Large Magellanic Cloud Halo Research Articles

Discerning Parallax Amplitude in Astrometric Microlensing

Gravitational microlensing is a powerful method for discovering isolated stellar-mass black holes (ISMBHs). These objects make long-duration microlensing events. To characterize these lensing objects by fully resolving the microlensing degeneracy, measurements of parallax and astrometric deflections are necessary. Microlensing events due to ISMBHs have considerable astrometric deflections but small parallax amplitudes, , where M l is the lens mass. We numerically investigate the possibility of inferring parallax amplitude from astrometric deflection in microlensing events due to ISMBHs. The parallax amplitude in astrometric deflections is proportional to the relative parallax π rel, which means that it (i) does not strongly depend on M l and (ii) increases in microlensing observations toward the Magellanic Clouds. We assume that these events will be potentially detected in upcoming microlensing surveys such as (1) the Roman observations of the Galactic bulge (GB) and (2) the LSST observations of the Large Magellanic Cloud (LMC) and that the Extremely Large Telescope (ELT) will follow up on them with one data point every 10 days. We evaluate the probability of inferring parallax amplitude from these observations by calculating the Fisher and covariance matrices. For the GB, the efficiencies for discerning parallax amplitudes with a relative error of <4% through astrometric and photometric observations are 3.8% and 29.1%, respectively. For observations toward the LMC, these efficiencies are 41.1% and 23.0%, respectively. Measuring parallax amplitude through astrometric deflections is plausible in GB events with a lens distance of ≲2.7 kpc and in LMC halo lensing. By monitoring long-duration microlensing events, the ELT can detect astrometric deflections and their parallax-induced deviations.

How do the dynamics of the Milky Way–Large Magellanic Cloud system affect gamma-ray constraints on particle dark matter?

ABSTRACT Previous studies on astrophysical dark matter (DM) constraints have all assumed that the Milky Way’s (MW) DM halo can be modelled in isolation. However, recent work suggests that the MW’s largest dwarf satellite, the Large Magellanic Cloud (LMC), has a mass of 10–20${{\ \rm per\ cent}}$ that of the MW and is currently merging with our Galaxy. As a result, the DM haloes of the MW and LMC are expected to be strongly deformed. We here address and quantify the impact of the dynamical response caused by the passage of the LMC through the MW on the prospects for indirect DM searches. Utilizing a set of state-of-the-art numerical simulations of the evolution of the MW–LMC system, we derive the DM distribution in both galaxies at the present time based on the basis function expansion formalism. Consequently, we build $\mathcal {J}$-factor all-sky maps of the MW–LMC system to study the impact of the LMC passage on gamma-ray indirect searches for thermally produced DM annihilating in the outer MW halo as well as within the LMC halo stand-alone. We conduct a detailed analysis of 12 yr of the Fermi Large Area Telescope data that incorporates various large-scale gamma-ray emission components and we quantify the systematic uncertainty associated with the imperfect knowledge of the astrophysical gamma-ray sources. We find that the dynamical response caused by the LMC passage can alter the constraints on the velocity-averaged annihilation cross-section for weak-scale particle DM at a level comparable to the existing observational uncertainty of the MW halo’s density profile and total mass.

Cosmic-Ray-driven Outflows from the Large Magellanic Cloud: Contributions to the LMC Filament

Abstract In this paper, we build from previous work and present simulations of recent (within the past Gyr), magnetized, cosmic-ray driven outflows from the Large Magellanic Cloud (LMC), including our first attempts to explicitly use the derived star formation history of the LMC to seed outflow generation. We run a parameter set of simulations for different LMC gas masses and cosmic-ray transport treatments, and we make preliminary comparisons to published outflow flux estimates, neutral and ionized hydrogen observations, and Faraday rotation measure maps. We additionally report on the gas mass that becomes unbound from the LMC disk and swept by ram pressure into the Trailing Magellanic Stream. We find that, even for our largest outburst, the mass contribution to the Stream is still quite small, as much of the outflow-turned-halo gas is shielded on the LMCs far-side due to the LMCs primarily face-on infall through the Milky Way halo over the past Gyr. On the LMC’s near-side, past outflows have fought an uphill battle against ram pressure, with the near-side halo mass being at least a factor of a few smaller than that of the far-side. Absorption-line studies probing only the LMC foreground, then, may be severely underestimating the total mass of the LMC halo formed by outflows.

