160 research outputs found
On the evolution of clustering of 24um-selected galaxies
This paper investigates the clustering properties of a complete sample of
1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping
region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the
two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z
sample) as it is in these regions were we expect the mid-IR population to be
dominated by intense dust-enshrouded activity such as star formation and black
hole accretion. Investigations of the angular correlation function produce a
correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the
low-z one. Comparisons with physical models reveal that the high-z sources are
exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable
to those which locally host groups-to-clusters of galaxies, and are very common
within such (rare) structures. Conversely, lower-z galaxies are found to reside
in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems.
While recent studies have determined a strong evolution of the 24um luminosity
function between z~2 and z~0, they cannot provide information on the physical
nature of such an evolution. Our clustering results instead indicate that this
is due to the presence of different populations of objects inhabiting different
structures, as active systems at z<~1.5 are found to be exclusively associated
with low-mass galaxies, while very massive sources appear to have concluded
their active phase before this epoch. Finally, we note that the small-scale
clustering data seem to require steep profiles for the distribution of galaxies
within their halos. This is suggestive of close encounters and/or mergers which
could strongly favour both AGN and star-formation activity.Comment: 13 pages, 8 figures, to appear in MNRA
The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years
We combine deep UBVRIzJK photometry from the Multiwavelength Survey by
Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a
large-scale study of the rest-frame ultraviolet (UV) properties of 674
high-redshift (0.5<z<1) early-type galaxies, drawn from the Extended Chandra
Deep Field South (E-CDFS). Galaxy morphologies are determined through visual
inspection of Hubble Space Telescope (HST) images taken from the GEMS survey.
We harness the sensitivity of the UV to young (<1 Gyr old) stars to quantify
the recent star formation history of early-type galaxies across a range of
luminosities (-23.5 < M(V) < -18). Comparisons to simple stellar populations
forming at high redshift indicate that only ~1.1 percent of early-types in this
sample are consistent with purely passive ageing since z=2. Parametrising the
recent star formation (RSF) in terms of the mass fraction of stars less than a
Gyr old, we find that the early-type population as a whole shows a typical RSF
between 5 and 13% in the redshift range 0.5<z<1. Early-types on the UV red
sequence show RSF values less than 5% while the reddest early-types are
virtually quiescent with RSF values of ~1%. We find compelling evidence that
early-types of all luminosities form stars over the lifetime of the Universe,
although the bulk of their star formation is already complete at high redshift.
This tail-end of star formation is measurable and not negligible, with luminous
(-23<M(V)<-20.5) early-types potentially forming 10-15% of their mass since
z=1, with their less luminous (M(V)>-20.5) counterparts potentially forming
30-60 percent of their mass in the same redshift range. (abridged)Comment: Submitted to MNRA
Newborn spheroids at high redshift: when and how did the dominant, old stars in today's massive galaxies form?
We study ~330 massive (M* > 10^9.5 MSun), newborn spheroidal galaxies (SGs)
around the epoch of peak star formation (1<z<3), to explore the high-redshift
origin of SGs and gain insight into when and how the old stellar populations
that dominate today's Universe formed. The sample is drawn from the HST/WFC3
Early-Release Science programme, which provides deep 10-filter (0.2 - 1.7
micron) HST imaging over a third of the GOODS-South field. We find that the
star formation episodes that built the SGs likely peaked in the redshift range
2<z<5 (with a median of z~3) and have decay timescales shorter than ~1.5 Gyr.
Starburst timescales and ages show no trend with stellar mass in the range
10^9.5 < M* < 10^10.5 MSun. However, the timescales show increased scatter
towards lower values ( 10^10.5 MSun, and an age trend becomes
evident in this mass regime: SGs with M* > 10^11.5 MSun are ~2 Gyrs older than
their counterparts with M* < 10^10.5 MSun. Nevertheless, a smooth downsizing
trend with galaxy mass is not observed, and the large scatter in starburst ages
indicate that SGs are not a particularly coeval population. Around half of the
blue SGs appear not to drive their star formation via major mergers, and those
that have experienced a recent major merger, show only modest enhancements
(~40%) in their specific star formation rates. Our empirical study indicates
that processes other than major mergers (e.g. violent disk instability driven
by cold streams and/or minor mergers) likely play a dominant role in building
SGs, and creating a significant fraction of the old stellar populations that
dominate today's Universe.Comment: MNRAS in pres
A highly obscured and strongly clustered galaxy population discovered with the Spitzer Space Telescope
The ~800 optically unseen (R>25.5) 24mum-selected sources in the complete
Spitzer First Look Survey sample (Fadda et al. 2006) with F[24mum]>0.35 mJy are
found to be very strongly clustered. If, as indicated by several lines of
circumstantial evidence, they are ultraluminous far-IR galaxies at z ~
[1.6-2.7], the amplitude of their spatial correlation function is very high.
