Radio Selected Damped Lyman Systems

Outline: 1. Damped Lya Systems 2. Motivation 3. Intervening Absorption 4. Intrinsic Absorption

[5. H2CO Absorption] 6. Summary

Jeremy Darling (CASA, University of Colorado)

Radio Selected Damped Lyman Systems

Damped Lyman Damped Lyman Systems Systems

By definition,

For the 21 cm HI line,

In practice, we’ll refer to DLAs as any sufficient column, regardless of host or setting.

NHI ≥ 2 1020 cm-2

NHI = 1.8 1018 cm-2 (Tspin / ) d

DLAs: DLAs: Motivation for 21 cm SearchesMotivation for 21 cm Searches

Optical spectroscopic selection: Requires background UV source Redshift into atmospheric window (z > 1.65) Pencil beam (single los, single cloud)

DLA studies: Damped/saturated line (very important for EOR studies!) Optical identification of DLAs

Molecular absorption: Extremely rare Requires dust Fundamental physics Gastrophysics

DLAs: DLAs: Motivation for 21 cm SearchesMotivation for 21 cm Searches

Optical spectroscopic selection: Requires background UV source Redshift into atmospheric window (z > 1.65) Pencil beam (single los, single cloud)

DLA studies: Damped/saturated line (very important for EOR studies!) Optical identification of DLAs

Molecular absorption: Extremely rare Requires dust Fundamental physics Gastrophysics

HI 21 cm: Dust! Any z Multiple los, clouds (+ Einstein rings!)

21 cm HI: = 0.01-0.10 (cf Radio Probes of Reionization, 2007)

Optically faint QSOs

All molecular absorbers show HI 21 cm absorption

Molecular Absorbers: Molecular Absorbers: The Usual Suspects The Usual Suspects

Molecular Absorbers: Four known at z > 0.2

(OH only excluded) Large searches have produced no new objects Molecular Absorption Requires fortuitous alignment Requires flat or inverted continuum Detectability is independent of redshift

Gastrophysics Provides only means to detect unexceptional ISM at z > 0

Precision Measurements Can measure fundamental constants at high redshift

Molecular Absorption Systems at z > 0.2 Molecular Absorption Systems at z > 0.2

• PKS 1413+135 z = 0.2467 AGN in spiral

• B3 1504+377 z = 0.6734 AGN in spiral

• B 0218+357 z = 0.6847 Lens (Einstein ring)

• PKS 1830-211 z = 0.8858 Lens (Einstein ring)

Wiklind & Combes

1998

Wiklind & Combes

1996

Wiklind & Combes

1995

Wiklind & Combes

1997

Kanekar et al 2003

Kanekar et al 2003

Darling (in prep)

Darling (in prep)

Darling (in prep)

Darling (2004)

Conjugate OH lines

No “main” lines

Molecular Absorption Systems at z > 0.2 Molecular Absorption Systems at z > 0.2

• PKS 1413+135 z = 0.2467 AGN in spiral

• B3 1504+377 z = 0.6734 AGN in spiral

• B 0218+357 z = 0.6847 Lens (Einstein ring)

• PKS 1830-211 z = 0.8858 Lens (Einstein ring)

Wiklind & Combes

1998

Wiklind & Combes

1996

Wiklind & Combes

1995

Wiklind & Combes

1997

Kanekar et al 2003

Kanekar et al 2003

Darling (in prep)

Darling (in prep)

Darling (in prep)

Darling (2004)

Conjugate OH lines

No “main” lines

PKS 1413+135: PKS 1413+135: OH and HI AbsorptionOH and HI Absorption

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

PKS 1413+135: PKS 1413+135: OH, HI & COOH, HI & CO

HI, CO redshifts exceptionally well measured (< 10-6); systematics dominate (Carilli et al. 1998)

OH: Systematic offset from HI, CO

OH-only measure consistent with zero

Δν/HI: systematics can account for all Δα/αo

(1×10-5 ~ 10 km s-1)

HI: Darling 2004OH: Darling 2004CO: Wiklind & Combes 1997

PKS 1413+135: PKS 1413+135: OH, HI & COOH, HI & CO

HI, CO redshifts exceptionally well measured (< 10-6); systematics dominate

OH: Systematic offset from HI, CO

OH-only measure consistent with zero

Δν/HI: systematics can account for all Δα/αo

Intervening 21 cm Absorption:Intervening 21 cm Absorption:A “blind” survey at Green BankA “blind” survey at Green Bank

Goals: Conduct a DLA search analogous to optical surveys (large ∆z). Minimize DLA selection biases (z, dust).

