Filamentary structures of ionized gas in Cygnus X

Emig, K. L.; White, G. J.; Salas, P.; Karim, R. L.; van Weeren, R. J.; Teuben, P. J.; Zavagno, A.; Chiu, P.; Haverkorn, M.; Oonk, J. B. R.; Orrú, E.; Polderman, I. M.; Reich, W.; Röttgering, H. J. A. and Tielens, A. G. G. M. (2022). Filamentary structures of ionized gas in Cygnus X. Astronomy & Astrophysics, 664, article no. A88.

DOI: https://doi.org/10.1051/0004-6361/202142596

Abstract

Context. Ionized gas probes the influence of massive stars on their environment. The Cygnus X region (d ~ 1.5 kpc) is one of the most massive star-forming complexes in our Galaxy, within which the Cyg OB2 association (age of 3–5 Myr and stellar mass 2 × 10⁴ M_⊙) has a dominant influence.

Aims. We observe the Cygnus X region at 148 MHz using the Low Frequency Array (LOFAR) and take short-spacing information into account during image deconvolution into account. Together with data from the Canadian Galactic Plane Survey, we investigate the morphology, distribution, and physical conditions of low-density ionized gas in a 4° × 4° (~100 pc × 100 pc) region at a resolution of 2′ (0.9 pc).

Methods. The Galactic radio emission in the region analyzed is almost entirely thermal (free-free) at 148 MHz, with emission measures (EM) of 10³ < EM [pc cm⁻⁶] < 106. As filamentary structure is a prominent feature of the emission, we use DisPerSE and Fil ChaP to identify filamentary ridges and characterize their radial (EM) profiles.

Results. The distribution of radial profiles has a characteristic width of 4.3 pc and a power-law distribution (β = −1.8 ± 0.1) in peak EM down to our completeness limit of 4200 pc cm−6. The electron densities of the filamentary structure range between 10 ≲ n_e [cm⁻³] ≲ 400 with a median value of 35 cm⁻³, remarkably similar to [N II] surveys of ionized gas.

Conclusions. Cyg OB2 may ionize at most two-thirds of the total ionized gas and the ionized gas in filaments. More than half of the filamentary structures are likely photoevaporating surfaces flowing into a surrounding diffuse (~5 cm⁻³) medium. However, this is likely not the case for all ionized gas ridges. A characteristic width in the distribution of ionized gas indicates that the stellar winds of Cyg OB2 create a fraction of the ionized filaments through swept-up ionized gas or dissipated turbulence.

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