We present a stringent measurement of the dust-obscured star formation rate density (SFRD) at z = 4-6 from the ASPIRE JWST Cycle-1 medium and ALMA Cycle-9 large program. We obtained JWST/NIRCam grism spectroscopy and ALMA 1.2 mm continuum map along 25 independent quasar sightlines, covering a total survey area of similar to 35 arcmin2 where we search for dusty star-forming galaxies (DSFGs) at z = 0-7. We identify eight DSFGs in seven fields at z = 4-6 through the detection of H alpha or [O iii] lambda 5008 lines, including fainter lines such as H beta, [O iii] lambda 4960, [N ii] lambda 6585, and [S ii] lambda lambda 6718,6733 for six sources. With this spectroscopically complete DSFG sample at z = 4-6 and negligible impact from cosmic variance (shot noise), we measure the infrared luminosity function (IRLF) down to LIR similar to 2 x 1011 L circle dot. We find flattening of IRLF at z = 4-6 towards the faint end (power-law slope alpha=0.59-0.45+0.39 ). We determine the dust-obscured cosmic SFRD at this epoch to be log[rho SFR,IR/(M circle dot yr-1Mpc-3)]=-1.52-0.13+0.14 . This is significantly higher than previous determinations using ALMA data in the Hubble Ultra Deep Field, which is void of DSFGs at z = 4-6 because of strong cosmic variance (shot noise). We conclude that the majority (66% +/- 7%) of cosmic star formation at z similar to 5 is still obscured by dust. We also discuss the uncertainty of SFRD propagated from far-IR spectral energy distribution and IRLF at the bright end, which will need to be resolved with future ALMA and JWST observations.

We present constraints on the spacetime variation of the fine-structure constant α at redshifts 2.5 ≤ z < 9.5 using JWST emission-line galaxies (ELGs). The galaxy sample consists of 621 high-quality spectra with strong and narrow [O iii ] λλ 4959,5007 doublet emission lines from 578 galaxies, including 232 spectra at z > 5. The [O iii ] doublet lines are arguably the best emission lines to probe the variation in α . We divide our sample into six subsamples based on redshift and calculate the relative variation Δ α / α for the individual subsamples. The calculated Δ α / α values are consistent with zero within 1 σ at all redshifts, suggesting no time variation in α above a level of (1–2) × 10 ^−4 (1 σ ) in the past 13.2 billion yr. When the whole sample is combined, the constraint is improved to be Δ α / α = (0.2 ± 0.7) × 10 ^−4 . We further test the spatial variation in α using four subsamples of galaxies in four different directions on the sky. The measured Δ α / α values are consistent with zero at a 1 σ level of ∼2 × 10 ^−4 . While the constraints in this work are not as stringent as those from lower-redshift quasar absorption lines in previous studies, this work uses an independent tracer and provides the first constraints on Δ α / α at the highest redshifts. With the growing number of ELGs from JWST, we expect to achieve stronger constraints in the future.

We present JWST/NIRSpec integral field spectroscopy in the rest-frame optical bands of the system PJ308-21, a quasar at z = 6.2342 caught as its host galaxy interacts with companion galaxies. We detect the spatially extended emission of several emission lines (H alpha, H beta, [O III], [N II], [S II], and He II), which we used to study the properties of the ionized phase of the interstellar medium: the source and hardness of the photoionizing radiation field, metallicity, dust reddening, electron density and temperature, and star formation. We also marginally detected continuum starlight emission associated with the companion sources. We find that at least two independent satellite galaxies are part of the system. While the quasar host appears highly enriched and obscured, with photoionization conditions typical of an Active Galactic Nucleus, the western companion shows minimal dust extinction, low metallicity (Z similar to 0.4 Z(circle dot)), and star formation driven photoionization. The eastern companion shows higher extinction and metallicity (Z similar to 0.8 Z(circle dot)) compared to the western companion, and it is at least partially photoionized by the nearby quasar. We do not find any indication of AGN in the companion sources. Our study shows that while the quasar host galaxy is already very massive (M-dyn > 10(11) M-circle dot), it is still rapidly building up by accreting two relatively massive (M-star similar to 10(10) M-circle dot) companion sources. This dataset showcases the power of JWST in exposing the buildup of massive galaxies in the first gigayear of the Universe.

