Turbulence is investigated in the lee of an open-cell metal foam layer. In contrast to canonical grids, metal foams are locally irregular but statistically isotropic. The solid matrix is characterised by two lengths, the ligament thickness $d_f$ and the pore diameter $d_p$. A direct numerical simulation is conducted on a realistic metal foam geometry for which $d_f/d_p = 0.14$ and the porous layer thickness is five times the pore diameter. The Reynolds number based on the pore size is ${\textit {Re}}_{d_p} = 4000$, corresponding to a Taylor-scale Reynolds number ${\textit {Re}}_\lambda \approx 80$. Closer to the foam than two pore diameters, the pressure and turbulent transports of turbulent kinetic energy are non-negligible. In the same region, ${\textit {Re}}_\lambda$ undergoes a steep decrease whereas the dissipation coefficient $C_{\epsilon }$ increases like ${\textit {Re}}_\lambda ^{-1}$. At larger distances from the porous layer, the classical grid turbulence situation is recovered, where the mean advection of turbulent kinetic energy equals dissipation. This entails a power-law decay of turbulent quantities and characteristic lengths. The decaying exponents of integral, Taylor and Kolmogorov scales are close to one-half, indicating that the turbulence simulated here differs from Saffman turbulence. Analysis of the scaling exponents of structure functions and the decorrelation length of dissipation reveals that small-scale fluctuations are weakly intermittent.

We present the stellar populations properties of the interacting spiral NGC 5719, which is known to host two cospatial counter-rotating stellar discs.

The radial profiles of the Hβ, Mg, and Fe line-strength indices are presented for a sample of eight spiral galaxies with a low surface-brightness stellar disc and a bulge. The correlations between the central values of the line-strength indices and velocity dispersion are consistent to those known for early-type galaxies and bulges of high surface-brightness galaxies. The age, metallicity, and α/Fe enhancement of the stellar populations in the bulge-dominated region are obtained using stellar population models with variable element abundance ratios. Almost all the sample bulges are characterized by a young stellar population, on-going star formation, and a solar α/Fe enhancement. Their metallicity spans from high to sub-solar values. No significant gradient in age and α/Fe enhancement is measured, whereas only in a few cases a negative metallicity gradient is found. These properties suggest that a pure dissipative collapse is not able to explain formation of all the sample bulges and that other phenomena, like mergers or acquisition events, need to be invoked. Such a picture is also supported by the lack of a correlation between the central value and gradient of the metallicity in bulges with very low metallicity. The stellar populations of the bulges hosted by low surface-brightness discs share many properties with those of high surface-brightness galaxies. Therefore, they are likely to have common formation scenarios and evolution histories. A strong interplay between bulges and discs is ruled out by the fact that in spite of being hosted by discs with extremely different properties, the bulges of low and high surface-brightness discs are remarkably similar.

We studied the stellar populations, distribution of dark matter, and dynamical structure of a sample of 25 early-type galaxies in the Coma and Abell~262 clusters. We derived dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the ages, metallicities, and α-element abundances of the galaxies from single stellar population models. Most of the galaxies have a significant detection of dark matter and their halos are about 10 times denser than in spirals of the same stellar mass. Calibrating dark matter densities to cosmological simulations we find assembly redshifts zDM ≈ 1–3. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function, especially in galaxies with high velocity dispersion σeff inside the effective radius reff. We now have 5 of 25 galaxies where mass follows light to 1–3 reff, the dynamical mass-to-light ratio of all the mass that follows the light is large (≈ 8–10 in the Kron-Cousins R band), the dark matter fraction is negligible to 1–3 reff. This could indicate a ‘massive’ initial mass function in massive early-type galaxies. Alternatively, some of the dark matter in massive galaxies could follow the light very closely suggesting a significant degeneracy between luminous and dark matter.

We present extensive photometric and spectroscopic study to give a new insight in the bulge stellar population. Super-solar α/Fe and its constant value along the radial profile, in most of the galaxies, suggest that the star formation in these objects has been fast and occurred at the same time in the whole bulge.

Secure measurements of the mass of the central supermassive black hole, MBH, in external galaxies are traditionally obtained through the modeling of the stellar and/or gaseous kinematics, most often derived using Hubble Space Telescope (HST) observations in the optical domain. The modeling of the nuclear ionized-gas kinematics has led to accurate MBH measurements at a relatively cheap cost in terms of observation time compared to stellar-dynamical MBH determinations. But only a handful of the objects have turned out to have sufficiently regular gas velocity fields for the purpose of modeling. Nevertheless, the HST archive contains a yet untapped resource that can be used to better constrain the MBH budget across the different morphological types of galaxies, which consists of the vast number of the Space Telescope Imaging Spectrograph (STIS) spectra from which a central emission-line width can be measured. These data allow to put an upper limit on MBH for a large number of galaxies and promise to compensate for the lack of exact measurements when studying the MBH–host galaxy relationships.

