Hideo Matsuhara

ABSTRACT Galaxy clusters provide an excellent probe in various research fields in astrophysics and cosmology. However, the number of galaxy clusters detected so far in the AKARI North Ecliptic Pole (NEP) field is limited. In this work, we provide galaxy cluster candidates in the AKARI NEP field with the minimum requisites based only on the coordinates and photometric redshift (photo-z) of galaxies. We used galaxies detected in five optical bands (g, r, i, z, and Y) by the Subaru Hyper Suprime-Cam (HSC), with additional data from the u band obtained from the Canada-France-Hawaii Telescope (CFHT) MegaPrime/MegaCam, and from the IRAC1 and IRAC2 bands from the Spitzer space telescope for photo-z estimation. We calculated the local density around every galaxy using the 10th-nearest neighbourhood. Cluster candidates were determined by applying the friends-of-friends algorithm to over-densities. A total of 88 cluster candidates containing 4390 member galaxies below redshift 1.1 in 5.4 deg2 were identified. The reliability of our method was examined through false-detection tests, redshift-uncertainty tests, and applications on the Cosmic Evolution Survey (COSMOS) data, giving false-detection rates of 0.01 to 0.05 and a recovery rate of 0.9 at high richness. Three X-ray clusters previously observed by ROSAT and Chandra were recovered. The cluster galaxies show a higher stellar mass and lower star formation rate compared with the field galaxies in two-sample Z-tests. These cluster candidates are useful for environmental studies of galaxy evolution and future astronomical surveys in the NEP, where AKARI has performed unique nine-band mid-infrared photometry for tens of thousands of galaxies.

The $AKARI$ space infrared telescope has performed near- to mid-infrared (MIR) observations on the North Ecliptic Pole Wide (NEPW) field (5.4 deg$^2$) for about one year. $AKARI$ took advantage of its continuous nine photometric bands, compared with NASA's $Spitzer$ and WISE space telescopes, which had only four filters with a wide gap in the MIR. The $AKARI$ NEPW field lacked deep and homogeneous optical data, limiting the use of nearly half of the IR sources for extra-galactic studies owing to the absence of photometric redshifts (photo-zs). To remedy this, we have recently obtained deep optical imaging over the NEPW field with 5 bands ($g$, $r$, $i$, $z$, and $Y$) of the Hyper Suprime-Camera (HSC) on the Subaru 8m telescope. We optically identify AKARI-IR sources along with supplementary $Spitzer$ and WISE data as well as pre-existing optical data. In this work, we derive new photo-zs using a $\chi^2$ template-fitting method code ($Le$ $Phare$) and reliable photometry from 26 selected filters including HSC, $AKARI$, CFHT, Maidanak, KPNO, $Spitzer$ and WISE data. We take 2026 spectroscopic redshifts (spec-z) from all available spectroscopic surveys over the NEPW to calibrate and assess the accuracy of the photo-zs. At z < 1.5, we achieve a weighted photo-z dispersion of $\sigma_{\Delta{z/(1+z) } }$ = 0.053 with $\eta$ = 11.3% catastrophic errors.

The north ecliptic pole (NEP) field is a natural deep field location for many satellite observations. It has been targeted manytimes 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 and made this field one of the most frequently observed areas witha variety of facilities, accumulating abundant panchromatic data from X-ray to radio wavelength range. Recently, a deep opticalsurvey with the Hyper Suprime-Cam (HSC) at the Subaru telescope covered the NEP-Wide (NEPW) field, which enabled us toidentify 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 multi-band photometry for 91,861 AKARI sourcesobserved over the NEPW field. We release a new band-merged catalogue combining various photometric data from GALEXUV to the submillimetre (sub-mm) bands (e.g., Herschel/SPIRE, JCMT/SCUBA-2). About 20,000 AKARI sources are newlymatched to the HSC data, most of which seem to be faint galaxies in the near- to mid-infrared AKARI bands. This cataloguemotivates a variety of current research, and will be increasingly useful as recently launched (eROSITA/ART-XC) and futurespace missions (such as JWST, Euclid, and SPHEREx) plan to take deep observations in the NEP field.

