arXiv subjects

Enrique Lopez-Rodriguez

Publications and source records attributed to Enrique Lopez-Rodriguez.

66 records · Page 4Linked to original sources

arXiv2021

The strength and structure of the magnetic field in the galactic outflow of M82

Galactic outflows driven by starbursts can modify the galactic magnetic fields and drive them away from the galactic planes. Here, we quantify how these fields may magnetize the intergalactic medium. We estimate the strength and structure of the fields in the starburst galaxy M82 using thermal polarized emission observations from SOFIA/HAWC+ and a potential field extrapolation commonly used in solar physics. We modified the Davis-Chandrasekhar-Fermi method to account for the large-scale flow and the turbulent field. Results show that the observed magnetic fields arise from the combination of a large-scale ordered potential field associated with the outflow and a small-scale turbulent field associated with bow-shock-like features. Within the central $900$ pc radius, the large-scale field accounts for $53\pm4$% of the observed turbulent magnetic energy with a median field strength of $305\pm15$ $μ$G, while small-scale turbulent magnetic fields account for the remaining $40\pm5$% with a median field strength of $222\pm19$ $μ$G. We estimate that the turbulent kinetic and turbulent magnetic energies are in close equipartition up to $\sim2$ kpc (measured), while the turbulent kinetic energy dominates at $\sim7$ kpc (extrapolated). We conclude that the fields are frozen into the ionized outflowing medium and driven away kinetically. The magnetic field lines in the galactic wind of M82 are `open,' providing a direct channel between the starburst core and the intergalactic medium. Our novel approach offers the tools needed to quantify the effects of outflows on galactic magnetic fields as well as their influence on the intergalactic medium and evolution of energetic particles.

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arXiv2021

The Magnetic Field Across the Molecular Warped Disk of Centaurus A

Magnetic fields are amplified as a consequence of galaxy formation and turbulence-driven dynamos. Galaxy mergers can potentially amplify the magnetic fields from their progenitors, making the magnetic fields dynamically important. However, the effect of mergers on magnetic fields is still poorly understood. We use thermal polarized emission observations to trace the magnetic fields in the molecular disk of the nearest radio active galaxy, Centaurus A, which is thought to be the remnant of a merger. Here, we detect that the magnetic field orientations in the plane of the sky are tightly following the $\sim3.0$ kpc-scale molecular warped disk. Our simple regular large-scale axisymmetric spiral magnetic field model can explain, to some extent, the averaged magnetic field orientations across the disk projected on the sky. Our observations also suggest the presence of small-scale turbulent fields, whose relative strength increases with velocity dispersion and column density. These results have strong implications for understanding the generation and role of magnetic fields in the formation of galaxies across cosmic time.

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arXiv2020

Magnetized filamentary gas flows feeding the young embedded cluster in Serpens South

Observations indicate that molecular clouds are strongly magnetized, and that magnetic fields influence the formation of stars. A key observation supporting the conclusion that molecular clouds are significantly magnetized is that the orientation of their internal structure is closely related to that of the magnetic field. At low column densities the structure aligns parallel with the field, whereas at higher column densities, the gas structure is typically oriented perpendicular to magnetic fields, with a transition at visual extinctions $A_V\gtrsim{}3~\rm{}mag$. Here we use far-infrared polarimetric observations from the HAWC+ polarimeter on SOFIA to report the discovery of a further transition in relative orientation, i.e., a return to parallel alignment at $A_V\gtrsim{}21~\rm{}mag$ in parts of the Serpens South cloud. This transition appears to be caused by gas flow and indicates that magnetic supercriticality sets in near $A_V\gtrsim{}21~\rm{}mag$, allowing gravitational collapse and star cluster formation to occur even in the presence of relatively strong magnetic fields.

