UWCScholar :: Browsing by Author "Jarvis, Matt"

Browsing by Author "Jarvis, Matt"

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Calibrating photometric redshifts with intensity mapping observations
(American Physical Society, 2017) Alonso, David; Ferreira, Pedro G.; Jarvis, Matt; Moodley, Kavilan
Imaging surveys of galaxies will have a high number density and angular resolution yet a poor redshift precision. Intensity maps of neutral hydrogen (HI) will have accurate redshift resolution yet will not resolve individual sources. Using this complementarity, we show how the clustering redshifts approach, proposed for spectroscopic surveys can also be used in combination with intensity mapping observations to calibrate the redshift distribution of galaxies in an imaging survey and, as a result, reduce uncertainties in photometric redshift measurements. We show how the intensity mapping surveys to be carried out with the MeerKAT, HIRAX and SKA instruments can improve photometric redshift uncertainties to well below the requirements of DES and LSST. The effectiveness of this method as a function of instrumental parameters, foreground subtraction and other potential systematic errors is discussed in detail.
Comparison of Hi and optical redshifts of galaxies - The impact of redshift uncertainties on spectral line stacking
(Oxford University Press, 2013) Maddox, Natasha; Hess, Kelley M.; Blyth, S.-L.; Jarvis, Matt
Accurate optical redshifts will be critical for spectral co-adding techniques used to extract detections from below the noise level in ongoing and upcoming surveys for Hi, which will extend our current understanding of gas reservoirs in galaxies to lower column densities and higher redshifts. We have used existing, high quality optical and radio data from the SDSS and ALFALFA surveys to investigate the relationship be- tween redshifts derived from optical spectroscopy and neutral hydrogen (Hi) spectral line observations.We find that the two redshift measurements agree well, with a negli- gible systematic offset and a small distribution width. Employing simple simulations, we determine how the width of an ideal stacked Hi profile depends on these redshift offsets, as well as larger redshift errors more appropriate for high redshift galaxy sur- veys. The width of the stacked profile is dominated by the width distribution of the input individual profiles when the redshift errors are less than the median width of the input profiles, and only when the redshift errors become large, 150 kms−1, do they significantly affect the width of the stacked profile. This redshift accuracy can be achieved with moderate resolution optical spectra. We provide guidelines for the number of spectra required for stacking to reach a specified mass sensitivity, given tele- scope and survey parameters, which will be useful for planning optical spectroscopy observing campaigns to supplement the radio data.
Constraining the bright-end of the UV luminosity function for z ~ 7-9 galaxies: results from CANDELS/GOODS-South
(OUP, 2013) Lorenzoni, Silvio; Bunker, Andrew J.; Wilkins, Stephen M.; Caruana, Joseph; Stanway, Elizabeth R.; Jarvis, Matt
The recent Hubble Space Telescope near-infrared imaging with the Wide-Field Camera #3 (WFC3) of the GOODS-South field in the CANDELS program 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 < 27mag) 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 WFC3 Early Release Science observations). We also look at the agreement with previous luminosity functions derived from WFC3 dropout counts, finding a generally good agreement, except for the luminosity function of Yan et al. (2010) at z ~ 8, which is strongly ruled out.
Cosmology with a SKA HI intensity mapping survey
(Proceedings of Science, 2014) Santos, Mario G.; Bull, Philip; Alonso, David; Camera, Stefano; Ferreira, Pedro G.; Bernardi, Gianni; Maartens, Roy; Viel, Matteo; Villaescusa-Navarro, Francisco; Abdalla, Filipe B.; Jarvis, Matt; Metcalf, R. Benton; Pourtsidou, A.; Wolz, Laura
HI intensity mapping (IM) is a novel technique capable of mapping the large-scale structure of the Universe in three dimensions and delivering exquisite constraints on cosmology, by using HI as a biased tracer of the dark matter density field. This is achieved by measuring the intensity of the redshifted 21cm line over the sky in a range of redshifts without the requirement to resolve individual galaxies. In this chapter, we investigate the potential of SKA1 to deliver HI intensity maps over a broad range of frequencies and a substantial fraction of the sky. By pinning down the baryon acoustic oscillation and redshift space distortion features in the matter power spectrum – thus determining the expansion and growth history of the Universe – these surveys can provide powerful tests of dark energy models and modifications to General Relativity. They can also be used to probe physics on extremely large scales, where precise measurements of spatial curvature and primordial non-Gaussianity can be used to test inflation; on small scales, by measuring the sum of neutrino masses; and at high redshifts where non-standard evolution models can be probed. We discuss the impact of foregrounds as well as various instrumental and survey design parameters on the achievable constraints. In particular we analyse the feasibility of using the SKA1 autocorrelations to probe the large-scale signal.
