Despite consistent progress in numerical simulations, the observable properties of galaxy clusters are difficult to predict ab initio. It is therefore important to compare both theoretical and ...observational results to a direct measure of the cluster mass. This can be done by measuring the gravitational lensing effects caused by the bending of light by the cluster mass distribution. In this review we discuss how this phenomenon can be used to determine cluster masses and study the mass distribution itself. As sample sizes increase, the accuracy of the weak lensing mass estimates needs to improve accordingly. We discuss the main practical aspects of these measurements. We review a number of applications and highlight some recent results.
Abstract
The gravitational lens system PS J0147+4630 (Andromeda’s Parachute) consists of four quasar images ABCD and a lensing galaxy. We obtained
r
-band light curves of ABCD in the 2017−2022 period ...from monitoring with two 2 m class telescopes. Applying state-of-the-art curve-shifting algorithms to these light curves led to measurements of time delays between images, and the three independent delays relative to image D are accurate enough to be used in cosmological studies (uncertainty of about 4%): Δ
t
AD
= −170.5 ± 7.0, Δ
t
BD
= −170.4 ± 6.0, and Δ
t
CD
= −177.0 ± 6.5 days, where image D is trailing all the other images. Our finely sampled light curves and some additional fluxes in the years 2010−2013 also demonstrated the presence of significant microlensing variations. From the measured delays relative to image D and typical values of the external convergence, recent lens mass models yielded a Hubble constant that is in clear disagreement with currently accepted values around 70 km s
−1
Mpc
−1
. We discuss how to account for a standard value of the Hubble constant without invoking the presence of an extraordinary high external convergence.
We study the abundance of star-forming and quiescent galaxies in a sample of 21 clusters at 0.5 < z < 0.7, detected with the Planck satellite. Thanks to the large volume probed by Planck, these ...systems are extremely massive, and provide an excellent laboratory to study any environmental effects on their galaxies’ properties. We measure the cluster galaxy stellar mass function (SMF), which is a fundamental observable to study and constrain the formation and evolution of galaxies. Our measurements are based on homogeneous and deep multi-band photometry spanning from the u- to the Ks-band for each cluster and are supported by spectroscopic data from different programs. The galaxy population is separated into quiescent and star-forming galaxies based on their rest-frame U−V and V−J colours. The SMF is compared to that of field galaxies at the same redshifts using data from the COSMOS/UltraVISTA survey. We find that the shape of the SMF of star-forming galaxies does not depend on environment, while the SMF of quiescent galaxies has a significantly steeper low-mass slope in the clusters compared to the field. This indicates that a different quenching mechanism is at play in clusters compared to the field, accentuated by a quenched fraction that is much higher in the clusters. We estimate the environmental quenching efficiency (fEQ), that is, the probability for a galaxy that would normally be star forming in the field to be quenched due to its environment. The fEQ shows no stellar-mass dependence in any environment, but it increases from 40% in the cluster outskirts to ∼90% in the cluster centres. The radial signature of fEQ provides constraints on where the dominant quenching mechanism operates in these clusters and on what timescale. Exploring these using a simple model based on galaxy orbits obtained from an N-body simulation, we find a clear degeneracy between both parameters. For example, the quenching process may either be triggered on a long (∼3 Gyr) timescale at large radii (r ∼ 8 R500), or happen well within 1 Gyr at r < R500. The radius where quenching is triggered is at least rquench > 0.67 R500 (95%CL). The ICM density at this location (as probed with XMM-Newton) suggests that ram-pressure stripping of the cold gas is a likely cause of quenching. In addition to this cluster-quenching mechanism, we find that 20–32%, depending on the cluster-specific quenching process, of accreted galaxies were already pre-processed (i.e. quenched by the surrounding overdensities) before they fell into the clusters.
