arXiv subjects

Miguel A. Requena-Torres

Publications and source records attributed to Miguel A. Requena-Torres.

25 records · Page 2Linked to original sources

arXiv2020

Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud-cloud collision from SiO emission maps

We present SiO J=2-1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10,40] km s$^{-1}$ and an arc at velocities of [-20,10] km s$^{-1}$. The spatial anti-correlation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud-cloud collision. Some of the known compact HII regions spatially overlap with sites of strong SiO emission at velocities of [40,85] km s$^{-1}$, and are between or along the edges of SiO gas features at [100,120] km s$^{-1}$, suggesting that the stars responsible for ionizing the compact HII regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of $n_{\rm H_2}\sim 10^5\rm cm^{-3}$ and $\sim$30 K, respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are $\sim$10$^{-9}$, $\sim$11 K km s$^{-1}$, and $\sim$31 km s$^{-1}$, respectively. These values agree with those obtained with chemical models that mimic grain sputtering by C-type shocks. A comparison of our observations with hydrodynamical simulations shows that a cloud-cloud collision that took place $\lesssim$ 0.5 Myr ago can explain the density distribution with a mean column density of $\bar{N}_{\rm H_2}\gtrsim 5\times10^{22}$ cm$^{-2}$, and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities $\sim$5-50 km $s^{-1}$. High-velocity shocks are produced during the early stages of the collision and can readily ignite star formation, while moderate- and low-velocity shocks are important over longer timescales and can explain the widespread SiO emission in Sgr B2.

astro-ph.GA↗

arXiv2020

Prebiotic precursors of the primordial RNA world in space: Detection of NH$_{2}$OH

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, NH$_2$OH, which, despite several observational attempts, it has not been detected in space yet. Here we present the first detection of NH$_2$OH in the interstellar medium towards 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$-$1, 3$-$2, and 4$-$3 rotational lines, detecting 5 transitions that are unblended or only slightly blended. The derived molecular abundance of NH$_2$OH is (2.1$\pm$0.9)$\times$10$^{-10}$. From the comparison of the derived abundance of NH$_2$OH and chemically related species, with those predicted by chemical models and measured in laboratory experiments, we favor the formation of NH$_2$OH in the interstellar medium via hydrogenation of NO on dust grain surfaces, with possibly a contribution of ice mantle NH$_3$ oxidation processes. Further laboratory studies and quantum chemical calculations are needed to completely rule out the formation of NH$_2$OH in the gas phase.

astro-ph.GA↗

arXiv2020

Propargylimine in the laboratory and in space: millimetre-wave spectroscopy and first detection in the ISM

Small imines containing up to three carbon atoms are present in the interstellar medium. As alkynyl compounds are abundant in this medium, propargylimine thus represents a promising candidate for a new interstellar detection. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of propargylimine in its ground vibrational state in order to obtain a highly precise set of rest-frequencies and to search it in space. The rotational spectra of $E$ and $Z$ geometrical isomers of propargylimine have been recorded in laboratory in the 83-500 GHz frequency interval. The measurements have been performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic quantities. The improved spectral data allow us to perform a successful search for this new imine in the quiescent G+0.693-0.027 molecular cloud. Eighteen lines of $Z$-propargylimine have been detected at level $>2.5 σ$, resulting in a column density estimate of $N = (0.24\pm 0.02)\times 10^{14}$ cm$^{-2}$. An upper limit was retrieved for the higher-energy $E$ isomer, which was not detected in the data. The fractional abundance (w.r.t. H$_2$) derived for $Z$-propargylimine is $1.8\times 10^{-10}$. We discuss the possible formation routes by comparing the derived abundance with those measured in the source for possible chemical precursors.

astro-ph.GA↗

arXiv2017

Characterizing the transition from diffuse atomic to dense molecular clouds in the Magellanic clouds with [CII], [CI], and CO

We present and analyze deep Herschel/HIFI observations of the [CII] 158um, [CI] 609um, and [CI] 370um lines towards 54 lines-of-sight (LOS) in the Large and Small Magellanic clouds. These observations are used to determine the physical conditions of the line--emitting gas, which we use to study the transition from atomic to molecular gas and from C^+ to C^0 to CO in their low metallicity environments. We trace gas with molecular fractions in the range 0.1 0.45 in both the LMC and SMC. Ionized carbon is the dominant gas-phase form of this element that is associated with molecular gas, with C^0 and CO representing a small fraction, implying that most (89% in the LMC and 77% in the SMC) of the molecular gas in our sample is CO-dark H2. The mean X_CO conversion factors in our LMC and SMC sample are larger than the value typically found in the Milky Way. When applying a correction based on the filling factor of the CO emission, we find that the values of X_CO in the LMC and SMC are closer to that in the Milky Way. The observed [CII] intensity in our sample represents about 1% of the total far-infrared intensity from the LOSs observed in both Magellanic Clouds.