The effects of environment on radio-loud AGN activity in Stripe 82
(University of the Western Cape, 2016) Kolwa, Sthabile; Jarvis, Matt; McAlpine, Kim
We investigate the link between environment and radiative accretion efficiency using a sample of 8946 radio-loud AGN detected at 1 − 2 GHz in the SDSS Stripe 82 region. We quantify their environments using the surface-density parameter, ƩN, which measures galaxy density based on distances to Nth nearest neighbours. Comparing Ʃ2 and Ʃ5 between AGN and control galaxies, we obtain relative densities that quantify the degree of galaxy clustering around each AGN. Using this, we examine the relation between density and the HERG-LERG dichotomy (accretion-modes) classified using a 1.4 GHz luminosity (L1.4GHz) threshold. Our results indicate that, in the low-redshift interval (0.1 < z < 0.2), LERGs occupy environments denser than the field. At intermediate redshifts (0.2 < z < 1.2), both LERGs and HERGs occupy regions denser than the field. Spearman’s rank tests show that correlations between density and L1.4GHz in both redshift intervals are weak. We conclude that the absence of a strong correlation is confirmation of the idea that galaxy density plays a more secondary role on AGN activity and also, accretion-mode classification (both measured using L1.4GHz). It is likely that the rate of gas accretion or properties of galactic-scale magnetic fields correlate more strongly with L1.4GHz, hence being primarily influential.
Evolution of faint radio sources in the VIDEO-XMM3 field
(OUP, 2013) McAlpine, K.; Jarvis, Matt; Bonfield, David G.
It has been speculated that low luminosity radio-loud AGN have the potential to serve as an important source of AGN feedback, and may be responsible for suppressing star-formation activity in massive elliptical galaxies at late times. As such the cosmic evolution of these sources is vitally important to understanding the significance of such AGN feedback processes and their influence on the global star-formation history of the universe. In this paper we present a new investigation of the evolution of faint radio sources out to z~2.5. We combine a 1 square degree VLA radio survey, complete to a depth of 100 μJy, with accurate 10 band photometric redshifts from the VIDEO and CFHTLS surveys. The results indicate that the radio population experiences mild positive evo- lution out to z~1.2 increasing their space density by a factor of ~3, consistent with results of several previous studies. Beyond z=1.2 there is evidence of a slowing down of this evolution. Star-forming galaxies drive the more rapid evolution at low redshifts, z<1.2, while more slowly evolving AGN populations dominate at higher redshifts resulting in a decline in the evolution of the radio luminosity function at z>1.2. The evolution is best fit by pure luminosity evolution with star-forming galaxies evolving as (1 + z)2.47±0.12 and AGN as (1 + z)1.18±0.21.