Requires: Large instantaneous z coverage Good velocity resolution (∆v < 10 km s-1) Sensitivity to all DLAs in short integrations

Bonus: Simultaneous search for OH lines Two Surveys: 1. 100 continuum sources (S > 0.8 Jy) in 0.6 < z < 1.1 (Darling & Giovanelli)

2. 182 flat-spectrum sources from z = 0 to z = zsys (Bolatto & Darling)

Feed Resonance

Green Bank Blind HI Survey:Observe 200 MHz at 800 MHz with 6 kHz (~2 km s-1) resolution

λ /Δλ = 132,000

BW/λ = 0.25

Radio Freq Interference (RFI) is problematic andreduces z coverage

RFI

z = 1.1z = 1.1ttll = 8.1 Gyr = 8.1 Gyr

ttUU = 5.6 Gyr = 5.6 Gyr

z = 0.63z = 0.63ttll = 5.9 Gyr = 5.9 Gyr

ttUU = 7.8 Gyr = 7.8 Gyr2.2 Gyr, 1.2 Gpc

Chengalur, deBruyn, & Narasimha 1999

Patnaik et al. 1994

Nair et al. 1993

FWHM = 57 km s-1

τc = 0.22

NHI = 24.3 x 1018 (Ts/f) cm-2

Pure radio HI absorption detection!

Proof-of-concept for blind searches.

• Molecules?• Lens?

Green Bank Blind HI Survey

PKS 1830-211

Chengalur, deBruyn, & Narasimha 1999

Patnaik et al. 1994

Nair et al. 1993

FWHM = 57 km s-1

τc = 0.22

NHI = 24.3 x 1018 (Ts/f) cm-2

PKS 1830-211

Pure radio HI absorption detection!

Proof-of-concept for blind searches.

• Molecules?• Lens?

Green Bank Blind HI Survey

BIMA (Bolatto)

Intervening 21 cm Absorption:Intervening 21 cm Absorption:A “blind” survey at Green BankA “blind” survey at Green Bank

Goals: Conduct a DLA search analogous to optical surveys (large ∆z). Minimize DLA selection biases (z, dust).

Requires: Large instantaneous z coverage Good velocity resolution (∆v < 10 km s-1) Sensitivity to all DLAs in short integrations

Proof of Concept: Detection of 2351+456 at z = 0.78 (no a priori knowledge of this DLA)

Recovery of known absorbers Expectations: ∆z ~ 150 (including RFI losses)

Estimate of ΩHI (but depends on Tspin)

Intrinsic 21 cm Absorption: Intrinsic 21 cm Absorption: CSOsCSOs

Compact Symmetric Objects: Compact (< 1 kpc) Symmetric (jets) Post-Mergers Inside-out virialization (t ~ 108 yr, Perlman et al 2001) Jet advance shows radio source turn-on Crossing time of nucleus « jet lifetime nucleus at birth of RL AGN

Dust and gas still in cores (yet to be expelled) Peck & Taylor 2002

Intrinsic Absorption: Intrinsic Absorption: Survey ExpectationsSurvey Expectations

DLAs

Observe: 71 sources 0.5 < z < 4 CSOs GPS sources CSS sources Expect: Detect all DLAs in 1-2 hours Bonus: OH lines

Intrinsic AbsorptionIntrinsic AbsorptionExpected HI

Intrinsic AbsorptionIntrinsic AbsorptionExpected HI

Flu

x D

ensi

ty (

Jy)

Barycentric Frequency (MHz)

PKS 0500+019z = 0.58

Previous detection:Carilli et al 1998

Intrinsic Absorption: Intrinsic Absorption: Survey Results Survey Results (so far…)(so far…)

z < 0.7 redetections

Intrinsic Absorption: Intrinsic Absorption: Survey Results Survey Results (so far…)(so far…)

No new detections Previous surveys have 30-50% detection rate atz < 0.7 (Vermeulen et al 2003)

Sub-DLAs detectable

Adequate sensitivity to z ~ 3, including RFI losses

Work continues…

z < 0.7 redetections

HH22CO: CO: The Swiss Army Knife MoleculeThe Swiss Army Knife Molecule

Galactic

Extragalactic

Gastrophysics

Galaxy Evolution

(Cosmology ?)

Darling & Goldsmith (in prep)

NGC 2264

Galactic HGalactic H22CO CO

Dark Clouds: - “Anomalous” H2CO absorption (e.g. Palmer et al.

1969)

- Absorption in multiple cm lines- No radio continuum source!



