Book chapters will be unavailable on Saturday 24th August between 8am-12pm BST. This is for essential maintenance which will provide improved performance going forwards. Please accept our apologies for any inconvenience caused.
To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
A radio continuum survey of the galactic plane has been made with the 45-m telescope of the Nobeyama Radio Observatory at 10.55 GHz, which is the highest frequency among such surveys. The sensitivity of the telescope was Tb/S = 0.47 K/Jy and the HPBW was 2!6, which was a great advantage because of the same beam size of the Bonn 5-GHz survey (Altenhoff et al. 1978). The receiver was a cooled parametric amplifier. The instantaneous bandwidth was 500 MHz, and the system noise temperature was about 100 K. The calibration source was NGC 7027, which was assumed to be 6.6 Jy. One circular polarization component was observed. The observational parameters are summarized in Table I.
CO observations of the nuclear region of the SABc galaxy M83 have been made with the 45-m telescope at NRO. A bar-like elongation of the CO emission along the optical bar and a velocity field which suggests noncircular motions are found. These results are consistent with predictions based on the theoretical model of barred spiral galaxies. The inflow and concentration of molecular gas in the nucleus of M83 may supply raw material which maintains a burst of star formation there.
A large radio continuum loop of diameter was discovered at G16.5+0.7 on the Bonn 2.7 GHz and NRO 10 GHz galactic plane surveys. The loop is associated with the H II region M16, and the diameter is 60 pc at a distance of 2.8 kpc. Figure 1 shows the loop at 2.7 GHz in gray scale. The spectrum is thermal and the total H II mass is estimated at 3×103 M⊙. If the loop is due to a shell of the same diameter, the mean electron density on the shell is about 4 cm−3. The total thermal energy is about 6×1048ergs. The characteristics are summarized in Table 1.
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.
The distribution of Faraday rotation measure (RM) of extragalactic radio sources shows that a large-scale magnetic field in the Galaxy is oriented along the spiral arms. The field lines change direction from one arm to the next in the inter-arm region.
The CO (J=1-0) emission in M82 has been mapped with the Nobeyama 45-m telescope. The CO intensity distribution in the central region is resolved into two peaks. An axisymmetric model reveals a ring structure of molecular gas at a distance of 80-400 pc (centered near 200 pc) from the nucleus. This “200-pc ring” corresponds to just the region of a star formation burst. The molecular gas in M82 is also expanding out of the galactic plane with a velocity of 100-500 km s−1. The expansion energy of (0.1-1.4) x 1056 erg can be explained by the energy supply of supernovae in the central region.
The rotation velocity of molecular gas in the halos of M82 and NGC4631 decreases with the height from the galactic plane. The slower rotation of halo gas can be explained if the gas is supplied from the central region of the galaxies due to some ejection.
The interacting edge-on galaxy NGC 4631 has been observed in the 12CO(J = 2 − 1) line emission using the IRAM 30-m telescope with a resolution of 13″ (330 pc). The molecular gas is strongly concentrated in a ring-like disk of 1 kpc radius, which is rotating rigidly. Line proriles show several velocity components, which are attributable to spiral arms. Although the J=2−1 to 1−0 transition line ratio indicates that the gas is generally opaque against the lines, we find some optically thinner regions, as well.
The CO emission from the almost entire disk of M51 was mapped with the Nobeyama 45-m telescope. Using the high spatial resolution and high sensitivity data, we examine formation mechanisms of massive stars and molecular clouds both in arms and in interarms. The N(H2)/CO ratio is also evaluated in the galaxy.
CO(J=1−0) line observations of the southern arm of the barred-spiral galaxy M83 were made with the 45-m telescope of the Nobeyama Radio Observatory with a 17″-beam. The CO emission is concentrated to the spiral arm, but it is much weaker than in the bar. The comparison between the CO flux and the far ultraviolet flux suggests the star forming efficiency is much lower in the bar than in the spiral arm.
Optical photographs of highly-tilted, dust-rich nearby spiral galaxies like NGC253 have revealed numerous vertical dark filaments which we call vertical dust jets (VDJ). The VDJ exdend more than a few kpc from the disk in an almost coherent manner, while they are as thin as a few tens of pc. They are most likely due to boiling-steaming galactic disk, which ejects gas into the halo. The coherency suggests that VDJ trace large-scale poloidal magnetic lines of force.
Symmetrical structures do exist, in the Galactic Centre region, In this article we attempt to summarize their properties and draw the attention of the scientific community to the advantages of taking them into account when working with models of the Centre of our Galaxy, Our work is corroborated by two new maps of the region at 10.7 GHz.
