Growing evidence for a core formation threshold traced in Herschel ^† Gould Belt survey clouds

It has already been suggested that a threshold in column density – or in visual extinction – may need to be exceeded to form dense cores and then protostars. Based on Herschel Gould Belt survey results in the Aquila and Orion B molecular cloud complexes we observe clear connection between the locations of the detected prestellar cores and their background column density values. This finding appears to support a core formation scenario where such threshold corresponds to the extinction above which interstellar filaments become gravitationally unstable and fragment into cores. In these two actively star-forming regions we find the vast majority of the gravitationally bound prestellar cores above a high column density of about (6–7) × 10²¹ cm^–2 (AV ∼ 6–7). This limit similarly appears in the column density probability distribution function (PDF) of the regions as well. The spatial distribution of the protostars and young stellar objects (YSOs) also shows a tight connection with the densest sites of both clouds, as more than 70 % of them appear above the mentioned AV thresholds. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)