Minoru Sasaki

A Study of the Distribution of Star-forming Regions in Luminous Infrared Galaxies by Means of H? Imaging Observations

We performed Hα imaging observations of 22 luminous infrared galaxies to investigate how the distribution of star-forming regions in these galaxies is related to galaxy interactions. Based on correlation diagrams between Hα flux and continuum emission for individual galaxies, a sequence for the distribution of star-forming regions was found: very compact (~100 pc) nuclear starbursts with almost no star-forming activity in the outer regions (type 1), dominant nuclear starbursts 1 kpc in size with a negligible contribution from the outer regions (type 2), nuclear starbursts 1 kpc in size with a significant contribution from the outer regions (type 3), and extended starbursts with relatively faint nuclei (type 4). These classes of star-forming regions were found to be strongly related to global star-forming properties, such as star formation efficiency, far-infrared color, and dust extinction. There was a clear tendency for the objects with more compact distributions of star-forming regions to show a higher star formation efficiency and hotter far-infrared color. An appreciable fraction of the sample objects were dominated by extended starbursts (type 4), which is unexpected in the standard scenario of interaction-induced starburst galaxies. We also found that the distribution of star-forming regions was weakly but clearly related to galaxy morphology: severely disturbed objects had a more concentrated distribution of star-forming regions. This suggests that the properties of galaxy interactions, such as dynamical phase and orbital parameters, play a more important role than the internal properties of progenitor galaxies, such as dynamical structure or gas mass fraction. We also discuss the evolution of the distribution of star-forming regions in interacting galaxies.

The effect of ultraviolet B irradiation on nitric oxide synthase expression in murine keratinocytes.

Abstract: Nitric oxide (NO), which has several physiological functions in skin, is generated by NO synthase (NOS). NOS has at least three isoforms; endothelial NOS (eNOS), brain NOS (bNOS), and inducible NOS (iNOS). Ultraviolet B (UVB) irradiation has been reported to stimulate NO production in skin via induction or activation of NOS, however, the exact mechanism of NOS induction by UVB irradiation remains obscure. In this study, we investigated the direct effect of UVB on the expression of NOS isoforms in murine keratinocytes, and found a significant increase in NO production within 48 h. mRNA and protein expressions of bNOS were both enhanced by UVB irradiation in murine keratinocytes, whereas iNOS mRNA expression was suppressed at 4 and 12 h after UVB irradiation. These results suggest that the enhancement of NO production observed after UVB irradiation in murine keratinocytes may be explained in part by the upregulation of bNOS expression, but not iNOS expression.

Ultraviolet B radiation downregulates inducible nitric oxide synthase expression induced by interferon-γ or tumor necrosis factor-α in murine keratinocyte Pam 212 cells

Abstractu2002 Ultraviolet radiation causes inflammation characterized by erythema and swelling, but also exhibits antiinflammatory effects which have led to the use of ultraviolet B radiation (UVBR) and psoralen plus ultraviolet A (PUVA) in the treatment of psoriasis, chronic severe atopic dermatitis and uremic pruritus. In inflammatory dermatoses, a pathogenic role of nitric oxide (NO) derived from inducible nitric oxide synthase (iNOS) has been suggested. To elucidate how UVBR regulates iNOS expression in skin under inflammatory conditions, we investigated the effect of UVBR on NO production and iNOS expression in cultured murine keratinocyte Pam 212 cells stimulated with interferon-Á (IFN-Á) or tumor necrosis factor-· (TNF-·). Low doses of UVBR significantly suppressed IFN-Á- or TNF-·-induced NO production. UVBR also downregulated IFN-Á- or TNF-·-induced iNOS expression at both the mRNA level and the protein level. These findings suggest the possibility that the downregulatory effect of UVBR on IFN-Á- or TNF-·-induced iNOS expression may, in part, explain the antiinflammatory and therapeutic properties of UVBR in inflammatory dermatoses.

Suppression of melanogenesis by induction of endogenous intracellular metallothionein in human melanocytes.

