We present measurements of the intergalactic medium (IGM) temperature within ∼5 proper Mpc of seven luminous quasars at z ≃ 6. The constraints are obtained from the Doppler widths of Lyα absorption lines in the quasar near zones and build upon our previous measurement for the z = 6.02 quasar SDSS J0818+1722. The expanded data set, combined with an improved treatment of systematic uncertainties, yields an average temperature at the mean density of () at 68 (95) per cent confidence for a flat prior distribution over 3.2 ≤ log (T0/K) ≤ 4.8. In comparison, temperatures measured from the general IGM at z ≃ 5 are ∼0.3 dex cooler, implying an additional source of heating around these quasars which is not yet present in the general IGM at slightly lower redshift. This heating is most likely due to the recent reionization of He ii in vicinity of these quasars, which have hard and non‐thermal ionizing spectra. The elevated temperatures may therefore represent evidence for the earliest stages of He ii reionization in the most biased regions of the high‐redshift Universe. The temperature as a function of distance from the quasars is consistent with being constant, log (T0/K) ≃ 4.2, with no evidence for a line‐of‐sight thermal proximity effect. However, the limited extent of the quasar near zones prevents the detection of He iii regions larger than ∼5 proper Mpc. Under the assumption that the quasars have reionized the He ii in their vicinity, we infer that the data are consistent with an average optically bright phase of duration in excess of 106.5 yr. These measurements represent the highest redshift IGM temperature constraints to date, and thus provide a valuable data set for confronting models of H i reionization.

Radiation feedback from stellar clusters is expected to play a key role in setting the rate and efficiency of star formation in giant molecular clouds (GMCs). To investigate how radiation forces influence realistic turbulent systems, we have conducted a series of numerical simulations employing the Hyperion radiation hydrodynamics solver, considering the regime that is optically thick to ultraviolet (UV) and optically thin to infrared (IR) radiation. Our model clouds cover initial surface densities between Σ cl,0 ∼ 10 − 300 M pc −2 , with varying initial turbulence. We follow them through turbulent, self-gravitating collapse, formation of star clusters, and cloud dispersal by stellar radiation. All our models display a lognormal distribution of gas surface density Σ; for an initial virial parameter α vir,0 = 2, the lognormal standard deviation is σ lnΣ = 1 − 1.5 and the star formation rate coefficient ε ff,ρ = 0.3 − 0.5, both of which are sensitive to turbulence but not radiation feedback. The net star formation efficiency ε final increases with Σ cl,0 and decreases with α vir,0 . We interpret these results via a simple conceptual framework, whereby steady star formation increases the radiation force, such that local gas patches at successively higher Σ become unbound. Based on this formalism (with fixed σ lnΣ ), we provide an analytic upper bound on ε final , which is in good agreement with our numerical results. The final star formation efficiency depends on the distribution of Eddington ratios in the cloud and is strongly increased by turbulent compression of gas.

We study the radial dependence in stellar populations of 33 nearby early-type galaxies with central stellar velocity dispersions σ * ∼ > 150 km s −1 . We measure stellar population properties in composite spectra, and use ratios of these composites to highlight the largest spectral changes as a function of radius. Based on stellar population modeling, the typical star at 2R e is old (∼ 10 Gyr), relatively metal poor ([Fe/H]≈ −0.5), and α-enhanced ([Mg/Fe]≈ 0.3). The stars were made rapidly at z ≈ 1.5 − 2 in shallow potential wells. Declining radial gradients in [C/Fe], which follow [Fe/H], also arise from rapid star formation timescales due to declining carbon yields from low-metallicity massive stars. In contrast, [N/Fe] remains high at large radius. Stars at large radius have different abundance ratio patterns from stars in the center of any present-day galaxy, but are similar to Milky Way thick disk stars. Our observations are thus consistent with a picture in which the stellar outskirts are built up through minor mergers with disky galaxies whose star formation is truncated early (z ≈ 1.5 − 2).

We present a 2D kinematic analysis out to ∼ 2−5 effective radii (R e ) of 33 massive elliptical galaxies with stellar velocity dispersions σ > 150 km s −1 . Our observations were taken using the Mitchell Spectrograph (formerly VIRUS-P), a spectrograph with a large 107 × 107 arcsec 2 field-of-view that allows us to construct robust, spatially resolved kinematic maps of V and σ for each galaxy extending to at least 2 R e . Using these maps we study the radial dependence of the stellar angular momentum and other kinematic properties. We see the familiar division between slow and fast rotators persisting out to large radius in our sample. Centrally slow rotating galaxies, which are almost universally characterised by some form of kinematic decoupling or misalignment, remain slowly rotating in their halos. The majority of fast rotating galaxies show either increases in specific angular momentum outwards or no change beyond R e . The generally triaxial nature of the slow rotators suggests that they formed through mergers, consistent with a "two-phase" picture of elliptical galaxy formation. However, we do not observe the sharp transitions in kinematics proposed in the literature as a signpost of moving from central dissipationally-formed components to outer accretion-dominated haloes.

Measurements of the intergalactic medium (IGM) temperature provide a potentially powerful constraint on the reionization history due to the thermal imprint left by the photoionization of neutral hydrogen. However, until recently IGM temperature measurements were limited to redshifts 2 ≤z≤ 4.8, restricting the ability of these data to probe the reionization history at z > 6. In this work, we use recent measurements of the IGM temperature in the near‐zones of seven quasars at z∼ 5.8–6.4, combined with a semi‐numerical model for inhomogeneous reionization, to establish new constraints on the redshift at which hydrogen reionization completed. We calibrate the model to reproduce observational constraints on the electron scattering optical depth and the H i photoionization rate, and compute the resulting spatially inhomogeneous temperature distribution at z∼ 6 for a variety of reionization scenarios. Under standard assumptions for the ionizing spectra of Population II sources, the near‐zone temperature measurements constrain the redshift by which hydrogen reionization was complete to be zr > 7.9 (6.5) at 68 (95) per cent confidence. We conclude that future temperature measurements around other high‐redshift quasars will significantly increase the power of this technique, enabling these results to be tightened and generalized.