ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

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CO近赤外線吸収から探る銀河中心pcスケールでのガスの物理状態：あかりと Spitzerによる低分散分光観測
馬場俊介（東大，ISAS/JAXA）
中川貴雄，磯部直樹（ISAS/JAXA），白旗麻衣（国立天文台）

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Introduction: Active Galactic Nuclei (AGNs)• Classification• Broad and Narrow lines -> type 1• Only Narrow lines -> type 2

Type 2• Unified Scheme• Central SMBH, accretion disc

• Broad Line Regions nearby thecenter• Optically and geometrically thickdusty molecular torus• Narrow Line Regions above thetorus• face-on → type 1• edge-on → type 2

Molecular torus is a key object!

∼ 𝟏 𝐩𝐜Type 1Urry & Padovani (1995)

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ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

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Introduction: observations of molecular tori
• Face-on• CO rotational emission

observer(milli, sub-millimeter)• spatial resolution ~mas~pc in nearby universe

Torus + Host Galaxy• Edge-on• near-infrared continuum• heated inner edge of tori
• CO ro-vibrational

absorption• gas in the torus absorbs
thermal radiation• NIR emission from hostgalaxies is negligibletorus

heated region
near infrared (NIR)

SMBH
accretion discabsorption

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

4Introduction: CO ro-vibrational transition• Band center 4.7 um

Energy(K)• vibration: 𝑣 = 1 ← 02166.1• rotation: Δ𝐽 = ±1𝑣′ = 02154.72147.12143.3• 2 branches• R-branch: Δ𝐽 = +1
• P-branch: Δ𝐽 = −1
• Absorption lines of different J

come in a small wavelength
range.
• Good probe for physical states

11.5𝑣 ′′ = 0

Normalized Flux

23.1
3.8
0.0

R-branchhigh energy

P-branchRest Wavelength (um)low energy

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Introduction: other researches• Spoon et al. 2004, ApJS, 154, 184• IRAS F00183-0711• LINER• Obscured AGN?

• Spitzer observation• Strong CO absorption• Lutz et al. 2004, A&A, 426, 5• Nearby 31 Seyfert galaxies• 19 type 1 and 12type 2• ISO observations• No detection of CO absorption

What makes the difference between the two groups ?

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ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Introduction: other researches• Shirahata (2005), Shirahata et al. (2013)• Obscured AGNs

Subaru observation (𝑅 = 5000)• High-resolution spectroscopy

with Subaru• Resolved rotational levels• Targets were limited byluminosity and redshift• 𝑀-band observation Æ 𝑧 < 0.13

• space telescopes enable complementary studies• Low-resolution• Large sample

In this study, we analyze CO ro-vibrational
absorption systematically using AKARI and Spitzer.

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ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Method: space observations
Spectral Resolution

Ground: 𝜆 Δ𝜆 ∼ 10000
Space: 𝜆 Δ𝜆 ∼ 100Redshift

Ground: 𝑧 < 0.13 for 𝑀-band
Space: Not limited by the atmosphere

Flux Limit

Ground: > 100 mJy for one-night observations in Subaru
Space: > 1 mJy for ten-minute observations with AKARIAKARISpitzer• NIR grism spectroscopy• SL, HL module• Wavelength: 2.5–5.0 um• Wavelength: 5.2–40 um•Redshift 𝑧 < 0.07•

Redshift 𝑧 > 0.13

• Spectral resolution: 𝜆 Δ𝜆 = 120 @3.6 μm• Spectral resolution: 𝜆 Δ𝜆 = 86 @5.2 um• Spatial resolution: ~5’’

• Spatial resolution: ~4’’

Resolution (𝜆/Δ𝜆)CO absorption (𝑧 = 0)

Wavelength (um)7

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

• AKARI and Spitzer observations

cannot resolve rotational levels• Model fitting assuming local

thermal equilibrium

Normalized Flux

Method: model fitting

Rest Wavelength (μm)

• Cami et al. (2000)

Low Spectral Resolution• Slab geometry and single component• Free parameters: column density 𝑁CO ,temperature 𝑇CO, line width 𝑣turb

𝑁CO × 5

𝑇CO × 5𝑣turb × 58

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Targets: selection and optical classification• AKARI• Mission Program “AGNUL”• Observations during Phase 1 and 2 ( LHe + mechanical cooler )• 3 targets that show the signature of CO absorption• Spitzer• 4 targets reported by Spoon et al. (2005)
𝑧 = 0.0583

LINER

UGC 5101

0.0392

LINER

IRAS 19254-7245

0.0617

Seyfert 2

IRAS F00183-7111

0.3270LINER

IRAS 00397-1312

0.2617H II

IRAS 00406-3127

0.3424Seyfert 2

IRAS 13352+6402

0.2370?

