Parallel Session P01: 1545-1730, Monday 12th April 2010

Galaxy Formation and Evolution in the Low-Redshift Universe With Multi-Wavelength Spectroscopic Surveys

Location: Bute

Abstract:

We can now study the low redshift Universe (z < 0.5) using extensive population statistics with very large galaxy numbers and high redshift completeness levels. In this session, we look forward to contributions on new galaxy survey analyses, which make extensive use of multi-wavelength datasets by combining information from SDSS, GALEX, Herschel, UKIDSS, etc., on highlights from the new GAMA survey, and on results from the most recent galaxy formation models.

The "Galaxy And Mass Assembly" (GAMA) survey is a major redshift survey for galaxy formation with an already unique spectral energy distribution coverage: GALEX-UV, SDSS-optical, UKIRT-NIR, Herschel-FIR and GMRT-radio. GAMA has measured since 2008 over 90k new spectra over ~150 sq.deg., probing in a systematic and comprehensive manner the faint galaxy population over a timespan of four billion years (z<0.5).

A NAM session focussed around GAMA science and similar multi-wavelength opportunities in the low redshift Universe is ideally timed with the first GAMA data release planned for mid-2010. The major science goals covered by GAMA comprise multi-wavelength galaxy group studies, the evolution of the baryonic content of the Universe and the efficiency with which galaxies form as function of environment.

Organisers:

  • Peder Norberg (IfA, University of Edinburgh)
  • Ivan Baldry (Liverpool John Moores University)

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Talks

12 April, 15:45Galaxy And Mass Assembly (GAMA): The next generation survey of surveys.
Aaron Robotham (St Andrews)
12 April, 16:05GAMA photometry and the Cosmic Spectral Energy Distribution
David Hill (University of St Andrews)
12 April, 16:20The colours, AGN properties, environments and star formation histories of bulge dominated post-mergers in the local universe
Alfredo Carpineti (Imperial College)
12 April, 16:40Modelling the UV/optical FIR/submm emission from Spiral Galaxies
Cristina C. Popescu (Jeremiah Horrocks Institute, UCLan)
12 April, 17:00Scale Size Evolution of Brightest Galaxies
Claire Burke (Astrophysics Research Institute LJMU)
12 April, 17:15Poster adverts

Posters

The radio spectral index of sub-millimetre galaxies.
Edo Ibar (UK Astronomy Technology Centre)

The ALFALFA HI Absorption Survey
Erin Macdonald (University of Glasgow)

Abundance gradients in simulated galaxy discs
Awat Rahimi (MSSL/UCL)

Galaxy Clustering Using Photometric Redshifts
Leonidas Christodoulou (University of Sussex)

A new sample of "blazars" to study the relationship between radio-loud AGN and galaxy formation
Jennifer Gupta (Jodrell Bank Centre for Astrophysics)

A new approach to disentangling star formation histories from survey data
Ignacio Ferreras (MSSL/UCL)

Red and Blue Satellite Galaxies in the Galaxy and Mass Assembly Survey
Matthew Prescott (LJMU Astrophysics Research Institute)

NGC 2976 & NGC 3351: 12CO(3-2) Observations and its Correlation with PAH 8um
Boon Kok Tan (University of Oxford)

Studying galaxy evolution with FMOS (Fibre Multi-Object Spectrograph)
Emma Curtis Lake (University of Oxford)

Modelling radiation fields in galaxies using a new radiation transfer code
Dmitrij Semionov (Jeremiah Horrocks Institute, UCLan)

GAMA: Single and Multi-Component Galaxy Modelling
Lee Kelvin (St Andrews)

Improved sky subtraction for spectroscopic pipelines
Hannah Parkinson (IfA, Edinburgh)

Robust methods to probe source evolution in galaxy redshift surveys
Russell Johnston (University of the Western Cape)


Talk Abstracts

Galaxy And Mass Assembly (GAMA): The next generation survey of surveys.
Robotham, Aaron, on behalf of the GAMA team
St Andrews
12 April, 15:45

The GAMA survey is the latest generation photometric and redshift survey. It will cover the full SED of galaxies, from the FUV to the radio, and is complemented by 130,000 redshifts obtained from the AAT over a 3 year period (finishing May 2010). GAMA will probe structure over the scales of 1kpc to 1Mpc, helping us to understand galaxy formation, the energy output of the Universe, and the role of groups and clusters in galaxy evolution.

