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Abstract We present a homogeneous spectroscopic dataset of 22,339 stars in 78 Milky Way dwarf galaxy satellites and globular clusters. All data were taken with the Keck II telescope and Deep Extragalactic Imaging Multiobject Spectrograph (DEIMOS) using the 1200G grating (spectral resolutionR≃ 6000). Based on a uniform data reduction of 411 DEIMOS masks, we present a catalog of individual stellar radial velocities, equivalent-width-based [Fe/H] metallicities, and membership estimates. The Milky Way satellites range fromM_V = 2 to −14 (M_⋆ = 10^1.5–10^7.5M_⊙); the majority of individual stars presented in these systems have magnitudes between 17 > r > 22. We additionally present redshifts for 2097 compact background galaxies and QSOs in the same magnitude range. The data were reduced to 1D spectra usingPypeIt, which provides near Poisson-statistics-level sky subtraction. Radial velocities were determined viadmost, a forward modeling method first presented here, which combines both synthetic telluric and stellar templates to determine stellar radial velocities. We assess the accuracy and precision our method via comparison to thousands of repeat measurements and literature values. We determine a velocity error floor of 1.1 km s⁻¹and a Caii-triplet-based metallicity error floor of 0.1 dex. We calculate internal velocity dispersions and compare to literature values, demonstrating 20%–50% improved precision over the literature in most cases. In a companion paper, we use our homogeneous catalogs to explore properties of these Milky Way satellites, including previously unpublished measurements in several systems including Boötes II and Draco II. We provide full access to the data catalogs to enable further studies. 

Linking quasars to their dark matter environments provides critical insights into the formation and early growth of supermassive black holes (SMBHs). We present JWST observations of the environments surrounding two high-redshift quasars, J0252−0503 atz = 7.0 and J1007+2115 atz = 7.5, which enable the first constraints on quasar–galaxy clustering atz ≃ 7.3. Galaxies in the vicinity of the quasars were selected through ground-based and JWST/NIRCam imaging and were then spectroscopically confirmed with JWST/NIRSpec using the multi-shutter assembly (MSA). Over both fields, we identified 51z > 5 galaxies, of which eight are found within a Δv_LOS= ± 1500 km s⁻¹line-of-sight velocity window from the quasars and another eight in the background. The galaxy J0252_8713, located just 7 pkpc and Δv_LOS≈ 360 km s⁻¹from quasar J0252−0503, emerges as a compelling candidate for one of the most distant quasar-galaxy mergers. Combining the galaxy discoveries over the two fields, we measured the quasar-galaxy cross-correlation and obtain a correlation length ofr₀^QG≈ 7.6^+1.7_−1.6h⁻¹cMpc, based on a power-law model with a fixed slope ofγ_QG = 2.0. Under the assumption that quasars and galaxies trace the same underlying dark matter density fluctuations, we infer a minimum dark matter halo mass forz ≃ 7.3 quasars of log₁₀(M_halo,min/M_⊙) = 11.6^+0.6_−0.7in a halo model framework. Compared to measurements from EIGER at ⟨z⟩ = 6.25 and ASPIRE at ⟨z⟩ = 6.7 (where log₁₀(M_halo, min/M_⊙)≳12.1), our clustering results provide tentative evidence for a nonmonotonic redshift evolution of quasar clustering properties. We further estimate a quasar duty cycle off_duty ≈ 0.05%, consistent with constraints from quasar proximity zones and intergalactic medium (IGM) damping wings. However, this implies very short phases of quasar activity, exacerbating the challenge to build billion solar mass SMBHs in only 700 Myr of cosmic time. 

