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Galaxies, Volume 6, Issue 3 (September 2018)

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Open AccessArticle Spectroscopy of Planetary Nebulae with Herschel: A Beginners Guide
Galaxies 2018, 6(3), 73; https://doi.org/10.3390/galaxies6030073 (registering DOI)
Received: 28 May 2018 / Revised: 11 July 2018 / Accepted: 13 July 2018 / Published: 17 July 2018
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Abstract
A brief overview of the Herschel Space Telescope PACS and SPIRE spectrographs is given, pointing out aspects of working with the data products that should be considered by anyone using them. Some preliminary results of Planetary Nebulae (PNe) taken from the Herschel Planetary
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A brief overview of the Herschel Space Telescope PACS and SPIRE spectrographs is given, pointing out aspects of working with the data products that should be considered by anyone using them. Some preliminary results of Planetary Nebulae (PNe) taken from the Herschel Planetary Nebula Survey (HerPlaNs) programme are then used to demonstrate what can be done with spectroscopy observations made with PACS. The take-home message is that using the full 3D information that PACS spectroscopy observations give will greatly aid in the interpretation of PNe. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
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Open AccessArticle The Collisional Atomic Processes of Rydberg Hydrogen and Helium Atoms: Astrophysical Relevance
Received: 17 June 2018 / Revised: 6 July 2018 / Accepted: 12 July 2018 / Published: 16 July 2018
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Abstract
Elementary processes in astrophysical environments traditionally attract researchers’ attention. We present the data needed for the inclusion of the specific atomic collisional processes in the investigation of the optical and kinetic properties of weakly ionized stellar atmosphere layers. The first type of processes
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Elementary processes in astrophysical environments traditionally attract researchers’ attention. We present the data needed for the inclusion of the specific atomic collisional processes in the investigation of the optical and kinetic properties of weakly ionized stellar atmosphere layers. The first type of processes are collisional ionisation (chemi-ionization) processes, and the second ones are excitation and de-excitation (i.e., (n-n)-mixing processes). We give the rate coefficients of the aforementioned processes for the conditions that exist in the solar photosphere, the atmosphere of DB white dwarfs, M-type red dwarfs, etc. Full article
(This article belongs to the Special Issue Atomic and Molecular Data Needs for Astronomy and Astrophysics)
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Open AccessFeature PaperArticle Photoelectric Polarimetry and the Gas Pixel Detector Yesterday, Today and Tomorrow
Received: 28 May 2018 / Revised: 10 July 2018 / Accepted: 10 July 2018 / Published: 16 July 2018
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Abstract
Since the very beginning of X-ray Astronomy, polarimetry has been suggested as a tool of diagnostics, of great potentiality. While almost all measurements of X-rays were based on detectors using the photoelectric effect, the first attempt to perform polarimetry were based on Compton
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Since the very beginning of X-ray Astronomy, polarimetry has been suggested as a tool of diagnostics, of great potentiality. While almost all measurements of X-rays were based on detectors using the photoelectric effect, the first attempt to perform polarimetry were based on Compton scattering and Bragg diffraction. The use of photoelectric effect also for polarimetry has been hypothesized and attempted for many years but never accomplished. Only 40 years from the start of X-ray astronomy, the Gas Pixel Detector (GPD) was developed, compatible with an X-ray optics, and capable of measuring energy, time, position and polarization simultaneously. Only after 20 more years, the Imaging X-ray Polarimetry Explorer, based on the GPD detectors, will be launched. I present the story of the development of photoelectric polarimetry that arrived to the Gas Pixel Detector, and discuss the possible future evolutions. Full article
(This article belongs to the Special Issue The Bright Future of Astronomical X-ray Polarimetry)
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Open AccessArticle A Simple Model for Explaining Galaxy Rotation Curves
Received: 7 June 2018 / Revised: 2 July 2018 / Accepted: 4 July 2018 / Published: 13 July 2018
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Abstract
A new simple expression for the circular velocity of spiral galaxies is proposed and tested against HI Nearby Galaxy Survey (THINGS) data set. Its accuracy is compared with the one coming from MOND. Full article
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Open AccessFeature PaperReview Hard X-ray and Soft Gamma Ray Polarimetry with CdTe/CZT Spectro-Imager
Received: 26 May 2018 / Revised: 2 July 2018 / Accepted: 2 July 2018 / Published: 8 July 2018
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Abstract
CdTe/CZT based spectroscopic two-dimensional (2D)/three-dimensional (3D) imagers when operated in the Compton regime can work as high performance scattering polarimeters, for high-energy astrophysics. Polarimetry in high-energy astrophysics has been little explored. To date, X- and γ-ray source emissions have been studied almost exclusively
