149 research outputs found
Hierarchical models of high redshift galaxies with thermally pulsing asymptotic giant branch stars: comparison with observations
In a recent paper we presented the first semi-analytic model of galaxy
formation in which the Thermally-Pulsing Asymptotic Giant Branch phase of
stellar evolution has been fully implemented. Here we address the comparison
with observations, and show how the TP-AGB recipe affects the performance of
the model in reproducing the colours and near-IR luminosities of high-redshift
galaxies. We find that the semi-analytic model with the TP-AGB better matches
the colour-magnitude and colour-colour relations at z ~ 2, both for
nearly-passive and for star-forming galaxies. The model with TP-AGB produces
star-forming galaxies with red V-K colours, thus revising the unique
interpretation of high-redshift red objects as 'red & dead'. We also show that
without the TP-AGB the semi-analytic model fails at reproducing the observed
colours, a situation that cannot be corrected by dust reddening. We also
explore the effect of nebular emission on the predicted colour-magnitude
relation of star-forming galaxies, to conclude that it does not play a
significant role in reddening their colours, at least in the range of
star-formation rates covered by the model. Finally, the rest-frame K-band
luminosity function at z ~ 2.5 is more luminous by almost 1 magnitude. This
indicates that the AGN feedback recipe that is adopted to regulate the
high-mass end of the luminosity function should be sophisticated to take the
effect of the stellar populations into account at high redshifts.Comment: 10 pages, 8 figures; effects of nebular emission included; accepted
for publication on MNRA
The impact of TP-AGB stars on hierarchical galaxy formation models
The spectro-photometric properties of galaxies in galaxy formation models are
obtained by combining the predicted history of star formation and mass
accretion with the physics of stellar evolution through stellar population
models. In the recent literature, significant differences have emerged
regarding the implementation of the Thermally-Pulsing Asymptotic Giant Branch
phase of stellar evolution. The emission in the TP-AGB phase dominates the
bolometric and near-IR spectrum of intermediate-age (~1 Gyr) stellar
populations, hence it is crucial for the correct modeling of the galaxy
luminosities and colours. In this paper for the first time, we incorporate a
full prescription of the TP-AGB phase in a semi-analytic model of galaxy
formation. We find that the inclusion of the TP-AGB in the model spectra
dramatically alters the predicted colour-magnitude relation and its evolution
with redshift. When the TP-AGB phase is active, the rest-frame V-K galaxy
colours are redder by almost 2 magnitudes in the redshift range z~2-3 and by 1
magnitude at z~1. Very red colours are produced in disk galaxies, so that the
V-K colour distributions of disk and spheroids are virtually undistinguishable
at low redshifts. We also find that the galaxy K-band emission is more than 1
magnitude higher in the range z~1-3. This may alleviate the difficulties met by
the hierarchical clustering scenario in predicting the red galaxy population at
high redshifts. The comparison between simulations and observations have to be
revisited in the light of our results.Comment: 6 pages, 4 figures. Accepted for publication on MNRAS Letter
Towards an understanding of the rapid decline of the cosmic star formation rate
We present a first analysis of deep 24 micron observations with the Spitzer
Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice,
0.65<z<0.75. We combine the infrared data with redshifts, rest-frame
luminosities, and colors from COMBO-17, and with morphologies from Hubble Space
Telescope images collected by the GEMS and GOODS projects. To characterize the
decline in star-formation rate (SFR) since z~0.7, we estimate the total thermal
infrared (IR) luminosities, SFRs, and stellar masses for the galaxies in this
sample. At z~0.7, nearly 40% of intermediate and high-mass galaxies (with
stellar masses >2x10^10 solar masses) are undergoing a period of intense star
formation above their past-averaged SFR. In contrast, less than 1% of
equally-massive galaxies in the local universe have similarly intense star
formation activity. Morphologically-undisturbed galaxies dominate the total
infrared luminosity density and SFR density: at z~0.7, more than half of the
intensely star-forming galaxies have spiral morphologies, whereas less than
\~30% are strongly interacting. Thus, a decline in major-merger rate is not the
underlying cause of the rapid decline in cosmic SFR since z~0.7. Physical
properties that do not strongly affect galaxy morphology - for example, gas