Stellar streams around the Magellanic Clouds in 4D

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.

Evolution of LMC/M33-mass dwarf galaxies in the eagle simulation

We investigate the population of dwarf galaxies with stellar masses similar to the Large Magellanic Cloud (LMC) and M33 in the EAGLE galaxy formation simulation. In the field, galaxies reside in haloes with stellar-to-halo mass ratios of $1.03^{+0.50}_{-0.31}\times10^{-2}$ (68% confidence level); systems like the LMC, which have an SMC-mass satellite, reside in haloes about 1.3 times more massive, which suggests an LMC halo mass at infall, $M_{200}=3.4^{+1.8}_{-1.2}\times10^{11}M_\odot$ (68% confidence level). The colour distribution of dwarfs is bimodal, with the red galaxies ($g-r>0.6$) being mostly satellites. The fraction of red LMC-mass dwarfs is 15% for centrals, and for satellites this fraction increases rapidly with host mass: from 10% for satellites of Milky Way (MW)-mass haloes to nearly 90% for satellites of groups and clusters. The quenching timescale, defined as the time after infall when half of the satellites have acquired red colours, decreases with host mass from ${>}5$ Gyrs for MW-mass hosts to $2.5$ Gyrs for cluster mass hosts. The satellites of MW-mass haloes have higher star formation rates and bluer colours than field galaxies. This is due to enhanced star formation triggered by gas compression shortly after accretion. Both the LMC and M33 have enhanced recent star formation that could be a manifestation of this process. After infall into their MW-mass hosts, the $g-r$ colours of LMC-mass dwarfs become bluer for the first 2 Gyrs, after which they rapidly redden. LMC-mass dwarfs fell into their MW-mass hosts only relatively recently, with more than half having an infall time of less than 3.5 Gyrs.

The Catalina Surveys Southern periodic variable star catalogue

U.S. National Science Foundation [AST-1313422, AST-1413600]; National Aeronautics and Space Administration [NNG05GF22G]; CONICYT's PCI program [DPI20140066]; Ministry for the Economy, Development, and Tourism's Iniciativa Cientifica Milenio [IC 120009]; Proyecto Fondecyt [1141141]; Proyecto Basal [PFB-06/2007]; National Aeronautics and Space Administration; National Science Foundation [1138766]

DISCOVERY AND ANALYSIS OF 21 μm FEATURE SOURCES IN THE MAGELLANIC CLOUDS

Spitzer Space Telescope mid-infrared spectroscopy has been obtained for 15 carbon-rich protoplanetary nebulae (PPNe) in the Large Magellanic Cloud (LMC) and for two other such stars in the Small Magellanic Cloud (SMC). Of these 17 PPNe, the unidentified 21 μm feature is strong in 7 spectra, weak in 2 spectra, and very weak or questionable in 4 spectra. Two of the four spectra without the 21 μm feature have a very strong feature near 11 μm, similar to a feature observed in some carbon-rich planetary nebulae (PNe) in the LMC. We attribute this feature to unusual SiC dust, although the feature-to-continuum ratio is much larger than for SiC features in Galactic or Magellanic Cloud carbon star spectra. The remaining two objects show typical carbon-rich PPNe spectra with no 21 μm features. One of the LMC objects that lacks the 21 μm feature and one SMC object with a questionable 21 μm detection may have mixed dust chemistries based upon their spectral similarity to Galactic [WC] PNe. The 13 objects that either definitely or may show the 21 μm feature have distinct dust shell properties compared to the Galactic 21 μm objects—the 21 μm features are weaker, the estimated dust temperatures are significantly higher, the unidentified infrared (UIR) bands are stronger, and the UIRs show more structure. Four of the 21 μm objects appear to show normal SiC emission features in their spectra. Many of the PPNe show strong 30 μm features, although this feature carries less of the total mid-infrared emission than is normally the case for the Galactic 21 μm PPNe. The LMC objects are in the LMC halo rather than in the LMC bar. The estimated luminosities of these PPNe vary from 4700 to 12,500 L� .

