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Register a new userMeasuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by ${S}^5$
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Stellar streams are excellent probes of the underlying gravitational potential in which they evolve. In this work, we fit dynamical models to five streams in the Southern Galactic hemisphere, combining observations from the Southern Stellar Stream Spectroscopic Survey (${S}^5$), Gaia EDR3, and the Dark Energy Survey (DES), to measure the mass of the Large Magellanic Cloud (LMC). With an ensemble of streams, we find a mass of the LMC ranging from 14 to $19 times 10^{10} mathrm{M}_{odot}$, probed over a range of closest approach times and distances. With the most constraining stream (Orphan-Chenab), we measure an LMC mass of $18.8^{+ 3.5}_{- 4.0} times 10^{10} mathrm{M}_{odot}$, probed at a closest approach time of 310 Myr and a closest approach distance of 25.4 kpc. This mass is compatible with previous measurements, showing that a consistent picture is emerging of the LMCs influence on structures in the Milky Way. Using this sample of streams, we find that the LMCs effect depends on the relative orientation of the stream and LMC at their point of closest approach. To better understand this, we present a simple model based on the impulse approximation and we show that the LMCs effect depends both on the magnitude of the velocity kick imparted to the stream and the direction of this kick.
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The Large Magellanic Cloud (LMC) is the closest and most studied example of an irregular galaxy. Among its principal defining morphological features, its off-centred bar and single spiral arm stand out, defining a whole family of galaxies known as the Magellanic spirals (Sm). These structures are thought to be triggered by tidal interactions and possibly maintained via gas accretion. However, it is still unknown whether they are long-lived stable structures. In this work, by combining photometry that reaches down to the oldest main sequence turn-off in the colour-magnitude diagrams (CMD, up to a distance of $sim$4.4 kpc from the LMC centre) from the SMASH survey and CMD fitting techniques, we find compelling evidence supporting the long-term stability of the LMC spiral arm, dating the origin of this structure to more than 2~Gyr ago. The evidence suggests that the close encounter between the LMC and the Small Magellanic Cloud (SMC) that produced the gaseous Magellanic Stream and its Leading Arm (LA) also triggered the formation of the LMCs spiral arm. Given the mass difference between the Clouds and the notable consequences of this interaction, we can speculate that this should have been one of their closest encounters. These results set important constraints on the timing of LMC-SMC collisions, as well as on the physics behind star formation induced by tidal encounters.
We carried out a spectroscopic follow-up program of the four new stellar stream candidates detected by Belokurov & Koposov (2016) in the outskirts of the Large Magellanic Cloud (LMC) using FORS2 (VLT). The medium-resolution spectra were used to measure the line-of-sight velocities, estimate stellar metallicities and to classify stars into Blue Horizontal Branch (BHB) and Blue Straggler (BS) stars. Using the 4-D phase-space information, we attribute approximately one half of our sample to the Magellanic Clouds, while the rest is part of the Galactic foreground. Only two of the four stream candidates are confirmed kinematically. While it is impossible to estimate the exact levels of MW contamination, the phase-space distribution of the entire sample of our Magellanic stars matches the expected velocity gradient for the LMC halo and extends as far as 33 deg (angular separation) or 29 kpc from the LMC center. Our detections reinforce the idea that the halo of the LMC seems to be larger than previously expected, and its debris can be spread in the sky out to very large separations from the LMC center. Finally, we provide some kinematic evidence that many of the stars analysed here have likely come from the Small Magellanic Cloud.
This paper explores the effect of the LMC on the mass estimates obtained from the timing argument. We show that accounting for the presence of the LMC systematically lowers the Local Group mass ($M_{rm LG}$) derived from the relative motion of the Milky Way--Andromeda pair. Motivated by this result we apply a Bayesian technique devised by Pe~narrubia et al. (2014) to simultaneously fit (i) distances and velocities of galaxies within 3~Mpc and (ii) the relative motion between the Milky Way and Andromeda derived from HST observations, with the LMC mass ($M_{rm LMC}$) as a free parameter. Our analysis returns a Local Group mass $M_{rm LG}=2.64^{+0.42}_{-0.38}times 10^{12}M_odot$ at a 68% confidence level. The masses of the Milky Way, $M_{rm MW}=1.04_{-0.23}^{+0.26}times 10^{12}M_odot$, and Andromeda, $M_{rm M31}=1.33_{-0.33}^{+0.39}times 10^{12}M_odot$, are consistent with previous estimates that neglect the impact of the LMC on the observed Hubble flow. We find a (total) LMC mass $M_{rm LMC}=0.25_{-0.08}^{+0.09}times 10^{12}M_odot$, which is indicative of an extended dark matter halo and supports the scenario where this galaxy is just past its first pericentric approach. Consequently, these results suggest that the LMC may induce significant perturbations on the Galactic potential.
(Abridged) Photometry of archival Spitzer observations of the Large Magellanic Cloud (LMC) are used to search for young stellar objects (YSOs). Simple mid-infrared selection criteria were used to exclude most normal and evolved stars and background galaxies. We identify a sample of 2,910 sources in the LMC that could potentially be YSOs. We then simultaneously considered images and photometry from the optical through mid-IR wavelengths to assess the source morphology, spectral energy distribution (SED), and the surrounding interstellar environment to determine the most likely nature of each source. From this examination of the initial sample, we suggest 1,172 sources are most likely YSOs and 1,075 probable background galaxies, consistent with expectations based on SWIRE survey data. Spitzer IRS observations of 269 of the brightest YSOs from our sample have confirmed that ~>95% are indeed YSOs. A comprehensive search for YSOs in the LMC has also been carried out by the SAGE team. There are three major differences between these two searches. (1) In the common region of color-magnitude space, ~850 of our 1,172 probable YSOs are missed in the SAGE YSO catalog because their conservative point source identification criteria have excluded YSOs superposed on complex diffuse emission. (2) About 20-30% of the YSOs identified by the SAGE team are sources we classify as background galaxies. (3) the SAGE YSO catalog identifies YSO in parts of color-magnitude space that we excluded and thus contains more evolved or fainter YSOs missed by our analysis. Finally, the mid-IR luminosity functions of our most likely YSO candidates in the LMC can be well described by N(L) propto L^-1, which is consistent with the Salpeter initial mass function if a mass-luminosity relation of L propto M^2.4 is adopted.
We report the results of a sensitive search for 12.2 GHz methanol maser emission towards a sample of eight high-mass star formation regions in the Large Magellanic Clouds which have been detected in other maser transitions. We detected one source towards the star formation region N105a. This is the first detection of a 12.2 GHz methanol maser outside our Galaxy. We also made near-contemporaneous observations of the 6.7 GHz methanol and 22 GHz water masers towards these sources, resulting in the detection of water maser emission in six new sources, including one associated with the strongest 6.7 GHz maser in the Magellanic Clouds IRAS 05011-6815. The majority of the maser sources are closely associated with objects identified as likely Young Stellar Objects (YSO) on the basis of Spitzer Space Telescope observations. We find that the YSOs associated with masers tend to be more luminous and have redder infrared colours than the sample as a whole. SED modeling of the YSOs shows that the masers are associated with sources of higher central mass, total luminosity and ambient density than the majority of YSOs in the LMC. This is consistent with the well-established relationship between luminous methanol and water masers and young, high-mass objects observed in the Galaxy.
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