arXiv subjects

L. S. Sparke

Publications and source records attributed to L. S. Sparke.

12 recordsLinked to original sources

arXiv2006

Stellar kinematics for the central spheroid in the Polar Disk Galaxy NGC4650A

We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically decoupled nucleus, and a flat velocity dispersion profile. The minor axis kinematics is determined for the first time: along this direction some rotation is measured, and the velocity dispersion is nearly constant and slightly increases at larger distances from the center. The new high resolution kinematic data suggest that the stellar component in NGC4650A resembles a nearly-exponential oblate spheroid supported by rotation. The main implications of these results on the previous mass models for NGC4650A are discussed. Moreover, the new kinematic data set constraints on current models for the formation scenarios of Polar Ring Galaxies (PRGs), supporting a slow accretion rather then a secondary strong dissipative event.

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arXiv2004

Radio Continuum Emission in Polar-Ring Galaxies

We have used the Very Large Array aperture synthesis telescope to conduct a radio continuum survey of polar-ring galaxies, at 20cm and 6cm. Forty objects were observed at 20cm with 5" resolution. Twenty (50%) of the program sources were detected at 20cm, down to our 5-sigma limit of 0.5 mJy/beam. This detection rate is similar to those in surveys with comparable sensitivity for early-type galaxies without polar rings. Sixteen of the objects we detected at 20cm were also observed at 6cm. We show radio continuum maps for the five objects in our sample that have noticeably extended emission. Our spatial resolution was sufficient to distinguish between emission originating in the host galaxy from that in the polar ring. The radio morphology of the extended sources, as well as the radio to far-infrared flux ratio and the radio spectral indices of our detected sources, indicate that star formation, not nuclear activity, is the dominant source of the radio continuum emission in polar-ring galaxies. However, the implied star-formation rates are modest, and only one of our sample galaxies will consume its supply of cool gas within 500 Myr.

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arXiv2004

Photometric structure of the peculiar galaxy ESO 235-G58

We present the near-infrared and optical properties of the peculiar galaxy ESO 235-G58, which resembles a late-type ringed barred spiral seen close to face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk galaxy of relatively low luminosity. We have analyzed the light and color distributions of ESO 235-G58 in the NIR and optical bands and compared them with the typical properties observed for other morphological galaxy types, including polar ring galaxies. Similar properties are observed for ESO 235-G58, polar ring galaxies, and spiral galaxies, which leads us to conclude that this peculiar system is a polar-ring-related galaxy, characterized by a low inclined ring/disk structure, as pointed out by Buta & Crocker in an earlier study, rather than a barred galaxy.

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arXiv2002

Polar Ring Galaxies and the Tully Fisher relation: implications for the dark halo shape

We have investigated the Tully-Fisher relation for Polar Ring Galaxies (PRGs), based on near infrared, optical and HI data available for a sample of these peculiar objects. The total K-band luminosity, which mainly comes from the central host galaxy, and the measured HI linewidth at 20% of the peak line flux density, which traces the potential in the polar plane, place most polar rings of the sample far from the Tully-Fisher relation defined for spiral galaxies, with many PRGs showing larger HI linewidths than expected for the observed K band luminosity. This result is confirmed by a larger sample of objects, based on B-band data. This observational evidence may be related to the dark halo shape and orientation in these systems, which we study by numerical modeling of PRG formation and dynamics: the larger rotation velocities observed in PRGs can be explained by a flattened polar halo, aligned with the polar ring.

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arXiv2002

Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: I. Data, structural parameters

We present new Near-Infrared (NIR) observations, in the J, H and Kn bands, for a sample of Polar Ring Galaxies (PRGs), selected from the Polar Ring Catalogue (Whitmore et al. 1990). Data were acquired with the CASPIR near-IR camera at the 2.3 m telescope of Mount Stromlo and Siding Spring Observatory. We report here on the detail morphological study for the central host galaxy and the polar structure in all PRGs of our sample. Total magnitudes, bulge-to-disk decomposition and structural parameters are computed for all objects. These data are crucial for an accurate modeling of the stellar population and the estimate of the star formation rates in the two components.

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arXiv2002

Near-Infrared photometry in the J, H and Kn bands for Polar Ring Galaxies: II. Global Properties

We discuss the properties of the host galaxy and ring light distributions in the optical and near infrared bands for a sample of Polar Ring Galaxies (PRGs), presented in Paper I (Iodice et al. 2002, Paper I). The goal of this work is to test different formation scenarios for PRGs, proposed by different authors in the last decades, by comparing their predictions with these new data. The strategy is twofold: i) the integrated colors of the main components in these systems are compared with those of standard morphological galaxy types, to investigate whether differences in colors are caused by dust absorption or difference in stellar populations. We then derived an estimate of the stellar population ages in PRGs, which can be used to set constrains on the dynamical modeling and the time evolution of these systems; ii) we analyse the structural parameters of the host galaxy in order to understand whether this component is a standard early-type system as its morphology suggests, and the light distribution in the polar ring to measure its radial extension. These observational results indicate that the global properties of PRGs are better explained by dissipative merging of disks with un-equal masses as proposed by Bekki (1998), rather than the accretion-or stripping-of gas by a pre-existing early-type galaxy.

