Breaking tidal stream degeneracies with lamost
This presentation is the property of its rightful owner.
Sponsored Links
1 / 14

Breaking tidal stream degeneracies with LAMOST PowerPoint PPT Presentation


  • 67 Views
  • Uploaded on
  • Presentation posted in: General

Breaking tidal stream degeneracies with LAMOST. Jorge Peñarrubia (IoA). Cambridge 2nd December 08. Local Group Cosmology. Cosmological Paradigm predicts that galaxies form through mergers of smaller galaxies. This process continues nowadays in the Milky Way…. Local Group Cosmology.

Download Presentation

Breaking tidal stream degeneracies with LAMOST

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Breaking tidal stream degeneracies with lamost

Breaking tidal stream degeneracies with LAMOST

Jorge Peñarrubia (IoA)

Cambridge 2nd December 08


Local group cosmology

Local Group Cosmology

Cosmological Paradigm predicts that galaxies form through mergers of smaller galaxies

This process continues

nowadays in the Milky Way…


Local group cosmology1

Local Group Cosmology

The Local Group is the only system where the kinematics of individual stars can be measured with high precision

why is this important?

We want to decompose the hierarchical formation

of our galaxy = set of individual mergers

However, the remnants of accreted satellites

blurwith time

Photometric surveys can only reveal

the most recent accretions


Full 3d kinematics

Full 3D Kinematics

  • Unbound particles escape through leadingand trailing tails

  • Tails approx. follow the orbit of the progenitor system ….

  • strong constraints on the

  • presenthost potential

  • progenitor’sorbit

  • progenitor’smass lost fraction

  • progenitor’s luminosity

for each accretion event

Peñarrubia et al. (2005)

cosmological merger tree


Radial velocity surveys

Radial velocity surveys

Proper motions can only be measured in a small volume (GAIA<20 kpc)

In contrast, radial velocities can be measured < 1 Mpc (DEIMOS @ Keck)

Mapping the sky via Radial velocity surveys:

  • RAVE: m<16 => D< 1.6 kpc (M=5) 120 objects - field

  • LAMOST: m<20 => D< 10 kpc (M=5) 4000objects - field

Position + radial velocity = 4D info of stellar streams

to infer the orbit+mass of progenitor

we need numerical modelling


Numerical modelling of tidal streams

Numerical modelling of tidal streams

Owing to the large parameter spacemodel degeneracies

are unavoidable

Free parameters

  • Flattening (q) of the host potential

  • Orbital apocentre

  • Orbital inclination

  • Orbital eccentricity

  • Mass and concentration of the satellite’s DM halo

  • Segregation of the satellite’s stellar component

  • Satellite luminosity

  • Accretion time

    (ifprogenitor is unknown)

  • Present progenitor position + velocity (6 param.)

Constraints:

  • position of stream pieces from photometric surveys

spectroscopic surveys will break fundamental model degeneracies


Ideal targets for lamost

Ideal Targets for LAMOST

Previous photometric surveys have revealed a large number of stream-like structures at D< 50 kpc

Potential targets for LAMOST are:

  • Sagittarius stream

  • Monoceros stream

  • Virgo over-density

  • Hercules-Aquila over-density

  • Palomar 5 stream

  • …….. etc

All located in the Northern Galactic Hemisphere !!

(the South remains terra incognita)

What could we learn if we had LAMOST data now??


Example 1 the sgr stream and the shape of the milky way potential

Example 1: The Sgr stream and the shape of the Milky Way potential

Belokurov et al. 2006

(SDSS+2MASS)

Sgr core


Example 1 the sgr stream and the shape of the milky way potential1

Example 1: The Sgr stream and the shape of the Milky Way potential

  • Constraints:

  • Sgr dwarf’s position: (D,l,b) = (25 kpc, 5.60,-14.50)

  • Sgr dwarf’s radial velocity: vrad = 171 km/s

  • Orbital plane inclination: i=76o

  • Free parameters

  • tangential vel. (vtan) (eccentricity==rapo)

  • halo axis-ratio (qh)


Example 1 the sgr stream and the shape of the milky way potential2

Example 1: The Sgr stream and the shape of the Milky Way potential

from 2-MASS (M-giants) :

  • Oblatehalo models (0.85<q<0.95) matchprecession rate

  • Prolate halo models (q>1) matchradial velocitiesalong the stream

Johnston et al. 2005

using the same data

inconsistent results !!

Law et al. 2005


Example 2 the monoceros stream

Example 2: The Monoceros stream

Again, M-Giant over-densities

  • M-giants show a large dispersion on the sky

  • They move on nearly circular orbits

Do all over-densities belong to the Mon stream?

Penarrubia et al. 2005


Example 2 the monoceros stream1

Example 2: The Monoceros stream

Degenerated model : Prograde vs Retrograde orbits

Radial velocities between

l > 220o

l < 110o

will break model degeneracy


Example 3 field s of streams

Example 3: Field(s) of streams

In the next few years, the number of streams detected via photometric

surveys (SDSS I,II,III; Pan-STARRS) will dramatically increase.

Monoceros

Orphan

Sgr

Pal 5

Virgo

Kinematics will be crucial for their modelling….


Example 4 halo clumpiness

Example 4: Halo clumpiness

According to CDM, there are ~104 subhaloes in the MW with M>107 Msol

Cold tidal streams (e.g from GCs with ~ 1 km/s) may be heated by encounters with DM subhaloes

kinematical surveys of GC streams could potentially constrain the number density of DM clumps

Grillmair & Dionatos 2006


  • Login