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J. Bland-Hawthorn

Publications and source records attributed to J. Bland-Hawthorn.

At least 307 records · Page 17Linked to original sources
arXiv2006

The 2dF-SDSS LRG and QSO survey: Evolution of the Luminosity Function of Luminous Red Galaxies to z=0.6

We present new measurements of the luminosity function (LF) of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) and the 2dF-SDSS LRG and Quasar (2SLAQ) survey. We have carefully quantified, and corrected for, uncertainties in the K and evolutionary corrections, differences in the colour selection methods, and the effects of photometric errors, thus ensuring we are studying the same galaxy population in both surveys. Using a limited subset of 6326 SDSS LRGs (with 0.17<z<0.24) and 1725 2SLAQ LRGs (with 0.5 <z<0.6), for which the matching colour selection is most reliable, we find no evidence for any additional evolution in the LRG LF, over this redshift range, beyond that expected from a simple passive evolution model. This lack of additional evolution is quantified using the comoving luminosity density of SDSS and 2SLAQ LRGs, brighter than M_r - 5logh = -22.5, which are 2.51+/-0.03 x 10^-7 L_sun Mpc^-3 and 2.44+/-0.15 x 10^-7 L_sun Mpc^-3 respectively (<10% uncertainty). We compare our LFs to the COMBO-17 data and find excellent agreement over the same redshift range. Together, these surveys show no evidence for additional evolution (beyond passive) in the LF of LRGs brighter than M_r - 5logh = -21 (or brighter than L*). We test our SDSS and 2SLAQ LFs against a simple ``dry merger'' model for the evolution of massive red galaxies and find that at least half of the LRGs at z=0.2 must already have been well-assembled (with more than half their stellar mass) by z=0.6. This limit is barely consistent with recent results from semi-analytical models of galaxy evolution.

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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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arXiv2006

Instruments without optics: an integrated photonic spectrograph

In recent years, a great deal of emphasis has been placed on achieving the diffraction limit with large aperture telescopes. For a well matched focal-plane instrument, the diffraction limit provides the highest possible angular resolution and sensitivity per pixel. But it offers another key advantage as we now show. Conventionally, as the telescope aperture D grows, the instrument size grows in proportion to D, and cost increases as D^2 or faster. However, an instrument that operates at the diffraction limit can break the trend of spiralling costs. In traditional instruments, the light must pass through a succession of large lenses, mirrors and gratings, making it difficult to conserve the integrity of such as small psf. An alternative approach, as we now show, is to couple the diffraction limited beam directly into an integrated photonic spectrograph operating in low-order modes.

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arXiv2006

The Radial Velocity Experiment (RAVE): first data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution spectra (median R=7,500) in the Ca-triplet region ($λλ$ 8,410--8,795 Å) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9<I<12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including re-observations). Those data were obtained on 67 nights between 11 April 2003 to 03 April 2004. The total sky coverage within this data release is $\sim$4,760 square degrees. The average signal to noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km/s. Combining internal errors and zero-point errors, the mode is found to be 2 km/s. Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km/s. We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal to noise. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2 and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS and 2MASS). The data release can be accessed via the RAVE webpage: http://www.rave-survey.org.

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arXiv2006

NGC922 - A new drop-through ring galaxy

We have found the peculiar galaxy NGC922 to be a new drop-through ring galaxy using multi-wavelength (UV-radio) imaging and spectroscopic observations. Its `C'-shaped morphology and tidal plume indicate a recent strong interaction with its companion which was identified with these observations. Using numerical simulations we demonstrate that the main properties of the system can be generated by a high-speed off-axis drop-through collision of a small galaxy with a larger disk system, thus making NGC922 one of the nearest known collisional ring galaxies. While these systems are rare in the local Universe, recent deep HST images suggest they were more common in the early Universe.

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arXiv2006

The Survey for Ionization in Neutral Gas Galaxies- II. The Star Formation Rate Density of the Local Universe

