adsabs/FOCAL huggingface dataset:
The Hubble Frontier Fields program1 (or HFF hereafter, Lotz et al. 2017) provides the most remarkably detailed examples of gravitational lensing by galaxy clusters, registering hundreds of multiply lensed galaxies for charting galaxy formation to unprecedented depths (see e.g. Jauzac et al. 2014, 2015a,b; Lam et al. 2014; Zitrin et al. 2014; Diego et al. 2015b,c, 2016; Kawamata et al. 2016; Limousin et al. 2016; Mahler et al. 2017). Furthermore, most of these HFF clusters are in a state of collision, enhancing their value for assessing the collisionality of dark matter (DM), a basic assumption of the standard particle interpretation of DM (Markevitch et al. 2002, 2004; Springel & Farrar 2007; Randall et al. 2008). Many clusters exhibit significant, but modest, offsets between the peak of the DM distribution and the centroid of the X-ray emission (Markevitch et al. 2004; Clowe et al. 2006; Mahdavi et al. 2007; Dawson et al. 2012; Menanteau et al. 2012), which is expected if DM is collisionless. These observations can provide a constraint on the DM cross-section (Markevitch et al. 2004; Randall et al. 2008). It is important that these differences are evaluated with the guidance of hydrodynamical models, as complex multibody interactions may also separate the DM from the plasma that can be explained without new physics, as is clearly evident in extreme cases of the bullet cluster (Mastropietro & Burkert 2008), and like the El Gordo cluster (Molnar & Broadhurst 2015), where high-speed collisions between pairs of clusters are ongoing. More direct evidence for collisional DM would be concluded from differences between the stellar and DM distributions as the stars behave like collisionless particles and we should expect the collisionless DM to follow the gravitational potential in the same way. Offsets between the position of the DM central peak and the peak of the luminous matter are difficult to explain with a standard Λcold dark matter but are naturally produced for reasonable values of the DM cross-section (Rocha et al. 2013). A difference of this nature has been claimed recently based on detailed lensing data in the centre of a cluster that contains four bright member galaxies (Massey et al. 2015). In case of the HFF clusters, it is interesting that our free-form analysis of MACS0146 also indicates a possible offset between the lensing-based centroids of the brightest galaxies and their luminous stellar centroids. These differences are subtle and it will be important to look at a larger sample and the model dependencies, and systematic uncertainties, in detail to support any claim of new physics.
Citation: Markevitch et al. 2002
Citation function: Motivation
There are several popular scenarios employed to explain the observational features of CL AGNs. One scenario is that the broad emission lines are obscured by the torus or moving clouds over the observer’s line of sight (Goodrich & Miller 1989), while only several CL AGNs can be explained by this scenario (Wang et al. 2019; Jaffarian & Gaskell 2020; Kokubo & Minezaki 2020). The features observed in most CL AGNs, e.g., the complex multiband spectral variabilities, and strong changes seen in the infrared or low level of polarization, strongly argue against the scattering (or obscuration) scenario (e.g., Sheng et al. 2017; Mathur et al. 2018; Stern et al. 2018; Hutsemékers et al. 2019; Kynoch et al. 2019, and the references therein). Another attractive scenario is that the CL AGNs are indeed tidal disruption events (Merloni et al. 2015; Kawamuro et al. 2016; Yang et al. 2019; Padmanabhan & Loeb 2020; Ricci et al. 2020; Zhang 2021), while it is not a general mechanism to explain all CL AGNs, such as repeating CL AGNs. The changing look phenomenon triggered by the change of the mass accretion rate of the accretion disk is a rather straightforward model (Husemann et al. 2016; Liu et al. 2019; Ruan et al. 2019; Ai et al. 2020; Sniegowska et al. 2020); however, it has a fatal problem that propagation timescale of the gas in a thin accretion disk is much longer than the observed timescale in CL AGNs, unless the viscous thin disk model is somewhat revised (Lawrence 2018). Dexter & Begelman (2019) proposed that the magnetically elevated disk model could help to explain the changing look timescale. Based on this scenario, Scepi et al. (2021) suggested that a magnetic flux inversion in a magnetically arrested disk is able to explain the CL event in 1ES 1927+654. Sniegowska et al. (2020) suggested that a narrow unstable zone between the outer thin disk and the inner ADAF could cause the periodic outbursts in repeating CL AGNs. Recently, the effects of large-scale magnetic fields on this scenario for repeating CL AGNs have been studied in detail by Pan et al. (2021), and Lyu et al. (2021) suggested that the change of broad emission lines in Mrk 1018 might be regulated by the evolution of accretion disk.
Citation: Hutsemékers et al. 2019
Citation function: Compare/Contrast
Once corrected for dust attenuation, Hα luminosities can be transformed into star formation rates (SFR, in M⊙ yr-1) using a factor that depends on the assumed IMF and stellar model7: (10)\begin{equation} {SFR = k({\rm H}\alpha) \times L({\rm H}\alpha)_{\rm cor}} . \end{equation}SFR=k(Hα)×L(Hα)cor.We recall that this relation is valid only under the assumption that the mean star formation activity of the emitting galaxies is constant on a timescale of a few Myr, roughly comparable to the typical time spent by the stellar population responsible for the ionisation of the gas on the main sequence (Boselli et al. 2009; Boissier 2013; Boquien et al. 2014). The ionising stars are O and early-B stars, whose typical age is ≲107 yr. The stationarity condition is generally satisfied in massive, normal, star-forming galaxies undergoing secular evolution. In these objects, the total number of OB associations is significantly larger than the number of HII regions under formation and of OB stars reaching the final stage of their evolution, thus their total Hα luminosity is fairly constant with time. This might not be the case in strongly perturbed systems or in dwarf galaxies, where the total star formation activity can be dominated by individual giant HII regions (Boselli et al. 2009; Weisz et al. 2012), and the IMF is only stochastically sampled (Lee et al. 2009; Fumagalli et al. 2011; da Silva et al. 2014). The HRS sample is dominated by relatively massive galaxies undergoing secular evolution. For these objects, Eq. (10) can thus be applied. The sample, however, also includes galaxies in the Virgo cluster region, where the perturbation induced by the cluster environment might have affected their star formation rate (e.g. Boselli & Gavazzi 2006, 2014). Models and simulations have shown that in these objects the suppression of star formation occurs on timescales of a few hundred Myr (Boselli et al. 2006, 2008a,b, 2014d). These timescales are relatively long compared to the typical age of O-B stars. The recent work of Boquien et al. (2014) has clearly shown that the Lyman continuum emission tightly follows the rapid variations in the star formation activity of simulated galaxies down to timescales of a few Myrs. We can thus safely consider that the linear relation between the Hα luminosity and the star formation rate given in Eq. (10) is satisfied in the HRS sample.
Citation: Boselli et al. 2009
Citation function: Uses
Citation: Boselli et al. 2009
Citation function: Compare/Contrast
We have tested the pixel-ICA algorithm, i.e., a non-parametric method proposed by Morello et al. (2014, 2015) to detrend Spitzer/IRAC primary transit observations, on simulated data sets. Systematics similar to the ones present in Spitzer/IRAC data sets are obtained by combining instrumental jitter with inter- or intra-pixel sensitivity variations. A variety of jitter timeseries is used to test the pixel-ICA method with:

1.
periodic signals with different frequencies, phasing, and shape;


2.
non-stationary signals with varying amplitudes or frequencies;


3.
sudden change.

The detrending performances of pixel-ICA method have been compared with division by a polynomial function of the centroid, in this paper PCD method, and PLD method (Deming et al. 2015). Here we summarize the main results found:

1.
Pixel-ICA algorithm can detrend non-stationary signals and sudden changes, as well as periodic signals with different frequencies and phasing, relative to the transit.


2.
Inter-pixel effects are well-detrended with pixel-ICA method.


3.
Even if the instrument PSF is not entirely within the array of pixels, pixel-ICA leads to results which are consistent at ∼1σ with the input parameters.


4.
In most cases, pixel-ICA outperforms PCD method, especially if the instrument PSF is narrow, or it is not entirely within the photometric aperture.


5.
Intra-pixel effects are only detectable if the PSF is relatively small.


6.
Intra-pixel effects cannot be totally detrended by any of the three methods, but pixel-ICA, in most cases, outperforms PCD method, which is largely case-dependent. Also, pixel-ICA method provides consistent results within the error bars.


7.
It is possible to fit the astrophysical signal after detrending or together with the other components. The only differences are registered if at least one of the non-transit components has a similar shape at the time of transit, in which case the first approach is preferable, but the two results were consistent within 1σ.


8.
The PLD method, updated to include cross-term between pixel fluctuations and the astrophysical signals, lead to very similar results than pixel-ICA, particularly if the astrophysical signal is fitted together with the other components.

In conclusion, we have found in a variety of simulated cases that pixel-ICA performs as well or better than other methods used in the literature, in particular polynomial centroid corrections and PLD (Deming et al. 2015). The main advantage of pixel-ICA over other methods relies on its purely statistical foundation without the need of imposing prior knowledge on the instrument systematics, therefore avoiding a potential source of error. The results of this paper, together with previous analyses of real Spitzer/IRAC data sets (Morello et al. 2014, 2015), suggest that photometric precision and repeatability at the level of one part in 104 can be achieved with current infrared space instruments.
Citation: Deming et al. 2015
Citation function: Compare/Contrast
To obtain a more complete picture of the physical processes that shape star formation in the early Universe, very deep radio surveys overwide areas of sky are required to complement deep submillimetre surveys. Previous work has used high-resolution radio observations, typically at 1.4 GHz, as a method of pinpointing the position of submillimetre sources detected in single-dish surveys (Ivison et al. 2002; Chapman et al. 2005); however, such work has been limited by the depth of available radio sky surveys,with dedicated deep surveys over only small regions of sky, resulting in a view biased towards the brighter radio sources. Studies have largely included limited radio spectral coverage of SMGs, focusing on the nature of the FIRC and its relation to properties such as stellar mass and redshift (e.g. Yun et al. 2001; Ivison et al. 2010; Smith et al. 2014). The Low Frequency Array (LOFAR; van Haarlem et al. 2013) has opened up new ways of studying galaxies in the radio, and a number of studies have used LOFAR’s capabilities to investigate this relationship between star formation and radio luminosity in the low-frequency regime – for example Gürkan et al. (2018), Read et al. (2018), Smith et al. (2021), and Wang et al. (2019a). However, these studies generally investigate the statistical properties of large samples of galaxies, in optically selected samples at low redshift (z ≲2), rather than probing the shapes of individual radio spectra. Thomson et al. (2019) conducted an in-depth study of high-frequency (>610 GHz) spectral curvature in SMGs, finding evidence of curved spectra that they attributed to spectral ageing of the synchrotron emission from star formation; their results implied estimated starburst ages consistent with expected SMG lifetimes. Studies at low frequencies, where we may be able to observe absorption processes affecting the shape of the spectrum, have been hampered by a lack of sufficiently deep, wide-area data. More comprehensive observations of the shape of the radio spectrum, extending to lower frequencies, can provide a probe of the physical conditions that give rise to extreme star formation in SMGs. Calistro Rivera et al. (2017) exploit LOFAR’s frequency range to investigate the spectral shapes of star-forming galaxies and AGN, finding evidence of low-frequency spectral flattening in the star-forming sample. This sample is also constrained in redshift, focusing on local galaxies rather than the peak of star formation at z > 2, and so does not probe the bulk of the highly star-forming SMG population. Chyży et al. (2018) also find weak spectral flattening in local star-forming galaxies with LOFAR but largely attribute this slight effect to synchrotron losses, predicting stronger low-frequency spectral flattening due to free–free absorption at high redshift, where galaxies with high SFRs are more common.
Citation: Gürkan et al. (2018)
Citation function: Background; Background; Background
It is now clear that binary stars hold the key to understanding the formation of many planetary nebulae (PNe; Jones & Boffin 2017a). However, with much of the recent focus being placed on common envelope evolution (Boffin & Jones 2019), the role of wider binaries remains almost completely unconstrained (Tyndall et al. 2013). To date, only three wide binary central stars of PNe have confirmed periods (Jones et al. 2017) with other systems either being so wide that they are resolved (Ciardullo et al. 1999) or displaying composite spectra with giant companions (Tyndall et al. 2013). Four central star systems are known to be barium stars (Bond, Pollacco & Webbink 2003; Miszalski et al. 2012, 2013; Löbling, Boffin & Jones 2019) with only one having a known orbital period (LoTr 5; Jones et al. 2017; Aller et al. 2018). Barium stars are mostly – but not only: see e.g. Escorza et al. (2019) – giant stars of spectral type G-K that display enhanced abundances of carbon and s-process elements such as barium and strontium, and are now known to all be long-period binaries (100 d ≲ Porb ≲ 104 d; McClure, Fletcher & Nemec 1980; Jorissen et al. 2019). The chemical contamination of barium stars is believed to be due to accretion of chemically enriched material from an evolved binary companion, likely through wind (Boffin & Jorissen 1988) or wind Roche lobe overflow (WRLOF; Theuns & Jorissen 1993; Nagae et al. 2004). WRLOF will occur when the acceleration radius of the asymptotic giant branch (now a white dwarf in these barium star systems) star’s stellar wind is comparable to or greater than its Roche lobe radius (Mohamed & Podsiadlowski 2012), meaning that the wind itself is strongly influenced by the binary potential and can be accreted on to the companion via the first Lagrangian point. This accreted material chemically contaminates the surface of the companion as well as increases its spin rate due to the conservation of angular momentum (Theuns, Boffin & Jorissen 1996). Intriguingly, the amount of material required to account for the observed contamination is often in excess of that which would be expected to result in critical rotation rates in the companion, providing an indication that significant (and as yet not understood) angular momentum losses must be experienced in these systems (Matrozis, Abate & Stancliffe 2017). PNe with barium central stars offer an important window into this process as the presence of the short-lived nebula (τ ≤ 30 000 yr; Jacob, Schönberner & Steffen 2013) means that the mass transfer has occurred too recently for significant changes in the companion’s spin rate, and moreover the nebula itself traces the mass-loss history of the system as it is formed from the material that has escaped the binary potential (Jones 2018).
Citation: Boffin & Jorissen 1988
Citation function: Background
Sagittarius A* (Sgr A*) is a supermassive black hole system that allows one to observationally test the aforementioned GRMHD models of accretion flows (Goddi et al. 2017). Millimeter-Very Long Baseline Interferometry (mm-VLBI) is capable of resolving the shadow of the event horizon (Falcke et al. 2000), making this an ideal laboratory not only to tests Einstein’s General Theory of Relativity (GR) but also to investigate electron acceleration in the vicinity of a black hole. Most of the radiative models for Sgr A*, which are based on post-processing GRMHD simulations, assume that electrons have a thermal, relativistic (Maxwell–Jüttner) distribution function, and that the proton-to-electron temperature ratio is constant across the simulation domain (Goldston et al. 2005; Noble et al. 2007; Mościbrodzka et al. 2009; Dexter et al. 2010, 2012a; Shcherbakov et al. 2012). When the proton-to-electron temperature is constant, the disk dominates the images and spectra since most of the matter resides there. We have recently extended these radiative models by making the temperature ratios a function of the plasma β parameter, where 

$\beta = \frac{P_{\textrm{gas}}}{P_{\textrm{B}}}$


β=


P

gas




P
B





 is the ratio of gas to magnetic pressures. In these extended models, the electrons are hotter in the more magnetized plasma, which is usually outflowing from the system. The reason for this is that the previously mentioned models do not recover the flat radio spectra. The β parameterization enforces that the disk emission is suppressed by significantly decreasing the temperature of the electrons in those regions. As a consequence of this, the jet will be the dominant source of emission. These modifications to the electron temperature model allowed us to recover some basic observational characteristics of Sgr A* (a roughly flat radio spectral slope and a size vs. wavelength relationship that is in agreement with observations) (Mościbrodzka & Falcke 2013; Mościbrodzka et al. 2014; Chan et al. 2015b,a; Gold et al. 2017). Our model for the electron temperatures as a function of the β plasma parameter is now roughly confirmed with extended-GRMHD simulations that self-consistently take into account the evolution of the electron temperatures (Ressler et al. 2015, 2017). Moreover, GRMHD simulations with the new electron temperatures can naturally explain the symbiosis of disks and jets observed in many accreting black hole systems (Falcke & Biermann 1995; Mościbrodzka et al. 2016a).
Citation: Dexter et al. 2010
Citation function: Background
The ice layer covering refractory grains in dense MCs consists mainly of amorphous water ice (Tielens & Allamandola 1987). A key property of the icy mantle is its porosity, which determines its ability to adsorb, desorb, and trap atoms and molecules. The actual degree of porosity of interstellar ices is still debated. There are indeed indications that the buildup of the ice in cold environments results in the formation of pores as shown by laboratory measurements (e.g., Dohnálek et al. 2003; Bossa et al. 2014) and simulations (Cuppen & Herbst 2007; Clements et al. 2018). These two studies, based on Monte Carlo simulations, suggest a significant level of porosity at the surface/subsurface, in particular in cold and dense environments. On the other hand, UV photons, exothermic reactions, and energetic ions tend to compact astrophysical ices. Estimates of the timescale for mantle compaction calculated from experiments range from a few up to 50 Myr (Raut et al. 2008; Palumbo et al. 2010; Accolla et al. 2011). It has also been suggested that the compaction of icy mantles may not be completed within the typical lifetime of MCs if they consist of ice mixtures, since compaction is slower for mixtures than for pure ices (Palumbo 2006). Transient events like the impact of energetic ions can also generate cavities in the ice surface and/or subsurface. Such energetic events induce a strong local increase of the ice temperature, produce fragments, and are associated with sputtering and evaporation along the ion track. Such cavities are short-lived since the heated ice rearranges while relaxing (Mainitz et al. 2016). The missing O–H dangling features near 3700 cm−1 in astronomical spectra have been taken as an indication of a low level of porosity of interstellar ices. However, laboratory data and simulations indicate that the absence of the O–H dangling modes does not necessarily imply the complete absence of porosity (Raut et al. 2007; Isokoski et al. 2014).
Citation: Clements et al. 2018
Citation function: Background; Background; Background
SHT has some inherent geometrical advantages, especially for large-angle and deep surveys. A significant advantage is that the spherical coordinates apply to wide-angle surveys like BOSS without any flat-sky approximation. A traditional P(k) analysis relies on the flat-sky approximation to distinguish between transverse and line-of-sight modes, which is critical for accurately representing RSDs and distinguishing continuum foregrounds from line signal. By contrast, in the SHT formalism, both foregrounds and linear RSDs take exact, simple forms. This geometric advantage is shared with the related analysis technique of spherical Fourier-Bessel (SFB) decomposition (Fisher et al. 1995; Heavens & Taylor 1995; Leistedt et al. 2012; Rassat & Refregier 2012; Yoo & Desjacques 2013; Lanusse et al. 2015; Liu, Zhang & Parsons 2016; Grasshorn Gebhardt & Doré 2021), which, in addtion to spherical harmonic decomposition, involves a further Fourier-Bessel transform and data-compression along the line-of-sight. However, SFB does not share another important feature of SHT, which is its ability to capture redshift-dependent change over cosmological time in deep surveys. For deep surveys, structure growth and changes in star formation rate break the assumption of translational invariance in the line-of-sight direction, rendering the P(k) or SFB statistic insufficient. However, since Cℓ(z, z′) does not compress data along the line-of-sight direction, it describes redshift evolution. A study (Mondal et al. 2022) of simulated 21-cm data from the EoR found that an implementation of the SHT technique, MAPS (Mondal, Bharadwaj & Datta 2018; Mondal et al. 2019, 2020), obtains ∼2 times more stringent error bars on model parameters than techniques that fail to capture redshift evolution due to data compression along the line-of-sight, such as P(k) or SFB. A final geometric advantage is that Cℓ(z, z′) describes the data in observing coordinates of angle and frequency (or, equivalently, redshift) rather than re-gridding the data on to cosmological distances in an assumed cosmological model. An MCMC likelihood analysis that constrains cosmological parameters would therefore not need to recompute the data statistic at each step, which in principle would be needed for a P(k) or SFB analysis.
Citation: Fisher et al. 1995
Citation function: Similarities; Background; Differences