adsabs/FOCAL huggingface dataset:
Another binary parameter is the stellar mass ratio distribution. The choice of the mass ratio can be called the pairing function, which is combining stars into binary systems. When random pairing is used (i.e., binary companions are randomly chosen from a given IMF), we find similar mass segregation results to those for star clusters containing only single stars. However, random pairing is ruled out observationally, and there is also a lack of theoretical backing for a random pairing function (Shatsky & Tokovinin 2002; Kouwenhoven et al. 2005, 2007a, 2007b). Indeed, massive stars preferentially choose other massive stars as their binary companions (Kouwenhoven et al. 2010). This implies that both the geometric average and the median MST method may be biased by the short MST edges from binary systems, although the LnND method is less influenced. An alternative binary pairing function is the so-called ordered pairing (i.e., mass ratio of the binary star components ∼1, in particular for massive stars; see e.g., Kouwenhoven et al. 2009; Oh & Kroupa 2012), which matches stars in order of their mass distribution. We re-pair our test model using ordered pairing and find some extremely high values of the mass segregation degree when using the MST method. This is illustrated in Figure 5, where we see that the mass segregation degree for ordered pairing functions is biased toward very high values for relatively small massive-star samples. These extremely high degrees of mass segregation are not physical, because they are mainly produced by the short MST edges in the binary systems. This is illustrated by the sharp steps in the solid curves, which greatly deviates from the non-mass-segregation distribution equal to unity. Therefore, the gmMST and mMST methods should not be considered as a global compactness measure of massive stars in cases where binary fractions are significant, i.e., >10%. Massive stars may have much shorter MST edges than low-mass stars, due to the preferential presence of binaries among massive stars (e.g., Sana et al. 2014).
Citation: Shatsky & Tokovinin 2002
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Due to the high luminosity and seemingly long-term flux stability, the Crab pulsar and its pulsar wind nebula (PWN) is one of the most studied sources in the very high energy (VHE, $\rm {E} \gt 100$ GeV) regime. For many years, Crab has been used as a standard candle in X- and gamma-ray astronomy (Hester 2008). The Crab nebula was the first TeV gamma-ray source discovered (in 1989 by the Whipple 10-m telescope; Weekes et al. 1989), and soon after detected by numerous facilities above 100 GeV (Smith et al. 2000; Aharonian et al. 2006; Abdo et al. 2012; Aleksić et al. 2015; Meagher & VERITAS Collaboration 2015; Abeysekara et al. 2017). It has a (energy-dependent) angular size of ∼0.1° and its distance has been estimated to be ≈2.2 kpc, corresponding to a physical size of ≈3.8 pc (Trimble 1973; Davidson & Fesen 1985; Kaplan et al. 2008). The nebula non-thermal spectrum can be described by two components, a synchrotron component extending from radio to high energy gamma-rays and a second component emerging above 1 GeV (Atoyan & Aharonian 1996). The latter is interpreted as inverse Compton scattering (IC) of the same particles against soft background photons: cosmic microwave background (CMB), far-infrared (FIR), and near-infrared (NIR) background, and the synchrotron photons of the nebula itself or Synchrotron Self-Compton (SSC). The pulsar has a spin period of $\rm {P} = 33$ ms, a spin-down rate of $\rm {\dot{P}} = 4.21\times 10^{-13}$ and a spin-down luminosity of $\rm {L_{spin}} = 3.8\times 10^{38}\ \rm {erg}\ \rm {s^{-1}}$. The pulsed emission between 0.1  and 100 GeV is believed to be due to synchrotron-curvature radiation (Abdo et al. 2010; Ansoldi et al. 2016) and its spectrum is well parametrized by a power law with a sub-exponential cut-off function of spectral index γP = 1.59, the break located at an energy of about 500 MeV and curvature index of κ = 0.43. In addition, a power-law component emerges above the cut-off extending above 100 GeV (Aliu et al. 2011; Aleksić et al. 2012; Ansoldi et al. 2016).
