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 Orbital Structure of Streams Pal 5 stream. Discovered by • Odenkirchen et al. (2001). This map was created by Bernard et al (2016)
Stellar Streams >40 Milky Way Streams (SDSS, Pan- STARRS1, DES, ATLAS…) • Malhan, Ibata & Martin (2018). ZEA projection of the Galactic sky. The plot was created using galstreams package ( Mateu et al 2017 )
STREAMFINDER Malhan & Ibata (2018) 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
STREAMFINDER Malhan & Ibata (2018) 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
STREAMFINDER Malhan & Ibata (2018) 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
STREAMFINDER Malhan & Ibata (2018) 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( σ w , σ v , t orbit )
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, Σ G =33 mag arcsec-2 (faint stream) Retained only 4D phase-space information – l , b, μ l , μ b (with errors) • v rad 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) Testing algorithm with N-body simulated ~Pal-5 stream PERFECT STREAM GAIA-like ERRORS
STREAMFINDER Malhan & Ibata (2018) • Stream (50 stars) + GUMS (330,000 stars) = Data ( 0.015% stream stars) • v rad 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 (-3 σ to +3 σ ) c) v rad space (s.t. v total < v escape ) • ~30,000 orbits for every datum. Sampled orbits Perfect orbit Data orbit
STREAMFINDER Malhan & Ibata (2018) • Log-likelihood of a star being associated with a stellar stream. L datum = L kinematics + L LF + L continuity Luminosity Stream continuity Data-orbit comparison Function criteria (given the observed errors) criteria
STREAMFINDER Malhan & Ibata (2018) • Log-likelihood of a star being associated with a stellar stream. L datum = L kinematics + L LF + L continuity Luminosity Stream continuity Data-orbit comparison Function criteria (given the uncertainties) criteria • L acts as ``weight’’ for every star used to obtain stream density plot
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 : SSP 1 • Age = 9-10 Gyrs • [Fe/H] = -1.5 to -2.5 • 50 stars per stream • Surface brightness SSP 2 ~ 33 mag arcsec -2 (very faint) • STREAMFINDER using different SSP 3 SSP models
MW Stellar Stream map from Gaia DR2 Malhan, Ibata & Martin (2018) results…? Gaia DR2 dataset STREAMFINDER • |b|>30 ◦ • GCs and DGs masked 1. Find GC streams (narrow and cold) 2. Dehnen & Binney (1998) 3. 7 SSP [Fe/H]=[-1.0, -2.2], Age=10Gyrs
Gaia-3* Gaia-2* Gaia-1* GD-1 Sagittarius Stream
Gaia-3* Gaia-2* Gaia-1* GD-1 Sagittarius Stream
Gaia-4* Jhelum Sagittarius Stream SMC Indus LMC
Gaia-4* Jhelum Sagittarius Stream SMC Indus LMC
Observations Orbital Solutions Phase-space-luminosity coherence of the structures. Malhan et al (2018)
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)
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