arXiv subjects

S. J. Maddox

Publications and source records attributed to S. J. Maddox.

At least 55 records · Page 3Linked to original sources

arXiv2010

Evolution of the Far-Infrared-Radio Correlation and Infrared SEDs of Massive Galaxies over z = 0 - 2

We investigate the far-infrared-radio correlation (FRC) of stellar-mass-selected galaxies in the Extended Chandra Deep Field South using far-infrared imaging from Spitzer and radio imaging from the Very Large Array and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe galaxies below the noise and confusion limits. Radio fluxes are K-corrected using observed flux ratios, leading to tentative evidence for an evolution in spectral index. We compare spectral energy distribution (SED) templates of local galaxies for K-correcting FIR fluxes, and show that the data are best fit by a quiescent spiral template (M51) rather than a warm starburst (M82) or ULIRG (Arp220), implying a predominance of cold dust in massive galaxies at high redshift. In contrast we measure total infrared luminosities that are consistent with high star-formation rates. We observe that the FRC index (q) does not evolve significantly over z=0-2 when computed from K-corrected 24 or 160-mum photometry, but that using 70-mum fluxes leads to an apparent decline in q beyond z~1. This suggests some change in the SED at high redshift, either a steepening of the spectrum at rest-frame ~25-35mum or a deficiency at ~70mum leading to a drop in the total infrared/radio ratios. We compare our results to other work in the literature and find synergies with recent findings on the high-redshift FRC, high specific star-formation rates of massive galaxies and the cold dust temperatures in these galaxies.

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arXiv2010

Herschel ATLAS: The angular correlation function of submillimetre galaxies at high and low redshift

We present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 micron-selected sample we detect no significant clustering, consistent with the expectation that the 250 micron-selected sources are mostly normal galaxies at z<~ 1. For our 350 micron and 500 micron-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z~2-3 we detect significant strong clustering, leading to an estimate of r_0 ~ 7-11 h^{-1} Mpc. The slope of our clustering measurements is very steep, delta~2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.

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arXiv2009

Cassiopeia A: dust factory revealed via submillimetre polarimetry

If Type-II supernovae - the evolutionary end points of short-lived, massive stars - produce a significant quantity of dust (>0.1 M_sun) then they can explain the rest-frame far-infrared emission seen in galaxies and quasars in the first Gyr of the Universe. Submillimetre observations of the Galactic supernova remnant, Cas A, provided the first observational evidence for the formation of significant quantities of dust in Type-II supernovae. In this paper we present new data which show that the submm emission from Cas A is polarised at a level significantly higher than that of its synchrotron emission. The orientation is consistent with that of the magnetic field in Cas A, implying that the polarised submm emission is associated with the remnant. No known mechanism would vary the synchrotron polarisation in this way and so we attribute the excess polarised submm flux to cold dust within the remnant, providing fresh evidence that cosmic dust can form rapidly. This is supported by the presence of both polarised and unpolarised dust emission in the north of the remnant, where there is no contamination from foreground molecular clouds. The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which, coupled with the brief timescale available for grain alignment (<300 yr), suggests that supernova dust differs from that seen in other Galactic sources (where f_pol=2-7%), or that a highly efficient grain alignment process must operate in the environment of a supernova remnant.

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arXiv2005

The [OII]/Halpha ratio of emission line galaxies in the 2dF redshift survey

We investigate the systematic variation of the [OII]3727/Halpha flux line ratio as a function of various galaxy properties, i.e., luminosity, metallicity, reddening, and excitation state, for a sample of 1124 emission-line galaxies, with a mean redshift z ~ 0.06, drawn from the Two Degree Field Galaxy Redshift Survey. The mean observed and extinction-corrected emission-line flux ratios agree well with the values derived from the $B$-band selected Nearby Field Galaxy Survey galaxy sample, but are significantly different from the values obtained from the Halpha-selected Universidad Complutense de Madrid Survey galaxy sample. This is because the different selection criteria applied in these surveys lead to a significant difference in the mean extinction and metallicity of different samples. We use the R_{23} parameter to estimate the gas-phase oxygen abundance and find that the extinction-corrected [OII]3727/Halpha ratio depends on the oxygen abundance. For 12+log(O/H)>8.4, we confirm that the emission-line ratio decreases with increasing metallicity. We have extended the relationship further to the metal-poor regime, 12+log(O/H)< 8.4, and find that the correlation between the extinction-corrected [OII]3727/Halpha ratio and the metallicity reverses in comparison to the relationship for metal-rich galaxies. For metal-poor galaxies, in contrast with metal-rich ones, the variation of extinction-corrected [OII]3727/Halpha ratio is correlated with the ionization states of the interstellar gas.

