We present the morphological analysis based on Hubble Space Telescope HST-NICMOS (Near-Infrared Camera and Multi-Object Spectrometer) observations in the F160W filter (λ≃ 1.6 μm) of a sample of 32 ...early-type galaxies (ETGs) at 1 < z < 2 with spectroscopic confirmation of their redshift and spectral type. The 32 ETGs at 〈z〉∼ 1.5 are placed on the (〈μ〉e, Re) plane according to the Kormendy relation (KR) with the same slope of the local one but with a different zero-point, which accounts for the evolution they undergo from z∼ 1.5–2 to z= 0. The best fitting of their spectral energy distribution shows that ETGs at 1 < z < 2 are composed of two distinct populations, an older population (oETGs) and a younger population (yETGs) whose mean ages differ by about 1.5–2 Gyr. Young ETGs are not denser than local ones since they follow the size–mass relation of local ETGs, and luminosity evolution brings them on to the local KR and size–luminosity relations without the need of size evolution. Old ETGs do not follow the size–mass relation of local ETGs, and luminosity evolution does not account for the discrepancy they show with respect to the local size–luminosity relation and KR. An increase in their Re by a factor of 2.5–3 (a density decrease by a factor of 15–30) from z∼ 1.5–2 to z∼ 0 is required to bring these galaxies on to the local scaling relations. The different properties and the different behaviour shown by the two populations with respect to the scaling relations imply different formation and evolution scenarios. The older population of ETGs must have formed at a higher z in a sort of dissipative gas-rich collapse able to produce remnants which at z∼ 2 are old and compact, a scenario which can be fitted qualitatively by some recent hydrodynamic simulations of gas-rich mergers. Given the typical time-scale of merging and the old age of their stellar population, oETGs should exist as they are up to z≳ 3–3.5. The size evolution they must experience from z∼ 2 to ∼0 must leave unchanged their mass to not exceed the local number of high-mass ETGs. Thus, major merging cannot fit this requirement. Satellite merging, close encounters and interactions can help at least qualitatively in solving this problem. The younger population of ETGs can be formed later through subsequent episodes of merging which increased progressively their size and assembled their mass down to z∼ 2. At z < 2, they evolve purely in luminosity since episodes of major merging would bring them far from the local scaling relations.
ABSTRACT
The mean size (effective radius Re) of massive galaxies (MGs; Mstar > 1011.2M⊙) is observed to increase steadily with cosmic time. It is still unclear whether this trend originates from the ...size growth of individual galaxies (via, e.g. mergers and/or AGN feedback) or from the inclusion of larger galaxies entering the selection at later epochs (progenitor bias). We here build a data-driven, flexible theoretical framework to probe the structural evolution of MGs. We assign galaxies to dark matter haloes via stellar mass–halo mass (SMHM) relations with varying high-mass slopes and scatters σSMHM in stellar mass at fixed halo mass, and assign sizes to galaxies using an empirically motivated, constant and linear relationship between Re and the host dark matter halo radius Rh. We find that (1) the fast mean size growth of MGs is well reproduced independently of the shape of the input SMHM relation; (2) the numbers of compact MGs grow steadily until z ≳ 2 and fall off at lower redshifts, suggesting a lesser role of progenitor bias at later epochs; (3) a time-independent scatter σSMHM is consistent with a scenario in which compact star-forming MGs transition into quiescent MGs in a few 108 yr with a negligible structural evolution during the compact phase, while a scatter increasing at high redshift implies significant size growth during the star-forming phase. A robust measurement of the size function of MGs at high redshift can set strong constraints on the scatter of the SMHM relation and, by extension, on models of galaxy evolution.
