stacey poster

Information about stacey poster

Published on November 15, 2007

Author: Margot

Source: authorstream.com

Content

Slide1:  The [NII] Line Ratio The ISO 122 m [NII] to SPIFI 205 m line ratio yields the density of the low ionization gas (Figure 5, blue line and circle) The ratio is ~ 1.2  ne ~ 30 cm-3 Even with a 50% calibration uncertainty, it is clear that the [NII] lines (tracing low ionization gas) arise from a very low density medium: 10 < ne < 100 cm-3 Therefore, the “halo” of emission seen in the [OII] lines also contains gas in lower ionization states This low ionization, diffuse gas is similar to the warm ionized medium in the Galaxy as a whole The SPIFI instrument mounted on the Nasmyth arm of the AST/RO telescope. Aurora over the South Pole August 22, 2005 (photo by Stephen Parshley) Observations The Carina Nebula was observed in the 205.178 m [NII] line with SPIFI (Bradford et al. 2002) on the 1.7 m AST/RO telescope (Stark et al. 2001) at the South Pole. The data presented here were obtained on 23 to 25 August 2005, near the middle of our 30 day run. We mapped the region outlined in red in Figure 1 in weather that was unusually poor for the South Pole site, with zenith transmission ~ 7.6%. SPIFI-AST/RO Parameters Beam size: ~ 54” (FWHM) Field of view: ~ 325”  325” Resolving Power: R  /~ 5000, or v ~ 60 km/sec Sensitivity: NEP ~ 3.4  10-15 W/Hz1/2 (front end) Trec(DSB) ~ 150 K Results The map of Figure 3 contains only about 20% of our data The [NII] line appears in emission over most of the region The observed line emission largely follows the free-free radio contours (Retallack, 1983) The line peaks at ~ 0.51 K on the position of the Carina II radio continuum peak (G287.57-0.59, Figure 4) The line velocity centroid well matches that of the radio recombination lines (Brooks, Storey, & Whiteoak, 2001) Acknowledgements This work was supported by NSF grants OPP-0094605, OPP-0338149, and NASA grant NNG05GK70H. We are indebted to the Cardiff group under P. A. R. Ade for their excellent filters, to the GSFC group (S.H. Moseley, D. J. Benford, & J. G. Staguhn) for their excellent bolometers, and to J.W. Kooi who set up LO’s for our frequency calibration at the pole. We also thank the many people who have contributed to the success of SPIFI both at AST/RO and the JCMT including, and especially C. M. Bradford, A. D. Bolatto, J.A. Davidson, & M. L. Savage Discussion Prior ISO Results ISO/LWS mapped much of the same regions in the [OIII] and [NII] 122 m lines (Mizutani, Onaka, and Shibai, 2002) O++ takes 35 eV to form so it traces gas exposed to UV light from high mass stars. From the [OIII] lines, they find the highly ionized gas has two components: Relatively dense (ne ~ 100 to 350 cm-3) component associated with the Carina I and II HII regions Relatively diffuse (ne < 100 cm-3) “halo” component encompassing the entire complex with a diameter of ~ 30 pc [NII] and [CII] The [CII] line was mapped with ISO LWS and the KAO, and is both bright and widespread over the Carina Nebula (Mizutani, Onaka, and Shibai, 2004, Brooks et al. 2003) In galaxies the [CII] line emission predominantly arises from the warm dense photodissociation regions (PDRs) on the far-UV exposed surfaces of molecular clouds (cf. Stacey et al. 1991) -- However, [CII] can also arise from low density ionized gas With an ionization potential of 14.5 eV, the 205 m [NII] line only arises from ionized gas regions Since the [NII] 205 m line has a nearly identical critical density for thermalization as [CII] in ionized regions (~ 50 cm-3), the [CII]/[NII] 205 m line intensity ratio yields the fraction of the observed [CII] that arises from the ionized medium – subject to relative C+ to N+ abundance estimates Figure 5 displays the predicted [CII]/[NII] line intensity ratio (red line) for ionized gas as a function of gas density The observed value (red dot) of 8 means that 4/8 ~ 50% of the observed [CII] line emission arises from the ionized medium This is a much larger fraction than the 10 to 25 % commonly assumed in neutral gas studies of external galaxies, and has implications for the modeling of photodissociation regions including gas density and temperature, and the strength of stellar radiation fields in these studies References Bradford et al. Ap. Opt. 41, 2561 (2002) Brooks, K.J. et al. A&A, 412, 751 (2003) Brooks, K.J., Storey, J.W.V., & Whiteoak, J.B. MNRAS 327, 46 (2001) Mizutani, Onaka, & Shibai A&A 382, 610 (2002) Mizutani, Onaka, & Shibai A&A 423, 579 (2004) Retallack, D.S. MNRAS 204, 669 (1983) Stacey et al. ApJ 373, 423 (1991) Stark, A.A. et al., PASP, 115, 567 (2001) Wright, E.L. et al. ApJ 381, 200 (1991)

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