Recent simulations predict that the presence of stellar bulge suppress the efficiency of star formation in early-type galaxies, and this `morphological quenching' scenario is supported by many observations. In this study, we discuss the net effect of galaxy morphologies on the star formation efficiency (SFE) during the phase of galaxy transition, on the basis of our CO($J=1-0$) observations of 28 local `green-valley' galaxies with the Nobeyama 45m Radio Telescope. We observed 13 `disk-dominated' and 15 `bulge-dominated' green-valley galaxies at fixed stellar mass ($M_*$) and star formation rate (SFR), supplemented by 1 disk- and 6 bulge-dominated galaxies satisfying the same criteria from the xCOLD~GASS survey. By using a total of 35 green-valley galaxies, we reveal that the distributions of molecular gas mass, molecular gas fraction, and SFE of green-valley galaxies do not change with their morphologies, suggesting little impact of galaxy morphologies on their SFE, and interestingly this result is also valid for normal star-forming galaxies on the SF main-sequence selected from the xCOLD~GASS galaxies. On the other hand, we find that $\sim$20 % of bulge-dominated green-valley galaxies do not show significant CO emission line, showing high SFEs for their M$_*$ and SFR. These molecular gas deficient sources identified only in the bulge-dominated green-valley galaxies may represent an important population during the quenching phase under the influence of stellar bulge, but our results suggest that the presence of stellar bulge does not decrease the efficiency of on-going star formation, in contrast to the prediction of the morphological quenching scenario.

We have developed an efficient Active Galactic Nucleus (AGN) selection method using 18-band Spectral Energy Distribution (SED) fitting in mid-infrared (mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend to be missed in optical, UV and soft X-ray observations. Mid-IR light can help us to recover them in an obscuration free way using their thermal emission. On the other hand, Star-Forming Galaxies (SFG) also have strong PAH emission features in mid-IR. Hence, establishing an accurate method to separate populations of AGN and SFG is important. However, in previous mid-IR surveys, only 3 or 4 filters were available, and thus the selection was limited. We combined AKARI's continuous 9 mid-IR bands with WISE and Spitzer data to create 18 mid-IR bands for AGN selection. Among 4682 galaxies in the AKARI NEP deep field, 1388 are selected to be AGN hosts, which implies an AGN fraction of 29.6$\pm$0.8$\%$ (among them 47$\%$ are Seyfert 1.8 and 2). Comparing the result from SED fitting into WISE and Spitzer colour-colour diagram reveals that Seyferts are often missed by previous studies. Our result has been tested by stacking median magnitude for each sample. Using X-ray data from Chandra, we compared the result of our SED fitting with WISE's colour box selection. We recovered more X-ray detected AGN than previous methods by 20$\%$.

We produce a catalogue of polycyclic aromatic hydrocarbon (PAH) 3.3 $\mu$m, Br$\alpha$ and infrared luminosity ($L$(IR)) of 412 local galaxies, and investigate a relation between these physical parameters. We measure the PAH 3.3 $\mu$m and Br$\alpha$ flux using AKARI 2-5 $\mu$m spectra and the $L$(IR) using the AKARI-all-sky-survey data. The $L$(IR) and redshift ranges of our sample are $L$(IR)=$10^{9.7-12.8}$L$_\odot$ and $z_{\rm spec}=0.002-0.3$, respectively. We found that the ratio of $L$(PAH 3.3 $\mu$m) to $L$(IR) is constant at $L$(IR) $<$ $10^{11} \rm L_\odot$ whereas it decreases with the $L$(IR) at higher $L$(IR). Also, the ratio of $L$(Br$\alpha$) to $L$(IR) decreases with the $L$(IR). The both $L$(PAH)/$L$(IR) and $L$(Br$\alpha$)/$L$(IR) ratios are not strongly dependent on galaxy type and dust temperature. The relative weakness of the two ratios could be attributed to destruction of PAH, a lack of UV photons exciting PAH molecules or ionising hydrogen gas, extremely high dust attenuation, or active galactic nucleus contribution to the $L$(IR). Although we cannot determine the cause of the decreases of the luminosity ratios, a clear correlation between them implies that they are related with each other. The catalogue presented in our work will be available at the AKARI archive web page.

We present an initial result from the 12CO (J=1-0) survey of 79 galaxies in 62 local luminous and ultra-luminous infrared galaxy (LIRG and ULIRG) systems obtained using the 45 m telescope at the Nobeyama Radio Observatory. This is the systematic 12CO (J=1-0) survey of the Great Observatories All-sky LIRGs Survey (GOALS) sample. The molecular gas mass of the sample ranges 2.2 x 10^8 - 7.0 x 10^9 Msun within the central several kiloparsecs subtending 15" beam. A method to estimate a size of a CO gas distribution is introduced, which is combined with the total CO flux in the literature. The method is applied to a part of our sample and we find that the median CO radius is 1-4 kpc. From the early stage to the late stage of mergers, we find that the CO size decreases while the median value of the molecular gas mass in the central several kpc region is constant. Our results statistically support a scenario where molecular gas inflows towards the central region from the outer disk, to replenish gas consumed by starburst, and that such a process is common in merging LIRGs.

