arXiv subjects

Simon P. Driver

Publications and source records attributed to Simon P. Driver.

At least 181 records · Page 10Linked to original sources

arXiv2004

The 2dF Galaxy Redshift Survey: Spherical Harmonics analysis of fluctuations in the final catalogue

We present the result of a decomposition of the 2dFGRS galaxy overdensity field into an orthonormal basis of spherical harmonics and spherical Bessel functions. Galaxies are expected to directly follow the bulk motion of the density field on large scales, so the absolute amplitude of the observed large-scale redshift-space distortions caused by this motion is expected to be independent of galaxy properties. By splitting the overdensity field into radial and angular components, we linearly model the observed distortion and obtain the cosmological constraint Omega_m^{0.6} sigma_8=0.46+/-0.06. The amplitude of the linear redshift-space distortions relative to the galaxy overdensity field is dependent on galaxy properties and, for L_* galaxies at redshift z=0, we measure beta(L_*,0)=0.58+/-0.08, and the amplitude of the overdensity fluctuations b(L_*,0) sigma_8=0.79+/-0.03, marginalising over the power spectrum shape parameters. Assuming a fixed power spectrum shape consistent with the full Fourier analysis produces very similar parameter constraints.

astro-ph↗

arXiv2004

The dwarf galaxy population in Abell 2218

We present results from a deep photometric study of the rich galaxy cluster Abell 2218 (z=0.18) based on archival HST WFPC2 F606W images. These have been used to derive the luminosity function to extremely faint limits (M_{F606W}=-13.2 mag, mu_{0}=24.7 mag arcsec^{-2}) over a wide field of view (1.3 h^{-2} Mpc^2). We find the faint-end slope of the luminosity function to vary with environment within the cluster, going from alpha=-1.23\pm0.13 within the projected central core of the cluster (100 < r < 300 h^{-1} kpc) to alpha=-1.49\pm 0.06 outside this radius (300 < r < 750 h^{-1} kpc). We infer that the core is 'dwarf depleted', and further quantify this by studying the ratio of 'dwarf' to 'giant' galaxies and its dependency as a function of cluster-centric radius and local galaxy density. We find that this ratio varies strongly with both quantities, and that the dwarf galaxy population in A2218 has a more extended distribution than the giant galaxy population.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: Clustering properties of radio galaxies

The clustering properties of local, S_{1.4 GHz} > 1 mJy, radio sources are investigated for a sample of 820 objects drawn from the joint use of the FIRST and 2dF Galaxy Redshift surveys. To this aim, we present 271 new bj < 19.45 spectroscopic counterparts of FIRST radio sources to be added to those already introduced in Magliocchetti et al. (2002). The two-point correlation function for the local radio population is found to be entirely consistent with estimates obtained for the whole sample of 2dFGRS galaxies. We estimate the parameters of the real-space correlation function xi(r)=(r/r_0)^{-γ}, r_0=6.7^{+0.9}_{-1.1} Mpc and γ=1.6\pm 0.1, where h=0.7 is assumed. Different results are instead obtained if we only consider sources that present signatures of AGN activity in their spectra. These objects are shown to be very strongly correlated, with r_0=10.9^{+1.0}_{-1.2} Mpc and γ=2\pm 0.1, a steeper slope than has been claimed in other recent works. No difference is found in the clustering properties of radio-AGNs of different radio luminosity. These results show that AGN-fuelled sources reside in dark matter halos more massive than \sim 10^{13.4} M_{\sun}},higher the corresponding figure for radio-quiet QSOs. This value can be converted into a minimum black hole mass associated with radio-loud, AGN-fuelled objects of M_{BH}^{min}\sim 10^9 M_{\sun}. The above results then suggest -at least for relatively faint radio objects -the existence of a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud AGNs; however, once the activity is triggered, there appears to be no evidence for a connection between black hole mass and level of radio output. (abridged)