Evolution of star formation in the UKIDSS ultra deep survey field - I. Luminosity functions and cosmic star formation rate out of z = 1.6
(OUP, 2013) Drake, Alyssa B.; Simpson, Chris; Collins, Chris A.; Jarvis, Matt
We present new results on the cosmic star formation history in the SXDS-UDS field out to z = 1.6. We compile narrow-band data from the Subaru Telescope and the Visible and Infrared Survey Telescope for Astronomy (VISTA) in conjunction with broad-band data from the SXDS and UDS, to make a selection of 5725 emission-line galaxies in 12 redshift slices, spanning 10 Gyr of cosmic time. We determine photometric redshifts for the sample using 11-band photometry, and use a spectroscopically confirmed subset to fine tune the resultant redshift distribution.We use themaximum-likelihood technique to determine luminosity functions in each redshift slice and model the selection effects inherent in any narrow-band selection statistically, to obviate the retrospective corrections ordinarily required. The deep narrow band data are sensitive to very low star formation rates (SFRs), and allow an accurate evaluation of the faint end slope of the Schechter function, α.We find that α is particularly sensitive to the assumed faintest broadband magnitude of a galaxy capable of hosting an emission line, and propose that this limit should be empirically motivated. For this analysis we base our threshold on the limiting observed equivalent widths of emission lines in the local Universe. We compute the characteristic SFR of galaxies in each redshift slice, and the integrated SFR density, ρSFR. We find our results to be in good agreement with the literature and parametrize the evolution of the SFR density as ρSFR (1 + z)4.58 confirming a steep decline in star formation activity since z ~ 1.6
Extracting the global signal from 21-cm fluctuations: the multitracer approach
(Oxford University Press, 2019) Jarvis, Matt; Fialkov, Anastasia; RBarkana, ennan
The multitracer technique employs a ratio of densities of two differently biased galaxy samples that trace the same underlying matter density field, and was proposed to alleviate the cosmic variance problem. Here, we propose a novel application of this approach, applying it to two different tracers one of which is the 21-cm signal of neutral hydrogen from the epochs of reionization and comic dawn.
The faint radio source population at 15.7 GHz - II. Multi-wavelength properties
(Oxford University Press, 2015) Whittam, I.H.; Riley, J.M.; Green, D.A.; Jarvis, Matt; Vaccari, M.
A complete, flux density limited sample of 96 faint (> 0:5 mJy) radio sources is selected from the 10C survey at 15.7 GHz in the Lockman Hole. We have matched this sample to a range of multi-wavelength catalogues, including SERVS, SWIRE, UKIDSS and optical data; multi-wavelength counterparts are found for 80 of the 96 sources and spectroscopic redshifts are available for 24 sources. Photometric reshifts are estimated for the sources with multiwavelength data available; the median redshift of the sample is 0.91 with an interquartile range of 0.84. Radio-to-optical ratios show that at least 94 per cent of the sample are radio loud, indicating that the 10C sample is dominated by radio galaxies. This is in contrast to samples selected at lower frequencies, where radio-quiet AGN and starforming galaxies are present in significant numbers at these flux density levels. All six radio-quiet sources have rising radio spectra, suggesting that they are dominated by AGN emission. These results confirm the conclusions of Paper I that the faint, flat-spectrum sources which are found to dominate the 10C sample below 1 mJy are the cores of radio galaxies. The properties of the 10C sample are compared to the SKADS Simulated Skies; a population of low-redshift starforming galaxies predicted by the simulation is not found in the observed sample.
The faint source population at 15.7 GHz - I. The radio properties
(Oxford University Press, 2013) Whittam, I.; Riley, J.; Jarvis, Matt; Green, D.A.; Prandoni, I.; Guglielmino, G.; Morganti, R.; Röttgering, H. J. A.; Garrett, M. A.
We have studied a sample of 296 faint (>0.5 mJy) radio sources selected from an area of the Tenth Cambridge (10C) survey at 15.7 GHz in the Lockman Hole. By matching this catalogue to several lower frequency surveys (e.g. including a deep GMRT survey at 610 MHz, aWSRT survey at 1.4 GHz, NVSS, FIRST and WENSS) we have investigated the radio spectral properties of the sources in this sample; all but 30 of the 10C sources are matched to one or more of these surveys. We have found a significant increase in the proportion of flat-spectrum sources at flux densities below ≈1 mJy – the median spectral index between 15.7 GHz and 610 MHz changes from 0.75 for flux densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8 mJy. This suggests that a population of faint, flat-spectrum sources are emerging at flux densities 1mJy. The spectral index distribution of this sample of sources selected at 15.7 GHz is compared to those of two samples selected at 1.4 GHz from FIRST and NVSS. We find that there is a significant flat-spectrum population present in the 10C sample which is missing from the samples selected at 1.4 GHz. The 10C sample is compared to a sample of sources selected from the SKADS Simulated Sky byWilman et al. and we find that this simulation fails to reproduce the observed spectral index distribution and significantly underpredicts the number of sources in the faintest flux density bin. It is likely that the observed faint, flat-spectrum sources are a result of the cores of Fanaroff–Riley type I sources becoming dominant at high frequencies. These results highlight the importance of studying this faint, high-frequency population.