Citation: Davidson & Fesen 1985
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Disk galaxies typically reveal out-of-equilibrium features due to incomplete equilibration. These may appear in the form of bars and spiral arms, which are large-scale perturbations in the radial and azimuthal directions, responsible for a slow, secular evolution of the disk. In the vertical direction, disks often reveal warps (Binney 1992). In the case of the Milky Way (MW) disk, which can be studied in much greater detail than any other system, recent data from astrometric and radial velocity surveys such as SEGUE (Yanny et al. 2009), RAVE (Steinmetz et al. 2006), GALAH (Bland-Hawthorn et al. 2019), LAMOST (Cui et al. 2012), and above all Gaia (Gaia Collaboration et al. 2016, 2018a, 2018b) have revealed a variety of additional vertical distortions. At large galactocentric radii (>10 kpc) this includes, among others, oscillations and corrugations (Xu et al. 2015; Schönrich & Dehnen 2018), and streams of stars kicked up from the disk that undergo phase mixing, sometimes referred to as “feathers” (e.g., Price-Whelan et al. 2015; Thomas et al. 2019; Laporte et al. 2022). Similar oscillations and vertical asymmetries have also been reported in the solar vicinity (e.g., Widrow et al. 2012; Williams et al. 2013; Yanny & Gardner 2013; Gaia Collaboration et al. 2018b; Quillen et al. 2018; Bennett & Bovy 2019; Carrillo et al. 2019). One of the most intriguing structures is the phase-space spiral discovered by Antoja et al. (2018) and studied in more detail in subsequent studies (e.g., Bland-Hawthorn et al. 2019; Li 2021; Li & Widrow 2021; Gandhi et al. 2022). Using data from Gaia DR2 (Gaia Collaboration et al. 2018a), Antoja et al. (2018) selected ∼900,000 stars within a narrow range of galactocentric radius and azimuthal angle centered around the Sun. When plotting the density of stars in the (z, v

z
)-plane of vertical position, z, and vertical velocity, v

z
, they noticed a faint, unexpected spiral pattern, which became more enhanced when color-coding the (z, v

z
)-“pixels” by the median radial or azimuthal velocities. The one-armed spiral makes two to three complete wraps, resembling a snail shell, and is interpreted as a signature of phase mixing in the vertical direction following a perturbation, which Antoja et al. (2018) estimate to have occurred between 300 and 900 Myr ago. More careful analyses in later studies (e.g., Bland-Hawthorn et al. 2019; Li 2021) have nailed down the interaction time to ∼500 Myr ago.
Citation: Thomas et al. 2019
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Several studies that analyzed the metallic content in the atmospheres of evolved stars hosting planets have been published in the last decade. The first results were based on small samples and/or the abundances were not obtained with a homogeneous technique. Schuler et al. (2005) derived the metallicity for one GWP and gathered abundances from the literature for another seven. They reported that, on average, GWP were metal-poor compared with planet hosting dwarfs. Similar results were found by Sadakane et al. (2005) analyzing 4 GWP. In 2007, Pasquini et al. studying 14 GWP (4 from the literature), concluded that in contrast to the distribution of main-sequence stars with planets, the GWP distribution does not favor high metallicity objects. Conversely, Hekker & Meléndez (2007), analyzing a sample of 380 GK giant stars including 20 with planets (15 from the literature), found an enhancement for GWP of 0.13 dex compared with stars without planets. Takeda et al. (2008), with a sample of 322 giants, including 10 planet-hosts, did not find any metallicity offset. Ghezzi et al. (2010a) found that the metallicity distribution of 16 GWP displays an average that is 0.17 dex more metal-poor than the sample of 117 planet-hosting dwarfs and, furthermore, that the subgiant sample is more metal-rich by 0.12 dex. Johnson et al. (2010) ruled out a flat metallicity relationship among their sample of 246 subgiants (36 with planets, including unpublished candidates). More recently, with larger samples, Mortier et al. (2013) did not find any metallicity enhancement in 71 evolved stars with planets in comparison with 733 evolved stars without planets, with metallicity values gathered from the literature. Finally, Maldonado et al. (2013) found a metallicity enhancement in 16 subgiants with planets relative to 55 without planets (50 from literature). These authors did not find evidence of a metallicity offset between giants with and without planets, analyzing 43 GWP and 67 GWOP. However, for stars with masses above 1.5 M⊙, they reported a slight metallicity enhancement for giants with planets relative to the control sample.
