The HI/OH/Recombination line survey of the inner Milky Way (THOR)
H. Beuther, S. Bihr, M. Rugel, K. Johnston, Y. Wang, F. Walter, A. Brunthaler, A. J. Walsh, J. Ott, J. Stil, Th. Henning, T. Schierhuber, J. Kainulainen, M. Hey… 展开作者
H. Beuther, S. Bihr, M. Rugel, K. Johnston, Y. Wang, F. Walter, A. Brunthaler, A. J. Walsh, J. Ott, J. Stil, Th. Henning, T. Schierhuber, J. Kainulainen, M. Heyer, P. F. Goldsmith, L. D. Anderson, S. N. Longmore, R. S. Klessen, S. C. O. Glover, J. S. Urquhart, R. Plume, S. E. Ragan, N. Schneider, N. M. McClure-Griffiths, K. M. Menten, R. Smith, N. Roy, R. Shanahan, Q. Nguyen-Luong, F. Bigiel
备注：
Accepted for Astronomy & Astrophysics, 23 pages, 17 figures, a high-resolution version can be found at http://www.mpia.de/thor
Context: The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20". However, no comparable high-resolution survey exists at long radio wavelengths around 21cm in line and continuum emission. Methods: Employing the Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21cm line, four OH lines, nineteen Halpha radio recombination lines as well as the continuum emission from 1 to 2GHz in full polarization over a large part of the first Galactic quadrant. Results: Covering Galactic longitudes from 14.5 to 67.4deg and latitudes between +-1.25deg, we image all of these lines and the continuum at ~20" resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Halpha radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page http://www.mpia.de/thor. Conclusions: The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from HII regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing different datasets allows us to address many open questions.
We performed a radio recombination line (RRL) survey to construct a high-mass star-forming region (HMSFR) sample in the Milky Way based on the all-sky Wide-Field Infrared Survey Explorer ($\textit{All-WISE}$) point source catalog. The survey was observed with the Shanghai 65m Tianma radio telescope (TMRT) covering 10 hydrogen RRL transitions ranging from H98$α$ to H113$α$ (corresponding to the rest frequencies of 4.5$-$6.9 GHz) simultaneously. Out of 3348 selected targets, we identified an HMSFR sample consisting of 517 sources traced by RRLs, a large fraction of this sample (486) locate near …
With the $Karl~G.~Jansky$ Very Large Array (VLA) in C-configuration, we observed a large portion of the first Galactic quadrant ($l=14.0-67.4^\circ $ and $\lvert b \rvert \leq 1.25^\circ $) achieving an angular resolution of $\leq 40^{\prime\prime}$. At $L$ Band, the WIDAR correlator at the VLA was set to cover the 21~cm HI line, four OH transitions, a series of H$nα$ radio recombination lines (RRLs; $n=151$ to 186), and eight 128~MHz wide continuum spectral windows (SPWs) simultaneously. The HI emission shows clear filamentary substructures at negative velocities with low velocity crowding. T…
To study the atomic, molecular and ionized emission of Giant Molecular Clouds (GMCs), we have initiated a Large Program with the VLA: 'THOR - The HI, OH, Recombination Line survey of the Milky Way'. We map the 21cm HI line, 4 OH lines, 19 H_alpha recombination lines and the continuum from 1 to 2 GHz of a significant fraction of the Milky Way (l=15-67deg, |b|<1deg) at ~20" resolution. In this paper, we focus on the HI emission from the W43 star-formation complex. Classically, the HI 21cm line is treated as optically thin with column densities calculated under this assumption. This might give re…
Context: OH masers trace diverse physical processes, from the expanding envelopes around evolved stars to star-forming regions or supernovae remnants. Aims: We identify the ground-state OH masers at 18cm wavelength in the area covered by ``The HI/OH/Recombination line survey of the Milky Way (THOR)''. We present a catalogue of all OH maser features and their possible associated environments. Methods: The THOR survey covers longitude and latitude ranges of 14.3<l<66.8 and b<1.25 deg. All OH ground state lines at 1612, 1665, 1667 and 1720MHz have been observed, employing the Very Large Array. Th…
We report the discovery of hydrogen radio recombination line (RRL) emission from two galaxies with star formation rates (SFRs) similar to that of the Milky Way: M51 and NGC628. We use the Green Bank Telescope (GBT) to measure $\sim$15 Hn$α$ recombination transitions simultaneously and average these data to improve our spectral signal-to-noise ratio. We show that our data can be used to estimate the total ionizing photon flux of these two sources, and we derive their SFRs within the GBT beam: $Ψ_{\rm OB} = 3.46$ M$_{\odot}$ yr$^{-1}$ for M51 and $Ψ_{\rm OB} = 0.56$ M$_{\odot}$ yr$^{-1}$ for NGC…
