An Old Supernova Remnant Within an H Ii Complex at ℓ ≈ 173°: FVW 172.8+1.5

Abstract

We present the results of H i 21 cm line observations to explore the nature of the high-velocity (HV) H i gas at ∼ 173• . In low-resolution H i surveys this HV gas appears as faint, wing-like, H i emission that extends to velocities beyond those allowed by Galactic rotation. We designate this feature as Forbidden Velocity Wing (FVW) 172.8+1.5. Our high-resolution (3. 4) Arecibo H i observations show that FVW 172.8+1.5 is composed of knots, filaments, and ring-like structures distributed over an area of a few degrees in extent. These HV H i emission features are confined within the limits of the H ii complex G173+1.5, which is composed of five Sharpless H ii regions distributed along a radio continuum loop of size 4.• 4 × 3.• 4, or ∼138 pc × 107 pc, at a distance of 1.8 kpc. G173+1.5 is one of the largest star-forming regions in the outer Galaxy. We demonstrate that the HV H i gas is well correlated with the radio continuum loop and that the two seem to trace an expanding shell. The expansion velocity of the shell is large (55 km s −1 ), suggesting that it represents a supernova remnant (SNR). We derive physical parameters for the shell and show these to be consistent with the object being an SNR. We also detect hot X-ray-emitting gas inside the H ii complex by analyzing the ROSAT all-sky X-ray background survey data. This also supports the SNR interpretation. We conclude that the HV H i gas and the X-rays are most likely the products of a supernova explosion(s) within the H ii complex, possibly in a cluster that triggered the formation of these H ii regions.

THE ARIZONA RADIO OBSERVATORY CO MAPPING SURVEY OF GALACTIC MOLECULAR CLOUDS. V. THE SH2-235 CLOUD IN CO J = 2 − 1, 13CO J = 2 − 1, AND CO J = 3 − 2

“…Triggered Star Formation. Kang et al (2012) found evidence that the entire Sh2-235 complex has been affected by a supernova remnant (SNR) with an age of ∼0.3 Myr, based on their observations of the H I 21 cm line. Their inferred age, however, is too short for the SNR to have triggered the formation of the ionizing stars in the most extended, oldest of the visible H II regions, namely .…”

Large-scale star formation in Auriga region

“…In addition it is reported that there are about 14 embedded SFRs having ages ∼3-5 Myrs (cf. Kang et al 2012, and references therein). It has also been proposed that the formation of these young objects could have been triggered by a older generation of stars (Kang et al 2012, and references therein).…”

“…region: a series of triggered star formation Kang et al (2012) estimated that the shell is expanding with a velocity of ∼55 km s −1 and the kinetic energy of the shell is ∼ 2.5 × 10 50 ergs. They also detected hard X-ray emitting hot gas inside the shell with a thermal energy of ∼ 3 × 10 50 ergs.…”

“…The most convincing evidence is the line broadening due to shocked molecular gas (Frail & Mitchell 1998;Reach & Rho 1999). Kang et al (2012) made H i 21 cm line observations and detected high velocity H i gas at l ∼173 • , b ∼1.5 • . They suggested a large scale star formation activity possibly associated with an SN explosion in the H ii complex G173+1.5.…”

G192.8-1.1: A Candidate of an Evolved Thermal Composite Supernova Remnant Reignited by Nearby Massive Stars

“…When the velocity dispersion is considered, the observed Hi profile would have a shape of a flat profile convolved with a Gaussian profile along the velocities (e.g., Park et al 2013;Kang et al 2012). The Hi mass follows the same shape of the Hi profile along the velocities.…”