ABSTRACT Until now, systematic errors in strong gravitational lens modeling have been acknowledged but have never been fully quantified. Here, we launch an investigation into the systematics induced ...by constraint selection. We model the simulated cluster Ares 362 times using random selections of image systems with and without spectroscopic redshifts and quantify the systematics using several diagnostics: image predictability, accuracy of model-predicted redshifts, enclosed mass, and magnification. We find that for models with >15 image systems, the image plane rms does not decrease significantly when more systems are added; however, the rms values quoted in the literature may be misleading as to the ability of a model to predict new multiple images. The mass is well constrained near the Einstein radius in all cases, and systematic error drops to <2% for models using >10 image systems. Magnification errors are smallest along the straight portions of the critical curve, and the value of the magnification is systematically lower near curved portions. For >15 systems, the systematic error on magnification is ∼2%. We report no trend in magnification error with the fraction of spectroscopic image systems when selecting constraints at random; however, when using the same selection of constraints, increasing this fraction up to ∼0.5 will increase model accuracy. The results suggest that the selection of constraints, rather than quantity alone, determines the accuracy of the magnification. We note that spectroscopic follow-up of at least a few image systems is crucial because models without any spectroscopic redshifts are inaccurate across all of our diagnostics.
We present a revised lens model of MACS J1149+2223, in which the first resolved multiply imaged lensed supernova (SN) was discovered. The lens model is based on the model of Johnson et al. with some ...modifications. We include more lensing constraints from the host galaxy of the newly discovered SN, and increase the flexibility of the model in order to better reproduce the lensing signal in the vicinity of this galaxy. The revised model accurately reconstructs the positions of the lensed SN, provides magnifications, and predicts the time delay between the instances of the SN. Finally, we reconstruct the source image of the host galaxy, and position the SN on one of its spiral arms. Products of this lens model are available to the community through MAST.
We present strong-lensing models as well as mass and magnification maps for the cores of the six Hubble Space Telescope (HST) Frontier Fields galaxy clusters. Our parametric lens models are ...constrained by the locations and redshifts of multiple image systems of lensed background galaxies. We use a combination of photometric redshifts and spectroscopic redshifts of the lensed background sources obtained by us (for A2744 and AS1063), collected from the literature, or kindly provided by the lensing community. Using our results, we (1) compare the derived mass distribution of each cluster to its light distribution, (2) quantify the cumulative magnification power of the HST Frontier Fields clusters, (3) describe how our models can be used to estimate the magnification and image multiplicity of lensed background sources at all redshifts and at any position within the cluster cores, and (4) discuss systematic effects and caveats resulting from our modeling methods. We specifically investigate the effect of the use of spectroscopic and photometric redshift constraints on the uncertainties of the resulting models. We find that the photometric redshift estimates of lensed galaxies are generally in excellent agreement with spectroscopic redshifts, where available. However, the flexibility associated with relaxed redshift priors may cause the complexity of large-scale structure that is needed to account for the lensing signal to be underestimated. Our findings thus underline the importance of spectroscopic arc redshifts, or tight photometric redshift constraints, for high precision lens models. All products from our best-fit lens models (magnification, convergence, shear, deflection field) and model simulations for estimating errors are made available via the Mikulski Archive for Space Telescopes.
Abstract
We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy ...SGAS J111020.0+645950.8 at a redshift of
z
= 2.481. The physical size scales that we probe, radii
r
= 30–50 pc, are considerably smaller scales than have yet been studied at these redshifts. The star formation surface density we find within these small clumps is consistent with surface densities measured previously for other lensed galaxies at similar redshift. Twenty-two percent of the rest-frame ultraviolet light in this lensed galaxy arises from small clumps, with
pc. Within the range of overlap, the clump luminosity function measured for this lensed galaxy is remarkably similar to those of
galaxies. In this galaxy, star-forming regions smaller than 100 pc—physical scales not usually resolved at these redshifts by current telescopes—are important locations of star formation in the distant universe. If this galaxy is representative, this may contradict the theoretical picture in which the critical size scale for star formation in the distant universe is of the order of 1 kpc. Instead, our results suggest that current telescopes have not yet resolved the critical size scales of star-forming activity in galaxies over most of cosmic time.