Galaxy And Mass Assembly (GAMA): spectroscopic analysis
(Oxford University Press, 2013) Hopkins, A.M.; Driver, S.P.; Brough, S.; Jarvis, Matt
The Galaxy And Mass Assembly (GAMA) survey is a multiwavelength photometric and spectroscopic survey, using the AAOmega spectrograph on the Anglo-Australian Telescope to obtain spectra for up to _ 300 000 galaxies over 280 square degrees, to a limiting magnitude of rpet < 19.8mag. The target galaxies are distributed over 0 < z . 0.5 with a median redshift of z _ 0.2, although the redshift distribution includes a small number of systems, primarily quasars, at higher redshifts, up to and beyond z = 1. The redshift accuracy ranges from σv _ 50 kms−1 to σv _ 100 kms−1 depending on the signal-to-noise of the spectrum. Here we describe the GAMA spectroscopic reduction and analysis pipeline. We present the steps involved in taking the raw two-dimensional spectroscopic images through to flux-calibrated one-dimensional spectra. The resulting GAMA spectra cover an observed wavelength range of 3750 . λ . 8850 °A at a resolution of R _ 1300. The final flux calibration is typically accurate to 10 − 20%, although the reliability is worse at the extreme wavelength ends, and poorer in the blue than the red. We present details of the measurement of emission and absorption features in the GAMA spectra. These measurements are characterised through a variety of quality control analyses detailing the robustness and reliability of the measurements. We illustrate the quality of the measurements with a brief exploration of elementary emission line properties of the galaxies in the GAMA sample. We demonstrate the luminosity dependence of the Balmer decrement, consistent with previously published results, and explore further how Balmer decrement varies with galaxy mass and redshift. We also investigate the mass and redshift dependencies of the [NII]/Hα vs [OIII]/Hβ spectral diagnostic diagram, commonly used to discriminate between star forming and nuclear activity in galaxies.
Gama/H-Atlas: The dust opacity-stellar mass surface density relation for spiral galaxies
(IOP Science, 2013) Grootes, M.W.; Tuffs, R.J.; Jarvis, Matt
We report the discovery of a well-defined correlation between B-band face-on central optical depth due to dust and the stellar mass surface density of nearby spiral galaxies. This relation was derived from a sample of spiral galaxies taken from the Galaxy and Mass Assembly (GAMA) survey, which were detected in the FIR/submm in the Herschel -ATLAS science demonstration phase field. Using a quantitative analysis of the NUV attenuation-inclination relation for complete samples of GAMA spirals categorized according to stellar mass surface density we demonstrate that this correlation can be used to statistically correct for dust attenuation purely on the basis of optical photometry and S´ersic-profile morphological fits.
H-Atlas: The cosmic abundance of dust from the far-infrared background power spectrum
(IOP Science, 2013) Thacker, Cameron; Cooray, Asantha; Jarvis, Matt
We present a measurement of the angular power spectrum of the cosmic far-infrared background (CFIRB) anisotropies in one of the extragalactic fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) at 250, 350 and 500 μm bands. Consistent with recent measurements of the CFIRB power spectrum in Herschel-SPIRE maps, we confirm the existence of a clear one-halo term of galaxy clustering on arcminute angular scales with large-scale two-halo term of clustering at 30 arcminutes to angular scales of a few degrees. The power spectrum at the largest angular scales, especially at 250 μm, is contaminated by the Galactic cirrus. The angular power spectrum is modeled using a conditional luminosity function approach to describe the spatial distribution of unresolved galaxies that make up the bulk of the CFIRB.
