45 research outputs found
Thermoregulatory strategy may shape immune investment in Drosophila melanogaster
As temperatures change, insects alter the amount of melanin in their cuticle to improve thermoregulation. However, melanin is also central to insect immunity, suggesting that thermoregulatory strategy may indirectly impact immune defense by altering the abundance of melanin pathway components (a hypothesis we refer to as thermoregulatory-dependent immune investment). This may be the case in the cricket Allonemobius socius, where warm environments (both seasonal and geographical) produced crickets with lighter cuticles and increased pathogen susceptibility. Unfortunately, the potential for thermoregulatory strategy to influence insect immunity has not been widely explored. Here we address the relationships between temperature, thermoregulatory strategy and immunity in the fruit fly Drosophila melanogaster. To this end, flies from two separate Canadian populations were reared in either a summer-or autumn-like environment. Shortly after adult eclosion, flies were moved to a common environment where their cuticle color and susceptibility to a bacterial pathogen (Pseudomonas aeruginosa) were measured. As with A. socius, individuals from summer-like environments exhibited lighter cuticles and increased pathogen susceptibility, suggesting that the thermoregulatory-immunity relationship is evolutionarily conserved across the hemimetabolous and holometabolous clades. If global temperatures continue to rise as expected, then thermoregulation might play an important role in host infection and mortality rates in systems that provide critical ecosystem services (e.g. pollination), or influence the prevalence of insect-vectored disease (e.g. malaria)
Wide-field weak lensing by RXJ1347-1145
We present an analysis of weak lensing observations for RXJ1347-1145 over a
43' X 43' field taken in B and R filters on the Blanco 4m telescope at CTIO.
RXJ1347-1145 is a massive cluster at redshift z=0.45. Using a population of
galaxies with 20<R<26, we detect a weak lensing signal at the p<0.0005 level,
finding best-fit parameters of \sigma_v=1400^{+130}_{-140} km s^{-1} for a
singular isothermal sphere model and r_{200} = 3.5^{+0.8}_{-0.2} Mpc with c =
15^{+64}_{-10} for a NFW model in an \Omega_m = 0.3, \Omega_\Lambda = 0.7
cosmology. In addition, a mass to light ratio M/L_R =90 \pm 20 M_\odot /
L_{R\odot} was determined. These values are consistent with the previous weak
lensing study of RXJ1347--1145 by Fischer and Tyson, 1997, giving strong
evidence that systemic bias was not introduced by the relatively small field of
view in that study. Our best-fit parameter values are also consistent with
recent X-ray studies by Allen et al, 2002 and Ettori et al, 2001, but are not
consistent with recent optical velocity dispersion measurements by Cohen and
Kneib, 2002.Comment: accepted to ApJ, tentative publication 10 May 2005, v624
SHELS: Testing Weak Lensing Maps with Redshift Surveys
Weak lensing surveys are emerging as an important tool for the construction
of "mass selected" clusters of galaxies. We evaluate both the efficiency and
completeness of a weak lensing selection by combining a dense, complete
redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), with a weak
lensing map from the Deep Lens Survey (DLS). SHELS includes 11,692 redshifts
for galaxies with R < 20.6 in the four square degree DLS field; the survey is a
solid basis for identifying massive clusters of galaxies with redshift z <
0.55. The range of sensitivity of the redshift survey is similar to the range
for the DLS convergence map. Only four the twelve convergence peaks with
signal-to-noise > 3.5 correspond to clusters of galaxies with M > 1.7 x 10^14
solar masses. Four of the eight massive clusters in SHELS are detected in the
weak lensing map yielding a completeness of roughly 50%. We examine the seven
known extended cluster x-ray sources in the DLS field: three can be detected in
the weak lensing map, three should not be detected without boosting from
superposed large-scale structure, and one is mysteriously undetected even
though its optical properties suggest that it should produce a detectable
lensing signal. Taken together, these results underscore the need for more
extensive comparisons among different methods of massive cluster
identification.Comment: 34 pages, 16 figures, ApJ accepte
Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived Masses for Shear-Selected Galaxy Clusters: I. A781
We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.Comment: 14 pages, 7 figures, matches version in Ap
Testing Weak Lensing Maps With Redshift Surveys: A Subaru Field
We use a dense redshift survey in the foreground of the Subaru GTO2deg^2 weak
lensing field (centered at = 16;
=43^\circ11^{\prime}24^{\prime\prime}$) to assess the completeness and comment
on the purity of massive halo identification in the weak lensing map. The
