Massive galaxies are unique for both cosmology and galaxy formation. Here we summarize recent results on the assembly of massive galaxies and their galaxy-halo connections using the deep images from the ambitious Hyper Suprime-Cam Survey.

1. Song Huang 黄崧
(UCSC, Kavli-IPMU
https://dr-guangtou.github.io)
and the HSC Collaboration
2017.11.02 Princeton
New Insights on the Stellar Halos of
Massive Galaxies
from the
HSC survey

2. 2
Picture: ESO 325-G004 in Abell S0740 by HST
Cover Model for Galaxy Formation since 1998
Picture: Cluster CL1358+62 by HST

3. “Compaction”/
Fast Quenching
Phase-I:
Intense Dissipation
Phase-II:
Minor/Major Mergers
Massive Ellipticals at Low Redshift
Inner: Dominated by
in situ stars
Outer: Dominated by “ex situ”
stars in the last 8-10 Gyrs

4. 4
Galaxy-Halo Connection at High-M* End
Leauthaud et al. (2012)Stellar Mass
HaloMass(M200b)M200b/Mstar
What’s the best definition
of stellar mass to study
galaxy-halo connection?
Tal et al. (2011)
LRGs @ z~0.4
Stacking SDSS images

5. 5

6. 6
HSC
SDSS
z~0.19 z~0.30 z~0.37
20” 20” 20”
Why Do We Need HSC?
• Average i-band seeing 0.6”
• i-band surface brightness limit:
~28.5 mag/arcsec2
• Huang et al. (2017c, PASJ Special Issue)

7. How does the Assembly of Stellar Halos Depend on
Stellar Mass ?
Does the Assembly of the Stellar Halo Depend on
Dark Matter Halo Mass (Environment) ?
Definition and Measurement of Stellar Mass
(and its Implications)

8. Part I:
How does the Assembly of Stellar Halos
Depend on Stellar Mass ?

9. Photometry of Massive Galaxies using HSC
•Large sample of massive galaxies
with spectroscopic redshift at
0.3<z<0.5.
•Estimate average M/L using 5-
band SED fitting (Chabrier IMF).
•Empirically correct the
background
•Build our own pipeline to detect
and mask surrounding objects.
Huang+ 2017a
Mask for Ellipse
/399

10. 10
PSF
100 kpc
Extracting of 1-D Mass Density Profiles
We also measure radial profiles for the isophotal shapes
Huang+ 2017a

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The scatter
is intrinsic!
Huang+ 2017a
Stellar Halos are NOT Self-Similar

12. 12
Redshift Evolution of the Extended Stellar Halo
30 kpc
Patel et al. (2013)
z~1.4

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Massive BCGs at Redshift = 1.1
140 kpc
Liu et al. (2013)
XDF

14. Rodriguez-Gomez+ (2016)
Qu+ 2017 EAGLE
FractionofEx-situComponents
/3914
Fraction of “Ex-situ” Stars

15. D’Souza+ (2014)
see also Huang+ (2013)
Stacked SDSS images
High-concentration
Galaxies
Based-on 3 Sersic
Fitting
log(Stellar Mass)
However, observational constraints are difficult…
Merritt+ (2017)
see also Harmsen+ (2017)
Dragonfly Nearby
Galaxy Survey
FractionofOuterComponent
Stellar Mass
Fraction of “Ex-situ” Stars

16. 10 kpc
100 kpc
Rodriguez-Gomez+
(2016)
Mass within 10 kpc:
Proxy of mass formed in-situ at
high redshift
Mass within 100 kpc:
Proxy of the “total stellar mass”
Better than cModel and single-Sersic

17. FAKE NEWS !
Huang+ 2017a /3917
FractionofExSituStars
Similar for
Illustris-TNG
Pillepich+2017
Fraction of “Ex-situ” Stars

18. 18
10 kpc
100 kpc Similar Stellar Mass within 10 Kpc

19. Difference in logM100 = 0.5 dex = a factor of 3
Similar Stellar Mass within 10 Kpc

20. NO Stacking!
Huang+ 2017a /3920
Shape of the Stellar Halo

21. 21
Shape of the Stellar Halo
Oh et al. (2017)
Huang et al. (2013)
2-D Dev+Exp Fitting

22. 22
Shape of the Stellar Halo
Oblate
Prolate
Li et al. (2016, 2017)

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Shape of the Stellar Halo
Wang et al. (2008)
Satellites align with the
central galaxy and the
dark matter halo
Also see Shin et al. (2017);
van Uitert et al. (2017);
Kang et al. (2007) etc.

