We measure the morphology-density relation ( MDR) and morphology-radius relation (MRR) for galaxies in seven z $ 1 clusters that have been observed with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. Simulations and independent comparisons of our visually derived morphologies indicate that ACS allows one to distinguish between E, S0, and spiral morphologies down to z 850 ¼ 24, corresponding to L /L Ã ¼ 0:21 and 0.30 at z ¼ 0:83 and 1.24, respectively. We adopt density and radius estimation methods that match those used at lower redshift in order to study the evolution of the MDR and MRR. We detect a change in the MDR between 0:8 < z < 1:2 and that observed at z $ 0, consistent with recent work; specifically, the growth in the bulge-dominated galaxy fraction, f EþS0 , with increasing density proceeds less rapidly at z $ 1 than it does at z $ 0. At z $ 1 and AE ! 500 galaxies Mpc À2 , we find h f EþS0 i ¼ 0:72 AE 0:10. At z $ 0, an E+S0 population fraction of this magnitude occurs at densities about 5 times smaller. The evolution in the MDR is confined to densities AE k 40 galaxies Mpc À2 and appears to be primarily due to a deficit of S0 galaxies and an excess of Sp+Irr galaxies relative to the local galaxy population. The f E -density relation exhibits no significant evolution between z ¼ 1 and 0. We find mild evidence to suggest that the MDR is dependent on the bolometric X-ray luminosity of the intracluster medium. Implications for the evolution of the disk galaxy population in dense regions are discussed in the context of these observations.

We present the Strong Lensing Legacy Survey -ARCS (SARCS) sample compiled from the final T0006 data release of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) covering a total non-overlapping area of 159 deg 2 . We adopt a semi-automatic method to find gravitational arcs in the survey that makes use of an arc-finding algorithm. The candidate list is pruned by visual inspection and ranking to form the final SARCS sample. This list also includes some serendipitously discovered lens candidates which the automated algorithm did not detect. The SARCS sample consists of 127 lens candidates which span arc radii ∼ 2 ′′ − 18 ′′ within the unmasked area of ∼150 deg 2 . Within the sample, 54 systems are promising lenses amongst which, we find 12 giant arcs (length-to-width ratio ≥ 8). We also find 2 radial arc candidates in SL2SJ141447+544704. From our sample, we detect a systematic alignment of the giant arcs with the major axis of the baryonic component of the putative lens in concordance with previous studies. This alignment is also observed for all arcs in the sample and does not vary significantly with increasing arc radius. The mean values of the photometric redshift distributions of lenses corresponding to the giant arcs and all arcs sample are at z ∼ 0.6. Owing to the large area and depth of the CFHTLS, we find the largest sample of lenses probing mass scales that are intermediate to cluster and galaxy lenses for the first time. We compare the observed image separation distribution (ISD) of our arcs with theoretical models. A two-component density profile for the lenses which accounts for both the central galaxy and the dark matter component is required by the data to explain the observed ISD. Unfortunately, current levels of uncertainties and degeneracies accommodate models both with and without adiabatic contraction. We also show the effects of changing parameters of the model that predict the ISD and that a larger lens sample might constrain relations such as the concentration-mass relation, mass-luminosity relation and the faint-end slope of the luminosity function.

We estimate the fraction of mass that is composed of compact objects in gravitational lens galaxies. This study is based on microlensing measurements (obtained from the literature) of a sample of 29 quasar image pairs seen through 20 lens galaxies. We determine the baseline for no microlensing magnification between two images from the ratios of emission line fluxes. Relative to this baseline, the ratio between the continua of the two images gives the difference in microlensing magnification. The histogram of observed microlensing events peaks close to no magnification and is concentrated below 0.6 magnitudes, although two events of high magnification, ∆m ∼ 1.5, are also present. We study the likelihood of the microlensing measurements using frequency distributions obtained from simulated microlensing magnification maps for different values of the fraction of mass in compact objects, α. The concentration of microlensing measurements close to ∆m ∼ 0 can be explained only by simulations corresponding to very low values of α (10% or less). A maximum likelihood test yields α = 0.05 +0.09 −0.03 (90% confidence interval) for a quasar continuum source of intrinsic size r s 0 ∼ 2.6 · 10 15 cm. This estimate is valid in the 0.1 − 10M ⊙ range of microlens masses. We study the dependence of the estimate of α with r s 0 , and find that α 0.1 for r s 0 1.3 · 10 16 cm. High values of α are possible only for source sizes much larger than commonly expected (r s 0 >> 2.6 · 10 16 cm). Regarding the current controversy about Milky Way/LMC and M31 microlensing studies, our work supports the hypothesis of a very low content in MACHOS (Massive Compact Halo Objects). In fact, according to our study, quasar microlensing probably arises from the normal star populations of lens galaxies and there is no statistical evidence for MACHOS in the dark halos.

