arXiv subjects

Luis F. Rodriguez

Publications and source records attributed to Luis F. Rodriguez.

At least 19 recordsLinked to original sources

arXiv2026

A Radio-Bright Local Little Red Dot Analog

The James Webb Space Telescope revealed the existence in the early Universe ($z >$ 4) of large populations of little red dots (LRDs), compact red luminous sources that host rapidly growing supermassive black holes (SMBHs) surrounded by coeval nuclear starbursts. LRDs have defining properties, one of which is the absence of radio detections. LRDs could be radio-undetected because of their large distances. A way to investigate the radio properties of LRDs is to search for radio emission in their local analogs, the Local Little Red Dot (LLRD) galaxies at $z <$ 1 with analogous properties to LRDs. We report the radio continuum detection of the LLRD analog J204837.26${-}$002437.2 ($z$ = 0.4332, hereinafter J2048). This adds to the previous radio detection of two other LLRDs. However, with a flux density of 3.0$\pm$0.2 mJy at 3.0 GHz, J2048 is two orders of magnitude more radio luminous than the previous detections. The spectral index of $\alpha$ = -0.39$\pm$0.04 is consistent with moderately optically-thick synchrotron emission. The radio luminosity of J2048 is $1.2 \times 10^{41}~ \mathrm{erg ~s^{-1}}$, in the lower end of the range defined by radio-loud giant elliptical galaxies and quasars of $L_R$ = $10^{41-46} ~\mathrm{erg ~s^{-1}}$. The expected radio luminosity of the SMBH associated with J2048 is estimated to be about an order of magnitude larger, suggesting that its radio luminosity could potentially be strongly dimmed. A cosmological ($z >$ 4) LRD with radio luminosity similar to that of J2048 would be detectable using the VLA with moderately long integrations.

astro-ph.GA↗

arXiv2025

Computational Aerothermal Framework and Analysis of Stetson Mach 6 Blunt Cone

Accurately predicting aerothermal behavior is paramount for the effective design of hypersonic vehicles, as aerodynamic heating plays a pivotal role in influencing performance metrics and structural integrity. This study introduces a computational aerothermal framework and analyzes a blunt cone subjected to Mach 6 conditions, drawing inspiration from Stetson foundational experimental work published in 1983. While the findings offer significant insights into the phenomena at play, the study highlights an urgent necessity for integrating chemical kinetics to comprehensively capture non-equilibrium effects, thereby enhancing the predictive accuracy of computational fluid dynamics (CFD) simulations. This research implements a one-way coupling method between CFD simulations and heat conduction analysis, facilitating a thorough investigation of surface heat transfer characteristics. The numerical results elucidate discrete roughness elements' impact on surface heating and fluid dynamics within high-speed airflow. Furthermore, the investigation underscores the critical importance of accounting for non-equilibrium thermochemical effects in aerothermal modeling to bolster the accuracy of high-enthalpy flow simulations. By refining predictive computational tools and deepening understanding of hypersonic aerothermal mechanisms, this research lays a robust groundwork for future experimental and computational endeavors, significantly contributing to advancing high-speed flight applications.

physics.flu-dyn↗

arXiv2025

Upper Limits to the Proper Motions of JuMBO 24, a Jupiter-Mass Binary Object Candidate in Orion

Using JWST near-infrared data of the inner Orion Nebula, \citet{Pearson_McCaughrean_2023} detected 40 binary systems they proposed to be Jupiter-Mass Binary Objects (JuMBOs) -- although their actual nature is still in debate. Only one of the objects, JuMBO\,24, was detected in the radio continuum. Here, we report on new radio continuum (10 GHz) Karl G. Jansky Very Large Array (VLA) detections of the radio counterpart to JuMBO\,24, and on an unsuccessful search for 5 GHz continuum emission with the High Sensitivity Array (HSA). From our new VLA detections and adopting a distance to the region, we set an upper limit of $\simeq 6$~km~s$^{-1}$ to the velocity of the radio source in the plane of the sky. This upper limit favors an origin for this source similar to that of stars, that is, from a stationary contracting core. The nature of the radio emission remains uncertain but the lack of strong variability (all VLA observations are consistent with a steady flux of $\sim$50 $\mu$Jy), of detection on long HSA baseline, and of detectable circular polarization in VLA data do not favor a non-thermal origin.

