共查询到20条相似文献，搜索用时 15 毫秒
1.
Using the “Updated Nearby Galaxy Catalog”, we consider different properties of companion galaxies around luminous hosts in the Local Volume. The data on stellar masses, linear diameters, surface brightnesses, HI‐richness, specific star formation rate (sSFR), and morphological types are discussed for members of the nearest groups, including the Milky Way and M 31 groups, as a function of their separation from the hosts. Companion galaxies in groups tend to have lower stellar masses, smaller linear diameters, and fainter mean surface brightnesses as the distance to their host decreases. The hydrogen‐to‐stellar mass ratio of the companions increases with their linear projected separation from the dominant luminous galaxy. This tendency is more expressed around the bulge‐dominated hosts. While linear separation of the companions decreases, their mean sSFR becomes lower, accompanied with the increasing sSFR scatter. the typical linear projected separation of dSphs around the bulge‐dominated hosts, 350 kpc, is substantially larger than that around the disk‐dominated ones, 130 kpc. This difference probably indicates the presence of larger hot/warm gas haloes around the early‐type host galaxies. The mean fraction of dSph (quenched) companions in the 11 nearest groups as a function of their projected separation Rp can be expressed as ƒ(E) = (0.55–0.69)×Rp. The fraction of dSphs around the Milky Way and M 31 looks much higher than in other nearby groups because the quenching efficiency dramatically increases towards the ultra‐low mass companions. We emphasize that the observed properties of the Local Group are not typical for other groups in the Local Volume due to the role of selection effects caused by our location inside the Local Group. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Noah Brosch Carmiya Bar-Or Doron Malka 《Monthly notices of the Royal Astronomical Society》2006,368(2):864-876
We report the discovery of small groups of uncatalogued, compact, star forming (SF) dwarf galaxies (DGs) by Hα mapping of the neighbourhoods of apparently isolated, catalogued, SF DGs. Our sample consists of dwarf ( M ≥−18 mag) galaxies at least 2 Mpc away from any other catalogued galaxy. The galaxies were selected to exhibit Hα emission of any intensity, i.e. not selecting only strong starbursts, as an indicator of recent or on-going star formation with the goal of understanding why are they presently forming stars. We identified possible neighbours by imaging the galaxies and their surroundings through Hα filters centred at or near the redshift of the galaxy, and searching for localized Hα emission with the characteristics of the line emission from the sample galaxies.
We identified 20 possible SF neighbour galaxies, 17 of them not previously catalogued, in three of the five search fields where we had good quality data, and present here their positions and, images and morphology, as well as some indications of binarity. The relatively large number of possible neighbour candidates, combined with their relative faintness, argue that it would be virtually impossible to identify truly isolated galaxies. It seems that the objects we selected as extremely isolated are probably the brightest members of sparse groups of galaxies, where the other members are also DGs that are presently forming stars. In order to enhance the confidence of this statement regular redshifts are required for our candidate neighbours. 相似文献
We identified 20 possible SF neighbour galaxies, 17 of them not previously catalogued, in three of the five search fields where we had good quality data, and present here their positions and, images and morphology, as well as some indications of binarity. The relatively large number of possible neighbour candidates, combined with their relative faintness, argue that it would be virtually impossible to identify truly isolated galaxies. It seems that the objects we selected as extremely isolated are probably the brightest members of sparse groups of galaxies, where the other members are also DGs that are presently forming stars. In order to enhance the confidence of this statement regular redshifts are required for our candidate neighbours. 相似文献
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A composite sample of NIR-selected galaxies having extended multicolor coverage has been used to probe the cosmological evolution
of the blue luminosity function and of the stellar mass function. The bright fraction of the sample has spectroscopic redshifts,
and the remaining fraction well-calibrated photometric redshifts. The resulting blue luminosity function shows an increasing
brightening with redshift respect to the local luminosity function. Hierarchical CDM models predictions are in agreement only
at low and intermediate redshifts but fail to reproduce the observed brightening at high redshifts (z ∼ 2–3). This brightening marks the epoch where starburst activity triggered by galaxy interactions could be an important
physical mechanism for the galaxy evolution. At the same time the NIR galaxy sample has been used to trace the evolution of
the cosmological stellar mass density up to ∼3. A clear decrease of the average mass density is apparent with a fraction ∼15%
of the local value at z ∼ 3. UV bright star-forming galaxies are substancial contributors to the evolution of the stellar mass density. Although
these results are globally consistent with Λ–CDM scenarios, they tend to underestimate the mass density produced by more massive
galaxies present at z > 2. 相似文献
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Barbara Lo Faro Pierluigi Monaco Eros Vanzella Fabio Fontanot Laura Silva Stefano Cristiani 《Monthly notices of the Royal Astronomical Society》2009,399(2):827-841
