586 research outputs found
Mechanosensitive Self-Replication Driven by Self-Organization
Self-replicating molecules are likely to have played an important role in the origin of life, and a small number of fully synthetic self-replicators have already been described. Yet it remains an open question which factors most effectively bias the replication toward the far-from-equilibrium distributions characterizing even simple organisms. We report here two self-replicating peptide-derived macrocycles that emerge from a small dynamic combinatorial library and compete for a common feedstock. Replication is driven by nanostructure formation, resulting from the assembly of the peptides into fibers held together by β sheets. Which of the two replicators becomes dominant is influenced by whether the sample is shaken or stirred. These results establish that mechanical forces can act as a selection pressure in the competition between replicators and can determine the outcome of a covalent synthesis.
The evolution of the galaxy stellar mass function over the last twelve billion years from a combination of ground-based and HST surveys
We present a new determination of the galaxy stellar mass function (GSMF)
over the redshift interval , derived from a combination
of ground-based and Hubble Space Telescope (HST) imaging surveys. Based on a
near-IR selected galaxy sample selected over a raw survey area of 3 deg
and spanning dex in stellar mass, we fit the GSMF with both single and
double Schechter functions, carefully accounting for Eddington bias to derive
both observed and intrinsic parameter values. We find that a double Schechter
function is a better fit to the GSMF at all redshifts, although the single and
double Schechter function fits are statistically indistinguishable by .
We find no evidence for significant evolution in , with the
intrinsic value consistent with over the full redshift range. Overall, our
determination of the GSMF is in good agreement with recent simulation results,
although differences persist at the highest stellar masses. Splitting our
sample according to location on the UVJ plane, we find that the star-forming
GSMF can be adequately described by a single Schechter function over the full
redshift range, and has not evolved significantly since . In
contrast, both the normalization and functional form of the passive GSMF
evolves dramatically with redshift, switching from a single to a double
Schechter function at . As a result, we find that while passive
galaxies dominate the integrated stellar-mass density at , they
only contribute per cent by . Finally, we provide a
simple parameterization that provides an accurate estimate of the GSMF, both
observed and intrinsic, at any redshift within the range .Comment: 24 pages, 16 figures, accepted for publication in MNRA
The VANDELS survey: Dust attenuation in star-forming galaxies at
We present the results of a new study of dust attenuation at redshifts based on a sample of star-forming galaxies from the VANDELS
spectroscopic survey. Motivated by results from the First Billion Years (FiBY)
simulation project, we argue that the intrinsic spectral energy distributions
(SEDs) of star-forming galaxies at these redshifts have a self-similar shape
across the mass range log probed by
our sample. Using FiBY data, we construct a set of intrinsic SED templates
which incorporate both detailed star formation and chemical abundance
histories, and a variety of stellar population synthesis (SPS) model
assumptions. With this set of intrinsic SEDs, we present a novel approach for
directly recovering the shape and normalization of the dust attenuation curve.
We find, across all of the intrinsic templates considered, that the average
attenuation curve for star-forming galaxies at is similar in shape
to the commonly-adopted Calzetti starburst law, with an average
total-to-selective attenuation ratio of . We show that the
optical attenuation () versus stellar mass () relation
predicted using our method is consistent with recent ALMA observations of
galaxies at in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field}
(HUDF), as well as empirical relations predicted by a
Calzetti-like law. Our results, combined with other literature data, suggest
that the relation does not evolve over the redshift range
, at least for galaxies with log.
Finally, we present tentative evidence which suggests that the attenuation
curve may become steeper at log.Comment: 16 pages, 12 figures, accepted for publication in MNRA
The VANDELS survey: Dust attenuation in star-forming galaxies at
We present the results of a new study of dust attenuation at redshifts based on a sample of star-forming galaxies from the VANDELS
spectroscopic survey. Motivated by results from the First Billion Years (FiBY)
simulation project, we argue that the intrinsic spectral energy distributions
(SEDs) of star-forming galaxies at these redshifts have a self-similar shape
across the mass range log probed by
our sample. Using FiBY data, we construct a set of intrinsic SED templates
which incorporate both detailed star formation and chemical abundance
histories, and a variety of stellar population synthesis (SPS) model
assumptions. With this set of intrinsic SEDs, we present a novel approach for
directly recovering the shape and normalization of the dust attenuation curve.
We find, across all of the intrinsic templates considered, that the average
attenuation curve for star-forming galaxies at is similar in shape
to the commonly-adopted Calzetti starburst law, with an average
total-to-selective attenuation ratio of . We show that the
optical attenuation () versus stellar mass () relation
predicted using our method is consistent with recent ALMA observations of
galaxies at in the \emph{Hubble} \emph{Ultra} \emph{Deep} \emph{Field}
(HUDF), as well as empirical relations predicted by a
Calzetti-like law. Our results, combined with other literature data, suggest
that the relation does not evolve over the redshift range
, at least for galaxies with log.