GAMA photometry and the Cosmic Spectral Energy Distribution
Hill, David, Lee Kelvin, Simon Driver, Aaron Robotham, GAMA team
University of St Andrews
12 April, 16:05

The cosmic spectral energy distribution (CSED) describes the mean radiation field within the sampled volume of the Universe. It can give insight into the star formation history, and the initial mass function. Its measurement requires accurate photometry from a number of filters, which has previously led to discrepancies between optical and NIR parameters. We introduce the GAMA photometric pipeline - a method for generating consistent colours over a range of passbands. We describe the generation of Gigapixel mosaics and matched aperture catalogues from UKIDSS and SDSS data. We quantify the systematic offsets in best-fitting luminosity function parameters produced by using different aperture types, detection thresholds or total magnitude systems. Finally, we introduce a CSED, produced using the GAMA survey, and compare it to theoretical models.

The colours, AGN properties, environments and star formation histories of bulge dominated post-mergers in the local universe
Carpineti, Alfredo, S. Kaviraj, Galaxy Zoo collaboration
Imperial College
12 April, 16:20

Galaxy merging is a fundamental aspect of the standard hierarchical galaxy formation paradigm. In Darg et al.(2010MNRAS.401.1043) we have created a large, homogeneous set of mergers through direct visual inspection of the entire SDSS using the GalaxyZoo project, a public user interface on the world wide web for the morphological classification of galaxies. At the time of writing, over 200,000 volunteers have submitted over 80 million classifications yielding a robust catalogue of around 3000 mergers which has been presented in Darg et al. We explore a subset of galaxies from this catalogue that are 'post-mergers', where the remnant appears to be in the final stages of relaxation. We focus on post-mergers that show evidence for a dominant bulge, making them plausible progenitors of early-type galaxies. For this set of galaxies we explore their GALEX-SDSS UV/optical colours, AGN activity, local environments and star formation histories. 64% of our galaxies are either quiescent or show LINER-like emission, while the rest are either star forming (9%) or have Seyfert AGNs (25%). We find that the plausible mass ratios for the mergers that created these systems are between 1:1 and 1:10, with a median value of around 1:3. The spheroidal postmergers have bluer colours than the general elliptical galaxy population, most likely due to merger-induced star formation. Comparison with stellar models suggests that the star formation activity in most of these systems peaked less than 1 Gyrs ago, suggesting that some of star formation recently discovered in early-type galaxies is merger-driven.

Modelling the UV/optical FIR/submm emission from Spiral Galaxies
Popescu, Cristina C., Richard J. Tuffs
Jeremiah Horrocks Institute, UCLan
12 April, 16:40

We present a comprehensive library of spectral energy distributions of spiral galaxies in the MIR-submm range calculated as a function of a minimal set of physical parameters using an updated and enhanced version of the model of Popescu et al. (2000). We describe how this set of dust/PAH re-emission SEDs can be self-consistently combined with the existing library of UV/optical dust attenuations calculated using the same model (Tuffs et al. 2004) to invert an observed set of broad-band photometry of a galaxy spanning the UV/optical - FIR/submm range to derive the intrinsic (i.e. as would be observed in the absence of dust) UV/optical emission of the galaxy. Using real and simulated data we illustrate the application of the SED modelling technique to the derivation of star formation rates and star formation histories of optically selected spiral galaxies in the local Universe observed by GAMA and Herschel. Specifically, we quantify how the amplitude and wavelength dependence of the UV/optical attenuation is related to the amplitude and colour of the FIR/submm continuum emission measured using the PACS and SPIRE instruments, and describe how to utilise morphological information from higher resolution optical observations of GAMA galaxies (such as linear sizes of disks and the bulge-disk decompositions) in the interpretation of the panchromatic observations.

Scale Size Evolution of Brightest Galaxies
Burke, Claire, C. Collins, J. Stott
Astrophysics Research Institute LJMU
12 April, 17:00

Scale sizes of elliptical galaxies have been a topic of discussion recently due to the unexpected result that these objects evolve from a compact state. We present our preliminary results of scale size measurements of brightest cluster galaxies (BCGs) at z~1, using deep imaging from HST and Subaru MOIRCS of ~10 BCGs in both the optical and near infra-red. We find robust BCG scale sizes of ~ 10kpc, and infer that this is evidence for mild size evolution of this homogeneous population since z~1. We discuss implications of this result, in concert with the recent result of no mass evolution of these galaxies over the same period, for cosmological models of the late time evolution of massive early type galaxies.

