Testing Cosmology with Phase-Space Correlations in Systems of Satellite Galaxies. Current Studies and Future Prospects

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1 Observed MW satellites Testing Cosmology with Phase-Space Correlations in Systems of Satellite Galaxies Current Studies and Future Prospects Marcel S. Pawlowski Hubble Fellow at University of California Irvine Web: marcelpawlowski.com Diemand et al. (2006) Simulated DM subhalos

2 Via Lactea project / J. Diemand Is the phase-space distribution of satellite galaxies consistent with ΛCDM expectations? known satellite galaxies for both Milky Way and Andromeda. Numerous small-scale problems known (missing satellites, core-cusp, TBTF) but affected by baryonic physics Positions and velocities of satellite subhalos on 100 kpc scales robust against internal baryonic physics and feedback processes. Radial distribution is affected. Ahmed+2017, Garrison-Kimmel+2017

3 Phase-space correlations Close pairs of galaxies Groups of galaxies / group infall Planes of satellite/dwarf galaxies Lopsided satellite systems

4 Phase-space correlations Close pairs of galaxies Groups of galaxies / group infall Planes of satellite/dwarf galaxies Lopsided satellite systems

5 Pairs of Satellites (of similar magnitude) Fattahi et al. (2013) Observed LG: 28% in close pairs with similar velocity ΛCDM simulations: 6% in close pairs with similar velocity

6 Phase-space correlations Close pairs of galaxies Groups of galaxies / group infall Planes of satellite/dwarf galaxies Lopsided satellite systems

7 Crater-Leo group of MW satellites Pawlowski, McGaugh & Sohn (in prep.) 4 satellite galaxies + 1 star cluster (Crater 1). Suggested by e.g. Torrealba et al. (2016) to be one infalling group. 1.Aligned along one common great circle. 2.Coherent distance trend along this direction (symbol sizes). 3.Similar, low Galactocentric velocities. 4.Typical number for normal ΛCDM subhalo groups found in simulations (2-5, e.g. Li & Helmi 2009). 5.Leo II and Leo IV stopped star formation ~5 Gyr ago: common infall at that time? 6.Leo II proper motion (Piatek et al. 2016) consistent with orbit along this direction (but VPOS too). VPOS

8 Phase-space correlations Close pairs of galaxies Groups of galaxies / group infall Planes of satellite/dwarf galaxies Lopsided satellite systems

9 The Vast Polar Structure of the Milky Way (VPOS) Pawlowski, Pflamm-Altenburg & Kroupa (2012, MNRAS, 423, 1109), Pawlowski & Kroupa (2013, MNRAS, 435, 2116), Pawlowski, McGaugh & Jerjen (2015, MNRAS, 453, 1047) Majority of MW satellites with measured proper motions co-orbit along VPOS CVn II UMa I Com Boo III Boo II Draco Crater-Leo group Segue 1 or part of the VPOS? Leo II Boo Willman 1 UMi UMa II CVn Leo V Leo I Leo IV Crater Hya II Sextans Her Segue 3 Sgr Kim 1 Kim 2 Tri II Both Segue 2 MW satellite pairs Peg III have similar PMs Pisces II Tuc II LMC SMC Pic I Gru I Phe II Scl Car Eri III For Ret II Hor II Hor I

10 The VPOS as seen from outside the Milky Way Pawlowski 2018 (brief review in MPLA, arxiv: )

11 How does the VPOS compare to ΛCDM? Pawlowski 2018 (brief review in MPLA, arxiv: ) (11 classical satellites only!) Measure of kinematic coherence Observed VPOS Frequency of similarly extreme satellite arrangements in cosmological simulations is 0.1% Measure of plane width

12 Is the Milky Way special? The Great Plane of Andromeda (GPoA) Ibata+2013 Both M31 satellite pairs are part of the GPoA Measure of kinematic coherence Measure of plane width Frequency of similarly extreme satellite arrangements in cosmological simulations is 1%, 0.1% if considering radial distribution.

