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Unfortunately, all of these cannot be tested with our spectroscopic data due to the large uncertainty in the metallicity measurements.

Forbes D. A. 2008). Alternatively, the photometry of the ring can be used to recover its stellar properties by modelling the continuum light and the blue star clusters as two distinct stellar populations. However, as pointed out by Appleton & Struck-Marcell (1996), the peculiar configuration of the core and the ring can be explained if Hoag’s Object is viewed at an oblique angle to our line of sight and exactly as the intruding companion reaches its farthest distance from the target, where it is at rest relative to the ring. The growing use of nitrogen fertilizers in the production of food worldwide is increasing atmospheric concentrations of nitrous oxide -- a greenhouse gas 300 times more potent than carbon dioxide that remains in the atmosphere for more th […].

To enhance fine structures along the ring, we created a model for the AALP of the galaxy using the ELLIPSE and BMODEL tasks and subtracted the model image from the original image. Giovanelli R. . To calibrate the FPI Hα emission flux, we obtained with SCORPIO a 900-s exposure with a narrow-band (FWHM = 20 Å) filter centred on the emission line and a 240-s exposure with an ‘off-line’ narrow-band (FWHM = 50 Å) filter. The data were obtained with the multimode focal reducer SCORPIO (Afanasiev & Moiseev 2005) and the integral-field Multi-Pupil Fibre Spectrograph (MPFS; Afanasiev, Dodonov & Moiseev 2001) at the prime focus of the BTA. This was done by measuring the intensity within circular apertures centred on the host galaxy photocentre, with radii increasing outwards, using ELLIPSE. Sparke L. S. 2009, and references therein). Finally, we turn to test the major accretion hypothesis from a kinematical point of view. Valdés J. R. Väisänen P.

The maximum observed rotation velocity along the major-axis is V = 70 ± 8 km s−1 at r = 4 arcsec, which should be taken as a lower limit since the galaxy is seen in projection. The HST imaging data were used to provide the morphological parameters, integrated magnitudes and colours of the central core and the ring of Hoag’s Object. Goudfrooij P. How Accurately Can We Detect the Splashback Radius of Dark Matter Halos and its Correlation With Accretion Rate? To estimate the star formation rate from our data, the Hα map has been calibrated into physical units by measuring the intensity within circular profiles extracted from the FPI map and the calibrated Hα continuum-subtracted direct image. The x-axis shows the rest-frame wavelengths. The core of Hoag’s Object. To draw definite conclusions about the metallicity and age gradients, and break the age–metallicity degeneracy, we determined them simultaneously in our model fit. If part of the gas is not shock-heated to the virial temperature of the halo and reaches a maximum temperature below 105 K, then it can cool to the neutral atomic state on a time-scale of several Gyr while forming dilute and extended atomic gas structures. To perform a coarse calibration, we also observed Hoag’s Object with the Wise Observatory (WO) 1-m telescope. The spectral analysis of the ring indicates the presence of a ∼2 Gyr old stellar population. The red colour gradient towards the centre of the core is also common of intermediate-luminosity ellipticals (Faber et al. The slit width was 1 arscec and the spatial sampling was 0.35 arcsec pixel−1. The metallicity of the central component of Hoag’s Object can provide an important clue to the formation of the core.

The authors could not detect CO in Hoag’s Object and put an upper limit of 7 × 108 M⊙ on the H2 mass. The obtained values are therefore not reliable and should provide only a consistency check of conclusions based on our spectroscopic measurements. (1987) put forward a new hypothesis that Hoag’s Object formed in a ‘major accretion event 2–3 Gyr ago’ by mass transfer or merger, in a mechanism similar to that forming polar ring galaxies. Appleton P. N. The MPFS was used to construct a detailed picture of the stellar kinematics in the central region of the galaxy.
. 3 shows the radial distributions of the line-of-sight velocities and velocity dispersion along the different slit positions. As demonstrated in Fig. Do our observational data agree with the Schweizer et al. Observations during 2009 May aimed to obtain deep exposures along the true kinematic axis were conducted under strong cirrus clouds and bad weather conditions. . Iodice E.
Milvang-Jensen B. Considering the age of the host galaxy and the massive, extended H i content, we concluded that the core formed more than ∼10 Gyr ago and that the H i disc probably formed a short time after.