Abstract:u2002 Nitric oxide (NO) is a potent intercellular mediator of melanogenesis, whereas metallothionein (MT) is an inducible intracellular antioxidant that has been reported to scavenge NO. We investigated the existence and induction of MT in melanocytes, and its inhibitory effect on NO‐induced melanogenesis. The expression of MT was detected in melanocytes, however, at a lower level than in keratinocytes, and its induction was possible by the addition of zinc chloride. Further, an NO‐stimulated increase of tyrosinase activity in melanocytes was remarkably suppressed, when MT was induced prior to NO stimulation. Melanogenesis was also suppressed, when dexamethasone was used to induce MT. However, an NO‐stimulated increase of tyrosinase expression was not suppressed at the gene and protein level, when MT was induced in melanocytes. The same suppressive effect of melanogenesis was also observed, when α‐melanocyte‐stimulating hormone or endothelin‐1 was used as a stimulator. Because these results implied a mechanism other than NO scavenging to explain the suppressive effect of MT induction on melanogenesis, the direct inhibition of tyrosinase by MT was examined. Melanosome fractions were prepared from melanocytes, whose melanogenesis was suppressed by the induction of MT. Tyrosinase suppression was observed in the melanosome fractions, which was neutralized by the addition of anti‐MT antibody. These results suggest that MT induction may be effective to suppress melanogenesis stimulated by NO as well as other melanogens, and these suppressive effects might be due to a direct inhibition of tyrosinase activity in melanosome and not a scavenging effect of NO.

SPECTRO-NEBULA GRAPH: A TRIDIMENSIONAL SPECTROSCOPIC SYSTEM BASED ON A LOCAL AREA NETWORK OF PERSONAL COMPUTERS

Spectro-nebula graph (SNG), a tridimensional-spectroscopic system, has been developed as a versatile observation system attached to the Cassegrain focus of the 1.88 m telescope at the Okayama Astrophysical Observatory. Tridimensional spectra, i.e., so-called data cubes, are obtained by sweeping the telescope in the direction perpendicular to the slit of a spectrograph step by step. From the data cube, various monochromatic images can be extracted by data processing. SNG consists of four devices, i.e., the telescope control system, the autoguider, the spectrograph, and the CCD camera, which are distributed on a personal computer network. The control software for SNG performs cooperative control of four devices in an automated fashion according to a programmed sequence of procedures. Some observational results taken with SNG are shown for 3C 120, NGC 4449, and NGC 3646.

Kyoto tridimensional spectrograph II: progress

We are building the Kyoto tridimensional spectrograph II and are planning to mount it on Subaru telescope. The spectrograph has four observational modes: Fabry-Perot imager, integral field spectrograph (IFS) with a microlens array, long-slit spectrograph, and filter-imaging modes. The optics is designed to be used in wide wavelength range from 360 nm to 900 nm. The design well matches with high spatial resolution of Subaru: 0 inch .06 pixel-1 in Fabry- Perot mode, for which we actually will use binning before adaptive optics at optical wavelengths becomes available, and 0 inch .1 lens-1 in microlens array mode. These well sample image sizes obtained by Subaru, which are about 0 inch .4 in relatively good conditions. We have evaluated a point spread function of our cylindrical microlens array and found that it consists of a diffraction pattern and more extended component which probably comes from border regions between microlenses. With a suitable mask at the micro pupil position, the crosstalk between spectra will be limited down to a few percent. With a suitable mask at the micro pupil position, the crosstalk between spectra will be limited down to a few percent. We have succeeded in synchronizing frequency switching of Fabry-Perot etalons with the movement of charge on the CCD. This technique enables to average out all temporal variations between each passband.

The Kyoto Tridimensional Spectrograph II on Subaru and the University of Hawaii 88 in Telescopes

In order to investigate physical conditions of ionized gas in galaxies, as well as its kinematics, we have developed the Kyoto tridimensional spectrograph II. It is a multimode optical instrument, including integral field spectrograph (IFS) and Fabry-Perot imager modes. We have designed it compact so that we can mount it on 2 m class telescopes as well as on the 8.2 m Subaru telescope. Special care was taken to obtain high-quality calibrations in the IFS mode. In order to remove the chromatic aberration of micropupil images produced by a lenslet array, we have introduced a corrector lens system behind the lenslet array. The internal calibration system simulates the telescope optics so that the system provides micropupil images identical to those produced by the telescope. The rigidness of the instrument provides the positional stability of micropupil images. We have succeeded in test observations of all the modes on Subaru and the University of Hawaii 88 in (UH88) telescopes and have verified the performance of the instrument. This includes the instrument efficiencies as well as the effective sky background subtraction and the minimization of crosstalk effects in the IFS mode. In the IFS mode a spatial resolution of 0.4 was obtained in good seeing conditions. Each of 37 × 37 lenslets subtends 0.1 in Subarus case. This samples the image size well. A wider field of view is emphasized in the case of UH88.

