adsabs/FOCAL huggingface dataset:
Molecular line ratio diagnostics are often used to investigate the physics and chemistry of the ISM in all of these environments. For example, as the gas chemistry located in the central, nuclear regions of galaxies is believed to be dominated by X-rays produced by the AGN, in so-called X-ray dominated regions (XDRs), the molecular content of the ISM surrounding such nuclei will greatly differ from that in starburst regions (Usero et al. 2004; García-Burillo et al. 2010). Hence, line ratios of specific molecules have been proposed as indicators of certain energetic or physical processes, for example HCN/HCO+ as a tracer of AGNs (Loenen et al. 2007), HCN/HNC as a mechanical heating tracer (Hacar et al. 2020), and HCN/CO as a density tracer (Leroy et al. 2017). In particular, the “submillimeter-HCN diagram”, first proposed in Izumi et al. (2013) and later expanded upon in Izumi et al. (2016), is a very notable example of the use of molecular line ratios as a probe of AGN-galaxies; this diagram makes use of two line ratios, HCN(4−3)/HCO+(4−3) and HCN(4−3)/CS(7−6), where all of the molecules involved are considered tracers of dense gas. Izumi et al. (2016) observed a clear trend that AGNs, including the Seyfert composite galaxy NGC 1068, tend to show higher HCN/HCO+ and/or HCN/CS than in SB galaxies as long as the observations were at high enough spatial resolutions to separate energetically discrete regions. Izumi et al. (2016) propose a scenario where it is the high temperature that is responsible for the HCN enhancement, whereby neutral-neutral reactions with high reaction barriers are enhanced (Harada et al. 2010), thus leading to the possible enhancement of HCN and the depletion of HCO+ via newly available formation and destruction paths, respectively. However, while of course higher gas temperatures are expected in AGN-dominated regions, these are not unique to these environments, as starburst regions and/or regions where outflows dominate can also harbour high enough temperatures for such enhancement to occur. Additionally, the higher temperatures could increase HCN excitation, relative to HCO+ and CS, without necessarily changing their relative abundances (Imanishi et al. 2018a). Finally, infrared radiative pumping is also a possible explanation of the HCN intensity enhancement relative to HCO+ and CS. Infrared pumping is a result of the emission of 14 μm infrared photons due to the presence of hot dust around AGN. These photons vibrationally excite HCN to the ν2 = 1 state. Upon de-exciting from this state back to the vibrational ground state, ν = 0, the HCN line intensities are thus pumped to higher fluxes (Imanishi et al. 2018a). However, we note that it is also not unlikely that the 12 μm infrared photons can similarly vibrationally excite HCO+, thus nullifying the extent of this effect (Imanishi et al. 2016).
Citation: Izumi et al. (2016)
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Citation: Izumi et al. (2016)
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Citation: Izumi et al. (2016)
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Owing to their brightness at rest-frame FIR wavelengths, the ionized and neutral species of Carbon, Nitrogen, and Oxygen are powerful diagnostic lines for tracing the ISM of nearby and distant galaxies. When combined with photodissociation region (PDR) models (Tielens & Hollenbach 1985), measurement of the emission from different lines provide a means to constrain quantities such as the ionization rate and metallicity of the ISM of galaxies. Multilevel FIR transition lines have now been widely surveyed in local galaxies, originally by ISO (e.g. Luhman et al. 1998; Malhotra et al. 2001) and more recently using the PACS spectrometer (Poglitsch et al. 2010) on the ESA Herschel Space Observatory (Pilbratt et al. 2010). The [C ii]158 μm line is typically the brightest in star-forming galaxies, arising from ionized, and even neutral gas where it is the main coolant (Wolfire et al. 2003). Another commonly observed FIR line tracer of the ionized ISM is [N ii]122 μm. It has the advantage that it can be found associated with lower excitation gas, close to that observed in our own Galaxy (e.g. Goldsmith et al. 2015; Herrera-Camus et al. 2016). Another major coolant of the ISM is [O i]63 μm (Wolfire et al. 2003). Owing to its high excitation temperature and critical density, it can dominate the cooling in regions of starburst activity (Kaufman et al. 1999; Kaufman, Wolfire & Hollenbach 2006; Brauher, Dale & Helou 2008; Croxall et al. 2012; Narayanan & Krumholz 2017). When combined with measurements of the [C ii]158 μm line intensity and FIR luminosity, the [O i]63 μm line intensity can constrain the FUV field, G, and the gas density using PDR models. The luminosity in these FIR lines generally exhibits a deficit in the most FIR luminous galaxies compared to the trend expected from lower luminosity galaxies (e.g. Malhotra et al. 2001; Graciá-Carpio et al. 2011; Díaz-Santos et al. 2017). This has made the emission from lines like [O i]63 μm more challenging to detect at high-redshifts.
