The measurement of Hα luminosity for large numbers of galaxies is important to investigate recent star formation history of galaxies. With SED fitting that includes emission line templates, we extract individual galaxy Hα luminosities from broad-band photometry. We compare Hα luminosity function with the result of a narrow-band survey, HiZELS, and find there are more luminous galaxies in Hα than previously reported. As a result, our derived star formation rate density at z ∼ 2.3 turns out to be 2.2 times higher than previous studies. Most of the offset in the results can be explained by missing Hα in the HiZELS photometric aperture and different methods for dust extinction correction.

We present the environmental properties of a sample of 260 Lyα emitters (LAEs) with extremely large equivalent widths (EW0 > 240 Å) at z ∼ 3. Such large EW LAEs may be very low-metal / young starbursts in void regions or Hi gas /galaxies illuminated by ionizing radiation from the QSO. We undertook Subaru/HSC Lyα imaging observations around a hyper luminous QSO at z = 2.84. We identified 3490 LAEs including 260 large EW LAEs. We found that the large EW LAEs tend to lie at galaxy over-dense regions surrounding the QSO, suggesting that most of the large EW LAEs are illuminated by the QSO. From the radial distribution of the large EW LAEs from the QSO, we found that the fraction of large EW LAE shows two excesses in the range of 2 to 5 Mpc and 14 to 16 Mpc from the QSO. If the two peaks are reflected with the QSO activity, the QSO should have episodic lifetimes with ∼10 Myr duration and ∼30 Myr separations. However, we require future spectroscopic observations to investigate if the large EW LAEs far from the QSO are low-metal young starbursts.

In order to clarify the dust production in the early Universe, we constrain the dust mass in high-redshift (z ≳ 5) galaxies using the upper limits obtained by ALMA. We perform fitting to the rest-frame UV–far-infrared spectral energy distribution (SED) of a giant Lyα emitter, Himiko, at z = 6.6 and a composite SED of z > 5 Lyman break galaxies (LBGs). For Himiko, we obtain a high dust temperature > 70 K. This high dust temperature puts a strong upper limit on the total dust mass Md ≲ 2 × 106 M⊙, and the dust mass produced per supernova (SN) md,SN ≲ 0.1 M⊙. Such a low md,SN suggests significant loss of dust by reverse shock destruction or outflow. For the LBG sample, we only obtain an upper limit for md,SN as ∼2 M⊙. This clarifies the importance of observing UV-bright objects (like Himiko) to constrain the dust production by SNe.

Panchromatic SED fitting allows us to better resolve degeneracies between quantities like the star formation rate and dust. This in turn allows us to more robustly extract information about the different stellar populations that comprise a galaxy’s Star Formation History (SFH). Using the Dense Basis SED fitting method (Iyer & Gawiser 2017), we reconstruct the SFHs with uncertainties for a large sample of galaxies using an atlas of SEDs corresponding to a physically motivated basis of SFHs. Using Gaussian Process Regression, we encode the parameters describing these SFHs in a functionally independent form. This give us more robust estimates for quantities like Stellar Masses and Star Formation Rates, that directly depend on the SFH. These SFHs can additionally be used to answer questions like the time at which a galaxy’s star formation peaked, and how many major episodes of star formation occurred in a galaxy’s past, allowing us to go beyond the traditionally estimated ‘Galaxy Age’, which is often poorly constrained. They also allow us to probe the high-redshift low-stellar mass regime of the SFR-M* correlation by constructing trajectories in SFR-M* space for each galaxy.

We report the first detection of [NII] 122 μm line toward a QSO-SMG pair, BRI 1202-0725, at z = 4.7 using ALMA. Combining with [NII] 205 μm line detection and taking the line ratio of [NII]122/[NII]205, we constrain electron densities of both galaxies. The derived electron densities are ${26_{ - 11}^{ + 12}$ and ${134_{ - 39}^{ + 50}$ cm−3 for the SMG and the QSO, respectively, which are the first measurements for galaxies at z > 4. The electron density of the SMG is comparable to the Galactic plane and the average of local spiral galaxies, while the value for the QSO is comparable to local starbursts and optical-line based measurements for star-forming galaxies at z ∼ 2–3. Considering the similar star-formation rates (SFRs) of ≍ 1000 M⊙ yr−1 for both galaxies, our results suggest a large scatter of electron densities at fixed SFR and caution against using optical lines for dusty starbursts. The details of this report are presented in Lee et al. 2019 (submitted).

