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P.Tisserand Rencontres du Vietnam 2006 1 Final results on galactic dark matter from the EROS-2 microlensing survey ~ 850 000 images processed - 55 million.

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Presentation on theme: "P.Tisserand Rencontres du Vietnam 2006 1 Final results on galactic dark matter from the EROS-2 microlensing survey ~ 850 000 images processed - 55 million."— Presentation transcript:

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

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

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

4 P.Tisserand Rencontres du Vietnam t E ~ 70 ( ) ½ days 1986ApJ P, B.Paczyński Light curve characteristics:  Symmetric  Achromatic  Unique ( ~1 evt / 10 6  ) M M  Microlensing effect : t E  t E (M, D d, V t ) Degeneracy !

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

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

7 P.Tisserand Rencontres du Vietnam Full Macho Halo:  LMC   SMC  Self lensing:  LMC-LMC   SMC-SMC  Lensing LMC-Galactic stars:  LMC-gal  Lensing Galactic-Galactic stars:  gal-gal  Events rate comparison : (  MACHO  )

8 P.Tisserand Rencontres du Vietnam : B. Paczyński propose microlensing effect to probe the halo : EROS1/MACHO/OGLE start the adventure :  First candidates ! : First alert system by MACHO & OGLE  Detection of exotic events (binary lenses) : EROS1/MACHO : No short timescale events discovered (10 -7 M 

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

10 P.Tisserand Rencontres du Vietnam Status before this analysis

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

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

13 P.Tisserand Rencontres du Vietnam Physical Microlensing Background

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

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

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

17 P.Tisserand Rencontres du Vietnam 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 !

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

19 P.Tisserand Rencontres du Vietnam Halo microlensing candidates status EROS MACHO 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 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 Only 1 on 9 candidates remain 10 on 13 could be considered as halo candidates

20 P.Tisserand Rencontres du Vietnam Data Analysis

21 P.Tisserand Rencontres du Vietnam 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!

22 P.Tisserand Rencontres du Vietnam 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% Blending problem Star cataloged and surveyed Fainter star located in the seeing disk (less than 2”) Optical depth estimate : Using bright star, we considerably reduce that problem under-estimated

23 P.Tisserand Rencontres du Vietnam Crowded field:

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

25 P.Tisserand Rencontres du Vietnam Number of events expected Macho mass Duration t E Number Magellanic events (full halo) effi. = 100%Real effi M  ~ 2.2 days~ 2500~ M  ~ 7 days~ 785~173 1 M  ~ 70 days~ 78~35 10 M  ~7.4 months~ 25~9 100 M  ~ 2 years~ 8~0.4 in the case of a dark halo 100% machos τ LMC ~ τ SMC ~ For 6.9 million bright stars monitored during 6.7 years × Efficiency t E ~ 70 ( ) ½ days M M  We need ~13 events to confirm the positive signal of MACHO at 20%

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

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

28 P.Tisserand Rencontres du Vietnam Comparison : EROS-2/MACHO 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) ~2 Million bright stars in common ! MACHO field EROS2 field LMC 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

29 P.Tisserand Rencontres du Vietnam 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 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 ) Discussion of the EROS2 result

30 P.Tisserand Rencontres du Vietnam 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


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