Testing diagnostics of triggered star formation

Abstract

We produce synthetic images and SEDs from radiation hydrodynamical simulations of radiatively driven implosion. The synthetically imaged bright rimmed clouds (BRCs) are morphologically similar to those observed in star forming regions. Using nebular diagnostic line-ratios, simulated Very Large Array (VLA) radio images, H{\alpha} imaging and SED fitting we compute the neutral cloud and ionized boundary layer gas densities and temperatures and perform a virial stability analysis for each model cloud. We determine that the neutral cloud temperatures derived by SED fitting are hotter than the dominant neutral cloud temperature by 1 - 2 K due to emission from warm dust. This translates into a change in the calculated cloud mass by 8-35 %. Using a constant mass conversion factor (C{\nu}) for BRCs of different class is found to give rise to errors in the cloud mass of up to a factor of 3.6. The ionized boundary layer (IBL) electron temperature calculated using diagnostic line ratios is more accurate than assuming the canonical value adopted for radio diagnostics of 10^4 K. Both radio diagnostics and diagnostic line ratios are found to underestimate the electron density in the IBL. Each system is qualitatively correctly found to be in a state in which the pressure in the ionized boundary layer is greater than the supporting cloud pressure, implying that the objects are being compressed. We find that observationally derived mass loss estimates agree with those on the simulation grid and introduce the concept of using the mass loss flux to give an indication of the relative strength of photo-evaporative flow between clouds. The effect of beam size on these diagnostics in radio observations is found to be a mixing of the bright rim and ambient cloud and HII region fluxes, which leads to an underestimate of the cloud properties relative to a control diagnostic.Comment: 17 pages. Post reviewer comment

Modelling multiwavelength observational characteristics of bow shocks from runaway early-type stars

“…It is considerably more computationally expensive to run such a coupled calculation using Monte-Carlo radiative transfer, however such calculations have already been shown to be tractable in 3D using the torus code (Haworth & Harries 2012). Our current hydrodynamical model also does not include magnetic fields.…”

“…A Monte-Carlo sampling technique (Harries 2000) is then used to sample the emission with a number of photon packets which are propagated through the grid (accounting for scattering and absorption events) to determine the flux in a prescribed image plane. The method has previously been applied to output from torus photoionisation calculations by Haworth et al (2012).…”

Study of a bright-rimmed cloud at the border of the infrared dust bubble CN20

“…Gritschneder et al 2010;Bisbas et al 2011;Haworth et al 2013;Kinnear et al 2014). Haworth, Harries & Acreman (2012) have shown, based on synthetic observations derived from their numerical simulations, that the diagnostic tools used to analyse the evolution of the BRCs are reliable. However, distinguishing between triggered and spontaneously formed stars is not an easy task.…”

High-resolution Near-infrared Observations of a Small Cluster Associated with a Bright-rimmed Cloud in W5

“…Theoretical investigation on the formation of BRCs under RDI mechanism (Miao et al 2009;Haworth et al 2012;Kinnear et al 2015) revealed that the morphology of a BRC is dependent on both the ionising radiation field and the initial density of the molecular cloud. When an ionising source is fixed, the morphology of a BRC after RDI is decided by the initial density of the molecular cloud (Miao et al 2009;Kinnear et al 2015).…”

“…They are considered to be the sites for triggered star formation by UV radiation from OB stars. Many theorists consider radiation-driven implosion (RDI) as an efficient way of inducing star formation in such clouds (e.g., Sandford, Whitaker & Klein 1982;Bertoldi 1989;Lefloch & Lazareff 1994;Kessel-Deynet & Burkert 2003;Miao et al 2009;Gritschneder et al 2009;Bisbas et al 2011;Haworth et al 2012;Kinnear et al 2014Kinnear et al , 2015. Sugitani et al (1991) and Sugitani & Ogura (1994) cataloged 89 BRCs associated with IRAS point sources as candidate sites for induced star formation, and they classified them into three morphological types of BRCs (type "A"; moderately curved rims, "B"; tightly curved rims, and "C"; cometary rims).…”