6,107 research outputs found
Superdense and normal early-type galaxies at 1<z<2
We combined proprietary and archival HST observations to collect a sample of
62 early-type galaxies (ETGs) at 0.9<z<2 with spectroscopic confirmation of
their redshift and spectral type. The whole sample is covered by ACS or NICMOS
observations and partially by Spitzer and AKARI observations. We derived
morphological parameters by fitting their HST light profiles and physical
parameters by fitting their spectral energy distributions. The study of the
size-mass and the size-luminosity relations of these early-types shows that a
large fraction of them (~50) follows the local relations. These 'normal' ETGs
are not smaller than local counterparts with comparable mass. The remaining
half of the sample is composed of compact ETGs with sizes (densities) 2.5-3
(15-30) times smaller (higher) than local counterparts and, most importantly,
than the other normal ETGs at the same redshift and with the same stellar mass.
This suggests that normal and superdense ETGs at z~2 come from different
histories of mass assembly.Comment: 4 pages, 3 figures. To appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and
C.C. Popescu, AIP Conf. (in press
The SDSS-GALEX viewpoint of the truncated red sequence in field environments at z~0
We combine GALEX near-UV photometry with a volume-limited sample of local
(0.005<z<0.037) SDSS DR4 galaxies to examine the composition and the
environmental dependencies of the optical and UV-optical colour-magnitude (C-M)
diagrams. We find that ~30% of red sequence galaxies in the optical C-M diagram
show signs of ongoing star-formation from their spectra having EW(Halpha)>2A.
This contamination is greatest at faint magnitudes (Mr>-19) and in field
regions where as many as three-quarters of red sequence galaxies are
star-forming, and as such has important consequences for following the build-up
of the red sequence. We find that the NUV-r colour instead allows a much more
robust separation of passively-evolving and star-forming galaxies, which allows
the build-up of the UV-selected red sequence with redshift and environment to
be directly interpreted in terms of the assembly of stellar mass in
passively-evolving galaxies. We find that in isolated field regions the number
density of UV-optical red sequence galaxies declines rapidly at magnitudes
fainter than Mr~-19 and appears completely truncated at Mr~-18. This confirms
the findings of Haines et al. (2007) that no passively-evolving dwarf galaxies
are found more than two virial radii from a massive halo, whether that be a
group, cluster or massive galaxy. These results support the downsizing paradigm
whereby the red sequence is assembled from the top down, being already largely
in place at the bright end by z~1, and the faint end filled in at later epochs
in clusters and groups through environment-related processes such as
ram-pressure stripping or galaxy harassment.Comment: 12 pages, 7 figures, MNRAS submitte
Cluster and field elliptical galaxies at z~1.3. The marginal role of the environment and the relevance of the galaxy central regions
We compared the properties of 56 elliptical galaxies selected from three
clusters at with those of field galaxies in the GOODS-S (~30),
COSMOS (~180) and CANDELS (~220) fields. We studied the relationships among
effective radius, surface brightness, stellar mass, stellar mass density
and central mass density within 1 kpc radius. We
find that cluster ellipticals do not differ from field ellipticals: they share
the same structural parameters at fixed mass and the same scaling relations. On
the other hand, the population of field ellipticals at shows a
significant lack of massive ( M) and large (R kpc) ellipticals with respect to the cluster. Nonetheless, at
M, the two populations are similar. The size-mass
relation of ellipticals at z~1.3 defines two different regimes, above and below
a transition mass M: at lower masses the
relation is nearly flat (R), the mean radius is
constant at ~1 kpc and while, at larger masses,
the relation is R. The transition mass marks the
mass at which galaxies reach the maximum . Also the
-mass relation follows two different regimes,
, defining a transition mass
density M pc. The mass density
does not correlate with mass, dense/compact galaxies can be
assembled over a wide mass regime, independently of the environment. The
central mass density, , besides to be correlated with the mass,
is correlated to the age of the stellar population: the higher the central
stellar mass density, the higher the mass, the older the age of the stellar
population. [Abridged]Comment: Accepted for publication in A&A; 20 pages, 13 figures (replaced to
match the A&A version
Lower mass normalization of the stellar initial mass function for dense massive early-type galaxies at z ~ 1.4
This paper aims at understanding if the normalization of the stellar initial
mass function (IMF) of massive early-type galaxies (ETGs) varies with cosmic
time and/or with mean stellar mass density Sigma (M*/2\pi Re^2). For this
purpose we collected a sample of 18 dense (Sigma>2500 M_sun/pc^2) ETGs at
