163 research outputs found
The Galaxy Octopole Moment as a Probe of Weak Lensing Shear Fields
In this paper, we introduce the octopole moment of the light distribution in
galaxies as a probe of the weak lensing shear field. While traditional
ellipticity estimates of the local shear derived from the quadrupole moment are
limited by the width of the intrinsic ellipticity distribution of background
galaxies, the dispersion in the intrinsic octopole distribution is expected to
be much smaller, implying that the signal from this higher order moment is
ultimately limited by measurement noise, and not by intrinsic scatter. We
present the computation of the octopole moment and show that current
observations are at the regime where the octopole estimates will soon be able
to contribute to the overall accuracy of the estimates of local shear fields.
Therefore, the prospects for this estimator from future datasets like the
Advanced Camera for Survey and the Next Generation Space Telescope are very
promising.Comment: 9 pages, 2 PostScript figures; Submitted to Astrophysical Journa
The alignment of disk and black hole spins in active galactic nuclei
The inner parts of an accretion disk around a spinning black hole are forced
to align with the spin of the hole by the Bardeen-Petterson effect. Assuming
that any jet produced by such a system is aligned with the angular momentum of
either the hole or the inner disk, this can, in principle provide a mechanism
for producing steady jets in AGN whose direction is independent of the angular
momentum of the accreted material. However, the torque which aligns the inner
disk with the hole, also, by Newton's third law, tends to align the spin of the
hole with the outer accretion disk. In this letter, we calculate this alignment
timescale for a black hole powering an AGN, and show that it is relatively
short. This timescale is typically much less than the derived ages for jets in
radio loud AGN, and implies that the jet directions are not in general
controlled by the spin of the black hole. We speculate that the jet directions
are most likely controlled either by the angular momentum of the accreted
material or by the gravitational potential of the host galaxy.Comment: 4 pages, LateX file, accepted for publication in ApJ Letter
The Virial Mass Function of Nearby SDSS Galaxy Clusters
We present a new determination of the cluster mass function and velocity
dispersion function in a volume Mpc using the Fourth Data
Release of the Sloan Digital Sky Survey (SDSS). We use the caustic technique to
remove foreground and background galaxies. The cluster virial mass function
agrees well with recent estimates from both X-ray observations and cluster
richnesses. The mass function lies between those predicted by the First-Year
and Three-Year WMAP data. We constrain the cosmological parameters
and and find good agreement with WMAP and constraints from other
techniques. With the CIRS mass function alone, we estimate
and , or
0.03 when holding fixed. We also use the WMAP
parameters as priors and constrain velocity segregation in clusters. Using the
First and Third-Year results, we infer velocity segregation of
0.05 or 1.280.06 respectively. We
compare the velocity dispersion function of clusters to that of early-type
galaxies and conclude that clusters comprise the high-velocity end of the
velocity dispersion function of dark matter haloes. The evolution of cluster
abundances provides constraints on dark energy models; the mass function
presented here offers an important low redshift calibration benchmark.Comment: 22 pages, 11 figures, ApJ in press, revised figure
Inhibition of vaccinia virus L1 N-myristoylation by the host N-myristoyltransferase inhibitor IMP-1088 generates non-infectious virions defective in cell entry
We have recently shown that the replication of rhinovirus, poliovirus and foot-and-mouth disease virus requires the co-translational N-myristoylation of viral proteins by human host cell N-myristoyltransferases (NMTs), and is inhibited by treatment with IMP-1088, an ultrapotent small molecule NMT inhibitor. Here, we examine the importance of N-myristoylation during vaccinia virus (VACV) infection in primate cells and demonstrate the anti-poxviral effects of IMP-1088. N-myristoylated proteins from VACV and the host were metabolically labelled with myristic acid alkyne during infection using quantitative chemical proteomics. We identified VACV proteins A16, G9 and L1 to be N-myristoylated. Treatment with NMT inhibitor IMP-1088 potently abrogated VACV infection, while VACV gene expression, DNA replication, morphogenesis and EV formation remained unaffected. Importantly, we observed that loss of N-myristoylation resulted in greatly reduced infectivity of assembled mature virus particles, characterized by significantly reduced host cell entry and a decline in membrane fusion activity of progeny virus. While the N-myristoylation of VACV entry proteins L1, A16 and G9 was inhibited by IMP-1088, mutational and genetic studies demonstrated that the N-myristoylation of L1 was the most critical for VACV entry. Given the significant genetic identity between VACV, monkeypox virus and variola virus L1 homologs, our data provides a basis for further investigating the role of N-myristoylation in poxviral infections as well as the potential of selective NMT inhibitors like IMP-1088 as broad-spectrum poxvirus inhibitors
