1,165 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
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
Clustering at high redshift
The addition of deep near infrared images to the database provided by the
HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline
and address a number of key issues including the total stellar content of
baryonic mass, the effects of dust extinction, the dependence of morphology on
the rest frame wavelength, the photometric redshifts, the detection and nature
of extremely red objects (EROs). For these reasons deep near infrared images
were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks
bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A
multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the
HDF-S has been produced. Photometric redshifts have been generated both fitting
templates to the observed SEDs and with neural network techniques.
Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed
all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the
galaxies brighter than I_AB< 27.5 have been used to study the evolution of
galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies
at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A.
Renzini (ESO Astrophysics Symposia, Springer-Verlag
Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites
In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites
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
IR Colors and Sizes of Faint Galaxies
We present J and Ks band galaxy counts down to J=24 and Ks=22.5 obtained with
the new infrared imager/spectrometer, SOFI, at the ESO New Technology
Telescope. The co-addition of short, dithered, images led to a total exposure
time of 256 and 624 minutes respectively, over an area of arcmin
centered on the NTT Deep Field. The total number of sources with S/N is
1569 in the J sample and 1025 in the Ks-selected sample. These are the largest
samples currently available at these depths. A d/d relation with slope
of in J and in Ks is found with no evident sign of a
decline at the magnitude limit. The observed surface density of ``small''
sources is much lower than ``large'' ones at bright magnitudes and rises more
steeply than the large sources to fainter magnitudes. Fainter than
and Ks, small sources dominate the number counts. Galaxies get redder
in J-K down to
J and Ks. At fainter magnitudes, the median color becomes
bluer with an accompanying increase in the compactness of the galaxies. We show
that the blue, small sources which dominate the faint IR counts are not
compatible with a high redshift () population. On the contrary, the
observed color and compactness trends, together with the absence of a turnover
at faint magnitudes and the dominance of small sources, can be naturally
explained by an increasing contribution of sub- galaxies when going to
fainter apparent magnitudes. Such evidence strongly supports the existence of a
steeply rising () faint end of the local infrared luminosity
function of galaxies - at least for luminosities .Comment: Accepted for publication on A&A; 15 pages, 13 figure
Tracing the Mass-Assembly History of Galaxies with Deep Surveys
We use the optical and near-infrared galaxy samples from the Munich
Near-Infrared Cluster Survey (MUNICS), the FORS Deep Field (FDF) and GOODS-S to
probe the stellar mass assembly history of field galaxies out to z ~ 5.
Combining information on the galaxies' stellar mass with their star-formation
rate and the age of the stellar population, we can draw important conclusions
on the assembly of the most massive galaxies in the universe: These objects
contain the oldest stellar populations at all redshifts probed. Furthermore, we
show that with increasing redshift the contribution of star-formation to the
mass assembly for massive galaxies increases dramatically, reaching the era of
their formation at z ~ 2 and beyond. These findings can be interpreted as
evidence for an early epoch of star formation in the most massive galaxies in
the universe.Comment: 3 pages, 2 figures; published in B. Aschenbach, V. Burwitz, G.
Hasinger, B. Leibundgut (eds.): "Relativistic Astrophysics and Cosmology -
Einstein's Legacy. Proceedings of the Conference held in Munich, 2006", ESO
Astrophysics Symposia, Springer Verlag, 2007, p. 310. Replaced to match final
published versio
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