1.2<z<1.6 with available velocity dispersion sigma_e. We have constrained their
mass-normalization by comparing their true stellar masses (M_true) derived
through virial theorem, hence IMF independent, with those inferred through the
fit of the photometry assuming a reference IMF (M_ref). Adopting the virial
estimator as proxy of the true stellar mass, we have assumed for these ETGs
zero dark matter (DM). However, dynamical models and numerical simulations of
galaxy evolution have shown that the DM fraction within Re in dense high-z ETGs
is negligible. We have considered the possible bias of virial theorem in
recovering the total masses and have shown that for dense ETGs the virial
masses are in agreement with those derived through more sophisticated dynamical
models. The variation of the parameter Gamma = M_true/M_ref with sigma_e shows
that, on average, dense ETGs at = 1.4 follow the same IMF-sigma_e trend of
typical local ETGs, but with a lower mass-normalization. Nonetheless, once the
IMF-sigma_e trend we have found for high-z dense ETGs is compared with that of
local ETGs with similar Sigma and sigma_e, they turn out to be consistent. The
similarity between the IMF-sigma_e trends of dense high-z and low-z ETGs over 9
Gyr of evolution and their lower mass-normalization with respect to the mean
value of local ETGs suggest that, independently on formation redshift, the
physical conditions characterizing the formation of a dense spheroid lead to a
mass spectrum of new formed stars with an higher ratio of high- to low-mass
stars with respect to the IMF of normal local ETGs.Comment: 9 pages, 4 figures, accepted for pubblication in A&A, updated to
match final journal versio
Density distribution of particles upon jamming after an avalanche in a 2D silo
We present a complete analysis of the density distribution of particles in a
two dimensional silo after discharge. Simulations through a pseudo-dynamic
algorithm are performed for filling and subsequent discharge of a plane silo.
Particles are monosized hard disks deposited in the container and subjected to
a tapping process for compaction. Then, a hole of a given size is open at the
bottom of the silo and the discharge is triggered. After a clogging at the
opening is produced, and equilibrium is restored, the final distribution of the
remaining particles at the silo is analyzed by dividing the space into cells
with different geometrical arrangements to visualize the way in which the
density depression near the opening is propagated throughout the system. The
different behavior as a function of the compaction degree is discussed.Comment: 11 pages, 10 figure
The population of early-type galaxies: how it evolves with time and how it differs from passive and late-type galaxies
The aim of our analysis is twofold. On the one hand we are interested in
addressing whether a sample of ETGs morphologically selected differs from a
sample of passive galaxies in terms of galaxy statistics. On the other hand we
study how the relative abundance of galaxies, the number density and the
stellar mass density for different morphological types change over the redshift
range 0.6<z<2.5. From the 1302 galaxies brighter than Ks=22 selected from the
GOODS-MUSIC catalogue, we classified the ETGs on the basis of their morphology
and the passive galaxies on the basis of their sSFR. We proved how the
definition of passive galaxy depends on the IMF adopted in the models and on
the assumed sSFR threshold. We find that ETGs cannot be distinguished from the
other morphological classes on the basis of their low sSFR, irrespective of the
IMF adopted in the models. Using the sample of 1302 galaxies morphologically
classified into spheroidal galaxies (ETGs) and not spheroidal galaxies (LTGs),
we find that their fractions are constant over the redshift range 0.6<z<2.5
(20-30% ETGs vs 70-80% LTGs). However, at z<1 these fractions change among the
population of the most massive (M*>=10^(11) M_sol) galaxies, with the fraction
of massive ETGs rising up to 40% and the fraction of massive LTGs decreasing
down to 60%. Moreover, we find that the number density and the stellar mass
density of the whole population of massive galaxies increase almost by a factor
of ~10 between 0.6<z<2.5, with a faster increase of these densities for the
ETGs than for the LTGs. Finally, we find that the number density of the
highest-mass galaxies (M*>3-4x10^(11) M_sol) both ETGs and LTGs do not increase
since z~2.5, contrary to the lower mass galaxies. This suggests that the
population of the most massive galaxies formed at z>2.5-3 and that the assembly
of such high-mass galaxies is not effective at lower redshift.Comment: 15 pages, 14 figures. Published in A&
Measuring Areas on Large Scale Nautical Charts on Mercator-Secant
This short paper presents a highly accurate module of surface deformation which permit to calculate, once and for all, the ellipsoid area corresponding to the area measured on nautical charts on Mercator-Secant. The accuracy of the measured surface increases together with the increase of the scale because it depends on the graphic error
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