adsabs/FOCAL huggingface dataset:
Submillimetre galaxies (SMGs) are ultraluminous dusty star-forming galaxies (SFGs) with the vast majority of radiation energy in the far-infrared (FIR) and submillimetre bands (Smail, Ivison & Blain 1997; Barger et al. 1998; Hughes et al. 1998; Michałowski et al. 2012; Casey, Narayanan & Cooray 2014). They are extreme starbursts with high star formation rate (SFR) of $\sim 10^2\, -\, 10^3$ M⊙ yr−1 and high stellar mass of ∼1010–11 M⊙, located preferentially at z ∼ 2–3 (Chapman et al. 2005; Wardlow et al. 2011; Smolčić et al. 2012; Simpson et al. 2014; Brisbin et al. 2017; Danielson et al. 2017; Michałowski et al. 2017; Smith et al. 2017; Hodge & da Cunha 2020, and references therein). The physical properties of SMGs derived from detailed studies of individual sources and large sky area submillimetre surveys suggest that SMGs represent an early evolutionary phase of all local ellipticals (Smail et al. 2002; Swinbank et al. 2006; Fu et al. 2013; Toft et al. 2014; Ikarashi et al. 2015; Miettinen et al. 2017; An et al. 2019; Gullberg et al. 2019; Dudzevičiūtė et al. 2020; Rennehan et al. 2020). Although SMGs are a rare population (∼400 deg−2 down to S850 = 4 mJy; Simpson et al. 2019; Shim et al. 2020), they contribute a significant fraction (∼20 per cent) of the cosmic SFR density at z > 2 (Bourne et al. 2017; Koprowski et al. 2017; Zavala et al. 2021). Their extreme SFRs are correlated with higher gas fractions compared to normal SFGs at the same epoch (Bothwell et al. 2013; Scoville et al. 2016; Decarli et al. 2016; Tacconi et al. 2018). The large amount gas is thought to be supplied by gas infall via cold streams from surrounding gas reservoirs (Narayanan et al. 2015; Ginolfi et al. 2017). The extreme starbursts of this population are partially triggered by galaxy major mergers (Tacconi et al. 2008; Engel et al. 2010, but see Davé et al. 2010; Narayanan et al. 2015; McAlpine et al. 2019), while a diversity of morphologies unveiled from the rest-frame ultraviolet (UV) and optical imaging indicate galaxy interactions and disc instabilities to be important mechanisms for enhancing star formation in SMGs (Swinbank et al. 2010; Kartaltepe et al. 2012; Chen et al. 2015), as well as AGN activities (Chapman et al. 2005; Wang et al. 2013). Because the rarity and high SFR of SMGs are sensitive to the physical processes governing galaxy formation (e.g. star formation, stellar and AGN feedback, gas infall, metal enrichment, and galaxy merging/interactions), the SMG population is used to constrain cosmological models. It remains challenging to reproduce the SMG population with high SFRs matching observations at high z (Davé et al. 2010; McAlpine et al. 2019; Hayward et al. 2021; Lovell et al. 2021).
Citation: Bourne et al. 2017
Citation function: Background; Background
Many factors can affect the prevalence of AGN activity. One important question is how gas is brought down to the galaxy center to fuel supermassive black holes (SMBHs). In the literature, two kinds of mechanisms are proposed. One is the internal secular evolution process. The torque induced by non-axisymmetric galactic structures can drive slow and significant inflow (Kormendy & Kennicutt 2004; Hopkins & Quataert 2011; Sellwood 2014; Fanali et al. 2015). The galactic bar is one of the most prominent non-axisymmetric structures and it exists in about 40% of spiral galaxies (Oh et al. 2012). In addition, there is evidence demonstrating that bars can enhance star formation in the central regions of galaxies (e.g. Oh et al. 2012; Chown et al. 2019). However, the question of whether galactic bars can significantly affect AGN activity is still under debate (Arsenault 1989; Mulchaey & Regan 1997; Oh et al. 2012; Galloway et al. 2015; Goulding et al. 2017; Alonso et al. 2018). Other mechanisms, such as galaxy merger and interaction, are also expected to displace the angular momentum of the gas and transport the gas inward (e.g. Hopkins et al. 2006; Di Matteo et al. 2008; Bhowmick et al. 2020). Similarly to studies of secular evolution, observational evidence for this scenario is also mixed. Some studies have found significant environmental dependence of AGN activity (e.g. Koulouridis et al. 2006; Koss et al. 2010; Ellison et al. 2011; Sabater et al. 2013; Khabiboulline et al. 2014; Lackner et al. 2014; Satyapal et al. 2014; Hong et al. 2015; Kocevski et al. 2015; Goulding et al. 2018; Gao et al. 2020), while others have found no or only weak environmental effects (e.g. Grogin et al. 2005; Li et al. 2006a, 2008; Pierce et al. 2007; Ellison et al. 2008; Gabor et al. 2009; Darg et al. 2010; Wang & Li 2019; Man et al. 2019). The contradictory results may be caused by the difference in AGN selection criterion, observational bias, control sample, and environmental indicator used. As we show below, understanding the environmental effects on AGNs also requires knowledge about the evolutionary status of their host galaxies, as it can help us to better understand how to construct control samples and to adopt appropriate environmental indicators.
