arXiv subjects

Martin Meyer

Publications and source records attributed to Martin Meyer.

At least 55 records · Page 3Linked to original sources

arXiv2015

SoFiA: a flexible source finder for 3D spectral line data

We introduce SoFiA, a flexible software application for the detection and parameterization of sources in 3D spectral-line datasets. SoFiA combines for the first time in a single piece of software a set of new source-finding and parameterization algorithms developed on the way to future HI surveys with ASKAP (WALLABY, DINGO) and APERTIF. It is designed to enable the general use of these new algorithms by the community on a broad range of datasets. The key advantages of SoFiA are the ability to: search for line emission on multiple scales to detect 3D sources in a complete and reliable way, taking into account noise level variations and the presence of artefacts in a data cube; estimate the reliability of individual detections; look for signal in arbitrarily large data cubes using a catalogue of 3D coordinates as a prior; provide a wide range of source parameters and output products which facilitate further analysis by the user. We highlight the modularity of SoFiA, which makes it a flexible package allowing users to select and apply only the algorithms useful for their data and science questions. This modularity makes it also possible to easily expand SoFiA in order to include additional methods as they become available. The full SoFiA distribution, including a dedicated graphical user interface, is publicly available for download.

astro-ph.IM↗

arXiv2015

Connecting the Baryons: Multiwavelength Data for SKA HI Surveys

The science achievable with SKA HI surveys will be greatly increased through the combination of HI data with that at other wavelengths. These multiwavelength datasets will enable studies to move beyond an understanding of HI gas in isolation to instead understand HI as an integral part of the highly complex baryonic processes that drive galaxy evolution. As they evolve, galaxies experience a host of environmental and feedback influences, many of which can radically impact their gas content. Important processes include: accretion (hot and cold mode, mergers), depletion (star formation, galactic winds, AGN), phase changes (ionised/atomic/molecular), and environmental effects (ram pressure stripping, tidal effects, strangulation). Governing all of these to various extents is the underlying dark matter distribution. In turn, the result of these processes can significantly alter the baryonic states in which material is finally observed (stellar populations, dust, chemistry) and its morphology (galaxy type, bulge/disk ratio, bars, warps, radial profile). To fully understand the evolution of HI and the role it plays in galactic evolution requires the ability to quantify each of these separate processes, and hence to coordinate SKA HI surveys with extensive multi-band photometric and spectroscopic campaigns. In addition, multiwavelength data is essential for statistical methods of HI analysis such as HI stacking and intensity mapping cross-correlations. In this chapter, we examine some of the principal science motivations for acquiring multiwavelength data to match that from the extragalactic SKA HI surveys, and review the currently planned capacity to achieve this (eg. LSST, Euclid, W-FIRST, SPICA, ALMA, and 4MOST).

astro-ph.GA↗

arXiv2014

100 deg$^2$ Mock Galaxy Cone for HI Surveys with the Early SKA

We distribute an easy-to-use mock catalog of galaxies with detailed neutral atomic hydrogen (HI) and auxiliary molecular and optical properties. The catalog covers a field of 10-by-10 degrees and a redshift range of z=0-1.2. It contains galaxies with 21cm peak flux densities down to 1uJy and is, within this flux limit, complete for HI masses above 10^8 solar masses. Five random realisations of the catalog in ASCII format (~4GB/file) and subtables with HI flux limits of 10u Jy (~500MB/file) and 100uJy$ (~30MB/file) can be downloaded at http://ict.icrar.org/store/staff/do/s3sax.

astro-ph.GA↗

arXiv2013

Detection of HI in distant galaxies using spectral stacking

Using the Parkes radio telescope, we study the 21cm neutral hydrogen (HI) properties of a sample of galaxies with redshifts z<0.13 extracted from the optical 2dF Galaxy Redshift Survey (2dFGRS). Galaxies at 0.04<z<0.13 are studied using new Parkes observations of a 42deg^2 field near the South Galactic Pole (SGP). A spectral stacking analysis of the 3,277 2dFGRS objects within this field results in a convincing 12sigma detection. For the low-redshift sample at 0<z<0.04, we use the 15,093 2dFGRS galaxies observed by the HI Parkes All-Sky Survey (HIPASS) and find a 31sigma stacked detection. We measure average HI masses of (6.93 +/- 0.17)*10^9 h^{-2} Msun and (1.48 +/- 0.03)*10^9 h^{-2} Msun for the SGP and HIPASS samples, respectively. Accounting for source confusion and sample bias, we find a cosmic HI mass density of Omega_HI=(3.19_{-0.59} ^{+0.43})*10^{-4} h^{-1} for the SGP sample and (2.82_{-0.59}^{+0.30})*10^{-4} h^{-1} for the HIPASS sample. This suggests no (12 +/- 23%) evolution in the cosmic HI density over the last ~1h^{-1} Gyr. Due to the very large effective volumes, cosmic variance in our determination of Omega_HI is considerably lower than previous estimates. Our stacking analysis reproduces and quantifies the expected trends in the HI mass and mass-to-light ratio of galaxies with redshift, luminosity and colour.