Large Magellanic Cloud self-lensing for OGLE-II microlensing observations

In the framework of microlensing searches towards the Large Magellanic Cloud (LMC), we discuss the results presented by the OGLE collaboration for their OGLE-II campaign \citep{lukas09}. We evaluate the optical depth, the duration and the expected rate of events for the different possible lens populations: both luminous, dominated by the LMC self lensing, and "dark", the would be compact halo objects (MACHOs) belonging to either the Galactic or to the LMC halo. The OGLE-II observational results, 2 microlensing candidate events located in the LMC bar region with duration of 24.2 and 57.2 days, compare well with the expected signal from the luminous lens populations: $n_\mathrm{exp}=1.5$, with typical duration, for LMC self lensing, of about 50 days. Because of the small statistics at disposal, however, the conclusions that can be drawn as for the halo mass fraction, $f$, in form of compact halo objects are not too severe. By means of a likelihood analysis we find an \emph{upper} limit for $f$, at 95% confidence level, of about 15% in the mass range $(10^{-2}-10^{-1}) \mathrm{M}_\odot$ and 26% for $0.5 \mathrm{M}_\odot$.

Highly ionized plasma in the Large Magellanic Cloud: evidence for outflows and a possible galactic wind

Based on an analysis of the interstellar highly ionised species C IV, Si IV, N V, and O VI observed in the FUSE and HST/STIS E140M spectra of four hot stars in the Large Magellanic Cloud (LMC), we find evidence for a hot LMC halo fed by energetic outflows from the LMC disk and even possibly an LMC galactic wind. Signatures for such outflows are the intermediate and high-velocity components (v_LSR>100 km/s) relative to the LMC disk observed in the high- and low-ion absorption profiles. The stellar environments produce strong, narrow (T<20,000 K) components of C IV and Si IV associated with the LMC disk; in particular they are likely signatures of H II regions and expanding shells. Broad components are observed in the profiles of C IV, Si IV, and O VI with their widths implying hot, collisionally ionised gas at temperatures of a few times 100,000 K. There is a striking similarity in the O VI/C IV ratios for the broad LMC and high-velocity components, suggesting much of the material at v_LSR>100 km/s is associated with the LMC. The velocity of the high-velocity component is large enough to escape altogether the LMC, polluting the intergalactic space between the LMC and the Milky Way. The observed high-ion ratios of the broad LMC and high-velocity components are consistent with those produced in conductive interfaces; such models are also favored by the apparent kinematically coupling between the high and the weakly ionised species.

LMC self-lensing from a new perspective

We present a new analysis on the issue of the location of the observed microlensing events in direction of the Large Magellanic Cloud (LMC). This is carried out starting from a recently drawn coherent picture of the geometrical structure and dynamics of the LMC disk and by considering different configurations for the LMC bar. In this framework it clearly emerges that the spatial distribution of the events observed so far shows a near--far asymmetry. This turns out to be compatible with the optical depth calculated for the LMC halo objects. In this perspective, our main conclusion, supported by a statistical analysis on the outcome of an evaluation of the microlensing rate, is that self lensing can not account for all the observed events. Finally we propose a general inequality to calculate quickly an upper limit to the optical depth along a line of view through the LMC center.

The Stellar Halo in the Large Magellanic Cloud: Mass, Luminosity, and Microlensing Predictions

Recently obtained kinematic data has shown that the Large Magellanic Cloud (LMC) possesses an old stellar halo. In order to further characterize the properties of this halo, parametric King models are fit to the surface density of RR Lyrae stars. Using data from both the MACHO and OGLE II microlensing surveys, the model fits yield the center of their distribution at RA = 05:21.1+-0.8, Dec = -69:45+-6 (J2000) and a core radius of 1.42+-0.12 kpc. As a check the halo model is compared with RR Lyrae star counts in fields near the LMC's periphery previously surveyed with photographic plates. These data, however, require a cautious interpretation. Several topics regarding the LMC stellar halo are discussed. First, the properties of the halo imply a global mass-to-light ratio of M/L_V = 5.3+-2.1 and a total mass of 1.6+-0.6 10^10 M_sun for the LMC in good agreement with estimates based on the rotation curve. Second, although the LMC's disk and halo are kinematically distinct, the shape of the surface density profile of the halo is remarkably similar to that of the young disk. For example, the best-fit exponential scale length for the RR Lyrae stars is 1.47+-0.08 kpc, which compares to 1.46 kpc for the LMC's blue light. In the Galaxy, the halo and disk do not resemble each other like this. Finally, a local maximum in the LMC's microlensing optical depth due to halo-on-disk stellar self-lensing is predicted. For the parameters of the stellar halo obtained, this maximum is located near MACHO events LMC-4 and LMC-23, and is large enough to possibly account for these two events, but not for all of the observed microlensing.

