Polar Ring Galaxies Research Articles

The stellar content of the ring in NGC 660

We present the results of stellar photometry of the polar-ring galaxy NGC 660 using the Hubble Space Telescope's archival data obtained with the Wide Field Planetary Camera 2. The final list of the resolved stars contains 550 objects, a considerable part of which are blue and red supergiants belonging to the polar ring. The analysis of the Colour-Magnitude Diagram for polar ring stars shows that it is best represented by the isochrones with metallicity Z = 0.008. The process of star formation in the polar ring was continuous and the age of the youngest detected stars is about 7 Myr.

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.

Photometric structure of polar-ring galaxies

The results of B, V, R surface photometry of three polar-ring galaxies (PRGs) – A 0017+2212, UGC 1198, UGC 4385 – are presented. The data were acquired at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. It was shown that all three galaxies are peculiar late-type spirals in the state of ongoing interaction or merging. We discuss available photometric properties of the PRGs with spiral hosts and consider the Tully-Fisher relation for different types of PRGs. In agreement with Iodice et al. ([CITE]), we have shown that true PRGs demonstrate ~1/3 larger maximum rotation velocities than spiral galaxies of the same luminosity. Peculiar objects with forming polar structures satisfy, on average, the Tully-Fisher relation for disk galaxies but with large scatter.

The Stellar Content of the Polar Rings in the Galaxies NGC 2685 and NGC 4650A

We present the results of stellar photometry of polar ring galaxies NGC 2685 and NGC 4650A, using the archival data obtained with the Hubble Space Telescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were resolved into ~800 and ~430 stellar objects in the B, V, and IC bands, a considerable part of which are blue supergiants located in the young stellar complexes. The stellar features in the CM diagrams are best represented by isochrones with metallicity Z = 0.008. The process of star formation in the polar rings of both galaxies was continuous, and the age of the youngest detected stars is about 9 Myr for NGC 2685 and 6.5 Myr for NGC 4650A.

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 line-widths 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.

Formation of polar ring galaxies

Polar ring galaxies are peculiar systems in which a gas rich, nearly polar ring surrounds an early-type or elliptical host galaxy. Two formation scenarios for these objects have been proposed: they are thought to form either in major galaxy mergers or by tidal accretion of the polar material from a gas rich donor galaxy. Both scenarios are studied through N-body simulations including gas dynamics and star formation. Constraints on physical parameters are drawn out, in order to determine which scenario is the most likely to occur. Polar ring galaxies from each scenario are compared with observations and we discuss whether the accretion scenario and the merging scenario account for observational properties of polar ring galaxies. The conclusion of this study is that the accretion scenario is both the most likely and the most supported by observations. Even if the merging scenario is rather robust, most polar ring galaxies are shown to be the result of tidal gas accretion events.

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.

Near-Infrared photometry in $\vec{J}$ $\vec{H}$ and $\vec{Kn}$ bands for polar ring galaxies

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. 2002b). The goal of this work is to test dierent formation scenarios for PRGs, proposed by dierent 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 dierences in colors are caused by dust absorption or dierence 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.

Near-Infrared photometry in the J, H and ${\it Kn}$ bands for Polar Ring Galaxies

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. [CITE]). 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.

Extended H [CSC]i[/CSC] Spiral Structure and the Figure Rotation of Triaxial Dark Halos

The HI disk of the blue compact dwarf (BCD) galaxy NGC 2915 extends to 22 optical scalelengths and shows spiral arms reaching far beyond the optical component. None of the previous theories for spiral structure provide likely explanations for these very extended spiral arms. Our numerical simulations first demonstrate that such large spiral arms can form in an extended gas disk embedded in a massive triaxial dark matter halo with slow figure rotation, through the strong gravitational torque of the rotating halo. We then show that the detailed morphological properties of the developed spirals and rings depend strongly on the pattern speed of the figure rotation, the shape of the triaxial halo, and the inclination of the disk with respect to the plane including the triaxial halo's long and middle axes. These results strongly suggest that the dark matter halo of NGC 2915 is triaxial and has figure rotation. Based on these results, we also suggest that dynamical effects of triaxial halos with figure rotation are important in various aspect of galaxy formation and evolution, such as formation of polar ring galaxies, excitation of non-axisymmetric structures in low surface-brightness galaxies, and gas fueling to the central starburst regions of BCDs.