The recent detection of optical emission lines from the circumgalactic medium (CGM) in combined, large samples of low-redshift, normal galaxy spectra hints at the potential to map the cool (∼104 kelvin) CGM in individual, representative galaxies. Using archival data from a forefront instrument (MUSE) on the VLT, we present a source-blind, wide-redshift-range (z ∼ 0 to 5) narrowband imaging survey for CGM emission. Our detected, resolved emission line sources are cataloged and include a 30-kiloparsec-wide Hα source likely tracing the CGM of a low-mass galaxy (stellar mass ∼ 108.78±0.42 solar mass) at z = 0.1723, a 60-kiloparsec-wide Ly α structure associated with a galaxy at z = 3.9076, and a 130-kiloparsec (∼rvir)-wide [O II] feature revealing an interaction between a galaxy pair at z = 1.2480. The Hα velocity field for the low-mass galaxy suggests that the CGM is more chaotic or turbulent than the galaxy disk, while that for the interacting galaxies shows large-scale (∼50 kiloparsec) coherent motions.

We characterize the multiphase circumgalactic medium and galaxy properties at z = 6.0-6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305-3150 to identify one new metal absorber at z = 6.2713 with multiple transitions (OI, MgI, FeII and CII). They are combined with the published absorbing systems in Davies et al. (2023a) at the same redshift range to form of a sample of nine metal absorbers at z = 6.03 to 6.49. We identify eight galaxies within 1000 km s$^{-1}$ and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [OIII]($\lambda\lambda$4959, 5007) doublets and H$\beta$ emission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar mass ranging from 10$^{7.2}$ to 10$^{8.8}M_{\odot}$ and metallicity between 0.02 and 0.4 solar. Notably, the z = 6.2713 system in the J0305-3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances of $\alpha$ elements to iron ([$\alpha$/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [$\alpha$/Fe] ratio. Our modeling of the galaxy's chemical abundance favors a top-heavy stellar initial mass function, and hints that we may be witnessing the contribution of the first generation Population III stars to the CGM at the end of reionization epoch.

We present a machine learning search for high-redshift (5.0 < z < 6.5) quasars using the combined photometric data from the Dark Energy Spectroscopic Instrument (DESI) Imaging Legacy Surveys and the Wide-field Infrared Survey Explorer survey. We explore the imputation of missing values for high-redshift quasars, discuss the feature selections, compare different machine learning algorithms, and investigate the selections of class ensemble for the training sample, then we find that the random forest model is very effective in separating the high-redshift quasars from various contaminators. The 11 class random forest model can achieve a precision of 96.43% and a recall of 91.53% for high-redshift quasars for the test set. We demonstrate that the completeness of the high-redshift quasars can reach as high as 82.20%. The final catalog consists of 216,949 high-redshift quasar candidates with 476 high probable ones in the entire Legacy Surveys DR9 footprint, and we make the catalog publicly available. Using Multi Unit Spectroscopic Explorer (MUSE) and DESI early data release (EDR) public spectra, we find that 14 true high-redshift quasars (11 in the training sample) out of 21 candidates are correctly identified for MUSE, and 20 true high-redshift quasars (11 in the training sample) out of 21 candidates are correctly identified for DESI-EDR. Additionally, we estimate photometric redshift for the high-redshift quasar candidates using a random forest regression model with a high precision.

We present the completed catalog of ultra-diffuse galaxy (UDG) candidates (7070 objects) from our search of the DR9 Legacy Survey images, including distance and total mass estimates for 1529 and 1436 galaxies, respectively, that we provide and describe in detail. From the sample with estimated distances, we obtain a sample of 585 UDGs ($\mu_{0,g} \ge 24$ mag arcsec$^{-2}$ and $r_e \ge 1.5$ kpc) over 20,000 sq. deg of sky in various environments. We conclude that UDGs in our sample are limited to $10^{10} \lesssim$ M$_h$/M$_\odot \lesssim 10^{11.5}$ and are on average a factor of 1.5 to 7 deficient in stars relative to the general population of galaxies of the same total mass. That factor increases with increasing galaxy size and mass up to a factor of $\sim$10 when the total mass of the UDG increases beyond M$_h = 10^{11}$ M$_\odot$. We do not find evidence that this factor has a dependence on the UDG's large-scale environment.

