85,055 research outputs found
Modelling Intermediate Age and Old Stellar Populations in the Infrared
We have investigated the spectro-photometric properties of the Asymptotic
Giant Branch (AGB) stars and their contribution to the integrated infrared
emission in simple stellar populations (SSP). Adopting analytical relations
describing the evolution of these stars in the HR diagram and empirical
relations for the mass-loss rate and the wind terminal velocity, we were able
to model the effects of the dusty envelope around these stars, with a minimal
number of parameters. We computed isochrones at different age and initial metal
content. We compare our models with existing infrared colors of M giants and
Mira stars and with IRAS PSC data. Contrary to previous models, in the new
isochrones the mass-loss rate, which establishes the duration of the AGB phase,
also determines the spectral properties of the stars. The contribution of these
stars to the integrated light of the population is thus obtained in a
consistent way. We find that the emission in the mid infrared is about one
order of magnitude larger when dust is taken into account in an intermediate
age population, irrespective of the particular mixture adopted. The dependence
of the integrated colors on the metallicity and age is discussed, with
particular emphasis on the problem of age-metallicity degeneracy. We show that,
contrary to the case of optical or near infrared colors, the adoption of a
suitable pass-band in the mid infrared allows a fair separation of the two
effects. We suggest intermediate redshift elliptical galaxies as possible
targets of this method of solving the age-metallicity dilemma. The new SSP
models constitute a first step in a more extended study aimed at modelling the
spectral properties of the galaxies from the ultraviolet to the far infrared.Comment: 16 pages, 10 figures, to appear in A&
An evolutionary model for GHz Peaked Spectrum Sources. Predictions for high frequency surveys
We have explored, in the general framework of the ``young source'' scenario,
evolutionary models for GHz Peaked Spectrum (GPS) galaxies and quasars which
reproduce the observed counts, redshift and peak frequency distributions of
currently available samples. Substantially different cosmological evolution
properties are found for the two populations: the quasar luminosity function
must evolve strongly up to , while the data on galaxies may be
consistent with no evolution. The models show that GPS sources (mostly quasars)
may comprise quite a significant fraction of bright (Jy) radio sources
at GHz if the intrinsic distribution of peak frequencies extends
up to GHz. In any case, however, their fraction decreases rapidly
with decreasing flux and their contribution to small scale fluctuations in the
frequency range covered by the forthcoming space missions MAP and Planck
Surveyor is expected to be minor.Comment: 7 pages, 4 figures, A&A accepte
Joint Formation of QSOs and Spheroids: QSOs as clocks of star formation in Spheroids
Direct and indirect observational evidence leads to the conclusion that high
redshift QSOs did shine in the core of early type proto-galaxies during their
main episode of star formation. Exploting this fact, we derive the rate of
formation of this kind of stellar systems at high redshift by using the QSO
Luminosity Function. The elemental proportions in elliptical galaxies, the
descendents of the QSO hosts, suggest that the star formation was more rapid in
more massive objects. We show that this is expected to occur in Dark Matter
haloes, when the processes of cooling and heating is considered. This is also
confirmed by comparing the observed sub-mm counts to those derived by coupling
the formation rate and the star formation rate of the spheroidal galaxies with
a detailed model for their SED evolution. In this scenario SCUBA galaxies and
Lyman Break Galaxies are early type proto-galaxies forming the bulk of their
stars before the onset of QSO activity.Comment: 13 pages, 8 figures, accepted by MNRAS, major revision of the
formalis
Labyrinthine pathways towards supercycle attractors in unimodal maps
We uncover previously unknown properties of the family of periodic
superstable cycles in unimodal maps characterized each by a Lyapunov exponent
that diverges to minus infinity. Amongst the main novel properties are the
following: i) The basins of attraction for the phases of the cycles develop
fractal boundaries of increasing complexity as the period-doubling structure
advances towards the transition to chaos. ii) The fractal boundaries, formed by
the preimages of the repellor, display hierarchical structures organized
according to exponential clusterings that manifest in the dynamics as
sensitivity to the final state and transient chaos. iii) There is a functional
composition renormalization group (RG) fixed-point map associated to the family
of supercycles. iv) This map is given in closed form by the same kind of
-exponential function found for both the pitchfork and tangent bifurcation
attractors. v) There is a final stage ultra-fast dynamics towards the attractor
with a sensitivity to initial conditions that decreases as an exponential of an
exponential of time.Comment: 8 pages, 13 figure
Panchromatic models of galaxies: GRASIL
We present here a model for simulating the panchromatic spectral energy
distribution of galaxies, which aims to be a complete tool to study the complex
multi-wavelength picture of the universe. The model take into account all
important components that concur to the SED of galaxies at wavelengths from
X-rays to the radio. We review the modeling of each component and provide
several applications, interpreting observations of galaxy of different types at
all the wavelengths.Comment: 10 pages, 4 figures, invited talk, to appear in the proceedings of:
"The Spectral Energy Distribution of Gas-Rich Galaxies: Confronting Models
with Data", Heidelberg, 4-8 Oct. 2004, eds. C.C. Popescu and R.J. Tuffs, AIP
Conf. Ser., in pres
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