Citation: Takeda et al. (2008)
Citation function: Compare/Contrast
When a galaxy is isolated, star formation quenching is mostly driven by internal processes (Larson 1974; Dekel & Silk 1986; Vulcani et al. 2021). Active galatic nuclei (AGNs) feedback create an outflow of gas preventing further hot gas accretion from the circumgalactic medium (Dalla Vecchia & Schaye 2008; Bongiorno et al. 2016; Trussler et al. 2020). Star formation depends on gravitational instabilities, which may be prevented due to a transition from a stellar disc to a spheroid (‘morphological quenching’; Martig et al. 2009). Bars in spiral galaxies may drive gas inflows, which enhance central star formation (bar-driven evolution; Spinoso et al. 2017). However, in the local Universe most of the galaxies live in groups/clusters (Geller & Huchra 1983). Even before crossing the virial radius, infalling galaxies can stop accreting new gas (‘Starvation’; Larson, Tinsley & Caldwell 1980; Balogh, Navarro & Morris 2000; van de Voort et al. 2017). For instance, Trussler et al. (2020) suggest galaxy quenching has an extended phase (∼5 Gyr) of starvation. In addition, infalling galaxies can lose gas, stars and even dark matter via gravitational tides (‘tidal mass-loss’ - TML; Johnston, Sigurdsson & Hernquist 1999; Read et al. 2006). Within the virial radius, the hot gas in the intracluster medium (ICM) exerts pressure on galaxies moving within the cluster and may remove gas via Ram Pressure Stripping (RPS; Gunn & Gott 1972; Abadi, Moore & Bower 1999). Clusters provide a suitable environment for both direct and indirect galaxy interactions, especially in its core. Direct encounters may lead to galaxy mergers and cause a starburst event over a short time-scale and quickly exhaust a galaxy’s gas supply (Springel & Hernquist 2005; Cox et al. 2008; Teyssier, Chapon & Bournaud 2010), whereas repeated indirect encounters may leave interacting galaxies with disturbed morphologies. At last, it is important to note that clusters are built up by the accretion of galaxy groups. Cluster galaxies may therefore be affected by ‘pre-processing’, in which galaxy properties were altered even before entering the cluster (Fujita 2004; Mahajan 2013; Sarron et al. 2019).
Citation: Spinoso et al. 2017
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Figure 2 shows solar wind plasma and magnetic field measurements for a CIR that occurred between July 26 and 27, 2003 (days of year 207–208). Following Chotoo et al. (2000), Richardson et al. (1993), we marked four regions in the plot: the slow wind region (S), the compressed slow wind region (S′), the compressed fast wind region (F′), and the fast wind itself (F). Throughout four regions, the mean charge states of iron measured by ACE/SWICS lies around 11+, consistent with typical values in the solar wind (Lepri et al. 2001). The stream interface (S′-F′) is indicated by the vertical line in Fig. 2 and is characterized by a drop of the O7+/O6+ abundance ratio measured with SWICS in the bulk solar wind (Wimmer-Schweingruber et al. 1997, 1999). The leading (S-S′) and trailing edge (F′-F) of the CIR were determined by the total pressure (Jian et al. 2006). Bučík et al. (2009) found that CIR boundaries can be well defined when the total pressure exceeds 50 pPa (indicated by the horizontal dashed line in Fig. 2), which is slightly higher than that in the background solar wind, which typically is 20−30 pPa, according to Jian et al. (2006). The total pressure P was obtained from the sum of plasma and magnetic field pressure, that is, \hbox{$P=n_{\rm p}v^{2}_{\rm th}m+B^2/2\mu_0$}P=npvth2m+B2/2μ0, where np and vth are the proton density and thermal speed, respectively, and B is the magnitude of the magnetic field. Because SOHO has no magnetometer, we used magnetic field data from ACE/MAG (which is also around L1). Comparing plasma parameters (bulk speed, thermal speed, and proton density) measured by PM with those of SWEPAM, we see that the physical conditions at SOHO and ACE were almost the same, and that the time difference between passages of the CIR boundaries is less than ten minutes. The CIR shown in Fig. 2 was bounded by a reverse shock (vertical line separating F′ from F). We clearly see that the suprathermal He++ intensity peaks inside the decelerated and compressed fast-wind region (F′), close to the reverse shock. In contrast, suprathermal particles are very rare in the S and S′ regions. After passage of the reverse shock, suprathermal particles continue to be observable for more than one day. They are commonly believed to be the sunward particles accelerated by the reverse shock far beyond the Earth orbit. In other words, the observer saw the duration of the CIR particle event, which was longer than that of the CIR compression region itself. The background level shown in green was estimated using the method described above. The signal-to-noise ratio (S/N) in the F and F′ regions is higher than 100, confirming that our observations are due to real He++ particles.