Citation: Oh et al. 2012
Citation function: Background
The oldest and most metal-poor stars contain a fossil record of the star formation processes in the early Universe. These first stars would have been composed solely of hydrogen, helium, and trace amounts of lithium (Steigman 2007; Cyburt et al. 2016); without metals to efficiently cool the gas, large Jeans masses, and thereby very massive stars ($M_* \gtrsim 100 \, \mathrm{M}_{\odot }$) are predicted to have formed (Silk 1983; Tegmark et al. 1997; Bromm, Coppi & Larson 1999; Abel, Bryan & Norman 2002; Yoshida et al. 2006). In addition, improved gas fragmentation models (e.g. Clark et al. 2011; Schneider et al. 2012) and the discovery of very low-mass ultrametal-poor stars ([Fe/H]  −4; Keller et al. 2014; Starkenburg et al. 2017b; Schlaufman, Thompson & Casey 2018; Nordlander et al. 2019) have suggested that lower mass, long-lived stars may have also formed in these pristine environments (e.g. Nakamura & Umemura 2001; Wise et al. 2012). Notably, if ≤0.8 M⊙ stars were to form, they could still exist today on the main sequence, and are expected to have undergone very little surface chemical evolution over their lifetimes. Detailed studies could provide invaluable constraints on (1) the nucleosynthetic yields from the first stars and the earliest supernovae (e.g. Heger & Woosley 2010; Ishigaki et al. 2014; Tominaga, Iwamoto & Nomoto 2014; Clarkson, Herwig & Pignatari 2018; Nordlander et al. 2019), (2) the physical conditions in the high-redshift universe (where stars are too faint to be observed individually; Tegmark et al. 1997; Freeman & Bland-Hawthorn 2002; Cooke & Madau 2014; Hartwig et al. 2018; Salvadori et al. 2019), (3) the primordial initial mass function (e.g. Greif et al. 2012; Susa, Hasegawa & Tominaga 2014), and (4) early Galactic chemical evolution processes (see Sneden, Cowan & Gallino 2008; Tolstoy, Hill & Tosi 2009; Roederer et al. 2014; Yoon et al. 2016; Wanajo et al. 2018; Kobayashi, Karakas & Lugaro 2020, and references therein).
Citation: Schneider et al. 2012
Citation function: Motivation; Motivation
Star-forming galaxies at redshifts z ∼ 1–3 probe the cosmic epoch when most of the stellar mass assembly in the universe took place (Madau & Dickinson 2014, and references therein). A better understanding of star formation (SF) during this epoch is therefore imperative to understand SF across cosmic time. Locally, less than 5% of the galaxy population has a star formation rate (SFR) that is significantly higher than the empirical main sequence for star-forming galaxies, i.e., the tight correlation (∼0.3 dex) between the SFR and stellar mass, M⋆ (Brinchmann et al. 2004; Elbaz et al. 2007, 2011; Noeske et al. 2007; Goto et al. 2011; Rodighiero et al. 2011; Sargent et al. 2012; Whitaker et al. 2012, 2014; Salmon et al. 2015). These often-called starburst galaxies, with an IR luminosity LIR ∼ (0.1–5) × 1012 L⊙ (e.g., Sanders & Mirabel 1996; Downes & Solomon 1998), become increasingly more common at high z. In fact, (sub)millimeter number counts reveal that galaxies with LIR > 1012–13 L⊙, at z > 0.5, are many hundreds of times more likely to exist than in the local universe (Blain et al. 2002; Chapman et al. 2005; Berta et al. 2011; Magnelli et al. 2011; Béthermin et al. 2012; Magnelli et al. 2013; Casey et al. 2013, 2014; Geach et al. 2013; Simpson et al. 2014; Strandet et al. 2016; Brisbin et al. 2017). Meanwhile, the cosmic molecular gas density also peaks at z ∼ 1–3 (Decarli et al. 2014, 2016a, 2016b, 2019; Walter et al. 2014; Lentati et al. 2015; Pavesi et al. 2018; Liu et al. 2019; Riechers et al. 2019). This suggests a strong link between molecular gas and SF. Rest-frame far-IR (FIR) measurements of spectral lines and thermal dust continuum emission have been used to investigate the cooling and heating processes of the interstellar medium (ISM) in star-forming galaxies; however, the physical conditions at high z are still, in general, poorly investigated (Popesso et al. 2012; Bothwell et al. 2013; Carilli & Walter 2013; Genzel et al. 2013; Yang et al. 2017; Tacconi et al. 2018, 2020; Aravena et al. 2020; Birkin et al. 2020; Boogaard et al. 2020; Lenkić et al. 2020).
