Robert Estalella

Context. Molecular outflows from massive protostars can impact the interstellar medium in different ways, adding turbulence on different spatial scales, dragging material at supersonic velocities, producing shocks and heating, and physically impinging onto dense structures that may be harboring other protostars. Aims. We aim to quantify the impact of the outflow associated with the high-mass protostar GGD 27-MM2(E) on its parent envelope and how this outflow affects its environment. Methods. We present Atacama Large Millimeter/submillimeter Array Band 3 observations of N₂H⁺ (1–0) and CH₃CN (5–4), as well as Band 7 observations of the H₂CO molecular line emissions from the protostellar system GGD 27-MM2(E). Through position–velocity diagrams along and across the outflow axis, we studied the kinematics and structure of the outflow. We also fit extracted spectra of the CH₃CN emission to obtain the physical conditions of the gas. We use the results to discuss the impact of the outflow on its surroundings. Results. We find that N₂H⁺ emission traces a dense molecular cloud surrounding GGD 27-MM2(E). We estimate that the mass of this cloud is ~13.3–26.5 M_⊙. The molecular cloud contains an internal cavity aligned with the H₂CO-traced molecular outflow. The outflow, also traced by CH₃CN, shows evidence of a collision with a molecular core (MC), as indicated by the distinctive increases in the distinct physical properties of the gas such as the excitation temperature, column density, line width, and velocity. This collision results in an X-shaped structure in the northern part of the outflow around the position of the MC, which produces spray-shocked material downstream in the north of MC, as observed in position–velocity diagrams both along and across the outflow axis. The outflow has a mass of 1.7–2.1 M_⊙, a momentum of 7.8–10.1 M_⊙ km s⁻¹, a kinetic energy of 5.0–6.6×10⁴⁴ erg, and a mass-loss rate of 4.9–6.0×10⁻⁴ M_⊙ yr⁻¹. Conclusions. The molecular outflow from GGD 27-MM2(E) significantly perturbs and erodes its parent cloud, compressing the gas of sources such as the MC and ALMA 12. The feedback from this powerful protostellar outflow helps maintain the turbulence in the surrounding area.

We report high angular resolution observations, made with the Atacama Large Millimeter Array in band 6, of high excitation molecular lines of CH 3 CN and SO₂ and of the H29α radio recombination line toward the G345.0061+01.794 B HC H ii region in order to investigate the physical and kinematical characteristics of its surroundings. Emission was detected in all observed components of the J = 14 →13 rotational ladder of CH 3 CN and in the 30_4,26–30_3,27, and 32_4,28–32_3,29 lines of SO₂. The peak of the velocity-integrated molecular emission is located ∼0.″4 northwest of the peak of the continuum emission. The first-order moment images and channel maps show a velocity gradient of 1.1 km s⁻¹ arcsec⁻¹ across the source and a distinctive spot of blueshifted emission toward the peak of the zero-order moment. The rotational temperature is found to decrease from 252±24 K at the peak position to 166±16 K at its edge, indicating that our molecular observations are probing a hot molecular core that is internally excited. The emission in the H29α line arises from a region of 0.″65 in size, where its peak coincides with that of the dust continuum. We model the kinematical characteristics of the “central blue spot” feature as due to infalling motions, suggesting a central mass of 172.8±8.8 M _⊙. Our observations indicate that this HC H ii region is surrounded by a compact structure of hot molecular gas, which is rotating and infalling toward a central mass, that is most likely confining the ionized region. The observed scenario is reminiscent of a “butterfly pattern” with an approximately edge-on torus and ionized gas roughly parallel to its rotation axis.

Context. The infrared dark cloud (IRDC) G14.225-0.506 is part of the extended and massive molecular cloud located to the southwest of the H II region M17. The cloud is associated with a network of filaments, which result in two different dense hubs, as well as with several signposts of star formation activity and a rich population of protostars and young stellar objects (YSOs). Aims. The aim of this work is to study the centimeter continuum emission in order to characterize the stellar population in both regions, as well as to study the evolutionary sequence across the IRDC G14.225-0.506. Methods. We performed deep (~ 1.5–3 μJy) radio continuum observations at 6 and 3.6 cm toward the IRDC G14.225-0.506 using the Karl G. Jansky Very Large Array (VLA) in its most extended A configuration (~0.3″). Data at both C and X bands were imaged using the same (u,v) range in order to derive spectral indices. We have also made use of observations taken during different days to study the presence of variability at short timescales toward the detected sources. Results. We detected a total of 66 sources, 32 in the northern region G14.2-N and 34 in the southern region G14.2-S. Ten of the sources are found to be variable, with three located in G14.2-N and seven in G14.2-S. Based on their spectral index, the emission in G14.2-N is mainly dominated by nonthermal sources while G14.2-S contains more thermal emitters. Approximately 75% of the sources present a counterpart at other wavelengths. When considering the inner 0.4 pc region around the center of each hub, the number of infrared (IR) sources in G14.2-N is larger than in G14.2-S by a factor of 4. We also studied the relation between the radio luminosity and the bolometric luminosity, finding that the thermal emission of the studied sources is compatible with thermal radio jets. For our sources with X-ray counterparts, the nonthermal emitters follow a Güdel-Benz relation with κ = 0.03, as previously suggested for other similar regions. Conclusions. We found similar levels of fragmentation between G14.2-N and G14.2-S, suggesting that both regions are most likely twin hubs. The nonthermal emission found in the less evolved objects, mainly coming from G14.2-N, suggests that G14.2-N may be composed of more massive YSOs as well as being in a more advanced evolutionary stage, consistent with the “filament-halo” gradient in age and mass from previous works. Overall, our results confirm a wider evolutionary sequence from the southwest to northeast starting in G14.2-S as the youngest part, followed by G14.2-N, and ending with the most evolved region M17.

A number of works infer radial temperature profiles of envelopes surrounding young stellar objects using several rotational transitions in a pixel-by-pixel or azimuthally-averaged basis. However, in many cases the assumption that the rotational temperature is constant along the line of sight is made, while this is not the case when a partially resolved envelope, assumed to be spherically symmetric, is used to obtain values of temperature for different projected radii. This kind of analysis (homogeneous analysis) is intrinsically inconsistent. By using a spherical envelope model to interpret NH3 (1, 1) and (2, 2) observations, we tested how robust it is to infer radial temperature profiles of an envelope. The temperature and density of the model envelope are power laws of radius, but the density can be flat for an inner central part. The homogeneous analysis was applied to obtain radial temperature profiles, and resulted that for small projected radii, where the optical depth of the lines is high, the homogeneous temperature can be much higher than the actual envelope temperature. In general, for larger projected radii, both the temperature and the temperature power-law index can be underestimated by as much as 40%, and 0.15, respectively. We applied this study to the infrared dark cloud G14.225-0.506 for which the radial temperature profile was previously derived from the dust emission at submillimeter wavelengths and the spectral energy distribution. As expected, the homogeneous analysis underestimated both the temperature and the temperature power-law index.

A number of works infer radial temperature profiles of envelopes surrounding young stellar objects using several rotational transitions in a pixel-by-pixel or azimuthally-averaged basis. However, in many cases the assumption that the rotational temperature is constant along the line of sight is made, while this is not the case when a partially resolved envelope, assumed to be spherically symmetric, is used to obtain values of temperature for different projected radii. This kind of analysis (homogeneous analysis) is intrinsically inconsistent. By using a spherical envelope model to interpret NH₃ (1,1) and (2,2) observations, we tested how robust it is to infer radial temperature profiles of an envelope. The temperature and density of the model envelope are power laws of radius, but the density can be flat for an inner central part. The homogeneous analysis was applied to obtain radial temperature profiles, and resulted that for small projected radii, where the optical depth of the lines is high, the homogeneous temperature can be much higher than the actual envelope temperature. In general, for larger projected radii, both the temperature and the temperature power-law index can be underestimated by as much as 40%, and 0.15, respectively. We applied this study to the infrared dark cloud G14.225−0.506 for which the radial temperature profile was previously derived from the dust emission at submillimeter wavelengths and the spectral energy distribution. As expected, the homogeneous analysis underestimated both the temperature and the temperature power-law index.

We present new Atacama Large Millimeter/submillimeter Array 0.98 mm observations of the continuum emission and several molecular lines toward the high-mass protostellar system GGD 27-MM1, driving the HH 80-81 radio jet. The detailed analysis of the continuum and the CH₃CN molecular emission allows us to separate the contributions from the dust content of the disk (extending up to 190 au), the molecular content of the disk (extending from 140–360 au), and the content of the envelope, revealing the presence of several possible accretion streamers (also seen in other molecular tracers, such as CH₃OH). We analyze the physical properties of the system, producing temperature and column density maps, and radial profiles for the disk and the envelope. We qualitatively reproduce the trajectories and line-of-sight velocities of the possible streamers using a theoretical model approach. An ad hoc model of a flared disk comprising a hot dust disk embedded in cold gas fits the H₂S emission, which revealed the molecular disk as a crescent shape with a prominent central absorption. Another fit to the central absorption spectrum suggests that the absorption is probably caused by different external cold layers from the envelope or the accretion streamers. Finally, the analysis of the rotation pattern of the different molecular transitions in the molecular disk suggests that there is an inner zone devoid of molecular content.

We present new Atacama Large (sub)Millimeter Array 0.98 mm observations of the continuum emission and several molecular lines toward the high-mass protostellar system GGD27-MM1, driving the HH 80-81 radio-jet. The detailed analysis of the continuum and the CH$_3$CN molecular emission allows us to separate the contributions from the dust content of the disk (extending up to 190 au), the molecular content of the disk (extending from 140 to 360 au), and the content of the envelope, revealing the presence of several possible accretion streamers (also seen in other molecular tracers, such as CH$_3$OH). We analyze the physical properties of the system, producing temperature and column density maps, and radial profiles for the disk and the envelope. We qualitatively reproduce the trajectories and line-of-sight velocities of the possible streamers using a theoretical model approach. An ad-hoc model of a flared disk comprising a hot dust disk embedded in cold gas fits the H$_2$S emission, which revealed the molecular disk as crescent-shape with a prominent central absorption. Another fit to the central absorption spectrum suggests that the absorption is probably caused by different external cold layers from the envelope or the accretion streamers. Finally, the analysis of the rotation pattern of the different molecular transitions in the molecular disk, suggests that there is an inner zone devoid of molecular content.

We present Very Large Array (VLA) and Atacama Large Millimeter/submillimeter Array (ALMA) observations of the close (0.″3 = 90 au separation) protobinary system SVS 13. We detect two small circumstellar disks (radii ∼12 and ∼9 au in dust, and ∼30 au in gas) with masses of ∼0.004–0.009 M _☉ for VLA 4A (the western component) and ∼0.009–0.030 M _☉ for VLA 4B (the eastern component). A circumbinary disk with prominent spiral arms extending ∼500 au and a mass of ∼0.052 M _☉ appears to be in the earliest stages of formation. The dust emission is more compact and with a very high optical depth toward VLA 4B, while toward VLA 4A the dust column density is lower, allowing the detection of stronger molecular transitions. We infer rotational temperatures of ∼140 K, on scales of ∼30 au, across the whole source, and a rich chemistry. Molecular transitions typical of hot corinos are detected toward both protostars, being stronger toward VLA 4A, with several ethylene glycol transitions detected only toward this source. There are clear velocity gradients, which we interpret in terms of infall plus rotation of the circumbinary disk, and pure rotation of the circumstellar disk of VLA 4A. We measured orbital proper motions and determined a total stellar mass of 1 M _☉. From the molecular kinematics, we infer the geometry and orientation of the system, and stellar masses of ∼0.26 M _☉ for VLA 4A and ∼0.60 M _☉ for VLA 4B.

Theoretical and numerical works indicate that a strong magnetic field should suppress fragmentation in dense cores. However, this has never been tested observationally in a relatively large sample of fragmenting massive dense cores. Here, we use the polarization data obtained in the Submillimeter Array Legacy Survey of Zhang et al. to build a sample of 18 massive dense cores where both fragmentation and magnetic field properties are studied in a uniform way. We measured the fragmentation level, N _mm, within the field of view common to all regions of ∼0.15 pc, with a mass sensitivity of ∼0.5 M _☉, and a spatial resolution of ∼1000 au. In order to obtain the magnetic field strength using the Davis–Chandrasekhar–Fermi method, we estimated the dispersion of the polarization position angles, the velocity dispersion of the H¹³CO⁺(4–3) gas, and the density of each core, all averaged within 0.15 pc. A strong correlation is found between N _mm and the average density of the parental core, although with significant scatter. When large-scale systematic motions are separated from the velocity dispersion and only the small-scale (turbulent) contribution is taken into account, a tentative correlation is found between N _mm and the mass-to-flux ratio, as suggested by numerical and theoretical works.

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