A limit on a possible cosmological variation of the proton-to-electron mass ratio μ is derived from methanol (CH3OH) absorption lines in the benchmark PKS1830-211 lensing galaxy at redshift z=0.89 ...observed with the Effelsberg 100-m radio telescope, the Institute de Radio Astronomie Millimétrique 30-m telescope, and the Atacama Large Millimeter/submillimeter Array. Ten different absorption lines of CH3OH covering a wide range of sensitivity coefficients K(μ) are used to derive a purely statistical 1σ constraint of Δμ/μ=(1.5±1.5)×10(-7) for a lookback time of 7.5 billion years. Systematic effects of chemical segregation, excitation temperature, frequency dependence, and time variability of the background source are quantified. A multidimensional linear regression analysis leads to a robust constraint of Δμ/μ=(-1.0±0.8(stat)±1.0(sys))×10(-7).
ABSTRACT
We present results from Atacama Large Millimeter/submillimeter Array (ALMA) observations of CS from the nearby galaxy NGC 1068 (∼14 Mpc). This Seyfert 2 barred galaxy possesses a ...circumnuclear disc (CND, r ∼ 200 pc) and a starburst ring (SB ring, r ∼ 1.3 kpc). These high-resolution maps (∼0.5 arcsec, ∼35 pc) allow us to analyse specific sub-regions in the galaxy and investigate differences in line intensity ratios and physical conditions, particularly those between the CND and SB ring. Local thermodynamic equilibrium (LTE) analysis of the gas is used to calculate CS densities in each sub-region, followed by the non-LTE analysis conducted using the radiative transfer code radex to fit observations and constrain gas temperature, CS column density and hydrogen density. Finally, the chemical code uclchem is used to reconstruct the gas, allowing an insight into its origin and chemical history. The density of hydrogen in the CND is found to be ≥105 cm−2, although exact values vary, reaching 106 cm−2 at the active galactic nucleus. The conditions in the two arms of the SB ring appear similar to one another, though the density found (∼104 cm−2) is lower than in the CND. The temperature in the CND increases from east to west, and is also overall greater than found in the SB ring. These modelling methods indicate the requirement for multiphase gas components in order to fit the observed emission over the galaxy. A larger number of high-resolution transitions across the SLED may allow for further constraining of the conditions, particularly in the SB ring.
We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 Band 7 observations of an extremely metal-poor dwarf starburst galaxy in the Local Universe, SBS 0335−052 (12 + log (O/H) ~ ...7.2). With these observations, dust is detected at 870 μm (ALMA Band 7), but 87% of the flux in this band is due to free-free emission from the starburst. We have compiled a spectral energy distribution (SED) of SBS 0335−052 that spans almost 6 orders of magnitude in wavelength and fit it with a spherical dust shell heated by a single-age stellar population; the best-fit model gives a dust mass of (3.8 ± 0.6) × 104 M⊙. We have also constructed a SED including Herschel archival data for I Zw 18, another low-metallicity dwarf starburst (12 + log (O/H) ~ 7.17), and fit it with a similar model to obtain a dust mass of (3.4 ± 1.0) × 102 M⊙. It appears that for such low-metallicity dwarf galaxies, the ratio of their stellar mass to their dust mass is within the range of values found for spirals and other star-forming galaxies. However, compared with their atomic gas mass, the dust mass of SBS 0335−052 far exceeds the prediction of a linear trend of dust-to-gas mass ratio with metallicity, while I Zw 18 falls far below. We use gas scaling relations to assess a putative missing gas component in both galaxies and find that the missing, possibly molecular, gas in SBS 0335−052 is a factor of 6 times higher than the value inferred from the observed Hi column density; in I Zw 18 the missing component is much smaller. Finally, we constrain the H2 surface density conversion factor αCO with our upper limit for CO J = 3−2 line in SBS 0335−052, and find that this is consistent with a linear or even super-linear trend of increasing αCO with decreasing metallicity. Ultimately, despite their similarly low metallicity, the differences in gas and dust column densities in SBS 0335−052 and I Zw 18 suggest that metal abundance does not uniquely define star-formation processes. At some level, self-shielding and the survival of molecules may depend just as much on gas and dust column density as on metallicity. The effects of low metallicity may at least be partially compensated for by large column densities in the interstellar medium.
