J/A+A/646/A97 Molecular emission from the Perseus cloud (Tafalla+, 2021)
Characterizing the emission from molecular clouds.
Stratified random sampling of the Perseus cloud.
Tafalla M., Usero A., Hacar A.
<Astron. Astrophys. 646, A97 (2021)>
=2021A&A...646A..97T 2021A&A...646A..97T (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Abundances
Keywords: ISM: abundances - ISM: clouds -
ISM: individual objects: Perseus Cloud - ISM: molecules -
ISM: structure - Stars: formation
Abstract:
The traditional technique to characterize the structure of molecular
clouds is mapping their line emission.
We aim to test and apply a sampling technique that can characterize
the line emission from a molecular cloud more efficiently than
mapping.
We have sampled the molecular emission from the Perseus cloud using
the H2 column density as a proxy. We have divided the cloud into 10
logarithmically- spaced column density bins, and we have selected 10
random positions from each bin. The resulting 100 cloud positions have
been observed with the IRAM 30m telescope covering the 3mm-wavelength
band and parts of the 2mm and 1mm bands.
We focus our analysis on the eleven molecular species (plus
isotopologs) detected toward most column density bins. In all cases,
the line intensity is tightly correlated with the H2 column density.
For the CO isotopologs, the correlation is relatively flat, while for
most dense gas tracers, the correlation is approximately linear. To
reproduce these trends, we have developed a cloud model in which most
species have abundance profiles characterized by an outer
photo-dissociation edge and an inner freeze-out drop. With this model
we determine that the intensity behavior of the dense gas tracers
arises from a combination of excitation effects and molecular freeze
out, with some modulation from optical depth. The quasi-linear
dependence of the dense-gas tracer emission with H2 column density
makes the gas at low column densities dominate the cloud- integrated
emission. It also makes this emission proportional to the cloud mass
inside the photodissociation edge.
Stratified random sampling is an efficient technique to characterize
the emission from molecular clouds. Despite its complex appearance,
the molecular emission from Perseus presents a relatively simple
behavior that, from a limited comparison with other clouds, seems to
reflect a general pattern.
Description:
This dataset contains coordinates of the 100 Perseus positions
selected by using stratified random sampling, their estimated H2
column density, and the velocity-integrated intensities for the
brightest lines in the 3mm wavelength band as observed with the
IRAM-30m telescope. The first digit in the source name indicates the
column density bin to which it belongs (10 denotes the highest column
density bin). The H2 column densities are derived from the data of
Zari et al. (2016A&A...587A.106Z 2016A&A...587A.106Z, Cat. J/A+A/587/A106) using their
recommended parameters. The line intensities are in the main beam
brightness temperature scale.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 316 100 Sample positions and integrated intensities
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See also:
J/A+A/587/A106 : Perseus dust optical depth & column density maps (Zari+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name
12- 13 I2 h RAh Right ascension (J2000)
15- 16 I2 min RAm Right ascension (J2000)
18- 21 F4.1 s RAs Right ascension (J2000)
23 A1 --- DE- Declination sign (J2000)
24- 25 I2 deg DEd Declination (J2000)
27- 28 I2 arcmin DEm Declination (J2000)
30- 31 I2 arcsec DEs Declination (J2000)
34- 41 E8.2 cm-2 NH2 H2 column density
44- 50 E7.1 cm-2 e_NH2 H2 column density uncertainty
53- 60 E8.2 K.km/s Int1 12CO(1-0) intensity
63- 69 E7.1 K.km/s e_Int1 12CO(1-0) intensity uncertainty
72- 79 E8.2 K.km/s Int2 13CO(1-0) intensity
82- 88 E7.1 K.km/s e_Int2 13CO(1-0) intensity uncertainty
90- 98 E9.2 K.km/s Int3 C18O(1-0) intensity
101-107 E7.1 K.km/s e_Int3 C18O(1-0) intensity uncertainty
109-117 E9.2 K.km/s Int4 C17O(1-0) intensity
120-126 E7.1 K.km/s e_Int4 C17O(1-0) intensity uncertainty
128-136 E9.2 K.km/s Int5 HCN(1-0) intensity (1)
139-145 E7.1 K.km/s e_Int5 HCN(1-0) intensity uncertainty (1)
148-155 E8.2 K.km/s Int6 CS(2-1) intensity
158-164 E7.1 K.km/s e_Int6 CS(2-1) intensity uncertainty
166-174 E9.2 K.km/s Int7 HNC(1-0) intensity
177-183 E7.1 K.km/s e_Int7 HNC(1-0) intensity uncertainty
186-193 E8.2 K.km/s Int8 HCO+(1-0) intensity
196-202 E7.1 K.km/s e_Int8 HCO+(1-0) intensity uncertainty
204-212 E9.2 K.km/s Int9 SO(23-12) intensity
215-221 E7.1 K.km/s e_Int9 SO(23-12) intensity uncertainty
223-231 E9.2 K.km/s Int10 CH3OH(2-1) intensity (2)
234-240 E7.1 K.km/s e_Int10 CH3OH(2-1) intensity uncertainty (2)
242-250 E9.2 K.km/s Int11 CN(1-0) intensity (1)
253-259 E7.1 K.km/s e_Int11 CN(1-0) intensity uncertainty (1)
261-269 E9.2 K.km/s Int12 C3H2(212-101) intensity
272-278 E7.1 K.km/s e_Int12 C3H2(212-101) intensity uncertainty
280-288 E9.2 K.km/s Int13 N2H+(1-0) intensity (1)
291-297 E7.1 K.km/s e_Int13 N2H+(1-0) intensity uncertainty (1)
299-307 E9.2 K.km/s Int14 C2H(1-0) intensity (1)
310-316 E7.1 K.km/s e_Int14 C2H(1-0) intensity uncertainty (1)
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Note (1): For HCN(1-0), CN(1-0), N2H+(1-0), and C2H(1-0), the intensity
includes the contribution from all detected hyperfine components.
Note (2): For CH3OH(2-1), the intensity includes the contribution from
the A+ and E components.
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Acknowledgements:
Mario Tafalla, m.tafalla(at)oan.es
(End) Patricia Vannier [CDS] 04-Jan-2021