The bandwith, sensitivity and sheer survey speed of the SKA offers unique potential for deep spectroscopic surveys of the Milky Way. Within the frequency bands available to the SKA lie many transitions that trace the ionised, radical and molecular components of the interstellar medium and which will revolutionise our understanding of many physical processes. In this chapter we describe the impact on our understanding of the Milky Way that can be achieved by spectroscopic SKA surveys, including "out of the box" early science with radio recombination lines, Phase 1 surveys of the molecular ISM u…
The hydroxyl radical (OH) is present in the diffuse molecular and partially atomic phases of the interstellar medium (ISM), but its abundance relative to hydrogen is not clear. We aim to evaluate the abundance of OH with respect to molecular hydrogen using OH absorption against cm-continuum sources over the first Galactic quadrant. This OH study is part of the HI/OH/Recombination line survey (THOR). THOR is a Karl G. Jansky Very Large Array large program of atomic, molecular and ionized gas in the range 15°$\leq$l$\leq$67° and |b|$\leq$1°. It is the highest-resolution unbiased OH absorption su…
The relations between star formation and properties of molecular clouds are studied based on a sample of star forming regions in the Galactic Plane. Sources were selected by having radio recombination lines to provide identification of associated molecular clouds and dense clumps. Radio continuum and mid-infrared emission were used to determine star formation rates, while 13CO and submillimeter dust continuum emission were used to obtain masses of molecular and dense gas, respectively. We test whether total molecular gas or dense gas provides the best predictor of star formation rate. We also …
We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 $\text{H}\thinspace \text{II}$ regions and ring nebulae surrounding massive O stars. We revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He$^{+}$ in a homogeneous way, using between 3 and 10 $\text{He}\thinspace \text{I}$ recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slo…
Anderson et al. (2017) identified seventy six candidate supernova remnants (SNRs) using data from The HI, OH, Recombination line survey of the Milky Way (THOR). The spectral index and polarization properties can help distinguish between SNRs and H II regions, which are often confused. We confirm two SNR candidates using spectral index data and morphology. However, we observe that the fractional linear polarization cannot distinguish between SNRs and H II regions, likely due to contamination by diffuse Galactic synchrotron emission. We also comment on the association of SNR candidates with puls…
HII regions made of gas ionized by radiations from young massive stars, are widely distributed in the Milky Way. They are tracers for star formation, and their distributions are correlated with the Galactic spiral structure. Radio recombination lines (RRLs) of hydrogen and other atoms allows for the precisest determination of physical parameters such as temperature and density. However, RRLs at around 1.4 GHz from HII regions are weak and their detections are difficult. As a result, only a limited number of detections have been obtained yet. The 19-beam receiver on board of the Five-hundred-me…
Spectroscopic surveys with the SKA probing the ionized and molecular Milky Way
Nicolaus Copernicus University in Toruń（托伦尼古拉·哥白尼大学）；Macquarie University（麦考瑞大学）；California State University, Chico（奇科加州州立大学）；University of Kent（肯特大学）；University of Bonn（波恩大学）；West Virginia University（西弗吉尼亚大学）；Tata Institute of Fundamental Research（塔塔基础研究所）；University of Leeds（利兹大学）；Royal Observatory Edinburgh（爱丁堡皇家天文台）；Max Planck Institute for Astronomy（马克斯·普朗克天体物理学研究所）
We present very deep spectrophotometry of 14 bright extragalactic HII regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the HIRES echelle spectrograph on the Keck I telescope. We have measured CII recombination lines in 10 of the objects and OII recombination lines in 8 of them. We have determined electron temperatures from line ratios of several ions, specially of low ionization potential ones. We have found a rather tight linear empirical relation between Te([NII]) and Te([OIII]). We have found that OII lines give always larger abundan…
We carried out a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The HI, OH, Recombination line survey of the Milky Way". We observed a significant portion of the Galactic plane in the first quadrant of the Milky Way in the 21cm HI line, 4 OH transitions, 19 radio recombination lines, and continuum from 1 to 2 GHz. In this paper we present a catalog of the continuum sources in the first half of the survey (l=14.0-37.9deg and l=47.1-51.2deg, |b|<1.1deg) at a spatial resolution of 10-25", with a spatially varying noise level of ~0.3-1 mJy/beam. The catalog contains ~4400 sou…
