Showing papers by "Carlton M. Baugh published in 1998"

The Epoch of Galaxy Formation

Abstract: We use a semianalytic model of galaxy formation in hierarchical clustering theories to interpret recent data on galaxy formation and evolution, focusing primarily on the recently discovered population of Lyman-break galaxies at z 3. For a variety of cold dark matter (CDM) cosmologies, we construct mock galaxy catalogs subject to selection criteria identical to those applied to the real data. We find that the expected number of Lyman-break galaxies is very sensitive to the assumed stellar initial mass function and to the normalization of the primordial power spectrum. For reasonable choices of these and other model parameters, it is possible to reproduce the observed abundance of Lyman-break galaxies in CDM models with ?0 = 1 and ?0 < 1. The characteristic masses, circular velocities, and star formation rates of the model Lyman-break galaxies depend somewhat on the values of the cosmological parameters, but are broadly in agreement with available data. These galaxies generally form from rare peaks at high redshift, and as a result their spatial distribution is strongly biased, with a typical bias parameter of b 4 and a comoving correlation length of r0 4 h-1 Mpc. The typical sizes of these galaxies, ~0.5 h-1 kpc, are substantially smaller than those of present-day bright galaxies. In combination with data at lower redshifts, the Lyman-break galaxies can be used to trace the cosmic star formation history. We compare theoretical predictions for this history with a compilation of recent data. The observational data match the theoretical predictions reasonably well, both for the distribution of star formation rates at various redshifts and for the integrated star formation rate as a function of redshift. Most galaxies (in our models and in the data) never experience star formation rates in excess of a few solar masses per year. Our models predict that even at z = 5, the integrated star formation rate is similar to that measured locally, although less than 1% of all the stars have formed prior to this redshift. The weak dependence of the predicted star formation histories on cosmological parameters allows us to propose a fairly general interpretation of the significance of the Lyman-break galaxies as the first galaxy-sized objects that experience significant amounts of star formation. These galaxies mark the onset of the epoch of galaxy formation that continues into the present day. The basic ingredients of a consistent picture of galaxy formation may well now be in place.

The K-band Hubble diagram for the brightest cluster galaxies: a test of hierarchical galaxy formation models

Abstract: We analyse the K-band Hubble diagram for a sample of brightest cluster galax-ies (BCGs) in the redshift range 0 < z < 1 In good agreement with earlier stud-ies, we confirm that the scatter in the absolute magnitudes of the galaxies is small(03magnitudes) The BCGs exhibit very little luminosity evolution in this redshiftrange: if q 0 = 00 we detect no luminosity evolution; for q 0 = 05 we measure a smallnegative evolution (ie, BCGs were about 05magnitudes fainter at z = 1 than to-day) If the mass in stars of these galaxies had remained constant over this periodof time, substantial positive luminosity evolution would be expected: BCGs shouldhave been brighter in the past since their stars were younger A likely explanationfor the observed zero or negative evolution is that the stellar mass of the BCGs hasbeen assembled over time through merging and accretion, as expected in hierarchi-cal models of galaxy formation The colour evolution of the BCGs is consistent withthat of an old stellar population (z

The seeds of rich galaxy clusters in the Universe

Abstract: The discovery1 of a population of young galaxies at a redshift when the Universe was about a tenth of its current age has shed new light on the question of when and how galaxies formed. Within the context of popular models2, this is the population of primeval galaxies that built themselves up to the size of present-day galaxies through the process of repeated mergers called hierarchical clustering. But the recent detection3 of a large concentration of these primeval galaxies appears to be incompatible with hierarchical clustering models, which generally predict that clusters of this size are fully formed later in time. Here we use a combination of theoretical techniques — semi-analytic modelling and n-body simulations — to show that such large concentrations should be quite common in a universe dominated by cold dark matter, and that they are the progenitors of the rich galaxy clusters seen today. We predict the clustering properties of primeval galaxies which should, when compared with data that will be collected in the near future, test our current understanding of galaxy formation within the framework of a universe dominated by cold dark matter.