Citation: Wimmer-Schweingruber et al. 1997
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Citation: Bučík et al. (2009)
Citation function: Uses
Since the free-fall time-scale tff depends on the gravity law, we study how changing the gravity law affects the value of n in the KS law. Our main aim in this paper is to derive for the first time the KS law from a basic description in the framework of Milgromian dynamics (MOND; Milgrom 1983; Famaey & McGaugh 2012). MOND is an alternative approach to a cold dark matter-dominated universe deduced from the flattening of observed rotation curves of spiral galaxies under the assumption of Newtonian dynamics. In MOND, these dynamical discrepancies are addressed by a generalization of Newtonian gravity (for a thorough review, see e.g. Famaey & McGaugh 2012). Within the classical MOND framework, the Newtonian gravitational acceleration gN is replaced in the spherically symmetric case by $g=\sqrt{g_{\rm {N}} a_0}$ when the gravitational acceleration is far smaller than the critical acceleration a0 = 1.2 × 10−10 m s−2 (Begeman, Broeils & Sanders 1991; Gentile, Famaey & de Blok 2011). In less symmetric configurations, the equations of motion are derived from a Lagrangian, yielding standard equations of motion but with a generalized Poisson equation for the gravitational field (Bekenstein & Milgrom 1984; Milgrom 2010). MOND predicted the very tight radial acceleration relation (RAR) between the gravity g implied by disc galaxy rotation curves and the Newtonian gravity gN, resulting from their baryonic distribution (Lelli et al. 2017; Li et al. 2018). The RAR is also evident in stacked galaxy–galaxy weak lensing measurements that probe out to larger radii (Milgrom 2013; Brouwer et al. 2021). The external field effect (EFE) predicted by MOND (Bekenstein & Milgrom 1984) and required for consistency with data on Solar neighbourhood wide binaries (Banik & Zhao 2018c; Pittordis & Sutherland 2019) has recently been confirmed at high significance by comparing galaxies in isolated and more crowded environments (Haghi et al. 2016; Chae et al. 2020). Detailed numerical simulations of disc galaxy secular evolution in MOND have recently been conducted for the case of M33 (Banik et al. 2020) and for a Milky Way or M31-like surface density (Roshan et al. 2021), while star formation has also been explored with high-resolution simulations (Renaud, Famaey & Kroupa 2016). The possible cosmological context has been explored in e.g. Haslbauer, Banik & Kroupa (2020) and Asencio, Banik & Kroupa (2021). The MOND corrections to Newtonian gravity might be capturing effects of the quantum vacuum (Milgrom 1999; Smolin 2017; Verlinde 2017; Senay, Mohammadi Sabet & Moradpour 2021).
Citation: Begeman, Broeils & Sanders 1991
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The most commonly used technique to create a mock lens system from simulated galaxies is to extract a mass map from a particle-based simulation and use it to calculate lensing quantities (i.e. lensing potential and its first and second derivatives) needed to emulate the gravitationally lensed images. For this purpose, galaxies from high resolution hydrodynamical simulations, including, for example, EAGLE (Evolution and Assembly of GaLaxies and their Environments, Schaye et al. 2015; Crain et al. 2015) or Illustris (Vogelsberger et al. 2014b,a), have been widely used. Different types of software, such as lenstronomy (Birrer & Amara 2018) and GLAMER (Gravitational Lensing Simulations with Adaptive Mesh Refinement, Metcalf & Petkova 2014), can handle the inference of lensing quantities from mass maps using fast Fourier transform convolution. Fast Fourier is a commonly used technique to speed up the calculation of lensing quantities, which imply computationally expansive numerical integration but it remains a demanding procedure (Metcalf & Petkova 2014; Plazas 2020). One could wonder what mass map resolution should be used and what size of map is relevant to be sufficiently precise in the mock creation while minimising the computational time. One generally considers that a strongly lensed system is determined by the projected mass inner to the lensed images. This would suggest that a region extending over a few Einstein radii (θE) is sufficient for the simulations. However, this consists in effectively ignoring any source of shear, and/or perturbations caused by substructures and/or anisotropy in the mass distributions. Moreover, depending on the symmetry of the problem, cutting the mass distribution at a given radius not only automatically removes the mass beyond that radius, but it may also introduce numerical artefacts that could wrongly be attributed to properties of the examined lens mass distribution. In this paper we focus on this latter point and quantify the impact of the shape (and size) of the integration domain on the lensing quantities inference.
