The Murchison Widefield Array (MWA) is an electronically steered low-frequency (<300 MHz) radio interferometer, with a ‘slew’ time less than 8 s. Low-frequency (∼100 MHz) radio telescopes are ideally suited for rapid response follow-up of transients due to their large field of view, the inverted spectrum of coherent emission, and the fact that the dispersion delay between a 1 GHz and 100 MHz pulse is on the order of 1–10 min for dispersion measures of 100–2000 pc/cm3. The MWA has previously been used to provide fast follow-up for transient events including gamma-ray bursts (GRBs), fast radio bursts (FRBs), and gravitational waves, using systems that respond to gamma-ray coordinates network packet-based notifications. We describe a system for automatically triggering MWA observations of such events, based on Virtual Observatory Event standard triggers, which is more flexible, capable, and accurate than previous systems. The system can respond to external multi-messenger triggers, which makes it well-suited to searching for prompt coherent radio emission from GRBs, the study of FRBs and gravitational waves, single pulse studies of pulsars, and rapid follow-up of high-energy superflares from flare stars. The new triggering system has the capability to trigger observations in both the regular correlator mode (limited to ≥0.5 s integrations) and using the Voltage Capture System (VCS, 0.1 ms integration) of the MWA and represents a new mode of operation for the MWA. The upgraded standard correlator triggering capability has been in use since MWA observing semester 2018B (July–Dec 2018), and the VCS and buffered mode triggers will become available for observing in a future semester.

Hα emission is one of the most prominent features of young stellar objects in the optical range, and importantly, the equivalent width (EW) of Hα emission [EW(Hα)] is used to characterise an evolutionary stage of young stars. The aim of this work is to identify and study the stellar objects with variable EW(Hα) in the young stellar cluster IC 348. We performed photometric and slit-less observations at several epochs in order to reveal the variable objects. Significant variability of EW(Hα) was found in 90 out of 127 examined stars. From all epochs of observations, 32 objects were classified as CTT (classical T Tauri) and 69 as WTT (weak-line T Tauri) objects. The fraction of the variables in these samples is ~60%. We also identified 20 stellar objects, which showed not only a significant variability of the EW, but which also change their apparent evolutionary stage (CTT ⇆ WTT). For six stars, Hα line was observed in both emission and absorption.

The analysis of data obtained over a wide wavelength range (from X-ray to mid-infrared) has shown that Hα activity and the measure of its variability are in good agreement with the activity of stellar objects measured with its other parameters, such as X-ray radiation and the mass accretion rate. The EW(Hα) differs not only between objects at different evolutionary stages, but also between variable and non-variable objects. The variables in the CTT and WTT samples are more active than non-variables although they have almost the same evolutionary age. Another distinct difference between these variables and non-variables is their average masses. The variables from both CTT and WTT samples are noticeably more massive than non-variables. Our data confirm the assumption made for other star formation regions that the decay of accretion activity occurs more slowly for more massive CTT objects. Apparently, a similar trend is also present in WTT objects, which are at a later stage of evolution. The variability of the stellar objects, which change their evolutionary classes (CTT ⇆ WTT), at least in a fraction of them, is due to the fact that they are close binaries, which affects and modulates their Hα emission activity.

We use the results of a supernova light-curve population synthesis to predict the range of possible supernova light curves arising from a population of single-star progenitors that lead to type IIP supernovae. We calculate multiple models varying the initial mass, explosion energy, nickel mass and nickel mixing and then compare these to type IIP supernovae with detailed light curve data and pre-explosion imaging progenitor constraints. Where a good fit is obtained to observations, we are able to achieve initial progenitor and nickel mass estimates from the supernova lightcurve that are comparable in precision to those obtained from progenitor imaging. For 2 of the 11 IIP supernovae considered our fits are poor, indicating that more progenitor models should be included in our synthesis or that our assumptions, regarding factors such as stellar mass loss rates or the rapid final stages of stellar evolution, may need to be revisited in certain cases. Using the results of our analysis we are able to show that most of the type IIP supernovae have an explosion energy of the order of log(Eexp/ergs) = 50.52 ± 0.10 and that both the amount of nickel in the supernovae and the amount of mixing may have a dependence on initial progenitor mass.

We have designed and developed the digital correlation receiver for Mingantu Spectral Radioheliograph (MUSER). The MUSER digital correlation receiver is implemented to sample, channelise, and correlate a 400 MHz wide solar radio signal of 40-antenna output from MUSER intermediate-frequency array and 60-antenna output from MUSER high-frequency array. The polyphase filter channeliser is used for wide-band channelisation and proved to be efficient to realise narrow-band filtering (${\sim}25$ MHz) in a high-speed digital signal-processing pipeline (sampling rate ${\sim}1$ Gsps). All modules of the digital correlation receiver are implemented on FPGA-based hardware and integrated via high-speed backplane, which makes a well-performed and economical correlator system for MUSER array. The future upgrade is also addressed including spectral resolution enhancement and radio-frequency-interference excision.

The substantial number of binary central stars of planetary nebulae (CSPNe) now known ($\sim 50$) has revealed a strong connection between binarity and some morphological features including jets and low-ionisation structures. However, some morphological features and asymmetries might be too complex or subtle to ascribe to binary interactions alone. In these cases, a tertiary component, that is, a triple nucleus, could be the missing ingredient required to produce these features. The only proven triple, NGC 246, is alone insufficient to investigate the shaping role of triple nuclei, but one straightforward way to identify more triples is to search for binaries in nuclei with known visual companions. Here we demonstrate this approach with the SALT HRS (High Resolution Spectrograph on the Southern African Large Telescope) discovery of a 4.81-d orbital period in the CSPN of Sp 3 which has a visual companion 0.31 arcsec away. The spectroscopic distance of the visual companion is in agreement with distance estimates to the nebula, the Gaia DR2 parallax of the central star, and the gravity distance of the central star. This supports a physical association between the visual companion and the inner 4.81 d binary, making the nucleus of Sp 3 a likely triple. We determine $T_\mathrm{eff}=68^{+12}_{-6}\ \text{kK},\ \log g=4.6\pm0.2\ \text{cm s}^{-2}$, and $v_\mathrm{rot}=80\pm20\ \text{km s}^{-1}$ for the primary from non-local thermodynamic equilibrium model atmosphere analysis. The peculiar nebula presents an apparent bipolar morphology, jets, and an unexpected ‘extreme’ oxygen abundance discrepancy factor (adf) of $24.6^{+4.1}_{-3.4}$. The adf is inconsistent with the purported trend for longer orbital period post-common-envelope (CE) PNe to exhibit normal adfs, further highlighting the dominant influence of selection effects in post-CE PNe. Lastly, the Type I nebular abundances of Sp 3, whose origin is often attributed to more massive progenitors, are incongruous with the likely Galactic Thick Disk membership of Sp 3, possibly suggesting that rotation and binarity may play an important role in influencing the AGB nucleosynthesis of PNe.

Atacama Large Millimeter/submillimeter Array (ALMA) has enabled us to detect [Oiii] 88 μm line even at z > 9. To study the properties of high-redshift [Oiii] emitters, we calculate [Oiii] luminosities of galaxies in a cosmological simulation by applying a physical model of Hii region and using the photoionization code cloudy. We find that the [Oiii] 88 μm luminosity, LOIII,88, scales with SFR with slightly larger LOIII,88 than a local relation. Some [Oiii] emitters have extended disk-like structure. We propose to use the ratio between [Oiii] 88 μm line and [Oiii] 5007 Å line, which can be detected with James Webb Space Telescope (JWST), to estimate the gas density and the metallicity in HII region of high-redshift [Oiii] emitters.

In this IAU symposium, we present results of our recent paper, Hashimoto et al. (2018a) focusing on its spectral energy distribution modeling. We present spectroscopic observations of MACS1149-JD1, a gravitationally lensed galaxy originally discovered by Zheng et al. (2012) via the dropout technique. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we detect an emission line of doubly ionized oxygen, [Oiii] 88 μm, at a redshift of 9.1096±0.0006. This precisely determined redshift indicates that the red rest-frame optical colour observed with the Spitzer Space Telescope arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. MACS1149-JD1 clearly demonstrates the importance and power of spectral energy distribution modeling to understand the earliest star formation history of the Universe.

Fitting the multi-wavelength spectral energy distributions (SEDs) of galaxies is a widely used technique to extract information about the physical properties of galaxies. However, a major difficulty lies in the numerous uncertainties regarding almost all ingredients of the SED modeling of galaxies. The Bayesian methods provide a consistent conceptual basis for dealing with the problem of inference with many uncertainties. While the Bayesian parameter estimation method have become quite popular in the field of SED fitting of galaxies, the Bayesian model comparison method, which is based on the same Bayes’ rule, is still not widely used in this field. With the application of Bayesian model comparison method in a series of papers, we show that the results obtained with Bayesian model comparison are understandable in the context of stellar/galaxy physics. These results indicate that Bayesian model comparison is a reliable and very powerful method for the SED fitting of galaxies.

This paper summarizes my thoughts, given in an invited review at the IAU symposium 341 “Challenges in Panchromatical Galaxy Modelling with Next Generation Facilities”, about how machine learning methods can help us solve some of the big data problems associated with current and upcoming large galaxy surveys.

Modelling and interpreting the SEDs of galaxies has become one of the key tools at the disposal of extragalactic astronomers. Ideally, we could hope that, through a detailed study of its SED, we can infer the correct physical properties and the evolutionary history of a galaxy. In the past decade, panchromatic SED fitting, i.e. modelling the SED over the entire UV–submm wavelength regime, has seen an enormous advance. Several advanced new codes have been developed, nearly all based on Bayesian inference modelling. In this review, we briefly touch upon the different ingredients necessary for panchromatic SED modelling, and discuss the methodology and some important aspects of Bayesian SED modelling. The current uncertainties and limitations of panchromatic SED modelling are discussed, and we explore some avenues how the models and techniques can potentially be improved in the near future.

We show our work on the L-Galaxies semi-analytic models of galaxy formation, which includes the radial resolved distribution of star, gas, SFR and metallicity on each galaxy disk. The newest version of the codes include the H22-to-HI gas transition prescriptions and the chemical enrichment of various elements. Our revised model can give results on cold gas components, radial metallicity gradients and scaling relations, which can fit the recent observations.

At high redshift, the contribution of strong emission lines to the broadband photometry can cause large uncertainties when estimating galaxy physical properties. To examine this effect, we investigate a sample of 54 LBGs at 3 < zspec < 3.8 with detected [OIII] line emissions. We use CIGALE to fit simultaneously the rest-frame UV-to-NIR SEDs of these galaxies and their emission line data. By comparing the results with and without emission line data, we show that spectroscopic data are necessary to constrain the nebular model. We examine the K-band excess, which is usually used to estimate the emissions of [OIII]+Hβ lines when there is no spectral data, and find that the difference between the estimation and observation can reach up to > 1 dex for some galaxies, showing the importance of obtaining spectroscopic measurements of these lines. We also estimate the equivalent width of the Hβ absorption and find it negligible compared to the Hβ emission.

We present the physical properties of Lyα emitters (LAEs) in a “DLA-concentrated regions” where there are 3 or more DLA within (50 Mpc)3 cubic box. We observed LAEs in a DLA-concentrated region at z = 2.3, the J1230+34 field, with Subaru/Suprime-Cam. In the 50 Mpc scale, we found no deferences in properties of LAEs such as Lyα luminosity function in the DLA-concentrated region compared to other fields at similar redshift. On the other hand, we found a ∼10 Mpc scale LAE overdensity around a strong DLA with NHI= 1021.08 cm−2.

Recent discoveries of high-redshift galaxies have revealed the diversity of their physical properties, from normal star-forming galaxies to starburst galaxies. To understand the properties of these observed galaxies, it is crucial to understand the star formation (SF) history, and the radiation properties associated with the SF activity. Here we present the results of cosmological hydrodynamic simulations with zoom-in initial conditions, and show the formation of the first galaxies and their evolution towards observable galaxies at z = 6. In addition, we show their multi-wavelength radiative properties. We find that star formation occurs intermittently due to supernova (SN) feedback at z > 10, and their radiation properties rapidly change with time. We suggest that the first galaxies are bright at UV wavelengths just after the starburst phase, and become extended Lyman-alpha sources. We also show that massive galaxies cause dusty starburst and become bright at infrared wavelengths.

In this paper, I review several dust evolution studies based on the DustPedia nearby galaxy sample. I first present the dust spectral energy distribution model, implementing a hierarchical Bayesian method, that we have developed. I then discuss the dust evolution trends we have derived among (integrated) and within (resolved) galaxies. In particular, we show that the trend of dust-to-gas ratio with metallicity is clearly non-linear, indicating the need for grain growth in the interstellar medium. Our trend is closer to the one derived with damped Lyα systems than what was suggested by previous studies. We finally demonstrate the universal processing of small amorphous carbon grains by stellar photons.

In Panda et al.2018a, we constructed a refined sample from the original Shen et al.(2011) QSO catalog. Based on our hypothesis — the main driver of the Quasar Main Sequence is the maximum of the accretion disk temperature (TBBB) defined by the Big Blue Bump on the Spectral Energy Distribution (Panda et al.2017; Panda et al.2018b). We select the four extreme sources that have RFeII ⩾ 4.0 and use {CIGALE (Boquien et al.2018) to fit their multi—band photometric data. We also perform detailed spectral fitting including the Fe II pseudo—continuum (based on Śniegowska et al.2018)) to estimate and compare the value of RFEII. We show the dependence of FeII strength on changing metallicity.

Dust absorbs stellar emission and reradiates this energy in the far-infrared (FIR). FIR observations hence give us a direct view of the dust, and allow us to study its properties. Unfortunately, FIR observations are only available for a small subset of galaxies. In this work, we estimate the global FIR emission from global UV-NIR observations. We show that a machine learning method clearly outperforms a SED modelling approach. For each galaxy, we not only predict the FIR flux across the 6 Herschel bands, but also estimate individual uncertainties. We inspect the worst predictions, and investigate how the machine learning predictor generalizes on new data. Our predictor can be used as a virtual observatory, which is especially useful now that there is still no confirmed next-generation FIR telescope.

Recently huge amount of dust Mdust ≃ 106−7M⊙ in galaxies at z = 7–8 has been discovered by ALMA observations. The suggested timescale of the dust production was a few–several×108 yr, while the stellar mass was several × 109M⊙. This amount of dust cannot be easily explained only by a supply from supernovae if we consider the dust destruction by reverse shocks. We propose that these values can be consistently explained if we take into account the grain growth in the interstellar medium (ISM). This scenario successfully reproduces the evolution of the dust mass, as well as the SFR, and stellar mass simultaneously. We conclude that even at such an early epoch of the Universe, the dust grain growth in the ISM plays a significant role in galaxies.

Numerical simulations of disk galaxies with steady (long-lived) and dynamic (short-lived) spiral arms suggest that offsets between stellar and gas spiral arms depend on their nature or lifetime (Baba et al.2015). Based on this theoretical study, we investigated gas-star offsets in the nearby grand-design spiral galaxy M51, and found that its two spiral arms exhibit different offset dependences against radius. One arm is consistent with a steady arm, while the other is consistent with a dynamic arm. We deduce that this difference is likely due to a tidal interaction with the companion galaxy (Egusa et al.2017). For this study, a stellar mass distribution with a high accuracy at a high spatial resolution is essential, which has come to be available by applying recent SED fitting techniques to multi-wavelength images. We are now working to extend this study to other nearby spiral galaxies.

The spectral energy distribution (SED) model should treat the evolution of a galaxy from its birth. Dust in galaxies affects the formation and evolution of galaxies in various ways. For example, dust grains scatter and absorb stellar emitted ultraviolet (UV) photons and re-emit the radiation at infrared (IR) wavelengths. In this work, we construct a galaxy SED model based on our dust evolution model (Asano et al. 2013a,b, 2014) with a rigorous treatment of the chemical evolution. To reduce the computational cost, we adopt mega-grain approximation (MGA; (MGA; Inoue, 2005). MGA regards a high density dusty region as a huge size (10 pc) dust grain for calculating dust scattering. In this approximation, we can solve the radiative transfer easily and provide SEDs and attenuation curves of galaxies. This model can be used to fit any galaxy in the wavelength range of 10 nm-3 mm.