4,400 research outputs found
Radio Galaxy populations and the multi-tracer technique: pushing the limits on primordial non-Gaussianity
We explore the use of different radio galaxy populations as tracers of
different mass halos and therefore, with different bias properties, to
constrain primordial non-Gaussianity of the local type. We perform a Fisher
matrix analysis based on the predicted auto and cross angular power spectra of
these populations, using simulated redshift distributions as a function of
detection flux and the evolution of the bias for the different galaxy types
(Star forming galaxies, Starburst galaxies, Radio-Quiet Quasars, FRI and FRII
AGN galaxies). We show that such a multi-tracer analysis greatly improves the
information on non-Gaussianity by drastically reducing the cosmic variance
contribution to the overall error budget. By using this method applied to
future surveys, we predict a constraint of sigma_fnl=3.6 on the local
non-Gaussian parameter for a galaxy detection flux limit of 10 \muJy and
sigma_fnl=2.2 for 1 \muJy. We show that this significantly improves on the
constraints obtained when using the whole undifferentiated populations
(sigma_fnl=48 for 10 \muJy and sigma_fnl=12 for 1 \muJy). We conclude that
continuum radio surveys alone have the potential to constrain primordial
non-Gaussianity to an accuracy at least a factor of two better than the present
constraints obtained with Planck data on the CMB bispectrum, opening a window
to obtain sigma_fnl~1 with the Square Kilometer Array.Comment: 9 pages, 5 figures, submitted to MNRA
Probing the Complex and Variable X-ray Absorption of Markarian 6 with XMM-Newton
We report on an X-ray observation of the Seyfert 1.5 galaxy Mrk 6 obtained
with the EPIC instruments onboard XMM-Newton. Archival BeppoSAX PDS data from
18-120 keV were also used to constrain the underlying hard power-law continuum.
The results from our spectral analyses generally favor a double
partial-covering model, although other spectral models such as absorption by a
mixture of partially ionized and neutral gas cannot be firmly ruled out. Our
best-fitting model consists of a power law with a photon index of 1.81+/-0.20
and partial covering with large column densities up to 10^{23} cm**-2. We also
detect a narrow emission line consistent with Fe Kalpha fluorescence at
6.45+/-0.04 keV with an equivalent width of ~93+/-25 eV. Joint analyses of
XMM-Newton, ASCA, and BeppoSAX data further provide evidence for both spectral
variability (a factor of ~2 change in absorbing column) and
absorption-corrected flux variations (by ~60%) during the ~4 year period probed
by the observations.Comment: 7 pages, 2 figures. accepted for publication in the Astronomical
Journa
Resonant Absorption in the AGN spectra emerging from photoionized gas: differences between steep and flat ionizing continua
We present photoionization models accounting for both photoelectric and
resonant absorption. Resonance absorption lines from C, O, Ne, Mg, Si S and Fe
between 0.1 and 10 keV are treated. In particular we consider the complex of
almost 60 strong Fe L absorption lines around 1 keV. We calculate profiles,
intensities and equivalent widths of each line, considering both Doppler and
natural broadening mechanisms. Doppler broadening includes a term accounting
for turbulence of the gas along the line of sight. We computed spectra
transmitted by gas illuminated by drastically different ionizing continua and
compared them to spectra observed in flat X-ray spectrum, broad optical
emission line type 1 AGN, and steep X-ray spectrum, narrow optical emission
line type 1 AGN. We show that the keV absorption feature observed in
moderate resolution X-ray spectra of several Narrow Line Seyfert 1 galaxies can
be explained by photoionization models, taking into account for resonance
absorption, without requiring relativistic outflowing velocities of the gas, if
the physical properties of these absorbers are close to those found in flat
X-ray spectrum Seyfert 1 galaxies.Comment: 22 pages, 10 figures. Accepted for publication on Ap
A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548
We report the spectral analysis of a long XMM-Newton observation of the
well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The
source was at an historically average brightness and we find the hard (3-10
keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75,
together with reflection. The only feature in the hard X-ray spectrum is a
narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The
energy and strength of this line is consistent with fluorescence from `neutral'
iron distant from the central continuum source. We find no evidence for a broad
Fe K line, with an upper limit well below previous reports, suggesting the
inner accretion disc is now absent or highly ionised. The addition of
simultaneous BeppoSAX data allows the analysis to be extended to 200 keV,
yielding important constraints on the total reflection. Extrapolation of the
hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7
keV. After due allowance for the effects of a complex warm absorber, measured
with the XMM-Newton RGS, we find the soft excess is better described as a
smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess
can be modelled either by Comptonised thermal emission or by enhanced
reflection from the surface of a highly ionised disc.Comment: 9 pages, 11 figures, accepted by MNRAS; minor changes to text and
figure
Line Emission from an Accretion Disk around a Black hole: Effects of Disk Structure
The observed iron K-alpha fluorescence lines in Seyfert-1 galaxies provide
strong evidence for an accretion disk near a supermassive black hole as a
source of the line emission. These lines serve as powerful probes for examining
the structure of inner regions of accretion disks. Previous studies of line
emission have considered geometrically thin disks only, where the gas moves
along geodesics in the equatorial plane of a black hole. Here we extend this
work to consider effects on line profiles from finite disk thickness, radial
accretion flow and turbulence. We adopt the Novikov and Thorne (1973) solution,
and find that within this framework, turbulent broadening is the dominant new
effect. The most prominent change in the skewed, double-horned line profiles is
a substantial reduction in the maximum flux at both red and blue peaks. The
effect is most pronounced when the inclination angle is large, and when the
accretion rate is high. Thus, the effects discussed here may be important for
future detailed modeling of high quality observational data.Comment: 21 pages including 8 figures; LaTeX; ApJ format; accepted by ApJ;
short results of this paper appeared before as a conference proceedings
(astro-ph/9711214
Angular momentum evolution of young low-mass stars and brown dwarfs: observations and theory
This chapter aims at providing the most complete review of both the emerging
concepts and the latest observational results regarding the angular momentum
evolution of young low-mass stars and brown dwarfs. In the time since
Protostars & Planets V, there have been major developments in the availability
of rotation period measurements at multiple ages and in different star-forming
environments that are essential for testing theory. In parallel, substantial
theoretical developments have been carried out in the last few years, including
the physics of the star-disk interaction, numerical simulations of stellar
winds, and the investigation of angular momentum transport processes in stellar
interiors. This chapter reviews both the recent observational and theoretical
advances that prompted the development of renewed angular momentum evolution
models for cool stars and brown dwarfs. While the main observational trends of
the rotational history of low mass objects seem to be accounted for by these
new models, a number of critical open issues remain that are outlined in this
review.Comment: 22 pages, 8 figures, accepted for publication in Protostars & Planets
VI, 2014, University of Arizona Press, eds. H. Beuther, R. Klessen, K.
