Keywords

The emission from dark ages halos in the lines of transitions between the lowest rotational levels of hydrogen and hydrogen deuteride molecules is analyzed. It is assumed that molecules are excited by the cosmic microwave background (CMB) and collisions with hydrogen atoms. The physical parameters of halos and the number density of molecules are precalculated assuming that halos are homogeneous top-hat spheres formed from the cosmological density perturbations in the four-component universe with post-Planck cosmological parameters. The differential brightness temperatures and differential spectral fluxes in the rotational lines of H₂–HD molecules are computed for two phenomena: thermal luminescence and resonant scattering of CMB radiation. The results show that the expected maximal values of differential brightness temperature of warm halos (T_K ∼ 200–800 K) are at the level of nanokelvins, are comparable for both phenomena, and are below the sensitivity of modern submillimeter radio telescopes. For hot halos (T_K ∼ 2000–5000 K) the thermal emission of H₂-ortho molecules dominates and the differential brightness temperatures are predicted to be of a few microkelvins at the frequencies 300–600 GHz, which could be detectable with next-generation telescopes.

The MAMMOTH-I Nebula at redshift 2.3 is one of the largest known Lyα nebulae in the universe, spanning ∼440 kpc. Enormous Lyα nebulae like MAMMOTH-I typically trace the densest and most active regions of galaxy formation. Using sensitive low-surface-brightness observations of CO(1−0) with the Very Large Array, we trace the cold molecular gas in the inner 150 kpc of the MAMMOTH-I Nebula. CO is found in four regions that are associated with either galaxies or groups of galaxies that lie inside the nebula. In three of the regions, the CO stretches up to ∼30 kpc into the circumgalactic medium (CGM). In the centermost region, the CO has a very low velocity dispersion (FWHM_CO ∼ 85 km s⁻¹), indicating that this gas is dynamically cold. This dynamically cold gas coincides with diffuse rest-frame optical light in the CGM around a central group of galaxies, as discovered with the Hubble Space Telescope. We argue that this likely represents cooling of settled and enriched gas in the center of MAMMOTH-I. This implies that the dynamically cold gas in the CGM, rather than the obscured active galactic nucleus, marks the core of the potential well of this Lyα nebula. In total, the CO in the MAMMOTH-I Nebula traces a molecular gas mass of M_H2 ∼ 1.4(α_CO/3.6) × 10¹¹ M_⊙, with roughly 50% of the CO(1−0) emission found in the CGM. Our results add to the increasing evidence that extended reservoirs of molecular gas exist in the CGM of massive high-z galaxies and protoclusters.

Recent Lyα forest tomography measurements of the intergalactic medium (IGM) have revealed a wealth of cosmic structures at high redshift (z ∼ 2.5). In this work, we present the Tomographic Absorption Reconstruction and Density Inference Scheme (TARDIS), a new chronocosmographic analysis tool for understanding the formation and evolution of these observed structures. We use maximum likelihood techniques with a fast nonlinear gravitational model to reconstruct the initial density field of the observed regions. We find that TARDIS allows accurate reconstruction of smaller-scale structures than standard Wiener-filtering techniques. Applying this technique to mock Lyα forest data sets that simulate ongoing and future surveys such as CLAMATO, Subaru PFS, or the ELTs, we are able to infer the underlying matter density field at observed redshift and classify the cosmic web structures. We find good agreement with the underlying truth in both the characteristic eigenvalues and eigenvectors of the pseudo-deformation tensor, with the eigenvalues inferred from 30 m class telescopes correlated at r = 0.95 relative to the truth. As an output of this method, we are able to further evolve the inferred structures to late time (z = 0) and also track the trajectories of coeval z = 2.5 galaxies to their z = 0 cosmic web environments.

We calculate the dispersion measure (DM) contributed by the intergalactic medium (IGM) to the total measured DM for fast radio bursts (FRBs). We use the MareNostrum Instituto de Ciencias del Espacio (MICE) Onion Universe simulation to track the evolution of the dark matter particle density over a large range of redshifts. We convert this dark matter particle number density to the corresponding free electron density and then integrate it to find the DM as a function of redshift. This approach yields an intergalactic DM of ${\mathrm{DM}}_{\mathrm{IGM}}(z=1)={800}_{-170}^{+7000}$ pc cm⁻³, with the large errors representative of the structure in the IGM. We place limits on the redshifts of the current population of observed FRBs. We also use our results to estimate the host galaxy contribution to the DM for the first repeater, FRB 121102, and show that the most probable host galaxy DM contribution, ${\mathrm{DM}}_{\mathrm{host}}\approx 310$ pc cm⁻³, is consistent with the estimate made using the Balmer emission lines in the spectrum of the host galaxy, ${\mathrm{DM}}_{\mathrm{Balmer}}=324$ pc cm⁻³. We also compare our predictions for the host galaxy contribution to the DM for the observations of FRB 180924 and FRB 190523, both of which have been localized to a host galaxy.

