adsabs/FOCAL huggingface dataset:
We first discuss the relative bulk enrichment. From internal structure models one can derive the MZ necessary to reproduce the observed mass and radius, and—for the Solar System planets—the gravitational moments. Studies inferring in this way eZ,rel,int of transiting exoplanets have found that eZ,rel,int decreases with increasing mass (left panel of Figure 3). The planetary mass where 





 defines the parity mass M1 (see Appendix B). It is shown in the right panel of Figure 3. It is extrapolated to be between ∼13 and 60 MJup (Miller & Fortney 2011; Thorngren et al. 2015). The planets analyzed in these studies have equilibrium temperatures of less than ∼1000 K (corresponding to an orbital distance of about 0.08 au for a solar-like star) so that they are not affected by the aforementioned bloating mechanisms. A similar decrease of eZ,rel,int with increasing mass is found for the bulk metal content of Solar System giants (Saumon & Guillot 2004; Helled et al. 2011), where the mass where eZ,rel,int reaches 1 is extrapolated to be at about 11 MJup. From theoretical planet population syntheses based on the core accretion theory one finally finds that the parity mass is at about 10 to 18 MJup (Mordasini et al. 2014). Considering that of the 255 extrasolar giant planets (M sin i > 0.1 M) inside of 0.1 au currently listed on www.exoplanets.org (Han et al. 2014) only 4 have a mass exceeding 10 M (which is not an observational bias). We thus deduce that at least based on their masses regarding the bulk composition of hot Jupiters, it appears that almost all of them should be dominated by planetesimal enrichment. We add the caveat that the bulk heavy element content cannot be inferred directly for typical hot Jupiters at equilibrium temperatures of Teq ≳ 1500 K because of bloating mechanisms. But the fact that both the planets analyzed by Miller & Fortney (2011), Thorngren et al. (2015) (a = 0.03–1 au, Teq ≲ 1000 K) and the solar system planets (a ≈ 5–30 au) follow the same trend, makes it appear unlikely—even though in principle not excluded—that the hot Jupiters at a ∼ 0.04 au do not follow the same enrichment pattern.
Citation: Helled et al. 2011
Citation function: Similarities; Similarities
(i) Our capability of reproducing the lensed images down to the noise level without fully correctly modelling the cored central mass density distribution of the lenses indicates some form of the source-position transformation (SPT; Schneider & Sluse 2014), in line with the previous findings by Unruh et al. (2017). As a consequence, our reconstructions lead to a systematic fractional error on the Hubble constant of $25_{-19}^{+37}$ per cent (in comparison to a statical error of $12_{-3}^{+6}$ per cent when the shape of the lensing potential is perfectly known). This result is in agreement with the latest analysis of Blum, Castorina & Simonović (2020) that shows that cored (dark matter) mass density distributions give rise to approximate MSDs, and an error on the inferred Hubble constant. The latest cosmographic analyses (see e.g. Wong et al. 2019) have attempted to break these degeneracies by including the information contained in the kinematic properties of the lens galaxies and the positions of the lensed quasar images. However, the validity of this approach has been recently debated by Kochanek (2020), who has demonstrated that departures from single power-law mass distributions are responsible for a fractional error on the Hubble constant of 30 per cent. While the cores in the simulations analysed in this paper are artefacts related to limited resolution, cored mass density distribution in real galaxies may be developed by the effect of baryonic processes (see e.g. Chan et al. 2015) or changes in the dark matter properties (Schive, Chiueh & Broadhurst 2014; Spergel & Steinhardt 2000). Moreover, similar additional complexities exist in real galaxies are related, for example, to the presence of faint discs (Hsueh et al. 2018), bars, or other (baryonic) structures (Gilman et al. 2018; Xu et al. 2013). More generally, there exist many plausible deviations from a smooth power-law distribution, such as broken power laws (see e.g. Du et al. 2020) or multiple component models (see e.g. Nightingale, Dye & Massey 2018), which can produce comparable degeneracies. Together with the findings of Blum et al. (2020), our results have important implications for the analysis of time delays and a potential solution to the H0 tension (Wong et al. 2019).
