arXiv subjects

J. R. Mould

Publications and source records attributed to J. R. Mould.

At least 19 recordsLinked to original sources

arXiv2023

WALLABY Pilot Survey: the Potential Polar Ring Galaxies NGC~4632 and NGC~6156

We report on the discovery of two potential polar ring galaxies (PRGs) in the WALLABY Pilot Data Release 1 (PDR1). These untargetted detections, cross-matched to NGC 4632 and NGC 6156, are some of the first galaxies where the Hi observations show two distinct components. We used the iDaVIE virtual reality software to separate the anomalous gas from the galactic gas and find that the anomalous gas comprises ~ 50% of the total H i content of both systems. We have generated plausible 3D kinematic models for each galaxy assuming that the rings are circular and inclined at 90 degrees to the galaxy bodies. These models show that the data are consistent with PRGs, but do not definitively prove that the galaxies are PRGs. By projecting these models at different combinations of main disk inclinations, ring orientations, and angular resolutions in mock datacubes, we have further investigated the detectability of similar PRGs in WALLABY. Assuming that these galaxies are indeed PRGs, the detectability fraction, combined with the size distribution of WALLABY PDR1 galaxies, implies an incidence rate of ~ 1% - 3%. If this rate holds true, the WALLABY survey will detect hundreds of new polar ring galaxies.

astro-ph.GA↗

arXiv2021

SoFiA 2 -- An automated, parallel HI source finding pipeline for the WALLABY survey

We present SoFiA 2, the fully automated 3D source finding pipeline for the WALLABY extragalactic HI survey with the Australian SKA Pathfinder (ASKAP). SoFiA 2 is a reimplementation of parts of the original SoFiA pipeline in the C programming language and makes use of OpenMP for multi-threading of the most time-critical algorithms. In addition, we have developed a parallel framework called SoFiA-X that allows the processing of large data cubes to be split across multiple computing nodes. As a result of these efforts, SoFiA 2 is substantially faster and comes with a much reduced memory footprint compared to its predecessor, thus allowing the large WALLABY data volumes of hundreds of gigabytes of imaging data per epoch to be processed in real-time. The source code has been made publicly available to the entire community under an open-source licence. Performance tests using mock galaxies injected into genuine ASKAP data suggest that in the absence of significant imaging artefacts SoFiA 2 is capable of achieving near-100% completeness and reliability above an integrated signal-to-noise ratio of about 5-6. We also demonstrate that SoFiA 2 generally recovers the location, integrated flux and w20 line width of galaxies with high accuracy. Other parameters, including the peak flux density and w50 line width, are more strongly biased due to the influence of the noise on the measurement. In addition, very faint galaxies below an integrated signal-to-noise ratio of about 10 may get broken up into multiple components, thus requiring a strategy to identify fragmented sources and ensure that they do not affect the integrity of any scientific analysis based on the SoFiA 2 output.

astro-ph.IM↗

arXiv2019

The Southern Stellar Stream Spectroscopic Survey (${S}^5$): Overview, Target Selection, Data Reduction, Validation, and Early Science

We introduce the Southern Stellar Stream Spectroscopy Survey (${S}^5$), an on-going program to map the kinematics and chemistry of stellar streams in the Southern Hemisphere. The initial focus of ${S}^5$ has been spectroscopic observations of recently identified streams within the footprint of the Dark Energy Survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9-m Anglo-Australian Telescope's 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from $Gaia$ DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far ${S}^5$ has mapped 9 DES streams and 3 streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the ${S}^5$ program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on ${S}^5$, including future public data release, can be found at \url{http://s5collab.github.io}.