We present results from the Keck Baryonic Structure Survey (KBSS) including the first detailed measurements of the column densities, kinematics, and internal energy of metal-bearing gas within the virial radius (35–100 physical kpc) of eight ∼L* galaxies at z ∼ 2. From our full sample of 130 metal-bearing absorbers, we infer that halo gas is kinematically complex when viewed in singly, doubly, and triply ionized species. Broad O vi and C iv absorbers are detected at velocities similar to the lower-ionization gas but with a very different kinematic structure, indicating that the circumgalactic medium (CGM) is multiphase. There is a high covering fraction of metal-bearing gas within 100 kpc, including highly ionized gas such as O vi; however, observations of a single galaxy probed by a lensed background QSO suggest the size of metal-bearing clouds is small (<400 pc for all but the O vi-bearing gas). The mass in metals found within the halo is substantial, equivalent to ≳25% of the metal mass within the interstellar medium. The gas kinematics unambiguously show that 70% of galaxies with detected metal absorption have some unbound metal-enriched gas, suggesting galactic winds may commonly eject gas from halos at z ∼ 2. When modeled assuming that ions with different ionization potentials can originate within a single gaseous structure, significant thermal broadening is detected in CGM absorbers that dominates the internal energy of the gas. Some 40% of the detected gas has temperatures in the range 10^4.5–5.5 K where cooling times are short, suggesting the CGM is dynamic, with constant heating or cooling to produce this short-lived thermal phase.

We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 [O iii] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg², surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Lyα emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.

We present Keck/OSIRIS infrared IFU observations of the z = 3.153 sub-DLA DLA2233+131, previously detected in absorption to a background quasar and studied with single-slit spectroscopy and Potsdam Multi Aperture Spectrophotometer integral field spectroscopy (IFU). We used the Laser Guide Star Adaptive Optics and OSIRIS IFU to reduce the point-spread function of the background quasar to FWHM ∼ 015 and marginally resolve extended, foreground DLA emission. We detect $[{\rm{O}}\,{\rm{iii}}]\lambda 5007$ emission with a flux ${F}^{[{\rm{O}}{\rm{iii}}]\lambda 5007}\,=(2.4\pm 0.5)\times {10}^{-17}$ erg s⁻¹ cm⁻², as well as unresolved $[{\rm{O}}\,{\rm{iii}}]\lambda 4959$ and Hβλ4861 emission. Using a composite spectrum over the emission region, we measure dynamical mass $\sim 3.1\,\times \,{10}^{9}$ M_⊙. We made several estimates of star formation rate (SFR) using $[{\rm{O}}\,{\rm{iii}}]\lambda 5007$ and Hβλ4861 emission, and measured a SFR of ∼7.1 − 13.6 M_⊙ yr⁻¹. We map $[{\rm{O}}\,{\rm{iii}}]\lambda 5007$ and Hβλ4861 emission and the corresponding velocity fields to search for signs of kinematic structure. These maps allow for a more detailed kinematic analysis than previously possible for this galaxy. While some regions show slightly red and blueshifted emission indicative of potential edge-on disk rotation, the data are insufficient to support this interpretation.

