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Dense gas in Active Galaxies
or

"What can we learn from molecules?"

Edo Loenen1,2
Willem Baan2 & Marco Spaans1
1 Kapteyn Astronomical Institute, University of Groningen 2 ASTRON, Dwingeloo


Why molecules?
Located in the interesting regions
Dense molecular gas is site of (massive) SF Gas provides fuel for central black holes

Direct view to the source of activity
"long" wavelengths (mm), less obscuration

Sensitive to environment:
type & strength of radiation field temperature (column) densities
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The Data
Own observations + literature data Submitted to A&A: Baan et al. 2007 Database very incomplete Individual lines don't reveal much
OH-MM

Use line ratios for diagnostics
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Other
3/16


Starburst Evolution: data
High density gas (HD) is consumed/destroyed during star formation Large scale, low density gas [CO(1-0)] mostly unaffected use HD/CO(1-0)
OH-MM H2O-MM Other
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Starburst Evolution: the model
LFIR (t ) = 1.35 LFIR
, max



T e t

2.5

-T

t

HD(t) LFIR(t) dt = 1 - LD LFIR,int

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SB Evolution: comparison

OH-MM H2O-MM Other
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Chemistry
Different molecules react different to environment, so line ratios can give diagnostics. To investigate this we use models by Meijerink, Spaans & Israel.
(Also see talk by Spaans/Baan)

So far only done for HCN(1-0), HNC(1-0) & HCO+(1-0) (due to lack of data)
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Chemistry: diagnostic diagram

OH-MM H2O-MM Other

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Chemistry: PDR models

[erg cm-2 s-1]

FUV

n
[cm-3]

1.6 16 160

104.5 105 105.5

N = [1022 - 1024] cm-2
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Chemistry: PDR models

Models separate based on density along HCO+/HCN & HNC/HCO+ axes.

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Chemistry: PDR models

OH-MM occupy region traced by high n (>105), high N (>1022) PDRs

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Chemistry: XDR models

[erg cm-2 s-1]

Fx

n
[cm-3]

1.6 16 160

105.5 106

N = [1021 - 1025] cm-2
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Chemistry: XDR models

Can't separate XDR models XDR and PDR separate in HNC/HCN XDR models don't trace H2O-MM
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Chemistry: Terra Incognita

Region of diagram not covered by models Other physical processes influencing results

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Chemistry: Terra Incognita

Possible answer: Shocks can destroy HNC and enhance HCO+ Then: H2O-MM are extremely shocked systems
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Conclusions
Molecules provide good diagnostics:
Environment:
HCO+ / (HCN or HNC) ratio good proxy for density HNC/HCN line ratio can discriminate PDR and XDR chemistry

Mega Masers:
OH: - young starburst systems - high (column) densities H2O: - systems with strong shocks?
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