The Central Gas Systems of Early-Type Galaxies Traced by Dust Feature: Based on the HST WFPC2 Archival Images

We investigated the central gas systems of E/S0 galaxies by making use of the WFPC2 images of the Hubble Space Telescope archive. We searched the gas systems that were traced by the dust with a new method of making color excess images in F555W - F814W (V-I). Out of 25 sample galaxies, we detected gas system in 14 galaxies. The dust was newly detected in two galaxies that were thought to contain no dust based on single band, pre-refurbishment data. The full extents of the gas systems are 0.1 to 3.5 kpc, and the masses of the gas, log M(gas) [M(solar)], are 4.2 to 7.2. The AGN activity is well correlated with existence of the gas systems. None of galaxies without the gas systems show the AGN activity. On the other hand, some galaxies with the gas systems show the AGN activity; optical AGN activities are shown in 5 out of 11 galaxies of which AGNs are optically studied, and radio activities are shown in 6 out of 14 galaxies. This shows that the AGN activity is driven with the gas system.Comment: gzipped tarred file containing 7 files: Tomita.tex (main text, needs aaspp4.sty), Tomita.tab[1,2].tex (tables, need aj_pt4.sty), Tomita.fig [1a,1b,1c,2].ps (PS figures). To be appeared in AJ, Vol.120, No.1 (July 2000

MOIRCS Deep Survey V: A Universal Relation for Stellar Mass and Surface Brightness of Galaxies

We present a universal linear correlation between the stellar mass and surface brightness (SB) of galaxies at 0.3<z<3, using a deep K-band selected catalog in the GOODS-North region. The correlation has a nearly constant slope, independent of redshift and color of galaxies in the rest-z frame. Considering unresolved compact galaxies, the tight correlation gives a lower boundary of SB for a given stellar mass; lower SB galaxies are prohibited over the boundary. The universal slope suggests that the stellar mass in galaxies was build up over their cosmic histories in a similar manner irrelevant to galaxy mass, as oppose to the scenario that massive galaxies mainly accumulated their stellar mass by major merging. In contrast, SB shows a strong dependence on redshift for a given stellar mass. It evolves as (1+z)^(-2.0~-0.8), in addition to dimming as (1+z)^4 by the cosmological expansion effect. The brightening depends on galaxy color and stellar mass. The blue population (rest-frame U-V<0), which is dominated by young and star-forming galaxies, evolves as ~(1+z)^(-0.8 +-0.3) in the rest-V band. On the other hand, the red population (U-V>0) and the massive galaxies (M_*>10^(10)M_sun) shows stronger brightening, (1+z)^(-1.5+-0.1). Based on the comparison with galaxy evolution models, we find that the phenomena are well explained by the pure luminosity evolution of galaxies out to z~3.Comment: 10 pages, 9 figures. Accepted for publication in Ap

MOIRCS Deep Survey. X. Evolution of Quiescent Galaxies as a Function of Stellar Mass at 0.5<z<2.5

We study the evolution of quiescent galaxies at 0.5<z<2.5 as a function of stellar mass, using very deep NIR imaging data taken with the Multi-Object Infrared Camera and Spectrograph on the Subaru Telescope in the GOODS-North region. The deep NIR data allow us to construct a stellar mass-limited sample of quiescent galaxies down to ~10^{10} Msun even at z~2 for the first time. We selected quiescent galaxies with age/tau>6 by performing SED fitting of the multi broad-band photometry from the U to Spitzer 5.8um bands with the population synthesis model of Bruzual & Charlot (2003) where exponentially decaying star formation histories are assumed. The number density of quiescent galaxies increases by a factor of ~3 from 1.0<z<1.5 to 0.5<z<1.0, and by a factor of ~10 from 1.5<z<2.5 to 0.5<z<1.0, while that of star-forming galaxies with age/tau<4 increases only by factors of ~2 and ~3 in the same redshift ranges. At 0.5<z<2.5, the low-mass slope of the stellar mass function of quiescent galaxies is alpha ~ 0 -- 0.6, which is significantly flatter than those of star-forming galaxies (alpha ~ -1.3 -- -1.5). As a result, the fraction of quiescent galaxies in the overall galaxy population increases with stellar mass in the redshift range. The fraction of quiescent galaxies at 10^{11}-10^{11.5} Msun increases from ~20-30% at z~2 to ~40-60% at z~0.75, while that at 10^{10}-10^{10.5} Msun increases from <~ 5% to ~15% in the same redshift range. These results could suggest that the quenching of star formation had been more effective in more massive galaxies at 1<~z<~2. Such a mass-dependent quenching could explain the rapid increase of the number density of ~M* galaxies relative to lower-mass galaxies at z >~ 1-1.5.Comment: 12 pages, 7 figures, accepted for publication in PASJ (Subaru special issue). Updated to accepted versio