The MACHO Project: Microlensing Results from 5.7 Years of Large Magellanic Cloud Observations

We report on our search for microlensing toward the Large Magellanic Cloud (LMC). Analysis of 5.7 yr of photometry on 11.9 million stars in the LMC reveals 13-17 microlensing events. A detailed treatment of our detection efficiency shows that this is significantly more than the ~2-4 events expected from lensing by known stellar populations. The timescales () of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < < 400 days to be τ = 1.2 × 10-7, with an additional 20% to 30% of systematic error. The spatial distribution of events is mildly inconsistent with LMC/LMC disk self-lensing, but is consistent with an extended lens distribution such as a Milky Way or LMC halo. Interpreted in the context of a Galactic dark matter halo, consisting partially of compact objects, a maximum-likelihood analysis gives a MACHO halo fraction of 20% for a typical halo model with a 95% confidence interval of 8%-50%. A 100% MACHO halo is ruled out at the 95% confidence level for all except our most extreme halo model. Interpreted as a Galactic halo population, the most likely MACHO mass is between 0.15 and 0.9 M☉, depending on the halo model, and the total mass in MACHOs out to 50 kpc is found to be 9 × 1010 M☉, independent of the halo model. These results are marginally consistent with our previous results, but are lower by about a factor of 2. This is mostly due to Poisson noise, because with 3.4 times more exposure and increased sensitivity to long-timescale events, we did not find the expected factor of ~4 more events. In addition to a larger data set, this work also includes an improved efficiency determination, improved likelihood analysis, and more thorough testing of systematic errors, especially with respect to the treatment of potential backgrounds to microlensing. We note that an important source of background are supernovae (SNe) in galaxies behind the LMC.

RX J050736−6847.8: A Large Supernova Remnant around an X-Ray Binary in the Large Magellanic Cloud

RX J050736-6847.8 in the Large Magellanic Cloud (LMC) is an intriguing X-ray source consisting of a large ring (diameter ~ 150 pc) of diffuse emission and a central compact source. It is projected in the vicinity of the superbubble N103 around the star cluster NGC 1850. RX J050736-6847.8's ring of diffuse X-ray emission, offset from the superbubble N103, is not bounded by any optical shell structure, while RX J050736-6847.8's central compact X-ray source is projected within the cluster HS122. We have analyzed archival ROSAT observations of RX J050736-6847.8 to determine the physical properties of its X-ray–emitting gas. The X-ray luminosity of the diffuse X-ray emission is 5–6 × 1035 ergs s-1 in the 0.1–2.4 keV band, within the range for supernova remnants (SNRs). Assuming a shell geometry with a fractional shell thickness (ΔR/R) of 0.05–0.2, we find the density of the hot gas to be 0.05–0.09 cm-3 and a hot gas mass of ~820 M⊙. The physical properties of this shell of hot gas are consistent with Sedov's solution for a ~5 × 104 yr old SNR in a low-density (~0.015 cm-3) medium formed by a supernova of an explosion energy of 3 × 1051 ergs. The density is so low that no detectable optical emission is expected. Therefore, we suggest that this ring of X-ray emission originates in a SNR, the largest known in the LMC. The large size, low density, and the regular X-ray morphology suggest that this SNR is located in the halo of the LMC; the small absorption column density further suggests that this SNR is on the near side of the LMC halo. The central compact source of RX J050736-6847.8 is probably an X-ray binary in the cluster HS122. The relationship between the compact source and the diffuse ring is unknown.

