Substructures, expected in cold dark matter haloes, have been proposed to explain the anomalous flux ratios in gravitational lenses. About 25% of lenses in the Cosmic Lens All-Sky Survey (CLASS) appear to have luminous satellites within ~ 5 kpc/h of the main lensing galaxies, which are usually at redshift z ~ 0.2-1. In this work we use the Millennium Simulation combined with galaxy catalogues from semi-analytical techniques to study the predicted frequency of such satellites in simulated haloes. The fraction of haloes that host bright satellites within the (projected) central regions is similar for red and blue hosts and is found to increase as a function of host halo mass and redshift. Specifically, at z = 1, about 11% of galaxy-sized haloes (with masses between 10^{12} M_sun/h and 10^{13} M_sun/h) host bright satellite galaxies within a projected radius of 5 kpc/h. This fraction increases to about 17% (25%) if we consider bright (all) satellites of only group-sized haloes (with masses between 10^{13} M_sun/h and 10^{14} M_sun/h). These results are roughly consistent with the fraction (~ 25%) of CLASS lensing galaxies observed to host luminous satellites. At z = 0, only ~ 3% of galaxy-sized haloes host bright satellite galaxies. The fraction rises to ~ 6%, (10%) if we consider bright (all) satellites of only group-sized haloes at z = 0. However, most of the satellites found in the inner regions are `orphan' galaxies where the dark matter haloes have been completely stripped. Thus the agreement crucially depends on the true survival rate of these `orphan' galaxies. We also discuss the effects of numerical resolution and cosmologies on our results.
We present H-band observations of gravitationally lensed QSO host galaxies obtained with NICMOS on HST as part of the CfA-Arizona-Gravitational-Lens-Survey (CASTLES). The detections are greatly facilitated by the lensing magnification in these systems; we find that most hosts of radio-quiet QSOs (RQQ) at z~2 are of modest luminosity (L<L_*). They are 2-5 times fainter than the hosts of radio-loud QSOs at the same epoch. Compared to low redshifts, RQQ hosts at z~2 also support higher nuclear luminosities at given stellar host mass. This suggests that the supermassive black holes at their center…
Caustic-crossing binary lenses make up about 5% of all detected microlenses. The relative proper motion of a caustic-crossing binary lens can be measured with observations from a single terrestrial telescope. Thus, uniquely, binary lenses can be completely solved with only the addition of a measurement of the microlensing parallax. This solution will yield the mass, distance, and transverse velocity of the lens relative to the source. To date, only one of the $\sim 1000$ observed microlensing events has been so solved. We examine the ability of a parallax satellite combined with ground-based o…
Surveys for gravitational lens systems have typically found a significantly larger fraction of lenses with four (or more) images than are predicted by standard ellipsoidal lens models (50% versus 25-30%). We show that including the effects of smaller satellite galaxies, with an abundance normalized by the observations, significantly increases the expected number of systems with more than two images and largely explains the discrepancy. The effect is dominated by satellites with ~20% the luminosity of the primary lens, in rough agreement with the typical luminosities of the observed satellites.…
We present a catalog of 49 spectroscopic strong gravitational lens candidates selected from a Sloan Digital Sky Survey sample of 50996 luminous red galaxies. Potentially lensed star-forming galaxies are detected through the presence of background oxygen and hydrogen nebular emission lines in the spectra of these massive foreground galaxies. This multiline selection eliminates the ambiguity of single-line identification and provides a very promising sample of candidate galaxy-galaxy lens systems at low to intermediate redshift, with foreground redshifts ranging from 0.16 to 0.49 and background …
In this paper we present a rather extensive error budget for the difference of the perigees of a pair of supplementary SLR satellites aimed to the detection of the Lense-Thirring effect.
