS 0723 field
with SED-derived distances consistent with the Magellanic system is 7.3
times larger than that of the blank field. The candidate stars at these
distances are consistent with a stellar population at the same distance modulus
with [Fe/H] and an age of Gyr. On the assumption that all
of the 68 stars are associated with the LMC, then the stellar density of the
LMC at the location of the SMACS 0723 field is stars kpc,
which helps trace the density of stars in the LMC outskirts.Comment: Submitted to ApJ, comments welcom
JWST's PEARLS: a new lens model for ACT-CL J01024915, "EL Gordo'', and the first red supergiant star at cosmological distances discovered by JWST
The first JWST data on the massive colliding cluster El Gordo confirm 23
known families of multiply lensed images and identify 8 new members of these
families. Based on these families, which have been confirmed spectroscopically
by MUSE, we derived an initial lens model. This model guided the identification
of 37 additional families of multiply lensed galaxies, among which 28 are
entirely new systems, and 9 were previously known. The initial lens model
determined geometric redshifts for the 37 new systems. The geometric redshifts
agree reasonably well with spectroscopic or photometric redshifts when those
are available. The geometric redshifts enable two additional models that
include all 60 families of multiply lensed galaxies spanning a redshift range
. The derived dark-matter distribution confirms the double-peak
configuration of mass found by earlier work with the southern and northern
clumps having similar masses. We confirm that El Gordo is the most massive
known cluster at and has an estimated virial mass close the maximum
mass allowed by standard cosmological models. The JWST images also reveal the
presence of small-mass perturbers that produce small lensing distortions. The
smallest of these is consistent with being a dwarf galaxy at and has
an estimated mass of ~\Msol, making it the smallest substructure
found at . The JWST images also show several candidate caustic-crossing
events. One of them is detected at high significance at the expected position
of the critical curve and is likely a red supergiant star at . This
would be the first red supergiant found at cosmological distances. The cluster
lensing should magnify background objects at , making more of them visible
than in blank fields of similar size, but there appears to be a deficiency of
such objects.Comment: 27 pages, 21 figure
JWST's PEARLS: TN J1338-1942 -- I. Extreme jet triggered star-formation in a z=4.11 luminous radio galaxy
We present the first JWST observations of the z = 4.11 luminous radio galaxy TN J1338–1942, obtained as part of the ‘Prime Extragalactic Areas for Reionization and Lensing Science’ (‘PEARLS’) project. Our NIRCam observations, designed to probe the key rest-frame optical continuum and emission line features at this redshift, enable resolved spectral energy distribution modelling that incorporates both a range of stellar population assumptions and radiative shock models. With an estimated stellar mass of log10(M/M) ∼ 10.9, TN J1338–1942 is confirmed to be one of the most massive galaxies known at this epoch. Our observations also reveal extremely high equivalent-width nebular emission coincident with the luminous AGN jets that is best fit by radiative shocks surrounded by extensive recent star formation. We estimate the total star-formation rate (SFR) could be as high as ∼ 1600 M yr−1 , with the SFR that we attribute to the jet induced burst conservatively 500 M yr−1. The mass-weighted age of the star-formation, tmass < 4 Myr, is consistent with the likely age of the jets responsible for the triggered activity and significantly younger than that measured in the core of the host galaxy. The extreme scale of the potential jet-triggered star-formation activity indicates the potential importance of positive AGN feedback in the earliest stages of massive galaxy formation, with our observations also illustrating the extraordinary prospects for detailed studies of high-redshift galaxies with JWST.KJD acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement number 892117 (HIZRAD) and support from the STFC through an Ernest Rutherford Fellowship (grant number ST/W003120/1). RAW, SHC, and RAJ acknowledge support from NASA JWST Interdisciplinary Scientist grants NAG5-12460, NNX14AN10G, and 80NSSC18K0200 from GSFC. Work by CJC acknowledges support from the European Research Council (ERC) Advanced Investigator Grant EPOCHS (788113). BLF thanks the Berkeley Center for Theoretical Physics for their hospitality during the writing of this paper. MAM acknowledges the support of a National Research Council of Canada Plaskett Fellowship, and the Australian Research Council center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE17010001. CNAW acknowledges funding from the JWST/NIRCam contract NASS-0215 to the University of Arizona. TAH is supported by an appointment to the NASA Postdoctoral Program (NPP) at NASA Goddard Space Flight Center, administered by Oak Ridge Associated Universities under contract with NASA.Peer reviewe
EPOCHS IX. When cosmic dawn breaks: Evidence for evolved stellar populations in galaxies from PEARLS GTO and public NIRCam imaging
The presence of evolved stars in high-redshift galaxies can place valuable
indirect constraints on the onset of star formation in the Universe. Thus we
use PEARLS GTO and public NIRCam photometric data to search for Balmer-break
candidate galaxies at . We find that our Balmer-break candidates at
tend to be older (115 Myr), have lower inferred [O III] +
H emission line equivalent widths (120 \r{A}), have lower specific star
formation rates (6 Gyr) and redder UV slopes () than our
control sample of galaxies. However, these trends all become less strong at , where the F444W filter now probes the strong rest-frame optical
emission lines, thus providing additional constraints on the current star
formation activity of these galaxies. Indeed, the bursty nature of Epoch of
Reionisation galaxies can lead to a disconnect between their current SED
profiles and their more extended star-formation histories. We discuss how
strong emission lines, the cumulative effect of weak emission lines, dusty
continua and AGN can all contribute to the photometric excess seen in the
rest-frame optical, thus mimicking the signature of a Balmer break. Additional
medium-band imaging will thus be essential to more robustly identify
Balmer-break galaxies. However, the Balmer break alone cannot serve as a
definitive proxy for the stellar age of galaxies, being complexly dependent on
the star-formation history. Ultimately, deep NIRSpec continuum spectroscopy and
MIRI imaging will provide the strongest indirect constraints on the formation
era of the first galaxies in the Universe, thereby revealing when cosmic dawn
breaks.Comment: 25 pages, 16 figures, 2 tables. Updated to published version in MNRA
JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models
We report the discovery of Mothra, an extremely magnified monster star,
likely a binary system of two supergiant stars, in one of the strongly lensed
galaxies behind the galaxy cluster MACS0416. The star is in a galaxy with
spectroscopic redshift in a portion of the galaxy that is parsecs
away from the cluster caustic. The binary star is observed only on the side of
the critical curve with negative parity but has been detectable for at least
eight years, implying the presence of a small lensing perturber.