Antagonistic interactions between bacteriophage (phage) and its bacterial host drives the continual selection for resistance and counter-defence. To date, much remains unknown about the genomic ...evolution that occurs as part of the underlying mechanisms. Such is the case for the marine cyanobacteria Synechococcus and viruses (cyanophages) that infect them. Here, we monitored host and phage abundances, alongside genomic changes to the phage populations, in a 500-day (~55 bacterial generations) infection experiment between Synechococcus sp. WH7803 and the T4-type cyanophage S-PM2d, run parallel in three replicate chemostats (plus one control chemostat). Flow cytometric count of total abundances revealed relatively similar host-phage population dynamics across the chemostats, starting with a cycle of host population collapse and recovery that led to phases of host-phage coexistence. Whole-genome analysis of the S-PM2d populations detected an assemblage of strongly selected and repeatable genomic changes, and therefore parallel evolution in the phage populations, early in the experiment (sampled on day 39). These consisted mostly of non-synonymous single-nucleotide-polymorphisms and a few instances of indel, altogether affecting 18 open-reading-frames, the majority of which were predicted to encode virion structures including those involved in phage adsorption onto host (i.e., baseplate wedge, short tail fibre, adhesin component). Mutations that emerged later (sampled on day 500), on the other hand, were found at a larger range of frequencies, with many lacking repeatability across the chemostats. This is indicative of some degree of between-population divergence in the phage evolutionary trajectory over time. A few of the early and late mutations were detected within putative auxiliary metabolic genes, but these generally occurred in only one or two of the chemostats. Less repeatable mutations may have higher fitness costs, thus drawing our attention onto the role of trade-offs in modulating the trajectory of a host-phage coevolution.
Abstract
We present the first results of a 4.5 yr monitoring campaign of the three bright images of multiply imaged
z
= 2.805 quasar SDSS J2222+2745 using the Gemini North Multi-Object Spectrograph ...and the Nordic Optical Telescope. We take advantage of gravitational time delays to construct light curves surpassing 6 yr in duration in the observed frame and achieve an average spectroscopic cadence of 10 days during the 8 months of visibility per season. Using multiple secondary calibrators and advanced reduction techniques, we achieve percent-level spectrophotometric precision and carry out an unprecedented reverberation mapping analysis, measuring both integrated and velocity-resolved time lags for the C
iv
emission line. The full line lags the continuum by
τ
cen
=
36.5
−
3.9
+
2.9
rest-frame days. We combine our measurement with published C
iv
emission line lags and derive the
r
BLR
−
L
relationship
log
10
(
τ
/
d
a
y
)
=
(
0.99
±
0.07
)
+
(
0.48
±
0.03
)
log
10
λ
L
λ
(
1350
A
A
)
/
10
44
e
r
g
s
−
1
with 0.30 ± 0.06 dex intrinsic scatter. The velocity-resolved lags are consistent with circular Keplerian orbits, with
τ
cen
=
86.2
−
5.0
+
4.5
,
25
−
15
+
11
, and
7.5
−
3.5
+
4.2
rest-frame days for the core, blue wing, and red wing, respectively. Using
σ
line
with the mean spectrum and assuming
log
10
(
f
mean
,
σ
)
=
0.52
±
0.26
, we derive
log
10
(
M
BH
/
M
⊙
)
=
8.63
±
0.27
. Given the quality of the data, this system represents a unique benchmark for calibration of
M
BH
estimators at high redshift. Future work will present dynamical modeling of the data to constrain the virial factor
f
and
M
BH
.
Abstract
We present high-resolution optical images from the Hubble Space Telescope, X-ray images from the Chandra X-ray Observatory, and optical spectra from the Nordic Optical Telescope for a newly ...discovered galaxy cluster, CHIPS1911+4455, at
z
= 0.485 ± 0.005. CHIPS1911+4455 was discovered in the Clusters Hiding in Plain Sight survey, which sought to discover galaxy clusters with extreme central galaxies that were misidentified as isolated X-ray point sources in the ROSAT All-Sky Survey. With new Chandra X-ray observations, we find the core (
r
= 10 kpc) entropy to be
, suggesting a strong cool core, which is typically found at the centers of relaxed clusters. However, the large-scale morphology of CHIPS1911+4455 is highly asymmetric, pointing to a more dynamically active and turbulent cluster. Furthermore, the Hubble images reveal a massive, filamentary starburst near the brightest cluster galaxy (BCG). We measure the star formation rate for the BCG to be 140–190
M
⊙
yr
−1
, which is one of the highest rates measured in a central cluster galaxy to date. One possible scenario for CHIPS1911+4455 is that the cool core was displaced during a major merger and rapidly cooled, with cool, star-forming gas raining back toward the core. This unique system is an excellent case study for high-redshift clusters, where such phenomena are proving to be more common. Further studies of such systems will drastically improve our understanding of the relation between cluster mergers and cooling, and how these fit in the bigger picture of active galactic nuclei feedback.
Abstract
Tension between cosmic microwave background–based and distance ladder–based determinations of the Hubble constant
H
0
motivates the pursuit of independent methods that are not subject to the ...same systematic effects. A promising alternative, proposed by Refsdal in 1964, relies on the inverse scaling of
H
0
with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. To date, Refsdal’s method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. Using the three quasars strongly lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745) that have both multiband Hubble Space Telescope data and published time delay measurements, we derive
H
0
, accounting for the systematic and statistical sources of uncertainty. While a single time delay measurement does not yield a well-constrained
H
0
value, analyzing the systems together tightens the constraint. Combining the six time delays measured in the three cluster-lensed quasars gives
H
0
= 74.1 ± 8.0 km s
−1
Mpc
−1
. To reach 1% uncertainty in
H
0
, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745 would be needed. Improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade.
