Optical views of dense gas clouds
at the circum-nuclear region in AGNs

Tohru Nagao
Ehime Univ., JapanALMA workshop
21-22 Dec. 2015, NAOJ/Mitaka

Schematic view of the AGN structure
BLR clouds: nH > 108 cm-3 at R < ~1 pc
typical total mass of the BLR: < 10 Msun (e.g., Petersonʼs textbook)! not important for circum-nuclear SF and mass reservoir! (probably) not important in this workshop
NLR clouds: at R ~ 101-3 pc
typical total mass of the NLR: ~ 105-6 Msun
! target of this workshop

2C. Ricciʼs webpage (http://www.isdc.unige.ch/~ricci/Website/Active̲Galactic̲Nuclei.html)

Narrow-Line Regions (NLRs) in AGNs
1 arcsec = 72 persec

NGC 1068
HST narrow-band image
Capetti et al. (1997)

Clumpy gas seen in the direction of the torus opening angle! NLRs are photoionized by anisotropic ionizing radiation3

from「星間物理学」小暮智一[SII]
6717,6731[OII]
3726,3729

5000
6000
Wavelength (Angstrom)from Osterbrockʼs textbook

4000

Intensity ratio

from Petersonʼs textbook

Optical spectrum of NLR clouds

Electron density (cm-3)

4

Gas density of NLR clouds
Kawasaki, TN, et al., in prep.

Seyfert sample (11,360)

normalized Nobj

1.0

[SII] ﬂux ratio of
SDSS Seyfertslog([NII]/Hα)>-0.5(11360)log([NII]/Hα)<-0.5
(59)

0.8
0.6

nNLR ~ 102-3 cm-3

0.4
0.2
0.0

1.5

2.0

2.5

3.0

3.5

log (ne cm-3)

4.0

4.5

※ measurements of
the [OII] ﬂux ratio arevery diﬃcult for NLRs
due to the line blending

What are these dashed lines?
5Gas density of NLR clouds: Caveat
from Osterbrockʼs textbookIntensity ratio" Low-density limit

[SII]
[OII]

6717/6731

3729/3726

High-density limit !

Electron density (cm-3)

6[SII] and [OII] ﬂux ratios
are saturated at lowand high-density limits

These indices work at~ 101.5-4.0 cm-3 for [SII]~ 101.0-3.5 cm-3 for [OII]

We cannot recognize possible dense clouds (nH >105-6 cm-3)
with [SII] and [OII] ﬂux ratios, even if they exist in the NLR.
~ due to the saturation at the high-density limit~ due to the collisional de-excitation eﬀect6

Seyfert-type dependence of NLR line flux ratios
TN+01a[SII]6717/[SII]6731[OII]doublet/[SII]doublet[SII]doublet/[NII]6584

No Seyfert-type dependence in the [SII]6717/[SII]6731 ratio.
No Seyfert-type dependence in other NLR line ﬂux ratios.
7

Seyfert-type dependence of NLR line flux ratios
TN+01a; see also Murayama+98a, TN+00[NeIII]3869/[OIII]5007[OIII]4363/[OIII]5007[FeVII]6087/[OIII]5007

Lines with a high critical density are stronger in Sy1.
Lines with a high ionization potential are stronger in Sy1.
8

F4959+5007 7.90 exp(3.29 × 10 4 /Te )[OIII]=F4363
1+ 4.5 × 10 −4 ⋅ n e /Te1/ 2€

log Ne (cm-3)

Note: [OIII]4363/[OIII]5007 in AGNs

[OIII]4363/5007: A reliable Te
indicator for HII regions and starforming galaxies, whose gas
density is always below 105 cm-3.
This may not be true for NLRs.
(also [NII]5755/6584, [SIII]6312/9532, etc.)

log Te (K)from「星間物理学」小暮智一

9

A two-component NLR model: An idea
Murayama+98a

The innermost partof the NLR is also
obscured by thedusty torus, wherethe gas clouds arecharacterized byvery high density
and high ionization.
What are thoseclouds? Probably
dense gas clump or
inner wall of torus.

