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Final results on galactic dark matter from the EROS-2 microlensing survey

Final results on galactic dark matter from the EROS-2 microlensing survey. Astro-ph/0607207. Patrick Tisserand Mount Stromlo Obs., Australia. EROS-2 Expérience de Recherche d’Objets Sombres Observation : 1996-2003 at La Silla (Chile) CEA/DAPNIA/SPP-Saclay.

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Final results on galactic dark matter from the EROS-2 microlensing survey

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  1. Final results on galactic dark matter from the EROS-2 microlensing survey Astro-ph/0607207 Patrick Tisserand Mount Stromlo Obs., Australia EROS-2 Expérience de Recherche d’Objets Sombres Observation : 1996-2003 at La Silla (Chile) CEA/DAPNIA/SPP-Saclay ~ 850 000 images processed - 55 million stars monitored Microlensing formalism History and the EROS-2 experiment Situation before this analysis Microlensing Background Analysis and Candidates status Final Result of EROS-2 Discussions Large Magellanic Cloud (LMC) Small Magellanic Cloud (SMC) Rencontres du Vietnam 2006

  2. Problem : Galaxy rotation curve Onehypothesis:A halo full of machos... A large amount of dark matter exists at the galaxy’s scale Machos «  Massive Astronomical Compact Halo Objects » Surface luminosity (mag/arcsec2) _ Planets  _ Brown dwarfs _ Stellar remnants _ Unknown compact matter Halo Rotation velocity (km.sec-1) Characteristics: - spherical isothermal distribution - Radius between 50 and 200 kpc - Mass : M(r) α r - Total Mass ~ 1012 M - Density : (r) α 1/r2 Disc Van Albada et al., 1985 Rencontres du Vietnam 2006

  3. Tool : lensing effect • Lensing effect : Indirect detection • For 1 M: • Image Separation ~ 0.2 milli arcsec Σ Exp: EROS MACHO OGLE ~ milli arcsec ~ arcsec Rencontres du Vietnam 2006

  4. 1986ApJ...304....1P, B.Paczyński Microlensing effect : tE~ 70 ( )½ days tE tE (M, Dd, Vt ) Degeneracy ! • Light curve characteristics: • Symmetric • Achromatic • Unique ( ~1 evt / 106) Rencontres du Vietnam 2006

  5. Some microlensing events observed : Appeared in 1993 tE = 17 days, Amplification ~ 7.5 MACHO – LMC#1 EROS2-LMC#8 OGLE2-99-LMC#1 Increase by 3.5 magnitudes ! Appeared in 2000 tE ~10 days Alert 1999 tE ~66 days, Amplification ~ 50 Rencontres du Vietnam 2006

  6. Event rate predictions from «standard» isothermal halo model • Probability (τ=Optical Depth): τ = Probability that, a given time, a source star is inside one Einstein disk (Amplification > 1.34) τ depends mainly on the halo density Independent of machos velocity and mass Virialised System:  ~ ( v / c )2 Typical Value (in the case of a dark halo 100% machos) LMC 0.45 10-6 SMC 0.65 10-6 Rencontres du Vietnam 2006

  7. Events rate comparison : Lensing Galactic-Galactic stars: gal-gal 2.0 10-6 Lensing LMC-Galactic stars: LMC-gal 0.01 10-6 Full Macho Halo: LMC 0.45 10-6 SMC 0.65 10-6 (MACHO 0.12 10-6) Self lensing: LMC-LMC 0.005 - 0.05 10-6 SMC-SMC 0.04 10-6 Rencontres du Vietnam 2006

  8. History : 1986 : B. Paczyński propose microlensing effect to probe the halo. 1990-92 : EROS1/MACHO/OGLE start the adventure. 1993 : First candidates ! 1994-95 : First alert system by MACHO & OGLE Detection of exotic events (binary lenses) 1994-98 : EROS1/MACHO : No short timescale events discovered (10-7M<M<10-3M) 1996 : Start of EROS-2. jan 2000 : End of the MACHO experiment. 2000 : EROS2/MACHO : First result up to Mass=10M ~ 2002 : Start of the SuperMACHO experiment + 3rd OGLE phase. feb 2003 : End of the EROS-2 observations. Rencontres du Vietnam 2006

