Detection of satellite remnants in the Galactic Halo with Gaia– I. The effect of the Galactic background, observational errors and sampling     

Anthony G. A. Brown  Hector M. Velázquez  Luis A. Aguilar 《Monthly notices of the Royal Astronomical Society》2005,359(4):1287-1305

  相似文献   

The Qso Hosts I Zw 1 and 3C 48: Prototypes of a Merger-Driven Quasar Evolution?     

Julia Scharwächter  Andreas Eckart  Susanne Pfalzner  Jens Zuther  Melanie Krips  Eva Schinnerer  Johannes Staguhn 《Astrophysics and Space Science》2005,295(1-2):101-106

I Zw 1 and 3C 48 are two neighboring template objects at a later stage of the hypothesized merger-driven evolutionary sequence from ultra-luminous infrared galaxies (ULIRGs) to quasi-stellar objects (QSOs). Since galaxy mergers are assumed to trigger the evolution, it is important to confirm the merger properties of transitionary objects. Using multi-wavelength observations and N-body simulations, the merger histories of I Zw 1 and 3C 48 have been investigated in two separate case studies. Here, the results from both studies are compared and their relevance for the evolutionary hypothesis is discussed.This research is partly based on observations with ISAAC at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) under projects 67.B-0009 and 67.B-0019.  相似文献   

The angular momentum of dark haloes: merger and accretion effects     

Sébastien Peirani  Roya Mohayaee  José A. de Freitas Pacheco 《Monthly notices of the Royal Astronomical Society》2004,348(3):921-931

  相似文献   

Orientation dependency of broad-line widths in quasars and consequences for black hole mass estimation     

Matt J. Jarvis  Ross J. McLure 《Monthly notices of the Royal Astronomical Society》2006,369(1):182-188

We have identified two new galaxies with gas counter-rotation (NGC 1596 and 3203) and have confirmed similar behaviour in another one (NGC 128), this using results from separate studies of the ionized-gas and stellar kinematics of a well-defined sample of 30 edge-on disc galaxies. Gas counter-rotators thus represent 10 ± 5 per cent of our sample, but the fraction climbs to 21 ± 11 per cent when only lenticular (S0) galaxies are considered and to 27 ± 13 per cent for S0 galaxies with detected ionized gas only. Those fractions are consistent with but slightly higher than previous studies. A compilation from well-defined studies of S0 galaxies in the literature yields fractions of 15 ± 4 and 23 ± 5 per cent, respectively. Although mainly based on circumstantial evidence, we argue that the counter-rotating gas originates primarily from minor mergers and tidally induced transfer of material from nearby objects. Assuming isotropic accretion, twice those fractions of objects must have undergone similar processes, underlining the importance of (minor) accretion for galaxy evolution. Applications of gas counter-rotators to barred galaxy dynamics are also discussed.  相似文献   

Origin of the counterrotating gas in NGC 1596     

Aeree Chung  Bärbel Koribalski  Martin Bureau  J. H. van Gorkom 《Monthly notices of the Royal Astronomical Society》2006,370(3):1565-1572

  相似文献   

The formation of ultracompact dwarf galaxies     

MichaelFellhauer  PavelKroupa 《Monthly notices of the Royal Astronomical Society》2002,330(3):642-650

Recent spectroscopic observations of galaxies in the Fornax Cluster reveal nearly unresolved 'star-like' objects with redshifts appropriate to the Fornax Cluster. These objects have intrinsic sizes of ≈100 pc and absolute B -band magnitudes in the range  −14< M _B<−11.5 mag  and lower limits for the central surface brightness   μ _B≳23 mag arcsec⁻²  , and so appear to constitute a new population of ultracompact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar superclusters (by Kroupa) , which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of superclusters in a tidal field. The YMCs merge on a few supercluster crossing times. Superclusters that are initially as concentrated and massive as knot S in the interacting Antennae galaxies evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs. Less massive superclusters resembling knot 430 in the Antennae may evolve to ω Cen-type systems. Low-concentration superclusters are disrupted by the tidal field, dispersing their surviving star clusters while the remaining merger objects rapidly evolve into the   μ _B− M _B  region populated by low-mass Milky Way dSph satellites.  相似文献   

Neutral hydrogen gas in interacting galaxies: the NGC 1511 galaxy group     

Bärbel Koribalski  Eva Manthey 《Monthly notices of the Royal Astronomical Society》2005,358(1):202-210

