Showing papers by "Stuart D. Ryder published in 2005"

The HIPASS catalogue - III. Optical counterparts and isolated dark galaxies

Abstract: We present the largest catalogue to date of optical counterparts for H I radio-selected galaxies, HOPCAT. Of the 4315 H I radio-detected sources from the H I Parkes All Sky Survey (HIPASS) catalogue, we find optical counterparts for 3618 (84 percent) galaxies. Of these, 1798 (42 per cent) have confirmed optical velocities and 848 (20 per cent) are single matches without confirmed velocities. Some galaxy matches are members of galaxy groups. From these multiple galaxy matches, 714 (16 per cent) have confirmed optical velocities and a further 258 (6 per cent) galaxies are without confirmed velocities. For 481 (11 per cent), multiple galaxies are present but no single optical counterpart can be chosen and 216 (5 per cent) have no obvious optical galaxy present. Most of these 'blank fields' are in crowded fields along the Galactic plane or have high extinctions. Isolated 'dark galaxy' candidates are investigated using an extinction cut of A Bj < 1 mag and the blank-fields category. Of the 3692 galaxies with an A Bj extinction < 1 mag, only 13 are also blank fields. Of these, 12 are eliminated either with follow-up Parkes observations or are in crowded fields. The remaining one has a low surface brightness optical counterpart. Hence, no isolated optically dark galaxies have been found within the limits of the HIPASS survey. © 2005 RAS.

The HIPASS Catalogue: III - Optical Counterparts & Isolated Dark Galaxies

Abstract: We present the largest catalogue to date of optical counterparts for HI radio-selected galaxies, Hopcat. Of the 4315 HI radio-detected sources from the HI Parkes All Sky Survey (Hipass) catalogue, we find optical counterparts for 3618 (84%) galaxies. Of these, 1798 (42%) have confirmed optical velocities and 848 (20%) are single matches without confirmed velocities. Some galaxy matches are members of galaxy groups. From these multiple galaxy matches, 714 (16%) have confirmed optical velocities and a further 258 (6%) galaxies are without confirmed velocities. For 481 (11%), multiple galaxies are present but no single optical counterpart can be chosen and 216 (5%) have no obvious optical galaxy present. Most of these 'blank fields' are in crowded fields along the Galactic plane or have high extinctions. Isolated 'Dark galaxy' candidates are investigated using an extinction cut of ABj < 1 mag and the blank fields category. Of the 3692 galaxies with an ABj extinction < 1 mag, only 13 are also blank fields. Of these, 12 are eliminated either with follow-up Parkes observations or are in crowded fields. The remaining one has a low surface brightness optical counterpart. Hence, no isolated optically dark galaxies have been found within the limits of the Hipass survey.

Science Programs for a 2-m Class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope

Abstract: The cold, dry, and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-millimetre wavelengths to be found on the Earth. Pathfinder for an International Large Optical Telescope (PILOT) is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near diffraction-limited performance with simple tip–tilt wavefront correction. PILOT would also be capable of near diffraction-limited performance in the optical wavebands, as well be able to open new wavebands for regular ground-based observation, in the mid-IR from 17 to 40 μm and in the sub-millimetre at 200 μm.

Massive H i clouds with no optical counterparts as high-density regions of intragroup H i rings and arcs

Abstract: We present a new scenario in which massive intragroup HI clouds are the high-density parts of large HI rings/arcs formed by dynamical interaction between galaxy groups and gas-rich, low surface brightness (LSB) galaxies with extended gas disks. Our hydrodynamical simulations demonstrate that the group tidal field is very efficient at stripping the outer HI gas of the disk if the gaseous disk of the LSB galaxy extends $2 - 5$ times further than the stellar disk. We find that a massive, extended `leading stream' orbiting the group's center can form out of the stripped outer HI envelope, while the severely shrunk LSB galaxy, whose stellar disk remains unaffected, continues on its path. The result is a relatively isolated, massive HI cloud with a ring- or arc-like shape, a very inhomogeneous density distribution ($N_{\\rm HI} \\sim 1.0 \\times 10^{17} - 1.1 \\times 10^{20}$ atoms cm$^{-2}$), and, initially, no stellar content. Only the high density peaks of the simulated intragroup HI ring/arc can be detected in many current HI observations. These will appear as relatively isolated `HI islands' near the group center. We also find that star formation can occur within the ring/arc, if the total gas mass within the intragroup ring/arc is very large ($\\sim$ 4 $\\times$ $10^9$ ${\\rm M}_{\\odot}$). We discuss these results in terms of existing observations of intragroup gas (e.g., the Leo Ring and HIPASS J0731--69) and intergalactic HII regions.

