arXiv subjects

S. Maddox

Publications and source records attributed to S. Maddox.

At least 91 records · Page 5Linked to original sources

arXiv2009

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 510 square degrees of the extragalactic sky, four times larger than all the other Herschel surveys combined, in five far-infrared and submillimetre bands. We describe the survey, the complementary multi-wavelength datasets that will be combined with the Herschel data, and the six major science programmes we are undertaking. Using new models based on a previous submillimetre survey of galaxies, we present predictions of the properties of the ATLAS sources in other wavebands.

astro-ph.CO↗

arXiv2009

Accounting for the Foreground Contribution to the Dust Emission towards Kepler's Supernova Remnant

Whether or not supernovae contribute significantly to the overall dust budget is a controversial subject. Submillimetre (submm) observations, sensitive to cold dust, have shown an excess at 450 and 850 microns in young remnants Cassiopeia A (Cas A) and Kepler. Some of the submm emission from Cas A has been shown to be contaminated by unrelated material along the line of sight. In this paper we explore the emission from material towards Kepler using submm continuum imaging and spectroscopic observations of atomic and molecular gas, via HI, 12CO (J=2-1) and 13CO (J=2-1). We detect weak CO emission (peak TA* = 0.2-1K, 1-2km/s fwhm) from diffuse, optically thin gas at the locations of some of the submm clumps. The contribution to the submm emission from foreground molecular and atomic clouds is negligible. The revised dust mass for Kepler's remnant is 0.1--1.2 solar masses, about half of the quoted values in the original study by Morgan et al. (2003), but still sufficient to explain the origin of dust at high redshifts.

astro-ph.GA↗

arXiv2009

The star-formation history of K-selected galaxies

We have studied the uJy radio properties of K-selected galaxies detected in the Ultra-Deep Survey portion of UKIDSS using 610- and 1,400-MHz images from the VLA and GMRT. These deep radio mosaics, combined with the largest and deepest K image currently available, allow high-S/N detections of many K-selected sub-populations, including sBzK and pBzK star-forming and passive galaxies. We find a strong correlation between the radio and K fluxes and a linear relationship between SFR and K luminosity. We find no evidence, from either radio spectral indices or a comparison with submm-derived SFRs, that the full sample is strongly contaminated by AGN. The sBzK and pBzK galaxies have similar levels of radio flux, SFR and specific SFR (SSFR) at z < 1.4, suggesting there is strong contamination of the pBzK sample by star-forming galaxies. At z > 1.4, pBzK galaxies become difficult to detect in the radio stack, though the implied SFRs are still much higher than expected for passively evolving galaxies. Their radio emission may come from low-luminosity AGN. EROs straddle the passive and star-forming regions of the BzK diagram and also straddle the two groups in terms of their radio properties. K-bright ERO samples are dominated by passive galaxies and faint ERO samples contain more star-forming galaxies. The star-formation history (SFH) from stacking all K sources in the UDS agrees well with that derived for other wavebands and other radio surveys, at least out to z ~ 2. The radio-derived SFH then appears to fall more steeply than that measured at other wavelengths. The SSFR for K-selected sources rises strongly with redshift at all stellar masses, and shows a weak dependence on stellar mass. High- and low-mass galaxies show a similar decline in SSFR since z ~ 2 (abridged).