Testing deprojection algorithms on mock angular catalogues: evidence for a break in the power spectrum

Abstract: We produce mock angular catalogues from simulations with different initial power spectra to test methods that recover measures of clustering in three dimensions, such as the power spectrum, variance and higher order cumulants. We find that the statistical properties derived from the angular mock catalogues are in good agreement with the intrinsic clustering in the simulations. In particular, we concentrate on the detailed predictions for the shape of the power spectrum, P (k). We find that there is good evidence for a break in the galaxy P (k) at scales between 0.02 < k < 0.06 hMpc using an inversion technique applied to the angular correlation function measured from the APM Galaxy Survey. For variants on the standard Cold Dark Matter model, a fit at the location of the break implies Ωh = 0.45 ± 0.10, where Ω is the ratio of the total matter density to the critical density and Hubble’s constant is parameterised as H0 = 100 hkm s Mpc. On slightly smaller, though still quasi-linear scales, there is a feature in the APM power spectrum where the local slope changes appreciably, with the best match to CDM models obtained for Ωh ≃ 0.2. Hence the location and narrowness of the break in the APM power spectrum combined with the rapid change in its slope on quasi-linear scales cannot be matched by any variant of CDM, including models that have a non-zero cosmological constant or a tilt to the slope of the primordial P (k). These results are independent of the overall normalization of the CDM models or any simple bias that exists between the galaxy and mass distributions.

Early type galaxies in the hierarchical universe

Abstract: Any realistic theory of galaxy formation must be set in the context of a model for the formation of structure in the universe. We describe a powerful approach -- semi-analytic modelling -- that combines a set of simple rules describing the gas processes involved in galaxy formation with a scheme to follow the hierarchical growth of dark matter haloes. Surprisingly few free parameters are required to specify the model, and these are fixed with reference to a subset of local observational data. The model produces the full star formation history of a galaxy, allowing a wide range of predictions to be made. We review some of the successes of the models, namely the star formation history of the universe and the evolution of galaxy clustering, before focusing our attention on early-type galaxies. We discuss the observational evidence against the classical picture in which early-type galaxies form at some arbitrarily high redshift in a single monolithic collapse and burst of star formation. The alternative scenario in which spheroidal systems are formed by the merger of disk galaxies is outlined. We review some of the predictions of this model, namely the colour-magnitude relation, the faint counts and the evolution of cluster membership.

Hybrid galaxy formation

Abstract: We model the two-point correlation function of galaxies in a cold dark matter Universe by combining two powerful theoretical tools - dissipationless N-body simulations of dark matter clustering (specifically the GIF simulations carried out by MPIA and the Virgo Consortium) and semi-analytic modelling of galaxy formation. We construct catalogues of galaxies containing a wide range of information for each galaxy, including magnitudes in various bands, star formation rates, disk and bulge sizes (from the semi-analytic model described by Cole et al 1998) and, importantly, spatial positions and peculiar velocities from the N-body simulation. We then use this information to study the clustering properties of galaxies.

Semi-analytical galaxy formation models and the high redshift universe

Abstract: Semi-analytical models of galaxy formation based on hierarchical clustering now make a wide range of predictions for observable properties of galaxies at low and high redshift. This article concentrates on 2 aspects: (1) Self-consistent modelling of dust absorption predicts a mean UV extinction A_{UV} ~ 1 mag, depending only weakly on redshift, and similar to observational estimates. (2) The models predict that the Lyman-break galaxies found at z ~ 3 should be strongly clustered with a comoving correlation length r_0 = 4-7 Mpc/h (depending on the cosmology), in good agreement with subsequent observational determinations.

