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Radio Recombination Line Observations of HII Regions with ALMA & the EVLA

Radio Recombination Line Observations of HII Regions with ALMA & the EVLA. Stan Kurtz Center for Radioastronomy & Astrophysics National Autonomous University of Mexico. What is an HII Region, anyway?. Objectives and challenges depend on the class of region. Why observe RRLs at all?.

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Radio Recombination Line Observations of HII Regions with ALMA & the EVLA

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  1. Radio Recombination LineObservations of HII Regions with ALMA & the EVLA Stan Kurtz Center for Radioastronomy & Astrophysics National Autonomous University of Mexico

  2. What is an HII Region, anyway? Objectives and challenges depend on the class of region

  3. Why observe RRLs at all? Optical & infrared recombination lines are much brighter than RRL Embedded HII regions are highly obscured by dust Optical lines may be affected by nearby reflection nebulae Higher angular resolution than offered by optical seeing Higher velocity resolution than offered by optical lines Intrinsic interest in the recomb line (masing, velocity shifts)

  4. Many ways to produce radio free-free emission many ways to produce RRL Keto (2005) • Photo-ionized HII regions • Externally ionized clumps • Thermal radio jets • Stellar winds • Ionized accretion flows • Photo-evaporated disks • Accretion shocks Neufeld & Hollenbach(1994) many of these are relatively weak: mJy or less; all could be profitably studied in RRL

  5. Some basic RRL facts • Band 2 covers H45α – H42α • Band 3 covers H42α – H38α • TL/TC ~ ν1.1 low-n lines are stronger • H76α has TL/TC ~ 0.15 H44α has TL/TC ~ 0.75 • Pressure broadening ~ n7.4 low-n lines better velocity tracers • Lines are more closely spaced at high n • line stacking improves S/N for e-VLA and e-MERLIN

  6. Hypercompact HII Regions andBroad Recombination Line Objects H92a G28.20-0.04 FWHM 75 km/s H92a FWHM 35 km/s Sewilo et al. 2004

  7. VLA observations of the 7mm H53 line Shell-like morphology 1100 AU inner radius 2500 AU outer radius Velocity gradient ~ 100 km/s/pc If Keplerian rotation, then central mass is ~28 M Sewiloet al. (2008)

  8. The Sub-Millimeter Array allows 1 arcsec resolution in the H30 line at 1mm (band 6) n(H30) > n(H66 & H92) suggests density gradients but so Keto, Zhang & Kurtz (2009) Green is H66 x190, Red is H30 blueshift of H30 implies outflow Blue is H53 x10, Red is H30 redshift of H30 implies infall

  9. Classical HII Regions • arc minute sizes  mosaicing (FOV ~ 1-1.5’) • Zeeman splitting & metallicity in cold HII regions G14.6-0.1 (Sánchez-Monge et al. in prep.) H79α Δv < 15 km/s T < 5000 K 24 μm + 20 cm

  10. Do RRL really need Band 2? • TL/TC is about 30% lower than in Band 3 • Pressure broadening is ~ 2x worse than in Band 3 H45α – H42α not so different from H42α – H38a

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