J/MNRAS/497/1972 LEGO II. 3mm molecular line study (Barnes+, 2020)
LEGO II: A 3mm molecular line study covering 100pc of one of the most actively.
Barnes A.T., Kauffmann J., Bigiel F., Brinkmann N., Colombo D., Guzman A.E,
Kim W.J., Szucs L., Wakelam V., Aalto S., Albertsson T., Evans N.J. II,
Glover S.C.O., Goldsmith P.F., Kramer C., Menten K., Nishimura Y., Viti S.,
Watanabe Y., Weiss A., Wienen M., Wiesemeyer H., Wyrowski F.
<Mon. Not. R. Astron. Soc. 497, 1972 (2020)>
=2020MNRAS.497.1972B 2020MNRAS.497.1972B (SIMBAD/NED BibCode)
ADC_Keywords: Star Forming Region ; Molecular data ; Interstellar medium
Keywords: stars: formation - ISM: clouds - ISM: molecules -
galaxies: evolution - galaxies: ISM - galaxies: star formation
Abstract:
The current generation of (sub)mm-telescopes have allowed molecular
line emission to become a major tool for studying the physical,
kinematic, and chemical properties of extra-galactic systems, yet
exploiting these observations requires a detailed understanding of
where emission lines originate within the Milky Way. In this paper, we
present 60" (∼3pc) resolution observations of many 3mm-band molecular
lines across a large map of the W49 massive star-forming region
(∼100pcx100pc at 11kpc), which were taken as part of the "LEGO"
IRAM-30m large project. We find that the spatial extent or brightness
of the molecular line transitions are not well correlated with their
critical densities, highlighting abundance and optical depth must be
considered when estimating line emission characteristics. We explore
how the total emission and emission efficiency (i.e. line brightness
per H2 column density) of the line emission vary as a function of
molecular hydrogen column density and dust temperature. We find that
there is not a single region of this parameter space responsible for
the brightest and most efficiently emitting gas for all species. For
example, we find that the HCN transition shows high emission
efficiency at high column density (1022cm-2) and moderate
temperatures (35K), whilst e.g. N2H+ emits most efficiently
towards lower temperatures (1022cm-2; <20K). We determine
XCO(1-0)∼0.3x1020cm-2/(K.km/s), and
αHCN(1-0)∼30M☉/(K.(km/s)pc2), which both differ
significantly from the commonly adopted values. In all, these results
suggest caution in interpreting molecular line emission.
Description:
table2.dat contains information on the selected observed molecular
lines, ordered by increasing rest frequency. Section 2.1.2 of the
paper describes how the lines recorded in this table were selected,
and how the line characteristics recorded here were obtained. Columns
1 to 10 show the name of each molecule, the transition information,
the frequency of the transition (Lovas, 2004JPCRD..33..177L 2004JPCRD..33..177L), the upper
energy level of the transition, the Einstein spontaneous decay
coefficient, the collisional deexcitation rate coefficients at a
kinetic temperature of 20K, and the critical and effective densities
for emission. Transitions that are not available within the LAMDA
database have the corresponding information blanked. Additional
information on the molecular line database used within this work can
be found in Table A1 of the paper.
table3b1.dat contains observational properties across the mapped
region (i.e. that covered with both vertical and horizontal on-the-fly
scans). The columns show the molecule name, the average cube rms (in a
1kms-1 channel), mean uncertainty of the integrated intensity, the
minimum values of all pixels within the map, and the minimum, mean,
and 5, 16, 50, 84, and 95 percentile ranges for the intensities at
positions above a 3-sigma uncertainty threshold. Also given is the
area percentage, within the mapped region that has an integrated
intensity above five times the uncertainty. The information given is
for maps that have been smoothed to an angular resolution of 60arcsec,
and have a spectral resolution of 0.6km/s.
table4.dat contains properties determined from the cumulative
distributions of the emission from each molecular line. Tabulated is
the molecule, and its characteristic column density, which is defined
as the column density that contains half the total line intensity. The
uncertainties show the range of characteristic densities after adding
a synthetic noise of 1 sigma (see shaded region on Figure 9 in the
paper). We provide the results of the analysis across the whole mapped
region (i.e. using the cumulative distributions shown in Section 4.1),
and when limited to W49A (i.e. using the cumulative distributions
shown in Section 5.2). Also shown for W49A is the characteristic
density (see Section 5.2).
tableA1.dat contains details on the emission lines covered by the LEGO
survey, and processed by our pipeline. Section 2.1.2 explains how
lines examined in this study were selected. Each of the selected lines
was given a LEGO reference code in the reduction pipeline, which are
presented in the first column of the Table. The rest frequency
recorded in this table refers to the specific full transition (Lovas,
2004JPCRD..33..177L 2004JPCRD..33..177L). These transitions are sometimes part of larger
groups, as explained in Sec. 2.1.2 (see the final column of this
Table). In those cases, the minimum and maximum frequencies of the
lines considered to form a group.
tablee1a.dat contains calculated conversion factors for the various
molecular line transitions. The values shown in this half of the Table
have been calculated using the column density and mass of Av>8mag
gas divided by the mean integrated intensity and total luminosity of
the given line across the region.
tablee1b.dat contains calculated conversion factors for the various
molecular line transitions. The values shown in this half of the Table
have been calculated using both the column density and mass, and
integrated intensity and luminosity above the Av>8mag threshold.
