Stellar Stream map of the Milky Way Halo : Application of STREAMFINDER onto ESA/Gaia DR2

Transcription

1 Stellar Stream map of the Milky Way Halo : Application of STREAMFINDER onto ESA/Gaia DR2 w/ Rodrigo A. Ibata and Nicolas F. Khyati Malhan PhD Student Supervisor: Dr. Rodrigo Ibata

2 Stellar Streams Pal 5 stream. Discovered by Odenkirchen et al. (2001). This map was created by Bernard et al (2016)

3 Stellar Streams Orbital Structure of Streams Pal 5 stream. Discovered by Odenkirchen et al. (2001). This map was created by Bernard et al (2016)

4 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)

5 Maximize stream detection by: STREAMFINDER Using all the prior information about the stellar stream ( analyzing phase-space-color-magnitude distribution simultaneously) This is possible with Gaia DR2

6 Maximize stream detection by: STREAMFINDER 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

7 Maximize stream detection by: STREAMFINDER 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

8 Maximize stream detection by: STREAMFINDER 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 )

9 STREAMFINDER 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)

10 GAIA-like ERRORS PERFECT STREAM STREAMFINDER Testing algorithm with N-body simulated ~Pal-5 stream

11 STREAMFINDER Stream (50 stars) + GUMS (330,000 stars) = Data (0.015% stream stars) v rad and ω information was deleted. Convolved Gaia like errors.

12 Orbit sampling STREAMFINDER 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) v rad space (s.t. v total < v escape ) ~30,000 orbits for every datum. Sampled orbits Perfect orbit Data orbit

13 STREAMFINDER Log-likelihood of a star being associated with a stellar stream. L datum = L kinematics + L LF + L continuity Data-orbit comparison (given the observed errors) Luminosity Function criteria Stream continuity criteria

14 STREAMFINDER Log-likelihood of a star being associated with a stellar stream. L datum = L kinematics + L LF + L continuity Data-orbit comparison (given the uncertainties) Luminosity Function criteria Stream continuity criteria L acts as ``weight for every star used to obtain stream density plot

15 STREAMFINDER Stream output log-likelihood density plot

16 Multiple stream case : Age = 9-10 Gyrs [Fe/H] = -1.5 to stars per stream Surface brightness ~ 33 mag arcsec -2 (very faint) STREAMFINDER

17 STREAMFINDER Multiple stream case : Age = 9-10 Gyrs [Fe/H] = -1.5 to stars per stream Surface brightness ~ 33 mag arcsec -2 (very faint) STREAMFINDER using different SSP models SSP 1 SSP 2 SSP 3

18 MW Stellar Stream map from Gaia DR2 Malhan, Ibata & Martin (2018) results? Gaia DR2 dataset b >30 GCs and DGs masked STREAMFINDER 1. Find GC streams (narrow and cold) 2. Dehnen & Binney (1998) 3. 7 SSP [Fe/H]=[-1.0, -2.2], Age=10Gyrs

19 Gaia-3* Gaia-2* Gaia-1* GD-1 Sagittarius Stream

20 Gaia-3* Gaia-2* Gaia-1* GD-1 Sagittarius Stream

21 Gaia-4* Sagittarius Stream LMC SMC Jhelum Indus

22 Gaia-4* Sagittarius Stream LMC SMC Jhelum Indus

23 Observations Orbital Solutions Phase-space-luminosity coherence of the structures. Malhan et al (2018)

24 Testing the phase-space-luminosity coherence of the structures. Malhan et al (2018)

25 STREAMFINDER 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)

26