Using the FirstLight database of 300 zoom-in cosmological simulations we provide rest-frame UV-optical spectral energy distributions of galaxies with complex star-formation histories that are coupled to the non-uniform gas accretion history of galactic halos during cosmic dawn. The population at any redshift is very diverse ranging from starbursts to quiescent galaxies even at a fixed stellar mass. The FirstLight simulations make predictions on the rest-frame UV-optical absolute magnitudes, colors and optical emission lines of galaxies at z = 6–12 that will be observed for the first time with JWST and the next generation of telescopes in the coming decade.

We present a velocity of galactic outflows in star-forming galaxies at the highest redshift, z ∼ 6, so far studied with metal absorption lines. Absorption-line studies of galactic outflows need well-determined redshifts, but there are few strong emission lines in the observed-frame optical spectra of galaxies at high redshifts. In this work, we use the systemic redshifts determined by the ALMA [CII]158 μm emission lines. The sample consists of seven Lyman break galaxies at 5.1 < z < 5.7 whose Keck/DEIMOS and ALMA data are available in the archive. The outflow maximum velocity (νmax) is estimated by a fitting of line profiles to metal absorption lines in a composite spectrum. We find that νmax monotonically increases from z ∼ 0 to 6 and that νmax tightly correlates with the halo circular velocity estimated from the stellar mass.

Panchromatic modeling is one of the most powerful tools at our disposal to measure reliably the physical properties of galaxies across cosmic times. We present here an entirely new implementation in python of one such tool: CIGALE. Developed along three main design principles: simplicity, modularity, and efficiency, it has proven to be a versatile code that in addition to estimating the physical properties of galaxies (or regions within galaxies), can generate arbitrary sets of theoretical models or be used as a library to build other tools. Among its defining features, it is a truly panchromatic code ranging from the far-ultraviolet to the radio that takes into account numerous physical components (including active nuclei or synchrotron emission), that can fit non-photometric data, handle upper limits, determine photometric redshifts, and even build mock catalogs.

Studying the density profiles of galaxy groups offers an important insight on how large-scale structure in the Universe formed and evolved, since galaxy groups bridge the gap between individual galaxies and galaxy clusters. We aim to probe the total density profile of the galaxy group that is gravitational lensing HELMS18, a submillimeter galaxy at z = 2.39 from the Herschel’s HerMES Large Mode Survey (HELMS), by combining strong gravitational lensing with kinematics of the centrally-located galaxies and kinematics of the group members. We will use high-resolution data of HELMS18 obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) and multi-object spectroscopic data of the group members from Gemini-GMOS. Our final goal is to combine these observations to probe the stellar and dark matter density profiles and to build a complete description of this galaxy group.

Radio continuum emission from galaxies is powered by a combination of distinct physical processes, each providing unique diagnostic information. Over frequencies spanning ∼ 1–120 GHz, radio spectra of star-forming galaxies are primarily comprised of: (1) non-thermal synchrotron emission powered by accelerated cosmic-ray electrons/positrons; (2) free-free emission from young massive star-forming (H ii) regions; (3) anomalous microwave emission, which is a dominant, but completely unconstrained, foreground in cosmic microwave background experiments; and (4) cold, thermal dust emission that accounts for most of the dust and total mass content in the interstellar medium in galaxies. In this proceeding, we discuss these key energetic processes that contribute to the radio emission from star-forming galaxies, with an emphasis on frequencies ≳30 GHz, where current investigations of star formation within nearby galaxies show that the free-free emission begins to dominate over non-thermal synchrotron emission. We also discuss how planned radio facilities that will access these frequencies, such as a next-generation Very Large Array (ngVLA), will be transformative to our understanding of the star formation process in galaxies.