10A two-component NLR model: Cloudy results
A photoionization model
TN+01b(see also Murayama+98b)

A classical NLR component~ nH = 101-6 cm-3
~ U = 10-2
~ ionization-bounded (opt. thick)A dense gas component⎞+∞~ nH = 107 cm-3 ⎛Lvdν
⎜⎟~ U = 10-1.5
13.6eV hν~ NH ~ 1021 cm-2 ⎜U = 4 πr 2 cn ⎟H ⎟⎜(truncated)⎝⎠∫(reddening eﬀect)

Combining these two components~ Contribution of dense gas to[OIII]5007, from 0% to 50%€ metallicity~ both solar~ a typical AGN SED adopted

Photoionization model explains well the observed trend.
Nuclear dense gas explains the AGN-type dependence.

11

A two-component NLR model: Kinematics
Subaru high-dispersion spectroscopy

TN+03a~ target: NGC 4151
~ 900sec x 4 = 1hr~ R = 45,000~ v ~ 7 km s-1

Consistent with thepicture of 2 comp. model(see also Filippenko+84;
De Robertis+84,86; Filippenko 85;
Veilleux 91; Alloin+92; etc...)12

A two-component NLR model: Kinematics in IR
Spitzer/IRS spectra~ 10-37 micron~ R = 600 ( v ~ 500 km/s)~ stacking analysis ofvarious populations of galaxies

High-ionization lines show larger
velocity dispersion! more ionization at smaller scales

Dasyra et al. (2011)

Tommasin et al. (2010)

A two-component NLR model: Spectro-pol.
Subaru spectropolarimetry~ Mrk 573, 208 min in total

TN+04

14

A two-component NLR model: Spectro-pol.
Keck spectropolarimetry~ NGC 4258

Murayama+98a

Barth+9915

A two-component NLR model: Dust grains?
物理状態に寄らず化学組成比に敏感な輝線の組合せとしては、[Ne V]3426 と [Fe VII]6087 の組合せがある。
これらはいずれも電離度が高く、NLR の中で最も中心核に近い領域から放射される。
この輝線強度比の観測値と光電離モデル計算を見比べると、高電離輝線を放射する領域にはダストが存在しないことが示唆される。
これは、NLR 中の高電離輝線放射領域がトーラス内壁あたりに相当するという二成分モデルと合致。

[右図のモデル]実線：
ダストがなく、鉄が気相に存在する場合。
破線：ダストが存在し、鉄の大部分がダストに吸着して、気相にはあまり存在しない場合。

TN+03b16

At high redshiftA “strange” rest-opt spectrum isobtained through near-infrared
spectroscopy serendipitously(SDSS J1707+6443 @ z=3.2)

atmos. transmission
Subaru/MOIRCS

Very strong [NeIII] but no [OII]...

sky emission

Araki, TN+12
Nitta, TN, in prep.

low-z
QSOs

Lv
∫13.6eV hν dν
U=4 πr 2 cn H+∞a QSO@z=3.2
Araki, TN+12

Photoionization model says that theNLR in this QSO is characterized bya very high density (>105 cm-3), but
probably distributed in the host.
But this is out of the scope of thismeeting...
17

fgas = M(gas)/M(gas+star)

At high redshift

Geach et al. (2011)

Riechers+10(CARMA)

Kewley et al. (2013)(Upper Left)
Higher gas fraction at
higher redshift,measured through CO(Right)
BPT diagram at various
redshifts; higher-z data
may be (?) consistent
with models withhigher gas density andharder ionizing SED(Lower Left)
HCN & HCO+ molecular lines
detected in a lensed quasar
APM 0879+255 at =3.91,
suggesting the presence ofabundant dense gas clouds
in the host galaxy (??)

z=0.1

z=0.8

z=1.5z=2.518

Expectations to ALMA
#Both Sy1 and Sy2 are expected to have dense clouds
at the circum-nuclear region~ should be tested with ALMA (no extinction!!)~ comparison of the frequency distribution ofdense-gas tracers between Sy1s and Sy2s
~ is the nuclear dense gas seen in “all” Seyferts?
~ but... NGC 1097 (?) Has LLAGN a diﬀerent picture?
#How dense?
~ multi-lines + LVG analysis#How compact is their spatial distribution?
~ now ALMA achieve higher resolution than optical~ <10pc expected from optical high-ionization lines
but should be tested#And... at higher redshifts?
19