Microlenses alone cannot explain the earlier observations of this object made
with the Hubble Space Telescope. A larger perturber with a mass of at least
\,\Msun\ offers a more satisfactory explanation. Based on the lack of
perturbation on other nearby sources in the same arc, the maximum mass of the
perturber is \,\Msun, making it the smallest substructure
constrained by lensing above redshift 0.3. The existence of this millilens is
fully consistent with the expectations from the standard cold dark matter
model. On the other hand, the existence of such small substructure in a cluster
environment has implications for other dark matter models. In particular, warm
dark matter models with particle masses below 8.7\,keV are excluded by our
observations. Similarly, axion dark matter models are consistent with the
observations only if the axion mass is in the range .Comment: 26 pages and 27 figure
SKYSURF: Constraints on Zodiacal Light and Extragalactic Background Light through Panchromatic HST All-Sky Surface-Brightness Measurements: I. Survey Overview and Methods
We give an overview and describe the rationale, methods, and testing of the
Hubble Space Telescope (HST) Archival Legacy project "SKYSURF." SKYSURF uses
HST's unique capability as an absolute photometer to measure the ~0.2-1.7
m sky surface brightness (SB) from 249,861 WFPC2, ACS, and WFC3 exposures
in ~1400 independent HST fields. SKYSURF's panchromatic dataset is designed to
constrain the discrete and diffuse UV to near-IR sky components: Zodiacal Light
(ZL; inner Solar System), Kuiper Belt Objects (KBOs; outer Solar System),
Diffuse Galactic Light (DGL), and the discrete plus diffuse Extragalactic
Background Light (EBL). We outline SKYSURF's methods to: (1) measure sky-SB
levels between its detected objects; (2) measure the integrated discrete EBL,
most of which comes from AB17-22 mag galaxies; and (3) estimate how
much diffuse light may exist in addition to the extrapolated discrete galaxy
counts. Simulations of HST WFC3/IR images with known sky-values and gradients,
realistic cosmic ray (CR) distributions, and star plus galaxy counts were
processed with nine different algorithms to measure the "Lowest Estimated
Sky-SB" (LES) in each image between the discrete objects. The best algorithms
recover the inserted LES values within 0.2% when there are no image gradients,
and within 0.2-0.4% when there are 5-10% gradients. SKYSURF requires
non-standard re-processing of these HST images that includes restoring the
lowest sky-level from each visit into each drizzled image. We provide a proof
of concept of our methods from the WFC3/IR F125W images, where any residual
diffuse light that HST sees in excess of the Kelsall et al. (1998) Zodiacal
model prediction does not depend on the total object flux that each image
contains. This enables us to present our first SKYSURF results on diffuse light
in Carleton et al. (2022).Comment: Accepted to AJ; see accompanying paper Carleton et al. 2022:
arXiv:2205.06347. Comments welcome
A search for high-redshift direct collapse black hole candidates in the PEARLS north ecliptic pole field
Direct-collapse black holes (DCBHs) of mass - that
form in HI-cooling halos in the early Universe are promising progenitors of the
supermassive black holes that fuel the observed quasars. Efficient accretion of the surrounding gas onto such DCBH
seeds may render them sufficiently bright for detection with the James Webb
Space Telescope (JWST) up to . Additionally, the very steep and
red spectral slope predicted across the -5 m wavelength range
of the JWST/NIRSpec instrument during their initial growth phase should make
them photometrically identifiable up to very high redshifts. Here, we present a
search for such DCBH candidates across the 34 arcmin in the first two
spokes of the JWST cycle-1 "Prime Extragalactic Areas for Reionization and
Lensing Science" (PEARLS) survey of the North Ecliptic Pole Time Domain Field
(NEP), covering 8 NIRCam filters down to a maximum depth of 29 AB mag.
We identify three objects with spectral energy distributions consistent with
the Pacucci et al. (2016) DCBH models. However, we also note that even with
data in 8 NIRCam filters, objects of this type remain degenerate with dusty
galaxies and obscured active galactic nuclei over a wide range of redshifts.
Follow-up spectroscopy would be required to pin down the nature of these
objects, and two of our DCBH candidates are sufficiently bright to make this
practical. Based on our sample of DCBH candidates and assumptions on the
typical duration of the DCBH steep-slope state, we set a conservative upper
limit of comoving Mpc (cMpc) on the
comoving density of host halos capable of hosting DCBHs with spectral energy
distributions similar to the Pacucci et al. (2016) models at -13.Comment: 10 pages, 6 figures, 1 table, submitted to A&
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