Adenosine monophosphate (AMP)-activated protein kinase (AMPK) acts as a master regulator of cellular energy homeostasis by directly phosphorylating metabolic enzymes and nutrient transporters and by ...indirectly promoting the transactivation of nuclear genes involved in mitochondrial biogenesis and function. We explored the mechanism of AMPK-mediated induction of gene expression. We identified AMPK consensus phosphorylation sequences in three proteins involved in nucleosome remodeling: DNA methyltransferase 1 (DNMT1), retinoblastoma binding protein 7 (RBBP7), and histone acetyltransferase 1 (HAT1). DNMT1 mediates DNA methylation that limits transcription factor access to promoters and is inhibited by RBBP7. Acetylation of histones by HAT1 creates a more relaxed chromatin-DNA structure that favors transcription. AMPK-mediated phosphorylation resulted in the activation of HAT1 and inhibition of DNMT1. For DNMT1, this inhibition was both a direct effect of phosphorylation and the result of increased interaction with RBBP7. In human umbilical vein cells, pharmacological AMPK activation or pulsatile shear stress triggered nucleosome remodeling and decreased cytosine methylation, leading to increased expression of nuclear genes encoding factors involved in mitochondrial biogenesis and function, such as peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), transcription factor A (Tfam), and uncoupling proteins 2 and 3 (UCP2 and UCP3). Similar effects were seen in the aortas of mice given pharmacological AMPK activators, and these effects required AMPK2α. These results enhance our understanding of AMPK-mediated mitochondrial gene expression through nucleosome remodeling.
Abstract
Using the combined resolving power of the
Hubble Space Telescope
and gravitational lensing, we resolve star-forming structures in a
galaxy on scales much smaller than the usual kiloparsec ...diffraction limit of
HST
. SGAS J111020.0+645950.8 is a clumpy, star-forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at
, with a total magnification
across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray-trace the model to the image plane, convolve with the instrumental point-spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray-tracing, of accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift.
Abstract
We present strong gravitational lensing models for 37 galaxy clusters from the Sloan Digital Sky Survey Giant Arcs Survey. We combine data from multi-band
Hubble Space Telescope
Wide Field ...Camera 3 (WFC3) imaging, with ground-based imaging and spectroscopy from
Magellan
, Gemini, Apache Point Observatory, and the Multiple Mirror Telescope, in order to detect and spectroscopically confirm new multiply imaged lensed background sources behind the clusters. We report spectroscopic or photometric redshifts of sources in these fields, including cluster galaxies and background sources. Based on all available lensing evidence, we construct and present strong-lensing mass models for these galaxy clusters. The clusters span a redshift range of 0.176 <
z
< 0.66 with a median redshift of
z
= 0.45, and sample a wide range of dynamical masses, 1.5 <
M
200
< 35 × 10
14
, as estimated from their velocity dispersions. As these clusters were selected as lenses primarily owing to a fortuitous alignment with background galaxies that results in giant arcs, they exhibit a wide range in Einstein radii, 1.″3 <
θ
E
< 23.″1 for a source at
z
= 2, with a median
θ
E
= 10.″8. The reduced
HST
images and lens model outputs are made available to the scientific community as high-level data products with this publication.