Citation: Wong et al. 2019
Citation function: Compare/Contrast
The equations of motions and hydrodynamics are solved by the ramses code (Teyssier 2002). The gas follows a piecewise polytropic equation of state (EoS) fitting the heating/cooling equilibrium (see Kraljic et al. 2014, and references therein). A Jeans polytrope sets a pressure floor in the most refined volumes, to prevent artificial fragmentation. We refer the reader specifically to sections 2.2, 2.3 and 4.2 of R+13 and Kraljic et al. (2014) for further discussions on this and specific EoS (see Robertson & Kravtsov 2008; Tasker & Bryan 2008; Dobbs, Burkert & Pringle 2011; Bonnell, Dobbs & Smith 2013, for a few other implementation schemes). The resulting gas density probability distribution function (PDF; McKee & Ostriker 2007, and references therein) in the present simulation follows a classic log-normal shape (Nordlund & Padoan 1999; Padoan & Nordlund 2002) with an additional few per cent of the mass in a power-law tail at high density (Choi, Shlosman & Begelman 2013; R+13), as expected from gravity and observed in real molecular clouds and galaxies (Lombardi, Alves & Lada 2010; Druard et al. 2014). While changes in the AMR grid refinement can locally bias the velocity dispersion, the density and velocity power spectra are thus clearly dominated by a single turbulence cascade with a well-identified injection scale at the average Jeans length (Bournaud et al. 2010; R+13). The very high resolution of the present simulation allows to resolve the turbulent cascade with a realistic power spectrum (Combes et al. 2013; R+13) and density distribution (Druard et al. 2014) down to the parsec scale. The simulation comprises conversion of gas into stellar particles (down to 160 M⊙) where the volume density ρ0 exceed 2000 cm−3, assuming that the local star formation rate depends on the free-fall time and with the star formation efficiency set at 3 per cent (R+13). This recipe does not take into account additional physics that may impact on the formation of molecules, and we thus rely on the EoS to follow the cloud collapse, the low temperatures and the high density which triggers the formation of new stars. These newly formed ‘stars’ are evolved on the AMR grid, i.e. with gravitational softening down to 0.05 pc, much smaller than the dark matter and primordial stellar components. The implementation of stellar feedback includes photoionization through heating, radiative pressure via injection of momentum and supernova explosions in the kinetic form (see R+13 for more details). A more thorough study of the impact of resolution or metallicity in such simulations was conducted by Kraljic et al. (2014), who have shown that the artificial density threshold ρ0 does not tune the efficiency of star formation, which mostly depends on the turbulence level (e.g. Mach number; see Klessen 2000; Li et al. 2004; Audit & Hennebelle 2010; Renaud, Kraljic & Bournaud 2012).
Citation: Choi, Shlosman & Begelman
Citation function: Uses; Uses
The photoionization of the disc surface is characterized by two main parameters: irradiating X-ray continuum flux and disc density. Thus the measurement of the disc ionization parameter can address various aspects of the disc/corona interplay. According to Ballantyne, McDuffie & Rusin (2011), the ionization parameter of a radiation pressure supported disc illuminated by a geometrically thick corona in the SS73 model can be approximated as
(11)$$\begin{eqnarray*}
\xi &amp;\approx &amp; 4.33\times 10^{9}\left(\frac{\eta }{0.1}\right)^{-2}\left(\frac{\alpha }{0.1}\right)\left(\frac{r}{r_{\rm g}}\right)^{-\frac{7}{2}} \nonumber\\
&amp;&amp;\times \,f_{\rm c}(1-f_{\rm c})^{3}\Big (\frac{L_{{\rm bol}}}{L_{{\rm E}}}\Big)^{3}GR_{{\rm corr}},
\end{eqnarray*}$$where radiative efficiency η ≈ 0.1 (Davis & Laor 2011); viscosity parameter α = 0.1 (Shakura & Sunyaev 1973); coronal dissipation fraction fc ≈ 0.45 (Vasudevan & Fabian 2007); r is the disc radius in units of rg; $GR_{{\rm corr}}=R_{{\rm R}}^{3}R_{{\rm z}}^{-2}R_{{\rm T}}^{-1}$ is a general relativistic correction factor and is solely dependent on the dimensionless black hole spin a (e.g. Novikov & Thorne 1993; Krolik 1999). Therefore, the dependence of disc ionization log ξ on the Eddington ratio (Lbol/LE) is predominantly determined by two parameters: r and a:
(12)$$\begin{eqnarray*}
\log \xi \simeq \varPsi (r,a)\Big (\frac{L_{\rm bol}}{L_{\rm E}}\Big).
\end{eqnarray*}$$Fig. 4 shows the dependence of the disc ionization parameter on the Eddington ratio for the low-mass sample. We show the SS73 model predicted log ξ–Lbol/LE relationships for five different combinations of BH spin and inner disc radius: (a = 0.998, r = 2rg), (a = 0.998, r = 6rg), (a = 0.75, r = 6rg), (a = 0.5, r = 6rg), and (a = 0.25, r = 6rg). We noticed that the inferred ionization states of low-mass AGN discs are consistent with the SS73 model predicted solutions. The derived log ξ–Lbol/LE plane suggests that if the relativistic reflection originated from within 6rg of the inner accretion disc, then the measured ionization parameters of the low-mass sample require spins to be in the range of a ∈ [0.25, 0.998] with a median value of ∼0.75.
