IRAS observations of starburst galaxies

Far infrared properties of Starburst galaxies were analyzed using IRAS observations at 25, 60, and 100 micrometers. Seventy-nine of 102 Starburst galaxies from the list of Balzano were detected. These galaxies have high IR luminosities of up to a few 10 to the 12th power L sub 0 and concentrate in a small area of the IR color - color diagram. The IR power law spectral indices, alpha, lie within the ranges -2.5 <alpha(60,25)< -1.5 and -1.5 <alpha(100,60)< 0. These observed indices can be interpreted in terms of a cold disk component and a warm component. More than 80% of the 60 micrometer emission comes from the warm component. The fraction of the 60 micrometer emission attributable to the warm component can be used as an activity indicator

The Subaru/XMM-Newton Deep Survey (SXDS) -VII. Clustering Segregation with Ultraviolet and Optical Luminosities of Lyman-Break Galaxies at z~3

We investigate clustering properties of Lyman-break galaxies (LBGs) at z~3 based on deep multi-waveband imaging data from optical to near-infrared wavelengths in the Subaru/XMM-Newton Deep Field. The LBGs are selected by U-V and V-z' colors in one contiguous area of 561 arcmin^2 down to z'=25.5. We study the dependence of the clustering strength on rest-frame UV and optical magnitudes, which can be indicators of star formation rate and stellar mass, respectively. The correlation length is found to be a strong function of both UV and optical magnitudes with brighter galaxies being more clustered than faint ones in both cases. Furthermore, the correlation length is dependent on a combination of UV and optical magnitudes in the sense that galaxies bright in optical magnitude have large correlation lengths irrespective of UV magnitude, while galaxies faint in optical magnitude have correlation lengths decreasing with decreasing UV brightness. These results suggest that galaxies with large stellar masses always belong to massive halos in which they can have various star formation rates, while galaxies with small stellar masses reside in less massive halos only if they have low star formation rates. There appears to be an upper limit to the stellar mass and the star formation rate which is determined by the mass of hosting dark halos.Comment: 16 pages, 15 figures, accepted for publication in Ap

An electrically powered binary star?

We propose a model for stellar binary systems consisting of a magnetic and a non-magnetic white-dwarf pair which is powered principally by electrical energy. In our model the luminosity is caused by resistive heating of the stellar atmospheres due to induced currents driven within the binary. This process is reminiscent of the Jupiter-Io system, but greatly increased in power because of the larger companion and stronger magnetic field of the primary. Electrical power is an alternative stellar luminosity source, following on from nuclear fusion and accretion. We find that this source of heating is sufficient to account for the observed X-ray luminosity of the 9.5-min binary RX J1914+24, and provides an explanation for its puzzling characteristics.Comment: accepted by MNRA

Evidence for a large fraction of Compton-thick quasars at high redshift

Using mid-infrared and radio selection criteria, we pre-select a sample of candidate high-redshift type-2 quasars in the Subaru XMM-Newton Deep Field (SXDF). To filter out starburst contaminants, we use a bayesian method to fit the spectral energy distributions (SEDs) between 24-microns and B-band, obtain photometric redshifts, and identify the best candidates for high-z type-2 quasars. This leaves us with 12 z_phot >= 1.7 type-2 quasar candidates in an area ~0.8 deg^2, of which only two have secure X-ray detections. The two detected sources have estimated column densities N_H~2 & 3x10^27 m^-2, i.e. heavily obscured but Compton-thin quasars. Given the large bolometric luminosities and redshifts of the undetected objects, the lack of X-ray detections suggests extreme absorbing columns N_H >= 10^28 m^-2 are typical. We have found evidence for a population of ``Compton-thick'' high-redshift type-2 quasars, at least comparable to, and probably larger than the type-1 quasar population, although spectroscopic confirmation of their AGN nature is important.Comment: 6 pages, 2 colour figures. Accepted by MNRAS. Full resolution version and supplementary figures can be found at: http://www.mpia.de/homes/martinez/publications.htm

Secondary electron emission from freely supported nanowires

We present secondary electron (SE) emission results from freely supported carbon/silicon nitride (Si3N4) hybrid nanowires using scanning electron microscopy. We found that, contrary to bulk materials, the SE emission from insulating or electrically isolated metallic nanowires is strongly suppressed by the penetrating beam. A mechanism of the SE suppression by the positive specimen charging is proposed, which is based on a total emission yield calculation using the Monte Carlo technique. This finding provides an important basis for studying low-energy electron emission from nanostructures under a penetrating electron beam

A New Constraint on the Lyα\alpha Fraction of UV Very Bright Galaxies at Redshift 7

We study the extent to which very bright (-23.0 < MUV < -21.75) Lyman-break selected galaxies at redshifts z~7 display detectable Lya emission. To explore this issue, we have obtained follow-up optical spectroscopy of 9 z~7 galaxies from a parent sample of 24 z~7 galaxy candidates selected from the 1.65 sq.deg COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z'-band imaging (which we also present and describe in this paper). Our spectroscopy has yielded only one possible detection of Lya at z=7.168 with a rest-frame equivalent width EW_0 = 3.7 (+1.7/-1.1) Angstrom. The relative weakness of this line, combined with our failure to detect Lya emission from the other spectroscopic targets allows us to place a new upper limit on the prevalence of strong Lya emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1-sigma upper limit on the fraction of UV bright galaxies at z~7 that display EW_0 > 50 Angstrom, which we estimate to be < 0.23. This result may indicate a weak trend where the fraction of strong Lya emitters ceases to rise, and possibly falls between z~6 and z~7. Our results also leave open the possibility that strong Lya may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction at z~7 based on the Lya fraction in the bright galaxies.Comment: 20 pages, 7 figures, 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

The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lya Emitters from z=3.1 to 5.7 in the 1 deg^2 Field: Luminosity Functions and AGN

We present luminosity functions (LFs) and various properties of Lya emitters (LAEs) at z=3.1, 3.7, and 5.7, in a 1 deg^2 sky of the Subaru/XMM-Newton Deep Survey (SXDS) Field. We obtain a photometric sample of 858 LAE candidates based on deep Subaru/Suprime-Cam imaging data, and a spectroscopic sample of 84 confirmed LAEs from Subaru/FOCAS and VLT/VIMOS spectroscopy in a survey volume of ~10^6 Mpc^3 with a limiting Lya luminosity of ~3x10^42 erg/s. We derive the LFs of Lya and UV-continuum (~1500 \AA) for each redshift, taking into account the statistical error and the field-to-field variation. We find that the apparent Lya LF shows no significant evolution between z=3.1 and 5.7 within factors of 1.8 and 2.7 in L* and phi*, respectively. On the other hand, the UV LF of LAEs increases from z=3.1 to 5.7, indicating that galaxies with Lya emission are more common at earlier epochs. We identify six LAEs with AGN activities from our spectra combined with VLA, Spitzer, and XMM-Newton data. Among the photometrically selected LAEs at z=3.1 and 3.7, only ~1 % show AGN activities, while the brightest LAEs with logL(Lya) >~ 43.4-43.6 erg/s appear to always host AGNs. Our LAEs are bluer in UV-continuum color than dropout galaxies, suggesting lower extinction and/or younger stellar populations. Our stacking analyses provide upper limits to the radio luminosity and the f(HeII)/f(Lya) line fraction, and constrain the hidden star formation (+low-luminosity AGN) and the primordial population in LAEs.Comment: 75 pages, 27 figures; ApJS in press. High resolution version at http://www.ociw.edu/~ouchi/work/astroph/sxds_LAEs/ouchi_SXDSLAE_ApJS.pd