arXiv subjects

Sergio Martin

Publications and source records attributed to Sergio Martin.

At least 19 recordsLinked to original sources

arXiv2026

ACES VII. Compact Continuum Source Catalog of the Central Molecular Zone

The Central Molecular Zone (CMZ) resides in the inner few hundred parsecs of our Galaxy, and despite being the largest reservoir of dense molecular gas in the Milky Way, it has a relatively low present-day star formation rate (SFR) of $\sim0.08~M_{\odot}~\text{yr}^{-1}$. Continuum and spectral line observations from the Atacama Large Millimeter/submillimeter Array (ALMA) CMZ Exploration Survey (ACES) provide the first full-coverage, high-resolution map of the inner 200 parsecs of the CMZ at 3 mm. In this paper we present the ACES catalog of compact continuum sources, the most complete catalog of potential sites of star formation in the CMZ to date. Using an automated dendrogram-based source extraction procedure in combination with a by-eye morphological classification scheme, we produce a `full' catalog of 1735 detections in total. Additionally, we use spectral index measurements to generate a `filtered' catalog of 567 sources with minimal contamination from non-thermal filaments and extended free-free emission. We find that 359 ($\sim63\%$) of the filtered catalog sources are located at column densities $< 10^{23}$ cm$^{-2}$, outside of the densest molecular cloud regions, 195 of which have not been identified in previous surveys. After cross-referencing with various catalogs generated from data at different wavelengths, we consider it likely that many of these newly discovered detections are produced by pre/protostellar sources or compact HII regions.

astro-ph.GA↗

arXiv2026

Detection of a four-carbon sugar in interstellar space

Sugars are essential biomolecules, serving as metabolic fuels, nucleic acid backbone components, and structural or energy-storage polymers. A central question in origin-of-life research is how monosaccharides formed on the primitive Earth, as laboratory experiments under prebiotic conditions yield insufficient concentrations. The detection of ribose, glucose and other monosaccharides in asteroids and meteorites suggests an exogenous origin, possibly in the interstellar medium (ISM) prior to meteoritic parent-body formation. However, no sugar has been observed in the ISM so far. We report the discovery of erythrulose, a chiral four-carbon ketose, in the ISM. The detection has been achieved thanks to ultrasensitive, broadband spectral surveys toward the Galactic Center molecular cloud G+0.693-0.027 obtained using the Yebes 40m and IRAM 30m telescopes. Erythrulose appears to be at least eight times more abundant than analogous three-carbon sugars, which remain undetected in our ultrasensitive observations. Quantum chemical and astrochemical models indicate that erythrulose forms efficiently on interstellar dust grains from simpler two-carbon aldehydes and alcohols. As ketoses readily isomerize into aldoses in aqueous conditions, interstellar erythrulose could have contributed to the sugar inventory available for early metabolic and replication processes.

astro-ph.GA↗

arXiv2026

ALMA Central Molecular Zone Exploration Survey (ACES)-IV. Data of the two intermediate-width spectral windows

We release the intermediate-width spectral window data from the ALMA Central Molecular Zone Exploration Survey (ACES) Large Program, which covers SiO(2-1), SO(2_2-1_1), H13CO+(1-0), H13CN(1-0), HN13C(1-0), and HC15N (1-0), among other molecular line transitions, with an angular resolution of ~2 arcsec and a velocity resolution of 1.7 km s-1 . The full cubes of the two spectral windows as well as the key data products will be available to the community. We also present the integrated brightness, peak brightness, centroid velocity, and Galactic longitude-velocity maps of the six lines. We briefly discuss morphological correlations between the continuum and the molecular line emission, and brightness ratios between pairs of isotopologue or isotopomer lines. We highlight features and trends in the data that will be followed up in upcoming ACES science papers.

