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Resolved kinematic work at significant redshifts began with the commissioning of the 10-m W.M. Keck telescope, which was the first optical telescope in this aperture class. Previous 4-m telescope work had studied normal galaxies to redshifts z~ 1 using multi-slit spectrographs — examples include the LDSS2 redshift survey (Glazebrook et al. 1995a) and the Canada France Hawaii Redshift Survey (Lilly et al. 1995), but had only attempted integrated spectroscopy due to signal:noise limitations. Early Keck work focussed on integrated velocity dispersions (Koo et al. 1995, Forbes et al. 1996) using the optical line width in a manner similar to early radio HI line widths. Trends were found of this velocity dispersion with luminosity which was interpreted by Forbes et al. as echoing the local Tully-Fisher relationship (with the large scatter being due to the much broader sample selection and crudity of the method) and by Koo et al. as representing galaxies which might 'fade' to become local low-luminosity spheroids.

The first resolved long-slit work at significant redshift, i.e. constructing true rotation curves, was done by Nicole Vogt et al. (Vogt et al. 1996) again using the Keck telescope. Galaxy rotation curves, with signatures of a turnover towards flatness at large radii, were measured to radii ~ 2 arcsec for galaxies at 0.1 < z < 1 in 0.8-0.95 arcsec seeing. An important finding was that high-redshift galaxies have similar rotation curves to low-redshift counterparts and that 'some massive discs were in place by z ~ 1', the first harbinger of the modern picture and in tension with the Ωm = 1 flat CDM cosmology favoured at the time. Vogt et al. found evidence for a Tully-Fisher relationship with only mild evolution.

A key problem in these early studies, and one that remains with us today, is the limited spatial resolution compared to the scale of the objects being studied. In our current cosmology, 1 arcsec corresponds to 6.2-8.5 kpc for 0.5 < z < 4. Given a typical spiral disc today has an exponential scale length of only 1-5 kpc (Freeman 1970a) it can be seen that these high-redshift discs were only marginally resolved in good natural seeing (0.5-1 arcsec). However, the situation is tractable as the exponential is a soft profile detectable to several scale lengths. Because of this, an important development in kinematic modelling was the use of maximum likelihood techniques to fit kinematic models convolved with the observational Point Spread Function (PSF).

Vogt herself pioneered this technique in her 1996 paper. Another similar approach was that of Simard & Pritchet (1998), who applied this to star-forming galaxies at z ~ 0.3 observed with the Canda-France Hawaii Telescope (CFHT) to derive a Tully-Fisher relationship. Important conclusions from these early works (that echo later results) were (i) at least some star-forming galaxies at these redshifts displayed clear rotation, (ii) significant fractions (25% in Simard & Pritchet 1998) do not and are 'kinematically anomalous', (iii) rotating galaxies appear to follow a Tully-Fisher relationship, (iv) the existence of very compact star-forming galaxies at intermediate redshifts, (v) the Tully-Fisher relationship displays significantly increased scatter compared to the local relation, and (vi) disagreement as to whether the zeropoint of the Tully-Fisher relationship evolves or not. Note that these early works used a relatively low spectral resolution and could not measure the internal velocity dispersions in the galaxy discs. As we will see at the end of this review the evolution (or not) of the Tully-Fisher relationship zeropoint is still a matter of debate.

Later, long-slit work built on these. For redshifts z ≲ 1, there was work by Ziegler et al. (2002) and Böhm et al. (2004) who found evidence for 'mass dependent' evolution in the Tully-Fisher relationship (in the B-band, little evolution for more massive galaxies, up to 2 mags in brightening for the fainter galaxies) using the Very Large Telescope (VLT) and the FORS2 spectrograph to study 113 galaxies. Again, spectral resolution was low (σ ≃ 100 km s-1). It is interesting to note that the fraction of anomalous galaxies was ~ 30% in these papers though that excited negligible comment. Conselice et al. (2005) was the first to look at the stellar mass Tully-Fisher relationship at significant redshift using a sample with near-IR photometry and found no evidence for an evolution of the relation from now to z > 0.7.

At higher redshifts (z > 2), the earliest kinematic work with long slits focussed on the kinematic follow-up of the so-called 'Lyman Break galaxies' (LBGs). These are ultraviolet (UV)-selected star-forming galaxies first characterised by Steidel et al. (1996) at z ~ 3. At these redshifts, the galaxies are observed to have low flux (i.e. 'dropouts') in the U-band from neutral hydrogen absorption bluewards of the Lyman limit together with blue colours (i.e. nearly constant fν flux) in redder filters. Pettini et al. (1998) and Pettini et al. (2001) presented near-IR spectra of 15 z ~ 3 LBGs. Integrated velocity dispersions were measured from [OII], [OIII] and Hβ emission lines but found to have no correlation with optical or UV continuum properties. In two cases, resolved velocity shear (i.e. tilted emission lines) were detected, but Pettini et al. could not conclude if these were rotating discs.

The UV selection technique has subsequently been pushed to lower redshifts (Steidel et al. 2004) (1.5 < z < 2.5) where the galaxies do have U-band flux and selection relies on them being bluer in their U-band to optical colours than lower redshift galaxies. It is important to note that UV selection does not pick out all galaxies at these redshifts — in particular it can miss out massive quiescent galaxies (e.g. Cimatti et al. 2004, McCarthy et al. 2004, van Dokkum et al. 2004) and populations of dusty star-forming galaxies (Yan et al. 2004) which are picked out by red/near-IR colour/magnitude selections (see review on high-redshift red galaxies of McCarthy (2004); an excellent recent review of physical properties and selection techniques of high-redshift galaxies is given by Shapley (2011). Erb et al. (2006b) performed near-IR long-slit spectroscopy of 114 z ~ 2 UV-selected galaxies in the Hα emission line. In most cases, resolved information was not measurable and only total line widths were measured. Very little correlation was found between these integrated velocity dispersions, or derived dynamical masses, and stellar mass. A stronger correlation was found between dispersion and rest-frame V luminosity though with a lot of scatter (factors of 3-4 in dispersion at a given luminosity). In 14 cases (some due to exceptional seeing), resolved velocity shear was measurable and even displayed flat rotation curve tops; the dispersion was well correlated with the rotation velocity suggesting that rotation was the primary contribution to the line widths. Erb et al. also inferred from their sample's star-formation rate densities that they were gas rich (mean gas fraction ~ 50%) an important point to which I will return later. Finally, I note that they found that their sub-sample with shear tended to be the galaxies with older stellar population ages and larger stellar masses leading to the (in hindsight) quite prescient conclusion that 'the rotation of mature, dynamically relaxed galaxies is a more important contribution to our observed shear than merging, which should not have a preference for older, more massive galaxies'.

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