1,721,133 research outputs found
HI in the Dusty Elliptical Galaxy NGC5266
No full textRecent observations with the Australia Telescope Compact Array show that the elliptical galaxy NGC 5266 has a disk of neutral hydrogen extending to almost 10Re. This HI disk lies along the galaxy's major axis, at right angles to the inner minor-axis dust lane. The geometry and kinematics of the gas will allow us to determine both the intrinsic shape of the stellar galaxy and the mass distribution. The mass-to-light ratio M/L_B rises from about 2 in the central regions to ~12 at 9Re (H0=50 km/s/Mpc)
The Asiago-ESO/RASS QSO Survey. I. The Catalog and the Local QSO Luminosity Function
Full text linkThis paper presents the first results of a survey for bright quasars (V30°. The photometric database is derived from the Guide Star and USNO catalogs. Quasars are identified on the basis of their X-ray emission measured in the ROSAT All-Sky Survey. The surface density of quasars brighter than 15.5 mag turns out to be (10+/-2)×10-3 deg-2, about 3 times higher than that estimated by the PG survey. The quasar optical luminosity function (LF) at 0.04<z<=0.3 is computed and shown to be consistent with a luminosity-dependent luminosity evolution of the type derived by La Franca & Cristiani in the range 0.3<z<=2.2. The predictions of semianalytical models of hierarchical structure formation agree remarkably well with the present observations
THE EFFECT OF SURFACE BRIGHTNESS DIMMING IN THE SELECTION OF HIGH-zGALAXIES
No full textCosmological surface brightness (SB) dimming of the form (1 + z)−4 affects all sources. The strong dependence
of SB dimming on redshift z suggests the presence of a selection bias when searching for high-z galaxies, i.e., we
tend to detect only those galaxies with a high SB. However, unresolved knots of emission are not affected by SB
dimming, thus providing a way to test the clumpiness of high-z galaxies. Our strategy relies on the comparison
of the total flux detected for the same source in surveys characterized by different depth. For all galaxies, deeper
images permit the better investigation of low-SB features. Cosmological SB dimming makes these low-SB features
hard to detect when going to higher and higher redshifts.We used the GOODS and HUDF Hubble Space Telescope
legacy data sets to study the effect of SB dimming on low-SB features of high-z galaxies and compare it to the
prediction for smooth sources. We selected a sample of Lyman-break galaxies at z ∼ 4 (i.e., B435-band dropouts)
detected in all of the data sets and found no significant trend when comparing the total magnitudes measured
from images with different depth. Through Monte Carlo simulations we derived the expected trend for galaxies
with different SB profiles. The comparison to the data hints at a compact distribution for most of the rest-frame
ultraviolet light emitted from high-z galaxies
Inner polar disks in early-type spiral galaxies
No full textWe measured a remarkable gas velocity gradient along the minor axis of a number of early-type spiral galaxies. This phenomenon suggests the presence of a kinematically-decoupled component in orthogonal rotation with respect to the galaxy disk which we named inner polar disk. If this is the case a second event has taken place in the history of the galaxy. Alternatively the gas velocity gradient is the result of non-circular motions induced by the potential of a triaxial bulge
SMBH mass function from velocity dispersion and luminosity
No full textBlack-hole masses are tightly correlated with the stellar velocity dispersion of host galaxies, and slightly less-well correlated with the bulge luminosities; the M• -σ relation predicts fewer massive black holes than does the M• -L relation.
This is because the L-σ in currently available black-hole samples is inconsistent with that in the samples from which the distributions of L or σ are based. This suggests that current black-hole samples are biased and that the M• -σ and M• -L relations currently in the literature are also biased from their intrinsic values. Our analysis suggests that the bias in the M• -σ relation is likely to be small, whereas the M• -L relation is biased towards predicting more massive black holes for a given luminosity
CDM or pseudo-isothermal halos in LSB galaxies
No full textWe present preliminary results of the spectroscopic observations of a sample of 12 bulge-dominated low surface brightness galaxies (LSB). We measured the stellar and gaseous kinematics along their major and minor axes. Such combined information will allow us to accurately investigate the dark matter (DM) content within their optical regions, providing further constraints on cosmological models. In particular we are going to test the consistency of the observed DM density radial profiles with the predictions of standard CDM models. Preliminary constant M/L modeling indicates the presence of dark matter at all radii. In order to derive the DM density radial profiles we need to construct dynamical mass models with a dark matter halo (work in progress)
The orthogonal gaseous kinematical decoupling in the Sa spiral NGC 2855
Full text linkWe present major and minor-axis kinematics of stars and ionized gas as well as narrow and broad-band surface photometry of the Sa spiral NGC 2855. In the nuclear regions of this unbarred and apparently undisturbed spiral galaxy the gas is rotating perpendicularly to the galaxy disk. We suggest that this kinematically-decoupled component is the signature of an acquisition process in the history of this galaxy
Satellites of Late-Type Spiral Galaxies
No full textUsing VIMOS (VLT) we carried out a spectroscopic survey around seven late-type spiral galaxies and we discovered 55 satellites. After obtaining the radial velocities and spatial distribution of the satellites, we analyze their properties
Kinematics of low surface brightness galaxies
No full textWe analyzed the kinematic of 12 low surface-brightness (LSB) galaxies to study the correlation between the disk circular velocity V_c and the central velocity dispersion of the spheroidal component σ_0. This relation has been claimed to be either the same power-law relation or a different linear one with respect to high surface-brightness (HSB) galaxies. We confirm here that LSB and HSB galaxies follow two different linear V_c-σ_0 relations
Kinematical decouplings in spiral galaxies
No full textLike fossils, multiple stellar and gaseous components with a misaligned or even opposite angular momentum with respect to that of their host conserve memory of processes driving galaxy formation and evolution. In disk galaxies, apart few cases like polar rings, they usually lurk to morphological inspection, they are serendipitously discovered by measuring detailed kinematics and generally interpreted as the end result of one or more second events. This is the case of a variety of kinematically-decoupled components, like the counterrotating gas observed in several S0's, the counterrotating stellar or gaseous disks found in a number of early-type spirals, and the orthogonally-rotating stellar cores we recently discovered in the bulges of two Sa spirals, namely NGC 4698 and NGC 4672. In this contribution we present the results of a survey aimed to measure the stellar and ionized-gas kinematics in a sample of nearby S0/a's and Sa's, which have been selected to be morphologically similar to the few spiral galaxies hosting counterrotating stellar and/or gaseous disks. In spite of their undisturbed appearance, all the sample galaxies host a kinematically decoupled gas component since they are characterized by a sharp gas velocity gradient along their minor axes. In some cases the nuclear gas is even rotating perpendicularly to the galaxy disk. In the past numerical experiments predicted that observable consequences of second events in disk galaxies (e.g. bulge growing, disk heating) result in a change of the host morphology toward earlier spiral types. Now we attempt to investigate the possible link between morphology and second events (unveiled by kinematical decouplings) in early-type spirals
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