The stellar population of the Milky Way bulge is thoroughly studied, with a plethora of measurements from virtually the full suite of instruments available to astronomers. It is thus perhaps surprising that alongside well-established results lies some substantial uncertainty in its star-formation history. Cosmological models predict the bulge to host the Galaxy's oldest stars for [Fe/H]$\lesssim -1$, and this is demonstrated by RR Lyrae stars and globular cluster observations. There is consensus that bulge stars with [Fe/H]$\lesssim0$ are older than $t \approx10$ Gyr. However, at super-solar m…
We present images of radio recombination lines (RRLs) at wavelengths around 17 cm from the star-forming region W49A to determine the kinematics of ionized gas in the THOR survey (The HI/OH/Recombination line survey of the inner Milky Way) at an angular resolution of 16.8"x13.8". The distribution of ionized gas appears to be affected by feedback processes from the star clusters in W49A. The velocity structure of the RRLs shows a complex behavior with respect to the molecular gas. We find a shell-like distribution of ionized gas as traced by RRL emission surrounding the central cluster of OB sta…
We use Gaia photometry and astrometry to estimate the vertical spatial structure of the Milky Way at the Solar radius, formally accounting for sample incompleteness (the selection function) and parallax measurement uncertainty. Our results show impressive precision demonstrating the power of the Gaia data. However, systematic errors dominate the parameter value uncertainties. We thoroughly test and quantify the impacts of all systematic uncertainties. The vertical tracer density is modelled as a sum of two exponential profiles for the thin and thick discs, together with a spherically symmetric…
The metallicity structure of the Milky Way disk stems from the chemodynamical evolutionary history of the Galaxy. We use the National Radio Astronomy Observatory Karl G. Jansky Very Large Array to observe ~8-10 GHz hydrogen radio recombination line and radio continuum emission toward 82 Galactic HII regions. We use these data to derive the electron temperatures and metallicities for these nebulae. Since collisionally excited lines from metals (e.g., oxygen, nitrogen) are the dominant cooling mechanism in HII regions, the nebular metallicity can be inferred from the electron temperature. Includ…
We report on observations of the hydroxyl radical (OH) within The H{\sc I}, OH Recombination line survey (THOR) pilot region. The region is bounded approximately between Galactic coordinates l=29.2 to 31.5$^\circ$ and b=-1.0 to +1.0$^\circ$ and includes the high-mass star forming region W43. We identify 103 maser sites, including 72 with 1612\,MHz masers, 42 showing masers in either of the main line transitions at 1665 and 1667\,MHz and four showing 1720\,MHz masers. Most maser sites with either main-line or 1720\,MHz emission are associated with star formation, whereas most of the 1612\,MHz m…
Spiral arms shown by different components may not be spatially coincident, which can constrain formation mechanisms of spiral structure in a galaxy. We reassess the spiral arm tangency directions in the Milky Way through identifying the bump features in the longitude plots of survey data for infrared stars, radio recombination lines (RRLs), star formation sites, CO, high density regions in clouds, and HI. The bump peaks are taken as indications for arm tangencies, which are close to the real density peaks near the spiral arm tangency point but often have $\sim$ 1$^\circ$ offset to the interior…
The field of Galactic Archaeology aims to understand the origins and evolution of the stellar populations in the Milky Way, as a way to understand galaxy formation and evolution in general. The GALAH (Galactic Archaeology with HERMES) Survey is an ambitious Australian-led project to explore the Galactic history of star formation, chemical evolution, minor mergers and stellar migration. GALAH is using the HERMES spectrograph, a novel, highly multiplexed, four-channel high-resolution optical spectrograph, to collect high-quality R ~ 28,000 spectra for one million stars in the Milky Way. From the…
We summarize our comprehensive gas surveys of some of the most luminous, deeply embedded (optically obscured) star formation regions in the Milky Way, which are the local cases of massive star clusters and/or associations in the making. Our approach emphasizes multi-scale, multi-resolution imaging in dust and free-free continuum, as well as in molecular- and hydrogen recombination lines, to trace the multiple gas components from 0.1 pc (core scale) all the way up to the scales of the entire giant molecular cloud (GMC), or $\sim 100$ pc. We highlight our results in W49A, the most luminous Galac…