The associated comoving clustering length is estimated to be
r_0=14.0_{-2.4}^{+2.1} Mpc, value which puts these sources amongst the most
strongly clustered populations of our known universe. Their 8mum-24mum colours
suggest that the AGN contribution dominates above F[24mum] ~ 0.8 mJy,
consistent with earlier analyses. The properties of these objects (number
counts, redshift distribution, clustering amplitude) are fully consistent with
those of proto-spheroidal galaxies in the process of forming most of their
stars and of growing their active nucleus, as described by the Granato et al.
(2004) model. In particular, the inferred space density of such galaxies at z ~
2 is much higher than what expected from most semi-analytic models. Matches of
the observed projected correlation function w(\theta) with models derived
within the so-called Halo Occupation Scenario show that these sources have to
be hosted by haloes more massive than ~10^{13.4} M_\odot. This value is
significantly higher than that for the typical galactic haloes hosting massive
elliptical galaxies, suggesting a duration of the starburst phase of massive
high-redshift dusty galaxies of T_B ~ 0.5 Gyr.Comment: 14 pages, 10 figures, minor revisions, to appear on MNRA
A metacognitive model of procrastination
BACKGROUND:
procrastination refers to the delay or postponement of task or decision-making initiation or completion and is often conceptualised as a failure of self-regulation. Recent research has suggested that metacognitions play a role in procrastination and that unintentional procrastination (UP), as opposed to intentional procrastination (IP), may be the most problematic form of this behaviour. We aimed to test a metacognitive model of procrastination that was grounded in the Self-Regulatory Executive Function model.
METHODS:
a convenience sample of 400 participants were recruited and completed (at least partially) a battery of online questionnaires that measured IP and UP, metacognitions about procrastination, depression, and Cognitive Attentional Syndrome (CAS) configurations. Initially, we tested series of hypotheses to establish the relationships between the experimental variables and to test whether CAS configurations would independently predict UP when controlling for age, depression, IP, metacognitions about procrastination, and whether an individual reported that they had been diagnosed with a psychiatric disorder.
RESULTS:
CAS configurations, depression, and metacognitions independently predicted UP. Additionally, path analysis revealed that the study data was an excellent fit to the proposed metacognitive model of procrastination.
LIMITATIONS:
the study is cross-sectional.
CONCLUSIONS:
the metacognitive model of procrastination presented in this paper can be used to generate novel interventions to treat this problematic behaviour
Environmental DNA metabarcoding for fish diversity assessment in a macrotidal estuary: A comparison with established fish survey methods
Fishes are a dominant component of the macrofauna in estuaries and are important for assessing the health of these threatened ecosystems. Several studies have applied environmental DNA (eDNA) metabarcoding to assess the biodiversity of fishes in estuaries. However, none have combined measurement of physicochemical variables with a spatially extensive sampling design across the full salinity gradient. This study aimed to compare spatial fish assemblage composition detected via eDNA metabarcoding of surface water samples with conventional fishing gear surveys in a macrotidal estuary (river Dee, North Wales, UK). In addition, eDNA assemblage composition across seasons was investigated. In autumn 2018, triplicate eDNA samples were taken at 13 stations in a spatially systematic design alongside seine, fyke and beam trawl sampling. In summer 2019, eDNA samples from eight of the 13 original stations were collected again in the upper and lower estuary. DNA was extracted from samples and subjected to metabarcoding analysis using an established assay targeting teleost fishes. The key findings were that in autumn, eDNA detected 17 of the 26 (71%) species caught by fishing gears, which included the most abundant species. Overall, eDNA detected a greater species richness, per 30 samples, than seine or fyke nets (but not beam trawling). Additionally, there was a clear correlation between salinity and assemblage composition, which was consistent across seasons. Overall, the study indicates that eDNA metabarcoding could enhance existing fish sampling methods, by generating a more comprehensive picture of estuarine fish biodiversity and providing additional information for ecological inference and management actions
Thermodynamic evolution of the cosmological baryonic gas : II. Galaxy formation