They also mentioned that the bright knots in the ring are aligned in a narrow ring which is off-centre with respect to the main ring, implying that the ring has not yet settled since the event took place. The different symbols show the long-slit spectrum measurements of stars and ionized gas; the deepest spectrum was taken along PA = 45° in 2009 August. Longo G. 2. . . In particular, recent studies revealed extended, low-level star formation activity in the form of outer rings and spiral arms around a surprisingly high fraction of these galaxies (Thilker et al.

This approach fundamentally differs from the tilted-rings model since the model is first constructed for the entire velocity field and only then is fitted to the observations. Surface B-magnitude and colour profiles derived by fitting ellipses to the isophotes of the core. Fraternali F. Matthews L. D.

2008; Bournaud & Elmegreen 2009; Dekel, Sari & Ceverino 2009) and the extremely high specific angular momentum of the core.

At first, he chalked its peculiar ring-like shape off as an optical illusion caused by gravitational lensing. Metal enrichment influenced by the stellar evolution of the old core itself is expected to produce a metallicity gradient along the ring. The authors also pointed out that Hoag’s Object itself might eventually turn out to be an E0 galaxy with a polar ring. Representative spectra of the core and the ring (black lines) and their best-fitting models (red lines).

(1987) scenario, such as the alignment of bright knots along ‘a narrower ring which appears off-centre from the main ring’. . . 2011). Brosch N. The major accretion event can also be tested by looking for signatures of extended fine structure or of morphological distortion and asymmetries.

Deep H i imaging is necessary to map the extended halo of cold gas clouds around Hoag’s Object, or to detect tidally disrupted dwarf companions. The specific kinematical properties of the merger remnant depend strongly on the details of the merging process and specifically on the relative angular momenta of the two merging galaxies (Toomre 1977; Mihos & Hernquist 1996; Barnes 2002; Bournaud, Jog & Combes 2005; Di Matteo et al. Non-circular velocity residuals of ≲20 km s−1 are probably related to the optical spiral pattern across the ring. Hibbard & Mihos 1995; Duc et al. Forbes D. A. Bottom panels: the geometrical properties of the core derived by isophotal ellipse fitting. Hoag’s Object (Hoag 1950) has been fascinating professional and non-professional astronomers for more than 60 years. Kinematic information for Hoag’s Object. We checked the neighbourhood of Hoag’s Object by searching the NASA/IPAC Extragalactic Database (NED) for nearby galaxies with known redshift. However, an analysis of the spectroscopic data showed that the kinematic major-axes of both the core and the ring coincide and lie at about 45°, in contrast to the Schweizer et al.

Instead of using analytic functions, as in Moiseev (2008), the PA, i and Vrot radial variations were determined with four fixed radial nodes and were interpolated to all radii using spline functions. Lower panels: the line-of-sight velocity field (lower left-hand panel) and velocity dispersion field (lower right-hand panel) of Hoag’s Object from FPI and MPFS observations.

Proctor R. N. Whether or not this unique evolutionary track is related to the galaxy residing in an underdensed environment remains to be solved. Closely examining the detached ring structure constrains the age of the presumed accretion event. 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.

However, the role of internal non-linear mechanisms in forming the outer ring was not yet completely ruled out. The WO R-band observations allowed us to estimate the zero-point magnitude of the SCORPIO image with an accuracy of ∼0.1 mag.

Our extrapolation of the inward gas rotation curve significantly disagrees with any reliable mass distribution along the central core or with the stellar rotation derived from the MPFS data. We help brands stay relevant and gain visibility in search results. To obtain the central velocity dispersion, we used the deepest spectral measurements (along PA = 45°, which also has the best seeing) and averaged the data inside r < re = 2.8 arcsec.

Macció A. V. The HST colour image of Hoag’s Object, displayed in the left-hand panel of Fig. (1987) results. The Cartwheel contains an exceptionally large number of these black hole binary X-ray sources, because many massive stars formed in the ring.>> Art Neuendorffer.

This implies that genuine Hoag-type galaxies belong to a class of galaxies with massive, extended H i discs.

2007) code hints at such a late event in the evolution of the core. Hayward C. C. Different possible formation scenarios have been proposed for isolated ellipticals by observational studies, but their nature remains debated and a detailed study of their properties is still required (Niemi et al.

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