Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHST Observations of 10 Two-Image Gravitational Lenses
106
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on a program to obtain HST observations of galaxy-mass gravitational lens systems at optical and infrared wavelengths. Here we discuss the properties of 10 two-image gravitational lens systems (Q0142-100=UM673, B0218+357, SBS0909+532, BRI0952-0115, LBQS1009-0252, Q1017-207=J03.13, B1030+074, HE1104-1805, Q1208+1011, and PKS1830-211). We grouped these 10 systems because they have limited lens model constraints and often show poor contrast between the images and the lens galaxy. Of the 10 lens galaxies, 7 are probably early-type galaxies, 2 are probably late-type galaxies (B0218+357 and PKS1830-211), and one was not detected (Q1208+1011). We detect the host galaxies of the z_s=4.50 lensed quasar in BRI0952-0115, the z_s=2.32 lensed quasar in HE1104-1805, and the unlensed z=1.63 quasar near LBQS1009-0252. We fit a set of four standard lens models to each lens that had sufficient constraints to compare isothermal dark matter and constant mass-to-light lens models, and to explore the effects of local tidal shears.
rate research
Read More
We present multi-frequency VLA polarisation observations of nine gravitational lenses. The aim of these observations was to determine Faraday rotation measures (RM) for the individual lensed images, and to measure their continuum spectra over a wide range of frequencies.
We present deep spectroscopic observations of a Lyman-break galaxy candidate (hereafter MACS1149-JD) at $zsim9.5$ with the $textit{Hubble}$ Space Telescope ($textit{HST}$) WFC3/IR grisms. The grism observations were taken at 4 distinct position angles, totaling 34 orbits with the G141 grism, although only 19 of the orbits are relatively uncontaminated along the trace of MACS1149-JD. We fit a 3-parameter ($z$, F160W mag, and Ly$alpha$ equivalent width) Lyman-break galaxy template to the three least contaminated grism position angles using an MCMC approach. The grism data alone are best fit with a redshift of $z_{mathrm{grism}}=9.53^{+0.39}_{-0.60}$ ($68%$ confidence), in good agreement with our photometric estimate of $z_{mathrm{phot}}=9.51^{+0.06}_{-0.12}$ ($68%$ confidence). Our analysis rules out Lyman-alpha emission from MACS1149-JD above a $3sigma$ equivalent width of 21 AA{}, consistent with a highly neutral IGM. We explore a scenario where the red $textit{Spitzer}$/IRAC $[3.6] - [4.5]$ color of the galaxy previously pointed out in the literature is due to strong rest-frame optical emission lines from a very young stellar population rather than a 4000 AA{} break. We find that while this can provide an explanation for the observed IRAC color, it requires a lower redshift ($zlesssim9.1$), which is less preferred by the $textit{HST}$ imaging data. The grism data are consistent with both scenarios, indicating that the red IRAC color can still be explained by a 4000 AA{} break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicate that a $340^{+29}_{-35}$ Myr stellar population is already present in this galaxy only $sim500~mathrm{Myr}$ after the Big Bang.
We present discovery images, together with follow-up imaging and spectroscopy, of two large separation gravitational lenses found by our survey for wide arcs (the CASSOWARY). The survey exploits the multicolor photometry of the Sloan Digital Sky Survey to find multiple blue components around red galaxies. CASSOWARY~2 (or the Cheshire Cat) is composed of two massive early-type galaxies at z = 0.426 and 0.432 respectively lensing two background sources, the first a star-forming galaxy at z = 0.97 and the second a high redshift galaxy (z> 1.4). There are at least three images of the former source and probably four or more of the latter, arranged in two giant arcs. The mass enclosed within the larger arc of radius 11 arcsecs is about 33 x 10^{12} solar masses. CASSOWARY~3 comprises an arc of three bright images of a z = 0.725 source, lensed by a foreground elliptical at z = 0.274. The radius of the arc is about 4 arcsecs and the enclosed mass is 2.5 x 10^{12} solar masses. Together with earlier discoveries like the Cosmic Horseshoe and the 8 OClock Arc, these new systems, with separations intermediate between the arcsecond separation lenses of typical strong galaxy lensing and the larger separation cluster lenses, probe the very high end of the galaxy mass function.
We use convolutional neural networks (CNNs) and recurrent neural networks (RNNs) to estimate the parameters of strong gravitational lenses from interferometric observations. We explore multiple strategies and find that the best results are obtained when the effects of the dirty beam are first removed from the images with a deconvolution performed with an RNN-based structure before estimating the parameters. For this purpose, we use the recurrent inference machine (RIM) introduced in Putzky & Welling (2017). This provides a fast and automated alternative to the traditional CLEAN algorithm. We obtain the uncertainties of the estimated parameters using variational inference with Bernoulli distributions. We test the performance of the networks with a simulated test dataset as well as with five ALMA observations of strong lenses. For the observed ALMA data we compare our estimates with values obtained from a maximum-likelihood lens modeling method which operates in the visibility space and find consistent results. We show that we can estimate the lensing parameters with high accuracy using a combination of an RNN structure performing image deconvolution and a CNN performing lensing analysis, with uncertainties less than a factor of two higher than those achieved with maximum-likelihood methods. Including the deconvolution procedure performed by RIM, a single evaluation can be done in about a second on a single GPU, providing a more than six orders of magnitude increase in analysis speed while using about eight orders of magnitude less computational resources compared to maximum-likelihood lens modeling in the uv-plane. We conclude that this is a promising method for the analysis of mm and cm interferometric data from current facilities (e.g., ALMA, JVLA) and future large interferometric observatories (e.g., SKA), where an analysis in the uv-plane could be difficult or unfeasible.
Recent observations of galaxy luminosity profiles and dark matter simulations find luminosity and mass distributions characterized by central cusps rather than finite core radii. We introduce and implement a set of cusped ellipsoidal lens models which include limits similar to the Jaffe, Hernquist, eta and NFW models and apply them to the gravitational lenses APM 08279+5255 and B 1933+503. A successful model of APM 08279+5255 with its central, odd image requires a very shallow cusp, $gamma ltorder 0.4$ where $rho propto r^{-gamma}$ as $rto 0$, which is similar to a core rather than the favored $1 ltorder gamma ltorder 2$ cusps. B~1933+503, by contrast, is well modeled with a steep density cusp, $1.6 ltorder gamma ltorder 2.0$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