SUBARCSECOND STRUCTURE AND VELOCITY FIELD OF OPTICAL LINE-EMITTING GAS IN NGC 1052

We have obtained integral field spectra of the low-ionization emission-line region in the galaxy NGC 1052 by using the Kyoto Tridimensional Spectrograph II mounted on the Subaru Telescope. Our high signal-to-noise ratio data with precise template subtraction have revealed weaker features at the nucleus, including the [Fe III] and He II emission lines, as well as a broad component of the Hβ emission. The broad Hβ component suggests the existence of a broad-line region. The spatial structure and velocity field derived from the data cube suggest the existence of three main components: a high-velocity bipolar outflow, low-velocity disk rotation, and a spatially unresolved nuclear component. The outflow axis does not coincide with the disk rotation axis. The opening angle of the outflow decreases with velocity shift from the systemic velocity both in bluer and redder velocity channels. This is explained only if the outflow has intrinsically higher velocity components inside, i.e., in regions closer to the outflow axis. At both sides of the bipolar outflow, we find that the highest velocity components are detached from the nucleus. This gap can be explained by an acceleration of at least a part of the flow or the surrounding matter, or by bow shocks that may be produced by even higher velocity outflow components that are not yet detected. Along the edges of the outflow and extending east-northeast and west-southwest, there exist strong [O III] emission ridges. These are closely related to the radio jet-counterjet structure. The abrupt change in the velocity field of the ionized gas and a large [O ]/Hβ line flux ratio in this region suggest a strong interaction of the jets, and possibly also of some ridge components of the line-emitting gas, with the interstellar matter.

Observations of the Velocity Curves of NGC-1068

For 132 spectra of NGC 1068 taken at 24 position angles of every 15° from an isophotal major axis (P.A. = 52°) of the inner arm region, we measured Hα, Hβ, [N II] λ6583, and [O III] λλ4959, 5007 to present the velocity curves in tabular form. Comparisons are made with previous observations to show that our measurements are consistent with the recent observations, but inconsistent with Walkers measurements (1968, ApJ, 151). Combined with CO velocity data, the velocity field was analyzed to reveal large-scale noncircular motions to occur within the galaxy

Test observations of the Kyoto Tridimensional Spectrograph II at the University of Hawaii 88-in and Subaru Telescopes

In order to investigate the physical conditions of ionized gas in galaxies, as well as its kinematics, we have developed the Kyoto tridimensional spectrograph II (3DII). It is a multi-mode instrument designed for Cassegrain focus, including integral field spectrograph (IFS) and Fabry-Perot imager modes. We have designed it compact so that we can mount it at 2-m class telescopes as well as at 8-m Subaru telescope. We have succeeded in test observations of the 3DII. In the IFS mode the spatial resolution of ~ 0.5 and 0.4 was obtained in 30-minute exposures at University of Hawaii 88-inch (UH88) and Subaru, respectively, in relatively good weather conditions. Each of 37 × 37 microlenses subtends ~ 0.1 in Subarus case. This samples well the image size. A wider field of view is emphasized in the case of UH88. Because our micropupil spectroscopy is free from a slit effect, we have reached the accuracy of an order of one tenth of a pixel for deriving velocity fields in terms of velocity center while the full width at half maximum of the instrumental profile corresponds to two pixels. At Subaru we have used a container designed in a collaboration with National Astronomical Observatory, Japan: it fits with a robotic instrument exchanger. The containerincludes two heat exchangers to keep its surface cool and void degrading the image quality. We have established effective observational equences by realizing a software interface with Subaru operating system. ome results from target observations are shown.