562 research outputs found
Cosmological interpretation of the color-magnitude diagrams of galaxy clusters
We investigate the color-magnitude diagram (CMD) of cluster galaxies in the
hierarchical -CDM cosmological scenario using both single stellar
populations and simple galaxy models. First, we analyze the effect of bursts
and mergers and companion chemical pollution and rejuvenation of the stellar
content on the integrated light emitted by galaxies. The dispersion of the
galaxy magnitudes and colors on the plane is mainly due to mixing
of ages and metallicities of the stellar populations, with mergers weighting
more than bursts of similar mass fractions. The analysis is made using the
Monte-Carlo technique applied to ideal model galaxies reduced to single stellar
populations with galaxy-size mass to evaluate mass, age and metallicity of each
object. We show that separately determining the contributions by bursts and
mergers leads to a better understanding of observed properties of CMD of
cluster galaxies. Then we repeat the analysis using suitable chemo-photometric
models of galaxies whose mass is derived from the cosmological predictions of
the galaxy content of typical clusters. Using the halo mass function and the
Monte-Carlo technique, we derive the formation redshift of each galaxy and its
photometric history. These are used to simulate the CMD of the cluster
galaxies. The main conclusion is that most massive galaxies have acquired the
red color they show today in very early epochs and remained the same ever
since. The simulations nicely reproduce the Red Sequence, the Green Valley and
the Blue Cloud, the three main regions of the CMD in which galaxies crowd.Comment: Accepted for publication in Ap
The transformation of Spirals into S0 galaxies in the cluster environment
We discuss the observational evidences of the morphological transformation of
Spirals into S0 galaxies in the cluster environment exploiting two big
databases of galaxy clusters: WINGS (0.04 < z < 0.07) and EDisCS (0.4 < z <
0.8). The most important results are: 1) the average number of S0 galaxies in
clusters is almost a factor of larger today than at redshift ; 2) the fraction of S0's to Spirals increases on average by a factor
2 every Gyr; 3) the average rate of transformation for Spirals (not
considering the infall of new galaxies from the cosmic web) is: 5 Sp
into S0's per Gyr and 2 Sp into E's per Gyr; 4) there are evidences that
the interstellar gas of Spirals is stripped by an hot intergalactic medium; 5)
there are also indirect hints that major/minor merging events have played a
role in the transformation of Spiral galaxies. In particular, we show that: 1)
the ratio between the number of S0's and Spirals (NS0/NSp) in the WINGS
clusters is correlated with their X-ray luminosity ; 2) that the
brightest and massive S0's are always close to the cluster center; 3) that the
mean Sersic index of S0's is always larger than that of Spirals (and lower than
E's) for galaxy stellar masses above Msun; 4) that the number of E's
in clusters cannot be constant; 5) that the largest difference between the mean
mass of S0's and E's with respect to Spirals is observed in clusters with low
velocity dispersion. Finally, by comparing the properties of the various
morphological types for galaxies in clusters and in the field, we find that the
most significant effect of the environment is the stripping of the outer galaxy
regions, resulting in a systematic difference in effective radius and Sersic
index.Comment: 38 pages, 20 figure
The parallelism between galaxy clusters and early-type galaxies: I. The light and mass profiles
We have analyzed the parallelism between the properties of galaxy clusters
and early-type galaxies (ETGs) by looking at the similarity between their light
profiles. We find that the equivalent luminosity profiles of all these systems
in the \vfilt\ band, once normalized to the effective radius \re\ and shifted
in surface brightness, can be fitted by the S\'ersic's law \Sers\ and
superposed with a small scatter ( mag). By grouping objects in
different classes of luminosity, the average profile of each class slightly
deviates from the other only in the inner and outer regions (outside ), but the range of values of remains ample for the members of
each class, indicating that objects with similar luminosity have quite
different shapes. The "Illustris" simulation reproduces quite well the
luminosity profiles of ETGs, with the exception of in the inner and outer
regions where feedback from supernovae and active galactic nuclei, wet and dry
