共查询到20条相似文献，搜索用时 218 毫秒
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M. Covington † A. Dekel T. J. Cox P. Jonsson J. R. Primack 《Monthly notices of the Royal Astronomical Society》2008,384(1):94-106
We construct a physically motivated model for predicting the properties of the remnants of gaseous galaxy mergers, given the properties of the progenitors and the orbit. The model is calibrated using a large suite of smoothed particle hydrodynamics (SPH) merger simulations. It implements generalized energy conservation while accounting for dissipative energy losses and star formation. The dissipative effects are evaluated from the initial gas fractions and from the orbital parameters via an 'impulse' parameter, which characterizes the strength of the encounter. Given the progenitor properties, the model predicts the remnant stellar mass, half-mass radius and velocity dispersion to an accuracy of 25 per cent. The model is valid for both major and minor mergers. We provide an explicit recipe for semi-analytic models of galaxy formation. 相似文献
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I. K. Baldry K. Glazebrook S. P. Driver 《Monthly notices of the Royal Astronomical Society》2008,388(3):945-959
A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4–8 per cent of the baryon density (assuming Ωb = 0.045 ). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the z < 0.05 GSMF using the New York University Value-Added Galaxy Catalog sample of 49 968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has α2 ≃−1.6 . At masses below ∼108.5 M⊙ , the GSMF may be significantly incomplete because of missing low-surface-brightness galaxies. One interpretation of the stellar mass–metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principle, we determine a simple relationship between baryonic mass and stellar mass and present an 'implied baryonic mass function'. This function has a faint-end slope, α2 ≃−1.9 . Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function → galaxy baryonic mass function → GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses ∼1011 M⊙ corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses. 相似文献
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Lilia P. Bassino Tom Richtler Boris Dirsch 《Monthly notices of the Royal Astronomical Society》2006,367(1):156-168
We present a photometric study of the globular cluster systems (GCSs) of the Fornax cluster galaxies NGC 1374, NGC 1379 and NGC 1387. The data consist of images from the wide-field MOSAIC imager of the Cerro Tololo Inter-American Observatory (CTIO) 4-m telescope, obtained with Washington C and Kron–Cousins R filters. The images cover a field of 36 × 36 arcmin2 , corresponding to 200 × 200 kpc2 at the Fornax distance. Two of the galaxies, NGC 1374 and NGC 1379, are low-luminosity ellipticals while NGC 1387 is a low-luminosity lenticular. Their cluster systems are still embedded in the cluster system of NGC 1399. Therefore, the use of a large field is crucial and some differences to previous work can be explained by this. The colour distributions of all GCSs are bimodal. NGC 1387 presents a particularly distinct separation between red and blue clusters and an overproportionally large population of red clusters. The radial distribution is different for blue and red clusters, red clusters being more concentrated towards the respective galaxies. The different colour and radial distributions point to the existence of two globular cluster subpopulations in these galaxies. Specific frequencies are in the range SN = 1.4–2.4 , smaller than the typical values for elliptical galaxies. These galaxies might have suffered tidal stripping of blue globular clusters by NGC 1399. 相似文献
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K. I. Caputi R. J. McLure J. S. Dunlop M. Cirasuolo A. M. Schael 《Monthly notices of the Royal Astronomical Society》2006,366(2):609-623
We have selected and analysed the properties of a sample of 2905 Ks < 21.5 galaxies in ∼131 arcmin2 of the Great Observatories Origins Deep Survey (GOODS) Chandra Deep Field South (CDFS), to obtain further constraints on the evolution of Ks -selected galaxies with respect to the results already obtained in previous studies. We made use of the public deep multiwavelength imaging from the optical B through the infrared (IR) 4.5-μm bands, in conjunction with available spectroscopic and COMBO17 data in the CDFS, to construct an optimized redshift catalogue for our galaxy sample. We computed the Ks -band luminosity function and determined that its characteristic magnitude has a substantial brightening and a decreasing total density from z = 0 to 〈 z 〉= 2.5 . We also analysed the colours and number density evolution of galaxies with different stellar masses. Within our sample, and in contrast to what is observed for less massive systems, the vast majority (∼85–90 per cent) of the most massive ( M > 2.5 × 1011 M⊙ ) local galaxies appear to be in place before redshift z ∼ 1 . Around 65–70 per cent of the total assemble between redshifts z = 1 and 3 and most of them display extremely red colours, suggesting that plausible star formation in these very massive systems should mainly proceed in obscured, short-time-scale bursts. The remaining fraction (up to ∼20 per cent) could be in place at even higher redshifts z = 3–4 , pushing the first epoch of formation of massive galaxies beyond the limits of current near-IR surveys. 相似文献
