Joe Michail

Joe Michail

Astronomy Ph.D. student at Northwestern University studying the radio variability of the nearest supermassive blackhole Sgr A*.

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APOD: Our Galaxy’s Magnetic Center (June 19, 2019)

The magnetic field of the Circumnuclear Disk (CND) observed by HAWC+ in the central 5 parsecs of the Milky Way. The background is a combination of far- and near-IR views of this dusty region as seen by SOFIA and Hubble.

publications

HAWC+, the Far-Infrared Camera and Polarimeter for SOFIA

Published in Journal of Astronomical Instrumentation, 2018

Abstract: High-resolution Airborne Wide-band Camera (HAWC+) is the facility far-infrared imager and polarimeter for SOFIA, NASA’s Stratospheric Observatory for Infrared Astronomy. It is designed to cover the portion of the infrared spectrum that is completely inaccessible to ground-based observatories and which is essential for studies of astronomical sources with temperatures between tens and hundreds of degrees Kelvin. Its ability to make polarimetric measurements of aligned dust grains provides a unique new capability for studying interstellar magnetic fields. HAWC+ began commissioning flights in April 2016 and was accepted as a facility instrument in early 2018. In this paper, we describe the instrument, its operational procedures, and its performance on the observatory.

Recommended citation: Harper et al. (2018). "HAWC+, the Far-Infrared Camera and Polarimeter for SOFIA." Journal of Astronomical Instrumentation https://ui.adsabs.harvard.edu/abs/2018JAI.....740008H/abstract

Evidence of a Decreasing Orbital Period for the Prototype Hot Jupiter System HD 189733: Implications for the Angular Momentum Evolution of Hot Jupiter Systems

Published in Research Notes of the American Astronomical Society, 2018

Download paper here

Recommended citation: Dowling Jones et al. (2018). "Evidence of a Decreasing Orbital Period for the Prototype Hot Jupiter System HD 189733: Implications for the Angular Momentum Evolution of Hot Jupiter Systems." RNAAS https://iopscience.iop.org/article/10.3847/2515-5172/aab437

SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic Wind

Published in The Astrophysical Journal Letters, 2019

Abstract: We present far-infrared polarimetry observations of M82 at 53 and 154 μm and NGC 253 at 89 μm, which were taken with High-resolution Airborne Wideband Camera-plus (HAWC+) in polarimetry mode on the Stratospheric Observatory for Infrared Astronomy. The polarization of M82 at 53 μm clearly shows a magnetic field geometry perpendicular to the disk in the hot dust emission. For M82 the polarization at 154 μm shows a combination of field geometry perpendicular to the disk in the nuclear region, but closer to parallel to the disk away from the nucleus. The fractional polarization at 53 μm (154 μm) ranges from 7% (3%) off nucleus to 0.5% (0.3%) near the nucleus. A simple interpretation of the observations of M82 invokes a massive polar outflow, dragging the field along, from a region ∼700 pc in diameter that has entrained some of the gas and dust, creating a vertical field geometry seen mostly in the hotter (53 μm) dust emission. This outflow sits within a larger disk with a more typical planar geometry that more strongly contributes to the cooler (154 μm) dust emission. For NGC 253, the polarization at 89 μm is dominated by a planar geometry in the tilted disk, with weak indication of a vertical geometry above and below the plane from the nucleus. The polarization observations of NGC 253 at 53 μm were of a insufficient signal-to-noise ratio for a detailed analysis.

Recommended citation: Jones et al. (2019). "SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic Wind" ApJL https://ui.adsabs.harvard.edu/abs/2019ApJ...870L...9J/abstract

HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1

Published in The Astrophysical Journal, 2019

Abstract: We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 μm at angular resolutions of 5″, 8″, 14″, and 19″ for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the “hourglass” configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin-Neugebauer/Kleinman-Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.

Recommended citation: Chuss et al. (2019). "HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1" ApJ https://ui.adsabs.harvard.edu/abs/2019ApJ...872..187C/abstract

The Far-infrared Polarization Spectrum of ρ Ophiuchi A from HAWC+/SOFIA Observations

Published in The Astrophysical Journal, 2019

Abstract: We report on polarimetric maps made with HAWC+/SOFIA toward ρ Oph A, the densest portion of the ρ Ophiuchi molecular complex. We employed HAWC+ bands C (89 μm) and D (154 μm). The slope of the polarization spectrum was investigated by defining the quantity R_DC=p_D/p_C, where p_C and p_D represent polarization degrees in bands C and D, respectively. We find a clear correlation between R_DC and the molecular hydrogen column density across the cloud. A positive slope (R_DC > 1) dominates the lower-density and well-illuminated portions of the cloud, which are heated by the high-mass star Oph S1, whereas a transition to a negative slope (R_DC < 1) is observed toward the denser and less evenly illuminated cloud core. We interpret the trends as due to a combination of (1) warm grains at the cloud outskirts, which are efficiently aligned by the abundant exposure to radiation from Oph S1, as proposed in the radiative torques theory; and (2) cold grains deep in the cloud core, which are poorly aligned owing to shielding from external radiation. To assess this interpretation, we developed a very simple toy model using a spherically symmetric cloud core based on Herschel data and verified that the predicted variation of R_DC is consistent with the observations. This result introduces a new method that can be used to probe the grain alignment efficiency in molecular clouds, based on the analysis of trends in the far-infrared polarization spectrum.

