Significance
The detection of ethanolamine (
N
H
2
C
H
2
C
H
2
OH) in a molecular cloud in the interstellar medium confirms that a precursor of phospholipids is efficiently formed by interstellar ...chemistry. Hence, ethanolamine could have been transferred from the proto-Solar nebula to planetesimals and minor bodies of the Solar System and thereafter to our planet. The prebiotic availability of ethanolamine on early Earth could have triggered the formation of efficient and permeable amphiphilic molecules such as phospholipids, thus playing a relevant role in the evolution of the first cellular membranes needed for the emergence of life.
Cell membranes are a key element of life because they keep the genetic material and metabolic machinery together. All present cell membranes are made of phospholipids, yet the nature of the first membranes and the origin of phospholipids are still under debate. We report here the presence of ethanolamine in space,
N
H
2
C
H
2
C
H
2
OH, which forms the hydrophilic head of the simplest and second-most-abundant phospholipid in membranes. The molecular column density of ethanolamine in interstellar space is
N
= (1.51
±
0.07)
×
10
13
c
m
−
2
, implying a molecular abundance with respect to
H
2
of
(
0.9
−
1.4
)
×
10
−
10
. Previous studies reported its presence in meteoritic material, but they suggested that it is synthesized in the meteorite itself by decomposition of amino acids. However, we find that the proportion of the molecule with respect to water in the interstellar medium is similar to the one found in the meteorite (
10
−
6
). These results indicate that ethanolamine forms efficiently in space and, if delivered onto early Earth, could have contributed to the assembling and early evolution of primitive membranes.
One of the proposed scenarios for the origin of life is the primordial RNA world, which considers that RNA molecules were likely responsible for the storage of genetic information and the catalysis ...of biochemical reactions in primitive cells, before the advent of proteins and DNA. In the last decade, experiments in the field of prebiotic chemistry have shown that RNA nucleotides can be synthesized from relatively simple molecular precursors, most of which have been found in space. An important exception is hydroxylamine, NH2OH, which, despite several observational attempts, it has not been detected in space yet. Here we present the first detection of NH2OH in the interstellar medium toward the quiescent molecular cloud G+0.693-0.027 located in the Galactic Center. We have targeted the three groups of transitions from the J = 2−1, 3−2, and 4−3 rotational lines, detecting five transitions that are unblended or only slightly blended. The derived molecular abundance of NH2OH is (2.1 0.9) × 10−10. From the comparison of the derived abundance of NH2OH and chemically related species, with those predicted by chemical models and measured in laboratory experiments, we favor the formation of NH2OH in the interstellar medium via hydrogenation of NO on dust grain surfaces, with possibly a contribution of ice-mantle NH3 oxidation processes. Further laboratory studies and quantum chemical calculations are needed to completely rule out the formation of NH2OH in the gas phase.
The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of ...compound toward the Galactic Center quiescent cloud G+0.693–0.027. We report the first detection in the interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with an abundance of ∼1 נ10−10. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C2H5SH) with an abundance of ∼3 נ10−10, and we also detect methyl mercaptan (CH3SH) with an abundance of ∼5 נ10−9. Abundance ratios were calculated for the three SH-bearing species and their OH analogs, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH3SH, and C2H5SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.
Abstract
A quarter century after the detection of the last interstellar carboxylic acid, acetic acid (CH
3
COOH), we report the discovery of a new one, the
cis-trans
form of carbonic acid (HOCOOH), ...toward the Galactic center molecular cloud G+0.693–0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also directly identified several pairs of unblended lines in the astronomical data (between 75 and 120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for
cis-trans
HOCOOH of
N
= (6.4 ± 0.4) × 10
12
cm
−2
, which yields an abundance with respect to molecular H
2
of 4.7 × 10
−11
. Meanwhile, the extremely low dipole moment (about 15 times lower) of the lower-energy conformer,
cis-cis
HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H
2
of ≤1.2 × 10
−9
, which suggests that
cis-cis
HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a
cis-cis
/
cis-trans
ratio of ≤25, consistent with the smaller energy difference between both conformers compared with the relative stability of
trans-
and
cis
-formic acid. Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the solar system, which could be inherited during the star formation process.