consumption and weak interactions with small satellite galaxies - appear to be
responsible.Comment: To appear in the Astrophysical Journal 1 June 2005. 14 pages with 8
embedded figure
Virotyping and genetic antimicrobial susceptibility testing of porcine ETEC/STEC strains and associated plasmid types
IntroductionEnterotoxigenic Escherichia coli (ETEC) infections are the most common cause of secretory diarrhea in suckling and post-weaning piglets. For the latter, Shiga toxin-producing Escherichia coli (STEC) also cause edema disease. This pathogen leads to significant economic losses. ETEC/STEC strains can be distinguished from general E. coli by the presence of different host colonization factors (e.g., F4 and F18 fimbriae) and various toxins (e.g., LT, Stx2e, STa, STb, EAST-1). Increased resistance against a wide variety of antimicrobial drugs, such as paromomycin, trimethoprim, and tetracyclines, has been observed. Nowadays, diagnosing an ETEC/STEC infection requires culture-dependent antimicrobial susceptibility testing (AST) and multiplex PCRs, which are costly and time-consuming.MethodsHere, nanopore sequencing was used on 94 field isolates to assess the predictive power, using the meta R package to determine sensitivity and specificity and associated credibility intervals of genotypes associated with virulence and AMR.ResultsGenetic markers associated with resistance for amoxicillin (plasmid-encoded TEM genes), cephalosporins (ampC promoter mutations), colistin (mcr genes), aminoglycosides (aac(3) and aph(3) genes), florfenicol (floR), tetracyclines (tet genes), and trimethoprim-sulfa (dfrA genes) could explain most acquired resistance phenotypes. Most of the genes were plasmid-encoded, of which some collocated on a multi-resistance plasmid (12 genes against 4 antimicrobial classes). For fluoroquinolones, AMR was addressed by point mutations within the ParC and GyrA proteins and the qnrS1 gene. In addition, long-read data allowed to study the genetic landscape of virulence- and AMR-carrying plasmids, highlighting a complex interplay of multi-replicon plasmids with varying host ranges.ConclusionOur results showed promising sensitivity and specificity for the detection of all common virulence factors and most resistance genotypes. The use of the identified genetic hallmarks will contribute to the simultaneous identification, pathotyping, and genetic AST within a single diagnostic test. This will revolutionize future quicker and more cost-efficient (meta)genomics-driven diagnostics in veterinary medicine and contribute to epidemiological studies, monitoring, tailored vaccination, and management
Mid-Infrared Selection of Active Galaxies
Mid-infrared photometry provides a robust technique for identifying active
galaxies. While the ultraviolet to mid-infrared continuum of normal galaxies is
dominated by the composite stellar black body curve and peaks at approximately
1.6 microns, the ultraviolet to mid-infrared continuum of active galaxies is
dominated by a power law. Consequently, with sufficient wavelength baseline,
one can easily distinguish AGN from stellar populations. Mirroring the tendency
of AGN to be bluer than galaxies in the ultraviolet, where galaxies (and stars)
sample the blue, rising portion of stellar spectra, AGN tend to be redder than
galaxies in the mid-infrared, where galaxies sample the red, falling portion of
the stellar spectra. We report on Spitzer Space Telescope mid-infrared colors,
derived from the IRAC Shallow Survey, of nearly 10,000 spectroscopically
identified sources from the AGN and Galaxy Evolution Survey. Based on this
spectroscopic sample, we find that simple mid-infrared color criteria provide
remarkably robust separation of active galaxies from normal galaxies and
Galactic stars, with over 80% completeness and less than 20% contamination.
Considering only broad-lined AGN, these mid-infrared color criteria identify
over 90% of spectroscopically identified quasars and Seyfert 1s. Applying these
color criteria to the full imaging data set, we discuss the implied surface
density of AGN and find evidence for a large population of optically obscured
active galaxies.Comment: 13 pages, 3 figures; submitted to the Astrophysical Journal Letter
Metal mining and birth defects : a case-control study in Lubumbashi, Democratic Republic of the Congo
Background Widespread environmental contamination caused by mining of copper and cobalt has led to concerns about the possible association between birth defects and exposure to several toxic metals in southern Katanga, Democratic Republic of the Congo (DRC). We therefore aimed to assess the possible contribution of parental and antenatal exposure to trace metals to the occurrence of visible birth defects among neonates.
