Molecular Absorption Lines in the Circumnuclear Region

Satoko Sawada-Satoh 澤田-佐藤 聡子 Kagoshima University 鹿児島大学

Background & Motivations

AGN circumnuclear torusFuel tank of mass accretion onto SMBHInvented by astronomers, to explain Seyfert 1 & 2The size : < 10pc

How can we confirm it ?Requirement of 1 milliarcsec (mas) resolution to imageVLBI can acheive it

Urry & Padovani 1995

<10pc

AGN torus/disk & VLBI

1990s mid ~ :A pc-scale masering molecular disk surrounding a SMBH.A pc-scale dense absorbing gas torus.

2000s ~ :A torus model with several physical-phase layers inside.

Miyoshi+ 1995

340pc

HST VLBAFerranres+ (1996)

Jones & Wehrle (1997)

Molecular lines & VLBI

Molecular gas in AGN regionImportant clues to study AGN fuelingCompact (pc scale)High column density (1023-24 cm-2)

Advantages of VLBI for absorptionCan display thermal absorption in silhouette against a background synchrtron emission.Not detect the thermail emission

No contamination of emissionsSensitive to detect the compact and dense absorbing gas

beam size smaller, filling factor larger

Emitting gas Absorbing gas

HI absorption with VLA

Irwin & Seaquist 1991

VLA-CVLA-BVLA-A

higher resolution

NGC3079

The target NGC 1052 (1)

A nearby radio gal.AGN : LINER/Sy2Two-sided radio jet

AGN torus suggestedSeveral layersFree-free absorption (FFA) due to plasmaH2O maserOH absorptionRedshifted from Vsys

Ongoing infall ?1 pc

Eastern approaching jet

Western receding jet

Circumnuclear torus

Plasma gas region

XDR

Centralengine Lines of sight

B

C3

C2

6 4 0 -4 -62 -2

4

2

0

-2

-4Relat

ive D

eclin

atio

n [m

as]

Relative Right Ascension [mas]

0

-1

1600 1650 1700 1750 1800VLSR (km s-1)

0 -1 -2

-16-14-12-10-8-6-4-2 0 2 4 6

1300 1400 1500 1600 1700

Flux D

ensit

y (Jy

/bea

m)

Velocity (km/s)

-4

-3

-2

-1

0

1

2

3

4

5

1300 1400 1500 1600 1700

Flux D

ensit

y (Jy

/bea

m)

Velocity (km/s)

-6

-4

-2

0

2

4

6

8

10

1300 1400 1500 1600 1700

Flux D

ensit

y (Jy

/bea

m)

Velocity (km/s)

NGC 1052

-10

-8

-6

-4

-2

0

2

4

6

8

1300 1400 1500 1600 1700

Flux D

ensit

y (Jy

/bea

m)

Velocity (km/s)

NGC 1052 − VLBA 2 cm

0.2 pc

Blank field

(a)

(b)

(c)

(d)

(e)approaching jet

receding jet

H2O maser spots

FFA opacity

OH absorption

0.1pc

Radio Continuum

0.2pc

Vsys

0.2pc

Sawada-Satoh+ 2008

Sawada-Satoh+ 2008

Impellizzeri+ 2009

Kameno+ 2003

Past VLBI images of NGC 1052

The target NGC 1052 (2)

Molecular absorption at mm bandHCO+(1-0), HCN(1-0), CO(1-0)Velocity: 1400-1800 km/sRedshifted with respect to Vsys

Similar to OH and H2OInfall from the torus ? or, another motion ? Location of the absorption is a key !

Need a high resolution image

Liszt & Lucas 2004 (PdBI)

Kameno+ 2008

H2O maser

Vsys

HCN (1-0) absorption

The first VLBI map of HCN (1-0) (Sawada-Satoh+ ApJ 830 L3, 2016)

Two redshifted features, detected.The features around Vsys, not detected.Localized on the receding jet side.A depth of >10%, deeper with PdBI

HCN 1-0 optical depth maps HCN spectral profileOptical Depth0 0.1 0.2 0.3

DEC

Offs

et [m

as]

RA Offset [mas]6 4 2 0 -2 -4 -6

4

2

0

-2

-4

1698-1741 km s-1(b)

Optical Depth0 0.1 0.2 0.3

DEC

Offs

et [m

as]

RA Offset [mas]6 4 2 0 -2 -4 -6

4

2

0

-2

-4

1634-1677 km s-1(a)

-40

-20

0

1400 1500 1600 1700Flu

x Den

sity [

mJy]

Radial Velocity [km s-1]

HCN(1-0)

Vsys (a) (b)

(c)

0.2pc 0.2pcreceding jetreceding jet

1656 1719

Sawada-Satoh+ (2016)

I

KVN

(I) (II)

II

0.00

-0.05

-0.10

line/

cont

inuu

m

(I) (II)

Vsys

Liszt & Lucas 2004PdBI

A possible model

Several layers + clumpy HCN clouds (Sawada-Satoh+ 2016)

High opacity localized on the receding jet => Inclined torusAt least two narrow absorptions => Inhomogeneous, clumpy Redshifted velocity => Ongoing infall onto SMBH

(maser)

The line of sightHCN clouds

(b)(a)

Circum-nuclear

torus

Eastern approaching

jet

Westernreceding

jet

XDRPlasmaregion

Sawada-Satoh+ ApJ 830 L3, 2016

0.2pc

Physical properties

N(H2) : 1024-1025 cm-2 (HCN-to-H2 ratio of 109; Smith & Wardle 14)1-2 order higher than N(e) by FFA opacity (~1023; Kameno+ 01)

Infall rate : ~0.05-0.5 Msun/yrComparable to the rate estimated from X-ray luminosities (~0.04 ; Wu & Cao 06)

Label Vp Vp-Vsys Δv NHCN(T=100K) NHCN(T=230K)

[km/s] [km/s] [km/s] [1014 cm-2] [1014 cm-2]

I 1656 149 31.7 9.5 50II 1719 212 52.9 20 101

M = fvRinNHmHVin�

Column density of HCN 1-0 absorption Sawada-Satoh+ ApJ 830 L3, 2016

Summary

Conducted KVN observations of the HCN(1-0) & HCO+(1-0) absorption in NGC 1052.Our HCN results are naturally explained by an AGN tors

Two HCN absorption features are identified at redshifted velocities.Reached a depth of >10%, deeper than that of PdBI.Found N(H2) of 1024--1025 cm-2 (HCN-to-H2 ratio of 109), assuming a Tex of 100--200 KHigh opacity of HCN absorption localized on the receding jetHCN gas is clumpy, and traces ongoing infall onto SMBH.

The first VLBI detection of HCO+(1-0) absorption A broad absorption feature (~500km/s), unlike HCNLocalised on the receding jet side. Torus ?