Astronomy Reports - The origin of several rings in lenticular galaxies with no signs of ongoing or recent star formation (without emission lines and a signal in the ultraviolet spectral range) is... 相似文献
Dark energy models inspired by the cosmological holographic principle are studied in homogeneous isotropic spacetime with a general choice for the dark energy density \(\rho_{d}=3(\alpha H^{2}+\beta\dot{H})\). Special choices of the parameters enable us to obtain three different holographic models, including the holographic Ricci dark energy (RDE) model. Effect of interaction between dark matter and dark energy on the dynamics of those models are investigated for different popular forms of interaction. It is found that crossing of phantom divide can be avoided in RDE models for β>0.5 irrespective of the presence of interaction. A choice of α=1 and β=2/3 leads to a varying Λ-like model introducing an IR cutoff length Λ?1/2. It is concluded that among the popular choices an interaction of the form Q∝Hρm suits the best in avoiding the coincidence problem in this model. 相似文献
With the means of panoramic spectroscopy at the SAO RAS BTA telescope, we investigated the properties of stellar populations
in the central regions of five early-type galaxies—the NGC524 group members. The evolution of the central regions of galaxies
looks synchronized: the average age of stars in the bulges of all the five galaxies lies in the range of 3–6Gyr.Four of the
five galaxies revealed synchronized bursts of star formation in the nuclei 1–2 Gyr ago. The only galaxy, in which the ages
of stellar population in the nucleus and in the bulge coincide (i.e. the nuclear burst of star formation did not take place)
isNGC502, the farthest from the center of the group of all the galaxies studied. 相似文献
Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the
structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies.
The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ∼ 1–3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies,
more precisely in all of them brighter than MB ∼ −18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential
segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies
with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of
S0 galaxies on distance from the center of the group is found. Morphological signs of a “minor merger” are found in the lenticular
galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation
of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions). 相似文献
Surface photometry data are presented for 12 southern lenticular galaxies located in regions of low density. Digital images in the gri bands were obtained on the LCOGT network of meter-class telescopes. Structural parameters of the global stellar disks of the galaxies are calculated—the exponential scale and relative thickness. The presence of substructure in the disks is noted; in particular, more than half the studied galaxies possess ring structures, sometimes more than one. The color maps presented indicate complex evolution of the substructure of the disks of lenticular galaxies: they can be classified as blue (ongoing star formation) or red (concentration of dust). The rings do not always lie in the main plane of the disk; there are cases of clearly inclined, or even polar, compact rings. 相似文献
We have investigated the stellar population properties in the central regions of a sample of lenticular galaxies with bars
and single-exponential outer stellar disks using the data from the SAURON integral-field spectrograph retrieved from the open
Isaac Newton Group Archive. We have detected chemically decoupled compact stellar nuclei with a metallicity twice that of
the stellar population in the bulges in seven of the eight galaxies. A starburst is currently going on at the center of the
eighth galaxy and we have failed to determine the stellar population properties from its spectrum. The mean stellar ages in
the chemically decoupled nuclei found range from 1 to 11 Gyr. The scenarios for the origin of both decoupled nuclei and lenticular
galaxies as a whole are discussed. 相似文献
Results of spectroscopic and photometric studies for the locally isolated lenticular galaxy NGC 4124 are presented. A model of the mass distribution consistent with photometric data has been constructed on the basis of a kinematic analysis. In this model, the halo mass within the optical radius is almost half the diskmass. The disk is shown to be in a dynamical state close to amarginally stable one. This rules out dynamical disk heating for the galaxy through a strong external action or a merger with a massive system. However, the presence of a gaseous disk inclined to the main plane of the galaxy in the central kiloparsec region suggests probable cannibalization of a small satellite that also produced a late starburst in the central region. This is confirmed by the younger mean age (~2 Gyr) of the stellar population in the galaxy’s central region than the disk age (5–7 Gyr). 相似文献
Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11°N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at ~ 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October–December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.
Based on GALEX (Galaxy Ultraviolet Explorer) data, we have compiled a list of lenticular galaxies with ultraviolet rings—radially
localized star-forming regions. We have analyzed the optical structure of these galaxies using SDSS (Sloan Digital Sky Survey)
surface photometry, measured the colors of the rings, and compared the radial localizations of the ring structures in the
optical and ultraviolet spectral ranges. Possible scenarios for the formation of ring star-forming regions in lenticular galaxies
having no other structural peculiarities and exhibiting a homogeneous old stellar population outside the rings are discussed. 相似文献