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1.
Dejan Urošević 《Astrophysics and Space Science》2003,283(1):75-86
This paper represents the updated empirical Galactic andextragalactic Σ-D relations (relations between the surface brightness Σ and the diameter D) for supernova remnants(SNRs), with checking the connection of the main Galactic radio loops (Loop I, II, III and IV) with
these relations. We present results which suggest, once again, that the radio loops may have an SNR origin. The updated relations
for old SNRs have been measured to have slopes, β ≈ 2 in log-log space. The best Σ-D relations for M31 and M33 galaxies were derived and these relations are shown to be flatter (β ≲2) than those for Galactic
SNRs alone. A Σ-D relation with168 reliable calibrators (both Galactic and extragalactic) is derived.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
In this paper, we discuss known discrepancies between theoretically derived and empirically measured relations between the radio surface brightness Σ and the diameter D of supernova remnants (SNRs): these relations are commonly known as the Σ–D relations. We argue that these discrepancies may be at least partially explained by taking into account thermal emission at radio frequencies from SNRs at particular evolutionary stages and located in particular environments. The major contributions of this paper may be summarized as follows: (i) we consider thermal emission at radio frequencies from SNRs in the following scenarios: a relatively young SNR evolving in a dense molecular cloud environment (n 100–1000 cm−3) and an extremely evolved SNR expanding in a dense warm medium (n 1–10 cm−3). Both of these SNRs are assumed to be in the adiabatic phase of evolution. We develop models of the radio emission from both of these types of SNRs and each of these models demonstrate that through the thermal bremsstrahlung process significant thermal emission at radio frequencies is expected from both types of SNR. Based on a literature search, we claim that thermal absorption or emission at radio frequencies has been detected for one evolved Galactic SNR and four young Galactic SNRs with similar properties to our modelled evolved and young SNRs. (ii) We construct artificial radio spectra for both of these two types of SNRs: in particular, we discuss our simulated spectrum for the evolved Galactic SNR OA 184. By including thermal emission in our simulated spectra, we obtain different slopes in Σ–D relations: these new slopes are in closer agreement to empirically obtained relations than the theoretically derived relations which do not take thermal emission into account. (iii) Lastly, we present an additional modification to the theoretical Σ–D relation for SNRs in the adiabatic expansion phase. This modification is based on the convolution of the synchrotron emissivity with the emissivity derived in this paper for thermal bremsstrahlung emission from an ionized gas cloud (that is, a theoretical construct of an SNR). 相似文献
3.
T. Morel R. Doyon N. St-Louis 《Monthly notices of the Royal Astronomical Society》2002,329(2):398-410
In an effort better to calibrate the supernova rate of starburst galaxies as determined from near-infrared [Fe ii ] features, we report on a [Fe ii ] λ 1.644 μm line-imaging survey of a sample of 42 optically selected supernova remnants (SNRs) in M33. A wide range of [Fe ii ] luminosities are observed within our sample (from less than 6 to 695 L⊙ ). Our data suggest that the bright [Fe ii ] SNRs are entering the radiative phase and that the density of the local interstellar medium (ISM) largely controls the amount of [Fe ii ] emission. We derive the following relation between the [Fe ii ] λ 1.644 μm line luminosity of radiative SNRs and the electronic density of the post-shock gas, n e : L [Fe ii ] (cm−3 ). We also find a correlation in our data between L [Fe ii ] and the metallicity of the shock-heated gas, but the physical interpretation of this result remains inconclusive, as our data also show a correlation between the metallicity and n e . The dramatically higher level of [Fe ii ] emission from SNRs in the central regions of starburst galaxies is most likely due to their dense environments, although metallicity effects might also be important. The typical [Fe ii ]-emitting lifetime of a SNR in the central regions of starburst galaxies is found to be of the order of 104 yr. On the basis of these results, we provide a new empirical relation allowing the determination of the current supernova rate of starburst galaxies from their integrated near-infrared [Fe ii ] luminosity. 相似文献
4.
B. J. Maughan † L. R. Jones H. Ebeling C. Scharf 《Monthly notices of the Royal Astronomical Society》2006,365(2):509-529
The X-ray properties of a sample of 11 high-redshift (0.6 < z < 1.0) clusters observed with Chandra and/or XMM–Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L – T , M – T , M g – T and M – L relations is consistent with simple self-similar predictions, in which the properties of clusters reflect the properties of the Universe at their redshift of observation. Under the assumption that the model of self-similar evolution is correct and that the local systems formed via a single spherical collapse, the high-redshift L – T relation is consistent with the high- z clusters having virialized at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material.
