adsabs/FOCAL huggingface dataset:
In particular, stellar wind P-Cygni profiles and photospheric absorption lines are detected with high significance (green and yellow dashed lines in Fig. 2). The detection of photospheric lines in J0121+0025 indicates unambiguously that the UV luminosity is dominated by stellar emission, rather than an AGN. We identify more than ten photospheric features. Some of them are resolved and detected with high significance (e.g. C ii 1324 Å, O iv 1343 Å, and S v 1501 Å; see Fig. 3). We use these to determine the systemic redshift zsys = 3.244 ± 0.001 of J0121+0025. Others are seen in blends from multiple transitions (e.g. Si iii 1417 Å, C iii 1427 Å, and Fe v 1430 Å at λ0 ≃ 1415–1435 Å). These stellar absorption lines are intrinsically weak in star-forming galaxies, with EW0 typically well bellow 1 Å (e.g. Shapley et al. 2003; Steidel et al. 2016; Rigby et al. 2018). As they are formed in the photospheres of hot stars and are seen in absorption, the background radiation should be dominated by the starlight, otherwise they would not be detected. Even a small contribution of an AGN to the UV continuum (≲ 25 per cent), that is featureless in these spectral regions, would make these lines disappear at the SNR of our spectrum. In addition, the observed P-Cygni profiles in N v 1240 Å and C iv 1550 Å can be also well explained/modelled by stellar models with a very young age (≃3 Myr burst; see Fig. 3 and Section 3.2 for details), similar to those seen in other very young starbursts (e.g. Rivera-Thorsen et al. 2019; Vanzella et al. ), some of them also very/extremely luminous (Vanzella et al. 2018; Marques-Chaves et al. 2020b). While some rare AGNs, such as broad or narrow absorption line QSOs (BAL/NAL QSOs), can show N v and C iv profiles mimic those of stellar P-Cygni, from the combination of a broad emission and a redshifted absorption (see for example Bentz, Osmer & Weinberg 2004; Appenzeller et al. 2005), photospheric lines are not present in the spectra of AGNs.
Citation: Steidel et al. 2016
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A comparison of the He and O abundances in RWT 152 with evolutionary models of stellar yields by Marigo (2001) suggests a progenitor star with an initial mass of ∼1.3 M⊙ and very low metallicity Z = 0.004. The stellar mass is compatible with that expected for sdOs (Heber 2009) and the low metallicity indicates that the progenitor was formed in a poor-metal environment. In contrast, similar models of initial mass ∼1.25 M⊙ and Z = 0.004 by Karakas (2010) predict abundances substantially different from those found in RWT 152. Even for the lowest metallicity in the Karakas models (Z = 0.0001), we do not recover the chemical abundances of RWT 152. Therefore, it is clear that drawing conclusions about the progenitor star of RWT 152 from the chemical abundances of the nebula may be a bit misleading. For this reason, we have obtained information about the progenitor from the current status of its CS. Fig. 6 shows the position of RWT 152 in the Hertzsprung-Russell diagram log g–Teff with the post-AGB tracks by Bloecker (1995) and Schoenberner (1983). The location of the star (Teff ≃ 45 000 K, log g ≃ 4.5; Ebbets & Savage 1982) is consistent with a current mass of M∼0.55 M⊙ which implies an initial mass in the main sequence of ∼1 M⊙. For such a low-mass star, the ejected mass during the AGB evolution is expected to be small. In fact, with the electron density derived above and the size of the nebula, we obtain values of 1.3 × 10−2–1.6 × 10−1 M⊙ for the ionized nebular mass (assuming 2.4 and 6.5 kpc, respectively, and a filling factor of 0.6). These values are much smaller than ionized masses usually obtained for PNe (see e.g. Hua & Kwok 1999), further supporting a low-mass progenitor for RWT 152. Moreover, taking into account that 0.1–0.3 M⊙ are lost in the red giant branch phase of a low-mass star (Dorman, Rood & O'Connell 1993), the current mass of the CS and the obtained ionized mass, we recover a progenitor star with a ∼0.8–1.0 M⊙, in agreement with the value obtained from the position of the CS in the log g–Teff diagram. Such a low ionized mass, combined with a relatively high kinematical age, may explain the low surface brightness of RWT 152. If a low-mass progenitor is involved in the evolution of other PNe+sdO systems, it is not surprising that these PNe are very faint and, in some cases, may have faded beyond detection.
