16 research outputs found
Isotopic fractionation study towards massive star-forming regions across the Galaxy
One of the most important tools to investigate the chemical history of our Galaxy and our own Solar System is to measure the isotopic fractionation of chemical elements. In the present study new astronomical observations devoted to the study of hydrogen and nitrogen fractionation (D/H and 14N/15N ratios) of molecules, towards massive star-forming regions in different evolutionary phases, have been presented. Moreover, a new detailed theoretical study of carbon fractionation, 12C/13C ratios, has been done. One of the main results was the confirmation that the 14N/15N ratio increases with the galactocentric distance, as predicted by stellar nucleosynthesis Galactic chemical evolution models. This work gives new important inputs on the understanding of local chemical processes that favor the production of molecules with different isotopes in star-forming regions
A sequential acid-base (SAB) mechanism in the interstellar medium: The emergence of cis formic acid in dark molecular clouds
The abundance ratios between isomers of a COM observed in the ISM provides
valuable information about the chemistry and physics of the gas and eventually,
the history of molecular clouds. In this context, the origin of an abundance of
c-HCOOH acid of only 6% the isomer c-HCOOH abundance in cold cores, remains
unknown. Herein, we explain the presence of c-HCOOH in dark molecular clouds
through the destruction and back formation of c-HCOOH and t-HCOOH in a cyclic
process that involves HCOOH and highly abundant molecules such as HCO+ and NH3.
We use high-level ab initio methods to compute the potential energy profiles
for the cyclic destruction/formation routes of c-HCOOH and t-HCOOH. Global rate
constants and branching ratios were calculated based on the transition state
theory and the master equation formalism under the typical conditions of the
ISM. The destruction of HCOOH by reaction with HCO+ in the gas phase leads to
three isomers of the cation HC(OH)2+. The most abundant cation can react in a
second step with other abundant molecules of the ISM like NH3 to form back
c-HCOOH and t-HCOOH. This mechanism explains the formation of c-HCOOH in dark
molecular clouds. Considering this mechanism, the fraction of c-HCOOH with
respect t-HCOOH is 25.7%. To explain the 6% reported by the observations we
propose that further destruction mechanisms of the cations of HCOOH should be
taken into account. The sequential acid-base (SAB) mechanism proposed in this
work involves fast processes with very abundant molecules in the ISM. Thus,
HCOOH very likely suffers our proposed transformations in the conditions of
dark molecular clouds. This is a new approach in the framework of the isomerism
of organic molecules in the ISM which has the potential to try to explain the
ratio between isomers of organic molecules detected in the ISM
H2CN/H2NC abundance ratio: a new potential temperature tracer for the interstellar medium
The radical is the high-energy metastable isomer of radical, which has been recently detected for the first time in the
interstellar medium towards a handful of cold galactic sources, besides a warm
galaxy in front of the PKS 1830-211 quasar. These detections have shown that
the / isomeric ratio, likewise the HCN/HNC ratio,
might increase with the kinetic temperature (), but the shortage
of them in warm sources still prevents us to confirm this hypothesis and shed
light about their chemistry. In this work, we present the first detection of
and towards a warm galactic source, the
G+0.693-0.027 molecular cloud (with ), using IRAM
30m observations. We have detected multiple hyperfine components of the
and transitions.