Abstract
Recent astronomical observations of both isomers E and Z of imines such as cyanomethanimine, ethanimine, and 2-propyn-1-imine have revealed that the abundances in the interstellar medium ...(ISM) of these isomers differ by factors of ∼3–10. Several theories have been proposed to explain the observed behavior, but none of them successfully explains the E/Z ratios. In this work we present a detailed study of the kinetics of the one-step E-Z isomerization reactions of cyanomethanimine, ethanimine, and 2-propyn-1-imine under interstellar conditions (in the 10–400 K temperature range). This reaction was previously thought to be nonviable in the ISM due to its associated high-energy barrier (about 13,000 K). In this Letter, we show that considering the multidimensional small curvature tunneling approximation, the tunneling effect enables the isomerization even at low temperatures. This is due to the fact that the representative tunneling energy lies in the vibrational ground state of the least stable isomer up to approximately 150 K, making the reaction constants of the isomerization from the least stable to the most stable isomer basically constant. The predicted E/Z ratios are almost the same as those reported from the astronomical observations for all imines observed. This study demonstrates that the E/Z ratio of imines in the ISM strongly depends on their relative stability.
Galaxies with nuclear bars are believed to efficiently drive gas inward, generating a nuclear starburst and possibly an active galactic nucleus. We confirm this scenario for the isolated, ...double-barred, luminous infrared galaxy ESO 320-G030 based on an analysis of
Herschel
and ALMA spectroscopic observations.
Herschel
/PACS and SPIRE observations of ESO 320-G030 show absorption or emission in 18 lines of H
2
O, which we combine with the ALMA H
2
O 4
23
− 3
30
448 GHz line (
E
upper
∼ 400 K) and continuum images to study the physical properties of the nuclear region. Radiative transfer models indicate that three nuclear components are required to account for the multi-transition H
2
O and continuum data. An envelope, with radius
R
∼ 130 − 150 pc, dust temperature
T
dust
≈ 50 K, and
N
H2
∼ 2 × 10
23
cm
−2
, surrounds a nuclear disk with
R
∼ 40 pc that is optically thick in the far-infrared (
τ
100 μm
∼ 1.5 − 3,
N
H2
∼ 2 × 10
24
cm
−2
). In addition, an extremely compact (
R
∼ 12 pc), warm (≈100 K), and buried (
τ
100 μm
> 5,
N
H2
≳ 5 × 10
24
cm
−2
) core component is required to account for the very high-lying H
2
O absorption lines. The three nuclear components account for 70% of the galaxy luminosity (SFR ∼ 16 − 18
M
⊙
yr
−1
). The nucleus is fed by a molecular inflow observed in CO 2-1 with ALMA, which is associated with the nuclear bar. With decreasing radius (
r
= 450 − 225 pc), the mass inflow rate increases up to
Ṁ
inf
∼ 20
Ṁ
yr
−1
, which is similar to the nuclear star formation rate (SFR), indicating that the starburst is sustained by the inflow. At lower
r
, ∼100 − 150 pc, the inflow is best probed by the far-infrared OH ground-state doublets, with an estimated
Ṁ
inf
∼ 30
Ṁ
yr
−1
. The inferred short timescale of ∼20 Myr for nuclear gas replenishment indicates quick secular evolution, and indicates that we are witnessing an intermediate stage (< 100 Myr) proto-pseudobulge fed by a massive inflow that is driven by a strong nuclear bar. We also apply the H
2
O model to the
Herschel
far-infrared spectroscopic observations of H
2
18
O, OH,
18
OH, OH
+
, H
2
O
+
, H
3
O
+
, NH, NH
2
, NH
3
, CH, CH
+
,
13
CH
+
, HF, SH, and C
3
, and we estimate their abundances.
Abstract
MWC 349A is a massive star with a well-known circumstellar disk rotating following a Keplerian law, and an ionized wind launched from the disk surface. Recent observations with the Atacama ...Large Millimeter/submillimeter Array (ALMA) carried out toward this system, however, have revealed an additional high-velocity component in the strong, maser emission of hydrogen radio recombination lines (RRLs), suggesting the presence of a high-velocity ionized jet. In this work, we present 3D non-LTE radiative transfer modeling of the emission of the H30
α
and H26
α
maser lines, and of their associated radio continuum emission, toward MWC 349A. By using the MORELI code, we reproduce the spatial distribution and kinematics of the high-velocity emission of the H30
α
and H26
α
maser lines with a high-velocity ionized jet expanding at a velocity of ∼250 km s
−1
, surrounded by MWC 349A’s wide-angle ionized wind. The bipolar jet, which is launched from MWC 349A’s disk, is poorly collimated and slightly misaligned with respect to the disk rotation axis. Thanks to the unprecedented sensitivity and spatial accuracy provided by ALMA, we also find that the already known, wide-angle ionized wind decelerates as it expands radially from the ionized disk. We briefly discuss the implications of our findings for understanding the formation and evolution of massive stars. Our results show the huge potential of RRL masers as powerful probes of the innermost ionized regions around massive stars and of their high-velocity jets.