Methods We did a case-control study between March 1, 2013, and Feb 28, 2015, in Lubumbashi, DRC. We included newborns with visible birth defects (cases) and healthy neonates born in the same maternity ward (controls). Mothers were interviewed about potentially relevant exposures, including their partners' jobs. Various trace metals were measured by inductively coupled plasma mass spectrometry in maternal urine, maternal blood, umbilical cord blood, placental tissue, and surface dust at home. Multivariable logistic regression analyses were done to calculate adjusted odds ratios and their 95% CIs (CI).
Findings Our study included 138 neonates with visible birth defects (about 0.1% of the 133 662 births in Lubumbashi during the study period) and 108 control neonates. Potential confounders were similarly distributed between cases and controls. Vitamin consumption during pregnancy was associated with a lower risk of birth defects (adjusted odds ratio 0.2, 95% CI 0.1-0.5). Mothers having paid jobs outside the home (2.8, 1.2-6.9) and fathers having mining-related jobs (5.5, 1.2-25.0) were associated with a higher risk of birth defects. We found no associations for trace metal concentrations in biological samples, except for a doubling of manganese (Mn; 1.7, 1.1-2.7) and zinc (Zn; 1.6, 0.9-2.8) in cord blood. In a separate model including placentas, a doubling of Mn at the fetal side of the placenta was associated with an increased risk of birth defects (3.3, 1.2-8.0), as was a doubling of cord blood Zn (5.3, 1.6-16.6).
Interpretation To our knowledge, this is the first study of the effects of mining-related pollution on newborns in sub-Saharan Africa. Paternal occupational mining exposure was the factor most strongly associated with birth defects. Because neither Mn nor Zn are mined in Lubumbashi, the mechanism of the association between their increased prenatal concentrations and birth defects is unclear
Semi-analytic modeling of the EBL and consequences for extragalactic gamma-ray spectra
Attenuation of high-energy gamma rays by pair-production with UV, optical and
IR extragalactic background light (EBL) photons provides a link between the
history of galaxy formation and high-energy astrophysics. We present results
from our latest semi-analytic models (SAMs), which employ the main ingredients
thought to be important to galaxy formation and evolution, as well as an
improved model for reprocessing of starlight by dust to mid- and far-IR
wavelengths. These SAMs are based upon a Lambda-CDM hierarchical structural
formation scenario, and are successful in reproducing a large variety of
observational constraints such as number counts, luminosity and mass functions,
and color bimodality. Our fiducial model is based upon a WMAP5 cosmology, and
treats dust emission using empirical templates. This model predicts a
background flux considerably lower than optical and near-IR measurements that
rely on subtraction of zodiacal and galactic foregrounds, and near the lower
bounds set by number counts of resolvable sources at a large number of
wavelengths. We also show the results of varying cosmological parameters and
dust attenuation model used in our SAM. For each EBL prediction, we show how
the optical depth due to electron-positron pair-production is affected by
redshift and gamma-ray energy, and the effect of gamma-ray absorption on the
spectra of a variety of extragalactic sources. We conclude with a discussion of
the implications of our work, comparisons to other models and key measurements
of the EBL and a discussion of how the burgeoning science of gamma-ray
astronomy will continue to help constrain cosmology. The low EBL flux predicted
by our fiducial model suggests an optimistic future for further studies of
distant gamma-ray sources.Comment: 23 pages, 11 figures, 3 tables, accepted by MNRAS; this preprint
matches accepted versio
The Spitzer High Redshift Radio Galaxy Survey
We present results from a comprehensive imaging survey of 70 radio galaxies
at redshifts 1<z<5.2 using all three cameras onboard the Spitzer Space
Telescope. The resulting spectral energy distributions unambiguously show a
stellar population in 46 sources and hot dust emission associated with the
active nucleus in 59. Using a new restframe S_3um/S_1.6um versus S_um/S_3um
criterion, we identify 42 sources where the restframe 1.6um emission from the
stellar population can be measured. For these radio galaxies, the median
stellar mass is high, 2x10^11 M_sun, and remarkably constant within the range
13, there is tentative evidence for a factor of two decrease in
stellar mass. This suggests that radio galaxies have assembled the bulk of
their stellar mass by z~3, but confirmation by more detailed decomposition of
stellar and AGN emission is needed.
