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A1689-zD1 is one of the most distant galaxies, discovered with the aid of gravitational lensing, providing us with an important opportunity to study galaxy formation in the very early Universe. In this study, we report the detection of [C II]158$\mu$m and [O III]88$\mu$m emission lines of A1689-zD1 in the ALMA Bands 6 and 8. We measure the redshift of this galaxy as $z_{\rm{sys}}=7.133\pm0.005$ based on the [C II] and [O III] emission lines, consistent with that adopted by Bakx et al. (2021). The observed $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ ratio is $2.09\pm0.09$, higher than most of the local galaxies, but consistent with other $z\sim7$ galaxies. The moderate-spatial resolution of ALMA data provided us with a precious opportunity to investigate spatial variation of $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$. In contrast to the average value of 2.09, we find a much higher $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ of $\sim 7$ at the center of the galaxy. This spatial variation of $L_{[\rm{O\,III]}}/L_{[\rm{C\,II]}}$ was seldom reported for other high-z galaxies. It is also interesting that the peak of the ratio does not overlap with optical peaks. Possible physical reasons include a central AGN, shock heating from merging, and starburst. Our moderate-spatial resolution data also reveals that in addition to the observed two clumps shown in previous HST images, there is a redshifted segment to the west of the northern optical clump. Such a structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected materials, or that the northern redshifted materials being from a third more highly obscured region of the galaxy., Comment: 11 pages, 5 figures, accepted for publication in ApJ. A video summary is available at https://youtu.be/VkR9FlclAp4

Fast radio bursts (FRBs) are mysterious millisecond pulses in radio, most of which originate from distant galaxies. Revealing the origin of FRBs is becoming central in astronomy. The redshift evolution of the FRB energy function, i.e., the number density of FRB sources as a function of energy, provides important implications for the FRB progenitors. Here we show the energy functions of FRBs selected from the recently released Canadian Hydrogen Intensity Mapping Experiment (CHIME) catalogue using the $V_{\rm max}$ method. The $V_{\rm max}$ method allows us to measure the redshift evolution of the energy functions as it is without any prior assumption on the evolution. We use a homogeneous sample of 164 non-repeating FRB sources, which are about one order of magnitude larger than previously investigated samples. The energy functions of non-repeating FRBs show Schechter function-like shapes at $z\lesssim1$. The energy functions and volumetric rates of non-repeating FRBs decrease towards higher redshifts similar to the cosmic stellar-mass density evolution: there is no significant difference between the non-repeating FRB rate and cosmic stellar-mass density evolution with a 1\% significance threshold, whereas the cosmic star-formation rate scenario is rejected with a more than 99\% confidence level. Our results indicate that the event rate of non-repeating FRBs is likely controlled by old populations rather than young populations which are traced by the cosmic star-formation rate density. This suggests old populations such as old neutron stars and black holes as more likely progenitors of non-repeating FRBs., Comment: Accepted for publication in MNRAS. A summary video is available at https://youtu.be/qbUctrFHLAs

Fast radio bursts (FRBs) are astronomical transients with millisecond timescales occurring at cosmological distances. The observed time lag between different energies of each FRB is well described by the inverse-square law of the observed frequency, i.e., dispersion measure. Therefore, FRBs provide one of the ideal laboratories to test Einstein's weak equivalence principle (WEP): the hypothetical time lag between photons with different energies under a gravitational potential. If WEP is violated, such evidence should be exposed within the observational uncertainties of dispersion measures, unless the WEP violation also depends on the inverse-square of the observed frequency. In this work, we constrain the difference of gamma parameters ($\Delta\gamma$) between photons with different energies using the observational uncertainties of FRB dispersion measures, where $\Delta\gamma=0$ for Einstein's general relativity. Adopting the averaged 'Shapiro time delay' for cosmological sources, FRB 121002 at $z=1.6\pm0.3$ and FRB 180817.J1533+42 at $z=1.0\pm0.2$ place the most stringent constraints of $\log\Delta\gamma<-20.8\pm0.1$ and $\log(\Delta\gamma/r_{E}) < -20.9\pm0.2$, respectively, where $r_{E}$ is the energy ratio between the photons. The former is about three orders of magnitude lower than those of other astrophysical sources in previous works under the same formalization of the Shapiro time delay while the latter is comparable to the tightest constraint so far., Comment: Accepted for publication in Physical Review D. A summary video is available at https://youtu.be/Rt7tXN02wpQ