mergers, are at work. The total mass and luminosity of galaxy clusters as well
as their light profiles are not well reproduced. By exploiting simulations we
have followed the variation of the effective half-light and half-mass radius of
ETGs up to , noting that progenitors are not necessarily smaller in size
than current objects. We have also analyzed the projected dark+baryonic and
dark-only mass profiles discovering that after a normalization to the half-mass
radius, they can be well superposed and fitted by the S\'ersic's law.Comment: 25 pages, 19 figure
The scaling relations of galaxies back in time: the road toward virialization
Context. The structural scaling relations (SSRs) of galaxies, i.e. the
observed correlations between effective radius, effective surface intensity and
velocity dispersion, are important tools for understanding how evolution
proceeds. Aims. In this paper we aim to demonstrate that the evolution of the
SSRs back in time is governed by the combination of the virial theorem (VT) and
the relation , where the parameters and
vary with time and from galaxy to galaxy. Methods. Using the WINGS
database for the galaxies at redshift and the Illustris-1 and
Illustris-TNG databases of artificial galaxies, for the galaxies up to redshift
, we analyse the SSRs back in time and, by means of simple algebraic
expressions for and (functions of time and other physical
quantities), we derive the expected paths followed by galaxies in the various
SSRs toward the distributions observed at . Results. The distribution of
galaxies in the SSRs is ultimately related to the evolution in luminosity and
velocity dispersion that are empirically mirrored by the law. Furthermore, the parameter works as a
thermometer of the virialization of a galaxy. This parameter can assume either
positive or negative values, and its absolute value attains high values when
the galaxy is close to the virial condition, while it tends to zero when the
galaxy is far from it. Conclusions. As the SSRs change with time, the method we
are proposing allows us to decipher the temporal evolution of galaxies.Comment: 21 pages, 20 figure
A new framework for understanding the evolution of early-type galaxies
We have recently suggested that the combination of the scalar virial theorem
() and the law, with L'_0 and
changing from galaxy to galaxy (and with time), can provide a new set
of equations valid for investigating the evolution of early-type galaxies
(ETGs) (Donofrio & Chiosi, 2022). These equations are able to account for the
tilt of the Fundamental Plane (FP) and to explain the observed distributions of
ETGs in all its projections. In this paper we analyze the advantages offered by
those equations, derive the and parameters for real and
simulated galaxies, and demonstrate that, according to the value of ,
galaxies can move only along some permitted directions in the FP projections.
Then, we show that simple galaxy models that grow in mass by infall of gas and
form stars with a star formation rate depending on the stellar velocity
dispersion nicely reproduce the observed distributions of ETGs in the FP
projections and yield s that agree with the measured ones. We derive the
mutual relationships among the stellar mass, effective radius, velocity
dispersion, and luminosity of ETGs as a function of and calculate the
coefficients of the FP. Then, using the simple infall models, we show that the
star formation history of ETGs is compatible with the -dependent star
formation rate, and that both positive and negative values of are
possible in a standard theory of galaxy evolution. The parameter
offers a new view of the evolution of ETGs. In brief, i) it gives a coherent
interpretation of the FP and of the motions of galaxies in its projections; ii)
it is the fingerprint of their evolution; iii) it measures the degree of
virialization of ETGs; iv) and finally it allows us to infer their evolution in
the near past.Comment: 25 pages, 30 figures, 5 table
A multimessenger view of galaxies and quasars from now to mid-century
In the next 30 years, a new generation of space and ground-based telescopes
will permit to obtain multi-frequency observations of faint sources and, for
the first time in human history, to achieve a deep, almost synoptical
monitoring of the whole sky. Gravitational wave observatories will detect a
Universe of unseen black holes in the merging process over a broad spectrum of
mass. Computing facilities will permit new high-resolution simulations with a
deeper physical analysis of the main phenomena occurring at different scales.