Thanks to deep optical to near-IR imaging and spectroscopy, significant progress is made in characterizing the rest-frame UV to optical properties of galaxies in the early universe (z > 4. Surveys with Hubble, Spitzer, and ground-based facilities (Keck, Subaru, and VLT) provide spectroscopic and photometric redshifts, measurements of the spatial structure, stellar masses, and optical emission lines for large samples of galaxies. Recently, the Atacama Large (Sub) Millimeter Array (ALMA) has become a major player in pushing studies of high redshift galaxies to far-infrared wavelengths, hence making panchromatic surveys over many orders of frequencies possible. While past studies focused mostly on bright sub-millimeter galaxies, the sensitivity of ALMA now enables surveys like ALPINE, which focuses on measuring the gas and dust properties of a large sample of normal main-sequence galaxies at z > 4. Combining observations across different wavelengths into a single, panchromatic picture of galaxy formation and evolution is currently and in the future an important focus of the astronomical community.

Observing high resolution optical to infrared spectra is crucial to understanding how energy is generated in galaxies. We present follow-up optical Keck-II/DEIMOS and infrared Keck-I/MOSFIRE spectra of ∼200 galaxies in the AKARI/North Ecliptic Pole Deep survey region at intermediate redshift. From rest-frame optical emission lines, we classify most of our objects as star-forming (53%), with the MIR selection favoring relatively massive galaxies (median log M/M⊙∼ 10.3). In addition, we combine our spectroscopic redshifts with UV to FIR photometry as inputs in order to model SEDs with CIGALE, and we measure the PAH 7.7 μm luminosity as an SFR indicator.

The infrared Astronomical Satellite AKARI conducted deep (∼0.4 deg2) and wide (∼ 5.4 deg2) surveys around the North Ecliptic Pole (NEP) with its InfraRed Camera (IRC) with nine filters continuously covering the 2–25 μm range. These photometric bands include three filters that fill the “ Spitzer gap” between the wavelength coverages of IRAC and MIPS. This unique feature has enabled us to make sensitive mid-infrared detection of AGN candidates at z∼1-2, based on the Spectral Energy Distribution (SED) fitting including hot dust emission in the AGN torus. This enables us to compare X-rays and the AGN torus component of the infrared emission to help us identify highly absorbed AGNs, including Compton-thick ones. We report our results of the Chandra observation of the AKARI NEP Deep Field and discuss the prospects for upcoming Spectrum-RG (eROSITA+ART-XC) on the AKARI Wide field.

We present ALMA detection of the [O iii] 88 μm line and 850 μm dust continuum emission in a Y-dropout Lyman break galaxy, MACS0416_Y1. The [O iii] detection confirms the object with a spectroscopic redshift to be z = 8.3118±0.0003. The 850 μm continuum intensity (0.14 mJy) implies a large dust mass on the order of 4×106M⊙. The ultraviolet-to-far infrared spectral energy distribution modeling, where the [O iii] emissivity model is incorporated, suggests the presence of a young (τage ≍ 4 Myr), star-forming (SFR ≍ 60M⊙yr−1), and moderately metal-polluted (Z ≍ 0.2Z⊙) stellar component with a stellar mass of 3 × 108M⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in ≍ 4 Myr, suggesting an underlying evolved stellar component as the origin of the dust mass.

Astronomy has changed from data-starving science to data-flooding science about 20 years ago due to advances of observational technology in all the wavelength regimes of electromagnetic waves. This paper gives a historical overview of galaxy surveys. We start from the impact of the technology development. Then, old imaging surveys and redshift surveys based on photography, especially using Schmidt telescopes, in the era of data-starving science are described in some detail. Several features of modern surveys are given and two highlights obtained from the exploitation of modern galaxy surveys are introduced.

