Lensed Arcs Research Articles

Constraints on dark energy models from galaxy clusters with multiple arcs

We make an exploratory study of how well dark energy models can be constrained using lensed arcs at different redshifts behind cluster lenses. Arcs trace the critical curves of clusters, and the growth of critical curves with source redshift is sensitive to the dark-energy equation of state. Using analytical models and numerically simulated clusters, we explore the key factors involved in using cluster arcs as a probe of dark energy. We quantify the sensitivity to lens mass, concentration and ellipticity with analytical models that include the effects of dark energy on halo structure. We show with simple examples how degeneracies between mass models and cosmography may be broken using arcs at multiple redshifts or additional constraints on the lens density profile. However we conclude that the requirements on the data are so stringent that it is very unlikely that robust constraints can be obtained from individual clusters. We argue that surveys of clusters, analyzed in conjunction with numerical simulations, are a more promising prospect for arc-cosmography. We use such numerically simulated clusters to estimate how large a sample of clusters/arcs could provide interesting constraints on dark energy models. We focus on the scatter produced by differences in the mass distribution of individual clusters. We find from our sample of simulated clusters that at least 1000 pairs of arcs are needed to obtain constraints if the mass distribution of individual clusters is taken to be undetermined. We discuss several unsolved problems that need study to fully develop this method for precision studies with future surveys.

An ISOCAM survey through gravitationally lensing galaxy clusters

The massive cluster of galaxies Abell 2219 (z = 0.228) with two spectacular gravitational lensing arcs was observed at 14.3 μm (hereafter 15 μm) with the Infrared Space Observatory and results were published by Barvainis et al. ([CITE]). These observations have been reanalyzed using a method specifically designed for the detection of faint sources that had been applied to other clusters. Five new sources were detected and the resulting cumulative total of ten sources all have optical counterparts. The mid-infrared sources are identified with three cluster members, three foreground galaxies, an Extremely Red Object, a star and two galaxies of unknown redshift. The spectral energy distributions (SEDs) of the galaxies are fit with models from a selection, using the program GRASIL. Best-fits are obtained, in general, with models of galaxies with ongoing star formation. Infrared luminosities and star formation rates are obtained for six sources: the cluster members and the foreground galaxies. For the three cluster members the infrared luminosities derived from the model SEDs are between ~5.7 and 1.4 , corresponding to infrared star formation rates between 10 and 24 . The two cluster galaxies that have optical classifications are in the Butcher-Oemler region of the color–magnitude diagramme. The three foreground galaxies have infrared luminosities between 1.5 and 9.4 yielding infrared star formation rates between 3 and 16 . Two of the foreground galaxies are located in two foreground galaxy enhancements (Boschin et al. [CITE]). Including Abell 2219, six distant clusters of galaxies have been mapped with ISOCAM and luminous infrared galaxies (LIRGs) have been found in three of them. The presence of LIRGs in Abell 2219 strengthens the association between luminous infrared galaxies in clusters and recent or ongoing cluster merger activity.

TheChandraLarge Area Synoptic X-Ray Survey (CLASXS) of the Lockman Hole-Northwest: The X-Ray Catalog

We present the X-ray catalog and basic results from our Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest field. Our 9 ACIS-I fields cover a contiguous solid angle of approx. 0.4 sq deg and reach fluxes of 5 x 10(exp -16) ergs/sq cm/s (0.4-2 keV) and 3 x 10(exp -15) ergs/sq cm/s (2-8 keV). Our survey bridges the gap between ultradeep pencil-beam surveys, such as the Chandra Deep Fields (CDFs), and shallower, large area surveys, allowing a better probe of the X-ray sources that contribute most of the 2-10 keV cosmic X-ray background (CXB). We find a total of 525 X-ray point sources and 4 extended sources. At approx. 10(exp -14)ergs/sq cm/s (2-8 keV), our number counts are significantly higher than those of several non-contiguous, large area surveys. Such a large difference is an indication of clustering in the X-ray sources. On the other hand, the integrated flux from the CLASXS field, combined with ASCA and Chandra ultradeep surveys, is consistent with results from other large area surveys, within the variance of the CXB. We see spectral evolution in the hardening of the sources at fluxes below 10(exp -14) ergs/sq cm/s, which agrees with previous observations from Chandra and XMM-Newton. About 1/3 of the sources in the CLASXS field have multiple observations, allowing variability tests. Above 4 x 10(exp -14) ergs/sq cm/s (0.4-8 keV), approx. 61% of the sources are variable. We also investigated the spectral variability of the variable sources. While most show spectral softening with increasing flux, or no significant spectral change, there are a few sources that show a different trend. Four extended sources in CLASXS is consistent with the previously measured LogN-LogS of galaxy clusters. Using X-ray spectra and optical colors, we argue that 3 of the 4 extended sources are galaxy clusters or galaxy groups. We report the discovery of a gravitational lensing arc associated with one of these sources. Using red sequence and brightest cluster galaxy methods, we find that the redshifts of the extended sources are in the range z approx. 0.5 - 1. The inferred masses within the Einstein radii are consistent with the mass profiles of local groups scaled to the same virial radii.

