Science So Far from the NANTEN Telescope (a.k.a. What regions have been observed now in CO in the Southern Hemisphere, and what can be said about them?)

CfA Star Formation Journal Club, November 3, 1999, Alyssa A. Goodman

For reference:


General Concerns:

The papers summarized in the table below are all to appear in an upcoming special issue of the Publications of the Astronomical Society of Japan, and were presented by Y. Fukui, A. Mizuno et al. at the October 1999 ALMA meeting at the Carnegie Institution of Washington. Papers& abstracts already published are listed in the ADS printout handout.





AG Comments

Hara et al. A Study of Dense Cloud Cores and Star Formation in Lupus: C18O and 13CO J=1-0 Observations with NANTEN C18O, 13CO


  • Distances ~150 pc
  • C18O is done as follow-up to 13CO, in regions where 13CO column density is high.(see Fig. 2)
  • YSO density (including TTS) correlated with C18O "core" distribution (e.g. Fig. 5)
  • Typical C18O Core properties: 9.7 Msun; 0.17 pc; 4.1 ¥ 1021 cm-2; 0.90 km s-1 (see Fig. 6)
  • Mass spectrum dN/dM~M-1.7± 0.6 for M>3Msun
  • Claim is that Taurus is unusual in having very small Mvir/Mcore; Lupus more like Oph North or L1333 (see Figs 8,9)


  • t(C18O) is determined from 12CO excitation temperature (true for most of the NANTEN papers)
  • Is depletion of C18O (as found by Kramer et al. 1999 above 10 mag AV) a problem?
  • General comment--for discussion: Is a C18O clump really a "core"? (See L1251 example in handouts from Toth & Walmsley 1996; Goodman et al. 1998)

Mizuno et al.

(see also Mizuno et al. 1998, ApJL, 507, L83.)

Dense Cores and Star Formation Activities in the Chamaeleon Dark-Cloud Complex C18O, 13CO
  • Distances ~150 pc
  • Star formation activity highest in Cha I and lowest in Cha III (evolutionary sequence suggested where Cha I is most "gravitationally relaxed"). Cha I comparable with Taurus.
  • Typical C18O Core properties: 22 Msun; 0.22 pc; 9.7 ¥ 1021 cm-2; 0.82 km s-1
  • "Threshold Effect" proposed as explanation for better correlation of CTTS (actually YSOs identified with DENIS) with areas with N>1022 cm-2 (see Figs. 8-12) Effect strongest for sources with FIR excess.
  • Mizuno et al. 1998 suggested cloud dissipation by ouflows to explain lack of (13CO-traced) molecular gas around many (X-ray identified) YSOs in the area. (see their Fig 1 & 3)
  • Does IR identification (rather than X-ray, etc.) choose a different set of YSOs?
  • Does C18O trace different gas than 13CO?
  • IR vs. X-ray identification alone can explain apparent discrepancies between Mizuno et al 98 & 99, but line choice may matter too.
  • Hayakawa et al. A New Derivation of the Extinction-to-CO Column Density Ratio in the Chamaeleon I Dark Cloud C18O, 13CO
    • Table 1a presents summary of all previous AV-N(13CO) relations and the present ones.
    • Figure 5 shows significant region-to-region variations in correlation slope, even just within Chamaeleon. Slope is steeper (¥ 2) near cluster of TTS.
  • Neither 13CO nor C18O observations in this paper probe range above 10 mag AV, so no comments on Kramer et al. 1999 depletion results.
  • The jury's still out on whether the dust in these regions is the best tracer of the matter, or whether spectral lines are reliable.
  • Yonekura et al. NANTEN Observations of Dense Cores in Corona Australis Molecular Cloud C18O
    • 2.2 sq. deg area observed, nearly 2000 spectra
    • Identified 8 "C18O cores"
    • Typical C18O Core properties: 18 Msun; 0.13 pc; 1.1 ¥ 1022 cm-2; 0.66 km s-1 ; 1.4 ¥ 104 cm-3
    • For most "active" star-forming core(s?), line width, column density, size, mass and density are all higher than average, and M is also higher w.r.t. virial mass (see Fig. 5)
  • What was YSO sourcelist source? (e.g. are any embedded sources missing?)
  • Results are intriguing, but sample is very small.
  • Saito et al. A study of the molecular cloud toward HII regions S35 and S37 with NANTEN

    12CO, C18O, 13CO

    • 10 sq. deg. observed
    • GMC found with ~1.3 ¥ 105 MSun
    • Extends ~100 pc off plane
    • Four strong outflows discovered, in addition to one previously known, all associated with C18O clumps
    • CO is located at the edge of an H I hole that has 55 pc radius
    • Supershell proposed as origin of GMC
  • HH80/81 is in this region
  • Supershell ass'n. very interesting
  • Yamaguchi et al. Molecular Clouds and Star Formation in the Southern HII Regions


    • 23 H II regions observed
    • Significant increase of SF activity on side of molecular clouds facing H II region
    • Suggestion is that about 30% of stars in the M.W. form through such compression by H II regions
  • Someone should review this very long paper, on its own, for J.C.