Citation: Ebbets & Savage 1982
Citation function: Similarities; Similarities
As done by Le Fèvre et al. (2020), we visually inspect the ancillary data, the intensity maps, the velocity and velocity dispersion fields presented in Sect. 3.1 to search for the presence of multiple components or disturbed morphology near the position of the targets. The channel maps, the spectra and the PVDs are checked together searching for consistent emission features. By taking into account the results of the initial qualitative classification by Le Fèvre et al. (2020) and of the more recent quantitative analysis of a subsample of the ALPINE targets by Jones et al. (2021), we proceed with a more in-depth characterization of the [CII]-detected galaxies aimed at obtaining a robust merger fraction at z ∼ 5. Adopting the same criteria described in Sect. 2 to differentiate the targets and considering the S/N of the minor merger component as described in Sect. 3.1, we find a slightly lower fraction (∼31%, 23 out of 75 [CII]-detected sources) of mergers7 if compared to the 40% found by Le Fèvre et al. (2020), with 12, 20 and 7% of the sample made by rotating, extended and compact dispersion dominated sources, respectively. To be more conservative in the classification of the galaxies (especially for obtaining a more robust merger statistics), we define the remaining 30% of the sample as ‘uncertain’, a new category that includes the weak galaxies (as described in Le Fèvre et al. 2020) and also objects that, by visual inspection, present features that are intermediate to those of various classes. This category is similar to the ‘uncertain’ (UNC) class introduced in Jones et al. (2021) that, based on the results of the 3DBarolo fits, contains sources they are unable to classify because of the low S/N and/or spectral resolution, or contrasting evidence in their classification criteria. Although the uncertain category is populated by a significantly larger fraction of sources with respect to the weak class (∼16%) in Le Fèvre et al. (2020), we recover the same qualitative morpho-kinematic distribution of the previous analysis, confirming the high fraction of rotators and mergers at these early epochs.
Citation: Jones et al. (2021)
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Citation: Jones et al. (2021)
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Altogether, the approximately thirty molecules recently detected have confirmed the chemical complexity in the nebula, and generated our interest for the present study. Of these species, we will focus our attention on the seventeen species listed by molecular families in Table 1. As can be seen in this table, the WHISPER survey allowed the detection of some organic molecules in the Horsehead nebula, such as formaldehyde (H2CO) and methanol (CH3OH), which constitute key species in the likely synthesis of more complex organic molecules such as some prebiotic molecules (Bernstein et al. 2002; Muñoz Caro et al. 2002; Garrod et al. 2008). Because they are detected in a wide variety of interstellar sources – in hot cores (Sutton et al. 1995; Ceccarelli et al. 2000), dark clouds (Bergman et al. 2011), shocked regions (e.g. Sakai et al. 2012; Codella et al. 2012; Tafalla et al. 2010) and even in comets (Mumma & Charnley 2011; Cordiner et al. 2015) – it is of prime importance to understand well how these precursor molecules form. H2CO is commonly thought to form both in the gas-phase and on grain surfaces, while CH3OH is believed to be only formed on grain surfaces (Garrod et al. 2006; Geppert et al. 2006). Guzman et al. (2013) reported the observations of these two molecules toward the Horsehead nebula in both the PDR and Core positions. Unable to reproduce the observed abundances of either H2CO or CH3OH at the PDR position with only pure gas-phase models, they concluded that, for this region, both species are formed on grain surfaces and then photodesorbed into the gas phase. On the other hand, at the Core position, a pure gas-phase model can reproduce the observed H2CO abundance, while photodesorption of ices is still needed to explain the observed abundance of CH3OH. Other organic molecules were reported in the Horsehead nebula as first detections in a PDR environment, including HCOOH (formic acid), CH2CO (ketene), CH3CHO (acetaldehyde), and CH3CCH (propyne) (Guzman et al. 2014). Their abundances were found to be higher at the PDR position than at the Core, revealing that complex organic chemistry is also occurring in UV-illuminated neutral gas (Guzman et al. 2014). Of these molecules, some – HCOOH, CH2CO, and CH3CHO – have now also been detected in the Orion bar PDR (Cuadrado et al. 2016, 2017).