Efficient survey design for finding high-redshift galaxies with JWST
Several large JWST blank field observing programs have not yet discovered the
first galaxies expected to form at . This has motivated the
search for more effective survey strategies that will be able to effectively
probe this redshift range. Here, we explore the use of gravitationally lensed
cluster fields, that have historically been the most effective discovery tool
with HST. In this paper, we analyze the effectiveness of the most massive
galaxy clusters that provide the highest median magnification factor within a
single JWST NIRCam module in uncovering this population. The results of
exploiting these lensing clusters to break the barrier are compared
against the results from large area, blank field surveys such as JADES and
CEERS in order to determine the most effective survey strategy for JWST. We
report that the fields containing massive foreground galaxy clusters
specifically chosen to occupy the largest fraction of a single NIRCam module
with high magnification factors in the source plane, whilst containing all
multiple images in the image plane within a single module provide the highest
probability of both probing the regime, as well as
discovering the highest redshift galaxy possible with JWST. We also find that
using multiple massive clusters in exchange for shallower survey depths is a
more time efficient method of probing the regime.Comment: 12 pages, 5 figure
Structures of the CCR5 N Terminus and of a Tyrosine-Sulfated Antibody with HIV-1 gp120 and CD4
The CCR5 co-receptor binds to the HIV-l gp120 envelope glycoprotein and facilitates HIV-l entry into cells. Its N terminus is tyrosine-sulfated, as are many antibodies that react with the co-receptor binding site on gp120. We applied nuclear magnetic resonance and crystallographic techniques to analyze the structure of the CCR5 N terminus and that of the tyrosine-sulfated antibody 412d in complex with gp120 and CD4. The conformations of tyrosine-sulfated regions of CCR5 (α-helix) and 412d (extendedloop) are surprisingly different. Nonetheless, a critical sulfotyrosine on CCR5 and on 412d induces similar structural rearrangements in gp120. These results now provide a framework for understanding HIV-l interactions with the CCR5 N terminus during viral entry and define a conserved site on gp120, whose recognition of sulfotyrosine engenders posttranslational mimicry by the immune system
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Microsecond dynamics control the HIV-1 Envelope conformation
The HIV-1 Envelope (Env) glycoprotein facilitates host cell fusion through a complex series of receptor-induced structural changes. Although remarkable progress has been made in understanding the structures of various Env conformations, microsecond timescale dynamics have not been studied experimentally. Here, we used time-resolved, temperature-jump small-angle x-ray scattering to monitor structural rearrangements in an HIV-1 Env SOSIP ectodomain construct with microsecond precision. In two distinct Env variants, we detected a transition that correlated with known Env structure rearrangements with a time constant in the hundreds of microseconds range. A previously unknown structural transition was also observed, which occurred with a time constant below 10 μs, and involved an order-to-disorder transition in the trimer apex. Using this information, we engineered an Env SOSIP construct that locks the trimer in the prefusion closed state by connecting adjacent protomers via disulfides. Our findings show that the microsecond timescale structural dynamics play an essential role in controlling the Env conformation with impacts on vaccine design
Structures of the CCR5 N Terminus and of a Tyrosine-Sulfated Antibody with HIV-1 gp120 and CD4
The CCR5 co-receptor binds to the HIV-l gp120 envelope glycoprotein and facilitates HIV-l entry into cells. Its N terminus is tyrosine-sulfated, as are many antibodies that react with the co-receptor binding site on gp120. We applied nuclear magnetic resonance and crystallographic techniques to analyze the structure of the CCR5 N terminus and that of the tyrosine-sulfated antibody 412d in complex with gp120 and CD4. The conformations of tyrosine-sulfated regions of CCR5 (α-helix) and 412d (extendedloop) are surprisingly different. Nonetheless, a critical sulfotyrosine on CCR5 and on 412d induces similar structural rearrangements in gp120. These results now provide a framework for understanding HIV-l interactions with the CCR5 N terminus during viral entry and define a conserved site on gp120, whose recognition of sulfotyrosine engenders posttranslational mimicry by the immune system
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