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Register a new userSOFIA Community Science I: HAWC+ Polarimetry of 30 Doradus
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The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a Boeing 747SP aircraft modified to accommodate a 2.7 meter gyro-stabilized telescope, which is mainly focused to studying the Universe at infrared wavelengths. As part of the Strategic Directors Discretionary Time (S-DDT) program, SOFIA performs observations of relevant science cases and immediately offers science-ready data products to the astronomical community. We present the first data release of the S-DDT program on far-infrared imaging polarimetric observations of 30 Doradus using the High-resolution Airborne Wideband Camera-Plus (HAWC+) at 53, 89, 154, and 214 micron. We present the status and quality of the observations, an overview of the SOFIA data products, and examples of working with HAWC+ polarimetric data that will enhance the scientific analysis of this, and future, data sets. These observations illustrate the potential influence of magnetic fields and turbulence in a star-forming region within the Tarantula Nebula.
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We present a study of the relative orientation between the magnetic field and elongated cloud structures for the $rho$ Oph A and $rho$ Oph E regions in L1688 in the Ophiuchus molecular cloud. Combining inferred magnetic field orientation from HAWC+ 154 $mu$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+.
Located in the Large Magellanic cloud and mostly irradiated by a massive-star cluster R$,$136, 30 Doradus is an ideal target to test the leading theory of the grain alignment and rotational disruption by RAdiative Torques (RATs). Here, we use publicly available polarized thermal dust emission observations of 30 Doradus at 89, 154, and 214$,mu$m using SOFIA/HAWC+. We analyse the variation of the dust polarization degree ($p$) with the total emission intensity ($I$), the dust temperature ($T_{rm d}$), and the gas column density ($N_{rm H}$) constructed from ${it Herschel}$ data. The 30 Doradus complex is divided into two main regions relative to R$,$136, namely North and South. In the North, we find that the polarization degree first decreases and then increases before decreasing again when the dust temperature increases toward the irradiating cluster R$,$136. The first depolarization likely arises from the decrease of grain alignment efficiency toward the dense medium due to the attenuation of the interstellar radiation field and the increase of the gas density. The second trend (the increase of $p$ with $T_{rm d}$) is consistent with the RAT alignment theory. The final trend (the decrease of $p$ with $T_{rm d}$) is consistent with the RAT alignment theory only when the grain rotational disruption by RATs is taken into account. In the South, we find that the polarization degree is nearly independent of the dust temperature, while the grain alignment efficiency is higher around the peak of the gas column density and decreases toward the radiation source. The latter feature is also consistent with the prediction of the rotational disruption by RATs.
We present the first fully calibrated H$_2$, 1-0 S(1) image of the entire 30 Doradus nebula. The observations were conducted using the NOAO Extremely Wide-Field Infrared Imager on the CTIO 4-meter Blanco Telescope. Together with a NEWFIRM Br$gamma$ image of 30 Doradus, our data reveal the morphologies of the warm molecular gas and ionized gas in 30 Doradus. The brightest H$_2$-emitting area, which extends from the northeast to the southwest of R136, is a photodissociation region viewed face-on, while many clumps and pillar features located at the outer shells of 30 Doradus are photodissociation regions viewed edge-on. Based on the morphologies of H$_2$, Br$gamma$, $^{12}$CO, and 8$mu$m emission, the H$_2$ to Br$gamma$ line ratio and Cloudy models, we find that the H$_2$ emission is formed inside the photodissociation regions of 30 Doradus, 2 - 3 pc to the ionization front of the HII region, in a relatively low-density environment $<$ 10$^4$ cm$^{-3}$. Comparisons with Br$gamma$, 8$mu$m, and CO emission indicate that H$_2$ emission is due to fluorescence, and provide no evidence for shock excited emission of this line.
Using observations obtained with the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope (HST), we have studied the properties of the stellar populations in the central regions of 30 Dor, in the Large Magellanic Cloud. The observations clearly reveal the presence of considerable differential extinction across the field. We characterise and quantify this effect using young massive main sequence stars to derive a statistical reddening correction for most objects in the field. We then search for pre-main sequence (PMS) stars by looking for objects with a strong (> 4 sigma) Halpha excess emission and find about 1150 of them over the entire field. Comparison of their location in the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for the appropriate metallicity reveals that about one third of these objects are younger than ~4Myr, compatible with the age of the massive stars in the central ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median age of ~12Myr. This indicates that star formation has proceeded over an extended period of time, although we cannot discriminate between an extended episode and a series of short and frequent bursts that are not resolved in time. While the younger PMS population preferentially occupies the central regions of the cluster, older PMS objects are more uniformly distributed across the field and are remarkably few at the very centre of the cluster. We attribute this latter effect to photoevaporation of the older circumstellar discs caused by the massive ionising members of R136.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7-m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 micron to 1.6 mm, SOFIA operates above 99.8 % of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center DLR, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This article provides an overview of the observatory and its early performance.
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