Wide Field Planetary Camera 2 Observations of the Polar Ring Galaxy NGC 4650A

We present multicolor Wide Field Planetary Camera 2 images of the polar ring galaxy NGC 4650A (D = 35 Mpc), taken with the Hubble Space Telescope. These data allow a detailed examination of the morphology of the central S0 component and the surrounding polar ring of stars, gas, and dust, which are spatially extended and form a polar disk. The nuclear complex, located near the common center of the two components, consists of an unresolved compact source less than 20 pc across, embedded in a more extended light distribution about 60 pc in radius. A complicated pattern of dust lanes crosses the high surface brightness central region of the S0, where dust features appear to extend inward to small radii. In areas of the S0 exterior to the projected polar disk, the light distribution is relatively smooth on small spatial scales, with few candidates for old star clusters or signs of internal dust features. Outer regions of the S0 galaxy have uniformly red colors of a stellar population where major star formation ceased ~3-5 Gyr in the past. The polar disk appears to be warped, with a complex morphology. On small spatial scales, features are produced mainly by dust and clumps of star formation; gas seems to be piling up in a dusty ring that encircles the central S0 at a radius of ~1 kpc (6''). The polar disk is inclined by about 63° near its center, twists toward edge-on at intermediate radii, and again becomes more nearly face-on further out, where two spiral arms are marked by young stars. We do not detect any regions with a prominent Baade sheet of older red stars in the polar disk; most of the optical light is supplied by moderately young stars, with lifetimes of ~1 Gyr. The polar material appears relatively unevolved, especially when compared to the S0 component of NGC 4650A. Either the polar disk is a late addition to the system or the outer gas has formed very few stars until recently.

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.

The gas content of peculiar galaxies: Counterrotators and polar rings

This paper studies the global ISM content in a sample of 104 accreting galaxies, including counterrotators and polar rings, which spans the entire Hubble sequence. The molecular, atomic and hot gas content of accretors is compared to a newly compiled sample of normal galaxies. We present results of a small survey of the line of 12CO with the 15 m SEST telescope on a sample of 11 accretors (10 counterrotators and 1 polar ring). The SEST sample is enlarged with published data from 48 galaxies, for which observational evidence of counterrotation in the gas and/or the stars has been found. Furthermore, the available data on a sample of 46 polar ring galaxies has been compiled. In order to explore the existence of an evolutionary path linking the two families of accretors, the gas content of counterrotators and polar rings is compared. It was found that the normalized content of cold gas () in polar rings is ~1 order of magnitude higher than the reference value derived for normal galaxies. The inferred gas masses are sufficient to stabilize polar rings through self-gravity. In contrast, it was found that the cold gas content of counterrotators is close to normal for all galaxy types. Although counterrotators and polar rings probably share a common origin, the gas masses estimated here confirm that light gas rings accreted by future counterrotators may have evolved faster than the self-gravitating structures of polar rings. In this scenario, the transformation of atomic into molecular gas could be enhanced near the transition region between the prograde and the retrograde disks, especially in late-type accretors characterized by a high content of primordial gas. This is tentatively confirmed in this work: the measured H2/HI ratio seems larger in counterrotators than in normal or polar ring galaxies for types later than S0s.

Photometric and spectral investigation of candidates for polar-ring galaxies

Abstract Some results of the observational investigation of four candidates for polar-ring galaxies (PRGs) are reported.

Nuclear spectra of polar-ring galaxies

We report the results of spectroscopic observations of eight southern polar-ring galaxies (PRGs), in the wavelength range 5900–7300 A. We find that five out of eight galaxies contain LINERs or Sy nuclei. Taking into consideration all PRGs with available spectral data, we estimate that about half of all PRGs and PRG candidates have either LINER or Seyfert nuclei. The observed widths of the [N ii]λ6583 line in the nuclei of early-type PRGs follow the linewidth–absolute luminosity relation for normal E/S0 galaxies. We found that one of the observed galaxies – ESO 576-G69 – is a new kinematically-confirmed polar-ring galaxy with a spiral host.

