adsabs/FOCAL huggingface dataset:
Observations of large-scale magnetic fields offer clear insights about regular ordered patterns of the field lines, suggesting that mean-field dynamo processes are responsible for their order and structure, as well as the existence of additional transport processes carrying magnetic energy into huge regions of space (Clarke, Kronberg & B”ohringer 2001; Bonafede et al. 2010; Arlen et al. 2012; Govoni, F. et al. 2017; Han 2017). Magnetic fields cannot be directly observed, so their impact on radiation processes need to be considered (see, for instance, Rybicki & Lightman 1979, and references therein). In addition, observations of magnetic fields in voids provide bounds on their strength, depending on the analytical model: From the simplest ones, it is possible to obtain lower bounds, although when improving such models a bounded range of magnetic field strength values can be provided, ranging from 10−25 to 10−15 nG (Neronov & Vovk 2010; Tavecchio et al. 2010; Essey, Ando & Kusenko 2011; Takahashi et al. 2013). Other authors argue magnetic field strengths between 10−16 and 10−15 G (Einstein 1915; Einstein 1916; Hubble 1929; Hubble & Humason 1931; Bull et al. 2016). Magnetic fields from astrophysical voids are relevant since they could evidence truly cosmological magnetic fields, which could have served as seeds for magnetic fields in lower scales (such as galactic fields). Observations in galaxy clusters yield values of the order of 10−6 G (Boulanger et al. 2018). Interest in primordial magnetic fields generated during inflation has recently increased. This scenario has driven the search for phenomenologically viable mechanisms to explain the observed magnetic fields in a broad set of scales (Grasso & Rubinstein 2001; Brandenburg & Subramanian 2005; Demozzi, Mukhanov & Rubinstein 2009; Ferreira, Jain & Sloth 2013; Green & Kobayashi 2016). The latest data on reionization and the observed UV luminosity function of high-redshift galaxies place limits on the magnetic field strength due to its impact on the reionization process.
Citation: Neronov & Vovk 2010
Citation function: Compare/Contrast
GCs formed in dwarf galaxies may differ from those found in the Galactic halo, depending on their age and metallicity. Dwarf galaxies show a wide variety of star formation histories (Hidalgo et al. 2011, 2013; Weisz et al. 2014) that are predicted to lead to variations in their metallicity distribution functions and chemical abundances. It has also been suggested these variations could be attributed to differences in the IMFs of these galaxies (McWilliam, Wallerstein & Mottini 2013). If the IMFs are the root cause of these differences, then this would also lead to differences in the age–metallicity relationship, which is observed by both Forbes & Bridges (2010) and Leaman et al. (2013). From observations, field stars in dwarf galaxies do exhibit different abundance ratios from MW field stars, e.g. lower [α/Fe] ratios and variations in neutron-capture element ratios at intermediate metallicities. However, these typically do not show up until [Fe/H] ∼ −1.5 (Shetrone, Bolte & Stetson 1998; Shetrone, Côté & Sargent 2001; Shetrone et al. 2003; Venn et al. 2004; Okamoto et al. 2012; Tolstoy, Hill & Tosi 2009; Frebel 2010). At metallicities below [Fe/H] = −1.5, the abundance variations between field and GC stars become less pronounced in dwarfs and the MW (Hill et al. 2000; Pritzl, Venn & Irwin 2005; Carretta et al. 2010; Letarte et al. 2010); a good example of this is M54, located at the heart of the Sagittarius (Sgr) dwarf accretion remnant. M54 has a much lower metallicity than the Sgr field stars (e.g. Carretta et al. 2010) and the [α/Fe] ratios resemble the field stars in the MW halo and its detailed chemical abundance ratios resemble the patterns seen in other GC systems (e.g. the Na–O anticorrelation; Carretta et al. 2009). Therefore, other than its physical association with the Sgr remnant, M54 does not stand out from other GCs in terms of its chemical abundance patterns, similar to the metal-poor GCs Terzan 8 and Arp 2 (both also kinematically and spatial associated with the Sgr stream; Mottini, Wallerstein & McWilliam 2008). On the other hand, Hodge 11 in the large magellanic cloud at [Fe/H] = −2.0 does have lower [α/Fe] than MW field and GC stars(Mateluna et al. 2012), and Ruprecht 106 has an anomalously low [α/Fe] ratio for a MW GC (Villanova et al. 2013).
Citation: Shetrone et al. 2003
Citation function: Background
