25 research outputs found
PKS 1830-211: A Face-On Spiral Galaxy Lens
We present new Hubble Space Telescope images of the gravitational lens PKS
1830-211, which allow us to characterize the lens galaxy and update the
determination of the Hubble constant from this system. The I-band image shows
that the lens galaxy is a face-on spiral galaxy with clearly delineated spiral
arms. The southwestern image of the background quasar passes through one of the
spiral arms, explaining the previous detections of large quantities of
molecular gas and dust in front of this image. The lens galaxy photometry is
consistent with the Tully-Fisher relation, suggesting the lens galaxy is a
typical spiral galaxy for its redshift. The lens galaxy position, which was the
main source of uncertainty in previous attempts to determine H_0, is now known
precisely. Given the current time delay measurement and assuming the lens
galaxy has an isothermal mass distribution, we compute H_0 = 44 +/- 9 km/s/Mpc
for an Omega_m = 0.3 flat cosmological model. We describe some possible
systematic errors and how to reduce them. We also discuss the possibility
raised by Courbin et al. (2002), that what we have identified as a single lens
galaxy is actually a foreground star and two separate galaxies.Comment: 21 pp., 4 figs., accepted by ApJ, section added to discuss related
work by Courbin et al. (astro-ph/0202026
Spectropolarimetric Evidence for Radiatively Inefficient Accretion in an Optically Dull Active Galaxy
We present Subaru/FOCAS spectropolarimetry of two active galaxies in the
Cosmic Evolution Survey. These objects were selected to be optically dull, with
the bright X-ray emission of an AGN but missing optical emission lines in our
previous spectroscopy. Our new observations show that one target has very weak
emission lines consistent with an optically dull AGN, while the other object
has strong emission lines typical of a host-diluted Type 2 Seyfert galaxy. In
neither source do we observe polarized emission lines, with 3-sigma upper
limits of P_BLR < 2%. This means that the missing broad emission lines (and
weaker narrow emission lines) are not due to simple anisotropic obscuration,
e.g., by the canonical AGN torus. The weak-lined optically dull AGN exhibits a
blue polarized continuum with P = 0.78 +/- 0.07% at 4400 A < lambda_rest < 7200
A (P = 1.37 +/- 0.16% at 4400 A < lambda_rest < 5050 A). The wavelength
dependence of this polarized flux is similar to that of an unobscured AGN
continuum and represents the intrinsic AGN emission, either as synchrotron
emission or the outer part of an accretion disk reflected by a clumpy dust
scatterer. Because this intrinsic AGN emission lacks emission lines, this
source is likely to have a radiatively inefficient accretion flow.Comment: Accepted to ApJ. 6 pages, 2 figure
Galaxy morphology and evolution from SWAN Adaptive Optics imaging
We present the results from adaptive optics (AO) assisted imaging in the Ks
band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We
derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in
the first 21 SWAN fields around bright guide stars, carefully taking into
account the survey selection effects and using an accurate treatment of the
anisoplanatic AO PSF. The detected galaxies are sorted into two morphological
classes according to their Sersic index. The extracted morphological properties
and number counts of the galaxies are compared with the predictions of
different galaxy formation and evolution models, both for the whole galaxy
population and separately for late-type and early-type galaxies. This is one of
the first times such a comparison has been done in the near-IR, as AO
observations and accurate PSF modeling are needed to obtain reliable
morphological classification of faint field galaxies at these wavelengths. For
early-type galaxies we find that a pure luminosity evolution model, without
evidence for relevant number and size evolution, better reproduces the observed
properties of our Ks-selected sample than current semi-analytic models based on
the hierarchical picture of galaxy formation. In particular, we find that the
observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in
good agreement with the prediction of the pure luminosity evolution model that
was calculated prior to the observation. For late-type galaxies, while both
models are able to reproduce the number counts, we find some hints of a
possible size growth. These results demonstrate the unique power of AO
observations to derive high resolution details of faint galaxies' morphology in
the near-IR and drive studies of galaxy evolution.Comment: 15 pages, 10 figures. A&A, in press. Final version with corrected
typo
Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts
In the present-day universe, supermassive black hole masses (MBH) appear to
be strongly correlated with their galaxy's bulge luminosity, among other
properties. In this study, we explore the analogous relationship between MBH,
derived using the virial method, and the stellar R-band bulge luminosity (Lr)
or stellar bulge mass (M*) at epochs of 1 < z < 4.5 using a sample of 31
gravitationally lensed AGNs and 20 non-lensed AGNs. At redshifts z > 1.7
(10--12 Gyrs ago), we find that the observed MBH--Lr relation is nearly the
same (to within ~0.3 mag) as it is today. When the observed Lr are corrected
for luminosity evolution, this means that the black holes grew in mass faster
than their hosts, with the MBH/M* mass ratio being a factor of > 4(+2)(-1)
times larger at z > 1.7 than it is today. By the redshift range 1<z<1.7 (8-10
Gyrs ago), the MBH/M* ratio is at most two times higher than today, but it may
be consistent with no evolution. Combining the results, we conclude that the
ratio MBH/M* rises with look-back time, although it may saturate at ~6 times
the local value. Scenarios in which moderately luminous quasar hosts at z>1.7
were fully formed bulges that passively faded to the present epoch are ruled
out.Comment: ApJ accepted, includes Referee comments and statistics to better
quantify the statistical significance of results. 23 pages, 11 figures, 4
table
Accretion Rate and the Physical Nature of Unobscured Active Galaxies
We show how accretion rate governs the physical properties of a sample of
unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs).