In this paper we reply to recent claims by Ciufolini and Pavlis about certain aspects of the measurement of the general relativistic Lense-Thirring effect in the gravitational field of the Earth. I) The proposal by such authors of using the existing satellites endowed with some active mechanism of compensation of the non-gravitational perturbations as an alternative strategy to improve the currently ongoing Lense-Thirring tests is unfeasible because of the impact of the uncancelled even zonal harmonics of the geopotential and of some time-dependent tidal perturbations. II) It is shown that the…
We present a halo model prediction of the image separation distribution of strong lenses. Our model takes account of the subhalo population, which has been ignored in previous studies, as well as the conventional halo population. Halos and subhalos are linked to central and satellite galaxies by adopting an universal scaling relation between masses of (sub-)halos and luminosities of galaxies. Our model predicts that 10%-20% of lenses should be caused by the subhalo population. The fraction of lensing by satellite galaxies (subhalos) peaks at ~1'' and decreases rapidly with increasing image sep…
In this paper we analyze quantitatively the concept of LAGEOS--type satellites in critical supplementary orbit configuration (CSOC) which has proven capable of yielding various observables for many tests of General Relativity in the terrestrial gravitational field, with particular emphasis on the measurement of the Lense--Thirring effect.
The most important uncertainty in the results of gravitational microlensing experiments comes from the difficulties of photometry caused by blending of source stars. Recently Nemiroff (1997) pointed out that the results of microlensing experiments can also be affected by the blending of light from the lens itself if a significant fraction of lenses are composed of stars. In this paper, we estimate the effects of lens blending on the optical depth determination and the derived matter distribution toward the Galactic bulge by using realistic models of the lens matter distribution and a well-cons…
The Lenses Structure & Dynamics (LSD) Survey aims at studying the internal structure of luminous and dark matter - as well as their evolution - of field early-type (E/SO) galaxies to z~1. In particular, E/S0 lens galaxies are studied by combining gravitational lensing, photometric and kinematic data obtained with ground-based (VLA/Keck/VLT) and space-based telescopes (HST). Here, we report on preliminary results from the LSD Survey, in particular on (i) the constraints set on the luminous and dark-matter distributions in the inner several R_eff of E/S0 galaxies, (ii) the evolution of their ste…
In this letter we further analyze the concept of the use of a pair of identical geodetic satellites placed in identical orbits except for the inclinations which should be supplementary for measuring the Lense-Thirring effect in the terrestrial gravitational field. It turns out that not only the sum of the nodes, as already proposed for the LAGEOS-LARES mission, but also the difference of the perigees could be fruitfully adopted.
In this Chapter we deal with the attempts to measure the general relativistic gravitomagnetic Lense-Thirring effect with the Satellite Laser Ranging (SLR) technique applied to the existing LAGEOS and LAGEOS II terrestrial satellites and to the recently approved LARES.
We present the results of a survey for Extremely Red Objects (EROs) in the fields of ten galaxy cluster lenses at z~0.2, combining high-resolution Hubble Space Telescope imaging with deep K-band imaging from UKIRT. We detect 60 EROs with R-K>=5.3, of which 26 have R-K>=6.0 in a total image plane survey area of 49arcmin^2 down to K=20.6. We use detailed models of the cluster lenses to quantify the lens amplification and thus correct the observed number counts and survey area for the effects of gravitational lensing. After making these corrections, we estimate surface densities at K<=21.6 of 2.5…
This paper explores the dynamical interaction between extended halo and spheroid components of a disk galaxy and an environmental disturbance. One finds that resonant interaction between a galaxy and passing interlopers or satellite companions can carry the disturbance inward, deep inside the halo, where it can perturb the disk. Applied to the Milky Way for example, the LMC and SMC appear to be sufficient to cause the observed Galactic warp and possibly seed other asymmetries. A polar satellite orbit produces the largest warp and therefore the inferred LMC orbit is nearly optimal for maximum w…