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arXiv2004

Spectro-photometric and Weak Lensing Survey of a Supercluster and Typical Field Region -- I. Spectroscopic Redshift Measurements

We present results from a spectroscopic study of ~4000 galaxies in a 6.2 square degree field in the direction of the Aquarius supercluster and a smaller typical field region in Cetus, down to R<19.5. Galaxy redshifts were measured using the Two Degree Field system on the Anglo-Australian Telescope, and form part of our wider efforts to conduct a spectro-photometric and weak gravitational lensing study of these regions. At the magnitude limit of the survey, we are capable of probing L_* galaxies out to z~0.4. We construct median spectra as a function of various survey parameters as a diagnostic of the quality of the sample. We use the redshift data to identify galaxy clusters and groups within the survey volume. In the Aquarius region, we find a total of 48 clusters and groups, of which 26 are previously unknown systems, and in Cetus we find 14 clusters and groups, of which 12 are new. We estimate centroid redshifts and velocity dispersions for all these systems. In the Aquarius region, we see a superposition of two strong superclusters at z=0.08 and z=0.11, which both have estimated masses and overdensities similar to the Corona Borealis supercluster.

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arXiv2003

Weak Gravitational Lensing by a Sample of X-ray Luminous Clusters of Galaxies -- III. Serendipitous Weak Lensing Detections of Dark and Luminous Mass Concentrations

In the course of a weak gravitational lensing survey of 39 clusters of galaxies,covering a total sky area of ~1 square degree, we have serendipitously discovered mass concentrations in the fields of A1705 and A1722 which are most probably not associated with the main cluster target. By combining weak lensing information with two-color galaxy photometry in fields centered on our sample clusters, we identify a new cluster candidate at z~0.5 in the field of A1705. This cluster candidate also displays strong lensing in the form of a giant luminous arc. The new mass concentration in the field of A1722 also seems to be associated with an optically luminous cluster of galaxies at z~0.5, but in this case there is some evidence for additional structures along the line of sight that may contribute to the lensing signal. A third cluster, A959, has a dark sub-clump which shows interesting morphological evidence in the mass map for being associated with the main cluster. This is the first case where there is any significant evidence for a physical association between a dark sub-clump (discovered from weak lensing) and a normal cluster. Analysis of archival X-ray data shows that the three new mass concentrations are not firmly detected in X-rays and that they are X-ray underluminous.

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arXiv2002

Surface brightness measurements for APM galaxies

This paper considers some simple surface brightness (SB) estimates for galaxies in the Automated Plate Measuring Machine (APM) catalogue in order to derive homogeneous SB data for a very large sample of faint galaxies. The isophotal magnitude and area are used to estimate the central surface brightness and total magnitude based on the assumption of an exponential SB profile. The surface brightness measurements are corrected for field effects on each UK Schmidt plate and the zero-point of each plate is adjusted to give a uniform sample of SB and total magnitude estimates over the whole survey. Results are obtained for 2.4 million galaxies with blue photographic magnitudes brighter than b_J = 20.5 covering 4300 deg^2 in the region of the south galactic cap. Almost all galaxies in our sample have central surface brightness in the range 20 to 24 b_J mag per arcsec^2. The SB measurements we obtain are compared to previous SB measurements and we find an acceptable level of error of +/- 0.2 b_J mag per arcsec^2. The distribution of SB profiles is considered for different galaxy morphologies for the bright APM galaxies. We find that early-type galaxies have more centrally concentrated profiles.

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arXiv2002

The Ha luminosity function and star formation rate up to z~1

We describe ISAAC/ESO-VLT observations of the Ha(6563) Balmer line of 33 field galaxies from the Canada-France Redshift Survey (CFRS) with redshifts selected between 0.5 and 1.1. We detect Ha in emission in 30 galaxies and compare the properties of this sample with the low-redshift sample of CFRS galaxies at z~0.2 (Tresse & Maddox 1998). We find that the Ha luminosity, L(Ha), is tightly correlated to M(B(AB)) in the same way for both the low- and high-redshift samples. L(Ha) is also correlated to L([OII]3727), and again the relation appears to be similar at low and high redshifts. The ratio L([OII])/L(Ha) decreases for brighter galaxies by as much as a factor 2 on average. Derived from the Ha luminosity function, the comoving Ha luminosity density increases by a factor 12 from =0.2 to =1.3. Our results confirm a strong rise of the star formation rate (SFR) at z<1.3, proportional to (1+z)^{4.1+/-0.3} (with H_0=50 km/s/Mpc, q_0=0.5). We find an average SFR(2800 Ang)/SFR(Ha) ratio of 3.2 using the Kennicutt (1998) SFR transformations. This corresponds to the dust correction that is required to make the near UV data consistent with the reddening-corrected Ha data within the self-contained, I-selected CFRS sample.

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arXiv2002

No Periodicities in 2dF Redshift Survey Data

We have used the publicly available data from the 2dF Galaxy Redshift Survey and the 2dF QSO Redshift Survey to test the hypothesis that there is a periodicity in the redshift distribution of quasi-stellar objects (QSOs) found projected close to foreground galaxies. These data provide by far the largest and most homogeneous sample for such a study, yielding 1647 QSO-galaxy pairs. There is no evidence for a periodicity at the predicted frequency in log(1+z), or at any other frequency.

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arXiv2002

Weak Gravitational Lensing by a Sample of X-Ray Luminous Clusters of Galaxies -- II. Comparison with Virial Masses

Dynamic velocity dispersion and mass estimates are given for a sample of five X-ray luminous rich clusters of galaxies at intermediate redshifts (z~0.3) drawn from a sample of 39 clusters for which we have obtained gravitational lens mass estimates. The velocity dispersions are determined from between 9 and 20 redshifts measured with the LDSS spectrograph of the William Herschel Telescope, and virial radii are determined from imaging using the UH8K mosaic CCD camera on the University of Hawaii 2.24m telescope. Including clusters with velocity dispersions taken from the literature, we have velocity dispersion estimates for 12 clusters in our gravitational lensing sample. For this sample we compare the dynamical velocity dispersion estimates with our estimates of the velocity dispersions made from gravitational lensing by fitting a singular isothermal sphere profile to the observed tangential weak lensing distortion as a function of radius. In all but two clusters, we find a good agreement between the velocity dispersion estimates based on spectroscopy and on weak lensing.

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arXiv2002

Studying large-scale structure with the 2dF Galaxy Redshift Survey

The 2dF Galaxy Redshift Survey is the first to observe more than 100,000 redshifts. This allows precise measurements of many of the key statistics of galaxy clustering, in particular redshift-space distortions and the large-scale power spectrum. This paper presents the current 2dFGRS results in these areas. Redshift-space distortions are detected with a high degree of significance, confirming the detailed Kaiser distortion from large-scale infall velocities, and measuring the distortion parameter beta equiv Omega_m^{0.6}/b = 0.43 +- 0.07. The power spectrum is measured to < 10% accuracy for k > 0.02 h Mpc^{-1}, and is well fitted by a CDM model with Omega_m h = 0.20 +- 0.03 and a baryon fraction of 0.15 +- 0.07. A joint analysis with CMB data requires Omega_m = 0.29 +- 0.05, assuming scalar fluctuations, but no priors on other parameters. Two methods are used to determine the large-scale bias parameter: an internal bispectrum analysis yields b = 1.04 +- 0.11, in very good agreement with the b = 1.10 +- 0.08 obtained from a joint 2dFGRS+CMB analysis, again assuming scalar fluctuations. These figures refer to galaxies of approximate luminosity 2L^*; luminosity dependence of clustering is detected at high significance, and is well described by b/b^* = 0.85 + 0.15(L/L^*).

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arXiv2002

The 2dF Galaxy Redshift Survey: The population of nearby radio galaxies at the 1 mJy level

We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with $S\ge 1$ mJy. 557 objects drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS cataloge within the area $9^h 48^m \simlt {\rm RA}({\rm 2000}) \simlt 14^h 32^m$ and $-2.77^\circ \simlt {\rm dec}({\rm 2000}) \simlt 2.25^\circ$, down to a magnitude limit $b_J= 19.45$. The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra. Radio galaxies (i.e. absorption systems, mainly belonging to the class of FR I sources, whose spectra may or may not show emission lines due to AGN activity) make up 63 per cent of the spectroscopic sample; they are characterized by relatively high radio-to-optical ratios, red colours and luminosities $10^{21}\simlt P_{1.4{\rm GHz}} W Hz^${-1}$ sr$^{-1}$ \simlt 10^{24}$. Actively star-forming galaxies instead contribute with 30 per cent to the total sample. These objects -- principally found at low redshifts ($z \simlt 0.1$) -- in general show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies and 4 Seyfert 1's. Analysis of the local radio luminosity function shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers $P_{1.4{\rm GHz}}\simlt 10^{20.5} W Hz$^{-1}$ sr$^{-1}$ Late-type galaxies, whose relative contribution to the RLF is found to be lower than was predicted by previous work, present a luminosity function which is compatible with the IRAS galaxy LF, and therefore plausibly constitute the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 $μ$m.

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arXiv2001

The 2dF Galaxy Redshift Survey: Spectra and redshifts

The 2dF Galaxy Redshift Survey (2dFGRS) is designed to measure redshifts for approximately 250000 galaxies. This paper describes the survey design, the spectroscopic observations, the redshift measurements and the survey database. The 2dFGRS uses the 2dF multi-fibre spectrograph on the Anglo-Australian Telescope, which is capable of observing 400 objects simultaneously over a 2-degree diameter field. The source catalogue for the survey is a revised and extended version of the APM galaxy catalogue, and the targets are galaxies with extinction-corrected magnitudes brighter than b_J=19.45. The main survey regions are two declination strips, one in the southern Galactic hemisphere spanning 80deg x 15deg around the SGP, and the other in the northern Galactic hemisphere spanning 75deg x 10deg along the celestial equator; in addition, there are 99 fields spread over the southern Galactic cap. The survey covers 2000 sq.deg and has a median depth of z=0.11. Adaptive tiling is used to give a highly uniform sampling rate of 93% over the whole survey region. Redshifts are measured from spectra covering 3600A-8000A at a two-pixel resolution of 9.0A and a median S/N of 13 per pixel. All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q>=3 redshifts are 98.4% reliable and have an rms uncertainty of 85 km/s. The overall redshift completeness for Q>=3 redshifts is 91.8%, but this varies with magnitude from 99% for the brightest galaxies to 90% for objects at the survey limit. The 2dFGRS database is available on the WWW at http://www.mso.anu.edu.au/2dFGRS

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arXiv2001

Star Formation, Metallicity and Dust Properties Derived from the SAPM Galaxy Survey Spectra

We have derived star formation rates (SFRs), gas-phase oxygen abundances and effective dust absorption optical depths for a sample of galaxies drawn from the Stromlo-APM redshift survey using the new Charlot and Longhetti (2001; CL01) models, which provide a physically consistent description of the effects of stars, gas and dust on the integrated spectra of galaxies. Our sample consists of 705 galaxies with measurements of the fluxes and equivalent widths of Halpha, [OII], and one or both of [NII] and [SII]. For a subset of the galaxies, 60 and 100 micron IRAS fluxes are available. We compare the star formation rates derived using the models with those derived using standard estimators based on the Halpha, the [OII] and the far-infrared luminosities of the galaxies. The CL01 SFR estimates agree well with those derived from the IRAS fluxes, but are typically a factor of ~3 higher than those derived from the Halpha or the [OII] fluxes, even after the usual mean attenuation correction of A_Halpha=1 mag is applied to the data. We show that the reason for this discrepancy is that the standard Halpha estimator neglects the absorption of ionizing photons by dust in HII regions and the contamination of Halpha emission by stellar absorption. We also use our sample to study variations in star formation and metallicity as a function of galaxy absolute bJ magnitude. For this sample, the star formation rate per unit bJ luminosity is independent of magnitude. The gas-phase oxygen abundance does increase with bJ luminosity, although the scatter in metallicity at fixed magnitude is large.