Finally, we present tentative evidence which suggests that the attenuation
curve may become steeper at log.Comment: 16 pages, 12 figures, accepted for publication in MNRA
Maximising the power of deep extragalactic imaging surveys with the James Webb Space Telescope
We present a new analysis of the potential power of deep, near-infrared,
imaging surveys with the James Webb Space Telescope (JWST) to improve our
knowledge of galaxy evolution. In this work we properly simulate what can be
achieved with realistic survey strategies, and utilise rigorous signal:noise
calculations to calculate the resulting posterior constraints on the physical
properties of galaxies. We explore a broad range of assumed input galaxy types
(>20,000 models, including extremely dusty objects) across a wide redshift
range (out to z~12), while at the same time considering a realistic mix of
galaxy properties based on our current knowledge of the evolving population (as
quantified through the Empirical Galaxy Generator: EGG). While our main focus
is on imaging surveys with NIRCam, spanning lambda(obs) = 0.6-5.0 microns, an
important goal of this work is to quantify the impact/added-value of: i)
parallel imaging observations with MIRI at longer wavelengths, and ii) deeper
supporting optical/UV imaging with HST (potentially prior to JWST launch) in
maximising the power and robustness of a major extragalactic NIRCam survey. We
show that MIRI parallel 7.7-micron imaging is of most value for better
constraining the redshifts and stellar masses of the dustiest (A_V > 3)
galaxies, while deep B-band imaging (reaching~28.5 AB mag) with ACS on HST is
vital for determining the redshifts of the large numbers of faint/low-mass, z <
5 galaxies that will be detected in a deep JWST NIRCam survey.Comment: 19 Pages, 11 Figures, Submitted to MNRA
The vandels survey: The star-formation histories of massive quiescent galaxies at 1.0 < z < 1.3
We present a Bayesian full-spectral-fitting analysis of 75 massive (â Mâ>1010.3Mââ ) UVJ-selected galaxies at redshifts of 1.0 1011Mâ
On the simultaneous modelling of dust and stellar populations for interpretation of galaxy properties
The physical properties of galaxies are encoded within their spectral energy distribution and require comparison with models to be extracted. These models must contain a synthetic stellar population and, where infrared data are to be used, also consider prescriptions for energy reprocessing and re-emission by dust. While many such models have been constructed, there are few analyses of the impact of stellar population model choice on derived dust parameters, or vice versa. Here, we apply a simple framework to compare the impact of these choices, combining three commonly used stellar population synthesis models and three dust emission models. We compare fits to the ultraviolet to far-infrared spectral energy distributions of a validation sample of infrared-luminous galaxies. We find that including different physics, such as binary stellar evolution, in the stellar synthesis model can introduce biases and uncertainties in the derived parameters of the dust and stellar emission models, largely due to differences in the far-ultraviolet emission available for reprocessing. This may help to reconcile the discrepancy between the cosmic star formation rate and stellar mass density histories. Notably the inclusion of a dusty stellar birth cloud component in the dust emission model provides more flexibility in accommodating the stellar population model, as its re-emission is highly sensitive to the ultraviolet radiation field spectrum and density. Binary populations favour a longer birth cloud dissipation time-scale than is found when assuming only single star population synthesis
The VANDELS survey: A strong correlation between Ly equivalent width and stellar metallicity at
We present the results of a new study investigating the relationship between
observed Ly equivalent width ((Ly)) and the
metallicity of the ionizing stellar population () for a sample of
star-forming galaxies at drawn from the VANDELS survey.
Dividing our sample into quartiles of rest-frame (Ly)
across the range -58 \unicode{xC5} \lesssim (Ly)
\lesssim 110 \unicode{xC5} we determine from full spectral
fitting of composite far-ultraviolet (FUV) spectra and find a clear
anti-correlation between (Ly) and . Our results
indicate that decreases by a factor between the lowest
(Ly) quartile
((Ly)\rangle=-18\unicode{xC5}) and the highest
(Ly) quartile
((Ly)\rangle=24\unicode{xC5}). Similarly,
galaxies typically defined as Lyman Alpha Emitters (LAEs;
(Ly) >20\unicode{xC5}) are, on average, metal poor with
respect to the non-LAE galaxy population ((Ly)
\leq20\unicode{xC5}) with
. Finally, based on the best-fitting stellar models, we
estimate that the increasing strength of the stellar ionizing spectrum towards
lower is responsible for of the observed variation
in (Ly) across our sample, with the remaining contribution
() being due to a decrease in the HI/dust covering fractions in
low galaxies.Comment: 10 pages, 6 figures, MNRAS accepte
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