In order to understand the nature of the lenses that generate microlensing events, one would like to measure their mass, distance, and velocity. Unfortunately, current microlensing experiments measure only one parameter of the events, the characteristic timescale, which is a combination of the underlying physical parameters. Other methods are required to extract additional information. Parallax measurements using a satellite in an Earth-like orbit yield the projected velocity of the lens: ${\bf{\tilde v}} ={\bf{v}}/(1-z)$, where ${\bf{v}}$ is the transverse velocity (speed and direction) of th…
In this paper we investigate the possibility of measuring the post-Newtonian general relativistic gravitomagnetic Lense-Thirring effect in the Jovian system of its Galilean satellites Io, Europa, Ganymede and Callisto in view of recent developments in processing and modelling their optical observations spanning a large time interval (125 years). The present day best observations have an accuracy between several kilometers to few tens of kilometers, which is just the order of magnitude of the Lense-Thirring shifts of the orbits of the Galilean satellites over almost a century. From a comparison…
We discuss the impact of the present-day uncertainties in the recently released CHAMP and/or GRACE Earth gravity models on the measurement of the Lense-Thirring effect with the nodes of the LAGEOS satellites. Also the role of the secular variations Jdots of the even zonal harmonics is quantitatively assessed via numerical simulations and tests. While the systematic error due to the static part of the geopotential ranges from 4% (EIGEN-GRACE02S) to 9% (GGM02S), the impact of the Jdots amounts to 13% over 11 years. This yields a 19% 1-sigma total error in the test recently performed with EIGEN-G…
With quantitative numerical simulations we show that the secular variations of the even zonal harmonics of the geopotential do affect the measurement of the Lense-Thirring effect with the nodes of LAGEOS and LAGEOS II at a \sim 14% level. Thus, the 1-sigma total error in the performed test with the 2nd generation CHAMP-only EIGEN2 Earth gravity model amounts to 51%, contrary to 18% claimed by Ciufolini.
We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low luminosity (M_V = -1.5) Milky Way satellite companion. While the combined size and luminosity of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we present spectroscopic evidence that this object is a dark matter-dominated dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean heliocentric recession velocity of 206 +/- 1.3 kms. We measure an internal velocity dispersion of 4.3+/-1.2 kms. Under the assumption that these stars are in dynamical equilibrium, we infer a total mass of 4.5^{+4.7}_{-2.5…
Among the effects predicted by the General Theory of Relativity for the orbital motion of a test particle, the post-Newtonian gravitomagnetic Lense-Thirring effect is very interesting and, up to now, there is not yet an undisputable experimental direct test of it. To date, the data analysis of the orbits of the existing geodetic LAGEOS and LAGEOS II satellites has yielded a test of the Lense-Thirring effect with a claimed accuracy of 20%-30%. According to some scientists such estimates could be optimistic. Here we wish to discuss the improvements obtainable in this measurement, in terms of rel…
In this paper we will show in detail that the performed attempts aimed at the detection of the general relativistic Lense-Thirring effect in the gravitational field of the Earth with the existing LAGEOS satellites are often presented in an optimistic and misleading way which is inadequate for such an important test of fundamental physics. E.g., in the latest reported measurement of the gravitomagnetic shift with the nodes of the LAGEOS satellites and the 2nd generation GRACE-only EIGEN-GRACE02S Earth gravity model over an observational time span of 11 years a 5-10% total accuracy is claimed at…
The impact of the latest combined CHAMP/GRACE/terrestrial measurements Earth gravity model EIGEN-CG03C on the measurement of the Lense-Thirring effect with some linear combinations of the nodes of some of the existing Earth's artificial satellites is presented. The 1-sigma upper bound of the systematic error in the node-node LAGEOS-LAGEOS II combination is 3.9% (4% with EIGEN-GRACE02S, \sim 6% with EIGEN-CG01C and \sim 9% with GGM02S), while it is 1$% for the node-only LAGEOS-LAGEOS II-Ajisai-Jason-1 combination (2% with EIGEN-GRACE02S, 1.6% with EIGEN-CG01C and 2.7% with GGM02S).
In this brief note some comments about the observable used in a recently published paper on the measurement of the general relativistic Lense-Thirring in the gravitational field of the Earth are presented. It turns out that, among other things, the authors might have yielded an optimistic evaluation of the error budget because of an underestimation of the impact of the secular variations of the even zonal harmonics of the geopotential. More realistic evaluations point towards a 15-45% error at 1-3sigma level, respectively.
