2,332 research outputs found
Bimodal AGNs in Bimodal Galaxies
By their star content, the galaxies split out into a red and a blue
population; their color index peaked around u-r=2.5 or u-r=1, respectively,
quantifies the ratio of the blue stars newly formed from cold galactic gas, to
the redder ones left over by past generations. On the other hand, upon
accreting substantial gas amounts the central massive black holes energize
active galactic nuclei (AGNs); here we investigate whether these show a
similar, and possibly related, bimodal partition as for current accretion
activity relative to the past. To this aim we use an updated semianalytic
model; based on Monte Carlo simulations, this follows with a large statistics
the galaxy assemblage, the star generations and the black hole accretions in
the cosmological framework over the redshift span from z=10 to z=0. We test our
simulations for yielding in close detail the observed split of galaxies into a
red, early and a blue, late population. We find that the black hole accretion
activities likewise give rise to two source populations: early, bright quasars
and later, dimmer AGNs. We predict for their Eddington parameter --
the ratio of the current to the past black hole accretions -- a bimodal
distribution; the two branches sit now under (mainly
contributed by low-luminosity AGNs) and around . These
not only mark out the two populations of AGNs, but also will turn out to
correlate strongly with the red or blue color of their host galaxies.Comment: 7 pages, accepted for publication in the Astrophysical Journa
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
Geocoding health data with Geographic Information Systems: a pilot study in northeast Italy for developing a standardized data-acquiring format
Introduction. Geographic Information Systems (GIS) have
become an innovative and somewhat crucial tool for analyzing
relationships between public health data and environment. This
study, though focusing on a Local Health Unit of northeastern
Italy, could be taken as a benchmark for developing a standardized
national data-acquiring format, providing a step-by-step
instructions on the manipulation of address elements specific for
Italian language and traditions.
Methods. Geocoding analysis was carried out on a health database
comprising 268,517 records of the Local Health Unit of
Rovigo in the Veneto region, covering a period of 10 years, starting
from 2001 up to 2010. The Map Service provided by the Environmental
Research System Institute (ESRI, Redlands, CA), and
ArcMap 10.0 by ESRI\uae were, respectively, the reference data and
the GIS software, employed in the geocoding process.
Results. The first attempt of geocoding produced a poor quality
result, having about 40% of the addresses matched. A procedure
of manual standardization was performed in order to enhance the
quality of the results, consequently a set of guiding principle were
expounded which should be pursued for geocoding health data.
High-level geocoding detail will provide a more precise geographic
representation of health related events.
Conclusions. The main achievement of this study was to outline
some of the difficulties encountered during the geocoding of
health data and to put forward a set of guidelines, which could
be useful to facilitate the process and enhance the quality of the
results. Public health informatics represents an emerging specialty
that highlights on the application of information science
and technology to public health practice and research. Therefore,
this study could draw the attention of the National Health Service
to the underestimated problem of geocoding accuracy in health
related data for environmental risk assessment
A revised Cepheid distance to NGC 4258 and a test of the distance scale
In a previous paper (Maoz et al. 1999), we reported a Hubble Space Telescope
(HST) Cepheid distance to the galaxy NGC 4258 obtained using the calibrations
and methods then standard for the Key Project on the Extragalactic Distance
Scale. Here, we reevaluate the Cepheid distance using the revised Key Project
procedures described in Freedman et al. (2001). These revisions alter the zero
points and slopes of the Cepheid Period-Luminosity (P-L) relations derived at
the Large Magellanic Cloud (LMC), the calibration of the HST WFPC2 camera, and
the treatment of metallicity differences. We also provide herein full
information on the Cepheids described in Maoz et al. 1999. Using the refined
Key Project techniques and calibrations, we determine the distance modulus of
NGC 4258 to be 29.47 +/- 0.09 mag (unique to this determination) +/- 0.15 mag
(systematic uncertainties in Key Project distances), corresponding to a metric
distance of 7.8 +/- 0.3 +/- 0.5 Mpc and 1.2 sigma from the maser distance of
7.2 +/- 0.5 Mpc. We also test the alternative Cepheid P-L relations of Feast
(1999), which yield more discrepant results. Additionally, we place weak limits
upon the distance to the LMC and upon the effect of metallicity in Cepheid
distance determinations.Comment: 26 pages in emulateapj5 format, including 6 figures and 5 tables.
Accepted for publication in the Astrophysical Journa
Comparing and calibrating black hole mass estimators for distant active galactic nuclei
Black hole mass is a fundamental property of active galactic nuclei (AGNs).
