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We present MArk-dependently THinned POint Process (Mathpop), a novel method to infer the globular cluster (GC) counts in ultra-diffuse galaxies (UDGs) and low-surface brightness galaxies (LSBGs). Many known UDGs have a surprisingly high ratio of GC number to surface brightness. However, standard methods to infer GC counts in UDGs face various challenges, such as photometric measurement uncertainties, GC membership uncertainties, and assumptions about the GC luminosity functions (GCLFs). Mathpop tackles these challenges using the mark-dependent thinned point process, enabling joint inference of the spatial and magnitude distributions of GCs. In doing so, Mathpop allows us to infer and quantify the uncertainties in both GC counts and GCLFs with minimal assumptions. As a precursor to Mathpop, we also address the data uncertainties coming from the selection process of GC candidates: we obtain probabilistic GC candidates instead of the traditional binary classification based on the color–magnitude diagram. We apply Mathpop to 40 LSBGs in the Perseus cluster using GC catalogs from a Hubble Space Telescope imaging program. We then compare our results to those from an independent study using the standard method. We further calibrate and validate our approach through extensive simulations. Our approach reveals two LSBGs having GCLF turnover points much brighter than the canonical value with Bayes’ factor being ∼4.5 and ∼2.5, respectively. An additional crude maximum-likelihood estimation and simulation study show that their GCLF TO points are approximately 0.9 mag and 1.1 mag brighter than the canonical value, with p-values of ∼10^−8 and ∼10^−5, respectively. 

High-resolution 3D maps of interstellar dust are critical for probing the underlying physics shaping the structure of the interstellar medium, and for foreground correction of astrophysical observations affected by dust. We aim to construct a new 3D map of the spatial distribution of interstellar dust extinction out to a distance of kpc from the Sun. We leveraged distance and extinction estimates to 54 million nearby stars derived from the Gaia BP/RP spectra. Using the stellar distance and extinction information, we inferred the spatial distribution of dust extinction. We modeled the logarithmic dust extinction with a Gaussian process in a spherical coordinate system via iterative charted refinement and a correlation kernel inferred in previous work. In total, our posterior has over 661 million degrees of freedom. We probed the posterior distribution using the variational inference method MGVI. Our 3D dust map has an angular resolution of up to $ $ ($$N_ side =256$$), and we achieve parsec-scale distance resolution, sampling the dust in $516$ logarithmically spaced distance bins spanning pc . We generated 12 samples from the variational posterior of the 3D dust distribution and release the samples alongside the mean 3D dust map and its corresponding uncertainty. Our map resolves the internal structure of hundreds of molecular clouds in the solar neighborhood and will be broadly useful for studies of star formation, Galactic structure, and young stellar populations. It is available for download in a variety of coordinate systems online and can also be queried via the publicly available dustmaps Python package. 

ABSTRACT We present the first detailed chemical-abundance analysis of stars from the dwarf-galaxy stellar stream Wukong/LMS-1 covering a wide metallicity range ($$-3.5 \lt \rm [Fe/H] \lesssim -1.3$$). We find abundance patterns that are effectively indistinguishable from the bulk of Indus and Jhelum, a pair of smaller stellar streams proposed to be dynamically associated with Wukong/LMS-1. We confirmed a carbon-enhanced metal-poor star ($$\rm [C/Fe] \gt +0.7$$ and $$\rm [Fe/H] \sim -2.9$$) in Wukong/LMS-1 with strong enhancements in Sr, Y, and Zr, which is peculiar given its solar-level [Ba/Fe]. Wukong/LMS-1 stars have high abundances of α elements up to $$\rm [Fe/H] \gtrsim -2$$, which is expected for relatively massive dwarfs. Towards the high-metallicity end, Wukong/LMS-1 becomes α-poor, revealing that it probably experienced fairly standard chemical evolution. We identified a pair of N- and Na-rich stars in Wukong/LMS-1, reminiscent of multiple stellar populations in globular clusters. This indicates that this dwarf galaxy contained at least one globular cluster that was completely disrupted in addition to two intact ones previously known to be associated with Wukong/LMS-1, which is possibly connected to similar evidence found in Indus. From these ≥3 globular clusters, we estimate the total mass of Wukong/LMS-1 to be $${\approx }10^{10} \, \mathrm{M}_\odot$$, representing ∼1 per cent of the present-day Milky Way. Finally, the [Eu/Mg] ratio in Wukong/LMS-1 continuously increases with metallicity, making this the first example of a dwarf galaxy where the production of r-process elements is clearly dominated by delayed sources, presumably neutron-star mergers. 