Barnard 227

NGC 2264

HH22CO: CO: The DASARThe DASAR

L ightA mplification byS timulated E mission ofR adiation

Inversion: “Heating” of lines Tx >> Tkin

Pump required: Chemical, collisional, radiative

D arkness*A mplification** byS timulated A bsorption ofR adiation

Townes et al (1953)

Anti-Inversion: “Cooling” of lines Tx < TCMB

Pump required: Collisions with H2

*Not really dark.**Not a true amplification.

Galactic HGalactic H22CO CO

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

NGC 2264

Darling & WiklindBiggs et al 2001

Extragalactic HExtragalactic H22CO CO

Maser Emission in (U)LIRGs (OH Megamasers)

Arp 220 III Zw 35

Absorption in starbursts (OH absorbers)

NGC 520NGC 660

Absorption in dense cloudsB0218+357

Ortho-HOrtho-H22CO Toward CO Toward

B0218+357 B0218+357 4.8 GHz (110-111) line detected at Arecibo

• Two gaussian components• app = 0.013 ± 0.003

• ∆v = 12.6 ± 0.6 km s-1

Previous Detections:Previous Detections: 14.5 GHz (211-212) (VLA; Menten & Reid 1996)

150.5 GHz (211-110) (IRAM; Wiklind & Combes)

Wiklind & Combes

Darling & Wiklind

HH22CO Toward B0218+357: Summary CO Toward B0218+357: Summary

Similar to Galactic Dark Clouds (but scaled to CMB at z = 0.67)

• Centimeter lines (4.8, 14.5 GHz) are anti-inverted- T4.8 ~ 2.3 K- T14.5 ~ 3.4 K (TCMB = 4.6 K)

• Millimeter lines (150.5, 140.8 GHz) have Tex ~ TCMB

• N(ortho-H2CO) = 1.5 1013 cm-2 • N(H2) = 1.5 1021-22 cm-2 • n(H2) = 104-5 cm-3

Future Prospects:• Ortho:para at z > 0• Prediction: H2CO can be observed in absorption against CMB in extragalactic ISM

- How does T decrement scale with z? - What is H2CO filling factor?

HH22CO Absorption Against the CMB CO Absorption Against the CMB

HH22CO: CO: The DASARThe DASAR

The CMB is the ultimate illumination source:

• Behind everything• Everywhere• Uniform on arcsec scales

H2CO absorption against the CMB offers an unrivaled probe of dense molecular gas, independent of redshift!

HH22CO Against the CMB: CO Against the CMB: ProspectsProspects

Step 1: Local Calibration• Survey local galaxies, from spirals to ULIRGs• Include sample with CO and HCN measurements• What is the filling factor on kpc scales? • What is the total H2CO mass? M(H2CO) M(dense)

GBT: large survey in 14.5 and 4.8 GHz lines (Darling, Mangum, Menten, & Henkel)

Step 2: Submm Galaxies• How does anti-inversion scale with redshift?• What is dense gas fraction?VLA: deep integrations in 312 - 313 line at z ~ 2.5

(Darling & Baker)

Radio-Selected Damped Lyman Radio-Selected Damped Lyman Systems Systems

New Radio Facilities Allow Optical-Style Surveys• Intervening absorption, independent of dust• Proof of concept detection of DLA• ∆z ~ 150 Intrinsic Absorption • Expect high detection rates• Sensitivie to DLAs to z = 4• OH search for free

Stimulated Absorption by H2CO (DASARs)• Uses CMB as illumination source• Traces gastrophysics in detail • Potentially very large pool of objects to observe (still much foundational/calibration work to be done…)

The End The End

Conjugate OH: Anti-masing Conjugate OH: Anti-masing

Selection rules: ΔF = ± 1,0

Intra-ladder transitions overpopulate F = 2: 1720 emission 1612 absorption

Inter-ladder transitions overpopulate F = 1: 1720 absorption 1612 emission

16121720

Conjugate OH lines:

Conjugate lines in NGC Conjugate lines in NGC 253 253

Frayer, Seaquist & Frail (1998)

Conjugate OH lines show changing structure along line of sight:

1720 emission N(OH)/V < 1015 cm-2 km-1 s N(H2) < 1022 cm-2

1612 emission N(OH)/V > 1015 cm-2 km-1 s N(H2) > 1022 cm-2

Note: Conjugate lines weakly amplify background continuum Detectability follows rules of absorption, not emission

HH22CO Absorption in Dark Clouds CO Absorption in Dark Clouds

“Anomalous absorption” in Galactic dark clouds (Palmer et al 1969)