How does the environment affect active galactic nucleus (AGN) activity? We investigated this question in an extinction-free way, by selecting 1120 infrared galaxies in the $AKARI$ North Ecliptic Pole Wide field at redshift $z$ $\leq$ 1.2. A unique feature of the $AKARI$ satellite is its continuous 9-band infrared (IR) filter coverage, providing us with an unprecedentedly large sample of IR spectral energy distributions (SEDs) of galaxies. By taking advantage of this, for the first time, we explored the AGN activity derived from SED modelling as a function of redshift, luminosity, and environment. We quantified AGN activity in two ways: AGN contribution fraction (ratio of AGN luminosity to the total IR luminosity), and AGN number fraction (ratio of number of AGNs to the total galaxy sample). We found that galaxy environment (normalised local density) does not greatly affect either definitions of AGN activity of our IRG/LIRG samples (log ${\rm L}_{\rm TIR}$ $\leq$ 12). However, we found a different behavior for ULIRGs (log ${\rm L}_{\rm TIR}$ $>$ 12). At our highest redshift bin (0.7 $\lesssim$ z $\lesssim$ 1.2), AGN activity increases with denser environments, but at the intermediate redshift bin (0.3 $\lesssim$ z $\lesssim$ 0.7), the opposite is observed. These results may hint at a different physical mechanism for ULIRGs. The trends are not statistically significant (p $\geq$ 0.060 at the intermediate redshift bin, and p $\geq$ 0.139 at the highest redshift bin). Possible different behavior of ULIRGs is a key direction to explore further with future space missions (e.g., $JWST$, $Euclid$, $SPHEREx$)., Comment: Accepted for publication in MNRAS. A summary video is available at https://www.youtube.com/watch?v=7Y_a0kJkLI4&ab_channel=NthuCosmology

The search for extraterrestrial intelligence (SETI) has been conducted for nearly 60 years. A Dyson Sphere, a spherical structure that surrounds a star and transports its radiative energy outward as an energy source for an advanced civilisation, is one of the main targets of SETI. In this study, we discuss whether building a Dyson Sphere around a black hole is effective. We consider six energy sources: (i) the cosmic microwave background, (ii) the Hawking radiation, (iii) an accretion disk, (iv) Bondi accretion, (v) a corona, and (vi) relativistic jets. To develop future civilisations (for example, a Type II civilisation), $4\times10^{26}\,{\rm W}$($1\,{\rm L_{\odot}}$) is expected to be needed. Among (iii) to (vi), the largest luminosity can be collected from an accretion disk, reaching $10^{5}\,{\rm L_{\odot}}$, enough to maintain a Type II civilisation. Moreover, if a Dyson Sphere collects not only the electromagnetic radiation but also other types of energy (e.g., kinetic energy) from the jets, the total collected energy would be approximately 5 times larger. Considering the emission from a Dyson Sphere, our results show that the Dyson Sphere around a stellar-mass black hole in the Milky Way ($10\,\rm kpc$ away from us) is detectable in the ultraviolet$(\rm 10-400\,{\rm nm)}$, optical$(\rm 400-760\,{\rm nm)}$, near-infrared($\rm 760\,{\rm nm}-5\,{\rm \mu m}$), and mid-infrared($\rm 5-40\,{\rm \mu m}$) wavelengths via the waste heat radiation using current telescopes such as Galaxy Evolution Explorer Ultraviolet Sky Surveys. Performing model fitting to observed spectral energy distributions and measuring the variability of radial velocity may help us to identify these possible artificial structures., Comment: This paper has been accepted for publication in MNRAS

Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent method using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM$_{\rm IGM}$) is an indicator of the amount of ionised material in the IGM. Since the differential of DM$_{\rm IGM}$ against redshift is proportional to the ionisation fraction, our method allows us to directly measure the reionisation history without any assumption on its functional shape. As a proof of concept, we constructed mock non-repeating FRB sources to be detected with the Square Kilometre Array, assuming three different reionisation histories with the same optical depth of Thomson scattering. We considered three cases of redshift measurements: (A) spectroscopic redshift for all mock data, (B) spectroscopic redshift for 10% of mock data, and (C) redshift estimated from an empirical relation of FRBs between their time-integrated luminosity and rest-frame intrinsic duration. In all cases, the reionisation histories are consistently reconstructed from the mock FRB data using our method. Our results demonstrate the capability of future FRBs in constraining the reionisation history., Comment: Accepted for publication in MNRAS. A summary video is available at https://youtu.be/uis6h_cBnpE