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arXiv2008

The clustering and abundance of star-forming and passive galaxies at $z \sim 2$

We use the UKIDSS Ultra-deep survey (UDS), currently the deepest panoramic near infra-red survey, together with deep Subaru optical imaging to measure the clustering, number counts and luminosity function of galaxies at $z\sim 2$ selected using the BzK selection technique. We find that both star-forming (sBzK) and passive (pBzK) galaxies, to a magnitude limit of $K_{AB} < 23$, are strongly clustered. The passive galaxies are the most strongly clustered population, with scale lengths of $r_0 = 15.0^{+1.9}_{-2.2}$h$^{-1}$Mpc compared with $r_0 = 6.75^{+0.34}_{-0.37}$h$^{-1}$Mpc for star-forming galaxies. The direct implication is that passive galaxies inhabit the most massive dark-matter halos, and are thus identified as the progenitors of the most massive galaxies at the present day. In addition, the pBzKs exhibit a sharp flattening and potential turn-over in their number counts, in agreement with other recent studies. This plateau cannot be explained by the effects of incompleteness. We conclude that only very massive galaxies are undergoing passive evolution at this early epoch, consistent with the downsizing scenario for galaxy evolution. Assuming a purely passive evolution for the pBzKs from their median redshift to the present day, their luminosity function suggests that only $\sim 2.5 %$ of present day massive ellipticals had a pBzK as a main progenitor.

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arXiv2006

An imaging survey of a uniform sample of Brightest Cluster Galaxies and Intracluster Light

We present deep, large area B and r' imaging for a sample of 49 brightest cluster galaxies (BCGs). The clusters were selected by their x-ray luminosity and redshift to form two volume limited samples, one with mean redshift ~ 0.07 and one at a mean redshift ~ 0.17. For each cluster the data cover 41' by 41'. We discuss our data reduction techniques in detail, and show that we can reliably measure the surface brightness at the levels of mu_B ~ 29 and mu_r' ~ 28. For each galaxy we present the B and r' images together with the surface brightness profile, B-r' colour, eccentricity and position angle as a function of radius. We investigate the distribution of positional offsets between the optical centroid of the BCG and the centre of the X-ray emission, and conclude that the mass profiles are cuspy, and do not have extended cores. We also introduce a method to objectively identify the transition from BCG to extended envelope of intra-cluster light, using the Petrosian index as a function of radius.

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arXiv2005

The 2dF Galaxy Redshift Survey: Power-spectrum analysis of the final dataset and cosmological implications

We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct Fourier method. The sample used comprises 221,414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys which are used to demonstrate that the input cosmological model can be correctly recovered. We are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the `baryon oscillations' that are predicted in CDM models. Fitting to a CDM model, assuming a primordial $n_{s}=1$ spectrum, $h=0.72$ and negligible neutrino mass, the preferred parameters are $Ω_{M} h = 0.168 \pm 0.016$ and a baryon fraction $Ω_{b} /Ω_{M} = 0.185\pm0.046$ (1$σ$ errors). The value of $Ω_{M} h$ is $1σ$ lower than the $0.20 \pm 0.03$ in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly-sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard $Ω_{M} =0.3$: in combination with CMB data from WMAP, we infer $Ω_{M} =0.231\pm 0.021$. (Abridged.)

astro-ph↗

arXiv2005

The 2dF Galaxy Redshift Survey: luminosity functions by density environment and galaxy type

We use the 2dF Galaxy Redshift Survey to measure the dependence of the bJ-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h-1Mpc, and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M_bJ-5log10h <-18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M_bJ-5log10h < -21. Differences in the mid to faint-end population between environments are significant: at M_bJ-5log10h=-18 early and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion which differs strikingly for early and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: voids and hierarchical scaling models

We measure the redshift space reduced void probability function (VPF) for 2dFGRS volume limited galaxy samples covering the absolute magnitude range M_bJ-5logh=-18 to -22. Theoretically, the VPF connects the distribution of voids to the moments of galaxy clustering of all orders, and can be used to discriminate clustering models in the weakly non-linear regime. The reduced VPF measured from the 2dFGRS is in excellent agreement with the paradigm of hierarchical scaling of the galaxy clustering moments. The accuracy of our measurement is such that we can rule out, at a very high significance, popular models for galaxy clustering, including the lognormal distribution. We demonstrate that the negative binomial model gives a very good approximation to the 2dFGRS data over a wide range of scales, out to at least 20h-1Mpc. Conversely, the reduced VPF for dark matter in a LambdaCDM universe does appear to be lognormal on small scales but deviates significantly beyond \approx 4h-1Mpc. We find little dependence of the 2dFGRS reduced VPF on galaxy luminosity. Our results hold independently in both the north and south Galactic pole survey regions.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: higher order galaxy correlation functions

