Diaspora in Cercetarea Stiintifica Bucuresti, 21-24 Sept. 2010 The Milky Way and its Satellite System in 3D Velocity Space: Its Place in the Current Cosmological

Diaspora in Cercetarea Stiintifica Diaspora in Cercetarea Stiintifica Bucuresti, 21-24 Sept. 2010Bucuresti, 21-24 Sept. 2010

The Milky Way and its The Milky Way and its Satellite System in 3D Satellite System in 3D

Velocity Space: Its Place in Velocity Space: Its Place in the Current Cosmological the Current Cosmological

FrameworkFramework

Dana I. Casetti - Dana I. Casetti - Yale UniversityYale University

APOD (10/20/2007);copyright: Larry Landolfi


Current Cosmological Framework: Current Cosmological Framework: CDMCDM

I. The makeup of the Universe, or the distribution of energy density of all I. The makeup of the Universe, or the distribution of energy density of all “matter”“matter”

WMAP - 2008 results

today

13.7 Gyr ago

map.gsfc.nasa.gov/news

Galaxy formation was initiated at around the epoch of reionization, (when first stars formed, ~ 400 Myr after Big Bang) => thus galaxy thus galaxy formation is governed formation is governed by the dark-matter by the dark-matter structure.structure.



II. Galaxy formationII. Galaxy formation

There are two stages of collapse:There are two stages of collapse:

- dark matter haloes (hierarchical built-up)dark matter haloes (hierarchical built-up)

- cooling of baryonic gas within haloes: if gas cooling of baryonic gas within haloes: if gas can cool efficiently (to below the halo virial can cool efficiently (to below the halo virial temperature), then it will lose pressure support temperature), then it will lose pressure support and can form a galaxyand can form a galaxy



QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

VL1 - formation history and zoom-in at z=0



* Far-field Cosmology (large to moderate redshift):* Far-field Cosmology (large to moderate redshift):

CMB, galaxy clusters, large-scale CMB, galaxy clusters, large-scale structure of galaxies structure of galaxies CDM confirmedCDM confirmed

* Near-field Cosmology (redshift ~ 0):* Near-field Cosmology (redshift ~ 0):

the domain of resolved stellar the domain of resolved stellar systems: Milky Way, and possibly systems: Milky Way, and possibly Andromeda Andromeda CDM challengedCDM challenged


Why is the MW a challenge for Why is the MW a challenge for CDM models ?CDM models ?

1)1) Missing satellite problem: hundreds to thousands predicted, MW has ~ 20Missing satellite problem: hundreds to thousands predicted, MW has ~ 20

(undetected? Are most of them dark matter haloes? Are some satellites (undetected? Are most of them dark matter haloes? Are some satellites formed via tidal interactions?)formed via tidal interactions?)

2)2) Predicted density profiles of subhaloes are cuspy (Predicted density profiles of subhaloes are cuspy ( ~ r ~ r-1-1); measured ones ); measured ones are less steepare less steep

(if correct: possibility of warm dark matter!, but there is degeneracy (if correct: possibility of warm dark matter!, but there is degeneracy between velocity anisotropy and slope of density, so we are unsure about between velocity anisotropy and slope of density, so we are unsure about the density profiles …)the density profiles …)

3)3) Simulated dark-matter haloes are prolate ellipsoids; measurements of the Simulated dark-matter haloes are prolate ellipsoids; measurements of the MW dark matter halo indicate it is spherical, but results are controversial.MW dark matter halo indicate it is spherical, but results are controversial.

4) In models, disks of spiral galaxies are difficult to built and maintain thin, 4) In models, disks of spiral galaxies are difficult to built and maintain thin, cold and extended.cold and extended.


