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How Young Can a Cloud Be –

How Young Can a Cloud Be –. HINSA as a New Molecular Cloud Probe. Di Li. Galactic HI Absorption. 1954: Clear Statement re. Absorption Features. Past Observations- Technical Limitations. Haystack 120ft: 25 ’ ; 0.5km/s (Myers et al. 1978) Green Bank 140ft: 21 ’ ; 0.4 km/s (Knapp 1974)

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How Young Can a Cloud Be –

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  1. How Young Can a Cloud Be – HINSA as a New Molecular Cloud Probe Di Li CfA Star Formation Symposium 2004

  2. Galactic HI Absorption CfA Star Formation Symposium 2004

  3. 1954: Clear Statement re. Absorption Features CfA Star Formation Symposium 2004

  4. Past Observations-Technical Limitations • Haystack 120ft: 25’; 0.5km/s (Myers et al. 1978) • Green Bank 140ft: 21’; 0.4 km/s(Knapp 1974) • 76m Lovell Telescope:12’; 0.5 km/s (McCutcheon et al.1978; Montgomery et al. 1995 ) • Effelsberg 100m: 9’, 0.5 km/s (Wilson & Minn 1977; Batrla et al. 1983; Poppel et al. 1983) • Arecibo 300m: 4’, 1 km/s (Baker & Burton 1979, Bania & Lockman 1984) • VLA & DRAO: 1’ - 1.5’, 1.3 km/s (Van der Werf et al. 1988, 1989; Gibson et al. 2000) CfA Star Formation Symposium 2004

  5. Arecibo: Upgraded Point-focused with secondary and tertiary Wider bandwidth LO and better backends Central panel patched Surface readjustment underway CfA Star Formation Symposium 2004

  6. Detecting Cold HI - HINarrow Self Absorption • Called ‘self-absorption’ in order to differentiate from absorption against continuum sources • HI Self-Absorption is different from the usual meaning of ‘self’, as in the case of thick tracer like CO. • In case of HI absorption caused by dark clouds, HINSA could be a less confusing alternative. -10 -5 0 5 10 15 Vlsr (km/s) (Li & Goldsmith 2003 ApJ, 585, 823) CfA Star Formation Symposium 2004

  7. HINSA: Definition HI Absorption with corresponding molecular emission and V(HI Absorption) < V(CO) (Li & Goldsmith 2003 ApJ, 585, 823) CfA Star Formation Symposium 2004

  8. Survey Statistics: HINSA Detection Rate • 23 sources with clear HI NSA • Detection rate: 77% • Similar Turbulent content HINSA vs. OH Average non-thermal line width (km/s) OH 0.83; HI 0.84 The raw line width of HI is on average ~1km/s, less than two channels in DRAO survey. The average depth is less than 2 RMS noise in DRAO survey. (Li & Goldsmith 2003 ApJ, 585, 823) CfA Star Formation Symposium 2004

  9. Extremely Good Correlation of HI Narrow Self-Absorption and Molecular Emission Lines (Goldsmith & Li 2004 submitted to ApJ) CfA Star Formation Symposium 2004

  10. The Real Globule? The “North” condensation was previously unknown and was found by mapping the HINSA and following up with 13CO and C18O This morphology confirms close connection between cold HI absorption and molecular emission position in CB catalog (Clemens & Barvanis 1988) (Goldsmith & Li 2004 submitted to ApJ) CfA Star Formation Symposium 2004

  11. Three-Component Radiative Transfer CfA Star Formation Symposium 2004

  12. Two Useful Limiting Cases • Without foreground: absorber is equivalent to an emitting cloud at the temperature differential • With optically thin foreground and Tb=Tf (Li & Goldsmith 2003 ApJ, 585, 823 cf. Van der Werf et al. 1988 ) CfA Star Formation Symposium 2004

  13. Column Density of HI • Total HI column density derived from optical depth of the 21cm line: • Average HI column density: • If using C18O, the abundance [HI/H2] is 0.15% • The third most abundant species inside molecular clouds after only H2 and He, but before CO! • 8x1018 cm-2 CfA Star Formation Symposium 2004

  14. How Fast Does Star Form? • Conventional View • Core: Ambipolar diffusion • Collapse: Inside-out • Jets: Deuterium Burning, Stellar energetic starts to take over • Accretion Disk: the termination of infall will determine the final mass of the new star. • Fast Star Formation? • Clouds form by HI stream interaction (Hartmann et al. 2001) • Stars are formed on a dynamical time scale (~Myr Elmegreen 2001). • Clouds are dispersed by stellar energy output (Elmegreen 2000) CfA Star Formation Symposium 2004

  15. Gas-Grain Reaction Network of H2 Formation • The variable set • The parameters set CfA Star Formation Symposium 2004

  16. HI Fractional Abundance Measures TIME since the start of Atomic to Molecular Conversion CfA Star Formation Symposium 2004

  17. From Atoms to Stars H=>H2 => Cloud Complex => Core=>Protostars ALFA-Tau Spitzer c2d + COMPLETE • Goodman • N. Ridge • S. Schnee • J. Foster • D. Li • … • (the COMPLETE team) P. Goldsmith C. Brunt M. Heyer R. Snell G. Narayanan D. Li H. Arce … and GALFA consortium N. Evans L. Allen P. Myers T. Burke … (the Spitzer legacy team) CfA Star Formation Symposium 2004

  18. HINSA: Conclusions • HINSA with v < 2 km s-1 is a widespread phenomenon associated with dark clouds . • The narrow line atomic hydrogen has significant column density N(HINSA)~8x1018 cm-2, making it the third most abundant species of molecular clouds after H2 and He. • HINSA places a lower limit on molecular cloud core age at > 5 million years • HINSA could be a good tracer for Zeeman measurement. • HINSA could provide a probe to galactic cosmic ray distribution. • Large scale HI, CO, and infrared surveys would build a picture of cloud formation and their evolution coupled with star formation. CfA Star Formation Symposium 2004

  19. Colder Gas in CNM Phases in neutral medium (Wolfire et al. 1995; McKee & Ostriker 1977; Field et al. 1962) Cold Neutral Medium: T~80 K Warm Neutral Medium: T~8000 K • Existence for colder CNM (T<40 K) • Continuum absorption: Heiles 2001, Kalbella et al. 1985 • HI self-absorption (HISA): Knee & Brunt 2001 CfA Star Formation Symposium 2004

  20. HI Self Absorption • Cold feature revealed in deficiency of emission GSH139-03-69 (Knee and Brunt, 2001) CfA Star Formation Symposium 2004

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