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Radio Selected Damped Lyman Systems. Jeremy Darling (CASA, University of Colorado). Outline: 1. Damped Lya Systems 2. Motivation 3. Intervening Absorption 4. Intrinsic Absorption [5. H 2 CO Absorption] 6. Summary. Damped Lyman Systems. By definition,
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Radio Selected Damped Lyman Systems Jeremy Darling (CASA, University of Colorado) Outline: 1. Damped Lya Systems 2. Motivation 3. Intervening Absorption 4. Intrinsic Absorption [5. H2CO Absorption] 6. Summary
Damped Lyman 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: Motivation 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: Motivation 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: 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 • 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) • Conjugate OH lines • No “main” lines Wiklind & Combes 1997 Darling (2004) Darling (in prep) Wiklind & Combes 1996 Darling (in prep) Kanekar et al 2003 Wiklind & Combes 1995 Kanekar et al 2003 Wiklind & Combes 1998 Darling (in prep)
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) • Conjugate OH lines • No “main” lines Wiklind & Combes 1997 Darling (2004) Darling (in prep) Wiklind & Combes 1996 Darling (in prep) Kanekar et al 2003 Wiklind & Combes 1995 Kanekar et al 2003 Wiklind & Combes 1998 Darling (in prep)
13 km s-1 PKS 1413+135: OH 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?
(1×10-5 ~ 10 km s-1) PKS 1413+135: OH, 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 forallΔα/αo HI: Darling 2004 OH: Darling 2004 CO: Wiklind & Combes 1997
PKS 1413+135: OH, 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 forallΔα/αo
Intervening 21 cm Absorption: A “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)
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 and reduces z coverage Feed Resonance RFI z = 1.1 tl = 8.1 Gyr tU = 5.6 Gyr z = 0.63 tl = 5.9 Gyr tU = 7.8 Gyr 2.2 Gyr, 1.2 Gpc
Chengalur, deBruyn, & Narasimha 1999 Patnaik et al. 1994 Nair et al. 1993 PKS 1830-211 FWHM = 57 km s-1 τc = 0.22 NHI = 24.3 x 1018 (Ts/f) cm-2 Green Bank Blind HI Survey Pure radio HI absorption detection! Proof-of-concept for blind searches. • Molecules? • Lens?
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 Green Bank Blind HI Survey BIMA (Bolatto) Pure radio HI absorption detection! Proof-of-concept for blind searches. PKS 1830-211 • Molecules? • Lens?
Intervening 21 cm Absorption: A “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: CSOs 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: Survey Expectations Observe: 71 sources 0.5 < z < 4 CSOs GPS sources CSS sources Expect: Detect all DLAs in 1-2 hours Bonus: OH lines DLAs
Intrinsic Absorption Expected HI
Intrinsic Absorption Expected HI PKS 0500+019 z = 0.58 Flux Density (Jy) Previous detection: Carilli et al 1998 Barycentric Frequency (MHz)
Intrinsic Absorption: Survey Results (so far…) z < 0.7 redetections
Intrinsic Absorption: Survey Results (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
NGC 2264 Darling & Goldsmith (in prep) H2CO: The Swiss Army Knife Molecule Galactic Extragalactic Gastrophysics Galaxy Evolution (Cosmology ?)
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)
H2CO: The DASAR L ight A mplification by S timulated E mission of R adiation Inversion: “Heating” of lines Tx >> Tkin Pumprequired: 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 Pumprequired: Collisions with H2 *Not really dark. **Not a true amplification.
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)
Biggs et al 2001 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 B0218+357
Darling & Wiklind Ortho-H2CO Toward 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: • 14.5 GHz (211-212) (VLA; Menten & Reid 1996) • 150.5 GHz (211-110) (IRAM; Wiklind & Combes) Wiklind & Combes
H2CO 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?
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 probe of dense molecular gas, independent of redshift!
H2CO Against the CMB: Prospects • 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 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…)
Conjugate OH: Anti-masing Conjugate OH lines: 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 1720 1612
Conjugate lines in NGC 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
H2CO 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
H2CO: The Swiss Army Knife Molecule 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
Baan, Guesten, & Haschick (1986) 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 B0218+357 Darling & Henkel
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 B0218+357 Darling & Henkel (in prep) NGC 660, 8.4 GHz Filho, Barthel, & Ho (2002)
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 B0218+357 Darling & Henkel (in prep) ~375 km/s NGC 660, 8.4 GHz ~350 pc Mencl = 1.4109 M Filho, Barthel, & Ho (2002)
H2CO: A Planar Asymmetric Top Molecule Wiklind & Combes
H2CO: Anti-Inversion in Centimeter Lines Allow 4 excitation temps: No physical solution with Tcm > TCMB No solution with Tmm= Tcm No solution with Tmm= T4.8 If T14.5 = T4.8 then all lines have Tex < TCMB If Tmm ≥ TCMB then TCMB > T14.5 > T4.8
Chengalur, deBruyn, & Narasimha 1999 Patnaik et al. 1994 Nair et al. 1993 Extended 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 PKS 1830-211 Menten et al. 1999 300 km/s Darling (in prep)
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
Scaling Relations • Detection of cm H2CO Lines vs z Depends on: • (Anti) Inversion vs z • How does Tcm - TCMB scale vs z? • Tcm - TCMB (1+z) • Filling factor on kpc scales • Filling factor vs z • Angular size vs z
Scaling Relations • Detection of cm H2CO Lines vs z Depends on: • (Anti) Inversion vs z • How does Tcm - TCMB scale vs z? • Tcm - TCMB (1+z) • Filling factor on kpc scales • Filling factor vs z • Angular size vs z
Scaling Relations • Detection of cm H2CO Lines vs z Depends on: • (Anti) Inversion vs z • How does Tcm - TCMB scale vs z? • Tcm - TCMB (1+z) • Filling factor on kpc scales • Filling factor vs 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
H2CO Against the CMB: Prospects The Future: - Molecule of choice for studies of star formation, molecular gas from present day to arbitrary redshift EVLA ALMA High Sensitivity Array Ortho:Para H2CO gives astrochemistry channel (dust vs gas, hot vs cold) H2CO mm + cm lines yield gastrophysics Tkin n(H2) Tx TCMB No redshift limit to detection (in fact, angular size grows at high z)
H2CO 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 • 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…)