We report the detection of a 4-kpc long, highly collimated radio feature emanating from the galactic center. This feature, which may be cylindrical in shape, is some 200 pc in diameter and extends almost perpendicular to the galactic plane. The structure may possibly be the remnant of a one-sided or highly asymmetric jet from the nucleus, or it might be a magnetic tornado produced by a twisted poloidal magnetic field between the disk and halo.
As a mechanism to generate asymmetric radio features in the central 50 pc of the Galaxy (Sofue and Fujimoto 1987), we consider a gaseous jet from the tilted accretion disk at the center and the interaction of the jet with ambient gas on the galactic plane. It is shown schematically in figure 1 that the magnetic torques N1,2,3 exert on a gaseous element ρhΔsΔr of a ring to change its tilted orbital plane,
where γ1,2,3 are constants of a factor of unity and e1,2,3 unit vectors. The azimuthal angle ϕ is measured along the rotation from the lowest part of the ring below the galactic plane. The orbital plane is tilted against the galactic plane by the angle θ The change of the angular momentum of the disk element L = ρhΔsΔrr × v is,
where 〈〉 means the average over one rotation period T or over ϕ = 0 to 2π in equations (1) to (3).
We present the results of a high-resolution CO-line survey using the Nobeyama Millimeter-wave Array at high-angular (⋐ 2–3″) and high spectral resolutions for the 15 CO-richest Virgo spirals. We derived exact rotation curves using position-velocity diagrams by applying the iteration method. the obtained RCs rise steeply in the central 100 pc. Surface-mass-density distributions by direct deconvolution of the RCs show massive cores of ⋐ 109M⊙ within 100 pc, suggesting the existence of DM cusps in the centres. Five galaxies were found to nest single-peaked extremely high-density molecular cores, where star formation is currently suppressed by the high differential rotation. We show that the deeper is the gravitational potential, the higher is the central gas density.
Rotation curves of spiral galaxies have been thought to rise rigidly in the central a few kpc, while they are flat in the outer regions (Rubin et al 1982; Persic 1996). On the other hand, CO-line and recent Hα observations have revealed steeply rising rotation curves near the nucleus (Sofue 1996,1997; Sofue et al 1997a,b; Rubin et al 1997).
We have investigated the masses and extents of dark halos of spiral galaxies by two methods. First, we have reanalyzed HI outer rotation curves so far obtained considering the velocity uncertainties. We confirmed that many HI rotation curves indicate the existence of dark matter to some extent. However, we also found that only few rotation curves provide direct evidences for halos extended beyond 10 disk scale length. On the other hand, recent HI observations revealed that several galaxies have declining rotation curves that are approximated by Keplerian in the outermost regions. Considering the velocity uncertainties in the outer rotation curves, we found that these declining rotation curves are not rare compared to flat rotation curves. If these declining rotation curves indeed trace the mass truncation, these results indicate that some dark halos have moderate masses that are comparable or slightly larger than disk masses.
The CO Tully-Fisher (TF) relation is able to measure the distances to farther galaxies than the HI TF relation reaches (Sofue et al. 1997). The galaxies observed for the CO TF relation at the high redshift are often infrared luminous galaxies. The fraction of interacting galaxies is large in the infrared luminous galaxies. Therefore, first we have analyzed the CO and HI linewidths for nearby interacting galaxies in order to examine the influence of the interaction on the linewidths. We found that HI linewidths for the interacting galaxies are significantly larger than CO (Tutui and Sofue 1997a). It suggests that the influence of the interaction is smaller at the inner region of galaxies where the CO gas exists, and that the CO TF relation is more reliable tool for the galaxies which have the evidence of the galaxy interaction as well as galaxies in rich clusters.
The accuracy of measurement of the Hubble constant depends not only on the accuracy of distance measurement but also on how small is the effect of local flows: The larger are redshifts of used galaxies, the higher is the accuracy of H0, if the error in distance measurement is comparable. The HI Tully-Fisher relation has been the standard tool for distance measurement up to cz ∼ 10,000 km s–1 (Tully and Fisher 1977), where, however, the local flow is not negligible.
Sofue (1996, 1997) presented accurate rotation curves of nearby galaxies, which are almost completely sampled from the inner to outer regions. The conspicuous common feature of the rotation curves is a steep rise at the inner bulge. The rise suggests a compact massive concentration near the nucleus (Sofue 1996). The study of the light distribution at the inner bulge demands accurate surface photometry at near-infrared wavelengths, where dust extinction is much less effective than in the optical. Most of Sofue's samples are nearby large galaxies, so that observations with a wide field view is clue to constructing reliable light distribution models.