Dark Matter in Galaxies. A. Bosma. Observatoire de Marseille. (actually LAM /
OAMP). History of the problem (incomplete and perhaps biased). Focus on recent
...
Dark Matter in Galaxies A. Bosma Observatoire de Marseille (actually LAM / OAMP) History of the problem (incomplete and perhaps biased) Focus on recent problems in the field a. dark matter in spirals b. core/cusp problem c. dark matter in ellipticals d. galaxy formation & the future
Galactic dark matter ? Oort (1932) dynamics 0.092 visible 0.038
Galactic dark matter
The strong outlyer is Bahcall, yet we were urged to believe him
Discussion in IAU 117
Zwicky 1933 : dunkle Materie
Coma = 7038 ± 1020 Colless & Dunn 1996 : 6917 ± 1038
Zwicky (1937) suggests lensing can give simple and accurate masses Schwarschild (1954) finds low values for M/L for M31 and other gas rich galaxies, he also says elsewhere in the paper :
DM ''proof''' Clowe et al. (2006) ApJ 648, L109
Schwarschild (1954)
M31 – RubinFord curve can be fitted with exponential disk without need for dark matter (blue curve) – For the bulge, see Athanassoula & Beaton (2006)
Disk stability argument
Even though the stability argument is now disputed, (cf. Athanassoula), the idea of a dark halo slowly gained acceptance
Dark halo : proposed for spirals also Ostriker , Peebles & Yahil (1974)
M33 – problem of the warp : again hardly any need for dark matter if one takes data out to the edge of the optical image
Flat rotation curves beyond the optical image Bosma, 1978, 1981a,b
velocity field & rotation curve
The last point ...matters
Kalnajs 1983 Kent 1986/7 Athanassoula et al.1987 Palunas & Williams 2000
better use HI, since it goes farther out
Expect peak at 2.2 scalelengths, discrepancy is seen out to > 10 15 scalelengths
Fukugita & Peebles 2004
Steigman astroph/0511534 Fields/Sarkar astroph/0601514
Core/cusp problem Springel et al. 2005
has problems on galaxy scales cuspy halos lots of satellites
Open problems concerning galaxy mass distributions at z = 0 (possible conflict with LambdaCDM) : Dominance of baryonic matter in the central parts of bright spirals The core/cusp problem in LSB galaxies
Dark Matter in Galaxies “predicted” observed
Data on LSB's De Blok, Bosma & McGaugh (& Rubin) 2001 2003 Criticisms : 1D data slit placement noncircular motions etc...
“Clean sample” De Blok, Bosma & McGaugh 2003
Dark Matter in Galaxies Bosma 2004
NGC 5055 SDSS – 2MASS
LSB galaxies are almost invisible in the 2MASS survey, hence we use WHT and LIRIS at Kband
UGC 4325
No cusp here, either
Milgrom & Sanders 2006
core/cusp debate
Kuzio de Naray et al. (ApJS, august 2006)
Dark Matter in Galaxies
Simon et al. (2003)
Simon et al. 2005
NGC 5963, a case unlike the others
Gentile et al. 2005 : no cusp in DDO 47
Hayashi et al. 2004, 2006 consider a disk in triaxial halo
Newer theoretical studies Cusps confirmed : slope 1.2 with billion particles simulation (Diemand et al. 2005) but whole approach put into question (Xiao et al. 2005) also research on what sets the slope theoretically
Diemand et al. (2006)
Galaxy formation in
Feedback helps: TFrelation zero point OK, but halos still too concentrated... resolution problem ... Governato et al. (2006)
Bar – Halo interaction Athanassoula 2002, 2003, 2005, 2006 Mechanism is the exchange of angular momentum via the resonances As a result, during the slow evolution, the mass concentration of the galaxy increases with time, and a bar/bulge forms from the disk Voie Lactée
seen in COSMOS data Sargent et al. (2006)
Local Group – all (badly) barred ?
MW
M31 is barred
Beaton et al. 2006 with 2MASS 6X; Athanassoula & Beaton, 2006
Dark Matter in M31
Lavalle et al. (2006)
Dark Matter in M31
Dark Matter in M31 Seigar et al. (2006)
M31 The RubinFord (1970) data do not argue for dark matter The Braun (1991) curve is not confirmed by the new work of Carignan et al. (2007)
No cusp in our own Galaxy ? Microlensing towards LMC/SMC : no evidence for much baryonic DM Microlensing towards bulge : not much room for NFWlike profile
Tisserand et al. (2006) Bissantz & Gerhard (2002) Hamadache et al. (2006)
Are the local galaxies exceptional ?
Hammer et al. (2007)
Dwarf spheroidal galaxies Wilkinson et al. (2006)
Dwarf spheroidal galaxies
Here the existence of clumps, or globular clusters, is used to argue that a cored potential is preferred, since a cusped potential will lead to rapid disruption and/or migration towards the center Kleyna et al. (2003) Goerdt et al. (2006)
Future constraints from SIM/GAIA Strigari et al. 2007 LOS velocities and proper motions in dSph galaxies
Dark Matter : jump into the unknown
Careful observer ... or Bold theorist ?
Concluding remarks The core/cusp problem is a tough problem for CDM theory It cannot be wished away Further development of galaxy formation theory is necessary Further observations will put better constraints on it Expected dark matter signals depend on its resolution Maybe you can detect the dark matter ?? Further literature in NED – level 5 http://nedwww.ipac.caltech.edu/level5/dark_matter.html http://nedwww.ipac.caltech.edu/level5/normal_galaxies.html