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IV: Milky Way / Local Group Tomography. Hans-Walter Rix MPI for Astronomy Heidelberg. The stellar distribution in the Milky Way is not smooth. What can it tell us bout its formation history?. “Substructure”: Signposts of Hierarchical Formation.

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Iv milky way local group tomography l.jpg
IV: Milky Way / Local Group Tomography

Hans-Walter Rix

MPI for Astronomy

Heidelberg

The stellar distribution in the Milky Way is not smooth.

What can it tell us bout its formation history?


Substructure signposts of hierarchical formation l.jpg
“Substructure”: Signposts of Hierarchical Formation

  • The motions of stars (or groups) still reflect their formation history after many dynamical periods.

  • In collissionless systems, the phase-space density/distribution is preserved.

  • Phase mixing may lead to a smooth appearance in r or v space.


2 seeing galaxies 2d 6d or the right 3d l.jpg

P. Harding

2. Seeing Galaxies: 2D, 6D or (the right) 3D



But all is well in phase space e g helmi de zeeuw 2000 l.jpg

initial

12 Gyrs later

..but all is well in phase space…(e.g. Helmi, de Zeeuw 2000)

Also holds true if the overall potential changes adiabatically (Penarrubbia et al 2005)

Scattering off sub-structure to be checked!


Questions l.jpg
Questions

  • Is there direct evidence for such sub-structure?

    • In all galaxies? In the Milky Way?

  • What is the mass spectrum of “pieces”?

  • Is hierarchical accretion still going on?

  • Can we use the streams to measure the gravitational potential?

  • How tightly is chemical enrichment coupled to kinematics (i.e. to formation episode)?


Slide8 l.jpg

Is (sub-)structure of the phase-space distribution observable in galaxies with unresolved stellar populations?


Tomography of unresolved galaxies ngc 4473 data model cappellari de zeeuw et al sauron l.jpg
Tomography of Unresolved Galaxies? observable in galaxies with unresolved stellar populations?NGC 4473: data-modelCappellari, de Zeeuw et al SAURON

2D-binned data

V s h3 h4

Symmetrized data

Axisymmetric model

Are the V-shaped velocity and high major-axis dispersion produced by a counter rotating stellar component?


Schwarzschild s approach l.jpg
Schwarzschild's approach observable in galaxies with unresolved stellar populations?

  • Compute all orbits possible in a given galaxy

  • The goal is to find the combination of orbits that actually appear in the galaxy  dynamical model

  • But images alone don't contain enough information

Observed

galaxy image

images of model orbits


Ngc 4473 orbital structure cappellari de zeeuw in prep l.jpg
NGC 4473: orbital structure observable in galaxies with unresolved stellar populations?Cappellari, de Zeeuw in prep.

Counter-rotating stars

Main galaxy rotation


Are spiral galaxies smooth let s step back and look at m31 l.jpg

Ferguson et al 2004

  • Step 1: select stars in color-magnitude space

blue RGB (= metal poor)

red RGB (= metal rich)

Are spiral galaxies smooth?Let’s step back and look at M31


Probing the halo of m31 with sdss zucker et al 2004 l.jpg

And NE observable in galaxies with unresolved stellar populations?

And V

SDSS Scan of M31: 45 sq. deg. in 3 hr

20 kpc

And IX

Spatial Density of Probable M31 RGB Stars by Color

Probing the Halo of M31 with SDSSZucker et al 2004

Advantage: large volume-filling factor easy

Disadvatage: 3D information limited


M 31 status quo lewis et al 2004 l.jpg
M 31 Status Quo observable in galaxies with unresolved stellar populations?Lewis et al 2004


4 substructure in the milky way halo l.jpg
4. Substructure in the Milky Way Halo observable in galaxies with unresolved stellar populations?

  • How to find it?

  • Status quo

  • How to interpret what has been found?


A clear case the sagittarius stream l.jpg

Ibata et al 1995 observable in galaxies with unresolved stellar populations?

Majewski et al 2003

A clear case: the Sagittarius stream


Slide17 l.jpg

Newberg, Yanny et al 2002 observable in galaxies with unresolved stellar populations?

Sagittarius Stream

Pal 5

The density of “turn-off” colored stars

in the SDSS equatorial stripe

Galactic Plane


Slide18 l.jpg

SEGUE (unpublished) observable in galaxies with unresolved stellar populations?

“Hess diagrams” as diagnostic tools


The wilky way s low latitude ring monoceros tri and cma etc l.jpg
The Wilky Way’s Low-Latitude Ring observable in galaxies with unresolved stellar populations?(Monoceros, Tri/And, CMa, etc…)

Kicked out (of the plane)

or

Dragged in (disrupting satellite)?


Slide20 l.jpg

THE FIRST SCENARIO: observable in galaxies with unresolved stellar populations? TIDALLY DISRUPTING DWARF GALAXY


Slide21 l.jpg

15 kpc observable in galaxies with unresolved stellar populations?

1.5 kpc

Galaxy ESO 510-13. Conselice et al 2003

THE SECOND SCENARIO: THE MILKY WAY WARP (Momany et al 2004)


Low latitude stellar overdensities in the mw l.jpg
Low-Latitude Stellar Overdensities in the MW observable in galaxies with unresolved stellar populations?