The coalescence of a binary compact object system (either a neutron star (NS) binary or a stellar-mass black hole (BH) and NS binary) has been widely suggested to account for short-duration gamma-ray burst (SGRB) events (Eichler et al. 1989; Narayan et al. 1992; Nakar 2007; Berger 2014) that last typically less than 2 s in the soft γ–ray band (Kouveliotou et al. 1993). Since 2006, it has been suspected that mergers of compact objects could also produce the so-called long–short GRBs (also known as the supernova-less long GRBs, which are apparently long-lasting but do not show any signal of supernovae down to very stringent limits), which share some properties of both long- and short-duration GRBs (Della Valle et al. 2006; Gal-Yam et al. 2006; Gehrels et al. 2006; Zhang et al. 2007). Compact binary coalescence (CBC) is generally expected to be a strong source of gravitational wave (GW) radiation and such events are prime targets for some GW detectors like advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)/VIRGO (Abadie et al. 2015; Acernese et al. 2015; Belczynski et al. 2010, 2016; see also the latest LSC–Virgo white paper at https://dcc.ligo.org/LIGO-T1400054/public). On 2015 September 14, the two detectors of the LIGO simultaneously detected a transient gravitational wave signal from the merger of two BHs (GW150914, Abbott et al. 2016). GW150914 is the first direct detection of gravitational waves and the first identification of a binary BH merger (Abbott et al. 2016). Surprisingly, the observations from the Fermi Gamma-ray Burst Monitor (GBM) at the time of GW150914 claimed a detection of a weak gamma-ray transient (i.e., GBM transient 150914) 0.4 s after GW150914 with a false alarm probability of 0.0022 (Connaughton et al. 2016). If true, this is the first GW/SGRB association (see, however, Savchenko et al. 2016 for some arguments). Li et al. (2016) compared GBM transient 150914 with other SGRBs and found that such an event is remarkably different in its prompt emission properties. The binary BH merger origin as well as its property of “distinguished” prompt emission suggest that GW150914/GBM transient 150914 is not a typical GW/SGRB association.
Citation: Gal-Yam et al. 2006
Citation function: Background
After the detection of V391 Peg b, some other planet or brown dwarf (BD) candidates orbiting sdB stars were proposed using different detection methods. From eclipse timing, about one-third of the known detached sdB/sdO + dM (dM = M-dwarf) post-common-envelope binaries (PCEB) are suspected to host planets/BDs: HW Vir (Beuermann et al. 2012 and references therein), HS 0705+6700 (alias V470 Cam, Qian et al. 2013 and references therein), HS 2231+2441 (Qian et al. 2010 and references therein; but see also Lohr et al. 2014), NSVS 14256825 (Almeida et al. 2013; Hinse et al. 2014 and references therein), NY Vir (Lee et al. 2014 and references therein), and 2M 1938+4603 (Baran et al. 2015). Interesting explorations on the origin of PCEB (and specifically sdB+MS/BD) circumbinary planets can be found in Zorotovic & Schreiber (2013), Schleicher & Dreizler (2014), Bear & Soker (2014), and Völschow et al. (2016). Very different planets or planetary remnants with terrestrial radii have been proposed from tiny reflection effects detected by the Kepler spacecraft in KIC 05807616 (Charpinet et al. 2011) and KIC 10001893 (Silvotti et al. 2014). However, none of these sdB planet/BD candidates has been confirmed with at least two independent detection methods. More robust detections of a few brown dwarfs (BDs) in eclipsing sdB binaries (also called HW Vir systems from the sdB+dM protoptype) were obtained by combining stellar radial velocities (RVs) with photometric measurements: J08205+0008, J1622+4730 and V2008-1753 have companion masses of about 71, 67, and 69 MJup, respectively (Geier et al. 2011; Schaffenroth et al. 2014a, 2015). At least two more sdB+BD eclipsing systems were recently found from the OGLE survey (Schaffenroth, in prep., priv. comm.). Finally, two more BD candidates in sdB binaries were found by combining radial velocities (RVs) with photometric reflection effects: CPD-64°6481 and PHL 457, with minimum masses of 50 and 28 MJup, respectively (Schaffenroth et al. 2014b).
Citation: Schleicher & Dreizler (2014)
Citation function: Background; Background
The global magnetospheric structures for the oblique rotator are very similar to the aligned one. We show the structure of magnetic field lines and the distribution of the accelerating electric field E0 in the x–z plane for a 60° rotator with the pair multiplicity κ = {0, 1, 3} in Figure 4. As the pair multiplicity κ increases, the field structure tends to the force-free solution with an equatorial current sheet outside the LC. We observer a dissipative region where E > B outside the LC. The spatial extension of the dissipative region decreases with increasing pair multiplicity and the E0 region is more confined to the equatorial current sheet outside the LC as the pair multiplicity κ increases. In fact, the E0 distribution for the high κ solution is qualitatively similar to the FIDO one (see, e.g., Kalapotharakos et al. 2014; Cao & Yang 2019). We also compare the field structures for κ = 0 with Figure 1 of Contopoulos (2016) for α = 0° and α = 60° respectively. We find that the field structures are qualitatively very similar to those of Contopoulos (2016). For comparison, we also show the magnetic field lines and the E0 distributions for a 60° rotator with the pair multiplicity κ = 0 by implementing the AE formulation everywhere in Figure 