astro-ph.EP↗

arXiv2025

An Unusual Change in the Radio Jets of GRS 1915+105

We compare Very Large Array observations of GRS 1915+105 made in 1994 and 2023, with nearly three decades of difference. The source has experienced intriguing major changes. The position angle of the bipolar ejecta in the plane of the sky has increased counterclockwise by 24$^\circ$. The inclination angle of the flow with respect to the line of sight has increased by 17$^\circ$. Both sets of observations show the temporal quasi-sinusoidal radio oscillations previously reported for other epochs. However, the 2023 oscillations are faster than ever before, with a period of about 8 minutes as opposed to the periods in the range of 20 to 40 minutes observed in previous epochs. Analysis of GRS 1915+105 images over the years suggest that the observed changes took place within a year or less. Our analysis indicates that during 2023 the plane of the accretion disk was aligned with the line of sight, which may explain the deep X-ray obscured state and the high mid-infrared luminosity observed with JWST in that epoch. More recent 2024 observations show that the position angle of the ejecta has returned to its historic values. Future monitoring of the time evolution of the source may clarify the cause of these remarkable changes.

astro-ph.HE↗

arXiv2024

Understanding the Radio Emission from the $\beta$ Cep star V2187 Cyg

We analyze the radio emission from the $\beta$ Cep star V2187 Cyg using archive data from the Jansky Very Large Array. The observations were made in ten epochs at 1.39 and 4.96 GHz in the highest angular resolution A configuration. We determine a spectral index of of $\alpha = 0.6\pm0.2$ ($S_{\nu} \propto \nu^\alpha$), consistent with an ionized wind or a partially optically-thick synchrotron or gyrosynchrotron source. The emission is spatially unresolved at both frequencies. The 4.96 GHz data shows a radio pulse with a duration of about one month that can be modeled in terms of an internal shock in the stellar wind produced by a sudden increase in the mass-loss rate and the terminal velocity. The quiescent radio emission of V2187 Cyg at 4.96 GHz (with a flux density of $\simeq 150~\mu Jy$), cannot be explained in terms of an internally (by V2187 Cyg) or externally (by a nearby O star) photoionized wind. We conclude that, despite the spectral index suggestive of free-free emission from an ionized wind, the radio emission of V2187 Cyg most likely has a magnetic origin, a possibility that can be tested with a sensitive search for circular polarization in the radio, as expected from gyro-synchrotron radiation, and also by trying to measure the stellar magnetic field, that is expected to be in the range of several kGauss.

astro-ph.SR↗

arXiv2024

Partition of Unity Physics-Informed Neural Networks (POU-PINNs): An Unsupervised Framework for Physics-Informed Domain Decomposition and Mixtures of Experts

Physics-informed neural networks (PINNs) commonly address ill-posed inverse problems by uncovering unknown physics. This study presents a novel unsupervised learning framework that identifies spatial subdomains with specific governing physics. It uses the partition of unity networks (POUs) to divide the space into subdomains, assigning unique nonlinear model parameters to each, which are integrated into the physics model. A vital feature of this method is a physics residual-based loss function that detects variations in physical properties without requiring labeled data. This approach enables the discovery of spatial decompositions and nonlinear parameters in partial differential equations (PDEs), optimizing the solution space by dividing it into subdomains and improving accuracy. Its effectiveness is demonstrated through applications in porous media thermal ablation and ice-sheet modeling, showcasing its potential for tackling real-world physics challenges.

cs.LG↗

arXiv2024

Designing an Optimal Scoop for Holloman High-Speed Test Track Water Braking Mechanism using Computational Fluid Dynamics

