Galactic Center

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14 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

67 εμφανίσεις

CO
J
=1
-
0 +
J
=3
-
2 map
(Oka+ 1999, 2007)

Galactic Center

Kunihiko Tanaka
(1)
,
Tomoharu Oka
(1)
, Shinji Matsumura
(1)
,
Kazuhisa Kamegai
(2)
, Makoto Nagai
(3)
, Testuo Hasegawa
(4)


(1) Keio University (2) ISAS/JAXA(3) KEK (4) Joint Alma Office

Outline

Galactic Center as Starburst/AGN nucleus


Results of the ASTE Galactic Center Key Science Project


What we can do with a Large Aperture Sub
-
mm Telescope


Central Molecular Zone (CMZ)

CMZ : Central

㈰〠p挠潦 瑨攠䵩Mk礠Way


5


7

M


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3 Most Massive Stellar Clusters


The Most Active Star Formation Site


Supermassive Black Hole (SMBH)


CO
J
=1
-
0 +
J
=3
-
2 map
(Oka+ 1999, 2007)

Massive Compact Clusters in GC

GC is Quiescent

Sgr A
*




Super Massive Black Hole (4x10
6
M

)


‘Spectacularly Dark’



Low Luminosity AGN (LLAGN)


L

x
< 10
-
9

L
edd



Moderate SF activity


SFR = 10
-
2

M


-
1

(Yusef
-
Zadeh+ 2009)


SFE = 10
-
8~
-
9

yr
-
1


cf.

SFE@ Galactic Disk = 5x10
-
9

yr
-
1


Yusef
-
Zadeh+ 2009

GC

Galactic

Disk

Past
Acticity
?


Fermi Bubbles


Past AGN event?
(
Zubovas
+

2011)



Past Starburst
?
(
Crocker
+ 2011
)





Past Starburst?


SFR = 0.14
M


-
1

(Yusef
-
Zadeh+ 2009)

@10
5

yr ago


cf.

present

SFR ~ 10
-
2

M


-
1


Bar
-
driven flow?
(
Binney

1991)

Gas Structure & Kinematics in the GC

Bar
-
Driven Inflow


Starburst?


Herschel
Obs

(Molinari+ 2011)



CMZ is a Twisted
Ellipitical

Ring?

Goals of the GC Key
-
science Project

SF history of the GC



Did starburst took place in the past?


How the physical condition and kinematics of the molecular gas are
related to the SF in the CMZ?


e.g.

Bar
-
Driven Flow



Activity of the Central SMBH Sgr A*


Did Sgr A* burst in the past?


How did the SMBH form?


ASTE observations

CO
J
=3
-
2 Survey (2005


2009)
Oka+ 2007, Nagai+2007



HCN
J
=4
-
3 Survey (2010
-
)



[CI]
3
P
1
-
3
P
0

Survey (2011
-
)
Tanaka+
ApJL

submitted
(
^・
ω
・^
)

KT (1.75 m)

ASTE (10 m)

High Velocity Compact Clouds (HVCCs)

Molecular Clumps with Very Large Velocity Width (~ 100 km s
-
1
)

High Velocity Compact Clouds

HVCCs


~100 HVCCs are in the GC?


Very energetic internal motion (10
49
-
52

ergs!)


Often has high CO
J
=3
-
2/
J
=1
-
0 ratio > 1
(~50 %;
Nagai PhD Thesis 2008
)


Intense [CI]
3
P
1
-
3
P
0

emission
(Tanaka+
ApJL

submitted)


What are the energy sources?


Shocked feature


Dissipating (=

unbound)



Tidal Shear?


Cloud
-
Cloud Collision ?


SN interaction


High Velocity Compact Clouds

HVCCs are often related to Expanding Shells


Multiple Expanding Molecular Shell


E
kin

~ 10
53

erg : driven by SN explosions in stellar cluster of > 10
5

M


Tanaka+2007


Galactic equivalent to ‘Molecular
Superbubbles
’ in the Starburst galaxies ?(NGC253, M82)

Study of HVCCs will tell us :

SF History of the Galactic Center


Cluster formation in the past ( ~ 10
Myr
)


Total Kinetic energy of HVCCs > 5x10
52

erg


N
SN

=
E
kin
/(10
51

h
SN

[erg])


h
SN

: conversion
efficiency to
E
kin





SFR ~ (0.08
-

0.5)
h
SN

-
1

M




1


Cf.

IR : 0.01
M


-
1

(Yusef
-
Zadeh+ 2009)





@p r e s e n t

I R : 0.1 4
M


-
1

(Yusef
-
Zadeh+ 2009)



@0.1
Myr

ago

X
-
ray: (1.1
-
2.1)
M



yr

1



(
Yamauchi+ 1990)



@10
Myr

ago




HVCCs identified in the CO
J
=1
-
0 map

(Matsumura 2011)

HVCCs as wombs of IMBH

Intermediate mass
blackholes

(IMBHs)


Formed in massive stellar clusters
(
Ebisuzaki
+ 2001
)


IMBHs merge to form a SMBH at the nucleus?


IMBH candidates are found in nearby galaxies (Ultra Luminous X
-
ray Objects)


IMBHs may have been formed in the HVCCs or Molecular Bubbles


Most energetic HVCCs may be remnant of clusters with mass 10
3
-
5

M




cf.

NIR/FIR
idensified

GC clusters 10
3
-
4

M




IMBHs of similar mass can be formed.



The formation process of the SMBH may be studied by
observations of HVCCs … ?


Current Problems

Origin of HVCCs


We want direct evidence that they were really created by
SNe
!


Do they have expanding motion?


… or they may be rotating disks around IMBHs


This observation requires high resolution (< 0.1 pc)


䅌䵁


Complete List of HVCCs


Statistical Study


How many HVCCs? How much energy? Where they are?




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䵹M



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-
ra祳


Requires
a survey covering the entire CMZ




Why do we need a Large Aperture Submillimeter
telescope

To

make reliable detection of HVCCs:


High

resolution

(< 1 pc) is required


ASTE resolution @345 GHz


0.7 pc


We have to avoid confusion by the ambient

gas


HCN/HCO
+

line are good tracers


Only small fraction of HVCCs are detectable
with the current ASTE observation.




Deep & high resolution survey


HCN/HCO
+

J
=4
-
3, CS
J
=7
-
6, [CI]
3
P
1
-
3
P
0





ASTE HCN
J
=4
-
3 survey

Correlation between

Clusters and HVCCs ?

How Much Time is Required for the GC survey ?

Impossible with ALMA

Needs better resolution/sensitivity than ASTE

I would be
happy with Multi
-
Beam receiver

IMBHs might be detectable

… ?

IMBHs might be detectable?


Sgr A* often flares up in wide wavelength (radio


X
-
ray)


~

1
Jy

@870
m
m


IMBHs may have similar time
-
variable emission


~
mJy

order?


…. If they really are in the GC !

?

[CI]
3
P
1
-
3
P
0

Observation

C
0

traces :


Chemically Immature Molecular gas


SNR
-
Molecular Cloud interaction


Cosmic
-
ray/X
-
ray ionization rate


[CI]

3
P
1
-
3
P
0

(500 GHz) Survey


Tanaka+
ApJL

submitted


Evidence of GMC formation


Gas inflow (bar
-
driven?)




䍬Cs瑥t⁆潲ma瑩潮 楮 晵瑵f攡


[CI]
-
excess

Conclusions

GC survey in the Submillimeter is still important


SF
in the past, at present and in future


Evolution of Sgr A*





Singledish

Telescope is necessary for the GC survey


Multibeam

Heterodyne Receiver


230, 350, 500 GHz