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arXiv2020

ALMA polarimetry measures magnetically aligned dust grains in the torus of NGC 1068

The obscuring structure surrounding active galactic nuclei (AGN) can be explained as a dust and gas flow cycle that fundamentally connects the AGN with their host galaxies. This structure is believed to be associated with dusty winds driven by radiation pressure. However, the role of magnetic fields, which are invoked in almost all models for accretion onto a supermassive black hole and outflows, is not thoroughly studied. Here we report the first detection of polarized thermal emission by means of magnetically aligned dust grains in the dusty torus of NGC 1068 using ALMA Cycle 4 polarimetric dust continuum observations ($0.07"$, $4.2$ pc; 348.5 GHz, $860$ $μ$m). The polarized torus has an asymmetric variation across the equatorial axis with a peak polarization of $3.7\pm0.5$\% and position angle of $109\pm2^{\circ}$ (B-vector) at $\sim8$ pc east from the core. We compute synthetic polarimetric observations of magnetically aligned dust grains assuming a toroidal magnetic field and homogeneous grain alignment. We conclude that the measured 860 $μ$m continuum polarization arises from magnetically aligned dust grains in an optically thin region of the torus. The asymmetric polarization across the equatorial axis of the torus arises from 1) an inhomogeneous optical depth, and 2) a variation of the velocity dispersion, i.e. variation of the magnetic field turbulence at sub-pc scales, from the eastern to the western region of the torus. These observations and modeling constrain the torus properties beyond spectral energy distribution results. This study strongly supports that magnetic fields up to a few pc contribute to the accretion flow onto the active nuclei.

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arXiv2019

Review: Far-Infrared Instrumentation and Technology Development for the Next Decade

Far-infrared astronomy has advanced rapidly since its inception in the late 1950's, driven by a maturing technology base and an expanding community of researchers. This advancement has shown that observations at far-infrared wavelengths are important in nearly all areas of astrophysics, from the search for habitable planets and the origin of life, to the earliest stages of galaxy assembly in the first few hundred million years of cosmic history. The combination of a still developing portfolio of technologies, particularly in the field of detectors, and a widening ensemble of platforms within which these technologies can be deployed, means that far-infrared astronomy holds the potential for paradigm-shifting advances over the next decade. In this review, we examine current and future far-infrared observing platforms, including ground-based, sub-orbital, and space-based facilities, and discuss the technology development pathways that will enable and enhance these platforms to best address the challenges facing far-infrared astronomy in the 21st century.

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arXiv2018

SOFIA/FORCAST resolves 30 - 40 um extended dust emission in nearby active galactic nuclei

We present arcsecond-scale observations of the active galactic nuclei (AGNs) of seven nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the 31.5 and 37.1 um filters of the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We isolate unresolved emission from the torus and find extended diffuse emission in six 37.1 um residual images in our sample. Using Spitzer/IRS spectra, we determine the dominant mid-infrared (MIR) extended emission source and attribute it to dust in the narrow line region (NLR) or star formation. We compare the optical NLR and radio jet axes to the extended 37.1 um emission and find coincident axes for three sources. For those AGNs with extended emission coincident with the optical axis, we find that spatial scales of the residual images are consistent with 0.1 - 1 kpc scale distances to which dust can be heated by the AGN. Using previously published subarcsecond 1 - 20 um imaging and spectroscopic data along with our new observations, we construct broadband spectral energy distributions (SEDs) of the AGNs at wavelengths 1 - 40 um. We find that three AGNs in our sample tentatively show a turnover in the SED between 30 - 40 um. Using results from Clumpy torus models and the Bayesian inference tool BayesClumpy, we find that the posterior outputs for AGNs with MIR turnover revealed by SOFIA/FORCAST have smaller uncertainties than AGNs that do not show a turnover.

