The evolution of quiescent galaxies at high redshifts (z ≥ 1.4)

The goal of this work is to study the evolution of high-redshift (z ≥ 1.4) quiescent galaxies over an effective area of ~ 1.7 deg^2 in the COSMOS field. Galaxies have been divided according to their star formation activity and the evolution of the different populations, in particular of the quiescent galaxies, has been investigated in detail. We have studied an IRAC (ma_( 3.6 μm) 2.5 (log_ρ[M_⊙ Mpc^(−3)]~ 6), meaning that efficient star formation had to take place before that time

Hidden AGN in dwarf galaxies revealed by MaNGA: light echoes, off-nuclear wanderers, and a new broad-line AGN

Active galactic nuclei (AGN) in dwarf galaxies could possibly host the relics of those early Universe seed black holes that did not grow into supermassive black holes. Using MaNGA integral field unit (IFU) spectroscopy we have found a sample of 37 dwarf galaxies that show AGN ionisation signatures in spatially-resolved emission line diagnostic diagrams. The AGN signatures are largely missed by integrated emission line diagnostics for 23 of them. The bolometric luminosity of these 23 new AGN candidates is $\lesssim 10^{40}$ erg s$^{-1}$, fainter than that of single-fiber SDSS AGN, X-ray AGN, and radio AGN in dwarf galaxies, which stands IFU spectroscopy as a powerful tool for identifying hidden and faint AGN in dwarf galaxies. The AGN emission is in most cases offset from the optical center of the dwarf galaxy and shows a symmetric morphology, which indicates that either the AGN are off-nuclear, that the central emission of the galaxy is dominated by star formation, or that the AGN are turned-off and we are observing a past ionisation burst. One of the new AGN shows a broad H$\alpha$ emission line component, from which we derive a black hole mass in the realm of intermediate-mass black holes. This constitutes the first hidden type 1 AGN discovered in a dwarf galaxy based on IFU spectroscopy. The finding of this sample of hidden and faint AGN has important implications for population studies of AGN in dwarf galaxies and for seed black hole formation models.Comment: 13 pages, 5 figures, accepted for publication in ApJ Letter

Frenkel Excitons in Random Systems With Correlated Gaussian Disorder

Optical absorption spectra of Frenkel excitons in random one-dimensional systems are presented. Two models of inhomogeneous broadening, arising from a Gaussian distribution of on-site energies, are considered. In one case the on-site energies are uncorrelated variables whereas in the second model the on-site energies are pairwise correlated (dimers). We observe a red shift and a broadening of the absorption line on increasing the width of the Gaussian distribution. In the two cases we find that the shift is the same, within our numerical accuracy, whereas the broadening is larger when dimers are introduced. The increase of the width of the Gaussian distribution leads to larger differences between uncorrelated and correlated disordered models. We suggest that this higher broadening is due to stronger scattering effects from dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review

Three-dimensional effects on extended states in disordered models of polymers

We study electronic transport properties of disordered polymers in the presence of both uncorrelated and short-range correlated impurities. In our procedure, the actual physical potential acting upon the electrons is replaced by a set of nonlocal separable potentials, leading to a Schr\"odinger equation that is exactly solvable in the momentum representation. We then show that the reflection coefficient of a pair of impurities placed at neighboring sites (dimer defect) vanishes for a particular resonant energy. When there is a finite number of such defects randomly distributed over the whole lattice, we find that the transmission coefficient is almost unity for states close to the resonant energy, and that those states present a very large localization length. Multifractal analysis techniques applied to very long systems demonstrate that these states are truly extended in the thermodynamic limit. These results reinforce the possibility to verify experimentally theoretical predictions about absence of localization in quasi-one-dimensional disordered systems.Comment: 16 pages, REVTeX 3.0, 5 figures on request from FDA ([email protected]). Submitted to Phys. Rev. B. MA/UC3M/09/9

Bridging the gap in the mass-size relation of compact galaxies with MaNGA

We present the analysis of the full MaNGA DR17 sample to characterize its population of compact galaxies. We focus on galaxies that fill the stellar mass (M$_{\star}$) gap between compact elliptical galaxies (cEs; $8 \lesssim \log \left(M_{\star} / M_{\odot} \right) \lesssim 10$) and compact massive galaxies (CMGs; $10 \lesssim \log \left(M_{\star} / M_{\odot} \right)$). We study their stellar populations and kinematics to reveal how their properties depend on stellar mass. We select compact galaxies in the MaNGA DR17 sample according to their effective radius ($R_e$) and stellar mass. 37 galaxies fulfill our selection criteria in the bridging region between cEs and CMGs. We derive their kinematics and stellar population parameters from the stacked spectra at 1~$R_e$ using a full spectral fitting routine. We then classify the selected compact galaxies in three main groups based on their stellar population properties. One of the groups shows characteristics compatible with relic galaxies, i.e. galaxies that have remained mostly unchanged since their early formation epoch ($z \sim 2$). Another group shows more extended and continuous star formation histories (SFHs). The third group shows a low star-forming rate at initial times, which increases at around $\sim4$ Gyr. We compare the derived properties of the selected galaxies with those of previously studied compact galaxies at different mass ranges. The selected galaxies successfully fill the mass gap between cEs and CMGs. Their properties are compatible with the assumption that the scaling relations of compact galaxies at different mass ranges are related, although galaxies in the first group are clear outliers in the fundamental plane, suggesting different formation mechanisms for this relic population.Comment: 16 pages, 14 figures, 2 table

Link between the chromospheric network and magnetic structures of the corona

Recent work suggested that the traditional picture of the corona above the quiet Sun being rooted in the magnetic concentrations of the chromospheric network alone is strongly questionable. Building on that previous study we explore the impact of magnetic configurations in the photosphere and the low corona on the magnetic connectivity from the network to the corona. Observational studies of this connectivity are often utilizing magnetic field extrapolations. However, it is open to which extent such extrapolations really represent the connectivity found on the Sun, as observations are not able to resolve all fine scale magnetic structures. The present numerical experiments aim at contributing to this question. We investigated random salt-and-pepper-type distributions of kilo-Gauss internetwork flux elements carrying some $10^{15}$ to $10^{17}$ Mx, which are hardly distinguishable by current observational techniques. These photospheric distributions are then extrapolated into the corona using different sets of boundary conditions at the bottom and the top. This allows us to investigate the fraction of network flux which is connected to the corona, as well as the locations of those coronal regions which are connected to the network patches. We find that with current instrumentation one cannot really determine from observations, which regions on the quiet Sun surface, i.e. in the network and internetwork, are connected to which parts of the corona through extrapolation techniques. Future spectro-polarimetric instruments, such as with Solar B or GREGOR, will provide a higher sensitivity, and studies like the present one could help to estimate to which extent one can then pinpoint the connection from the chromosphere to the corona.Comment: 8 pages, 5 figures, acceped for publication in A&