Citation: Ceccarelli et al. 2000
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Citation: Bernstein et al. 2002
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Citation: Cordiner et al. 2015
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The duration of the manually scheduled follow-up observations were also increased to improve the likelihood of a radio detection. The recent investigation of the entire sample of radio-detected GRBs before 2011 April by Chandra & Frail (2012) demonstrated that the majority of GRBs detected in the radio band at 8.5 GHz had a peak flux between 0.1 and 0.2 mJy beam−1 at 5–10 d post-burst (see fig. 4 of Chandra & Frail 2012). A 4 h AMI observation is therefore required to reach an rms noise of ∼0.03–0.04 mJy beam−1 that will allow the reliable detection of >0.1–0.2 mJy beam−1 sources. However, it is worth noting that since GRB relativistic blast waves generate synchrotron radiation as they expand into the circumstellar (wind generated) medium (Granot & Sari 2002), we expect the forward-shock of the afterglow to peak more brightly at 15.7 GHz and at earlier times than the peaks recorded by Chandra & Frail (2012). We therefore require a higher monitoring cadence at early times (within 5 d post-burst) to detect similar radio peaks. As the range of radio peaks observed by Chandra & Frail (2012) will be brighter at 15.7 GHz, the rms achieved by a 4 h AMI observation will be sufficient for detecting events similar to those seen in their sample. The follow-up observations are manually scheduled to occur near transit approximately 24 h, 3, 7, and 10 d post-burst, with this temporal spacing designed to catch the peak of the forward- or reverse-shock at 15.7 GHz at a range of redshifts (z ≲ 5; e.g. see figs 22 and 23 of Chandra & Frail 2012). In the event that a GRB radio counterpart was detected, the AMI observing cadence was increased to a 4 h observation every 1 or 2 d. As part of the AMI GRB observing programme, we also obtained manually scheduled observations of GRBs that were detected with the Fermi Large Area Telescope (LAT; Atwood et al. 2009), the Fermi Gamma-ray Burst Monitor (GBM; Meegan et al. 2009) and the International Gamma-Ray Astrophysics Laboratory (INTEGRAL; Winkler et al. 2003), whose positions had been more precisely localized through the identification of X-ray and/or optical counterparts, usually by the Swift-XRT, Swift-UVOT, or one of the ground-based GRB follow-up programmes.
Citation: Granot & Sari 2002
Citation function: Uses; Compare/Contrast; Uses
Eigenbrod et al. (2006) first modelled this system with HST imaging and suspected that the second set of bluer arcs in F814W band (see Fig. 1) inside and outside the area delimited by the red arcs in F160W band could be either a second source at a different redshift or a star-forming region in the source galaxy. We examine the possibility of a second source plane existing at a lower redshift than the source (z = 1.52) due to the bluer colour of the arc and find that the scenario is very unlikely, as the macro model determined by the red arc cannot reproduce a reasonable source for the blue arcs given a possible range of the source redshift from z = 0.5 to z  1.52. In contrast, we do find that a star-forming region can be reconstructed at the same source redshift. Faure et al. (2011) modelled the lens with high-resolution H and Ks imaging obtained using the European Southern Obseratory (ESO) Very Large Telescope (VLT) with AO and the laser guide star system. They identified a luminous object, located ∼0.3 arcsec to the north of the lens galaxy, but showed that it cannot be responsible for the anomalous flux ratios. Many studies (e.g. Metcalf & Madau 2001; Bradač et al. 2002; Dalal & Kochanek 2002; Pooley et al. 2012; Schechter et al. 2014; Glikman et al. 2018; Badole et al. 2020) have shown that the macro model cannot explain the flux ratios in this lens, which suggested the presence of microlensing or dark matter substructures. Thus, to avoid possible biases caused by flux ratios, we only use the lensed quasar positions and the extended arc to constrain the mass model, which is also the standard procedure for H0 measurements in TDCOSMO Collaboration. Ignoring the fluxes of the lensed quasar images will not affect the constraining power of the imaging data, since the lensed arc emission is much more constraining than the lensed quasar fluxes. In addition, For the error budget of H0 contributed from the uncertainties of the lensed quasar positions, Chen et al. (2021a) have showed that with high-resolution AO imaging it is a subdominate term given configuration of the J0924+0219 lens system. Gilman et al. (2020) also show that the presence of substructures do not bias H0 above the per cent level. We use glee, a strong lens modelling code to model (Suyu & Halkola 2010; Suyu et al. 2012) the three HST bands and one Keck AO band simultaneously. We describe the models in the following for fitting the high-resolution imaging data. We show the imaging, models, normalized residuals, and reconstructed sources in Fig. 4. Note that since the source in F555W band has more clumpy star-forming regions, the reconstructed source is less regular, with small-scale structures and more noise.5 In addition, the noise-overfitting problem is due to the fact that the outer region of the source plane is under-regularized, but this effect will not affect the uncertainty because the uncertainty will be dominated by the time delay and velocity dispersion measurements. Besides, we model the imaging with different source resolutions and marginalize over them to control the systematics.