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arXiv2018

The highly polarized dusty emission core of Cygnus A

We report the detection of linearly polarized emission at 53 and 89 $μ$m, from the radio-loud active galactic nucleus (AGN) Cygnus A using HAWC+ onboard SOFIA. We measure a highly polarized core of $11\pm3$% and $9\pm2$% with a position angle (P.A.) of polarization of $43\pm8^{\circ}$ and $39\pm7^{\circ}$ at 53 and 89 $μ$m, respectively. We find (1) a synchrotron dominated core with a flat spectrum ($+0.21\pm0.05$) and a turn-over at $543\pm120$ $μ$m, which implies synchrotron emission is insignificant in the infrared (IR), and (2) a $2-500$ $μ$m bump peaking at $\sim40$ $μ$m described by a blackbody component with color temperature of $107\pm9$ K. The polarized SED has the same shape as the IR bump of the total flux SED. We observe a change in the P.A. of polarization of $\sim20^{\circ}$ from 2 to 89 $μ$m, which suggests a change of polarization mechanisms. The ultraviolet, optical and near-IR polarization has been convincingly attributed to scattering by polar dust, consistent with the usual torus scenario, though this scattered component can only be directly observed from the core in the near-IR. By contrast, the gradual rotation by $\sim20^{\circ}$ towards the far-IR, and the near-perfect match between the total and polarized IR bumps, indicate that dust emission from aligned dust grains becomes dominant at $10-100$ $μ$m, with a large polarization of 10% at a nearly constant P.A. This result suggests that a coherent dusty and magnetic field structure dominates the $10-100$ $μ$m emission around the AGN.

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arXiv2018

The emission and distribution of dust of the torus of NGC 1068

We present observations of NGC 1068 covering the $19.7-53.0$ $μ$m wavelength range using FORCAST and HAWC+ onboard SOFIA. Using these observations, high-angular resolution infrared (IR) and sub-mm observations, we find an observational turn-over of the torus emission in the $30-40$ $μ$m wavelength range with a characteristic temperature of $70-100$ K. This component is clearly different from the diffuse extended emission in the narrow line and star formation regions at 10-100 $μ$m within the central 700 pc. We compute $2.2-432$ $μ$m 2D images using the best inferred \textsc{clumpy} torus model based on several nuclear spectral energy distribution (SED) coverages. We find that when $1-20$ $μ$m SED is used, the inferred result gives a small torus size ($<4$ pc radius) and a steep radial dust distribution. The computed torus using the $1-432$ $μ$m SED provides comparable torus sizes, $5.1^{+0.4}_{-0.4}$ pc radius, and morphology to the recently resolved 432 $μ$m ALMA observations. This result indicates that the $1-20$ $μ$m wavelength range is not able to probe the full extent of the torus. The characterization of the turn-over emission of the torus using the $30-60$ $μ$m wavelength range is sensitive to the detection of cold dust in the torus. The morphology of the dust emission in our 2D image at 432 $μ$m is spatially coincident with the cloud distribution, while the morphology of the emission in the $1-20$ $μ$m wavelength range shows an elongated morphology perpendicular to the cloud distribution. We find that our 2D \textsc{clumpy} torus image at 12 $μ$m can produce comparable results to those observed using IR interferometry.

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arXiv2016

The InfraRed Imaging Spectrograph (IRIS) for TMT: latest science cases and simulations

The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared Imaging Spectrograph) will complete its preliminary design phase in 2016. The IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral field spectrograph (IFS) and imager that are able to conduct simultaneous diffraction-limited observations behind the advanced adaptive optics system NFIRAOS. The IRIS science cases have continued to be developed and new science studies have been investigated to aid in technical performance and design requirements. In this development phase, the IRIS science team has paid particular attention to the selection of filters, gratings, sensitivities of the entire system, and science cases that will benefit from the parallel mode of the IFS and imaging camera. We present new science cases for IRIS using the latest end-to-end data simulator on the following topics: Solar System bodies, the Galactic center, active galactic nuclei (AGN), and distant gravitationally-lensed galaxies. We then briefly discuss the necessity of an advanced data management system and data reduction pipeline.

