We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (< 10 degrees from the LMC center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the south. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the Dark Energy Survey data by Mackey et al. at similar to 15 degrees. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC's interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf-dwarf interactions.

We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the Carina. II ( Car II) and Carina. III ( Car III) dwarf galaxy candidates, recently discovered in the Magellanic Satellites Survey ( MagLiteS). We identify 18 member stars in Car. II, including two binaries with variable radial velocities and two RR Lyrae stars. The other 14 members have a mean heliocentric velocity v(hel) = 477.2 +/- 1.2 km s(-1) and a velocity dispersion of sigma(v) 3.4(-0.8)(vertical bar 1.2) km s(-1). Assuming Car II is in dynamical equilibrium, we derive a total mass within the half-light radius of 1.0(-0.4)(+0.8) x 10(6) M circle dot, indicating a mass-to-light ratio of 369(-161)(+309) M circle dot/L circle dot. From equivalent width measurements of the calcium triplet lines of nine red giant branch (RGB) stars, we derive a mean metallicity of [Fe/H] = -2.44 +/- 0.09 with dispersion sigma([Fe/H]) = 0.22(-0.07)(+0.10). Considering both the kinematic and chemical properties, we conclude that Car II is a dark-matter-dominated dwarf galaxy. For Car III, we identify four member stars, from which we calculate a systemic velocity of vhel = 284.6(-3.1)(+3.4) km S-1. The brightest RGB member of Car. III has a metallicity of [Fe/H] = -1.97 +/- 0.12. Due to the small size of the Car III spectroscopic sample, we cannot conclusively determine its nature. Although these two systems have the smallest known physical separation (Delta d similar to 10 kpc) among Local Group satellites, the large difference in their systemic velocities, similar to 200 km s(-1), indicates that they are unlikely to be a bound pair. One or both systems are likely associated with the Large Magellanic Cloud (LMC), and may remain LMC satellites today. No statistically significant excess of gamma-ray emission is found at the locations of Car II and Car III in eight years of Fermi-LAT data.

We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS). Situated 18 deg (similar to 20 kpc) from the LMC and separated from each other by only 18 arcmin, Carina II and III form an intriguing pair. By simultaneously modelling the spatial and the colour-magnitude stellar distributions, we find that both Carina II and Carina III are likely dwarf galaxies, although this is less clear for Carina III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina II is located at similar to 36 kpc from the Sun, with M-V similar to -4.5 and r(h) similar to 90 pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina III is much more elongated, measured to be fainter (M-V similar to -2.4), significantly more compact (r(h) similar to 30 pc), and closer to the Sun, at similar to 28 kpc, placing it only 8 kpc away from Car II. Together with several other systems detected by the Dark Energy Camera, Carina II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.

Context. Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions.

We report the discovery of a new ultra-faint stellar system found near the Magellanic Clouds in the DECam Local Volume Exploration Survey. This new system, DELVE J0155-6815 (DELVE 2), is located at a heliocentric distance of D-circle dot = 71 +/- 4 kpc, which places it at a 3D physical separation of 12 +/- 3 kpc from the center of the Small Magellanic Cloud and 28(-3)(+4) kpc from the center of the Large Magellanic Cloud ( LMC). DELVE 2 is identified as a resolved overdensity of old (tau > 13.3 Gyr) and metal-poor ([Fe/H] = -2.0(-0.5)(+0.2) dex) stars with a projected half-light radius of r(1/2) = 21(-3)(+4) pc and an absolute magnitude of M-V = -2.1(-0.5)(+0.4) mag. The size and luminosity of DELVE 2 are consistent with both the population of recently discovered ultra-faint globular clusters and the smallest ultra-faint dwarf galaxies. However, its photometrically derived age and metallicity would place it among the oldest and most metal-poor globular clusters in the Magellanic system. In the absence of spectroscopic measurements of the system's metallicity dispersion and internal kinematics, we are unable to conclusively classify this system at this time. DELVE 2 is detected in Gaia DR2 with a clear proper-motion signal, with multiple blue horizontal-branch stars near the centroid of the system with proper motions consistent with the systemic mean. We measure the system proper motion to be (mu(alpha) cos delta, mu(delta)) = (1.02(-0.25)(+0.24), -0.85(-0.19)(+0.18) mas yr(-1). We compare the spatial position and proper motion of DELVE 2 with simulations of the accreted satellite population of the LMC and find that it is very likely to be associated with the LMC.

