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Register a new userNuclear-to-Disk Rotation Curves of Galaxies in the H_alpha and [NII] Emission Lines
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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 : http://www.ioa.s.u-tokyo.ac.jp/]
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A homogeneous sample of ~2200 low redshift disk galaxies with both high sensitivity long-slit optical spectroscopy and detailed I-band photometry is used to construct average, or template, rotation curves in separate luminosity classes, spanning 6 magnitudes in I-band luminosity. The template rotation curves are expressed as functions both of exponential disk scale lengths r_d and of optical radii Ropt, and extend out to 4.5-6.5 r_d, depending on the luminosity bin. The two parameterizations yield slightly different results beyond Ropt because galaxies whose Halpha emission can be traced to larger extents in the disks are typically of higher optical surface brightness and are characterized by larger values of Ropt/r_d. By either parameterization, these template rotation curves show no convincing evidence of velocity decline within the spatial scales over which they are sampled, even in the case of the most luminous systems. In contrast to some previous expectations, the fastest rotators (most luminous galaxies) have, on average, rotation curves that are flat or mildly rising beyond the optical radius, implying that the dark matter halo makes an important contribution to the kinematics also in these systems. The template rotation curves and the derived functional fits provide quantitative constraints for studies of the structure and evolution of disk galaxies, which aim at reproducing the internal kinematics properties of disks at the present cosmological epoch.
We present an investigation of the structure of the emission line region in a sample of 12 single-peaked Active Galactic Nuclei (AGNs). Using the high resolution H-beta and H-alpha line profiles observed with the Isaac Newton Telescope (La Palma) we study the substructure in the lines (such as shoulders or bumps) which can indicate a disk or disk-like emission in Broad Line Regions (BLRs). Applying Gaussian analysis we found that both kinds of emission regions, BLR and NLR, are complex. In this sample the narrow [OIII] lines are composites of two components; NLR1 which have random velocities from sim 200 to 500 km/s and systematic velocities toward the blue from 20 to 350 km/s, and NLR2 with smaller random velocities (sim 100-200 km/s) and a redshift corresponding to the cosmological one. The BLR also have complex structure and we apply a two-component model assuming that the line wings originate in a very broad line region (VBLR) and the line core in an intermediate line region (ILR). The VBLR is assumed to be an accretion disk and the ILR a spherical emission region. The model fits very well the H-alpha and H-beta line profiles of the AGNs.
We present rotation curves for 19, mostly luminous, early-type disk galaxies. Rotation velocities are measured from a combination of HI velocity fields and long-slit optical emission line spectra along the major axis. We find that the rotation curves generally rise rapidly in the central regions and often reach rotation velocities of 200 - 300 km/s within a few hundred parsecs of the centre. The detailed shape of the central rotation curves shows a clear dependence on the concentration of the stellar light distribution and the bulge-to-disk luminosity ratio: galaxies with highly concentrated stellar light distributions reach the maximum in their rotation curves at relatively smaller radii than galaxies with small bulges and a relatively diffuse light distribution. We interpret this as a strong indication that the dynamics in the central regions are dominated by the stellar mass. At intermediate radii, many rotation curves decline. The strength of the decline is correlated with the total luminosity of the galaxies, more luminous galaxies having on average more strongly declining rotation curves. At large radii, however, all declining rotation curves flatten out, indicating that substantial amounts of dark matter must be present in these galaxies too. A comparison of our rotation curves with the Universal Rotation Curve from Persic et al. (1996) reveals large discrepancies between the observed and predicted rotation curves; we argue that rotation curves form a multi-parameter family which is too complex to describe with a simple formula depending on total luminosity only. (abridged)
After explaining the motivation for this article, I briefly recapitulate the methods used to determine, somewhat coarsely, the rotation curves of our Milky Way Galaxy and other spiral galaxies, especially in their outer parts, and the results of applying these methods. Recent observations and models of the very inner central parts of galaxian rotation curves are only briefly described. I then present the essential Newtonian theory of (disk) galaxy rotation curves. The next two sections present two numerical simulation schemes and brief results. Application of modified Newtonian dynamics to the outer parts of disk galaxies is then described. Finally, attempts to apply Einsteinian general relativity to the dynamics are summarized. The article ends with a summary and prospects for further work in this area.
We use N-body hydrodynamical simulations to study the structure of disks in triaxial potentials resembling CDM halos. Our analysis focuses on the accuracy of the dark mass distribution inferred from rotation curves derived from simulated long-slit spectra. We consider a massless disk embedded in a halo with axis ratios of 0.5:0.6:1.0 and with its rotation axis aligned with the minor axis of the halo. Closed orbits for the gaseous particles deviate from coplanar circular symmetry, resulting in a variety of long-slit rotation curve shapes, depending on the orientation of the disk relative to the line of sight. Rotation curves may thus differ significantly from the spherically-averaged circular velocity profile of the dark matter halo. Solid-body rotation curves--typically interpreted as a signature of a constant density core in the dark matter distribution--are obtained about 25% of the time for random orientations although the dark matter follows the cuspy density profile proposed by Navarro, Frenk & White (NFW). We conclude that the discrepancies reported between the shape of the rotation curve of low surface brightness galaxies and the structure of CDM halos may be resolved once the complex effects of halo triaxiality on the dynamics of the gas component is properly taken into account.
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