Physical Conditions and Kinematics of the Filamentary Structure in Orion Molecular Cloud 1

Abstract

We have studied the structure and kinematics of the dense molecular gas in the Orion Molecular Cloud 1 (OMC1) region with the N 2 H + 3-2 line. The 6 × 9 (∼ 0.7 × 1.1 pc) region surrounding the Orion KL core has been mapped with the Submillimeter Array (SMA) and the Submillimeter Telescope (SMT). The combined SMA and SMT image having a resolution of ∼ 5.4 (∼ 2300 au) reveals multiple filaments with a typical width of 0.02-0.03 pc. On the basis of the non-LTE analysis using the N 2 H + 3-2 and 1-0 data, the density and temperature of the filaments are estimated to be ∼ 10 7 cm −3 and ∼ 15-20 K, respectively. The core fragmentation is observed in three massive filaments, one of which shows the oscillations in the velocity and intensity that could be the signature of core-forming gas motions. The gas kinetic temperature is significantly enhanced in the eastern part of OMC1, likely due to the external heating from the high mass stars in M42 and M43. In addition, the filaments are colder than their surrounding regions, suggesting the shielding from the external heating due to the dense gas in the filaments. The OMC1 region consists of three sub-regions, i.e. north, west, and south of Orion KL, having different radial velocities with sharp velocity transitions. There is a north-to-south velocity gradient from the western to the southern regions. The observed velocity pattern suggests that dense gas in OMC1 is collapsing globally toward the high-mass star-forming region, Orion Nebula Cluster.

Probing the structure of a massive filament: ArTéMiS 350 and 450 μm mapping of the integral-shaped filament in Orion A

“…i = 0). The mean central density we infer for the OMC-1 portion of the ISF is a factor of three lower than the nominal volume density of 3 × 10 6 cm −3 found by Teng & Hirano (2020) for N 2 H + filamentary structures in OMC-1 (outside of cores) through non-LTE modelling of the N 2 H + (3-2) and (1-0) lines. Our dust continuum estimate of the volume density is, however, affected by a rather large uncertainty of a factor of ∼2-3 or more in the OMC-1 subregion, which is due to particularly uncertain dust opacity and temperature gradient effects in this unusually dense and strongly irradiated area (see e.g.…”

“…In any event, a comparison of the N 2 H + map of Hacar et al (2018) with the NH 3 map of Monsch et al (2018) clearly indicates that the abundance of N 2 H + is far from uniform in the OMC-1 region. The most extreme difference between the two maps is that no N 2 H + emission is detected in the immediate vicinity of Orion KL (see also Teng & Hirano 2020), presumably due to the destruction of N 2 H + by CO, while strong NH 3 (1,1) and NH 3 (2,2) emission is seen in the Monsch et al (2018) data and a prominent column density peak is observed in our data (cf. Figs.…”

“…A.1 and A.2 in Appendix A). The N 2 H + density estimates of Teng & Hirano (2020) are also uncertain by a factor of ∼3 (see their Table 3). Given these uncertainties, the two sets of density estimates are broadly consistent.…”

APEX-SEPIA660 Early Science: gas at densities above 107 cm−3 towards OMC-1

“…A detailed analysis of the N 2 H + (1-0) hyperfine line opacities and excitation suggest that the density of these fibers reaches values of n(H 2 ) > 10 7 cm −3 (see Hacar et al 2018, for a discussion). This hypothesis is supported by the recent detection of extended N 2 H + (3-2) emission towards the entire OMC-1 region (Teng & Hirano 2020).…”

“…The relatively higher abundances of N 2 H + also makes this molecule a favourable target for observations in comparison with other deuterated isotopologues (e.g., N 2 D + ) and species (e.g., DCO + ). Most studies typically investigate low-frequency transitions of this molecule, such as N 2 H + (1-0) (93 GHz; e.g., Hacar et al 2018) or N 2 H + (3-2) (279 GHz; e.g., Teng & Hirano 2020), limiting the dynamic range of these observations to densities of n(H 2 ) 10 6 cm −3 . However, the observation of high-J transitions (J > 4-3) necessary to confirm the existence of gas at higher densities has been largely hampered by the more challenging access to frequencies above >300 GHz.…”