NGC 2655: From Inner Polar Ring to Outer Shells and Tails

Sparke, Linda S.; Moorsel, G. van; Erwin, Peter; Wehner, E. M.

doi:10.1088/0004-6256/135/1/99

Cited by 16 publications

(19 citation statements)

References 41 publications

(59 reference statements)

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“…12, even the warped‐disc model cannot reproduce all the features of the velocity field, implying that at least part of the motion is non‐circular. Secondly, galaxies with helical structures always present extended high‐ or low‐contrast features (shells and envelopes, see Makarov, Reshetnikov & Yakovleva 1989; Sparke et al 2008; Sparke et al 2009), whereas we could not detect any such features outside the ring of Hoag’s Object down to very low surface brightnesses (see Fig. 4).…”

Section: The Structure Of Hoag’s Objectmentioning

confidence: 58%

Hoag’s Object: evidence for cold accretion on to an elliptical galaxy

Finkelman

Моисеев

Brosch

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present new photometric and spectroscopic observations of the famous Hoag's Object, a peculiar ring galaxy with a central roundish core. The nature of Hoag's Object is still under controversy. Previous studies demonstrated that a major accretion event that took place at least 2-3 Gyr ago can account for the observational evidence. However, the role of internal non-linear mechanisms in forming the outer ring was not yet completely ruled out.The observations reported here consist of WFPC2 optical data retrieved from the Hubble Space Telescope archive as well as long-slit and 3D spectroscopic data obtained at the Russian BTA 6-m telescope. These new data, together with H I and optical information from the literature, are used to demonstrate that Hoag's Object is a relatively isolated system surrounded by a luminous quasi-spiral pattern and a massive, low-density H I disc. The main stellar body is an old, mildly triaxial elliptical galaxy with very high angular momentum.We review previous formation scenarios of Hoag's Object in light of the new data and conclude that the peculiar morphology could not represent a late phase in barred early-type galaxies evolution. In addition, no observational evidence supports late merging events in the evolution of the galaxy, although further tests are required before safely dismissing this idea. Combining all the information, we propose a new scenario where the elliptical core formed in the early Universe with the H I disc forming shortly after the core by prolonged 'cold' accretion of primordial gas from the intergalactic medium.The low gas density does not allow intense star formation to occur everywhere in the disc, but only along a tightly wound spiral pattern of enhanced density induced by the triaxial gravitational potential. According to this view, the physical mechanism that forms rings in Hoag-like galaxies is closely linked with that in some non-barred disc galaxies, although the formation and evolution of both classes of galaxies are clearly distinct. Whether or not this unique evolutionary track is related to the galaxy residing in an underdensed environment remains to be solved. A detailed H I mapping of Hoag's Object and its environment is required to test our hypothesis and to examine the nature of the H I disc.

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Section: The Structure Of Hoag’s Objectmentioning

confidence: 58%

Hoag’s Object: evidence for cold accretion on to an elliptical galaxy

Finkelman

Моисеев

Brosch

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…Above we already pointed out some similarities between Arp 212 and NGC 2655-another galaxy with a warped polar disk. Deep images of this galaxy, presented by Sparke et al (2008), show low surface brightness tidal features within two optical diameters. However, our image of Arp 212 lacks tidal features brighter than 25.2 m /✷ ′′ (see Section 3).…”

Section: The Origin Of the Outer Gaseous Subsystemmentioning

confidence: 89%

Warped polar ring in the Arp 212 galaxy

Моисеев

2008

Astrophys. Bull.

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Abstract. The Fabry-Perot scanning interferometer mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences is used to study the distribution and kinematics of ionized gas in the peculiar galaxy Arp 212 (NGC 7625, III Zw 102). Two kinematically distinct subsystems-the inner disk and outer emission filaments-are found within the optical radius of the galaxy. The first subsystem, at galactocentric distances r < 3.5 kpc, rotates in the plane of the stellar disk. The inner part of the ionized-gas disk (r < 1.5-2 kpc) exactly coincides with the previously known disk consisting of molecular gas. The second subsystem of ionized gas is located at galactocentric distances 2-6 kpc. This subsystem rotates in a plane tilted by a significant angle to the stellar disk. The angle of orbital inclination in the outer disk increases with galactocentric distance and reaches 50• at r ≈ 6 kpc. The ionized fraction of the gaseous disk does not show up beyond this galactocentric distance, but we believe that the HI disk continues to warp and approaches the plane that is polar with respect to the inner disk of the galaxy. Hence Arp 212 can be classified as a galaxy with a polar ring (or a polar disk). The observed kinematics of the ionized and neutral gas can be explained assuming that the distribution of gravitational potential in the galaxy is not spherically symmetric. Most probably, the polar ring have formed via accretion of gas from the dwarf satellite galaxy UGC 12549.

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“…The sample here is the unbarred subset of the parent sample: those galaxies with RC3 classifications of SA or S (the latter formally means that no bar classification is available), as well as those SB and SAB galaxies which were judged to lack true bars by Erwin & Sparke (2003) and Erwin (2005). (We excluded NGC 2655 from the latter set because it appears to be in the midst of an interaction; see Sparke et al 2008. ) See Section 4 for more details on previously undetected bars.…”

Section: Sample Selection Criteriamentioning

confidence: 99%

The Outer Disks of Early-Type Galaxies. Ii. Surface-Brightness Profiles of Unbarred Galaxies and Trends With Hubble Type

Gutiérrez

Erwin

Aladro

et al. 2011

The Astronomical Journal

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150

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We present azimuthally averaged radial profiles of R-band surface brightness for a complete sample of 47 early-type, unbarred galaxies, as a complement to our previous study of early-type barred galaxies. Following very careful sky subtraction, the profiles can typically be determined down to brightness levels well below 27 mag arcsec −2 and in the best cases below 28 mag arcsec −2 . We classified the profiles according to the scheme used previously for the barred sample: Type I profiles are single unbroken exponential radial declines in brightness; Type II profiles ("truncations") have an inner shallow slope (usually exponential) which changes at a well-defined break radius to a steeper exponential; and Type III profiles ("antitruncations") have an inner exponential that is steeper, giving way to a shallower outer (usually exponential) decline. By combining these profiles with previous studies, we can make the first clear statements about the trends of outer-disk-profile types along the Hubble sequence (including both barred and unbarred galaxies), and their global frequencies. We find that Type I profiles are most frequent in early-type disks, decreasing from one-third of all S0-Sa disks to barely 10% of the latest-type spirals. Conversely, Type II profiles (truncations) increase in frequency with Hubble type, from only ∼25% of S0 galaxies to ∼80% of Sd-Sm spirals. Overall, the fractions of Type I, II, and III profiles for all disk galaxies (Hubble types S0-Sm) are 21%, 50%, and 38%, respectively; this includes galaxies (∼8% of the total) with composite Type II+III profiles (counted twice). Finally, we note the presence of bars in 10 galaxies previously classified (optically) as "unbarred." This suggests that ∼20% of optically unbarred galaxies are actually barred; the bars in such cases can be weak, obscured by dust, or so large as to be mistaken for the main disk of the galaxy.

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NGC 2655: From Inner Polar Ring to Outer Shells and Tails

Cited by 16 publications

References 41 publications

Hoag’s Object: evidence for cold accretion on to an elliptical galaxy

Hoag’s Object: evidence for cold accretion on to an elliptical galaxy

Warped polar ring in the Arp 212 galaxy

The Outer Disks of Early-Type Galaxies. Ii. Surface-Brightness Profiles of Unbarred Galaxies and Trends With Hubble Type

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