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CdTe/CZT based spectroscopic two-dimensional (2D)/three-dimensional (3D) imagers when operated in the Compton regime can work as high performance scattering polarimeters, for high-energy astrophysics. Polarimetry in high-energy astrophysics has been little explored. To date, X- and γ-ray source emissions have been studied almost exclusively through spectral, imaging, and timing analysis. Polarization measurements provide two additional observational parameters: the polarization angle and the level of linear polarization. These additional parameters should allow for a better discrimination between the physical mechanisms of different emission models characterizing a celestial object. Therefore, polarimetry will play a strategic role in new instrumentations for future high-energy astronomy missions. 2D and 3D CZT/CdTe spectroscopic imagers provided with coincidence readout logic can efficiently handle scattering events to perform simultaneously polarization, spectroscopy, imaging, and timing measurements. Herein, we describe the results obtained, both experimentally and by MC simulations, with CdTe/CZT pixel detector prototypes in high-energy polarimetry. We give an overview on the achievable polarimetric performance with spectroscopic imagers and on how these performances are affected by detector configuration parameters. Finally, we address the perspective of scattering polarimetry opened by the recent implementation of new high energy focusing optics, as broadband Laue lens, in next generation of hard X- and soft γ-ray astronomy instrumentation. The unprecedented sensitivity achievable by these telescopes will definitely open the window of polarimetry in this high-energy range. Full article
(This article belongs to the Special Issue The Bright Future of Astronomical X-ray Polarimetry)
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Open AccessFeature PaperArticle Fast γ-ray Variability: A Common Feature and Powerful Probe for Jetted AGNs
Received: 17 May 2018 / Revised: 26 June 2018 / Accepted: 28 June 2018 / Published: 3 July 2018
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Abstract
Among the highly dynamical non-thermal universe, flashes of γ-ray photons from jets in active galactic nuclei (AGNs) are always attractive. Not only are they extraordinary observational phenomena, but they also become powerful probes of the jets. Benefiting from the current advanced γ
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Among the highly dynamical non-thermal universe, flashes of γ-ray photons from jets in active galactic nuclei (AGNs) are always attractive. Not only are they extraordinary observational phenomena, but they also become powerful probes of the jets. Benefiting from the current advanced γ-ray observational facilities, especially the Large Area Telescope aboard the Fermi space γ-ray observatory and Imaging Atmospheric Cherenkov Telescope arrays, fast (intraday) γ-ray variability has become a common feature detected in various subtypes of jetted AGNs. Moreover, extreme events with variability timescales down to a few minutes have been occasionally detected, which put a severe constraint on the classical jet model. Herein, recent studies on the detection of fast γ-ray variability in jetted AGNs are summarized, and corresponding implications are discussed. Scenarios proposed to explain the minute-scale γ-ray variability as well as future observational opportunities are also briefly summarized. Full article
(This article belongs to the Special Issue Microvariability of Blazars)
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Open AccessArticle On the Dwarf Galaxy Rotation Curve Diversity Problem
Received: 24 May 2018 / Revised: 25 June 2018 / Accepted: 25 June 2018 / Published: 29 June 2018
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Abstract
In this paper, we show how baryonic physics can solve the problem of the striking diversity in dwarf galaxy rotation curves shapes. To this aim, we compare the distribution of galaxies of the SPARC sample, in the plane V2kpc-V
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In this paper, we show how baryonic physics can solve the problem of the striking diversity in dwarf galaxy rotation curves shapes. To this aim, we compare the distribution of galaxies of the SPARC sample, in the plane V2kpc-VRlast (V2kpc being the galaxy rotation velocity at 2 kpc, and VRlast being the outermost one), with that of galaxies that we simulated, taking account of baryonic effects. The scatter in the rotation curves in the V2kpc-VRlast plane, as well as the trend of the SPARC sample, and our simulated galaxy distribution is in good agreement. The solution of the “diversity” problem lies in the ability of the baryonic process to produce non-self-similar haloes, contrary to DM-only simulations. We show also that baryonic effects can reproduce the rotation curves of galaxies such as IC2574, which are characterized by a slow rise in radius. A solution to the diversity problem can be obtained taking the baryon physics effects appropriately into account. Full article
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Open AccessArticle On the Origin of Morphological Structures of Planetary Nebulae
Received: 24 May 2018 / Revised: 17 June 2018 / Accepted: 22 June 2018 / Published: 26 June 2018
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Abstract
We suggest that most of the mass in planetary nebulae (PNe) resides in the equatorial region and the spherical envelope and the optically bright lobes of PNe are in fact low-density cavities cleared out by fast outflows and photoionized by UV photons leaked
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We suggest that most of the mass in planetary nebulae (PNe) resides in the equatorial region and the spherical envelope and the optically bright lobes of PNe are in fact low-density cavities cleared out by fast outflows and photoionized by UV photons leaked from the torus. The nature of multi-polar PNe is discussed under this framework. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
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