5. The magnetospheric structure is very similar to the aligned one with a force-free zone bounded by a radiation zone. We observe a strong E0 distribution inside the LC, which is very different from those in the SG and OG models. A strong E0 region with E > B also appears outside the LC. We show the distributions of magnetic field lines and the accelerating electric field E0 in the x–z plane for a 30° rotator with the pair multiplicity κ = 3 in Figure 6. We see that the field structure is very close to the force-free one and the E0 region is restricted to only near the current sheet outside the LC for this high κ value. We also show the normalized Poynting flux L/Laligned as a function of radius r for a 90° rotator with different pair multiplicities in Figure 7. We see that the Poynting flux increases with increasing κ values and approaches the force-free solution for the high κ value. Our simulation shows a more than 1% dissipation rate outside the LC for a 90° dissipative rotator. A similar dissipation rate is also found by the PIC simulation for the aligned and perpendicular rotator (Philippov et al. 2015). In fact, the spectral numerical methods present an unphysical dissipation beyond the LC due to discontinuity in the current sheet. A higher resolution is necessary to catch the discontinuity in the current sheet and reduce the unphysical dissipation.
Citation: Kalapotharakos et al. 2014
Citation function: Similarities
In both models, as we will see, the thick disc scale length is about a factor of two shorter than that of the thin disc, in agreement with the results by Bovy et al. (2012a). The choice of presenting two mass models for the mass distribution of our Galaxy is mainly dictated by two reasons. First, the need to add a central bulge to the global gravitational potential to reproduce the rotation curve in the inner kpcs of the Milky Way strongly depends on the observational data with which one compares the theoretical curve: to reproduce the rise observed in the inner kpcs (see the observational data adopted by Caldwell & Ostriker 1981), Allen & Santillan (1991) introduced a central mass concentration, whose mass is about 15% of the disc mass. However, the central rise observed in the rotation of the molecular gas in the inner Galaxy (for more recent estimates see, for example,  Sofue 2012) may be an effect of non circular motions generated by large scale asymmetries like the bar, as has been shown recently by Chemin et al. (2015). Moreover, this feature is not reported in all the observational studies (see, for example, Reid et al. 2014). Secondly, there is growing evidence that the mass of any classical bulge, if present in the Milky Way, must be small (Shen et al. 2010; Kunder et al. 2012, 2016; Di Matteo et al. 2014, 2015). For these reasons, we prefer to present a second model, our Model II, which does not include any spherical central component, and which is still compatible with the rotation curve of the Galaxy, as given by Reid et al. (2014). Because it has been widely used in the last decades, and due to the facility of its implementation, we explicitly aim at generating Galactic models similar to the Allen & Santillan (1991) model, so to make any implementation of these new models, and any comparison with Allen & Santillan (1991), straightforward. As for the model proposed by Allen & Santillan (1991), Models I and II are axisymmetric and time-independent, and do not include stellar asymmetries such as a bar or spiral arms. No truncation is assumed for the discs, while the halo is truncated at 100 kpc, in agreement with the choice of Allen & Santillan (1991). As we describe in the following section, the analytic forms for the discs, halo, and bulge potentials are the same as those adopted by Allen & Santillan (1991). To allow an easy comparison with the Allen & Santillan (1991) model, in the following we will make use of the same system of units adopted by these authors: the potential is given in units of 100 km2/ s2, lengths are in kpc, masses in units of 2.32 × 107M⊙, time in units of 0.1 Gyr, velocities in units of 10 km s-1 and the vertical force in units of 10-9 cm s2. In these units, the gravitational constant G is equal to 1 and the mass volume density is in units of 2.32 × 107M⊙/ kpc3.
Citation: Kunder et al.; 2016
Citation function: Background; Motivation