ABSTRACT We introduce a new approach for analysing the intergalactic medium (IGM) damping wings imprinted on the proximity zones of quasars in the epoch of reionization (EoR). Whereas past work has typically forgone the additional constraining power afforded by the blue side continuum ($$\lambda \lesssim 1280\,$$ Å) and/or opted not to model the large correlated IGM transmission fluctuations in the proximity zone ($$\lambda \lesssim 1216\,$$ Å), we construct a generative probabilistic model for the entire spectrum accounting for all sources of error – the stochasticity induced by patchy reionization, the impact of the quasar’s ionizing radiation on the IGM, the unknown intrinsic spectrum of the quasar, and spectral noise. This principled Bayesian method allows us to marginalize out nuisance parameters associated with the quasar’s radiation and its unknown intrinsic spectrum to precisely measure the IGM neutral fraction, $$\langle x_{\rm H\,\small{I}}\rangle$$. A key element of our analysis is the use of dimensionality reduction (DR) to describe the intrinsic quasar spectrum via a small number of nuisance parameters. Using a large sample of 15 559 SDSS/BOSS quasars at $$z \gtrsim 2.15$$ we trained and quantified the performance of six distinct DR methods, and find that a six parameter principal component analysis model (five coefficients plus a normalization) performs best, with complex machine-learning approaches providing no advantage. By conducting statistical inference on 100 realistic mock EoR quasar spectra, we demonstrate the reliability of the credibility contours that we obtain on $$\langle x_{\rm H\,{\small{I}}}\rangle$$ and the quasar lifetime, $$t_{\rm Q}$$. The new method introduced here will transform IGM damping wings into a precision probe of reionization, on the same solid methodological and statistical footing as other precision cosmological measurements. 

ABSTRACT Thus far, Lyman-$$\alpha$$ damping wings towards quasars have been used to probe the global ionization state of the foreground intergalactic medium (IGM). A new parametrization has demonstrated that the damping wing signature also carries local information about the distribution of neutral hydrogen (H i) in front of the quasar before it started shining. Leveraging a recently introduced Bayesian jax-based Hamiltonian Monte Carlo inference framework, we derive constraints on the Lorentzian-weighted H i column density $$N_\mathrm{H\, {\small I}}^\mathrm{DW}$$, the quasar’s distance $$r_\mathrm{patch}$$ to the first neutral patch, and its lifetime $$t_\mathrm{Q}$$ based on James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) spectra of the two $$z \sim 7.5$$ quasars J1007+2115 and J1342+0928. After folding in model-dependent topology information, we find that J1007+2115 (and J1342+0928) is most likely to reside in a $$\langle x_\mathrm{H\, {\small I}} \rangle = 0.32_{-0.20}^{+0.22}$$ ($$0.58_{-0.23}^{+0.23}$$) neutral IGM while shining for a remarkably short lifetime of $$\log _{10} t_\mathrm{Q}/\mathrm{yr}= 4.14_{-0.18}^{+0.74}$$ (an intermediate lifetime of $$5.64_{-0.43}^{+0.25}$$) along a sightline with $$\log _{10} N_\mathrm{H\, {\small I}}^\mathrm{DW}/\mathrm{cm}^{-2}= 19.70_{-0.86}^{+0.35}$$ ($$20.24_{-0.22}^{+0.25}$$) and $$r_\mathrm{patch}= 28.9_{-14.4}^{+54.0} \, \mathrm{cMpc}$$ ($$10.9_{-5.9}^{+5.6} \, \mathrm{cMpc}$$). In light of the potential presence of local absorbers in the foreground of J1342+0928 as has been recently suggested, we also demonstrate how the Lorentzian-weighted column density $$N_\mathrm{H\, {\small I}}^\mathrm{DW}$$ provides a natural means for quantifying their contribution to the observed damping wing signal. 

Abstract The nature of ‘little red dots’ and their relation to other forms of accreting supermassive black holes remain an open question. Here we report the discovery of a little red dot atz = 7.3. It is attenuated by moderate amounts of dust,A_V = 2.79 mag, and has an intrinsic bolometric luminosity of 10^46.6 erg s⁻¹and a supermassive black hole mass of 5 × 10⁸ M_⊙. Most notably, this object is embedded in an overdensity of eight nearby galaxies, allowing us to calculate a spectroscopic estimate of the clustering of galaxies around little red dots. We find a little red dot versus galaxy cross-correlation length ofr₀ = 8 ± 2 h⁻¹ cMpc, comparable to that ofz ≈ 6 ultraviolet-luminous quasars. The resulting estimate of their minimum dark matter halo mass$$\log_{10}({M}_{{\rm{halo}},\min }/{{{M}}}_{\odot })=12.{0}_{-1.0}^{+0.8}$$ ${\log }_{10}\left(M_{\mathrm{halo},\min }/M_{\odot }\right)=12.0_{-1.0}^{+0.8}$ indicates that nearly all haloes above this mass must host actively accreting supermassive black holes atz ≈ 7, in strong contrast with the far smaller duty cycle of luminous quasars (<1%). Our results, taken at face value, motivate a picture in which supermassive black holes in little red dot phases could serve as the obscured precursors of ultraviolet-luminous quasars, which provides a natural explanation for the short ultraviolet-luminous lifetimes inferred from both quasar clustering and quasar proximity zones. 

