IC 5181: An S0 Galaxy with Ionized Gas on Polar Orbits

The nearby S0 galaxy IC 5181 is studied to address the origin of the ionized gas component that orbits the galaxy on polar orbit. We perform detailed photometric and spectroscopic observations measuring the surface brightness distribution of the stars (I-band), ionized gas of IC 5181 (H-alpha narrow band), the ionized-gas and stellar kinematics along both the major and minor axis, and the corresponding line strengths of the Lick indices. We conclude that the galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. The result is suggesting that the gas component is not related to the stars having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment.Comment: 4 pages, 5 figures, To appear in ASP Conf. Ser., Multi-Spin Galaxies, E. Iodice and E. M. Corsini (eds.

The properties and the formation mechanism of the stellar counter-rotating components in NGC 4191

We disentangle two counter-rotating stellar components in NGC 4191 and characterize their physical properties (kinematics, morphology, age, metallicity, and abundance ratio). We performed a spectroscopic decomposition on integral field data to separate the contribution of two stellar components to the observed galaxy spectrum across the field of view. We also performed a photometric decomposition, modelling the galaxy with a S\'ersic bulge and two exponential disks of different scale length, with the aim of associating these structural components with the kinematic components. We measured the equivalent width of the absorption line indices on the best fit that represent the kinematic components and compared our measurements to the predictions of stellar population models. We have evidence that the line-of-sight velocity distributions (LOSVDs) are consistent with the presence of two distinct kinematic components. The combined information of the intensity of the LOSVDs and photometry allows us to associate the S\'ersic bulge and the outer disk with the main kinematic component, and the inner disk with the secondary kinematic component. The two kinematic stellar components counter-rotate with respect to each other. The main component is the most luminous and massive, and it rotates slower than the secondary component, which rotates along the same direction as the ionized gas. We also found that the two kinematic components have the same solar metallicity and sub-solar abundance ratio, without the presence of significant radial gradients. On the other hand, their ages show strong negative gradients and the possible indication that the secondary component is the youngest. We interpret our results in light of recent cosmological simulations and suggest gas accretion along two filaments as the formation mechanism of the stellar counter-rotating components in NGC 4191 (Abridged).Comment: 10 pages, 10 figure. Accepted for publication in Astronomy and Astrophysic

Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366

Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the \u3b1/Fe overabundance. Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less \u3b1/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy. \ua9 ESO 2017

AGN STORM 2: V. Anomalous Behavior of the CIV Light Curve in Mrk 817

An intensive reverberation mapping campaign on the Seyfert 1 galaxy Mrk817 using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) revealed significant variations in the response of the broad UV emission lines to fluctuations in the continuum emission. The response of the prominent UV emission lines changes over a $\sim$60-day duration, resulting in distinctly different time lags in the various segments of the light curve over the 14 months observing campaign. One-dimensional echo-mapping models fit these variations if a slowly varying background is included for each emission line. These variations are more evident in the CIV light curve, which is the line least affected by intrinsic absorption in Mrk817 and least blended with neighboring emission lines. We identify five temporal windows with distinct emission line response, and measure their corresponding time delays, which range from 2 to 13 days. These temporal windows are plausibly linked to changes in the UV and X-ray obscuration occurring during these same intervals. The shortest time lags occur during periods with diminishing obscuration, whereas the longest lags occur during periods with rising obscuration. We propose that the obscuring outflow shields the ultraviolet broad lines from the ionizing continuum. The resulting change in the spectral energy distribution of the ionizing continuum, as seen by clouds at a range of distances from the nucleus, is responsible for the changes in the line response.Comment: 20 pages, 8 figures, submitted to Ap

AGN STORM 2. IV. Swift X-ray and ultraviolet/optical monitoring of Mrk 817

The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble UV continuum light curves, we measure interband continuum lags, $\tau(\lambda)$, that increase with increasing wavelength roughly following $\tau(\lambda) \propto \lambda^{4/3}$, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curve - the light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad line region gas that sees an absorbed ionizing continuum.Comment: 20 pages, 13 figures, 3 tables, accepted for publication in Ap