We present a search for H i in the circumgalactic medium (CGM) of 21 massive ($\langle \mathrm{log}{M}_{\star }\rangle \sim 11.4$), luminous red galaxies (LRGs) at z ∼ 0.5. Using UV spectroscopy of QSO sightlines projected within 500 kpc (∼${R}_{\mathrm{vir}}$) of these galaxies, we detect H i absorption in 11/21 sightlines, including two partial Lyman limit systems and two Lyman limit systems. The covering factor of $\mathrm{log}N({\rm{H}}\,{\rm{I}})\geqslant 16.0$ gas within the virial radius of these LRGs is ${f}_{c}(\rho \leqslant \,{R}_{\mathrm{vir}})={0.27}_{-0.10}^{+0.11}$, while for optically thick gas ($\mathrm{log}N({\rm{H}}\,{\rm{I}})\geqslant 17.2$) it is ${f}_{c}(\rho \leqslant \,{R}_{\mathrm{vir}})={0.15}_{-0.07}^{+0.10}$. Combining this sample of massive galaxies with previous galaxy-selected CGM studies, we find no strong dependence of the H i covering factor on galaxy mass, although star-forming galaxies show marginally higher covering factors. There is no evidence for a critical mass above which dense, cold (T ∼ 10⁴ K) gas is suppressed in the CGM of galaxies (spanning stellar masses $9.5\lesssim \mathrm{log}{M}_{\star }\lesssim 11.8$). The metallicity distribution in LRGs is indistinguishable from those found about lower-mass star-forming galaxies, and we find low-metallicity gas with $[{\rm{X}}/{\rm{H}}]\approx -1.8$ (1.5% solar) and below about massive galaxies. About half the cases show supersolar [Fe ii/$\mathrm{Mg}\,{\rm{II}}$] abundances as seen previously in cool gas near massive galaxies. While the high-metallicity cold gas seen in LRGs could plausibly result from condensation from a corona, the low-metallicity gas is inconsistent with this interpretation.

The intense radiation emitted by luminous quasars dramatically alters the ionization state of their surrounding IGM. This so-called proximity effect extends out to tens of Mpc, and manifests as large coherent regions of enhanced Lyα (Lyα) forest transmission in absorption spectra of background sightlines. Here, we present a novel method based on Lyα forest tomography, which is capable of mapping these quasar "light echoes" in three dimensions. Using a dense grid (10–100) of faint (${m}_{r}\approx 24.7\,\mathrm{mag}$) background galaxies as absorption probes, one can measure the ionization state of the IGM in the vicinity of a foreground quasar, yielding detailed information about the quasar's radiative history and emission geometry. An end-to-end analysis—combining cosmological hydrodynamical simulations post-processed with a quasar emission model, realistic estimates of galaxy number densities, and instrument + telescope throughput—is conducted to explore the feasibility of detecting quasar light echoes. We present a new, fully Bayesian statistical method that allows one to reconstruct quasar light echoes from thousands of individual low-S/N transmission measurements. Armed with this tool, we undertake an exhaustive parameter study and show that light echoes can be convincingly detected for luminous (M₁₄₅₀ < −27.5 mag, corresponding to m₁₄₅₀ < 18.4 mag at $z\simeq 3.6$) quasars at redshifts 3 < z_QSO < 5, and that a relative precision better than 20% on the quasar age can be achieved for individual objects in the expected range of ages between 1 and 100 Myr. The observational requirements are relatively modest: moderate-resolution (R ≳ 750), multiobject spectroscopy at a low signal-to-noise ratio (S/N > 5) is sufficient, requiring three-hour integrations using existing instruments on 8 m class telescopes.

Ratios of different ions of the same element encode ionization information independently from relative abundances in quasar absorption line systems, crucial for understanding the multiphase nature and origin of absorbing gas, particularly at z > 6 where H i cannot be observed. Observational considerations have limited such studies to a small number of sightlines, with most surveys at z > 6 focused upon the statistical properties of individual ions such as Mg ii or C iv. Here we compare high- and low-ionization absorption within 69 intervening systems at z > 5, including 16 systems at z > 6, from Magellan/FIRE spectra of 47 quasars together with a Keck/High Resolution Echelle Spectrometer (HIRES) spectrum of the "ultraluminous" z = 6.3 quasar SDSSJ010013.02+280225.8. The highest redshift absorbers increasingly exhibit low-ionization species alone, consistent with previous single-ion surveys that show the frequency of Mg ii is unchanging with redshift, while C iv absorption drops markedly toward z = 6. We detect no C iv or Si iv in half of all metal-line absorbers at z > 5.7, with stacks not revealing any slightly weaker C iv just below our detection threshold, and most of the other half have ${N}_{{\rm{C}}{\rm{II}}}\gt {N}_{{\rm{C}}{\rm{IV}}}$. In contrast, only 20% of absorbers at 5.0–5.7 lack high-ionization gas, and a search of 25 HIRES sightlines at z ∼ 3 yielded zero such examples. We infer that these low-ionization high-redshift absorption systems may be analogous to metal-poor damped Lyα systems (∼1% of the absorber population at z ∼ 3), based on incidence rates and absolute and relative column densities. Simple photoionization models suggest that circumgalactic matter at redshift six has systematically lower chemical abundances and experiences a softer ionizing background relative to redshift three.