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

Dwarf Galaxy Scales Problems with Galaxy Formation Missing Satellites Too Big to Fail Problem + Solution Defined in MW/LG Genereralizable?

Boylan-Kolchin+2011 A Lonely Giant: The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina

Bullock, Boylan-Kolchin, Pawlowski 2017

Müller et al. 2018 Geha et al. 2017

Motivates satellite searches around MW-analogs

Crnojevic et al. 2016 Smercina et al. 2017 Romanowsky et al. 2017

A Subaru HSC Survey of M94’s Satellites

• M94: An isolated MW-mass galaxy

§ Mass: M* ~ 4×1010 M⊙ § Distance: 4.2 Mpc

• 6 pointings with HSC (g-band)

§ ~150 kpc radial coverage in g-band § Discovered 2 low-mass satellites

A Lonely Giant: The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina

There are only 2 satellites >4×105 M⊙!

50 kpc Deep Deep 50 kpc Deep Deep

Dw2 Dw1

5 kpc 5 kpc

−60 −40 −20 20 40 60

∆α (arcsec)

−60 −40 −20 20 40 60

∆δ (arcsec)

−1 1 2

(g − r)0

24.5 25 25.5 26

r0

M94-Dw1

−60 −40 −20 20 40 60

∆α (arcsec)

−60 −40 −20 20 40 60

∆δ (arcsec)

−1 1 2

(g − r)0

24.5 25 25.5 26

r0

M94-Dw1

−30 −20 −10 10 20 30

∆α (arcsec)

−30 −20 −10 10 20 30

∆δ (arcsec)

−1 1 2

(g − r)0

24.5 25 25.5 26

r0

M94-Dw2

−30 −20 −10 10 20 30

∆α (arcsec)

−30 −20 −10 10 20 30

∆δ (arcsec)

−1 1 2

(g − r)0

24.5 25 25.5 26

r0

M94-Dw2

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

0.01

P Most Massive Satellite

6 7 8 9 10 11

log10 M? (M)

100 101

Nsat(>M?)

0.05

P

10 20 30 40

Standard

Halo Occup. Nsat(4⇥105M)

M94’s satellite population is very unlikely in a ‘Standard’ Halo Occupation Context

−20 −18 −16 −14 −12 −10

MV

100 101

N(<MV )

Cen A (Crnojevi´ c + 18) MW (McConnachie + 12) M31 (McConnachie + 12) M81 (Karachentsev& Kudrya 14) M101 (Bennet + 19) M94 (Smercina + 18)

Known galaxies EAGLE (Halo Occupation) <0.2% in 1500 galaxies! No most massive satellites ≤106 M☉ FIRE

(Garrison-Kimmel+19)

A ‘Stochastic’ Halo Occupation model produces M94-like systems much more frequently

0.01

P Most Massive Satellite

6 7 8 9 10 11

log10 M? (M)

100 101

Nsat(>M?)

MW M31 M81 M101 M94 M-II, Med. M-II, 50% M-II, 90% M-II, 99%

0.1

P

10 20 30 40

Stochastic

Halo Occup. Nsat(4⇥105M)

~4-5% in 1500 galaxies

Some systems have a most massive satellites ≤106 M☉

Missing Satellites Too Big to Fail Galaxy formation at ALL dwarf-galaxy scales may be much more stochastic

M94’s Sparse Satellite System suggests that galaxy formation is surprisingly stochastic for <1011 M☉ halos

M94’s Satellites

MW-mass galaxies have large scatter in their # of satellites Scatter from best current simulations is much lower! M94 lacks any satellite >106 M☉ Large scatter may persist for halos >1010 à the TBTF mass

A Lonely Giant: The Sparse Satellite Population of M94 Challenges Galaxy Formation Adam Smercina