ABSTRACT The fraction of ‘dark pixels’ in the Ly$$\alpha$$ and other Lyman-series forests at $$z\sim 5$$–6 provides a powerful constraint on the end of the reionization process. Any spectral region showing transmission must be highly ionized, while dark regions could be ionized or neutral, thus the dark pixel fraction provides a (nearly) model independent upper limit to the volume-filling fraction of the neutral intergalactic medium, modulo choices in binning scale and dark pixel definition. Here, we provide updated measurements of the 3.3 comoving Mpc dark pixel fraction at $z=4.85$–6.25 in the Ly$$\alpha$$, Ly$$\beta$$, and Ly$$\gamma$$ forests of 34 deep $$5.8 \lesssim z\lesssim 6.6$$ quasar spectra from the (enlarged) XQR−30 sample. Using the negative pixel method to measure the dark pixel fraction, we derive fiducial $$1\sigma$$ upper limits on the volume-average neutral hydrogen fraction of $$\langle x_{\rm HI} \rangle \le \lbrace 0.030+0.048,0.095+0.037,0.191+0.056,0.199+0.087\rbrace$$ at $$\bar{z}=\lbrace 5.481,5.654,5.831,6.043\rbrace$$ from the optimally sensitive combination of the Ly$$\beta$$ and Ly$$\gamma$$ forests. We further demonstrate an alternative method that treats the forest flux as a mixture of dark and transparent regions, where the latter are modelled using a physically motivated parametric form for the intrinsic opacity distribution. The resulting model-dependent upper limits on $$\langle x_{\rm HI} \rangle$$ are similar to those derived from our fiducial model-independent analysis. We confirm that the bulk of reionization must be finished at $z>6$, while leaving room for an extended ‘soft landing’ to the reionization history down to $$z\sim 5.4$$ suggested by Ly$$\alpha$$ forest opacity fluctuations. 

ABSTRACT We present optical and near-infrared (NIR) spectroscopic observations for a sample of 45 quasars at $$6.50 < z \le 7.64$$ with absolute magnitudes at 1450 Å in the range $$-28.82 \le M_{1450} \le -24.13$$ and their composite spectrum. The median redshift and $$M_{1450}$$ of the quasars in the sample are $$z_{\rm {median}}=6.71$$ and $$M_{1450,\rm {median}} \simeq -26.1$$, respectively. The NIR spectra are taken with Echelle spectrographs, complemented with additional data from optical long slit instruments, and then reduced consistently using the open-source Python-based spectroscopic data reduction pipeline PypeIt. The median of the mean signal-to-noise ratios per 110 km s$$^{-1}$$ pixel in the J, H, and K band [median $$\langle \rm {SNR}_{\lambda } \rangle$$] is median $$\langle \rm {SNR}_{J} \rangle =9.7$$, median $$\langle \rm {SNR}_{H} \rangle =10.3$$, and median $$\langle \rm {SNR}_{K} \rangle =11.7$$; demonstrating the good data quality. This work presents the largest medium-/moderate-resolution sample of quasars at $z>6.5$ from ground-based instruments. Despite the diversity in instrumental set-ups and spectral quality, the data set is uniformly processed and well-characterized, making it ideally suited for several scientific goals, including the study of the quasar proximity zones and damping wings, the Ly $$\alpha$$ forest, the intergalactic medium’s metal content, as well as other properties such as the distribution of SMBH masses and Eddington ratios. Our composite spectrum is compared to others at both high and low z from the literature, showing differences in the strengths of many emission lines, probably due to differences in luminosity among the samples, but a consistent continuum slope, which proves that the same spectral features are preserved in quasars at different redshift ranges. 

