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 ～ 200 pc of the Milky Way– 5 ｘ 107 M☉ Molecular Gas (several % of

Milky Way)– 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 (4x106 M☉)

– ‘Spectacularly Dark’ Low Luminosity AGN (LLAGN)

– L x< 10-9 Ledd

Moderate SF activity– SFR = 10-2 M☉yr-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☉yr-1 (Yusef-Zadeh+ 2009) @105 yr ago

– cf. present SFR ~ 10-2 M☉yr-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] 3P1-3P0 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 (1049-52

ergs!)– Often has high CO J=3-2/J=1-0 ratio >

1 (~50 %; Nagai PhD Thesis 2008) – Intense [CI] 3P1-3P0 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•Ekin ~ 1053 erg : driven by SN explosions in stellar cluster of > 105 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 >

5x1052 erg– NSN = Ekin/(1051 hSN [erg]) 　 hSN :

conversion efficiency to Ekin

⇒ 　 SFR ~ (0.08 - 0.5) hSN -1

M☉ yr–1

Cf. IR : 0.01 M☉yr-1 (Yusef-Zadeh+ 2009)

　　 @presentIR : 0.14 M☉yr-1 (Yusef-Zadeh+ 2009)

@0.1 Myr agoX-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 103-5 M ☉

• cf. NIR/FIR idensified GC clusters 103-4 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) ⇒

ALMA

Complete List of HVCCs– Statistical Study – How many HVCCs? How much energy? Where they are?

⇒ SFR in the past 10 Myr⇒Formation process of massive clusters ⇒ Counterparts in radio continuum/X-rays

– 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] 3P1-3P0

…

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 mm– IMBHs may have similar time-variable emission

• ~ mJy order?

…. If they really are

in the GC !

?

[CI] 3P1-3P0 Observation

C0 traces :– Chemically Immature Molecular gas– SNR-Molecular Cloud interaction – Cosmic-ray/X-ray ionization rate

[CI] 3P1-3P0 (500 GHz) Survey

Tanaka+ ApJL submitted– Evidence of GMC formation– Gas inflow (bar-driven?)⇒ Cluster Formation in future!

[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