tablee2.dat contains calculated conversion factors for the various
molecular line transitions. The values in this table have been
calculated without imposing any extinction threshold on the gas column
density and gas mass, and the integrated intensity and luminosity of
the given line.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 166 25 Selected observed molecular line information
table3b1.dat 258 24 Molecular line cube and integrated intensity
map statistics (Table 3 and B1)
table4.dat 148 24 Characteristic column and number densities of
molecular hydrogen
tablea1.dat 108 25 Molecular line information for the LEGO survey
pipeline
tablee1a.dat 195 23 Molecular hydrogen column density and mass
conversion factors calculated using the column
density and mass of Av>8mag gas divided by the
mean integrated intensity and total luminosity
of the given line across the region
(top half of Table E1)
tablee1b.dat 194 23 Molecular hydrogen column density and mass
conversion factors calculated using both the
column density and mass, and integrated
intensity and luminosity above the Av>8mag
threshold (bottom half of Table E1)
tablee2.dat 195 23 Molecular hydrogen column density and mass
conversion factors calculated without imposing
any extinction threshold on the gas column
density and gas mass, and the integrated
intensity and luminosity of the given line
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- LEGO Identifier
12- 21 A10 --- Mol Molecule
23- 49 A27 --- Trans Transition
51- 61 F11.7 GHz Freq Rest frequency (1)
63- 69 F7.3 K Eu ? Upper energy level (2)
71- 82 E12.7 s-1 Aij ? Einstein coefficient for spontaneous
emission (2)
84- 92 E9.4 cm3/s Cij-2lvl ? Two-level approximation for downward
collisional rates coefficient (2)
94-115 E22.17 cm3/s Cij-tot ? Full-level approximation for downward
collisional rates coefficient (2)
117-137 F21.13 cm-3 ncrit-2lvl ? Two-level approximation for critical
density for emission
139-159 F21.14 cm-3 ncrit-tot ? Full-level approximation for critical
density for emission
161-166 I6 cm-3 effncrit Effective density for emission
--------------------------------------------------------------------------------
Note (1): Lovas/NIST database; Lovas 2004JPCRD..33..177L 2004JPCRD..33..177L
Note (2): (LAMDA database; Schoeier et al., 2005, Cat. J/A+A/432/369)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3b1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- LEGO Identifier
12- 31 F20.18 K rms Average rms within the cubes within a 1km/s
channel
33- 51 F19.17 K.km/s sigma Mean uncertainty of the integrated intensity
53- 73 F21.17 % coverage Area percentage containing significant
emission
75- 94 F20.17 K.km/s min-ns Minimum integrated intensity of all pixels
within the map
95-114 F20.17 K.km/s min Minimum integrated intensity of significant
pixels within the map
115-134 F20.17 K.km/s p5 5 percentile integrated intensity of
significant pixels within the map
135-154 F20.17 K.km/s p16 16 percentile integrated intensity of
significant pixels within the map
155-175 F21.18 K.km/s mean Mean integrated intensity of significant
pixels within the map
177-196 F20.17 K.km/s median Median integrated intensity of significant
pixels within the map
197-216 F20.16 K.km/s p84 84 percentile integrated intensity of
significant pixels within the map
218-238 F21.17 K.km/s p95 95 percentile integrated intensity of
significant pixels within the map
239-259 F21.17 K.km/s maximum Maximum integrated intensity of significant
pixels within the map
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- LEGO Identifier
12- 33 E22.16 cm-2 Nchar-all Characteristic column density across the
whole map
35- 56 E22.16 cm-2 e_Nchar-all Error on the characteristic column density
across the whole map
58- 79 E22.16 cm-2 Nchar-w49a Characteristic column density across W49A
only
81-102 E22.16 cm-2 e_Nchar-w49a Error on the characteristic column density
across W49A only
104-125 E22.16 cm-3 nchar-w49a Characteristic number density across W49A
only
127-148 E22.16 cm-3 e_nchar-w49a Error on the characteristic number density
across W49A only
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- LEGO Identifier
12- 21 A10 --- Mol Molecule
23- 49 A27 --- Trans Transition
51- 61 F11.7 GHz Freq [86.3/115.3]? Rest frequency (Lovas/NIST
database; Lovas 2004JPCRD..33..177L 2004JPCRD..33..177L)
63- 73 F11.7 GHz FreqMin [86.3/113.5]? Minimum group frequency
75- 85 F11.7 GHz FreqMax [86.3/113.6]? Maximum group frequency
87-108 A22 --- Comm Comments on group
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablee1a.dat tablee1b.dat tablee2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- LEGO Identifier
12- 32 F21.18 [K.km/s] logW ? Mean integrated intensity (log10)
35- 55 F21.18 [K.km/s] e_logW [] Error on integrated intensity
(log10)
57- 74 F18.16 [K.(km/s).pc2] logL ? Sum luminosity (log10)
76- 97 F22.19 [K.(km/s).pc2] e_logL [] Error on sum luminosity (log10)
99-122 E24.19 cm-2/(K.km/s) XQ Column density conversion factor
(Xfactor)
123-146 E24.19 cm-2/(K.km/s) e_XQ [] Error on column density
conversion factor (X-factor)
147-168 F22.16 Msun/(K.(km/s).pc2) aQ Mass conversion factor
(alpha-factor)
171-195 F25.18 Msun/(K.(km/s).pc2) e_aQ [] Error on mass conversion factor
(alpha-factor)
--------------------------------------------------------------------------------
Acknowledgements:
Ashley Barnes, ashleybarnes.astro(at)gmail.com
References:
Kauffmann et al., Paper 2017A&A...605L...5K 2017A&A...605L...5K
(End) Patricia Vannier [CDS] 03-Sep-2020