Context. Methanol is an important tracer to probe physical and chemical conditions in the interstellar medium of galaxies. Methanol is also the most sensitive target molecule for probing potential ...space-time variations of the proton-electron mass ratio, μ, a dimensionless constant of nature. Aims. We present an extensive study of the strongest submillimeter absorption lines of methanol (with rest frequencies between 300 and 520 GHz) in the z = 0.89 molecular absorber toward PKS 1830−211, the only high-redshift object in which methanol has been detected. Our goals are to constrain the excitation of the methanol lines and to investigate the cosmological invariance of μ based on their relative kinematics. Methods. We observed 14 transitions of methanol, five of the A-form and nine of the E-form, and three transitions of A-13CH3OH, with ALMA. We analyzed the line profiles with a Gaussian fitting and constructed a global line profile that is able to match all observations after allowing for variations of the source covering factor, line opacity scaling, and relative bulk velocity offsets. We explore methanol excitation by running the non local thermal equilibrium radiative transfer code RADEX on a grid of kinetic temperatures and H2 volume densities. Results. Methanol absorption is detected in only one of the two lines of sight (the southwest) to PKS 1830−211. There, the excitation analysis points to a cool (∼10 − 20 K) and dense (∼104 − 5 cm−3) methanol gas. Under these conditions, several methanol transitions become anti-inverted, with excitation temperatures below the temperature of the cosmic microwave background. In addition, we measure an abundance ratio A/E = 1.0 ± 0.1, an abundance ratio CH3OH/H2 ∼ 2 × 10−8, and a 12CH3OH/13CH3OH ratio 62 ± 3. Our analysis shows that the bulk velocities of the different transitions are primarily correlated with the observing epoch due to morphological changes in the background quasar’s emission. There is a weaker correlation between bulk velocities and the lower level energies of the transitions, which could be a signature of temperature-velocity gradients in the absorbing gas. As a result, we do not find evidence for variations of μ, and we estimate Δμ/μ=(−1.8 ± 1.2) × 10−7 at 1-σ from our multivariate linear regression. Conclusions. We set a robust upper limit |Δμ/μ| < 3.6 × 10−7 (3σ) for the invariance of μ at a look-back time of half the present age of the Universe. Our analysis highlights that systematics need to be carefully taken into account in future radio molecular absorption studies aimed at testing Δμ/μ below the 10−7 horizon.
Context. According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This ...relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. Aims. We aim to measure the temperature of the CMB with an accuracy of a few percent at z = 0.89 toward the molecular absorber in the galaxy lensing the quasar PKS 1830−211. Methods. We adopted a Monte-Carlo Markov chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation conditions of a set of various molecular species directly from their spectra. Results. We determine TCMB = 5.08 ± 0.10 K at 68% confidence level. Our measurement is consistent with the value TCMB = 5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of TCMB at z > 0 to date.
We present the first unbiased molecular line survey toward an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 ...GHz, i.e., most of the 2 mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers super(34)SO and HC super(18)O super(+). Tentative detections of two deuterated species, DNC and N sub(2)D super(+), are reported for the first time from a target beyond the Magellanic Clouds. In addition, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.
Aims. We derive the physical properties of a filament discovered in the dark cometary-shaped cloud L1251. Methods. Mapping observations in the NH3(1, 1) and (2, 2) inversion lines, encompassing 300 ...positions toward L1251, were performed with the Effelsberg 100-m telescope at a spatial resolution of 40′′ and a spectral resolution of 0.045 km s-1. Results. The filament L1251A consists of three condensations (α, β, and γ) of elongated morphology, which are combined in a long and narrow structure covering a 38′ × 3′ angular range (∼3.3 pc × 0.3 pc). Comparing the kinematics with the more extended envelope (∼61′ × 33′) emitting in 13CO, we find that: (1) the angular velocity of the envelope around the horizontal axis E → W is ΩEWCO ≈−2 × 10-14 rad s-1 (the line-of-sight velocity is more negative to the north); (2) approximately one half of the filament (combined α and β condensations) exhibits counter-rotation with ΩEWαβ ≈2 × 10-14 rad s-1; (3) one third of the filament (the γ condensation) co-rotates with ΩEWγ ≈−2 × 10-14 rad s-1; (4) the central part of the filament between these two kinematically distinct regions does not show any rotation around this axis; (5) the whole filament revolves slowly around the vertical axis S → N with ΩSNtot ≈7 × 10-15 rad s-1. The opposite chirality (dextral and sinistral) of the αβ and γ condensations indicates magnetic field helicities of two types, negative and positive, which were most probably caused by dynamo mechanisms. We estimated the magnetic Reynolds number Rm ≳ 600 and the Rossby number ℛ < 1, which means that dynamo action is important.
Currently the majority of non-culturable microbes in sea water are yet to be discovered, Nanopore offers a solution to overcome the challenging tasks to identify the genomes and complex composition ...of oceanic microbiomes. In this study we evaluate the utility of Oxford Nanopore Technologies (ONT) sequencing to characterize microbial diversity in seawater from multiple locations. We compared the microbial species diversity of retrieved environmental samples from two different locations and time points.
With only three ONT flow cells we were able to identify thousands of organisms, including bacteriophages, from which a large part at species level. It was possible to assemble genomes from environmental samples with Flye. In several cases this resulted in > 1 Mbp contigs and in the particular case of a Thioglobus singularis species it even produced a near complete genome. k-mer analysis reveals that a large part of the data represents species of which close relatives have not yet been deposited to the database. These results show that our approach is suitable for scalable genomic investigations such as monitoring oceanic biodiversity and provides a new platform for education in biodiversity.
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