Change of macrobenthic communities in the 1930s, 1970s and 2015 in the mesotrophic Lake Nojiri, Central Japan

We documented the current status of the macrobenthic community of Lake Nojiri (surface area: 4.56 km2; maximum depth: 38.5 m; altitude: 654 m above sea level; mesotrophic lake), and examined changes over time in the densities of chironomids and oligochaetes, by comparison with previous quantitative data of the lake reported in 1931 and 1973. We discussed the succession of benthic macroinvertebrates in relation to changes in the lake bottom environment, as evidence of lake eutrophication. On March 10, 2015, a bathymetrical sampling survey was carried out using a standard Ekman grab at each of the 5 stations (min. ca. 6 m – max. ca. 27 m) in Lake Nojiri. The average densities of the benthic communities for all the stations were ca. 5000m-2, comprised principally of oligochaetes ca. 2800 m-2 (57%) and chironomids ca. 2100 m-2 (43%), whereas their benthic biomass averaged ca. 9.7 g m-2, chironomids ca. 7.6 g m-2 (77%) and oligochaetes ca. 2.3 g m-2 (23%). In the shallower stations, the dominant species was Heterotrissocladius sp., but Chironomus nipponensis Tokunaga was the dominant species in the deeper stations. The densities of C. nipponensis was ca. 14 times higher than those reported by Miyadi in 1931 and 4 times higher than reported by Kitagawa in 1973a. In recent years the density of the oligochaete Tubifex tubifex, has tended to increase and the anoxic- and anaerobic-layer have thickened, especially in deeper regions where they are widely distributed. Moreover, we found differences in the C. nipponensis larval growth rate with water depth, i.e., small IV-instar larvae that dominated at the deepest Station 5. At this station, we suggest that low dissolved oxygen concentration and low water temperature during summer-fall suppresses growth of C. nipponensis. Large environmental changes must have affected chironomid and oligochaete densities and growth rate of C. nipponensis, especially in the deeper regions with low dissolved oxygen concentrations, low water temperature and high organic matter (ignition loss; 15.0% in St. 4 and 13.9% in St. 5) in the sediments. This is a strong evidence that the eutrophication of this lake is continuing

Heat Transfer and Thermographic Analysis of Catalyst Surface during Multiphase Phenomena under Spray-Pulsed Conditions for Dehydrogenation of Cyclohexane over Pt Catalysts

Dehydrogenation of cyclohexane over Pt/alumite and Pt/activated carbon catalysts has been carried out for hydrogen storage and supply to fuel cell applications. An unsteady state has been created using spray pulsed injection of cyclohexane over the catalyst surface to facilitate the endothermic reaction to occur efficiently. Higher temperature of the catalyst surface is more favorable for the reaction, thus the heat transfer phenomena and temperature profile under alternate wet and dry conditions created using spray pulsed injection becomes important. IR thermography has been used for monitoring of temperature profile of the catalyst surface simultaneously with product analysis. The heat flux from the plate-type heater to the catalyst has been estimated using a rapid temperature recording and thermocouple arrangement. The estimated heat flux under transient conditions was in the range of 10-15 kW/m2, which equates the requirement for endothermic reactions to the injection frequency of 0.5 Hz, as used in this study. The analysis of temperature profiles, reaction products over two different supports namely activated carbon cloth and alumite, reveals that the more conductive support such as alumite is more suitable for dehydrogenation of cyclohexane