stellar stream map of the milky way halo : application of streamfinder onto esa/gaia … · 2018....

Stellar Stream map of the Milky Way Halo :

Application of STREAMFINDER onto ESA/Gaia

DR2

w/ Rodrigo A. Ibata and Nicolas F. Martin

@kmalhan07

Khyati Malhan

PhD Student

Supervisor: Dr. Rodrigo Ibata

Stellar Streams

Pal 5 stream. Discovered by

• Odenkirchen et al. (2001). This map was created by Bernard et al (2016)

Stellar Streams

Pal 5 stream. Discovered by

• Odenkirchen et al. (2001). This map was created by Bernard et al (2016)

Orbital Structure of Streams

Stellar Streams

• Malhan, Ibata & Martin (2018). ZEA projection of the Galactic sky. The plot was created using galstreams package (Mateu et al 2017)

>40 Milky Way Streams (SDSS, Pan-STARRS1, DES, ATLAS…)

STREAMFINDER

Maximize stream detection by:

• Using all the prior information about the stellar stream ( analyzing phase-space-color-magnitude distribution simultaneously)

• This is possible with Gaia DR2

Malhan & Ibata (2018)

STREAMFINDER

Maximize stream detection by:

• Using all the prior information about the stellar stream ( analyzing phase-space-color-magnitude distribution simultaneously)

• This is possible with Gaia DR2

Best way to detect stream : LOOK ALONG THE ORBITS

Malhan & Ibata (2018)

STREAMFINDER

Maximize stream detection by:

• Using all the prior information about the stellar stream ( analyzing phase-space-color-magnitude distribution simultaneously)

• This is possible with Gaia DR2

Best way to detect stream : LOOK ALONG THE ORBITS

Malhan & Ibata (2018)

STREAMFINDER

Maximize stream detection by:

• Using all the prior information about the stellar stream ( analyzing phase-space-color-magnitude distribution simultaneously)

• This is possible with Gaia DR2

Best way to detect stream : LOOK ALONG THE ORBITS. stream members contained in a 6D hypertube and its 6D volume ~ f(σw, σv, torbit)

Malhan & Ibata (2018)

STREAMFINDER Malhan & Ibata (2018)

Testing algorithm with N-body simulated stream • Simulated a globular cluster stream in a realistic galactic model (Dehnen & Binney 1998)

• Retained only 50 objects in the stream, ΣG =33 mag arcsec-2 (faint stream)

• Retained only 4D phase-space information – l , b, μl ,μb (with errors)

vrad and ω information was deleted. • Convolved Gaia like errors in proper motions. • Also assigned a SSP model to the stream of ([Fe/H], Age)= (-1.5, 10 Gyr)

STREAMFINDER Malhan & Ibata (2018)

GA

IA-l

ike

ER

RO

RS

PER

FEC

T ST

REA

M

Testing algorithm with N-body simulated ~Pal-5 stream

STREAMFINDER Malhan & Ibata (2018)

• Stream (50 stars) + GUMS (330,000 stars) = Data (0.015% stream stars)

• vrad and ω information was deleted. Convolved Gaia like errors.

STREAMFINDER Malhan & Ibata (2018)

Orbit sampling • Blindness and uncertainty in stellar phase-space position. • Sample orbits in: a) distance space (3 solutions based on SSP model) b) proper motion space (-3σ to +3σ) c) vrad space (s.t. vtotal< vescape) • ~30,000 orbits for every datum.

Sampled orbits

Data orbit Perfect orbit

STREAMFINDER Malhan & Ibata (2018)

Ldatum = Lkinematics + LLF + Lcontinuity

• Log-likelihood of a star being associated with a stellar stream.

Data-orbit comparison (given the observed errors)

Luminosity Function criteria

Stream continuity criteria

STREAMFINDER Malhan & Ibata (2018)

Ldatum = Lkinematics + LLF + Lcontinuity

• Log-likelihood of a star being associated with a stellar stream.

• L acts as ``weight’’ for every star used to obtain stream density plot

Data-orbit comparison (given the uncertainties)

Luminosity Function criteria

Stream continuity criteria

STREAMFINDER Malhan & Ibata (2018)

• Stream output – log-likelihood density plot

STREAMFINDER Malhan & Ibata (2018)

Multiple stream case :

• Age = 9-10 Gyrs

• [Fe/H] = -1.5 to -2.5

• 50 stars per stream

• Surface brightness

~ 33 mag arcsec-2

(very faint)

STREAMFINDER Malhan & Ibata (2018)

Multiple stream case :

• Age = 9-10 Gyrs

• [Fe/H] = -1.5 to -2.5

• 50 stars per stream

• Surface brightness

~ 33 mag arcsec-2

(very faint)

• STREAMFINDER

using different

SSP models

SSP 1

SSP 2

SSP 3

MW Stellar Stream map from Gaia DR2 Malhan, Ibata & Martin (2018)

Gaia DR2 dataset • |b|>30 ◦ • GCs and DGs

masked

STREAMFINDER

results…?

1. Find GC streams (narrow and cold) 2. Dehnen & Binney (1998) 3. 7 SSP [Fe/H]=[-1.0, -2.2], Age=10Gyrs

GD-1

Sagittarius Stream

Gaia-1*

Gaia-2* Gaia-3*

GD-1

Sagittarius Stream

Gaia-1*

Gaia-2* Gaia-3*

Sagittarius Stream Jhelum

Indus

Gaia-4*

LMC

SMC

Sagittarius Stream Jhelum

Indus

Gaia-4*

LMC

SMC

Phase-space-luminosity coherence of the structures. Malhan et al (2018)

Observations Orbital Solutions

Testing the phase-space-luminosity coherence of the structures.

Malhan et al (2018)

STREAMFINDER Malhan & Ibata (2018)

Main advantages of the algorithm : • Detection of v. faint structures, even if on complex orbits • Completing the 6D DF(x,v) of detected stellar streams -useful in the context of galaxy formation .

GD-1 stream

observations (Koposov et al 2010)

STREAMFINDER solutions

• STREAMFINDER BLOBFINDER (find blob of stars – star clusters and dwarf galaxies)