Studies of rest-frame optical emission in quasars at $z>6$ have historically been limited by the wavelengths accessible by ground-based telescopes. The James Webb Space Telescope (JWST) now offers the opportunity to probe this emission deep into the reionization epoch. We report the observations of eight quasars at $z>6.5$ using the JWST/NIRCam Wide Field Slitless Spectroscopy, as a part of the ''A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE)" program. Our JWST spectra cover the quasars' emission between rest frame $\sim$ 4100 and 5100 \r{A}. The profiles of these quasars' broad H$\beta$ emission lines span a FWHM from 3000 to 6000 $\rm{km~s^{-1}}$. The H$\beta$-based virial black hole (BH) masses, ranging from 0.6 to 2.1 billion solar masses, are generally consistent with their MgII-based BH masses. The new measurements based on the more reliable H$\beta$ tracer thus confirm the existence of billion solar-mass BHs in the reionization epoch. In the observed [OIII] $\lambda\lambda$4960,5008 doublets of these luminous quasars, broad components are more common than narrow core components ($\le~1200~\rm{km~s^{-1}}$), and only one quasar shows stronger narrow components than broad. Two quasars exhibit significantly broad and blueshifted [OIII] emission, thought to trace galactic-scale outflows, with median velocities of $-610~\rm{km~s^{-1}}$ and $-1430~\rm{km~s^{-1}}$ relative to the [CII] $158\,\mu$m line. All eight quasars show strong optical FeII emission, and follow the Eigenvector 1 relations defined by low-redshift quasars. The entire ASPIRE program will eventually cover 25 quasars and provide a statistical sample for the studies of the BHs and quasar spectral properties.

We present the first results from the JWST program A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE). This program represents an imaging and spectroscopic survey of 25 reionization-era quasars and their environments by utilizing the unprecedented capabilities of NIRCam Wide Field Slitless Spectroscopy (WFSS) mode. ASPIRE will deliver the largest (similar to 280 arcmin(2)) galaxy redshift survey at 3-4 mu m among JWST Cycle 1 programs and provide extensive legacy values for studying the formation of the earliest supermassive black holes, the assembly of galaxies, early metal enrichment, and cosmic reionization. In this first ASPIRE paper, we report the discovery of a filamentary structure traced by the luminous quasar J0305-3150 and 10 [O III] emitters at z = 6.6. This structure has a 3D galaxy overdensity of delta(gal) = 12.6 over 637 cMpc(3), one of the most overdense structures known in the early universe, and could eventually evolve into a massive galaxy cluster. Together with existing VLT/MUSE and ALMA observations of this field, our JWST observations reveal that J0305-3150 traces a complex environment where both UV-bright and dusty galaxies are present and indicate that the early evolution of galaxies around the quasar is not simultaneous. In addition, we discovered 31 [O III] emitters in this field at other redshifts, 5.3 < z < 6.7, with half of them situated at z similar to 5.4 and 6.2. This indicates that star-forming galaxies, such as [O III] emitters, are generally clustered at high redshifts. These discoveries demonstrate the unparalleled redshift survey capabilities of NIRCam WFSS and the potential of the full ASPIRE survey data set.

Using measurements of the [O iii ], H α , and [N ii ] emission line fluxes originating in the cool ( T ∼10 4 K) gas that populates the halos of massive early-type galaxies with stellar masses greater than 10 10.4 M ⊙ , we explore the recent conjecture that active galactic nucleus (AGN) activity preferentially removes the circumgalactic medium (CGM) along the polar (minor-axis) direction. We find deficits in the mean emission line flux of [O iii ] and H α (65% and 43%, respectively) along the polar versus planar directions, although due to the large uncertainties in these difficult measurements the results are of marginal statistical significance (1.5 σ ). More robustly (97%–99.9% confidence depending on the statistical test), diagnostic line ratios show stronger AGN ionization signatures along the polar direction at small radii than at other angles or radii. Our results are consistent with the conjecture of an anisotropic CGM in massive early-type galaxies, suggested on independent grounds, that is tied to AGN activity and begin to show the potential of CGM mapping using emission lines.