The problem of galaxy formation and its dependence on thermodynamic
properties is addressed by using Eulerian hydrodynamic numerical simulations of
large scale structure formation. Global galaxy properties are explored in
simulations including gravitation, shock heating and cooling processes, and
following self-consistently the chemical evolution of a primordial composition
hydrogen-helium plasma without assuming collisional ionization equilibrium. The
galaxy formation model is mainly based on the identification of converging
dense cold gas regions. We show that the evolution at low redshift of the
observed cosmic star formation rate density is reproduced, and that the
galaxy-like object mass function is dominated by low-mass objects. The galaxy
mass functions are well described by a two power-law Schechter function whose
parameters are in good agreement with observational fits of the galaxy
luminosity function. The high-mass end of the galaxy mass function includes
objects formed at early epochs and residing in high-mass dark matter halos
whereas the low-mass end includes galaxies formed at later epochs and active in
their ``stellar'' mass formation. Finally, the influence of two other physical
processes, photoionization and non-equipartition processes between electrons,
ions and neutrals of the cosmological plasma is discussed and the modifications
on galaxy formation are examined.Comment: 17 pages, 19 figures, 6 tables. Accepted for publication in A&
Cosmic evolution of the galaxy mass and luminosity functions by morphological type from multi-wavelength data in the CDF-South
We constrain the evolution of the galaxy mass and luminosity functions from
the analysis of (public) multi-wavelength data in the Chandra Deep Field South
(CDFS) area, obtained from the GOODS and other projects, and including very
deep high-resolution imaging by HST/ACS. Our reference catalogue of faint
high-redshift galaxies, which we have thoroughly tested for completeness and
reliability, comes from a deep (S(3.6micron)>1 microJy) image by IRAC on the
Spitzer Observatory. These imaging data in the field are complemented with
extensive optical spectroscopy by the ESO VLT/FORS2 and VIMOS spectrographs,
while deep K-band VLT/ISAAC imaging is also used to derive further
complementary statistical constraints and to assist the source identification
and SED analysis. We have selected a highly reliable IRAC 3.6micron sub-sample
of 1478 galaxies with S(3.6)>10microJy, 47% of which have spectroscopic
redshift, while for the remaining objects both COMBO-17 and Hyperz are used to
estimate the photometric redshift. This very extensive dataset is exploited to
assess evolutionary effects in the galaxy luminosity and stellar mass
functions, while luminosity/density evolution is further constrained with the
number counts and redshift distributions. The deep ACS imaging allows us to
differentiate these evolutionary paths by morphological type, which our
simulations show to be reliable at least up to z=1.5 for the two main early-
(E/S0) and late-type (Sp/Irr) classes. These data, as well as our direct
estimate of the stellar mass function above M=10^(10)M_sun for the spheroidal
subclass, consistently evidence a progressive dearth of such objects to occur
starting at z=0.7, paralleled by an increase in luminosity. (abridged)Comment: paper accepted for publication in A&
The Gene Ontology resource: enriching a GOld mine
The Gene Ontology Consortium (GOC) provides the most comprehensive resource currently available for computable knowledge regarding the functions of genes and gene products. Here, we report the advances of the consortium over the past two years. The new GO-CAM annotation framework was notably improved, and we formalized the model with a computational schema to check and validate the rapidly increasing repository of 2838 GO-CAMs. In addition, we describe the impacts of several collaborations to refine GO and report a 10% increase in the number of GO annotations, a 25% increase in annotated gene products, and over 9,400 new scientific articles annotated. As the project matures, we continue our efforts to review older annotations in light of newer findings, and, to maintain consistency with other ontologies. As a result, 20 000 annotations derived from experimental data were reviewed, corresponding to 2.5% of experimental GO annotations. The website (http://geneontology.org) was redesigned for quick access to documentation, downloads and tools. To maintain an accurate resource and support traceability and reproducibility, we have made available a historical archive covering the past 15 years of GO data with a consistent format and file structure for both the ontology and annotations
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