山田 亨

The fraction of-star-forming galaxies in rich clusters of galaxies increases rapidly with the redshift. This is interpreted as the result of a rapid evolution of cluster galaxies, though its mechanism is not yet dear. One hypothesis is that if galaxies run into the dense intracluster medium (ICM) regions, starbursts can be induced due to the compression of molecular clouds in the galaxies by a raised ''external'' ICM pressure. In a merging cluster, there would be dense ICM regions and some galaxies may experience a rapid increase of external pressure. Thus, if the mechanism works, starbursts would occur in such galaxies. Such a situation is considered to be realized in Coma cluster, and galaxies showing a recent starburst have a characteristic spatial distribution; they populate an elongated region between two subclusters. We examined the above hypothesis by measuring the spatial distribution of blue galaxies, regarded as star-forming galaxies in Abell 168 to check whether a case Like Coma is realized in this recently merging cluster. However, we could not find an enhanced blue-galaxy distribution between two subclusters. We discuss the causes of our result, including the possibilities of surviving the hypothesis. (C) 1996 American Astronomical Society.

We observed a high redshift radio galaxy 53W002 at z=2.390 with the Nobeyama 45 m telescope aiming at a detection of a redshifted (CO)-C-12 (J=1-0) emission line. The galaxy was discovered in the Leiden Berkeley Deep Survey and is known to have a blue SED and is a candidate for a genuinely young galaxy. We detected a weak (similar to 5 mJy) emission-line feature at z=2.392; the feature was significant in our November 1993 observations and marginally confirmed in the follow-up observations held in December 1993 and February 1994. If the detected emission-line feature is really a redshifted CO emission line associated with 53W002, its luminosity is 1.2x10(11) h(-2) K km s(-1) pc(2) (q(0)=0.5), or, H(H-2)similar to 5 X 10(11) h(-2) H-circle dot, adopting the galactic CO-to-H-2 conversion factor. (C) 1995 American Astronomical Society.

We carried out a complete search for IRAS galaxies in the Taurus molecular cloud region at l=169 degrees to 177 degrees and b = -19 degrees to -12 degrees We selected a total number of 36 galaxies and galaxy candidates and looked for the 21- cm H I line in 25 objects; we detected H I emission in five of them including one with previously unknown redshift. The spatial density of IRAS galaxies with cz =4000 to 6000 km s(-1) is lower in this region than in the adjacent regions at both sides along galactic longitude, where the Perseus supercluster and the Gemini-Monoceros filament are respectively located.

MG 0414 + 0534 is a gravitational-lens system at z = 2.64 having a steep power-law continuum and an unusually red color in optical light. We searched for redshifted (CO)-C-12 (J = 3 - 2) emission from MG 0414 + 0534 and (CO)-C-12 (J = 1 - 0) emission from its lensing galaxy at z = 0.468 using the Nobeyama 45-m radio telescope. No significant emission was detected with a rms noise of 5 mK at a velocity resolution of 20 km s(-1). Assuming a velocity width of 400 km s(-1), we obtained 3 sigma upper limits on the molecular gas mass of 1.1 x 10(11) h(-2) M. for MG 0414 + 0534 and 5.7 x 10(10) h(-2) M. for the lensing galaxy (q(0) = 0.5, H-0 = 100 h km s(-1) Mpc(-1)), adopting a standard Galactic CO-to-H-2 conversion factor and neglecting the influence of the lensing event. We examined two views: MG 0414 + 0534 is a quasar reddened by the interstellar matter in the lensing galaxy or by the interstellar matter surrounding the power-law source.

We observed a high-redshift luminous radio-quiet quasar Q1235+0857 at z = 2.880 with the Nobeyama 45 m radio telescope aiming at detection of a redshifted (CO)-C-12 (J = 3-2) emission line. We have marginally (3-5 sigma significance) detected an emission-line-like feature at similar to 89.8 GHz (z = 2.883) with similar to 150 km s(-1) width (FWHM). Adopting the standard CO to H-2 conversion factor obtained for galactic giant molecular clouds, the CO luminosity can be roughly converted to H-2 gas mass of similar to 10(12) M., which is much larger than the molecular gas content of any galaxies at preent epoch and nearly equal to the total stellar mass of a giant elliptical galaxy. Although we should note that a confirmation of the detection by an independent facility is absolutely needed, the results discussed in this Letter would support the idea that luminous quasars at high redshift are associated with the massive galaxies in their forming phase.

We investigate the radial velocity distribution of the galaxies in the Puppis region behind the Milky Way around (l, b) approximately (245-degrees, 0-degrees), where a concentration of galaxies was recently recognized through the systematic search for galaxies behind the zone of avoidance. Using the lower limit sample of the 60-mum flux-limited sample of IRAS galaxies brighter than f60 = 0.6 Jy, we find a large nearby clustering of galaxies at about 20 h-1 Mpc, whose peak spatial density at 7.5 h-1 Mpc scale is at least twice the whole-sky average. This Puppis concentration is probably associated with the S1 supercluster at (l, b) = (220-degrees, -15-degrees) detected in the QDOT survey, and this association is likely to be comparable to other nearby superclusters such as the Virgo, the Hydra, the Centaurus and the Fornax-Eridanus superclusters. Consequently, the effect of the Puppis concentration on the peculiar motions of the Local Group and other nearby galaxies should be considerable. There is no prominent individual cluster in the Puppis region, however, although some galaxies are concentrated into the regions around (l, b) = (245-degrees, -7-degrees) and (237-degrees, -15-degrees); the richness of these individual clusters in IRAS galaxies is as large as that of the Fornax cluster, and perhaps half or more of that of the Virgo cluster. We also study the radial velocity distribution of the galaxies selected by an optical limiting diameter, although uncertainty in the selection is large because of galactic extinction. The distribution of these diameter-selected galaxies shows good agreement with that of the IRAS-selected ones.

In the course of our redshift; survey of IRAS galaxies behind the Milky Way, we newly detected four galaxies with active galactic nuclei, including one quasar and two Seyfert-type galaxies. The quasar, IRAS 07483+0328, is at z approximate to 0.1 and Mv = -24.0 mag. The quasar may be appropriate for investigating the nature of quasars because of its low redshift as well as the bright apparent magnitude.

A search for redshifted (CO)-C-12 (J = 1-0) emission from the damped Lya system at z = 2.00 toward QSO 1215+333 was made. No emission was found, and the upper limit of the molecular-hydrogen mass is 1.6 x 10(11)h(-2)M. (q(0) = 0.5) if we assume a velocity width of 400 km s(-1) and the Galactic CO-to-H-2 conversion factor. We estimated the far-infrared luminosity from the HP luminosity, and found that the upper limit of the molecular-hydrogen mass and far-infrared luminosity are comparable to those of ultraluminous far-infrared galaxies. However, the upper limit of the molecular-hydrogen mass obtained in this system is much smaller than the molecular-hydrogen mass found in other damped Lya systems at z = 2-3. It seems that the star-formation properties in these damped Lya systems are quite different from those of the system toward QSO 1215+333 and nearby galaxies. Further observations of more damped Lya systems in CO lines as well as in other wavelengths are indispensable to trace the star-formation history of damped Lya systems.

We systematically searched for IRAS galaxies with 60 μm flux density larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-J Atlases in the Milky Way region (|b| &lt 15°) between l = 210° and 360°. We first selected about 4000 IRAS point sources by using our far-infrared criteria, which are optimized for the search of IRAS galaxies behind the Milky Way region, and then inspected visually the optical counterparts of them on the Schmidt Atlas film copies. We found 966 IRAS sources associated with galaxy-like objects. The list of the objects is presented here with the IRAS source name, Galactic coordinates, IRAS flux densities, field number and emulsion of the Atlas, type and size of galaxy (-like) image, redshift, multiplicity, and cross-identification. Of these, 423 galaxies are already cataloged in the Catalog of Galaxies and Quasars Observed in the IRAS Survey, and most of the remaining 543 galaxy candidates are newly identified in this search. Although the radial velocities are known for only 387 galaxies, of which 60 were newly measured by us so far, we inferred the contamination by Galactic objects to be small from the good correlation between the sky distributions of the newly identified galaxy candidates and the previously cataloged galaxies. In the regions where the Galactic molecular clouds dominate, almost all the sources were not identified as galaxies. The detected galaxies are clustered in the three regions around l = 240°, 280°, and 315°, where the projected number densities are higher than the whole-sky average of IRAS galaxies of the same flux limit.

Slit spectral observations of the irregular galaxy IC 10 were made for the Halpha emission line in the central 4.'2 x 1.'0 region covering most of the star-forming regions of the galaxy; the Halpha velocities were obtained at about 500 points with a spatial resolution of about 3''. The Halpha velocities are similar to the velocities of CO molecules, while on most of the observed H II regions the Halpha velocities are redshifted by 5-10 km s-1 or so relative to the velocities of the surrounding H I gas. It is suggested from a simple hydrodynamical consideration that the star-forming clouds originated due to the collision of high-velocity infalling gas with the central H I disk.

We carried out aperture synthesis observations of the dwarf irregular galaxy IC 10 with the Nobeyama Millimeter Array in the (CO)-C-12 (j = 1-0) line. The observations have revealed the presence of three molecular clouds in the most active star-forming region; the line widths, masses, and deconvolved sizes of the molecular clouds axe approximately 7 km s-1, approximately 10(5) M., and 30-40 pc, respectively. The sizes and line widths of the molecular clouds are consistent with the size-line width relation for giant molecular clouds in our Galaxy. The H II regions and other features showing star-formation activity are adjacent to these molecular clouds. All of these properties of the molecular clouds are very similar to those of the giant molecular clouds in our Galaxy, M31, and M33, indicating that giant molecular clouds are formed in the dwarf irregular galaxy without any density wave. The results of CO and optical observations suggest that the molecular clouds are receding from the galactic plane of IC 10 with velocities of a few km s-1.