J/A+A/613/A11 SDC13 NH3(1,1) and NH3(2,2) datacubes (Williams+, 2018)
Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13.
Williams G.M., Peretto N., Avison A., Duarte-Cabral A., Fuller G.A.
<Astron. Astrophys. 613, A11 (2018)>
=2018A&A...613A..11W 2018A&A...613A..11W (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Interferometry ; Molecular clouds
Keywords: stars: formation - stars: massive - ISM: clouds -
ISM: kinematics and dynamics - ISM: structure
Abstract:
Converging networks of interstellar filaments, that is hubs, have been
recently linked to the formation of stellar clusters and massive
stars. Understanding the relationship between the evolution of these
systems and the formation of cores and stars inside them is at the
heart of current star formation research. The goal is to study the
kinematic and density structure of the SDC13 prototypical hub at high
angular resolution to determine what drives its evolution and
fragmentation. We have mapped SDC13, a ∼1000M☉ infrared dark
hub, in NH3(1,1) and NH3(2,2) emission lines, with both the Jansky
Very Large Array and Green Bank Telescope. The high angular resolution
achieved in the combined dataset allowed us to probe scales down to
0.07pc. After fitting the ammonia lines, we computed the integrated
intensities, centroid velocities and line widths, along with gas
temperatures and H2 column densities. The mass-per-unit-lengths of
all four hub filaments are thermally super- critical, consistent with
the presence of tens of gravitationally bound cores identified along
them. These cores exhibit a regular separation of ∼0.37±0.16pc
suggesting gravitational instabilities running along these
super-critical filaments are responsible for their fragmentation. The
observed local increase of the dense gas velocity dispersion towards
starless cores is believed to be a consequence of such fragmentation
process. Using energy conservation arguments, we estimate that the
gravitational to kinetic energy conversion efficiency in the SDC13
cores is ∼35%. We see velocity gradient peaks towards ∼63% of cores as
expected during the early stages of filament fragmentation. Another
clear observational signature is the presence of the most massive
cores at the filaments' junction, where the velocity dispersion is
largest. We interpret this as the result of the hub morphology
generating the largest acceleration gradients near the hub centre. We
propose a scenario for the evolution of the SDC13 hub in which
filaments first form as post-shock structures in a supersonic
turbulent flow. As a result of the turbulent energy dissipation in the
shock, the dense gas within the filaments is initially mostly
subsonic. Then gravity takes over and starts shaping the evolution of
the hub, both fragmenting filaments and pulling the gas towards the
centre of the gravitational well. By doing so, gravitational energy is
converted into kinetic energy in both local (cores) and global (hub
centre) potential well minima. Furthermore, the generation of larger
gravitational acceleration gradients at the filament junctions
promotes the formation of more massive cores.
Description:
The FITS files of the JVLA+GBT combined data cubes in NH3(1,1) and
NH3(2,2) molecular line emission, towards the SDC13 infrared dark
cloud. The combined spectral resolution is 0.049km/s. The rest
frequencies of the NH3(1,1) and NH3(2,2) lines are 23.694GHz and
23.723GHz. The brightness intensity unit is Jy per beam. The data was
combined in CASA feather. Right ascension and declination coordinates
are in the J2000 epoch. The central cloud coordinate is
18:14:30.0, -17:32:50.0, with a systemic cloud velocity of 37km/s.
Objects:
-----------------------------------------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------------------------------------
18 14 30.0 -17 32 50 SDC13 = [PFA2014] SDC13
-----------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 175 2 List of fits datacubes
fits/* . 2 Individual datacubes
--------------------------------------------------------------------------------
See also:
J/A+A/561/A83 : SDC13 infrared dark clouds spectra (Peretto+, 2014)
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 --- Nz Number of slices
32- 52 A21 --- Obs.Date Observation date
54- 60 F7.1 m/s bVRAD Lower value of VRAD interval
62- 68 F7.1 m/s BVRAD Upper value of VRAD interval
70- 76 F7.4 m/s dVRAD VRAD resolution
78- 83 I6 Kibyte size Size of FITS file
85- 96 A12 --- FileName Name of FITS file, in subdirectory fits
98-175 A78 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Gwenllian Williams, williamsgm8(at)cf.ac.uk>
(End) Gwenllian Williams [Cardiff Univ., UK], Patricia Vannier [CDS] 26-Jan-2018