From downtown to the outskirts: a radio survey of the Orion Nebula Cluster

Abstract

We present a newly enlarged census of the compact radio population towards the Orion Nebula Cluster (ONC) using high-sensitivity continuum maps (3–10 μJy bm−1) from a total of ∼30 h centimeter-wavelength observations over an area of ∼20′ × 20′ obtained in the C-band (4−8 GHz) with the Karl G. Jansky Very Large Array (VLA) in its high-resolution A-configuration. We thus complement our previous deep survey of the innermost areas of the ONC, now covering the field of view of the Chandra Orion Ultra-deep Project (COUP). Our catalog contains 521 compact radio sources of which 198 are new detections. Overall, we find that 17 per cent of the (mostly stellar) COUP sources have radio counterparts, while 53 per cent of the radio sources have COUP counterparts. Most notably, the radio detection fraction of X-ray sources is higher in the inner cluster and almost constant for r > 3′ (0.36 pc) from θ1 Ori C suggesting a correlation between the radio emission mechanism of these sources and their distance from the most massive stars at the center of the cluster, for example due to increased photoionisation of circumstellar disks. The combination with our previous observations four years prior lead to the discovery of fast proper motions of up to ∼373 km s−1 from faint radio sources associated with ejecta of the OMC1 explosion. Finally, we search for strong radio variability. We found changes in flux density by a factor of ≲5 within our observations and a few sources with changes by a factor >10 on long timescales of a few years.

The external photoevaporation of planet-forming discs

“…Nonetheless, in recent years there have been important detections of proplyds in lower EUV environments. Proplyds can be found in the ONC at separations of up to ∼ 1 pc from θ 1 C [20,110,111]. Meanwhile, [112] found proplyds in the vicinity of the B1V star 42 Ori in NGC 1977, demonstrating that B stars can drive external photoevaporative winds.…”

A global view on star formation: The GLOSTAR Galactic plane survey

“…Compact radio sources have been found to be related to HII regions. The best-known and closest case is the Orion Nebula Cluster (ONC), where around 600 compact radio sources are found in the HII region ionized by the Trapezium stars (Forbrich et al 2016;Vargas-González et al 2021). As first suggested by Garay et al (1987); Garay (1987), most of these fall into two broad categories: first, sources with thermal radio emission from circumstellar matter, often protoplanetary disks ("Proplyds"), which are photo-evaporated in the intense UV field of the brightest Trapezium star θ 1 Ori C (O7Vp); second, nonthermal sources associated with the coronal activity of magnetically active low-mass members of the ONC, many of which also show X-ray emission and are (highly) variable (Forbrich et al 2021;Dzib et al 2021).…”

A systematic survey of millimetre-wavelength flaring variability of Young Stellar Objects in the Orion Nebula Cluster

“…Even after applying additional spatial filtering, this often remains as uneven noise with occasional spurious point-like emission, and therefore automated source extraction methods typically require significant manual intervention to deal with artifacts. We thus searched for compact sources by visual inspection of the concatenated image followed by an automatic search only on the position of known X-ray sources in the Chandra Orion Ultra-deep Project (COUP; Getman et al 2005b), known sources detected at cm-wavelengths with the VLA reported by Forbrich et al (2016) and Vargas-González et al (2021), and millimeter sources reported in Friedel & Widicus Weaver (2011), Eisner et al (2016), andOtter et al (2021). These catalogues provide an updated and well characterized sample of X-ray and radio sources likely tracing the young stellar population in the Orion BN/KL region.…”

“…Centimeter radio emission from Young Stellar Objects (YSOs) has been explored in more detail in the last few years due to the improved sensitivity of radio facilities such as the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) (Rivilla et al 2015;Forbrich et al 2016;Sheehan et al 2016;Tobin et al 2016;Forbrich et al 2021;Vargas-González et al 2021). Recent analysis of deep VLA observations at cm-wavelengths towards hundreds of YSOs in the Orion Nebula Cluster (ONC) revealed intense radio flares with changes in flux density by a factor of 10 in less than 30 min and denominated as extreme radio variability events (Forbrich et al 2017, see also Vargas-González et al 2021).…”

“…Centimeter radio emission from Young Stellar Objects (YSOs) has been explored in more detail in the last few years due to the improved sensitivity of radio facilities such as the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) (Rivilla et al 2015;Forbrich et al 2016;Sheehan et al 2016;Tobin et al 2016;Forbrich et al 2021;Vargas-González et al 2021). Recent analysis of deep VLA observations at cm-wavelengths towards hundreds of YSOs in the Orion Nebula Cluster (ONC) revealed intense radio flares with changes in flux density by a factor of 10 in less than 30 min and denominated as extreme radio variability events (Forbrich et al 2017, see also Vargas-González et al 2021). These studies comprise a systematic search for YSOs variability at cm-wavelengths totaling up to ∼7440 h of cumulative YSO observing time and leading to a mean time between extreme radio variability events of 2482±1433 h. On the other hand, millimeter continuum observations of YSOs are typically used to study the thermal component of circumstellar disks that arises from dust emission assumed to be constant on short timescales.…”