CO J 10 J 32 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 ISASJAXA3 KEK 4 Joint Alma Office ID: 762814
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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 ProjectWhat we can do with a Large Aperture Sub-mm Telescope
Central Molecula r Zone (CMZ) CMZ : Central ～ 200 pc of the Milky Way 5 ｘ 10 7 M ☉ Molecular Gas (several % of Milky Way)3 Most Massive Stellar ClustersThe Most Active Star Formation SiteSupermassive 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 L eddModerate SF activity SFR = 10 -2 M ☉ yr -1 (Yusef-Zadeh+ 2009)SFE = 10-8~-9 yr-1cf. 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) @10 5 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+2007HCN J=4-3 Survey (2010-)[CI] 3 P1-3P0 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] 3P1-3 P0 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 > 5x1052 ergNSN = Ekin/(1051 hSN [erg]) hSN : conversion efficiency to E kin ⇒ SFR ~ (0.08 - 0.5) h SN -1 M☉ yr–1Cf. 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 BubblesMost energetic HVCCs may be remnant of clusters with mass 103-5 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) ⇒ ALMAComplete List of HVCCsStatistical 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 pcWe 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 mmIMBHs may have similar time-variable emission ~ mJy order? …. If they really are in the GC ! ?
[CI] 3P1 -3P0 Observation C0 traces :Chemically Immature Molecular gasSNR-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?) ⇒ Cluster Formation in future! [CI]-excess
Conclusions GC survey in the Submillimeter is still important SF in the past, at present and in futureEvolution of Sgr A* Singledish Telescope is necessary for the GC surveyMultibeam Heterodyne Receiver230, 350, 500 GHz