ABSTRACT We model the stellar abundances and ages of two disrupted dwarf galaxies in the Milky Way stellar halo: Gaia-Sausage Enceladus (GSE) and Wukong/LMS-1. Using a statistically robust likelihood function, we fit one-zone models of galactic chemical evolution with exponential infall histories to both systems, deriving e-folding time-scales of τin = 1.01 ± 0.13 Gyr for GSE and $$\tau _\text{in} = 3.08^{+3.19}_{-1.16}$$ Gyr for Wukong/LMS-1. GSE formed stars for $$\tau _\text{tot} = 5.40^{+0.32}_{-0.31}$$ Gyr, sustaining star formation for ∼1.5–2 Gyr after its first infall into the Milky Way ∼10 Gyr ago. Our fit suggests that star formation lasted for $$\tau _\text{tot} = 3.36^{+0.55}_{-0.47}$$ Gyr in Wukong/LMS-1, though our sample does not contain any age measurements. The differences in evolutionary parameters between the two are qualitatively consistent with trends with stellar mass M⋆ predicted by simulations and semi-analytic models of galaxy formation. Our inferred values of the outflow mass-loading factor reasonably match $$\eta \propto M_\star ^{-1/3}$$ as predicted by galactic wind models. Our fitting method is based only on Poisson sampling from an evolutionary track and requires no binning of the data. We demonstrate its accuracy by testing against mock data, showing that it accurately recovers the input model across a broad range of sample sizes (20 ≤ N ≤ 2000) and measurement uncertainties (0.01 ≤ σ[α/Fe], σ[Fe/H] ≤ 0.5; $$0.02 \le \sigma _{\log _{10}(\text{age})} \le 1$$). Due to the generic nature of our derivation, this likelihood function should be applicable to one-zone models of any parametrization and easily extensible to other astrophysical models which predict tracks in some observed space. 

Abstract We present an analysis of the kinematics of the Radcliffe Wave, a 2.7 kpc long sinusoidal band of molecular clouds in the solar neighborhood recently detected via 3D dust mapping. With Gaia DR2 astrometry and spectroscopy, we analyze the 3D space velocities of ∼1500 young stars along the Radcliffe Wave in action-angle space, using the motion of the wave’s newly born stars as a proxy for its gas motion. We find that the vertical angle of young stars—corresponding to their orbital phase perpendicular to the Galactic plane—varies significantly as a function of position along the structure, in a pattern potentially consistent with a wavelike oscillation. This kind of oscillation is not seen in a control sample of older stars from Gaia occupying the same volume, disfavoring formation channels caused by long-lived physical processes. We use a “wavy midplane” model to try to account for the trend in vertical angles seen in young stars, and find that while the best-fit parameters for the wave’s spatial period and amplitude are qualitatively consistent with the existing morphology defined by 3D dust, there is no evidence for additional velocity structure. These results support more recent and/or transitory processes in the formation of the Radcliffe Wave, which would primarily affect the motion of the wave’s gaseous material. Comparisons of our results with new and upcoming simulations, in conjunction with new stellar radial velocity measurements in Gaia DR3, should allow us to further discriminate between various competing hypotheses. 

Abstract Modern Galactic surveys have revealed an ancient merger that dominates the stellar halo of our galaxy (Gaia–Sausage–Enceladus, GSE). Using chemical abundances and kinematics from the H3 Survey, we identify 5559 halo stars from this merger in the radial range r Gal = 6–60kpc. We forward model the full selection function of H3 to infer the density profile of this accreted component of the stellar halo. We consider a general ellipsoid with principal axes allowed to rotate with respect to the galactocentric axes, coupled with a multiply broken power law. The best-fit model is a triaxial ellipsoid (axes ratios 10:8:7) tilted 25° above the Galactic plane toward the Sun and a doubly broken power law with breaking radii at 12 kpc and 28 kpc. The doubly broken power law resolves a long-standing dichotomy in literature values of the halo breaking radius, being at either ∼15 kpc or ∼30 kpc assuming a singly broken power law. N -body simulations suggest that the breaking radii are connected to apocenter pile-ups of stellar orbits, and so the observed double-break provides new insight into the initial conditions and evolution of the GSE merger. Furthermore, the tilt and triaxiality of the stellar halo could imply that a fraction of the underlying dark matter halo is also tilted and triaxial. This has important implications for dynamical mass modeling of the galaxy as well as direct dark matter detection experiments. 

