Cosmology

Abstract:

We have constructed a sample of radio-loud objects with optical spectroscopy from the Galaxy and Mass Assembly (GAMA) project over the Herschel Astrophysical Terahertz Large Area Survey (Herschel-ATLAS) Phase 1 fields. Classifying the radio sources in terms of their optical spectra, we find that strong-emission-line sources ('high-excitation radio galaxies') have, on average, a factor of ~4 higher 250-μm Herschel luminosity than weak-line ('lowexcitation') radio galaxies and are also more luminous than magnitude-matched radio-quiet galaxies at the same redshift. Using all five H-ATLAS bands, we show that this difference in luminosity between the emission-line classes arises mostly from a difference in the average dust temperature; strong-emission-line sources tend to have comparable dust masses to, but higher dust temperatures than, radio galaxies with weak emission lines. We interpret this as showing that radio galaxies with strong nuclear emission lines are much more likely to be associated with star formation in their host galaxy, although there is certainly not a one-to-one relationship between star formation and strong-line active galactic nuclei (AGN) activity. The strong-line sources are estimated to have star formation rates at least a factor of 3-4 higher than those in the weak-line objects. Our conclusion is consistent with earlier work, generally carried out using much smaller samples, and reinforces the general picture of high-excitation radio galaxies as being located in lower-mass, less evolved host galaxies than their low-excitation counterparts. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the massive cluster A1689 at z = 0.183. Conducting an analysis similar to that of ATLAS3D, we extend the baseline of the kinematic morphology-density relation by an order of magnitude in projected density and show that it is possible to use existing instruments to identify slow and fast rotators beyond the local Universe. We find 4.5 ± 1.0 slow rotators with a distribution in magnitude similar to those in the Virgo cluster. The overall slow rotator fraction of our A1689 sample is 0.15 ± 0.03, the same as in Virgo using our selection criteria. This suggests that the fraction of slow rotators in a cluster is not strongly dependent on its density. However, within A1689, we find that the fraction of slow rotators increases towards the centre, as was also found in the Virgo cluster. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

The recent Hubble Space Telescope near-infrared imaging with the Wide-Field Camera #3 (WFC 3) of the Great Observatories Origins Deep Survey South (GOODS-S) field in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) programme covering nearly 100 arcmin2, along with already existing Advanced Camera for Surveys optical data, makes possible the search for bright galaxy candidates at redshift z≈7-9 using the Lyman break technique. We present the first analysis of z'-drop z≈7 candidate galaxies in this area, finding 19 objects. We also analyse Y-drops at z≈8, trebling the number of bright (HAB < 27 mag) Y-drops from our previous work, and compare our results with those of other groups based on the same data. The bright high-redshift galaxy candidates we find serve to better constrain the bright end of the luminosity function at those redshift, and may also be more amenable to spectroscopic confirmation than the fainter ones presented in various previous work on the smaller fields (the Hubble Ultra Deep Field and the WFC 3 Early Release Science observations).We also look at the agreement with previous luminosity functions derived from WFC3 drop-out counts, finding a generally good agreement, except for the luminosity function of Yan et al. at z≈8, which is strongly ruled out. ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

The first half of this paper explores the origin of systematic biases in the measurement of weak gravitational lensing. Compared to previous work, we expand the investigation of point spread function instability and fold in for the first time the effects of non-idealities in electronic imaging detectors and imperfect galaxy shape measurement algorithms. Together, these now explain the additive A(l) and multiplicative M(l) systematics typically reported in current lensing measurements. We find that overall performance is driven by a product of a telescope/camera's absolute performance, and our knowledge about its performance. The second half of this paper propagates any residual shear measurement biases through to their effect on cosmological parameter constraints. Fully exploiting the statistical power of Stage IV weak lensing surveys will require additive biasesA 1.8 × 10-12 and multiplicative biases M 4.0 × -3. These can be allocated between individual budgets in hardware, calibration data and software, using results from the first half of the paper. If instrumentation is stable and well calibrated, we find extant shear measurement software from Gravitational Lensing Accuracy Testing 2010 (GREAT10) already meet requirements on galaxies detected at signal-to-noise ratio = 40. Averaging over a population of galaxies with a realistic distribution of sizes, it also meets requirements for a 2D cosmic shear analysis from space. If used on fainter galaxies or for 3D cosmic shear tomography, existing algorithms would need calibration on simulations to avoid introducing bias at a level similar to the statistical error. Requirements on hardware and calibration data are discussed in more detail in a companion paper. Our analysis is intentionally general, but is specifically being used to drive the hardware and ground segment performance budget for the design of the European Space Agency's recently selected Euclid mission. ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Abstract:

We use interferometric 12CO(1-0) observations to compare and contrast the extent, surface brightness profiles and kinematics of the molecular gas in CO-rich ATLAS3D early-type galaxies (ETGs) and spiral galaxies. We find that the molecular gas extent is smaller in absolute terms in ETGs than in late-type galaxies, but that the size distributions are similar once scaled by the galaxies optical/stellar characteristic scalelengths. Amongst ETGs, we find that the extent of the gas is independent of its kinematic misalignment (with respect to the stars), but does depend on the environment, with Virgo cluster ETGs having less extended molecular gas reservoirs, further emphasizing that cluster ETGs follow different evolutionary pathways from those in the field. Approximately half of ETGs have molecular gas surface brightness profiles that follow the stellar light profile. These systems often have relaxed gas out to large radii, suggesting they are unlikely to have had recent merger/accretion events. A third of the sample galaxies show molecular gas surface brightness profiles that fall off slower than the light, and sometimes show a truncation. These galaxies often have a low mass, and eitherhave disturbed molecular gas or are in the Virgo cluster, suggesting that recent mergers, ram pressure stripping and/or the presence of hot gas can compress/truncate the gas. The remaining galaxies have rings, or composite profiles, that we argue can be caused by the effects of bars. We investigated the kinematics of the molecular gas using position-velocity diagrams, and compared the observed kinematics with dynamical model predictions, and the observed stellar and ionized gas velocities. We confirm that the molecular gas reaches beyond the turnover of the circular velocity curve in~70 per cent of our CO-rich ATLAS3D ETGs, validating previous work on the CO Tully-Fisher relation. In general we find that in most galaxies the molecular gas is dynamically cold, and the observed CO rotation matches well model predictions of the circular velocity. In the galaxies with the largest molecular masses, dust obscuration and/or population gradients can cause model predictions of the circular velocity to disagree with observations of the molecular gas rotation; however, these effects are confined to the most star forming systems. Bars and non-equilibrium conditions can also make the gas deviate from circular orbits. In both these cases, one expects the model circular velocity to be higher than the observed CO velocity, in agreement with our observations. Molecular gas is a better direct tracer of the circular velocity than the ionized gas, justifying its use as a kinematic tracer for Tully-Fisher and similar analyses.