Star Formation and AGN activity in Galaxies classified using the 1.6 {\mu}m Bump and PAH features at z=0.4−2z = 0.4-2

We have studied the star-formation and AGN activity of massive galaxies in the redshift range $z=0.4-2$, which are detected in a deep survey field using the AKARI InfraRed (IR) astronomical satellite and {\em Subaru} telescope toward the North Ecliptic Pole (NEP). The AKARI/IRC Mid-InfraRed (MIR) multiband photometry is used to trace their star-forming activities with the Polycyclic-Aromatic Hydrocarbon (PAH) emissions, which is also used to distinguish star-forming populations from AGN dominated ones and to estimate the Star Formation Rate (SFR) derived from their total emitting IR (TIR) luminosities. In combination with analyses of their stellar components, we have studied the MIR SED features of star-forming and AGN-harboring galaxies.Comment: 45 pages and 63 figures, will be published in PASJ Vol.64 No.

Hyper Suprime-Camera Survey of the Akari NEP Wide Field

The extragalactic background suggests half the energy generated by stars was reprocessed into the infrared (IR) by dust. At z ∼1.3, 90% of star formation is obscured by dust. To fully understand the cosmic star formation history, it is critical to investigate infrared emission. AKARI has made deep mid-IR observation using its continuous 9-band filters in the NEP field (5.4 deg2), using ∼10% of the entire pointed observations available throughout its lifetime. However, there remain 11,000 AKARI infrared sources undetected with the previous CFHT/Megacam imaging (r ∼25.9ABmag). Redshift and IR luminosity of these sources are unknown. These sources may contribute significantly to the cosmic star-formation rate density (CSFRD). For example, if they all lie at 1 z g, r, i, z, and y) using Hyper Suprime-Camera (HSC), which has 1.5 deg field of view in diameter on Subaru 8m telescope. This will provide photometric redshift information, and thereby IR luminosity for the previously-undetected 11,000 faint AKARI IR sources. Combined with AKARI's mid-IR AGN/SF diagnosis, and accurate mid-IR luminosity measurement, this will allow a complete census of cosmic star-formation/AGN accretion history obscured by dust

Torus Constraints in ANEPD-CXO245: A Compton-thick AGN with Double-peaked Narrow Lines

We report on the torus constraints of the Compton-thick active galactic nucleus (AGN) with double-peaked optical narrow-line region emission lines, ANEPD-CXO245, at z = 0.449 in the AKARI NEP Deep Field. The unique infrared data on this field, including those from the nine-band photometry over 2–24 μm with the AKARI Infrared Camera, and the X-ray spectrum from Chandra allow us to constrain torus parameters such as the torus optical depth, X-ray absorbing column, torus angular width (σ), and viewing angle (i). We analyze the X-ray spectrum as well as the UV–optical–infrared spectral energy distribution (UOI-SED) with clumpy torus models in X-ray (XCLUMPY) and infrared (CLUMPY), respectively. From our current data, the constraints on σ–i from both X-rays and UOI show that the line of sight crosses the torus as expected for a type 2 AGN. We obtain a small X-ray scattering fraction (NH from the X-ray spectrum, we find that the gas-to-dust ratio is <4 times larger than the Galactic value

Infrared luminosity functions based on 18 mid-infrared bands: revealing cosmic star formation history with AKARI and Hyper Suprime-Cam*

Much of star formation is obscured by dust. For a complete understanding of the cosmic star formation history (CSFH), infrared (IR) census is indispensable. AKARI carried out deep mid-infrared observations using its continuous nine-band filters in the North Ecliptic Pole (NEP) field (5.4 deg2). This took a significant amount of the satellite’s lifetime, ∼10% of the entire pointed observations. By combining archival Spitzer (five bands) and WISE (four bands) mid-IR photometry, we have, in total, 18-band mid-IR photometry, which is the most comprehensive photometric coverage in the mid-IR for thousands of galaxies. However, we only had shallow optical imaging (∼25.9 AB magnitude) in a small area, 1.0 deg2. As a result, thousands of AKARI’s infrared sources remained undetected in the optical. Using the new Hyper Suprime-Cam on the Subaru telescope, we obtained deep enough optical images of the entire AKARI NEP field in five broad bands (g ∼ 27.5 mag). These provided photometric redshift, and thereby IR luminosity, for the previously undetected faint AKARI IR sources. Combined with the accurate mid-IR luminosity measurement, we constructed mid-IR luminosity functions (LFs), and thereby performed a census of dust-obscured CSFH in the entire AKARI NEP field. We have measured restframe 8 μm and 12 μm LFs, and estimated total infrared LFs at 0.35 z z ∼ 2