Poster Abstracts

Galaxy Clustering Using Photometric Redshifts
Christodoulou, Leonidas, Jon Loveday, GAMA Team
University of Sussex

The GAMA spectroscopic release offers a unique opportunity to calibrate photometric redshifts from SDSS down to r=19.4. Taking advantage of the fact that GAMA offers a truly representative subset of SDSS we construct a catalogue of ~5 million objects, using an artificial neural network (ANNz). Moreover, we carry out an extensive error analysis to check for possible biases in our redshifts estimation. We also show independent estimations of the underlying redshift distribution, using a weighting method (Cunha et al, 2009), which recovers more accurately the redshift distribution. This allows as to reveal the weakness and the strengths of the two methods. Having done that, we measure the two point angular correlation function in luminosity bins and then using Limber's approximation we calculate the spatial correlation function. Finally we compare with the results in the literature from spectroscopic surveys. However, because of the use of photometric redshifts our work extends to intrinsically faint objects with magnitude down to M=-14.

Studying galaxy evolution with FMOS (Fibre Multi-Object Spectrograph)
Curtis Lake, Emma, Gavin Dalton, Thomas Mauch, Naruhisa Takato, Naoyuki Tamura, Ian Smail, Philip Best, Jim Geach, David Sobral, FMOS team
University of Oxford

FMOS (Fibre Multi-Object Spectrograph) is now available on the Subaru Telescope for obtaining near-infrared spectra in the J and H bands. With 400 target fibres, within a wide field of view, this instrument provides the means to extend the results from low redshift spectroscopic surveys using the same lines as detected in the optical. In particular, star formation can be traced by H-alpha emission between ~0.5

A new approach to disentangling star formation histories from survey data
Ferreras, Ignacio
MSSL/UCL

Large, homogeneous surveys such as SDSS or GAMA allow us to apply multivariate techniques based at extracting differences between the stellar populations of galaxies in a model-independent way. In this talk I will present recent and ongoing research focused on a volume-limited sample of early-type galaxies from SDSS. Principal Component Analysis (PCA) is used to define two estimators of average age and recent star formation which is then applied to subsamples of close pairs of early-types (i.e. the precursors of dry mergers) or to samples classified according to the mass of the parent halo in order to quantify the effect of environment on the star formation history of galaxies. Future directions for the promising field of multivariate analysis of photo-spectroscopic data will be presented.

A new sample of "blazars" to study the relationship between radio-loud AGN and galaxy formation
Gupta, Jennifer, Ian Browne
Jodrell Bank Centre for Astrophysics

Radio-loud active galactic nuclei are now recognised to be vital in the process of galaxy formation, by providing feedback which regulates the star-formation process. Logically it follows that in order to understand galaxy formation and evolution, we must understand AGN. However, the details of how AGN feedback happens is a difficult problem; there are many unanswered questions, such as what triggers the bursts of AGN activity, how long do the bursts of activity last and how do the bursts evolve. Blazars are a subset of radio-loud AGN where one of the radio jets is directed towards the observer at a small angle to the line of sight. Therefore in blazars we get the most direct view of the relativistic jets that may ultimately provide the feedback. We have defined a new sample of nearby blazar-like objects, attempting to minimise the selection effects in order to understand the fundamental and intrinsic properties of these objects. The Survey of Extragalactic Nuclear Spectral Energies (SENSE) sample contains 151 compact radio core objects within z < 0.2. Here we present the SENSE sample with an emphasis on the ways in which we are using multiwavelength observations of the sample to probe the physics of blazars in the low-redshift Universe.