IRAS 08572+3915

cf. NGC 1068 (z=0.0038)

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ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 201510

Targets: spectra
AKARI＋Spitzer

Spitzer

redshift 𝑧 < 0.07

redshift 𝑧 > 0.13

COCO

IRAS 19254-7245

Rest Wavelength (µm)

IRAS F00183-7111

IRAS 00397-1312

COIRAS 00406-3127
Flux (Jy)

Flux (Jy)

Flux (Jy)UGC 5101

Flux (Jy)

IRAS 08572+3915

IRAS 13352+6402

COCO
Rest Wavelength (µm)

COCO
Rest Wavelength (µm)

Rest Wavelength (µm)

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 201511

Results: 𝜒2 in the parameter space
Calculated 𝜒 2 in the3D parameter space
searched the best fitlog 𝑇COlog 𝑁CO𝑣turb

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Results: best fit

Normalized Flux

IRAS 08572+3915
Spitzer−2log 𝑁CO = 19.03 +0.30−0.08 cm

AKARI

𝑇CO = 456 +38−34 K−1𝑣turb = 73 +13−8 km s

Rest Wavelength (µm)

High Temperature
andLarge Column Density

Cf: molecular clouds in star-forming regions, 𝑇 < 50 K

12ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Results: best fit

Column Density 𝑁COMedian

Each Unc.

1 × 1019 cm−240%

Temperature𝑇CO350 K

10–40%

Line Width𝑣turb

70 km/s

10–30%

𝑁H∼ 1 × 1023 cm−2WarmandAbundant

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ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015Discussion• Origin of NIR continuum• NIR continuum ( ~5 µm ) -> Thermal radiation ( ≳ 103 K )• Heated by central nuclei• Dust sublimation temperature is ∼ 1500 K
Æ inner edge of the torus is a good candidate
Dust

Absorbinglayer

sublimation
nuclei
NIR continuum• Absorber• Absorption line of each J is almost

saturated

High-resolution spectrum• Molecular clouds in star-forming regions• Molecular cloud of systematic geometry

surrounding the nucleus

Normalized Flux

distribute randomly and cannot cover
the background entirely

1014

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

15Discussion• Heating mechanism• Observed gas has high temperature (350 K) and large column density(𝑁Hobs ∼ 1023 cm−2 )Scale of heating

𝑁Hobs
1021 cm−2 1023 cm−2

• 3 candidates are examined• 1. Photo Dissociation Region (PDR)• The accretion disk emits UV light and heats surrounding gas up to104 K (Tielens & Hollenbach 1985).
• But UV flux is attenuated by neutral gas and penetrates column
density of only 𝑁H ∼ 1021 cm−2 ≪ 𝑁Hobs (Diplas & Savage 1994).
• PDR can hardly explain the observed large column density.

• 2. Shock Heating• Shock layers caused by such as outflows can be heated up to ∼ 1000 K.
• But the scale of shock layers is only 𝑁𝐻 ∼ 1021 cm−2 ≪ 𝑁Hobs (McKeeet al. 1984)• The observed large column density cannot be explained by shockheating.

UVShock

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 201516Discussion• 3. X-ray Dissociation Region (XDR)

Scale of heating𝑁Hobs• AGN nucleus emits hard X-ray photons (2—10 keV) and1021 cm−2 1023 cm−2heats surrounding gas.
• The temperature of the gas can reach ∼ 104 K.
• Hard X-ray can penetrate neutral gas ofUV𝑁H ∼ 1024 cm−2 ∼ 𝑁Hobs before photoelectrically absorbed(Meijerink & Spaans 2005).
• XDR can explain the observed large column density.

ShockÆ XDR is a good candidate as the heating mechanism
X-ray

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹21 Dec. 2015

Discussion• When CO absorption is observed?
• Geometrical effects?

tgas << 1SMBH
diskDust
Sublimation
Layertgas ~ 1
tdust ~1
tdust >> 1
WarmMolecular
CloudKawaguchi et al. 2010, 201117

ALMAワークショップ「AGN銀河質量降着 @sub-kpc」＠国立天文台三鷹

21 Dec. 2015

Summary• We observed CO ro-vibrational absorption (4.7 um) to study the physical state ofmolecular tori.
• From observations by AKARI and Spitzer, we obtained spectra of low resolution andwide wavelength range for 7 targets.
• CO absorptions were almost saturated and implied background emitters heated by thenuclei and molecular clouds of systematic geometry surrounding them.
• From the model-fitting analysis, in spite of low-resolution spectra that does not resolve

rotational levels, we succeeded to obtain column densities, temperatures, and line
widths with uncertainties of several × 10%.
• Medians of them were, 𝑁CO = 1 × 1019 cm−2 , 𝑇CO = 350 K, 𝑣turb = 70 km s −1

• The result indicates warm and abundant gas.
• XDR is a good candidate of the heating mechanism

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