The star formation history (SFH) of galaxies allow us to investigate when galaxies formed their stars and assembled their mass. We can constrain the SFH with high level of precision from galaxies with resolved stellar populations, since we are able to discriminate between stars of different ages from the spectrum they emit. However, the relative importance of secular evolution (nature) over nurture is not yet clear, and separating the effects of interaction-driven evolution in the observed galaxy properties is not trivial. The aim of this study is to use MaNGA (Mapping Nearby Galaxies at APO) Integral Field Unit (IFU) data, in combination with multi-wavelength data, to constrain the SFH of nearby isolated galaxies. We present here the new techniques we are developing to constrain the SFH with high level of precision from Spectral Energy Distribution (SED) fitting. This study is part of a China-Chile collaboration program where we are applying these new techniques to investigate how galaxies formed and evolve in different environments.

We build a theoretical picture of how the light from galaxies evolves across cosmic time. In particular, we predict the evolution of the galaxy spectral energy distribution (SED) by carefully integrating the star formation and metal enrichment histories of semi-analytic model (SAM) galaxies and combining these with stellar population synthesis models which we call mentari. Our SAM combines prescriptions to model the interplay between gas accretion, star formation, feedback process, and chemical enrichment in galaxy evolution. From this, the SED of any simulated galaxy at any point in its history can be constructed and compared with telescope data to reverse engineer the various physical processes that may have led to a particular set of observations. The synthetic SEDs of millions of simulated galaxies from mentari can cover wavelengths from the far UV to infrared, and thus can tell a near complete story of the history of galaxy evolution.

New challenges in the modelling of galaxy spectra are bound to emerge as upcoming telescopes like the James Webb Space Telescope will allow us to detect galaxies at fainter flux levels and higher redshifts than ever before. Here, we highlight three modelling problems that may become relevant for upcoming observations in the rest-frame ultraviolet/optical at the high-redshift frontier: stellar initial mass function sampling effects, Population III signatures and the leakage of ionizing radiation into the intergalactic medium.

In this study, we show that the characteristic radius rs, mass Ms, and the X-ray temperature, TX, of galaxy clusters form a thin plane in the space of (log rs, log Ms, log TX). This tight correlation indicates that the cluster structure including the temperature is affected by the formation time of individual clusters. Numerical simulations show that clusters move along the fundamental plane as they evolve. The plane and the cluster evolution within the plane can be explained by a similarity solution of structure formation. The angle of the plane shows that clusters have not achieved “virial equilibrium”. The details of this study are written in Fujita et al. (2018a,b).

Combining cosmological hydrodynamic simulations and radiative transfer (RT) calculations, we present predictions of multi-wavelength radiative properties of the first galaxies at z ∼ 6–5. We find that intermittent star formation due to supernova (SN) feedback causes the escape fraction of UV photons to fluctuate rapidly, which then produces the observed diversity of SEDs for high-z galaxies. The simulated galaxies make rapid transition between UV-bright and IR-bright phase, and our RT calculations suggest that dust temperatures in the first galaxies are higher than z < 3 galaxies with ∼ 60 K.

We study star formation and metallicity enrichment histories of 24 massive galaxies at 1.6 < z < 2.5. Deep slitless spectroscopy + imaging data set collected from multiple HST surveys allows robust determination of their SEDs. Our new SED modeling with no functional assumptions on star formation histories revels that 1. most of the sample galaxies have already formed >50% of their extant masses ∼1.5 Gyr before the time of observed redshifts, with a trend where more massive galaxies form earlier, 2. most of our galaxies already have stellar metallicities compatible with those of local early-type galaxies, and 3. inferred metallicities are on average ∼ 0.25 dex higher than observed gas-phase metallicities of star forming galaxies at the time of their formation. Continuation of low-level star formation, rather than abrupt termination of star forming activity, may explain the observed gap of metallicities.