-Dwarf satellite galaxiesDwarf satellite galaxies

-Streams from tidally disrupted systemsStreams from tidally disrupted systems

-Globular clustersGlobular clusters

The Galactic GadaboutsThe Galactic Gadabouts

Excellent probes of the gravitational Excellent probes of the gravitational potential of the MW and of its potential of the MW and of its subhalo structuresubhalo structure

Determine orbits and velocity dispersions Determine orbits and velocity dispersions or 3D velocitiesor 3D velocities

Need: radial velocities, distances and Need: radial velocities, distances and proper motionsproper motions


Proper Motions, Velocities and UncertaintiesProper Motions, Velocities and Uncertainties

Current formal errors in Current formal errors in absolute proper motions of absolute proper motions of stellar systems:stellar systems:

Ground based:Ground based: between between 0.06 and ~1.5 mas/yr0.06 and ~1.5 mas/yr

Space based (HST):Space based (HST): between 0.04 and 0.5 between 0.04 and 0.5 mas/yrmas/yr


Case Study I - Known satellites of the MWCase Study I - Known satellites of the MW

Bullock et al. 2010Bullock et al. 2010

Metz et al. 2008, 2009Metz et al. 2008, 2009

-Spatial alignment of the traditional 11 dwarf sph. -Spatial alignment of the traditional 11 dwarf sph. (Lynden-Bell 1976, 1982, Kunkel & Deemers 1976).(Lynden-Bell 1976, 1982, Kunkel & Deemers 1976).

-Newly found ultra-faint dwarfs follow this alignment -Newly found ultra-faint dwarfs follow this alignment (Metz et al. 2009).(Metz et al. 2009).

-Proper motions of 6 dwarf satellites indicate that their -Proper motions of 6 dwarf satellites indicate that their orbital angular momenta are aligned -> rotationally orbital angular momenta are aligned -> rotationally supported disk of satellites (Metz et al. 2008).supported disk of satellites (Metz et al. 2008).



Only 7 satellites have proper motions measured (with 0.04 to 0.25 mas/yr errors). Only 7 satellites have proper motions measured (with 0.04 to 0.25 mas/yr errors). HST and ground-based observations do not agree.HST and ground-based observations do not agree.

Example: Fornax at ~ 140 kpcExample: Fornax at ~ 140 kpc

Piatek et al. 2002 (before CTI correction)

Dinescu et al. 2004

Piatek et al. 2006






Dinescu et al. 2004

Piatek et al. 2006






Dinescu et al. 2004

Piatek et al. 2006



Example: The Magellanic CloudsExample: The Magellanic Clouds

HST-based proper motions (Kallivayalil et al. 2006, Piatek et al. 2009) indicate HST-based proper motions (Kallivayalil et al. 2006, Piatek et al. 2009) indicate that the Clouds are unbound to the MW (if its mass implies a rotation of the LSR that the Clouds are unbound to the MW (if its mass implies a rotation of the LSR of 220 km/s), and likely unbound to each other…Recent ground-based results of 220 km/s), and likely unbound to each other…Recent ground-based results partially agree with HST results (Costa et al. 2009, Vieira et al. 2010).partially agree with HST results (Costa et al. 2009, Vieira et al. 2010).


Case Study II - Stellar Streams of the MWCase Study II - Stellar Streams of the MW

Example: The Sagittarius Dwarf Galaxy and its Tidal StreamExample: The Sagittarius Dwarf Galaxy and its Tidal Stream

G. Gilmore and R. Sword

Ibata, Gilmore, Irwin 1994

P. Cseresnjes

Found via Found via radial radial velocitiesvelocities




Connecting 2MASS with SDSS along the Sagittarius tidal stream

Belokurov et al. 2006, 2007, 2008, Majewski et al. 2003




Connecting 2MASS with SDSS along the Sagittarius tidal stream

Belokurov et al. 2006, 2007, 2008, Majewski et al. 2003




The geometry of the orbit allows a direct determination of The geometry of the orbit allows a direct determination of LSRLSR: :

the proper motions in longitude provides this.the proper motions in longitude provides this.




Carlin 2010, Law et al. 2010

SA 71

SA 94SA 93 SA 117

SA 116

Sgr core




LSRLSR = 267 +- 23 km/s = 267 +- 23 km/s

The traditional value of 220 The traditional value of 220 km/s appears to be ruled out!km/s appears to be ruled out!


The FutureThe Future

-ESA: Gaia satellite ESA: Gaia satellite

-LSST (Large Synoptic Survey Telescope 8m class)LSST (Large Synoptic Survey Telescope 8m class)

-other more limited ground-based surveys, and a few more HST other more limited ground-based surveys, and a few more HST resultsresults

Documents

Diaspora in Cercetarea Stiintifica Bucuresti, 21-24 Sept. 2010 The Milky Way and its Satellite System in 3D Velocity Space: Its Place in the Current Cosmological