We present a spectroscopic analysis based on measurements of two mainly age-dependent spectrophotometric indices in the 4000 Å rest-frame region, i.e. H+K(Ca ii) and Δ4000, for a sample of 15 ...early-type galaxies (ETGs) at 0.7 < z
spec < 1.1, morphologically selected in the GOODS-South field. Ages derived from the two different indices by means of the comparison with stellar population synthesis models are not consistent with each other for at least nine galaxies (60 per cent of the sample), while for the remaining six galaxies, the ages derived from their global spectral energy distribution (SED) fitting are not consistent with those derived from the two indices. We then hypothesized that the stellar content of many galaxies is made of two stellar components with different ages. The double-component analysis, performed by taking into account both the index values and the observed SED, fully explains the observational data and improves the results of the standard one-component SED fitting in 9 out of the 15 objects, i.e. those for which the two indices point towards two different ages. In all of them, the bulk of the mass belongs to rather evolved stars, while a small mass fraction is many Gyr younger. In some cases, thanks to the sensitivity of the H+K(Ca ii) index, we find that the minor younger component reveals signs of recent star formation. The distribution of the ages of the younger stellar components appears uniformly in time and this suggests that small amounts of star formation could be common during the evolution of high-z ETGs. We argue the possibility that these new star formation episodes could be frequently triggered by internal causes due to the presence of small gas reservoir.
Although thousands of galaxy mergers are known, only a handful of sub-kiloparsec-scale supermassive black hole (SMBH) pairs have been confirmed so far, leaving a huge gap between the observed and ...predicted numbers of such objects. In this work, we present a detailed analysis of the Sloan Digital Sky Survey optical spectrum and of near-infrared (NIR) diffraction limited imaging of
SDSS J1431+4358
. This object is a local radio-quiet type 2 active galactic nucleus (AGN) previously selected as a double AGN candidate on the basis of the double-peaked OIII emission line. The NIR adaptive optics-assisted observations were obtained at the Large Binocular Telescope with the LUCI+FLAO camera. We found that most of the prominent optical emission lines are characterized by a double-peaked profile, mainly produced by AGN photoionization. Our spectroscopical analysis disfavors the hypothesis that the double-peaked emission lines in the source are the signatures of outflow kinematics, leaving open the possibility that we are detecting either the rotation of a single narrow-line region or the presence of two SMBHs orbiting around a common central potential. The latter scenario is further supported by the high-spatial resolution NIR imaging: after subtracting the dominant contribution of the stellar bulge component in the host galaxy, we detect two faint nuclear sources at
r
< 0.5 kpc projected separation. Interestingly, the two sources have a position angle consistent with that defined by the two regions where the OIII double peaks most likely originate. Aside from the discovery of a promising sub-kiloparsec scale dual AGN, our analysis shows the importance of an appropriate host galaxy subtraction in order to achieve a reliable estimate of the incidence of dual AGNs at small projected separations.
We present the first estimate of age, stellar metallicity and chemical abundance ratios, for an individual early-type galaxy at high-redshift (z = 1.426) in the COSMOS (Cosmological Evolution Survey) ...field. Our analysis is based on observations obtained with the X-Shooter instrument at the Very Large Telescope (VLT), which cover the visual and near-infrared spectrum at high (R > 5000) spectral resolution. We measure the values of several spectral absorptions tracing chemical species, in particular magnesium and iron, besides determining the age-sensitive D4000 break. We compare the measured indices to stellar population models, finding good agreement. We find that our target is an old (t > 3 Gyr), high-metallicity (Z/H > 0.5) galaxy which formed its stars at z
form >5 within a short time-scale ∼0.1 Gyr, as testified by the strong α/Fe ratio (>0.4), and has passively evolved in the first >3–4 Gyr of its life. We have verified that this result is robust against the choice and number of fitted spectral features, and stellar population model. The result of an old age and high-metallicity has important implications for galaxy formation and evolution confirming an early and rapid formation of the most massive galaxies in the Universe.