We present F435W (B), F606W ( broad V ), and F814W ( broad I ) coronagraphic images of the debris disk around Pictoris obtained with the Hubble Space Telescope's Advanced Camera for Surveys. These images provide the most photometrically accurate and morphologically detailed views of the disk between 30 and 300 AU from the star ever recorded in scattered light. We confirm that the previously reported warp in the inner disk is a distinct secondary disk inclined by $5 from the main disk. The projected spine of the secondary disk coincides with the isophotal inflections, or ''butterfly asymmetry,'' previously seen at large distances from the star. We also confirm that the opposing extensions of the main disk have different position angles, but we find that this ''wing-tilt asymmetry'' is centered on the star rather than offset from it, as previously reported. The main disk's northeast extension is linear from 80 to 250 AU, but the southwest extension is distinctly bowed with an amplitude of $1 AU over the same region. Both extensions of the secondary disk appear linear, but not collinear, from 80 to 150 AU. Within $120 AU of the star, the main disk is $50% thinner than previously reported. The surface brightness profiles along the spine of the main disk are fitted with four distinct radial power laws between 40 and 250 AU, while those of the secondary disk between 80 and 150 AU are fitted with single power laws. These discrepancies suggest that the two disks have different grain compositions or size distributions. The F606W/ F435W and F814W/ F435W flux ratios of the composite disk are nonuniform and asymmetric about both projected axes of the disk. The disk's northwest region appears 20%-30% redder than its southeast region, which is inconsistent with the notion that forward scattering from the nearer northwest side of the disk should diminish with increasing wavelength. Within $120 AU, the m F435W À m F606W and m F435W À m F814W colors along the spine of the main disk are $10% and $20% redder, respectively, than those of Pic. These colors increasingly redden beyond $120 AU, becoming 25% and 40% redder, respectively, than the star at 250 AU. These measurements overrule previous determinations that the disk is composed of neutrally scattering grains. The change in color gradient at $120 AU nearly coincides with the prominent inflection in the surface brightness profile at $115 AU and the expected waterice sublimation boundary. We compare the observed red colors within $120 AU with the simulated colors of nonicy grains having a radial number density /r À3 and different compositions, porosities, and minimum grain sizes. The observed colors are consistent with those of compact or moderately porous grains of astronomical silicate and /or graphite with sizes k0.15-0.20 m, but the colors are inconsistent with the blue colors expected from grains with porosities k90%. The increasingly red colors beyond the ice sublimation zone may indicate the condensation of icy mantles on the refractory grains, or they may reflect...

Using Hubble Space Telescope (HST ) and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z $ 7:6 in the field of the massive galaxy cluster Abell 1689 (z ¼ 0:18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong z 850 À J 110 break of at least 2.2 mag and is completely undetected (<1 ) in HST Advanced Camera for Surveys (ACS) g 475 , r 625 , i 775 , and z 850 data. These properties, combined with the very blue J 110 À H 160 and H 160 À ½4:5 m colors, are exactly the properties of an z $ 7:6 LBG, and can only be reasonably fit by a star-forming galaxy at z ¼ 7:6 AE 0:4 ( 2 ¼ 1:1). Attempts to reproduce these properties with a model galaxy at z < 4 yield particularly poor fits ( 2 ! 25). A1689-zD1 has an observed ( lensed) magnitude of 24.7 AB (8 ) in the NICMOS H 160 band and is $1.3 mag brighter than the brightest known z 850 -dropout galaxy. When corrected for the cluster magnification of $9.3 at z $ 7:6, the candidate has an intrinsic magnitude of H 160 ¼ 27:1 AB, or about an L Ã galaxy at z $ 7:6. The source-plane deprojection shows that the star formation is occurring in compact knots of size P300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1:6Y3:9) ; 10 9 M , stellar ages 45Y320 Myr, star formation rates P7.6 M yr À1 , and low reddening with A V 0:3. These properties are generally similar to those of LBGs found at z $ 5Y 6. The inferred stellar ages suggest a formation redshift of z $ 8Y10 (t P 0:63 Gyr). A1689-zD1 is the brightest observed, highly reliable z > 7:0 galaxy candidate found to date.