Mass, metallicity, and star formation rate (SFR) of a galaxy are crucial parameters in understanding galaxy formation and evolution. However, the relation among these is still a matter of debate for luminous infrared galaxies, which carry a bulk of SFR budget of the universe at $z\sim1$. We have investigated the relation among stellar mass, gas-phase oxygen abundance, and SFR of AKARI-detected mid-IR galaxies at $z\sim0.88$ in the AKARI NEP deep field. We observed about 350 AKARI sources with Subaru/FMOS NIR spectrograph, and detected secure and expected H$\alpha$ emission lines from 25 and 44 galaxies, respectively. The SFR of our sample is almost constant ($\sim 25M_{\odot}/yr$) over the stellar mass range of our sample. Compared with main-sequence (MS) galaxies at a similar redshift range, the average SFR of our detected sample is comparable for massive galaxies ($\sim10^{10.58}~M_{\odot}$), while higher by $\sim$0.6dex for less massive galaxies ($\sim 10^{10.05}~M_{\odot}$). We measure metallicities from the [NII]/H$\alpha$ emission line ratio. We find that the mass-metallicity relation of our individually measured sources agrees with that for optical-selected star-forming galaxies at $z\sim0.1$, while metallicities of stacked spectra agree with that of MS galaxies at $z\sim0.78$. Considering high SFR of individually measured sources, FMR of the IR galaxies is different from that at $z\sim0.1$. However, on the mass-metallicity plane, they are consistent with the MS galaxies, highlighting higher SFR of the IR galaxies. This suggests the evolutionary path of our IR galaxies is different from that of MS galaxies. A possible physical interpretation includes that the star-formation activities of IR galaxies at $z\sim0.88$ in our sample are enhanced by interaction and/or merger of galaxies, but the inflow of metal-poor gas is not yet induced, keeping the metallicity intact.

We present measurements of the clustering properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining 125 deg$^2$ of wide and deep optical images obtained with the Hyper Suprime-Cam on the Subaru Telescope and all-sky mid-IR (MIR) images taken with Wide-Field Infrared Survey Explorer, we have discovered 4,367 IR-bright DOGs with $(i - [22])_{\rm AB}$ $>$ 7.0 and flux density at 22 $\mu$m $>$ 1.0 mJy. We calculate the angular autocorrelation function (ACF) for a uniform subsample of 1411 DOGs with 3.0 mJy $<$ flux (22 $mu$m) $<$ 5.0 mJy and $i_{\rm AB}$ $<$ 24.0. The ACF of our DOG subsample is well-fit with a single power-law, $\omega (\theta)$ = (0.010 $\pm$ 0.003) $\theta^{-0.9}$, where $\theta$ in degrees. The correlation amplitude of IR-bright DOGs is larger than that of IR-faint DOGs, which reflects a flux-dependence of the DOG clustering, as suggested by Brodwin et al. (2008). We assume that the redshift distribution for our DOG sample is Gaussian, and consider 2 cases: (1) the redshift distribution is the same as IR-faint DOGs with flux at 22 $\mu$m $<$ 1.0 mJy, mean and sigma $z$ = 1.99 $\pm$ 0.45, and (2) $z$ = 1.19 $\pm$ 0.30, as inferred from their photometric redshifts. The inferred correlation length of IR-bright DOGs is $r_0$ = 12.0 $\pm$ 2.0 and 10.3 $\pm$ 1.7 $h^{-1}$ Mpc, respectively. IR-bright DOGs reside in massive dark matter halos with a mass of $\log [\langle M_{\mathrm{h } } \rangle / (h^{-1} M_{\odot})]$ = 13.57$_{-0.55}^{+0.50}$ and 13.65$_{-0.52}^{+0.45}$ in the two cases, respectively.

Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

Aims. Dust-obscured star-formation increases with increasing intensity and increasing redshift. We aim to reveal the cosmic star-formation history obscured by dust using deep infrared observation with AKARI. Methods. We constructed restframe 8 mu m, 12 mu m, and total infrared (TIR) luminosity functions (LFs) at 0.15 &lt; z &lt; 2.2 using 4128 infrared sources in the AKARI NEP-deep field. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24 mu m) by the AKARI satellite allowed us to estimate restframe 8 mu m and 12 mu m luminosities without using a large extrapolation based on an SED fit, which was the largest uncertainty in previous work. Results. We find that all 8 mu m (0.38 &lt; z &lt; 2.2), 12 mu m (0.15 &lt; z &lt; 1.16), and TIR LFs (0.2 &lt; z &lt; 1.6) show continuous and strong evolution toward higher redshift. Our direct estimate of 8 mu m LFs is useful since previous work often had to use a large extrapolation from the Spitzer 24 mu m to 8 mu m, where SED modeling is more difficult because of the PAH emissions. In terms of cosmic infrared luminosity density (Omega(IR)), which was obtained by integrating analytic fits to the LFs, we find good agreement with previous work at z &lt; 1.2. We find the Omega(IR) evolves as proportional to(1 + z)(4.4 +/- 1.0). When we separate contributions to Omega(IR) by LIRGs and ULIRGs, we found more IR luminous sources are increasingly more important at higher redshift. We find that the ULIRG (LIRG) contribution increases by a factor of 10 (1.8) from z = 0.35 to z = 1.4.