astro-ph.GA↗

arXiv2025

The Emergence of Prebiotic Chemistry in the ISM

Contrary to popular belief, the interstellar medium (ISM) is not empty; it is filled with atoms, dust particles, and molecules. Some of these molecules may have been the very building blocks of life that, delivered to Earth via comets and meteorites, could have given rise to Life itself. A large-area single-dish telescope with superb sensitivity, field-of-view and multi-band instruments will allow us to explore the limits of chemical complexity in the interstellar medium, across our Galaxy and in external galaxies, determining whether amino acids, sugars, or RNA/DNA nucleobases can form in space.

astro-ph.IM↗

arXiv2025

Clumpy, dense gas in the outflow of NGC 1266

Outflows are one of the most spectacular mechanisms through which active galactic nuclei (AGN) impact their host galaxy, though the role of AGN-driven outflows in global star formation regulation across the galaxy population is unclear. NGC 1266 is an excellent case study for investigating the outflows and star formation quenching because it is a nearby (D\sim30 Mpc) AGN host galaxy with an outflow driving shocks through the interstellar medium (ISM) and has recently quenched its star formation outside the nucleus. While previous works have studied the molecular outflow from its CO emission, to fully characterize the impact the outflow has on the ISM observations probing the dense, cold gas are necessary. Our ALMA cycle 0 observations do not detect a molecular outflow in 13CO(2-1) and yield a lower limit 12CO/13CO \geq 250, suggesting a highly optically thin CO outflow with low 13CO abundance. In contrast, we detect substantial HCN(1-0) emission in the outflow, with an HCN(1-0)/12CO(1-0) ratio of 0.09, consistent with global measurements of many star-forming galaxies and Luminous InfraRed Galaxies (LIRGs). We conclude that the CO emission traces a diffuse component of the molecular gas with a low optical depth, whereas the HCN(1-0) traces dense clumps of gas entrained in the outflow. We measure an upper limit molecular outflow rate of < 85 Msun/yr. Assuming the ongoing nuclear star formation and outflow continue at the same rates, NGC 1266 will deplete its gas reservoirs in 450 Myr or longer, indicating that relatively low-level AGN feedback is capable of gradually expelling the molecular gas reservoir after a rapid quenching event.

astro-ph.GA↗

arXiv2024

SambaMixer: State of Health Prediction of Li-ion Batteries using Mamba State Space Models

The state of health (SOH) of a Li-ion battery is a critical parameter that determines the remaining capacity and the remaining lifetime of the battery. In this paper, we propose SambaMixer a novel structured state space model (SSM) for predicting the state of health of Li-ion batteries. The proposed SSM is based on the MambaMixer architecture, which is designed to handle multi-variate time signals. We evaluate our model on the NASA battery discharge dataset and show that our model outperforms the state-of-the-art on this dataset. We further introduce a novel anchor-based resampling method which ensures time signals are of the expected length while also serving as augmentation technique. Finally, we condition prediction on the sample time and the cycle time difference using positional encodings to improve the performance of our model and to learn recuperation effects. Our results proof that our model is able to predict the SOH of Li-ion batteries with high accuracy and robustness.

cs.LG↗

arXiv2024

Neural Network Constraints on the Cosmic-Ray Ionization Rate and Other Physical Conditions in NGC 253 with ALCHEMI Measurements of HCN and HNC

We use a neural network model and ALMA observations of HCN and HNC to constrain the physical conditions, most notably the cosmic-ray ionization rate (CRIR, zeta), in the Central Molecular Zone (CMZ) of the starburst galaxy NGC 253. Using output from the chemical code UCLCHEM, we train a neural network model to emulate UCLCHEM and derive HCN and HNC molecular abundances from a given set of physical conditions. We combine the neural network with radiative transfer modeling to generate modeled integrated intensities, which we compare to measurements of HCN and HNC from the ALMA Large Program ALCHEMI. Using a Bayesian nested sampling framework, we constrain the CRIR, molecular gas volume and column densities, kinetic temperature, and beam-filling factor across NGC 253's CMZ. The neural network model successfully recovers UCLCHEM molecular abundances with about 3 percent error and, when used with our Bayesian inference algorithm, increases the parameter inference speed tenfold. We create images of these physical parameters across NGC 253's CMZ at 50 pc resolution and find that the CRIR, in addition to the other gas parameters, is spatially variable with zeta a few times 10^{14} s^{-1} at greater than 100 pc from the nucleus, increasing to zeta greater than 10^{-13} s^{-1} at its center. These inferred CRIRs are consistent within 1 dex with theoretical predictions based on non-thermal emission. Additionally, the high CRIRs estimated in NGC 253's CMZ can be explained by the large number of cosmic-ray-producing sources as well as a potential suppression of cosmic-ray diffusion near their injection sites.