astro-ph.CO↗

arXiv2013

Precise Tully-Fisher Relations without Galaxy Inclinations

Power-law relations between tracers of baryonic mass and rotational velocities of disk galaxies, so-called Tully-Fisher relations (TFRs), offer a wealth of applications in galaxy evolution and cosmology. However, measurements of rotational velocities require galaxy inclinations, which are difficult to measure, thus limiting the range of TFR studies. This work introduces a maximum likelihood estimation (MLE) method for recovering the TFR in galaxy samples with limited or no information on inclinations. The robustness and accuracy of this method is demonstrated using virtual and real galaxy samples. Intriguingly, the MLE reliably recovers the TFR of all test samples, even without using any inclination measurements - that is, assuming a sin(i)-distribution for galaxy inclinations. Explicitly, this 'inclination-free MLE' recovers the three TFR parameters (zero-point, slope, scatter) with statistical errors only about 1.5-times larger than the best estimates based on perfectly known galaxy inclinations with zero uncertainty. Thus, given realistic uncertainties, the inclination-free MLE is highly competitive. If inclination measurements have mean errors larger than 10 degrees, it is better not to use any inclinations, than to consider the inclination measurements to be exact. The inclination-free MLE opens interesting perspectives for future HI surveys by the SKA and its pathfinders.

astro-ph.CO↗

arXiv2013

Confronting Cold Dark Matter Predictions with Observed Galaxy Rotations

The rich statistics of galaxy rotations as captured by the velocity function (VF) provides invaluable constraints on galactic baryon physics and the nature of dark matter (DM). However, the comparison of observed galaxy rotations against cosmological models is prone to subtle caveats that can easily lead to misinterpretations. Our analysis reveals full statistical consistency between ~5000 galaxy rotations, observed in line-of-sight projection, and predictions based on the standard cosmological model (LCDM) at the mass-resolution of the Millennium simulation (HI line-based circular velocities above ~50 km/s). Explicitly, the HI linewidths in the HI Parkes All Sky Survey (HIPASS) are found consistent with those in S3-SAX, a post-processed semi-analytic model for the Millennium simulation. Previously found anomalies in the VF can be plausibly attributed to (1) the mass-limit of the Millennium simulation, (2) confused sources in HIPASS, (3) inaccurate inclination measurements for optically faint sources, and (4) the non-detectability of gas-poor early-type galaxies. These issues can be bypassed by comparing observations and models using linewidth source counts rather than VFs. We investigate if and how well such source counts can constrain the temperature of DM.

astro-ph.CO↗

arXiv2013

Choirs, HI Galaxy Groups: Catalogue and Detection of Star-forming Dwarf Group Members

Hα observations centred on galaxies selected from the HI Parkes All Sky Survey (HIPASS, Barnes et al. 2001) typically show one and sometimes two star-forming galaxies within the approximately 15-arcminute beam of the Parkes 64-m HI detections. In our Survey of Ionization in Neutral Gas Galaxies (SINGG, Meurer et al. 2006) we found fifteen cases of HIPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case we found a field with at least nine ELGs. In this paper we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HIPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total HI mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, Hα equivalent width, and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly HI-deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190 kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (the ratio of star formation rate to HI mass; SFE), showing an increasing trend in SFE with stellar mass.

astro-ph.CO↗

arXiv2013

Technology Transfer and the End of the Bayh-Dole Effect: Patents as an Analytical Lens on University-Industry-Government Relations

Three periods can be distinguished in university patenting at the U.S. Patent and Trade Office (USPTO) since the Bayh-Dole Act of 1980: (1) a first period of exponential increase in university patenting till 1995 (filing date) or 1999 (issuing date); (2) a period of relative decline since 1999; and (3) in most recent years -- since 2008 -- a linear increase in university patenting. We argue that this last period is driven by specific non-US universities (e.g., Tokyo University and Chinese universities) patenting increasingly in the U.S.A. as the most competitive market for high-tech patents.