A wealth of observations recently challenged the notion of a universal stellar initial mass function (IMF) by showing evidences in favour of a variability of this statistical indicator as a function of galaxy properties. I present predictions from the semi-analytic model gaea (GAlaxy Evolution and Assembly), which features (a) a detailed treatment of chemical enrichment, (b) an improved stellar feedback scheme, and (c) implements theoretical prescriptions for IMF variations. Our variable IMF realizations predict intrinsic stellar masses and mass-to-light ratios larger than those estimated from synthetic photometry assuming a universal IMF. This provides a self-consistent interpretation for the observed mismatch between photometrically inferred stellar masses of local early-type galaxies and those derived by dynamical and spectroscopic studies. At higher redshifts, the assumption of a variable IMF has a deep impact on our ability to reconstruct the evolution of the galaxy stellar mass function and the star formation history of galaxies.

We present results of our zoom-in cosmological hydrodynamic simulations of direct collapse (DC) to supermassive black hole (SMBH) seeds with radiative transfer (RT). The DC has been modeled in dark matter halos of ∼108M⊙, using adaptive mesh refinement (AMR) code Enzo. For the first time, the baryonic collapse has been followed down to 10−7 pc (∼0.01 AU) with on-the-fly RT and the flux-limited diffusion (FLD) approximation. We find a complex behavior involving accretion flow and associated outflows driven by the radiation force. The resulting gas dynamics around the central density peak differs profoundly from that in previous works which adopted adiabatic approximation in the core. The core forms with a photosphere at ∼1 AU, and its growth starts to saturate at ∼100M⊙. The unrelaxed core radiates intermittently near the Eddington luminosity, correlated with strong anisotropic outflows.

Dust radiative transfer simulations provide us with the unique opportunity to study the heating mechanisms of dust by the stellar radiation field. From 2D observational images we derive the 3D distributions of stars and dust. Our aim is to analyze the contribution of the different stellar populations to the radiative dust heating processes in the nearby face-on barred galaxies NGC 1365, M 83 and M 95. We wish to decompose the FIR-submm SED and quantify the fraction directly related to star formation. To model the complex geometries mentioned above, we used SKIRT, a state-of-the-art, 3D Monte Carlo radiative transfer code designed to simulate the absorption, scattering and thermal re-emission of dust in a variety of environments. We find that the contribution of the evolved stars (8 Gyr) to the dust heating is non-negligible (∼35%) and can reach as high as 70%. We also find a tight correlation between the heating fraction by the unevolved stars (⩽ 100 Myr) and the specific star formation rate.

It is well known that X-ray luminosity (Lx) originating from high mass X-ray binaries (HMXBs) is tightly correlated with the host galaxy’s star formation rate (SFR). We explore this connection using a sample representative of the star-formation activity in the local Universe (Star-Formation Reference Survey; SFRS) along with a comprehensive set of star-formation (radio, FIR, 24μm, 8 μm, Hα, UV, SED fitting) and stellar mass (K-band, 3.6 μm, SED fitting) indicators, and Chandra observations. We investigate the Lx–SFR and Lx– stellar mass (M*) scaling relations down to sub-galactic scales of ∼lkpc2. This way we extend these relations to extremely low SFR (∼10−6M⊙.yr−1) and M* (∼104M⊙). We also quantify their scatter and their dependence on the age of the local stellar populations as inferred from the different age sensitive SFR indicators. These results are particularly important for setting the benchmark for the formation of X-ray binaries in vigorous, but low SFR objects such as galaxies in the early Universe.

Brightest cluster galaxies (BCGs) residing in cool-core clusters are known to be the stage of intricate baryon cycle phenomena (e.g. gas inflows, AGN outflows, star formation feedback). The scenarios describing the observed properties of these galaxies are still controversial, suffering from limitations due to the spatial resolving power of the instruments, specifically for galaxies beyond the Local Universe. However, the dramatic improvements introduced by the integral-field unit instruments (e.g. MUSE) could shed light on the physical processes driving the evolution of these galaxies. We present an extensive analysis of the stellar and gas properties (i.e. kinematics, stellar mass, star formation rate) of the radio-loud BCG sitting at the centre of the X-ray luminous cool-core cluster Abell 2667 (z = 0.23), based on MUSE data. Our results indicate that the BCG is a massive elliptical, hosting an AGN that is possibly undergoing accretion of cold star-forming clouds of ICM or galactic cannibalism.