We measure moments of the galaxy count probability distribution function in the two-degree field galaxy redshift survey (2dFGRS). The survey is divided into volume limited subsamples in order to examine the dependence of the higher order clustering on galaxy luminosity. We demonstrate the hierarchical scaling of the averaged p-point galaxy correlation functions, xibar_p, up to p=6. The hierarchical amplitudes, S_p = xibar_p/xibar_2^{p-1}, are approximately independent of the cell radius used to smooth the galaxy distribution on small to medium scales. On larger scales we find the higher order moments can be strongly affected by the presence of rare, massive superstructures in the galaxy distribution. The skewness S_3 has a weak dependence on luminosity, approximated by a linear dependence on log luminosity. We discuss the implications of our results for simple models of linear and non-linear bias that relate the galaxy distribution to the underlying mass.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: The clustering of galaxy groups

We measure the clustering of galaxy groups in the 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue. The 2PIGG sample has 29,000 groups with at least two members. The clustering amplitude of the full 2PIGG catalogue is weaker than that of 2dFGRS galaxies, in agreement with theoretical predictions. We have subdivided the 2PIGG catalogue into samples that span a factor of 25 in median total luminosity. Our correlation function measurements span an unprecedented range of clustering strengths, connecting the regimes probed by groups fainter than L* galaxies and rich clusters. There is a steady increase in clustering strength with group luminosity; the most luminous groups are ten times more strongly clustered than the full 2PIGG catalogue. We demonstrate that the 2PIGG results are in very good agreement with the clustering of groups expected in the LCDM model.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: Hierarchical galaxy clustering

We use the two-degree field Galaxy Redshift Survey (2dFGRS) to test the hierarchical scaling hypothesis: namely, that the $p$-point galaxy correlation functions can be written in terms of the two point correlation function or variance. This scaling is expected if an initially Gaussian distribution of density fluctuations evolves under the action of gravitational instability. We measure the volume averaged $p$-point correlation functions using a counts in cells technique applied to a volume limited sample of 44,931 $L_*$ galaxies. We demonstrate that $L_{*}$ galaxies display hierarchical clustering up to order $p=6$ in redshift space. The variance measured for $L_{*}$ galaxies is in excellent agreement with the predictions from a $Λ$-cold dark matter N-body simulation. This applies to all cell radii considered, $0.3<(R/h^{-1}{\rm Mpc})<30$. However, the higher order correlation functions of $L_*$ galaxies have a significantly smaller amplitude than is predicted for the dark matter for $R<10h^{-1}$Mpc. This disagreement implies that a non-linear bias exists between the dark matter and $L_*$ galaxies on these scales. We also show that the presence of two rare, massive superclusters in the 2dFGRS has an impact on the higher-order clustering moments measured on large scales.

astro-ph↗

arXiv2004

The nature of the relative bias between galaxies of different spectral type in 2dFGRS

We present an analysis of the relative bias between early- and late-type galaxies in the Two-degree Field Galaxy Redshift Survey (2dFGRS). Our analysis examines the joint counts in cells between early- and late-type galaxies, using approximately cubical cells with sides ranging from 7h^{-1}Mpc to 42h^{-1}Mpc. We measure the variance of the counts in cells using the method of Efstathiou et al. (1990), which we find requires a correction for a finite volume effect. We fit lognormal models to the one-point density distribution and develop methods of dealing with biases in the recovered variances resulting from this technique. We directly fit deterministic models for the joint density distribution function, f(delta_E,delta_L), to the joint counts in cells using a maximum likelihood technique. Our results are consistent with a scale invariant relative bias factor on all scales studied. Linear bias is ruled out on scales less than l=28h^{-1}Mpc. A power-law bias model is a significantly better fit to the data on all but the largest scales studied; the relative goodness of fit of this model as compared to that of the linear bias model suggests that any nonlinearity is negligible for l>~40h^{-1}Mpc, consistent with the expectation from theory that the bias should become linear on large scales. (abridged)

