Diego Mardones - Profile on Academia.edu (original) (raw)

Papers by Diego Mardones

Star Formation from Cores To Clusters - Conference Summary

Conference summary

arXiv (Cornell University), Mar 5, 2023

We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze ... more We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from ALMA 1.3 mm observations with resolution of 0.2 ′′ (∼1,000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., H 2 CO, CH 3 OH, CH 3 OCH 3), sulfur-bearing (SO 2 , H 2 S) and nitrogenbearing (e.g., HNCO, NH 2 CHO, C 2 H 3 CN, C 2 H 5 CN) molecules. We discuss their spatial distributions, physical conditions, correlation between different species and possible chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 is part of a mm continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of ∼ 300 K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of ∼ 250 K, and is of intermediate chemical complexity. HMC3 is further away, ∼ 3, 000au in projection, cooler (∼ 70K) and is the least line-rich. The three HMCs have similar mass surface densities (∼ 10g cm −2), number densities (n H ∼ 10 9 cm −3) and masses of a few M ⊙. The total gas mass in the cores and in the region out to 3, 000 au is ∼ 25 M ⊙ , which is comparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities and abundances of the detected species and discuss the implications for hot core astrochemistry.

The HH30 T-Tauri star

sf2a, Dec 1, 2019

Astronomical Society of the Pacific eBooks, Dec 1, 2015

We present preliminary analysis of ALMA cycle 1 12m array 12 CO / 13 CO /C 18 O data of the HH 46... more We present preliminary analysis of ALMA cycle 1 12m array 12 CO / 13 CO /C 18 O data of the HH 46/47 molecular outflow. 13 CO and C 18 O trace relatively denser outflow material than 12 CO and allow us to trace the outflow to lower velocities than what it possible using only the 12 CO emission. Interestingly, the cavity wall of the red lobe can be seen at velocity as low as 0.2 km/s. Using C 18 O, we are now able to estimate the optical depth of 13 CO, and then use the corrected 13 CO emission to further and better correct the 12 CO emission and estimate the mass, momentum, and kinetic energy of the outflow. Moreover, C 18 O reveals a flattened rotational structure at the center, likely to be a rotational envelope infalling onto an inner Keplerian disk.

arXiv (Cornell University), Nov 11, 2018

We report molecular line observations of the massive protostellar source G339.88-1.26 with the At... more We report molecular line observations of the massive protostellar source G339.88-1.26 with the Atacama Large Millimeter/Submillimeter Array. The observations reveal a highly collimated SiO jet extending from the 1.3 mm continuum source, which connects to a slightly wider but still highly collimated CO outflow. Rotational features perpendicular to the outflow axis are detected in various molecular emissions, including SiO, SO$_2$, H$_2$S, CH$_3$OH, and H$_2$CO emissions. Based on their spatial distributions and kinematics, we find that they trace different parts of the envelope-disk system. The SiO traces the disk and inner envelope in addition to the jet, the CH$_3$OH and H$_2$CO trace the infalling-rotating envelope outside of the disk, and the SO$_2$ and H$_2$S appear enhanced around the transition region between envelope and disk, i.e., the centrifugal barrier, as well as the outer part of the disk. Envelope kinematics are consistent with rotating-infalling motion, while those of the disk are consistent with Keplerian rotation. The radius and velocity of the centrifugal barrier are estimated to be about 530 au and 6 km s$^{-1}$, leading to a central mass of about 11M˜odot11~M_\odot11M˜odot, consistent with estimates based on spectral energy distribution fitting. These results indicate that an ordered transition from an infalling-rotating envelope to a Keplerian disk through a centrifugal barrier, accompanied by change of chemical composition, is a valid description of this massive protostellar source. This implies that at least some massive stars form in a similar way as low-mass stars via Core Accretion.

arXiv (Cornell University), Jun 14, 2018

We consider the problem of analyzing the structure of spectroscopic cubes using unsupervised mach... more We consider the problem of analyzing the structure of spectroscopic cubes using unsupervised machine learning techniques. We propose representing the target's signal as an homogeneous set of volumes through an iterative algorithm that separates the structured emission from the background while not overestimating the flux. Besides verifying some basic theoretical properties, the algorithm is designed to be tuned by domain experts, because its parameters have meaningful values in the astronomical context. Nevertheless, we propose an heuristic to automatically estimate the signal-to-noise ratio parameter of the algorithm directly from data. The resulting light-weighted set of samples (≤ 1% compared to the original data) offer several advantages. For instance, it is statistically correct and computationally inexpensive to apply well-established techniques of the pattern recognition and machine learning domains; such as clustering and dimensionality reduction algorithms. We use ALMA science verification data to validate our method, and present examples of the operations that can be performed by using the proposed representation. Even though this approach is focused on providing faster and better analysis tools for the end-user astronomer, it also opens the possibility of content-aware data discovery by applying our algorithm to big data.

