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Register a new userKinematics in the Central Kiloparsec of Spiral Galaxies
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Johan H. Knapen
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Results from kinematic observations of the central regions of spiral galaxies are reviewed, with particular emphasis on starburst and AGN hosts. While morphological studies lead to important insight, a more complete understanding of the physical processes that drive the evolution of the central regions can be achieved with measurements of the kinematics of gas and stars. Here, a variety of observational techniques at different wavelengths is critically discussed, and specific areas of interest are highlighted, such as inflow in barred galaxies and the origin of nuclear spiral arms. A brief discussion of a number of case studies is presented to illustrate recent progress.
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(Abridged) We trace the interaction processes of galaxies at intermediate redshift by measuring the irregularity of their ionized gas kinematics, and investigate these irregularities as a function of the environment (cluster versus field) and of morphological type (spiral versus irregular). Our sample consists of 92 distant galaxies. 16 cluster (z~0.3 and z~0.5) and 29 field galaxies (mean z=0.44) of these have velocity fields with sufficient signal to be analyzed. We find that the fraction of galaxies that have irregular gas kinematics is remarkably similar in galaxy clusters and in the field at intermediate redshifts. The distribution of the field and cluster galaxies in (ir)regularity parameters space is also similar. On the other hand galaxies with small central concentration of light, that we see in the field sample, are absent in the cluster sample. We find that field galaxies at intermediate redshifts have more irregular velocity fields as well as more clumpy and less centrally concentrated light distributions than their local counterparts. Comparison with a SINS sample of 11 z ~ 2 galaxies shows that these distant galaxies have more irregular gas kinematics than our intermediate redshift cluster and field sample. We do not find a dependence of the irregularities in gas kinematics on morphological type. We find that two different indicators of star formation correlate with irregularity in the gas kinematics. More irregular gas kinematics, also more clumpy and less centrally concentrated light distributions of spiral field galaxies at intermediate redshifts in comparison to their local counterparts indicate that these galaxies are probably still in the process of building their disks via mechanisms such as accretion and mergers. On the other hand, they have less irregular gas kinematics compared to galaxies at z ~ 2.
We present first results from our project to examine the internal kinematics of disk galaxies in 7 rich clusters with 0.3<=z<0.6. Spatially resolved MOS spectra have been obtained with FORS at the VLT. We concentrate here on the clusters MS1008.1-1224 at z=0.30 and Cl0413-6559 (F1557.19TC) at z=0.51. Out of 22 cluster members, 12 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing over into a flat part. The other members have intrinsically peculiar kinematics. The 12 cluster galaxies for which a maximum rotation velocity could be derived are distributed in the Tully-Fisher diagram very similar to field galaxies from the FORS Deep Field with corresponding redshifts. The same is true for 6 galaxies observed in the cluster fields that turned out not to be members. In particular, these cluster spirals do not show any significant luminosity evolution as might be expected from certain clusterspecific phenomena. Contrary to that, the other half of the cluster sample with disturbed kinematics also shows a higher degree of structural assymetries on average indicating ongoing or recent interaction processes.
Context: The morphology of massive star formation in the central regions of galaxies is an important tracer of the dynamical processes that govern the evolution of disk, bulge, and nuclear activity. Aims: We present optical imaging of the central regions of a sample of 73 spiral galaxies in the H alpha line and in optical broad bands, and derive information on the morphology of massive star formation. Methods: We obtained images with the William Herschel Telescope, mostly at a spatial resolution of below one second of arc. For most galaxies, no H alpha imaging is available in the literature. We outline the observing and data reduction procedures, list basic properties, and present the I-band and continuum-subtracted H alpha images. We classify the morphology of the nuclear and circumnuclear H alpha emission and explore trends with host galaxy parameters. Results: We confirm that late-type galaxies have a patchy circumnuclear appearance in H alpha, and that nuclear rings occur primarily in spiral types Sa-Sbc. We identify a number of previously unknown nuclear rings, and confirm that nuclear rings are predominantly hosted by barred galaxies. Conclusions: Other than in stimulating nuclear rings, bars do not influence the relative strength of the nuclear H alpha peak, nor the circumnuclear H alpha morphology. Even though our selection criteria led to an over-abundance of galaxies with close massive companions, we do not find any significant influence of the presence or absence of a close companion on the relative strength of the nuclear H alpha peak, nor on the H alpha morphology around the nucleus.
We introduce our project on galaxy evolution in the environment of rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of galaxies in the field. Emphasis is laid on the examination of the internal kinematics of disk galaxies through spatially resolved MOS spectroscopy with FORS at the VLT. First results are presented for the clusters MS1008.1-1224 (z=0.30), Cl0303+1706 (z=0.42), and Cl0413-6559 (F1557.19TC) (z=0.51). Out of 30 cluster members with emission-lines, 13 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing over into a flat part. The other members have either intrinsically peculiar kinematics (4), or too strong geometric distortions (9) or too low S/N (4 galaxies) for a reliable classification of their velocity profiles. The 13 cluster galaxies for which a maximum rotation velocity could be derived are distributed in the Tully--Fisher diagram very similar to field galaxies from the FORS Deep Field that have corresponding redshifts and do not show any significant luminosity evolution with respect to local samples. The same is true for seven galaxies observed in the cluster fields that turned out not to be members. The mass-to-light ratios of the 13 TF cluster spirals cover the same range as the distant field population indicating that their stellar populations were not dramatically changed by possible clusterspecific interaction phenomena. The cluster members with distorted kinematics may be subject to interaction processes but it is impossible to determine whether these processes also lead to changes in the overall luminosity of their stellar populations.
We present our project on galaxy evolution in the environment of distant rich clusters aiming at disentangling the importance of specific interaction and galaxy transformation processes from the hierarchical evolution of field galaxies. Spatially resolved MOS spectra were gained with VLT/FORS to analyze the internal kinematics of disk galaxies. First results are shown for the clusters MS 1008.1-1224 (z=0.30), Cl 0303+1706 (z=0.42), and Cl 0413-6559 (z=0.51). Out of 35 late type cluster members, 13 galaxies exhibit a rotation curve of the universal form rising in the inner region and passing over into a flat part. The other members have peculiar kinematics. The 13 cluster galaxies for which a maximum rotation velocity could be derived are distributed in the Tully-Fisher diagram very similar to field galaxies from the FORS Deep Field with corresponding redshifts. The same is true for seven non-cluster galaxies observed in the cluster fields. The TF-cluster spirals do not show any significant luminosity evolution as might be expected from certain clusterspecific phenomena. Contrary to that, the disturbed kinematics of the non--TF cluster spirals indicate ongoing or recent interaction processes.
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