[en] Direct measurements of dark matter distributions in galaxies are currently only possible through the use of gravitational lensing observations. Combinations of lens modeling and stellar velocity dispersion measurements provide the best constraints on dark matter distributions in individual galaxies, however they can be quite complex. In this paper, we use observations and simulations of gravitational microlensing to measure the smooth (dark) matter mass fraction at the position of lensed images in three lens galaxies: MG 0414+0534, SDSS J0924+0219, and Q2237+0305. The first two systems consist of early-type lens galaxies, and both display a flux ratio anomaly in their close image pair. Anomalies such as these suggest that a high smooth matter percentage is likely, and indeed we prefer ∼50% smooth matter in MG 0414+0534 and ∼80% in SDSS J0924+0219 at the projected locations of the lensed images. Q2237+0305 differs somewhat in that its lensed images lie in the central kiloparsec of the barred spiral lens galaxy, where we expect stars to dominate the mass distribution. In this system, we find a smooth matter percentage that is consistent with zero.

[en] We investigate the effects of gravitational waves (GWs) from a simulated population of binary supermassive black holes (SMBHs) on pulsar timing array data sets. We construct a distribution describing the binary SMBH population from an existing semi-analytic galaxy formation model. Using realizations of the binary SMBH population generated from this distribution, we simulate pulsar timing data sets with GW-induced variations. We find that the statistics of these variations do not correspond to an isotropic, stochastic GW background. The ''Hellings and Downs'' correlations between simulated data sets for different pulsars are recovered on average, though the scatter of the correlation estimates is greater than expected for an isotropic, stochastic GW background. These results are attributable to the fact that just a few GW sources dominate the GW-induced variations in every Fourier frequency bin of a five-year data set. Current constraints on the amplitude of the GW signal from binary SMBHs will be biased. Individual binary systems are likely to be detectable in five-year pulsar timing array data sets where the noise is dominated by GW-induced variations. Searches for GWs in pulsar timing array data therefore need to account for the effects of individual sources of GWs.

[en] Lyman-break galaxy (LBG) samples observed during reionization (z ≳ 6) with the Hubble Space Telescope's Wide Field Camera 3 are reaching sizes sufficient to characterize their clustering properties. Using a combined catalog from the Hubble eXtreme Deep Field and CANDELS surveys, containing N = 743 LBG candidates at z ≥ 6.5 at a mean redshift of z-bar =7.2, we detect a clear clustering signal in the angular correlation function (ACF) at ≳ 4σ, corresponding to a real-space correlation length r₀=6.7_−1.0^+0.9h⁻¹cMpc. The derived galaxy bias b=8.6_−1.0^+0.9 is that of dark matter halos of M=10^{11.1_−0.3+0.2} M_⊙ at z = 7.2, and highlights that galaxies below the current detection limit (M_AB ∼ –17.7) are expected in lower-mass halos (M ∼ 10⁸-10^10.5 M_⊙ ). We compute the ACF of LBGs at z ∼ 3.8 – z ∼ 5.9 in the same surveys. A trend of increasing bias is found from z-bar =3.8 (b ∼ 3.0) to z-bar =7.2 (b ∼ 8.6), broadly consistent with galaxies at fixed luminosity being hosted in dark matter halos of similar mass at 4 ≲ z ≲ 6, followed by a slight rise in halo masses at z ≳ 7 (∼2σ confidence). Separating the data at the median luminosity of the z-bar =7.2 sample (M _UV = –19.4) shows higher clustering at z-bar =5.9 for bright galaxies (r₀=5.5_−1.6^+1.4h⁻¹cMpc, b=6.2_−1.5^+1.2) compared to faint galaxies (r₀=1.9_−1.0^+1.1h⁻¹cMpc, b=2.7_−1.2^+1.2) implying a constant mass-to-light ratio (dlogM/dlogL)∼1.2_−0.8^+1.8. A similar trend is present in the z-bar =7.2 sample with larger uncertainty. Finally, our bias measurements allow us to investigate the fraction of dark matter halos hosting UV-bright galaxies (the duty cycle, ε_DC). At z-bar =7.2 values near unity are preferred, which may be explained by the shortened halo assembly time at high redshift.

[en] We report on a Hubble Space Telescope search for rest-frame ultraviolet emission from the host galaxies of five far-infrared-luminous z ≃ 6 quasars and the z = 5.85 hot-dust-free quasar SDSS J0005–0006. We perform 2D surface brightness modeling for each quasar using a Markov Chain Monte Carlo estimator, to simultaneously fit and subtract the quasar point source in order to constrain the underlying host galaxy emission. We measure upper limits for the quasar host galaxies of m _J > 22.7 mag and m _H > 22.4 mag, corresponding to stellar masses of M _* < 2 × 10¹¹ M _⊙. These stellar mass limits are consistent with the local M _BH − M _* relation. Our flux limits are consistent with those predicted for the UV stellar populations of z ≃ 6 host galaxies, but likely in the presence of significant dust ($⟨<!--\; ???\; -->A_{\mathrm{U}\mathrm{V}}⟩<!--\; ???\; -->\simeq <!--\; ???\; -->2.6$ mag). We also detect a total of up to nine potential z ≃ 6 quasar companion galaxies surrounding five of the six quasars, separated from the quasars by 1.″4–3.″2, or 8.4–19.4 kpc, which may be interacting with the quasar hosts. These nearby companion galaxies have UV absolute magnitudes of −22.1 to −19.9 mag and UV spectral slopes β of −2.0 to −0.2, consistent with luminous star-forming galaxies at z ≃ 6. These results suggest that the quasars are in dense environments typical of luminous z ≃ 6 galaxies. However, we cannot rule out the possibility that some of these companions are foreground interlopers. Infrared observations with the James Webb Space Telescope will be needed to detect the z ≃ 6 quasar host galaxies and better constrain their stellar mass and dust content.