cs.DL↗

arXiv2012

Comparison of potential ASKAP HI survey source finders

The large size of the ASKAP HI surveys DINGO and WALLABY necessitates automated 3D source finding. A performance difference of a few percent corresponds to a significant number of galaxies being detected or undetected. As such, the performance of the automated source finding is of paramount importance to both of these surveys. We have analysed the performance of various source finders to determine which will allow us to meet our survey goals during the DINGO and WALLABY design studies. Here we present a comparison of the performance of five different methods of automated source finding. These source finders are Duchamp, the Gamma-finder, CNHI, a 2D-1D Wavelet Reconstruction and S+C finder, a sigma clipping method. Each source finder was applied on the same three-dimensional data cubes containing (a) point sources with a Gaussian velocity profile and (b) spatially extended model-galaxies with inclinations and rotation profiles. We focus on the completeness and reliability of each algorithm when comparing the performance of the different source finders.

astro-ph.IM↗

arXiv2010

Deep 21-cm HI Observations at z~0.1: The Precursor to the Arecibo Ultra Deep Survey

The "ALFA Ultra Deep Survey" (AUDS) is an ongoing 21-cm spectral survey with the Arecibo 305m telescope. AUDS will be the most sensitive blind survey undertaken with Arecibo's 300 MHz Mock spectrometer. The survey searches for 21-cm HI line emission at redshifts between 0 and 0.16. The main goals of the survey are to investigate the HI content and probe the evolution of HI gas within that redshift region. In this paper, we report on a set of precursor observations with a total integration time of 53 hours. The survey detected a total of eighteen 21-cm emission lines at redshifts between 0.07 and 0.15 in a region centered around ra~0:00h, dec= 15:42deg. The rate of detection is consistent with the one expected from the local HI mass function. The derived relative HI density at the median redshift of the survey is rho_HI[z=0.125]=(1.0+/-0.3)*rho_0, where rho_0 is the HI density at zero redshift.

astro-ph.CO↗

arXiv2010

The Decline of University Patenting and the End of the Bayh-Dole Effect

University patenting has been heralded as a symbol of changing relations between universities and their social environments. The Bayh-Dole Act of 1980 in the USA was eagerly promoted by the OECD as a recipe for the commercialization of university research, and the law was imitated by a number of national governments. However, since the 2000s university patenting in the most advanced economies has been on the decline both as a percentage and in absolute terms. We suggest that the institutional incentives for university patenting have disappeared with the new regime of university ranking. Patents and spin-offs are not counted in university rankings. In the new arrangements of university-industry-government relations, universities have become very responsive to changes in their relevant environments.

physics.soc-ph↗

arXiv2009

Exploring the HI Universe with ASKAP

The survey speed of ASKAP makes it a prime instrument with which to survey the HI universe, enabling it to carry out both wide surveys of the entire sky, as well as deep surveys covering cosmologically representative volumes. Here, the use of ASKAP to study deep HI fields is discussed as proposed by the Deep Investigation of Neutral Gas Origins (DINGO) survey. This ASKAP science survey project anticipates observing in excess of 10^5 sources out to redshift z~0.4. Key science goals include: Omega_HI and its evolution, the cosmic web as traced by distributions such as the HI mass function and the 2pt correlation function, and the formation and evolution of galaxies. Science returns are maximised by targeting the GAMA survey regions, enabling the HI content of galaxies to be studied and understood in full context with all the major galactic constituents over the past 4 Gyr.

astro-ph.CO↗

arXiv2009

The velocity function of gas-rich galaxies

We measure the distribution function of rotational velocities phi(V_c) of late-type galaxies from the HIPASS galaxy catalogue. Previous measurements of the late-type velocity function are indirect, derived by converting the galaxy luminosity function using the relation between galaxy luminosity and rotation velocity (the Tully-Fisher relation). The advantage of HIPASS is that space densities and velocity widths are both derived from the same survey data. We find good agreement with earlier inferred measurements of phi(V_c), but we are able to define the space density of objects with V_c as low as 30 km/s. The measured velocity function is `flat' (power-law slope alpha ~ -1.0) below V_c = 100 km/s. We compare our results with predictions based on LCDM simulations and find good agreement for rotational velocities in excess of 100 km/s, but at lower velocities current models over-predict the space density of objects. At V_c=30 km/s this discrepancy is approximately a factor 20.

