Environmental effects on
massive galaxy formation in a
distant X-ray cluster at z=2.51
Tao Wang (U. Tokyo/NAOJ)

The TAO telescope

Galaxy evolution workshop@IPMU, 2019/06/07

Environmental effects on galaxyformation and evolution

Morphology-density relation (Cappellari+2011)

Increasing quiescent fraction as
increasing local density up to z~2

ZFOURGE survey, Kawinwanichakij+2017

(Minor) Environmental effects on starformation properties of galaxies up to z~2“MAHALO-Subaru” ,Koyama+2013

Indications: the quenching processes must be quite rapid in clusters.Star formation history of massive galaxies

Thomas+2010

The more massive galaxies assembled their masses at earlier times.
Large galaxies die early.

To uncover the role of (densest) environment
in shaping galaxies:

hunting for high-z clustersz~0

The Hubble Space Telescope Treasury
Survey of the Coma Cluster of Galaxies

z~2

JKCS 041@z=1.803
Newman+2014

A large number of protoclusters
at high redshiftz=5.7, Jiang+2018, Nature astronomy

z=2.53, Hayashi+2016

low galaxy densities;
extended structure; not yet collapsed

J1001: A starbursting, X-ray cluster at
z=2.51, the furthest ever known

Wang, T., et al. 2016, ApJ, 828, 56

J1001: A starbursting, X-ray cluster at
z=2.51, the furthest ever known

Wang, T., et al. 2016, ApJ, 828, 56

J1001 bridges the gap between matureclusters and protoclustersz~0z=0z~2.5J1001@z=2.5z~3z=3.1
SMGs
LAEs

Coma Cluster

J1001: presence of both an X-ray
halo and a starbursting core, ideal
laboratory for studying environmental SSA22, Umehata+2015
eﬀects on massive galaxy formation

A census of CO(1-0) in J1001 with JVLA

CO(1-0) detections towards a mass-complete sampleof cluster galaxies
Wang, T., et al. 2018, ApJL, 867, 29

Evidence for strong environmental dependence of(molecular) gas content

Decreasing gas content as decreasing cluster-centric radius
Wang, T., et al. 2018, ApJL, 867, 29

Evidence for strong environmental dependence of(molecular) gas content

Decreasing gas content as decreasing cluster-centric radius
Wang, T., et al. 2018, ApJL, 867, 29

Elevated star formation efficiency (SFE=SFR/M_gas) for galaxies in the cluster center

Environmental effects on the SFR of galaxies are likely delayed comparedto that on the gas content.
The gas depletion time ranges 100 to 400 Myrs, comparable to thedynamical time of the cluster
Wang, T., et al. 2018, ApJL, 867, 29

The physical origin of the rapid
quenching in cluster cores:
tidal and ram pressure stripping at z=2.5?

HST/WFC3 F160W
Contour:CO(1-0)

Wang+2019, in prep

Next:
Radio selection of distant galaxy clusters

Daddi,+Wang,…et al.,+2017, ApJ

Great potential for SKA

Square Kilometer ArrayGreat potential for SKA:
200~2000 clusters like J1001

Summary•

We have discovered the most distant X-ray cluster J1001 at z=2.51 known todate. This structure is unique in the presence of both an X-ray emitting halo
and a starbursting core, bridging the gap between mature clusters andprotoclusters.

•Based on CO(1-0) detections towards a mass-complete sample of member
galaxies in J1001, we have found a strong clustercentric radius dependenceof molecular gas content, with galaxies closer to the cluster core being
increasingly gas-poor.

•Despite their low gas content, galaxies in the cluster center suggest anelevated star formation efficiency, suggesting that the effects on the SFR are
likely delayed compared to that on the gas content.

•Future wide-field, deep radio continuum surveys with SKA could help to reveal
thousands of similar clusters at high redshifts, which will revolutionize the fieldon both galaxy formation and cosmology.