1. Redshifted Extragalactic Molecular Lines
Jeremy Darling
(CASA, University of Colorado)
Mechanisms
1. Thermal
2. Masers
3. Dasars
Science
A. High Redshift
B. Galaxy Evolution
C. Star Formation/ISM
D. Massive Black Holes
E. Cosmology
F. Physical Constants

2. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)

3. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
Out of reach
(Existence of molecules?)

4. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
z = 0.9 gravitational lens
(e.g. Muller et al. 2006)
high dipole moment
expect detections in submm
galaxies soon!
dense gas tracer
star formation
(akin to HCN, HCO+)

5. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
Chengalur, deBruyn, &
Narasimha 1999
Patnaik et al. 1994
Nair et al. 1993
z = 0.7, 0.9 gravitational lenses
(Henkel et al. 2005, Menten et al. in prep)
Tunneling transitions (many)
Thermometer
Constancy of me/mp
(Flambaum & Kozlov 2007)

6. Ammonia (NH3): “Umbrella” Tunneling
Symmetric top molecule
Electrostatic repulsion between
N and H3 plane
“Umbrella” inversion possible via
tunneling (for low vibration states)
Each rotation ladder has inversion
splitting
Inversion transitions can be masers
(first maser was NH3 24 GHz!)
Rohlfs & Wilson 1996

7. Ammonia (NH3): “Umbrella” Tunneling
Symmetric top molecule
Electrostatic repulsion between
N and H3 plane
“Umbrella” inversion possible via
tunneling (for low vibration states)
Each rotation ladder has inversion
splitting
Gastrophysics
Multiple inversion lines give Trot
B :
z = 0.67; Trot = 35 K
PKS :
z = 0.89; up to (J,K) = (10,10) detected! (Menten et al in prep)
(Henkel et al 2005)

8. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
z = 0.66 maser (Barvanis & Antonucci 2005)
5 mJy line
Acceleration search (disks)
HSN targets
Cosmology

9. H2O Megamasers Associated with Type 2 nuclei Highly beamed NGC 4258:
- VLBI proper motions
of maser spots
- Line accelerations
Geometric distance
7.2  0.5 Mpc
(Herrnstein et al. 1999)
Herrnstein et al. 1999
NGC 4258
(H2O masers can also occur in jets and outflows)

10. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
No megamasers
(Phillips et al 1998, Darling et al 2003)
* Menten predicts broad shallow
absorption akin to Galactic Center

11. Redshifted Molecular Lines
Biggs et al 2001
Line
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
z = 0.7,0.9 gravitational lenses
(Menten & Reid 1996, Menten et al. 1999)

12. Darling & Goldsmith (in prep) Darling & Goldsmith (in prep)
Galactic H2CO
Dark Clouds:
- “Anomalous” H2CO absorption
(e.g. Palmer et al. 1969)
- Absorption in multiple cm lines
- No radio continuum source!
Barnard 227
Darling & Goldsmith (in prep)
NGC 2264
Darling & Goldsmith (in prep)

13. H2CO: The DASAR L ight A mplification by S timulated E mission of
R adiation
Inversion:
“Heating” of lines
Tx >> Tkin
Pump required:
Chemical, collisional, radiative
D arkness*
A mplification** by
S timulated
A bsorption of
R adiation
Townes et al (1953)
Anti-Inversion:
“Cooling” of lines
Tx < TCMB
Pump required:
Collisions with H2
*Not really dark.
**Not a true amplification.

14. Darling & Goldsmith (in prep) Darling & Goldsmith (in prep)
Galactic H2CO
Dark Clouds:
- “Anomalous” H2CO absorption
(e.g. Palmer et al. 1969)
- Absorption in multiple cm lines
- No radio continuum source!
Can H2CO be observed in other galaxies?
2. Can “anomalous” H2CO absorption be observed in galaxy-scale analogs of Dark Clouds?
Barnard 227
Darling & Goldsmith (in prep)
NGC 2264
Darling & Goldsmith (in prep)

15. H2CO Absorption Against the CMB

16. H2CO: The DASAR The CMB is the ultimate illumination source:
Behind everything
Everywhere
Uniform on arcsec scales
H2CO absorption against the CMB offers an unrivaled, extinction-free, mass-limited probe of dense (star-forming) molecular gas, independent of redshift!