We derived molecular abundances with respect to of
(6.81.3) for and of (3.10.7) for , and a / abundance ratio
of 2.20.5. These detections confirm that the /
ratio is 2 for sources with , larger than
the 1 ratios previously found in colder cores (). This isomeric ratio dependence with temperature cannot be fully explained
with the currently proposed gas-phase formation and destruction pathways. Grain
surface reactions, including the
isomerization, deserve consideration to explain the higher isomeric ratios and
abundances observed in warm sources, where the molecules can be
desorbed into the gas phase through thermal and/or shock-induced mechanisms.Comment: 12 pages, 5 figures, 3 tables, 2 appendix - Accepted for publication
in Monthly Notices of the Royal Astronomical Societ
Discovery of the elusive carbonic acid (HOCOOH) in space
After a quarter century since the detection of the last interstellar
carboxylic acid, acetic acid (CHCOOH), 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 also the third carboxylic acid detected so
far in the interstellar medium. Albeit the limited available laboratory
measurements (up to 65 GHz), we have also identified several pairs of unblended
lines directly in the astronomical data (between 75-120 GHz), which allowed us
to slightly improve the set of spectroscopic constants. We derive a column
density for cis-trans HOCOOH of = (6.4 0.4) 10
cm, which yields an abundance with respect to molecular H of 4.7
10. Meanwhile, the extremely low dipole moment (about fifteen
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 of
1.2 10, 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 25,
consistent with the smaller energy difference between both conformers compared
with the relative stability of trans- and cis-formic acid (HCOOH). 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.Comment: Accepted for publication in The Astrophysical Journa
Precursors of fatty alcohols in the ISM: Discovery of n-propanol
Theories on the origins of life propose that early cell membranes were
synthesized from amphiphilic molecules simpler than phospholipids such as fatty
alcohols. The discovery in the interstellar medium (ISM) of ethanolamine, the
simplest phospholipid head group, raises the question whether simple
amphiphilic molecules are also synthesized in space. We investigate whether
precursors of fatty alcohols are present in the ISM. For this, we have carried
out a spectral survey at 7, 3, 2 and 1 mm toward the Giant Molecular Cloud
G+0.693-0.027 located in the Galactic Center using the IRAM 30m and Yebes 40m
telescopes. Here, we report the detection in the ISM of the primary alcohol
n-propanol (in both conformers Ga-n-C3H7OH and Aa-n-C3H7OH), a precursor of
fatty alcohols. The derived column densities of n-propanol are (5.5+-0.4)x10^13
cm^-2 for the Ga conformer and (3.4+-0.3)x10^13 cm^-2 for the Aa conformer,
which imply molecular abundances of (4.1+-0.3)x10^-10 for Ga-n-C3H7OH and of
(2.5+-0.2)x10^-10 for Aa-n-C3H7OH. We also searched for the AGa conformer of
n-butanol (AGa-n-C4H9OH) without success yielding an upper limit to its
abundance of <4.1x10^-11. The inferred CH3OH:C2H5OH:C3H7OH:C4H9OH abundance
ratios go as 1:0.04:0.006:<0.0004 toward G+0.693-0.027, i.e. they decrease
roughly by one order of magnitude for increasing complexity. We also report the
detection of both syn and anti conformers of vinyl alcohol, with column
densities of (1.11+-0.08)x10^14 cm^-2 and (1.3+-0.4)x10^13 cm^-2, and
abundances of (8.2+-0.6)x10^-10 and (9.6+-3.0)x10^-11, respectively. The
detection of n-propanol, together with the recent discovery of ethanolamine in
the ISM, opens the possibility that precursors of lipids according to theories
of the origin of life, could have been brought to Earth from outer space.Comment: 15 pages, 10 figures, accepted for A&
First glycine isomer detected in the interstellar medium: glycolamide (NHC(O)CHOH)
We report the first detection in the interstellar medium of a
CHON isomer: -glycolamide (NHC(O)CHOH). The exquisite
sensitivity at sub-mK levels of an ultra-deep spectral survey carried out with
the Yebes 40m and IRAM 30m telescopes towards the G+0.693-0.027 molecular cloud
have allowed us to unambiguously identify multiple transitions of this species.