Specializing in high-speed testing, Holloman High-Speed Test Track (HHSTT) uses water braking to stop vehicles on the test track. This method takes advantage of the higher density of water, compared to air, to increase braking capability through momentum exchange by increasing the water content in that section at the end of the track. By studying water braking using computational fluid dynamics (CFD), the forces acting on tracked vehicles can be approximated and prepared before actual testing through numerical simulations. In this study, emphasis will be placed on the brake component of the tracked sled, which is responsible for interacting with water to brake. By discretizing a volume space around our brake, we accelerate the water and air to simulate the brake coupling relatively. The multiphase flow model uses the governing equations of the gas and liquid phases with the finite volume method to perform 3D simulations. By adjusting the air and water inlet velocity, it is possible to simulate HHSTT sled tests at various operating speeds.

physics.flu-dyn↗

arXiv2024

Computational Investigation of Roughness Effects on Boundary Layer Transition for Stetson's Blunt Cone at Mach 6

In this aerothermal study, we performed a two-dimensional steady-state Computational Fluid Dynamics (CFD) and heat conduction simulation at Mach 6. The key to our methodology was a one-way coupling between CFD surface temperature as a boundary condition and the calculation of the heat transfer flux and temperatures inside the solid stainless-steel body of a nose geometry. This approach allowed us to gain insight into surface heat transfer signatures with corresponding fluid flow regimes, such as the one experienced in laminar fluid flow. We have also examined this heat transfer under roughness values encountered in Stetson's studies at the Wright-Patterson Air Force Base Ludwig tube. To validate our findings, we have performed this type of work on a blunt cone, specifically for the U.S. Air Force. The research focuses on predicting transition onset using laminar correlations derived from Stetson's experimental studies, examining the role of discrete roughness elements. Findings emphasize the importance of incorporating non-equilibrium effects in future computational frameworks to enhance predictive accuracy for high-speed aerodynamic applications.

physics.flu-dyn↗

arXiv2024

Radio Proper Motions and a Search for the Origin of PSR B1849+00

Until now it has not been possible to obtain the proper motions of PSR B1849+00 with timing techniques or VLBI imaging given the enhanced interstellar scattering along its line of sight. We present an analysis of archive Very Large Array observations at epochs from 2012 to 2022 that indicates a total proper motion of 23.9$\pm$5.5 mas yr$^{-1}$ toward the southwest. After correction for the proper motions produced by galactic rotation, we find a peculiar transverse velocity of $\simeq$740 km s$^{-1}$. We searched unsuccessfully along the past trajectory of the pulsar for an associated supernova remnant. In particular, W44 is in this trajectory but its distance is different to that of PSR B1849+00.

astro-ph.HE↗

arXiv2024

The Radio Continuum Source Projected Near HR 8799

HR 8799 is an A5/F0 V star where exoplanets were first directly imaged. Four exoplanets were found within $\simeq 2\rlap.{''}0$ from the star. Here we report the VLA detection of a faint (19.1$\pm$2.7 $\mu$Jy) radio continuum (3.0 GHz) source projected at $\simeq 2\rlap.{''}2$ from the star. The \sl a priori \rm probability of finding a background source with this flux density within a radius of $2\rlap.{''}2$ is only 0.0046. However, the astrometry made with the VLA and ALMA images, separated by 5.5 years, indicates no significant proper motions and rules out the association of the radio source with the HR 8799 system and suggests it is a background millimeter galaxy with dust emission in the millimeter and partially thick synchrotron emission in the centimeter.

astro-ph.SR↗

arXiv2024

A Radio Counterpart to a Jupiter-Mass Binary Object in Orion

Using James Webb Space Telescope near-infrared data of the inner Orion Nebula, \citet{Pearson_McCaughrean_2023} detected 40 Jupiter-Mass Binary Objects (JuMBOS). These systems are not associated with stars and their components have masses of giant Jupiter-like planets and separations in the plane of the sky of order $\sim$100 au. The existence of these wide free-floating planetary mass binaries was unexpected in our current theories of star and planet formation. Here we report the radio continuum (6.1 and 10.0 GHz) Karl G.\ Jansky Very Large Array detection of a counterpart to JuMBO\,24. The radio emission appears to be steady at a level of $\sim$50 $\mu$Jy over timescales of days and years. We set an upper limit of $\simeq15$~km~s$^{-1}$ to the velocity of the radio source in the plane of the sky. As in the near-infrared, the radio emission seems to be coming from both components of the binary.