We derive observed Halpha and R band luminosity densities of an HI-selected sample of nearby galaxies using the SINGG sample to be l_Halpha' = (9.4 +/- 1.8)e38 h_70 erg s^-1 Mpc^-3 for Halpha and l_R' = (4.4 +/- 0.7)e37 h_70 erg s^-1 A^-1 Mpc^-3 in the R band. This R band luminosity density is approximately 70% of that found by the Sloan Digital Sky Survey. This leads to a local star formation rate density of log(SFRD) = -1.80 +0.13/-0.07(random) +/- 0.03(systematic) + log(h_70) after applying a mean internal extinction correction of 0.82 magnitudes. The gas cycling time of this sample is found to be t_gas = 7.5 +1.3/-2.1 Gyr, and the volume-averaged equivalent width of the SINGG galaxies is EW(Halpha) = 28.8 +7.2/-4.7 A (21.2 +4.2/-3.5 A without internal dust correction). As with similar surveys, these results imply that SFRD(z) decreases drastically from z ~ 1.5 to the present. A comparison of the dynamical masses of the SINGG galaxies evaluated at their optical limits with their stellar and HI masses shows significant evidence of downsizing: the most massive galaxies have a larger fraction of their mass locked up in stars compared with HI, while the opposite is true for less massive galaxies. We show that the application of the Kennicutt star formation law to a galaxy having the median orbital time at the optical limit of this sample results in a star formation rate decay with cosmic time similar to that given by the SFRD(z) evolution. This implies that the SFRD(z) evolution is primarily due to the secular evolution of galaxies, rather than interactions or mergers. This is consistent with the morphologies predominantly seen in the SINGG sample.

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arXiv2005

Chemical Homogeneity in the Hyades

We present an abundance analysis of the heavy elements Zr, Ba, La, Ce, and Nd for Hyades cluster F-K dwarfs based on high resolution, high S/N ratio spectra from Keck/HIRES. The derived abundances show the stellar members to be highly uniform, although some elements show a small residual trend with temperature. The rms scatter for each element for the cluster members is as follows; Zr = 0.055 dex, Ba = 0.049 dex, Ce = 0.025 dex, La = 0.025 dex, Nd = 0.032 dex. This is consistent with the measurement errors, and implies that there is little or no intrinsic scatter among the Hyades members. Several stars thought to be non-members of the cluster based on their kinematics are found to deviate from the cluster mean abundances by about 2sigma. Establishing chemical homogeneity in open clusters is the primary requirement for the viability of chemically tagging Galactic disk stars to common formation sites, in order to unravel the dissipative history of early disk formation.

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arXiv2005

Imaging Fabry-Perot Spectroscopy of NGC 5775: Kinematics of the Diffuse Ionized Gas Halo

We present imaging Fabry-Perot observations of Halpha emission in the nearly edge-on spiral galaxy NGC 5775. We have derived a rotation curve and a radial density profile along the major axis by examining position-velocity (PV) diagrams from the Fabry-Perot data cube as well as a CO 2-1 data cube from the literature. PV diagrams constructed parallel to the major axis are used to examine changes in azimuthal velocity as a function of height above the midplane. The results of this analysis reveal the presence of a vertical gradient in azimuthal velocity. The magnitude of this gradient is approximately 1 km/s/arcsec, or about 8 km/s/kpc, though a higher value of the gradient may be appropriate in localized regions of the halo. The evidence for an azimuthal velocity gradient is much stronger for the approaching half of the galaxy, although earlier slit spectra are consistent with a gradient on both sides. There is evidence for an outward radial redistribution of gas in the halo. The form of the rotation curve may also change with height, but this is not certain. We compare these results with those of an entirely ballistic model of a disk-halo flow. The model predicts a vertical gradient in azimuthal velocity which is shallower than the observed gradient, indicating that an additional mechanism is required to further slow the rotation speeds in the halo.

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arXiv2005

The Millennium Galaxy Catalogue: On the natural sub-division of galaxies

The distribution of global photometric, spectroscopic, structural and morphological parameters for a well defined sample of 350 nearby galaxies has been examined. The usual trends were recovered demonstrating that E/S0 galaxies are redder, more quiescent, more centrally concentrated and possess larger Sersic indices than later type galaxies. Multivariate statistical analyses were performed to examine the distribution of all parameters simultaneously. The main result of these analyses was the existence of only two classes of galaxies, corresponding closely to early and late types. Linear discriminant analysis was able to reproduce the classifications of early and late types galaxies with high success, but further refinement of galaxy types was not reproduced in the distribution of observed galaxy properties. A principal components analysis showed that the major variance of the parameter set corresponded to a distinction between early and late types, highlighting the importance of the distinction. A hierarchical clustering analysis revealed only two clear natural classes within the parameter set, closely corresponding to early and late types. Early and late types are clearly distinct and the distinction is of fundamental importance. In contrast, late types from Sa to Irr are smoothly distributed throughout the parameter space. A population of galaxies classified by eye as elliptical/lenticular, and exhibiting concentration indices similar to early-types were found to have a significant star-formation activity. These galaxies are preferentially faint, suggesting they are low-mass systems.

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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.)

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arXiv2005

Galactic Winds

Galactic winds are the primary mechanism by which energy and metals are recycled in galaxies and are deposited into the intergalactic medium. New observations are revealing the ubiquity of this process, particularly at high redshift. We describe the physics behind these winds, discuss the observational evidence for them in nearby star-forming and active galaxies and in the high-redshift universe, and consider the implications of energetic winds for the formation and evolution of galaxies and the intergalactic medium. To inspire future research, we conclude with a set of observational and theoretical challenges.