astro-ph↗

arXiv2004

Galaxy ecology: groups and low-density environments in the SDSS and 2dFGRS

We analyse the observed correlation between galaxy environment and H-alpha emission line strength, using volume-limited samples and group catalogues of 24968 galaxies drawn from the 2dF Galaxy Redshift Survey (Mb<-19.5) and the Sloan Digital Sky Survey (Mr<-20.6). We characterise the environment by 1) Sigma_5, the surface number density of galaxies determined by the projected distance to the 5th nearest neighbour; and 2) rho1.1 and rho5.5, three-dimensional density estimates obtained by convolving the galaxy distribution with Gaussian kernels of dispersion 1.1 Mpc and 5.5 Mpc, respectively. We find that star-forming and quiescent galaxies form two distinct populations, as characterised by their H-alpha equivalent width, EW(Ha). The relative numbers of star-forming and quiescent galaxies varies strongly and continuously with local density. However, the distribution of EW(Ha) amongst the star-forming population is independent of environment. The fraction of star-forming galaxies shows strong sensitivity to the density on large scales, rho5.5, which is likely independent of the trend with local density, rho1.1. We use two differently-selected group catalogues to demonstrate that the correlation with galaxy density is approximately independent of group velocity dispersion, for sigma=200-1000 km/s. Even in the lowest density environments, no more than ~70 per cent of galaxies show significant H-alpha emission. Based on these results, we conclude that the present-day correlation between star formation rate and environment is a result of short-timescale mechanisms that take place preferentially at high redshift, such as starbursts induced by galaxy-galaxy interactions.

astro-ph↗

arXiv2003

The 2dF Galaxy Redshift Survey: Wiener Reconstruction of the Cosmic Web

We reconstruct the underlying density field of the 2 degree Field Galaxy Redshift Survey (2dFGRS) for the redshift range 0.035<z<0.200 using the Wiener Filtering method. The Wiener Filter suppresses shot noise and accounts for selection and incompleteness effects. The method relies on prior knowledge of the 2dF power spectrum of fluctuations and the combination of matter density and bias parameters however the results are only slightly affected by changes to these parameters. We present maps of the density field in two different resolutions: 5 Mpc/h and 10 Mpc/h. We identify all major superclusters and voids in the survey. In particular, we find two large superclusters and two large local voids. A version of this paper with full set of colour maps can be found at http://www.ast.cam.ac.uk/~pirin.

astro-ph↗

arXiv2003

The 2dF Galaxy Redshift Survey: Final Data Release

The 2dF Galaxy Redshift Survey (2dFGRS) has obtained spectra for 245591 sources, mainly galaxies, brighter than a nominal extinction-corrected magnitude limit of b_J=19.45. Reliable redshifts were measured for 221414 galaxies. The galaxies are selected from the extended APM Galaxy Survey and cover an area of approximately 1500 square degrees in three regions: an NGP strip, an SGP strip and random fields scattered around the SGP strip. This paper describes the 2dFGRS final data release of 30 June 2003 and complements Colless et al. (2001), which described the survey and the initial 100k data release. The 2dFGRS database and full documentation are available on the WWW at http://www.mso.anu.edu.au/2dFGRS/

astro-ph↗

arXiv2003

The Hubble Space Telescope WFPC2 B-Band Parallel Survey: A Study of Galaxy Morphology for 18 < B < 27 mag