astro-ph.EP↗

arXiv2023

Compact Radio Sources in the Field of Tycho's Supernova Remnant

We present sensitive, high angular resolution Jansky Very Large Array observations made in 2014 at 1.50 GHz toward the field of Tycho's supernova remnant. We detect a total of 36 compact sources in a field with radius of 13 arcmin. This number is consistent with the expected number of background sources. We use older observations made with the classic Very Large Array to compare with the 2014 observations and search for sources showing large proper motions that could be related to the donor companion of the exploding white dwarf that produced the supernova in 1572. The comparison of the positions for the two sets of observations does not show sources with large proper motions and supports the conclusion that all sources detected are extragalactic and unrelated to the supernova field.

astro-ph.HE↗

arXiv2023

One, Two, Three ... An Explosive Outflow in IRAS 12326$-$6245 revealed by ALMA

In the last years there has been a substantial increase in the number of the reported massive and luminous star-forming regions with related explosive outflows thanks to the superb sensitivity and angular resolution provided by the new radio, infrared, and optical facilities. Here, we report one more explosive outflow related with the massive and bright star-forming region IRAS 12326$-$6245 using Band 6 sensitive and high angular resolution ($\sim$0.2$"$) Atacama Large Millimeter/Submillimeter Array (ALMA) observations. We find over 10 molecular and collimated well-defined streamers, with Hubble-Lemaitre like expansion motions, and pointing right to the center of a dusty and molecular shell (reported for the first time here) localized in the northern part of the UCHII region known as G301.1A. The estimated kinematic age, and energy for the explosion are $\sim$700 yrs, and 10$^{48}$ erg, respectively. Taking into account the recently reported explosive outflows together with IRAS 12326$-$6245, we estimate an event rate of once every 90 yr in our Galaxy, similar to the formation rate of massive stars.

astro-ph.GA↗

arXiv2023

Radio Proper Motions of the Nearby Ultra-cool dwarf binary VHS 1256$-$1257AB

The proper motions of a source obtained at different epochs or in different spectral regions should in principle be consistent. However, in the case of a binary source or a source with associated ejecta, they could be different depending on the epochs when the observations were made and on what emission is traced in each spectral region. In this paper we determine the radio proper motions of the ultra-cool dwarf binary VHS 1256$-$1257AB from Very Large Array (VLA) observations, that we find are consistent within error ($\simeq 2-3\%$) with those reported by Gaia DR3. The comparison of the proper motions and the analysis of the VLA data imply that, as in the optical, the radio emission is coming in comparable amounts from both components of the unresolved binary.

astro-ph.SR↗

arXiv2023

Understanding the Radio Emission from $\epsilon$ Eridani

Some solar-type stars are known to present faint, time-variable radio continuum emission whose nature is not clearly established. We report on Jansky Very Large Array observations of the nearby star $\epsilon$ Eridani at 10.0 and 33.0 GHz. We find that this star has flux density variations on scales down to days, hours and minutes. On 2020 Apr 15 it exhibited a radio pulse at 10.0 GHz with a total duration of about 20 minutes and a peak four times larger than the plateau of 40 $\mu$Jy present in that epoch. We were able to model the time behavior of this radio pulse in terms of the radiation from shocks ramming into the stellar wind. Such shocks can be produced by the wind interaction of violently expanding gas heated suddenly by energetic electrons from a stellar flare, similar to the observed solar flares. Because of the large temperature needed in the working surface to produce the observed emission, this has to be non thermal. It could be gyrosynchrotron or synchrotron emission. Unfortunately, the spectral index or polarization measurements from the radio pulse do not have enough signal-to-noise ratio to determine its nature.