Tex < TCMB

2 cm lines also observed in absorption against CMB “Anti-inversion” due to collisional pumping (Evans et al 1975)

cm line ratio proxy for n(H2)

2 mm emission observed in Galactic dark clouds (Evans & Kutner 1976)

gastrophysics

HH22CO: The Swiss Army Knife CO: The Swiss Army Knife MoleculeMolecule

Anti-inverted (cm) line ratios yield n(H2), nearly independent of Tkin

Line ratios between species give ortho:para ratio H2CO formation channel (hot/cold; gas/dust)

Line ratios from different Ka

ladders of a given species (ortho/para) yield Tkin

∆J = ±1 line ratios within a Ka ladder yield Trot



Arp 220 III Zw 35


NGC 520NGC 660


Darling & Henkel

Baan, Guesten, & Haschick (1986)



Arp 220 III Zw 35


NGC 520NGC 660


Filho, Barthel, & Ho (2002)

NGC 660, 8.4 GHz

Darling & Henkel (in prep)


Darling & Henkel (in prep)


Arp 220 III Zw 35


NGC 520NGC 660


Filho, Barthel, & Ho (2002)

NGC 660, 8.4 GHz

~350 pc

~375 km/s

Mencl = 1.4109 M

HH22CO: CO: A Planar Asymmetric Top MoleculeA Planar Asymmetric Top Molecule

Wiklind & Combes

HH22CO: CO: Anti-Inversion in Centimeter LinesAnti-Inversion in Centimeter Lines

Allow 4 excitation temps:

1. No physical solution with

Tcm > TCMB

2. No solution with Tmm= Tcm

3. No solution with Tmm= T4.8

4. If T14.5 = T4.8 then all lines

have Tex < TCMB

5. If Tmm ≥ TCMB then

TCMB > T14.5 > T4.8

Chengalur, deBruyn, &Chengalur, deBruyn, & Narasimha 1999Narasimha 1999

Patnaik et al. 1994Patnaik et al. 1994

Nair et al. 1993Nair et al. 1993

PKS 1830-211

Darling (in prep)

Menten et al. 1999300 km/s

Extended Illumination: PKS 1830-211Extended Illumination: PKS 1830-211

PKS 1830-211: - Einstein ring at z = 0.89

- HI and OH absorption

- CO, HCN, HCO+,… absorption

- Moleculear isotope absorption

- H2CO absorption

Scaling Relations Scaling Relations

Detection of cm H2CO Lines vs z Depends on:

• (Anti) Inversion vs z How does Tcm - TCMB scale vs z?

(TCMB = 2.73 (1+z) K)

• Filling factor on kpc scales

• Filling factor vs z

• Angular size vs z




Tcm - TCMB (1+z)







Tcm - TCMB (1+z)







Tcm - TCMB (1+z)



• Angular size vs z - CMB power in small beams

Rayleigh-Jeans Law

CMB power scales as beam

arcmin:arcsec 3600:1

~100 mJy ~30 µJy

HH22CO Against the CMB: CO Against the CMB: ProspectsProspects

The Future:

- Molecule of choice for studies of star formation, molecular gas from present day to arbitrary redshift

EVLAALMAHigh Sensitivity Array

Ortho:Para H2CO gives astrochemistry channel(dust vs gas, hot vs cold)

H2CO mm + cm lines yield gastrophysicsTkin n(H2) Tx TCMB

No redshift limit to detection (in fact, angular size grows at high z)

HH22CO as z-Machine CO as z-Machine

If H2CO can be observed against the CMB, • Anti-inversion obviates need for chance alignments• Unique probe of gastrophysics of dense molecular ISM

Much foundational work yet to be done… Scaling relations Filling factor on kpc scales Total H2CO mass in galaxies: M(H2CO) M(dense)

Regardless, H2CO should be observable with ALMA:• Absorption and emission• Similar abundance, line luminosity to HCN (~10%)• Ortho:para H2CO at z > 0• Line Tex floor set by CMB, scales with z

Pathologies as Probes Pathologies as Probes

Masers provide exceptional Tb • Precision positions (H2O in NGC 4258)• Probes of intervening gas (scintillation)• Signposts at cosmological distances Tunneling • NH3 is a maser and molecular ISM thermometer

Conjugate Lines• Local H2 density indicator• Probe of fundamental physical constants

Stimulated Absorption (DASARs)• Uses CMB as illumination source• Traces gastrophysics in detail • Potentially very large pool of objects to observe (still much foundational/calibration work to be done…)

Documents

Radio Selected Damped Lyman Systems