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
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ER
RO
RS
PER
FEC
T ST
REA
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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)