astro-ph.GA↗

arXiv2024

MagMar III -- Resisting the Pressure, Is the Magnetic Field Overwhelmed in NGC6334I?

We report on ALMA observations of polarized dust emission at 1.2 mm from NGC6334I, a source known for its significant flux outbursts. Between five months, our data show no substantial change in total intensity and a modest 8\% variation in linear polarization, suggesting a phase of stability or the conclusion of the outburst. The magnetic field, inferred from this polarized emission, displays a predominantly radial pattern from North-West to South-East with intricate disturbances across major cores, hinting at spiral structures. Energy analysis of CS$(J=5 \rightarrow 4)$ emission yields an outflow energy of approximately $3.5\times10^{45}$ ergs, aligning with previous interferometric studies. Utilizing the Davis-Chandrasekhar-Fermi method, we determined magnetic field strengths ranging from 1 to 11 mG, averaging at 1.9 mG. This average increases to 4 $\pm 1$ mG when incorporating Zeeman measurements. Comparative analyses using gravitational, thermal, and kinetic energy maps reveal that magnetic energy is significantly weaker, possibly explaining the observed field morphology. We also find that the energy in the outflows and the expanding cometary {\HII} region is also larger than the magnetic energy, suggesting that protostellar feedback maybe the dominant driver behind the injection of turbulence in NGC6334I at the scales sampled by our data. The gas in NGC6334I predominantly exhibits supersonic and trans-Alfvenic conditions, transitioning towards a super-Alfvenic regime, underscoring a diminished influence of the magnetic field with increasing gas density. These observations are in agreement with prior polarization studies at 220 GHz, enriching our understanding of the dynamic processes in high-mass star-forming regions.

astro-ph.GA↗

arXiv2023

Volume density structure of the NGC253 CMZ through ALCHEMI excitation analysis

We present a spatially-resolved excitation analysis for the central molecular zone (CMZ) of the starburst galaxy NGC 253 using the data from the ALMA Large program ALCHEMI, whereby we explore parameters distinguishing NGC 253 from the quiescent Milky Way's Galactic Center (GC). Non-LTE analyses employing a hierarchical Bayesian framework are applied to Band 3-7 transitions from nine molecular species to delineate the position-position-velocity distributions of column density ($N_\mathrm{H_2}$), volume density ($n_\mathrm{H_2}$), and temperature ($T_\mathrm{kin}$) at 27 pc resolution. Two distinct components are detected: a low-density component with $(n_\mathrm{H_2},\ T_\mathrm{kin})\sim(10^{3.3}\ \mathrm{cm}^{-3}, 85 K)$ and a high-density component with $(n_\mathrm{H_2},\ T_\mathrm{kin})\sim (10^{4.4}\ \mathrm{cm}^{-3}, 110\ \mathrm{K})$, separated at $n_\mathrm{H_2}\sim10^{3.8}\ \mathrm{cm}^{-3}$. NGC 253 has $\sim10$ times the high-density gas mass and $\sim3$ times the dense-gas mass fraction of the GC. These properties are consistent with their HCN/CO ratio but cannot alone explain the factor of $\sim30$ difference in their star formation efficiencies (SFEs), contradicting the dense-gas mass to star formation rate scaling law. The $n_\mathrm{H_2}$ histogram toward NGC 253 exhibits a shallow declining slope up to $n_\mathrm{H_2}\sim10^6\ \mathrm{cm}^{-3}$, while that of the GC steeply drops in $n_\mathrm{H_2}\gtrsim10^{4.5}\ \mathrm{cm}^{-3}$ and vanishes at $10^5\ \mathrm{cm}^{-3}$. Their dense-gas mass fraction ratio becomes consistent with their SFEs when the threshold $n_\mathrm{H_2}$ for the dense gas is taken at $\sim 10^{4.2\mbox{-}4.6}\ \mathrm{cm}^{-3}$. The rich abundance of gas above this density range in the NGC 253 CMZ, or its scarcity in the GC, is likely to be the critical difference characterizing the contrasting star formation in the centers of the two galaxies.