Citation: Sargent et al. 2012
Citation function: Background
The photoevaporation model successfully explains the ‘two-time-scale’ nature of protoplanetary disc evolution, where the inner regions of protoplanetary discs appear to evolve slowly on Myr time-scales, before dispersing on a much more rapid time-scale (e.g. Kenyon & Hartmann 1995; Ercolano, Clarke & Hall 2011; Koepferl et al. 2013; Ercolano et al. 2014). Furthermore, slow-moving (∼5–10 km s−1) ionized winds are observed to be occurring in many nearby discs hosting young stars (e.g. Hartigan, Edwards & Ghandour 1995; Pascucci & Sterzik 2009; Rigliaco et al. 2013) and are consistent with the photoevaporation model (Alexander 2008; Ercolano & Owen 2010; Pascucci et al. 2011; Owen, Scaife & Ercolano 2013a; Ercolano & Owen 2016). The photoevaporation model can also explain a large fraction of observed ‘transition discs’ (e.g. Owen & Clarke 2012; Espaillat et al. 2014), specifically those with holes ≲10 au and accretion rates ≲10−9 M⊙ yr−1 (Owen et al. 2011b) and even those with larger holes and higher accretion rates in more recent models that incorporate CO depletion in the outer disc (Ercolano, Weber & Owen 2018). Transition discs are protoplanetary discs with evidence for a large hole or cavity in their discs (e.g. Espaillat et al. 2014), but they are known to be a heterogeneous class of objects (e.g. Owen & Clarke 2012; van der Marel et al. 2016) and their origins are not always clear. However, a specific prediction of the standard photoevaporation scenario is that there should be a large number of transition discs with hole sizes ≳10 au but that are no longer accreting. This final long-lived stage of disc dispersal gives rise to transition discs which have lifetimes between 105 and 106 yr, but remain optically thick – ‘relic discs’ (Owen et al. 2011b). The long disc lifetimes emerge from the simple fact that discs store most of their mass at large radii, but photoevaporative clearing proceeds from the inside out, so it will always take longer to remove the larger disc mass that resides at larger distance. While several discs satisfy this criterion (Dong et al. 2017), the number of observed non-accreting transition discs with large holes falls far below the theoretical expectations (Owen et al. 2011b; Owen & Clarke 2012). Studies by Cieza et al. (2013) and Hardy et al. (2015) showed that optically thick relic discs are rare and many non-accreting stars that show evidence for a circumstellar disc are more consistent with young, radially optically thin, debris discs.