We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the LOw Frequency ARray in the 33 to 57 MHz range. These low frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. To our knowledge this is the first time that foreground Milky Way recombination line absorption has been observed against a bright extragalactic background source. By stacking 48 carbon $α$ lines in the observed frequency range we detect carbon absorption with a signal-to…
Elemental abundance patterns in the Galactic disk constrain theories of the formation and evolution of the Milky Way. HII region abundances are the result of billions of years of chemical evolution. We made radio recombination line and continuum measurements of 21 HII regions located between Galactic azimuth Az = 90-130 degree, a previously unexplored region. We derive the plasma electron temperatures using the line-to-continuum ratios and use them as proxies for the nebular [O/H] abundances, because in thermal equilibrium the abundance of the coolants (O, N, and other heavy elements) in the i…
The distribution of metals in the Galaxy provides important information about galaxy formation and evolution. HII regions are the most luminous objects in the Milky Way at mid-infrared to radio wavelengths and can be seen across the entire Galactic disk. We used the NRAO Green Bank Telescope (GBT) to measure radio recombination line and continuum emission in 81 Galactic HII regions. We calculated LTE electron temperatures using these data. In thermal equilibrium metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. Our HII region…
Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines
Green Bank Observatory（格林班克天文台）；National Radio Astronomy Observatory（国家射电天文台）；Westminster College（威斯敏斯特学院）；Florida Space Institute, University of Central Florida（中佛罗里达大学佛罗里达航天研究所）；Arecibo Observatory（阿雷西博天文台）；Center for Advanced Research in Science and Engineering, University of Puerto Rico（波多黎各大学先进科学与工程研究中心）；West Virginia University（西弗吉尼亚大学）
We analyze the diffuse ionized gas (DIG) in the first Galactic quadrant from l=18deg to 40deg using radio recombination line (RRL) data from the Green Bank Telescope. These data allow us to distinguish DIG emission from HII region emission and thus study the diffuse gas essentially unaffected by confusion from discrete sources. We find that the DIG has two dominant velocity components, one centered around 100km/s associated with the luminous HII region W43, and the other centered around 45km/s not associated with any large HII region. Our analysis suggests that the two velocity components near…
We present robust constraints from the Sloan Digital Sky Survey (SDSS) on the shape and distribution of the dark matter halo within the Milky Way (MW). Using the number density distribution and kinematics of SDSS halo stars, we probe the dark matter distribution to heliocentric distances exceeding 10 kpc and galactocentric distances exceeding 20 kpc. Our analysis utilizes Jeans equations to generate two-dimensional acceleration maps throughout the volume; this approach is thoroughly tested on a cosmologically derived N-body+SPH simulation of a MW-like galaxy. We show that the known acceleratio…
We present new 3 mm observations of the ionized gas toward the nuclear starburst in the nearby (D ~ 3.5 Mpc) galaxy NGC 253. With ALMA, we detect emission from the H40-alpha and He40-alpha lines in the central 200 pc of this galaxy on spatial scales of ~4 pc. The recombination line emission primarily originates from a population of approximately a dozen embedded super star clusters in the early stages of formation. We find that emission from these clusters is characterized by electron temperatures ranging from 7000-10000 K and measure an average singly-ionized helium abundance <Y+> = 0.25 +/- …
We discovered a large population of previously unknown Galactic H II regions by using the Green Bank Telescope to detect their hydrogen radio recombination line emission. Since recombination lines are optically thin at 3 cm wavelength, we can detect H II regions across the entire Galactic disk. Our targets were selected based on spatially coincident 24 micron and 21 cm continuum emission. For the Galactic zone -16 deg < L_gal < 67 deg and abs(B_gal) < 1 deg, we detected 602 discrete recombination line components from 448 lines of sight, 95% of the sample targets, which more than doubles the nu…
We summarize basic observational results on Sagittarius~A* obtained from the radio, infrared and X-ray domain. Infrared observations have revealed that a dusty S-cluster object (DSO/G2) passes by SgrA*, the central super-massive black hole of the Milky Way. It is still expected that this event will give rise to exceptionally intense activity in the entire electromagnetic spectrum. Based on February to September 2014 SINFONI observations. The detection of spatially compact and red-shifted hydrogen recombination line emission allows a us to obtain a new estimate of the orbital parameters of the …
