Formation of polar ring galaxies

Bournaud, F.; Combes, F.

doi:10.1051/0004-6361:20030150

Cited by 156 publications

(204 citation statements)

References 38 publications

(112 reference statements)

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“…We have used the N-body FFT code described in Bournaud & Combes (2003). The gravitational potential is computed on a cartesian grid of size 256 3 with a resolution of 700 pc.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics

Bournaud

Combes

Jog

2004

A&A

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108

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Abstract. It is generally believed that major galaxy mergers with mass ratios in the range 1:1-3:1 result in remnants that have properties similar to elliptical galaxies, and minor mergers below 10:1 result in disturbed spiral galaxies. The intermediate range of mass ratios 4:1-10:1 has not been studied so far. Using N-body simulations, we show that such mergers can result in very peculiar systems, that have the morphology of a disk galaxy with an exponential profile, but whose kinematics is closer to that of elliptical systems. These objects are similar to those recently observed by . We present two cases with mass ratios 4.5:1 and 7:1, and show that the merging causes major heating and results in the appearance of elliptical-type kinematics, while surprisingly the initial spiral-like mass profile is conserved.

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“…We have used the N-body FFT code described in Bournaud & Combes (2003). The gravitational potential is computed on a cartesian grid of size 256 3 with a resolution of 700 pc.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics

Bournaud

Combes

Jog

2004

A&A

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108

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“…Thus, this ring becomes an appropriate place for star formation. It is thought that these objects are formed as a consequence of the interaction between galaxies with a small impact parameter (Bournaud & Combes 2003). In the case of IIZw71, there are proofs from Article published by EDP Sciences interferometric observations of interaction with IIZw70, another BCD.…”

Section: Introductionmentioning

confidence: 99%

Long-slit spectrophotometry of the multiple knots of the polar ring galaxy IIZw71

Montero

García-Benito

Díaz

et al. 2009

A&A

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Aims. The blue compact dwarf galaxy IIZw71 is catalogued as a probable polar-ring galaxy, and along its long axis it has several very luminous knots showing recent episodes of star formation. Our main aim is to study the physical properties, the stellar content, and the kinematics in the brightest knots of the polar ring. Methods. We carried out long-slit spectroscopic observations of the polar ring in the spectral range 3500-10 000 Å taken with the William Herschel Telescope (WHT). The spectroscopic observations complemented by the available photometry of the galaxy in narrow Hα filters. Results. We measured the rotation curve of the ring, from which we infer a ratio M/L B ≈ 3.9 inside the star-forming ring. We measured the auroral [Oiii] line in the two brightest knots, allowing us to measure oxygen, sulphur, nitrogen, argon, and neon chemical abundances following the direct method. Different empirical calibrators were used to estimate the oxygen abundance in the two faintest knots where the temperature sensitive lines could not be measured. The metallicities obtained are very similar for all the knots, but lower than previously reported in the literature from integrated spectra. The N/O abundance, as derived from the N 2 O 2 parameter (the ratio of the [Nii] and [Oii] intensities), is remarkably constant over the ring, indicating that local polution processes are not conspicuous. Using synthetic stellar populations (SSPs) calculated with the code STARLIGHT, we studied the age distribution of the stellar populations in each knot, finding that in all of them there is a combination of a very young population with less than 10 Myr, responsible for the ionisation of the gas, with other populations older than 100 Myr, probably responsible for the chemical evolution of the knots. The small differences in metallicity and the age distributions among the different knots are indicative of a common chemical evolution, probably related to the process of interaction with the companion galaxy IIZw70. Finally, we calculated the SFR in the different knots from the Hα luminosities. The combined SFR rate for the ring amounts to half of the integrated SFR for this galaxy reported by previous authors. The average surface SFR is also higher than the average reported value of HII in polar rings by more than an order of magnitude.

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“…The final mass of M 32 in our model is 1/23 that of M 31, compatible with present-day mass estimates. 21 of a head-on encounter between M 31 and M 32. These N-body models include the gravitational dynamics of stars, interstellar matter, and dark matter in both M 31 and M 32.…”

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An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy

Block

Bournaud

Combes

et al. 2006

Nature

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117

161

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Abstract. The unusual morphology of the Andromeda Spiral (Messier 31, the closest spiral galaxy to the Milky Way) has long been an enigma. Although regarded for decades as showing little evidence of a violent history, M 31 has a well-known outer ring 1−7 of star formation at a radius of 10 kpc whose center is offset from the galaxy nucleus. In addition, the outer galaxy disk is warped as seen at both optical 8 and radio 9 wavelengths. The halo contains numerous loops and ripples. Here we report the discovery, based on analysis of previously-obtained data 10 , of a second, inner dust ring with projected dimensions 1.5 by 1 kpc and offset by ∼ 0.5 kpc from the center of the galaxy. The two rings appear to bedensity waves propagating in the disk.Numerical simulations offer a completely new interpretation for the morphology of M 31: both rings result from a companion galaxyplunging head-on through the center of the disk of M 31. The most likely interloper is M 32. Head-on collisions between galaxies are rare, but it appears nonetheless that one took place 210 million years ago in our Local Group of galaxies.Newly-acquired images 10 of M 31 secured by the Infrared Array Camera 11 (IRAC) onboard the Spitzer Space Telescope span the wavelength regime of 3.6 to 8.0 microns. These images offer unique probes of the morphologies of the stellar distribution and interstellar medium with no interference from extinction. Figure 1 shows the emission map of the interstellar medium at 8 microns, generated by subtracting a scaled 3.6 micron image (dominated by starlight) from the 8 micron image. The subtraction removes the contribution from stellar photospheres and leaves only the emission from dust grains 10 , which trace the interstellar medium of M 31. What is most striking in Figure 1 (and in the enlarged inset) is the presence of a complete though asymmetric inner ring of dust 6.9 by 4.4 arcmin in extent, translating to linear dimensions of about 1.5 by 1 kpc (assuming a distance 12 of 780 kpc). The inner ring lies between the two well known Baade spiral dust arms 13 , both of which are clearly seen in emission. The inner ring is elongated in a direction close to the minor axis and belongs to the central gas disk, which appears to be more face-on 14 . It is therefore not possible to know the inner rings precise ellipticity, but it is unlikely to be circular. IRAC imaging thus reveals two rings. The outer ring is offset by approximately 10 percent of its radius, while the inner ring is offset by about 40 percent or 0.5 kpc. The inner elliptical ring has been alluded to in earlier studies 15,16 , but all investigators have hitherto believed it to be a mini-spiral, related to a bar. Published Spitzer 24 micron images5 of M 31 show centrally-concentrated dust emission; the ring morphology is therefore disguised at these longer wavelengths. The IRAC images beautifully show the inner ring at high spatial resolution and furthermore confirm that this feature is a complete and continuous ring, even though offset and asymmetrical. Ther...

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Formation of polar ring galaxies

Cited by 156 publications

References 38 publications

Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics

Unequal-mass galaxy merger remnants: Spiral-like morphology but elliptical-like kinematics

Long-slit spectrophotometry of the multiple knots of the polar ring galaxy IIZw71

An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy

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