Citation: Bradač et al. 2002
Citation function: Uses; Uses
In the last two decades, it has been demonstrated that massive galaxies harbour supermassive black holes (SMBHs) in the centres of their bulge components (Kormendy & Ho 2013, and references therein). Also, at redshifts higher than 6, quasars are found that possess SMBHs with the mass higher than 109 M⊙ (Fan et al. 2001; Kurk et al. 2007). The formation history of these SMBHs is among the most significant unsolved issues in astrophysics (Volonteri & Bellovary 2012; Haiman 2013). Two recently discovered high-redshift quasars, ULAS J112010+641 with the mass of MBH = 2 × 109 M⊙ at redshift z = 7.085 (Mortlock et al. 2011) and SDSS J01001+2802 with MBH = 1.2 × 1010 M⊙ at z = 6.30 (Wu et al. 2015) have raised a serious problem for the formation of SMBHs. Possible building blocks for such high-redshift SMBHs are the remnants of first stars. The initial mass function of first stars is thought to be more or less top-heavy (Abel, Bryan & Norman 2000; Nakamura & Umemura 2001; Bromm, Coppi & Larson 2002; Yoshida et al. 2006; Greif et al. 2011; Hirano et al. 2014; Susa, Hasegawa & Tominaga 2014). First stars of several tens M⊙ undergo supernovae, leaving black holes (BHs) of few tens M⊙ (Heger & Woosley 2002). For SMBHs to grow from such first star remnants through mass accretion at z ≳ 6, a super-Eddington accretion rate is requisite. If SMBHs grow continuously by mass accretion from BH remnants of ∼20 M⊙, the Eddington ratio (λ) is required to be λ = 1.4 for ULAS J112010+641, or λ = 1.3 for SDSS J01001+2802. However, the continuous accretion is unlikely to be sustained due to feedbacks, and thus the average mass accretion rates should be lower than the Eddington rate (Alvarez, Wise & Abel 2009; Milosavljevic, Couch & Bromm 2009). On the other hand, seed BHs may stem from supermassive stars of 104–6 M⊙ as a result of the direct collapse of primordial density fluctuations (Umemura, Loeb & Turner 1993; Bromm & Loeb 2003; Inayoshi & Omukai 2012). These BHs are thought to be incorporated into a primordial galaxy of ∼108–109 M⊙ (Greene 2012). If an SMBH grows via gas accretion from such a massive BH (MBH), the constraint on the accretion rate can be alleviated.