One of the key questions of the observational cosmology is how the environmental dependence of galaxies today formed. Proto-clusters, galaxy overdense regions at high redshift are important laboratory to study the formation history of clusters of galaxies. We perform the first statistic study of far-infrared spectral energy distribution(SED)s of proto-clusters at z ∼ 4 by the stacking analysis of Planck/ AKARI/ IRAS images of proto-clusters at z ∼ 4 selected from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. By stacking ∼ 200 proto-clusters, we successfully constrain their average total SEDs in 60–850μm. Our results imply the excess of dusty starburst galaxies with star formation rate several 1000 M⊙yr−1 in total and obscured AGNs in proto-clusters at z ∼ 4.

We report fourteen and twenty-eight protocluster candidates at z = 5.7 and 6.6 over 14 and 19 deg2 areas, respectively, selected from 2,230 Lyα emitters (LAEs) photometrically identified with Subaru/Hyper Suprime-Cam (HSC) deep images. Six out of the 42 protocluster candidates include at least 1 spectroscopically confirmed LAEs at redshifts up to z = 6.574. By the comparisons with the cosmological Lyα radiative transfer (RT) model reproducing LAEs with the reionization effects, we find that more than a half of these protocluster candidates might be progenitors of the present-day clusters with a mass of ≳ 1014M⊙. We also investigate the correlation between LAE overdensity and Lya rest-frame equivalent width (EW), because the cosmological Lyα RT model suggests that a slope of EW-overdensity relation is steepened towards the epoch of cosmic reionization (EoR), due to the existence of the ionized bubbles around galaxy overdensities easing the escape of Lyα emission from the partly neutral intergalactic medium. The available HSC data suggest that the slope of the EW-overdensity correlation does not evolve from the post-reionization epoch z = 5.7 to the EoR z = 6.6 beyond the moderately large statistical errors.

The massive galaxies and their central supermassive black holes (SMBHs) co-evolution scenario proposes that a gas-rich major merger can trigger the central starburst and feeding the SMBH accretion, and then star formation is eventually quenched by quasar feedback. In this evolutionary sequence, dust-obscured quasars may represent the critical transition phase between starburst and unobscured quasars. Modeling the panchromatic emission of these hidden monsters provides a unique way to explore their physical properties and therefore the co-evolution between SMBHs and their hosts. However, most of modelling methods are not suitable for the extremely luminous systems with obscured Active Galactic Nucleus (AGN) emission. Here we present two case studies of panchromatic modeling of the extremely luminous dust-obscured quasars at the cosmic noon.

LSST and Euclid must address the daunting challenge of analyzing the unprecedented volumes of imaging and spectroscopic data that these next-generation instruments will generate. A promising approach to overcoming this challenge involves rapid, automatic image processing using appropriately trained Deep Learning (DL) algorithms. However, reliable application of DL requires large, accurately labeled samples of training data. Galaxy Zoo Express (GZX) is a recent experiment that simulated using Bayesian inference to dynamically aggregate binary responses provided by citizen scientists via the Zooniverse crowd-sourcing platform in real time. The GZX approach enables collaboration between human and machine classifiers and provides rapidly generated, reliably labeled datasets, thereby enabling online training of accurate machine classifiers. We present selected results from GZX and show how the Bayesian aggregation engine it uses can be extended to efficiently provide object-localization and bounding-box annotations of two-dimensional data with quantified reliability. DL algorithms that are trained using these annotations will facilitate numerous panchromatic data modeling tasks including morphological classification and substructure detection in direct imaging, as well as decontamination and emission line identification for slitless spectroscopy. Effectively combining the speed of modern computational analyses with the human capacity to extrapolate from few examples will be critical if the potential of forthcoming large-scale surveys is to be realized.