A Lonely Giant: The Sparse Satellite Population of M94 Challenges - PowerPoint PPT Presentation

A Lonely Giant: The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina Eric Bell, Richard D’Souza, Paul Price, Colin Slater, Jeremy Bailin, Antonela Monachesi, David Nidever Smercina et al. 2018, ApJ, 863, 152

Problems with Galaxy Formation Missing Satellites Dwarf Galaxy Scales Too Big to Fail Problem + Solution Defined in MW/LG Genereralizable? Boylan-Kolchin+2011 Bullock, Boylan-Kolchin, Pawlowski 2017 A Lonely Giant : The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina

Motivates satellite searches around MW-analogs Geha et al. 2017 Müller et al. 2018 Crnojevic et al. 2016 Romanowsky et al. 2017 Smercina et al. 2017

A Subaru HSC Survey of M94’s Satellites 5 kpc 5 kpc • M94: An isolated MW-mass galaxy 60 24 . 5 60 24 . 5 40 40 § Mass: M * ~ 4 × 10 10 M ⊙ 25 20 25 ∆ δ (arcsec) 20 ∆ δ (arcsec) r 0 0 § Distance: 4.2 Mpc r 0 0 25 . 5 25 . 5 − 20 − 20 − 40 26 Deep − 40 • 6 pointings with HSC ( g -band) 26 Deep − 60 Dw2 − 1 0 1 2 − 60 60 40 20 0 − 20 − 40 − 60 − 1 0 ( g − r ) 0 1 2 60 40 20 ∆ α (arcsec) 0 − 20 − 40 − 60 ( g − r ) 0 ∆ α (arcsec) M94-Dw1 M94-Dw1 § ~150 kpc radial coverage in g -band M94-Dw2 M94-Dw2 § Discovered 2 low-mass satellites 30 24 . 5 Dw1 30 24 . 5 20 Deep 20 Deep 25 10 ∆ δ (arcsec) 25 10 ∆ δ (arcsec) 0 r 0 0 r 0 25 . 5 There are only 2 satellites >4 × 10 5 M ⊙ ! 25 . 5 − 10 − 10 50 kpc − 20 26 50 kpc − 20 26 − 30 − 30 30 20 10 0 − 10 − 20 − 30 − 1 0 1 2 30 20 10 ∆ α (arcsec) 0 − 10 − 20 − 30 − 1 0 ( g − r ) 0 1 2 ∆ α (arcsec) ( g − r ) 0 A Lonely Giant : The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina

How does M94’s satellite population compare to other galaxies, and model predictions? A Lonely Giant : The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina

M94’s satellite population is very unlikely in a ‘Standard’ Halo Occupation Context <0.2% in 1500 galaxies! EAGLE FIRE No most massive Known galaxies satellites ≤ 10 6 M ☉ (Halo Occupation) (Garrison-Kimmel+19) Most Massive Satellite MW (McConnachie + 12) M31 (McConnachie + 12) 0.01 Standard P Halo Occup . M81 (Karachentsev& Kudrya 14) 10 1 M101 (Bennet + 19) 0 N sat ( � 4 ⇥ 10 5 M � ) Cen A (Crnojevi´ c + 18) MW M31 M94 (Smercina + 18) M81 N ( <M V ) M101 M94 40 M-II, Med. M-II, 50 % M-II, 90 % M-II, 99 % N sat ( >M ? ) 10 1 30 20 10 10 0 10 0 0 − 10 − 12 − 14 − 16 − 18 − 20 6 7 8 9 10 11 0.05 log 10 M ? ( M � ) M V P

A ‘Stochastic’ Halo Occupation model produces M94-like systems much more frequently Most Massive Satellite 0.01 Stochastic P Halo Occup . ~4-5% in 1500 galaxies 0 N sat ( � 4 ⇥ 10 5 M � ) MW M31 M81 M101 M94 40 M-II, Med. M-II, 50 % M-II, 90 % M-II, 99 % N sat ( >M ? ) 10 1 30 20 Some systems have a most 10 massive satellites ≤ 10 6 M ☉ 10 0 0 6 7 8 9 10 11 0.1 log 10 M ? ( M � ) P

M94’s Sparse Satellite System suggests that galaxy formation is surprisingly stochastic for <10 11 M ☉ halos Missing Satellites M94’s Satellites Too Big to Fail MW-mass galaxies have M94 lacks any satellite >10 6 M ☉ large scatter in their # of satellites Large scatter may persist for halos >10 10 à the TBTF mass Scatter from best current Galaxy formation at ALL simulations is much lower! dwarf-galaxy scales may be much more stochastic A Lonely Giant : The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina