arXiv subjects

S. Driver

Publications and source records attributed to S. Driver.

47 records · Page 3Linked to original sources

arXiv2011

The environment and characteristics of low redshift galaxies detected by the Herschel-ATLAS

We investigate the ultraviolet and optical properties and environment of low redshift galaxies detected in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) science demonstration data. We use the Sloan Digital Sky Survey seventh release and the Galaxy And Mass Assembly database to select galaxies with r_Petro < 19.0 mag in the redshift range 0.02 < z < 0.2 and look for their submillimeter counterparts in H-ATLAS. Our results show that at low redshift, H-ATLAS detects mainly blue/star-forming galaxies with a minor contribution from red systems which are highly obscured by dust. In addition we find that the colour of a galaxy rather than the local density of its environment determines whether it is detectable by H-ATLAS. The average dust temperature of galaxies that are simultaneously detected by both PACS and SPIRE is 25K \pm 4K, independent of environment. This analysis provides a glimpse of the potential of the H-ATLAS data to investigate the submillimeter properties of galaxies in the local universe.

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arXiv2011

GAMA/H-ATLAS: The ultraviolet spectral slope and obscuration in galaxies

We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various dust obscuration measures in galaxies. We explore the connections between the ultraviolet (UV) spectral slope, $β$, the Balmer decrement, and the far infrared (IR) to $150\,$nm far ultraviolet (FUV) luminosity ratio. We explore trends with galaxy mass, star formation rate (SFR) and redshift in order to identify possible systematics in these various measures. We reiterate the finding of other authors that there is a large scatter between the Balmer decrement and the $β$ parameter, and that $β$ may be poorly constrained when derived from only two broad passbands in the UV. We also emphasise that FUV derived SFRs, corrected for dust obscuration using $β$, will be overestimated unless a modified relation between $β$ and the attenuation factor is used. Even in the optimum case, the resulting SFRs have a significant scatter, well over an order of magnitude. While there is a stronger correlation between the IR to FUV luminosity ratio and $β$ parameter than with the Balmer decrement, neither of these correlations are particularly tight, and dust corrections based on $β$ for high redshift galaxy SFRs must be treated with caution. We conclude with a description of the extent to which the different obscuration measures are consistent with each other as well as the effects of including other galactic properties on these correlations.

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arXiv2010

Which halos host Herschel-ATLAS galaxies in the local Universe?

We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies, this indicates that most of the low redshift H-ATLAS sources are hosted by halos with masses comparable to that of the Milky Way. The correlation function appears to depend on the 250 um luminosity, L_250, with bright (median luminosity νL_250 ~ 1.6 x 10^10 L_sun) objects being somewhat more strongly clustered than faint (νL_250 ~ 4.0 x 10^9 L_sun) objects. This implies that galaxies with higher dust-obscured star formation rates are hosted by more massive halos.

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arXiv2010

Galaxy and Mass Assembly (GAMA): Dust obscuration in galaxies and their recent star formation histories

We present self-consistent star formation rates derived through pan-spectral analysis of galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. We determine the most appropriate form of dust obscuration correction via application of a range of extinction laws drawn from the literature as applied to Halpha, [O{II}] and UV luminosities. These corrections are applied to a sample of 31,508 galaxies from the GAMA survey at z < 0.35. We consider several different obscuration curves, including those of Milky Way, Calzetti (2001) and Fischera and Dopita (2005) curves and their effects on the observed luminosities. At the core of this technique is the observed Balmer decrement, and we provide a prescription to apply optimal obscuration corrections using the Balmer decrement. We carry out an analysis of the star formation history (SFH) using stellar population synthesis tools to investigate the evolutionary history of our sample of galaxies as well as to understand the effects of variation in the Initial Mass Function (IMF) and the effects this has on the evolutionary history of galaxies. We find that the Fischera and Dopita (2005) obscuration curve with an R_{v} value of 4.5 gives the best agreement between the different SFR indicators. The 2200A feature needed to be removed from this curve to obtain complete consistency between all SFR indicators suggesting that this feature may not be common in the average integrated attenuation of galaxy emission. We also find that the UV dust obscuration is strongly dependent on the SFR.

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arXiv2010

The Herschel-ATLAS: Evolution of the 250um luminosity function out to z=0.5

We have determined the luminosity function of 250um-selected galaxies detected in the ~14 sq.deg science demonstration region of the Herschel-ATLAS project out to a redshift of z=0.5. Our findings very clearly show that the luminosity function evolves steadily out to this redshift. By selecting a sub-group of sources within a fixed luminosity interval where incompleteness effects are minimal, we have measured a smooth increase in the comoving 250um luminosity density out to z=0.2 where it is 3.6+1.4-0.9 times higher than the local value.

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arXiv2010

Herschel-ATLAS: Dust temperature and redshift distribution of SPIRE and PACS detected sources using submillimetre colours

We present colour-colour diagrams of detected sources in the Herschel-ATLAS Science Demonstration Field from 100 to 500 microns using both PACS and SPIRE. We fit isothermal modified black bodies to the spectral energy distribution (SED) to extract the dust temperature of sources with counterparts in Galaxy And Mass Assembly (GAMA) or SDSS surveys with either a spectroscopic or a photometric redshift. For a subsample of 330 sources detected in at least three FIR bands with a significance greater than 3 $σ$, we find an average dust temperature of $(28 \pm 8)$K. For sources with no known redshift, we populate the colour-colour diagram with a large number of SEDs generated with a broad range of dust temperatures and emissivity parameters, and compare to colours of observed sources to establish the redshift distribution of this sample. For another subsample of 1686 sources with fluxes above 35 mJy at 350 microns and detected at 250 and 500 microns with a significance greater than 3$σ$, we find an average redshift of $2.2 \pm 0.6$.

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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.

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arXiv2006

The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey

We present a spectroscopic survey of almost 15,000 candidate intermediate-redshift Luminous Red Galaxies (LRGs) brighter than i=19.8, observed with 2dF on the Anglo-Australian Telescope. The targets were selected photometrically from the Sloan Digital Sky Survey (SDSS) and lie along two narrow equatorial strips covering 180 sq deg. Reliable redshifts were obtained for 92% of the targets and the selection is very efficient: over 90% have redshifts between 0.45 and 0.8. More than 80% of the ~11,000 red galaxies have pure absorption-line spectra consistent with a passively-evolving old stellar population. The redshift, photometric and spatial distributions of the LRGs are described. The 2SLAQ data will be released publicly from mid-2006, providing a powerful resource for observational cosmology and the study of galaxy evolution.

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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.

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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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arXiv2002

The 2dF Galaxy Redshift Survey: The b_J-band galaxy luminosity function and survey selection function

We use more than 110500 galaxies from the 2dF galaxy redshift survey (2dFGRS) to estimate the b_J-band galaxy luminosity function at redshift z=0, taking account of evolution, the distribution of magnitude measurement errors and small corrections for incompletenessin the galaxy catalogue. Throughout the interval -16.5>M- 5log h>-22, the luminosity function is accurately described by a Schechter function with M* -5log h =-19.66+/-0.07, alpha=-1.21+/-0.03 and phistar=(1.61+/-0.08) 10^{-2} h^3/Mpc^3, giving an integrated luminosity density of rho_L=(1.82+/-0.17) 10^8 h L_sol/Mpc^3 (assuming an Omega_0=0.3, Lambda_0=0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zeropoint, large scale structure in the galaxy distribution and, importantly, from the uncertainty in the appropriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the b_J-band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on apparent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented.

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