Deep learning (DL) is the paradigm of machine learning which uses multilayer neural networks. Neural networks are ML models inspired from the network of brain cells or neurons. The differentiating factor between DL and conventional ML is in the process of feature selection. In conventional ML, performance strongly depends on the features used. More often than not, new features are created for a task to better capture correlations in the data. This is called feature engineering. ML models perform poorly if not given good features to learn from. Deep learning eliminates this dependence by defining its own features to learn from, which are relevant to the task at hand. This makes deep learning a versatile, high performing solution for a variety of supervised ML tasks. The Artificial Neural Networks (ANNs) have found application in not only the traditional tasks in extragalactic astronomy such as photometric redshift estimation (e.g. Firth, Lahav & Somerville 2003; Tagliaferri et al. 2003; Collister & Lahav 2004; Vanzella et al. 2004; Sadeh, Abdalla & Lahav 2016; Bilicki et al. 2018; Pasquet et al. 2019), but also in more specialized problems such as predicting infrared luminosity of galaxies (Ellison et al. 2016), estimation of star formation properties (Surana et al. 2020), and ranking the quenching parameters of galaxies (Teimoorinia, Bluck & Ellison 2016). In particular, Convolutional Neural Networks (CNN) are now becoming increasingly popular in studies using imaging data on galaxies. The CNNs are deep learning models designed to extract features from images. They have provided state-of-the-art performance in majority of computer vision tasks in recent times (Krizhevsky, Sutskever & Hinton 2012; He et al. 2017). CNNs have been utilized for galaxy morphological classification e.g. classifying the optical morphologies broadly into spheroidal, disc, and irregular types (Huertas-Company et al. 2015) and even for classification of various radio galaxy morphologies (Wu et al. 2019). Recently, Ribli, Dobos & Csabai (2019) have shown that CNNs can be used to predict galaxy shapes, needed for weak lensing studies, from a wide field but shallow sky survey images using the ‘ground truth’ images from a deeper but narrower field survey. CNNs have also found application in the automated detection of features in sky-survey images such as galactic bars (Abraham et al. 2018) and strong gravitational lenses (Canameras et al. 2020; Li et al. 2020). Further, ML and CNNs in particular have also been used to detect outliers in large area Sloan Digital Sky Survey (SDSS) data (e.g. Baron & Poznanski 2017; Sharma et al. 2019). In this study, we want to determine the bulge to total luminosity ratio (B/T) of a galaxy using its optical multiband images as input. Due to the use of a data set with galaxy images labelled by $B/T\, \in [0,1]$ in a continuous space $\rm I\!R$, we have performed CNN based regression in this work.
Citation: Surana et al. 2020
Citation function: Background; Background; Background
To explain the observed evolution, the physical processes invoked have to result in a large growth in size but not in stellar mass, nor drastic increase in the star formation rate. Most plausible candidates are mass-loss driven adiabatic expansion (‘puffing-up’) (e.g. Fan et al. 2008, 2010; Ragone-Figueroa & Granato 2011) and dry mergers scenarios (e.g. Bezanson et al. 2009; Naab, Johansson & Ostriker 2009; Trujillo, Ferreras & de La Rosa 2011). In the former scenario, galaxies experience a mass-loss from wind driven by active galactic nuclei (AGNs) or supernovae feedback, which lead to an expansion in size due to a change in the gravitational potential. In the latter, mergers either major involving merging with another galaxy of comparable mass, or minor that involves accretion of low mass companions, have to be dry to keep the low star formation rate (Trujillo et al. 2011). Nevertheless, major mergers are not compatible with the observed growth in mass function in clusters as well as the observed major merger rates since z ∼ 1 (e.g. Nipoti, Londrillo & Ciotti 2003; Bundy et al. 2009). On the other hand, minor mergers are able to produce an efficient size growth (see e.g. Trujillo et al. 2011; Shankar et al. 2013). The rates of minor mergers are roughly enough to account for the size evolution only up to z ≲ 1 Newman et al. (2012), at z ∼ 2 additional mechanisms are required (e.g. AGN feedback-driven star formation Ishibashi, Fabian & Canning 2013). In addition, the effect of continual quenched galaxies on to the red sequence as well as morphological mixing (known as the ‘progenitor bias’) further complicates the situation (e.g van Dokkum & Franx 2001). Processes that are specific in clusters such as harassment, strangulation and ram-pressure stripping (e.g. Treu et al. 2003; Moran et al. 2007) might play an important role in quenching and morphologically transforming galaxies. Several studies have already shown that the progenitor bias has a non-negligible effect on the size evolution (e.g. Saglia et al. 2010; Valentinuzzi et al. 2010b; Carollo et al. 2013; Poggianti et al. 2013; Beifiori et al. 2014; Delaye et al. 2014; Belli, Newman & Ellis 2015; Shankar et al. 2015).
Citation: Trujillo et al. 2011
Citation function: Compare/Contrast
We note that during these encounters, energy is also lost due to tidal oscillations in the neutron star excited by the black hole (e.g., Press & Teukolsky 1977), and contributes to σ. To check whether we should include this effect in our calculations or whether it can be safely neglected, we approximate the tidal energy dissipated during a parabolic encounter according to the formalism presented in Press & Teukolsky (1977):
6





