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Register a new userDecomposition of the rotation curves of distant field galaxies
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B.Fuchs
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We present decompositions of the rotation curves of distant spiral galaxies into contributions due to their bulges, disks, and putative dark haloes. In order to set constraints on the ambiguities of the decompositions we interpret the morphology of the spiral structures quantitatively in the framework of density wave theory. Galaxy models constrained in such a way show that the distant galaxies, which are much younger than nearby galaxies, are indeed also imbedded in dark haloes as expected from contemporary theories of the cosmonogy of galaxies.
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Spatially resolved velocity profiles are presented for nine faint field galaxies in the redshift range 0.1 < z < 1, based on moderate-resolution spectroscopy obtained with the Keck 10 m telescope. These data were augmented with high-resolution HST images from WFPC2, which provided V and I photometry, galaxy type, orientation, and inclination. The effects of seeing, slit width, and slit misalignment with respect to galaxy major axis were modeled along with inclination for each source, in order to derive a maximum circular velocity from the observed rotation curve. The lowest redshift galaxy, though highly elongated, shows a distorted low-amplitude rotation curve that suggests a merger in progress seen perpendicular to the collision path. The remaining rotation curves appear similar to those of local galaxies in both form and amplitude, implying that some massive disks were in place at z ~ 1. The key result is that the kinematics of these distant galaxies show evidence for only a modest increase in luminosity of delta M_B < 0.6 compared to velocity-luminosity (Tully-Fisher) relations for local galaxies.
We have undertaken a pilot project to measure the rotation velocities of spiral galaxies in the redshift range 0.18 < z < 0.4 using high dispersion long slit spectroscopy obtained with the Palomar 5m telescope. One field galaxy and three cluster objects known to have strong emission lines were observed over wavelength ranges covering the redshifted lines of [OII], CaII K, H beta, and [OIII]. Two of the objects show extended line emission that allows the tracing of the rotation curve in one or more lines. A line width similar to that obtained with single dish telescopes for the 21-cm HI line observed in lower redshift galaxies can be derived from the observed H beta, [OII], and [OIII] emission by measuring a characteristic width from the velocity histogram. These moderately distant galaxies have much stronger emission lines than typical low-redshift spirals but they appear to be kinematically similar. Application of the Tully-Fisher relation suggests that the two galaxies with rotation curves are intrinsically brighter at R-band than nearby galaxies.
We present rotation curves derived for a sample of 62 late-type dwarf galaxies that have been observed as part of the Westerbork HI Survey of Spiral and Irregular Galaxies (WHISP) project. The rotation curves were derived by interactively fitting model data cubes to the observed cubes, taking rotation curve shape, HI distribution, inclination, and the size of the beam into account. This makes it possible to correct for the effects of beam smearing. The dwarf galaxies in our sample have rotation-curve shapes that are similar to those of late-type spiral galaxies, in the sense that their rotation curves, when expressed in units of disk scale lengths, rise as steeply in the inner parts and start to flatten at two disk scale lengths. None of the galaxies in our sample have solid-body rotation curves that extend beyond three scale lengths. The logarithmic outer rotation curve slopes are similar between late-type dwarf and spiral galaxies. Thus, whether the flat part of the rotation curve is reached seems to depend more on the extent of the rotation curve than on its amplitude. We also find that the outer rotation curve shape does not strongly depend on luminosity, at least for galaxies fainter than M_R~-19. We find that in spiral galaxies and in the central regions of late-type dwarf galaxies, the shape of the central distribution of light and the inner rise of the rotation curve are related. This implies that galaxies with stronger central concentrations of light also have higher central mass densities, and it suggests that the luminous mass dominates the gravitational potential in the central regions, even in low surface brightness dwarf galaxies.
In this work we study rotation curves of spiral galaxies using a model of dark matter based on a scalar-tensor theory of gravity. We show how to estimate the scalar field dark matter parameters using a sample of observed rotation curves.
We examine the evolution of the Tully-Fisher relation (TFR) using a sample of 89 field spirals, with 0.1 < z < 1, for which we have measured confident rotation velocities (Vrot). By plotting the residuals from the local TFR versus redshift, or alternatively fitting the TFR to our data in several redshift bins, we find evidence that luminous spiral galaxies are increasingly offset from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, for a given Vrot, by approximately z = 1. Since selection effects would generally increase the fraction of intrinsically-bright galaxies at higher redshifts, we argue that the observed evolution is probably an upper limit. Previous studies have used an observed correlation between the TFR residuals and Vrot to argue that low mass galaxies have evolved significantly more than those with higher mass. However, we demonstrate that such a correlation may exist purely due to an intrinsic coupling between the Vrot scatter and TFR residuals, acting in combination with the TFR scatter and restrictions on the magnitude range of the data, and therefore it does not necessarily indicate a physical difference in the evolution of galaxies with different Vrot. Finally, if we interpret the luminosity evolution derived from the TFR as due to the evolution of the star formation rate (SFR) in these luminous spiral galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1), slower than commonly derived for the overall field galaxy population. This suggests that the rapid evolution in the SFR density of the universe observed since approximately z = 1 is not driven by the evolution of the SFR in individual bright spiral galaxies. (Abridged.)
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