The analysis of Abell 1835 using a deprojection technique

We present the results from a detailed deprojection analysis of Abell 1835 as observed by {\it XMM-Newton}. If we fit the spectra with an isothermal plasma model, the deprojected temperature profile is flat in the outer region around 7.6 keV and decreases to $\sim$ 5.6 keV in the center, which may be connected with the gas cooling. In the central part, a two-component thermal plasma model can fit the spectrum significantly better. Moreover, the cool component (T $\sim$ 1.8 keV) has a much lower metal abundance than the hot component (T $\sim$ 8 keV), which may be due to the longer cooling time for the cool gas with lower abundance. In addition, it was found that without a main isothermal component, the standard cooling flow model cannot fit the spectrum satisfactorily. From the isothermal model fitting results we also derived the electron density $n_e$, and fitted its radial distribution with a double-$\beta$ model. The $n_e$ profile inferred with the double-$\beta$ model and the deprojected X-ray gas temperature profile were then combined to derive the total mass and the total projected mass of the cluster. The projected mass is lower than that derived from the weak lensing method. However, assuming that the cluster extends to a larger radius $\sim15'$ as found by Clowe & Schneider (2002), the two results are consistent within the error bars. Furthermore, we calculated the projected mass within the radius of $\sim$ 153 kpc implied by the presence of a gravitational lensing arc, which is about half of the mass determined from the optical lensing.

Arc Statistics in Triaxial Dark Matter Halos: Testing the Collisionless Cold Dark Matter Paradigm

Statistics of lensed arcs in clusters of galaxies serve as a powerful probe of both the non-sphericity and the inner slope of dark matter halos. We develop a semi-analytic method to compute the number of arcs in triaxial dark matter halos. This combines the lensing cross section from the Monte Carlo ray-tracing simulations, and the probability distribution function (PDF) of the axis ratios evaluated from cosmological N-body simulations. This approach enables one to incorporate both asymmetries in the projected mass density and elongations along the line-of-sight analytically, for the first time in cosmological lensed arc statistics. As expected, triaxial dark matter halos significantly increase the number of arcs relative to spherical models; the difference amounts to more than one order of magnitude while the value of enhancement depends on the specific properties of density profiles. Then we compare our theoretical predictions with the observed number of arcs from 38 X-ray selected clusters. In contrast to the previous claims, our triaxial dark matter halos with inner density profile \rho \propto r^{-1.5} in a Lambda-dominated cold dark matter (CDM) universe reproduces well the observation. Since both the central mass concentration and triaxial axis ratios (minor to major axis ratio ~0.5) required to account for the observed data are consistent with cosmological N-body simulations, our result may be interpreted to lend strong support for the collisionless CDM paradigm at the mass scale of clusters.

Gravitational Lens Models of Arcs in Abell 2218

view Abstract Citations (10) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gravitational Lens Models of Arcs in Abell 2218 Saraniti, David W. ; Petrosian, Vahe ; Lynds, Roger Abstract Abell 2218, with redshift z = 0.17, is one of the first clusters in which gravitationally lensed arcs have been found. Abell 2218 contains several arcs, and although none are as large as some of the more studied arcs (Abell 370, Cl 2244-02), they are interesting nonetheless. We present photometric and spectroscopic data of the cluster taken at the NOAO 4 m telescope. We show broadband spectra of some of the more interesting objects in the field. One arc in the cluster is redder than a typical galaxy, which is unusual since most lensed arcs have a bluer color. The spectrum of this arc reveals a redshift of 0.703. There is an almost perfectly circular blue ring surrounding one galaxy. There are several other blue arclets including two, called the twin arcs, that are on either side of two close galaxies. We model the system with a simple mass distribution consisting of the visible galaxies and a diffuse dark matter component. We are able to model the red arc and the twin arcs, but we find that the ring is most likely not a gravitationally lensed image. Combining this with the observed velocity dispersion of galaxies, we set limits on the masses of some of the galaxies and on the parameters describing the distribution of dark matter. We compare the distributions with the X-ray surface brightness variation of the cluster and find that the dark matter component for the lensing models is more compact than the X-ray distribution. We shall discuss this in a future publication. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176792 Bibcode: 1996ApJ...458...57S Keywords: GALAXIES: CLUSTERS: INDIVIDUAL NAME: ABELL 2218; COSMOLOGY: GRAVITATIONAL LENSING full text sources ADS | data products NED (16) SIMBAD (3)