Citation: Yoshida et al. 2006
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So far, the discussion has emphasized particle energization by local plasma regions of contracting and fast reconnecting (merging) small-scale flux ropes generated in the vicinity of large-scale primary current sheets through turbulent current sheet reconnection. However, one can also approach this topic from the perspective of MHD turbulence theory, simulations, and related solar wind observations. Theoretical considerations and simulations of MHD turbulence in the presence of a significant background/guide magnetic field suggest that solar wind turbulence can to lowest order be modeled in terms of a combination of a dominant quasi-2D turbulence component of coherent structures (small-scale magnetic islands) perpendicular to the background/guide field and a minor parallel-propagating Alfvén wave turbulence component (Shebalin et al. 1983; Zank & Matthaeus 1992, 1993; Dmitruk et al. 2004; Zank et al. 2017), a view that is consistent with analysis of solar wind observations (Matthaeus et al. 1990; Bieber et al. 1996) and with the finding that quasi-2D turbulence alone is not sufficient to explain observed solar wind turbulence (Turner et al. 2012). A recent analysis of Wind data to identify inertial-scale flux ropes indicates that these structures are much more commonplace in the solar wind near 1 au than previously thought. Zheng (2017), Zheng et al. (2017), and Zheng & Hu (2018) identified an unprecedented number of small-scale flux ropes at 1 au with scales in the inertial range using the Grad–Shafranov reconstruction approach (∼3500 per year on average) with a clear solar cycle dependence, a number that is expected to grow when the data analysis shifts to shorter timescales. Furthermore, an axial (out-of-plane) current density distribution constructed from the Grad–Shafranov-based data analysis yielded a non-Gaussian probability density function (pdf) entirely consistent with the out-of-plane current density pdf produced from compressible 2D MHD turbulence simulations with a strong out-of-plane guide field, in which merging magnetic island structures are a common occurrence (Greco et al. 2009). This result, combined with the sheer number of small-scale flux ropes being identified, suggests that the common occurrence of small-scale flux ropes in the low-latitude solar wind near 1 au is a natural consequence of local MHD turbulence evolution in a highly conductive plasma with a strong guide field, independent of additional flux-rope production at primary current sheets. Furthermore, observational evidence of merging (magnetic reconnection) of neighboring small-scale flux ropes at Earth (Khabarova et al. 2015, 2016), including evidence on the basis of Grad–Shafranov reconstruction of small-scale flux ropes (Zheng & Hu 2016; Zheng 2017; Zheng et al. 2017), is consistent with the concept of quasi-2D turbulence theory of an inverse cascade of magnetic island energy to smaller wavenumbers.
Citation: Zank & Matthaeus 1992
Citation function: Background; Similarities; Similarities
The realistic structures of the pulsar magnetosphere still remain uncertain. Knowledge about the pulsar magnetosphere structures can be used to identify the potential sites of particle acceleration and gamma-ray emission. A vacuum dipole field is generally adopted in the early study of pulsar emission, because it has an exact analytical solution given by Deutsch (1955). Based on this field structure, different theoretical models have been developed to explain the observed pulsar emission. In these models, it is widely believed that particles are accelerated in the gap region where an accelerating electric field is created because of the deficit of charges. Gamma-ray emission is produced by the curvature or inverse-Compton radiation from high-energy particles accelerated in these gaps. Due to different emission zone locations, standard pulsar radiation models include the polar cap (PC; e.g., Ruderman & Sutherland 1975; Daugherty & Harding 1982), the slot-gap (SG) (e.g., Dyks & Rudak 2003; Dyks et al. 2004; Muslimov & Harding 2004), and the outer gap (OG; e.g., Cheng et al. 1986, 2000; Zhang & Cheng 1997, 2001; Zhang et al. 2004) models. These gap models have achieved great successes in explaining pulsar high-energy emissions and light curves (e.g., Watters et al. 2009; Romani & Watters 2010). However, the vacuum solution has no plasma; it is not able to reproduce any pulsar phenomena. It is well known that the pulsar magnetosphere should be filled with plasma (Goldreich & Julian 1969). In the presence of abundant plasma, all accelerating electric fields can be efficiently screened to form a force-free (FF) magnetosphere. The FF solution for an aligned rotator was first obtained by Contopoulos et al. (1999). The CKF solution consists of a closed field line region extending to the light cylinder (LC), an open field line region, and an equatorial current sheet beyond the LC. Moreover, the time-dependent simulations for the FF axisymmetric rotator also confirmed the closed–open CKF solution (e.g., Komissarov 2006; McKinney 2006; Timokhin 2006; Yu 2011; Parfrey et al. 2012; Cao et al. 2016a; Etienne et al. 2017).
Citation: Dyks et al. 2004
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