astro-ph.GA↗

arXiv2016

The 492 GHz emission of Sgr A* constrained by ALMA

We report linearly polarized continuum emission properties of Sgr A* at $\sim$492 GHz, based on the Atacama Large Millimeter Array (ALMA) observations. We used the observations of the likely unpolarized continuum emission of Titan, and the observations of C\textsc{i} line emission, to gauge the degree of spurious polarization. The Stokes I flux of 3.6$\pm$0.72 Jy during our run is consistent with extrapolations from the previous, lower frequency observations. We found that the continuum emission of Sgr A* at $\sim$492 GHz shows large amplitude differences between the XX and the YY correlations. The observed intensity ratio between the XX and YY correlations as a function of parallactic angle may be explained by a constant polarization position angle of $\sim$158$^{\circ}$$\pm$3$^{\circ}$. The fitted polarization percentage of Sgr A* during our observational period is 14\%$\pm$1.2\%. The calibrator quasar J1744-3116 we observed at the same night can be fitted to Stokes I = 252 mJy, with 7.9\%$\pm$0.9\% polarization in position angle P.A. = 4.1$^{\circ}$$\pm$4.2$^{\circ}$. The observed polarization percentage and polarization position angle in the present work appear consistent with those expected from longer wavelength observations in the period of 1999-2005. In particular, the polarization position angle at 492 GHz, expected from the previously fitted 167$^{\circ}$$\pm$7$^{\circ}$ intrinsic polarization position angle and (-5.6$\pm$0.7)$\times$10$^{5}$ rotation measure, is 155$^{+9}_{-8}$, which is consistent with our new measurement of polarization position angle within 1$σ$. The polarization percentage and the polarization position angle may be varying over the period of our ALMA 12m Array observations, which demands further investigation with future polarization observations.

astro-ph.HE↗

arXiv2015

Dense gas in the Galactic central molecular zone is warm and heated by turbulence

The Galactic center is the closest region in which we can study star formation under extreme physical conditions like those in high-redshift galaxies. We measure the temperature of the dense gas in the central molecular zone (CMZ) and examine what drives it. We mapped the inner 300 pc of the CMZ in the temperature-sensitive J = 3-2 para-formaldehyde (p-H$_2$CO) transitions. We used the $3_{2,1} - 2_{2,0} / 3_{0,3} - 2_{0,2}$ line ratio to determine the gas temperature in $n \sim 10^4 - 10^5 $cm$^{-3}$ gas. We have produced temperature maps and cubes with 30" and 1 km/s resolution and published all data in FITS form. Dense gas temperatures in the Galactic center range from ~60 K to > 100 K in selected regions. The highest gas temperatures T_G > 100 K are observed around the Sgr B2 cores, in the extended Sgr B2 cloud, the 20 km/s and 50 km/s clouds, and in "The Brick" (G0.253+0.016). We infer an upper limit on the cosmic ray ionization rate $ζ_{CR} < 10^{-14}$ 1/s. The dense molecular gas temperature of the region around our Galactic center is similar to values found in the central regions of other galaxies, in particular starburst systems. The gas temperature is uniformly higher than the dust temperature, confirming that dust is a coolant in the dense gas. Turbulent heating can readily explain the observed temperatures given the observed line widths. Cosmic rays cannot explain the observed variation in gas temperatures, so CMZ dense gas temperatures are not dominated by cosmic ray heating. The gas temperatures previously observed to be high in the inner ~75 pc are confirmed to be high in the entire CMZ.

astro-ph.GA↗

arXiv2012

CARMA CO(J = 2 - 1) Observations of the Circumstellar Envelope of Betelgeuse

We report radio interferometric observations of the 12C16O 1.3 mm J = 2-1 emission line in the circumstellar envelope of the M supergiant Alpha Ori and have detected and separated both the S1 and S2 flow components for the first time. Observations were made with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometer in the C, D, and E antenna configurations. We obtain good u-v coverage (5-280 klambda) by combining data from all three configurations allowing us to trace spatial scales as small as 0.9\arcsec over a 32\arcsec field of view. The high spectral and spatial resolution C configuration line profile shows that the inner S1 flow has slightly asymmetric outflow velocities ranging from -9.0 km s-1 to +10.6 km s-1 with respect to the stellar rest frame. We find little evidence for the outer S2 flow in this configuration because the majority of this emission has been spatially-filtered (resolved out) by the array. We also report a SOFIA-GREAT CO(J= 12-11) emission line profile which we associate with this inner higher excitation S1 flow. The outer S2 flow appears in the D and E configuration maps and its outflow velocity is found to be in good agreement with high resolution optical spectroscopy of K I obtained at the McDonald Observatory. We image both S1 and S2 in the multi-configuration maps and see a gradual change in the angular size of the emission in the high absolute velocity maps. We assign an outer radius of 4\arcsec to S1 and propose that S2 extends beyond CARMA's field of view (32\arcsec at 1.3 mm) out to a radius of 17\arcsec which is larger than recent single-dish observations have indicated. When azimuthally averaged, the intensity fall-off for both flows is found to be proportional to R^{-1}, where R is the projected radius, indicating optically thin winds with ρ\propto R^{-2}.

astro-ph.SR↗