Filamentary structures of ionized gas in Cygnus X
K. L. Emig, G. J. White, P. Salas, R. Karim, R. J. van Weeren, Peter Teuben, A. Zavagno, Ping‐Gin Chiu, M. Haverkorn, J. B. R. Oonk, E. Orrú, I. M. Polderman, W. Reich, H. J. A. Röttgering, A. G. G. M. Tielens
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 × 10 4 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 10 3 < EM [pc cm −6 ] < 10 6 . 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.