THE STAR FORMATION NEWSLETTER
No.266 - 12 February 2015
2015/5/29
46-50“Understanding star formation in molecularclouds II. Signatures of gravitational collapseof IRDCs”
to“Cloud-cloud collision as a trigger of the highmass star formation; a molecular line study inRCW120”
泉奈都子 (D3)

Understanding star formation in molecular clouds II.
Signatures of gravitational collapse of IRDCs!
N.Schneider et al. Accepted by A&A http://arxiv.org/pdf/1406.3134.pdf

IRDCs (infrared dark clouds) の実態をさぐる• IRDCs- Dark, cold (< 25 K) absorption features, with high column density(N > 1022-1023 cm-2)- いくつかはGMC中に存在している (not isolated features)- Span a large of mass and size, with and without star formation activity‣ Massive and largest IRDCs:
1. The earliest stage of massive star formation (e.g. Rathborne et al. 2006)?
2. Active and ongoing (massive) star formation (e.g. Carey et al. 2000)→ 詳細な性質を調べる• Sample: 4 prominent, massive IRDCs• Data (全てarchive data): 70, 170, 250, 350, 500 µm- Herschel Infrared GALactic plane survey- Galactic Ring Survey (by FCRAO) : 13CO(1-0)- CO High-Resolution Survey (by JCMT) : 12CO(3-2)- APEX Telescope Large Area Survey of the Galaxy : 870 µm• Results• Results- Massive IRDCs are embedded in more extended molecular clouds

clouds, surface density)- Similar physical properties (peak and average molecular23-2
as ridges (high column density regions with N > 10cm over small areas)- Probability distribution function (PDF) ofcolumn density‣ 4つのIRDCsは進化段階が違うにも関らず(3つは(proto) starsを含み、1つは星形成見られない)

power-law

全て power-law を示す↑ Large scale gravitational collapse
Free-fall collapse of pre- and protostellar coresfor the highest column densities

log-normalpower-law

An Ammonia Spectral Map of the L1495-B218 Filaments in
the Taurus Molecular Cloud: I. Physical Properties ofFilaments and Dense cores!
Young Min Seo et al. Accepted by ApJ http://arxiv.org/pdf/1503.05179

The formation filaments and the evolution from filaments to dense core

• Target : L1495-B218 filament- Prominent in the Taurus molecular cloud extending over 3 degrees on the sky- Contain cores that range from chemically young starless cores (e.g. L1521B,L1521E) to more evolved protostellar cores (in B7/L1495)- 既に多くのデータあり(e.g. dust extinction, dust continuum emission, 12CO, 13CO, C18O, N2H+)• Observation- Telescope : 100 m Green Bank Telescope- Frequency : NH3(1,1) (23.6944955 GHz), NH3(2,2) (23.7226333 GHz)
- Angular resolution : 31” , velocity resolution : 0.038 km s-1• Results- 55個の NH structures を同定（39 leaves, 16 branches）
3‣ Gravitationally bound : 9 （7/9が星生成領域に付随）,‣ Gravitationally unbound : 30 （12/30はpressure-confined）
Dense core → pressure-confirmed structure → gravitationally bound core
→ collapse to form a protostar
500 μm dust continuum

NH3 (1,1)

The properties of discs around planets and brown dwarfs asevidence for disc fragmentation!
Dimitris Stamatellos and Gregory J. Herczeg Accepted by MNRAS http://arxiv.org/pdf/1503.05209

Predictions of the disc fragmentation model regarding the properties of thediscs around low-mass objects (planets, brown dwarfs): Simulation• Method- 詳細は Stamatellos & Whitworth, 2009

- Initial condition : M* = 0.7 M⊙, MD = 0.7 M⊙ , RD = 400 AU!
!
!

- Numerical method : SPH code DRAGON(Treats the radiation transport within the disc with thediffusion approximation of Stamatellos et al. 2007)‣ The code uses time dependent viscosity with parameters α = 0.1, β = 2α• Results- Disk fragmentation で生成された low-mass objectsのdiskの mass, accretion rateは・Mdisk - M* relation, M* - M* relation から導出される値よりも大きい↑ 観測結果もこれに矛盾しない!
- このようなscaling relationは high-mass, low-massで異なるだろう

A Sub-arcsecond Survey Toward Class 0 Protostars inPerseus: Searching for Signatures of Protostellar Disks!
John J. Tobin et al. 2015 Accepted by ApJ http://arxiv.org/pdf/1503.05189

CARMA 1.3 mm continuum survey toward 9 Class 0 protostars in thePerseus molecular cloud• Observation- Telescope: CALMA- Frequency: 225.0491 GHz (1.3 mm), 12CO(2-1), 13CO(2-1), C18O(2-1) も- Resolution: ~0.3” (~70 AU)- Follow-up observation: 12CO(2-1), 13CO(2-1), C18O(2-1), H13CO+, HCO+(4-3)
by SMA• Sample: 9 Class 0, 2 Class I

• Results- 100 AU 以上の半径を持つdisk候補を2つ発見 （L1448 IRS2, Per-emb-14）- Outflow に垂直なmarginally resolved structureを3つ検出 (L1448 IRS3C, IRAS03282+3035, L1448C)→ disk候補- 2 Resolved structure (L1448 IRS3B, IRAS 03292+3039) → massive innerenvelopes or disks- L1448 IRAS3Bではcompanionを検出 (separeted by 0.9” (~ 210 AU))

Cloud-cloud collision as a trigger of the high-mass starformation; a molecular line study in RCW 120!
K.Trii et al. 2015 Accepted by ApJ http://arxiv.org/pdf/1503.00070

The present cloud-cloud collision scenario explains the observed
signatures of RCW 120• Target : RCW 120- Galactic HII region- Beautiful ring-like structureを持つ- O8V, O9V starあり• Observation- Telescope : NANTEN, Mopra, ASTE
- Emission : 12CO(1-0), 13CO(1-0) (by NANTEN, Mopra),

C18O(1-0) (by Mopra), 12CO(3-2) (by ASTE)- Resolution : 200” (NANTEN), 33” (Mopra), 22” (ASTE)- Velocity resolution : 0.17 km s-1 (NANTEN), 0.088 km s-1 (Mopra),
0.43 km s-1(ASTE)

• Results- Blue cloud (-28 km s ) , red cloud (-8 km s ) を検出-1-1- 両cloudsのkinetic temperatures > ~ 30 K ← heated by O star and/or HII region- Expansion model を示す特徴見られない- Blue cloud, red cloudの衝突によって O star が形成されたと考えられる（short timescale 0.2-0.4 Myr）