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 HI-based V_c 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_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.Comment: 2 pages, 2 figures, to appear in Proc. IAU Symp. 222, "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei" eds. Th. Storchi Bergmann, L.C. Ho & H.R. Schmitt (Cambridge University Press

The Black Hole Mass of Abell 1836-BCG and Abell 3565-BCG

Two brightest cluster galaxies (BCGs), namely Abell 1836-BCG and Abell 3565-BCG, were observed with the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. By modeling the available photometric and kinematic data, it resulted that the mass of Abell 1836-BCG and Abell 3565-BCG are M_bh=4.8(+0.8,-0.7)x10^9 M_sun and M_bh=1.3(+0.3,-0.4)x10^9 M_sun at 1 sigma confidence level, respectively.Comment: 4 pages, 3 figures, Mem SAIt in press, Proceedings of the 51st Annual Meeting of the Italian Astronomical Society, Florence, April 17-20, 200

The Infrared Telescope Facility (IRTF) spectral library: spectral diagnostics for cool stars

The near-infrared (NIR) wavelength range offers some unique spectral features, and it is less prone to the extinction than the optical one. Recently, the first flux calibrated NIR library of cool stars from the NASA Infrared Telescope Facility (IRTF) have become available, and it has not been fully exploited yet. We want to develop spectroscopic diagnostics for stellar physical parameters based on features in the wavelength range 1-5 micron. In this work we test the technique in the I and K bands. The study of the Y, J, H, and L bands will be presented in the following paper. An objective method for semi-empirical definition of spectral features sensitive to various physical parameters is applied to the spectra. It is based on sensitivity map--i.e., derivative of the flux in the spectra with respect to the stellar parameters at a fixed wavelength. New optimized indices are defined and their equivalent widths (EWs) are measured. A number of sensitive features to the effective temperature and surface gravity are re-identified or newly identified clearly showing the reliability of the sensitivity map analysis. The sensitivity map allows to identify the best bandpass limits for the line and nearby continuum. It reliably predicts the trends of spectral features with respect to a given physical parameter but not their absolute strengths. Line blends are easy to recognize when blended features have different behavior with respect to some physical stellar parameter. The use of sensitivity map is therefore complementary to the use of indices. We give the EWs of the new indices measured for the IRTF star sample. This new and homogeneous set of EWs will be useful for stellar population synthesis models and can be used to get element-by-element abundances for unresolved stellar population studies in galaxies.Comment: 46 pages, 27 figures, accepted for publication on Astronomy and Astrophysic

Dissecting Kinematics and Stellar Populations of Counter-Rotating Galaxies with 2-Dimensional Spectroscopy

We present a spectral decomposition technique and its applications to a sample of galaxies hosting large-scale counter-rotating stellar disks. Our spectral decomposition technique allows to separate and measure the kinematics and the properties of the stellar populations of both the two counter-rotating disks in the observed galaxies at the same time. Our results provide new insights on the epoch and mechanism of formation of these galaxies.Comment: 4 pages, 3 figures. Contributed talk presented at the Conference "Multi-Spin galaxies", September 30 - October 3, 2013, INAF-Astronomical Observatory of Capodimonte, Naples, Italy. To be published in ASP Conf. Ser., Multi-Spin Galaxies, ed. E. Iodice & E. M. Corsini (San Francisco: ASP

Could the Fermi-LAT detect gamma-rays from dark matter annihilation in the dwarf galaxies of the Local Group?

The detection of gamma-rays from dark matter (DM) annihilation is among the scientific goals of the Fermi Large Area Telescope (formerly known as GLAST) and Cherenkov telescopes. In this paper we investigate the existence of realistic chances of such a discovery selecting some nearby dwarf spheroidal galaxies (dSph) as a target. We study the detectability with the Fermi-LAT of the gamma-ray flux from DM annihilation in Draco, Ursa Minor, Carina, and Sextans, for which the state-of-art DM density profiles were available. We assume the DM is made of Weakly Interacting Massive Particles such as the Lightest Supersymmetric Particle (LSP) and compute the expected gamma-ray flux for optimistic choices of the unknown underlying particle physics parameters. We then compute the boost factors due to the presence of DM clumps and of a central supermassive black hole. Finally, we compare our predictions with the Fermi-LAT sensitivity maps. We find that the dSph galaxies shine above the Galactic smooth halo: e.g., the Galactic halo is brighter than the Draco dSph only for angles smaller than 2.3 degrees above the Galactic Center. We also find that the presence of a cusp or a constant density core in the DM mass density profile does not produce any relevant effect in the gamma-ray flux due to the fortunate combination of the geometrical acceptance of the Fermi-LAT detector and the distance of the galaxies and that no significant enhancement is given by the presence of a central black hole or a population of sub-subhalos. We conclude that, even for the most optimistic scenario of particle physics, the gamma-ray flux from DM annihilation in the dSph galaxies of the LG would be too low to be detected with the Fermi-LAT.Comment: 11 pages, 11 figures, accepted for publication in A&

On the distribution of galaxy ellipticity in clusters

We study the distribution of projected ellipticity n(ϵ) for galaxies in a sample of 20 rich (Richness ≥ 2) nearby (z 0.4), therefore it is not a consequence of the increasing fraction of round slow rotator galaxies near cluster centers. Furthermore, the ϵ-R relation persists for just smooth flattened galaxies and for galaxies with de Vaucouleurs-like light profiles, suggesting that the variation of the spiral fraction with radius is not the underlying cause of the trend. We interpret our findings in light of the classification of early type galaxies (ETGs) as fast and slow rotators. We conclude that the observed trend of decreasing ϵ towards the centres of clusters is evidence for physical effects in clusters causing fast rotator ETGs to have a lower average intrinsic ellipticity near the centres of rich clusters

Super massive black holes in spiral galaxies: HST/STIS observations for 3 new objects

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 H_alpha and [NII] 6583 AA 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 one order of magnitude lower than the one expected from the M-sigma relation for galaxies (Ferrarese & Merritt 2000; Gebhardt et al. 2000).Comment: 2 pages, 1 figure, to appear in "The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", IAU Symposium 222, eds. Th. Storchi Bergmann, L.C. Ho & H.R. Schmit

Supermassive Black Holes in BCGs

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 Halpha and [NII]lambda6583 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_bh=4.8(-0.7,+0.8)10**9 M_sun and M_bh=1.3(-0.4,+0.3)10**9 M_sun at 1 sigma confidence level, respectively. For the SBH of Abell 2052-BCG, we found M_bh < 7.3 10**9 M_sun.Comment: 2 pages, 1 figure. To appear in the proceedings of "Black Holes: from Stars to Galaxies", IAU Symp. No. 238, V. Karas & G. Matt (eds.), Cambridge University Pres

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