Authors

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:

C¹⁸O (J=1-0) is at 109.78 GHz
13CO (J=1-0) is at 110.20 GHz
A 4-m telescope at 110 GHz has 1.2l/D of 2.7 arcmin

NANTEN:

Joint venture of Nagoya University and Carnegie Institution, located on Las Campanas in Chile
Receiver uses 4 K cryogenically cooled Nb S-I-S mixer which gives T_sys~140 K near zenith at 3 mm
Spectrometer is AOS with 2048 channels and usual BW=40 MHz
Typical frequency resolution is 40 kHz, giving 0.1 km s^-1 at 3 mm

General Concerns:

What are effects of depletion and/or optical depth on ability of C¹⁸O (J=1-0) to trace dense gas—does this line really trace"cores"?
Is resolution an issue w.r.t. the above question? (See L1251 example).

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.

Authors

Title

Lines

Data/Results

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 M_sun; 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>3M_sun
Claim is that Taurus is unusual in having very small M_vir/M_core; 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 A_V) 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 M_sun; 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 A_V-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 A_V, 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 M_sun; 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 ¥ 10⁵M_Sun
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 ^13CO

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.

Authors	Title	Lines	Data/Results	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 M_sun; 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>3M_sun Claim is that Taurus is unusual in having very small M_vir/M_core; 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 A_V) 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 M_sun; 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 A_V-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 A_V, 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 M_sun; 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 ¥ 10⁵M_Sun 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	^13CO	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.