[Abridged] We present the results of the HST B-Band Parallel Survey (BBPS). It covers 0.0370 sq. deg. and consists of 31 shallow (4-6 orbit), randomly selected high latitude HST WFPC2 parallel fields with images taken in both the B (F450W) and I (F814W) filters. The goal is to morphologically classify the galaxies in a homogeneous manner and study galaxy properties as a function of type and B-band magnitude for 18<b_J<23.5 mag. The B-band selected galaxies are classified using an artificial neural network (ANN) galaxy classifier on the higher S/N I-band images. These provide reliable types for I<24 mag (or b_J<26 mag), since these I-band classifications are less subject to the uncertain redshifted rest-frame UV morphology. The ANN classification depends on the shape of the surface brightness profile, but not on color. These results are combined with deeper studies in the HDF-N and the deep WFPC2 field surrounding the radio galaxy 53W002, for which galaxies have been classified to b_J<27 mag. The galaxy counts for the combined B-band selected samples show adequate statistics for a range 19<b_J<27 mag, and are in good agreement with other studies in the flux range where they overlap, while showing improved statistics at the bright end. The galaxies are divided into 3 morphological classes: E/S0, Sabc and Sd/Irr, and the B-band counts are presented for each class, as well as the total counts. The faint end of the counts is dominated by the Sd/Irr galaxies. These type dependent counts are compared to models based on local luminosity functions which include the effects of the Cosmological Constant. The BBPS sample, along with the two deeper fields, is used to delineate the general trends of effective radius and (B-I) color as a function of both morphological type and apparent magnitude 18<b_J<27 mag.

astro-ph↗

arXiv2002

The Global, Local and Cluster Galaxy Luminosity Function

We review selected measurements of the galaxy luminosity function including the global field, the local group, the local sphere, nearby clusters (Virgo, Coma and Fornax) and clusters in general. We conclude that the overall cluster luminosity function is consistent with the global luminosity function over the magnitude range in common (-22 < M_B -5logh_0.68 < -17). We find that only in the core regions of clusters (r < 300 kpc) does the overall form of the luminosity function show significant variation. However when the luminosity function is subdivided by spectral type some further variations are seen. We argue that these results imply: substantial late infall, efficient star-formation suppression, and the confinement of mass-changing evolutionary processes to the core regions only.

astro-ph↗

arXiv2002

Parameter constraints for flat cosmologies from CMB and 2dFGRS power spectra

We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega_m, which arises mainly from preserving the location of the peaks in the angular power spectrum. This `horizon-angle degeneracy' is considered in some detail and shown to follow a simple relation Omega_m h^{3.4} = constant. Adding the 2dFGRS power spectrum constrains Omega_m h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant h=0.665 +/- 0.047, the matter density Omega_m=0.313 +/- 0.055, and the physical CDM and baryon densities Omega_c h^2 = 0.115 +/- 0.009, Omega_b h^2 = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set a upper limit to the tensor-to-scalar ratio of r<0.7 at 95% confidence. We then show how these data can be used to constrain the equation of state of the vacuum, and find w<-0.52 at 95% confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/~wjp/

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: The amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing

We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey and by the latest measurements of the Cosmic Microwave Background anisotropies. By combining the 2dFGRS and CMB data we find the linear-theory rms mass fluctuations in 8 Mpc/h spheres to be sigma_8 = 0.73 +-0.05 (after marginalization over the matter density parameter Omega_m and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L_s = 1.9L_* APM-selected galaxies to be b(L_s,z=0) = 1.10 +- 0.08 on comoving scales of 0.02 < k < 0.15 h/Mpc. If luminosity segregation operates on these scales, L_* galaxies would be almost un-biased, b(L_*,z=0) = 0.96. These results are derived by assuming a flat Lambda-CDM Universe, and by marginalizing over other free parameters and fixing the spectral index n=1 and the optical depth due to reionization tau=0. We also study the best fit pair (Omega_m,b), and the robustness of the results to varying n and tau. Various modelling corrections can each change the resulting b by 5-15 per cent. The results are compared with other independent measurements from the 2dFGRS itself, and from the SDSS, cluster abundance and cosmic shear.

