Boxy/Peanut/X Bulges, Barlenses and the Thick Part of Galactic Bars: What Are They and How Did They Form?

Athanassoula, E.

doi:10.1007/978-3-319-19378-6_14

Cited by 55 publications

(34 citation statements)

References 72 publications

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“…The field has advanced significantly, with three-dimensional simulations becoming ever more refined (e.g., Quillen et al 2014;Athanassoula et al 2015;Li & Shen 2015) and peanuts being detected at lower inclinations (e.g., Erwin & Debattista 2013). For a more in-depth overview we refer the reader to the review articles of Laurikainen & Salo (2016) and Athanassoula (2016), and references therein.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the (X/peanut)-shaped structure in edge-on disc galaxies: length, strength, and nested peanuts

Ciambur

Graham

2016

Mon. Not. R. Astron. Soc.

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X-shaped or peanut-shaped (X/P) bulges are observed in more than 40% of (nearly) edge-on disc galaxies, though to date a robust method to quantify them is lacking. Using Fourier harmonics to describe the deviation of galaxy isophotes from ellipses, we demonstrate with a sample of 11 such galaxies (including NGC 128) that the sixth Fourier component (B 6 ) carries physical meaning by tracing this X/P structure. We introduce five quantitative diagnostics based on the radial B 6 profile, namely: its 'peak' amplitude (Π max ); the (projected major-axis) 'length' where this peak occurs (R Π ,max ); its vertical 'height' above the disc plane (z Π ,max ); a measure of the B 6 profile's integrated 'strength' (S Π ); and the B 6 peak 'width' (W Π ). We also introduce different 'classes' of B 6 profile shape. Furthermore, we convincingly detect and measure the properties of multiple (nested) X/P structures in individual galaxies which additionally display the signatures of multiple bars in their surface brightness profiles, thus consolidating further the scenario in which peanuts are associated with bars. We reveal that the peanut parameter space ('length', 'strength' and 'height') for real galaxies is not randomly populated, but the three metrics are inter-correlated (both in kpc and disc scale-length h). Additionally, the X/P 'length' and 'strength' appear to correlate with (v rot /σ ), lending further support to the notion that peanuts 'know' about the galactic disc in which they reside. Such constraints are important for numerical simulations, as they provide a direct link between peanuts and their host disc. Our diagnostics reveal a spectrum of X/P properties and could provide a means of distinguishing between different peanut formation scenarios discussed in the literature. Moreover, nested peanuts, as remnants of bar buckling events, can provide insights into the disc and bar instability history.

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Section: Introductionmentioning

confidence: 99%

Quantifying the (X/peanut)-shaped structure in edge-on disc galaxies: length, strength, and nested peanuts

Ciambur

Graham

2016

Mon. Not. R. Astron. Soc.

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“…The coldness of the superthin component may reflect young stars trapped in resonances at the bar ends. Such morphological features, called 'ansae', are seen in external galaxies and simulations (Martinez-Valpuesta, Knapen & Buta 2008, Athanassoula 2016. Complex structures like these may complicate the determination of the long bar length and, indeed, the projected properties here are not symmetric about the Galactic Centre, even accounting for the different distances (Wegg, Gerhard & Portail 2015).…”

Section: The End Of the Barmentioning

confidence: 93%

Quantifying the (X/peanut)-shaped structure of the Milky Way – new constraints on the bar geometry

Ciambur

Graham

Bland-Hawthorn

2017

Monthly Notices of the Royal Astronomical Society

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The nature, size and orientation of the dominant structural components in the Milky Way's inner ∼ 4 kpc -specifically the bulge and bar -have been the subject of conflicting interpretations in the literature. We present a different approach to inferring the properties of the long bar which extends beyond the inner bulge, via the information encoded in the Galaxy's X/peanut (X/P)-shaped structure. We perform a quantitative analysis of the X/P feature seen in wise wide-field imaging at 3.4 µm and 4.6 µm. We measure the deviations of the isophotes from pure ellipses, and quantify the X/P structure via the radial profile of the Fourier n = 6 harmonic (cosine term B 6 ). In addition to the vertical height and integrated 'strength' of the X/P instability, we report an intrinsic radius of R Π ,int = 1.67 ± 0.27 kpc, and an orientation angle of α = 37•+7• −10 • with respect to our line-of-sight to the Galactic Centre. Based on X/P structures observed in other galaxies, we make three assumptions: (i) the peanut is intrinsically symmetric, (ii) the peanut is aligned with the long Galactic bar, and (iii) their sizes are correlated. Thus the implication for the Galactic bar is that it is oriented at the same 37• angle and has an expected radius of ≈ 4.2 kpc, but possibly as low as ≈ 3.2 kpc. We further investigate how the Milky Way's X/P structure compares with other analogues, and find that the Galaxy is broadly consistent with our recently established scaling relations, though with a moderately stronger peanut instability than expected. We additionally perform a photometric decomposition of the Milky Way's major axis surface brightness profile, accounting for spiral structure, and determine an average disc scale length of h = 2.54 ± 0.16 kpc in the wise bands, in good agreement with the literature.

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“…In particular, real bars as well as N-body bars are composed of two parts: an inner part which is thick both horizontally and vertically, and an outer part which is thin in both these directions, while as yet no analytical potential with such a property has been developed (see Athanassoula 2016 for a review). N-body bar potentials, however, are much more complex to use and there are therefore relatively few studies relying on them, compared to the large number of studies relying on analytic potentials.…”

Section: Introductionmentioning

confidence: 99%

Orbital classification in anN-body bar

Wang¹,

Athanassoula²,

Mao³

2016

Mon. Not. R. Astron. Soc.

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The dynamics and evolution of any galactic structure are strongly influenced by the properties of the orbits that constitute it. In this paper, we compare two orbit classification schemes, one by Laskar (NAFF) , and the other by Carpintero and Aguilar (CA), by applying both of them to orbits obtained by following individual particles in a numerical simulation of a barred galaxy. We find that, at least for our case and some provisos, the main frequencies calculated by the two methods are in good agreement: for 80% of the orbits the difference between the results of the two methods is less than 5% for all three main frequencies. However, it is difficult to evaluate the amount of regular or chaotic bar orbits in a given system. The fraction of regular orbits obtained by the NAFF method strongly depends on the critical frequency drift parameter, while in the CA method the number of fundamental frequencies strongly depends on the frequency difference parameter L r and the maximum integer used for searching the linear independence of the fundamental frequencies. We also find that, for a given particle, in general the projection of its motion along the bar minor axis is more regular than the other two projections, while the projection along the intermediate axis is the least regular.

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Boxy/Peanut/X Bulges, Barlenses and the Thick Part of Galactic Bars: What Are They and How Did They Form?

Cited by 55 publications

References 72 publications

Quantifying the (X/peanut)-shaped structure in edge-on disc galaxies: length, strength, and nested peanuts

Quantifying the (X/peanut)-shaped structure in edge-on disc galaxies: length, strength, and nested peanuts

Quantifying the (X/peanut)-shaped structure of the Milky Way – new constraints on the bar geometry

Orbital classification in anN-body bar

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