Structure, star formation and magnetic fields in the OMC 1 region

1. Structure, star formation and magnetic fields in the OMC 1 region Coppin et al., A&A, 356, 1031 (2000) UMEKAWA Michihisa (ASAFAS) Plasma seminar Feb. 2

2. Observation of OMC1 using 450 and 850 micro m • clump mass function • polarimetry (direction of magnetic fields)

3. Orion star forming region • ~４５０ｐｃ • 5h20m-6h00m • +5°- -10°

4. OMC1

5. James Clerk Maxwell Telescope (JCMT) • SCUBA (Submillimetre Common-User Bolometer Array) • Dec. 1997 • Jan. 1999 for polarimetry data, with a rotating half-wave plate and a fixed etched grid in front of the SCUBA 15m, the largest submillimetre tele- scope in the world.

6. SCUBA 450 micro m: hexagonal array of 91 bolometers 850 micro m: 37 bolometers field of view: 2’.3 Calibration sources: Uranus, Mars, OH231.8, CRL618...... Nine over lapping fields of view over two nights Bright bar region could be observed only second night

8. north-east bar KL

9. Clump identification • part of a clumpbeing truncated by the map edge • having a negative flux • having a higher mean signal in larger areas • having a peak flux above the local background • lower than the noise cut-off • reject criteria The fluxes of the peaks above the local backgroud for clumps

10. 39 clumps at 850 micro m, 28 clumps at 450 micro m • 55 source are finally listed • 3 clumps are on common regions 850 and 450 micro m • covered, but not seen on 450 micro m map. All have • some emission on 450 micro m map although not a distinct • centroid. • Clumps are generally circle, however at 850 micro m 7 clumps and at 450 micro m 4 clumps are elongated. • ～20% of the flux within their beam size region • <7% of the total flux of the whole jiggle-map region. • S_ν∝ν^(2+β) (black body). The mean βis 0.5. • This is small than 1.75 to 2.5 of the previous work at • 350 and 1100 micro m. For clouds This is 1.8 to 2.3. • Expecting the growth of grains?

12. Clump mass function • The number of clumps dN in mass bin M to M+dM is • dN/dM ∝ M^(-α) • S_clumps directly traces mass of the clumps. • β and temperature of dust are approximately constant. • log(dN/dS_clump) vs log S_clump is plotted.

13. α= 1.51 at 850 micro m and 1.54 at 450 micro m.

14. Polarimetry data

15. Conclusions • 4 clouds larger than 0.1 pc contain most of the mass and flux in the region, while the 55 clumps identified on ~0.02pc scales have <7% of the total flux. • magnetic field may have influenced the formation of the brightest cores, Orion-KL and Orion-S, but overall the HII region expansion and fragmentation on the Jeans length appear to be more important dynamically. • a single power-law function of slope -1.5 provides a good fit to the clump masses over a very wide range from 0.1 to 100 Msun. • One more NEXT

16. Cloud mass function in Motte et al. (1998) Motte et al., A&A 336, 150 (1998) ρOphiuchi dark cloud : 160pc from the sun. IRAM 30-m telescope located near Granada Spain 1.3mm dust continuum emission from the ρOphiuchi main cloud MPIfR 19-channel bolometer run: 1995 Mar. 17 to 21, 1996 Mar. 13 to 17, 1996 Apr. 3 to 4, and 1997 Feb. 17 to 23

17. Results

18. dN/dM ∝ M^-α • α~2.5 for 1 – 10 Msun • α~1.5 for less than 1Msun • The mass distribution for clumps mimics the behavior of the stellar initial mass function.

19. Comments in Coppin et al. • Motte et al. found two slopes of cloud mass function in ρOphiuchi. In contrust their result has only -1.5. • The changes in mas function slope are potentially a difference between regions of high-mass and low-mass star formation. Statistical problem: only afew high mass objects identified in each cloud.

20. Umekawa’s simulations

21. (a) (b)

22. Umekawa’s simulations • (a) Mc~3.5x10 Msun • (b) Mc~1.1x10^-1Msun • 微妙である