Observations of [C II] 158 micron Line and Far-infrared Continuum Emission toward the High-latitude Molecular Clouds in Ursa Major

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.Comment: 15 pages, LaTeX (aaspp4.sty) + 2 tables(apjpt4.sty) + 6 postscript figures; accepted for publication in the Astrophysical Journal; Astrophys. J. in press (Vol. 490, December 1, 1997 issue

Exploring Galaxy Evolution from Infrared Number Counts and Cosmic Infrared Background

Recently reported infrared (IR) galaxy number counts and cosmic infrared background (CIRB) all suggest that galaxies have experienced a strong evolution sometime in their lifetime. We statistically estimate the galaxy evolution history from these data. We find that an order of magnitude increase of the far-infrared (FIR) luminosity at redshift z = 0.5 - 1.0 is necessary to reproduce the very high CIRB intensity at 140 um reported by Hauser et al. (1998). z \sim 0.75 and decreases to, even at most, a factor of 10 toward z \sim 5, though many variants are allowed within these constraints. This evolution history also satisfies the constraints from the galaxy number counts obtained by IRAS, ISO and, roughly, SCUBA. The rapid evolution of the comoving IR luminosity density required from the CIRB well reproduces the very steep slope of galaxy number counts obtained by ISO. We also estimate the cosmic star formation history (SFH) from the obtained FIR luminosity density, considering the effect of the metal enrichment in galaxies. The derived SFH increases steeply with redshift in 0 0.75. This is consistent with the SFH estimated from the reported ultraviolet luminosity density. In addition, we present the performance of the Japanese ASTRO-F FIR galaxy survey. We show the expected number counts in the survey. We also evaluate how large a sky area is necessary to derive a secure information of galaxy evolution up to z \sim 1 from the survey, and find that at least 50 - 300 deg^2 is required.Comment: 18 pages LaTeX, PASJ in press. Abstract abridge

Spatially Resolved Spectroscopy of Passive Spiral Galaxies

Passive spiral galaxies, despite their spiral morphological appearance, do not have any emission lines indicative of ongoing star formation in their optical spectra. Previous studies have suggested that passive spiral galaxies preferentially exist in infall regions of galaxy clusters, suggesting that the cluster environment is likely to be responsible for creating these galaxies. By carrying out spatially resolved long-slit spectroscopy on four nearby passive spiral galaxies with the Apache Point Observatory 3.5-m telescope, we investigated the stellar populations of passive spiral galaxies separately for their inner and outer regions. In the two unambiguously passive spiral galaxies among the four observed galaxies, H$\delta$ absorption lines are more prominent in the outer regions of the galaxies, whereas the 4000-{\AA} breaks (D$_{4000}$) are strongest in the inner regions of the galaxies. A comparison with a simple stellar population model for the two passive spiral galaxies indicates that the outer regions of the galaxies tend to harbour younger populations of stars. The strong H$\delta$ absorption observed in the outer regions of the sample galaxies is consistent with that of galaxies whose star formation ceased a few Gyrs ago. Because of the large uncertainty in the absorption indices in our samples, further observations are needed in order to place constraints on the mechanisms that quench star formation in passive spiral galaxies.Comment: MNRAS,382,27

<i>AKARI</i>/IRC source catalogues and source counts for the IRAC Dark Field, ELAIS North and the <i>AKARI</i> Deep Field South

We present the first detailed analysis of three extragalactic fields (IRAC Dark Field, ELAIS-N1, ADF-S) observed by the infrared satellite, AKARI, using an optimized data analysis toolkit specifically for the processing of extragalactic point sources. The InfaRed Camera (IRC) on AKARI complements the SpitzerSpace Telescope via its comprehensive coverage between 8–24 μm filling the gap between the Spitzer/IRAC and MIPS instruments. Source counts in the AKARI bands at 3.2, 4.1, 7, 11, 15 and 18 μm are presented. At near-infrared wavelengths, our source counts are consistent with counts made in other AKARI fields and in general with SpitzerIRAC (except at 3.2 μm where our counts lie above). In the mid-infrared (11 – 18 μm), we find our counts are consistent with both previous surveys by AKARI and the Spitzer peak-up imaging survey with the InfraRed Spectrograph (IRS). Using our counts to constrain contemporary evolutionary models, we find that although the models and counts are in agreement at mid-infrared wavelengths there are inconsistencies at wavelengths shortward of 7 μm, suggesting either a problem with stellar subtraction or indicating the need for refinement of the stellar population models. We have also investigated the AKARI/IRC filters, and find an active galactic nucleus selection criteria out to z AKARI 4.1, 11, 15 and 18 μm colours