The velocity distribution of stars is a sensitive probe of the gravitational potential of the Galaxy, and hence of its dark matter distribution. In particular, the shape of the dark halo (e.g. spherical, oblate, or prolate) determines velocity correlations, and different halo geometries are expected to result in measurable differences. Here we explore and interpret the correlations in the $(v_R, v_z)$-velocity distribution as a function of position in the Milky Way. We selected a high-quality sample of stars from the Gaia DR2 catalogue and characterised the orientation of the velocity distribu…
As one of the major components of the interstellar medium, the ionized gas in our Milky Way, especially the low-density diffuse component, has not been extensively observed in the radio band. The Galactic Plane Pulsar Snapshot (GPPS) survey covers the sky area within the Galactic latitude of $\pm10^\circ$ around the Galactic plane visible by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and the spectral line data are simultaneously recorded during the pulsar survey observations. With an integration time of 5 minutes for each beam, the GPPS survey project provides the most s…
This is a brief note to comment on some recent papers addressing the Monoceros ring. In our view, nothing new was delivered on the matter: No new evidence or arguments are presented which lead to think that the over-densities in Monoceros must not be due to the flared thick disc of the Milky Way. Again, we restate that extrapolations are easily misleading and that a model of the Galaxy is not the Galaxy. Raising and discussing exciting possibilities is healthy. However, enthusiasm should not overtake and produce strong claims before thoroughly checking simpler and more sensible possibilities w…
The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey of the inner Milky Way (THOR) at $\lesssim$18" resolution covers $\sim 132$ square degrees of the Galactic plane and detects 10387 sources. Similarly, the first data release of the Global View of Star Formation in the Milky Way (GLOSTAR) surveys covers $\sim 16$ square degrees of the Galactic plane from 4-8 GHz at 18" resolution and detects 1575 sources. However, a large fraction of the unresolved discrete sources detected in these radio continuum surveys of the Galactic plane remain unclassified. Here, we study the …
We present polarization and Faraday rotation for the supernova remnants (SNRs) G46.8-0.3, G43.3-0.2, G41.1-0.3, and G39.2-0.3 in L-band (1-2 GHz) radio continuum in The HI/OH/Recombination line (THOR) survey. We detect polarization from G46.8-0.3, G43.3-0.2 and G39.2-0.3 but find upper limits at the 1% level of Stokes I for G41.1-0.3. For G46.8-0.3 and G39.2-0.3 the fractional polarization varies on small scales from 1% to ~6%. G43.3-0.2 is less polarized with fractional polarization <~3%. We find upper limits at the 1% level for the brighter regions in each SNR with no evidence for associated…
There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of HII regions makes identifying such features challenging. SNRs can, however, be separated from HII regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-res…
We present imaging of the recently discovered Hercules Milky Way satellite and its surrounding regions to study its structure, star formation history and to thoroughly search for signs of disruption. We robustly determine the distance, luminosity, size and morphology of Hercules utilizing a bootstrap approach to characterize our uncertainties. We derive a distance to Hercules of $133 \pm 6$ kpc via a comparison to empirical and theoretical isochrones. As previous studies have found, Hercules is very elongated, with $ε=0.67\pm0.03$ and a half light radius of $r_{h} \simeq 230$ pc. Using the col…
The close environment of the central supermassive black hole of our Galaxy is studied thoroughly since decades in order to shed light on the behavior of the central regions of galaxies in general and of active galaxies in particular. The Galactic Center has shown a wealth of structures on different scales with a complicated mixture of early- and late-type stars, ionized and molecular gas, dust and winds. Here we aim at studying the distribution of water ices and hydrocarbons in the central parsec as well as along the line of sight. This study is made possible thanks to L-band spectroscopy. Thi…
