The Dawes Review 1: Kinematic studies of star-forming galaxies across cosmic time

The last seven years have seen an explosion in the number of Integral Field galaxy surveys, obtaining resolved 2D spectroscopy, especially at high-redshift. These have taken advantage of the mature capabilities of 8-10 m class telescopes and the development of associated technology such as AO. Surveys have leveraged both high spectroscopic resolution enabling internal velocity measurements and high spatial resolution from AO techniques and sites with excellent natural seeing. For the first time, we have been able to glimpse the kinematic state of matter in young, assembling star-forming galaxies and learn detailed astrophysical information about the physical processes and compare their kinematic scaling relations with those in the local Universe. Observers have measured disc galaxy rotation, merger signatures, and turbulence-enhanced velocity dispersions of gas-rich discs. Theorists have interpreted kinematic signatures of galaxies in a variety of ways (rotation, merging, outflows, and feedback) and attempted to discuss evolution vs. theoretical models and relate it to the evolution in galaxy morphology. A key point that has emerged from this activity is that substantial fractions of high-redshift galaxies have regular kinematic morphologies despite irregular photometric morphologies and this is likely due to the presence of a large number of highly gas-rich discs. There has not yet been a review of this burgeoning topic. In this first Dawes review, I will discuss the extensive kinematic surveys that have been done and the physical models that have arisen for young galaxies at high-redshift.Comment: 51 pages, 34,000 words, 16 figures. A few minor corrections have been made to the journal version. High-resolution PDF and iPad optimised ePUB versions available from http://astronomy.swin.edu.au/karl/dawe

Future prospects in observational galaxy evolution: towards increased resolution

Future prospects in observational galaxy evolution are reviewed from a personal perspective. New insights will especially come from high-redshift integral field kinematic data and similar low-redshift observations in very large and definitive surveys. We will start to systematically probe the mass structures of galaxies and their haloes via lensing from new imaging surveys and upcoming near-IR spectroscopic surveys will finally obtain large numbers of rest frame optical spectra at high-redshift routinely. ALMA will be an important new ingredient, spatially resolving the molecular gas fuelling the high star-formation rates seen in the early Universe.Comment: 8 pages, 2 figures, Proceedings IAU Symposium No. 295, Beijing, 2013, eds. D. Thomas, A. Pasquali & I. Ferrera

Microslit Nod-shuffle Spectroscopy - a technique for achieving very high densities of spectra

We describe a new approach to obtaining very high surface densities of optical spectra in astronomical observations with extremely accurate subtraction of night sky emission. The observing technique requires that the telescope is nodded rapidly between targets and adjacent sky positions; object and sky spectra are recorded on adjacent regions of a low-noise CCD through charge shuffling. This permits the use of extremely high densities of small slit apertures (`microslits') since an extended slit is not required for sky interpolation. The overall multi-object advantage of this technique is as large as 2.9x that of conventional multi-slit observing for an instrument configuration which has an underfilled CCD detector and is always >1.5 for high target densities. The `nod-shuffle' technique has been practically implemented at the Anglo-Australian Telescope as the `LDSS++ project' and achieves sky-subtraction accuracies as good as 0.04%, with even better performance possible. This is a factor of ten better than is routinely achieved with long-slits. LDSS++ has been used in various observational modes, which we describe, and for a wide variety of astronomical projects. The nod-shuffle approach should be of great benefit to most spectroscopic (e.g. long-slit, fiber, integral field) methods and would allow much deeper spectroscopy on very large telescopes (10m or greater) than is currently possible. Finally we discuss the prospects of using nod-shuffle to pursue extremely long spectroscopic exposures (many days) and of mimicking nod-shuffle observations with infrared arrays.Comment: Accepted for publication in PASP; 25 pages, 12 figures. A higher-quality compressed Postscript file (2.2Mb) is available from http://www.pha.jhu.edu/~kgb/papers/nodshuffle2000hq.ps.g

An infrared study of galaxy evolution

This thesis describes a large -area 2μm survey undertaken on the U.K. Infrared Telescope in Hawaii, using a new infrared imaging camera. The survey covers 5940' and is complete and uniform to a limit of K = 17. The main aim of the survey was to construct a sample of galaxies, selected by their 2μm flux, for studies of galaxy evolution. The subsidiary aim was to survey the 2μm Universe and search for any new populations of infrared objects, such as protogalaxies and brown dwarf stars.The first half of this thesis is concerned with the analysis of astronomical data. The detailed methods for constructing the infrared survey are described, including flatfielding, astrometry, mosaicing and photometry. Also described are optical CCD observations which cover the survey area to provide optical- infrared colours of almost all the objects in the sample. The methods of reducing, calibrating and matching the CCD data with the infrared data are detailed. For the study of galaxy evolution the redshifts of 53 K band selected galaxies, with a well defined completeness, were measured using multiple object spectrographs. The reduction of the spectra and the methods used for securing the redshifts, including the cross -correlation technique, are described.The second half of this thesis is about the scientific results from this survey. Firstly, it appears that no new large populations of objects appear, in particular there appear to be no objects only detected in K. A few extremely red objects objects are found, however their true nature is unclear in the absence of spectra. The best evidence is that a few of them are very cool stars. Secondly the galaxy population appears to have very red R -K colours, although not necessarily so red in B - K, and the K band number -magnitude counts exhibit a much smaller excess over the no- evolution prediction than do the B band optical counts. The K band counts are consistent with only a small amount of luminosity evolution.It is possible to reconcile the B counts, K counts, and the colours of the galaxies, by introducing a model of galaxy merging in which galaxy numbers per unit volume are no longer conserved with lookback time. This model naturally predicts the surprisingly low redshifts found by other workers in B band selected redshift surveys. This model also predicts that the mean redshift of a K selected survey should be less than the no- evolution prediction. This is indeed found - the redshift distribution for the sample studied here is less than the no- evolution model at the 5% significance level.Finally the limitations of this survey are reviewed, and the prospects for future deep infrared and spectroscopic surveys discussed

Angular Momentum Regulates Atomic Gas Fractions of Galactic Disks

We show that the mass fraction f_atm = 1.35*MHI/M of neutral atomic gas (HI and He) in isolated local disk galaxies of baryonic mass M is well described by a straightforward stability model for flat exponential disks. In the outer disk parts, where gas at the characteristic dispersion of the warm neutral medium is stable in the sense of Toomre (1964), the disk consists of neutral atomic gas; conversely the inner part where this medium would be Toomre-unstable, is dominated by stars and molecules. Within this model, f_atm only depends on a global stability parameter q=j*sigma/(GM), where j is the baryonic specific angular momentum of the disk and sigma the velocity dispersion of the atomic gas. The analytically derived first-order solution f_atm = min{1,2.5q^1.12} provides a good fit to all plausible rotation curves. This model, with no free parameters, agrees remarkably well (+-0.2 dex) with measurements of f_atm in isolated local disk galaxies, even with galaxies that are extremely HI-rich or HI-poor for their mass. The finding that f_atm increases monotonically with q for pure stability reasons offers a powerful intuitive explanation for the mean variation of f_atm with M: in a cold dark matter universe galaxies are expected to follow j~M^(2/3), which implies the average scaling q~M^(-1/3) and hence f_atm~M^(-0.37), in agreement with observations.Comment: 5 pages, 3 figure