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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 2006 1 Final results on galactic dark matter from the EROS-2 microlensing survey ~ 850 000 images processed - 55 million stars monitored Large Magellanic Cloud (LMC)Small Magellanic Cloud (SMC) EROS-2 Expérience de Recherche d’Objets Sombres Observation : 1996-2003 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/0607207

2 P.Tisserand Rencontres du Vietnam 2006 2 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 ~ 10 12 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 2006 3 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 2006 4 t E ~ 70 ( ) ½ days 1986ApJ...304....1P, 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 2006 5 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 2006 6 Event rate predictions from «standard» isothermal halo model Typical Value (in the case of a dark halo 100% machos)  LMC  0.45 10 -6  SMC  0.65 10 -6 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 2006 7 Full Macho Halo:  LMC  0.45 10 -6  SMC  0.65 10 -6 Self lensing:  LMC-LMC  0.005 - 0.05 10 -6  SMC-SMC  0.04 10 -6 Lensing LMC-Galactic stars:  LMC-gal  0.01 10 -6 Lensing Galactic-Galactic stars:  gal-gal  2.0 10 -6 Events rate comparison : (  MACHO  0.12 10 -6 )

8 P.Tisserand Rencontres du Vietnam 2006 8 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 -7 M  { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/12/3706391/slides/slide_8.jpg", "name": "P.Tisserand Rencontres du Vietnam 2006 8 1986 : B.", "description": "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 -7 M 

9 P.Tisserand Rencontres du Vietnam 2006 9 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 1996 - 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 2006 10 Status before this analysis

11 P.Tisserand Rencontres du Vietnam 2006 11 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 2006 12 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 2006 13 Physical Microlensing Background

14 P.Tisserand Rencontres du Vietnam 2006 14 « 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 2006 15 Candidates follow-up : longer baseline ( + 3 yrs)  EROS 1 – LMC#1 :  MACHO – LMC#23 : ~ 1992 ~ 1998 ~ 2001 ~ 1995 3 candidates show a new bump a few years later !!  Variable Stars = Background Withdrawn !

16 P.Tisserand Rencontres du Vietnam 2006 16 (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 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 !

18 P.Tisserand Rencontres du Vietnam 2006 18 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 2006 19 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 2006 20 Data Analysis

21 P.Tisserand 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!

22 P.Tisserand Rencontres du Vietnam 2006 22 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 2006 23 Crowded field:

24 P.Tisserand Rencontres du Vietnam 2006 24 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 [18.2-19.7] 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 2006 25 Number of events expected Macho mass Duration t E Number Magellanic events (full halo) effi. = 100%Real effi. 10 -3 M  ~ 2.2 days~ 2500~63 10 -2 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 ~ 0.45 10 -6 τ SMC ~ 0.65 10 -6 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 2006 26 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 2006 27 _3% at 10 -2 M  Final EROS combined limit (1990-2003) _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 2006 28 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 2006 29 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 ) Discussion of the EROS2 result

30 P.Tisserand 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


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