13 Is the LG special? Cen A Satellite Plane Müller, Pawlowski, Jerjen & Lelli (2018) Measure of kinematic coherence Measure of plane width Frequency of similarly extreme satellite arrangements in cosmological simulations is 0.5% (DMO & hydro simulations)

14 Searching for a Satellite Planes Signal in a Statistical Sample of Systems Ibata et al Identify hosts with 2 satellites with measured los velocities in SDSS. Select satellites on opposite sides -> increases chance to see satellite plane edge-on. Check velocity relative to host: ΛCDM expectation: 50% have correlated, 50% have anti-correlated velocity sign. Rotating satellite planes: satellite pairs should show anti-correlated velocities. Observed velocity anti-correlation consistent with > 60% of satellites in thin planes. (Ibata et al. 2014)

15 Phase-space correlations Close pairs of galaxies Groups of galaxies / group infall Planes of satellite/dwarf galaxies Lopsided satellite systems

16 Libeskind et al. (2016): Lopsidedness in stacked host pairs in SDSS θ

17 θ

18 Lopsidedness of Satellite Systems in Simulations Pawlowski, Ibata & Bullock (2017) Cumulative number of satellites in wedges of opening angle θ. Observed overabundance (black). Libeskind+2016 Millennium 1+2 simulations show such an excess! Pawlowski+2017 ΛCDM passes this test. θ ratio of found vs. expected from isotropy Observed vs. Simulated MS1 (no orphans) facing partner MS1 (no orphans) opposite partner MS2 (no orphans) facing partner MS2 (no orphans) opposite partner SDSS facing partner SDSS opposite partner cos ( )

19 Limitations of Studying Phase-Space Correlations in Satellite Galaxy System Target (distance) Milky Way (~100 kpc) Andromeda (~800 kpc) Centaurus A (~4 Mpc) Local Volume (~10 Mpc) (~ 100 Mpc) Angular size of viral volume (rvir~ 250 kpc) 5% distance uncertainty all-sky 18º 4º 1.4º 9 ± 5 kpc ± 40 kpc ± 200 kpc ~ 500 kpc ~ 5 Mpc Positions 3D 3D ~3D 2D 2D Kinematics 3D LoS + PM 1D - 3D LoS (+ PM?) 1D LoS 1D LoS 1D LoS Angular size of dwarf (rh ~ 250 pc)

20 Limitations of Studying Phase-Space Correlations in Satellite Galaxy System Less phase-space information available for distant satellite systems. Must test correlations in projection. Need to study more host systems. Need better statistics to investigate connections between different types of phase-space correlations. Is is universal or incidental? Velocity information is crucial (2D -> 3D). Not only for top 1-2 satellites, but for 10, i.e. down to MV ~ -8

21 Some Current Surveys Dec ( ) Spectroscopic Satellite Survey Around NGC 4258 (Spencer, Loebman & Yoachim, 2014) d=7.6 Mpc, luminosity limit for satellite velocities: MV < 11 (Sculptor) 1.5 SAGA survey (Geha et al. 2017) Possible Satellites Aim: dwarf satellite galaxy systems down to Mr < 12.3 (Leo I) in 300 kpc viral radius around Limits correspond to top 5-6 MW sats. (LMC, Not enough 092 to study phase-space structures Probable Satellites MW analogs between Mpc. SMC, Sag, For, Leo I, Scu) RA ( ) V V NGC4258 (km/s) V NGC 4258 (kms 1 ) Probable Satellites Possible Satellites R Proj (kpc)

22 Conclusions 1. The phase-space distribution of satellite galaxies is a powerful test of cosmological models: Does not depend strongly on baryonic physics. LCDM predicts correlations which haven t been observationally confirmed (e.g. groups of satellites). 2. Satellite phase-space distributions show a number of conflicts with ΛCDM expectations: Planes of Satellite galaxies, too many satellite pairs, 3. Most severe tension with LCDM due to kinematics, not distribution alone. Need line-of-sight velocities! 4. Have to study a statistical sample of satellite systems. For more on satellite planes, see my review in MPLA: arxiv: