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Dominique Segura-Cox

Publications and source records attributed to Dominique Segura-Cox.

At least 19 recordsLinked to original sources
arXiv2026

Preferential alignment of Class 0, Class I protostellar disks in multiple systems across nine nearby molecular clouds

Protostellar disk orientations in multiple systems provide critical insights into the primary mechanisms that govern the formation of multiple-star systems, their subsequent dynamical evolution, and their impact on planet-forming disks. We present a disk alignment study of 512 Class 0, Class I, and flat-spectrum protostars across nine nearby molecular clouds within 500 pc, utilizing data from the CAMPOS and VANDAM surveys. Our sample includes 74 binaries and 31 high-order multiple systems. We find that multiple systems with projected pair separations up to 6000 au exhibit preferential disk alignment with respect to each other across all evolutionary classes, deviating significantly from the random distribution predicted by turbulent fragmentation models. This suggests that the formation of multiple systems cannot be explained by turbulent fragmentation alone. Disk alignment on scales of a few thousand au is also difficult to explain by disk fragmentation as the dominant origin. We further find that the degree of nearest-neighbor disk alignment in higher-order multiples is comparable to that in binaries. Finally, we identify a significant deficit of flat-spectrum protostellar disks in high-order multiple systems as compared to younger Class 0 and Class I phases. The decline is consistent with rapid dynamical evolution, in which most higher-order systems dissolve by the end of the Class I phase.

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arXiv2026

Ice Deposition Fronts In Porous Bodies From Transient Heating Events In a Protoplanetary Disk

Using a 1D mass and heat transport model, we numerically integrate heat flow and gas transport in a porous body exposed to a transient heating event while embedded in a protoplanetary disk. When small icy grains are heated, volatiles sublimate, enriching the disk with volatile gases. When a porous body enters this heated, volatile-rich environment, volatile gases diffuse throughout the cool, porous body and deposit ice where the partial pressure of a volatile exceeds its vapor pressure. We simulate sublimation and deposition fronts of water, carbon dioxide, and carbon monoxide. Our simulations show that an ice deposition front forms and moves deeper into the porous body as the body warms. The amount of nebular gas deposited in an initially dry body is usually extremely low; however, in an initially icy body, an ice deposition front contains locally sublimated volatiles. In this case, the front can increase the ice volume fraction (by a factor of 2) in a thin layer below the surface. We find that the propagation speed, propagation strength, and final depth of an ice deposition front primarily depend on pore size. We propose that nebular heating events can alter the subsurface morphology and physical properties of porous icy objects embedded in a protoplanetary disk.

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arXiv2025

CAMPOS II. The onset of protostellar disk substructures and planet formation

The 1.3 mm CAMPOS survey has resolved 90 protostellar disks with ~15 au resolution across the Ophiuchus, Corona Australis, and Chamaeleon star-forming regions. To address the fundamental question, `When does planet formation begin?', we combined the CAMPOS sample with literature observations of Class 0-II disks (bolometric temperature, $T_{bol} \le 1900 K$). To investigate substructure detection rates as a function of $T_{bol}$, we restricted the sample to disks observed at the 1.3 mm wavelength, with inclinations below 75$^\circ$, linear resolution $\le 20$ au and resolved with at least 4 resolution elements ($θ_{disk}/θ_{res} \ge 4$). We also considered the effects of extinction correction and the inclusion of Herschel Space Telescope data on the $T_{bol}$ measurements to constrain the lower and upper limits of $T_{bol}$ for each source. We find that by $T_{bol}$ ~200-400 K, substructure detection rates increased sharply to ~60%, corresponding to an age of ~0.2-0.4 Myr. No substructures are detected in Class 0 disks. The ratio of disk-averaged brightness temperature to predicted dust temperature shows a trend of increasing values toward the youngest Class 0 disks, suggesting higher optical depths in these early stages. Our statistical analysis confirms that substructures similar to those in Class II disks are already common by the Class I stage, and the emergence of structures at early Class I could represent only an upper limit. Classifying disks with substructures into those with and without large central cavities, we find both populations coexisting across evolutionary stages, suggesting they are not necessarily evolutionarily linked. If protostellar disk substructures do follow an evolutionary sequence, then our results imply that disk substructures evolve very rapidly and thus can be present in all Class I/II stages and/or that they can be triggered at different times.

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arXiv2025

Mapping the merging zone of late infall in the AB Aur planet-forming system

Late infall events challenge the traditional view that planet formation occurs without external influence. Here we present deep ALMA $^{12}$CO $J=2-1$ and SO $J_{N}=5_6-4_5$ observations toward AB Aurigae, a Class II disk system with strong signs of gravitational instability and ongoing planet formation. By applying Keplerian and anti-Keplerian masks, we separate disk-like and non-disk-like motions of $^{12}$CO, considering the two outputs as the 'disk' and 'exo-disk' (out of disk) emission components, respectively. The disk component of $^{12}$CO extends to $\sim 1600$ au in radius and exhibits a stunningly rich architecture of global spiral structure. The exo-disk emission consists predominantly of three spiral structures -- S1, S2 and S3 -- whose projections are co-spatial with the disk. We successfully reproduce their trajectories with a ballistic accretion flow model, finding that S1 and S2 (both redshifted) are infalling toward the disk from in front, and S3 (blueshifted) is infalling from behind. Where the terminal ends of S1 and S2 become indistinguishable from the disk, we observe a brightness peak in SO emission $2.5\times$ the azimuthal average of a background SO ring. This merging zone lies within a relatively confined region $15-100$ degrees east of north, and between $\sim150-300$ au from the star, at scales relevant to where planet candidates have been previously identified. The AB Aur system provides a unified picture of late infall inducing replenishment of the disk, triggering gravitational instability, and modifying the conditions of forming planets.

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arXiv2024

Sites of Planet Formation in Binary Systems. II. Double the Disks in DF Tau

This article presents the latest results of our ALMA program to study circumstellar disk characteristics as a function of orbital and stellar properties in a sample of young binary star systems known to host at least one disk. Optical and infrared observations of the eccentric, ~48-year period binary DF Tau indicated the presence of only one disk around the brighter component. However, our 1.3 mm ALMA thermal continuum maps show two nearly-equal brightness components in this system. We present these observations within the context of updated stellar and orbital properties which indicate that the inner disk of the secondary is absent. Because the two stars likely formed together, with the same composition, in the same environment, and at the same time, we expect their disks to be co-eval. However the absence of an inner disk around the secondary suggests uneven dissipation. We consider several processes which have the potential to accelerate inner disk evolution. Rapid inner disk dissipation has important implications for planet formation, particularly in the terrestrial-planet-forming region.

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arXiv2024

The ALMA Legacy survey of Class 0/I disks in Corona australis, Aquila, chaMaeleon, oPhiuchus north, Ophiuchus, Serpens (CAMPOS). I. Evolution of Protostellar disk radii

We surveyed nearly all the embedded protostars in seven nearby clouds (Corona Australis, Aquila, Chamaeleon I & II, Ophiuchus North, Ophiuchus, Serpens) with the Atacama Large Millimeter/submillimeter Array at 1.3mm observations with a resolution of 0.1$"$. This survey detected 184 protostellar disks, 90 of which were observed at a resolution of 14-18 au, making it one of the most comprehensive high-resolution disk samples across various protostellar evolutionary stages to date. Our key findings include the detection of new annular substructures in two Class I and two flat-spectrum sources, while 21 embedded protostars exhibit distinct asymmetries or substructures in their disks. We find that protostellar disks have a substantially large variability in their radii across all evolutionary classes. In particular, the fraction of large disks with sizes above 60\,au decreases as the protostar evolves from Class 0 to Class I. Compiling the literature data, we discovered an increasing trend of the gas disk radii to dust disk radii ratio ($R_{\rm gas,Kep}/R_{\rm mm}$) with increasing bolometric temperature (${\rm T}_{\rm bol}$). Our results indicate that the dust and gas disk radii decouple during the early Class I stage. However, in the Class 0 stage, the dust and gas disk sizes are similar, which allows a direct comparison between models and observational data at the earliest stages of protostellar evolution. We show that the distribution of radii in the 52 Class 0 disks in our sample is in high tension with various disk formation models, indicating that protostellar disk formation remains an unsolved question.

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arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

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arXiv2024

On the magnetic field properties of protostellar envelopes in Orion

We present 870 um polarimetric observations toward 61 protostars in the Orion molecular clouds, with ~400 au (1") resolution using the Atacama Large Millimeter/submillimeter Array. We successfully detect dust polarization and outflow emission in 56 protostars, in 16 of them the polarization is likely produced by self-scattering. Self-scattering signatures are seen in several Class 0 sources, suggesting that grain growth appears to be significant in disks at earlier protostellar phases. For the rest of the protostars, the dust polarization traces the magnetic field, whose morphology can be approximately classified into three categories: standard-hourglass, rotated-hourglass (with its axis perpendicular to outflow), and spiral-like morphology. 40.0% (+-3.0%) of the protostars exhibit a mean magnetic field direction approximately perpendicular to the outflow on several 100--1000 au scales. However, in the remaining sample, this relative orientation appears to be random, probably due to the complex set of morphologies observed. Furthermore, we classify the protostars into three types based on the C17O (3--2) velocity envelope's gradient: perpendicular to outflow, non-perpendicular to outflow, and unresolved gradient (<1.0~km/s/arcsec). In protostars with a velocity gradient perpendicular to outflow, the magnetic field lines are preferentially perpendicular to outflow, most of them exhibit a rotated hourglass morphology, suggesting that the magnetic field has been overwhelmed by gravity and angular momentum. Spiral-like magnetic fields are associated with envelopes having large velocity gradients, indicating that the rotation motions are strong enough to twist the field lines. All of the protostars with a standard-hourglass field morphology show no significant velocity gradient due to the strong magnetic braking.

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arXiv2024

Sites of Planet Formation in Binary Systems. I. Evidence for Disk-Orbit Alignment in the Close Binary FO Tau

Close binary systems present challenges to planet formation. As binary separations decrease, so too do the occurrence rates of protoplanetary disks in young systems and planets in mature systems. For systems that do retain disks, their disk masses and sizes are altered by the presence of the binary companion. Through the study of protoplanetary disks in binary systems with known orbital parameters, we seek to determine the properties that promote disk retention and, therefore, planet formation. In this work, we characterize the young binary-disk system, FO Tau. We determine the first full orbital solution for the system, finding masses of $0.35^{+0.06}_{-0.05}\ M_\odot$ and $0.34\pm0.05\ M_\odot$ for the stellar components, a semi-major axis of $22(^{+2}_{-1})$ AU, and an eccentricity of $0.21(^{+0.04}_{-0.03})$. With long-baseline ALMA interferometry, we detect 1.3mm continuum and $^{12}{\mathrm{CO}} \ (J=2-1)$ line emission toward each of the binary components; no circumbinary emission is detected. The protoplanetary disks are compact, consistent with being truncated by the binary orbit. The dust disks are unresolved in the image plane and the more extended gas disks are only marginally resolved. Fitting the continuum and CO visibilities, we determine the inclination of each disk, finding evidence for alignment of the disk and binary orbital planes. This study is the first of its kind linking the properties of circumstellar protoplanetary disks to a precisely known binary orbit. In the case of FO Tau, we find a dynamically placid environment (coplanar, low eccentricity), which may foster its potential for planet formation.

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arXiv2024

870 Micron Dust Continuum of the Youngest Protostars in Ophiuchus

We present a 0.15$^{\prime\prime}$ resolution (21 au) ALMA 870 $μ$m continuum survey of 25 pointings containing 31 young stellar objects in the Ophiuchus molecular clouds. Using the dust continuum as a proxy for dust mass and circumstellar disk radius in our sample, we report a mean mass of 2.8$^{+2.1}_{-1.3}$ and 2.5$^{+9.2}_{-1.1}$ M$_{\oplus}$ and a mean radii of 23.5$^{+1.8}_{-1.2}$ and 16.5$^{+2.8}_{-0.9}$ au, for Class I and Flat spectrum protostars, respectively. In addition, we calculate the multiplicity statistics of the dust surrounding young stellar objects in Ophiuchus. The multiplicity fraction (MF) and companion star fraction (CSF) of the combined Class I and Flats based solely on this work is 0.25 $\pm$ 0.09 and 0.33 $\pm$ 0.10, respectively, which are consistent with the values for Perseus and Orion. While we see clear differences in mass and radius between the Ophiuchus and Perseus/Orion protostellar surveys, we do not see any significant differences in the multiplicities of the various regions. We posit there are some differences in the conditions for star formation in Ophiuchus that strongly affects disk size (and consequently disk mass), but does not affect system multiplicity, which could imply important variation in planet formation processes.

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arXiv2024

Cloudlet Capture Model for the Accretion Streamer onto the disk of DG Tau

DG Tau is a nearby T Tauri star associated with a collimated jet, a circumstellar disk and a streamer a few hundred au long. The streamer connects to the disk at $\sim$50 au from DG Tau. At this location SO emission is observed, likely due to the release of sulphur from dust grains caused by the shock of the impact of the accretion streamer onto the disk. We investigate the possibility that the DG Tau streamer was produced via cloudlet capture on the basis of hydrodynamic simulations, considering a cloudlet initiating infall at 600 au from DG Tau with low angular momentum so that the centrifugal force is smaller than the gravitational force, even at 50 au. The elongation of the cloudlet into a streamer is caused by the tidal force when its initial velocity is much less than the free-fall velocity. The elongated cloudlet reaches the disk and forms a high density gas clump. Our hydrodynamic model reproduces the morphology and line-of-sight velocity of CS ($5-4$) emission from the Northern streamer observed with ALMA. We discuss the conditions for forming a streamer based on the simulations. We also show that the streamer should perturb the disk after impact for several thousands of years.

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arXiv2023

Exploring the dust grain size and polarization mechanism in the hot and massive Class 0 disk IRAS 16293-2422 B

Multiwavelength dust continuum and polarization observations arising from self-scattering have been used to investigate grain sizes in young disks. However, the polarization by self-scattering is low in face-on optically thick disks and puts some of the size constraints from polarization on hold, particularly for the younger and more massive disks. The 1.3 mm emission detected toward the hot ($\gtrsim$400 K) Class 0 disk IRAS 16293-2422 B has been attributed to self-scattering, predicting grain sizes between 200-2000 $μ$m. We investigate the effects of grain size in the resultant flux and polarization fractions from self-scattering using a hot and massive Class 0 disk model and compare with observations. We compared new and archival high-resolution observations between 1.3 and 18 mm to a set of synthetic models. We have developed a new public tool to automate this process called Synthesizer. This is an easy-to-use program to generate synthetic observations from numerical simulations. Optical depths are in the range of 130 to 2 from 1.3 to 18 mm, respectively. Predictions from significant grain growth populations, including millimetric grains are comparable to the observations at all wavelengths. The polarization fraction produced by self-scattering reaches a maximum of $\sim$0.1% at 1.3 mm for a maximum grain size of 100 $μ$m, being an order of magnitude lower than that observed with ALMA. From the comparison of Stokes I fluxes, we conclude that significant grain growth could be present in the young Class 0 disk IRAS 16293 B, particularly in the inner hot region ($<10$ au, $T>$ 300 K) where refractory organics evaporate. The polarization produced by self-scattering in our model is not high enough to explain the observations at 1.3 and 7 mm, and effects like dichroic extinction or polarization reversal of elongated aligned grains remain other possible but untested scenarios.

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arXiv2023

Panchromatic (Sub)millimeter Polarization Observations of HL Tau Unveil Aligned Scattering Grains

Polarization is a unique tool to study the properties of dust grains of protoplanetary disks and detail the initial conditions of planet formation. Polarization around HL Tau was previously imaged using the Atacama Large Millimeter/submillimeter Array (ALMA) at Bands 3 (3.1 mm), 6 (1.3 mm), and 7 (0.87 mm), showing that the polarization orientation changes across wavelength $λ$. The polarization morphology at Band 7 is predominantly parallel to the disk minor axis but appears azimuthally oriented at Band 3, with the morphology at Band 6 in between the two. We present new ~0.2" (29 au) polarization observations at Q-Band (7.0 mm) using the Karl G. Jansky Very Large Array (VLA) and at Bands 4 (2.1 mm), 5 (1.5 mm), and 7 using ALMA, consolidating HL Tau's position as the protoplanetary disk with the most complete wavelength coverage in dust polarization. The polarization patterns at Bands 4 and 5 continue to follow the morphological transition with wavelength previously identified in Bands 3, 6, and 7. Based on the azimuthal variation, we decompose the polarization into contributions from scattering ($s$) and thermal emission ($t$). We find that $s$ decreases slowly with increasing $λ$, and $t$ increases more rapidly with $λ$ which are expected from optical depth effects of toroidally aligned, scattering prolate grains. The relatively weak $λ$ dependence of $s$ is consistent with large, porous grains. The sparse polarization detections from the Q-band image are also consistent with toroidally aligned prolate grains.

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arXiv2022

CH$_3$CN deuteration in the SVS13-A Class I hot-corino. SOLIS XV

We studied the line emission from CH3CN and its deuterated isotopologue CH$_2$DCN towards the prototypical Class I object SVS13-A, where the deuteration of a large number of species has already been reported. Our goal is to measure the CH$_3$CN deuteration in a Class I protostar, for the first time, in order to constrain the CH$_3$CN formation pathways and the chemical evolution from the early prestellar core and Class 0 to the evolved Class I stages. We imaged CH2DCN towards SVS13-A using the IRAM NOEMA interferometer at 3mm in the context of the Large Program SOLIS (with a spatial resolution of 1.8"x1.2"). The NOEMA images have been complemented by the CH$_3$CN and CH$_2$DCN spectra collected by the IRAM-30m Large Program ASAI, that provided an unbiased spectral survey at 3mm, 2mm, and 1.3mm. The observed line emission has been analysed using LTE and non-LTE LVG approaches. The NOEMA/SOLIS images of CH2DCN show that this species emits in an unresolved area centered towards the SVS13-A continuum emission peak, suggesting that methyl cyanide and its isotopologues are associated with the hot corino of SVS13-A, previously imaged via other iCOMs. In addition, we detected 41 and 11 ASAI transitions of CH$_3$CN and CH2DCN, respectively, which cover upper level energies (Eup) from 13 to 442 K and from 18 K to 200 K, respectively. The derived [CH2DCN]/[CH3CN] ratio is $\sim$9\%. This value is consistent with those measured towards prestellar cores and a factor 2-3 higher than those measured in Class 0 protostars. Contrarily to what expected for other molecular species, the CH3CN deuteration does not show a decrease in SVS13-A with respect to measurements in younger prestellar cores and Class 0 protostars. Finally, we discuss why our new results suggest that CH3CN was likely synthesised via gas-phase reactions and frozen onto the dust grain mantles during the cold prestellar phase.

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arXiv2022

FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple protostellar system of VLA 1623$-$2417

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

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arXiv2021

The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars V. A Characterization of Protostellar Multiplicity

We characterize protostellar multiplicity in the Orion molecular clouds using ALMA 0.87~mm and VLA 9~mm continuum surveys toward 328 protostars. These observations are sensitive to projected spatial separations as small as $\sim$20~au, and we consider source separations up to 10$^4$~au as potential companions. The overall multiplicity fraction (MF) and companion fraction (CF) for the Orion protostars are 0.30$\pm$0.03 and 0.44$\pm$0.03, respectively, considering separations from 20 to 10$^4$~au. The MFs and CFs are corrected for potential contamination by unassociated young stars using a probabilistic scheme based on the surface density of young stars around each protostar. The companion separation distribution as a whole is double peaked and inconsistent with the separation distribution of solar-type field stars, while the separation distribution of Flat Spectrum protostars is consistent solar-type field stars. The multiplicity statistics and companion separation distributions of the Perseus star-forming region are consistent with those of Orion. Based on the observed peaks in the Class 0 separations at $\sim$100~au and $\sim$10$^3$~au, we argue that multiples with separations $<$500~au are likely produced by both disk fragmentation and turbulent fragmentation with migration, and those at $\ga$10$^3$~au result primarily from turbulent fragmentation. We also find that MFs/CFs may rise from Class 0 to Flat Spectrum protostars between 100 and 10$^3$~au in regions of high YSO density. This finding may be evidence for migration of companions from $>$10$^3$~au to $<$10$^3$~au, and that some companions between 10$^3$ and 10$^4$~au must be (or become) unbound.

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arXiv2021

VLA and NOEMA view of the Bok Globule CB 17: the starless nature of a proposed FHSC candidate

We use 3mm continuum NOEMA and NH$_3$ VLA observations towards the First Hydrostatic Core (FHSC) candidate CB 17 MMS to reveal the dust structure and gas properties down to 600-1,100 au scales and constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise of 9. The gas traced by NH$_3$ exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius $\sim$1,800 au and a central density of $\sim$6$\times10^5$ cm$^{-3}$. Virial and density structure analysis reveals the core is marginally bound ($α_{vir}$= 0.73). The region is entirely consistent with a young starless core, hence ruling out CB 17 MMS as a FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the p-v diagram and an off-center region with high-velocity dispersion caused by two distinct velocity peaks. These features could be due to interaction with the nearby outflow, which appears to deflect due to the dense gas near the NH$_3$ column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of such radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1,000 au scales are determined by large-scale dense cloud motions and may be preserved through the early stages of star formation.

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arXiv2021

HAWC+/SOFIA Polarimetry in L1688: Relative Orientation of Magnetic Field and Elongated Cloud Structure

We present a study of the relative orientation between the magnetic field and elongated cloud structures for the $ρ$ Oph A and $ρ$ Oph E regions in L1688 in the Ophiuchus molecular cloud. Combining inferred magnetic field orientation from HAWC+ 154 $μ$m observations of polarized thermal emission with column density maps created using Herschel submillimeter observations, we find consistent perpendicular relative alignment at scales of $0.02$ pc ($33.6"$ at $d \approx 137$ pc) using the histogram of relative orientations (HRO) technique. This supports the conclusions of previous work using Planck polarimetry and extends the results to higher column densities. Combining this HAWC+ HRO analysis with a new Planck HRO analysis of L1688, the transition from parallel to perpendicular alignment in L1688 is observed to occur at a molecular hydrogen column density of approximately $10^{21.7}$ cm$^{-2}$. This value for the alignment transition column density agrees well with values found for nearby clouds via previous studies using only Planck observations. Using existing turbulent, magnetohydrodynamic simulations of molecular clouds formed by colliding flows as a model for L1688, we conclude that the molecular hydrogen volume density associated with this transition is approximately $\sim10^{4}$ cm$^{-3}$. We discuss the limitations of our analysis, including incomplete sampling of the dense regions in L1688 by HAWC+.

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