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تسجيل مستخدم جديدConstraints on the dynamical evolution of the galaxy group M81
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According to the standard model of cosmology, galaxies are embedded in dark matter halos which are made of particles beyond the standard model of particle physics, thus extending the mass and the size of the visible baryonic matter by typically two orders of magnitude. The observed gas distribution throughout the nearby M81 group of galaxies shows evidence for past significant galaxy--galaxy interactions but without a merger having occurred. This group is here studied for possible dynamical solutions within the dark-matter standard model. In order to cover a comprehensive set of initial conditions, the inner three core members M81, M82 and NGC3077 are treated as a three-body model based on Navarro-Frenk-White profiles. The possible orbits of these galaxies are examined statistically taking into account dynamical friction. Long living, non-merging initial constellations which allow multiple galaxy-galaxy encounters comprise unbound galaxies only, which are arriving from a far distance and happen to simultaneously encounter each other within the recent 500 Myr. Our results are derived by the employment of two separate and independent statistical methods, namely a Markov chain Monte Carlo method and the genetic algorithm using the SAP system environment. The conclusions reached are confirmed by high-resolution simulations of live self-consistent systems (N-body calculations). Given the observed positions of the three galaxies the solutions found comprise predictions for their proper motions.
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According to the standard model of cosmology the visible, baryonic matter of galaxies is embedded in dark matter haloes, thus extending the mass and the size of galaxies by one to two orders of magnitude. Taking into account dynamical friction betwee
n the dark matter haloes, the nearby located M81 group of galaxies as well as the Hickson compact groups of galaxies are here investigated with regard to their dynamical behaviour. The results of the employment of the Markov Chain Monte Carlo method and the genetic algorithm show statistically substantial merger rates between galaxies, and long living constellations without merging galaxies comprise - apart from very few instances - initially unbound systems only. This result is derived based on three- and four-body calculations for a model of rigid Navarro-Frenk-White profiles for the dark matter haloes, but verified by the comparison to randomly chosen individual solutions for the M81 galaxy group with high-resolution simulations of live self-consistent systems (N-body calculations). In consequence, the observed compact configurations of major galaxies are a very unlikely occurence if dark matter haloes exist.
GC-1 and GC-2 are two globular clusters (GCs) in the remote halo of M81 and M82 in the M81 group discovered by Jang et al. using the {it Hubble Space Telescope} ({it HST}) images. These two GCs were observed as part of the Beijing--Arizona--Taiwan--C
onnecticut (BATC) Multicolor Sky Survey, using 14 intermediate-band filters covering a wavelength range of 4000--10000 AA. We accurately determine these two clusters ages and masses by comparing their spectral energy distributions (from 2267 to 20000~{AA}, comprising photometric data in the near-ultraviolet of the {it Galaxy Evolution Explorer}, 14 BATC intermediate-band, and Two Micron All Sky Survey near-infrared $JHK_{rm s}$ filters) with theoretical stellar population-synthesis models, resulting in ages of $15.50pm3.20$ for GC-1 and $15.10pm2.70$ Gyr for GC-2. The masses of GC-1 and GC-2 obtained here are $1.77-2.04times 10^6$ and $5.20-7.11times 10^6 rm~M_odot$, respectively. In addition, the deep observations with the Advanced Camera for Surveys and Wide Field Camera 3 on the {it HST} are used to provide the surface brightness profiles of GC-1 and GC-2. The structural and dynamical parameters are derived from fitting the profiles to three different models; in particular, the internal velocity dispersions of GC-1 and GC-2 are derived, which can be compared with ones obtained based on spectral observations in the future. For the first time, in this paper, the $r_h$ versus $M_V$ diagram shows that GC-2 is an ultra-compact dwarf in the M81 group.
We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by
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Galactic cirrus emission at far-infrared wavelengths affects many extragalactic observations. Separating this emission from that associated with extragalactic objects is both important and difficult. In this paper we discuss a particular case, the M8
1 group, and the identification of diffuse structures prominent in the infrared, but also detected at optical wavelengths. The origin of these structures has previously been controversial, ranging from them being the result of a past interaction between M81 and M82 or due to more local Galactic emission. We show that over of order a few arcminute scales the far-infrared (Herschel 250 &mu&m) emission correlates spatially very well with a particular narrow velocity (2-3 km/s) component of the Galactic HI. We find no evidence that any of the far-infrared emission associated with these features actually originates in the M81 group. Thus we infer that the associated diffuse optical emission must be due to galactic light back scattered off dust in our galaxy. Ultra-violet observations pick out young stellar associations around M81, but no detectable far-infrared emission. We consider in detail one of the Galactic cirrus features, finding that the far-infrared HI relation breaks down below arc minute scales and that at smaller scales there can be quite large dust temperature variations.
We present the first results of a wide-field mapping survey of the M81 group conducted with Hyper Suprime-Cam on the Subaru Telescope. Our deep photometry reaches $sim2$ magnitudes below the tip of the red giant branch (RGB) and reveals the spatial d
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