The Fossil Nuclear Outflow in the Central 30 pc of
the Galactic Center
Pei-Ying Hsieh1,2; Paul T. P. Ho1,3; Chorng-Yuan Hwang2; Yoshito Shimajiri4; Satoki Matsushita1; Patrick Koch1; Daisuke Iono5,61 Academia Sinica Institute of Astronomy and Astrophysics (ASIAA); 2 Institute of Astronomy, National Central University; 3 East Asian Observatory; 4 CEA; 5 National Astronomical Observatory of Japan; 6The Graduate University for Advanced Studies (SOKENDAI)

Hsieh et al. 2015 ApJ , 811, 142; Hsieh et al. 2016 ApJ, accepted (astro-ph->arXiv:1607.03673)

Dense Molecular Gas in the Galactic Center
We present the dense gas maps in the central 30 pc of the0.150
0.150
1.000
Galactic Center (GC). We observed the CS(Ju=5,4,2) lines with
Polar Arc
Polar Arc
0.100
0.100
1.000
the Nobeyama 45m (NRO 45m) and the Caltech Submillimeter
0.800
0.050
0.050
Observatory(CSO)(Hsieh+15,16).
Our
goal
istoobtainreliable
Connecting
Ridge
Connecting Ridge
0.800
Galactic Center Lobe (GCL)
0.000
0.000
maps less affected by the foreground/ambient cold gas in the0.600
Galactic Center Lobe (GCL)
CO0.02-0.02
CO0.02-0.02
GC. We focus on the complex activities and physical conditions-0.050-0.050
0.600
PA
SgrB
0.400
in
the
nuclearregionprobedbythedensegas.
Thearchival
SgrC
20
MCPA
-0.100-0.100
50
MC
SgrA*
20 MC
50 MC
SgrB
0.400
CS(1-0)line
map(Tsuboi+99)
is
also
shown
in
theleft
figures
for
SgrC
0.200
-0.150SgrA*-0.150comparison. We reported a new feature called the connecting
0.200-0.200-0.200ridge (CR) which was detected with the CS(4−3) line. The CR has
0.000-0.250-0.250avelocity
gradientperpendicular
tothedisk
rotation.
Itis
0.000
0.100
0.000
359.900
359.800
359.700
0.100
0.000
359.900
359.800
359.700
CS(J=5-4)
CS(J=4-3)-0.2000.150
0.150
physically associated with the extraplanar polar arc (PA) (Bally
Galactic longitude
Galactic longitude
Polar Arc
Polar Arc
-0.20020 km/s cloud
–22–
0.100
0.100
50 km/s cloud88; Henshaw+16). The PA extends from north of the SgrA* region-0.40020 km/s cloudat a 40 deg and shows a large velocity gradient from (l, b, Vsys)
0.050
0.050
50 km/s cloud-0.400
Connecting Ridge
Connecting Ridge-0.600=(0 , 0.05, 70 km/s) to (0.2, 0.25, 140 km/s) and becomes
0.000
0.000
100 pc-0.600confused with the molecular clouds in the SgrA* region. We findCO0.02-0.02
CO0.02-0.02
100 pc-0.050-0.050-0.800that the kinematic and spatial structures connect the Galactic
0.800
0.400
0.000
359.600
359.200
20MC20MC50
MC50
MC-0.100-0.100-0.800disk, the CR, and the PA. These results suggest that the0.800
0.400
0.000
359.600 359.200
Galactic longitude-0.150-0.150molecular gas might be lifted out of the Galactic plane. We,
Galactic
longitude
Dense Gas and Infrared Emission:CS(1-0)integrated intensity -0.200-0.200thus, propose the idea of a molecular outflow in the central 30
map (Tsuboi+99; contours) overlaid on the MSX E-band map (Pricepcof
theGCandsuggest
thatthePA
ispushedaway,possiblyby-0.250-0.250+01; color). The Galactic Center Lobe (GCL) (e.g., Bland-Hawthorn
0.100
0.000
359.900
359.800
359.700
0.100
0.000
359.900
359.800
359.700
the energy of 8-80 supernovae explosions (Hsieh+15). We also
Longitude (deg)+03, Law+09) is a double-horn feature that straddles the Galactic
Galactic longitude
Galactic longitudeconfirmed
the PA belongs to the eastern protrusion of the GCL.
Plane.
0.30
CS(J=2-1)