  9. EROS-2 :Expérience de Recherche d’Objets Sombres • Second Phase : July 1996 - February 2003 • Dedicated telescope 1m Ø (Marly), at La Silla (Chile) • 2 cameras : test for achromaticity • 2×8 CCDs : wide field (~1deg²) Red filter Blue filter Collaboration: CEA/DAPNIA, LAL-IN2P3, IAP-INSU, Observatoire de Marseille, Collège de France (PCC), OHP BEros ~ between V and R & REros ~ I Rencontres du Vietnam 2006

  10. Status before this analysis Rencontres du Vietnam 2006

  11. Toward the Galactic center …. Hundreds of microlensing effect have been observed EROS2 : 120 MACHO : 62 OGLE : 33 Only Clump giant stars have been used !! Galactic latitude (deg) Rencontres du Vietnam 2006

  12. Halo constraints in 2003: Microlensing halo candidates: EROS1 : 1 LMC EROS2 : 4 LMC + 3 SMC MACHO : 13 LMC Exclusion diagram at 95% C.L. Excluded at 95% C.L. Rencontres du Vietnam 2006

  13. Physical Microlensing Background Rencontres du Vietnam 2006

  14. known physical background : (discovered by MACHO) « BLUE BUMPER » Bright stars of the upper main sequence Amplification < 2 + Chromatic Variation Easy to reject ! Rencontres du Vietnam 2006

  15. Candidates follow-up : longer baseline ( + 3 yrs) 3 candidates show a new bump a few years later !!  Variable Stars = Background Withdrawn ! • EROS 1 – LMC#1 : ~ 1992 ~ 1998 • MACHO – LMC#23 :  ~ 1995 ~ 2001 Rencontres du Vietnam 2006

  16. (Probable) New background: Be type Stars. EROS1-LMC#1 source star have emission features. ZOOM on the 2nd fluctuation: Rencontres du Vietnam 2006

  17. Supernovae : ~ 590 Supernovae detectable If :  Appeared close to a cataloged star.  or SN cataloged.  26 Supernovae detected at low S/N . (Similar rate for MACHO) == Serious background ! Rencontres du Vietnam 2006

  18. Supernovae elimination : • Galaxies seen on reference images • Fit of an “asymmetric” microlensing light curve : and / or Elimination if |S| > 0.3 • Elimination of the 3 remaining EROS-2 LMC candidates (#5, #6 et #7) : Better Photometry! EROS2-LMC#5 : S = 0.5 EROS2-LMC#7 : S = 0.62 Rencontres du Vietnam 2006

  19. Halo microlensing candidates status MACHO EROS MACHO-A-LMC#1 MACHO-A-LMC#4 MACHO-A-LMC#5 : galactic red dwarf lens MACHO-A-LMC#6 MACHO-A-LMC#7 MACHO-A-LMC#8 MACHO-A-LMC#13 MACHO-A-LMC#14 : self-lensing MACHO-A-LMC#15 MACHO-A-LMC#18 MACHO-A-LMC#21 MACHO-A-LMC#23 : Variable star MACHO-A-LMC#25 EROS1-LMC#1 : Variable star EROS2-LMC#3 : Variable star EROS2-LMC#5 : Supernovae EROS2-LMC#6 : Supernovae EROS2-LMC#7 : Supernovae EROS2-SMC#1 EROS2-SMC#2 : Long Period Variable EROS2-SMC#3 : Long Period Variable EROS2-SMC#4 : Long Period Variable Only 1 on 9 candidates remain 10 on 13 could be considered as halo candidates Rencontres du Vietnam 2006

  20. Data Analysis Rencontres du Vietnam 2006

  21. Principe of the analysis: Detection efficiency controlled by a MONTE-CARLO simulation: => False microlensing effects added on real light curve (~ 99% stable) They passed the same selection cuts! Rencontres du Vietnam 2006

  22. Blending problem Star cataloged and surveyed Fainter star located in the seeing disk (less than 2”) Optical depth estimate : MACHO : estimate an additional 30% error due to blending EROS2 : With HST LMC luminosity function weighted with the probability to generate an observable event. → ~1% under-estimated Using bright star, we considerably reduce that problem Rencontres du Vietnam 2006

