[Fe II] 1.64 um Imaging Observations of the Outflow Features around Ultracompact H II Regions in the 1st Galactic Quadrant

TL;DR

This study investigates [Fe II] 1.64 um features around ultracompact H II regions in the first Galactic quadrant, suggesting they may be shock-excited outflow footprints from massive young stellar objects, with implications for understanding stellar outflows.

Contribution

First survey of [Fe II] features around UCHIIs in the Galactic quadrant, proposing these features as potential outflow footprints and estimating associated mass loss rates.

Findings

[Fe II] features found around 5 UCHIIs out of 237 surveyed.

Estimated outflow mass loss rates range from 1 x 10^-6 to 4 x 10^-5 Ms yr^-1.

Low detection rate of [Fe II] features compared to high-velocity CO gas detection rate.

Abstract

We present [Fe II] 1.644 um features around ultracompact H II regions (UCHIIs) found on a quest for the "footprint" outflow features of UCHIIs---the feature produced by the outflowing materials ejected during the earlier, active accretion phase of massive young stellar objects (MYSOs). We surveyed 237 UCHIIs in the 1st Galactic quadrant, employing the CORNISH UCHII catalog and UWIFE data which is an imaging survey in [Fe II] 1.644 um performed with UKIRT-WFCAM under ~ 0.8" seeing condition. The [Fe II] features were found around five UCHIIs, one of which is of low plausibility. We interpret that the [Fe II] features are shock-excited by outflows from YSOs, and estimate the outflow mass loss rates from the [Fe II] flux, which are ~ 1 x 10^-6 - 4 x 10^-5 Ms yr^-1. We propose that the [Fe II] features might be the "footprint" outflow features, but more studies are required to clarify it. This is based on the morphological relation between the [Fe II] and 5 GHz radio features, the outflow mass loss rate, the travel time of the [Fe II] features, and the existence of several YSO candidates near the UCHIIs. The UCHIIs accompanying the [Fe II] features have a relatively higher peak flux density. The fraction of UCHIIs accompanying the [Fe II] features, 5/237, is small when compared to the ~ 90 % detection rate of high-velocity CO gas around UCHIIs. We discuss some possible explanations on the low detection rate.