The relation between bulge velocity dispersion and disk circular velocity in galaxies

We investigate the relation between the central velocity dispersion, \u3c3_c, and the circular velocity, V_circ, in galaxies, which could be interpreted as a relation between the masses of central black holes and dark matter halos. We consider an observationally homogeneous sample of 52 high surface brightness (HSB) spiral galaxies and 11 low surface brightness (LSB) spiral galaxies in addition to HSB literature data. We performed a straight line regression analysis in a linear scale, finding a good fit, also for low \u3c3_c galaxies, always rejected in the previous studies. LSB galaxies, for the first time considered for this purpose, seem to behave differently, showing either higher values of V_circ or lower values of \u3c3_c with respect to their HSB counterparts

The \u3c3_c-V_circ correlation in high and low surface brightness galaxies

We investigate the relation between the central velocity dispersion, \u3c3_c, and the circular velocity, V_circ, in galaxies. In addition to previously obtained data, we consider an observationally homogeneous 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 \u3c3_c galaxies, always rejected in the previous studies. Low surface brightness galaxies seem to behave differently, showing either higher values of V_circ or lower values of \u3c3_c with respect to their high surface brightness counterparts

The external origin of the polar gaseous disk of the S0 galaxy IC 5181

Context. Galaxies accrete material from the environment through acquisition and merging events. These processes contribute to galaxy assembly and leave their fingerprints on the galactic morphology, internal kinematics of gas and stars, and stellar populations. Aims: We study the nearby S0 galaxy IC 5181 to address the origin of the ionized gas component that orbits the galaxy on polar orbits. Methods: We measure the surface brightness distribution of the stars and ionized gas of IC 5181 from broadband and narrow-band imaging. The structural parameters of the galaxy are obtained with a photometric decomposition assuming a S\ue9rsic and exponential profile for the bulge and disk, respectively. We measure the ionized-gas and stellar kinematics and the line strengths of the Lick indices of the stellar component along both the major and minor axis. The age, metallicity, and [\u3b1/Fe] enhancement of the stellar populations are derived using single stellar population models with variable element abundance ratios. The ionized-gas metallicity is obtained from the equivalent width of the emission lines. Results: The galaxy IC 5181 is a morphologically undisturbed S0 galaxy with a classical bulge made by old stars with super solar metallicity and overabundance. Stellar age and metallicity decrease in the disk region. The galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. Conclusions: We interpret the kinematical decoupling as suggesting that there is a component of gas, which is not related to the stars and having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment

The V_c- sigma_c relation in high and low surface brightness galaxies

We investigate the relation between the asymptotic circular velocity, V_c , and the central stellar velocity dispersion, sigma_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 H I-based V_c measurements. We find that: 1) elliptical galaxies with H I 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_c < 70 km/s; 3) LSB galaxies, considered for the first time with this respect, seem to behave differently, showing either larger V_c values or smaller sigma_c values. If the V_c-sigma_c relation is equivalent to one between the mass of the dark matter halo and that of the supermassive black hole, these results suggest that the LSB galaxies host a supermassive black hole with a smaller mass compared to HSB galaxies of equal dark matter halo. On the other hand, if the fundamental correlation of SMBH mass is with the halo circular velocity, then LSBs should have larger black hole masses for given bulge dispersion

Counter-rotating disks in galaxies: Dissecting kinematics and stellar populations with 3D spectroscopy

We present a spectral decomposition technique that separates the contribution of different kinematic components in galaxies from the observed spectrum. This allows to study the kinematics and properties of the stellar populations of the individual components (e.g., bulge, disk, counter-rotating cores, orthogonal structures). Here, we discuss the results of this technique for galaxies that host counter-rotating stellar disks of comparable size. In all the studied cases, the counter-rotating stellar disk is the less massive, the youngest and has different chemical content (metallicity and \u3b1-elements abundance ratio) than the main galaxy disk. Further applications of the spectral decomposition technique are also discussed