Naomasa Nakai

BeppoSAX Observation of NGC 3079

Using the BeppoSAX observatory, we have observed a nearby LINER/Seyfert 2 galaxy, NGC 3079, which is known as an outflow galaxy and a bright H2O maser source. Using the Phoswich Detection System, we have revealed that the NGC 3079 nucleus suffers from a Compton-thick absorption, with a hydrogen column density ~1025 cm-2. After corrected the absorption, the 2-10 keV luminosity becomes 1042-1043 ergs s-1 at a distance of 16 Mpc. It is 2-3 orders of magnitude higher than that observed in the Medium Energy Concentrator Spectrometer band (below 10 keV). We also detected a strong Fe K line at 6.4 keV with an equivalent width of 2.4 keV, which is consistent with the heavy absorption.

CO Survey of a Distance-limited Seyfert Sample. I. The Data

We present the data of 12CO (J = 1–0) observations of the central regions of a sample of 43 nearby Seyfert galaxies (cz ≤ 5000 km s-1) with the NRO 45 m telescope. The general properties of this sample are also discussed, but a more detailed analysis is deferred to Paper II. The CO detection rate of this sample (i.e., almost 50%) is comparable to that of other spiral galaxy surveys in similar redshift ranges made with that telescope. There seems to be no difference in the detection rates of Seyfert galaxies types 1 and 2. Since we observed a single point centered at the nucleus, and the average ratio of the beam HPBW of the 45 m telescope to the apparent optical diameter of these objects was 0.13, only a small fraction of the total molecular gas is recovered. However, a clear correlation of the CO contents with the IRAS FIR luminosities is also seen, and there seems to be a tendency for Seyfert galaxies to be closer to normal galaxies than to starbursts. The radial distribution of the molecular gas in these galaxies is compatible in most cases with a steeply decreasing function. Our high spatial resolution observations trace the interface region between the large scale properties of the disks of the host galaxies and the active nuclear regions. This interface region is the one most directly associated to the fuelling of the nuclear energy source in these objects and can be thus compared with data on samples of nonactive galaxies at similar spatial scales to deduce the possible relation of the circumnuclear gas contents and dynamics with nuclear activity (see Paper II).

CO emission from the polar-ring S0 galaxy NGC 2685 and origin of the ring structure

A CO emission line has been detected in the polar-ring S0 galaxy NGC 2685 and the possible origin of the circumnuclear molecular gas is discussed. It is suggested that the gas has been fed by the helix structure and may have little relation to the star-forming activity of the galaxy. As a formation mechanism of the helix and the faint outer ring of NGC 2685, a possibility of interaction with a distant partner UGC 4683 is suggested. The age of the helix and the outer ring is estimated to be more than 1 billion years, since such an interval of time is necessary for the formation of the ring structures and for the accumulation of molecular gas in the central 820 pc region of the galaxy. The accretion rate is estimated to be about 0.01 solar mass/yr. 46 refs.

The Polar Ring Starburst Galaxy NGC 660

NGC 660 is a gas-rich, peculiar polar ring RSBa-type starburst galaxy with two distinct morphological and kinematic components: an inner disc, seen almost edge-on, with a major axis position angle of 45° and a diameter of ~11 kpc [D=13 Mpc, H o =75 kms −1 Mpc −1 ], and an outer polar ring (p.a. 170°) with a diameter of 31 kpc, inclined on average about 55° with respect to the major axis of the inner disc. We obtained deep, 30 min. exposure CCD images of NGC 660 with the 105 cm Schmidt telescope of Kiso Observatory in the B, V, R, and I bands. A preliminary reduction shows that the inner disc is clearly redder than the polar ring and the nucleus. Optical spectra indicate that the galaxy has a LINER-type spectrum, suggesting intense massive star formation in the nucleus. We obtained a long-slit Ha spectrum along the major axis of the inner disc at ESO, which shows a very steep gradient near the nucleus. Assuming an inclination of 80°, it implies a rotational velocity of about 150 km s −1 for the inner disc.

A 10-Ghz Radio-Continuum Survey of the Galactic-Plane Region at the Nobeyama Radio Observatory - A Complex Region at l = 22° – 25°

Preliminary results of a 10-GHz radio-continuum survey of the galactic-plane region using the 45-m telescope at NRO are presented. An extensive study of a complex region at 22° ≦ l ≦ 25°, | b | ≲ 1° has been made.