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Hubble Space Telescope observations of distant clusters have suggested a steep increase in the proportion of S0 galaxies between clusters at high redshifts and similar systems at the present day. It has been proposed that this increase results from the transformation of the morphologies of accreted field galaxies from spirals to S0s. We have simulated the evolution of the morphological mix in clusters based on a simple phenomenological model where the clusters accrete a mix of galaxies from the surrounding field, the spiral galaxies are transformed to S0s (through an unspecified process) and are added to the existing cluster population. We find that in order to reproduce the apparently rapid increase in the ratio of S0 galaxies to ellipticals in the clusters, our model requires that: (1) the galaxy accretion rate has to be high (typically, more than half of the present-day cluster population must have been accreted since z ∼0.5) , and (2) most of the accreted spirals, with morphological types as late as Scdm, must have transformed to S0s. Although the latter requirement may be difficult to meet, it is possible that such bulge-weak spirals have already been 'pre-processed' into the bulge-strong galaxies prior to entering the cluster core and are eventually transformed into S0s in the cluster environment. On the basis of the evolution of the general morphological mix in clusters our model suggests that the process responsible for the morphological transformation takes a relatively long time (∼ 1–3 Gyr) after the galaxy has entered the cluster environment. 相似文献
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Y. Fukazawa K. Makishima T. Tamura K. Nakazawa H. Ezawa Y. Ikebe K. Kikuchi T. Ohashi 《Monthly notices of the Royal Astronomical Society》2000,313(1):21-31
We measured metal abundances of the intracluster medium in the central regions of 34 nearby clusters of galaxies, using ASCA data. Clusters that have a sharp X-ray emission centred on a cD galaxy are commonly found to exhibit a central increment in the Fe abundance, which is more pronounced in lower temperature clusters; +(0.1–0.2) solar at kT >5 keV, compared with +(0.2–0.3) solar at 1.5< kT <4 keV. These central excess metals are thought to be ejected from cD galaxies. Several low-temperature cD type clusters also show significant Si abundance increase by +(0.1–0.2) solar at the central region. Compared with the Si-rich abundances observed in the outer regions of rich clusters, the Si to Fe abundance ratio of central excess metals tends to be near the solar ratio, implying that type Ia products from cD galaxies are dominant for the central excess metals. On the other hand, some other clusters do not show the central Fe abundance increase. As these clusters tend to contain two or three central giant galaxies, it is suggested that galaxy interactions have removed the central abundance increase. 相似文献
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Hiroyuki Hirashita Tomohiro T. Ichikawa 《Monthly notices of the Royal Astronomical Society》2009,396(1):500-510
We investigate the far-infrared (FIR) properties of a sample of blue compact dwarf galaxies (BCDs) observed by AKARI . By utilizing the data at wavelengths of λ= 65 , 90 and 140 μm, we find that the FIR colours of the BCDs are located at the natural high-temperature extension of those of the Milky Way and the Magellanic Clouds. This implies that the optical properties of dust in BCDs are similar to those in the Milky Way. Indeed, we explain the FIR colours by assuming the same grain optical properties, which may be appropriate for amorphous dust grains, and the same size distribution as those adopted for the Milky Way dust. Since both interstellar radiation field and dust optical depth affect the dust temperature, it is difficult to distinguish which of these two physical properties is responsible for the change of FIR colours. Then, in order to examine if the dust optical depth plays an important role in determining the dust temperature, we investigate the correlation between FIR colour (dust temperature) and dust-to-gas ratio. We find that the dust temperature tends to be high as the dust-to-gas ratio decreases but that this trend cannot be explained by the effect of dust optical depth. Rather, it indicates a correlation between dust-to-gas ratio and interstellar radiation field. Although the metallicity may also play a role in this correlation, we suggest that the dust optical depth could regulate the star formation activities, which govern the interstellar radiation field. We also mention the importance of submillimetre data in tracing the emission from highly shielded low-temperature dust. 相似文献
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Giulia Rodighiero Alberto Franceschini Giovanni Fasano 《Monthly notices of the Royal Astronomical Society》2001,324(2):491-497
We have extended our previous analysis of morphologically selected elliptical and S0 galaxies in the Hubble Deep Field (HDF) North to include Hubble Space Telescope ( HST ) data in the HDF South and the HDFS–NICMOS areas. Our final sample amounts to 69 E/S0 galaxies with K <20.15 over an area of 11 arcmin2 . Although a moderately small number over a modest sky area, this sample benefits from the best imaging and photometric data available on high-redshift galaxies. Multi-waveband photometry allows us to estimate with good accuracy the redshifts for the majority of these galaxies, which lack a spectroscopic measure. We confirm our previous findings that massive E/S0s tend to disappear from flux-limited samples at z >1.4. This adds to the evidence that the rest-frame colours and spectral energy distributions (SEDs) of the numerous objects found at 0.8< z <1.2 are inconsistent with a very high redshift of formation for the bulk of stars, while they are more consistent with protracted (either continuous or episodic) star formation down to z ≤1. These results based on high-quality imaging on a small field can be complemented with data from colour-selected extremely red objects (EROs) on much larger sky areas: our claimed demise of E/S0s going from z =1 to z =1.5 is paralleled by a similarly fast decrease in the areal density of EROs when the colour limit is changed from ( R − K )=5 to ( R − K )=6 (corresponding to z ≃1 and z ≃1.3 respectively). Altogether, the redshift interval from 1 to 2 seems to correspond to a very active phase for the assembly of massive E/S0 galaxies in the field, and also probably one where a substantial fraction of their stars are formed. 相似文献