Neutral hydrogen gas in 7 high-inclination spiral galaxies - I. The data

Abstract: High-sensitivity interferometric H i line observations of a small sample of seven galaxies with limiting column densities of a few times 10 19 cm -2 are presented. A tilted ring model fitting routine was used to determine some global characteristics of the H i distribution and kinematics in the galaxy disks. 4 of the 7 galaxies have low maximum rotation velocities of $\la$125 km s -1 , indicating that they are low-mass systems. Visual inspection shows that at least one galaxy, NGC 4700, exhibits signs of extraplanar H i emission. An in-depth search for H i gas in the galaxy halos and the determination of halo gas properties, based on three-dimensional modeling, will follow in a separate publication. Companion galaxies were detected in H i line emission near 3 of the 7 sample galaxies: NGC 1511, NGC 4565 and NGC 4700. One of these, NGC 1511, is found to be strongly interacting and is therefore not suitable for a study of the dependence of its halo properties on the level of star formation activity in the underlying disk. In the case of NGC 4700 the companion galaxy has no visible influence on its gas kinematics, while NGC 4565 might be affected by its interaction with two small companions.

Examining the Seyfert - Starburst Connection with Arcsecond Resolution Radio Continuum Observations

Abstract: We compare the arcsecond-scale circumnuclear radio continuum properties between five Seyfert and five starburst galaxies, concentrating on the search for any structures that could imply a spatial or causal connection between the nuclear activity and a circumnuclear starburst ring. No evidence is found in the radio emission for a link between the triggering or feeding of nuclear activity and the properties of circumnuclear star formation. Conversely, there is no clear evidence of nuclear outflows or jets triggering activity in the circumnuclear rings of star formation. Interestingly, the difference in the angle between the apparent orientation of the most elongated radio emission and the orientation of the major axis of the galaxy is on average larger in Seyferts than in starburst galaxies, and Seyferts appear to have a larger physical size scale of the circumnuclear radio continuum emission. The concentration, asymmetry, and clumpiness parameters of radio continuum emission in Seyferts and starbursts are comparable, as are the radial profiles of radio continuum and near-infrared line emission. The circumnuclear star formation and supernova rates do not depend on the level of nuclear activity. The radio emission usually traces the near-infrared Br-gamma and H2 1-0 S(1) line emission on large spatial scales, but locally their distributions are different, most likely because of the effects of varying local magnetic fields and dust absorption and scattering.

Stellar abundance gradients in galactic discs — I. Method and spectral line gradients

Abstract: We describe the technique of absorption-line imaging of galaxy discs using the Taurus Tunable Filter on the Anglo-Australian Telescope and demonstrate its sensitivity to the behaviour of spectral features associated with Mg and Fe. Radial profiles of Mg 2 and Fe5270 line strengths are presented for a sample of eight face-on spiral galaxies spanning a range of Hubble types. Signatures of phenomena including merger-induced star formation, H II rings and galactic bars are also reported. This study demonstrates the capacity of tunable filters to measure Mg and Fe line strengths across the face of spiral galaxies, which can ultimately reveal clues about the star formation history and chemical evolution.

The Circumnuclear Starburst in M83

Abstract: We present results from near‐infrared integral‐field spectroscopy of the circumnuclear starburst in M83, using the CIRPASS instrument on Gemini South. The combination of Paβ, CO (6,3), and [Fe II] equivalent width measurements over large contiguous regions allows us to track the spatial propagation of star formation across the ringlet, which is too heavily obscured to be properly analysed at optical wavelengths. We find the clearest evidence yet for an age gradient, with the youngest clusters found closest to where the dust lane crosses the ringlet. We discuss the implications for gas fueling by the bar.

Radio Monitoring of Supernova 2001ig: The First Year

Abstract: Supernova 2001ig in NGC 7424 has been observed with the Australia Telescope Compact Array at ∼2 week intervals since its discovery, making this the best-studied Type IIb radio supernova since SN 1993J.We present radio light curves for frequencies from 1.4 to 20 GHz, and preliminary attempts to model the observed behavior. Since peaking in radio luminosity at 8.6 and 4.8 GHz some 1–2 months after the explosion, SN 2001ig has on at least two occasions deviated significantly from a smooth decline, indicative of interaction with a dense circumstellar medium and possibly of periodic progenitor mass-loss.

Stellar abundance gradients in galactic disks. I. Method and spectral line gradients

Abstract: We describe the technique of absorption line imaging of galaxy disks using the Taurus Tunable Filter on the Anglo-Australian Telescope and demonstrate its sensitivity to the behaviour of spectral features associated with Mg and Fe. Radial profiles of Mg2 and Fe5270 line-strengths are presented for a sample of eight face-on spiral galaxies spanning a range of Hubble types. Signatures of phenomena including merger-induced star formation, HII rings and galactic bars are also reported. This study demonstrates the capacity of tunable filters to measure Mg and Fe line-strengths across the face of spiral galaxies, which can ultimately reveal clues about the star formation history and chemical evolution.