We avoid the systematic errors plaguing previous studies of AGN accretion rate
by using accurate accretion luminosities (L_int) from well-sampled
multiwavelength SEDs from the Cosmic Evolution Survey (COSMOS), and accurate
black hole masses derived from virial scaling relations (for broad-line AGNs)
or host-AGN relations (for narrow-line and lineless AGNs). In general, broad
emission lines are present only at the highest accretion rates (L_int/L_Edd >
0.01), and these rapidly accreting AGNs are observed as broad-line AGNs or
possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower
specific accretion rates (L_int/L_Edd < 0.01) are unobscured and yet lack a
broad line region. The disappearance of the broad emission lines is caused by
an expanding radiatively inefficient accretion flow (RIAF) at the inner radius
of the accretion disk. The presence of the RIAF also drives L_int/L_Edd < 10^-2
narrow-line and lineless AGNs to 10 times higher ratios of radio to optical/UV
emission than L_int/L_Edd > 0.01 broad-line AGNs, since the unbound nature of
the RIAF means it is easier to form a radio outflow. The IR torus signature
also tends to become weaker or disappear from L_int/L_Edd < 0.01 AGNs, although
there may be additional mid-IR synchrotron emission associated with the RIAF.
Together these results suggest that specific accretion rate is an important
physical "axis" of AGN unification, described by a simple model.Comment: Accepted for publication in the Astrophysical Journal. 15 pages, 9
figure
Transcriptional Regulation of BMP2 Expression by the PTH-CREB Signaling Pathway in Osteoblasts
Intermittent application of parathyroid hormone (PTH) has well established anabolic effects on bone mass in rodents and humans. Although transcriptional mechanisms responsible for these effects are not fully understood, it is recognized that transcriptional factor cAMP response element binding protein (CREB) mediates PTH signaling in osteoblasts, and that there is a communication between the PTH-CREB pathway and the BMP2 signaling pathway, which is important for osteoblast differentiation and bone formations. These findings, in conjunction with putative cAMP response elements (CREs) in the BMP2 promoter, led us to hypothesize that the PTH-CREB pathway could be a positive regulator of BMP2 transcription in osteoblasts. To test this hypothesis, we first demonstrated that PTH signaling activated CREB by phosphorylation in osteoblasts, and that both PTH and CREB were capable of promoting osteoblastic differentiation of primary mouse osteoblast cells and multiple rodent osteoblast cell lines. Importantly, we found that the PTH-CREB signaling pathway functioned as an effective activator of BMP2 expression, as pharmacologic and genetic modulation of PTH-CREB activity significantly affected BMP2 expression levels in these cells. Lastly, through multiple promoter assays, including promoter reporter deletion, mutation, chromatin immunoprecipitation (ChIP), and electrophoretic mobility shift assay (EMSA), we identified a specific CRE in the BMP2 promoter which is responsible for CREB transactivation of the BMP2 gene in osteoblasts. Together, these results demonstrate that the anabolic function of PTH signaling in bone is mediated, at least in part, by CREB transactivation of BMP2 expression in osteoblasts
Evaluating the Effects of SARS-CoV-2 Spike Mutation D614G on Transmissibility and Pathogenicity.