It has recently been shown that galaxy formation models within the Λ cold dark matter cosmology predict that, compared to the observed population, small galaxies (with stellar masses <1011 M⊙ ) form too early, are too passive since z ∼ 3 and host too old stellar populations at z = 0 . We then expect an overproduction of small galaxies at z ≳ 4 that should be visible as an excess of faint Lyman-break galaxies. To check whether this excess is present, we use the morgana galaxy formation model and grasil spectrophotometric + radiative transfer code to generate mock catalogues of deep fields observed with Hubble Space Telescope Advanced Camera for Surveys. We add observational noise and the effect of Lyman α emission, and perform colour–colour selections to identify Lyman-break galaxies. The resulting mock candidates have plausible properties that closely resemble those of observed galaxies. We are able to reproduce the evolution of the bright tail of the luminosity function of Lyman-break galaxies (with a possible underestimate of the number of the brightest i -dropouts), but uncertainties and degeneracies in dust absorption parameters do not allow to give strong constraints to the model. Besides, our model shows a clear excess with respect to observations of faint Lyman-break galaxies, especially of z 850 ∼ 27 V -dropouts at z ∼ 5 . We quantify the properties of these 'excess' galaxies and discuss the implications: these galaxies are hosted in dark matter haloes with circular velocities in excess of 100 km s−1 , and their suppression may require a deep rethinking of stellar feedback processes taking place in galaxy formation. 相似文献
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Francesca Matteucci Antonio Pipino 《Monthly notices of the Royal Astronomical Society》2005,357(2):489-496
We have studied the effects of a hypothetical initial generation containing very massive stars [ M > 100 M⊙ , pair-creation supernovae] on the chemical and photometric evolution of elliptical galaxies. To this purpose, we have computed the evolution of a typical elliptical galaxy with luminous mass of the order of 1011 M⊙ and adopted chemical evolution models already tested to reproduce the main features of ellipticals. We have tested several sets of yields for very massive zero-metallicity stars: these stars should produce quite different amounts of heavy elements than lower-mass stars. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results are at variance with the main observational constraints of ellipticals such as the average [〈α/ Fe〉* ] ratio in stars and the integrated colours. Therefore, we conclude that if Population III stars ever existed they must have been present for a very short period of time and their effects on the following evolution of the parent galaxy must have been negligible. This effect is minimum if a more realistic model with initial infall of gas rather than the classic monolithic model is adopted. Ultimately, we conclude that there is no need to invoke a generation of very massive stars in ellipticals to explain their chemical and photometric properties. 相似文献
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D. Kilkenny L. A. Crause F. van Wyk 《Monthly notices of the Royal Astronomical Society》2005,361(2):559-564
A new statement of the eigenvalue problem of studying small perturbations in arbitrary integrable self-gravitating systems is presented. An example of such a system, a 2D stellar disc, is considered in detail. The theory, based on the general equation for disc eigenmodes, reveals mechanisms for the formation and growth of global galactic structures. This new point of view specifies the limits of the unified theory of bar-like and spiral modes that was based on the assumption that global galactic structures could be understood in terms of low-frequency disc modes. 相似文献
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Understanding the formation and evolution of massive galaxies provides important keys to constrain the baryon assembly processes
in the ΛCDM hierarchical scenario. We review the main results obtained so far with the K20 and other recent near-IR surveys
on the redshift distribution, the evolution of the luminosity function and luminosity density, the nature of old and dusty
EROs, the evolution of the galaxy stellar mass function and the nature of luminous starbursts at z∼2 which may be the progenitors of the present-day massive spheroidal galaxies. 相似文献
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Vimal Simha David H. Weinberg Romeel Davé Oleg Y. Gnedin Neal Katz Du&#;an Kere&#; 《Monthly notices of the Royal Astronomical Society》2009,399(2):650-662
We examine the accretion and merger histories of central and satellite galaxies in a smoothed particle hydrodynamics (SPH) cosmological simulation that resolves galaxies down to 7 × 109 M⊙ . Most friends-of-friends haloes in the simulation have a distinct central galaxy, typically 2–5 times more massive than the most massive satellite. As expected, satellites have systematically higher assembly redshifts than central galaxies of the same baryonic mass, and satellites in more massive haloes form earlier. However, contrary to the simplest expectations, satellite galaxies continue to accrete gas and convert it to stars; the gas accretion declines steadily over a period of 0.5–1 Gyr after the satellite halo merges with a larger parent halo. Satellites in a cluster mass halo eventually begin to lose baryonic mass. Typically, satellites in our simulation are 0.1–0.2 mag bluer than in models that assume no gas accretion on to satellites after a halo merger. Since z = 1 , 27 per cent of central galaxies (above 3 × 1010 M⊙ ) and 22 per cent of present-day satellite galaxies have merged with a smaller system above a 1:4 mass ratio; about half of the satellite mergers occurred after the galaxy became a satellite and half before. In effect, satellite galaxies can remain 'central' objects of halo substructures, with continuing accretion and mergers, making the transition in assembly histories and physical properties a gradual one. Implementing such a gradual transformation in semi-analytic models would improve their agreement with observed colour distributions of satellite galaxies in groups and with the observed colour dependence of galaxy clustering. 相似文献
