Eﬀects of X-ray Emitting Hot
Plasmas on the Galaxy Evolution
Kazuo Makishima
Senior Aﬃliate Member, Kavli IPMU
Prof. Emeritus, Dept. Physics, Univ. Tokyo
OB and Visiting Member at RIKEN

X-ray emitting plasma (ICM=Intra Cluster Medium),
more massive than galaxies, may provide a major
origin of the environmental eﬀects(1) Makishima+01, PASJ 53, 401 (2) Takahashi+09, ApJ 701, 377(3) Gu+13 ApJ 767, id. 157(4) Gu+16 ApJ 826, id. 72(5) Gu, Makishima, & Kawaharada, in prep.
2019/06/07

Galaxy Evolution WS 20191Hereafter
CLG

1. Introduction

PhD Thesis, Rukumani Vijayaraghavan (2015 U. Illinois)“Clusters of galaxies are harsh environments for theirconstituent galaxies. A variety of physical processes
eﬀective in these dense environments transform gasrich, spiral, star-forming galaxies to elliptical orOver tH, a galaxy
spheroidal galaxies with very little gas.”“sweeps” an ICM
mass comparable
to its own mass
100 kpc
Temperaturemaps of ICM
in a simulated
young CLG(Vijayaraghavan
500 kpc+Ricker 2017)2019/06/07

Galaxy Evolution WS 201922. There are no Cooling Flows!
² ASCA (1993~2001)：The worldsʼ ﬁrst X-ray imaging
spectroscopy mission in a broad (0.3~10 keV) band.
² Contrary to the group hypnosis (集団催眠) of Cooling
Flow picture, ICM at the CLG center was not coolingbelow kT~1 keV (Makishima+01, PASJ )The emperor’s
new clothes² The ICM is heated by some mechanism.
² Moving galʼs strongly interact with
the ICM, and create turbulence.
² The turbulence is dissipated as
ICM entropy, which stops CFs.
² Galʼs thus loose dynamical energy,
and fall to the CLG bottom on ~tH.
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Galaxy Evolution WS 2019

劇団四季「はだかの王様」

台本は寺山修司

3

3. How Galaxies interacts with ICM• ICM, in-ﬂowing with velocity v,exerts ram pressure to ISM.
• If it is mild, ISM is displaced
by xR (Roediger +2015).
• By gravity, the displaced ISM
pulls the whole galaxy.

galaxyISM
xR

ICM ﬂowRx〜0.5 (γ/0.01)-1 (R/10kpc)4 (ne/10-3) (Mg/1011M0)-2 (v/108)2

fractional
ISM massICM
densitygalaxymass

in-ﬂow
velocity• When x<1, ISM is bound, and keep interacting.
• Even an elliptical galaxy (γ~0.01) can interact
with the in-ﬂowing ICM and create ICM turbulence.
• Dynamical friction provides additional interaction.
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Galaxy Evolution WS 20194

4. Cosmological Galaxy Infall
Using two samples, the optical/X-ray angular extent
ratios of CLGs were studied for its evolution.

Sample I: selected 34 relaxed CLGs
² Over z=0.08 〜0.89² Optical: Own data with UH88 multi-band photo² X-ray: Archives from Chandra ＆ XMM-Newton² Gu,..Kodama, Shimasaku, KM+13, ApJ 767, 157

Sample II: 340 relaxed CLGs
² over z=0.01 〜 0.50
² Optical: SDSS, partially spectroscopic² X-ray: the same as above² Gu, Makishima +16, ApJ, 826, id 72
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Galaxy Evolution WS 20195

Gal. number/ICM mass

2D integ. gal. num./ 2D integ. ICM mass

Sample Iz = 0.4-0.89
z = 0.22-0.45
z = 0.08-0.22

normalized
to 1.0Sample II

Various sys.
biases havebeen carefully
evaluated,and foundinsigniﬁcant.

z = 0.22-0.5
z = 0.08-0.22
z = 0-0.08

Normalized Radius Relative to ICM, galʼs havebeen falling to the center!

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Galaxy Evolution WS 20196

5. Mild ICM Turbulence
Hitomi results on the Perseus CLG: The ICM turbulenceis subsonic, σ=160 km/s 〜s/5, and rather uniform
over the central ~100 kpc (Hitomi collaboration 2017).

dyn. energyof galaxies

ICM
turbulence
M. F.
ampliﬁcation

thermalizationion
tc
enecon

ICM heating
acceleraionr² This view can provide a suﬃcient ICM heating luminosity
over tH, and explain the Hitomi results (Gu, KM+in prep.).
² A contrasting view of “turbulence/heating due to AGN jets”
fails to explain the Hitomi results.

² The overall process should signiﬁcantly aﬀect thegalaxy evolution, and drive the environmental eﬀects !
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6. A Lesson (教訓)
Optical astronomers
considered only galaxies,
neglecting the dense
plasma environment.

X-ray astrophysicists
considered only ICM,
neglecting the role ofmoving galaxies.

Because of insuﬃcient interactions between thetwo communities, the important subject of galaxy
vs. ICM interaction remained unexplored.
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Galaxy Evolution WS 20198

7. Conclusion
The galaxy-ICM interaction scenario can explain:
1. The ICM heating mechanism to stop Cooling Flows.
2. The observed cosmological (z~1 to 0) galaxy in-fall.
3. Distributions in z~0 clusters: Gals＜DM＜ICM~metals.
4. The subsonic and uniform turbulence in Perseus.

The scenario will also explain the environmental
eﬀects, via gas removal and “quenching”.
In order to explore this novel possibility, enhanced
interactions are highly encouraged between theoptical and X-ray communities.
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Galaxy Evolution WS 20199