ABSTRACT Lyman α emitters (LAEs) are excellent probes of the reionization process, as they must be surrounded by large ionized bubbles in order to be visible during the reionization era. Large ionized regions are thought to correspond to overdense regions and may be protoclusters, making them interesting test-beds for early massive structures. Close associations containing several LAEs are often assumed to mark overdense, ionized bubbles. Here, we develop the first framework to quantify the ionization and density fields of high-z galaxy associations. We explore the interplay between (i) the large-scale density of a survey field, (ii) Poisson noise due to the small number density of bright sources at high redshifts (z ∼ 7), and (iii) the effects of the ionized fraction on the observation of LAEs. We use Bayesian statistics, a simple model of reionization, and a Monte Carlo simulation to construct a more comprehensive method for calculating the large-scale density of LAE regions than previous works. We find that Poisson noise has a strong effect on the inferred density of a region and show how the ionized fraction can be inferred. We then apply our framework to the strongest association yet identified: Hu et al. found 14 LAEs in a volume of ∼50 000 cMpc3 inside the COSMOS field at z ∼ 7. We show that this is most likely a 2.4σ overdensity inside of an ionized or nearly ionized bubble. We also show that this LAE association implies that the global ionized fraction is $$\bar{Q} = 0.59^{+0.10}_{-0.11}$$, within the context of a simple reionization model. 

Abstract We present a systematic study of the environments of 25 luminous quasars atz > 6.5 from the ASPIRE program. Using JWST/NIRCam wide-field slitless spectroscopy data, we identified 487 galaxies at 5.3 ≲ z ≲ 7.0 exhibiting [Oiii] emission. Among these, 122 [Oiii] emitters lie within ∣Δv_los∣ < 1000 km s⁻¹of the quasars, corresponding to a ∼9.4-fold enhancement relative to the average galaxy density at other redshifts. Furthermore, we identified 16 [Cii]-emitting galaxies at the quasar redshifts from Atacama Large Millimeter/submillimeter Array (ALMA) mosaic observations. A cross-correlation function analysis between quasars and [Oiii]+[Cii] emitters yields a cross-correlation length of $r_0^{\mathrm{QG}}=8.68_{-0.55}^{+0.51}{h}^{-1}\mathrm{cMpc}$ and an autocorrelation of $r_0^{\mathrm{QQ}}=15.76_{-2.70}^{+2.48}{h}^{-1}\mathrm{cMpc}$ , indicating thatz ∼ 7 quasars reside in dark matter halos with $M_{\mathrm{halo}}=10^{12.27_{-0.26}^{+0.21}}{M}_{\odot }$ and have a quasar lifetime of $t_Q=10^{{7.05}_{-1.01}^{+0.95}}\mathrm{yr}$ . Notably, the number of [Oiii]-emitting galaxies at quasar redshifts varies significantly from field to field, ranging from 0 to 20, highlighting a diverse quasar environment. Remarkably, seven quasars trace significant galaxy overdensities (i.e., protoclusters), withδ_gal > 5 within a volume ofV ∼ 500 cMpc³. We also find that ∣Δv_los∣ increases rapidly toward smaller galaxy–quasar separations in protocluster fields, consistent with galaxy kinematics around extremely massive halos in cosmological simulations. By combining JWST and ALMA data, we reveal the complex and diverse environments of these early quasars, providing robust evidence that the earliest luminous quasars are effective tracers of galaxy overdensities, albeit with substantial field-to-field variation. 

Abstract Fluctuations in Lyman-α (Lyα) forest transmission towards high-z quasars are partially sourced from spatial fluctuations in the ultraviolet background (UVB), the level of which are set by the mean free path of ionizing photons (λmfp). The auto-correlation function of Lyα forest flux characterizes the strength and scale of transmission fluctuations and, as we show, is thus sensitive to λmfp. Recent measurements at z ∼ 6 suggest a rapid evolution of λmfp at z > 5.0 which would leave a signature in the evolution of the auto-correlation function. For this forecast, we model mock Lyα forest data with properties similar to the XQR-30 extended data set at 5.4 ≤ z ≤ 6.0. At each z we investigate 100 mock data sets and an ideal case where mock data matches model values of the auto-correlation function. For ideal data with λmfp = 9.0 cMpc at z = 6.0, we recover $$\lambda _{\text{mfp}}=12^{+6}_{-3}$$ cMpc. This precision is comparable to direct measurements of λmfp from the stacking of quasar spectra beyond the Lyman limit. Hypothetical high-resolution data leads to a $$\sim 40{{\%}}$$ reduction in the error bars over all z. The distribution of mock values of the auto-correlation function in this work is highly non-Gaussian for high-z, which should caution work with other statistics of the high-z Lyα forest against making this assumption. We use a rigorous statistical method to pass an inference test, however future work on non-Gaussian methods will enable higher precision measurements.