The neutral hydrogen 21 cm line is an excellent tracer of the atomic interstellar medium in the cold and the warm phases. Combined 21 cm emission and absorption observations are very useful to study the properties of the gas over a wide range of density and temperature. In this work, we have used 21 cm absorption spectra from recent interferometric surveys, along with the corresponding emission spectra from earlier single dish surveys to study the properties of the atomic gas in the Milky Way. In particular, we focus on a comparison of properties between lines of sight through the gas disk in …
The Milky Way contains thousands of H II region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as H II regions. With only $\sim$2500 confirmed H II regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array (VLA), we explore a sample of H II …
We report the detection of a dispersed Fast Radio Burst (FRB) in archival intermediate-latitude Parkes Radio Telescope data. The burst appears to be of the same physical origin as the four purported extragalactic FRBs reported by Thornton et al. (2013). This burst's arrival time precedes the Thornton et al.~bursts by ten years. We consider that this survey, and many other archival low-latitude (|gb|<30deg) pulsar surveys, have been searched for FRBs but produced fewer detections than the comparatively brief Thornton et al.~search. Such a rate dependence on Galactic position could provide criti…
We present a study of the filamentary structure in the emission from the neutral atomic hydrogen (HI) at 21 cm across velocity channels in the 40'' and 1.5-km/s resolution position-position-velocity cube resulting from the combination of the single-dish and interferometric observations in The HI/OH/Recombination (THOR) line survey. Using the Hessian matrix method in combination with tools from circular statistics, we find that the majority of the filamentary structures in the HI emission are aligned with the Galactic plane. Part of this trend can be assigned to long filamentary structures that…
We simulate the evolution of supernova remnant (SNR) W51C. The simulation shows the existence of a new northeast edge. We present magnetic field structure of the W51 complex (SNR W51C and two HII regions W51A/B) by employing the 11 cm survey data of Effelsberg. This new edge is identified and overlaps with W51A along the line of sight, which gives a new angular diameter of about 37' for the quasi-circular remnant. In addition, we assemble the OH spectral lines (1612/1665/1720 MHz) towards the complex by employing the newly released THOR (The HI OH Recombination line survey of Milky Way) data. …
The Multi-phase HI of the Milky Way and Nearby Galaxies
Laboratoire de Physique de l’Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Observatoire de Paris（巴黎高等师范学院物理实验室，ENS，PSL大学，CNRS，索邦大学，巴黎第七大学，索邦巴黎城，巴黎天文台）；Macquarie University（麦考瑞大学）；Indian Institute of Technology Indore（印度理工学院印多尔分校）；Indian Institute of Astrophysics（印度天体物理研究所）；Stanford University（斯坦福大学）；University of Tasmania（塔斯马尼亚大学）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，CEA，CNRS，AIM）；University of British Columbia（不列颠哥伦比亚大学）；National Research Council Canada（加拿大国家研究委员会）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究所）；University of Science and Technology（科学技术大学）；The Australian National University（澳大利亚国立大学）；Space Telescope Science Institute（太空望远镜科学研究所）；University of Wisconsin–Madison（威斯康星大学麦迪逊分校）；Indiana University（印第安纳大学）；Columbia University（哥伦比亚大学）；Indian Institute of Science（印度科学学院）；California State University, Chico（加州州立大学奇科分校）
We use the Green Bank Telescope to search for $^3He^+$ emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis the light elements $^2H$, $^3He$, $^4He$, and $^7Li$ were produced in significant amounts and these abundances have since been modified primarily by stars. Observations of $^3He^+$ in H II regions located throughout the Milky Way disk reveal very little variation in the $^3He/H$ abundance ratio -- the "$^3He$ Plateau" -- indicating that the net effect of $^3He$ production in stars is negligible…
In this work, we investigate the contribution of dust scattering to the diffuse H-alpha emission observed in nearby galaxies. As initial conditions for the spatial distribution of HII regions, gas, and dust, we take three Milky Way-like galaxies from state-of-the-art cosmological hydrodynamical simulations that implement different prescriptions for star formation, feedback, and chemical enrichment. Radiative transfer has been solved a posteriori, using the publicly-available Monte Carlo code Sunrise to take into account dust absorption and scattering of the H-alpha photons, originating exclusi…
Radio continuum surveys of the Galactic plane can find and characterize HII regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at high angular resolution (<25") at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21cm. We observed a large fraction of the Galactic plane in the first quadrant of the Milky Way (l=14.0-67.4deg and |b| < 1.25deg) with the Karl G. Jansky Very Large Array (VLA) in the C-configuration covering…