The slope of the L – T relation at high redshift ( B = 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2 . This suggests that the same non-gravitational processes are responsible for steepening the local and high- z relations, possibly occurring universally at z ≳ 1 or in the early stages of the cluster formation, prior to their observation.
The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is β= 0.66 ± 0.05 , the mean gas mass fractions within R2500( z ) and R 200( z ) are 0.069 ± 0.012 and 0.11 ± 0.02 , respectively, and the mean metallicity of the sample is 0.28 ± 0.11 Z⊙ . 相似文献
The slope of the L – T relation at high redshift ( B = 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self-similar prediction of B = 2 . This suggests that the same non-gravitational processes are responsible for steepening the local and high- z relations, possibly occurring universally at z ≳ 1 or in the early stages of the cluster formation, prior to their observation.
The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface-brightness profile slope for the sample is β= 0.66 ± 0.05 , the mean gas mass fractions within R
5.
We present velocity dispersion measurements for 69 faint early-type galaxies in the core of the Coma cluster, spanning −22.0 ≲ MR ≲−17.5 mag . We examine the L –σ relation for our sample and compare it to that of bright elliptical galaxies (Es) from the literature. The distribution of the the faint early-type galaxies in the L –σ plane follows the relation L ∝σ2.01±0.36 , which is significantly shallower from L ∝σ4 as defined for the bright Es. While increased rotational support for fainter early-type galaxies could account for some of the difference in slope, we show that it cannot explain it. We also investigate the colour–σ relation for our Coma galaxies. Using the scatter in this relation, we constrain the range of galaxy ages as a function of their formation epoch for different formation scenarios. Assuming a strong coordination in the formation epoch of faint early-type systems in Coma, we find that most had to be formed at least 6 Gyr ago and over a short 1-Gyr period. 相似文献
6.
Jian-Wen Xu Xi-Zhen Zhang Jin-Lin Han National Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(2):165-174
We collected the basic parameters of 231 supernova remnants (SNRs) in our Galaxy, namely, distances (d) from the Sun, linear diameters (D), Galactic heights (Z), estimated ages (t), luminosities (L), surface brightness (∑) and flux densities (S1) at 1-GHz frequency and spectral indices (α). We tried to find possible correlations between these parameters. As expected, the linear diameters were found to increase with ages for the shell-type remnants, and also to have a tendency to increase with the Galactic heights. Both the surface brightness and luminosity of SNRs at 1-GHz tend to decrease with the linear diameter and with age. No other relations between the parameters were found. 相似文献
7.
Jian Hu 《Monthly notices of the Royal Astronomical Society》2008,386(4):2242-2252
We investigate the correlation between the supermassive black holes (SMBHs) mass ( M bh ) and the stellar velocity dispersion (σ* ) in two types of host galaxies: the early-type bulges (disc galaxies with classical bulges or elliptical galaxies) and pseudo-bulges. In the form log ( M bh /M⊙ ) =α+β log (σ* /200 km s−1 ) , the best-fitting results for the 39 early-type bulges are the slope β= 4.06 ± 0.28 and the normalization α= 8.28 ± 0.05 ; the best-fitting results for the nine pseudo-bulges are β= 4.5 ± 1.3 and α= 7.50 ± 0.18 . Both relations have intrinsic scatter in log M bh of ≲0.27 dex. The M bh –σ* relation for pseudo-bulges is different from the relation in the early-type bulges over the 3σ significance level. The contrasting relations indicate the formation and growth histories of SMBHs depend on their host type. The discrepancy between the slope of the M bh –σ* relations using different definition of velocity dispersion vanishes in our sample, a uniform slope will constrain the coevolution theories of the SMBHs and their host galaxies more effectively. We also find the slope for the 'core' elliptical galaxies at the high-mass range of the relation appears steeper (β≃ 5–6) , which may be the imprint of their origin of dissipationless mergers. 相似文献
8.