The restframe 500 MHz radio luminosities are only marginally correlated with
stellar mass but are strongly correlated with the restframe 5um hot dust
luminosity. This suggests that the radio galaxies have a large range of
Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz
imaging of 14 radio galaxies and find that radio core dominance --- an
indicator of jet orientation --- is strongly correlated with hot dust
luminosity. While all of our targets were selected as narrow-lined, type 2
AGNs, this result can be understood in the context of orientation-dependent
models if there is a continuous distribution of orientations from obscured type
2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio
galaxies have nearby (<6") companions whose mid-IR colors are suggestive of
their being AGNs. This may indicate an association between radio galaxy
activity and major mergers.Comment: 31 pages, 125 figures. Accepted for publication in the Astrophysical
Journa
The hierarchical build-up of the Tully-Fisher relation
We use the semi-analytic model GalICS to predict the Tully-Fisher relation in
the B, I and for the first time, in the K band, and its evolution with
redshift, up to z~1. We refined the determination of the disk galaxies rotation
velocity, with a dynamical recipe for the rotation curve, rather than a simple
conversion from the total mass to maximum velocity. The new recipe takes into
account the disk shape factor, and the angular momentum transfer occurring
during secular evolution leading to the formation of bulges. This produces
model rotation velocities that are lower by ~20-25% for the majority of the
spirals. We implemented stellar population models with a complete treatment of
the TP-AGB, which leads to a revision of the mass-to-light ratio in the
near-IR. I/K band luminosities increase by ~0.3/0.5 mags at redshift z=0 and by
~0.5/1 mags at z=3. With these two new recipes in place, the comparison between
the predicted Tully-Fisher relation with a series of datasets in the optical
and near-IR, at redshifts between 0 and 1, is used as a diagnostics of the
assembly and evolution of spiral galaxies in the model. At 0.4<z<1.2 the match
between the new model and data is remarkably good, especially for later-type
spirals (Sb/Sc). At z=0 the new model shows a net improvement in comparison
with its original version of 2003, and in accord with recent observations in
the K band, the model Tully-Fisher also shows a morphological differentiation.
However, in all bands the z=0 model Tully-Fisher is too bright. We argue that
this behaviour is caused by inadequate star formation histories in the model
galaxies at low redshifts. The star-formation rate declines too slowly, due to
continuous gas infall that is not efficiently suppressed. An analysis of the
model disk scale lengths, at odds with observations, hints to some missing
physics in the modeling of disk formation inside dark matter halos.Comment: Accepted for publication on MNRAS. 2 new plots, 1 new section, and
extended discussion. 21 pages, 11 figures in tota
Less than 10 percent of star formation in z=0.6 massive galaxies is triggered by major interactions
Both observations and simulations show that major tidal interactions or
mergers between gas-rich galaxies can lead to intense bursts of starformation.
Yet, the average enhancement in star formation rate (SFR) in major mergers and
the contribution of such events to the cosmic SFR are not well estimated. Here
we use photometric redshifts, stellar masses and UV SFRs from COMBO-17, 24
micron SFRs from Spitzer and morphologies from two deep HST cosmological survey
fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a
function of projected galaxy separation. We apply two-point projected
correlation function techniques, which we augment with morphologically-selected
very close pairs (separation <2 arcsec) and merger remnants from the HST
imaging. Our analysis confirms that the most intensely star-forming systems are
indeed interacting or merging. Yet, for massive (M* > 10^10 Msun) star-forming
galaxies at 0.4<z<0.8, we find that the SFRs of galaxies undergoing a major
interaction (mass ratios <1:4 and separations < 40 kpc) are only 1.80 +/- 0.30
times higher than the SFRs of non-interacting galaxies when averaged over all
interactions and all stages of the interaction, in good agreement with other
observational works.
We demonstrate that these results imply that <10% of star formation at 0.4 <
z < 0.8 is triggered directly by major mergers and interactions; these events
are not important factors in the build-up of stellar mass since z=1.Comment: Submitted to ApJ. 41 pages, 11 figure
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