Publications (10)0 Total impact
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D. Thomas,
O. Steele,
C. Maraston,
J. Johansson, A. Beifiori,
J. Pforr,
G. Strombaeck,
C. A. Tremonti,
D. Wake,
D. Bizyaev, [......],
D. Oravetz,
K. Pan,
J. K. Parejko,
D. P. Schneider,
A. Shelden,
A. Simmons,
S. Snedden,
M. Tanaka,
B. A. Weaver,
R. Yan
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ABSTRACT: We perform a spectroscopic analysis of 492,450 galaxy spectra from the first
two years of observations of the Sloan Digital Sky Survey-III/Baryonic
Oscillation Spectroscopic Survey (BOSS) collaboration. This data set has been
released in the ninth SDSS data release, the first public data release of BOSS
spectra. We show that the typical signal-to-noise ratio of BOSS spectra is
sufficient to measure stellar velocity dispersion and emission line fluxes for
individual objects. The typical velocity dispersion of a BOSS galaxy is 240
km/s, with an accuracy of better than 30 per cent for 93 per cent of BOSS
galaxies. The distribution in velocity dispersion is redshift independent
between redshifts 0.15 and 0.7, which reflects the survey design targeting
massive galaxies with an approximately uniform mass distribution in this
redshift interval. The majority of BOSS galaxies lack detectable emission
lines. We analyse the emission line properties and present diagnostic diagrams
using the emission lines [OII], Hbeta, [OIII], Halpha, and [NII] (detected in
about 4 per cent of the galaxies). We show that the emission line properties
are strongly redshift dependent and that there is a clear correlation between
observed frame colours and emission line properties. Within in the low-z sample
around 0.15<z<0.3, half of the emission-line galaxies have LINER-like emission
line ratios, followed by Seyfert-AGN dominated spectra, and only a small
fraction of a few per cent are purely star forming galaxies. AGN and LINER-like
objects, instead, are less prevalent in the high-z sample around 0.4<z<0.7,
where more than half of the emission line objects are star forming. This is a
pure selection effect caused by the non-detection of weak Hbeta emission lines
in the BOSS spectra. Finally, we show that star forming, AGN and emission line
free galaxies are well separated in the g-r vs r-i target selection diagram.
07/2012;
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ABSTRACT: The early-type spiral NGC 4698 is known to host a nuclear disc of gas and
stars which is rotating perpendicularly with respect to the galaxy main disc.
In addition, the bulge and main disc are characterised by a remarkable
geometrical decoupling. Indeed they appear elongated orthogonally to each
other. In this work the complex structure of the galaxy is investigated by a
detailed photometric decomposition of optical and near-infrared images. The
intrinsic shape of the bulge was constrained from its apparent ellipticity, its
twist angle with respect to the major axis of the main disc, and the
inclination of the main disc. The bulge is actually elongated perpendicular to
the main disc and it is equally likely to be triaxial or axisymmetric. The
central surface brightness, scalelength, inclination, and position angle of the
nuclear disc were derived by assuming it is infinitesimally thin and
exponential. Its size, orientation, and location do not depend on the observed
passband. These findings support a scenario in which the nuclear disc is the
end result of the acquisition of external gas by the pre-existing triaxial
bulge on the principal plane perpendicular to its shortest axis and
perpendicular to the galaxy main disc. The subsequent star formation either
occurred homogeneously all over the extension of the nuclear disc or through an
inside-out process that ended more than 5 Gyr ago.
04/2012;
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ABSTRACT: We use a large sample of upper limits and accurate estimates of supermassive
black holes masses coupled with libraries of host galaxy velocity dispersions,
rotational velocities and photometric parameters extracted from Sloan Digital
Sky Survey i-band images to establish correlations between the SMBH and host
galaxy parameters. We test whether the mass of the black hole, MBH, is
fundamentally driven by either local or global galaxy properties. We explore
correlations between MBH and stellar velocity dispersion sigma, bulge
luminosity, bulge mass Sersic index, bulge mean effective surface brightness,
luminosity of the galaxy, galaxy stellar mass, maximum circular velocity Vc,
galaxy dynamical and effective masses. We verify the tightness of the MBH-sigma
relation and find that correlations with other galaxy parameters do not yield
tighter trends. We do not find differences in the MBH-sigma relation of barred
and unbarred galaxies. The MBH-sigma relation of pseudo-bulges is also coarser
and has a different slope than that involving classical bulges. The MBH-bulge
mass is not as tight as the MBH-sigma relation, despite the bulge mass proving
to be a better proxy of MBH than bulge luminosity. We find a rather poor
correlation between MBH and Sersic index suggesting that MBH is not related to
the bulge light concentration. The correlations between MBH and galaxy
luminosity or mass are not a marked improvement over the MBH sigma relation. If
Vc is a proxy for the dark matter halo mass, the large scatter of the MBH-Vc
relation then suggests that MBH is more coupled to the baryonic rather than the
dark matter. We have tested the need for a third parameter in the MBH scaling
relations, through various linear correlations with bulge and galaxy
parameters, only to confirm that the fundamental plane of the SMBH is mainly
driven by sigma, with a small tilt due to the effective radius. (Abridged)
09/2011;
