Constraining the CNM with LOFAR.

Transcription

1 Constraining the CNM with LOFAR. JBRO, R. van Weeren, F. Salgado, L. Morabito, C. Toribio, X. Tielens, H. Rottgering, A. Asgekar & G. White + assistance: J. McKean, R. Fallows, J. Hessels (1) Interstellar medium (2) Recombination lines (3) LOFAR 'baby steps' (4) SKA1 LOFAR: Cassiopeia A (60 MHz, 10'') 'growing up ' Carbon RRL (n=576)

2 The Interstellar Medium (ISM) Phase T [K] nh [cm-3] H-state HIM WIM 104 WNM 8000 Xe Obsv. H+ 1 X-ray, UV 0.04 H+ 1 UV-IR 0.1 H0 0.1 HI (em) CNM (HI) H0 <10-3 HI (abs) CNM (H2) 30 >1000 H2 <10-7 CO Galaxy evolution is driven by (SF) recycling of ISM => What is the role of the atomic CNM? => HI em (contaminated), HI abs (difficult)

3 Outstanding questions. Galaxy evolution is driven by recycling of the ISM but, what is the role of the cold atomic gas in galaxy evolution? In particular: - What is its morphology, dynamics and how does this compare to molecular, starforming & hot gas? - What is its thermal, pressure balance? - What is its ionization rate? - What is its chemical enrichment? - What is the CNM fraction of the HI 21 cm signal?

4 Radio Recombination Lines (RRL's) Spectral lines from ions recombining with electrons in a diffuse ionized plasma are called recombination lines Occur at all quantum levels (n): ν = R c [ 1/n2 1/(n+Δn)2 ] n < 50: UV-IR (RL) n > 50: Radio (RRL) RRL types: classical diffuse ( ν > 1 GHz ) ( ν < 1 GHz ) Palmer & Zuckerman 1966 Konovalenko & Sodin 1980 Diffuse RRLs: - weak ( Milky Way τpeak ~10-4 to 10-3 ) + many ( 500 α lines LOFAR )

5 Diffuse RRL's ( 1 GHz) - Carbon, Hydrogen RRL's Absorption 130 MHz Emission 130 MHz - Associated with CNM / PDR's Te ~ [K] ne ~ [cm-3] - properties : Te, ne, EM - ionisation : ζ(h) - metallicity : [C/H] Cassiopeia A (Payne+1989) - kinematics : v, Δv (?) unstable gas : (?) WNM : T ~ [K] T ~ [K]

6 RRL models: Line width broadening Total (solid) width Contributions: (1) Doppler (dash) (2) Pressure (dash-dot) (3) Radiation (dash-dot-dot) ΔVP ~ ( ne n5.2 ) / ( Te1.5 ν ) ΔVR ~ ( TR n5.8 ) / ν [N(HI)=1020 cm-2]

7 RRL models: Integrated Optical Depth (τ) Phases: CNM (atomic): - ne = 0.05 cm-3 - Te = 100 K WNM: - ne = 0.01 cm-3 - Te = 104 K HII: - ne = 300 cm-3 - Te = 104 K * i.e. RRL can disentangle CNM, WNM in HI 21 cm τc ~ Te-5/2 EMC ( bn βn )C [N(HI)=1020 cm-2]

8 Returning to the BIG question. Galaxy evolution is driven by recycling of the ISM but, what is the role of the cold atomic gas in galaxy evolution? Method: - Localize the (C)RRL gas & compare with CO, HI and HII. - Thermal properties of RRL gas ( Te, ne, EM ) - Ionization rate of the RRL gas ( ζh ) - Carbon abundance ( [C/H] ) - Kinematics of the RRL gas ( v, Δv )

9 Diffuse Radio Recombination Lines with LOFAR The Power of LOFAR: - sensitivity - resolution - field of view - bandwidth => Survey speed (α, δ, λ) * LBA MHz : 400 RRL α-lines * HBA MHz : 100 RRL α-lines

10 LOFAR: (a) Galactic Diffuse RRL Survey 1 Degree Survey (stepping-stone) Goal: - Morphology RRL gas Thermal balance ( Λth, Pth ) Ionization rate CNM Carbon abundance (end goal is 10' survey)

