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Cluster-Cluster MicrolensingA New Probe of Cosmological Dark Compact Objects in Unexplored Mass Range: 

Cluster-Cluster Microlensing A New Probe of Cosmological Dark Compact Objects in Unexplored Mass Range T. Totani1, T. Sumi2, N. Yasuda3, G. Kosugi3, andamp; M. Doi4 1.Kyoto University 2.Princeton University 3.NAO, Japan 4.Univ. of Tokyo

Contents: 

Contents The cluster-cluster system towards the Hercules supercluster (Abell 2152) Search for MACHOs in 30-104 Msun by microlensing search in this system First observation by Subaru Telescope in May-June, 2003

The Hercules Supercluster: 

The Hercules Supercluster A complex of three rich Abell clusters, 2147, 2151, and 2152 Distance: z ~ 0.04 or 170 Mpc (h=0.7) Estimated dynamical mass M~1015 Msun for each LR~(1-2) x 1012 h-2 Lsun ~8 x 1015 Msun as total (marginally bounded) cz (km/s) R.A. cone Decl. cone

The Hercules Supercluster (2): 

The Hercules Supercluster (2) A2152 A2147 A2151

Cluster-Cluster System: A2152: 

Cluster-Cluster System: A2152 Another, even more rich cluster found just behind A2152 (Blakeslee et al. 2001) A2152-B @ z = 0.13 Angular offset of the centers: 2’.4 (0.09h-1 Mpc at z=0.04) Optical depth of A2152 ~ 0.01 Abell 2152, 30’ x 30’

Cluster-Cluster System: A2152 (2): 

Cluster-Cluster System: A2152 (2) A2152 center A2152-B center X-ray center 6’ x 6’ image of A2152 center A2152-B CM A2152 CM

Galaxy Counts in the A2152 Region: 

Galaxy Counts in the A2152 Region Circles and Dashed: galaxies within 5’ Crosses and Solid: galaxies within 15’ Field counts Number Surface Number Density

Cluster-Cluster Microlensing: 

Cluster-Cluster Microlensing Search intracluster MACHOs in A2152 by ultra-magnified microlensing event of a star in A2152-B

Is it detectable?: 

Is it detectable? New wide-field cameras on large telescopes e.g., Subaru/Suprime-Cam: 8m, 30’x30’ Wide and deep transient search is suitable for new microlensing experiments in distant galaxies

Wide-field deep imaging by Subaru/Suprime-Cam: 

Wide-field deep imaging by Subaru/Suprime-Cam

Extreme Magnification Required : 

Extreme Magnification Required Distance modulus to A2152-B = 38.7 Magnification to reach a detection limit m~26:

Point-mass lens versus caustic-crossing: 

Point-mass lens versus caustic-crossing

Caustic-crossing light curves : 

Caustic-crossing light curves

Typical Quantities: 

Typical Quantities

Event rate estimate: 

Event rate estimate M=1015h-1Msun for A2152, A2152-B (M/LI)=180h(Msun/LI,sun) for A2152-B Stellar luminosity function (LF) Our Galaxy disk for spirals Our Galaxy bulge for ellipticals Density profile: Isothermal sphere with core for DM in A2152 King profile for stars in A2152-B Relative velocity of lens and source: 1000 km/s spiral elliptical Totani 2003, ApJ in press (astro-ph/0211222)

Event Rate Estimate Result:: 

Event Rate Estimate Result: Assuming continuous observation during 10 nights for Subaru/Suprime-Cam Sensitivity limit: I=26.0 @ S/N=5, 1 hr exposure Surprisingly wide sensitivity to the lens mass (m~10-5 – 108 Msun), at a level of a few % in the mass fraction of compact objects in the dark matter (fCO) Elliptical Spiral mean

Effect of diffuse light of host galaxies?: 

Effect of diffuse light of host galaxies? Host galaxies at z=0.13 m*~19 for M*~ -20 Much brighter than lensing event of m~26? Image subtraction  host galaxy flux becomes zero level Noise level? Most galaxies have SB lower than the sky brightness We can use normal sensitivity limit for ground-based observations

Scientific Implications: 

Scientific Implications compact objects as the dark matter: Past constraints exclude compact object DM in: 10-7 andlt; M andlt;~ 30Msun from EROS/MACHO M andgt;~105 Msun from strong lensing of QSOs, no GRB recurrence No strong constraint yet by lensing in ~30 andlt; M andlt; 105 Msun, which can be probed by the cluster-cluster microlensing A recent constraint from binary separation distribution by Yoo, Chaname, andamp; Gould (2003) andgt;105 Msun DM MACHOs may solve the core/cups problem in dwarf galaxies (Jin, Ostriker, andamp; Wilkinson 2003)

Unique Points of Cluster-Cluster Microlensing : 

Unique Points of Cluster-Cluster Microlensing No known contaminating astronomical transient events Supernovae: too low event rate, different time scale Variable stars, novae: too faint Self-lensing: negligible event rate Event rate asymmetry between the foreground A2152 and the background A2152-B If observed, it provides undoubted proof for microlensing, different from variable sources or noise false detection Lens mass estimate: Not easy because of unresolved source stars Color, host galaxy types, and finite source size effect could constrain the absolute source star luminosity, making a rough lens mass estimate possible

Observations by Subaru: 

Observations by Subaru First observation has been done Subaru Open Use Intensive Program, 5 nights 2003/05/05, 2003/06/01-04 Condition was pretty good I, V, one field-of-view centered on A2152 ~1 hour exposure for I and V, and repeated. 1 day includes 3 sets for both I and V.

Slide21: 

The Suprime-Cam Image of the A2152 Cluster-Cluster System

Slide22: 

Close-up of the central region

Image Subtraction and Event Search (1): 

Image Subtraction and Event Search (1) Image subtraction (Alard andamp; Lupton argorithm) Source detection by SExtractor search around host galaxies of A2152-B (surface area fraction ~a few %) Test of detection efficiency by artificial stars Distributed on Abell 2152-B member galaxies Detection efficiency ~50% at I=24.7 and V=26.2 @ 40min exposure V andamp; I correlation Saturated region removed from analysis Often occur in the center of elliptical galaxies

Center of A2152: before subtraction: 

Center of A2152: before subtraction

Center of A2152: after subtraction: 

Center of A2152: after subtraction

Slide26: 

Examples of variable candidates I(May) I(June) I(sub) V(May) V(June) V(sub)

Image Subtraction and Event Search (2): 

Image Subtraction and Event Search (2) Event candidates False signals (bad pix, saturated region, etc.) AGNs SNe Number that can be examined by eyes Expected event number (preliminary) ~1 event for the first run

Summary : 

Summary First observation has been made for the cluster-cluster microlensing to Abell 2152 The achieved sensitivity is about ~1 event if dark matter is MACHOs in the 30-104 Msun window No microlensing candidate More observation is necessary to reject MACHOs as dark matter Several AGNs, and supernovae found Studies on low luminosity AGNs and supernova rate evolution are now underway

Cooling flows in galaxy clusters and dark matter neutralinos: 

Cooling flows in galaxy clusters and dark matter neutralinos No cooling flow revealed by recent X-ray observation, and some heat source necessary (conduction, AGNs, ..??) DM Neutralino annihilation provides a sufficient heat with Standard annihilation cross section Standard (initial) DM density profile (e.g. NFW) Adiabatic growth of central density cusp by SMBH in cD galaxies Annihilation gamma-rays should be detected by GLAST Totani 2004, astro-ph/0401140