The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). IV. Free–Free Emission from Protostars: Links to Infrared Properties, Outflow Tracers, and Protostellar Disk Masses

Abstract

Emission from protostars at centimeter radio wavelengths has been shown to trace the free–free emission arising from ionizing shocks as a result of jets and outflows driven by protostars. Therefore, measuring properties of protostars at radio frequencies can provide valuable insights into the nature of their outflows and jets. We present a C-band (4.1 and 6.4 cm) survey of all known protostars (Class 0 and Class I) in Perseus as part of the VLA Nascent Disk and Multiplicity (VANDAM) Survey. We examine the known correlations between radio flux density and protostellar parameters, such as bolometric luminosity and outflow force, for our sample. We also investigate the relationship between radio flux density and far-infrared line luminosities from Herschel. We show that free–free emission most likely originates from J-type shocks; however, the large scatter indicates that those two types of emission probe different time and spatial scales. Using C-band fluxes, we removed an estimation of free–free contamination from the corresponding Ka-band (9 mm) flux densities that primarily probe dust emission from embedded disks. We find that the compact (<1″) dust emission is lower for Class I sources (median dust mass 96 M ⊕) relative to Class 0 (248 M ⊕), but several times higher than in Class II (5–15 M ⊕). If this compact dust emission is tracing primarily the embedded disk, as is likely for many sources, this result provides evidence of decreasing disk masses with protostellar evolution, with sufficient mass for forming giant planet cores primarily at early times.

VLA cm-wave survey of young stellar objects in the Oph A cluster: constraining extreme UV- and X-ray-driven disk photoevaporation

“…Observations also indicate that the fluxes of thermal (freefree) sources vary rarely more than 20-30%, while, in general, non-thermal sources show larger variability (Ortiz-León et al 2017;Tychoniec et al 2018). The spectral indices of each type of emission can also differ.…”

“…The detection of transition disks where dust has been cleared in the inner regions (e.g., Strom et al 1989;Pascucci et al 2016;van der Marel et al 2018;Ansdell et al 2018) favored the development of theoretical models where disk dispersal occurs from the inside out (e.g., photoevaporation, grain growth, giant planet formation). In particular, models of disk dispersal through photoevaporation can successfully explain the inner hole sizes and accretion rates of a large number of transition disks (e.g., Alexander & Armitage 2009;Owen et al 2011Owen et al , 2012Ercolano et al 2018).…”

Constraining disk evolution prescriptions of planet population synthesis models with observed disk masses and accretion rates

“…As described by Mordasini et al (2009Mordasini et al ( , 2012, the Bern planet population synthesis models are based on the core accretion paradigm for planet formation, coupled to a model of disk evolution and tidal migration of the planets (Alibert et al 2005 2x10 −3 , coupled with a prescription for external far-ultraviolet photo-evaporation (Matsuyama et al 2003) with a mass loss rate randomly sampled to disperse the disk according to a typical disk lifetime (Haisch et al 2001), and internal extreme-ultraviolet radiation (Clarke et al 2001), which is responsible for opening a gap in the disk whenṀ acc 10 −11 M /yr, plus mass removal because of accretion by growing planets. In the models the initial disk mass distribution is taken from Tychoniec et al (2018) and has a mean value 30 M Jup and a dispersion of ∼0.2 dex. The initial radii distribution is set using the relation between disk mass and disk characteristic radius (R c ) described by Andrews et al (2010), assuming this is valid for the initial disk masses.…”

The Role of Magnetic Fields in Protostellar Outflows and Star Formation

“…Of course this has a dramatic impact on radio studies of jets from young stars. Complete radio surveys of YSOs in nearby star formation regions, for example, have become possible for the first time [Dzib et al, 2015;Tychoniec et al, 2018].…”