Abstract
We report the first 3D kinematical measurements of 88 stars in the direction of several recently discovered substructures in the southern periphery of the Large Magellanic Cloud (LMC) using ...a combination of Gaia proper motions and radial velocities from the APOGEE-2 survey. More specifically, we explore stars in assorted APOGEE-2 pointings in a region of the LMC periphery where various overdensities of stars have previously been identified in maps of stars from Gaia and DECam. By using a model of the LMC disk rotation, we find that a sizable fraction of the APOGEE-2 stars have extreme space velocities that are distinct from, and not a simple extension of, the LMC disk. Using
N
-body hydrodynamical simulations of the past dynamical evolution and interaction of the LMC and Small Magellanic Cloud (SMC), we explore whether the extreme-velocity stars may be accounted for as tidal debris created in the course of that interaction. We conclude that the combination of LMC and SMC debris produced from their interaction is a promising explanation, although we cannot rule out other possible origins, and that these new data should be used to constrain future simulations of the LMC–SMC interaction. We also conclude that many of the stars in the southern periphery of the LMC lie outside of the LMC plane by several kiloparsecs. Given that the metallicity of these stars suggests that they are likely of Magellanic origin, our results suggest that a wider exploration of the past interaction history of the Magellanic Clouds is needed.
ABSTRACT We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data from the ongoing Survey of the Magellanic Stellar History conducted with the Dark Energy ...Camera on the Blanco 4 m Telescope. The new satellite is compact ( 11 pc) and faint ( 0.3), but well within the realm of dwarf galaxies. The stellar distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ( ) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric distance of 134 10 kpc, Hydra II is located in a region of the Galactic halo that models have suggested may host material from the leading arm of the Magellanic Stream. A comparison with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite of the Magellanic Clouds.
Abstract
Multiple populations (MPs), characterized by variations in light elemental abundances, have been found in stellar clusters in the Milky Way, Magellanic Clouds, as well as several other dwarf ...galaxies. Based on a large number of observations, mass has been suggested to be a key parameter affecting the presence and appearance of MPs in stellar clusters. To further investigate the existence of MPs in low-mass clusters and explore the mass threshold for the formation of MPs, we carried out a project studying the composition of the stellar population in several low-mass Galactic globular clusters. Here we present our study on the cluster Eridanus. With blue-UV low-resolution spectra obtained with the OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed the spectral indices of CH and CN for a sample of giant stars and derived their carbon and nitrogen abundances using model spectra. A significant dispersion in the initial surface abundance of nitrogen was found in the sample, indicating the existence of MPs in Eridanus. Inspecting the age–initial mass distribution of in situ clusters with MPs, we find a slight trend that initial mass increases with increasing age, and the lowest initial masses of
log
M
initial
∼ 4.98 and 5.26 are found at the young and old end, respectively, which might provide a rough reference for the mass threshold for clusters to form MPs. However, more observations of clusters with low initial masses are still necessary before any firm conclusion can be drawn.
The central (‘bulge’) region of the Milky Way is teeming with a significant fraction of mildly metal-deficient stars with atmospheres that are strongly enriched in cyanogen (
12
C
14
N). Some of ...these objects, which are also known as nitrogen-enhanced stars, are hypothesised to be relics of the ancient assembly history of the Milky Way. Although the chemical similarity of nitrogen-enhanced stars to the unique chemical patterns observed in globular clusters has been observed, a direct connection between field stars and globular clusters has not yet been proven. In this work, we report on high-resolution, near-infrared spectroscopic observations of the bulge globular cluster NGC 6723, and the serendipitous discovery of a star, 2M18594405−3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio (N/Fe ≳ + 0.94) is well above the typical Galactic field-star levels, and it exhibits noticeable enrichment in the heavy
s
-process elements (Ce, Nd, and Yb), along with moderate carbon enrichment; all characteristics are known examples in globular clusters. This result suggests that some of the nitrogen-enhanced stars in the bulge likely originated from the tidal disruption of globular clusters.
SMASHing the low surface brightness SMC Massana, Pol; Noël, Noelia E D; Nidever, David L ...
Monthly notices of the Royal Astronomical Society,
10/2020, Letnik:
498, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
The periphery of the Small Magellanic Cloud (SMC) can unlock important information regarding galaxy formation and evolution in interacting systems. Here, we present a detailed study of the ...extended stellar structure of the SMC using deep colour–magnitude diagrams, obtained as part of the Survey of the MAgellanic Stellar History (SMASH). Special care was taken in the decontamination of our data from Milky Way (MW) foreground stars, including from foreground globular clusters NGC 362 and 47 Tuc. We derived the SMC surface brightness using a ‘conservative’ approach from which we calculated the general parameters of the SMC, finding a staggered surface brightness profile. We also traced the fainter outskirts by constructing a stellar density profile. This approach, based on stellar counts of the oldest main-sequence turn-off stars, uncovered a tidally disrupted stellar feature that reaches as far out as 12 deg from the SMC centre. We also serendipitously found a faint feature of unknown origin located at ∼14 deg from the centre of the SMC and that we tentatively associated with a more distant structure. We compared our results to in-house simulations of a 1 × 109 M⊙ SMC, finding that its elliptical shape can be explained by its tidal disruption under the combined presence of the MW and the Large Magellanic Cloud. Finally, we found that the older stellar populations show a smooth profile while the younger component presents a jump in the density followed by a flat profile, confirming the heavily disturbed nature of the SMC.