ABSTRACT
This paper presents the third data release of the INvestigating Stellar Population In RElics (INSPIRE) project, comprising 52 ultra-compact massive galaxies (UCMGs) observed with the ...X-Shooter spectrograph. We measure integrated stellar velocity dispersion, Mg/Fe abundances, ages, and metallicities for all the INSPIRE objects. We thus infer star formation histories and confirm the existence of a degree of relicness (DoR), defined in terms of the fraction of stellar mass formed by z = 2, the time at which a galaxy has assembled 75 per cent of its mass, and the final assembly time. Objects with a high DoR assembled their stellar mass at early epochs, while low-DoR objects show a non-negligible fraction of later formed populations and hence a spread in ages and metallicities. A higher DoR correlates with larger Mg/Fe, supersolar metallicity, and larger velocity dispersion values. The 52 UMCGs span a large range of DoR from 0.83 to 0.06, with 38 of them having formed more than 75 per cent of their mass by z = 2. Of these, nine are extreme relics (DoR>0.7), since they formed the totality ($\gt 99~{{\ \rm per\ cent}}$) of their stellar mass by redshift z = 2. The remaining 14 UCMGs cannot be considered relics, as they are characterized by more extended star formation histories. With INSPIRE we built the first sizeable sample of relics outside the local Universe, up to z ∼ 0.4, increasing the number of confirmed relics by a factor of >10, and opening up an important window to explain the mass assembly of massive galaxies in the high-z Universe.
The study of the eigenvalues of the neutron transport operator yields an important insight into the physical features of the neutronic phenomena taking place in a nuclear reactor. Although the ...multiplication eigenvalue is the most popular because of its implication in the engineering design of multiplying structures, alternative interesting formulations are possible. In this paper the interest is focused on the multiplication, collision and time eigenvalues. The transport model is considered in the spherical harmonics approximation and the study is restricted to the one-dimensional plane geometry in the monokinetic case. The spectra of the different eigenvalues are investigated using a numerical code, validating its performance against the results available in the literature. The observation of the convergence trends allows to establish the performance of even- and odd-order approximations. It is shown that in general even-order approximations yield slightly less accurate results, nevertheless they appear to converge to the reference values.
The effect of the choice of the boundary conditions according to the methodologies proposed by either Mark or Marshak is also investigated. The analysis of all the results presented allows to characterize the convergence properties of the spherical harmonics approach to neutron transport.
The spectrum of the time eigenvalues retains a very rich physical meaning, as they are the actual time constants of the time-dependent solution of the transport problem. Therefore, in the last part of the paper the behavior of the pattern of the spectrum of the time eigenvalues when changing the scattering ratio and the order of the approximation is examined.
Magnetic hyperthermia is an oncological therapy where magnetic nanostructures, under a radiofrequency field, act as heat transducers increasing tumour temperature and killing cancerous cells. ...Nanostructure heating efficiency depends both on the field conditions and on the nanostructure properties and mobility inside the tumour. Such nanostructures are often incorrectly bench-marketed in the colloidal state and using field settings far off from the recommended therapeutic values. Here, we prepared nanoclusters composed of iron oxide magnetite nanoparticles crystallographically aligned and their specific absorption rate (SAR) values were calorimetrically determined in physiological fluids, agarose-gel-phantoms and ex vivo tumours extracted from mice challenged with B16-F0 melanoma cells. A portable, multipurpose applicator using medical field settings; 100 kHz and 9.3 kA m
, was developed and the results were fully analysed in terms of nanoclusters' structural and magnetic properties. A careful evaluation of the nanoclusters' heating capacity in the three milieus clearly indicates that the SAR values of fluid suspensions or agarose-gel-phantoms are not adequate to predict the real tissue temperature increase or the dosage needed to heat a tumour. Our results show that besides nanostructure mobility, perfusion and local thermoregulation, the nanostructure distribution inside the tumour plays a key role in effective heating. A suppression of the magnetic material effective heating efficiency appears in tumour tissue. In fact, dosage had to be increased considerably, from the SAR values predicted from fluid or agarose, to achieve the desired temperature increase. These results represent an important contribution towards the design of more efficient nanostructures and towards the clinical translation of hyperthermia.
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