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arXiv2001

Optical identifications of $\sim 4000$ radio sources at the 1 mJy level

We present an analysis of the properties of optical counterparts of radio sources down to 1 mJy. Optical identifications have been obtained by matching together objects from the APM and FIRST surveys over the region $148.13^\circ\simlt {\rm RA(2000)}\simlt 218.13^\circ$, $-2.77^\circ\simlt {\rm Dec} \simlt 2.25^\circ$. Selecting radio sources down to 1 mJy, and adopting a uniform optical limit of $b_J = 21.5$ we find 3176 have a counterpart in the APM catalogue, corresponding to 13 per cent of the radio sample. For $b_J \le 20.5$ we can divide radio sources into resolved radio galaxies and stellar-like objects (principally QSO). We find the population of radio galaxies to be mainly made by early-type galaxies with very red colours ($b_J-R$ up to $\sim 4$) and a radio-to-optical ratio $10^2\simlt r\simlt 10^4$. The contribution of starbursting objects is negligible. In general QSO show $r\simgt 10^4$ and $0\simlt b_J -R \simlt 1$. On the basis of the $R$ magnitudes, we estimate the sample of radio galaxies to be complete up to $z\simeq 0.3$. We can therefore divide the whole sample of radio sources into a low-z and high-z population. The low-z one includes the objects identified as galaxies in the APM survey, the high-z one includes sources either identified as QSO or with no optical counterpart for $b_J \le 20.5$. We find that radio galaxies are strongly clustered and highly biased tracers of the underlying mass distribution. Models for the angular correlation function $w(θ)$ show good agreement with the observations if we assume a bias factor $b\simeq 2$ at $z\simeq 0.3$.

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arXiv2000

The 1-point PDF of the Initial Conditions of our Local Universe from the IRAS PSC redshift catalogue

The algorithm ZTRACE of Monaco & Efstathiou (1999) is applied to the IRAS PSCz catalogue to reconstruct the initial conditions of our local Universe with a resolution down to ~5 Mpc/h. The 1-point PDF of the reconstructed initial conditions is consistent with the assumptions that (i) IRAS galaxies trace mass on scales of ~5 Mpc/h, and (ii) the statistics of primordial density fluctuations is Gaussian. We use simulated PSCz catalogues, constructed from N-body simulations with Gaussian initial conditions, to show that local non-linear bias can cause the recovered initial PDF (assuming no bias) to be non-Gaussian. However, for plausible bias models, the distortions of the recovered PDF would be difficult to detect using the volume finely sampled by the PSCz catalogue. So, for Gaussian initial conditions, a range of bias models remain compatible with our PSCz reconstruction results.

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arXiv2000

The PSCz Catalogue

We present the catalogue, mask, redshift data and selection function for the PSCz survey of 15411 IRAS galaxies across 84% of the sky. Most of the IRAS data is taken from the Point Source Catalog, but this has been supplemented and corrected in various ways to improve the completeness and uniformity. We quantify the known imperfections in the catalogue, and we assess the overall uniformity, completeness and data quality. We find that overall the catalogue is complete and uniform to within a few percent at high latitudes and 10% at low latitudes. Ancillary information, access details, guidelines and caveats for using the catalogue are given.

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arXiv2000

The Redshift Distribution of FIRST Radio Sources at 1 mJy

We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels.We targeted 365 sources and obtained 46 redshifts (13 per cent of the sample). We find that our sample is complete in redshift measurement to R $\sim 18.6$, corresponding to $z\sim 0.2$. Early-type galaxies represent the largest subset (45 per cent) of the sample and have redshifts $0.15\la z \la 0.5$ ; late-type galaxies make up 15 per cent of the sample and have redshifts $0.05\la z \la 0.2$; starbursting galaxies are a small fraction ($\sim 6$ per cent), and are very nearby ($z\la 0.05$). Some 9 per cent of the population have Seyfert1/quasar-type spectra, all at $z\ga 0.8$, and there are 4 per cent are Seyfert2 type galaxies at intermediate redshifts ($z\sim 0.2$). Using our measurements and data from the Phoenix survey, we obtain an estimate for $N(z)$ at $S_{1.4 \rm {GHz}}\ge 1$ mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up $\la 5 $ per cent of the radio population at S $\sim 1$ mJy.

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