On the prospect of inferring the halo structure and the masses of dark objects through parallax microlensing

We study the proposed use of parallax microlensing in the direction of the Large Magellanic Cloud (LMC) to separate the effects of the mass function of dark massive halo objects (MHOs or ‘machos’) on the one hand, and their spatial distribution and kinematics on the other. This disentanglement is supposed to allow a much better determination of the two than could be achieved entirely on the basis of the durations of events. We restrict our treatment to the same class of power-law spherical models for the halo of MHOs studied in a previous paper by Markovic 38 Sommer-Larsen, and assume that one can eliminate microlensing events caused by massive objects outside the halo (e.g., the LMC halo). Whereas the duration-based error in the average MHO mass, μ¯ ≡ M¯/M, exceeds (at N = 100 events) μ¯ by a factor of 2 or more, parallax microlensing remarkably brings it down to 15–20 per cent of μ¯, regardless of the shape of the mass function. In addition, the slope α of the mass function, dn/dμ ∝ μα, can be inferred relatively accurately (σα < 0.4) for a broader range, −3 < α < 0. The improvement in the inference of the halo structure is also significant: the index γ of the density profile ( ρ ∼ R−γ) can be obtained with the error σγ < 0.4. While in a typical situation the errors for the parameters specifying the velocity dispersion profile are of about the same magnitude as the parameters themselves, virtually all the uncertainty is ‘concentrated’ in linear combinations of the parameters that may have little influence on the profile, thus allowing its reasonably accurate inference.

Gravitational microlensing by the MACHOs of the Large Magellanic Cloud

view Abstract Citations (92) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gravitational Microlensing by the MACHOs of the Large Magellanic Cloud Wu, Xiang-Ping Abstract The expected microlensing events of the Large Magellanic Cloud (LMC) by the MACHOs of the LMC itself are calculated and compared with analog events by objects in the Galactic halo. The LMC matter distribution is modeled by a spherical halo and an exponential disk, while a face-on exponential disk is used for the stellar distribution of the LMC. Among the microlensing events discovered by the MACHO and EROS projects, a fraction of 22% could be caused by the lenses near the center of the LMC or 13% from lenses at 5^deg^ from the LMC center, provided that the halo of the Galaxy and of the LMC are composed of MACHOs. The LMC disk produces a relatively lower optical depth to microlensing of ~3 x 10^-8^ but contributes a fraction of ~40% of the observed microlensing events toward the LMC center, if the actual detection rate is taken to be (7-9) x 10^-8^. It is then likely that the presently detected microlensing events near the center of the LMC are due to some combination of the MACHOs of the Galactic halo, the Galactic spheroid, the LMC halo, and particularly the LMC disk. Therefore, any statistical study of these microlensing events must take the LMC lenses into account. Publication: The Astrophysical Journal Pub Date: November 1994 DOI: 10.1086/174794 arXiv: arXiv:astro-ph/9312059 Bibcode: 1994ApJ...435...66W Keywords: Astronomical Models; Galactic Halos; Gravitational Lenses; Magellanic Clouds; Mathematical Models; Optical Thickness; Star Distribution; Astronomy; COSMOLOGY: GRAVITATIONAL LENSING; GALAXIES: MAGELLANIC CLOUDS; Astrophysics E-Print: 12 pages, 6 figures (not included) by fax, ApJ submitted, DAEC-OPM-93 full text sources arXiv | ADS | data products SIMBAD (4) NED (1)

Probing the Large Magellanic Cloud halo for MACHOs

view Abstract Citations (32) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Probing the Large Magellanic Cloud Halo for MACHOS Gould, Andrew Abstract If galactic halos are composed of massive compact halo objects (MACHOs) in the mass range M <~ 0.01 M_sun_, then ongoing gravitational lensing experiments could be capable of detecting them in the Large Magellanic Cloud (LMC). The signature of LMC (as opposed to Galactic) MACHOs is a variation of the Optical depth to lensing as a function of sky position. Assuming that the LMC halo is spherical, the optical depth along lines of sight toward the far side of the LMC disk should be ~20% higher than those toward the near side because the former pass through more of the halo. If the LMC halo is oblate, the effect is diminished as the square of the halo flatness ratio. The amplitude of the spatial variation in the lensing rate can therefore provide information about the flattening of the LMC halo. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172298 Bibcode: 1993ApJ...404..451G Keywords: Galactic Halos; Gravitational Lenses; Magellanic Clouds; Dark Matter; Optical Thickness; Astrophysics; COSMOLOGY: GRAVITATIONAL LENSING; COSMOLOGY: DARK MATTER; GALAXIES: MAGELLANIC CLOUDS full text sources ADS | data products SIMBAD (3) NED (1)