We report the detection of three RR Lyrae (RRL) stars (two RRc and one RRab) in the ultra-faint dwarf (UFD) galaxy Centaurus I (Cen I) and two Milky Way (MW) delta Scuti/SX Phoenicis stars based on multi-epoch giz DECam observations. The two RRc stars are located within two times the half-light radius (r ( h )) of Cen I, while the RRab star (CenI-V3) is at similar to 6 r ( h ). The presence of three distant RRL stars clustered this tightly in space represents a 4.7 sigma excess relative to the smooth distribution of RRL in the Galactic halo. Using the newly detected RRL stars, we obtain a distance modulus to Cen I of mu (0) = 20.354 +/- 0.002 mag (sigma = 0.03 mag), a heliocentric distance of D (circle dot) = 117.7 +/- 0.1 kpc (sigma = 1.6 kpc), with systematic errors of 0.07 mag and 4 kpc. The location of the Cen I RRL stars in the Bailey diagram is in agreement with other UFD galaxies (mainly Oosterhoff II). Finally, we study the relative rate of RRc+RRd (RRcd) stars (f (cd)) in UFD and classical dwarf galaxies. The full sample of MW dwarf galaxies gives a mean of f (cd) = 0.28. While several UFD galaxies, such as Cen I, present higher RRcd ratios, if we combine the RRL populations of all UFD galaxies, the RRcd ratio is similar to the one obtained for the classical dwarfs (f (cd) similar to 0.3). Therefore, there is no evidence for a different fraction of RRcd stars in UFD and classical dwarf galaxies.

We present the discovery of a candidate ultra-faint Milky-Way satellite, Eridanus IV (DELVE J0505-0931), detected in photometric data from the DECam Local Volume Exploration survey (DELVE). Eridanus IV is a faint (M-V = - 4.7 +/- 0.2), extended (r(1/2)=75(-13)(+16) pc ), and elliptical (epsilon = 0.54 +/- 0.1) system at a heliocentric distance of 76.7(-6.1)(+4.0)kpc, with a stellar population that is well described by an old, metal-poor isochrone (age of tau similar to 13.0 Gyr and metallicity of [Fe/H] less than or similar to - 2.1 dex). These properties are consistent with the known population of ultra-faint Milky-Way satellite galaxies. Eridanus IV is also prominently detected using proper-motion measurements from Gaia Early Data Release 3, with a systemic proper motion of (mu(alpha) cos delta,mu(delta))=(+0.25 +/- 0.06,-0.10 +/- 0.05) mas yr(-1) measured from its horizontal branch and red-giant-branch member stars. We find that the spatial distribution of likely member stars hints at the possibility that the system is undergoing tidal disruption.

A fully sampled and hitherto highest resolution and sensitivity observation of neutral hydrogen (H I) in the Leo Triplet (NGC 3628, M 65/NGC 3623, and M 66/NGC 3627) reveals six H I structures beyond the three galaxies. We present detailed results of the morphologies and kinematics of these structures, which can be used for future simulations. In particular, we detect a two-arm structure in the plume of NGC 3628 for the first time, which can be explained by a tidal interaction model. The optical counterpart of the plume is mainly associated with the southern arm. The connecting part (base) of the plume (directed eastward) with NGC 3628 is located at the blueshifted (western) side of NGC 3628. Two bases appear to be associated with the two arms of the plume. A clump with a reversed velocity gradient (relative to the velocity gradient of M 66) and a newly detected tail, that is to say M 66SE, is found in the southeast of M 66. We suspect that M 66SE represents gas from NGC 3628, which was captured by M 66 in the recent interaction between the two galaxies. Meanwhile gas is falling toward M 66, resulting in features previously observed in the southeastern part of M 66, such as large line widths and double peaks. An upside-down "Y"-shaped H I gas component (M 65S) is detected in the south of M 65, which suggests that M 65 may also have been involved in the interaction. We strongly encourage modern hydrodynamical simulations of this interacting group of galaxies to reveal the origin of the gaseous debris surrounding all three galaxies.

We present the second public data release (DR2) from the DECam Local Volume Exploration survey (DELVE). DELVE DR2 combines new DECam observations with archival DECam data from the Dark Energy Survey, the DECam Legacy Survey, and other DECam community programs. DELVE DR2 consists of similar to 160,000 exposures that cover >21,000 deg(2) of the high-Galactic-latitude ( divide b divide > 10 degrees) sky in four broadband optical/near-infrared filters (g, r, i, z). DELVE DR2 provides point-source and automatic aperture photometry for similar to 2.5 billion astronomical sources with a median 5 sigma point-source depth of g = 24.3, r = 23.9, i = 23.5, and z = 22.8 mag. A region of similar to 17,000 deg(2) has been imaged in all four filters, providing four-band photometric measurements for similar to 618 million astronomical sources. DELVE DR2 covers more than 4 times the area of the previous DELVE data release and contains roughly 5 times as many astronomical objects. DELVE DR2 is publicly available via the NOIRLab Astro Data Lab science platform.