astro-ph.CO↗

arXiv2009

Triple Helix Indicators of Knowledge-Based Innovation Systems

When two selection environments operate upon each other, mutual shaping in a co-evolution along a particular trajectory is one possible outcome. When three selection environments are involved, more complex dynamics can be expected as a result of interactions involving bi-lateral and tri-lateral relations. Three selection environments are specified in the Triple Helix model: (1) wealth generation (industry), (2) novelty production (academia), and (3) public control (government). Furthermore, this model somewhat reduces the complexity by using university-industry-government relations for the specification of the historical conditions of the non-linear dynamics. One can no longer expect a one-to-one correspondence between institutions and functions; a statistics is needed for the evaluation of how, for how long, and to what extent institutional arrangements enhance synergies among different selection environments. The empirical contributions to this Triple Helix issue point in the direction of "rich ecologies": the construction of careful balances between differentiation and integration among the three functions.

physics.soc-ph↗

arXiv2009

The Scientometrics of a Triple Helix of University-Industry-Government Relations

We distinguish between an internal differentiation of science and technology that focuses on instrumentalities and an external differentiation in terms of the relations of the knowledge production process to other social domains, notably governance and industry. The external contexts bring into play indicators and statistical techniques other than publications, patents, and citations. Using regression analysis, for example, one can examine the importance of knowledge and knowledge spill-over for economic development. The relations can be expected to vary among nations and regions. The field-specificity of changes is emphasized as a major driver of the research agenda. In a knowledge-based economy, institutional arrangements can be considered as support structures for cognitive developments.

physics.soc-ph↗

arXiv2009

Diversity and network coherence as indicators of interdisciplinarity: Case studies in bionanoscience

The multidimensional character and inherent conflict with categorisation of interdisciplinarity makes its mapping and evaluation a challenging task. We propose a conceptual framework that aims to capture interdisciplinarity in the wider sense of knowledge integration, by exploring the concepts of diversity and coherence. Disciplinary diversity indicators are developed to describe the heterogeneity of a bibliometric set viewed from predefined categories, i.e. using a top-down approach that locates the set on the global map of science. Network coherence indicators are constructed to measure the intensity of similarity relations within a bibliometric set, i.e. using a bottom-up approach, which reveals the structural consistency of the publications network. We carry out case studies on individual articles in bionanoscience to illustrate how these two perspectives identify different aspects of interdisciplinarity: disciplinary diversity indicates the large-scale breadth of the knowledge base of a publication; network coherence reflects the novelty of its knowledge integration. We suggest that the combination of these two approaches may be useful for comparative studies of emergent scientific and technological fields, where new and controversial categorisations are accompanied by equally contested claims of novelty and interdisciplinarity.

physics.soc-ph↗

arXiv2007

Star Formation in NGC 5194 (M51a). II. The Spatially-Resolved Star Formation Law

We have studied the relationship between the star formation rate (SFR) surface density and gas surface density in the spiral galaxy M51a (NGC 5194), using multi-wavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of H-alpha emission-line and 24 micron continuum luminosities, that provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis HI and CO maps has allowed us to probe the form of the spatially-resolved star formation law on scales of 0.5 to 2 kpc. We find that the resolved SFR vs gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zeropoint and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parametrization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.

astro-ph↗

arXiv2007

Stellar Clusters in NGC 1313: Evidence for Infant Mortality

We present evidence that infant mortality of stellar clusters is likely to be a major and very efficient process for the dissolution of young clusters in the spiral galaxy NGC 1313. Performing stellar PSF photometry on archival HST/ACS images of the galaxy, we find that a large fraction of early B-type stars are seen outside of star clusters and well spread within the galactic disk, consistent with the scenario of infant mortality. We also calculate the UV flux produced by the stars in and out the clusters and find that 75 to 90% of the UV flux in NGC 1313 is produced by stars outside the clusters. These results suggest that the infant mortality of star clusters is probably the underlying cause of the diffuse UV emission in starburst galaxies. Infant mortality would also explain the numerous B-type stars observed in the background field of our Galaxy as well. We exclude the possibility that unresolved low-mass star clusters and scaled OB associations might be the main source for the diffuse UV emission.

astro-ph↗