astro-ph.GA↗

arXiv2023

RGB-D-Fusion: Image Conditioned Depth Diffusion of Humanoid Subjects

We present RGB-D-Fusion, a multi-modal conditional denoising diffusion probabilistic model to generate high resolution depth maps from low-resolution monocular RGB images of humanoid subjects. RGB-D-Fusion first generates a low-resolution depth map using an image conditioned denoising diffusion probabilistic model and then upsamples the depth map using a second denoising diffusion probabilistic model conditioned on a low-resolution RGB-D image. We further introduce a novel augmentation technique, depth noise augmentation, to increase the robustness of our super-resolution model.

cs.CV↗

arXiv2023

Diverse Molecular Structures Across The Whole Star-Forming Disk of M83: High fidelity Imaging at 40pc Resolution

We present high-fidelity CO(1-0) imaging of molecular gas across the full star-forming disk of M83, using ALMA's 12m, 7m, and TP arrays and the MIRIAD package. The data have a mass sensitivity and resolution of 10^4Msun and 40 pc. The full disk coverage shows that the characteristics of molecular gas change radially from the center to outer disk. The molecular gas distribution shows coherent large-scale structures in the inner part, including the central concentration, bar offset ridges, and prominent molecular spiral arms. In the outer disk, the spiral arms appear less spatially coherent, and even flocculent. Massive filamentary gas concentrations are abundant even in the interarm regions. Building up these structures in the interarm regions would require a very long time (~>100Myr). Instead, they must have formed within stellar spiral arms and been released into the interarm regions. For such structures to survive through the dynamical processes, the lifetimes of these structures and their constituent molecules and molecular clouds must be long (~>100Myr). These interarm structures host little or no star formation traced by Halpha. The new map also shows extended CO emission, which likely represents an ensemble of unresolved molecular clouds.

astro-ph.GA↗

arXiv2022

Tracing Interstellar Heating: An ALCHEMI Measurement of the HCN Isomers in NGC 253

We analyze HCN and HNC emission in the nearby starburst galaxy NGC 253 to investigate its effectiveness in tracing heating processes associated with star formation. This study uses multiple HCN and HNC rotational transitions observed using ALMA via the ALCHEMI Large Program. To understand the conditions and associated heating mechanisms within NGC 253's dense gas, we employ Bayesian nested sampling techniques applied to chemical and radiative transfer models which are constrained using our HCN and HNC measurements. We find that the volume density $n_{\text{H}_{2}}$ and cosmic ray ionization rate (CRIR) $\zeta$ are enhanced by about an order of magnitude in the galaxy's central regions as compared to those further from the nucleus. In NGC 253's central GMCs, where observed HCN/HNC abundance ratios are lowest, $n \sim 10^{5.5}$ cm$^{-3}$ and $\zeta \sim 10^{-12}$ s$^{-1}$ (greater than $10^4$ times the average Galactic rate). We find a positive correlation in the association of both density and CRIR with the number of star formation-related heating sources (supernova remnants, HII regions, and super hot cores) located in each GMC, as well as a correlation between CRIRs and supernova rates. Additionally, we see an anticorrelation between the HCN/HNC ratio and CRIR, indicating that this ratio will be lower in regions where $\zeta$ is higher. Though previous studies suggested HCN and HNC may reveal strong mechanical heating processes in NGC 253's CMZ, we find cosmic ray heating dominates the heating budget, and mechanical heating does not play a significant role in the HCN and HNC chemistry.

