An imaging line survey of OMC-1 to OMC-3

N Brinkmann,X D Tang,J Kauffmann,F Wyrowski,D Colombo,K M Menten,R Güsten

doi:10.1051/0004-6361/201936885

N Brinkmann, X D Tang + Show 5 more

Open Access

https://doi.org/10.1051/0004-6361/201936885

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Abstract

Context. Recently, sensitive wide-bandwidth receivers in the millimetre regime have enabled us to combine large spatial and spectral coverage for observations of molecular clouds. The resulting capability to map the distributions of lines from many molecules simultaneously yields unbiased coverage of the various environments within star-forming regions. Aims. Our aim is to identify the dominant molecular cooling lines and characteristic emission features in the 1.3 mm window of distinct regions in the northern part of the Orion A molecular cloud. By defining and analysing template regions, we also intend to help with the interpretation of observations from more distant sources which cannot be easily spatially resolved. Methods. We analyse an imaging line survey covering the area of OMC-1 to OMC-3 from 200.2 to 281.8 GHz obtained with the PI230 receiver at the APEX telescope. Masks are used to define regions with distinct properties (e.g. column density or temperature ranges) from which we obtain averaged spectra. Lines of 29 molecular species (55 isotopologues) are fitted for each region to obtain the respective total intensity. Results. We find that strong sources like Orion KL have a clear impact on the emission on larger scales. Although not spatially extended, their line emission contributes substantially to spectra averaged over large regions. Conversely, the emission signatures of dense, cold regions like OMC-2 and OMC-3 (e.g. enhanced N2H+ emission and low HCN/HNC ratio) seem to be difficult to pick up on larger scales, where they are eclipsed by signatures of stronger sources. In all regions, HCO+ appears to contribute between 3 and 6% to the total intensity, the most stable value for all bright species. N2H+ shows the strongest correlation with column density, but not with typical high-density tracers like HCN, HCO+, H2CO, or HNC. Common line ratios associated with UV illumination, CN/HNC and CN/HCO+, show ambiguous results on larger scales, suggesting that the identification of UV illuminated material may be more challenging. The HCN/HNC ratio may be related to temperature over varying scales.

Highlights

The northern part of the Orion A molecular cloud is one of the most prominent regions of current low- to intermediate-mass star formation, whose close proximity of just ∼400 pc (Menten et al 2007; Kounkel 2017) enables us to spatially resolve its physically and chemically different regions
The averaged total intensity for each species and region is listed in Table 4, together with the detection limit for each region
Removing just the region around KL and Orion South has a significant impact on the overall emission and reduces the averaged total intensity by 48%, the removed area represents only 8% of the high column density region

Summary

Introduction

The northern part of the Orion A molecular cloud is one of the most prominent regions of current low- to intermediate-mass star formation, whose close proximity of just ∼400 pc (Menten et al 2007; Kounkel 2017) enables us to spatially resolve its physically and chemically different regions. Continuum maps show substructures which divide Orion A into morphologically different regions: the bright OMC-1 in the south, with a group of filaments radiating away from its central region OMC-1 hosts star formation and is heavily influenced by intense UV radiation from the young massive Trapezium stars. In addition to the Trapezium, Orion BN/KL (hereafter KL) and Orion South are sites of recent of star formation (O’Dell et al 2008). Their positions are indicated in the later discussed Fig. 2. In contrast to OMC-1, there are no massive O/B stars, resulting in very different conditions with outflows driven by young embedded stars In contrast to OMC-1, there are no massive O/B stars, resulting in very different conditions with outflows driven by young embedded stars (Peterson & Megeath 2008 and references therein, e.g. Yu et al 1997), but without strong UV radiation

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