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We review the methodology adopted in computing chemical evolution models of galaxies of different morphological type (ellipticals,
spirals and irregulars). We discuss the importance of the history of star formation in different galaxies in order to interpret
the observed abundances. In particular, we discuss the time-delay model which allows us to interpret the observed abundance
patterns in galaxies as due to the different contributions of supernovae II and Ia. We show that the time-delay model applied
to galaxies of different morphological type predicts different [X/Fe] versus [Fe/H] relations in different galaxies. As a
consequence of this, these relations can be used to infer the nature and to date high redshift objects. Finally, we show our
predictions for the cosmic star formation rate. 相似文献
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Michael Boylan-Kolchin Chung-Pei Ma Eliot Quataert 《Monthly notices of the Royal Astronomical Society》2008,383(1):93-101
The time-scale for galaxies within merging dark matter haloes to merge with each other is an important ingredient in galaxy formation models. Accurate estimates of merging time-scales are required for predictions of astrophysical quantities such as black hole binary merger rates, the build-up of stellar mass in central galaxies and the statistical properties of satellite galaxies within dark matter haloes. In this paper, we study the merging time-scales of extended dark matter haloes using N -body simulations. We compare these results to standard estimates based on the Chandrasekhar theory of dynamical friction. We find that these standard predictions for merging time-scales, which are often used in semi-analytic galaxy formation models, are systematically shorter than those found in simulations. The discrepancy is approximately a factor of 1.7 for M sat / M host ≈ 0.1 and becomes larger for more disparate satellite-to-host mass ratios, reaching a factor of ∼3.3 for M sat / M host ≈ 0.01. Based on our simulations, we propose a new, easily implementable fitting formula that accurately predicts the time-scale for an extended satellite to sink from the virial radius of a host halo down to the halo's centre for a wide range of M sat / M host and orbits. Including a central bulge in each galaxy changes the merging time-scale by ≲10 per cent. To highlight one concrete application of our results, we show that merging time-scales often used in the literature overestimate the growth of stellar mass by satellite accretion by ≈40 per cent, with the extra mass gained in low mass ratio mergers. 相似文献
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R. Coziol 《Monthly notices of the Royal Astronomical Society》2003,344(1):181-187
The characteristics of the starburst galaxies from the Pico dos Dias survey (PDS) are compared with those of the nearby ultraviolet (UV) bright Markarian starburst galaxies, having the same limit in redshift ( v h < 7500 km s−1 ) and absolute B magnitude ( MB < −18). An important difference is found: the Markarian galaxies are generally undetected at 12 and 25 μm in IRAS . This is consistent with the UV excess shown by these galaxies and suggests that the youngest star-forming regions dominating these galaxies are relatively free of dust.
The far-infrared selection criteria for the PDS are shown to introduce a strong bias towards massive (luminous) and large size late-type spiral galaxies. This is contrary to the Markarian galaxies, which are found to be remarkably rich in smaller size early-type galaxies. These results suggest that only late-type spirals with a large and massive disc are strong emitters at 12 and 25 μm in IRAS in the nearby Universe.
The Markarian and PDS starburst galaxies are shown to share the same environment. This rules out an explanation of the differences observed in terms of external parameters. These differences may be explained by assuming two different levels of evolution, the Markarian being less evolved than the PDS galaxies. This interpretation is fully consistent with the disc formation hypothesis proposed by Coziol et al. to explain the special properties of the Markarian SBNG. 相似文献
The far-infrared selection criteria for the PDS are shown to introduce a strong bias towards massive (luminous) and large size late-type spiral galaxies. This is contrary to the Markarian galaxies, which are found to be remarkably rich in smaller size early-type galaxies. These results suggest that only late-type spirals with a large and massive disc are strong emitters at 12 and 25 μm in IRAS in the nearby Universe.
The Markarian and PDS starburst galaxies are shown to share the same environment. This rules out an explanation of the differences observed in terms of external parameters. These differences may be explained by assuming two different levels of evolution, the Markarian being less evolved than the PDS galaxies. This interpretation is fully consistent with the disc formation hypothesis proposed by Coziol et al. to explain the special properties of the Markarian SBNG. 相似文献
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B. Aryal S. Paudel W. Saurer 《Monthly notices of the Royal Astronomical Society》2007,379(3):1011-1021
As a concluding paper in this series, we present an analysis of the spatial orientations of galaxies in seven Abell clusters of BM type II and compare the results with previous works. Four BM type II clusters (A1767, A1809, A2554, A2721) show a similar preferred alignment: spin vectors of galaxies tend to lie in the local supercluster plane and the projections of the spin vector tend to be oriented perpendicular with respect to the Virgo cluster centre. A preferred alignment of galaxies in cluster A2554 is noticed in both the two- and three-dimensional analyses. In a comparison with previous work, we noticed a systematic change (with distance, radial velocity, morphology and magnitude) in the galaxy alignments from early-type (BM I) to late-type (BM III) clusters. Possible explanations of these systematic changes will be discussed. 相似文献