Browsing by Author "Iwasawa, Kazushi"

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    A Herschel Space Observatory Spectral Line Survey of Local Luminous Infrared Galaxies from 194 to 671 Microns
    (IOP PUBLISHING LTD, 2017) Lu, Nanyao; Zhao, Yinghe; Diaz Santos, Tanio; Kevin Xu, C.; Gao, Yu; Armus, Lee; Isaak, Kate G.; Mazzarella, Joseph M.; van der Werf, Paul P.; Appleton, Philip N.; Charmandaris, Vassilis; Evans, Aaron S.; Howell, Justin; Iwasawa, Kazushi; Leech, Jamie; Lord, Steven; Petric, Andreea O.; Privon, George C.; Sanders, David B.; Schulz, Bernhard; Surace, Jason A.
    We describe a Herschel Space Observatory 194-671 mu m spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO J to J-1 rotational transitions for 4 <= J <= 13, the [N II] 205 mu m line, the [C I] lines at 609 and 370 mu m, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at J less than or similar to 4 and likely represents the same gas phase traced by CO (1-0), and (ii) a warm component, which dominates over the mid-J regime (4 < J less than or similar to 10) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at J > 10. The flux ratios of the two [C I] lines imply modest excitation temperatures of 15-30 K; the [C I] 370 mu m line scales more linearly in flux with CO (4-3) than with CO (7-6). These findings suggest that the [C I] emission is predominantly associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of H2O vapor as a function of the FIR color in a direction consistent with infrared photon pumping.
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    SERENADE. II. An ALMA Multiband Dust Continuum Analysis of 28 Galaxies at 5<z<8 and the Physical Origin of the Dust Temperature Evolution
    (2024) Mitsuhashi, Ikki; Harikane, Yuichi; Bauer, Franz E.; Bakx, Tom J. L. C.; Ferrara, Andrea; Fujimoto, Seiji; Hashimoto, Takuya; Inoue, Akio K.; Iwasawa, Kazushi; Nishimura, Yuri; Imanishi, Masatoshi; Ono, Yoshiaki; Saito, Toshiki; Sugahara, Yuma; Umehata, Hideki; Vallini, Livia; Wang, Tao; Zavala, Jorge A.
    We present an analysis of the Atacama Large Millimeter-submillimeter Array (ALMA) multiband dust continuum observations for 28 spectroscopically confirmed bright Lyman break galaxies at 5 < z < 8. Our sample consists of 11 galaxies at z similar to 6 newly observed in our ALMA program, which substantially increases the number of 5 < z < 8 galaxies with both rest-frame 88 and 158 mu m continuum observations, allowing us to simultaneously measure the IR luminosity and dust temperature for a statistical sample of z greater than or similar to 5 galaxies for the first time. We derive the relationship between the ultraviolet (UV) slope (beta(UV)) and infrared excess (IRX) for the z similar to 6 galaxies, and find a shallower IRX-beta(UV) relation compared to the previous results at z similar to 2-4. Based on the IRX-beta(UV) relation consistent with our results and the beta(UV)-M-UV relation including fainter galaxies in the literature, we find a limited contribution of the dust-obscured star formation to the total star formation rate density, similar to 30% at z similar to 6. Our measurements of the dust temperature at z similar to 6-7, T-dust = 40.9(-9.1)(+10.0) K on average, support a gentle increase of T-dust from z = 0 to z similar to 6-7. Using an analytic model with parameters consistent with recent James Webb Space Telescope results, we discuss that the observed redshift evolution of the dust temperature can be reproduced by an similar to 0.6 dex decrease in the gas depletion timescale and similar to 0.4 dex decrease in the metallicity. The variety of T-dust observed at high redshifts can also be naturally explained by scatters around the star formation main sequence and average mass-metallicity relation including an extremely high dust temperature of T-dust > 80 K observed in a galaxy at z = 8.3.