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Register a new userCharacteristics of mid-infrared PAH emission from star-forming galaxies selected at 250 {mu}m in the North Ecliptic Pole (NEP) field
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Evolutionary properties of infrared (IR) luminous galaxies are important keys to understand dust-obscured star formation history and galaxy evolution. Based on the near- to mid-IR imaging with 9 continuous filters of AKARI space telescope, we present the characteristics of dusty star-forming (SF) galalxies showing polycyclic aromatic hydrocarbon (PAH) features observed by the North Ecliptic Pole (NEP) wide field survey of AKARI and Herschel. All the sample galaxies from the AKARI/NEP-Wide data are selected based both on the Herschel/SPIRE 250 {mu}m detection and optical spectroscopic redshift data. The physical modelling of spectral energy distribution (SED) using all available data points from u to sub-mm 500 {mu}m band, including WISE and PACS data where available, takes unique advantages of the continuous near to mid-IR coverage, reliable constraint on far-IR peak, spectroscopically determined accurate redshifts, as well as energy balance principle by MAGPHYS. This enables us to derive physically meaningful and accurate total infrared luminosity and 8 {mu}m (or PAH) luminosity consistently. Our sample galaxies are in the redshift range z <1, and majority of them appear to be normal SF/spiral populations showing PAH features near the 8 {mu}m. These SF galaxies showing PAHs in the mid-IR include various types from quiescent to starbursts. Some of our sample show shortage of 8 {mu}m luminosity compared to the total IR luminosity and this PAH deficit gets severe in more luminous IR galaxies, suggesting PAH molecules in these galaxies destroyed by strong radiation field from SF region or a large amount of cold dust in ISM. The specific SFR of our sample shows mass dependent time evolution which is consistent with downsizing evolutionary pattern.
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We present the mid-infrared (MIR) properties of galaxies within a supercluster in the North Ecliptic Pole region at z?0.087 observed with the AKARI satellite. We use data from the AKARI NEP-Wide (5.4 deg2) IR survey and the CLusters of galaxies EVoLution studies (CLEVL) mission program. We show that near-IR (3 {mu}m)-mid- IR (11 {mu}m) color can be used as an indicator of the specific star formation rate and the presence of intermediate age stellar populations. From the MIR observations, we find that red-sequence galaxies consist not only of passively evolving red early-type galaxies, but also of 1) weak-SFG (disk-dominated star-forming galaxies which have star formation rates lower by sim 4 times than blue-cloud galaxies), and 2) intermediate- MXG (bulge-dominated galaxies showing stronger MIR dust emission than normal red early-type galaxies). Those two populations can be a set of transition galaxies from blue, star-forming, late-type galaxies evolving into red, quiescent, early-type ones. We find that the weak-SFG are predominant at intermediate masses (1010Modot < Mstar < 1010.5Modot) and are typically found in local densities similar to the outskirts of galaxy clusters. As much as 40% of the supercluster member galaxies in this mass range can be classified as weak-SFGs, but their proportion decreases to < 10% at larger masses (Mstar > 1010.5 Modot) at any galaxy density. The fraction of the intermediate-MXG among red- sequence galaxies at 1010Modot < Mstar < 1011Modot also decreases as the density and mass increase. In particular, sim42% of the red-sequence galaxies with early-type morphologies are classified as intermediate-MXG at intermediate densities. These results suggest that the star formation activity is strongly dependent on the stellar mass, but that the morphological transformation is mainly controlled by the environment.