Given these development lines, we first sketch a panorama of the main
instrumental developments expected in the next thirty years, dealing not only
with electromagnetic radiation, but also from a multi-messenger perspective
that includes gravitational waves, neutrinos, and cosmic rays. We then present
how the new instrumentation will make it possible to foster advances in our
present understanding of galaxies and quasars. We focus on selected scientific
themes that are hotly debated today, in some cases advancing conjectures on the
solution of major problems that may become solved in the next 30 years.Comment: 43 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1801.03298 by other author
Dependency of halo concentration on mass, redshift and fossilness in Magneticum hydrodynamic simulations
We study the dependency of the concentration on mass and redshift using three
large N-body cosmological hydrodynamic simulations carried out by the
Magneticum project. We constrain the slope of the mass-concentration relation
with an unprecedented mass range for hydrodynamic simulations and find a
negative trend on the mass-concentration plane and a slightly negative redshift
dependency, in agreement with observations and other numerical works. We also
show how the concentration correlates with the fossil parameter, defined as the
stellar mass ratio between the central galaxy and the most massive satellite,
in agreement with observations. We find that haloes with high fossil parameter
have systematically higher concentration and investigate the cause in two
different ways. First we study the evolution of haloes that lives unperturbed
for a long period of time, where we find that the internal region keeps
accreting satellites as the fossil parameter increases and the scale radius
decreases (which increases the concentration). We also study the dependency of
the concentration on the virial ratio and the energy term from the surface
pressure . We conclude that fossil objects have higher concentration
because they are dynamically relaxed, with no in-fall/out-fall material and had
time to accrete their satellites.Comment: 13 pages, 10 figure
Cosmic Star Formation: a simple model of the SFRD(z)
We investigate the evolution of the cosmic star formation rate density (SFRD)
from redshift z=20 to z=0 and compare it with the observational one by Madau
and Dickinson derived from recent compilations of UV and IR data. The
theoretical SFRD(z) and its evolution are obtained using a simple model which
folds together the star formation histories of prototype galaxies designed to
represent real objects of different morphological type along the Hubble
sequence and the hierarchical growing of structures under the action of gravity
from small perturbations to large scale objects in \Lambda-CDM cosmogony, i.e.
the number density of dark matter halos N(M,z). Although the overall model is
very simple and easy to set up, it provides results that well mimic those
obtained from large scale N-body simulations of great complexity. The
simplicity of our approach allows us to test different assumptions for the star
formation law in galaxies, the effects of energy feedback from stars to
interstellar gas and the efficiency of galactic winds, and also the effect of
N(M,z). The result of our analysis is that in the framework of the hierarchical
assembly of galaxies the so-called time-delayed star formation under plain
assumptions mainly for the energy feedback and galactic winds can reproduce the
observational SFRD(z).Comment: ApJ (accepted for publication
The parallelism between galaxy clusters and early-type galaxies: II. Clues on the origin of the scaling relations
Context. This is the second work dedicated to the observed parallelism
between galaxy clusters and early-type galaxies. The focus is on the
distribution of these systems in the scaling relations (SRs) observed when
effective radii, effective surface brightness, total luminosities and velocity
dispersions are mutually correlated. Aims. Using the data of the Illustris
simulation we try to speculate on the origin of the observed SRs. Methods. We
compare the observational SRs extracted from the database of the WIde-field
Nearby Galaxy-cluster Survey (WINGS) with the relevant parameters coming from
the Illustris simulations. Then we use the simulated data at different redshift
to infer the evolution of the SRs. Results. The comparison demonstrate that
galaxy clusters (GCs) at z~0 follow the same log(L)-log(sigma) relation of
early-type galaxies (ETGs) and that both in the log(Ie)-log(Re) and
log(Re)-log(M*) planes the distribution of GCs is along the sequence defined by
the brightest and massive early-type galaxies (BCGs). The Illustris simulation
reproduces the tails of the massive galaxies visible both in the
log(Ie)-log(Re) and log(Re)-log(M*) planes, but fail to give the correct
estimate of the effective radii of the dwarf galaxies that appear too large and
those of GCs that are too small. The evolution of the SRs up to z=4 permits to
reveal the complex evolutionary paths of galaxies in the SRs and indicate that
the line marking the Zone of Exclusion (ZoE), visible both in the
log(Ie)-log(Re) and log(Re)-log(M*) planes, is the trend followed by virialized
and passively evolving systems. Conclusions. We speculate that the observed SRs
originate from the intersection of the virial theorem and a relation L=L_0 x
sigma^beta where the luminosities depend on the star formation history.Comment: 22 pages, 14 figures, 4 table
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