Millimeter-Wave Molecular Line Observations of the Galactic Circumnuclear Disk

Shunya TakekawaT. Oka, K. Tanaka, K. Miura, H. Suzuta

Keio University

Rotating velocity: ~110 km/sDensity: ~104–6 cm–3

Mass: ~104–5 M☉

The entity of the CND is possibly an infalling disk with a diameter of 10 pc(e.g. Oka et al. 2011)

contour: 5 GHz continuum

The Galactic Circumnuclear Disk

2 pc radius ring

(CND)HCN 1–0

blue shift (VLSR= –80 – –110 km/s)

Rotating velocity: ~110 km/sDensity: ~104–6 cm–3

Mass: ~104–5 M☉

The entity of the CND is possibly an infalling disk with a diameter of 10 pc(e.g. Oka et al. 2011)

contour: 5 GHz continuum

The Galactic Circumnuclear Disk

2 pc radius ring

(CND)HCN 1–0

red shift (VLSR=+80 – +110 km/s)

Single-dish obs.CO 1–0(Serabyn et al. 1986)

~ 10 pcSgr A*

mostly neglected!

The Galactic Circumnuclear Disk

• How is the CND affected by nuclear activities?

• How does the CND feed the nucleus?

• How was the CND formed?

• How is the physical condition?

etc…

The Galactic Circumnuclear Disk

In order to answer these questions, it is essential to reveal the accurate

distribution.

The Galactic Circumnuclear Disk

In order to answer these questions, it is essential to reveal the accurate

distribution.SINGLE DISH! ASTE 10 m

NRO 45 m

The Galactic Circumnuclear Disk

In order to answer these questions, it is essential to reveal the accurate

distribution.SINGLE DISH! appropriate tracer +ASTE 10 m

NRO 45 m

To search appropriate tracers of the CND,

We conducted 3 mm band spectral line surveystoward the CND and Sgr A* with the NRO 45 m.

(Takekawa et al. 2014)

TZ1 receiver + SAM45frequency : 81 – 116 GHzresolution : 15” –19”

50 lines were detected

We classified the detected lines into three types:– CND-type: mainly trace the CND – GMC-type: mainly trace the GMCs

(50 km/s and 20 km/s clouds)

– HBD-type: hybrid between the CND- and GMC-types

We classified the detected lines into three types:– CND-type: mainly trace the CND – GMC-type: mainly trace the GMCs

(50 km/s and 20 km/s clouds)

– HBD-type: hybrid between the CND- and GMC-types

HCO+

HCN

SiO CNH13CO+

H13CN

N2H+

CH3OHHC3N

CSSO

C2Hc-C3H2

We classified the detected lines into three types:– CND-type: mainly trace the CND – GMC-type: mainly trace the GMCs

(50 km/s and 20 km/s clouds)

– HBD-type: hybrid between the CND- and GMC-types

HCO+

HCN

SiO CNH13CO+

H13CN

N2H+

CH3OHHC3N

CSSO

C2Hc-C3H2

OTF mapping of the CND

The OTF mapping of the CND with the NRO 45 m

• date: 2014/2/5 – 2/12, 3/28 – 3/30 (33 hr) • line: HCN 1–0, HCO+ 1–0, SiO 2–1, CS 2–1, etc…

• mapping range: 6’×6’

• angular resolution: ~19” • receiver: TZ1 H/V

• spectrometer: SAM45– bandwidth: 1 GHz

(resolution: 244.14 kHz)

ResultHCN 1–0 integrated intensity map

2-pc ringNegative Longitude Extension

+50 km/s cloud+20 km/s cloud

The velocity structureVLSR= –150 〜 +150 km/s

HCN 1–0

The velocity structureVLSR= –150 〜 +150 km/s –150 〜 – 20 km/s, +80 〜 +150 km/s

HCN 1–0 HCN 1–0

C1 cloud and Negative Longitude Extension (NLE)

–150 〜 – 20 km/s, +80 〜 +150 km/sVLSR= –150 〜 – 20km/s

HCN 1–0 HCN 1–0

C1 cloud and Negative Longitude Extension (NLE)

–150 〜 – 20 km/s, +80 〜 +150 km/sVLSR= –150 〜 – 20km/s

first reported in Oka et al. 2011

HCN 1–0 HCN 1–0mostly neglected in recent studies!

New discovery 1

A velocity structure of the C1 cloudVLSR= –150 〜 – 20km/s

HCN 1–0

New discovery 1

A velocity structure of the C1 cloudVLSR= –150 〜 – 20km/s

VLSR= –150 〜 – 20km/s

HCN 1–0

CS 2–1

New discovery 1

A velocity structure of the C1 cloudVLSR= –150 〜 – 20km/s

VLSR= –150 〜 – 20km/s

HCN 1–0

CS 2–1

The C1 cloud is associated with the CND!

CND

CND

C1 cloud

C1 cloud

New discovery 1

New discovery 2

A streamer from the +20 km/s cloud to the CNDVLSR= –150 〜 – 20km/s

VLSR= –150 〜 – 20km/s

HCN 1–0

CS 2–1

New discovery 2

A streamer from the +20 km/s cloud to the CNDVLSR= –150 〜 – 20km/s

VLSR= –150 〜 – 20km/s

HCN 1–0

CS 2–1

+20 km/s cloud

+20 km/s cloud

CND

CND

New discovery 2

A streamer from the +20 km/s cloud to the CNDVLSR= –40 〜 +10km/s

CS 2–1

+20 km/s cloud

CND

New discovery 2

A streamer from the +20 km/s cloud to the CNDVLSR= –40 〜 +10km/s

CS 2–1

+20 km/s cloud

CND

A streamer feeding the CND from the +20 km/s cloud

New discovery 2

CND

A streamer from the +20 km/s cloud to the CNDVLSR= –40 〜 +10km/s

CS 2–1

+20 km/s cloud

★

The +20 km/s cloud may be feeding the CND through the NLE

A possible scheme of the central environment seen from the Galactic north pole

+50 km/s cloud

molecular ridge +20 km/s cloud

to observer

2-pc ring

NLE

streamer

CND

New discovery 2

ConclusionWe found that

1. The C1 cloud is associated with the CND2. The +20 km/s cloud may be feeding the CND

through the NLE

Single dish observations are very important for studies of the CND!

HCN 1–0

VLSR= –150 〜 – 20km/sA possible scheme of the central environment

Future works• Detailed analysis

– line ratios– estimation of physical parameters

• We have already obtained the J =4–3 lines of HCN and HCO+ using the ASTE 10 m

• Data reduction of the ASTE observations– We have conducted spectral line surveys

in 330 – 360 GHz band with the ASTE 10 m

HCN 4–3 HCN 1–0

Using the single-dish data, we will make effortsto reveal the actual entity of the CND

Summary• We conducted the OTF mapping

observations of the Galactic CND with the NRO 45 m

• We found that1. The C1 cloud is associated with the

CND2. The +20 km/s cloud may be feeding

the CND through the NLE

• Single dish observations are very importantfor studies of the CND!

HCN 1–0

A possible scheme of the central environment