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Extra-tidal features around globular clusters (GCs) are tracers of their disruption, stellar stream formation, and their host's gravitational potential. However, these features remain challenging to detect due to their low surface brightness. We conduct a systematic search for such features around 19 GCs in the DECam Local Volume Exploration (DELVE) survey Data Release 2, discovering a new extra-tidal envelope around NGC 5897 and find tentative evidence for an extended envelope surrounding NGC 7492. Through a combination of dynamical modeling and analyzing synthetic stellar populations, we demonstrate these envelopes may have formed through tidal disruption. We use these models to explore the detectability of these features in the upcoming Legacy Survey of Space and Time (LSST), finding that while LSST's deeper photometry will enhance detection significance, additional methods for foreground removal like proper motions or metallicities may be important for robust stream detection. Our results both add to the sample of globular clusters with extra-tidal features and provide insights on interpreting similar features in current and upcoming data.

Observations of density variations in stellar streams are a promising probe of low-mass dark matter substructure in the Milky Way. However, survey systematics such as variations in seeing and sky brightness can also induce artificial fluctuations in the observed densities of known stellar streams. These variations arise because survey conditions affect both object detection and star--galaxy misclassification rates. To mitigate these effects, we use Balrog synthetic source injections in the Dark Energy Survey (DES) Y3 data to calculate detection rate variations and classification rates as functions of survey properties. We show that these rates are nearly separable with respect to survey properties and can be estimated with sufficient statistics from the synthetic catalogs. Applying these corrections reduces the standard deviation of relative detection rates across the DES footprint by a factor of five, and our corrections significantly change the inferred linear density of the Phoenix stream when including faint objects. Additionally, for artificial streams with DES like survey properties we are able to recover density power spectra with reduced bias. We also find that uncorrected power-spectrum results for LSST-like data can be around five times more biased, highlighting the need for such corrections in future ground based surveys.

The properties of Milky Way satellite galaxies have important implications for galaxy formation, reionization, and the fundamental physics of dark matter. However, the population of Milky Way satellites includes the faintest known galaxies, and current observations are incomplete. To understand the impact of observational selection effects on the known satellite population, we perform rigorous, quantitative estimates of the Milky Way satellite galaxy detection efficiency in three wide-field survey datasets: the Dark Energy Survey Year 6, the DECam Local Volume Exploration Data Release 3, and the Pan-STARRS1 Data Release 1. Together, these surveys cover \\(\\sim\\)13,600 deg\\(^2\\) to \\(g \\sim 24.0\\) and \\(\\sim\\)27,700 deg\\(^2\\) to \\(g \\sim 22.5\\), spanning \\(\\sim\\)91% of the high-Galactic-latitude sky (\\(|b| \\geq 15^\\circ\\)). We apply multiple detection algorithms over the combined footprint and recover 49 known satellites above a strict census detection threshold. To characterize the sensitivity of our census, we run our detection algorithms on a large set of simulated galaxies injected into the survey data, which allows us to develop models that predict the detectability of satellites as a function of their properties. We then fit an empirical model to our data and infer the luminosity function, radial distribution, and size-luminosity relation of Milky Way satellite galaxies. Our empirical model predicts a total of \\(265^{+79}_{-47}\\) satellite galaxies with \\(-20 \\leq M_V \\leq 0\\), half-light radii of \\(15 \\leq r_{1/2} (\\rm pc) \\leq 3000\\), and galactocentric distances of \\(10 \\leq D_{\\rm GC} (\\rm kpc) \\leq 300\\). We also identify a mild anisotropy in the angular distribution of the observed galaxies, at a significance of $\\sim$$2\\sigma$, which can be attributed to the clustering of satellites associated with the LMC.

We report the discovery of three Milky Way satellite candidates: Carina IV, Phoenix III, and DELVE 7, in the third data release of the DECam Local Volume Exploration survey (DELVE). The candidate systems were identified by cross-matching results from two independent search algorithms. All three are extremely faint systems composed of old, metal-poor stellar populations (\\(\\tau \\gtrsim 10\\) Gyr, [Fe/H] \\( \\lesssim -1.4\\)). Carina IV (\\(M_V = -2.8;\\ r_{1/2} = 40 {\\rm pc}\\)) and Phoenix III (\\(M_V = -1.2;\\ r_{1/2} = 19 {\\rm pc}\\)) have half-light radii that are consistent with the known population of dwarf galaxies, while DELVE 7 (\\(M_V = 1.2;\\ r_{1/2} = 2 {\\rm pc}\\)) is very compact and seems more likely to be a star cluster, though its nature remains ambiguous without spectroscopic followup. The Gaia proper motions of stars in Carina IV (\\(M_* = 2250^{+1180}_{-830} {\\rm M_\\odot}\\)) indicate that it is unlikely to be associated with the LMC, while DECam CaHK photometry confirms that its member stars are metal-poor. Phoenix III (\\(M_* = 520^{+660}_{-290} {\\rm M_\\odot}\\)) is the faintest known satellite in the extreme outer stellar halo (\\(D_{\\rm GC} > 100\\) kpc), while DELVE 7 (\\(M_* = 60^{+120}_{-40} {\\rm M_\\odot}\\)) is the faintest known satellite with \\(D_{\\rm GC} > 20\\) kpc.