Modeling the CO outflow in DG Tauri B: Swept-up shells versus perturbed MHD disk wind

Astronomy and Astrophysics, Dec 1, 2022

Context. The origin of outflows and their exact impact on disk evolution and planet formation rem... more Context. The origin of outflows and their exact impact on disk evolution and planet formation remain crucial open questions. DG Tau B is a Class I protostar associated with a rotating conical CO outflow and a structured disk. Hence it is an ideal target to study these questions. Aims. We aim to characterize the morphology and kinematics of the DG Tau B outflow in order to elucidate its origin and potential impact on the disk. Methods. Our analysis is based on Atacama Large Millimeter Array (ALMA) 12CO(2–1) observations of DG Tau B at 0.15″ (20 au) angular resolution. We developed a tomographic method to recover 2D (R,Z) maps of vertical velocity VZ and specific angular momentum j = R × Vϕ. We created synthetic data cubes for parametric models of wind-driven shells and disk winds, which we fit to the observed channel maps. Results. Tomographic analysis of the bright inner conical outflow shows that both VZ and j remain roughly constant along conical surfaces, defining a shear-like structure. We characterize three different types of substructures in this outflow (arches, fingers, and cusps) with apparent acceleration. Wind-driven shell models with a Hubble law fail to explain these substructures. In contrast, both the morphology and kinematics of the conical flow can be explained by a steady conical magnetohydrodynamic (MHD) disk wind with foot-point radii r0 ≃ 0.7–3.4 au, a small magnetic level arm parameter (λ ≤ 1.6), and quasi periodic brightness enhancements. These might be caused by the impact of jet bow shocks, source orbital motion caused by a 25 MJ companion at 50 au, or disk density perturbations accreting through the wind launching region. The large CO wind mass flux (four times the accretion rate onto the central star) can also be explained if the MHD disk wind removes most of the angular momentum required for steady disk accretion. Conclusions. Our results provide the strongest evidence so far for the presence of massive MHD disk winds in Class I sources with residual infall, and they suggest that the initial stages of planet formation take place in a highly dynamic environment.

Springer eBooks, Feb 1, 2006

Using high-resolution SPH numerical simulations, we investigate the effects of gas on the in-spir... more Using high-resolution SPH numerical simulations, we investigate the effects of gas on the in-spiral and merger of a massive black hole binary. This study is motivated by the very massive nuclear gas disks observed in the central regions of merging galaxies. Here we present results that expand on the treatment in a previous work by studying models in which the gas is in a disk. We run a variety of models, ranging from simulations with a relatively smooth gas disk to cases in which the gas has a more clumpy spatial distribution. We also vary the inclination angle between the plane of the binary and the plane of the disk, and the mass ratio between the MBHs and the gaseous disk. We find that, as in our previous work, in the early evolution of the system the binary separation diminishes mainly due to dynamical friction exerted by the background gas, and in the later stages the gaseous medium responds by forming an ellipsoidal density enhancement whose axis lags behind the binary axis. This offset produces a gravitational torque on the binary that causes continuing loss of angular momentum and is able to reduce the separation to distances at which gravitational radiation is efficient. The main difference is that between these two regimes we now find a new transition regime that was not apparent in our previous paper, in which the evolution is temporarily slowed down when neither of these mechanisms is fully effective. In the variety of simulations that we perform, we find that the coalescence timescale for the MBH binary varies between 5 ; 10 6 and 2:5 ; 10 7 yr for typical ULIRGs. For MBHs that satisfy the observed ''mc '' relation, our simulations suggest that in a merger of galaxies that have at least 1% of their total mass in gas, the MBHs will coalesce soon after the galaxies merge.

Astronomy and Astrophysics, Feb 1, 2020

We present Atacama Large Millimeter Array (ALMA) Band 6 observations at 14−20 au spatial resoluti... more We present Atacama Large Millimeter Array (ALMA) Band 6 observations at 14−20 au spatial resolution of the disk and CO(2-1) outflow around the Class I protostar DG Tau B in Taurus. The disk is very large, both in dust continuum (R eff,95% = 174 au) and CO (R CO = 700 au). It shows Keplerian rotation around a 1.1 ± 0.2 M central star and two dust emission bumps at r = 62 and 135 au. These results confirm that large structured disks can form at an early stage where residual infall is still ongoing. The redshifted CO outflow at high velocity shows a striking hollow cone morphology out to 3000 au with a shear-like velocity structure within the cone walls. These walls coincide with the scattered light cavity, and they appear to be rooted within <60 au in the disk. We confirm their global average rotation in the same sense as the disk, with a specific angular momentum 65 au km s −1. The mass-flux rate of 1.7−2.9 × 10 −7 M yr −1 is 35 ± 10 times that in the atomic jet. We also detect a wider and slower outflow component surrounding this inner conical flow, which also rotates in the same direction as the disk. Our ALMA observations therefore demonstrate that the inner cone walls, and the associated scattered light cavity, do not trace the interface with infalling material, which is shown to be confined to much wider angles (>70 •). The properties of the conical walls are suggestive of the interaction between an episodic inner jet or wind with an outer disk wind, or of a massive disk wind originating from 2 to 5 au. However, further modeling is required to establish their origin. In either case, such massive outflow may significantly affect the disk structure and evolution.

Springer eBooks, 2004

We report multi-wavelength observations towards IRAS 16547-4247, a luminous infrared source with ... more We report multi-wavelength observations towards IRAS 16547-4247, a luminous infrared source with a bolometric luminosity of 6.2×10 4 L. Dust continuum observations at 1.2-mm indicate that this object is associated with a dust cloud with a size of about 0.4 pc in diameter and a mass of about 1.3 × 10 3 M. Radio continuum observations show the presence of a triple radio source consisting of a compact central object and two outer lobes, separated by about 0.3 pc, symmetrically located from the central source. Molecular hydrogen line observations show a chain of knots that trace a collimated flow extending over 1.5 pc. We suggest that IRAS 16547-4247 corresponds to a dense massive core which hosts near its central region a high-mass star in an early stage of evolution. This massive YSO is undergoing the ejection of a collimated stellar wind which drives the H 2 flow. The radio emission from the lobes arises in shocks resulting from the interaction of the collimated wind with the surrounding medium. We conclude that the thermal jets found in the formation of low-mass stars are also produced in high-mass stars.

Monthly Notices of the Royal Astronomical Society, Mar 2, 2023

The dust continuum and molecular distributions observed on the sky plane al w ays show irregular ... more The dust continuum and molecular distributions observed on the sky plane al w ays show irregular shapes of molecular clouds. Ho we ver, it is hard to directly reproduce the observed distributions using symmetrical models. In this work, for the first time, we present a three-dimensional (3D) gas-grain chemical simulation using an irregular 3D density structure derived by the Abel inversion taking the starless core L1544 as an example. We found that most (∼70 per cent) of the observed features (molecular distributions, peak positions, and column density values of 16 species) can be reproduced directly. The previously reached conclusion of non-uniform illumination at C 3 H 2 peak is confirmed as the contribution from the gas component with density of a few 10 4 cm −3 at distance of ∼3000-8000 au from the core centre along the line of sight.

arXiv (Cornell University), Dec 7, 2022

Models of the protostellar source, B335, are developed using axisymmetric three-dimensional model... more Models of the protostellar source, B335, are developed using axisymmetric three-dimensional models to resolve conflicts found in one-dimensional models. The models are constrained by a large number of observations, including ALMA, Herschel, and Spitzer data. Observations of the protostellar source B335 with ALMA show red-shifted absorption against a central continuum source indicative of infall in the HCO + and HCN J = 4 → 3 transitions. The data are combined with a new estimate of the distance to provide strong constraints to three-dimensional radiative transfer models including a rotating, infalling envelope, outflow cavities, and a very small disk. The models favor ages since the initiation of collapse between 3 × 10 4 and 4 × 10 4 yr for both the continuum and the lines, resolving a conflict found in one-dimensional models. The models under-predict the continuum emission seen by ALMA, suggesting an additional component such as a pseudo-disk. The best-fitting model is used to convert variations in the 4.5 µm flux in recent years into a model for a variation of a factor of 5-7 in luminosity over the last 8 years.