Viruses have long been viewed as entities possessing extremely limited metabolic capacities. Over the last decade, however, this view has been challenged, as metabolic genes have been identified in ...viruses possessing large genomes and virions-the synthesis of which is energetically demanding. Here, we unveil peculiar phenotypic and genomic features of
virus RF01 (PkV RF01), a giant virus of the
family. We found that this virus encodes an unprecedented number of proteins involved in energy metabolism, such as all four succinate dehydrogenase (SDH) subunits (A-D) as well as key enzymes in the
-oxidation pathway. The
gene was transcribed upon infection, indicating that the viral SDH is actively used by the virus- potentially to modulate its host's energy metabolism. We detected orthologous
and
genes in numerous genome fragments from uncultivated marine
viruses, which suggests that the viral SDH is widespread in oceans. PkV RF01 was less virulent compared with other cultured prymnesioviruses, a phenomenon possibly linked to the metabolic capacity of this virus and suggestive of relatively long co-evolution with its hosts. It also has a unique morphology, compared to other characterized viruses in the
family. Finally, we found that PkV RF01 is the only alga-infecting
virus encoding two aminoacyl-tRNA synthetases and enzymes corresponding to an entire base-excision repair pathway, as seen in heterotroph-infecting
These
encoded-enzymes were found to be monophyletic and branching at the root of the eukaryotic tree of life. This placement suggests that the last common ancestor of
was endowed with a large, complex genome prior to the divergence of known extant eukaryotes.
Viruses on Earth are tremendously diverse in terms of morphology, functionality, and genomic composition. Over the last decade, the conceptual gap separating viruses and cellular life has tightened because of the detection of metabolic genes in viral genomes that express complex virus phenotypes upon infection. Here, we describe
virus RF01, a large alga-infecting virus with a unique morphology, an atypical infection profile, and an unprecedented number of genes involved in energy metabolism (such as the tricarboxylic (TCA) cycle and the
-oxidation pathway). Moreover, we show that the gene corresponding to one of these enzymes (the succinate dehydrogenase subunit A) is transcribed during infection and is widespread among marine viruses. This discovery provides evidence that a virus has the potential to actively regulate energy metabolism with its own gene.
A recirculating aquaculture system (RAS) for rearing Atlantic salmon requires nitrifying microorganisms in the biofilter in order to be fully functional. These microorganisms play a crucial role in ...water quality improvement by removing ammonia, but the nitrifying population is time-consuming to establish in the biofilter due to their slow growth rates. An efficient biofilter activation strategy is therefore necessary for an improved and short maturation period of biofilters in new RAS. In this study, microbial growth cultures added two different inoculums for RAS were compared. The observed biofilm establishment on clean biofilm carriers and quantified nitrification in the cultures simulated activation of new RAS biofilters. The inoculums used in the experiments included commercial inoculum for marine RAS and transferred biofilm carriers from a marine RAS biofilter operated 1.5 years after activation. The growth experiments revealed that the enrichment cultures inoculated with biofilm carriers from RAS initiated nitrite and nitrate production from ammonia on day 4, which is much earlier than in enrichment cultures with commercial inoculum where nitrite and nitrate production were detectable on day 15 and 18, respectively. The concentration of nitrite and nitrate measured at the end of the experimental period was also substantially higher in enrichment cultures inoculated with biofilm carriers. These results were supported by microbial community analyses of the enrichment cultures, showing that the populations in cultures added biofilm carriers had the highest relative abundance of Nitrosococcus and Nitrospira. Overall, our study shows that biofilm carriers from an established RAS were applicable as inoculum for biofilter activation. However, more knowledge on optimized growth conditions for nitrifying bacteria in RAS could benefit the colonization efficiency and the enrichment of these microorganisms during biofilter activation. In addition, methodical screening for pathogenic bacteria or viruses is needed before biofilter material can be successfully transferred between RAS without risk for disease transfer.
•Bacterial growth experiments to study activation of marine recirculating aquaculture system (RAS) biofilters.•Comparison of commercial inoculum and biofilter material from RAS as inoculum in growth cultures.•Nitrifying bacteria were successfully enriched in growth cultures containing biofilter material from RAS.•Microbial nitrite and nitrate production occurred earlier in cultures containing biofilter material from RAS
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