Global dispersal and increasing frequency of the SARS-CoV-2 spike protein variant D614G are suggestive of a selective advantage but may also be due to a random founder effect. We investigate the hypothesis for positive selection of spike D614G in the United Kingdom using more than 25,000 whole genome SARS-CoV-2 sequences. Despite the availability of a large dataset, well represented by both spike 614 variants, not all approaches showed a conclusive signal of positive selection. Population genetic analysis indicates that 614G increases in frequency relative to 614D in a manner consistent with a selective advantage. We do not find any indication that patients infected with the spike 614G variant have higher COVID-19 mortality or clinical severity, but 614G is associated with higher viral load and younger age of patients. Significant differences in growth and size of 614G phylogenetic clusters indicate a need for continued study of this variant
SARS-CoV-2 Omicron is an immune escape variant with an altered cell entry pathway
Vaccines based on the spike protein of SARS-CoV-2 are a cornerstone of the public health response to COVID-19. The emergence of hypermutated, increasingly transmissible variants of concern (VOCs) threaten this strategy. Omicron (B.1.1.529), the fifth VOC to be described, harbours multiple amino acid mutations in spike, half of which lie within the receptor-binding domain. Here we demonstrate substantial evasion of neutralization by Omicron BA.1 and BA.2 variants in vitro using sera from individuals vaccinated with ChAdOx1, BNT162b2 and mRNA-1273. These data were mirrored by a substantial reduction in real-world vaccine effectiveness that was partially restored by booster vaccination. The Omicron variants BA.1 and BA.2 did not induce cell syncytia in vitro and favoured a TMPRSS2-independent endosomal entry pathway, these phenotypes mapping to distinct regions of the spike protein. Impaired cell fusion was determined by the receptor-binding domain, while endosomal entry mapped to the S2 domain. Such marked changes in antigenicity and replicative biology may underlie the rapid global spread and altered pathogenicity of the Omicron variant
Genomic epidemiology of SARS-CoV-2 in a UK university identifies dynamics of transmission
AbstractUnderstanding SARS-CoV-2 transmission in higher education settings is important to limit spread between students, and into at-risk populations. In this study, we sequenced 482 SARS-CoV-2 isolates from the University of Cambridge from 5 October to 6 December 2020. We perform a detailed phylogenetic comparison with 972 isolates from the surrounding community, complemented with epidemiological and contact tracing data, to determine transmission dynamics. We observe limited viral introductions into the university; the majority of student cases were linked to a single genetic cluster, likely following social gatherings at a venue outside the university. We identify considerable onward transmission associated with student accommodation and courses; this was effectively contained using local infection control measures and following a national lockdown. Transmission clusters were largely segregated within the university or the community. Our study highlights key determinants of SARS-CoV-2 transmission and effective interventions in a higher education setting that will inform public health policy during pandemics.</jats:p
Changes in symptomatology, reinfection, and transmissibility associated with the SARS-CoV-2 variant B.1.1.7: an ecological study
Background
The SARS-CoV-2 variant B.1.1.7 was first identified in December, 2020, in England. We aimed to investigate whether increases in the proportion of infections with this variant are associated with differences in symptoms or disease course, reinfection rates, or transmissibility.
Methods
We did an ecological study to examine the association between the regional proportion of infections with the SARS-CoV-2 B.1.1.7 variant and reported symptoms, disease course, rates of reinfection, and transmissibility. Data on types and duration of symptoms were obtained from longitudinal reports from users of the COVID Symptom Study app who reported a positive test for COVID-19 between Sept 28 and Dec 27, 2020 (during which the prevalence of B.1.1.7 increased most notably in parts of the UK). From this dataset, we also estimated the frequency of possible reinfection, defined as the presence of two reported positive tests separated by more than 90 days with a period of reporting no symptoms for more than 7 days before the second positive test. The proportion of SARS-CoV-2 infections with the B.1.1.7 variant across the UK was estimated with use of genomic data from the COVID-19 Genomics UK Consortium and data from Public Health England on spike-gene target failure (a non-specific indicator of the B.1.1.7 variant) in community cases in England. We used linear regression to examine the association between reported symptoms and proportion of B.1.1.7. We assessed the Spearman correlation between the proportion of B.1.1.7 cases and number of reinfections over time, and between the number of positive tests and reinfections. We estimated incidence for B.1.1.7 and previous variants, and compared the effective reproduction number, Rt, for the two incidence estimates.
Findings
From Sept 28 to Dec 27, 2020, positive COVID-19 tests were reported by 36 920 COVID Symptom Study app users whose region was known and who reported as healthy on app sign-up. We found no changes in reported symptoms or disease duration associated with B.1.1.7. For the same period, possible reinfections were identified in 249 (0·7% [95% CI 0·6–0·8]) of 36 509 app users who reported a positive swab test before Oct 1, 2020, but there was no evidence that the frequency of reinfections was higher for the B.1.1.7 variant than for pre-existing variants. Reinfection occurrences were more positively correlated with the overall regional rise in cases (Spearman correlation 0·56–0·69 for South East, London, and East of England) than with the regional increase in the proportion of infections with the B.1.1.7 variant (Spearman correlation 0·38–0·56 in the same regions), suggesting B.1.1.7 does not substantially alter the risk of reinfection. We found a multiplicative increase in the Rt of B.1.1.7 by a factor of 1·35 (95% CI 1·02–1·69) relative to pre-existing variants. However, Rt fell below 1 during regional and national lockdowns, even in regions with high proportions of infections with the B.1.1.7 variant.
Interpretation
The lack of change in symptoms identified in this study indicates that existing testing and surveillance infrastructure do not need to change specifically for the B.1.1.7 variant. In addition, given that there was no apparent increase in the reinfection rate, vaccines are likely to remain effective against the B.1.1.7 variant.
Funding
Zoe Global, Department of Health (UK), Wellcome Trust, Engineering and Physical Sciences Research Council (UK), National Institute for Health Research (UK), Medical Research Council (UK), Alzheimer's Society