H2O emission in high-z ultra-luminous infrared galaxies
(edp sciences, 2013) Omont, A.; Yang, Chentao; Cox, P.; Jarvis, Matt
Using the IRAM Plateau de Bure interferometer (PdBI), we report the detection of water vapor in six new lensed ultraluminous starburst galaxies at high redshift, discovered in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). The sources are detected either in the 202–111 or 211–202 H2O emission lines with integrated line fluxes ranging from 1.8 to 14 Jy km s−1. The corresponding apparent luminosities are μLH2O _ 3 − 12 x 108 L⊙, where μ is the lensing magnification factor (3 < μ < 12). These results confirm that H2O lines are among the strongest molecular lines in high-z ultra-luminous starburst galaxies, with intensities almost comparable to those of the high-J CO lines, and similar profiles and line widths (_200-900 km s−1). With the current sensitivity of the PdBI, the water lines can therefore easily be detected in high-z lensed galaxies (with F(500μm)>100mJy) discovered in the Herschel surveys. Correcting the luminosities for amplification, using existing lensing models, LH2O is found to have a strong dependence on the infrared luminosity, varying as _L1.2 IR . This relation, which needs to be confirmed with better statistics, may indicate a role of radiative (infrared) excitation of the H2O lines, and implies that high-z galaxies with LIR &1013 L⊙ tend to be very strong emitters in water vapor, that have no equivalent in the local universe.
The Herschel* view of the environment of the radio galaxy 4C+41.17 at z = 3.8
(Oxford University Press, 2013) Wylezalek, D.; Vernet, J.; De Breuck, C.; Stern, D.; Galametz, A.; Seymour, N.; Jarvis, Matt; Barthel, P.; Drouart, G.; Rottgering, H.J.A.; Greve, T.R.; Haas, M.; Hatch, N.; Ivison, R.J.; Lehnert, M.; Meisenheimer, K.; Miley, G.; Nesvadba, N.; Stevens, J.A.
We present Herschel observations at 70, 160, 250, 350 and 500 μm of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65 per cent of the extracted sources are securely identified with mid-infrared sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 μm.We derive simple photometric redshifts, also including existing 850 and 1200 μm data, using templates of active galactic nuclei, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the spectral energy distribution (SED) of the closest (∼25 arcsec offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multiwavelength data, in particular on the Rayleigh–Jeans side of the SED, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data sets.
Herschel*-ATLAS: correlations between dust and gas in local submm-selected galaxies
(2013) Dunne, L.; Bourne, N.; Bendo, G.J.; Smith, M.W.L.; Clark, C.J.R.; Smith, Daniel J.B.; Rigby, E.E.; Baes, M.; Leeuw, L.L.; Maddox, S.J.; Thompson, M.A.; Bremer, M.N.; Cooray, Asantha; Dariush, A.; de Zotti, G.; Dye, S.; Eales, S.; Hopwood, R.; Ibar, Edo; Ivison, R.J.; Jarvis, Matt; Michalowski, M.J.; Rowlands, K.; Valiante, E.
We present an analysis of CO molecular gas tracers in a sample of 500 μ m-selected Herschel -ATLAS galaxies at z < 0 . 05 ( cz < 14990 km s − 1 ). Using 22 − 500 μ m photom- etry from WISE , IRAS and Herschel , with H i data from the literature, we investigate correlations between warm and cold dust, and tracers of the gas in different phases. The correlation between global CO(3–2) line fluxes and FIR–submm fl uxes weakens with increasing IR wavelength ( λ & 60 μ m), as a result of colder dust being less strongly associated with dense gas. Conversely, CO(2–1) and H i line fluxes both ap- pear to be better correlated with longer wavelengths, suggesting that cold dust is more strongly associated with diffuse atomic and molecular gas phases, co nsistent with it being at least partially heated by radiation from old stellar populations . The increased scatter at long wavelengths implies that sub-millimetre fluxes are a po orer tracer of SFR. Fluxes at 22 and 60 μ m are also better correlated with diffuse gas tracers than dense CO(3–2), probably due to very-small-grain emission in the diffu se interstellar medium, which is not correlated with SFR. The FIR/CO luminosity ratio a nd the dust mass/CO luminosity ratio both decrease with increasing luminosit y, as a result of either correlations between mass and metallicity (changing CO/H 2 ) or between CO luminosity and excitation [changing CO(3–2)/CO(1–0)].
Herschel-atlas/Gama: a difference between star formation rates in strong-line and weak-line radio galaxies
(OUP, 2013) Hardcastle, M.J.; Ching, J.H.Y.; Jarvis, Matt
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.
Herschel-ATLAS/GAMA: What determines the far-infrared properties of radio galaxies?
