The Structures on Sub-Jeans Scales, Fragmentation, and the Chemical Properties in Two Extremely Dense Orion Cores Zhiyuan Ren, Di Li (NAOC) and Nicolas Chapman ( Center for Interdisciplinary Exploration and Research in Astrophysics(CIERA) )

Outline Introduction A sample of intermediate- to high-mass cores in Orion Molecular cloud Observation: CARMA observation of the unstable Orion cores Results - Density profile: extremely high central concentration - Gas morphology: fragmentation - Chemistry: Abundance ratio of [N2H+]/[HCO+] Summary

Introduction Formation of high-mass stars in Orion Molecular cloud: - How many high-mass cores? - Which of them may potentially form high-mass stars? - Is the fragmentation significant at the earliest stage? Observational Requirements: - An ideal sample of the high-mass pre- to protostellar cores - Ideal molecular tracers to demonstrate the structure and kinematics

Introductions CMF in two quiescent region in Orion Molecular Cloud (OMC) Li et al. (2007)

Introduction CMF in two quiescent region in Orion Molecular Cloud (OMC) Li et al. (2007)  Desirable for dense molecular tracers Instable

Observation

Results: Dust continuum in ORI8nw_2 3.2 mm continuum  n(H 2 )~10 9 cm -3 at the center. 350 micron  Flat envelope L bol =60 Lsolar ; Lstars= ~0.1 Lsolar  The dust core is subject to the external heating N 2 H + deviated from the densest gas.

Result: Gas Density in ORI2_6

ORI8nw_2: multiple condensations revealed in the molecular emissions. N2H+ declines towards the stellar objects; Opposite trend for HCO+ Gravitational instabilities of the condensations: M_LTE= Msun vs M_Jeans~0.25 Msun, M_virial~2 Msun  Plausible fragmentation; Gravitationally unbounded.

Outflow: - Major ingredient to Shaping the morphology; -Accelerating the gas; -Driving the chemical Evolution (at least for. ORI8nw_2: influence from a combination of cloud-cloud collision, outflow, and stellar emissions

Molecular gas: Also plausible influence from the Cloud-Cloud collision Results – ORI8nw_2 Nakamura et al. (2012)

Also a displacement between N2H+ and HCO+ Irregular, not fully isolated gas condensations in N2H+ Results – ORI2_6

Results – Chemical properties [N2H+]/[HCO+]~0.1 for IRDCs (Sanhueza et al. 2012) Versus Comparison with the chemical model Jorgensen et al. (2004)  CO depletion is a reasonable explanation

Conclusion Molecular cores in ORI8nw_2 and ORI2_6: - Gas distribution is highly concentrated into the center, but with a small amount a mass; - high-mass envelope: - fragmentation is not halted by the stellar heating. Impact from outflow - shaping the N2H+ morphology, causing a shift away from the densest dust component Chemistry - Chemical evolution that converts N2H+ into HCO+ is taking place, resulting in a spatial anti-correlation between the two species. - Overall abundance ratio >> IRDC values  CO depletion.

Thank you

backup

12CO (1-0) channel maps Red: ( ) km/s Blue: ( ) km/s Contour: 1.1 mm continuum Cloud-Cloud Collision

Local outflow structure (Stank et al. 2007, 133, 1307) Blue (-8,3); Red (12,30)

1. HCO+ appears along the edge of the N2H+ filament 2. N2H+ filament surrounded by the HCO+ emission N(CO)>3x10^18