Citation: Birrer & Amara 2018
Citation function: Background; Background
We derived the mean values of the 13CO/C18O abundance ratio for the three star-forming regions, obtaining values of 13CO/C18O = 10.9 ± 7.5 for Taurus, 13CO/C18O = 17.3 ± 11.5 for Perseus, and 13CO/C18O = 23.7 ± 10.4 for Orion. The expected value is 13CO/C18O = 7.5−9.8, assuming 12C/13C = 57−67 and 16O/18O = 500−600 (Gerin et al. 2015; Langer & Penzias 1990; Wilson & Rood 1994). As mentioned in Sect. 5.7, the 13CO/C18O abundance ratio increases in regions of enhanced UV field (Shimajiri et al. 2014; Ishii et al. 2019; Areal et al. 2018). This variation is interpreted in terms of the selective photodissociation and isotopic fractionation (see Bron et al. 2018; Fuente et al. 2019). This effect is produced because the more abundant CO isotopolog shields itself from the effect of UV photons more efficiently than less abundant isotopologs (Stark et al. 2014; Visser et al. 2009). Our data confirm this trend in Orion, although the observed positions are located at a distance >1 pc from the ionized nebula M 42, which shows that the whole cloud is illuminated by a strong UV field emitted by young massive stars in the Trapezium cluster (Pabst et al. 2019). In contrast to X(C18O), which presents uniform abundance in the three regions, the mean 13CO abundance is a factor of approximately two higher in Orion than in Taurus. One interesting question pertains to whether the observed variation in the 13CO abundance is related to a variation in the 12CO/13CO ratio (Roueff et al. 2015; Colzi et al. 2020) or is revealing variations for a higher 12CO abundance in Orion. Because of the higher gas temperature and incident UV field in Orion, selective photodissociation would work in the direction of increasing N(12CO)/N(13CO) in Orion with respect to Taurus. Therefore, a higher 12CO abundance in Orion stands as the most likely explanation. Our results are based on significant approximations (one single phase, gas-dust thermalization), and therefore a detailed multi-transition study of these compounds is required to confirm this result.
Citation: Shimajiri et al. 2014
Citation function: Uses
Hydrodynamical simulations of evolving galaxies allow us to calibrate these diagnostics by measuring their observability given a set of formation scenarios and physical processes (e.g. Jonsson et al. 2006; Rocha et al. 2007; Lotz et al. 2008a; Bush et al. 2010; Narayanan et al. 2010; Hayward et al. 2013; Snyder et al. 2013; Lanz et al. 2014). The quality and breadth of these experiments are limited by the availability of computational resources and the fidelity of models for galaxy physics such as star formation, supernovae, and the interstellar medium (ISM). It has only recently become widespread to model the formation of galaxies ab initio (e.g. Governato et al. 2004; Agertz, Teyssier & Moore 2011; Guedes et al. 2011; Marinacci, Pakmor & Springel 2013; Ceverino et al. 2014), and the realism continues to improve (Stinson et al. 2012; Hopkins et al. 2014; Torrey et al. 2014), albeit with still widely varying physics models (e.g. Scannapieco et al. 2012; Kim et al. 2014). Prior to these advances, studies were limited to small numbers of isolated galaxies or mergers to inform common diagnostics of galaxy evolution, an approach with a significant limitation: they do not fully account for cosmological context, such as gas accretion and the breadth of assembly histories. In addition to mergers, models of high-redshift galaxy formation (e.g. Dekel, Sari & Ceverino 2009; Dekel et al. 2013) have recently appreciated the tight coupling between gas accretion and disc evolution (e.g. Cacciato, Dekel & Genel 2012; Danovich et al. 2012; Dekel & Krumholz 2013), as well as bulge and super-massive black hole (SMBH) growth mediated by turbulent motions or violent disc instability (e.g. Bournaud et al. 2011; Porter et al. 2014) and the evolution of giant clumps (Dekel & Burkert 2013). These important processes likely complicate interpretation of a given observation, and recent studies of galaxy morphology have begun to exploit simulations including them (e.g. Scannapieco et al. 2010; Pedrosa, Tissera & De Rossi 2014).
Citation: Governato et al. 2004
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Citation: Torrey et al. 2014
Citation function: Motivation; Motivation; Motivation