Galactic latitude
Galactic latitude

Latitude (deg)Galactic latitude

Galactic latitude

Galactic latitude

Galactic latitude

CS(J=1-0)

Polar arc

Molecular Shell and Bipolar Outflow– 22 –
Shell-Like
Molecular Feature

0.30

0.20

15 pc

CO0.02-0.02

Polar arc

Galactic latitude

Galactic latitude

Galactic latitude

We display the color-composite map of the 0.30
Polar arc
150.20CO0.02-0.02
20-cm (Yusef-Zadeh+04) and the MSX 0.10
E15 pcband 21-µm map (Price+01; Simpson+99, 0.20
CO0.02-0.0207). We compare the low velocity CS(2−1)
line emission (same as left panel) with 0.00
the 0.10 0.10
dust (21 µm) and the emission from freeelectrons (20 cm). The map shows that thelow-velocity gas roughly surrounds -0.10
the 0.00 0.00
GC buble
infrared/radio features. The 21 µmemission shows the prominent Galactic -0.10-0.10GC buble
center bubble (Simpson+07) (GC bubble,-0.20
orGC buble
20 MC50MC
arc bubble in Ponti+15) near the SgrA radio(M-0.13-0.08)(M-0.02-0.07)
-0.20
20 MC
CS(2−1) (Hsieh+16) and CS(1−0) (Tsuboi+99) line emission (contours)
halo/arc. The northern part of the GC
50 MC(M-0.13-0.08)-0.20(M-0.02-0.07)−1
integrated from −10km/s
to
10km/soverlaidonarchival
VLA
20-cm
20 MC
Fig. 3.— Top: CS(J = 2 − 1) line emission (contours) integrated from −10 kms to 10km a radio feature known as -0.30
bubblehasthe50 MC(M-0.13-0.08)
continuum (color).s−1The
resolutionis30′′(1.1pc)forbothimages(blue(M-0.02-0.07)-0.30“radioarc”(e.g.
Serabyn&Guesten
1987;
overlaid on archival VLA 20-cm continuum (color; Jy/beam). Bottom: CS(J = 1 − 0)
circles in lower left corners). The molecular gas associated with theLang+99).
TheGC
bubblecould
beproduced
−1−1
0.4
0.3
0.2
0.1
0.0
359.9
359.8
359.7
359.6
-0.30
line
emission(contours)(Tsuboietal.
1999)
integrated
from−10kms
to10kms
molecular cloud called 20 MC and 50 MC shows an hourglass-shaped
0.4
0.3
0.2
0.1
0.0
359.9
359.8
359.7
359.6
by the starbursts in the past (Simpson+07;
feature (hereafter
HG-feature),
withcontinuum
a northwest-southeast
overlaid
on archival VLA 20-cm
emission (color). The contour Sofuelevels are03).
5, 10,We show the low-velocity CS(J =Galactic
longitude
Galactic longitude
orientation perpendicular
to the Galactic disk, with the openings or2−1)line(bluemap spatially coincides with the0.4 and0.3 GC bubble:
0.20.1 CS(2-1)
0.0
359.9
359.8
Outflow
integrated
20, 30, 40, 50×1.47 K km s−1 for both images. The beam size is 30′′ for bothimages– 24 –radio halo (Pedlar 89; Zhao+14). The HGcavities that surround theinfrared/radio features. The HG-featureintensity map (contours) overlaid
the VLA 20
Galacticonlongitude
circles
inlower
leftcorners).
TheHG-featureismarkedwithcyandots.
Ascalebarof15
feature is marked with cyan dots. The HG-feature has a size of ∼13
seems to surround the warm dust and thecm(blue)
andtheMSX
E-bandmaps(red).
◦pc.
free-electron emission.
pc (=0.11 ) is shown.

The Fossil Nuclear Outflow
DE0archival VLA0.1520-cm continuum (color; Jy/beam). Bottom: CS(J = 1 − CS(J=2−1)
0)Region A−E (average Tmb)

0.2 −1−1ontours) (Tsuboietal.
1999)
integrated
from−10kms
to10
kms
0.10

0.2val VLA 20-cm continuum emission (color). The contour levels are 5, 10,Polar
Arc
0.10.1

Galactic latitude

0.050.00

eft corners). The HG-feature is marked with cyan dots. A scale bar0.0of 15-0.05

own.