We present a model to estimate the effect of differential magnification on the SED of high-z ULIRGs. It is found that the ratio of the high temperature component to the low temperature component can vary with up to a factor of ten with source position on very small angular scales ~0.01". This means that a correction for differential magnification is needed when deriving dust properties from strongly lensed sources.
We use the fourth data release of the Sloan Digital Sky Survey to investigate the orientations of 4289 satellite galaxies with respect to their hosts. The orientation of the satellites is inconsistent with a random distribution at the 99.94% confidence level, and the satellites show a preference for elongation in the direction of their hosts. Further, on scales < 50 kpc the major axes of the host galaxies and their satellites are preferentially aligned. Phrased in the terminology of weak lensing, the images of the satellites have a mean shear of gamma_T = -0.045 +/- 0.010, averaged over scales…
The tiny general relativistic Lense-Thirring effect can be measured by means of a suitable combination of the orbital residuals of the nodes of LAGEOS and LAGEOS II and the perigee of LAGEOS II. This observable is affected, among other factors, by the Earth' s solid and ocean tides. They induce long-period orbital perturbations that, over observational periods of few years, may alias the detection of the gravitomagnetic secular trend of interest. In this paper we calculate explicitly the most relevant tidal perturbations acting upon LAGEOSs and assess their influence on the detection of the Le…
The existence of flux-ratio anomalies between fold and cusp images in galaxy-scale strong-lens systems has led to an interpretation based on the presence of a high mass-fraction of cold-dark-matter (CDM) substructures around galaxies, as predicted by numerical N-body simulations. The flux-ratio anomaly is particularly evident in the radio-loud quadruple gravitational lens system CLASS B2045+265. In this paper, new high-resolution radio, optical, and infrared imaging of B2045+265 is presented which sheds more light on this anomaly and its possible causes. First, deep Very Long Baseline Array ob…
We consider the possibility that the Magellanic Clouds were the largest members of a group of dwarf galaxies that entered the Milky Way (MW) halo at late times. Seven of the eleven brightest satellites of the MW may have been part of this system. The proximity of some dwarfs to the plane of the orbit of the Large Magellanic Cloud (LMC) has been used to argue that they formed from tidal debris from the LMC and Small Magellanic Cloud (SMC). Instead, they may owe to the tidal breakup of the Magellanic Group. This can explain the association of many of the dwarf galaxies in the Local Group with th…
We propose a new method to detect the gravitational lenses in the ongoing microlensing experiments using medium and high resolution spectroscopy (resolution > 6000). Since the radial velocity of the lens and lensed source typically differs by ~100km/s, the spectral lines from the lens and source will be shifted relative to each other by (1-2)A in the optical. We simulate realistic composite spectra assuming different spectral types for the lens and source and study the lens detectability as a function of the signal-to-noise ratio, spectral resolution and lens-to-source light ratio. We show tha…
We present the first three galaxy clusters of a larger sample of the most X-ray luminous galaxy clusters selected from the ROSAT Bright Survey. This project, which is a systematic search for strong lensing, aims at arc statistics, mass determinations and studies of distant lensed galaxies. The three galaxy clusters presented here have been observed with the Wide Field Imager at the ESO2.2m in the R- and V-band. The images show lensing features like distinct distorted galaxies and arcs. Mass distributions of the lensing galaxy clusters and photometric properties of some arc candidates are prese…
In cold dark matter models, a galaxy's dark matter halo is more spatially extended than its stars. However, even though the five well-constrained gravitational lenses with time delay measurements must have similar dark matter distributions, reconciling the Hubble constant estimated from their time delays with local estimates is possible only if that dark matter distribution is as compact as the luminous galaxy. The Hubble constant is H0=48-4+7 km/s Mpc (95% confidence) if the lenses have flat rotation curves and H0=71+/-6 km/s Mpc (95% confidence) if they have constant mass-to-light ratios, as…