  23. Crowded field: Rencontres du Vietnam 2006

  24. Bright Star Sample First time in LMC ! On our 33.4 Million stars sample, we retained : Better resolution → better rejection of variable stars Statistics still excellent due to a better <efficiency> Largely reduce the Blending problem Remember galactic center ! LMC : ~6 Million SMC : ~0.9 Million LMC Efficiency Magnitude cut different for each field: Mag  [16-Rmax] with Rmax [18.2-19.7] Homogeneous sample : ~uniform photometric resolution (~7%) CLUMP Rencontres du Vietnam 2006

  25. Number of events expected in the case of a dark halo 100% machos τLMC ~ 0.45 10-6 τSMC ~ 0.65 10-6 × Efficiency For 6.9 million bright stars monitored during 6.7 years tE~ 70( )½days We need ~13 events to confirm the positive signal of MACHO at 20% Rencontres du Vietnam 2006

  26. No new microlensing event detected 1 candidate in the SMC still selected EROS2-SMC#1 Known since 1997(EROS+MACHO) → Probably due to SMC lens (for a halo lens, earth motion would distort the light curve visibly) tE = 120 days Duration expected for SMC self-lensing Rencontres du Vietnam 2006

  27. Final EROS combined limit (1990-2003) _3% at 10-2M Domain excluded from all EROS data _7% at 0.4 M _10% at 1 M ZOOM LMC data set / No event LMC + SMC data set with 1 SMC halo candidate Rencontres du Vietnam 2006

  28. Comparison : EROS-2/MACHO LMC 2 different strategies : 2 different data sets EROS2: ~ 7 Million Bright stars in sparse wide field (~84 deg2 LMC + ~10deg2 SMC) MACHO: ~ 11 Million faint and bright stars in dense field (~13.4 deg2, LMC bar) MACHO field ~2 Million bright stars in common ! EROS2 field Our Measurement is mainly based on a less crowded area Photometry easier and result less affected by blending Remark : A positive result must be seen everywhere, not be concentrated in a special area Rencontres du Vietnam 2006

  29. Discussion of the EROS2 result • Our analysis is conservative : - Use only bright-well measured sub-sample of Magellanic stars (~20% total) - Largely reduce the blending effect • Measurement obtained mainly with stars in the outer part of the LMC (sparse field) • Machos in the mass range 10-7 M< M < 5 M are ruled out as the primary occupants of the Milky Way Halo. • Result compatible with the Optical depth expected from the known star distribution (self-lensing + galactic disk stars) • 2 different Monte-Carlo have been computed to estimate our detection efficiency: _ simulated microlensing effect on true light curve _ fake images that pass all the photometric chain with simulated microlensed star ► they are in excellent agreement for the bright star sample. • An all star sample analysis (33.4 millions) has been done with stricter cuts. Only 5 microlensing candidates have been selected : for one, the lens is a galactic red dwarf star located at about 300pc. (result also compatible with self-lensing) • Serious background : Supernovae & Variable stars Many former candidates died for these reasons (ex: EROS2-LMC#1 and MACHO-LMC#23) Rencontres du Vietnam 2006

  30. Difference between MACHO/EROS2 • 2 completely different data sets : _Most of the MACHO stars are considered too faint for us : ~9 millions. _MACHO observation concentrated in the LMC bar : crowded region • Blending effect : MACHO suggest an additional 30% systematic error on the result. • Our limit is at f<7% for 0.4 M , about 13 events would have been necessary to confirm the MACHO signal. • The higher MACHO optical depth may be due, in part, to self-lensing in central part of the LMC. But this would contradict LMC models (Mancini et al., 2004) which suggest that only 1-2 MACHO candidates should be expected to be due to self-lensing (#9 and #14 are already known to be self-lensing). • 5 MACHO candidates are really convincing : #1, #5, #9, #14 and #21. 3 are explained by LMC self-lensing or due to a galactic lens. Possible confirmation :_ OGLE III and SuperMACHO _ AGAPE, MEGA and WeCaPP (toward M31) _ Photometric follow-up of candidates Rencontres du Vietnam 2006

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