Montreal 12Sep2017 Galactic HI -...
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Future Canadian Prospects in the Galac4c Neutral Atomic Medium
Jeroen S4l Department of Physics and Astronomy
The University of Calgary
VGPS
CGPS
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Why Galac4c HI?
• It’s (almost) everywhere • Most of the mass of the ISM • Two orders of magnitude in temperature and density • Sub-‐parsec scale structure (10” 0.1 pc @ 2 kpc) • Physics that cannot be addressed in extragalac4c work (opacity, spin temperature, phases)
• Tracer for interstellar ex4nc4on
Movie credit: J. Peek, GALFA consor4um
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Cold HI Con4nuum Absorp4on
Instrumenta4on: High angular resolu4on (< 10”) ngVLA strength Modest UV coverage No short spacings required, unless structure in HI in front of extended sources (Leahy & Ranasinghe)
Astrophysics: Ø Galac4c distribu4on and opacity of
cold HI Ø Tracer of spiral arms Ø Kinema4c distances of Galac4c
con4nuum sources (HII regions, SNRs)
Point source sensi4vity propor4onal to third power of angular resolu4on.
CO
Average “off” spectrum
“on” spectrum
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Cold HI HI Self Absorp4on (HISA)
Instrumenta4on: Wide range of spa4al scales Short spacings required Complete UV coverage with 0.2 K sensi4vity on baselines up to ~ 5 km.
Astrophysics: Ø Structure of cold HI clouds Ø Transi4on state to or from molecular gas Ø Resolve near/far ambiguity in kinema4c
distances of molecular clouds Ø Rela4on to cold dust, molecular
filaments (0.1 pc scale requires ~ 10” resolu4on at few kpc)
“Arch of Darkness”, Knee & Brunt (2001) Nat, 412, 308
S. Gibson
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Instrumenta4on: µG field detectable in emission with DRAO 26m telescope in a few hours Single dish or interferometer. No short spacings necessary? Polariza4on purity in Stokes V and stray radia4on (single dish). Beam squint problem in JVLA because of off-‐axis feeds.
Astrophysics: Ø Local strength of (line of sight
component of) magne4c field. Ø Similar magne4c field strength in
cold and warm HI? Ø Magne4c field in IVC/HVC Ø Rela4on to molecular filaments? Ø Absorp4on or emission
McClure-‐Griffiths et al. (2006), Clark et al. (2014)
Troland et al. (2016) from absorp4on against M42 (one of 2 velocity components)
Magne4sm Zeeman effect, filaments
Stellar polariza4on Fiber structure
Also: Van Eck et al. (2016)
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Not just 21 cm Radio Recombina4on Lines of C+ (CRRL)
Astrophysics: Ø C+ can exist where H is neutral Ø Main source of cooling in HI regions
in crucial temperature and density range, T < 100 K, AV = 1-‐5 mag.
Ø CRRL probe electron temperature, density, and line-‐of-‐sight depth.
Detec4on of cold HI independent of background illumina4on Instrumenta4on: Low-‐frequency interferometer
For example: C272α at 327 MHz C441α and C555β at 76 MHz C575α at 34.5 MHz Roshi & Kantharia (2013)
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Stellar Feedback Astrophysics: Ø Stellar wind bubbles, SNRs, Superbubbles Ø Broad wings of HI spectra Ø Disk-‐halo interface Ø Mechanical energy input over life 4me of a
star cluster Ø Condi4ons for ouqlow into the halo
Image credit: Jayanne English et al. Normandeau et al. (1996), Nat 380, 687
Instrumenta4on: Wide range of spa4al scales + short spacings Good signal to noise and dynamic range Complete UV coverage
S4l & Irwin (2001) VGPS
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Galac4c Halo
Blagrave et al. (2017), DRAO ST
Astrophysics: Ø Dynamics of halo gas Ø Structure and kinema4cs of intermediate-‐
velocity and high-‐velocity clouds Ø Interac4on of disk with infalling gas Instrumenta4on: Wide range of spa4al scales + short spacings Good signal to noise and dynamic range Complete UV coverage Beware stray radia4on from bright Galac4c plane in single dish surveys.
NASA/ESA/Levay/STScI, Saxton/Lockman/NRAO/AUI/NSF/Mellinger
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LMC/SMC/Magellanic Stream
Astrophysics: Ø Bird’s eye view of stellar feedback on ISM in best
possible detail. Ø Structure and rela4on to other phases of the ISM
in a low-‐metallicity environment. Ø Dynamics of accre4on of maser on galaxies
Bart Wakker
Kim et al./CSIRO
Instrumenta4on: SKA. Match angular resolu4on and spa4al dynamic range of op4cal/IR surveys
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Conclusions Galac4c HI and other spectral lines probing the neutral atomic medium are essen4al for detailed observa4on of many astrophysical phenomena
– Stellar wind bubbles and Supernova remnants – Magne4sm – Molecular cloud forma4on and phase transi4ons in the ISM – Disk-‐halo connec4on, dynamics of halo gas
• Significant progress with 15” resolu4on, good spa4al and intensity dynamic range
• Many (not all) applica4ons require a 50 -‐ 100 m single dish to fill short spacings (Baseline < 15m): Arecibo, FAST, GBT, Parkes, ….
• Most applica4ons do not require full sky coverage • Loca4on: LMC/SMC favor SKA (but M31 favors ngVLA) • Circular polariza4on capability for Zeeman effect
Check out the THOR survey, JVLA 18” resolu4on HI in first quadrant (JVLA C-‐array + VGPS)