Simone Bianchi Raffaella Schneider 《Monthly notices of the Royal Astronomical Society》2007,378(3):973-982
The presence of dust at high redshift requires efficient condensation of grains in supernova (SN) ejecta, in accordance with current theoretical models. Yet observations of the few well-studied supernovae (SNe) and supernova remnants (SNRs) imply condensation efficiencies which are about two orders of magnitude smaller. Motivated by this tension, we have (i) revisited the model of Todini & Ferrara for dust formation in the ejecta of core collapse SNe, and (ii) followed, for the first time, the evolution of newly condensed grains from the time of formation to their survival – through the passage of the reverse shock – in the SNR. We find that 0.1–0.6 M⊙ of dust form in the ejecta of 12–40 M⊙ stellar progenitors. Depending on the density of the surrounding interstellar medium, between 2 and 20 per cent of the initial dust mass survives the passage of the reverse shock, on time-scales of about 4–8 × 104 yr from the stellar explosion. Sputtering by the hot gas induces a shift of the dust size distribution towards smaller grains. The resulting dust extinction curve shows a good agreement with that derived by observations of a reddened QSO at z = 6.2 . Stochastic heating of small grains leads to a wide distribution of dust temperatures. This supports the idea that large amounts (∼0.1 M⊙ ) of cold dust ( T ∼ 40 K) can be present in SNRs, without being in conflict with the observed infrared emission. 相似文献
9.
Chow-Choong Ngeow Shashi M. Kanbur 《Monthly notices of the Royal Astronomical Society》2006,369(2):723-733
The superb phase resolution and quality of the Optical Gravitational Lensing Experiment (OGLE) data on the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) Cepheids, together with existing data on Galactic Cepheids, are combined to study the period–colour (PC) and amplitude–colour (AC) relations as a function of pulsation phase. Our results confirm earlier work that the LMC PC relation (at mean light) is more consistent with two lines of differing slopes, separated at a period of 10 d. However, our multiphase PC relations reveal much new structure which can potentially increase our understanding of Cepheid variables. These multiphase PC relations provide insight into why the Galactic PC relation is linear but the LMC PC relation is non-linear. This is because the LMC PC relation is shallower for short (log P < 1) and steeper for long (log P > 1) period Cepheids than the corresponding Galactic PC relation. Both of the short- and long-period Cepheids in all three galaxies exhibit the steepest and shallowest slopes at phases around 0.75–0.85, respectively. A consequence is that the PC relation at phase ∼ 0.8 is highly non-linear. Further, the Galactic and LMC Cepheids with log P > 1 display a flat slope in the PC plane at phases close to the maximum light. When the LMC period–luminosity (PL) relation is studied as a function of phase, we confirm that it changes with the PC relation. The LMC PL relation in V and I band near the phase of 0.8 provides compelling evidence that this relation is also consistent with two lines of differing slopes joined at a period close to 10 d. 相似文献
10.
Matt J. Jarvis Steve Rawlings Steve Eales Katherine M. Blundell rew J. Bunker Steve Croft Ross J. McLure Chris J. Willott 《Monthly notices of the Royal Astronomical Society》2001,326(4):1585-1600
In this paper, the third and final of a series, we present complete K -band imaging and some complementary I -band imaging of the filtered 6C* sample. We find no systematic differences between the K – z relation of 6C* radio galaxies and those from complete samples, so the near-infrared properties of luminous radio galaxies are not obviously biased by the additional 6C* radio selection criteria (steep spectral index and small angular size). The 6C* K – z data significantly improve delineation of the K – z relation for radio galaxies at high redshift ( z >2) . Accounting for non-stellar contamination, and for correlations between radio luminosity and stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z >2 . In a particular spatially flat universe with a cosmological constant (ΩM =0.3 and ΩΛ =0.7) , the most luminous radio sources appear to be associated with galaxies with a luminosity distribution with a high mean (≈5 L *), and a low dispersion ( σ ∼0.5 mag) which formed their stars at epochs corresponding to z ≳2.5 . This result is in line with recent submillimetre studies of high-redshift radio galaxies and the inferred ages of extremely red objects from faint radio samples. 相似文献
11.
J. L. Payne G. L. White M. D. Filipovi 《Monthly notices of the Royal Astronomical Society》2008,383(3):1175-1194
We use long-slit spectra from shocked regions of radio supernova remnants (SNRs) in the Large Magellanic Cloud to estimate electron density and derive an average 'metal' abundance of 10−3.9 based on diagnostic line ratio plots. These simple diagnostics may be especially useful to determine abundances in more distant galaxies. Abundance values listed in this paper, in units of log(x/H) + 12, for nitrogen (7.3) and oxygen (8.2) agree with those reported in the literature. These estimates – which we assume to be dominated by the interstellar medium with little evolutionary interference – were obtained from spectral analysis of ∼50 per cent of known radio SNRs using the double beam spectrograph on the 2.3-m Advanced Technology Telescope at Siding Spring Observatory in Australia and the Cassegrain spectrograph on the 1.9-m Radcliffe telescope at the South African Astronomical Observatory. We also found optical evidence of shocked regions near 2 of 20 radio SNR candidates (J053620−693136 and J053731−662740), strengthening their identification as true remnants. 相似文献
12.