Citation: Owen et al. 2011b
Citation function: Differences; Differences
The broad-band SED of blazars, in a log(νFν) versus log(ν) representation, shows two prominent broad components, one (low-energy component) peaking form far-infrared frequencies to X-ray energies and another (high energy component) peaking at MeV/GeV energies. The peak of the low-energy component (νs) is used to further classify blazars as high synchrotron peaked BL Lacs (HBL when νs > 1015 Hz), intermediate synchrotron peaked BL Lacs (IBL when 1014  νs  1015 Hz), or low synchrotron peaked BL Lacs (LBL when νs  1014 Hz) objects (Padovani & Giommi 1995; Abdo et al. 2010). Sometimes the synchrotron peak can reach energies as high as ∼1 keV, (∼2 × 1017 Hz) or beyond, showing what is considered to be extreme behaviour, even for these highly peculiar sources (e.g. Giommi, Menna & Padovani 1999; Costamante et al. 2001; Biteau et al. 2020). Such a high synchrotron peak was first observed during a flare of Mkn 501 (Pian et al. 1998), and subsequently in many other objects (e.g. Costamante et al. 2018; Sahakyan 2020a). Independently of the location of the peak, the low-energy part of the SED is generally interpreted as synchrotron emission from the relativistic electrons in the jet. A proton synchrotron origin of the high energy end of this component during X-ray flares has also been considered (Mastichiadis & Petropoulou 2021; Stathopoulos et al. 2021). The nature of the high energy (HE; >100 MeV) component is instead still under debate. Within one-zone leptonic scenarios, the second component originates from inverse Compton scattering of the synchrotron photons (SSC) by the electron population producing the low-energy component (Ghisellini, Maraschi & Treves 1985
; Maraschi, Ghisellini & Celotti 1992; Bloom & Marscher 1996). Depending on the location of the emission region, the photons external to the jet [e.g. photons from the disc, or those reprocessed from the broad-line region (BLR) or those from the infrared torus] can up-scatter, producing the second component [external inverse Compton (EIC); Sikora, Begelman & Rees 1994; Błażejowski et al. 2000; Ghisellini & Tavecchio 2009
]. On the other hand, the HE component can be also produced from the interaction of relativistic protons either from their synchrotron emission (Mücke & Protheroe 2001) or from the secondary particles from pion decay (Mannheim & Biermann 1989; Mannheim 1993; Mücke & Protheroe 2001; Mücke et al. 2003; Böttcher et al. 2013). Recently, after associating TXS 0506+056 with the IceCube-170922A neutrino event (IceCube Collaboration 2018a, b; Padovani et al. 2018) the lepto-hadronic scenarios, when both electrons and protons contribute to the HE emission, have become more attractive. These models also predict very high energy (VHE; >100 GeV) neutrinos observable by the IceCube detector (Ansoldi et al. 2018; Keivani et al. 2018; Murase, Oikonomou & Petropoulou 2018; Padovani et al. 2018; Sahakyan 2018; Cerruti et al. 2019; Gao et al. 2019; Righi, Tavecchio & Pacciani 2019; Sahakyan 2019; Gasparyan, Bégué & Sahakyan 2022).
Citation: Stathopoulos et al. 2021
Citation function: Compare/Contrast; Compare/Contrast
These two isotopes are made by the rapid neutron-capture (r) process, and typical estimates for the time interval at which r-process nucleosynthetic events that are believed to enrich a parcel of gas in the Galaxy range between 200 and 500 Myr (Hotokezaka et al. 2015; Tsujimoto et al. 2017; Bartos & Marka 2019; Côté et al. 2021). Therefore the case of 247Cm/129I is the best example of Regime 3 because τeq = 5085 Myr (Table 2) is much longer than γ, while each τ (≃22.5 and 22.6 Myr, respectively) is much shorter than γ. The ratios to the long-lived or stable references isotopes, 247Cm/235U and 129I/127I, allow us to derive a TLE, for example, for the specific γ value of 316 Myr considered in Table 3, and derive typical production ratios of 1.35 for 129I/127I and 0.3 for 247Cm/235U. While our TLE values are not perfectly compatible with each other, the more detailed analysis shown by Côté et al. (2021) demonstrates that there is compatibility for TLE in the range between 100–200 Myr, depending on the exact choice of the K parameter (Côté et al. 2019a), γ, and the production ratios. The short mean lives of 247Cm and 129I ensure that there is no memory from previous events, while the long τeq of 247Cm/129I instead ensures that this ratio did not change significantly during TLE and has a high probability to be within the 10% of the production ratio. Therefore the production ratio of the last r-process event that polluted the ESS material can be accurately determined directly from the ESS ratio. If we assume that the last event produced a 247Cm/232Th ratio similar to the average predicted by Goriely & Janka (2016) and assume a solar ratio for 127I/232Th, then we find an inconsistency between the numbers in the last two columns of Table 3. The back-decayed value is more than five times lower than the assumed production ratio, which indicates a weaker production of the actinides from this last event with respect to the production ratios that we are using here. The number in the last column therefore represents a unique constraint on the nature of the astrophysical sites of the r process in the Galaxy at the time of the formation of the Sun and needs to be compared directly to different possible astrophysical and nuclear models (Côté et al. 2021).