In the distant universe, black hole mass is commonly estimated using the MgII,
Hbeta, or Halpha emission line widths and the optical/UV continuum or line
luminosities, as proxies for the characteristic velocity and size of the
broad-line region. Although they all have a common calibration in the local
universe, a number of different recipes are currently used in the literature.
It is important to verify the relative accuracy and consistency of the recipes,
as systematic changes could mimic evolutionary trends when comparing various
samples. At z=0.36, all three lines can be observed at optical wavelengths,
providing a unique opportunity to compare different empirical recipes. We use
spectra from the Keck Telescope and the Sloan Digital Sky Survey to compare
black hole mass estimators for a sample of nineteen AGNs at this redshift. We
compare popular recipes available from the literature, finding that mass
estimates can differ up to 0.38+-0.05 dex in the mean (or 0.13+-0.05 dex, if
the same virial coefficient is adopted). Finally, we provide a set of 30
internally self consistent recipes for determining black hole mass from a
variety of observables. The intrinsic scatter between cross-calibrated recipes
is in the range 0.1-0.3 dex. This should be considered as a lower limit to the
uncertainty of the black hole mass estimators.Comment: ApJ in press, 11 pages, 10 figure
Measuring supermassive black holes with gas kinematics - II. The LINERs IC 989, NGC 5077, and NGC 6500
We present results from a kinematical study of the gas in the nucleus of a
sample of three LINER galaxies, obtained from archival HST/STIS long-slit
spectra. We found that, while for the elliptical galaxy NGC 5077, the observed
velocity curves are consistent with gas in regular rotation around the galaxy's
center, this is not the case for the two remaining objects. By modeling the
surface brightness distribution and rotation curve from the emission lines in
NGC 5077, we found that the observed kinematics of the circumnuclear gas can be
accurately reproduced by adding to the stellar mass component a black hole mass
of M_bh = 6.8 (-2.8,+4.3) 10**8 M_sun (uncertainties at a 1 sigma level); the
radius of its sphere of influence (R_sph ~ 0".34) is well-resolved at the HST
resolution. The BH mass estimate in NGC 5077 is in fairly good agreement with
both the M_bh-M_bul (with an upward scatter of ~ 0.4 dex) and M_bh-sigma
correlations (with an upward scatter of 0.5 dex in the Tremaine et al. form and
essentially no scatter using the Ferrarese et al. form) and provides further
support for the presence of a connection between the ``residuals'' from the
M_bh-sigma correlation and the bulge effective radius. This indicates the
presence of a black hole's ``fundamental plane'' in the sense that a
combination of at least sigma and R_e drives the correlations between M_bh and
host bulge properties.Comment: Accepted for publication in A&
The Gemini spectral library of near-IR late type stellar templates and its application for velocity dispersion measurements
We present a spectroscopic library of late spectral type stellar templates in
the near-IR range 2.15-2.42microns, at R=5300-5900 resolution, oriented to
support stellar kinematics studies in external galaxies, such as the direct
determination of the masses of supermassive black-holes in nearby active (or
non-active) galaxies. The combination of high spectral resolution and
state-of-the-art instrumentation available in 8-m class telescopes has made the
analysis of circumnuclear stellar kinematics using the near-IR CO band heads
one of the most used techniques for such studies, and this library aims to
provide the supporting datasets required by the higher spectral resolution and
larger spectral coverage currently achieved with modern near-IR spectrographs.
Examples of the application for kinematical analysis are given for data
obtained with two Gemini instruments, but the templates can be easily adjusted
for use with other near-IR spectrographs at similar or lower resolution. The
example datasets are also used to revisit the "template mismatch" effect and
the dependence of the velocity dispersion values obtained from the fitting
process with the characteristics of the stellar templates. The library is
available in electronic form from the Gemini web pages (link above).Comment: To appear in the ApJ Supplement Series, December 2009. AASTex, 25
pages, 17 figures. The library spectra are available in standard FITS format
from the Gemini Observatory webpage at
http://www.gemini.edu/sciops/instruments/nearir-resources/?q=node/1016
Faint dwarf galaxies in the Next Generation Virgo cluster Survey
The Next Generation Virgo Cluster Survey (NGVS) is a CFHT Large Program that
is using the wide field of view capabilities of the MegaCam camera to map the
entire Virgo Cluster from its core to virial radius. The observing strategy has
been optimized to detect very low surface brightness structures in the cluster,
including intracluster stellar streams and faint dwarf spheroidal galaxies. We
present here the current status of this ongoing survey, with an emphasis on the
detection and analysis of the very low-mass galaxies in the cluster that have
been revealed by the NGVS.Comment: 6 pages, 2 figures, Conference Proceedings: "A Universe of Dwarf
Galaxies", 14-18 June 2010, Lyon, Franc
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