We present Magellan/IMACS and Magellan/MIKE spectroscopy of the ultra-faint dwarf (UFD) galaxy Pictor~II (Pic~II) that is located only 12 kpc from the Large Magellanic Cloud (LMC). From the IMACS spectroscopy, we identify 13 member stars and measure a mean heliocentric velocity of \\(326.9\\pm1.1~{\\rm km~s^{-1}}\\), a velocity dispersion of \\(3.5_{-0.9}^{+1.1}~{\\rm km~s^{-1}}\\), a mean metallicity of \\(\\overline{{\\rm [Fe/H]}}=-2.99\\pm0.06\\), and an upper limit on the metallicity dispersion of \\(\\sigma_{\\rm [Fe/H]}<0.18\\). We measure detailed elemental abundances for the brightest star, finding \\(\\mbox{[Fe/H]} = -3.3\\), high [\\(\\alpha\\)/Fe] ratios, and no detectable neutron capture elements, similar to stars in other UFDs. However, this star has an unusually high [Sc/Fe] ratio. The dynamical mass-to-light ratio (\\(M/L=760_{-420}^{+910}~M_{\\odot}~L^{-1}_{\\odot}\\)), size, and chemical abundances confirms that Pic~II is a dark matter-dominated dwarf galaxy. We perform detailed orbit modeling of Pic~II in a combined Milky Way (MW) and LMC potential and find that Pic~II is highly likely to be a long-term LMC satellite. Furthermore, we find that Pic II is likely still bound to the LMC today. Pic~II is the seventh LMC-associated UFD and among the most metal-poor UFDs known. We further update the morphological parameters with deeper Dark Energy Camera (DECam) photometry, compute the dark matter properties for dark matter indirect detection searches, verify the extremely low metallicity with narrowband CaHK imaging, and briefly discuss tidal influences of the LMC and MW.

We present the photometric redshift characterization and calibration for the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. The redshifts are estimated from a combination of wide-field photometry, deep-field photometry with associated redshift estimates, and a transfer function between the wide field and deep field that is estimated using a source injection catalog. We construct four tomographic bins for the galaxy catalog, and estimate the redshift distribution, \\(n(z)\\), within each one using the Self-organizing Map Photo-Z (SOMPZ) methodology. Our estimates include the contributions from sample variance, zeropoint calibration uncertainties, and redshift biases, as quantified for the deep-field dataset. The total uncertainties on the mean redshifts are \\(_ z 0.01\\). The SOMPZ estimates are then compared to those from the clustering redshift method, obtained by cross-correlating our source galaxies with galaxies in spectroscopic surveys, and are shown to be consistent with each other.

We present the pipeline for the cosmic shear analysis of the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog consisting of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. The catalog derives from a large number of disparate observing programs and is therefore more inhomogeneous across the sky compared to existing lensing surveys. First, we use simulated data-vectors to show the sensitivity of our constraints to different analysis choices in our inference pipeline, including sensitivity to residual systematics. Next we use simulations to validate our covariance modeling for inhomogeneous datasets. Finally, we show that our choices in the end-to-end cosmic shear pipeline are robust against inhomogeneities in the survey, by extracting relative shifts in the cosmology constraints across different subsets of the footprint/catalog and showing they are all consistent within \\(1\\) to \\(2\\). This is done for forty-six subsets of the data and is carried out in a fully consistent manner: for each subset of the data, we re-derive the photometric redshift estimates, shear calibrations, survey transfer functions, the data vector, measurement covariance, and finally, the cosmological constraints. Our results show that existing analysis methods for weak lensing cosmology can be fairly resilient towards inhomogeneous datasets. This also motivates exploring a wider range of image data for pursuing such cosmological constraints.

