The origin of the microlensing events observed towards the LMC and the stellar counterpart of the Magellanic stream

Gurtina Besla, Lars Hernquist, Abraham Loeb

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

We introduce a novel theoretical model to explain the longstanding puzzle of the nature of the microlensing events reported towards the Large Magellanic Cloud (LMC) by the massive compact halo object (MACHO) and Optical Gravitational Lensing Experiment (OGLE) collaborations. We propose that a population of tidally stripped stars from the Small Magellanic Cloud (SMC) located ~4-10 kpc behind a lensing population of LMC disc stars can naturally explain the observed event durations (17-71 d), event frequencies and spatial distribution of the reported events. Differences in the event frequencies reported by the OGLE (~0.33 yr-1) and MACHO (~1.75 yr-1) surveys appear to be naturally accounted for by their different detection efficiencies and sensitivity to faint sources. The presented models of the Magellanic System were constructed without prior consideration of the microlensing implications. These results favour a scenario for the interaction history of the Magellanic Clouds, wherein the Clouds are on their first infall towards the Milky Way and the SMC has recently collided with the LMC 100-300 Myr ago, leading to a large number of faint sources distributed nonuniformly behind the LMC disc. In contrast to self-lensing models, microlensing events are also expected to occur in fields off the LMC's stellar bar since the stellar debris is not expected to be concentrated in the bar region. This scenario leads to a number of observational tests: the sources are low-metallicity SMC stars; they exhibit high velocities relative to LMC disc stars that may be detectable via proper motion studies and, most notably, there should exist a stellar counterpart to the gaseous Magellanic Stream and Bridge with a V-band surface brightness of >34 mag arcsec-2. In particular, the stellar Bridge should contain enough RR Lyrae stars to be detected by the ongoing OGLE survey of this region.

Original languageEnglish (US)
Pages (from-to)2342-2365
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Volume428
Issue number3
DOIs
StatePublished - Jan 2013
Externally publishedYes

Fingerprint

Magellanic clouds
experiment
stars
massive compact halo objects
spatial distribution
history
frequency distribution
proper motion
extremely high frequencies
debris
metallicity
brightness
histories
sensitivity

Keywords

  • Dark matter
  • Galaxies: interactions
  • Galaxies: irregular
  • Galaxy: halo
  • Gravitational lensing: micro
  • Magellanic clouds

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The origin of the microlensing events observed towards the LMC and the stellar counterpart of the Magellanic stream. / Besla, Gurtina; Hernquist, Lars; Loeb, Abraham.

In: Monthly Notices of the Royal Astronomical Society, Vol. 428, No. 3, 01.2013, p. 2342-2365.

Research output: Contribution to journalArticle

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abstract = "We introduce a novel theoretical model to explain the longstanding puzzle of the nature of the microlensing events reported towards the Large Magellanic Cloud (LMC) by the massive compact halo object (MACHO) and Optical Gravitational Lensing Experiment (OGLE) collaborations. We propose that a population of tidally stripped stars from the Small Magellanic Cloud (SMC) located ~4-10 kpc behind a lensing population of LMC disc stars can naturally explain the observed event durations (17-71 d), event frequencies and spatial distribution of the reported events. Differences in the event frequencies reported by the OGLE (~0.33 yr-1) and MACHO (~1.75 yr-1) surveys appear to be naturally accounted for by their different detection efficiencies and sensitivity to faint sources. The presented models of the Magellanic System were constructed without prior consideration of the microlensing implications. These results favour a scenario for the interaction history of the Magellanic Clouds, wherein the Clouds are on their first infall towards the Milky Way and the SMC has recently collided with the LMC 100-300 Myr ago, leading to a large number of faint sources distributed nonuniformly behind the LMC disc. In contrast to self-lensing models, microlensing events are also expected to occur in fields off the LMC's stellar bar since the stellar debris is not expected to be concentrated in the bar region. This scenario leads to a number of observational tests: the sources are low-metallicity SMC stars; they exhibit high velocities relative to LMC disc stars that may be detectable via proper motion studies and, most notably, there should exist a stellar counterpart to the gaseous Magellanic Stream and Bridge with a V-band surface brightness of >34 mag arcsec-2. In particular, the stellar Bridge should contain enough RR Lyrae stars to be detected by the ongoing OGLE survey of this region.",
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AB - We introduce a novel theoretical model to explain the longstanding puzzle of the nature of the microlensing events reported towards the Large Magellanic Cloud (LMC) by the massive compact halo object (MACHO) and Optical Gravitational Lensing Experiment (OGLE) collaborations. We propose that a population of tidally stripped stars from the Small Magellanic Cloud (SMC) located ~4-10 kpc behind a lensing population of LMC disc stars can naturally explain the observed event durations (17-71 d), event frequencies and spatial distribution of the reported events. Differences in the event frequencies reported by the OGLE (~0.33 yr-1) and MACHO (~1.75 yr-1) surveys appear to be naturally accounted for by their different detection efficiencies and sensitivity to faint sources. The presented models of the Magellanic System were constructed without prior consideration of the microlensing implications. These results favour a scenario for the interaction history of the Magellanic Clouds, wherein the Clouds are on their first infall towards the Milky Way and the SMC has recently collided with the LMC 100-300 Myr ago, leading to a large number of faint sources distributed nonuniformly behind the LMC disc. In contrast to self-lensing models, microlensing events are also expected to occur in fields off the LMC's stellar bar since the stellar debris is not expected to be concentrated in the bar region. This scenario leads to a number of observational tests: the sources are low-metallicity SMC stars; they exhibit high velocities relative to LMC disc stars that may be detectable via proper motion studies and, most notably, there should exist a stellar counterpart to the gaseous Magellanic Stream and Bridge with a V-band surface brightness of >34 mag arcsec-2. In particular, the stellar Bridge should contain enough RR Lyrae stars to be detected by the ongoing OGLE survey of this region.

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