We investigate infrared colours and spectral energy distributions (SEDs) of 338 X-ray selected AGN from Swift-BAT 105-month survey catalogue that have AKARI detection, in order to find a new selection criteria for Compton-thick AGN. By combining data from Galaxy Evolution Explore (GALEX), Sloan Digital Sky Survey (SDSS) Data Release 14 (DR14), Two Micron All Sky Survey (2MASS), Wide-field Infrared Survey Explorer (WISE), AKARI and Herschel for the first time we perform ultraviolet (UV) to far-infrared (FIR) SED fitting 158 Swift BAT AGN by CIGALE and constrain the AGN model parameters of obscured and Compton-thick AGN. The comparison of average SEDs show while the mid-IR (MIR) SEDs are similar for the three AGN populations, optical/UV and FIR regions have differences. We measure the dust luminosity, the pure AGN luminosity and the total infrared (IR) luminosity. We examine the relationships between the measured infrared luminosities and the hard X-ray luminosity in the 14-195 keV band. We show that the average covering factor of Compton-thick AGN is higher compared to the obscured and unobscured AGN. We present a new infrared selection for Compton-thick AGN based on MIR and FIR colours ([9$\mu$m - 22$\mu$m]$ > 3.0$ and [22$\mu$m - 90$\mu$m]$ < 2.7$) from WISE and AKARI. We find two known Compton-thick AGN that are not included in the Swift-BAT sample, and conclude that MIR colours covering 9.7$\mu$m silicate absorption and MIR continuum can be a promising new tool to identify Compton-thick AGN., Comment: 20 pages, 12 figures. Accepted for publication in MNRAS

Local infrared (IR) luminosity functions (LFs) are necessary benchmarks for high-redshift IR galaxy evolution studies. Any accurate IR LF evolution studies require accordingly accurate local IR LFs. We present infrared galaxy LFs at redshifts redshifts of $z \leq 0.3$ from AKARI space telescope, which performed an all-sky survey in six IR bands (9, 18, 65, 90, 140 and 160 micron) with 10 times better sensitivity than its precursor IRAS. Availability of 160 micron filter is critically important in accurately measuring total IR luminosity of galaxies, covering across the peak of the dust emission. By combining data from Wide-field Infrared Survey Explorer (WISE), Sloan Digital Sky Survey (SDSS) Data Release 13 (DR13), 6-degree Field Galaxy Survey (6dFGS) and the 2MASS Redshift Survey (2MRS), we created a sample of 15,638 local IR galaxies with spectroscopic redshifts, factor of 7 larger compared to previously studied AKARI -SDSS sample. After carefully correcting for volume effects in both IR and optical, the obtained IR LFs agree well with previous studies, but comes with much smaller errors. Measured local IR luminosity density is $\Omega_{IR}=$ 1.19$\pm$0.05 $\times 10^{8}$ L$_{\odot}$ Mpc$^{-3}$. The contributions from luminous infrared galaxies and ultra luminous infrared galaxies to IR are very small, 9.3 per cent and 0.9 per cent, respectively. There exists no future all sky survey in far-infrared wavelengths in the foreseeable future. The IR LFs obtained in this work will therefore remain an important benchmark for high-redshift studies for decades., Comment: 10 pages, 3 figures, accepted for publication in MNRAS

We present and analyse quasi-simultaneous multi-epoch spectral energy distributions (SEDs) of seven reverberation-mapped AGNs for which accurate black hole mass measurements and suitable archival data are available from the 'AGN Watch' monitoring programs. We explore the potential of optical-UV and X-ray data, obtained within 2 days, to provide more accurate SED-based measurements of individual AGN and quantify the impact of source variability on key measurements typically used to characterise the black hole accretion process plus on bolometric correction factors at 5100 {\AA}, 1350 {\AA} and for the 2-10 keV X-ray band, respectively. The largest SED changes occur on long timescales (>1 year). For our small sample, the 1 micron to 10 keV integrated accretion luminosity typically changes by 10% on short time-scales (over 20 days), by ~30% over a year, but can change by 100% or more for individual AGN. The EUV gap is the most uncertain part of the intrinsic SED, introducing a ~25% uncertainty in the accretion-induced luminosity, relative to the model independent interpolation method that we adopt. That aside, our analysis shows that the uncertainty in the accretion-induced luminosity, the Eddington luminosity ratio and the bolometric correction factors can be reduced (by a factor of two or more) by use of SEDs built from data obtained within 20 days. However, mass accretion rate and mass accretion efficiency are mostly limited by the unknown EUV emission and the unknown details of the central engine and our aspect angle., Comment: Accepted for publication in MNRAS, 44 pages, 16 figures, updated with additional literature references and a corrected referencing to databases