A large fraction of otherwise normal galaxies shows weak nuclear activity. One of the signatures of the low-luminosity active galactic nuclei (LLAGNs) is the ultraviolet variability which was serendipitously discovered in the center of some low-ionization nuclear emission-line region (LINER) galaxies (see Ho 2008 for a review).

The growth of supermassive black holes (SMBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SMBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SMBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SMBHs that can be present in the center of all the nearby galaxies (D < 100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits will be derived by modeling the central emission-line widths ([N II] λλ6548, 6583, Hα and [S II] λλ6716, 6731) observed over an aperture of ~01 (R < 50 pc). Here we present our preliminary results for a subsample of 76 bulges.

We present extensive photometric and spectroscopic study to give a new insight in the bulge stellar population. Super-solar α/Fe and its constant value along the radial profile, in most of the galaxies, suggest that the star formation in these objects has been fast and occurred at the same time in the whole bulge.

The dynamics of a barred galaxy depends on the pattern speed of its bar. The only direct method for measuring the pattern speed of a bar is the Tremaine-Weinberg technique. This method is best suited to the analysis of the distribution and dynamics of the stellar component. Therefore it has been mostly used for early-type barred galaxies. Most of them host a classical bulge. On the other hand, a variety of indirect methods, which are based on the analysis of the distribution and dynamics of the gaseous component, has been used to measure the bar pattern speed in late-type barred galaxies. Nearly all the measured bars are as rapidly rotating as they can be. By comparing this result with high-resolution numerical simulations of bars in dark matter halos, it is possible to conclude that these bars reside in maximal disks.

Traditionally, the study of the structural parameters of galaxies have been used to understand the bulge formation processes. However, one piece lost in this study is the three-dimensional shape of the bulges. In this work, the structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived to study the correlations between bulge and disk parameters as well as the probability distribution function (PDF) of the intrinsic equatorial ellipticity of bulges. A new algorithm (GASP-2D) was used to perform the bidimensional bulge-disk decomposition of J-band galaxy images extracted from the archive of the 2MASS survey. The PDF of intrinsic ellipticities was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. About 80% of bulges in S0-Sb galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is 〈B/A〉=0.85. There is not significant dependence of their PDF on morphology, light concentration, and luminosity. The scenarios in which bulges assembled from mergers and/or grew over long times through disk secular evolution have to be tested against the derived PDF of bulge intrinsic ellipticities.

We present extensive photometric and spectroscopic study to give a new insight in the bulge stellar population. Super-solar α/Fe and its constant value along the radial profile, in most of the galaxies, suggest that the star formation in these objects has been fast and occurred at the same time in the whole bulge.

The growth of supermassive black holes (SBHs) appears to be closely linked with the formation of spheroids. There is a pressing need to acquire better statistics on SBH masses, since the existing samples are preferentially weighted toward early-type galaxies with very massive SBHs. With this motivation we started a project aimed at measuring upper limits on the mass of the SBHs in the center of all the nearby galaxies (D < 100 Mpc) for which STIS/G750M spectra are available in the HST archive. These upper limits will be derived by modeling the central emission-line widths observed in the Hα region over an aperture of ∼0.1″. Here we present our results for a subsample of 22 S0-Sb galaxies within 20 Mpc.

We analyzed the 2MASS images of a sample of 148 bright, nearby and unbarred galaxies to derive the photometric parameters of their bulge and disk by applying an accurate 2D decomposition algorithm. As a model for the bulge we have considered a system where the surfaces of equal density of light are coaxial and concentric ellipsoids with independent values of the principal axes A > B > C. If the emitting surfaces are concentric, coaxial but non-homologous ellipsoids, their projection on the plane of the sky will be concentric, non-homologous and non-coaxial ellipses (Stark 1977). Therefore if we identify the projected ellipses with the isophotal contours of a bulge, the observed twist between the position angle of the bulge and disk components can be understood as a hint for triaxiality.

Following the procedure described by Simonneau et al. (1998), we are able to express the intrinsic semi-axis values (A, B, C) of the triaxial ellipsoid as a function of the semi-axis measured on to its projected ellipse (a, b), position angle of the ellipse (δ), and angles which define the line of sight with respect to the ellipsoid (θ, φ).