Abstract
Amines, particularly primary amines (R-NH
2
), are closely related to the primordial synthesis of amino acids since they share the same structural backbone. However, only a limited number of ...amines has been identified in the interstellar medium, which prevents us from studying their chemistry as well as their relation to prebiotic species that could lead to the emergence of life. In this Letter, we report the first interstellar detection of vinylamine (C
2
H
3
NH
2
) and tentative detection of ethylamine (C
2
H
5
NH
2
) toward the Galactic center cloud G+0.693-0.027. The derived abundance with respect to H
2
is (3.3 ± 0.4) × 10
−10
and (1.9 ± 0.5) × 10
−10
, respectively. The inferred abundance ratios of C
2
H
3
NH
2
and C
2
H
5
NH
2
with respect to methylamine (CH
3
NH
2
) are ∼0.02 and ∼0.008, respectively. The derived abundance of C
2
H
3
NH
2
, C
2
H
5
NH
2
, and several other NH
2
-bearing species are compared to those obtained toward high-mass and low-mass star-forming regions. Based on recent chemical and laboratory studies, possible chemical routes for the interstellar synthesis of C
2
H
3
NH
2
and C
2
H
5
NH
2
are discussed.
We report the first detection in the interstellar medium (ISM) of a C2H5O2N isomer: syn-glycolamide (NH2C(O)CH2OH). The exquisite sensitivity at sub-mK levels of an ultradeep spectral survey carried ...out with the Yebes 40 m and IRAM 30 m telescopes toward the G+0.693–0.027 molecular cloud has allowed us to unambiguously identify multiple transitions of this species. We derived a column density of (7.4 ± 0.7) × 1012 cm−2, which implies a molecular abundance with respect to H2 of 5.5 × 10−11. The other C2H5O2N isomers, including the higher-energy anti conformer of glycolamide and two conformers of glycine, were not detected. The upper limit derived for the abundance of glycine indicates that this amino acid is surely less abundant than its isomer glycolamide in the ISM. The abundances of the C2H5O2N isomers cannot be explained in terms of thermodynamic equilibrium; thus, chemical kinetics need to be invoked. While the low abundance of glycine might not be surprising, based on the relative low abundances of acids in the ISM compared to other compounds (e.g., alcohols, aldehydes, or amines), several chemical pathways can favor the formation of its isomer glycolamide. It can be formed through radical–radical reactions on the surface of dust grains. The abundances of these radicals can be significantly boosted in an environment affected by a strong ultraviolet field induced by cosmic rays, such as that expected in G+0.693–0.027. Therefore, as shown by several recent molecular detections toward this molecular cloud, it stands out as the best target to discover new species with carbon, oxygen, and nitrogen with increasing chemical complexity.
Abstract
We present the first detection in space of O-protonated carbonyl sulfide (HOCS
+
), in the midst of an ultradeep molecular line survey toward the G+0.693-0.027 molecular cloud. From the ...observation of all
K
a
= 0 transitions ranging from
J
lo
= 2 to
J
lo
= 13 of HOCS
+
covered by our survey, we derive a column density of
N
= (9 ± 2) × 10
12
cm
−2
, translating into a fractional abundance relative to H
2
of ∼7 × 10
−11
. Conversely, the S-protonated HSCO
+
isomer remains undetected, and we derive an upper limit to its abundance with respect to H
2
of ≤3 × 10
−11
, a factor of ≥2.3 less abundant than HOCS
+
. We obtain an HOCS
+
/OCS ratio of ∼2.5 × 10
−3
, in good agreement with the prediction of astrochemical models. These models show that one of the main chemical routes to the interstellar formation of HOCS
+
is likely the protonation of OCS, which appears to be more efficient at the oxygen end. Also, we find that high values of cosmic-ray ionization rates (10
−15
–10
−14
s
−1
) are needed to reproduce the observed abundance of HOCS
+
. In addition, we compare the O/S ratio across different interstellar environments. G+0.693-0.027 appears as the source with the lowest O/S ratio. We find an HOCO
+
/HOCS
+
ratio of ∼31, in accordance with other O/S molecular pairs detected toward this region and also close to the O/S solar value (∼37). This fact indicates that S is not significantly depleted within this cloud due to the action of large-scale shocks, unlike in other sources where S-bearing species remain trapped on icy dust grains.
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