Polar Ring Galaxy NGC Research Articles

Beyond the rings: Polar ring galaxy NGC 4262 and its globular cluster system

ABSTRACT In the context of the hierarchical model of galaxy evolution, polar ring galaxies (PRGs) are considered the intermediate phase between ongoing mergers and quiescent galaxies. This study explores the globular cluster system (GCS) and its properties in the nearest PRG, NGC4262, serving as a pilot investigation to study GCS in nearby PRGs. We utilize wide and deep-field observations of the CFHT as part of the NGVS to investigate the GCS of NGC4262. We presented the first optical image of NGC4262 with an optically faint ring component. The photometric analysis of the GCS displays a distinct colour bimodality. We estimate the total number of GCs for NGC4262 to be 266 $\pm$ 16 GCs with a specific frequency of 4.2 $\pm$ 0.8 and a specific mass of 0.23 $\pm$ 0.01, which is relatively high compared to other galaxies of similar mass and environmental conditions. The spatial and azimuthal distributions of subpopulations reveal strong evidence of previous interactions within the host galaxy. The colour distribution of GCS in NGC4262 shows a gradient of –0.05 $\pm$ 0.01 within 5.5$^\prime$, supporting the notion of past interactions and evolutionary transitions. PRG NGC4262 conforms to the overall trend of the GCS mass with respect to the halo mass. Furthermore, our investigation of the global scaling relations between GCS and host galaxy parameters provides further support for the hypothesis that PRGs are an intermediate phase connecting ongoing mergers and quiescent galaxies.

X-ray source population in the polar ring galaxy NGC 660 as observed by Chandra

We present Chandra observations of the nearby polar ring galaxy NGC 660 to study its X-ray source population. Based on our analysis, we detected a total of 23 X-ray sources in the 0.5−8 keV band, with luminosities ranging from ∼1037 to ∼1039 erg s−1. Twenty-two of these sources are located off-nuclear and have luminosities below the ultraluminous X-ray source (ULX) threshold value of L 0.5−8 keV < 1039 erg s−1, suggesting that they are likely to be X-ray binary (XRB) candidates. The remaining source is located at the center of the galaxy, suggesting it is an active galactic nucleus (AGN). However, we estimated that four of the detected sources could be associated with background objects. Based on the source count rates in each of the Chandra observations, we found evidence for variability in nine of the 23 sources, including the AGN. However, further investigation with spectral analysis suggested no significant differences in the AGN luminosities between the observations. The X-ray luminosity distribution of the galaxy was found to be generally lower than that expected from previous studies on star forming and collisional ring galaxies. No ULX was also detected in the galaxy, in contrast with what was expected from the galaxyʼs SFR and metallicity (i.e., SFR = 14.43 ± 0.19 M ⊙ yr−1 and Z = 0.94 ± 0.01 Z ⊙, respectively). These results suggest a deficit in the X-ray sources detected. Based on source hardness ratio distribution, we found evidence that the fainter sources have a harder source spectrum, indicating higher absorption. This further suggests that there could be more X-ray sources that were not detected in the galaxy due to significant obscuration.

The Origin of Polar Ring Galaxies: Evidence for Galaxy Formation by Cold Accretion

Polar ring galaxies are flattened stellar systems with an extended ring of gas and stars rotating in a plane almost perpendicular to the central galaxy. We show that their formation can occur naturally in a hierarchical universe where most low-mass galaxies are assembled through the accretion of cold gas infalling along megaparsec-scale filamentary structures. Within a large cosmological hydrodynamical simulation, we find a system that closely resembles the classic polar ring galaxy NGC 4650A. How galaxies acquire their gas is a major uncertainty in models of galaxy formation, and recent theoretical work has argued that cold accretion plays a major role. This idea is supported by our numerical simulations and the fact that polar ring galaxies are typically low-mass systems.

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.

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)

New HI Observations of the prototype Polar Ring Galaxy NGC 4650A

AbstractNew, 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 NGC 4650A are presented. They 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 (NIR) images argues against previous warp models used to describe the dynamics of this object. Further analysis of the new B-band image obtained at the European Southern Observatories New Technology Telescope (NTT) indicates clearly that the polar structure extends continuously to within about 200 pc of the nucleus of the central host galaxy, ruling out the presence of a ‘hole’ in the central region of this component. 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.

The Rotation Curves of the Polar Ring Galaxy NGC 4650A under Modified Newtonian Dynamics

The Rotation Curves of the Polar Ring Galaxy NGC 4650A under Modified Newtonian Dynamics

The flattened dark halo of polar ring galaxy NGC 4650A: A conspiracy of shapes?

view Abstract Citations (149) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Flattened Dark Halo of Polar Ring Galaxy NGC 4650A: A Conspiracy of Shapes? Sackett, Penny D. ; Rix, Hans-Walter ; Jarvis, Brian J. ; Freeman, Kenneth C. Abstract Kinematics and photometry of the polar ring galaxy NGC 4650A, including new observations of the rotation and velocity dispersion of its central stellar disk, are used to infer the presence of a dark matter halo and to measure its shape. Fits to the observed disk and polar ring rotation curves from detailed mass and photometric modeling rule out a spherical dark halo. The best-fit models have halos with isodensity surfaces that are flattened to a shape between E6 and E7 (axis ratios between 0.4 and 0.3); the asymptotic equatorial speeds of these models are in excellent agreement with the I-band Tully-Fisher relation. This degree of dark halo flattening is larger than that expected from N-body collapse simulations of dissipationless dark matter. Since the kinematics and surface brightness profile of the central luminous body indicate that its light has an intrinsic axis ratio c/a <0~ .4, in NGC 4650A the radial "conspiracy" between the dark and luminous components that leads to flat rotation curves may extend to the shape of the mass distribution as well. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174938 arXiv: arXiv:astro-ph/9406015 Bibcode: 1994ApJ...436..629S Keywords: Astronomical Photometry; Dark Matter; Disk Galaxies; Galactic Halos; Galactic Rotation; Kinematics; Ring Galaxies; Stellar Luminosity; Astrodynamics; Galactic Mass; Mass Distribution; Astrophysics; COSMOLOGY: DARK MATTER; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4650A; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: PHOTOMETRY; Astrophysics E-Print: Uuencoded compressed tar file (complete with figures). Institute for Advanced Study number AST 94/22 full text sources arXiv | ADS | data products SIMBAD (6) NED (1)