B. M. Gaensler A. J. Green & R. N. Manchester 《Monthly notices of the Royal Astronomical Society》1998,299(3):812-824
We present Australia Telescope Compact Array observations of the supernova remnant (SNR) G309.2–00.6. In a 1.3-GHz continuum image the remnant appears as a near-circular shell, but with two brightened and distorted arcs of emission on opposite sides. H i absorption against the SNR yields a distance in the range 5.4 to 14.1 kpc, corresponding to an age (1−20) × 103 yr. On the basis of the morphology of the SNR we argue that it is a younger analogue of the W 50/SS 433 system, and that its unusual appearance is a result of opposed jets or outflows from a central source. A jet-like feature and breaks in the shell can both be seen along the axis of proposed outflow, providing further support for this interpretation; the central source itself is not detected. The SNR may be interacting with the adjacent H ii region RCW 80 through an extension of the proposed outflow beyond its shell. This would put the SNR at the lower limit of its distance range and would imply an age 4000 yr. We consider other SNRs similar to G309.2–00.6, and propose remnants whose shells are affected by jets as one of several classes of SNR from which the presence of a central source can be inferred. 相似文献
13.
I. K. Baldry M. L. Balogh R. G. Bower K. Glazebrook R. C. Nichol S. P. Bamford T. Budavari 《Monthly notices of the Royal Astronomical Society》2006,373(2):469-483
We analyse a z < 0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation in the galaxy colour bimodality with stellar mass and projected neighbour density Σ, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 1010.6 to (Kroupa initial mass function, H 0 = 70 ) for Σ in the range 0.1–10 Mpc−2 . The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour–mass and colour–concentration indices not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in log Σ and bins). The red fraction f r generally increases continuously in both Σ and such that there is a unified relation: . Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N -body simulation: the Bower et al. and Croton et al. models that incorporate active galactic nucleus feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies. 相似文献
14.
M. Stupar M. D. Filipović Q. A. Parker G. L. White T. G. Pannuti P. A. Jones 《Astrophysics and Space Science》2007,307(4):423-435
The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs)
at a common frequency of 4.85 GHz (λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample
of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide
reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within
carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from
the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam
together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature
values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria
are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution
from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin
are low. We also re-visit the contentious Σ–D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs
which yields β=−2.2±0.6. This new evaluation of the Σ–D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution.
We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height. 相似文献
15.
Ryo Yamazaki Kazunori Kohri Aya Bamba Tatsuo Yoshida Toru Tsuribe Fumio Takahara 《Monthly notices of the Royal Astronomical Society》2006,371(4):1975-1982
We study the emission from an old supernova remnant (SNR) with an age of around 105 yr and that from a giant molecular cloud (GMC) encountered by the SNR. When the SNR age is around 105 yr, proton acceleration is efficient enough to emit TeV γ-rays both at the shock of the SNR and that in the GMC. The maximum energy of primarily accelerated electrons is so small that TeV γ-rays and X-rays are dominated by hadronic processes, π0 -decay and synchrotron radiation from secondary electrons, respectively. However, if the SNR is older than several 105 yr, there are few high-energy particles emitting TeV γ-rays because of the energy-loss effect and/or the wave-damping effect occurring at low-velocity isothermal shocks. For old SNRs or SNR–GMC interacting systems capable of generating TeV γ-ray emitting particles, we calculated the ratio of TeV γ-ray (1–10 TeV) to X-ray (2–10 keV) energy flux and found that it can be more than ∼102 . Such a source showing large flux ratio may be a possible origin of recently discovered unidentified TeV sources. 相似文献
16.
Stephen Serjeant Duncan Farrah James Geach Toshinobu Takagi Aprajita Verma Ali Kaviani Matt Fox 《Monthly notices of the Royal Astronomical Society》2003,346(4):L51-L56
We present the K -band Hubble diagrams ( K – z relations) of submillimetre-selected galaxies and hyperluminous galaxies (HLIRGs). We report the discovery of a remarkably tight K – z relation of HLIRGs, indistinguishable from that of the most luminous radio galaxies. Like radio galaxies, the HLIRG K – z relation at z ≲ 3 is consistent with a passively evolving ∼3 L * instantaneous starburst starting from a redshift of z ∼ 10 . In contrast, many submillimetre-selected galaxies are ≳2 mag fainter, and the population has a much larger dispersion. We argue that dust obscuration and/or a larger mass range may be responsible for this scatter. The galaxies so far proved to be hyperluminous may have been biased towards higher AGN bolometric contributions than submillimetre-selected galaxies due to the 60-μm selection of some, so the location on the K – z relation may be related to the presence of the most massive active galactic nucleus. Alternatively, a particular host galaxy mass range may be responsible for both extreme star formation and the most massive active nuclei. 相似文献
17.