Citation: Wolfire et al. 2003
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Citation: Malhotra et al. 2001
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Citation: Wolfire et al. 2003
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Citation: Malhotra et al. 2001
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It is also possible that these clusters have a smaller extent and can just be missed by our extent selection as our detection algorithm sets the extent to zero if it is smaller than 6 (Brunner et al. 2022). Following the method presented in Ghirardini et al. (2021a), we estimated several dynamical properties of the clusters in the point source sample and compared them with the extent-selected sample presented in Ghirardini et al. (2021a). In Fig. 5 we compare the distributions of the core radii (Rcore) constrained by the V06 model and the concentration parameter (cSB) between these two samples. The concentration parameter is defined as the ratio of the surface brightness within 0.1 R500 to the surface brightness within R500 (Ghirardini et al. 2021a; Santos et al. 2008; Maughan et al. 2012). Intuitively, the expectation is that the smaller the core radius, the more compact the cluster. The left panel of Fig. 5 clearly shows that the clusters in the point source sample have relatively smaller core radii, hence the emission is more concentrated in a smaller area. Consistently, the concentration of the point source sample shows a clear excess in higher values than the extent-selected sample, indicating that a significantly larger fraction of cool-core clusters and clusters host a central AGN. We performed the same experiment by applying cuts in flux 1.5 × 10−14 ergs s−1 cm−2 and in detection likelihood to test whether the clusters are missed by the extent selection because they are fainter and/or more compact than the extent-selected clusters. The distribution of number density, core radius, and concentration parameter remains the same, indicating that the population of clusters in the point source catalog is more compact than the extent-selected sample. The extent-selected sample does not show a clear bias toward cool-core clusters or clusters with a central AGN, but contains the fraction of cool-cores is similar to that of SZ surveys (Ghirardini et al. 2021a). In this sample, we observe the opposite trend.
Citation: Ghirardini et al. (2021a)
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Citation: Ghirardini et al. (2021a)
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Citation: Ghirardini et al. 2021a
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Citation: Ghirardini et al. 2021a
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Citation: Santos et al. 2008
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We searched the literature carefully and selected all published GRB-DLAs and QSO-DLAs sightlines conforming to our requirements which are as follows. The object must have spectral energy distributions (SEDs) and optical spectroscopic data available with measurements of AV, column densities of Zn ii and Fe ii, or of S ii and Si ii. The GRBs are selected only if they had their optical extinction derived from simultaneous SED fitting to X-ray-to-optical/NIR data using either a single or broken power law (see Greiner et al. 2011; Zafar et al. 2011; Schady et al. 2012; Covino et al. 2013; Bolmer et al. 2018; Zafar et al. 2018a for discussion on AV determination). This is a reliable method to determine extinctions at higher redshifts where the intrinsic slopes are constrained by the X-ray data. Note that there is some degeneracy between broken power-law break frequency (see De Cia et al. 