In this paper we investigate the opportunities offered by the new Earth gravity models from the dedicated CHAMP and, especially, GRACE missions to the project of measuring the general relativistic Lense-Thirring effect with a new Earth's artificial satellite. It turns out that it would be possible to abandon the stringent, and expensive, requirements on the orbital geometry of the originally prosed LARES mission (same semimajor axis a=12270 km of the existing LAGEOS and inclination i=70 deg) by inserting the new spacecraft in a relatively low, and cheaper, orbit (a=7500-8000 km, i\sim 70 deg) …
We report redshifts in two gravitational lens systems, MG0414+0534 and MG0751+2716. The lens galaxy in MG0414+0534 lies at z_l=0.9584+/-0.0002. The luminosity and extreme red color of the lens are then typical of a passively evolving, early-type, ~2L* galaxy. The galaxy cannot have a significant global mean extinction without being anomalously luminous. The lens galaxy in MG0751+2716 has a redshift of z_l=0.3502+/-0.0003 and it is a member of a small group. The group includes the nearby, bright companion galaxy whose redshift we confirmed to be z=0.3501+/-0.0001 and a nearby emission line gala…
The general relativistic Lense-Thirring effect can be detected by means of a suitable combination of orbital residuals of the laser-ranged LAGEOS and LAGEOS II satellites. While this observable is not affected by the orbital perturbation induced by the zonal Earth solid and ocean tides, it is sensitive to those generated by the tesseral and sectorial tides. The assessment of their influence on the measurement of the parameter mu, with which the gravitomagnetic effect is accounted for, is the goal of this paper. After simulating the combined residual curve by calculating accurately the mismodel…
Gravitational lensing studies suggest that the Universe may contain a population of dark galaxies; we investigate this intriguing possibility and propose a mechanism to explain their nature. In this mechanism a dark galaxy is formed with a low density disk in a dark halo of high spin parameter; such galaxies can have surface densities below the critical Toomre value for instabilities to develop, and following Kennicutt's work we expect these galaxies to have low star formation rates. The only stellar component of the galaxies is a halo system, formed during the collapse of the proto-galactic c…
MG 2016+112 is a quadruply imaged lens system with two complete images A and B and a pair of merging partial images in region C as seen in the radio. The merging images are found to violate the expected mirror symmetry. This indicates an astrometric anomaly which could only be of gravitational origin and could arise due to substructure in the environment or line-of-sight of the lens galaxy. We present new high resolution multi-frequency VLBI observations at 1.7, 5 and 8.4 GHz. Three new components are detected in the new VLBI imaging of both the lensed images A and B. The expected opposite par…
During the course of a gravitational lensing survey of distant, X-ray selected, EMSS clusters of galaxies, we have studied 6 X-ray luminous (Lx > 5x10^44 h_{50}^{-2} erg s^{-1}) clusters at redshifts exceeding z=0.5. All of these clusters are apparently massive. In addition to their high X-ray luminosity, two of the clusters at z~0.6 exhibit gravitationally lensed arcs. Furthermore, the highest redshift cluster in our sample, MS1054-0321 at z=0.826, is both extremely X-ray luminous (L[0.3-3.5 keV]=9.3x10^{44} h_{50}^{-2} erg s^{-1}), and exceedingly rich with an optical richness comparable to …
Bright galaxy-galaxy strong lenses are much more powerful than lensed quasars for measuring the mass profiles of galaxies, but until this year only a handful have been known. Here we present five new examples, identified via the optimal line-of-sight gravitational lens search strategy applied to luminous red galaxies in the Sloan Digital Sky Survey (SDSS). Our survey largely complements a similar survey by Bolton et al., who recently presented several new lenses. The lensed background galaxies are selected from the SDSS spectra via the presence of narrow emission line signatures, including the…
