SuprimeCam Observation of Sporadic Meteors during Perseids 2004

We report the serendipitous findings of 13 faint meteors and 44 artificial space objects by Subaru SuprimeCam imaging observations during 11-16 August 2004. The meteors, at about 100km altitude, and artificial satellites/debris in orbit, at 500km altitude or higher, were clearly discriminated by their apparent defocused image sizes. CCD photometry of the 13 meteors, including 1 Perseid, 1 Aquarid, and 11 sporadic meteors, was performed. We defined a peak video-rate magnitude by comparing the integrated photon counts from the brightest portion of the track traversed within 33ms to those from a 0-mag star during the same time duration. This definition gives magnitudes in the range 4.0< V_{vr} <6.4 and 4.1< I_{vr}<5.9 for these 13 meteors. The corresponding magnitude for virtual naked-eye observers could be somewhat fainter especially for the V-band observation, in which the [OI] 5577 line lasting about 1 sec as an afterglow could contribute to the integrated flux of the present 5-10 min CCD exposures. Although the spatial resolution is insufficient to resolve the source size of anything smaller than about 1 m, we developed a new estimate of the collisionally excited column diameter of these meteors. A diameter as small as a few mm was derived from their collisionally excited photon rates, meteor speed, and the volume density of the oxygen atoms at the 100km altitude. The actual column diameter of the radiating zone, however, could be as large as few 100m because the excited atoms travel that distance before they emit forbidden lines in 0.7 sec of its average lifetime. Among the 44 artificial space objects, we confirmed that 17 were cataloged satellites/space debris.Comment: 14 pages, 13 figures, 5 tables, submitted to PAS

Morphologies and Color Gradients of Luminous Evolved Galaxies at z~1.5

We have examined in detail the morphologies of seven z~1.5 passively evolving luminous red galaxies using high resolution HST NICMOS and ACS imaging data. Almost all of these galaxies appear to be relaxed systems, with smooth morphologies at both rest-frame UV and visible wavelengths. Previous results from spectral synthesis modeling favor a single burst of star formation more than 1 Gyr before the observed epoch. The prevalence of old stellar populations, however, does not correlate exclusively with early-type morphologies as it does in the local universe; the light profiles for some of these galaxies appear to be dominated by massive exponential disks. This evidence for massive old disks, along with the apparent uniformity of stellar age across the disk, suggests formation by a mechanism better described as a form of monolithic collapse than as a hierarchical merger. These galaxies could not have undergone a single major merging event since the bulk of their stars were formed, more than 1 Gyr earlier. There is at least one case, however, that appears to be undergoing a "dry merger", which may be an example of the process that converts these unusual galaxies into the familiar spheroids that dominate galaxies comprising old stellar populations at the present epoch.Comment: 16 pages, 9 figures (8 in color), accepted for publication in Ap

JHK Spectra of the z=2.39 Radio Galaxy 53W002

We present low-resolution, near-IR JHK spectra of the weak z=2.39 radio galaxy 53W002, obtained with the OH-airglow Suppressor spectrograph (OHS) and Cooled Infrared Spectrograph and Camera for OHS (CISCO) on the Subaru Telescope. They cover rest-frame wavelengths of 3400-7200 A, and the emission lines of [O II]3727, Hb, [O III]4959, 5007, Ha, [N II]6548, 6583 and [S II]6716, 6731 were detected. Using the Ha/Hb line ratio, we find an extinction of E(B-V)=0.14. The emission-line ratios are reproduced by a cloud of electron density n_e=1x10^{3-4}(/cm3) with solar metallicity, ionized by an alpha=-0.7 power-law continuum with ionizing parameter U=1x10^-3. In addition to these emission lines, we make the first spectroscopic confirmation of the Balmer discontinuity in a high-z radio galaxy. Together with rest-frame UV photometry from the literature, we show that at least 1/3 of the present stellar mass was formed in the current starburst. The stellar mass was estimated to be (1-1.4)x10^11 M_sol by one-component model fitting, which is smaller than that of typical z~1 B2/6C radio galaxies. We suggest that 53W002 is currently assembling a large part of its stellar mass through merger events with the surrounding sub-galactic clumps, some of which can be identified with the Lya emitters detected in narrow-band imaging. After a few such events over the next few Gyr, 53W002 will evolve into a massive elliptical galaxy.Comment: 10 pages, including 11 figures. Accepted for publication in PASJ(2001). Revised 5/15/200

Pressure dependence of the superconducting transition temperature in C6_6Yb and C6_6Ca

We have studied the evolution, with hydrostatic pressure, of the recently discovered superconductivity in the graphite intercalation compounds C$_6$Yb and C$_6$Ca. We present pressure-temperature phase diagrams, for both superconductors, established by electrical transport and magnetization measurements. In the range 0-1.2 GPa the superconducting transition temperature increases linearly with pressure in both materials with $dT_c/dP = +0.39 K/GPa$ and $dT_c/dP = +0.50 K/GPa$ for C$_6$Yb and C$_6$Ca respectively. The transition temperature in C$_6$Yb, which has beenmeasured up to 2.3 GPa, reaches a peak at around 1.8 GPa and then starts to drop. We also discuss how this pressure dependence may be explained within a plasmon pairing mechanism.Comment: 4 pages, 3 figure

