An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud. I. Physical Properties of Filaments and Dense Cores

Abstract

We present deep NH 3 observations of the L1495-B218 filaments in the Taurus molecular cloud covering over a 3 degree angular range using the K-band focal plane array on the 100m Green Bank Telescope. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed NH 3 (1,1) and (2,2) with a spectral resolution of 0.038 km/s and a spatial resolution of 31 . Most of the ammonia peaks coincide with intensity peaks in dust continuum maps at 350 µm and 500 µm. We deduced physical properties by fitting a model to the observed spectra. We find gas kinetic temperatures of 8 − 15 K, velocity dispersions of 0.05 − 0.25 km/s, and NH 3 column densities of 5×10 12 − 1×10 14 cm −2 . The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithms, identifies a total of 55 NH 3 structures including 39 leaves and 16 branches. The masses of the NH 3 sources range from 0.05 M to 9.5 M . The masses of NH 3 leaves are mostly smaller than their corresponding virial mass estimated from their internal and gravitational energies, which suggests these leaves are gravitationally unbound structures. 9 out of 39 NH 3 leaves are gravitationally bound and 7 out of 9 gravitationally bound NH 3 leaves are associated with star formation. We also found that 12 out of 30 gravitationally unbound leaves are pressure-confined. Our data suggest that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and undergo collapse to form a protostar.

Submillimetre Studies of Prestellar and Starless Cores in the Ophiuchus, Taurus and Cepheus Molecular Clouds

“…The regions observed by Seo et al (2015) which were also observed as part of the JCMT GBS are those identified as B7, B10 and B211 on Figure 4.14. It can be seen that the NH 3 and 850-µm continuum emission appear to be tracing the same material -the dense cores within the filament (c.f.…”

“…We determine the internal energy of our cores using the linewidths determined for cores in L1495 in ammonia (NH 3 ) by Seo et al (2015). Seo et al (2015) observed the NH 3 (1,1) -rest frequency 23.694 GHz -and (2,2) -rest frequency 23.723 GHz -transitions using the 100-m Robert C. Byrd Green Bank Telescope, with a beam size of 31 arcsec and a velocity resolution of 3.05 kHz.…”

“…Seo et al (2015) observed the NH 3 (1,1) -rest frequency 23.694 GHz -and (2,2) -rest frequency 23.723 GHz -transitions using the 100-m Robert C. Byrd Green Bank Telescope, with a beam size of 31 arcsec and a velocity resolution of 3.05 kHz.…”

“…Figure 4.3). The cores identified by Seo et al (2015) are marked on Figure 4.14. These NH 3 cores were also extracted using CSAR , and should hence be comparable to our own set of sources.…”

“…We assume that the velocity dispersions given by Seo et al (2015) for their cores are applicable to their counterpart SCUBA-2 cores in our catalogue. For consistency with our previous assumptions, we adjust the velocity dispersions listed by Seo et al (2015) to account for their assumption of a mean atomic weight µ Seo = 2.33 (where we take µ = 2.86), and to assume a central core temperature of T gas = 7 K, in keeping with our analysis of the starless cores in Ophiuchus.…”