We present evidence for a Spitzer-selected luminous infrared galaxy (LIRG) behind the Bullet Cluster. The galaxy, originally identified in IRAC photometry as a multiply imaged source, has a spectral energy distribution consistent with a highly extincted (A_V~3.3), strongly star-forming galaxy at z=2.7. Using our strong gravitational lensing model presented in Bradac et al. (2006), we find that the magnifications are 10 to 50 for the three images of the galaxy. The implied infrared luminosity is consistent with the galaxy being a LIRG, with a stellar mass of M_*~2e11 M_Sun and a star formation …
We deal with the attempts to measure the Lense-Thirring effect with the Satellite Laser Ranging (SLR) technique applied to the existing LAGEOS and LAGEOS II terrestrial satellites and to the recently approved LARES spacecraft.The first issue addressed here is: are the so far published evaluations of the systematic uncertainty induced by the bad knowledge of the even zonal harmonic coefficients J_L of the multipolar expansion of the Earth's geopotential reliable and realistic? Our answer is negative. Indeed, if the differences Delta J_L among the even zonals estimated in different Earth's gravi…
While there is convincing evidence that the central regions (r<<Re) of early-type galaxies are dominated by stars and that the outer regions (r>>Re) are dominated by dark matter, the structure of early-type galaxies in the transition region (a few effective radii, Re) between the stars and the dark matter is unclear both locally and in gravitational lenses. Understanding the structure of galaxies in this transition region is a prerequisite for understanding dark matter halos and how they relate to the luminous galaxy. Potentially the best probe of this region is the sample of ~80 strong gravit…
We consider a nearly free falling Earth satellite where atomic wave interferometers are tied to a telescope pointing towards a faraway star. They measure the acceleration and the rotation relatively to the local inertial frame. We calculate the rotation of the telescope due to the aberrations and the deflection of the light in the gravitational field of the Earth. We show that the deflection due to the quadrupolar momentum of the gravity is not negligible if one wants to observe the Lense-Thirring effect of the Earth. We consider some perturbation to the ideal device and we discuss the orders …
(Abridged) We use numerical simulations to investigate the origin and structure of the luminous halos that surround isolated galaxies. These stellar structures extend out to several hundred kpc away from a galaxy, and consist of stars shed by merging subunits during the many accretion events that characterize the hierarchical assembly of galaxies. Such origin suggests that outer luminous halos are ubiquitous and that they should appear as an excess of light over extrapolations of the galaxy's inner profile beyond its traditional luminous radius. The mass profile of the accreted stellar compone…
We examine the relative fractions of passive (Type 1), quiet-SF (Type 2) and active-SF (Type 3+4) galaxies as a function of luminosity and number of neighbours in several volume limited samples selected from the 2dFGRS. Neighbours are counted within 1 $h_{75}^{-1}$ Mpc projected distance, and $\pm$ 1000 km s$^{-1}$ depth. We apply a maximum magnitude difference criterion and require neighbours to be fainter than the galaxy itself. We show that, whatever the environment, passive galaxies dominate in bright samples and active-SF galaxies in faint samples, whereas quiet-SF galaxies never dominate…
In this note we comment on a recent paper by I.Ciufolini about the possibility of placing the proposed terrestrial satellite LARES in a low-altitude, nearly polar orbit in order to measure the general relativistic Lense-Thirring effect with its node. Ciufolini claims that, for a departure of 4 deg in the satellite's inclination $i$ from the ideal polar configuration (i=90 deg), the impact of the errors in the even zonal harmonics of the geopotential, modelled with EIGEN-GRACE02S, would be nearly zero allowing for a few-percent measurement of the Lense-Thirring effect. Instead, we find that, wi…
After the approval by the Italian Space Agency of the LARES satellite, which should be launched at the end of 2009 with a VEGA rocket and whose claimed goal is a about 1% measurement of the general relativistic gravitomagnetic Lense-Thirring effect in the gravitational field of the spinning Earth, it is of the utmost importance to reliably assess the total realistic accuracy that can be reached by such a mission. The observable is a linear combination of the nodes of the existing LAGEOS and LAGEOS II satellites and of LARES able to cancel out the impact of the first two even zonal harmonic coe…