[Ultra] Luminous Infrared Galaxies selected at 90 μ\mum in the AKARI deep field: a study of AGN types contributing to their infrared emission

The aim of this work is to characterize physical properties of Ultra Luminous Infrared Galaxies (ULIRGs) and Luminous Infrared Galaxies (LIRGs) detected in the far-infrared (FIR) 90um band in the AKARI Deep Field-South (ADF-S) survey. In particular, we want to estimate the AGN contribution to the [U]LIRGs' infrared emission and which types of AGNs are related to their activity. We examined 69 galaxies at z>0.05 detected at 90um by the AKARI satellite in the ADF-S, with optical counterparts and spectral coverage from the ultraviolet to the FIR. We used two independent spectral energy distribution fitting codes: one fitting the SED from FIR to FUV (CIGALE) and gray-body + power spectrum fit for the infrared part of the spectra (CMCIRSED) in order to identify a subsample of [U]LIRGs, and to estimate their properties. Based on the CIGALE SED fitting, we have found that [U]LIRGs selected at the 90um AKARI band compose ~56% of our sample (we found 17 ULIRGs and 22 LIRGs, spanning over the redshift range 0.06<z<1.23). Their physical parameters, such as stellar mass, star formation rate (SFR), and specific SFR are consistent with the ones found for other samples selected at IR wavelengths. We have detected a significant AGN contribution to the MIR luminosity for 63% of LIRGs and ULIRGs. Our LIRGs contain Type 1, Type 2, and intermediate types of AGN, whereas for ULIRGs, a majority (more than 50%) of AGN emission originates from Type 2 AGNs. The temperature--luminosity and temperature--mass relations for the dust component of ADF--S LIRGs and ULIRGs indicate that these relations are shaped by the dust mass and not by the increased dust heating. We conclude that LIRGs contain Type 1, Type 2, and intermediate types of AGNs, with an AGN contribution to the MIR emission at the median level of 13+/-3%, whereas the majority of ULIRGs contain Type 2 AGNs, with a median AGN fraction equal to 19+/-8%.Comment: 24 pages, 21 figures, accepted for publication in Astronomy & Astrophysic

Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts

We present data products from the 300 ks Chandra survey in the AKARI North Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared photometry covering 2-24 micron from the AKARI Infrared Camera, including mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the deepest ever achieved at ~15 micron, and is by far the widest among those with similar depths in the MIR. This makes this field unique for the MIR-selection of AGN at z~1. We design a source detection procedure, which performs joint Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings covering an area of 0.34 square degree. The procedure has been highly optimized and tested by simulations. We provide a point source catalog with photometry and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2, 2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent confidence upper flux limits maps in all bands are provided as well. We search for optical MIR counterparts in the central 0.25 square degree, where deep Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit flux maps are available from the VizieR Servic

AKARI Detections of Hot Dust in Luminous Infrared Galaxies

We present a new sample of active galactic nuclei (AGNs) identified using the catalog of the AKARI Mid-infrared(MIR) All-Sky Survey. Our MIR search has an advantage in detecting AGNs that are obscured at optical wavelengths due to extinction. We first selected AKARI 9micron excess sources with F(9micron)/F(K_S)>2 where K_S magnitudes were taken from the Two Micron All Sky Survey. We then obtained follow-up near-infrared spectroscopy with the AKARI/IRC, to confirm that the excess is caused by hot dust. We also obtained optical spectroscopy with the Kast Double Spectrograph on the Shane 3-m telescope at Lick Observatory. On the basis of on these observations, we detected hot dust with a characteristic temperature of ~500K in two luminous infrared galaxies. The hot dust is suspected to be associated with AGNs that exhibit their nonstellar activity not in the optical, but in the near- and mid-infrared bands, i.e., they harbor buried AGNs. The host galaxy stellar masses of 4-6 x 10^9 M_sun are small compared with the hosts in optically-selected AGN populations. These objects were missed by previous surveys, demonstrating the power of the AKARI MIR All-Sky Survey to widen AGN searches to include more heavily obscured objects. The existence of multiple dusty star clusters with massive stars cannot be completely ruled out with our current data.Comment: 15 pages, 4 figures, to be published in Astronomy & Astrophysic