We present the Dark Energy Camera All Data Everywhere (DECADE) weak lensing dataset: a catalog of 107 million galaxies observed by the Dark Energy Camera (DECam) in the northern Galactic cap. This catalog was assembled from public DECam data including survey and standard observing programs. These data were consistently processed with the Dark Energy Survey Data Management pipeline as part of the DECADE campaign and serve as the basis of the DECam Local Volume Exploration survey (DELVE) Early Data Release 3 (EDR3). We apply the Metacalibration measurement algorithm to generate and calibrate galaxy shapes. After cuts, the resulting cosmology-ready galaxy shape catalog covers a region of \\(5,\\!412 \\,\\, deg^2\\) with an effective number density of \\(4.59\\,\\, arcmin^-2\\). The coadd images used to derive this data have a median limiting magnitude of \\(r = 23.6\\), \\(i = 23.2\\), and \\(z = 22.6\\), estimated at \\( S/N = 10\\) in a 2 arcsecond aperture. We present a suite of detailed studies to characterize the catalog, measure any residual systematic biases, and verify that the catalog is suitable for cosmology analyses. In parallel, we build an image simulation pipeline to characterize the remaining multiplicative shear bias in this catalog, which we measure to be \\(m = (-2.454 0.124) 10^-2\\) for the full sample. Despite the significantly inhomogeneous nature of the data set, due to it being an amalgamation of various observing programs, we find the resulting catalog has sufficient quality to yield competitive cosmological constraints.

We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way (MW) satellite in the constellation of Leo. This system was discovered as a spatial overdensity of resolved stars observed with Dark Energy Camera (DECam) data from an early version of the third data release of the DECam Local Volume Exploration survey (DELVE EDR3). The low luminosity (\\(M_V = -3.56_{-0.37}^{+0.47}\\) ; \\(L_V = 2300_{-700}^{+1200} L_\\odot\\)), large size (\\(R_{1/2} = 90_{-30}^{+30}\\) pc), and large heliocentric distance (\\(D = 111_{-6}^{+9}\\) kpc) are all consistent with the population of ultra-faint dwarf galaxies (UFDs). Using Keck/DEIMOS observations of the system, we were able to spectroscopically confirm nine member stars, while measuring a tentative mass-to-light ratio of \\(700_{-500}^{+1400} M_\\odot/L_\\odot\\) and a non-zero metallicity dispersion of \\(\\sigma_{[\\rm Fe/H]}=0.19_{-0.11}^{+0.14}\\), further confirming Leo VI's identity as an UFD. While the system has a highly elliptical shape, \\(\\epsilon = 0.54_{-0.29}^{+0.19}\\), we do not find any conclusive evidence that it is tidally disrupting. Moreover, despite the apparent on-sky proximity of Leo VI to members of the proposed Crater-Leo infall group, its smaller heliocentric distance and inconsistent position in energy-angular momentum space make it unlikely that Leo VI is part of the proposed infall group.

We report the discovery of Tucana B, an isolated ultra-faint dwarf galaxy at a distance of D=1.4 Mpc. Tucana B was found during a search for ultra-faint satellite companions to the known dwarfs in the outskirts of the Local Group, although its sky position and distance indicate the nearest galaxy to be \\(\\sim\\)500 kpc distant. Deep ground-based imaging resolves Tucana B into stars, and it displays a sparse red giant branch consistent with an old, metal poor stellar population analogous to that seen in the ultra-faint dwarf galaxies of the Milky Way, albeit at fainter apparent magnitudes. Tucana B has a half-light radius of 80\\(\\pm\\)40 pc, and an absolute magnitude of \\(M_V\\)=\\(-\\)6.9\\(^{+0.5}_{-0.6}\\) mag (\\(L_V\\)=\\((5^{+4}_{-2})\\times\\)10\\(^4\\) \\(L_{\\odot}\\)), which is again comparable to the Milky Way's ultra-faint satellites. There is no evidence for a population of young stars, either in the optical color magnitude diagram or in GALEX archival ultraviolet imaging, with the GALEX data indicating \\(\\log (\\mathrm{SFR_{NUV}/M_\\odot \\, yr^{-1}}) < -5.4\\) for star formation on \\(\\lesssim\\)100 Myr time scales. Given its isolation and physical properties, Tucana B may be a definitive example of an ultra-faint dwarf that has been quenched by reionization, providing strong confirmation of a key driver of galaxy formation and evolution at the lowest mass scales. It also signals a new era of ultra-faint dwarf galaxy discovery at the extreme edges of the Local Group.