However, since the φ angle is observationally undetermined, the intrinsic shape of bulges is still an ambiguous problem. Thus, it is customary to resort to a statistical approach for deducing the probability distribution function (PDF) of the intrinsic axis ratio of bulges. Since we have already inverted the problem, putting the intrinsic variables as a function of the measured variables (E, δ) and the variables (θ, φ) which are defined in a probabilistic way, and we have assumed that they are independent, the PDF can be determined simply by the multiplication of the integrated single probabilities of these variables.

We have found that integrating the derived PDF over the different ellipsoid regions (prolate, triaxial and oblate), ~45% of bulges have a triaxial structure, about 26% are oblate ellipsoids, 23% are prolate ellipsoids and the remaining 5% are spherical.

A typical bulge from our PDF, calculated as the mean value of the axis ratios of the ellipsoids weighted with the PDF, have axis ratios <P>=1.66 and <Q>=1.34. This means that the axis ratio in the equatorial plane of the galaxy is B/A=0.81, the ratio between the major and the polar axis is C/A=0.60 and the triaxiality parameter is T=0.55, which is in good agreement with the previous results by Bertola et al. (1991).

We also found a correlation between the Sérsic index and the intrinsic flattening of the bulges. We observed that bulges tend to be less flattened (C/A=0.64) in more-concentrated galaxies (n > 2) and more flattened (C/A=0.54) in less-concentrated galaxies.

We observed a sample of three Brightest Cluster Galaxies (BCGs), Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, with the Advanced Camera for Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Space Telescope. For each target galaxy we obtained high-resolution spectroscopy of the Hα and [N II] λ6583 emission lines at three slit positions, to measure the central ionized-gas kinematics. ACS images in three different filters (F435W, F625W, and FR656N) have been used to determine the optical depth of the dust, stellar mass distribution near the nucleus, and intensity map. We present supermassive black hole (SBH) mass estimates for two galaxies which show regular rotation curves and strong central velocity gradients, and an upper limit on the SBH mass of the third one. For the SBHs of Abell 1836-BCG and Abell 3565-BCG, we derived M• = 4.8+0.8−0.7 × 109 M⊙ and M• = 1.3+0.3−0.4 × 109 M⊙ at 1 σ confidence level, respectively. For the SBH of Abell 2052-BCG, we found M• ≤ 7.3 × 109 M⊙.

We present long-slit HST/STIS measurements of the ionized-gas kinematics in the nucleus of three disk galaxies, namely NGC 2179, NGC 4343, NGC 4435. The sample galaxies have been selected on the basis of their ground-based spectroscopy, for displaying a strong central velocity gradient for the ionized gas, which is consistent with the presence of a circum nuclear keplerian disk (CNKD, Bertola et al. 1998; Funes et al. 2002) rotating around a super massive black hole (SMBH). For each target galaxy we obtained the Hα and [NII] 6583 Å kinematics along the major axis and two 0."25 parallel offset positions. Out of three objects only NGC 4435 turned out to have a disk of ionized gas in regular motion and a regular dust-lane morphology. Preliminary modeling indicates a SMBH mass (M[bull ]) one order of magnitude lower than the one expected from the M[bull ]−σc relation for galaxies (Ferrarese & Merritt 2000; Gebhardt et al. 2000).To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the relation between the asymptotic circular velocity, $V_{\rm circ}$, and the central stellar velocity dispersion, $\sigma_{\rm c}$, in galaxies. We consider a new sample of high surface brightness spiral galaxies (HSB), low surface brightness spiral galaxies (LSB), and elliptical galaxies with HI-based $V_{\rm circ}$ measurements. We find that: 1) elliptical galaxies with HI measurements fit well within the relation; 2) a linear law can reproduce the data as well as a power law (used in previous works) even for galaxies with $\sigma_{\rm c} \lt 70$ km/s; 3) LSB galaxies, considered for the first time with this respect, seem to behave differently, showing either larger $V_{\rm circ}$ values or smaller $\sigma_{\rm c}$ values.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We investigate the relation between the central velocity dispersion, σc, and the circular velocity, Vcirc, in galaxies. in addition to previously obtained data, we consider an observationally homogeneus sample of 52 high surface brightness and 11 low surface brightness spiral galaxies. We performed a straight line regression analysis in a linear scale, finding a good fit, also for low σc galaxies, always rejected in the previous studies. Low surface brightness galaxies seem to behave differently, showing either higher values of Vcirc or lower values of σc with respect to their high surface brightness counterparts.