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

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: alvaro.hacar@univie.ac.at
² Department of Astrophysics, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
³ Anton Pannekoek Institute for Astonomy, University of Amsterdam, The Netherlands
⁴ Institute of Astronomy and Astrophysics, Academia Sinica, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, Republic of China
⁵ European Southern Observatory, Karl Schwarzschild Strasse 2, 85748 Garching, Germany
⁶ Netherlands Research School for Astronomy (NOVA), Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen, The Netherlands
⁷ Astro Space Center of Lebedev Physical Institute, Profsoyuznaya 84/32, 117997 Moscow, Russia
⁸ Netherlands Research School for Astronomy (NOVA), Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 9 April 2020
Accepted: 26 October 2020

Abstract

Context. The star-formation rates and stellar densities found in young massive clusters suggest that these stellar systems originate from gas at densities of n(H₂) > 10⁶ cm⁻³. Until today, however, the physical characterization of this ultra high density material remains largely unconstrained in observations.

Aims. We investigate the density properties of the star-forming gas in the OMC-1 region located in the vicinity of the Orion Nebula Cluster (ONC).

Methods. We mapped the molecular emission at 652 GHz in OMC-1 as part of the APEX-SEPIA660 Early Science.

Results. We detect bright and extended N₂H⁺ (J = 7–6) line emission along the entire OMC-1 region. Comparisons with previous ALMA data of the (J = 1–0) transition and radiative transfer models indicate that the line intensities observed in this N₂H⁺ (7–6) line are produced by large mass reservoirs of gas at densities n(H₂) > 10⁷ cm⁻³.

Conclusions. The first detection of this N₂H⁺ (7–6) line at parsec-scales demonstrates the extreme density conditions of the star-forming gas in young massive clusters such as the ONC. Our results highlight the unique combination of sensitivity and mapping capabilities of the new SEPIA660 receiver for the study of the ISM properties at high frequencies.