astro-ph.GA↗

arXiv2022

ALCHEMI finds a "shocking" carbon footprint in the starburst galaxy NGC~253

Centers of starburst galaxies may be characterized by a specific gas and ice chemistry due to their gas dynamics and the presence of various ice desorption mechanisms. This may result in a peculiar observable composition. We analyze abundances of $CO_2$, a reliable tracer of ice chemistry, from data collected as part of the ALMA large program ALCHEMI, a wide-frequency spectral scan toward the starburst galaxy NGC~253 with an angular resolution of 1.6$''$. We constrain the $CO_2$ abundances in the gas phase using its protonated form $HOCO^+$. The distribution of $HOCO^+$ is similar to that of methanol, which suggests that $HOCO^+$ is indeed produced from the protonation of $CO_2$ sublimated from ice. The $HOCO^+$ fractional abundances are found to be $(1-2)\times10^{-9}$ at the outer part of the central molecular zone (CMZ), while they are lower ($\sim10^{-10}$) near the kinematic center. This peak fractional abundance at the outer CMZ is comparable to that in the Milky Way CMZ, and orders of magnitude higher than that in Galactic disk star-forming regions. From the range of $HOCO^+/CO_2$ ratios suggested from chemical models, the gas-phase $CO_2$ fractional abundance is estimated to be $(1-20)\times10^{-7}$ at the outer CMZ, and orders of magnitude lower near the center. We estimate the $CO_2$ ice fractional abundances at the outer CMZ to be $(2-5)\times10^{-6}$ from the literature. A comparison between the ice and gas $CO_2$ abundances suggests an efficient sublimation mechanism. This sublimation is attributed to large-scale shocks at the orbital intersections of the bar and CMZ.

astro-ph.GA↗

arXiv2022

Starbursts with suppressed velocity dispersion revealed in a forming cluster at z=2.51

One of the most prominent features of galaxy clusters is the presence of a dominant population of massive ellipticals in their cores. Stellar archaeology suggests that these gigantic beasts assembled most of their stars in the early Universe via starbursts. However, the role of dense environments and their detailed physical mechanisms in triggering starburst activities remain unknown. Here we report spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of the CO $J= 3-2$ emission line, with a resolution of about 2.5 kiloparsecs, toward a forming galaxy cluster core with starburst galaxies at $z=2.51$. In contrast to starburst galaxies in the field often associated with galaxy mergers or highly turbulent gaseous disks, our observations show that the two starbursts in the cluster exhibit dynamically cold (rotation-dominated) gas-rich disks. Their gas disks have extremely low velocity dispersion ($\sigma_{\mathrm{0}} \sim 20-30$ km s$^{-1}$), which is three times lower than their field counterparts at similar redshifts. The high gas fraction and suppressed velocity dispersion yield gravitationally unstable gas disks, which enables highly efficient star formation. The suppressed velocity dispersion, likely induced by the accretion of corotating and coplanar cold gas, might serve as an essential avenue to trigger starbursts in massive halos at high redshifts.

astro-ph.GA↗

arXiv2022

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.

astro-ph.GA↗

arXiv2021

Magnetic Fields in Massive Star-Forming Regions (MagMaR) II. Tomography Through Dust and Molecular Line Polarization in NGC 6334I(N)