astro-ph.GA↗

arXiv2019

An Ultra Deep Field survey with WFIRST

Studying the formation and evolution of galaxies at the earliest cosmic times, and their role in reionization, requires the deepest imaging possible. Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB$\,\sim\,$30, revealing galaxies at the faint end of the LF to $z$$\,\sim\,$9$\,-\,$11 and constraining their role in reionization. However, a key limitation of these fields is their size, only a few arcminutes (less than a Mpc at these redshifts), too small to probe large-scale environments or clustering properties of these galaxies, crucial for advancing our understanding of reionization. Achieving HUDF-quality depth over areas $\sim$100 times larger becomes possible with a mission like the Wide Field Infrared Survey Telescope (WFIRST), a 2.4-m telescope with similar optical properties to HST, with a field of view of $\sim$1000 arcmin$^2$, $\sim$100$\times$ the area of the HST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering $\sim$100$\,-\,$300$\times$ the area of the HUDF, or up to $\sim$1 deg$^2$, to \mAB$\,\sim\,$30, potentially revealing thousands of galaxies and AGN at the faint end of the LF, at or beyond $z$\,$\sim$\,9$\,-\,$10 in the epoch of reionization, and tracing their LSS environments, dramatically increasing the discovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted as input to the Astro2020 Decadal Survey, with this version including an Appendix (which exceeded the Astro2020 page limits), describing how the science drivers for a WFIRST Ultra Deep Field might map into a notional observing program, including the filters used and exposure times needed to achieve these depths.)

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arXiv2017

Self-consistent bulge/disk/halo galaxy dynamical modeling using integral field kinematics

We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sersic-profile stellar bulge, exponential disk and parametric dark matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep $g$- and $r$-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge-disk decomposition. Our method returns broadly consistent results for shared parameters, while constraining the mass-to-light ratios of stellar components and reproducing the HI-inferred circular velocity well beyond the limits of the SAMI data. While the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fibre dispersions and \HI circular velocities, and is well-suited for modelling galaxies with a combination of deep imaging and HI and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors.

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arXiv2013

Spectroscopic Observations of SN 2012fr: A Luminous Normal Type Ia Supernova with Early High Velocity Features and Late Velocity Plateau

We present 65 optical spectra of the Type Ia supernova SN 2012fr, of which 33 were obtained before maximum light. At early times SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II 6355 line which can be cleanly decoupled from the lower velocity "photospheric" component. This Si II 6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of v~12,000 km/s until at least 5 weeks after maximum brightness. The Ca II infrared (IR) triplet exhibits similar evidence for both a photospheric component at v~12,000 km/s with narrow line width and long velocity plateau, as well as a high-velocity component beginning at v~31,000 km/s two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. (2009) classification scheme, and on the border between normal and "high-velocity" SNe Ia in the Wang et al. (2009a) system. Though it is a clear member of the "low velocity gradient" (LVG; Benetii et al., 2005) group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution, and a key transitional event between nominal spectroscopic subclasses of SNe Ia.

astro-ph.CO↗

arXiv2009

The effect of metallicity on Cepheid magnitudes and the distance to M33

We present the results from a multi-epoch survey of two regions of M33 using the 3.5m WIYN telescope. The inner field is located close to the centre of the galaxy, with the outer region situated about 5.1 kpc away in the southern spiral arm, allowing us to sample a large metallicity range. We have data for 167 fundamental mode Cepheids in the two regions. The reddening-free Wesenheit magnitude Wvi period-luminosity relations were used to establish the distance modulus of each region, with mu_{inner} = 24.37 +- 0.02 mag and mu_{outer} = 24.54 +- 0.03 mag. The apparent discrepancy between these two results can be explained by the significant metallicity gradient of the galaxy. We determine a value for the metallicity parameter of the Period--Luminosity relation gamma = d(m-M)/d log(Z) = -0.29 +- 0.11 mag/dex, consistent with previous measurements. This leads to a metallicity corrected distance modulus to M33 of 24.53 +- 0.11 mag.

astro-ph.CO↗

arXiv2006

Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams

Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).

astro-ph↗

arXiv2004

Far Infrared Source Counts at 70 and 160 microns in Spitzer Deep Surveys

We derive galaxy source counts at 70 and 160 microns using the Multiband Imaging Photometer for Spitzer (MIPS) to map the Chandra Deep Field South (CDFS) and other fields. At 70 microns, our observations extend upwards about 2 orders of magnitude in flux density from a threshold of 15 mJy, and at 160 microns they extend about an order of magnitude upward from 50 mJy. The counts are consistent with previous observations on the bright end. Significant evolution is detected at the faint end of the counts in both bands, by factors of 2-3 over no-evolution models. This evolution agrees well with models that indicate most ofthe faint galaxies lie at redshifts between 0.7 and 0.9. The new Spitzer data already resolve about 23% of the Cosmic Far Infrared Background at 70 microns and about 7% at 160 microns.

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arXiv2003

The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI

We present a new accurate measurement of the HI mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest HI peak flux densities in the southern hemisphere (Koribalski et al. 2003). This sample spans nearly four orders of magnitude in HI mass (from log M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies, and show that this is a robust method, insensitive to the effects of large scale structure. The resulting HI mass function can be fitted satisfactorily with a Schechter function with faint-end slope alpha=-1.30. This slope is found to be dependent on morphological type, with later type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the HI mass function, including peculiar motions of galaxies, large scale structure, selection bias, and inclination effects, and quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies contribute only 15% to this value, consistent with previous findings.

astro-ph↗

arXiv2001

NICMOS Observations of Extragalactic Cepheids. I. Photometry Database and a Test of the Standard Extinction Law

We present the results of near-infrared observations of extragalactic Cepheids made with the Near Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope. The variables are located in the galaxies IC 1613, IC 4182, M 31, M 81, M 101, NGC 925, NGC 1365, NGC 2090, NGC 3198, NGC 3621, NGC 4496A and NGC 4536. All fields were observed in the F160W bandpass; additional images were obtained in the F110W and F205W filters. Photometry was performed using the DAOPHOT II/ALLSTAR package. Self-consistent distance moduli and color excesses were obtained by fitting Period-Luminosity relations in the H, I and V bands. Our results support the assumption of a standard reddening law adopted by the HST Key Project on the Extragalactic Distance Scale. A companion paper will determine true distance moduli and explore the effects of metallicity on the Cepheid distance scale.

astro-ph↗

arXiv2000

Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant

We present here the final results of the Hubble Space Telescope Key Project to measure the Hubble constant. We summarize our method, the results and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. The analysis presented here benefits from a number of recent improvements and refinements, including (1) a larger LMC Cepheid sample to define the fiducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. New, revised distances are given for the 18 spiral galaxies for which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we find values (in km/sec/Mpc) of H0 = 71 +/- 2 (random) +/- 6 (systematic) (type Ia supernovae), 71 +/- 2 +/- 7 (Tully-Fisher relation), 70 +/- 5 +/- 6 (surface brightness fluctuations), 72 +/- 9 +/- 7 (type II supernovae), and 82 +/- 6 +/- 9 (fundamental plane). We combine these results for the different methods with 3 different weighting schemes, and find good agreement and consistency with H0 = 72 +/- 8. Finally, we compare these results with other, global methods for measuring the Hubble constant.

astro-ph↗

arXiv2000

An Extragalactic HI Cloud with No Optical Counterpart?

We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an estimated distance of ~3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits (mu(B)~ 27 mag arcsec^-2). HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, HI 1225+01 (the Virgo HI Cloud) and has a size of at least 15 kpc. The mean velocity dispersion, measured with the Australia Telescope Compact Array (ATCA), is only 4 km/s for the main component and because of the weak or non-existent star-formation, possibly reflects the thermal linewidth (T<2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 10^19 cm^-2, which is estimated to be a factor of two below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognised class of Compact High Velocity Clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud/Galaxy system at perigalacticon ~ 2 x 10^8 yr ago.

astro-ph↗

arXiv1999

Observations and Implications of the Star Formation History of the LMC

We present derivations of star formation histories based on color-magnitude diagrams of three fields in the LMC from HST/WFPC2 observations. A significant component of stars older than 4 Gyr is required to match the observed color-magnitude diagrams. Models with a dispersion-free age-metallicity relation are unable to reproduce the width of the observed main sequence; models with a range of metallicity at a given age provide a much better fit. Such models allow us to construct complete ``population boxes'' for the LMC based entirely on color-magnitude diagrams; remarkably, these qualitatively reproduce the age-metallicity relation observed in LMC clusters. We discuss some of the uncertainties in deriving star formation histories. We find, independently of the models, that the LMC bar field has a larger relative component of older stars than the outer fields. The main implications suggested by this study are: 1) the star formation history of field stars appears to differ from the age distribution of clusters, 2) there is no obvious evidence for bursty star formation, but our ability to measure bursts shorter in duration than $\sim$ 25% of any given age is limited by the statistics of the observed number of stars, 3) there may be some correlation of the star formation rate with the last close passage of the LMC/SMC/Milky Way, but there is no dramatic effect, and 4) the derived star formation history is probably consistent with observed abundances, based on recent chemical evolution models.