2011) and extinction, which could lead to inference of grey dust for some instances (Watson et al. 2006; Perley et al. 2008; Friis et al. 2015). However, overall a fixed spectral break change (Δβ = 0.5) between the optical and X-ray slopes is preferred for GRBs (Greiner et al. 2011; Zafar et al. 2011; Japelj et al. 2015). For QSO-DLAs, reddening must be determined either from QSO colours or extinctions through template fitting to the QSO SED. Those methods are less robust than the X-ray-supported GRB fits, but are widely adapted. We refer the reader to Zafar et al. (2015) and Krogager et al. (2015, 2016) for more discussions on AV determination for QSO. The requirement for the pairs of elements (Zn ii and Fe ii, or of S ii and Si ii) are in order to be able to derive depletions. Here, Zn and S are volatile elements and Fe and Si are refractory elements (e.g. Ledoux, Bergeron & Petitjean 2002; Draine 2003; Vladilo et al. 2011; De Cia et al. 2016). Defined this way our initial sample consists of 28 GRBs and 32 QSO-DLAs with the required measurements available. To this we add sources where only part of the required measurements are complete but where limits have been determined for the rest. The vast majority of the elemental abundances have been determined via detailed spectral line fitting, for eight GRBs elemental abundances (or limits) were derived from rest-frame equivalent widths of non-saturated lines provided by Fynbo et al. (2009) as described in Laskar, Berger & Chary (2011) and Zafar & Watson (2013, see references to Table 1).
Citation: Perley et al. 2008
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In Fig. 4, 29 observations of 15B-type asteroids are presented. As shown by Gil-Hutton & Cañada-Assandri (2012) and Gil-Hutton et al. (2014), in any plot of the observations of B-type objects a dispersion always appears in the whole phase angle range and it seems that these objects do not follow a single phase-polarization curve. The reason is probably that the asteroids classified by Bus & Binzel (2002) as members of this taxonomic class include objects that belong to the old F-class, originally proposed by Gradie & Tedesco (1982) and included in the Tholen taxonomy, due to its flat spectrum and low albedo; but several F-class objects have phase-polarization curves that are characterized by a comparatively low value of the inversion angle (Belskaya et al. 2005). Therefore, we also include in Fig. 4 nine observations of five asteroids classified as F-class by Tholen (1989) but included in other taxonomic types by Lazzaro et al.: (426) Hippo (X-type), (530) Turandot (C-type), (762) Pulcova (Cb-type), (778) Theobalda (C-type), and (877) Walkure (without a Bus taxonomy classification). The group of objects formed by (142) Polana, (213) Lilaea, (877) Walkure, and (1021) Flammario, all of them belonging to the old F-class, have observations indicating a low value of inversion angle, and the single observation of (314) Rosalia also indicates a similar polarimetric behavior even though it was not classified using the taxonomy of Tholen. On the other hand, the asteroids (62) Erato, (372) Palma, (635) Vundtia, and (981) Martina have measurements well below the theoretical phase-polarization curve for this taxonomic class, so it would seem to have a polarimetric behavior that corresponds more to a C-type than to a B-type. The apparent discrepancies might be indicative of some heterogeneity in the polarimetric properties within this particular taxonomic type, or alternatively, there might be some misclassification of the objects as could be the case for (635) Vundtia and (981) Martina, which were classified as C- and CFU-type by Tholen (1984).