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arXiv2002

A neutral hydrogen survey of polar ring galaxies IV. Parkes observations

A total of 33 polar ring galaxies and polar ring galaxy candidates were observed in the 21-cm HI line with the 64-m Parkes radio telescope. The objects, selected by their optical morphology, are all south of declination -39 degrees and in only 5 of them HI had been reported previously. HI line emission was detected towards 18 objects, though in 3 cases the detection may be confused by another galaxy in the telescope beam, and one is a marginal detection. Eight objects were detected for the first time in HI, of which 5 did not have previously known redshifts.

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arXiv2001

The puzzle of the polar structure in NGC 4650A

This work presents new surface photometry and two-dimensional modeling of the light distribution of the Polar Ring Galaxy NGC 4650A, based on near-infrared (NIR) observations and high resolution optical imaging acquired during the Hubble Heritage program. The NIR and optical integrated colors of the S0 and the polar ring, and their scale parameters, are compared with those for standard galaxy morphological types. The polar structure appears to be a disk of a very young age, while the colors and light distribution of the host galaxy do not resemble that of a typical early-type system. We compare these observational results with the predictions from different formation scenarios for polar ring galaxies. The peculiarities of the central S0 galaxy, the polar disk structure and stellar population ages suggest that the polar ring galaxy NGC 4650A may be the result of a dissipative merger event, rather than of an accretion process.

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arXiv2000

Stars & Gas in the Galaxy Pair II Zw 70/71

II Zw 71 (UGC 9562) was classified as a ``probable'' polar-ring galaxy in the Polar-Ring Catalog, based upon its optical appearance. We present 21 cm and optical observations of this galaxy and its companion, the blue star-forming dwarf II Zw 70. Our 21 cm observations show that 5e8 solar masses of HI is present in a polar ring orbiting II Zw 71, and show a spatially and kinematically contiguous streamer with 2.5e8 solar masses of HI gas between the two galaxies. This gaseous bridge, plus our observations of Halpha line emission in the polar ring and in II Zw 70, are strong evidence for an ongoing interaction between the two galaxies. However, the configuration of the streamer suggests that the polar ring itself may well have predated the current interaction, which then stimulated an outburst of star formation in the ring gas.

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arXiv2000

H-alpha Velocity Fields of Normal Spiral Disks

We present H-alpha velocity fields for a sample of nearly face--on spiral galaxies observed with DensePak on the WIYN telescope. We combine kinematic inclinations and position angles measured from these data with photometric inclinations and position angles measured from I-band images to show that spiral disks are intrinsically non-circular.

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arXiv1996

The Quadruple Gravitational Lens PG1115+080: Time Delays and Models

Optical photometry is presented for the quadruple gravitational lens PG1115+080. A preliminary reduction of data taken from November 1995 to June 1996 gives component ``C'' leading component ``B'' by 23.7+/-3.4 days and components ``A1'' and ``A2'' by 9.4 days. A range of models has been fit to the image positions, none of which gives an adequate fit. The best fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km/s/Mpc for Omega=1, with an observational uncertainty of 14%, as computed from the B-C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0=64 km/sec/Mpc while taking the galaxy to be a point mass gives H0=84 km/sec/Mpc. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned HST observations.

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arXiv1993

A Neutral Hydrogen Survey of Polar-Ring Galaxies: I. Green Bank Observations of the Northern Sample

We present the results of a neutral hydrogen survey conducted with the Green Bank 140-foot radio telescope of 47 northern objects in the polar-ring galaxy atlas of Whitmore \etal\ (1990). We detected 39 of these above our detection limit of 1.7 \hbox{Jy\CDOT\KMS}; the average measured flux of 21 Jy\CDOT\KMS\ corresponds to an average neutral hydrogen mass of $\rm 5.3 \times 10^9$ \MSUN for a Hubble constant of $\rm H_0 = 75$ \KMS \ Mpc$^{-1}$. For the polar-ring galaxies in our sample that have also been observed with radio arrays, we find that the 21\AMIN\ (FWHM) Green Bank beam often includes much more flux than found by the synthesis instruments for the polar rings alone; some of these galaxies are known to have gas-rich companions. We compare the neutral hydrogen content of the sample to the blue luminosity and IRAS fluxes. The \HI-to-blue- light ratios of the confirmed and probable polar rings are around unity in solar units, indicating that polar ring galaxies (or their environments) are as gas-rich as typical irregular galaxies. For their blue luminosity, the confirmed polar rings are underluminous in the far-infrared, as compared with the rest of the sample. They are also FIR-underluminous for their \HI\ masses, which suggests that most of the gas in the ring may be in stable orbits, rather than flowing inward to trigger star formation in the central galaxy. The more disordered class of `related objects,' which includes a number of obvious mergers, is highly luminous in the far-infrared.

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