Mareki Honma

CENTRAL ROTATION CURVES OF SPIRAL GALAXIES

We present high-resolution central-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies. We discuss their general characteristics, particularly their central behavior, as well as dependencies on morphological types, activity, and peculiarity. The rotation curves generally show a steep nuclear rise and high-velocity central rotation, followed by a broad maximum in the disk and then a flat rotation due to the massive halo. Since the central high velocity and steep rise are common to all massive galaxies, they cannot be due to noncircular motions. Disk rotation curves of barred galaxies show larger dispersion than those of normal galaxies, probably because of noncircular motions. Interacting galaxies often show perturbed outer rotation curves, while their central rotation shows no particular peculiarity. In addition, central activities, such as starbursts and active galactic nuclei, appear to show no particular correlation with the property of rotation curves. This would suggest that the central activities are triggered by a more local effect than the global dynamical property.

An Isotope Study of Carbon Monoxide in the Edge-on Galaxy NGC 891

We present high-resolution simultaneous observations of the edge-on galaxy NGC 891 in 12CO and 13CO emissions. The molecular thin-disk component within 10.7 kpc from the galactic center was completely covered. This data set with accurate relative calibrations of intensity scale and pointing is analyzed to examine radial variation in the physical properties of the molecular gas. The total 13CO/12CO luminosity ratio is 1/6.6. A low 13CO/12CO intensity ratio of 1/(15.4 ± 6.0) is observed in the nuclear disk of about 550 pc in radius. There exists a systematic gradient of the 13CO/12CO intensity ratio in the main galactic disk as a function of galactocentric distance: the 13CO/12CO intensity ratio exhibits a notable peak of 1/4.5 near 4 kpc, and decreases systematically outward down to 1/10 at 10 kpc. The observational results are analyzed on the basis of a CO excitation analysis. The low 13CO/12CO intensity ratio in the nuclear disk may be attributed to a predominance of warm molecular gas (40 K) of moderate gas density (~103 cm-3), while the systematic gradient of the 13CO/12CO intensity ratio in the main disk can be interpreted in terms of radial decrease in the dense molecular gas fraction. Since interstellar gas in the inner part of the galaxy is mostly molecular, this variation will be ascribed to compression of molecular gas with its strength dependent on galactocentric distance rather than dissociation of low-density molecular gas by UV photons from young stars in the inner part of the galaxy.

Mass of the Galaxy Inferred from Outer Rotation Curve

Using an outer rotation curve of the Galaxy, we explore the galactic constants and the mass of the Galaxy. We show that \Theta_0 of 200 km/s is more favorable than the IAU standard value of 220 km/s, and also show that if \Theta_0 is smaller than 207 km/s the rotation curve beyond 2R_0 is declining in Keplerian fashion. In the case of \Theta_0= 200 km/s and R_0= 7.6 kpc, the total mass and the extent of the Galaxy inferred from the rotation curve are 2.0+/-0.3x 10^{11} M_\odot and 15 kpc, respectively. These results may significantly change the previous view of the Galaxy, that its outer region is dominated by a massive dark halo extending out to several tens of kpc.

Nuclear Rotation Curves of Galaxies in the Co-Line Emission

We have obtained high-resolution position-velocity (PV) diagrams along the major axes of the central regions of nearby galaxies in the CO-line emission using the Nobeyama 45-m telescope and the Millimeter Array. Nuclear rotation curves for 14 galaxies have been derived based on the PV diagrams using the envelope-tracing method. The nuclear rotation curves for most of the galaxies show a steep rise within a few hundred pc, which indicates a high-density concentration of mass. Keywords: Galaxies: general - Galaxies: structure - ISM: molecular line

Ultra-High-Density Molecular Core and Warped Nuclear Disk in the Deep Potential of Radio Lobe Galaxy NGC 3079

We have performed high-resolution synthesis observations of the 12CO (J = 1-0) line emission from the radio lobe edge-on spiral galaxy NGC 3079 using a seven-element millimeter-wave interferometer at the Nobeyama Radio Observatory, which consisted of the 45 m telescope and six-element array. The nuclear molecular disk (NMD) of 750 pc radius is found to be inclined by 20° from the optical disk, and the NMD has spiral arms. An ultra-high-density core (UHC) of molecular gas was found at the nucleus. The gaseous mass of the UHC within 125 pc radius is as large as ~3 × 108 M☉, an order of magnitude more massive than that in the same area of the Galactic center, and the mean density is as high as ~3 × 103H2 cm-3. A position-velocity diagram along the major axis indicates that the rotation curve already starts at a finite velocity exceeding 300 km s-1 from the nucleus. The surface mass density in the central region is estimated to be as high as ~105 M☉ pc-2, producing a very deep gravitational potential. We argue that the very large differential rotation in such a deep potential will keep the UHC gravitationally stable during the current star formation.

On the Keplerian Rotation Curves of Galaxies

We propose a criterion for examining whether or not the uncertainty of the outer rotation curves is sufficiently small to distinguish a Keplerian rotation curve from flat ones. We have applied this criterion to both Keplerian and non-Keplerian rotation curves so far obtained, and investigated their relative fraction. We also studied the minimum extent of the dark halos indicated by non-Keplerian rotation curves using the criterion. We have found that one cannot rule out the possibility that a significant fraction of rotation curves become Keplerian within 10-times the disk scale length. If the Keplerian rotation curves so far observed trace the mass truncation, several galaxies may have rather small halos, the extent of which is not larger than twice that of the optical disk.

Nuclear-to-Disk Rotation Curves of Galaxies in the Ha and [N II] Emission Lines

We have obtained optical CCD spectroscopy along the major axes of 22 nearby spiral galaxies of Sb and Sc types in order to analyze their rotation curves. By subtracting the stellar continuum emission, we have obtained position velocity (PV) diagrams of the H alpha and [NII] lines. We point out that the H alphaline is often superposed by a broad stellar absorption feature (Balmer wind) in the nuclear regions, and, therefore, the [NII] line is a better tracer of kinematics in the central a few hundred pc regions. By applying the envelope-tracing technique to the H alpha and [NII] PV diagrams, we have derived nucleus-to-disk rotation curves of the observed galaxies. The rotation curves rise steeply within the central a few hundred parsecs, indicating rapidly rotating nuclear disk and mass concentration near the nucleus. [For more rotation curves : this http URL]

J-Net Galactic-Plane Survey of VLBI Radio Sources for VLBI Exploration of Radio Astrometry (VERA)

In order to search for new VLBI sources in the Galactic plane that can be used as phase reference sources in differential VLBI, we have conducted 22 GHz observations of radio sources in the Galactic plane using the Japanese VLBI Network (J-Net). We have observed 267 VLBI source candidates selected from existing radio surveys and have detected 93 sources at the signal-to-noise ratio larger than 5. While 42 of the 93 detected sources had already been detected with VLBI at relatively lower frequency (typically 2 to 8 GHz), the remaining 51 are found to be new VLBI sources detected for the first time. These VLBI sources are located within

The Mass-to-Light Ratio of Binary Galaxies

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MACHO Mass Determination Based on Space Telescope Observation

, and have a large number of Galactic maser sources around them. Thus, they are potential candidates for phase reference sources for VLBI Exploration of Radio Astrometry (VERA), which is the first VLBI array dedicated to the phase referencing VLBI astrometry aiming at measuring the parallax and proper motion of maser sources in the whole Galaxy.