redshift survey (published here) includes 4541 galaxies; 4405 are new redshifts
measured with the Hectospec on the MMT. Among the weak lensing peaks with a
signal-to-noise greater that 4.25, 2/3 correspond to individual massive
systems; this result is essentially identical to the Geller et al. (2010) test
of the Deep Lens Survey field F2. The Subaru map, based on images in
substantially better seeing than the DLS, enables detection of less massive
halos at fixed redshift as expected. We demonstrate that the procedure adopted
by Miyazaki et al. (2007) for removing some contaminated peaks from the weak
lensing map improves agreement between the lensing map and the redshift survey
in the identification of candidate massive systems.Comment: Astrophysical Journal accepted versio
Shear-Selected Clusters From the Deep Lens Survey III: Masses from Weak Lensing
We present weak lensing mass estimates of seven shear-selected galaxy cluster
candidates from the Deep Lens Survey. The clusters were previously identified
as mass peaks in convergence maps of 8.6 sq. deg of R band imaging, and
followed up with X-ray and spectroscopic confirmation, spanning a redshift
range 0.19 - 0.68. Most clusters contained multiple X-ray peaks, yielding 17
total mass concentrations. In this paper, we constrain the masses of these
X-ray sources with weak lensing, using photometric redshifts from the full set
of BVRz' imaging to properly weight background galaxies according to their
lensing distance ratios. We fit both NFW and singular isothermal sphere
profiles, and find that the results are insensitive to the assumed profile. We
also show that the results do not depend significantly on the assumed prior on
the position of the mass peak, but that this may become an issue in future
larger samples. The inferred velocity dispersions for the extended X-ray
sources range from 250-800 km/s, with the exception of one source for which no
lensing signal was found. This work further establishes shear selection as a
viable technique for finding clusters, but also highlights some unresolved
issues such as determination of the mass profile center without biasing the
mass estimate, and fully accounting for line-of-sight projections. A follow-up
paper will examine the mass-X-ray scaling relations of these clusters.Comment: Accepted for publication in ApJ, 27 pages, 4 figures. Some discussion
and clarification added. Cluster centre offset added to Table
SHELS: The Hectospec Lensing Survey
The Smithsonian Hectospec Lensing Survey (SHELS) combines a large deep
complete redshift survey with a weak lensing map from the Deep Lens Survey
(Wittman et al. 2002; 2005). We use maps of the velocity dispersion based on
systems identified in the redshift survey to compare the three-dimensional
matter distribution with the two-dimensional projection mapped by weak lensing.
We demonstrate directly that the lensing map images the three-dimensional
matter distribution obtained from the kinematic data.Comment: Astrophysical Journal Letters 9pages, 3 figures, accepted, corrected
typo
The Faint End of the Luminosity Function and Low Surface Brightness Galaxies
SHELS (Smithsonian Hectospec Lensing Survey) is a dense redshift survey
covering a 4 square degree region to a limiting R = 20.6. In the construction
of the galaxy catalog and in the acquisition of spectroscopic targets, we paid
careful attention to the survey completeness for lower surface brightness dwarf
galaxies. Thus, although the survey covers a small area, it is a robust basis
for computation of the slope of the faint end of the galaxy luminosity function
to a limiting M_R = -13.3 + 5logh. We calculate the faint end slope in the
R-band for the subset of SHELS galaxies with redshif ts in the range 0.02 <= z
< 0.1, SHELS_{0.1}. This sample contains 532 galaxies with R< 20.6 and with a
median surface brightness within the half light radius of SB_{50,R} = 21.82 mag
arcsec^{-2}. We used this sample to make one of the few direct measurements of
the dependence of the faint end of the galaxy luminosity function on surface
brightness. For the sample as a whole the faint end slope, alpha = -1.31 +/-
0.04, is consistent with both the Blanton et al. (2005b) analysis of the SDSS
and the Liu et al. (2008) analysis of the COSMOS field. This consistency is
impressive given the very different approaches of th ese three surveys. A
magnitude limited sample of 135 galaxies with optical spectroscopic reds hifts
with mean half-light surface brightness, SB_{50,R} >= 22.5 mag arcsec^{-2} is
unique to SHELS_{0.1}. The faint end slope is alpha_{22.5} = -1.52+/- 0.16.
SHELS_{0.1} shows that lower surface brightness objects dominate the faint end
slope of the l uminosity function in the field, underscoring the importance of
surface brightness limits in evaluating measurements of the faint end slope and
its evolution.Comment: 34 pages, 13 figures, 3 tables, Astronomical Journal, in press
(updated based on review