CND

Latitude (degree)

Latitude (degree).47 K km s−1 for both images. The beam size is 30′′ for both images (blue ML
B2−0.1

-0.10

ML

0.0

−0.1

50 km/s cloud

0.0

−0.2
-0.20
0.15

0.10

0.05

0.00

359.95 359.90 359.85 359.80 359.75 359.70−0.2
0Velocity (km/s)

4

Tmb (K)
1.0

61.5

02.0

100

Tmb (K)
2 21 00.2

0.2

0.2

0.1

Polar
Arc0.1Polar
western−HG
Arc
0.1−13 km/s cloud

ML0.0

ML

Tmb (K)
34460

B2

B2−0.1

ML0.0−0.2−13 km/s cloud

MLML0.0

B2
CND−0.1−100

B1−1000
0 100
Velocity (km/s)
Velocity (km/s)

1004CS(J=1−0) Region D (average Tmb)

Polar
Arc0.1Polar
Arc

western−HG
MLML

ML

0.0
CND

50 km/s cloud
20 km/s cloud

−0.2

3−0.1

50 km/s cloud 50 km/s cloud

B1

Polar
Arc

ML

CND

−0.1

Tmb (K)210.2

ML

20 km/s cloud

B1

−100

Tmb (K)
0.5

CS(J=2−1)
CS(J=1−0)
RegionRegion
A (averageA−E Tmb)(average Tmb)
CS(J=2−1)
CS(J=1−0)
Region DRegion(averageA (averageTmb) Tmb)

20 km/s cloud-0.15

2Latitude (degree)C

2.0

Latitude (degree)B

1.5

Latitude (degree)A

Tmb (K)
1.0

0.5

Latitude (degree)

S(J = 2 − 1) line emission (contours) integrated from −10 km s−1 to 10 km
0.0

20 km/s cloud
B1

−0.2
−100

−1000
0 100
Velocity (km/s)
Velocity (km/s)

−0.2
100

−1000Velocity (km/s)

100

Galactic longitude

Regions of the latitude-velocity diagrams We analyze the kinematics of the nuclear outflow with the latitude-velocity diagrams (bv-diagrams). We collapse longitudinal planein a cube onto one plane (see left panel). We show the bv-diagrams of the region A-E (averaged from A to E), region A, region D, andpanels)
are shown.
Eachare region
Fig. 5.—(rightRegions madefor the latitude
velocity diagrams
shown in the CS(J = 2 − 1)
the CS(2-1)/CS(1-0) ratios for averaging region A/B and C/D, respectively. The yellow/blue rectangles mark the HG-feature. Thecoversawidthof
2.6′′in longitude. Colorline map. Each region covers a width of 2.6 in longitude. The color map is identical to themap shows the CS(2-1) integrated intensity 50/20 MC are located in the Galactic disk. The PA extends out of the Galactic disk to b~0.23 deg with increasing velocity andone in Figure 1 and the contour image is identical to Figure 3. Regions A, B,C, D, E areto the Galactic disk via the molecular loop ((ML; see Hsieh+15). The B1/B2 labels show the position of an expanding bubble
connectsmap from -197 km/s to 197 km/s and themarked. The central large red cross marks the position of SgrA*. Small black
crosses ofmarkthe Galactic disk. Other known features of the CND and the HVCC CO0.02-0.02 are labeled. We find that the PA can besouthcontour map shows the CS(2-1) map′′
tracedbackto the Galactic disk. This provides clues of the launching point of the PA , roughly 6X10^6 years ago. Implications of thethe HG-feature.
The
spacing
betweenregions
correspondstotheconvolved
beamsizeof30.
integrated form -10 km/s to 10 km/s.
Regions A, B, C, D, E are marked. The dynamical time scale of the PA might be related to the GCL at parsec scale. The bv-diagrams show that the eastern edge of the HGcentral large red cross marks the position feature is associated with expanding bubble B1, ∼7 pc away from SgrA*. The dynamical time scale of bubble B1 is ∼ 3X10^5 years. Theof SgrA*. Small black crosses mark the HG- bubble B1 is interacting with the 50 MC. Part of the molecular gas from the 50 MC was swept away to the bubble B1 to b = −0.2 . Thefeature. The spacing between regions western edge of the HG-feature seems to be the molecular gas entrained from the 20 MC towards the north of the Galactic disk. Our
corresponds to the convolved beam size of results suggest a fossil explosion in the central 30 pc of the GC a few 10^(5-6) years ago. More information please see Hsieh+16.
30′′.
◦