Filamentary structures of ionized gas in Cygnus X

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, in 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 into account short-spacing information during image deconvolution. 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 FilChaP 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 points to the stellar winds of Cyg OB2 creating a fraction of the ionized filaments through swept-up ionized gas or dissipated turbulence.

Ionized filaments and ongoing physical processes in massive-star-forming sites around l = 345.°5

“…In recent years, a wealth of studies on dust and molecular filaments have been carried out in star-forming sites, which strongly support their key role in the formation of stellar clusters and massive stars. Despite the availability of numerous radio continuum surveys, so far a very limited number of studies have conducted to investigate elongated ionized structures with high aspect ratios (length/thickness) in massive star-forming regions (e.g., Lynds Bright Nebulae (Karr & Martin 2003), Eridanus filaments (Pon et al 2014), Cygnus X (Emig et al 2022)), which can be referred to as ionized filaments.…”

“…In the case of Eridanus filaments, Pon et al (2014) reported that these filaments are non-equilibrium structures, and might have produced when the Orion-Eridanus superbubble com-pressed a pre-existing gas cloud and swept up the gas into a dense ring around the outer boundary of the bubble. In the site Cygnus X, Emig et al (2022) proposed that the energetic feedback from Cyg OB2 (i.e., ultraviolet (UV) radiation, stellar winds, and radiation pressure) may be responsible for the observed ionized filaments via swept-up ionized gas or dissipated turbulence. Hence, the common ) emission (at velocity intervals of 1 km s −1 ) toward an area containing i17008 and i17009.…”

“…Apart from the molecular and dust filaments, one may also expect elongated filaments of ionized gas in star-forming regions, but such study is very limited in the literature (e.g., LBN 140.07+01.64 (Karr & Martin 2003;Dewangan et al 2021); Eridanus filaments (Pon et al 2014); Cygnus X (Emig et al 2022)). Hence, the simultaneous study of the ionized, dust, and molecular filaments is still lacking due to scarcity of the ionized filaments in star-forming regions (e.g., LBN 140.07+01.64; Dewangan et al 2021).…”

“…The ionizing radiation from OB-association (or OB-star complex) is thought to be responsible for the origin of ionized filaments. Such ionized filaments are found at far distances from the exciting stars/complex (e.g., Karr & Martin 2003;Pon et al 2014;Emig et al 2022). On the other hand, there is a possibility that several massive stars formed in molecular/dust filamentary clouds may locally produce the ionized filaments in the same clouds.…”