(OUP, 2013) Virdee, J.S.; Hardcastle, M.J.; Jarvis, Matt
We perform a stacking analysis of Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) data in order to obtain isothermal dust temperatures and rest-frame luminosities at 250 µm (L250), for a well-defined sample of 1599 radio sources over the H-ATLAS Phase 1/Galaxy and Mass Assembly (GAMA) area. The radio sample is generated using a combination of NRAO VLA Sky Survey data and K-band United Kingdom Infrared Telescope Deep Sky Survey–Large Area Survey data, over the redshift range 0.01 30 kpc) counterparts. The higher dust temperature suggests that this may be attributed to enhanced SFRs in compact radio galaxies, but whether this is directly or indirectly due to radio activity (e.g. jet-induced or merger-driven star formation) is as yet unknown. For matched samples in LK and g –r , sub-1.5L∗ K and super-1.5L∗ K radio-detected galaxies have 0.89±0.18 and 0.49±0.12 times the 250μm luminosity of their non-radio-detected counterparts. Thus, while no difference in L250 is observed in sub-1.5L∗ K radio-detected galaxies, a strong deficit is observed in super-1.5L∗ K radio-detected galaxies. We explain these results in terms of the hotter, denser and richer halo environments massive radio galaxies maintain and are embedded in. These environments are expected to quench the cold gas and dust supply needed for further star formation and therefore dust production. Our results indicate that all massive radio galaxies (>1.5L∗ K) may have systematically lower FIR luminosities (∼25 per cent) than their colour-matched non-radio-detected counterparts. Finally, no relation between radio spectral index and L250 is found for the subset of 1.4-GHz radio sources with detections at 330 MHz.
Herschel-ATLAS: A binary HyLIRG pinpointing a cluster of starbursting protoellipticals
(American Astronomical Society, 2013) Ivison, R.J.; Swinbank, A.M.; Jarvis, Matt
Panchromatic observations of the best candidate hyperluminous infrared galaxies from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z = 2.41 galaxies across an ≈100 kpc region—a cluster of starbursting protoellipticals. Via subarcsecond interferometric imaging we have measured accurate gas and star formation surface densities. The two brightest galaxies span ∼3 kpc FWHM in submillimeter/radio continuum and CO J = 4–3, and double that in CO J = 1–0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks—a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have Mdyn of several ×1011M , and gas fractions of ∼40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star formation rates place them 5×above the main sequence, which supposedly comprises large gas disks like these. Their high star formation efficiencies are difficult to reconcile with a simple volumetric star formation law. N-body and dark matter simulations suggest that this system is the progenitor of a B(inary)-type ≈1014.6-M cluster.
Improving photometric redshift estimation using GPz: size information, post processing and improved photometry
(Oxford University Press, 2017) Gomes, Zahra; Jarvis, Matt; Almosallam, Ibrahim A.; Roberts, Stephen J.
The next generation of large-scale imaging surveys (such as those conducted with the Large Synoptic Survey Telescope and Euclid) will require accurate photometric redshifts in order to optimally extract cosmological information. Gaussian Process for photometric redshift estimation (GPZ) is a promising new method that has been proven to provide efficient, accurate photometric redshift estimations with reliable variance predictions. In this paper, we investigate a number of methods for improving the photometric redshift estimations obtained using GPZ (but which are also applicable to others). We use spectroscopy from the Galaxy and Mass Assembly Data Release 2 with a limiting magnitude of r < 19.4 along with corresponding Sloan Digital Sky Survey visible (ugriz) photometry and the UKIRT Infrared Deep Sky Survey Large Area Survey near-IR (YJHK) photometry. We evaluate the effects of adding near-IR magnitudes and angular size as features for the training, validation, and testing of GPZ and find that these improve the accuracy of the results by ~15–20 per cent. In addition, we explore a post-processing method of shifting the probability distributions of the estimated redshifts based on their Quantile–Quantile plots and find that it improves the bias by ~40 per cent. Finally, we investigate the effects of using more precise photometry obtained from the Hyper Suprime-Cam Subaru Strategic Program Data Release 1 and find that it produces significant improvements in accuracy, similar to the effect of including additional features.

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