We study the sensitivities of space infrared interferometers. We formulate the signal-to-noise ratios of infrared images obtained by aperture synthesis in the presence of source shot noise, background shot noise and detector read noise. We consider the case in which n beams are pairwise combined at n(n-1)/2 detectors, and the case in which all the n beams are combined at a single detector. We apply the results to future missions, Terrestrial Planet Finder and Darwin. We also discuss the potential of a far-infrared interferometer for a deep galaxy survey.

We present the results of ground-based imaging spectroscopy of the [Ne II] 12.8 mu m line emitted from the ultracompact (UC) H II regions W51d, G45.12 +/- 0.13, G35.20 - 1.74, and Monoceros R2, with 2" spatial resolution. We found that the overall distribution of the [Ne II] emission is generally in good agreement with the radio (5 or 15 GHz) VLA distribution for each source. The Ne+ abundance ([Ne+/ H+]) distributions are also derived from the [Ne II] and the radio maps. As for G45.12 + 0.13 and W51d, the Ne+ abundance decreases steeply from the outer part of the map toward the radio peak. On the other hand, the Ne+ abundance distributions of G35.20-1.74 and Mon R2 appear rather uniform. These results can be interpreted by the variation of ionizing structures of neon, which is determined primarily by the spectral type of the ionizing stars. We have evaluated the effective temperature of the ionizing star by comparing the Ne+ abundance averaged over the whole observed region with that calculated by H II region models based on recent non-LTE stellar atmosphere models: 39,100(-500)(+1100) K (O7.5 V-O8 V) for W51d; 37,200(-700)(+1000) K (O8 V-O8.5 V) for G45.12 + 0.13; 35,00-37,600(-600)(+1500) K (O8 V-O9 V) for G35.20-1.74; and less than or equal to 34,000 K (less than or equal to B0 V) for Mon R2. These effective temperatures are consistent with those inferred from the observed Ne+ abundance distributions.

We report the results of a rocket-borne observation of [C II] 158\micron line and far-infrared continuum emission at 152.5\micron toward the high latitude molecular clouds in Ursa Major. We also present the results of a follow-up observation of the millimeter ^{12}CO J=1-0 line over a selected region observed by the rocket-borne experiment. We have discovered three small CO cloudlets from the follow-up ^{12}CO observations. We show that these molecular cloudlets, as well as the MBM clouds(MBM 27/28/29/30), are not gravitationally bound. Magnetic pressure and turbulent pressure dominate the dynamic balance of the clouds. After removing the HI-correlated and background contributions, we find that the [C II] emission peak is displaced from the 152.5\micron and CO peaks, while the 152.5\micron continuum emission is spatially correlated with the CO emission. We interpret this behavior by attributing the origin of [C II] emission to the photodissociation regions around the molecular clouds illuminated by the local UV radiation field. We also find that the ratio of the molecular hydrogen column density to velocity-integrated CO intensity is 1.19+-0.29x10^{20} cm^{-2} (K kms^{-1})^{-1} from the FIR continuum and the CO data. The average [C II] /FIR intensity ratio over the MBM clouds is 0.0071, which is close to the all sky average of 0.0082 reported by the FIRAS on the COBE satellite. The average [C II]/CO ratio over the same regions is 420, which is significantly lower than that of molecular clouds in the Galactic plane.

We give a detailed description of the design and flight performance of an instrument onboard the S-52015 rocket of the Institute of Space and Astronautical Science. The instrument, consisting of a near-infrared spectrometer and a far-infrared photometer at the focus of a 10 cm liquid-helium cooled telescope, was designed to observe both the brightness and distribution of diffuse emission with high sensitivity. The rocket was successfully launched and the instrument observed near-infrared and far-infrared continuum emission, as well as [C(II)] 157.7 mum line emission from regions at high Galactic latitude. We also give a brief description of the design and performance of an onboard attitude control system.

A wobbling mechanism for a secondary mirror has been developed for a balloon-borne infrared telescope. Friction of the wobbling mechanism is negligibly small, and hence the wobbling mechanism is very reliable for the use in a severe environment at balloon altitudes. Motion is controlled by servo electronics, whose transfer function includes the second-order differential term of the error signal in order to improve the waveform. Good performance of the drive mechanism has been confirmed in two balloon flights in 1988 at an altitude of 31 km.