The radio spectral index of sub-millimetre galaxies.
Ibar, Edo, Edo Ibar, R. J. Ivison, P. N. Best, K. Coppin, A. Pope, Ian Smail, J. S. Dunlop
UK Astronomy Technology Centre

We have employed the Giant Metre-wave Radio Telescope and the Very Large Array to map the Lockman Hole. At 610 and 1400MHz, we reach noise levels of 15 and 6microJy/beam, respectively, with well-matched resolutions (~5arcsec). At this depth, we obtained reliable detections for about half of the known sub-mm galaxies (SMGs) in the field (SCUBA, AzTEC and MAMBO). For radio-identified SMGs, which are typically at z ~ 2, we measure a mean radio spectral index of alpha(1400,610) = -0.75 ± 0.06 (where S_nu ~ nu^alpha) and standard deviation of 0.29, between approximate rest-frame frequencies of 1.8 and 4.2GHz. The slope of their continuum emission is indistinguishable from that of local star-forming galaxies and suggests that extended optically thin synchrotron emission dominates the radio output of SMGs. Cooling effects by synchrotron emission and Inverse Compton scattering off the cosmic microwave background do not seem to affect their radio spectral energy distributions. For those SMGs judged by Spitzer mid-infrared colours and spectroscopy to host obscured active galactic nuclei (AGN), we find a clear deviation from the rest of the sample - they typically have steeper radio spectral indices, alpha(1400,610) ~< -1.0. These findings suggest these mid-IR-/AGN-selected SMGs may have an intrinsically different injection mechanism for relativistic particles, or they might reside in denser environments. This work provides a reliable spectral template for the estimation of far-IR/radio photometric redshifts, and will enable accurate statistical K-corrections for the large samples of SMGs expected with SCUBA-2 and Herschel.

Robust methods to probe source evolution in galaxy redshift surveys
Johnston, Russell
University of the Western Cape

One of the most fundamental, and still relevant, statistical challenges in modern observational cosmology is accurately determining the galaxy luminosity function. Determining the luminosity function of galaxies remains a vital and fundamental tool for assessing the statistical nature of galaxy formation and evolution. Pertinent to this area of study is accurately characterising source evolution in galaxy redshift surveys.

I will present a recently developed method that robustly constrains luminosity evolutionary models by exploiting the properties of the magnitude completeness test developed by Rauzy (2001) and Johnston, Teodoro & Hendry (2007), combined with a maximum entropy approach. This statistical approach has the potential advantage over traditional approaches by not making any assumption of the parametric form of the underlying luminosity function and is also independent the spatial distribution of galaxies.

GAMA: Single and Multi-Component Galaxy Modelling
Kelvin, Lee, Aaron Robotham, Simon Driver, Ewan Cameron, David Hill, GAMA Team
St Andrews

I present results from the GAMA structural decomposition pipeline (GAMA-SIGMA; Structural Investigation of Galaxies via Model Analysis) for all GAMA objects with optical-to-near-IR imaging from the SDSS & UKIDSS-LAS surveys. I show that photometric modelling shorter than the i band restricts the recoverability of galactic properties, and discuss the role of dust in changing our view of the Universe. I also demonstrate how full bulge-disk-bar decomposition is required in order to gain further insight into the formation and evolution of galaxies, and discuss its application to ~12,000 nearby galaxies in the forthcoming high-resolution/deep VST & VISTA imaging of the GAMA fields.

The ALFALFA HI Absorption Survey
Macdonald, Erin, Jeremy Darling, ALFALFA Team
University of Glasgow

We present the results of a wide-area pilot survey to search for cold Neutral Hydrogen (HI) 21~cm absorption utilizing the Arecibo Legacy Fast Arecibo L-Band Feed Array (ALFALFA) Survey. This survey is the first to conduct a wide-area (517.0 deg$^2$) ''blind'' search for HI absorption in the local universe. The survey spans $10.9^h < \alpha < 14.95^h$ and $+7.7^\circ < \delta < 6.3^\circ$ centred on the Virgo Cluster. The full ALFALFA survey is an HI emission survey that covers $-650 ~{\rm km~s}^{-1}< cz < 17,500 ~{\rm kms}^{-1}$ (11$\%$ of this span is lost to radio frequency interference and Galactic HI emission) resulting in a $\Delta$z = 0.054 along each line of sight. When completed, the ALFALFA survey will span 7000~deg$^2$. Our survey is sensitive to HI absorption lines towards radio sources stronger than 8.4~mJy. This includes 8983 sources for a total search path of $\Delta z = 485.1$. There are 243 sources toward which all damped Ly-$\alpha$ systems (N(HI) $> 2\times10^{20}$~cm$^{-2}$) could be detected, and 3282 sources toward which N(HI)$ > 2\times 10^{21}$~cm$^{-2}$ columns could be detected. We detect one previously known HI absorption line in UGC 6081, confirming our method is feasible, but make no new detections. Using these data, we calculate an upper limit to the HI column density distribution function and its moments. This pilot survey demonstrates the value and feasibility of large-area radio absorption line searches that are not yet possible with optical telescopes and provides a baseline for future HI 21 cm absorption line surveys planned for new radio facilities, such as SKAMP, ASKAP, MEERKAT and the ATA.