astro-ph.SR↗

arXiv2022

Black holes at cosmic dawn in the redshifted 21cm signal of HI

Indirect insights of Pop III stars and Black Holes (BHs) at Cosmic Dawn (CD) may be imprinted as an absorption signal in the 21cm line of HI against the CMB, when the Universe was less than 200 Myr old. To explain the additional large amplitude of the 21cm HI absorption reported by EDGES there have been proposed models based on an additional synchrotron Cosmic Radio Background (CRB) from BH-jet sources that boost the HI absorption signal at CD. The recent observations of radio loud supermassive BHs (SMBHs) in high-z quasars up to z=7 suggest the existence of a CRB from growing BHs at z > 15, of unknown intensity. To match the onset of the EDGES signal a CRB of comparable intensity to that of the CMB is required. Here we provide approximate calculations to analyze this type of absorption signals, taking that of EDGES as an example. Assuming a BH mass to radio luminosity ratio as observed in radio-loud SMBHs of ~10^9 solar masses in quasars at z = 6-7, we find that rapidly growing radio luminous BHs of Intermediate Mass (IMBHs) in their way to become SMBHs, are the only type of astrophysical radio sources of a CRB that could explain the amplitude of the HI absorption reported by EDGES in the interval of z = 18-20. At those redshifts the EDGES signal would imply that the global mass density of IMBHs must be dominant over that of stars, more than 70% of the maximum Stellar Mass Density (SMD) expected at those high redshifts. This suggests that those IMBHs are formed before and grow faster than the bulk of stars, with no large mass contribution from stellar-mass BH remnants of typical Pop III stars. The highly redshifted signals from these IMBHs may be detected at long radio wavelengths with ultrasensitive interferometers such as the SKA, in the infrared with the JWST, and in the X-rays with future space missions.

astro-ph.CO↗

arXiv2020

Confirming the Explosive Outflow in G5.89 with ALMA

The explosive molecular outflow detected decades ago in the Orion BN/KL region of massive star formation was considered to be a bizarre event. This belief was strengthened by the non detection of similar cases over the years with the only exception of the marginal case of DR21. Here, we confim a similar explosive outflow associated with the UCH$_{\rm II}$ region G5.89$-$0.39 that indicates that this phenomenon is not unique to Orion or DR21. Sensitive and high angular resolution ($\sim$ 0.1$''$) ALMA CO(2$-$1) and SiO(5$-$4) observations show that the molecular outflow in the massive star forming region G5.89$-$0.39 is indeed an explosive outflow with an age of about 1000 yrs and a liberated kinetic energy of 10$^{46-49}$ erg. Our new CO(2$-$1) ALMA observations revealed over 30 molecular filaments, with Hubble-like expansion motions, pointing to the center of UCH$_{\rm II}$ region. In addition, the SiO(5$-$4) observations reveal warmer and strong shocks very close to the origin of the explosion, confirming the true nature of the flow. A simple estimation for the occurrence of these explosive events during the formation of the massive stars indicates an event rate of once every $\sim$100 yrs, which is close to the supernovae rate.

astro-ph.GA↗

arXiv2020

Proper Motions of the Radio Source Orion MR, Formerly Known as Orion n, and New Sources with Large Proper Motions in Orion BN/KL

The infrared source known as Orion n was detected in 1980 with observations made with the 3.8-m United Kingdom Infrared Telescope. About two decades later, sensitive observations made with the Very Large Array revealed the presence of a mJy double radio source apparently coincident in position with the infrared source n. The radio source was assumed to be the counterpart of the infrared source. However, over the years it has been concluded that the radio source shows large proper motions to the south while the infrared source n is stationary. Here we reanalyze the proper motions of the radio source adding both older and newer VLA observations than previously used. We confirm the proper motions of the radio source that at present no longer coincides positionally with the infrared source. The solution to this problem is, most probably, that the infrared source n and the radio source are not the same object: the infrared source is a stationary object in the region while the radio counterpart is moving as a result of the explosion that took place in this region some 500 years ago and that expelled large amounts of molecular gas as well as several compact sources. Considering the paper where it was first reported, we refer to this double radio source as Orion MR. In addition, we use these new observations to fully confirm the large proper motions of the sources IRc23 and Zapata 11. Together with sources BN, I, Orion MR, and x, there are at least six compact sources that recede from a point in common in Orion BN/KL. However, IRc23 is peculiar in that its ejection age appears to be only $\sim$300 years. The relatively large number of sources rules out as a possible mechanism the classic three-body scenario since then only two escaping bodies are expected: a tight binary plus the third star involved in the encounter.

astro-ph.SR↗