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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– ~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