Citation: Gradie & Tedesco (1982)
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However, if the magnetic curvature contraction term (last term in Equation (15)) is dominated by the compression term (second-to-last term in Equation (15)) so that 





, the contraction or merging is strongly compressible (∇ ·  VE  0), resulting in an increase in flux-rope magnetic energy instead. In this case the plasma environment is doing positive mechanical work on the flux-rope structure, pushing magnetic field lines together to enhance flux-rope magnetic energy. Although it appears that small-scale flux ropes tend to contract or merge predominantly incompressibly in discussions of particle simulations (e.g., Drake et al. 2006; Dahlin et al. 2016), and it is also thought of as intrinsically incompressible in its manifestation as the quasi-2D turbulence component in N i MHD theory of solar wind turbulence (Zank et al. 2017), there is observational evidence to the contrary. For example, when primary current sheets associated with interplanetary coronal mass ejections (ICMEs) interact with the heliospheric current sheet, these structures are disturbed and several small-scale flux-rope structures may be formed when turbulent magnetic reconnection occurs in these structures. The flux ropes, being trapped between the converging heliospheric current sheet and the primary current sheets of ICMEs, experience compression, which may lead to efficient particle acceleration (e.g., Khabarova et al. 2015). However, it is possible that the particles are bounded in space because they cannot escape easily the region filled with small-scale flux ropes, which implies more efficient acceleration. Furthermore, in N i MHD theory of quasi-2D magnetic island turbulence, incompressible flux ropes can be compressed by large-scale density and flow velocity gradients in the nonuniform solar wind (Zank et al. 2017; see also discussion of Equation (69) in Section 8.2). Closer to the Sun, Guidoni et al. (2016) discuss the possibility of strong plasma compression during magnetic island contraction for islands propagating sunward during a solar flare event.
Citation: Drake et al. 2006
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The gamma-ray emission from the solar disk due to CR cascades in the solar atmosphere is denoted as a disk component. This secondary gamma-ray produced by the hadronic interaction of cosmic ray with the solar surface was first proposed by Dolan & Fazio (1965). While only upper limits were obtained by early measurements over the range 20 keV–10 MeV (Peterson et al. 1966). A detailed theoretical model for gamma-rays from the collision of cosmic ray with the solar atmosphere was presented by Seckel et al. (1991). The predicted gamma-ray flux at energies from 10 MeV to 10 GeV has a large uncertainty, being sensitive to the assumptions about the cosmic-ray transport in the magnetic field near the Sun. Gamma rays from the Sun were first detected by the Energetic Gamma-ray Experiment Telescope (Orlando & Strong 2008). The measured flux from 100 MeV to 2 GeV was within the range of the theoretical predictions. The Fermi collaboration (Abdo et al. 2011) reported the detection of high energy gamma-rays at 0.1–10 GeV from the quiescent Sun using the first 1.5 yr data. However, the measured solar disk emission flux was about a factor of seven higher than that predicted about this disk component by a “nominal” model (Seckel et al. 1991). This mismatch motivated Ng et al. (2016) to analyze 6 yr of public Fermi-LAT data. The obtained gamma-ray spectrum follows a simple power-law shape (α = −2.3) in 1–100 GeV without any evident high energy cutoff. For the flux in 1–10 GeV, a significant time variation of the solar disk gamma-ray flux that anticorrelates with solar activity was discovered, suggesting that the solar magnetic field would play an important role. An updated analysis with 9 yr of Fermi-LAT data, from 2008 August 7 to 2017 July 27, was performed, and Tang et al. (2018) confirmed these results and extended the gamma-ray spectrum up to >200 GeV. Notably, the bright gamma-ray flux above 100 GeV is dominant only during solar minimum at the end of Cycle 23 (Linden et al. 2018). The HAWC measurements in periods of high solar activity may support these findings (Albert et al. 2018a). Data collected from 2014 November to 2017 December, the second half of solar cycle 24, have been used to set strong upper limits on the flux of 1–100 TeV gamma-rays from the solar disk, about 10% of the maximum gamma-ray flux estimated by Linden et al. (2018). The HAWC 95% upper limit at 1 TeV is about 13% of the flux extrapolated from the solar minimum Fermi-LAT gamma-ray spectrum.
