Globular Clusters as Tracers of Stellar and Dark Halos Asher - - PowerPoint PPT Presentation

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Feb 25, 2023 316 likes •527 views

Globular Clusters as Tracers of Stellar and Dark Halos Asher Wasserman University of California - Santa Cruz in collaboration with Jean Brodie, Aaron Romanowsky, Duncan Forbes, Adebusola Alabi, Alexa Villaume, and the SLUGGS survey

SLIDE 1

Globular Clusters as Tracers

f Stellar and Dark Halos

Asher Wasserman

University of California - Santa Cruz

in collaboration with Jean Brodie, Aaron Romanowsky, Duncan Forbes, Adebusola Alabi, Alexa Villaume, and the SLUGGS survey collaboration

SLIDE 2

Why study extragalactic globular clusters (GCs)?

If we want to spectroscopically study galactic outskirts much beyond ~ 2 Re, we should look beyond the extent of the stellar light.

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 3

Why study extragalactic globular clusters (GCs)?

If we want to spectroscopically study galactic outskirts much beyond ~ 2 Re, we should look beyond the extent of the stellar light.

~50 kpc

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 4

~50 kpc Observability:

GCs are bright and

compact

Can get radial

velocities of GCs out to ≲ 30 Mpc in ~2 hours on 10 m telescope

SLIDE 5

Sizes of GC systems

Re,GC ~ 2 Re,*

Data from Forbes 2017d

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 6

GCs as dynamical tracers of dark matter (DM)

GCs probe where DM dominates the potential.

“Typical” mass model: log M* = 11, log Mh = 13

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 7

GCs as tracers of accretion

Volume density r / rhalf

In-situ Ex-situ 2 rhalf

GCs, particularly the blue subpopulation, may be good tracers of the accretion history of galaxies Surface density

10 kpc 100 kpc

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

Rodriguez-Gomez+2016 Wasserman+2018 (submitted)

SLIDE 8

SLUGGS Survey

SAGES Legacy Unifying Galaxies and GlobularS -- Brodie+2014

Representative sample of 25 elliptical/lenticular galaxies out to

~30 Mpc

Keck/DEIMOS spectroscopy of GCs and integrated starlight

○ Use Calcium Triplet absorption lines at 8498, 8542 and 8662 Å ○ 1.5 Å resolution (σ ~23 km/s)

Publicly released GC radial velocities

○ Forbes+2017d ○ http://sluggs.swin.edu.au

Stellar kinematics

○ Foster+2016

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 9

SLUGGS Survey

DEIMOS as a wide-field IFU

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 10

SLUGGS Survey: GC and stellar kinematics

Stellar kinematics from Foster+2016 GC kinematics from Forbes+2017b

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 11

SLUGGS Survey: DM fractions

Alabi+2017 Tracer Mass Estimators MDM / Mtot within outermost kinematic tracer Lovell+2018, submitted (note: != arXiv:1801.10170) Comparison with IllustrisTNG, aperture definition matters!

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 12

SLUGGS Survey: DM fractions

Alabi+2017 Tracer Mass Estimators MDM / Mtot within outermost kinematic tracer Lovell+2018, submitted (note: != arXiv:1801.10170) Comparison with IllustrisTNG, aperture definition matters!

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 13

SLUGGS Survey: GC-DM connection

Forbes+2016
DM halo mass closely follows

the blue (accreted) GC population mass.

See also El-Badry+2018

Forbes+2016, with updates from Busola Alabi

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 14

SLUGGS Survey: Multi-population Jeans Modeling

Wasserman+2018 (submitted, arXiv:1712.01229) See also Napolitano+2014 , Pota+2015, Zhu+2016, Oldham & Auger 2016 Mitigating the mass-anisotropy degeneracy: Three tracers in the same potential with different orbital anisotropy and spatial density.

β = 1 - σ2

tan / σ2 rad

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 15

NGC 1407: DM density slope

γ = -d(log ρ) / d(log r) as r -> 0 γ ~ 1 = NFW γ c200 log M200

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 16

NGC 1407: Halo anisotropy

Expectation of radial bias (β > 0)
Evidence for a diversity of stellar

halo anisotropy?

βred ~ 0.4 (radially-biased orbits)
βblue ≲ -4 (tangentially-biased
rbits)

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 17

NGC 1407: Halo anisotropy

Expectation of radial bias. Evidence for a diversity of orbital anisotropy?

Amorisco 2018a

log Msat / Mhost

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

NGC 1407 from Wasserman+2018 (submitted) NGC 5846 from Zhu+2014 M87 from Li & Zhu (in prep), see Ling Zhu’s slides!

tangential radial radial tangential

SLIDE 18

Future work

SLUGGS GC probabilistic photometric catalogs

○ Better contamination modeling, assigning probabilities to point sources based on color, magnitude, and galactocentric distance

Orbital Anisotropy of SLUGGS galaxies
Hierarchical dynamical modeling of massive slow-rotators

○ Using Jeans models which can inform and be informed by galaxy/halo scaling relations

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018

SLIDE 19

Summary

1. GCs offer the opportunity to study stellar & dark matter halos of galaxies beyond the Local Group on spatial scales which are difficult to probe in integrated stellar light. 2. Modeling multiple tracer populations (metal-rich GCs, metal-poor GCs, field stars) help mitigate the mass-anisotropy degeneracy. 3. There is evidence for a mysterious diversity of halo orbital anisotropy.

Asher Wasserman -- Stellar Halos Across the Cosmos -- 5 July 2018