Here, we report ALMA detections of polarized emission from dust, CS($J=5 \rightarrow 4$), and C$^{33}$S($J=5 \rightarrow 4$) toward the high-mass star-forming region NGC6334I(N). A clear ``hourglass'' magnetic field morphology was inferred from the polarized dust emission which is also directly seen from the polarized CS emission across velocity, where the polarization appears to be parallel to the field. By considering previous findings, the field retains a pinched shape which can be traced to clump length-scales from the envelope scales traced by ALMA, suggesting that the field is dynamically important across multiple length-scales in this region. The CS total intensity emission is found to be optically thick ($τ_{\mathrm{CS}} = 32 \pm 12$) while the C$^{33}$S emission appears to be optically thin ($τ_{\mathrm{C^{33}S}} = 0.1 \pm 0.01$). This suggests that sources of anisotropy other than large velocity gradients, i.e. anisotropies in the radiation field are required to explain the polarized emission from CS seen by ALMA. By using four variants of the Davis-Chandrasekhar-Fermi technique and the angle dispersion function methods (ADF), we obtain an average of estimates for the magnetic field strength onto the plane of the sky of $\left< \mathrm{B}_{\mathrm{pos}} \right> = 16$ mG from the dust and $\left< \mathrm{B}_{\mathrm{pos}} \right> \sim 2$ mG from the CS emission, where each emission traces different molecular hydrogen number densities. This effectively enables a tomographic view of the magnetic field within a single ALMA observation.

astro-ph.GA↗

arXiv2021

Deeply Buried Nuclei in the Infrared-Luminous Galaxies NGC 4418 and Arp 220: II. Line Forests at $λ= $1.4--0.4 mm and Circumnuclear Gas Observed with ALMA

We present the line observations in our ALMA imaging spectral scan toward three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in $f_{\rm rest}$=215-697 GHz at about 0.2$"$ (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of $\sim$100 pc sizes. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, most of the major lines and many $^{13}$C isotopologues show absorption against even brighter continuum cores of the nuclei. The lines with higher upper-level energies, including those from vibrationally-excited molecules, tend to arise from smaller areas, indicating radially varying conditions in these nuclei. The outflows from the two Arp 220 nuclei cause blueshifted line absorption below the continuum level. The absorption mostly has small spatial offsets from the continuum peaks to indicate the outflow orientations. The bipolar outflow from the western nucleus is also imaged in multiple emission lines, showing the extent of $\sim$1$"$ (400 pc). Redshifted line absorption against the nucleus of NGC 4418 indicates either an inward gas motion or a small collimated outflow slanted to the nuclear disk. We also resolved some previous confusions due to line blending and misidentification.

astro-ph.GA↗

arXiv2021

Deeply Buried Nuclei in the Infrared-Luminous Galaxies NGC 4418 and Arp 220: I. ALMA Observations at $λ= $1.4-0.4 mm and Continuum Analysis

We observed with ALMA three deeply buried nuclei in two galaxies, NGC 4418 and Arp 220, at $\sim$0.2$''$ resolution over a total bandwidth of 67 GHz in $f_{\rm rest}$ = 215 - 697 GHz. Here we (1) introduce our program, (2) describe our data reduction method for wide-band, high-resolution imaging spectroscopy, (3) analyze in visibilities the compact nuclei with line forests, (4) develop a continuum-based estimation method of dust opacity and gas column density in heavily obscured nuclei, which uses the BGN (buried galactic nuclei) model and is sensitive to $\log(N_{\rm H_2}/{\rm cm}^{-2}) \sim $ 25 - 26 at $λ\sim 1$ mm, and (5) present the continuum data and diagnosis of our targets. The three continuum nuclei have major-axis FWHM of $\sim$0.1$''$-0.3$''$ (20-140 pc) aligned to their rotating nuclear disks of molecular gas. However, each nucleus is described better with two or three concentric components than with a single Gaussian. The innermost cores have sizes of 0.05$''$-0.10$''$ (8-40 pc), peak brightness temperatures of ~100-500 K at 350 GHz, and more fractional flux at lower frequencies. The intermediate components correspond to the nuclear disks. They have axial ratios of $\approx$0.5 and hence inclinations $\stackrel{>}{\sim} 60$ deg. The outermost elements include the bipolar outflow from Arp 220W. We estimate 1 mm dust opacity of $τ_{\rm d,1mm} \approx 2.2$, $1.2$, and $\stackrel{<}{\sim} 0.4$ respectively for NGC 4418, Arp 220W, and Arp 220E. The first two correspond to $\log(N_{\rm H}/{\rm cm}^{-2}) \sim 26$ for conventional dust-opacity laws, and hence the nuclei are highly Compton thick.

astro-ph.GA↗