J/A+A/643/A61 Prestellar cores H2D+ and N2H+ maps (Koumpia+, 2020)
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Mapping the H_2_D^+^ and N_2_H^+^ emission towards prestellar cores.
Testing dynamical models of the collapse using gas tracers.
Koumpia E., Evans L., Di Francesco J., van der Tak F.F.S., Oudmaijer R.D.
=2020A&A...643A..61K (SIMBAD/NED BibCode)
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ADC_Keywords: Molecular clouds ; Interstellar medium ; Radio lines
Keywords: stars: formation - ISM: clouds - ISM: kinematics and dynamics -
submillimeter: ISM
Abstract:
The study of prestellar cores is critical as they set the initial
conditions in star formation and determine the final mass of the
stellar object. To date, several hypotheses are describing their
gravitational collapse. Deriving the dynamical model that fits both
the observed dust and the gas emission from such cores is therefore of
great importance.
We perform detailed line analysis and modelling of H_2_D^+^
1_10_-1_11_ and N_2_H^+^ 4-3 emission at 372GHz, using 2'x2' maps
(JCMT).Our goal is to test the most prominent dynamical models by
comparing the modelled gas kinematics and spatial distribution
(H_2_D^+^ and N_2_H^+^) with observations towards four prestellar
(L1544, L183, L694-2, L1517B) and one protostellar core (L1521f).
We fit the line profiles at all offsets showing emission using single
Gaussian distributions. We investigate how the line parameters
(V_LSR_, FWHM and T_A_*) change with offset, to examine the velocity
field, the degree of non-thermal contributions to the line broadening,
and the distribution of the material in these cores. To assess the
thermal broadening, we derive the average gas kinetic temperature
towards all cores using the non-LTE radiative transfer code RADEX. We
perform a more detailed non-LTEradiative transfer modelling using
RATRAN, where we compare the predicted spatial distribution and line
profiles of H_2_D^+^ and N_2_H^+^ with observations towards all cores.
To do so, we adopt the physical structure for each core predicted by
three different dynamical models taken from literature:
Quasi-Equilibrium Bonnor-Ebert Sphere (QE-BES), Singular Isothermal
Sphere (SIS), and Larson-Penston (LP) flow. In addition, we compare
these results to those of a static sphere, whose density and
temperature profiles are based on the observed dust continuum. Lastly,
we constrain the abundance profiles of H_2_D^+^ and N_2_H^+^ towards
each core.
We find that variable non-thermal contributions (variations by a
factor of 2.5) are required to explain the observed line width of both
H_2_D^+^ and N_2_H^+^, while the non-thermal contributions are found
to be 50% higher for N_2_H^+^. The RADEX modelling results in average
core column densities of ~9x10^12^cm^-2^ for H_2_D+and N_2_H^+^. The
LP flow seems to be the dynamical model that can reproduce the
observed spatial distribution and line profiles of H_2_D^+^ on a
global scale of prestellar cores, while the SIS model systematically
and significantly overestimates the width of the line profiles and
underestimates the line peak intensity. We find similar abundance
profiles for the prestellar cores and the protostellar core. The
typical abundances of H_2_D^+^ vary between 10^-9^-10^-10^ for the
inner 5000au, and drop by about an order of magnitude for the outer
regions of the core (2x10^-10^-6x10^-11^). In addition, a higher
N_2_H^+^ abundance by about a factor of 4 compared to H_2_D^+^ is
found towards the two cores with detected emission. The presence
ofN_2_H^+^ 4-3 towards the protostellar core and towards one of the
prestellar cores reflects the increasing densities as the core
evolves.
Our analysis provides an updated picture of the physical structure of
prestellar cores. Although the dynamical models account for mass
differences by up to a factor of 7, the velocity structure drives the
shape of the line profiles, allowing for a robust comparison between
the models. We find that the SIS model can be cleary excluded in
explaining the gas emission towards the cores,but a larger sample is
required to differentiate clearly between the LP flow, the QE-BES and
the static models. All models of collapse underestimate the intensity
of the gas emission by up to several factors towards the only
protostellar core in our sample, indicating that different dynamics
take place in different evolutionary core stages. If the LP model is
confirmed towards a larger sample of prestellarcores, it would
indicate that they may form by compression or accretion of gas from
larger scales. If the QE-BES model is confirmed, it means that quasi
hydrostatic cores can exist within turbulent ISM.
Description:
The objective of this work is to test the most prominent dynamical
models of collapse by comparing the modelled gas kinematics and
spatial distribution (H_2_D^+^ and N_2_H^+^) with observations towards
four prestellar (L1544, L183, L694-2, L1517B) and one protostellar
core (L1521f). We performed detailed line analysis and modelling of
H_2_D^+^ 110-111 and N_2_H^+^ 4-3 emission at 372GHz, using 2'x2' maps
(JCMT).
These are the reduced JCMT 2'x2' data cubes. The data were reduced
using standard routines and procedures in the STARLINK reduction
package.
These files contain both the spatial and velocity information of the
molecular transition of interest towards each core.
Objects:
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RA (2000) DE Designation(s)
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04 55 18.3 +30 37 48 L1517B = [LM99] L1517B
04 28 39.3 +26 51 33 L1521f = [LM99] L1521F
05 04 17.2 +25 10 44 L1544 = [LM99] L1544-1
15 54 08.6 -02 52 45 L183 = LDN 183
19 41 04.5 +10 57 02 L694-2 = [LM99] L694-2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 158 10 List of fits datacubes
fits/* . 10 Individual fits datacubes
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 21 I2 --- Nx Number of pixels along X-axis
23- 24 I2 --- Ny Number of pixels along Y-axis
26- 28 I3 --- Nz Number of slices
30- 52 A23 "datime" Obs.date Observation date
54- 62 F9.5 m/s bVRAD Lower value of VRAD interval
64- 71 F8.5 m/s BVRAD Upper value of VRAD interval
72- 80 F9.7 m/s dVRAD VRAD resolution
82- 84 I3 Kibyte size Size of FITS file
86-101 A16 --- FileName Name of FITS file, in subdirectory fits
103-158 A56 --- Title Title of the FITS file
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Acknowledgements:
Evgenia Koumpia, ev.koumpia(at)gmail.com
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(End) Patricia Vannier [CDS] 20-Sep-2020