11 Galactic diffuse RRL's: All that was known sofar (Kantharia & Anantharamaiah 2001) Major issues: ΩL > 4 deg ΩL = 4 deg ΩL = 2 deg - Beam FWHM > 2 deg. i.e. unresolved cloud sizes - instrument resolution mismatch - limited frequency coverage Data: * Anantharamaiah 1988 (1985) 328 MHz (inner plane north) * Erickson et al MHz (inner plane south) * K & A MHz (few pointings)

12 LOFAR: Galactic RRL Survey LC0_028 : Galactic beamformed observations (6 stations, 1 degree beam) Fields P0, P1, P2 P0 (18:26:44 ; -12:11:29) P1 (18:52:01 ; +00:00:12) P2 (20:18:36 ; +41:19:14) LBA-Superterp (BF) 61 TAB (10x10 deg2) 81 SB/L (30-70 MHz) 256 channels

13 LOFAR: (b) Galactic Pinhole RRL survey Cassiopeia A (LCASS) Goal: - connect > 10' scales to < 1' scale ( primary sources: SNR's, FRI/II's )

14 Galactic pinhole RRL's: All that was known sofar Cas A issue: instrument resolution mismatch (Kantharia+1998) WSRT HBA LBA WSRT HBA LBA (LBA: 400 α lines) (HBA: 80 α lines) (Cas A: Kantharia+1998)

15 LOFAR: LOFAR Cas A Spectral Survey (LCASS) Cas A: 60 MHz (10'') Bandpass: Cas A (black), Cyg A (red) Cβ (PI: Oonk) Cα

16 LOFAR: Galactic pinhole studies Cygnus A (bright, extragalactic background source) Measurements: (MW CNM) LOFAR-LBA (10h) BW = Δf = Δv = MHz 0.4 khz 2-4 km/s τpeak = 2 x 10-4 vlsr = +4 km/s FWHM = 10 km/s Derived properties: Te ne EMC [C/H] ζh = 110 K = 0.06 cm-3 = cm-6 pc = 1.8x10-4 < 4x10-16 s-1

17 LOFAR RRL Universe: (HI 21 cm, 3C, SNR) [N(HI) > 3x1020 cm-2]

18 LOFAR: Results & Outlook LOFAR-RRL => CNM ( Te, ne, EM, ζh, [C/H] ) Cas A (LBA 60 MHz) (a) Scientific: - LOFAR can map the CNM in the Milky Way - Bright background sources give < 1' scale - First extragalactic (C)RRL detection (< 1 GHz) (a) Technical: - Spectroscopic results stable (>2 years) - Spectral RMS: (time), (chan), (#SB) (c) Future: - LOFAR (stay tuned) - SKA1-LOW...

19 SKA1-LOW: Transformational for RRL's Galactic: SKA1-LOW > LOFAR x 10!! Arecibo at low frequencies - LOFAR (northern hemisphere) : scales >10' for N(HI) > 3x1020 cm-2 - SKA1-LOW (southern hemisphere) : scales >3' for N(HI) > 5x1019 cm-2

20 SKA1-LOW: Transformational for RRL's Extragalactic: SKA1-LOW > LOFAR x 10!! Arecibo at low frequencies - LOFAR (northern hemisphere) : 3C limit - SKA1-LOW (southern hemisphere) : 7C limit

21 SKA1-LOW: Transformational for RRL's Extragalactic: SKA1-LOW > LOFAR x 10!! (far-away galaxies) SKA1-LOW (3πsr, 8h pointings) * Dramatic increase in (RRL) sources: LOFAR (7.0Jy) ~ 102 SKA1-LOW (0.5Jy) ~ 105 (x 103!!)

22 Conclusions Cas A (LBA 60 MHz) (a) Low-frequency RRLs can constrain the CNM and its role in starformation. CNM ( Te, ne, EM, ζh, [C/H] ) (b) LOFAR will open our eyes and provide the first glimpse of the RRL universe. Milky Way >= 10', N(HI)>3x1020 cm-2 Extragalactic <= 300 sources (c) SKA1-LOW will sharpen our focus by an order of magnitude (>10xLOFAR) Milky Way >= 3', N(HI)>5x1019 cm-2 Extragalactic >= sources