Abstract
ABSTRACT The Herschel Gould Belt survey mapped the nearby (d < 500 pc) star-forming regions to understand better how the prestellar phase influences the star formation process. Here, we report a complete census of dense cores in a ∼15 deg2 area of the Serpens star-forming region located between d ∼ 420 and 484 pc. The PACS and SPIRE cameras imaged this cloud from 70 to 500 μm. With the multiwavelength source extraction algorithm getsources, we extract 833 sources, of which 709 are starless cores and 124 are candidate protostellar cores. We obtain temperatures and masses for all the sample, classifying the starless cores in 604 prestellar cores and 105 unbound cores. Our census of sources is $80{{\ \rm per\ cent}}$ complete for M > 0.8 M⊙ overall. We produce the core mass function (CMF) and compare it with the initial mass function (IMF). The prestellar CMF is consistent with lognormal trend up to ∼2 M⊙, after which it follows a power law with slope of −2.05 ± 0.34. The tail of its CMF is steeper but still compatible with the IMF for the region we studied in this work. We also extract the filaments network of the Serpens region, finding that $81{{\ \rm per\ cent}}$ of prestellar cores lie on filamentary structures. The spatial association between cores and filamentary structure supports the paradigm, suggested by other Herschel observations, that prestellar cores mostly form on filaments. Serpens is confirmed to be a young, low-mass and active star-forming region.
Highlights
1 INTRODUCTION Solar-type stars form from the collapse of compact structures called prestellar cores, but how the physical properties of stars are determined during the prestellar core phase is still a matter of debate
We find that 455 starless cores are robust prestellar cores, i.e. with masses larger than MBE/2, where the factor 1/2 follows the analogy with the criterion of cloud collapse based on the virial condition
The temperature distributions of the two sub-regions appear quite different, with Aquila East being on average warmer than the Serpens Main, which is probably more shielded from the interstellar radiation field coming from the Galactic plane
Summary
Solar-type stars form from the collapse of compact structures called prestellar cores, but how the physical properties of stars are determined during the prestellar core phase is still a matter of debate. The HGBS is one of the largest projects with the Herschel Space Observatory (Pilbratt et al 2010), whose main objectives are to take a deep census of prestellar cores in nearby clouds, determine a reliable prestellar CMF, and investigate the link between the CMF and the IMF in detail, based on the observations of the nearest (d ≤ 500 pc) star-forming clouds in the Milky Way. Herschel observed with its far-infrared and sub-millimetre cameras PACS (Poglitsch et al 2010) and SPIRE (Griffin et al 2010), respectively, with unprecedented sensitivity and resolution in the range between 70 and 500 μm. The twofold purpose of our work, as a part of the HGBS project, is to characterize the earliest stages of star formation in the Serpens region and to verify whether accompanying results about its prestellar core mass function (CMF) are in agreement or not with ones obtained for other clouds and with previous studies of the Serpens Main subregion.
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