Citation: Côté et al. 2019a
Citation function: Compare/Contrast; Compare/Contrast
The source shows some preferred tracks in its movement along the HID. Dips occur as the source is in the SUL regime, either from SUL2 or from SUL3 regions; ingress and egress times populate the D3 and D2 spectra, whereas the D1 spectrum comes from the time segments characterized by the lowest count rate (deep dip). We noted that during the longest dips, the source occasionally switched to harder flaring episodes in D2 state. Most dips show the following pattern: SUL2/SUL3 → D3 → D2 → D1 → D2 → D3 → SUL2/SUL3. The passage from the SSUL to SUL state is only occasionally observed. We selected seven regions on the HID and extracted the corresponding spectra. For the normal branch spectra, the continuum emission is well fitted with two thermal components: a soft blackbody and a disc multicolour blackbody. The blackbody emission represents the bulk of the emitted power in each spectrum. It is likely due to strong reprocessing in an optically thick environment formed at Rsph, where disc inflow is mainly inflated by internal radiation pressure. This picture is consistent with the observed low temperature, large radius, and super-Eddington luminosity (see Shen et al. 2015; Soria & Kong 2016; Urquhart & Soria 2016; Guo et al. 2019). The hotter component, which we fitted using a diskbb, dominates the emission above 2 keV. Although its origin is still debated, it might come from internal hard X-ray emission, which has been inefficiently reprocessed, or simply scattered along our line of sight. Alternatively, it can be continuum emission (bremsshtrahlung and/or Comptonization) from an extended optically thin plasma where the emission lines are produced, or a tail of the blackbody emission which has been Compton upscattered in a coronal environment around the photosphere. In addition to the continuum, we added multiple emission and absorption lines derived by the combined averaged PN / RGS analysis to mimic the emitting and absorbing plasmas found in Paper I. Their shifts suggest different Doppler motions in several states as a consequence of a velocity field which changes depending on the launching site and on the geometry of the system. This seems supported by correlations among the parameters of the emission lines and the underneath hard X-ray flux (see Table 3). However, given the limited energy resolution of the EPIC we are not able to distinguish between a varying ionization state of the plasma, the effect of a different line broadening for the different ionized species, a complex absorption/emission pattern. A thorough study of the lines is left to a dedicated forthcoming study. For consistency the same spectral model has been applied also to the dipping branch spectra, although the physical conditions in and out of the dips might be different.
Citation: Urquhart & Soria 2016
Citation function: Similarities
The basically linear correlation between L′CO[5–4] and LIR is different from findings for low-J CO, where considering all galaxies together yields a trend more consistent with a slope of 1.7 (e.g., see the classical work of Solomon & van der Bout 2005) or, when distinguishing SB and MS galaxies, separate relations with slopes of 1.2 and different normalizations (e.g., Sargent et al. 2014). This suggests that CO[5–4] could behave as a tracer of the star-forming gas, meaning that the gas is dense enough to be directly related to the amount of stars formed, in a way that is insensitive of whether the star formation occurs in a quiescent disk or inside a violent merger. If this is the case, then CO[5–4] could be used as a more efficient and accessible tracer of the dense gas than standard molecules such as HCN or HCO, which also scale basically linearly with LIR, but are intrinsically 10–20 times fainter and harder to observe (Gao & Solomon 2004a,b; Gao et al. 2007)5. At the same time, given its fairly high frequency, CO[5–4] can be observed with reasonably high, subarcsec spatial resolution with both ALMA and IRAM PdBI. We caution, however, that the critical density of CO[5–4] is an order of magnitude lower than that of HCN (Carilli & Walter 2013). Strictly speaking, these are not equivalent as tracers. In addition, CO[5–4] has an excitation temperature of ~83 K, which is much higher than low-J HCN transitions. As such, the low-J lines of these molecules are clearer tracers of density because they do not require the medium to be both warm and dense; we will still need HCN[1–0] or other dense gas tracers at [1–0] to obtain the total dense gas including the much colder component that will be missed by high-J CO lines. We do not know, moreover, whether Eq. (4) manifests a direct connection between CO[5–4] and LIR or if both CO[5–4] and LIR are driven in similar ways by some other parameter, in which case their spatial distribution inside galaxies might differ. Evidence from local galaxies suggests that CO[5–4] emission with Tkin> 50 K, as favored by our LVG modeling, might not be excited by the photodissociation region, but more likely by mechanical heating from shocks (e.g., Rosenberg et al. 2014; Meijerink et al. 2013), which most likely are driven by winds connected to the SF regions. Future comparisons of high spatial resolution maps of CO[5–4] with HCN, for example, are required to clarify whether this is a viable approach or not, that is, to clarify if CO[5–4] can be used as a high-fidelity tracer of the star-forming gas.
Citation: Carilli & Walter 2013
Citation function: Uses