We present a catalog of 5598 ultra-diffuse galaxy (UDG) candidates with effective radius r e > 5.″3 distributed throughout the southern portion of the DESI Legacy Imaging Survey covering ∼15,000 deg2. The catalog is most complete for physically large (r e > 2.5 kpc) UDGs lying in the redshift range 1800 ≲ cz/km s−1 ≲ 7000, where the lower bound is defined by where incompleteness becomes significant for large objects on the sky and the upper bound by our minimum angular size selection criterion. Because physical size is integral to the definition of a UDG, we develop a method of distance estimation using existing redshift surveys. With three different galaxy samples, two of which contain UDGs with spectroscopic redshifts, we estimate that the method has a redshift accuracy of ∼75% when the method converges, although larger, more representative spectroscopic UDG samples are needed in order to fully understand the behavior of the method. We are able to estimate distances for 1079 of our UDG candidates (19%). Finally, to illustrate some uses of the catalog, we present both distance-independent and distance-dependent results. In the latter category, we establish that the red sequence of UDGs lies on the extrapolation of the red sequence relation for bright ellipticals and that the environment–color relation is at least qualitatively similar to that of high surface brightness galaxies. Both of these results challenge some of the models proposed for UDG evolution.

We present 226 large ultra-diffuse galaxy (UDG) candidates (r ( e ) > 5.'' 3, mu (0,g ) > 24 mag arcsec(-2)) in the SDSS Stripe 82 region recovered using our improved procedure developed in anticipation of processing the entire Legacy Surveys footprint. The advancements include less constrained structural parameter fitting, expanded wavelet filtering criteria, consideration of Galactic dust, estimates of parameter uncertainties and completeness based on simulated sources, and refinements of our automated candidate classification. We have a sensitivity similar to 1 mag fainter in mu (0,g ) than the largest published catalog of this region. Using our completeness-corrected sample, we find that (1) there is no significant decline in the number of UDG candidates as a function of mu (0,g ) to the limit of our survey (similar to 26.5 mag arcsec(-2)); (2) bluer candidates have smaller Sersic n; (3) most blue (g-r < 0.45 mag) candidates have mu (0,g ) less than or similar to 25 mag arcsec(-2) and will fade to populate the UDG red sequence we observe to similar to 26.5 mag arcsec(-2); (4) any red UDGs that exist significantly below our mu (0,g ) sensitivity limit are not descendent from blue UDGs in our sample; and (5) candidates with lower mu (0,g ) tend to smaller n. We anticipate that the final SMUDGes sample will contain similar to 30 x as many candidates.

Using our measurements of the H α emission line flux originating in the cool ( T ∼ 10 4 K) gas that populates the halos of galaxies, we build a joint model to describe the mass of the cool circumgalactic medium (CGM) as a function of galactic stellar mass ( 10 9.5 < M ∗ / M ⊙ < 10 11 ) and environment. Because the H α emission correlates with the main cooling channel for this gas, we are able to estimate the rate at which the CGM cools and becomes fuel for star formation in the central galaxy. We describe this calculation, which uses our observations, previous measurements of some critical CGM properties, and modeling of the cooling mechanism using the C loudy modeling suite. We find that the mass cooling rate is larger than the star formation rates of the central galaxies by a factor of ∼4–90, empirically confirming that there is sufficient fuel to resolve the gas consumption problem and that feedback is needed to avoid collecting too much cold gas in galaxies. We find excellent agreement between our estimates of both the mass cooling rates and mass loading factors and the predictions of independent theoretical studies. The convergence in results that we find from several completely different treatments of the problem, particularly at the lower end of the galactic mass range, is a strong indication that we have a relatively robust understanding of the quantitative effects of feedback across this mass range.

The timing argument provides a lower limit on the mass of the Milky Way. Using a sample of 32 stars at R > 60 kpc drawn from the H3 Spectroscopic Survey and mock catalogs created from published numerical simulations, we find that M 200 > 0.91 × 10 12 M ⊙ with 90% confidence. We recommend using this limit to refine the allowed prior mass range in more complex and sophisticated statistical treatments of Milky Way dynamics. The use of such a prior would have significantly reduced many previously published uncertainty ranges. Our analysis suggests that the most likely value of M 200 is ≈1.5 × 10 12 M ⊙ , but establishing this as the Milky Way mass requires a larger sample of outer halo stars and a more complete analysis of the inner halo stars in H3. The imminent growth in the sample of outer halo stars due to ongoing and planned surveys will make this possible.