Citation: Seckel et al. (1991)
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Citation: Seckel et al. 1991
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Generally, solar eruptions release their prestored magnetic energy via three phases, namely the precursor, impulsive, and gradual phases (Zhang et al. 2001; Zhou et al. 2016). Thereinto, the latter two, jointly termed as the main phase, correspond to the impulsive acceleration of the erupting CME flux rope, while the less-studied precursor phase includes key information on the eruptive structure and its trigger process. In the past, the limited observations showed that precursor activities of solar eruptions can come in various forms, in which preceding flux emergence (e.g., Palacios et al. 2015; Yan et al. 2017; Yang & Chen 2019) or cancellation (e.g., Green et al. 2011; Yang et al. 2016; Chen et al. 2018) in magnetograms, pre-eruption brightenings in Hα/EUV images (e.g., Bi et al. 2012; Dudík et al. 2016; Wang et al. 2017; Awasthi et al. 2018; Chen et al. 2018), as well as nonthermal processes in microwave or hard X-ray wavelength (Joshi et al. 2011; Altyntsev et al. 2012; Chen et al. 2017) are most common ones. In recent years, in the precursor phase of many CME/flare eruptive events, a type of new progenitor of CME flux ropes, namely hot channels (HCs, Cheng et al. 2011, 2013; Zhang et al. 2012), have been detected in the AIA high-temperature passbands (e.g., 131 and 94 Å). These newfound features commonly exist in the low corona with obvious helical/twisted fine fields or distinct writhed elbows (Cheng et al. 2013; Zhang et al. 2015), and they are found to be directly related to the occurrence of CMEs (Li & Zhang 2013; Patsourakos et al. 2013) and major eruptive flares (Nindos et al. 2015). To date, HCs have been evidenced as MFRs by some joint remote-sensing and in situ observations (e.g., Song et al. 2015), but for many HC eruption events, two problems are still elusive: (1) whether a corresponding MFR already exists before the HC eruption or is newly/partially built up during the eruption; and (2) whether its loss-of-equilibrium is initially facilitated by the preflare reconnection beneath/above the HC (Antiochos et al. 1999; Moore et al. 2001) or directly triggered the ideal magnetohydrodynamic (MHD) instabilities (Török et al. 2004; Kliem & Török 2006).
Citation: Joshi et al. 2011
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Owing to their dusty circumstellar environments, a large mid-infrared (mid-IR) excess is a characteristic feature of post-AGB stars and a detection of cold circumstellar material using mid-IR photometry can be used to identify these objects. The first extensive search for these objects was initiated in the mid-80's using results from the Infrared Astronomical Satellite (Neugebauer et al. 1984) which enabled the identification of post-AGB stars in our Galaxy (Kwok 1993). The Toru$\acute{\rm n}$ catalogue (Szczerba et al. 2007) for Galactic post-AGB stars lists around 391 very likely post-AGB objects. The Galactic sample of post-AGB stars have been found to be a very diverse group of objects (Van Winckel 2003). Studies showed that the majority of the optically visible Galactic post-AGB stars could be classified based on their spectral energy distributions (SEDs) into two groups: shell-sources and disc-sources (Van Winckel 2003). The shell-sources show a double-peaked SED with the hot central star peaking at shorter wavelengths while the cold, detached, expanding dust shell peaks at longer wavelengths. This type of SED is considered to be characteristic of objects that follow the single-star evolution scenario mentioned above. The disc-sources do not show two distinct flux peaks in the mid-IR but they do display a clear near-infrared (near-IR) excess indicating that circumstellar dust must be close to the central star, near sublimation temperature. It is now well established that this feature in the SED indicates the presence of a stable compact circumbinary disc, and therefore these sources are referred to as disc-sources (de Ruyter et al. 2006; Deroo et al. 2007; Gielen et al. 2011a; Hillen et al. 2013). The rotation of the disc was resolved with the ALMA array (Bujarrabal et al. 2013a) in one object and using single dish observations Bujarrabal et al. (2013b) confirmed that disc rotation is indeed widespread. Moreover, these disc-sources are confirmed to be binaries and show orbital periods between 100 and 2000 d (Van Winckel et al. 2009; Gorlova et al. 2014). In contrast, for the Galactic shell-sources long-term radial velocity monitoring efforts have not yet resulted in any clear detected binary orbit (Hrivnak et al. 2011), which either confirms the single-star nature of these objects or introduces a possibility that these systems can have companions on very wide orbits.
Citation: Van Winckel 2003
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Citation: Van Winckel et al. 2009
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