astro-ph↗

arXiv2004

Galaxy groups in the 2dFGRS: the group-finding algorithm and the 2PIGG catalogue

The construction of a catalogue of galaxy groups from the 2-degree Field Galaxy Redshift Survey (2dFGRS) is described. Groups are identified by means of a friends-of-friends percolation algorithm which has been thoroughly tested on mock versions of the 2dFGRS generated from cosmological N-body simulations. The tests suggest that the algorithm groups all galaxies that it should be grouping, with an additional 40% of interlopers. About 55% of the ~190000 galaxies considered are placed into groups containing at least two members of which ~29000 are found. Of these, ~7000 contain at least four galaxies, and these groups have a median redshift of 0.11 and a median velocity dispersion of 260km/s. This 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue represents the largest available homogeneous sample of galaxy groups. It is publicly available on the WWW.

astro-ph↗

arXiv2004

Galaxy groups in the 2dFGRS: the luminous content of the groups

The 2dFGRS Percolation-Inferred Galaxy Group (2PIGG) catalogue of ~29000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. A Schechter function is found to be a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data. The characteristic luminosity L* is larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. The variation of halo mass-to-light ratio with group size is studied in both these wavebands. A robust trend of increasing M/L with increasing group luminosity is found in the 2PIGG data. From groups with L_bj=10^{10}Lsol to those 100 times more luminous, the typical bj-band M/L increases by a factor of 5, whereas the rf-band M/L grows by a factor of 3.5. These trends agree well with the simulations, which also predict a minimum M/L on a scale corresponding to the Local Group. Our data indicate that if such a minimum exists, then it must occur at L<~10^{10}Lsol, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bj M/Ls of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data yields an estimate of Omega_m=0.26+/-0.03 (statistical).

astro-ph↗

arXiv2004

The Luminosity-Metallicity relation in the local universe from the 2dF Galaxy Redshift Survey

We investigate the Luminosity-Metallicity (L-Z) relation in the local universe (z < 0.15) using spectra of 6387 star-forming galaxies extracted from the 2dF Galaxy Redshift Survey. This sample is by far the largest to date used to perform such a study. We distinguish star-forming galaxies from AGNs using "standard" diagnostic diagrams to build a homogeneous sample of starburst galaxies for the L-Z study. We propose new diagnostic diagrams using "blue" emission lines ([OII]3727, [OIII]5007 and Hbeta) only to discriminate starbursts from AGNs in intermediate-redshift (z > 0.3) galaxies. Oxygen-to-hydrogen (O/H) abundance ratios are estimated using the "strong-line" method, which relates the strength of bright emission lines (parameters R23 and O32) to O/H. We confirm the existence of the luminosity-metallicity relation over a large range of abundances (~ 2 dex) and luminosities (~ 9 magnitudes). We find a linear relation between the gas-phase oxygen abundance and both the "raw" and extinction-corrected absolute B-band magnitude with a rms of 0.27. A similar relation, with nearly the same scatter, is found in the R band. This relation is in good agreement with the one derived by Melbourne & Salzer (2002) using the KISS data. However, our L-Z relation is much steeper than previous determinations using samples of "normal" irregular and spiral galaxies. This difference seems to be primarily due to the choice of the galaxy sample used to investigate the L-Z relation rather than any systematic error affecting the O/H determination. We anticipate that this luminosity-metallicity relation will be used as the local "reference" for future studies of the evolution with cosmic time of fundamental galaxy scaling relations. (Abridged version).