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arXiv2005

Science Programs for a 2 m-class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope

The cold, dry and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-mm wavelengths to be found on the Earth. PILOT is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of science projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near-diffraction limited performance with simple tip-tilt wavefront correction. PILOT would also be capable of near-diffraction limited performance in the optical wavebands, as well be able to open new wavebands for regular ground based observation; in the mid-IR from 17 to 40 microns and in the sub-mm at 200 microns.

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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.

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arXiv2004

A Wide-Field Survey of the Fornax Dwarf Spheroidal Galaxy

The results of a photometric survey of the Fornax dwarf spheroidal galaxy are presented herein. Accurate photometry in two colours (V and I) was collected over a 10 square degree area centred on the Fornax system with the aim of searching for extra-tidal structure. The data were complete to a magnitude of V=20, or approximately one magnitude brighter than the Fornax red clump stars. Stars were selected with a colour and magnitude lying near the Fornax red giant branch, thereby reducing contamination from the field star population. We were thus able to probe the outer structure of this dwarf galaxy. Immediately visible was a shell-like structure located 1.3 degrees NW from the centre of Fornax, approximately 30 arcmin beyond the nominal tidal radius at this position angle. We have measured the absolute visual magnitude of this feature to be M_V ~ -7. The feature is aligned with a previously reported shell (age approximately 2 Gyr) located near the core radius of Fornax. A statistical analysis of the extra-tidal stellar distribution further revealed two lobes situated on the Fornax minor axis which are aligned with the two shell-like features. The two-lobed structure combined with the two shells provide strong evidence that Fornax has experienced a merger event in the relatively recent past.

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arXiv2004

The 2dF Galaxy Redshift Survey: stochastic relative biasing between galaxy populations

It is well known that the clustering of galaxies depends on galaxy type.Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, eta, as early or late type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the nonlinearity and stochasticity of the relative bias, with cubical cells of side 10Mpc \leq L \leq 45Mpc (h=0.7). Exact linear bias is ruled out with high significance on all scales. Power law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero `stochasticity' - i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (r_LN) of 0.958 for cells of length L=10Mpc, increasing to 0.970 by L=45Mpc. This corresponds to a stochasticity sigma_b/bhat of 0.44\pm0.02 and 0.27\pm0.05 respectively. For smaller cells, the Poisson sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semianalytic galaxy formation models: these match the data well in terms of overall level of stochasticity, variation with scale, and fraction of empty cells.

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arXiv2004

Kinematics of the Ionized Halo of NGC 5775

Studies of the kinematics of gaseous halos in some spiral galaxies have shown that the rotational velocity of the gas decreases with height above the midplane (z). This vertical velocity gradient has been observed in both the neutral and ionized components of halos. We present imaging Fabry-Perot Halpha observations of the edge-on galaxy NGC 5775. These observations allow us to study the variation in the rotation curve (and, to some extent, the radial profile) of the ionized gas component as a function of z. We have used an iterative technique to infer the major axis rotation curve from the ionized gas observations as well as CO data. A preliminary analysis of position-velocity (PV) diagrams parallel to the major axis implies the presence of a vertical velocity gradient. The magnitude of this gradient is tentatively found to be ~2 km/s/arcsec, consistent with the results of Rand (2000) and Tullmann et al. (2000).

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arXiv2004

Tunable-filter imaging of quasar fields at z ~ 1. II. The star-forming galaxy environments of radio-loud quasars

We have scanned the fields of six radio-loud quasars using the Taurus Tunable Filter to detect redshifted [OII] 3727 line-emitting galaxies at redshifts 0.8 < z < 1.3. Forty-seven new emission-line galaxy (ELG) candidates are found. This number corresponds to an average space density about 100 times that found locally and, at L([OII]) < 10^{42} erg s^{-1} cm^{-2}, is 2 - 5 times greater than the field ELG density at similar redshifts, implying that radio-loud quasars inhabit sites of above-average star formation activity. The implied star-formation rates are consistent with surveys of field galaxies at z ~ 1. However, the variation in candidate density between fields is large and indicative of a range of environments, from the field to rich clusters. The ELG candidates also cluster -- both spatially and in terms of velocity -- about the radio sources. In fields known to contain rich galaxy clusters, the ELGs lie at the edges and outside the concentrated cores of red, evolved galaxies, consistent with the morphology-density relation seen in low-redshift clusters. This work, combined with other studies, suggests that the ELG environments of powerful AGN look very much the same from moderate to high redshifts, i.e. 0.8 < z < 4.

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