Spectroscopy of i-Dropout Galaxies with an NB921-Band Depression in the Subaru Deep Field

We report new spectroscopy of two star-forming galaxies with strong Ly_alpha emission at z=6.03 and z=6.04 in the Subaru Deep Field. These two objects are originally selected as i'-dropouts (i'-z' > 1.5) showing an interesting photometric property, the ``NB921 depression''. The NB921-band (centered at 9196A) magnitude is significantly depressed with respect to the z'-band magnitude. The optical spectra of these two objects exhibit asymmetric emission-lines at lambda_obs ~ 8540A and ~ 8560A, suggesting that these objects are Ly_alpha emitters at z~6. The rest-frame equivalent widths of the Ly_alpha emission of the two objects are 94A and 236A; the latter one is the Ly_alpha emitter with the largest Ly_alpha equivalent width at z > 6 ever spectroscopically confirmed. The spectroscopically measured Ly_alpha fluxes of these two objects are consistent with the interpretation that the NB921 depression is caused by the contribution of the strong Ly_alpha emission to the z'-band flux. Most of the NB921-depressed i'-dropout objects are thought to be strong Ly_alpha emitters at 6.0 < z < 6.5; Galactic L and T dwarfs and NB921-dropout galaxies at z > 6.6 do not dominate the NB921-depressed i'-dropout sample. Thus the NB921-depression method is very useful for finding high-z Ly_alpha emitters with a large Ly_alpha equivalent width over a large redshift range, 6.0 < z < 6.5. Although the broadband-selected sample at z ~ 3 contains only a small fraction of objects with a Ly_alpha equivalent width larger than 100A, the i'-dropout sample of the Subaru Deep Field contains a much larger fraction of such strong Ly_alpha emitters. This may imply a strong evolution of the Ly_alpha equivalent width from z > 6 to z ~ 3.Comment: 21 pages, 6 figures, to appear in The Astrophysical Journa

Discovery of H alpha absorption in the unusual broad absorption line quasar SDSS J083942.11+380526.3

We discovered an H alpha absorption in a broad H alpha emission line of an unusual broad absorption line quasar, SDSS J083942.11+380526.3 at z=2.318, by near-infrared spectroscopy with the Cooled Infrared Spectrograph and Camera for OHS (CISCO) on the Subaru telescope. The Presence of non-stellar H alpha absorption is known only in the Seyfert galaxy NGC 4151 to date, thus our discovery is the first case for quasars. The H alpha absorption line is blueshifted by 520 km/s relative to the H alpha emission line, and its redshift almost coincides with those of UV low-ionization metal absorption lines. The width of the H alpha absorption (~ 340 km/s) is similar to those of the UV low-ionization absorption lines. These facts suggest that the H alpha and the low-ionization metal absorption lines are produced by the same low-ionization gas which has a substantial amount of neutral gas. The column density of the neutral hydrogen is estimated to be ~ 10^18 cm^-2 by assuming a gas temperature of 10,000 K from the analysis of the curve of growth. The continuum spectrum is reproduced by a reddened (E(B-V) ~ 0.15 mag for the SMC-like reddening law) composite quasar spectrum. Furthermore, the UV spectrum of SDSS J083942.11+380526.3 shows a remarkable similarity to that of NGC 4151 in its low state, suggesting the physical condition of the absorber in SDSS J083942.11+380526.3 is similar to that of NGC 4151 in the low state. As proposed for NGC 4151, SDSS J083942.11+380526.3 may be also seen through the close direction of the surface of the obscuring torus.Comment: Accepted for publication in Ap

The Number Density of Old Passively-Evolving Galaxies at z=1 in the Subaru/XMM-Newton Deep Survey Field

We obtained the number counts and the rest-frame B-band luminosity function of the color-selected old passively-evolving galaxies (OPEGs) at z=1 with very high statistical accuracy using a large and homogeneous sample of about 4000 such objects with z' <25 detected in the area of 1.03 deg^2 in the Subaru/XMM-Newton Deep Survey (SXDS) field. Our selection criteria are defined on the i'-z' and R-z' color-magnitude plane so that OPEGs at z=0.9-1.1 with formation redshift z_f=2-10 are properly sampled. The limiting magnitude corresponds to the luminosity of galaxies with M_*+3 at z=0. We made a pilot redshift observations for 99 OPEG candidates with 19 < z' < 22 and found that at least 78% (73/93) of the entire sample, or 95% (73/77) of these whose redshifts were obtained are indeed lie between z=0.87 and 1.12 and the most of their spectra show the continuum break and strong Ca H and K lines, indicating that these objects are indeed dominated by the old stellar populations. We then compare our results with the luminosity functions of the color- or the morphologically-selected early type galaxies at z=0 taking the evolutionary factor into account and found that the number density of old passive galaxies with sim M_* magnitude at z~1 averaged over the SXDS area is 40-60% of the equivalently red galaxies and 60-85% of the morphologically-selected E/S0 galaxies at z=0 depending on their luminosity evolution. It is revealed that more than half, but not all, of the present-day early-type galaxies had already been formed into quiescent passive galaxies at z=1.Comment: 28 pages, accepted for publication in Astrophysical Journal. The full version of the paper including Fig.3 and Fig.4 (large size) in full resolution is put at http://optik2.mtk.nao.ac.jp/~yamada/astronomy/sxdsred.htm