24. Part II:
Does the Stellar Halo Depend on Dark Matter
Halo Mass?

25. Huertas-Company+2013
Does Size Depend on Environment ?
Shankar et al. (2014)
Allen et al. (2015)
Yes
No
z ⇠ 0.0 z 0
Nair et al. (2010) Kelkar et al. (2015)
Delaye et al. (2014)
Papovich et al. (2012)
/3925

26. Central Galaxies in Cluster-level Halos
BCGs of redMaPPer Clusters with λ>30 at 0.3<z<0.5
Rykoff et al. 2014; Rozo et al. 2015
cenHighMh
M200c 1.4 ⇥ 1014
M
Also see Baxter et al. (2016); Simet et al. (2016)
Farahi et al. (2016)
RedMaPPer Richness
HaloMass(M200c)

27. Massive galaxies at 0.3<z<0.5 that are NOT in clusters
(Cluster members removed)
cenLowMh
fSatellites  0.2
van Uitert et al. (2016)
Stellar Mass
FractionofSatellite
Central Galaxies in Less Mass Halos
/3927

28. Structure v.s. Environment (Halo Mass)
Huang+ in prep.
Subtle but
Systematic
Differences
Huang+ 2017b
Matched in
M100 kpc and
Redshift
/3928

29. Mass-Size Relation and Environment
Huang+ 2017b
More Massive
Halos
Less Massive
Halos
/3929

30. Much more
extended
outer halo
Huang+ 2017b
Matched in
M10 kpc and
Redshift
/3930
Structure v.s. Environment (Halo Mass)

31. MHalo, M100 kpc, and M10 kpc
Huang+ 2017b
More Massive
Halos
Less Massive
Halos
/3931

32. Red: High Mass Halo
Grey: Low Mass Halo
MassiveBlack-II
MassiveBlack-II
Huang+ in prep.
Khandai+2015
LOESS
Smooth
Michelle Cappellari
Color
Indicates
Halo
Mass
Preliminary
MHalo, M100 kpc, and M10 kpc
Also see in
UniverseMachine
(Behroozi+
in prep)

33. Part III:
Definition and Measurements of Stellar Mass

34. Deep 1-D profile
is better than CModel
or single-Sersic models
Huang+ 2017a
Does not depend on the SED fitting process
/3934
Measurements of “Total” Stellar Mass

35. 35
GAMA: Single-Sersic fit to
SDSS r-band image
Kelvin et al. (2012, 2014)
Comparison with Single-Sersic Model

36. 11.4 11.6 11.8 12.0
log (M?/M ) (HSC)
6.0
5.5
5.0
4.5
4.0
3.5dN/d?[Mpc3
dex1
]
hscMassive; cModel
11.4 11.6 11.8 12.0
log (M?/M ) (HSC)
6.0
5.5
5.0
4.5
4.0
3.5dN/dlogM?[Mpc3
dex1
]
hscMassive; cModel
hscMassive; 100 kpc
MassIncomplete
/3936
11.4 11.6 11.8 12.0
log (M?/M ) (HSC)
6.0
5.5
5.0
4.5
4.0
3.5dN/dlogM?[Mpc3
dex1
]
hscMassive; cModel
hscMassive; 100 kpc
hscMassive; Max
Additional
0.02-0.05 dex
Huang+ 2017a
Impacts on Stellar Mass Function

37. Huang+ 2017a /3937
Impacts on Stellar Mass Function

38. Huang + in prep.
Ignore the
crazy halo mass
value here…
Scatter of SHMR Introduced by Mass Measurement

39. 39
HSC
SDSS
0.19 z~0.30 z~0.37 z~0.44
20” 20” 20”

40. Future Directions
❖ Comparison with Hydro-simulations (with Felipe Arbilla)
❖ Intrinsic and observed scatter of SMHR (with Christopher Bradshaw)
❖ Better 2-D photometric models for massive galaxies (with Rajdipa
Chowdhury and Dane Cross)
❖ Forward modeling the M100kpc-M10kpc-Mhalo relations with help from
the UniverseMachine model (Peter Behroozi, Andrew Hearin)
❖ Better “cluster finder” using just properties of central galaxies
❖ Radial variation of isophote shapes and the intrinsic shape of
stellar halos
HSC Discussion Next Thursday !

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Thank You Very Much !