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: The Number and Luminosity Density of Galaxies

We present the bivariate brightness distribution (BBD) for the 2dF Galaxy Redshift Survey (2dFGRS) based on a preliminary subsample of 45,000 galaxies. The BBD is an extension of the galaxy luminosity function incorporating surface brightness information. It allows the measurement of the local luminosity density, j_B, and the galaxy luminosity and surface brightness distributions while accounting for surface brightness selection biases. The recovered 2dFGRS BBD shows a strong surface brightness-luminosity relation (M_B~2.4μ_e). The luminosity-density is dominated by normal galaxies and the luminosity-density peak lies away from the selection boundaries implying that the 2dFGRS is complete and that luminous low surface brightness galaxies are rare. The final value we derive for the local luminosity-density, inclusive of surface brightness corrections, is: j_B=2.49+/-0.20x10^8 h L_solar Mpc^-3. Representative Schechter function parameters are: M*=-19.75+/-0.05, phi*=2.02+/-0.02x10^-2 and alpha=-1.09+/-0.03. Extending the conventional methodology to incorporate surface brightness selection effects has resulted in an increase in the luminosity-density of 37%.

astro-ph↗

arXiv2002

Constraints on the [Omega_Matter-Omega_Lambda]-plane from Elliptical Galaxy Counts ?

Here we present a pilot study into whether elliptical galaxy counts alone, can place a useful constraint on the Omega_M - Omega_Lambda-plane. The elliptical galaxy counts are drawn from three surveys: The Millennium Galaxy Catalogue (16 > B_KPNO > 20), the B-band Parallel Survey (20 > B_AB >24) and the Hubble Deep Fields (23 > B_AB > 28). The elliptical luminosity function used in the modeling was derived from a combination of the Millennium Galaxy Catalogue, the two-degree field galaxy redshift survey and the Sloan Digital Sky Survey (M_*=-19.90, phi_*=0.0019/Mpc^3 and alpha =-0.75 for H_o=75km/s/Mpc). We adopt a benchmark model and tweak the various input parameters by their uncertainties to determine the impact upon the counts. We find that IF the faint-end slope of the elliptical galaxy luminosity function is known to better than 0.1$, then over the magnitude range 16 < B < 23 the counts depend most critically upon the cosmology, and can be used to place a weak constraint on the [Omega_Matter-Omega_Lambda]-plane.

astro-ph↗

arXiv2001

The Bivariate Brightness Function of Galaxies and a Demonstration of the Impact of Surface Brightness Selection Effects on Luminosity Function Estimations

In this paper we fit an analytic function to the Bivariate Brightness Distribution (BBD) of galaxies. It is a combination of the classical Schechter Function convolved with a Gaussian distribution in surface brightness: thus incorporating the luminosity-surface brightness correlation as seen in many recent datasets. We fit this function to a recent measurement of the BBD based on 45,000 galaxies from the two-degree field Galaxy Redshift Survey (Cross et al. 2001). Using a BBF we explore the impact of the limiting detection isophote on classical measures of the galaxy luminosity distribution. If Gaussian corrected magnitudes are used these change to $ΔM^*_{b_j} \sim 0.38 $ mags, $Δϕ^* \sim 11%$ and $Δα< 0.01$ for $μ_{lim,b_j}=24.0$ mag arcsec$^{-2}$. Hence while the faint-end slope, $α$, appears fairly robust to surface brightness issues, both the $M^*$ and $ϕ^*$ values are highly dependent. The range over which these parameters were seen to vary is fully consistent with the scatter in the published values, reproducing the range of observed luminosity densities ($1.1<j_{b_j}<2.2\times10^8h L_{\odot}$Mpc$^{-3}$ see Cross et al. 2001). We conclude that surface brightness selection effects are primarily responsible for this variation. After due consideration of these effects, we derive a value of $j_{b_j}=2.16\times10^8h L_{\odot}$Mpc$^{-3}$.

astro-ph↗

arXiv2001

Evidence for a non-zero Lambda and a low matter density from a combined analysis of the 2dF Galaxy Redshift Survey and Cosmic Microwave Background Anisotropies

We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n_s and n_t. On its own, the 2dFGRS sets tight limits on the parameter combination Omega_m h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega_b/Omega_m. The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a `geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons and cold dark matter. Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a pm 2sigma range of 0.65 < Omega_Lambda < 0.85, completely independently of constraints on Omega_Λderived from Type Ia supernovae.