Stars and Gas in the Galaxy Pair II [CLC]Zw[/CLC] 70/71

II Zw 71 (UGC 9562) has been classified as a "probable" polar ring galaxy, based on 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 5 × 108 solar masses of H I are present in a polar ring orbiting II Zw 71 and show a spatially and kinematically contiguous streamer with 2.5 × 108 solar masses of H I gas between the two galaxies. This gaseous bridge, plus our observations of Hα line emission in the polar ring and in II Zw 71, 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.

A neutral hydrogen survey of polar ring galaxies

A total of 50 optically selected polar ring galax- ies, polar ring galaxy candidates and related objects were observed in the 21-cm H i line with the Nan cay deci- metric radio telescope and 31 were detected. The ob- jects, selected by their optical morphology, are all north of declination 39, and generally relatively nearby (V< 8000 km s 1 ) and/or bright (mB < 15.5). The H i line data are presented for all 74 galaxies observed for the sur- vey with the Eelsberg, Green Bank or Nan cay radio tele- scopes, as well as all other published H i line parameters of these objects. Three objects were observed and detected by us at Parkes. A total of 59 objects were detected. For each object a brief description is given based on a litera- ture search.

An HI Line Survey of Polar Ring Galaxies

We have observed a total of 74 polar ring galaxies (PRGs), PRG candidates and related objects at 3 radio observatories: Green Bank (Richter et al. 1994, AJ, 107, 1), Effelsberg (Huchtmeier 1997, A&amp;A, 319, 401) and Nançay (van Driel et al. 1997, A&amp;AS, in press; van Driel et al. 1998, A&amp;A, in prep.). Our main aim is to identify systems suitable for HI synthesis mapping, crucial for an understanding of their dynamical state. Most objects were selected using one or more of the following 3 (&lt;8000 km/s), or blue magnitude brighter than 15.5 mag, or kinematically confirmed PRG or good PRG candidate. A total of 62 objects were detected, 39 of which with more than one telescope.

Formation of a Polar Ring Galaxy in a Galaxy Merger

We numerically investigate stellar and gas dynamics in star-forming and dissipative galaxy mergers between two disk galaxies with specific orbital configurations. We find that violent relaxation combined with gaseous dissipation in galaxy merging transforms two disk galaxies into one S0 galaxy with polar-rings: Both the central S0-like host and the polar-ring component in a polar-ring galaxy are originally disk galaxies. We also find that morphology of the developed polar-rings reflects both the initial orbit configuration of galaxy merging and the initial mass ratio of the two merger progenitor disk galaxies. Based upon these results, we discuss the origin of the fundamental observational properties of polar-ring galaxies, such as the prevalence of S0 galaxies among polar-ring galaxies, the rarity of polar-ring galaxies among S0 galaxies, the dichotomy between narrow polar-rings and annular ones, shapes of polar-ring warps, and an appreciably larger amount of interstellar gas in the polar-ring component.

New H I Observations of the Prototype Polar Ring Galaxy NGC 4650A

view Abstract Citations (67) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New H I Observations of the Prototype Polar Ring Galaxy NGC 4650A Arnaboldi, M. ; Oosterloo, T. ; Combes, F. ; Freeman, K. C. ; Koribalski, B. Abstract New, high resolution observations of the \hi\ emission line and 20-cm continuum at the Australia Telescope Compact Array (ATCA) for the prototype polar ring galaxy \n4650a\ are presented. We show the presence of a far more extended \hi\ distribution than previously observed with the VLA, and a very regular velocity field out to a distance of ~ 50 kpc. The combined analysis of the \hi\ data with optical and near infrared images argues against previous warp models used to describe the dynamics of this object. A comparison between the high resolution \hi\ images and a new B-band image obtained at the ESO NTT further weakens the interpretation of the optical morphology via warp geometries. The presence of two spiral arms stretching out in the polar disk seems to represent the most likely explanation for the observed morphology and kinematics. Publication: The Astronomical Journal Pub Date: February 1997 DOI: 10.1086/118278 Bibcode: 1997AJ....113..585A full text sources ADS | data products SIMBAD (6) NED (2)