Exploring Galaxy Proto-Cluster Cores
at z ~ 2
6th Galaxy Evolution Workshop @IPMU (2019.6.6)

Makoto Ando
(M2 student, Dept. of Astronomy, UTokyo)

Kazuhiro Shimasaku (UTokyo)

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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Contents(1) Introduction(2) Data & Method(3) Result & Dark Halo Mass Estimation(4) Member Galaxies

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)2(1) Introduction✦Galaxy Clusters• most massive system in the universe

Galaxy Cluster(Abell 1689)• member galaxies:- quiescent galaxies- elliptical galaxies- top-heavy stellar mass function
https://www.spacetelescope.org➡ How and when did these properties appear?
➡ need to search for the high-z counterpart: proto-cluster

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)3(1) Introduction✦Growth of Galaxy Clusters

based on Chiang+17
proto-matured-presentpastz• Growth of cluster -> host dark matter halo(DMH) growth.
✓cluster DMH mass: MDH 1014 M✓At high-z, whole structure have not collapsed yet.
✓Central DMH have already collapsed:➡ proto-cluster core

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

4(1) Introduction✦Growth of Galaxy Clusters

based on Chiang+17
proto-matured-presentMiller+18

Wang+16

pastz✦Proto-Cluster Core
•most massive DMHs
•active SF / BCG formation?
•core sample is still limited➡ systematic searchz~4z~2.5

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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z=0

M⇤ vs MD(1) Introduction - outlineM⇤z∼2cluster

1 ⇥ 1011 Mcore
MDH ⇠ 1 ⇥ 1014 MMDH ⇠ 2 3 ⇥ 1013 M
rvirial ⇠ 0.3 Mpc

Behroozi+13

M⇤ vs MDH

pair: multiple system of very massive galaxies

clustering-based mass estimation➡conﬁrming “core” candidates

Properties of member galaxies
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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Contents(1) Introduction(2) Data & Method(3) Result & Dark Halo Mass Estimation(4) Member Galaxies

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(2) Data & Method - samples✦Data- COSMOS 2015 catalog (Laigle et al. 2016)✓photo-z catalog
footprint✓stellar mass
✓Passive/SF classiﬁcation(UVJ)✦Subsample1 (massive galaxy)- redshift: 1.5  zphot  3.0- stellar mass: Mstar 1011 M- total: 1745 galaxies✦Subsample2- redshift: 1.25  zphot  3.25g(M⇤ /M) < 11.0 / mag(Ks)  24
- mag(Ks):(3sigma lim. of catalog)

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

8(2) Data & Method - “Pair” ﬁnding method✦Finding Massive Galaxy Pair
(1) Pick up one galaxy and count neighbors within:✓✓  2 ⇥ 2500 ⇠ 2 ⇥ 0.2 Mpc (z ⇠ 2)core size✓z  0.12z uncertainty(2) All neighbors are regarded as core members.
(3) 3D position of core = average position of member galaxies.

corecz

an✓
didz
atX

2⇥

ezsky

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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Contents(1) Introduction(2) Data & Method(3) Result- Core candidates- DMH mass estimation(4) Member Galaxies

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

10(2) Result

sample galaxies

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)11(2) Result

139 core candidates

N =2: 114
N>=3: 25
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(3) DH Mass Estimation✦ clustering analysis
They can- cross-correlation between core and galaxies
withgrow- 10.2 < log(M⇤ /M ) < 11.0 / mag(Ks)  24 into cluster!

!(✓)

CCF

tracerMass Growth(EPS model, code by T. Hamana)

ACF✓ [arcsec]
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MDH = 2.36+0.66
⇥10M
0.58
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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Contents(1) Introduction(2) Data & Massive Galaxy Pair
(3) Dark Halo Mass Estimation(4) Member Galaxies- Stellar Mass Function- Passive Fraction- QSO distribution

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(4) Member Galaxies - ﬁeld subtraction

core + ﬁeld

core position
core only

ﬁeld

random points(1) Stellar Mass Function(2) Passive Fraction

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(4) Member Galaxies - Stellar Mass Function

core✦core member galaxy✓top-heavy SMF- early formation ofmassive galaxies

ﬁeld- disruption and merger of
low-mass galaxies✓consistent with simulation(e.g. Muldrew+18)

core/ﬁeld
top-heavy
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(4) Member Galaxies - Passive Fraction
1.5 < z < 2.0

Npassive /Ntotal

whole mass range✓core: 16%✓ﬁeld: 5%✓3 times higher passive fraction (due to environmental eﬀect?)- core galaxies experience earlier quenching?
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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(4) Member Galaxies - QSO distribution

cores with QSO: 1/139 ( < 0.3 Mpc )8/139 ( < 1.0 Mpc )z✓zzskyz  0.12

Milliquas v6.0 2019 update, Flesch+15
6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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Summary• We have identiﬁed 139 galaxy proto-cluster cores using pairs of very
massive galaxies as tracers.
• Their viral masses are high enough to grow into present-day clusters.
• Core galaxies have✓Top-heavy SMF.
✓3 times higher passive fraction
than ﬁeld ones.
• Only one core harbors a QSO.

6th Galaxy Evolution Workshop @IPMU (2019.6.6) by Makoto Ando(UTokyo)

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