Citation: Vasudevan & Fabian 2007
Citation function: Uses
Several studies indicate that the solar wind produced by the WTD mechanism has higher AHe and vαp, while the solar wind may have lower AHe and vαp when the RLO mechanism is at work. While it is challenging to obtain direct observations of the AHe in the solar corona, first ionization potential (FIP) bias measurements are more readily available. It is found that generally the FIP bias is higher in AR and QS regions (mainly occupied by closed loops) than in CH regions (generally taken up by open magnetic field lines) (Widing & Feldman 2001; Feldman et al. 2005; Brooks & Warren 2011; Baker et al. 2013). It is believed that the reason for the enrichment of the low FIP ions in the corona and the solar wind is that they are ionized earlier in comparison to high FIP elements. The helium has the highest FIP and remains neutral longest. This results in the enrichment/depletion of low FIP elements/helium because only ions interact with waves (Laming 2012, 2015, 2017). It means that the helium abundance should be inversely proportional to the low FIP bias elements in the corona. Thus, the AHe is higher in open magnetic field structures and lower in closed loops if the above mechanism is valid. The helium abundance for the fast SW coming from large CHs is higher and remarkably stable (Schwenn 2006). In contrast, Rakowski & Laming (2012) suggested that the helium is depleted in closed loops and the depletion efficiency is higher in larger loops, and lower in smaller loops. Furthermore, from simulations, Laming (2017) showed that the AHe is higher in open magnetic field regions and it is lower in closed loops. Suess et al. (2009) found that the solar wind that comes from big streamers has lower helium abundance. The solar wind can be produced by interchange reconnection in the streamers (Huang et al. 2016). This gives the observational support to the notion that the AHe is lower in the closed loops as streamer structures are composed by very large closed loops.
Citation: Widing & Feldman 2001
Citation function: Background
The GW sources that LISA will observe at cosmological distances can be used as standard sirens. These include MBHBs, EMRIs, and SOBHBs. Unfortunately, only for the first of these types of sources are EM counterparts plausibly expected to be produced and observed by future EM facilities (Tamanini et al. 2016). MBHBs are in fact expected to emit a large amount of EM radiation in different bands at merger or during long-lasting (∼ weeks/months) afterglows (see, e.g. Palenzuela, Lehner & Liebling 2010; Dotti, Sesana & Decarli 2012; Giacomazzo et al. 2012; Moesta et al. 2012), and possibly even through pre-merger signals (Kocsis, Haiman & Menou 2008; Kaplan et al. 2011; O’Shaughnessy et al. 2011; Haiman 2017; Dal Canton et al. 2019). If sufficiently accurate sky localization can be attained from the GW parameter estimation analysis and if the EM counterpart is sufficiently powerful to be spotted by EM telescopes, then we expect to identify the host galaxy of up to a few LISA MBHB mergers per year (Tamanini et al. 2016; Tamanini 2017). These golden sources can then be used as high-redshift standard sirens to map the expansion of the Universe up to z ∼ 10. Although the low number of expected EM counterparts and the high redshift of MBHB mergers are not ideal to test standard cosmological models such as ΛCDM or to place constraints on late-time dark energy (DE) (Tamanini et al. 2016; Tamanini 2017; Belgacem et al. 2019b), they can efficiently be used to probe deviations from ΛCDM at earlier cosmological epochs, specifically in the interval 3 ≲ z ≲ 10 (Caprini & Tamanini 2016; Cai, Tamanini & Yang 2017; Belgacem et al. 2019b; Speri et al. 2020). Standard siren analyses with MBHBs would moreover definitely benefit from a network of space-based detectors, e.g. LISA and Taiji, which would greatly improve the sky location accuracy of each MBHBs and thus provide better chances to spot the EM counterpart (see, e.g. Shuman & Cornish 2021; Wang et al. 2021; Yang 2021).