CO(2-->1) and 13CO(1-->0) emission from luminous southern infrared galaxies

Astronomy and Astrophysics, Oct 1, 1993

, We observed, using the SEST 15-m telescope, the CO(2-1) line emission toward eight highly lumin... more , We observed, using the SEST 15-m telescope, the CO(2-1) line emission toward eight highly luminous infrared galaxies of the southern hemisphere which were previously detected in the CO(1-0) transition. While the shapes of the (2 - 1) and (1 - 0) line profiles (taken with angular resolutions of 24" and 45", respectively) are remarkably similar, the ratios of observed peak main-beam radiation temperatures vary between 1.2 and 2.6. The derived (2-1)/(1-0) ratios of velocity integrated brightness temperature range between 0.33 and 0.77, indicating that the physical conditions of the molecular gas varies from source to source. Assuming that the kinetic temperature of the molecular gas is similar to the temperature derived for the dust (~30-40 K), the low values of the integrated line ratios imply that the CO is subthermally excited and that the bulk of the emission arises from regions of moderate H_2_ density, between 100 and 500 cm^-3^. We find that the use of the Galactic CO-H_2_ conversion factor is appropriate, to within a factor of 1.5, to estimate the molecular mass in this type of galaxies. We also observed four of these galaxies in the ^13^CO(1-0) transition and one in the ^13^CO(2-1) line. The ^12^CO(1-0)/^13^CO(1-0) velocity integrated brightness temperature ratios range from 9 to 27. The largest values, about 5 times greater than the average ratio observed for molecular clouds in the Milky Way disk, are exhibited by the most luminous IR galaxies. They can be explained if molecular clouds in mergers have low and moderate optical depths in ^13^CO and ^12^CO, respectively.

Astronomy and Astrophysics, Jun 1, 2021

Context. Formaldehyde H 2 CO was the first organic polyatomic molecule discovered in the interste... more Context. Formaldehyde H 2 CO was the first organic polyatomic molecule discovered in the interstellar medium to have been detected in a variety of sources. However, pathways to synthesize this molecule under interstellar conditions have yet to be discussed. Aims. We carried out a systematic study to analyze the chemical processes that can explain the H 2 CO formation mechanism toward a decamer of methanol (CH 3 OH) 10 as target material to mimic an ice mantle bombarded by an OH + cation. Methods. We performed Born-Oppenheimer (ab initio) molecular dynamics simulations to obtain the formation mechanisms of complex organic molecules (COMs) such as formaldehyde H 2 CO and its HCOH isomer. Results. We found that CH 2 OH + and CH 2 (OH) 2 are the main precursors to form H 2 CO and HCOH. We discuss its formation mechanisms and the astrophysical implications in star-forming regions. These processes are likely relevant to the production of COMs.

arXiv (Cornell University), Feb 6, 2023

We present Atacama Large Millimeter/submillimeter Array observations of the ∼10 kAU environment s... more We present Atacama Large Millimeter/submillimeter Array observations of the ∼10 kAU environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full ∼1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the Pixel Flux-tracing Technique (PFT). Our results indicate that by the end of the protostellar phase, outflows will remove ∼2 to 4 M from the surrounding ∼1 M low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of "cores as well-defined mass reservoir", and hence to the simplified core to star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on 10 kAU scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.

A Co Survey in Planet-Forming Disks: Characterizing the Gas Content in the Epoch of Planet Formation

The Astronomical Journal, Jul 31, 2014

The Astrophysical Journal, Oct 26, 2017

Stellar feedback from high-mass stars (e.g., H II regions) can strongly influence the surrounding... more Stellar feedback from high-mass stars (e.g., H II regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one subvirial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM1-MM12) detected by ALMA are at very different evolutionary stages, from the starless core phase to the UC H II region phase. Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The massvelocity diagrams of the outflows associated with MM7/G and MM8/F can be well-fit by broken power laws. The mass-velocity diagram of the SiO outflow associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO, SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10) are massive starless core candidates whose masses are estimated to be larger than 25 M ☉ , assuming a dust temperature of 20 K. The shocks from the expanding H II regions ("B" and "C") to the west may have a great impact on the G9.62 clump by compressing it into a filament and inducing core collapse successively, leading to sequential star formation. Our findings suggest that stellar feedback from H II regions may enhance the star formation efficiency and suppress low-mass star formation in adjacent pre-existing massive clumps.

ALMA Observations of a Keplerian Disk in the Infalling Envelope of L1527

한국천문학회보, Apr 1, 2015