astro-ph↗

arXiv1999

The Extragalactic Distance Scale Key Project XVIII. The Discovery of Cepheids and a New Distance to NGC 4535 Using the Hubble Space Telescope

We report on the discovery of Cepheids in the Virgo spiral galaxy NGC 4535, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. NGC 4535 is one of 18 galaxies observed as a part of The HST Key Project on the Extragalactic Distance Scale which aims to measure the Hubble constant to 10% accuracy. NGC 4535 was observed over 13 epochs using the F555W filter, and over 9 epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent programs, DoPHOT and DAOPHOT II/ALLFRAME. Period-luminosity relations in the V and I bands were constructed using 39 high-quality Cepheids present in our set of 50 variable candidates. We obtain a distance modulus of 31.02+/-0.26 mag, corresponding to a distance of 16.0+/-1.9 Mpc. Our distance estimate is based on values of mu = 18.50 +/- 0.10 mag and E(V-I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.

astro-ph↗

arXiv1998

Detection of Surface Brightness Fluctuations in NGC 4373 Using the Hubble Space Telescope

Surface brightness fluctuations (SBF) have been detected for three elliptical galaxies-NGC 3379 in the Leo group, NGC 4406 in the Virgo cluster, and NGC 4373 in the Hydra-Centaurus supercluster-using marginally-sampled, deep images taken with the Planetary Camera of the WFPC-2 instrument on the Hubble Space Telescope (HST). The power spectrum of the fluctuations image is well-fit by an empirical model of the point-spread function (PSF) constructed using point sources identified in the field. The previous ground-based SBF measurements for NGC 3379 and NGC 4406 are recovered, thereby demonstrating the capability of the Planetary Camera of WFPC-2 to measure distances using the SBF technique despite the marginal sampling of the images. The residual variance due to unresolved sources in all three galaxies is only 2-5% of the detected fluctuations signal, which confirms the advantage of HST imaging in minimizing the uncertainty of this SBF correction. Extensive consistency checks, including an independent SBF analysis using an alternate software package, suggest that our internal uncertainties are < 0.02 mag. The fluctuations magnitude for NGC 4373 is I814bar = 31.31 +/- 0.05 mag, corresponding to a distance modulus of DM = 32.99 +/- 0.11. This implies a peculiar velocity for this galaxy of 415 +/- 330 km/s, which is smaller than derived from the D_n-sigma relation. These results demonstrate the power of the post-repair HST to measure distances to elliptical galaxies at significant redshifts using the SBF technique.

astro-ph↗

arXiv1998

A Cepheid Distance to the Fornax Cluster

The Hubble Space Telescope is being used to measure accurate Cepheid distances to nearby galaxies with the ultimate aim of determining the Hubble constant, H_0. For the first time, it has become feasible to use Cepheid variables to derive a distance to a galaxy in the southern hemisphere cluster of Fornax. Based on the discovery of 37 Cepheids in the Fornax galaxy NGC 1365, a distance to this galaxy of 18.6 +/- 0.6 Mpc (statistical error only) is obtained. This distance leads to a value of H_0 = 70 +/- 7 (random) +/- 18 (systematic) km/sec/Mpc in good agreement with estimates of the Hubble constant further afield.

astro-ph↗

arXiv1998

The disruption of nearby galaxies by the Milky Way

Interactions between galaxies are common and are an important factor in determining their physical properties such as position along the Hubble sequence and star-formation rate. There are many possible galaxy interaction mechanisms, including merging, ram-pressure stripping, gas compression, gravitational interaction and cluster tides. The relative importance of these mechanisms is often not clear, as their strength depends on poorly known parameters such as the density, extent and nature of the massive dark halos that surround galaxies. A nearby example of a galaxy interaction where the mechanism is controversial is that between our own Galaxy and two of its neighbours -- the Large and Small Magellanic Clouds. Here we present the first results of a new HI survey which provides a spectacular view of this interaction. In addition to the previously known Magellanic Stream, which trails 100 degrees behind the Clouds, the new data reveal a counter-stream which lies in the opposite direction and leads the motion of the Clouds. This result supports the gravitational model in which leading and trailing streams are tidally torn from the body of the Magellanic Clouds.

astro-ph↗