The irradiated ISM of ULIRGs

isc.astro.cornell.edu

The irradiated ISM of ULIRGs

The Irradiated ISM of ULIRGs

Rowin Meijerink (Leiden Obs)

Marco Spaans (Kapteyn Institute)

Frank Israel (Leiden Obs)

ULIRG Workshop Cornell


Context

- Radiative Feedback:

`Any process where photons impact the

properties of molecular gas from which

stars form´

- PDRs (FUV) and XDRs (X-ray):

`The energy of the photons matters’

- Wavelength: FIR/mm lines; so dust

absorption not an issue

ULIRG Workshop Cornell


PDRs: 6 < E < 13.6 eV

■ Heating: Photo-electric emission from

grains and cosmic rays

■ Cooling: Fine-structure lines like

[OI] 63, 145; [CII] 158 μm

and emission by H2, H , CO, H2OH

■ 10 eV photon penetrates ½ mag of dust

ULIRG Workshop Cornell


XDRs: E > 1 keV

■ Heating: X-ray photo-ionization -->

fast electrons;

H and H2 H 2 vib excitation;

UV emission (Ly α, Lyman-Werner)

■ Cooling: [FeII] 1.26, 1.64; [OI] 63;

[CII] 158; [SiII] 35 μm;

thermal H2vib; gas-dust

■ 1 keV photon penetrates 10 22 cm -2 of N H

ULIRG Workshop Cornell


■ Tielens et al. 1993; Orion Bar

ULIRG Workshop Cornell


■ Weaver et al. 2004; NGC 253

ULIRG Workshop Cornell


Energetics

G0 = 1.6x10 -3 erg cm -2 s -1

is the Habing flux over 6-13.6 eV

Orion Bar has 10 5 G 0

; SSC=many OB’s

F L

X

= 84 L44

r2 -2

-2 erg cm -2

-2 s -1

is the X-ray flux over 1-100 keV with a

power law E -0.9

Think of Seyfert nucleus at 100 pc or

TTauri star with 10 32 erg/s at 20 AU

ULIRG Workshop Cornell


■ PDR (left) with n=10 5 cm -3 and G=10 3.5

■ XDR with n=10 5 cm -3 and F X

= 5.1 erg s -1 cm

ULIRG Workshop Cornell

cm -3

■ Note N H

scale and depth dependence (CO, CI)


■ Atomic ions more abundant in XDRs

■ HCN/HCO + good indicator of this ionization

■ HCN ~cst. after a few mag (τ~1(

for large N H

)

ULIRG Workshop Cornell


■ PDR model with CR rate = 5x10 -15

rate for ~100 M 0

/yr

■ Note the changes in CI and OH

ULIRG Workshop Cornell

-15 s -1

-1 ; so SN


■ Cosmic rays mimic XDRs where HCO + is

concerned, but not so for atomic ions

ULIRG Workshop Cornell


ULIRG Workshop Cornell


Grid of Models (1D slabs)

■ n H

=10 2 – 10 6.5

6.5 cm -3 ,N

,N H

=10 22 – 10 25

■ G 0

& F X

~ 0.016-160 erg s -1

ULIRG Workshop Cornell

-1 cm -2

25 cm -2

-2 , 2Z/Z 0

■ Cloud sizes of 1, 10, 50 pc for

4-6.5

densities of 10 3-4

, 10 2-3

, 10 -3

cm ■ Also models with CR rate of 5 x 10 -15 s -1

■ www.strw.leidenuniv.nl/~meijerin/grid/

as of September 1st 2006


■ Atomic layers in XDRs are warmer, for

the same density and irradiation;

1pc cloud

ULIRG Workshop Cornell


There is more neutral carbon in XDRs

and CI is warmer

ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


■ CO gas in XDRs is warmer, for the same

density and irradiation (same for 13 CO)

■ Very high J CO lines, observable with

HIFI, are good diagnostics

■ Shirahata et al. poster: CO v=0-1 up to

J=17 with Subaru for IRAS 08572+3915

ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


Summary

■ HCO + /HCN and HNC/HCN are XDR vs

PDR diagnostics, same for high-J CO;

CN (~HCO + ), NO, HOC + , HCO, CH, CH +

■ Need collisional cross sections for CN,

NO, HOC + , HCO, CH, CH +

■ Cosmic rays matter and lead to lower

high/low J CO ratios (not XDR-like) and

higher HCO + /HCN ratios (XDR-like)

ULIRG Workshop Cornell


Outlook

■ Molecules have great diagnostic value:

starburst/FUV vs AGN/X-ray

■ Observe galaxies with Herschel (HIFI),

ALMA, Subaru, etc. in order to separate

PDR and XDR contributions

ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


■ Brandl et al. 2005

ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


Orion Bar

■ Generic high mass star-forming region

■ Template for starburst galaxies

■ Illuminated by Trapezium stars (θ¹ Ori)

G~10 5

■ Dense: nH n ~ 3x10 4 - 6x10 6 cm-³

■ Interface between HII region and OMC1

■ 6cm --> PAHs --> H2* H * / C+ --> CO

ULIRG Workshop Cornell


ULIRG Workshop Cornell


ULIRG Workshop Cornell


■ Concentrate on

irradiated gas

■ Such gas produces

lines/continuum

observable with ISO-

LWS/SWS, HIFI, ALMA,

SOFIA

■ So active galaxies are

bright because of

radiative feedback from

star-forming regions or a

central AGN

ULIRG Workshop Cornell


ULIRG Workshop Cornell

Maloney et al. 1996

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