Citation: Haiman 2017
Citation function: Background; Background
Galaxies hosting active galactic nuclei (AGN) are not only promising candidates for providing direct evidence for such a co-evolution, they can also be used to study the scaling relations over cosmic times. Many studies suggest that BH growth precedes spheroid assembly (Treu, Malkan & Blandford 2004; McLure et al. 2006; Peng et al. 2006a,b; Shields et al. 2006; Woo et al. 2006, 2008; Salviander et al. 2007; Treu et al. 2007; Gu, Chen & Cao 2009; Jahnke et al. 2009; Bennert et al. 2010, 2011; Decarli et al. 2010; Merloni et al. 2010; Wang et al. 2010); however, other studies find no significant evolution with redshift (e.g. Shields et al. 2003; Shen et al. 2008a; Salviander & Shields 2013; Schramm & Silverman 2013; Salviander, Shields & Bonning 2015; Shen et al. 2015; Sun et al. 2015). The likely reason for the disagreement is that the studies are differently affected by intrinsic scatter in the relation, selection effects, and observational biases (see e.g. Lauer et al. 2007; Volonteri & Stark 2011; Schulze & Wisotzki 2014). Another issue is that the MBH–σ* relation is not well constrained even for local AGN host galaxies at the high-mass end. Especially for the AGN appearing as quasi-stellar objects (QSOs), the bright nuclear point source often outshines its host galaxy. Measurements of the spheroid properties are therefore difficult, in particular the stellar velocity dispersion for which high signal-to-noise (S/N) spectra are needed. Thus, many studies focus on Seyfert galaxies often using aperture spectra which integrates over the central few kpc of the host galaxy (e.g. Greene & Ho 2006; Woo et al. 2006, 2008; Treu et al. 2007; Shen et al. 2008a; Matsuoka et al. 2015). The side effect is that, if present, a significant disc contribution may be included, questioning the definition of the spheroid stellar velocity dispersion in these cases. Bennert et al. (2015) study the effect of different definitions of σ* in the literature for a sample of 66 local Seyfert-1 galaxies and find that it can vary by up to 40 per cent.
Citation: Shields et al. 2003
Citation function: Compare/Contrast; Compare/Contrast
Historically, the explanation of soft state spectra of NSs demanded the presence of a blackbody emission from the boundary layer of an NS (Mitsuda et al. 1984). For the harder states with a power-law tail in the energy spectrum, the need of Compton scattering became evident (White et al. 1986; Mitsuda et al. 1989). The difference between these two models was that while the former assumed a cooler boundary layer, the latter assumed a hotter one, compared to the accretion disc. Sunyaev and his collaborators (Inogamov & Sunyaev 1999, hereafter IS99; Popham & Sunyaev 2001, hereafter PS01; Gilfanov & Sunyaev 2014 , hereafter GS14) assume that the KD reaches all the way to the NS and is connected with the boundary layer where the thickness increases due to higher temperature. Most of these studies were done to address the soft state spectra of NSs. The state transition of NSs in Low Mass X-ray Binaries (LMXBs), presented another problem. The fact that disc accretion rate was not the single factor that controlled the size or temperature of the Compton cloud, used to model the hard state spectra, lead to the conclusion that some unknown parameter, related to the truncation radius of the disc, is responsible for the hard X-ray tail (Barret 2001; Barret & Olive 2002; Di Salvo & Stella 2002). Paizis et al. (2006) found a systematic positive correlation between the X-ray hard tail and the radio luminosity, inferring that the Compton cloud might serve as the base of radio jets (see Chakrabarti 2016, and references therein). Recent phenomenological works places a transition layer (TL) or Compton cloud between the KD and the boundary layer (Farinelli et al. 2008; Titarchuk, Seifina & Shrader 2014, hereafter TSS14). It has been argued in the past (Chakrabarti 1989; C96; Chakrabarti & Sahu 1997) that while in black hole accretion, passing of the flow through the inner sonic point ensures that the flow becomes sub-Keplerian just outside the horizon, in the case of NSs, the Keplerian flow velocity must slow down to match with the sub-Keplerian surface velocity. Numerical simulations clearly showed that jumping from a KD to a sub-Keplerian disc is mediated by a super-Keplerian region (Chakrabarti & Molteni 1995). In Titarchuk, Lapidus & Muslimov (1998, hereafter TLM98), a super-Keplerian TL was invoked to explain the kHz quasi-periodic oscillations (QPOs) and in TSS14 the TL was expanded several fold to explain the spectral properties. In reality, there are two such layers simultaneously present in an NS accretion: One is similar to the NBOL and the other is similar to the CENBOL in a black hole accretion (CT95). In a black hole accretion, only CENBOL is present. All these approaches clearly point to the existence of a CENBOL type hot electron reservoir, which naturally occurred in black hole accretion, confirming Chakrabarti & Sahu (1997) conclusions that the solutions of the transonic flows are modified only in the last few Schwarzschild radii as per the boundary condition of the gravitating object.