astro-ph↗

arXiv2003

The 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the Universe

We present a detailed analysis of the two-point correlation function, from the 2dF Galaxy Redshift Survey (2dFGRS). We estimate the redshift-space correlation function, xi(s), from which we measure the redshift-space clustering length, s_0=6.82+/-0.28 Mpc/h. We also estimate the projected correlation function, Xi(sigma), and the real-space correlation function, xi(r), which can be fit by a power-law, with r_0=5.05+/-0.26Mpc/h, gamma_r=1.67+/-0.03. For r>20Mpc/h, xi drops below a power-law as is expected in the popular LCDM model. The ratio of amplitudes of the real and redshift-space correlation functions on scales of 8-30Mpc/h gives an estimate of the redshift-space distortion parameter beta. The quadrupole moment of xi on scales 30-40Mpc/h provides another estimate of beta. We also estimate the distribution function of pairwise peculiar velocities, f(v), including rigorously the effect of infall velocities, and find that it is well fit by an exponential. The accuracy of our xi measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of xi(r) and the two redshift-space distortion effects parameterized by beta and velocity dispersion, a. We find beta=0.49+/-0.09 and a=506+/-52km/s, though the best fit values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(sigma), and find that the shape is consistent with models and simulations. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that beta(L=L*,z=0)=0.47+/-0.08, and that the present day matter density of the Universe is 0.3, consistent with other 2dFGRS estimates and independent analyses.

astro-ph↗

arXiv2003

The 2dF Galaxy Redshift Survey: galaxy clustering per spectral type

We have calculated the two-point correlation functions in redshift space, xi(sigma,pi), for galaxies of different spectral types in the 2dF Galaxy Redshift Survey. Using these correlation functions we are able to estimate values of the linear redshift-space distortion parameter, beta = Omega_m^0.6/b, the pairwise velocity dispersion, a, and the real-space correlation function, xi(r), for galaxies with both relatively low star-formation rates (for which the present rate of star formation is less than 10% of its past averaged value) and galaxies with higher current star-formation activity. At small separations, the real-space clustering of passive galaxies is very much stronger than that of the more actively star-forming galaxies; the correlation-function slopes are respectively 1.93 and 1.50, and the relative bias between the two classes is a declining function of radius. On scales larger than 10 h^-1 Mpc there is evidence that the relative bias tends to a constant, b(passive)/b(active) ~ 1. This result is consistent with the similar degrees of redshift-space distortions seen in the correlation functions of the two classes -- the contours of xi(sigma,pi) require beta(active)=0.49+/-0.13, and beta(passive)=0.48+/-0.14. The pairwise velocity dispersion is highly correlated with beta. However, despite this a significant difference is seen between the two classes. Over the range 8-20 h^-1 Mpc, the pairwise velocity dispersion has mean values 416+/-76 km/s and 612+/-92 km/s for the active and passive galaxy samples respectively. This is consistent with the expectation from morphological segregation, in which passively evolving galaxies preferentially inhabit the cores of high-mass virialised regions.

astro-ph↗

arXiv2002

The 2dF Galaxy Redshift Survey: the luminosity function of cluster galaxies

We have determined the composite luminosity function (LF) for galaxies in 60 clusters from the 2dF Galaxy Redshift Survey. The LF spans the range $-22.5<M_{b_{\rm J}}<-15$, and is well-fitted by a Schechter function with ${M_{b_{\rm J}}}^{*}=-20.07\pm0.07$ and $α=-1.28\pm0.03$ ($H_0$=100 km s$^{-1}$ Mpc$^{-1}$, $Ω_M$=0.3, $Ω_Λ$=0.7). It differs significantly from the field LF of \cite{mad02}, having a characteristic magnitude that is approximately 0.3 mag brighter and a faint-end slope that is approximately 0.1 steeper. There is no evidence for variations in the LF across a wide range of cluster properties. However the LF of early-type galaxies in clusters is both brighter and steeper than its field counterpart. The differences between the field and cluster LFs for the various spectral types can be qualitatively explained by the suppression of star formation in the dense cluster environment, together with mergers to produce the brightest early-type galaxies.

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