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EXPLORING THE GALACTIC PLANE WITH HYDROGEN RADIO RECOMBINATION LINES (RRLs) Roberta Paladini

EXPLORING THE GALACTIC PLANE WITH HYDROGEN RADIO RECOMBINATION LINES (RRLs) Roberta Paladini NASA Herschel Science Center/Caltech. WHAT ARE (HYDROGEN) RADIO RECOMBINATION LINES (RRLs) ? . RRLs (n > 50) . Rydberg Equation. WHY DO WE CARE ? I - THE WARM IONIZED MEDIUM (WIM).

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EXPLORING THE GALACTIC PLANE WITH HYDROGEN RADIO RECOMBINATION LINES (RRLs) Roberta Paladini

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  1. EXPLORING THE GALACTIC PLANE WITH HYDROGEN RADIO RECOMBINATION LINES (RRLs) Roberta Paladini NASA Herschel Science Center/Caltech EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  2. WHAT ARE (HYDROGEN) RADIO RECOMBINATION LINES (RRLs) ? RRLs (n > 50) Rydberg Equation EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  3. WHY DO WE CARE ? I - THE WARM IONIZED MEDIUM (WIM) • FACTS ABOUT THE WIM • (Haffner et al. 2012 from Reynolds 1984, 1992,et al. 1998, 1999, etc.) • Comparable to molecular hydrogen in mass: ~ 1.6 x 109Msol (Ferriere ) • locally, in a vertical column through the solar neighborhood, H+ ~ 1/3 H0: • NH+ ~ 1 x 1020 cm-2 • Globally, 90% of the H+ mass is in the WIM, not in HII regions • Fills 20 – 40% of the volume over a 2-3 kpc thick layer about the midplane • Requires 1 x 10-4 erg s-1 cm-2 to sustain the 5 x 106 s-1 cm-2 recombination • rate ( ~15% of ionizing flux escapes HII regions and ~4% even escapes • the Galaxy !) The existence of a substantial amount of ionized gas outside of HII regions was first suggested by Hoyle & Ellis (1963) However, definitive assessment only with Wisconsin H-Alpha Mapper (WHAM, Haffner et al. 2003) survey EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  4. WHY DO WE CARE ? II – WE NEED A “CLEAN” TRACER OF IONIZED GAS To trace ionized gas, one can use: 1. Radio free-free emission (thermal bremsstrahlung)  but component separation problem (@ 5 GHz, 20% of emission along the Plane is synchrotron emission, Paladini et al. 2005) H-alpha emission (Balmer line: 3 2)  absorption (on the Galactic Plane, AV > 1 mag almost everywhere) AME synchrotron dust free-free Davies et al. 2006 Problem, e.g., to compute SFR (Msol yr-1) EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  5. WHY DO WE CARE ? III – THE PHYSICS 1. From RRLs: with 2. From free-free continuum: The combination of RRLs and free-free allows us to uniquely constrain the physics of the ionized gas component EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  6. HISTORICAL RRL SURVEYS NOTE: none of the surveys above covers the whole Galactic Plane. Also, all these surveys target (relatively bright) HII regions. EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  7. NEW GENERATION OF SURVEYS – I • The GBT HII Region Discovery Survey: HRDS(Anderson, Bania, Balser & Rood 2011) • Green Bank Telescope (GBT, 100 m) – sensitivity + power of anticorrelation spectrometer (ACS) • 3 cm (8 GHz -> X-band) • -160 < l < 67o, |b| < 1o • Q ~ 82’’, Dv ~ 1.86 km s-1, rms ~ 1 mJy • simultaneous observations of H86a to H93a • also free-free continuum (using Digital Continuum Receiver) EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  8. HRDS Survey : investigating Galactic structure Bania & Anderson 2010 •  Discovery of large number of new (bubble) HII regions • 25 new 1st quadrant HII regions (double known #) with negative • velocities, i.e. beyond solar circle (D > 12 kpc) •  also, HII regions located in the kinematic locus of 3 kpc Arm EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  9. NEW GENERATION OF SURVEYS – II • The HI Parkes All Sky Survey: HIPASS (Staveley-Smith et al. 1996) • Parkes telescope (64 m) • 21cm HI line survey over entire southern sky ( -900 < d < +20) • Q ~ 14.4’ , Dv ~ 13.19 km s-1, rms ~ 13 mJy • overall bandwidth : 64 MHz, from 1362 MHz to 1426 MHz • Zone of Avoidance (ZOA) Survey: osame equipment but deeper (~5.6 mJy) • (HIPASS by-product) • ocovers 196o < l < 20, |b| < 5o • o H166a, H167a, H168a EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  10. HIPASS Survey – I : resolving component separation problem Alves et al. 2010 & 2011 Alves et al. 2010 Alves et al. 2011 (l = 200 to 360) Alves et al. 2010 (l = 360 to 440) EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  11. HIPASS Survey – II : ISM dust properties Traficante et al. 2012 (submitted to MNRAS) (Bloemen et al. 1986, Sodroski et al. 1989, 1994, etc..) Neutral Phase Molecular Phase Ionized Phase GLIMPSE + MIPSGAL + Hi-GAL EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  12. HIPASS Survey – II : ISM dust properties Traficante et al. 2012 (submitted to MNRAS) (Bloemen et al. 1986, Sodroski et al. 1989, 1994, etc..) Neutral Phase Molecular Phase Ionized Phase GLIMPSE + MIPSGAL + Hi-GAL EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  13. EWASS 2012 –Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  14. RRLs AT DECAMETER WAVELENGTHS • Hydrogen transitions for 40 < n < ~300 are observable at centimeter wavelengths • Highest hydrogen transition ever detected: H300a detected in SgrA and W43 (Casse & Shaver 1977; Pedlar, Davies, Hart & Shaver 1978) • Q: Can atoms with still higher levels of excitation exist in the cosmos ? • C427a (l = 3.56 m), C486a (l = 5.25 m), C358a (l = 7.12 m) and C612b (l = 3.56 m) were successfully detected at PushcinoPadioastronomical Observatory (Ariskinet al. 1982) • To emit RRLs corresponding to transitions between extremely high excitation levels (n > 300) , the emitting region must have low ne (< 102 cm-3) and be sufficiently cold (Te < 100 K) EWASS 2012 –Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  15. CAS A @ 74 MHz Courtesy of VLA EWASS 2012 –Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  16. CARBON RRLs: PROSPECTS FOR THE FUTURE Peters et al. 2010 EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  17. SUMMARY • RRLs provide invaluable information about the thermodynamic and kinematic for the ionized gas (both HII regions and the WIM) • they trace ionized gas in a ‘’clean’’ fashion (no contamination from other emitting process or from dust absorption) • Hydrogen and carbon RRLs are complementary in providing information on the WIM: • o hydrogen RRLs trace denser/warmer gas • o carbon RRLs trace less dense/colder gas EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  18. EWASS 2012 – Galactic Plane Reloaded -July 5, 6 2012 - Rome, Italy

  19. EWASS 2012 –Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

  20. EWASS 2012 - July 5, 6 2012 - Rome, Italy

  21. EWASS 2012 - July 5, 6 2012 - Rome, Italy

  22. EWASS 2012 - July 5, 6 2012 - Rome, Italy

  23. THE POTENTIAL OF RRLs • RRLs not only are a powerful tool to investigate the thermodynamic structure of bright HII regions and other discrete sources • With the continuing improvements in the sensitivity of telescopes and receivers, they enable the study of: • o the structure of the Galaxy • o the diffuse gas along the Galactic Plane, not necessarily • associated with discrete sources EWASS 2012 – Galactic Plane Reloaded - July 5, 6 2012 - Rome, Italy

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