  • Is it a tidal stream? -- external

    • Can all “pieces” be fit as originating from one disrupted entity?

    • Is there a parent?

  • Is a warp (or more complex response to a perturbation)? – internal

  • Discriminants:

    • Kinematics – disk/warp-like

    • Spatial distribution

    • Chemical composition – diff. star-formation history


Modelling the low latitude ring penarrubbia rix et al 2005 l.jpg

Best retrograde orbit observable in galaxies with unresolved stellar populations?

Modelling the Low-Latitude Ring(Penarrubbia, Rix, et al. 2005)

  • Question:can all overdensities be attributed to one stream?

  • Approach:

  • semi-analytic point orbit (incl. dynamical friction)

  • full N-body realization

Best prograde semi-analytic orbit


The wilky way s low latitude ring monoceros tri and cma etc24 l.jpg

Penarrubia, Rix et al 2005 observable in galaxies with unresolved stellar populations?

The Wilky Way’s Low-Latitude Ring(Monoceros, Tri/And, CMa, etc…)


Slide25 l.jpg

Penarrubia, Rix et al 2005 observable in galaxies with unresolved stellar populations?

Peñarrubia 2004

Spatial Distribution:

wide z-range; little R range

 ? Not a warp


Results of the stream modeling l.jpg
Results of the stream modeling observable in galaxies with unresolved stellar populations?

  • The location of all known over-densities at low latitude (<30o) can be matched as leading and trailing tidal tails of a disrupted satellite

    • Geometry excludes warp

  • Satellite orbit prograde, very low ellipticity (~0.1+-0.05) at low inclination (20o+-5o)

  • “Parent” location not well determined

    • metallicity gradient of debris suggest l=250

    • Orbit model suggests distance dsun=12 kpc

    • Parent satellite mass 2x108-109Msun


Does the stream have a parent galaxy l.jpg
Does the stream have a parent galaxy? observable in galaxies with unresolved stellar populations?

Selecting stars with red giant colors and taking apparent magnitude as a distance proxy


Slide28 l.jpg

Martinez-Delgado, Rix et al 2005 observable in galaxies with unresolved stellar populations?

Can Maj Main Seq.

ThickDisk

Halo

Thin Disk Main Seq.


Slide29 l.jpg

Martinez-Delgado, Rix, et al 2004 observable in galaxies with unresolved stellar populations?

(see also Bellazzini et al 2004)

saturation

mV,0 ~ 24

(l,b)=(240,-8)


Density of ms stars towards cma as a function of distance app magnitude l.jpg

Martinez-Delgado, Rix et al 2005 observable in galaxies with unresolved stellar populations?

Density of MS stars towards CMa as a function of distance (app. magnitude)

Depth of CMa: r1/2~0.85kpc @ RGC~13kpc


What is the density profile of cma l.jpg
What is the density profile of CMa? observable in galaxies with unresolved stellar populations?

galactic plane

Butler, Martinez-Delgado, Rix ’05 (in prep.)


Slide32 l.jpg

Martinez-Delgado, Rix et al 2005 observable in galaxies with unresolved stellar populations?

Can Maj Main Seq.

ThickDisk

Halo

Thin Disk Main Seq.

  • Narrow MS (15% depth)

  • High-contrast (>3)

  • Two distinct (age?) populations

  • Distance 8kpc


Slide33 l.jpg

Rocha-Pinto et al 2005 observable in galaxies with unresolved stellar populations?

  • Buit life’s never easy!

  • CMa may not be the point of maximal density


Proper motions of canis majoris l.jpg

Rocha-Pinto et al 2005 observable in galaxies with unresolved stellar populations?

Warp motion

Dinescu et al 2005

Proper Motions of “Canis Majoris”

WCMa=-49+-15 km/s


What would the milky way s response be to such a disrupting satellite l.jpg

sun observable in galaxies with unresolved stellar populations?

(CMa) satellite

What would the Milky Way’s response be to such a disrupting satellite?

below


Sdss segue sky coverage l.jpg
SDSS+SEGUE Sky Coverage observable in galaxies with unresolved stellar populations?


Near term future astrometry l.jpg
Near–Term Future Astrometry observable in galaxies with unresolved stellar populations?

  • PRIMA: differential astrometry with VLTI

    • 2008

    • 10mas @ 17 mag across 30”


6 gaia 2012 l.jpg
6. GAIA 2012--- observable in galaxies with unresolved stellar populations?


Summary l.jpg
Summary observable in galaxies with unresolved stellar populations?

  • Sub-structure exists (may even be pervasive)

    • The observed parts were created recently (z<0.5)

  • We still have to learn how to best find it

    • Quantitatively

    • Objectively

  • Milky Way seems to be surrounded by at least two large streams

    • “parent” of the low-latitude stream is probably near Canis Majoris

  • Impact of those streams on the Milky Way is considerable

    • Milky Way subject to quite intense “gravitational noise”

  • SEGUE (SDSS-II) and GAIA can revolutionize the field.

    • The existing analysis tools for these data are still rudimentary


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