The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations

C. Alcock, R. A. Allsman, D. R. Alves, T. S. Axelrod, A. C. Becker, D. P. Bennett, K. H. Cook, N. Dalal, A. J. Drake, K. C. Freeman, M. Geha, K. Griest, M. J. Lehner, S. L. Marshall, D. Minniti, C. A. Nelson, B. A. Peterson, P. Popowski, M. R. Pratt, P. J. QuinnC. W. Stubbs, W. Sutherland, A. B. Tomaney, T. Vandehei, D. Welch

Resultado de la investigación: Article

538 Citas (Scopus)

Resumen

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 (t̂) of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < t̂ < 400 days to be τ400 2 = 1.2+0.4 -0:3 × 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+4 -3 × 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 noie that an important source of background are supernovae (SNe) in galaxies behind the LMC.

Idioma originalEnglish
Páginas (desde-hasta)281-307
Número de páginas27
PublicaciónAstrophysical Journal
Volumen542
N.º1 PART 1
EstadoPublished - 10 oct 2000

Huella dactilar

massive compact halo objects
Magellanic clouds
halos
timescale
maximum likelihood analysis
systematic errors
confidence interval
optical depth
confidence
spatial distribution
project
galactic halos
optical thickness
photometry
supernovae
dark matter
lenses
galaxies
intervals
stars

ASJC Scopus subject areas

  • Space and Planetary Science
  • Nuclear and High Energy Physics
  • Astronomy and Astrophysics

Citar esto

Alcock, C., Allsman, R. A., Alves, D. R., Axelrod, T. S., Becker, A. C., Bennett, D. P., ... Welch, D. (2000). The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations. Astrophysical Journal, 542(1 PART 1), 281-307.
Alcock, C. ; Allsman, R. A. ; Alves, D. R. ; Axelrod, T. S. ; Becker, A. C. ; Bennett, D. P. ; Cook, K. H. ; Dalal, N. ; Drake, A. J. ; Freeman, K. C. ; Geha, M. ; Griest, K. ; Lehner, M. J. ; Marshall, S. L. ; Minniti, D. ; Nelson, C. A. ; Peterson, B. A. ; Popowski, P. ; Pratt, M. R. ; Quinn, P. J. ; Stubbs, C. W. ; Sutherland, W. ; Tomaney, A. B. ; Vandehei, T. ; Welch, D. / The MACHO project : Microlensing results from 5.7 years of Large Magellanic Cloud observations. En: Astrophysical Journal. 2000 ; Vol. 542, N.º 1 PART 1. pp. 281-307.
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title = "The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations",
abstract = "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 (t̂) of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < t̂ < 400 days to be τ400 2 = 1.2+0.4 -0:3 × 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+4 -3 × 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 noie that an important source of background are supernovae (SNe) in galaxies behind the LMC.",
keywords = "Dark matter, Galaxy: halo, Galaxy: structure, Gravitational lensing, Stars: low-mass, brown dwarfs, White dwarfs",
author = "C. Alcock and Allsman, {R. A.} and Alves, {D. R.} and Axelrod, {T. S.} and Becker, {A. C.} and Bennett, {D. P.} and Cook, {K. H.} and N. Dalal and Drake, {A. J.} and Freeman, {K. C.} and M. Geha and K. Griest and Lehner, {M. J.} and Marshall, {S. L.} and D. Minniti and Nelson, {C. A.} and Peterson, {B. A.} and P. Popowski and Pratt, {M. R.} and Quinn, {P. J.} and Stubbs, {C. W.} and W. Sutherland and Tomaney, {A. B.} and T. Vandehei and D. Welch",
year = "2000",
month = "10",
day = "10",
language = "English",
volume = "542",
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journal = "Astrophysical Journal",
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Alcock, C, Allsman, RA, Alves, DR, Axelrod, TS, Becker, AC, Bennett, DP, Cook, KH, Dalal, N, Drake, AJ, Freeman, KC, Geha, M, Griest, K, Lehner, MJ, Marshall, SL, Minniti, D, Nelson, CA, Peterson, BA, Popowski, P, Pratt, MR, Quinn, PJ, Stubbs, CW, Sutherland, W, Tomaney, AB, Vandehei, T & Welch, D 2000, 'The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations', Astrophysical Journal, vol. 542, n.º 1 PART 1, pp. 281-307.

The MACHO project : Microlensing results from 5.7 years of Large Magellanic Cloud observations. / Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Dalal, N.; Drake, A. J.; Freeman, K. C.; Geha, M.; Griest, K.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Nelson, C. A.; Peterson, B. A.; Popowski, P.; Pratt, M. R.; Quinn, P. J.; Stubbs, C. W.; Sutherland, W.; Tomaney, A. B.; Vandehei, T.; Welch, D.

En: Astrophysical Journal, Vol. 542, N.º 1 PART 1, 10.10.2000, p. 281-307.

Resultado de la investigación: Article

TY - JOUR

T1 - The MACHO project

T2 - Microlensing results from 5.7 years of Large Magellanic Cloud observations

AU - Alcock, C.

AU - Allsman, R. A.

AU - Alves, D. R.

AU - Axelrod, T. S.

AU - Becker, A. C.

AU - Bennett, D. P.

AU - Cook, K. H.

AU - Dalal, N.

AU - Drake, A. J.

AU - Freeman, K. C.

AU - Geha, M.

AU - Griest, K.

AU - Lehner, M. J.

AU - Marshall, S. L.

AU - Minniti, D.

AU - Nelson, C. A.

AU - Peterson, B. A.

AU - Popowski, P.

AU - Pratt, M. R.

AU - Quinn, P. J.

AU - Stubbs, C. W.

AU - Sutherland, W.

AU - Tomaney, A. B.

AU - Vandehei, T.

AU - Welch, D.

PY - 2000/10/10

Y1 - 2000/10/10

N2 - 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 (t̂) of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < t̂ < 400 days to be τ400 2 = 1.2+0.4 -0:3 × 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+4 -3 × 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 noie that an important source of background are supernovae (SNe) in galaxies behind the LMC.

AB - 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 (t̂) of the events range from 34 to 230 days. We estimate the microlensing optical depth toward the LMC from events with 2 < t̂ < 400 days to be τ400 2 = 1.2+0.4 -0:3 × 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+4 -3 × 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 noie that an important source of background are supernovae (SNe) in galaxies behind the LMC.

KW - Dark matter

KW - Galaxy: halo

KW - Galaxy: structure

KW - Gravitational lensing

KW - Stars: low-mass, brown dwarfs

KW - White dwarfs

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M3 - Article

AN - SCOPUS:0034633466

VL - 542

SP - 281

EP - 307

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 PART 1

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Alcock C, Allsman RA, Alves DR, Axelrod TS, Becker AC, Bennett DP y otros. The MACHO project: Microlensing results from 5.7 years of Large Magellanic Cloud observations. Astrophysical Journal. 2000 oct 10;542(1 PART 1):281-307.