Dark Matter in Galaxies

Marc Verheijen

verheyen@astro.rug.nlRm 284

an observational perspective

Capita Selecta 2009

http://www.astro.rug.nl/~verheyen ! Teaching & Outreach ! Dark Matter in Galaxies

outline

• introduction, layout of activities

• seminal papers

• historical notes

• dark matter in spiral galaxies

• dark matter in elliptical galaxies

• discussion & selection of topics

introduction & layout of activities

• Tue, Apr 28, 11:15 - 13:00 introductory lecture, choice of topics

• Fri, May 1, 15:15 - 17:00 topical lecture & discussions

• Thu, May 7, 11:15 - 13:00 topical lecture & discussions

• Tue, May 12, 11:15 - 13:00 presentations + reviews

• Tue, May 19, 11:15 - 13:00 presentations + reviews

• Tue, May 26, 11:15 - 13:00 presentations + reviews

• Thu, May 28, 11:15 - 13:00 presentations + reviews

7 interactive meetings:

Capita Selecta - not part of mandatory curriculum requires basic knowledge of galaxy structure & dynamics

3 ECTS : presentation/participation/report

+ written summary reports before July 1st.

Seminal papers

• Bosma, A., 1986, AJ, 86, 1791(first indisputable evidence for DM in spirals)

• van Albada, T.S., Sancisi, R., 1986, Phil. Trans. R. Soc. Lond., 320, 447(interpretation of galaxy rotation curves)

• Trimble, V., 1987, ARAA, Vol. 25, 425-472 (§2.2, §2.3, §2.4)(classical, but somewhat outdated, review on Dark Matter in galaxies)

• Ashman, K.M., 1992, PASP, 104, 1109-1138 (§6, §7)(updated, but now incomplete, review on Dark Matter in galaxies)

• Loewenstein, M., White III, R.E.,1999, ApJ, 518, 50Kronawitter, A. et al, 2000, A&AS, 144, 53(first indisputable evidence for DM in ellipticals)

• Navarro, J.F., Frenk, C.S., White, S.D.M., 1997, ApJ, 490, 493(universal DM halo density profile from cosmological N-body simulations)

some historical notes

• The prediction of the existence of Neptune by Adams (1843) and Leverrier (1846), and confirmed by Galle in1846, was based on the gravitational interpretation of deviations in the orbit of Uranus.

• In 1932, Oort measures the vertical velocities of K-giant stars (from the thick disk) in the Solar neighbourhood, but derives the wrong corresponding density distribution (of the thin disk) and thus, using the Jeans equation, overestimates the gravitational restoring foce, wrongfully deducing the presence of dark matter in the disk.

• In 1988, Kuijken used modern data and the more general Boltzman equation to show that little or no dark matter exists in the disk.

• In 1998, Bienayme used Hipparcos data to conclude that the Galactic disk in the Solar Neighbourhood is more or less free of dark matter.

some historical notes

• In 1933, Zwicky infers M(dark) !50xM(lum) in the Coma cluster, based on the virial theorem.

• In 1936, Smith infers M(dark) !100xM(lum) in the Virgo cluster, also based on the virial theorem. The notion that M/L of the cluster as a whole is much larger than the M/L of an individual Virgo galaxy, leads to the suggestion that much of the mass is ‘inter-nebular’.

• Babcock measures, in 1939, the rotation of the stellar disk of M31, but unknown distance results in wrong numbers for the total mass.

some historical notes

• 21cm emission from HI is predicted in 1944 by van de Hulst and detected in 1951 by Ewen & Purcell.

• Radio interferometry techniques, developed in the 1960s, allowed for detailed mapping of extended rotating HI disks in the late 1970s.

• In 1978, Bosma provided compelling evidence for dark matter in the outer regions of galaxies with extended flat rotation curves.

The existence of dark matter on the scales of galaxies was finally and indisputably established.

extended rotation curves

NGC 2403

Fraternali et al (2001)

• Observational errorsbeam smearing, warps, non-circular (lopsided) motions

• disk-halo degeneracymaximum-disk hypothesis, stellar kinematics

Battaglia et al (2005)

NGC 5055

Boomsma (2007)

NGC 6946

dark matter in spiral galaxies

• extended rotation curves

• kinematics of satellite galaxies

• weak galaxy-galaxy lensing

• extent of tidal tails

• flaring outer disks

• kinematics of polar rings

mass, size and shape of the halo

maximum-disk hypothesis & disk-halo conspiracy

HI column density map velocity field

Radial HI distribution position-velocity map

luminosity profile

Begeman (1987)

dark matter ‘conspires’ with baryons to keep the rotation curve flat

amplitude ! " (M/L)

disk-halo degeneracy

need independent measure of M/L

van Albada & Sancisi, 1986

dark matter in spiral galaxies

• extended rotation curves

• kinematics of satellite galaxies

• weak galaxy-galaxy lensing

• extent of tidal tails

• flaring outer disks

• kinematics of polar rings

• micro-lensing (Milky Way only)

mass, size and shape of the halo