We present a method of selection of 24~$mu$m galaxies from the AKARI North Ecliptic Pole (NEP) Deep Field down to $150 mbox{ }mu$Jy and measurements of their two-point correlation function. We aim to associate various 24 $mu$m selected galaxy populations with present day galaxies and to investigate the impact of their environment on the direction of their subsequent evolution. We discuss using of Support Vector Machines (SVM) algorithm applied to infrared photometric data to perform star-galaxy separation, in which we achieve an accuracy higher than 80%. The photometric redshift information, obtained through the CIGALE code, is used to explore the redshift dependence of the correlation function parameter ($r_{0}$) as well as the linear bias evolution. This parameter relates galaxy distribution to the one of the underlying dark matter. We connect the investigated sources to their potential local descendants through a simplified model of the clustering evolution without interactions. We observe two different populations of star-forming galaxies, at $z_{med}sim 0.25$, $z_{med}sim 0.9$. Measurements of total infrared luminosities ($L_{TIR}$) show that the sample at $z_{med}sim 0.25$ is composed mostly of local star-forming galaxies, while the sample at $z_{med}sim0.9$ is composed of luminous infrared galaxies (LIRGs) with $L_{TIR}sim 10^{11.62}L_{odot}$. We find that dark halo mass is not necessarily correlated with the $L_{TIR}$: for subsamples with $L_{TIR}= 10^{11.15} L_{odot}$ at $z_{med}sim 0.7$ we observe a higher clustering length ($r_{0}=6.21pm0.78$ $[h^{-1} mbox{Mpc}]$) than for a subsample with mean $L_{TIR}=10^{11.84} L_{odot}$ at $z_{med}sim1.1$ ($r_{0}=5.86pm0.69$ $h^{-1} mbox{Mpc}$). We find that galaxies at $z_{med}sim 0.9$ can be ancestors of present day $L_{*}$ early type galaxies, which exhibit a very high $r_{0}sim 8$~$h^{-1} mbox{Mpc}$.
The recent updates of the North Ecliptic Pole deep (0.5~deg$^2$, NEP-Deep) multi-wavelength survey covering from X-ray to radio-wave is presented. The NEP-Deep provides us with several thousands of 15~$mu$m or 18~$mu$m selected sample of galaxies, which is the largest sample ever made at this wavelengths. A continuous filter coverage in the mid-infrared wavelength (7, 9, 11, 15, 18, and 24~$mu$m) is unique and vital to diagnose the contributions from starbursts and AGNs in the galaxies out to $z$=2.The new goal of the project is to resolve the nature of the cosmic star formation history at the violent epoch (e.g. $z$=1--2), and to find a clue to understand its decline from $z$=1 to present universe by utilizing the unique power of the multi-wavelength survey. The progress in this context is briefly mentioned.
We present mid-infrared (MIR) luminosity functions (LFs) of local star-forming (SF) galaxies in the AKARI NEP-Wide Survey field. In order to derive more accurate luminosity function, we used spectroscopic sample only. Based on the NEP-Wide point source catalogue containing a large number of infrared (IR) sources distributed over the wide (5.4 sq. deg.) field, we incorporated the spectroscopic redshift data for about 1790 selected targets obtained by optical follow-up surveys with MMT/Hectospec and WIYN/Hydra. The AKARI continuous 2 to 24 micron wavelength coverage as well as photometric data from optical u band to NIR H-band with the spectroscopic redshifts for our sample galaxies enable us to derive accurate spectral energy distributions (SEDs) in the mid-infrared. We carried out SED fit analysis and employed 1/Vmax method to derive the MIR (8, 12, and 15 micron rest-frame) luminosity functions. We fit our 8 micron LFs to the double power-law with the power index of alpha= 1.53 and beta= 2.85 at the break luminosity. We made extensive comparisons with various MIR LFs from several literatures. Our results for local galaxies from the NEP region are generally consistent with other works for different fields over wide luminosity ranges. The comparisons with the results from the NEP-Deep data as well as other LFs imply the luminosity evolution from higher redshifts towards the present epoch.
We present a photometric catalog for Spitzer Space Telescope warm mission observations of the North Ecliptic Pole (NEP; centered at $rm R.A.=18^h00^m00^s$, $rm Decl.=66^d33^m38^s.552$). The observations are conducted with IRAC in 3.6 $mu$m and 4.5 $mu$m bands over an area of 7.04 deg$^2$ reaching 1$sigma$ depths of 1.29 $mu$Jy and 0.79 $mu$Jy in the 3.6 $mu$m and 4.5 $mu$m bands respectively. The photometric catalog contains 380,858 sources with 3.6 $mu$m and 4.5 $mu$m band photometry over the full-depth NEP mosaic. Point source completeness simulations show that the catalog is 80% complete down to 19.7 AB. The accompanying catalog can be utilized in constraining the physical properties of extra-galactic objects, studying the AGN population, measuring the infrared colors of stellar objects, and studying the extra-galactic infrared background light.
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