The seeds of rich galaxy clusters in the Universe

Abstract: The discovery of a population of young galaxies at an epoch when the universe was about one tenth of its current age has shed new light on the question of when and how galaxies formed. Within the context of popular models this is the population of primeval galaxies that built themselves up to the size of present--day galaxies through the process of repeated mergers. But the recent detection of a large concentration of these primeval galaxies (Steidel et al. 1997) appears to be incompatible with hierarchical clustering models, which generally predict that clusters of this size are fully formed later in time. Here we use a combination of two powerful theoretical techniques --semi-analytic modelling and N-body simulations-- to show that such large concentrations should be quite common in a universe dominated by cold dark matter, and that they are the progenitors of the rich galaxy clusters seen today. We predict the clustering properties of primeval galaxies which should, when compared with data that will be collected in the near future, test our understanding of galaxy formation within the framework of a universe dominated by cold dark matter.

The Durham/UKST Galaxy Redshift Survey - VI. Power spectrum analysis of clustering

Abstract: We present the power spectrum analysis of clustering in the Durham/UKST Galaxy Redshift Survey, which covers 1450 square degrees and consists of 2501 galaxy redshifts sampled at a rate of 1 in 3 to b_J = 17. The fluctuations that we measure can be expressed as sigma_{8} = 1.01 +/- 0.17 . We find remarkably good agreement between the power spectrum measured for the Durham/UKST Survey and those from other optical studies, in spite of the very different sampling rates, magnitude limits and survey geometries employed, on scales up to lambda = (2 pi)/k = 80/h Mpc. On scales larger than this we find good agreement with the power measured from the Stromlo-APM Survey (Tadros & Efstathiou), but find more power than estimated from the Las Campanas Redshift Survey (Lin et al). We apply a simple model for redshift space distortions to the real space APM Galaxy Survey power spectrum and find a shape and amplitude that is in very good agreement with the power spectrum of the Durham/UKST Survey. This implies beta=Omega^{0.6}/b=0.60 +/- 0.35, where Omega is the density parameter and b is the bias between fluctuations in the galaxy and mass distributions, and also suggests a one dimensional velocity dispersion of sigma = 320 +/-140 km/s. We find that for any choice of normalisation, the standard CDM model has a shape that cannot be reconciled with the Durham/UKST Survey power spectrum, unless either unacceptably high values of the one dimensional velocity dispersion are adopted or the assumption that bias is constant is invalid on scales greater than 20/h Mpc. Over the range of wavenumbers for which we have a robust measurement of the power spectrum, we find the best agreement is obtained for a critical density CDM model in which the shape of the power spectrum is modified. (Abridged)

Semianalytic modelling of the formation and evolution of galaxies

Abstract: The high redshift observations of galaxies now becoming available from the Hubble Space Telescope and from large ground based telescopes are opening fresh windows on galaxy formation. Semianalytic models of galaxy formation provide us with a powerful tool to interpret and understand these exciting new data. In this review, we explain the philosophy behind this class of model and outline some of their remarkable successes, focussing our attention on the formation of elliptical galaxies and on the properties of galaxies at high redshift. Now that the recent discovery of star forming galaxies at z=3 has made possible the construction of the cosmic star formation history, which is in good agreement with our model predictions, it appears that a coherent, broadbrush picture of galaxy formation is beginning to emerge.

Semianalytic modelling of the formation and evolution of galaxies

Abstract: The high redshift observations of galaxies now becoming available from the Hubble Space Telescope and from large ground based telescopes are opening fresh windows on galaxy formation. Semianalytic models of galaxy formation provide us with a powerful tool to interpret and understand these exciting new data. In this review, we explain the philosophy behind this class of model and outline some of their remarkable successes, focussing our attention on the formation of elliptical galaxies and on the properties of galaxies at high redshift. Now that the recent discovery of star forming galaxies at z � 4 has made possible the construction of the cosmic star formation history, which is in good agreement with our model predictions, it appears that a coherent picture of galaxy formation is beginning to emerge.