Recommended citation: Santos et al. (2019). "The Far-infrared Polarization Spectrum of ρ Ophiuchi A from HAWC+/SOFIA Observations" ApJ https://ui.adsabs.harvard.edu/#abs/2019ApJ...882..113S/abstract

SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068

Published in The Astrophysical Journal, 2020

Abstract: We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 μm polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy’s inner-bar and active galactic nucleus (AGN). We find correlations between the 89 μm magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of 16.9 +/- 2.8 deg and a disk inclination of 48° +/- 2°. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk (<1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar.Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak ∼3″─6″ NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized (<1%) at both 53 and 89 μm.

Recommended citation: Lopez-Rodriguez et al. (2020). "SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068" ApJ https://ui.adsabs.harvard.edu/abs/2020ApJ...888...66L/abstract

Maps of Magnetic Field Strength in the OMC-1 using HAWC+ FIR Polarimetric data

Published in arXiv, 2020

Abstract: Far-infrared (FIR) dust polarimetry enables the study of interstellar magnetic fields via tracing of the polarized emission from dust grains that are partially aligned with the direction of the field. The advent of high quality polarimetric data has permitted the use of statistical methods to extract both the direction and magnitude of the magnetic field. This work presents an effort to produce maps (integrated along the line of sight) of the magnetic field strength in both the line-of-sight (LOS) direction and in the plane-of-sky (POS) in the Orion Molecular Cloud (OMC-1) using all four HAWC+ polarimetry bands (53, 89, 154 and 214 μm ). Using the statistics of the polarization data (angles and fractions) along with previously-reported Zeeman measurements, information about the three-dimensional magnetic field configuration was inferred over the OMC-1 region. POS magnetic field strengths of up to 2 mG were determined in OMC-1. The strongest fields were observed near the BN/KL object, while the OMC-1 bar shows strengths of up to few hundreds of μG. The LOS magnetic field has been determined to have comparable strengths to the POS components but it is differently distributed across the cloud. These estimates of the magnetic field components were used to produce more reliable maps of the mass-to-magnetic flux ratio ( M/Φ ) – a proxy for probing the conditions for star formation in molecular clouds – and determine regions of sub- and super-criticality in OMC-1. Such maps can provide invaluable input and comparison to MHD simulations of star formation processes in filamentary structures of molecular clouds.

Recommended citation: Guerra et al. (2020). "Maps of Magnetic Field Strength in the OMC-1 using HAWC+ FIR Polarimetric data" arXiV:2007.04923 (Submitted to ApJ) https://ui.adsabs.harvard.edu/#abs/2020arXiv200704923G/abstract

Far-Infrared Polarization Spectrum of the OMC-1 Star-Forming Region

Published in arXiv, 2020

Abstract: We analyze the wavelength-dependence of the far-infrared degree of polarization toward the OMC-1 star forming region using observations from HAWC+/SOFIA at 53, 89, 154, and 214 μ m. We find that the shape of the far-infrared polarization spectrum is variable across the cloud and that there is evidence of a correlation between the slope of the polarization spectrum and the average line-of-sight temperature. The slope of the polarization spectrum tends to be negative (falling towards longer wavelengths) in cooler regions and positive or flat in warmer regions. This is very similar to what was discovered in ρ Oph A via SOFIA polarimetry at 89 and 154 μ m. Like the authors of this earlier work, we argue that the most natural explanation for our falling spectra is line-of-sight superposition of differing grain populations, with polarized emission from the warmer regions and less-polarized emission from the cooler ones. In contrast with the earlier work on ρ Oph A, we do not find a clear correlation of polarization spectrum slope with column density. This suggests that falling spectra are attributable to variations in grain alignment efficiency in a heterogeneous cloud consistent with Radiative Alignment Torques theory. Alternative explanations in which variations in grain alignment efficiency are caused by varying gas density rather than by varying radiation intensity are disfavored.

Recommended citation: Michail et al. (2020). "Far-Infrared Polarization Spectrum of the OMC-1 Star-Forming Region" arXiv:2008.00310 (Submitted to ApJ) https://ui.adsabs.harvard.edu/#abs/2020arXiv200800310M/abstract

Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study

Published in arXiv, 2020

Abstract: We study the environment of Sgr A-star using spectral and continuum observations with the ALMA and VLA. Our analysis of sub-arcsecond H30alpha, H39alpha, H52alpha and H56alpha line emission towards Sgr A-star confirm the recently published broad peak ~500 km/s spectrum toward Sgr A-star. We also detect emission at more extreme radial velocities peaking near -2500 and 4000 km/s, within 0.2 arcsec. We then present broad band radio continuum images at multiple frequencies on scales from arcseconds to arcminutes. A number of elongated continuum structures lie parallel to the Galactic plane, extending from ~0.4 arcsec to 10 arcmin. We note a nonthermal elongated structure on an arcminute scale emanating from Sgr A-star at low frequencies between 1 and 1.4 GHz where thermal emission from the mini-spiral is depressed by optical depth effects. The position angle of this elongated structure and the sense of motion of ionized features with respect to Sgr A-star suggest a symmetric, collimated jet emerging from Sgr A-star with an opening angle of ~30 deg and a position angle of ~60 deg punching through the medium before accelerating a significant fraction of the orbiting ionized gas to high velocities. The jet with estimated mass flow rate ~1.4x10^{-5} solar mass/yr emerges perpendicular to the equatorial plane of the accretion flow near the event horizon of Sgr A-star and runs along the Galactic plane. To explain a number of east-west features near Sgr A-star, we also consider the possibility of an outflow component with a wider-angle launched from the accretion flow at larger radii.

Recommended citation: Yusef-Zadeh et al. (2020). "Evidence for a jet and outflow from Sgr A*: a continuum and spectral line study" arXiv:2008.04317 (Submitted to MNRAS) https://ui.adsabs.harvard.edu/#abs/2020arXiv200804317Y/abstract

Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL

Published in arXiv, 2020

Abstract: Complex Organic Molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of T_d >= 100K . However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to centrifugal stress induced by radiative torques (RATs) is proposed by Hoang & Tram (2020) that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region Orion BN/KL. We compare the abundance of COMs computed using the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the detection of COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submm decreases with increasing the grain temperature for T_d >= 71K . This is consistent with the theoretical prediction using the Radiative Torque (RAT) alignment theory and Radiative Torque Disruption (RATD) mechanism. Such an anti-correlation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.

Recommended citation: Tram et al. (2020). "Observational evidence for rotational desorption of Complex Molecules by radiative torques from Orion BN/KL" arXiv:2008.05537 (Submitted to ApJ) https://ui.adsabs.harvard.edu/#abs/2020arXiv200805537T/abstract

HAWC+ Far-Infrared Observations of the Magnetic Field Geometry in M51 and NGC 851

Published in The Astrophysical Journal, 2020

Abstract: SOFIA HAWC+ polarimetry at 154 μm is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 MJy/sr are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891 the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.

Recommended citation: Jones et al. (2020). "HAWC+ Far-Infrared Observations of the Magnetic Field Geometry in M51 and NGC 891" arXiv:2007.07897 (Accepted to ApJ) https://ui.adsabs.harvard.edu/#abs/2020arXiv200807897J/abstract

talks

HAWC+/SOFIA Instrumental Polarization Calibration

Published:

HAWC+ is a new far-infrared polarimeter for the NASA/DLR SOFIA (Stratospheric Observatory for Infrared Astronomy) telescope. HAWC+ has the capability to measure the polarization of astronomical sources with unprecedented sensitivity and angular resolution in four bands from 50-250 microns. Using data obtained during commissioning flights, we implemented a calibration strategy that separates the astronomical polarization signal from the induced instrumental polarization. The result of this analysis is a map of the instrumental polarization as a function of position in the instrument’s focal plane in each band. The results show consistency between bands, as well as with other methods used to determine preliminary instrumental polarization values.

HAWC+/SOFIA Observations of OMC-1: Spectral Energy Distributions

Published:

The Orion Molecular Cloud-1, OMC-1, has been well-studied as an example of a region that is actively forming massive stars. The High-resolution Airborne Wideband Camera+, HAWC+, on the SOFIA telescope has observed this region polarimetrically and photometrically at wavelengths of 53, 89, 154, and 214 microns. These new data will help determine the role of magnetic fields in the dynamics of the region. Combining the photometry from HAWC+ with other far-infrared, submillimeter and radio maps, we produce new spectral energy distributions across a ~5-arcminute region from ~50 microns to 3.5 cm. We fit the intensity with a single-temperature modified blackbody and a free-free component that contributes at long wavelengths. We present the resulting maps of temperature, column density and dust emissivity index at 19-arcsecond resolution.

Far-Infrared and Submillimeter Polarization Spectrum of the OMC-1 Region

Published:

We compile the most complete far-infrared multiwavelength polarization spectrum to date of the high-mass star-forming region, OMC-1, using data from the High-resolution Airborne Wideband Camera+ (HAWC+) polarimeter on the NASA / German Aerospace Center (DLR) Stratospheric Observatory for Infrared Astronomy (SOFIA). These observations are combined with ground-based polarimetry data at 350- and 450-micron from the SHARP instrument on the now-decommissioned Caltech Submillimeter Observatory (CSO) and 850-micron data from the POL-2 instrument on the James Clerk Maxwell Telescope (JCMT). Our analysis finds a nearly flat polarization spectrum in the far-infrared, characteristic of a single polarized dust species. We find evidence for a rising polarization spectrum in the high column density molecular gas and a flat spectrum in the low column density HII region. We also use previously published spectral energy distribution parameters of this region to determine possible correlations with polarization spectral shape.

teaching

Teaching experience 1

Undergraduate course, University 1, Department, 2014

This is a description of a teaching experience. You can use markdown like any other post.