We present the first systematic study of the stellar populations of ultra-diffuse galaxies (UDGs) in the field, integrating the large area search and characterization of UDGs by the SMUDGes survey with the twelve-band optical photometry of the S-PLUS survey. Based on Bayesian modeling of the optical colors of UDGs, we determine the ages, metallicities, and stellar masses of 100 UDGs distributed in an area of ∼330 deg 2 in the Stripe 82 region. We find that the stellar masses and metallicities of field UDGs are similar to those observed in clusters and follow the trends previously defined in studies of dwarf and giant galaxies. However, field UDGs have younger luminosity-weighted ages than do UDGs in clusters. We interpret this result to mean that field UDGs have more extended star formation histories, including some that continue to form stars at low levels to the present time. Finally, we examine stellar population scaling relations that show that UDGs are, as a population, similar to other low surface brightness galaxies.

We continue our empirical study of the emission line flux originating in the cool (T similar to 10(4) K) gas that populates the halos of galaxies and their environments. Specifically, we present results obtained for a sample of galaxy pairs with a range of projected separations, <CDATA <i , and mass ratios <1:5, intersected by 5443 Sloan Digital Sky Survey lines of sight at projected radii of 10-50 kpc from either or both of the two galaxies. We find significant enhancement in H alpha emission and a moderate enhancement in [N ii]6583 emission for low-mass pairs (mean stellar mass per galaxy, <CDATA <i ) relative to the results from a control sample. This enhanced H alpha emission comes almost entirely from sight lines located between the galaxies, consistent with a short-term, interaction-driven origin for the enhancement. We find no enhancement in H alpha emission, but significant enhancement in [N ii]6583 emission for high-mass ( <CDATA <i ) pairs. Furthermore, we find a dependence of the emission line properties on the galaxy pair mass ratio such that those with a mass ratio below 1:2.5 have enhanced [N ii]6583 and those with a mass ratio between 1:2.5 and 1:5 do not. In all cases, departures from the control sample are only detected for close pairs (S-p < 100 kpc). Attributing an elevated [N ii]6583/H alpha ratio to shocks, we infer that shocks play a role in determining the circumgalactic medium properties for close pairs that are among the more massive and have mass ratios closer to 1:1.

We continue our empirical study of the emission line flux originating in the cool ($T\sim10^4$ K) gas that populates the halos of galaxies and their environments. Specifically, we present results obtained for a sample of nearly half a million individual galaxies, groups, and clusters of galaxies, intersected by more than two million SDSS lines of sight at projected separations of up to a quarter of the virial radius. Adopting simple power law relationships between the circumgalactic (CGM) cool gas fraction and either the halo or stellar mass, we present expressions for the CGM cool gas fraction as a function of either halo or stellar mass, $f_{\rm cool}(M_h) = (0.25^{+0.07}_{-0.06}) \times (M_h/10^{12}M_\odot)^{(-0.39^{+0.06}_{-0.07})}$ or $f_{\rm cool}(M_{*}) = (0.28^{+0.07}_{-0.06}) \times (M_{\rm *}/10^{10.0}M_\odot)^{(-0.33\pm 0.06)}$. Where we can compare, our results are consistent with previous constraints from absorption line studies, our own previous emission line work, and simulations. The cool gas can be the dominant baryonic CGM component, comprising a fraction as high as $> 90\%$ of halo gaseous baryons, in low mass halos, $M_h\sim$ $10^{10.5} M_\odot$, and a minor fraction, $ 10^{14} M_\odot$.

Over the past decade, empirical constraints on the galaxy-dark matter halo connection have significantly advanced our understanding of galaxy evolution. Past techniques have focused on connections between halo properties and galaxy stellar mass and/or star formation rates. Empirical techniques in the next decade will link halo assembly histories with galaxies' circumgalactic media, supermassive black holes, morphologies, kinematics, sizes, colors, metallicities, and transient rates. Uncovering these links will resolve many critical uncertainties in galaxy formation and will enable much higher-fidelity mock catalogs essential for interpreting observations. Achieving these results will require broader and deeper spectroscopic coverage of galaxies and their circumgalactic media; survey teams will also need to meet several criteria (cross-comparisons, public access, and covariance matrices) to facilitate combining data across different surveys. Acting on these recommendations will continue enabling dramatic progress in both empirical modeling and galaxy evolution for the next decade.

The circumgalactic medium (CGM), which harbors > 50% of all the baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. As such, the CGM obviously plays a critical role in galaxy evolution. We discuss the opportunity to image this component using recombination line emission, beginning with the early results coming from recent statistical detection of this emission to the final goal of realizing spectral-line images of the CGM in individual nearby galaxies. Such work will happen in the next decade and provide new insights on the galactic baryon cycle.