17. Extragalactic H2CO Emission in (U)LIRGs (OH Megamasers) Arp 220
Baan, Guesten, &
Haschick (1986)
Extragalactic H2CO
Emission in (U)LIRGs
(OH Megamasers)
Arp 220
III Zw 35
Absorption in starbursts
(OH absorbers)
NGC 520
NGC 660
Henkel & Darling (in prep)

18. Extragalactic H2CO Emission in (U)LIRGs (OH Megamasers) Arp 220
III Zw 35
Absorption in starbursts
(OH absorbers)
NGC 520
NGC 660
Henkel & Darling (in prep)
NGC 660, 8.4 GHz
Filho, Barthel, & Ho (2002)

19. Extragalactic H2CO So far… All OHMs show 6 cm emission in H2CO
All OH absorbers show 6 cm absorption
H2CO 6 cm line flip at n(H2) ~ cm-3
A critical density threshold for OH megamasers?
(there must also be a density upper limit where inversion is quenched… n(H2) ~ 106 cm-3)
H2CO Survey of Local Star-Forming Galaxies
(Mangum, Darling, Menten, & Henkel, 2007)
M 82
Arp 220
6 cm
2 cm

20. Extragalactic H2CO So far… All OHMs show 6 cm emission in H2CO
(Mangum et al. 2007)
So far…
All OHMs show 6 cm emission in H2CO
All OH absorbers show 6 cm absorption
H2CO 6 cm line flip at n(H2) ~ cm-3
A critical density threshold for OH megamasers?
(there is also an upper density where 2 cm line flips… n(H2) ~ cm-3)
2 cm
(kilomaser)
6 cm
OHMs

21. Extragalactic H2CO
H2CO dasar effect spans 3 orders of magnitude in density
cm line ratio is sensitive to n(H2)
Darling & Zeiger

22. Extragalactic H2CO H2CO dasar effect is insensitive to TCMB
The effect likely becomes easier to detect with increasing redshift!
Darling & Zeiger

23. Extragalactic H2CO Maser Emission in (U)LIRGs (OH Megamasers) Arp 220
Darling & Wiklind
Extragalactic H2CO
Maser Emission in (U)LIRGs
(OH Megamasers)
Arp 220
III Zw 35
Absorption in starbursts
(OH absorbers)
NGC 520
NGC 660
Absorption in dense clouds B
PKS
Biggs et al 2001

24. Redshifted Molecular Lines
z when
 = 10 GHz
CO (1-0)
10.5
HCN (1-0)
7.9
HCO+ (1-0)
CS (1-0)
3.9
SiO (1-0)
3.3
NH3 (24 GHz)
1.4
H2O (22 GHz)
1.2
H2CO ( )
0.45
HC3N (1-0)
Any
CH3OH (6.7 GHz)
H2CO ( )
OH (1.8, 4.7, 6.0 GHz)
IRAS z = 0.18
PKS OH HI
z = 0.89
z = 0.26 megamaser
z = 0.9 gravitational lens

25. Merging Galaxies:

26. OH Megamasers:
Tracers of Major Mergers, Star Formation, and Massive Black Holes
OH  FIR and favors dusty
environments
OHMs seem to indicate massive
black holes (small sample)
OHMs seem to favor a specific
stage of merging, star formation
Sampling a specific stage of
merging
 BH binary formation rate
 long-period GW background
There are many approaches to these
problems; no single method will be
a panacea.