Abstract Deep optical and near-infrared imaging of the entire Galactic plane is essential for understanding our Galaxy’s stars, gas, and dust. The second data release of the Dark Energy Camera (DECam) Plane Survey extends the five-band optical and near-infrared survey of the southern Galactic plane to cover 6.5% of the sky, ∣ b ∣ ≤ 10°, and 6° > ℓ > −124°, complementary to coverage by Pan-STARRS1. Typical single-exposure effective depths, including crowding effects and other complications, are 23.5, 22.6, 22.1, 21.6, and 20.8 mag in g , r , i , z , and Y bands, respectively, with around 1″ seeing. The survey comprises 3.32 billion objects built from 34 billion detections in 21,400 exposures, totaling 260 hr open shutter time on the DECam at Cerro Tololo. The data reduction pipeline features several improvements, including the addition of synthetic source injection tests to validate photometric solutions across the entire survey footprint. A convenient functional form for the detection bias in the faint limit was derived and leveraged to characterize the photometric pipeline performance. A new postprocessing technique was applied to every detection to debias and improve uncertainty estimates of the flux in the presence of structured backgrounds, specifically targeting nebulosity. The images and source catalogs are publicly available at http://decaps.skymaps.info/ . 

Abstract We report the discovery of Specter, a disrupted ultrafaint dwarf galaxy revealed by the H3 Spectroscopic Survey. We detected this structure via a pair of comoving metal-poor stars at a distance of 12.5 kpc, and further characterized it with Gaia astrometry and follow-up spectroscopy. Specter is a 25° × 1° stream of stars that is entirely invisible until strict kinematic cuts are applied to remove the Galactic foreground. The spectroscopic members suggest a stellar age τ ≳ 12 Gyr and a mean metallicity 〈 [ Fe / H ] 〉 = − 1.84 − 0.18 + 0.16 , with a significant intrinsic metallicity dispersion σ [ Fe / H ] = 0.37 − 0.13 + 0.21 . We therefore argue that Specter is the disrupted remnant of an ancient dwarf galaxy. With an integrated luminosity M V ≈ −2.6, Specter is by far the least-luminous dwarf galaxy stream known. We estimate that dozens of similar streams are lurking below the detection threshold of current search techniques, and conclude that spectroscopic surveys offer a novel means to identify extremely low surface brightness structures. 

Abstract Recent observations of the stellar halo have uncovered the debris of an ancient merger, Gaia–Sausage–Enceladus (GSE), estimated to have occurred ≳8 Gyr ago. Follow-up studies have associated GSE with a large-scale tilt in the stellar halo that links two well-known stellar overdensities in diagonally opposing octants of the Galaxy (the Hercules–Aquila Cloud and Virgo Overdensity; HAC and VOD). In this paper, we study the plausibility of such unmixed merger debris persisting over several gigayears in the Galactic halo. We employ the simulated stellar halo from Naidu et al., which reproduces several key properties of the merger remnant, including the large-scale tilt. By integrating the orbits of these simulated stellar halo particles, we show that adoption of a spherical halo potential results in rapid phase mixing of the asymmetry. However, adopting a tilted halo potential preserves the initial asymmetry in the stellar halo for many gigayears. The asymmetry is preserved even when a realistic growing disk is added to the potential. These results suggest that HAC and VOD are long-lived structures that are associated with GSE and that the dark matter halo of the Galaxy is tilted with respect to the disk and aligned in the direction of HAC–VOD. Such halo–disk misalignment is common in modern cosmological simulations. Lastly, we study the relationship between the local and global stellar halo in light of a tilted global halo comprised of highly radial orbits. We find that the local halo offers a dynamically biased view of the global halo due to its displacement from the Galactic center. 

ABSTRACT Due to the different environments in the Milky Way’s disc and halo, comparing wide binaries in the disc and halo is key to understanding wide binary formation and evolution. By using Gaia Early Data Release 3, we search for resolved wide binary companions in the H3 survey, a spectroscopic survey that has compiled ∼150 000 spectra for thick-disc and halo stars to date. We identify 800 high-confidence (a contamination rate of 4 per cent) wide binaries and two resolved triples, with binary separations mostly between 103 and 105 au and a lowest [Fe/H] of −2.7. Based on their Galactic kinematics, 33 of them are halo wide binaries, and most of those are associated with the accreted Gaia-Sausage-Enceladus galaxy. The wide binary fraction in the thick disc decreases toward the low metallicity end, consistent with the previous findings for the thin disc. Our key finding is that the halo wide binary fraction is consistent with the thick-disc stars at a fixed [Fe/H]. There is no significant dependence of the wide binary fraction on the α-captured abundance. Therefore, the wide binary fraction is mainly determined by the iron abundance, not their disc or halo origin nor the α-captured abundance. Our results suggest that the formation environments play a major role for the wide binary fraction, instead of other processes like radial migration that only apply to disc stars.