astro-ph.IM↗

arXiv2016

Investigating the dusty torus of Seyfert galaxies using SOFIA/FORCAST photometry

We present 31.5 micron imaging photometry of 11 nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We tentatively detect extended 31 micron emission for the first time in our sample. In combination with this new data set, subarcsecond resolution 1-18 micron imaging and 7.5-13 micron spectroscopic observations were used to compute the nuclear spectral energy distribution (SED) of each galaxy. We found that the turnover of the torus emission does not occur at wavelengths <31.5 micron, which we interpret as a lower-limit for the wavelength of peak emission. We used CLUMPY torus models to fit the nuclear infrared (IR) SED and infer trends in the physical parameters of the AGN torus for the galaxies in the sample. Including the 31.5 micron nuclear flux in the SED 1) reduces the number of clumpy torus models compatible with the data, and 2) modifies the model output for the outer radial extent of the torus for 10 of the 11 objects. Specifically, six (60%) objects show a decrease in radial extent while four (40%) show an increase. We find torus outer radii ranging from <1pc to 8.4 pc

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arXiv2015

Probing Hypergiant Mass Loss with Adaptive Optics Imaging & Polarimetry in the Infrared: MMT-Pol and LMIRCam observations of IRC +10420 & VY Canis Majoris

We present 2 - 5 micron adaptive optics (AO) imaging and polarimetry of the famous hypergiant stars IRC +10420 and VY Canis Majoris. The imaging polarimetry of IRC +10420 with MMT-Pol at 2.2 micron resolves nebular emission with intrinsic polarization of 30%, with a high surface brightness indicating optically thick scattering. The relatively uniform distribution of this polarized emission both radially and azimuthally around the star confirms previous studies that place the scattering dust largely in the plane of the sky. Using constraints on scattered light consistent with the polarimetry at 2.2 micron, extrapolation to wavelengths in the 3 - 5 micron band predicts a scattered light component significantly below the nebular flux that is observed in our LBT/LMIRCam 3 - 5 micron AO imaging. Under the assumption this excess emission is thermal, we find a color temperature of ~ 500 K is required, well in excess of the emissivity-modified equilibrium temperature for typical astrophysical dust. The nebular features of VY CMa are found to be highly polarized (up to 60%) at 1.3 micron, again with optically thick scattering required to reproduce the observed surface brightness. This star's peculiar nebular feature dubbed the "Southwest Clump" is clearly detected in the 3.1 micron polarimetry as well, which, unlike IRC+10420, is consistent with scattered light alone. The high intrinsic polarizations of both hypergiants' nebulae are compatible with optically thick scattering for typical dust around evolved dusty stars, where the depolarizing effect of multiple scatters is mitigated by the grains' low albedos.

astro-ph.SR↗

arXiv2015

On the difference of torus geometry between hidden and non-hidden broad line active galactic nuclei

We present results from the fitting of infrared (IR) spectral energy distributions of 21 active galactic nuclei (AGN) with clumpy torus models. We compiled high spatial resolution ($\sim 0.3$--$0.7$ arcsec) mid-IR $N$-band spectroscopy, $Q$-band imaging and nuclear near- and mid-IR photometry from the literature. Combining these nuclear near- and mid-IR observations, far-IR photometry and clumpy torus models, enables us to put constraints on the torus properties and geometry. We divide the sample into three types according to the broad line region (BLR) properties; type-1s, type-2s with scattered or hidden broad line region (HBLR) previously observed, and type-2s without any published HBLR signature (NHBLR). Comparing the torus model parameters gives us the first quantitative torus geometrical view for each subgroup. We find that NHBLR AGN have smaller torus opening angles and larger covering factors than those of HBLR AGN. This suggests that the chance to observe scattered (polarized) flux from the BLR in NHBLR could be reduced by the dual effects of (a) less scattering medium due to the reduced scattering volume given the small torus opening angle and (b) the increased torus obscuration between the observer and the scattering region. These effects give a reasonable explanation for the lack of observed HBLR in some type-2 AGN.

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