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We report Hα imaging observations of nearby galaxies with the Kiso Schmidt telescope. For spiral galaxy NGC 628, we found no clear correlation between Hα and CO intensities, and we discuss the star formation efficiency of this galaxy. No nuclear Hα emission in this galaxy was detected. This is consistent with spectroscopic observations which indicate that the nuclear region is in the post starburst phase. We also describe the Hα image of Hickson's compact group 92 in which diffuse emission is detected extending within the group system.
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.
We present initial results of a deep mid-infrared survey
conducted in the high galactic latitude field SSA13 with ISO.
We have surveyed through the broad band filter
LW2 (5-8.5 μm)
of the mid-infrared camera ISOCAM
to probe the near-infrared light at high redshift.
The 80% completeness limit for point sources in the central
6 arcmin2 reaches 10 μJy at 6.7 μm.
65 sources are detected down to 6 μJy in 16 arcmin2.
The integral galaxy number counts
are 1.4 × 104 deg-2
at 10 μJy with the slope of -1.5.
The integrated 6.7 μm light down to 6 μJy
is estimated as 0.43 nWm-2sr-1.
Our counts are consistent with
the results in the HDF and
the model prediction
based on the K band local luminosity function.
It suggests that
the majority of the detected sources are
E/S0 galaxies at z>1.
Faint submillimeter sources detected with JCMT/SCUBA
have faced an identification problem due to their broad beam profiles.
Here we propose a new method to identify these sources
at the mid-infrared utilizing a finer point spread function.
ISOCAM has provided us a very deep 6.7 μm image of the Hawaii Deep Field SSA13.
For all three 850 μm sources in this field,
we have found their 6.7 μm counterparts.
All of them have been identified with interacting galaxy pairs at the optical.
Two of the pairs are very faint and red (I>24, I - K > 4),
one of the two has the hard X-ray detection with Chandra.
Assuming an Arp 220 SED,
we have found a typical redshift of z ~ 2.
that the sources should be a few times more luminous than Arp 220.
It appears that extremely high star formation rates
are occurring in galaxies at high redshift
with massive stellar contents already in place.
We present the characteristics of far-infrared (FIR) brightness fluctuations at 90 μm and 170 μm in the Lockman Hole, which were surveyed with the ISOPHOT instrument aboard the Infrared Space Observatory (ISO), and give constraints on the galaxy number counts down to 30 mJy at 90 μm and 50 mJy at 170 μm. The fluctuation power spectra of the FIR images are not dominated by IR cirrus, and are instead most likely due to star-forming galaxies. This analysis indicates the existence of strong evolution in the counts. Especially at 90 μm, the source density is much larger than that expected from the currently available galaxy count models. The galaxies responsible for the fluctuations also significantly contribute to the cosmic infrared background radiation recently derived from an analysis of the COBE data.
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.
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 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.
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).
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.
We have studied the bulge formation process by starbursts in young disk galaxies whose disks and halos are gas-rich. If such galaxies tidally encounter another galaxies, large starbursts are easily induced and create galactic superwinds. We study the interaction between the superwind and the halo gas by using a similarity solution and show that a massive, radiativelly-cooled, gaseous shell is formed and becomes gravitationally unstable. In this way, we expect that shells of stars are formed. In order to study further evolution of these shells and their interaction with the disk, we model both the shell and the disk by using an N-body code. Our numerical results show that a large bulge with de Vaucouleurs' density profile is formed from the shell. We also show that the disk is thickened due to the interaction with the shell. The large bulges and thick disks are very similar to these found in S0 galaxies.
Starburst galaxies release huge energy by frequent supernovae. In some starburst galaxies, hot gas and molecular outflows are observed. These outflows are called superwinds (Heckman et al. 1990; Tomisakak and Ikeuchi 1988; Mac Low and McCray 1989). Since some starburst galaxies are interacting galaxies, it was proposed that the starbursts occurs due to gravitational interaction between galaxies (e.g. Noguchi 1988). Such interactions induce bar formation in a galaxy, and the subsequent gas inflow towards the galactic center, as a result of gas-bar interaction and due to the self-gravity in the gas (e.g. Wada and Habe 1990).
NMA 12CO(J=1-0) observations of the radio lobe spiral galaxy, NGC 3079, reveal a dense, rigidly rotating ring of molecular gas with a radius of about 750 pc. In addition, a tilted CO component as well as several molecular gas “spurs” are interpreted as linear features which are accelerated outwards by the nuclear outflow.
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.
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.
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.
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).