Dullemond, Th. Hennin
The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848
IGR J16318-4848 is the prototype and one of the more extreme examples of the
new class of highly obscured Galactic X-ray sources discovered by INTEGRAL. A
monitoring campaign on this source has been carried out by XMM-Newton and
INTEGRAL, consisting in three simultaneous observations performed in February,
March and August 2004. The long-term variability of the Compton-thick
absorption and emission line complexes will be used to probe the properties of
the circumstellar matter. A detailed timing and spectral analysis of the three
observations is performed, along with the reanalysis of the XMM-Newton
observation performed in February 2003. The results are compared with
predictions from numerical radiative transfer simulations to derive the
parameters of the circumstellar matter. Despite the large flux dynamic range
observed (almost a factor 3 between observations performed a few months apart),
the source remained bright (suggesting it is a persistent source) and
Compton-thick (NH >1.2x10^24 cm-2). Large Equivalent Width (EW) emission lines
from Fe Kalpha, Fe Kbeta and Ni Kalpha were present in all spectra. The
addition of a Fe Kalpha Compton Shoulder improves the fits, especially in the
2004 observations. Sporadic occurrences of rapid X-ray flux risings were
observed in three of the four observations. The Fe Kalpha light curve followed
the continuum almost instantaneously, suggesting that the emission lines are
produced by illumination of small-scale optically-thick matter around the
high-energy continuum source. Using the iron line EW and Compton Shoulder as
diagnostic of the geometry of the matter, we suggest that the obscuring matter
is in a flattened configuration seen almost edge-on.Comment: accepted by Astronomy and Astrophysic
Handgun carrying among white youth increasing in the United States: new evidence from the national survey on drug use and health 2002–2013
The objective of the present study was to examine trends and correlates of handgun carrying among adolescents ages 12–17 in the United States. Data was derived from the National Survey on Drug Use and Health (NSDUH) involving non-Hispanic White, African American, and Hispanic respondents ages 12–17 (n = 197,313) and spanning the years 2002–2013. Logistic regression was used to examine significance of trend year and correlates of previous 12-month handgun carrying. The overall self-reported prevalence of handgun carrying was 3.4%. The prevalence of handgun carrying during 2004–2005 was significantly higher for African-Americans (4.39%) compared to non-Hispanic Whites (3.03%). However, by 2012–2013, non-Hispanic Whites (4.08%) completely diverged and reported carrying handguns significantly more than both African-American (2.96%) and Hispanic (2.82%) youth. Male gender and a number of externalizing behaviors were significant correlates of handgun carrying; however, we also found evidence of differential correlates with regard to such factors as drug selling, parental affirmation, and income by race/ethnicity. To our knowledge, this is the largest study of handgun carrying among youth in the United States. Findings indicate that although at historically low levels handgun carrying is on the rise but only among non-Hispanic Whites. Differential correlates among racial/ethnic groups suggest prevention programming and policies may need modifications depending on group and geographic locale targeted.R25 DA030310 - National Institute on Drug Abuse at the National Institutes of Healt
The Seyfert-Starburst Connection in X-rays. II. Results and Implications
We present the results of X-ray imaging and spectroscopic analysis of a
sample of Seyfert 2 galaxies that contain starbursts, based on their optical
and UV characteristics. These composite galaxies exhibit extended, soft,
thermal X-ray emission, which we attribute to their starburst components.
Comparing their X-ray and far-infrared properties with ordinary Seyfert and
starburst galaxies, we identify the spectral characteristics of their various
intrinsic emission sources. The observed far-infrared emission of the composite
galaxies may be associated almost exclusively with star formation, rather than
the active nucleus. The ratio of the hard X-ray luminosity to the far-infrared
and [O III] 5007 luminosity distinguishes most of these composite galaxies from
``pure'' Seyfert 2 galaxies, while their total observed hard X-ray luminosity
distinguishes them from ``pure'' starbursts. The hard nuclear X-ray source is
generally heavily absorbed (N_H > 10^{23} cm^{-2}) in the composite galaxies.
Based on these results, we suggest that the interstellar medium of the nuclear
starburst is a significant source of absorption. The majority of the sample are
located in groups or are interacting with other galaxies, which may trigger the
starburst or allow rapid mass infall to the central black hole, or both. We
conclude that starbursts are energetically important in a significant fraction
of active galaxies, and starbursts and active galactic nuclei may be part of a
common evolutionary sequence.Comment: 16 pages including 8 figures and 5 tables; to appear in the ApJ, Mar.
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