Improved sky subtraction for spectroscopic pipelines
Parkinson, Hannah, GAMA team
IfA, Edinburgh

Imperfect sky subtraction continues to be a problem for galaxy redshift surveys, with the effect increasing with wavelength. I will present a new application of Principle Component Analysis (PCA), developed for the Galaxy And Mass Assembly (GAMA) survey, which empirically models the residuals from sky subtraction and returns significantly cleaner galaxy spectra. This new approach does not require additional sky spectra, operates separately on each spectroscopic field acquired and, through its empirical nature, specific knowledge of the source spectrum in advance of the sky subtraction is not even required. Results using spectra from the GAMA survey will be presented.

Red and Blue Satellite Galaxies in the Galaxy and Mass Assembly Survey
Prescott, Matthew, Ivan K. Baldry, Phil A. James, GAMA Team
LJMU Astrophysics Research Institute

The role of blue-sequence satellite galaxies in the fuelling of disk galaxies. A long-standing problem for disk galaxies is the origin of the continuing gas supply required to explain their star formation and chemical abundance properties. One possible source is from gas-rich satellites, either through minor mergers ('cannibalism') or from the gas component only of the dwarf being transferred to the disk galaxy, with the gas removal occurring either through tides or through supernova-driven winds. An initial search for gas-rich companions of field disk galaxies using wide-field H alpha imaging shows that Magellanic Cloud-like satellites are surprisingly rare. The scarcity of gas-rich companions could be indicative of the efficiency with which they have been gas-stripped and transformed into red-sequence, passive dwarfs. In this talk I will present the preliminary results of a study on the red-to-blue ratio of dwarf galaxies around isolated field disk galaxies selected from the GAMA survey, and the variation in this ratio as a function of projected separation.

Abundance gradients in simulated galaxy discs
Rahimi, Awat, Daisuke Kawata, Chris B. Brook, Brad K. Gibson, Carlos Allende-Prieto
MSSL/UCL

TBC

Modelling radiation fields in galaxies using a new radiation transfer code
Semionov, Dmitrij
Jeremiah Horrocks Institute, UCLan

We describe a new ray tracing radiation transfer (RTR) code being developed at UCLan, optimised for calculating the distribution of radiation fields in dusty galaxies. Primary applications will be to model images and integrated SEDs in direct and dust re-radiated light of synthetic galaxies calculated self consistently with CDM cosmology.

NGC 2976 & NGC 3351: 12CO(3-2) Observations and its Correlation with PAH 8um
Tan, Boon Kok, Jamie Leech, Dimitra Rigopoulou, NGLS team members
University of Oxford

We present 12CO(3-2) maps of NGC 2976 and NGC 3351 obtained using the James Clerk Maxwell Telescope. Both galaxies are part of the Nearby Galaxy Legacy Survey (NGLS). We combine these data with the 12CO(3-2) maps from Nobeyama Radio Observatory and Berkeley Illinois Maryland Association interferometer to derive CO line-ratio map. The value of 12CO(3-2) to 12CO(1-0) line ratio we obtained was within 0.2--0.6 range. Using this ratio, we derived the total molecular gas mass of 3 \times 10^7 solar mass for NGC 2976 and 7.55x10^8 solar mass for NGC 3351. We present spectral maps and discuss the velocity field and the velocity dispersion of the two galaxies. We find that these velocity components are very similar to the data from the VLA survey of HI emission. Using 8 um Spitzer data, we investigated the correlation of the 12CO(3-2) intensity with the PAH 8 micron surface brightness. We study the radial distribution of these star formation tracers in the two galaxies and suggest that the correlation is good at high surface brightness region. We extend this study to include the total surface brightness of the 12CO(3-2) and the PAH 8 \mu m emission of 17 galaxies within the NGLS samples. We find that the correlation is very good at large spatial scale, as both physical parameters trace active star formation.