We derived a column density of (7.4 0.7)10 cm,
which implies a molecular abundance with respect to H of
5.510. The other CHON isomers, including the
higher-energy 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 CHON isomers cannot
be explained in terms of thermodynamic equilibrium, and 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
favour 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
towards this molecular cloud, it stands out as the best target to discover new
species with carbon, oxygen and nitrogen with increasing chemical complexity.Comment: Accepted in The Astrophysical Journal Letter
Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of HO and SO
The cosmic ray ionization rate (CRIR) is a key parameter in understanding the
physical and chemical processes in the interstellar medium. Cosmic rays are a
significant source of energy in star formation regions, which impacts the
physical and chemical processes which drive the formation of stars. Previous
studies of the circum-molecular zone (CMZ) of the starburst galaxy NGC 253 have
found evidence for a high CRIR value; times the average cosmic ray
ionization rate within the Milky Way. This is a broad constraint and one goal
of this study is to determine this value with much higher precision. We exploit
ALMA observations towards the central molecular zone of NGC 253 to measure the
CRIR. We first demonstrate that the abundance ratio of HO and SO is
strongly sensitive to the CRIR. We then combine chemical and radiative transfer
models with nested sampling to infer the gas properties and CRIR of several
star-forming regions in NGC 253 due to emission from their transitions. We find
that each of the four regions modelled has a CRIR in the range
s and that this result adequately fits the
abundances of other species that are believed to be sensitive to cosmic rays
including CH, HCO, HOC, and CO. From shock and PDR/XDR models, we
further find that neither UV/X-ray driven nor shock dominated chemistry are a
viable single alternative as none of these processes can adequately fit the
abundances of all of these species.Comment: 24 pages, 15 figures, accepted for publication in Ap
Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
The Central Molecular Zone (CMZ; the central ~ 500 pc of the Galaxy) is a
kinematically unusual environment relative to the Galactic disc, with high
velocity dispersions and a steep size-linewidth relation of the molecular
clouds. In addition, the CMZ region has a significantly lower star formation
rate (SFR) than expected by its large amount of dense gas. An important factor
in explaining the low SFR is the turbulent state of the star-forming gas, which
seems to be dominated by rotational modes. However, the turbulence driving
mechanism remains unclear. In this work, we investigate how the Galactic
gravitational potential affects the turbulence in CMZ clouds. We focus on the
CMZ cloud G0.253+0.016 (`the Brick'), which is very quiescent and unlikely to
be kinematically dominated by stellar feedback. We demonstrate that several
kinematic properties of the Brick arise naturally in a cloud-scale
hydrodynamics simulation that takes into account the Galactic gravitational
potential. These properties include the line-of-sight velocity distribution,
the steepened size-linewidth relation, and the predominantly solenoidal nature
of the turbulence. Within the simulation, these properties result from the
Galactic shear in combination with the cloud's gravitational collapse. This is
a strong indication that the Galactic gravitational potential plays a crucial
role in shaping the CMZ gas kinematics, and is a major contributor to
suppressing the SFR by inducing predominantly solenoidal turbulent modes.Comment: 7 pages, 8 figures; accepted to MNRAS (July 24th 2023
Precursors of the RNA-world in space: Detection of ()-1,2-ethenediol in the interstellar medium, a key intermediate in sugar formation
We present the first detection of ()-1,2-ethenediol, (CHOH), the enol
form of glycolaldehyde, in the interstellar medium towards the G+0.693-0.027
molecular cloud located in the Galactic Center. We have derived a column
density of (1.80.1)10 cm, which translates into a
molecular abundance with respect to molecular hydrogen of
1.310. The abundance ratio between glycolaldehyde and
()-1,2-ethenediol is 5.2. We discuss several viable formation routes
through chemical reactions from precursors such as HCO, HCO, CHOH or
CHCHOH. We also propose that this species might be an important precursor
in the formation of glyceraldehyde (HOCHCHOHCHO) in the interstellar medium
through combination with the hydroxymethylene (CHOH) radical.Comment: Accepted for publication in The Astrophysical Journal Letter
Isotopic fractionation study towards massive star-forming regions across the Galaxy
One of the most important tools to investigate the chemical history of our Galaxy and our own Solar System is to measure the isotopic fractionation of chemical elements. In the present study new astronomical observations devoted to the study of hydrogen and nitrogen fractionation (D/H and 14N/15N ratios) of molecules, towards massive star-forming regions in different evolutionary phases, have been presented. Moreover, a new detailed theoretical study of carbon fractionation, 12C/13C ratios, has been done. One of the main results was the confirmation that the 14N/15N ratio increases with the galactocentric distance, as predicted by stellar nucleosynthesis Galactic chemical evolution models.
This work gives new important inputs on the understanding of local chemical processes that favor the production of molecules with different isotopes in star-forming regions