where RNS is the radius of the neutron star, Rmin is the periastron of the approach, and Tl are dimensionless values associated with each spherical harmonic l (see Press & Teukolsky 1977 for calculation of Tl). We only consider the quadrupole mode (l = 2), which dominates over the other modes (Press & Teukolsky 1977). We approximate the NS as a polytropic star of index n = 0.5 (e.g., Finn 1987), and use values from Table 1 of Kokkotas & Schafer (1995) to aid in the calculation of Tl. Note that since there is a minimum impact parameter, there is a minimum possible value of Rmin. For a parabolic encounter the relationship between the impact parameter and the periastron distance is:
7





Thus, combining Equations (4) and (7), we find the minimum possible Rmin to be:
8





Encounters with Rmin  Rmin(bmin) will result in a direct collision between the BH and NS instead of a bound binary. In Figure 1 we plot 





—the ratio of energy lost to tidal oscillations to the energy lost to gravitational waves—as a function of Rmin, for a 5 





 BH and a 1.4 





 NS. We have also marked the region where 





. We see that in the region of interest where 





, i.e., where bound binaries can form, 





, an extremely small value. We have verified (not shown to avoid clutter) that for larger BH masses, 





 is even smaller. This is consistent with previous studies about NS–NS captures (e.g., Gold et al. 2012; Chirenti et al. 2017). Thus, we can safely neglect tides in our calculation of the capture cross section.
Citation: Finn 1987
Citation function: Uses
It is generally thought that the emission from radio to medium energy gamma rays is generated by the injected electrons through the synchrotron radiative mechanism. The high-energy photon emission mainly comes from inverse Compton (IC) scattering of the high-energy electrons on the background seed photons, which include the synchrotron background, the cosmic microwave background, and infrared photons in the PWNe (see, e.g., Zhang et al. 2008; Fang & Zhang 2010; Torres et al. 2013; Lu et al. 2020). On the other hand, it is also suggested that the gamma rays could be emitted by the hadronic processes. The relativistic protons accelerated in the Crab pulsar outer gap interact with the matter inside the nebula. and this process may contribute in the high-energy gamma-ray range (see, e.g., Cheng et al. 1990; Bednarek & Protheroe 1997; Khangulyan et al. 2020; Cao et al. 2021). Therefore, it has been long debated whether the high-energy emission from the PWNe is the leptonic or hadronic origin. The details of the high-energy radiation produced by leptonic process have been discussed for the Crab Nebula (see, e.g., Venter & de Jager 2007; Zhang et al. 2008; Martín et al. 2012), and that of the gamma-ray emission about the hadronic process have been also investigated (see, e.g., Cheng et al. 1990; Bednarek & Protheroe 1997; Bednarek 2003, 2007). However, with the establishment of more and more high-energy observatories, some telescopes have possessed the performance of observing photons of exceeding to the PeV from the astronomic objects. An increasing number of observational data has been reported by the different experiments. For example, the Amenomori et al. (2019) reported that the Tibet air shower array with the underground water-Cerenkov-type muon detector array observed the highest energy photons of exceeding 100 TeV with a 5.6σ statistical significance and pointed the measured spectrum with energy extended to the sub-PeV from the Crab Nebula have an absence of high-energy cutoff. Recently, more than 530 photons at energies above 100 TeV and up to 1.4 PeV from the 12 ultra-high-energy gamma-ray sources with a statistical significance greater than seven standard deviations were reported again by LHAASO (Cao et al. 2021). Together with the earlier investigations about the leptonic scenario, the radiative spectrum from the leptons has a cutoff around the sub-PeV region (see, e.g., Zhang et al. 2008; Martín et al. 2012; Zhang et al. 2020). It seems that the other components of gamma rays have a significant contribution.
Citation: Cheng et al. 1990
Citation function: Motivation
Citation: Cheng et al. 1990
Citation function: Background; Motivation