astro-ph↗

arXiv2001

The nature of the dwarf population in Abell 868

We present the results of a study of the morphology of the dwarf galaxy population in Abell 868, a rich, intermediate redshift (z=0.154) cluster which has a galaxy luminosity function with a steep faint-end slope (alpha=-1.26 +/- 0.05). A statistical background subtraction method is employed to study the B-R colour distribution of the cluster galaxies. This distribution suggests that the galaxies contributing to the faint-end of the measured cluster LF can be split into three populations: dIrrs with B-R<1.4; dEs with 1.4 2.5. The remvoal of the contribution of the background gEs from the counts only marginally lessens the faint-end slope (alpha=-1.22 +/- 0.16). However, the removal of the contribution of the dIrrs from the counts produces a flat LF (alpha=-0.91 +/- 0.16). The dEs and the dIrrs have similar spatial distributions within the cluster except that the dIrrs appear to be totally absent within a central projected radius of about 0.2 Mpc (Ho=75 km/s /Mpc). The number density of both dEs and dIrrs appear to fall off beyond a projected radius of about 0.35 Mpc. We suggest that the dE and dIrr populations of A868 have been associated with the cluster for similar timescales but that evolutionary processes such as `galaxy harassment' tend to fade the dIrr galaxies while having much less effect on the dE galaxies. The harassement would be expected to have the greatest effect on dwarfs residing in the central parts of the cluster.

astro-ph↗

arXiv2001

The 2dF Galaxy Redshift Survey: The power spectrum and the matter content of the universe

The 2dF Galaxy Redshift Survey has now measured in excess of 160000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct FFT-based technique. We argue that, within the k-space region 0.02<k<0.15 h Mpc^-1, the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analyzed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68% confidence limits on the total matter density times the Hubble parameter Ω_m h = 0.20 +/- 0.03, and the baryon fraction Ω_b/Ω_m = 0.15 +/- 0.07, assuming scale-invariant primordial fluctuations.

astro-ph↗

arXiv2000

The Parameter Space Occupied by Galaxies: The Optical Window

We discuss the optical parameter space (luminosity and surface brightness) over which galaxies are known to exist and report on the results from three recent datasets: the Two-degree Field Galaxy Redshift Survey, the Hubble Deep Field north, and the Local Group. These data are combined to provide a unique and comprehensive insight into the luminosity distribution of galaxies over the range -24 < M(B) < -8 mags, and the surface brightness distribution over the range 18 < SB(Effective) < 28 mags/sq arcsec. The main conclusions are: (1) luminous low surface brightness galaxies are rare; (2) there exists a universal luminosity-surface brightness relation; (3) the most numerous galaxies are low luminosity low surface brightness dwarfs.

astro-ph↗

arXiv1999

The Ccontribution of normal, dim and dwarf galaxies to the local luminosity density

From the Hubble Deep Field catalog presented in Driver et al. (1998) we derive the local (0.3 < z < 0.5) Bivariate Brightness Distribution (BBD) of field galaxies within a 326 Mpc**3 Volume-Limited sample. The sample contains 47 galaxies which uniformally sample the underlying galaxy population within the specified redshift, magnitude and surface brightness limits (0.3 < z < 0.5, -21.3 < M_{B} < -13.7 mags, 18.0 < mu_{B} < 24.55 mags/sq arcsec). We conclude: (i) A luminosity-surface brightness relation exists for both the field and cluster galaxy populations, M_{B} ~ 1.5 mu_{e} - 50, (ii) Luminous low surface brightness galaxies account for <10% of the L* population, (iii) Low luminosity low surface brightness galaxies outnumber Hubble types by a factor of ~ 1.4, however their space density is NOT sufficient to explain the faint blue excess either by themselves or as faded remnants. In terms of the local luminosity density and galaxy dynamical mass budget, normal galaxies (i.e. Hubble tuning fork) contribute 88% and 72% respectively. This compares to 7% and 12% for dim galaxies and 5% and 16% for dwarf galaxies (within the above specified limits).

astro-ph↗