We present H  i line and 20-cm radio continuum observations of the NGC 1511 galaxy group obtained with the Australia Telescope Compact Array. The data reveal an extended, rather disturbed H  i distribution for the peculiar starburst galaxy NGC 1511 and a narrow bridge to its small companion galaxy, NGC 1511B, which has been severely distorted by the interaction/collision between the two galaxies. No stellar counterpart to the gaseous bridge has been detected. In addition, we find that the peculiar optical ridge to the east of NGC 1511 is probably the stellar remnant of a galaxy completely disrupted by interactions with NGC 1511. The slightly more distant neighbour, NGC 1511A, shows a regular H  i velocity field and no obvious signs of interactions.
Radio continuum emission from NGC 1511 reveals three prominent sources on top of a more diffuse, extended distribution. We derive an overall star formation rate of  7 M_⊙ yr⁻¹  . The most enhanced star formation is found in the south-eastern part of the disc, coincident with several bright H  ii regions, and closest to the peculiar optical ridge. No continuum emission was detected in the companions, but NGC 1511B appears to show an H  ii region at its faint western edge, closest to NGC 1511. The group displays a prime example of interaction-induced star formation activity.  相似文献   

Investigating the central engine of ultraluminous infrared galaxies: near-infrared imaging     

R.I. Davies  A. Burston  M.J. Ward 《Monthly notices of the Royal Astronomical Society》2002,329(2):367-376

We present 0.5-arcsec-resolution near-infrared images of six ultraluminous infrared galaxies with known redshifts. Six of the eight bright nuclei are resolved on kiloparsec scales, suggesting that there is significant circumnuclear star formation or close progenitor nuclei. At this spatial resolution, the nuclei have very red colours that cannot in general be reproduced by reddening stellar light, but require an additional component of hot dust emission. In five of the six primary nuclei more than 20 per cent of the K -band continuum originates in hot dust, but the temperature cannot be determined by JHK broad-band colours alone. Comparison with the spectral shapes, however, does allow the temperature to be constrained, and we find in every case that it is at the upper end of the permissible range, ≳1000 K. This does not necessarily imply that there is an active galactic nucleus present, since there is evidence that stellar processes can also generate dust this hot via stochastic heating of small grains. The quantities of hot dust we have found here can make up to 0.5-mag difference to the K -band magnitude even at     , with implications for observations and population synthesis models of higher-redshift objects. Observations in the L or M bands, where hot dust is most important at     , could help to discriminate between models of dusty starbursts and ellipticals.  相似文献   

Tracing the star stream through M31 using planetary nebula kinematics     

H. R. Merrett  K. Kuijken  M. R. Merrifield  A. J. Romanowsky  N. G. Douglas  N. R. Napolitano  M. Arnaboldi  M. Capaccioli  K. C. Freeman  O. Gerhard  N. W. Evans  M. I. Wilkinson  C. Halliday  T. J. Bridges  D. Carter 《Monthly notices of the Royal Astronomical Society》2003,346(4):L62-L66

We present a possible orbit for the Southern Stream of stars in M31, which connects it to the Northern Spur. Support for this model comes from the dynamics of planetary nebulae (PNe) in the disc of M31: analysis of a new sample of 2611 PNe obtained using the Planetary Nebula Spectrograph reveals ∼20 objects with kinematics inconsistent with the normal components of the galaxy, but which lie at the right positions and velocities to connect the two photometric features via this orbit. The satellite galaxy M32 is coincident with the stream both in position and velocity, adding weight to the hypothesis that the stream comprises its tidal debris.  相似文献   

Tidal disruption model for the interacting pair of galaxies VV 117 (NGC 2444/45)     

K.S.V.S. Narasimhan  P.M.S. Namboodiri  S.M. Alladin 《Astrophysics and Space Science》2003,286(3-4):381-395

A series of N-body simulations have been performed to interpret the interacting pair of galaxies VV 117 (NGC 2444/45). The galaxies have been modelled assuming a mass ratio two. The simulations use various values for the distance of closest approach and the eccentricity of the relative orbit of the pair. A plausible scenario for the tidal disruption of the less massive galaxy is proposed. NGC2444, having double the mass of NGC 2445, has undergone penetrating collision with the latter in a hyperbolic or a parabolic orbit. After the first collision, the orbit has become bound. Our results show that VV 117 has either just emerged from the first collision or are on the verge of a second collision. NGC 2445suffers considerable disruption and mass loss. NGC 2444 is not affected much. The second collision is expected to culminate in the merger of the two galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献