O. Petruk G. Dubner G. Castelletti F. Bocchino D. Iakubovskyi M. G. F. Kirsch M. Miceli S. Orlando I. Telezhinsky 《Monthly notices of the Royal Astronomical Society》2009,393(3):1034-1040
A number of important processes taking place around strong shocks in supernova remnants (SNRs) depend on the shock obliquity. The measured synchrotron flux is a function of the aspect angle between interstellar magnetic field (ISMF) and the line of sight. Thus, a model of non-thermal emission from SNRs should account for the orientation of the ambient magnetic field. We develop a new method for the estimation of the aspect angle, based on the comparison between observed and synthesized radio maps of SNRs, making different assumptions about the dependence of electron injection efficiency on the shock obliquity. The method uses the azimuthal profile of radio surface brightness as a probe for orientation of ambient magnetic field because it is almost insensitive to the downstream distribution of magnetic field and emitting electrons. We apply our method to a new radio image of SN 1006 produced on the basis of archival Very Large Array and Parkes data. The image recovers emission from all spatial structures with angular scales from a few arcsec to 15 arcmin. We explore different models of injection efficiency and find the following best-fitting values for the aspect angle of SN 1006: φo = 70o ± 4.2o if the injection is isotropic, φo = 64o ± 2.8o for quasi-perpendicular injection (SNR has an equatorial belt in both cases) and φo = 11o ± 0.8o for quasi-parallel injection (polar-cap model of SNR). In the last case, SN 1006 is expected to have a centrally peaked morphology contrary to what is observed. Therefore, our analysis provides some indication against the quasi-parallel injection model. 相似文献
18.
Guillermo Bosch † Elena Terlevich ‡ Roberto Terlevich § 《Monthly notices of the Royal Astronomical Society》2002,329(3):481-496
We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the plane. 相似文献
19.
Shashi M. Kanbur Chow-Choong Ngeow Greg Feiden 《Monthly notices of the Royal Astronomical Society》2007,380(2):819-827
Period–colour (PC) and amplitude–colour (AC) relations at maximum, mean and minimum light are constructed from a large grid of full amplitude hydrodynamic models of Cepheids with a composition appropriate for the Small Magellanic Cloud (SMC). We compare these theoretical relations with those from observations. The theoretical relations are, in general, in good agreement with their observational counterparts, though there exist some discrepancy for short period (log [ P ] < 1) Cepheids. We outline a physical mechanism which can, in principle, be one factor to explain the observed PC/AC relations for the long and short period Cepheids in the Galaxy, Large Magellanic Cloud (LMC) and SMC. Our explanation relies on the hydrogen ionization front (HIF)–photosphere interaction and the way this interaction changes with pulsation period, pulsation phase and metallicity. Since the PC relation is connected with the period–luminosity (PL) relation, it is postulated that such a mechanism can also explain the observed properties of the PL relation in these three galaxies. 相似文献
20.
Antonio Pipino Francesca Matteucci 《Monthly notices of the Royal Astronomical Society》2006,365(4):1114-1122
The effects of late gas accretion episodes and subsequent merger-induced starbursts on the photochemical evolution of elliptical galaxies are studied and compared to the picture of galaxy formation occurring at high redshift with a unique and intense starburst modulated by a very short infall, as suggested by Pipino and Matteucci in Paper I. By means of the comparison with the colour–magnitude relations (CMRs) and the [〈Mg/Fe〉 V ]–σ relation observed in ellipticals, we conclude that either bursts involving a gas mass comparable to the mass already transformed into stars during the first episode of star formation (SF) and occurring at any redshift, or bursts occurring at low redshift (i.e. z ≤ 0.2) and with a large range of accreted mass, are ruled out. These models fail in matching the above relations even if the initial infalling hypothesis is relaxed, and the galaxies form either by means of more complicated SF histories or by means of the classical monolithic model. On the other hand, galaxies accreting a small amount of gas at high redshift (i.e. z ≥ 3) produce a spread in the model results, with respect to the best model of Paper I, which is consistent with the observational scatter of the CMRs, although there is only marginal agreement with the [〈Mg/Fe〉 V ]–σ relation. Therefore, only small perturbations to the standard scenario seem to be allowed. We stress that the strongest constraints to galaxy-formation mechanisms are represented by the chemical abundances, whereas the colours can be reproduced under several different hypotheses. 相似文献