Search for Optically Dark Infrared Galaxies without Counterparts of Subaru Hyper Suprime-Cam in the AKARI North Ecliptic Pole Wide Survey Field

We present the physical properties of AKARI sources without optical counterparts in optical images from the Hyper Suprime-Cam (HSC) on the Subaru telescope. Using the AKARI infrared (IR) source catalog and HSC optical catalog, we select 583 objects that do not have HSC counterparts in the AKARI North Ecliptic Pole wide survey field (~5 deg2). Because the HSC limiting magnitude is deep (gAB ~ 28.6), these are good candidates for extremely red star-forming galaxies (SFGs) and/or active galactic nuclei (AGNs), possibly at high redshifts. We compile multiwavelength data out to 500 μm and use them for fitting the spectral energy distribution with CIGALE to investigate the physical properties of AKARI galaxies without optical counterparts. We also compare their physical quantities with AKARI mid-IR selected galaxies with HSC counterparts. The estimated redshifts of AKARI objects without HSC counterparts range up to z ~ 4, significantly higher than for AKARI objects with HSC counterparts. We find that (i) 3.6 – 4.5 μm color, (ii) AGN luminosity, (iii) stellar mass, (iv) star formation rate, and (v) V-band dust attenuation in the interstellar medium of AKARI objects without HSC counterparts are systematically larger than those of AKARI objects with counterparts. These results suggest that our sample includes luminous, heavily dust-obscured SFGs/AGNs at z ~ 1–4 that are missed by previous optical surveys, providing very interesting targets for the coming era of the James Webb Space Telescope

The evolution of merger fraction of galaxies at z < 0.6 depending on the star formation mode in the <i>AKARI</i> NEP-Wide Field

We study the galaxy merger fraction and its dependence on star formation mode in the 5.4 deg2 of the North Ecliptic Pole-Wide Field. We select 6352 galaxies with AKARI 9 µm detections, and identify mergers among them using the Gini coefficient and M20 derived from the Subaru/Hyper Suprime-Cam (HSC) optical images. We obtain the total infrared luminosity and star formation rate of galaxies using the spectral energy distribution templates based on one band, AKARI 9 µm. We classify galaxies into three different star formation modes (i.e. starbursts, main-sequence, and quiescent galaxies) and calculate the merger fractions for each. We find that the merger fractions of galaxies increase with redshift at z Herschel/Spectral and Photometric Imaging Receiver (SPIRE). We find that Herschel-detected galaxies have higher merger fraction compared to non-Herschel-detected galaxies, and both Herschel-detected and non-Herschel-detected galaxies show clearly different merger fractions depending on the star formation modes

Identification of <i>AKARI</i> infrared sources by the Deep HSC Optical Survey: construction of a new band-merged catalogue in the North Ecliptic Pole Wide field

The North Ecliptic Pole field is a natural deep-field location for many satellite observations. It has been targeted many times since it was surveyed by the AKARI space telescope with its unique wavelength coverage from the near- to mid-infrared (mid-IR). Many follow-up observations have been carried out, making this field one of the most frequently observed areas with a variety of facilities, accumulating abundant panchromatic data from the X-ray to the radio wavelength range. Recently, a deep optical survey with the Hyper Suprime-Cam (HSC) at the Subaru telescope covered the NEP-Wide (NEPW) field, which enabled us to identify faint sources in the near- and mid-IR bands, and to improve the photometric redshift (photo-z) estimation. In this work, we present newly identified AKARI sources by the HSC survey, along with multiband photometry for 91 861 AKARI sources observed over the NEPW field. We release a new band-merged catalogue combining various photometric data from the GALEX UV to submillimetre (sub-mm) bands (e.g. Herschel/SPIRE, JCMT/SCUBA-2). About ∼20 000 AKARI sources are newly matched to the HSC data, most of which seem to be faint galaxies in the near- to mid-infrared AKARI bands. This catalogue is motivating a variety of current research, and will be increasingly useful as recently launched (eROSITA/ART-XC) and future space missions (such as JWST, Euclid, and SPHEREx) plan to take deep observations in the NEP field