384 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 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
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
The connection between stellar mass, age and quenching timescale in massive quiescent galaxies at
We present a spectro-photometric study of a mass-complete sample of quiescent
galaxies at with
drawn from the
VANDELS survey, exploring the relationship between stellar mass, age and
star-formation history. Within our sample of 114 galaxies, we derive a
stellar-mass vs stellar-age relation with a slope of Gyr
per decade in stellar mass. When combined with recent literature results, we
find evidence that the slope of this relation remains consistent over the
redshift interval . The galaxies within the VANDELS quiescent display a
wide range of star-formation histories, with a mean star-formation timescale of
Gyr and a mean quenching timescale of Gyr. We also
find a large scatter in the quenching timescales of the VANDELS quiescent
galaxies, in agreement with previous evidence that galaxies at cease
star formation via multiple mechanisms. We then focus on the oldest galaxies in
our sample, finding that the number density of galaxies that quenched before with stellar masses is . Although
uncertain, this estimate is in good agreement with the latest observational
results at , tentatively suggesting that neither rejuvenation nor merger
events are playing a major role in the evolution of the oldest massive
quiescent galaxies within the redshift interval .Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
A combined VANDELS and LEGA-C study: the evolution of quiescent galaxy size, stellar mass, and age from z = 0.6 to z = 1.3
We study the relationships between stellar mass, size and age within the
quiescent population, using two mass-complete spectroscopic samples with
, taken from VANDELS at
, and LEGA-C at . Using robust D4000 values, we
demonstrate that the well-known 'downsizing' signature is already in place by
, with D4000 increasing by across a 1
dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate
the evolution of the quiescent galaxy stellar mass-size relation from
to . We find the median size increases by a factor of
at , and
see tentative evidence for flattening of the relation, finding slopes of
and for VANDELS and LEGA-C
respectively. We finally split our sample into galaxies above and below our
fitted mass-size relations, to investigate how size and D4000 correlate.
For LEGA-C, we see a clear difference, with larger galaxies found to have
smaller D4000 at fixed stellar mass. Due to the faintness and smaller
numbers of the VANDELS sample, we cannot confirm whether a similar relation
exists at . We consider whether differences in stellar age or
metallicity are most likely to drive this size-D4000 relation, finding
that any metallicity differences are unlikely to fully explain the observed
offset, meaning smaller galaxies must be older than their larger counterparts.
We find the observed evolution in size, mass and D4000 across the
Gyr from to can be explained by a simple toy
model in which VANDELS galaxies evolve passively, whilst experiencing a series
of minor mergers.Comment: 14 pages, 9 figures, submitted to MNRA
A combined VANDELS and LEGA-C study: the evolution of quiescent galaxy size, stellar mass, and age from z = 0.6 to z = 1.3
We study the relationships between stellar mass, size, and age within the quiescent population, using two mass-complete spectroscopic samples with log10(M⊙/M⊙) > 10.3, taken from VANDELS at 1.0 < z < 1.3, and LEGA-C at 0.6 < z < 0.8. Using robust Dn4000 values, we demonstrate that the well-known 'downsizing' signature is already in place by z 1.1, with Dn4000 increasing by 0.1 across a 1 dex mass interval for both VANDELS and LEGA-C. We then proceed to investigate the evolution of the quiescent galaxy stellar mass-size relation from z -1.1 to z -0.7. We find the median size increases by a factor of 1.9 ± 0.1 at log10(M⊙/M⊙) = 10.5, and see tentative evidence for flattening of the relation, finding slopes of α = 0.72 ± 0.06 and α =\0.56\pm 0.04 for VANDELS and LEGA-C, respectively. We finally split our sample into galaxies above and below our fitted mass-size relations, to investigate how size and Dn4000 correlate. For LEGA-C, we see a clear difference, with larger galaxies found to have smaller Dn4000 at fixed stellar mass. Due to the faintness and smaller numbers of the VANDELS sample, we cannot confirm whether a similar relation exists at z -1.1. We consider whether differences in stellar age or metallicity are most likely to drive this size-Dn4000 relation, finding that any metallicity differences are unlikely to fully explain the observed offset, meaning smaller galaxies must be older than their larger counterparts. We find the observed evolution in size, mass, and Dn4000 across the -2 Gyr from z ∼1.1 to z ∼0.7 can be explained by a simple toy model in which VANDELS galaxies evolve passively whilst experiencing a series of minor mergers
Timing the earliest quenching events with a robust sample of massive quiescent galaxies at 2 <z <5
We present a sample of 151 massive ()
quiescent galaxies at , based on a sophisticated Bayesian spectral
energy distribution fitting analysis of the CANDELS UDS and GOODS-South fields.
Our sample includes a robust sub-sample of 61 objects for which we confidently
exclude low-redshift and star-forming solutions. We identify 10 robust objects
at , of which 2 are at . We report formation redshifts, demonstrating
that the oldest objects formed at , however individual ages from our
photometric data have significant uncertainties, typically Gyr. We
demonstrate that the UVJ colours of the quiescent population evolve with
redshift at , becoming bluer and more similar to post-starburst galaxies
at lower redshift. Based upon this we construct a model for the time-evolution
of quiescent galaxy UVJ colours, concluding that the oldest objects are
consistent with forming the bulk of their stellar mass at and
quenching at . We report spectroscopic redshifts for two of our objects
at and , which exhibit extremely weak Ly emission in
ultra-deep VANDELS spectra. We calculate star-formation rates based on these
line fluxes, finding that these galaxies are consistent with our quiescent
selection criteria, provided their Ly escape fractions are and
per cent respectively. We finally report that our highest-redshift robust
object exhibits a continuum break at A in a spectrum from
VUDS, consistent with our photometric redshift of
. If confirmed as quiescent this object
would be the highest-redshift known quiescent galaxy. To obtain stronger
constraints on the times of the earliest quenching events, high-SNR
spectroscopy must be extended to quiescent objects.Comment: 14 pages, 8 figures, MNRAS accepte
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