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ABSTRACT: A large fraction of otherwise normal galaxies shows a 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. There is a pressing need to acquire better statistics about UV flaring and variability in galaxy nuclei, both in terms of the number and monitoring of targets. The Science Data Archive of the Hubble Space Telescope was queried to find all the elliptical galaxies with UV images obtained in different epochs with the Wide Field Planetary Camera 2 (WFPC2) and possibly with nuclear spectra obtained with the Space Telescope Imaging Spectrograph (STIS) in the region of the Halpha emission line. These data were found only for the elliptical radiogalaxy NGC 4278. The UV flux of the nuclear source of NGC 4278 was measured by means of aperture photometry on the WFPC2/F218W images obtained between June 1994 and January 1995. The mass of the central supermassive black hole (SBH) was estimated by measuring the broad components of the emission lines observed in the STIS/G750M spectrum and assuming that the gas is uniformly distributed in a sphere. The nucleus of NGC 4278 hosts a barely resolved but strongly variable UV source. Its UV luminosity increased by a factor of 1.6 in a period of 6 months. The amplitude and scale time of the UV flare in NGC 4278 are remarkably similar to those of the brightest UV nuclear transients which were earlier found in other LLAGNs. The mass of the SBH was found to be in the range between 7x10^7 and 2x10^9 M_sun. This is in agreement with previous findings based on different assumptions about the gas distribution and with the predictions based on the galaxy velocity dispersion. Comment: 5 pages,3 figures, accepted for publication on A&A
09/2009;
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ABSTRACT: We present Hubble Space Telescope imaging and spectroscopic observations of three Brightest Cluster Galaxies, Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, obtained with the Wide Field and Planetary Camera 2, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph. The data provide detailed information on the structure and mass profile of the stellar component, the dust optical depth, and the spatial distribution and kinematics of the ionized gas within the innermost region of each galaxy. Dynamical models, which account for the observed stellar mass profile and include the contribution of a central supermassive black hole (SBH), are constructed to reproduce the kinematics derived from the Halpha and [N II](lambda 6548,6583) emission lines. Secure SBH detection with M_bh=3.61(+0.41,-0.50)x10^9 M_sun and M_bh=1.34(+0.21,-0.19)x10^9 M_sun, respectively, are obtained for Abell 1836-BCG and Abell 3565-BCG, which show regular rotation curves and strong central velocity gradients. In the case of Abell 2052-BCG, the lack of an orderly rotational motion prevents a secure determination, although an upper limit of M_bh < 4.60x10^9 M_sun can be placed on the mass of the central SBH. These measurements represent an important step forward in the characterization of the high-mass end of the SBH mass function.
10/2008;
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ABSTRACT: Based on the modeling of the central emission-line width measured over sub-arcsecond apertures with the Hubble Space Telescope, we present stringent upper bounds on the mass of the central supermassive black hole, MBH, for a sample of 105 nearby galaxies (D<100Mpc) spanning a wide range of Hubble types (E-Sc) and values of the central stellar velocity dispersion, sigma (58-419km/s). For the vast majority of the objects the derived MBH upper limits run parallel and above the well-known MBH-sigma relation independently of the galaxy distance, suggesting that our nebular line-width measurements trace rather well the nuclear gravitational potential. For values of sigma between 90 and 220km/s the 68% of our upper limits falls immediately above the MBH-sigma relation without exceeding the expected MBH values by more than a factor 4.1. No systematic trends or offsets are observed in this sigma range as a function of the galaxy Hubble type or with respect to the presence of a bar. For 6 of our 12 MBH upper limits with sigma<90km/s our line-width measurements are more sensitive to the stellar contribution to the gravitational potential, either due to the presence of a nuclear stellar cluster or because of a greater distance compared to the other galaxies at the low-sigma end of the MBH-sigma relation. Conversely, our MBH upper bounds appear to lie closer to the expected MBH in the most massive elliptical galaxies with values of sigma above 220km/s. Such a flattening of the MBH-sigma relation at its high-sigma end would appear consistent with a coevolution of supermassive black holes and galaxies driven by dry mergers, although better and more consistent measurements for sigma and K-band luminosity are needed for these kind of objects before systematic effects can be ruled out. Comment: 15 pages, 5 figures, 2 tables, accepted for publication on ApJ. An ascii version of Tab.1 is available upon request
09/2008;
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ABSTRACT: 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 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] λλ
6548,6583Å, Hα, and [S II] λλ
6716,6731Å) observed over an aperture of ˜0.1 arcsec
(R<50 pc).
09/2008; 396:49.
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ABSTRACT: The variability of the UV luminosity and mass of the supermassive black
hole (SBH) in the nucleus of the giant elliptical NGC 4278 were derived
by analyzing the UV images and Hα spectrum available in the Hubble
Space Telescope Science Archive. The UV nuclear source in NGC 4278 is
almost certainly associated to the low-luminosity AGN responsible for
its known radio emission. The properties of this UV flare and SBH are
remarkably similar to the UV-bright nuclear transients and SBHs
discovered earlier in other low-luminosity AGNs. This supports the idea
that UV flaring near the center of galaxies may be a common event and
offers a way to search for SBH-related activities in otherwise quiescent
galaxies.
09/2008; 396:53.
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[show abstract]
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ABSTRACT: 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 ([NII], Halpha and [SII]) observed over an aperture of ~0.1" (R<50 pc). Here we present our preliminary results for a subsample of 76 bulges.
10/2007;
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[show abstract]
[hide abstract]
ABSTRACT: 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 Halpha region over an aperture of ~0.1''. Here we present our results for a subsample of 20 S0-Sb galaxies within 20 Mpc.
11/2006;
Institutions
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2008
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University of Padua
Padova,
Veneto,
Italy