Abstract
Using 3D positions and kinematics of stars relative to the Sagittarius (Sgr) orbital plane and angular momentum, we identify 166 Sgr stream members observed by the Apache Point Observatory ...Galactic Evolution Experiment (APOGEE) that also have
Gaia
DR2 astrometry. This sample of 63/103 stars in the Sgr trailing/leading arm is combined with an APOGEE sample of 710 members of the Sgr dwarf spheroidal core (385 of them newly presented here) to establish differences of 0.6 dex in median metallicity and 0.1 dex in
α
/Fe between our Sgr core and dynamically older stream samples. Mild chemical gradients are found internally along each arm, but these steepen when anchored by core stars. With a model of Sgr tidal disruption providing estimated dynamical ages (i.e., stripping times) for each stream star, we find a mean metallicity gradient of 0.12 ± 0.03 dex Gyr
−1
for stars stripped from Sgr over time. For the first time, an
α
/Fe gradient is also measured within the stream, at 0.02 ± 0.01 dex Gyr
−1
using magnesium abundances and at 0.04 ± 0.01 dex Gyr
−1
using silicon, which imply that the Sgr progenitor had significant radial abundance gradients. We discuss the magnitude of those inferred gradients and their implication for the nature of the Sgr progenitor within the context of the current family of Milky Way satellite galaxies, and we suggest that more sophisticated Sgr models are needed to properly interpret the growing chemodynamical detail we have on the Sgr system.
We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using ∼2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To ...correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 deg2 area with ∼10′ resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map, yielding a best-fit inclination angle degrees with random errors of 0 19 and line-of-nodes position angle degrees with random errors of 0 49. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at ∼ 7° that departs from the defined LMC plane up to ∼4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5°-15° relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.
We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R ∼ 21°, or ∼18.5 kpc at the LMC distance of 50 kpc, as detected in the Survey of the ...Magellanic Stellar History (SMASH) performed with the Dark Energy Camera on the NOAO Blanco 4 m Telescope. The deep (g ∼ 24) SMASH color-magnitude diagrams (CMDs) clearly reveal old (∼9 Gyr), metal-poor (Fe/H −0.8 dex) main-sequence stars at a distance of ∼50 kpc. The surface brightness of these detections is extremely low with our most distant detection at g 34 mag arcsec−2. The SMASH radial density profile breaks from the inner LMC exponential decline at ∼13°-15° and a second component at larger radii has a shallower slope with power-law index = −2.2 that contributes ∼0.4% of the LMC's total stellar mass. In addition, the SMASH densities exhibit large scatter around our best-fit model of ∼70% indicating that the envelope of stellar material in the LMC periphery is highly disturbed. We also use data from the NOAO Source catalog to map the LMC main-sequence populations at intermediate radii and detect a steep dropoff in density on the eastern side of the LMC (at R 8°) as well as an extended structure to the far northeast. These combined results confirm the existence of a very extended, low-density envelope of stellar material with a disturbed shape around the LMC. The exact origin of this structure remains unclear, but the leading options include an accreted halo or tidally stripped outer disk material.
The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History ...(SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over ∼2400 square degrees at ∼20% filling factor) to ∼24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ∼15 mas and the accuracy is ∼2 mas with respect to the Gaia reference frame. The photometric precision is ∼0.5%-0.7% in griz and ∼1% in u with a calibration accuracy of ∼1.3% in all bands. The median 5 point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R ∼ 18.4 kpc. SMASH DR1 contains measurements of ∼100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.
Abstract
We present deep, wide-field Subaru Hyper Suprime-Cam photometry of two recently discovered satellites of the Milky Way (MW): Columba I (Col I) and Triangulum II (Tri II). The color–magnitude ...diagrams of both objects point to exclusively old and metal-poor stellar populations. We re-derive structural parameters and luminosities of these satellites, and find
for Col I and
for Tri II, with corresponding half-light radii of
pc and
pc. The properties of both systems are consistent with observed scaling relations for MW dwarf galaxies. Based on archival data, we derive upper limits on the neutral gas content of these dwarfs, and find that they lack H
i
, as do the majority of observed satellites within the MW virial radius. Neither satellite shows evidence of tidal stripping in the form of extensions or distortions in matched-filter stellar density maps or surface-density profiles. However, the smaller Tri II system is relatively metal-rich for its luminosity (compared to other MW satellites), possibly because it has been tidally stripped. Through a suite of orbit simulations, we show that Tri II is approaching pericenter of its eccentric orbit, a stage at which tidal debris is unlikely to be seen. In addition, we find that Tri II may be on its first infall into the MW, which helps explain its unique properties among MW dwarfs. Further evidence that Tri II is likely an ultra-faint dwarf comes from its stellar mass function, which is similar to those of other MW dwarfs.
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