Citation: Di Salvo & Stella 2002
Citation function: Background
Brown dwarfs and giant exoplanets populate the same temperature range and share many physical properties, such as their molecule-dominated atmospheres and gradual cooling from ~3000 K at formation to ~100 K like the solar system gas-giant planets. Recent discoveries of very massive planets (Chauvin et al. 2005; Marois et al. 2010; Delorme et al. 2013), some possibly more massive than the 13 MJup deuterium burning mass limit, hint that planets could overlap with brown dwarfs in mass. On the other hand, the discovery of isolated L dwarfs in young clusters (Zapatero Osorio et al. 2002, 2014; Peña Ramírez et al. 2012), in young moving groups (Liu et al. 2013; Gagné et al. 2015; Gauza et al. 2015), and very cold very nearby Y dwarf objects (e.g., Kirkpatrick et al. 2012; Luhman 2014) show that very low-mass isolated brown dwarfs exist and overlap with the planetary masses. When these low-mass brown dwarfs are close enough and bright enough to be observed spectroscopically their atmospheres are much easier to study than similar exoplanets that lie near their very bright host stars. Liu et al. (2013) notably showed that the ~8 MJup brown dwarf PSO J318.5−22, a β-pictoris moving group member shares the spectral characteristics of the young directly imaged exoplanets, as well as atypically red late-L spectral type objects (e.g., Faherty et al. 2013; Gizis et al. 2015; Kellogg et al. 2016; Schneider et al. 2014, 2016; Bonnefoy et al. 2016). When CFBDSIR J214947.2−040308.9, hereafter CFBDSIR 2149, was identified (Delorme et al. 2012), it seemed to be a candidate member of the AB Doradus young moving group and, together with the low-gravity features in its spectrum, made it a unique T-type isolated planetary-mass candidate. Another earlier-type, isolated young planetary-mass T-dwarf, SDSS J111010.01+011613.1, has been identified as a bona fide member of AB Doradus moving group (\hbox{$149^{+51}_{-19}$}149-19+51 Myr; Bell et al. 2015) by Gagné et al. (2015). The late-T spectral type of CFBDSIR 2149 is typical of the coolest known directly imaged exoplanets, such as GJ 504 b or 51 Eri b (Kuzuhara et al. 2013; Macintosh et al. 2015), that the latest generation of adaptive optics systems are detecting. We therefore carried out a multi-wavelength, multi-instrument follow-up of CFBDSIR 2149 to fully characterise it and constrain its nature.
Citation: Kirkpatrick et al. 2012
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The spectra from Sloan Digital Sky Survey (SDSS) have enabled the detection of the relatively faint He ii λ4686 line in large samples of star-forming galaxies (e.g. Shirazi & Brinchmann 2012). These studies find that the observed He ii λ4686/H β intensity ratio does not drop at low metallicities. In fact, recent studies find the ratio to be increasing as the metallicity decreases (Schaerer, Fragos & Izotov 2019). Furthermore, these low-metallicity He ii λ4686-emitting galaxies often show only a weak or no evidence of the presence of WR stars (Shirazi & Brinchmann 2012). Thus, questions have been raised on the WR stars as the sole source of ionization of He+ (Plat et al. 2019). Alternative mechanisms such as hard radiation from high-mass stars in binaries (Eldridge et al. 2017), shocks from supernova remnants (Garnett et al. 1991; Dopita & Sutherland 1996), and high-mass X-ray binaries (HMXBs; Schaerer et al. 2019; Kojima et al. 2020) are often invoked. Nearby low-metallicity systems offer an opportunity to address the He+ ionization problem by enabling study of individual star-forming knots. In a detailed study of the metal-poor (Z = 3–4 per cent Z⊙) galaxy SBS 0335−052E using MUSE, Kehrig et al. (2018) discard WR stars as the source of ionization and instead propose rotating metal-free stars or a binary population with Z = 10−5 and an extremely top-heavy initial mass function (IMF) as the only plausible way of getting around the problem of the ionization budget. In a recent study, Schaerer et al. (2019) find that the observed He ii λ4686 intensity in metal-poor star-forming galaxies can be naturally reproduced if the bulk of the He+ ionizing photons is emitted by the HMXB, whose number is found to increase with decreasing metallicity. X-ray binaries in a cluster appear only after the death of the most massive stars, and hence this scenario cannot explain the He+ ionization in young systems [H β equivalent widths (EWs) ≥ 200 Å], as illustrated by Plat et al. (2019).
Citation: Dopita & Sutherland 1996
Citation function: Background; Background; Background