In this paper we address two questions related to data analysis in large astronomical datasets, and we demonstrate how they can be answered making use of machine learning techniques. The first question is: how to efficiently find previously unknown or rare objects which can be expected to exist in big data samples? Using the largest existing extragalactic all-sky survey, provided by the WISE satellite, we demonstrate that, surprisingly, supervised classification methods can come to aid. The second question is: having a sufficiently large data sample, how can we look for new optimal classification schemes, possibly finding new and previously unknown classes and subclasses of sources? Based on the VIPERS cutting-edge galaxy catalog at redshift z > 0.5, we demonstrate that unsupervised classification methods can give unexpected but physically well-motivated results.

We measure the evolution of the UV upturn color for galaxies on the red sequence in clusters at 0 < z < 0.7 and to luminosity levels L ∼ L*. We show that the UV upturn color does not change until at least z = 0.55 but becomes significantly redder at z = 0.7. This is the first detection of evolution in the UV upturn. Our observations are inconsistent with all models proposed for its origin except the presence of a population of helium enriched stars, with helium abundances above 42 % and formed at z > 4.

We present results from high-resolution, zoom-in cosmological simulations to study the effect of feedback from galactic outflows on the physical and Lyα properties of high-redshift galaxies in highly overdense and normal environments at z >∼6. The Lyα properties have been obtained by post-processing the simulations with a Monte-Carlo radiative transfer (RT) code. Our results demonstrate that galactic outflows play an important role in regulating the growth of massive galaxies in overdense regions as well as the temperature and metallicity of the intergalactic medium. In particular, we find that galactic outflows are necessary to reproduce the observed Lyα luminosity functions as well as the apparent Lyα luminosity, line width and equivalent width distributions of luminous Lyα emitters at z ∼ 6.

We investigate rest-frame UV to far-infrared emission lines and SEDs from 1124 galaxies at z = 4.9 – 7.0. Our sample is composed of 1092 Lyα emitters (LAEs) at z = 4.9–7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys and 34 galaxies at z = 5.148–7.508 with deep [Cii]158μm ALMA data. The SEDs clearly show flux excesses in the Spitzer/IRAC 3.6 and 4.5μm bands, suggesting strong rest-frame optical emission lines of [Oiii] and/or Hα. We model the galaxy SEDs with a flexible code combining stellar population and photoionization models (BEAGLE; Chevallard & Charlot 2016), and investigate relations between the emission lines of Lyα, [Oiii], Hα, and [CII]. We find 1) a positive correlation between the rest-frame Hα equivalent width (EW) and the Lyα, EW, ${\EW {^0_Ly\alpha}} $, 2) an interesting turn-over trend that the [Oiii]/Hα flux ratio increases in ${\EW {^0_Ly\alpha}} $ ≃ 0–30 Å, and then decreases out to ${\EW {^0_Ly\alpha}} $ ≃ 130 Å, and 3) a > 99% anti-correlation between a [Cii] luminosity to star-formation rate ratio L[Cii]/SFR) and ${\EW {^0_Ly\alpha}} $. Modeling with BEAGLE also suggests that a simple anticorrelation between ${\EW {^0_Ly\alpha}} $ and metallicity explains self-consistently all of the relations of Lyα, Hα, [Oiii]/Hα, and [Cii] in our study, indicative of detections of very metal-poor (∼0.03Z⊙) galaxies with ${\EW {^0_Ly\alpha}} $ ∼200 Å.

We present ongoing work on the spectral energy distributions (SEDs) of active galactic nuclei (AGNs), derived from X-ray, ultraviolet, optical, infrared and radio photometry and spectroscopy. Our work is motivated by new wide-field imaging surveys that will identify vast numbers of AGNs, and by the need to benchmark AGN SED fitting codes. We have constructed 41 SEDs of individual AGNs and 80 additional SEDs that mimic Seyfert spectra. All of our SEDs span 0.09 to 30μm, while some extend into the X-ray and/or radio. We have tested the utility of the SEDs by using them to generate AGN photometric redshifts, and they outperform SEDs from the prior literature, including reduced redshift errors and flux density residuals.

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.