27. Begelman, Blandford & Rees 1980
OH Megamasers:
Tracers of Major Mergers, Star Formation, and Massive Black Holes
(CSOs?)
OH  FIR and favors dusty
environments
OHMs seem to indicate massive
black holes (small sample)
OHMs seem to favor a specific
stage of merging, star formation
Sampling a specific stage of
merging
 BH binary formation rate
 long-period GW background
There are many approaches to these
problems; no single method will be
a panacea.
OHMs
GWs
Begelman, Blandford & Rees 1980

28. OH Megamasers in HI Surveys
Power-law LF
Increasing Merger Rate
Increasing Star Formation
Briggs (1998):
The deeper the HI survey, the more confusion with OH megamasers
At z ~ 0.1 the OH line > HI line
(but remains rare)
At z ~ 1 there is ~ 1 OHM per deg2
Briggs (1988)
0.2 mJy
1 mJy
5 mJy
20 mJy

29. OH Megamaser Surveys: High(er) Redshift
Barriers
RFI
Receivers
Rarity
Boons
Half of OH megamasers are QSO-like
Current sensitivity is adequate for z ~ 1
More merging in past

30. Detecting OH
Megamasers at
High Redshift
Submm Galaxies

31. PKS 1413+135: OH and HI Absorption
Conjugate OH satellite lines:
1612, 1720 MHz
(see also Kanekar et al. 2004)
Systematic offset from HI
Is the offset physical?
How to assess offsets?
13 km s-1

32. Variability in OH Megamasers: Super-VLBI Resolution
Multiple independent variable features with different timescales:
 Segregates
sizescales
 May segregate
positions
 Offers sub-
milliarcsecond
resolution
 Sensitivity is key

33. 02524+2046 Observations: Day-to-day (and intraday) variation
Multiple narrow variable components
1665 MHz line varies, often (but not always) with 1667
Components often (but not always) correspond to peaks
Darling (in prep)

34.
Darling (in prep)
Observations:
Unprecedented matching between 1665 and 1667 MHz lines in average and variable fits, including flaring lines
Variation envelope shows proportional 1667:1665 modulation of ~20% (~30% expected for point source)
Size scales < 1 pc (0.3 milliarcsec)
Tb > 81011 K (!)
(What is line separation in sky?)

35. A Super-VLBI Single Dish Telescope
Variability Studies:
A Super-VLBI Single Dish Telescope
Variability studies can segregate size scales and on-sky projections of OH megamaser components with super-VLBI resolution (~pc at z = 0.2).
Roughly half of luminous OMHs at z > 0.1 are variable/compact.
We have identified compact 1665 MHz emission coincident with compact 1667 MHz lines.
Observed phenomena are consistent with strong refractive ISS (and detailed tests are possible)
ISS predictions are consistent with VLBI observations
Long-term monitoring can identify small accelerations

36. Characterizing Variability
10% modulation
4.5 day timescale
Assuming ISS
Variable features:
< 1.2 parsec
Quiescent features:
> 4 parsec

37. Characterizing Variability
10% modulation
4.5 day timescale
Assuming ISS
Variable features:
< 1.2 parsec
Quiescent features:
> 4 parsec
Robishaw, Heiles, & Quataert
z = 0.217

38. Magnetic Fields in OH Megamasers
Robishaw, Heiles, & Quataert have detected Zeeman splitting in multiple OH megamaser galaxies!
Prediction:
Zeeman splitting will also be observable in OH conjugate lines and OH in molecular absorption systems (detectable at arbitrary redshift).

39. Discussion Questions: High Frequency
What can be done to improve 5-10 GHz sensitivity?
Has double position switching been evaluated at high frequency?
What bandwidths can be correlated?
How good are baselines across 100 MHz? 1 GHz?
The H2CO “densitometer” offers tremendous promise
H2O surveys and studies (cosmology)
NH3 tunneling lines
High redshift CS
How high in frequency can Arecibo still work with the HSA?
What is the impact of strong continuum on Arecibo within the HSA?
Any hope for observations of molecular absorption systems?
Is there an irreducible noise floor?
How low can we go?
Can we have certainty when observing weak lines?

40. Discussion Questions: Low Frequency
Is 800 MHz feasible?
OH (megamasers, conjugate lines, absorption) at z~1
HI absorption (intrinsic, gravitational lenses, damped Ly systems)
Changing physical constants, peak of star formation, merging, BH growth
Interferometer with GBT, possibly WSRT
Are polarization observations possible with double position switching?
B fields in single clouds at high z via OH conjugate lines, absorption
Is there an irreducible noise floor in L-band or below?
(How low can we go?)