ABSTRACT
Recent observations have revealed the presence of strong C iii emission (EW$_{\rm {C\,{\small III}}}\gt 20$ Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to ...understand the nature of these line emitters, we have initiated a survey targeting C iii emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J125-band flux excesses indicative of intense O iii + H β emission (EW$_{\rm {O\,{\small III}+H\,\beta }}$ = 500–2000 Å), similar to what has been observed at z > 6. We detect C iii emission in three of the four sources, with the C iii EW reaching values seen in the reionization era (EW$_{\rm {C\,{\small III}}}\simeq 17\!-\!22$ Å) in the two sources with the strongest optical line emission (EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C iii emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C iii and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C iii has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C iii to measure redshifts of objects with IRAC excesses indicating EW$_{\rm {O\,{\small III}+H\,\beta }}\simeq 2000$ Å, providing a method of spectroscopic confirmation independent of Ly α.
Strong gravitational lensing by galaxy clusters magnifies background galaxies, enhancing our ability to discover statistically significant samples of galaxies at , in order to constrain the ...high-redshift galaxy luminosity functions. Here, we present the first five lens models out of the Reionization Lensing Cluster Survey (RELICS) Hubble Treasury Program, based on new HST WFC3/IR and ACS imaging of the clusters RXC J0142.9+4438, Abell 2537, Abell 2163, RXC J2211.7-0349, and ACT-CLJ0102-49151. The derived lensing magnification is essential for estimating the intrinsic properties of high-redshift galaxy candidates, and properly accounting for the survey volume. We report on new spectroscopic redshifts of multiply imaged lensed galaxies behind these clusters, which are used as constraints, and detail our strategy to reduce systematic uncertainties due to lack of spectroscopic information. In addition, we quantify the uncertainty on the lensing magnification due to statistical and systematic errors related to the lens modeling process, and find that in all but one cluster, the magnification is constrained to better than 20% in at least 80% of the field of view, including statistical and systematic uncertainties. The five clusters presented in this paper span the range of masses and redshifts of the clusters in the RELICS program. We find that they exhibit similar strong lensing efficiencies to the clusters targeted by the Hubble Frontier Fields within the WFC3/IR field of view. Outputs of the lens models are made available to the community through the Mikulski Archive for Space Telescopes.
Cortactin translocates to the cell periphery in vascular endothelial cells (ECs) on cortical-actin assembly in response to pulsatile shear stress. Because cortactin has putative sites for ...AMP-activated protein kinase (AMPK) phosphorylation and sirtuin 1 (SIRT1) deacetylation, we examined the hypothesis that AMPK and SIRT1 coregulate cortactin dynamics in response to shear stress.
Analysis of the ability of AMPK to phosphorylate recombinant cortactin and oligopeptides whose sequences matched AMPK consensus sequences in cortactin pointed to Thr-401 as the site of AMPK phosphorylation. Mass spectrometry confirmed Thr-401 as the site of AMPK phosphorylation. Immunoblot analysis with AMPK siRNA and SIRT1 siRNA in human umbilical vein ECs and EC-specific AMPKα2 knockout mice showed that AMPK phosphorylation of cortactin primes SIRT1 deacetylation in response to shear stress. Immunoblot analyses with cortactin siRNA in human umbilical vein ECs, phospho-deficient T401A and phospho-mimetic T401D mutant, or aceto-deficient (9K/R) and aceto-mimetic (9K/Q) showed that cortactin regulates endothelial nitric oxide synthase activity. Confocal imaging and sucrose-density gradient analyses revealed that the phosphorylated/deacetylated cortactin translocates to the EC periphery facilitating endothelial nitric oxide synthase translocation from lipid to nonlipid raft domains. Knockdown of cortactin in vitro or genetic reduction of cortactin expression in vivo in mice substantially decreased the endothelial nitric oxide synthase-derived NO bioavailability. In vivo, atherosclerotic lesions increase in ApoE
/cortactin
mice, when compared with ApoE
/cortactin
littermates.
AMPK phosphorylation of cortactin followed by SIRT1 deacetylation modulates the interaction of cortactin and cortical-actin in response to shear stress. Functionally, this AMPK/SIRT1 coregulated cortactin-F-actin dynamics is required for endothelial nitric oxide synthase subcellular translocation/activation and is atheroprotective.
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