The MACHO Project: Microlensing Optical Depth toward the Galactic Bulge from Difference Image Analysis

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Drake, A. J.; Freeman, K. C.; Geha, Marla; Griest, K.; Lehner, M. J.; Marshall, S.; Minniti, D.; Nelson, C A; Peterson, Bruce A.; Popowski, Piotr; Pratt, M. R.; Quinn, Peter J.; Stubbs, C. W.; Sutherland, William J.; Tomaney, A.; Vandehei, T.; Welch, D. L.

doi:10.1086/309484

Cited by 177 publications

(208 citation statements)

References 54 publications

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“…Many of the inner fields have been mapped by the microlensing experiments in optical passbands (Alcock et al 2000;Udalski et al 2002). However, such a split clump has never been reported, which seems to contradict our findings.…”

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confidence: 99%

Milky Way demographics with the VVV survey

Minniti

Saito

Gonzalez

et al. 2014

A&A

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The new generation of IR surveys are revealing and quantifying Galactic features that provide an improved 3D interpretation of our own Galaxy. We present an analysis of the global distribution of dust clouds in the bulge using the near-IR photometry of 157 million stars from the VVV survey. We investigate the color−magnitude diagram of the Milky Way bulge, which shows a red giant clump of core He burning stars that is split into two color components, with a mean color difference of (Z − K s ) = 0.55 mag that is equivalent to A V = 2.0 mag. We conclude that there is an optically thick dust lane at intermediate latitudes above and below the plane that stretches across several square degrees from l = −10• to l = +10• . We call this feature the great dark lane. Although its exact distance is uncertain, it is located in front of the bulge. The evidence for a large-scale great dark lane within the Galactic bulge is important for constraining models of the barred Milky Way bulge and for comparing our galaxy with external barred galaxies in which these types of features are prominent. We discuss two other potential implications of the great dark lane for microlensing and bulge stellar populations studies.

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confidence: 99%

Milky Way demographics with the VVV survey

Minniti

Saito

Gonzalez

et al. 2014

A&A

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“…More than ∼350 microlensing events detected towards the Galactic Centre have been published to date by several collaborations: MACHO (Alcock et al 1997b;Alcock et al 1999b;Alcock et al 2000, hereafter A00), OGLE Udalski et al 2000) and DUO (Alard & Guibert 1997). The resulting optical depth is > ∼ 3 10 −6 in Baade's window, a value that is higher than the theoretical expectation.…”

Section: Introductionmentioning

confidence: 99%

The Sagittarius dwarf galaxy as a microlensing target

Cseresnjes¹,

Alard²

2001

A&A

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Abstract. We estimate the optical depth, time-scale distribution and fraction of microlensing events originating from sources in the Sagittarius dwarf galaxy (Sgr) lensed by deflectors in the Milky Way. These events have a time-scale longer by a factor ∼1.3 than the MW/MW events and occur mainly on sources fainter than V ∼ 21 mag below Sgr's turn off. The fraction of events involving a source in Sgr depends on the location and extinction of the field and on the limiting magnitude of the survey. The contribution of the MW/Sgr events is negligible ( < ∼ 1%) at very low latitudes (|b| < ∼ 2 • ) but increases continuously towards higher |b| and becomes dominant near the highest density region of the dwarf galaxy. Sgr is present within the fields of current microlensing surveys and any optical depth map inferred from observations will become biased by the presence of Sgr towards higher |b| where the contribution of MW/Sgr events is significant. Systematic spectroscopic measurements on the sources of all the microlensing events may allow detection of this kind of event for which the degeneracy on the lens mass can be significantly reduced.

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“…Extensive photometric surveys, triggered by Paczyński's suggestion (1986), have led to the observation of microlensing effects toward the Magellanic clouds (EROS, Aubourg et al 1993;MACHO, Alcock et al 1993) and the Galactic bulge (OGLE, Udalski et al 1994;Udalski et al 2000;MACHO, Alcock et al 1995;Alcock et al 1997;Alcock et al 2000) 1 . The few hundred events observed toward the Galactic centre have strengthened the hypothesis of a barred structure.…”

Section: Introductionmentioning

confidence: 99%

Observation of microlensing toward the galactic spiral arms. EROS II 3 year survey

Derue

Afonso

Alard

et al. 2001

A&A

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Abstract.We present an analysis of the light curves of 9.1 million stars observed during three seasons by EROS (Expérience de Recherche d'Objets Sombres), in the Galactic plane away from the bulge. Seven stars exhibit luminosity variations compatible with gravitational microlensing effects due to unseen objects. The corresponding optical depth, averaged over four directions, isτ = 0.43 ± 0.2 × 10 −6 . While this value is compatible with expectations from simple Galactic models under reasonable assumptions on the target star distances, we find an excess of events with short timescales toward the direction closest to the Galactic centre. We discuss a possible interpretation involving the contribution of an elongated bar.

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The MACHO Project: Microlensing Optical Depth toward the Galactic Bulge from Difference Image Analysis

Cited by 177 publications

References 54 publications

Milky Way demographics with the VVV survey

Milky Way demographics with the VVV survey

The Sagittarius dwarf galaxy as a microlensing target

Observation of microlensing toward the galactic spiral arms. EROS II 3 year survey

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