459 research outputs found
Cultural distance and the permanence of acquired CEOs in crossâborder highâtech acquisitions: combining the acquirer's and CEO's perspectives
The cultural distance between the acquiring and acquired firms is a double-edged sword in
cross-border high-tech acquisitions. It magnifies the âcombination potentialâ of the acquisition
but also poses severe integration challenges. Scholars have highlighted that the retention
of acquired CEOs in combined entities is an effective integration action to address
these challenges but have generally considered it from the acquiring firmsâ perspective only.
In this study, we also take into account the acquired CEOsâ perspective and find that the
permanence of acquired CEOs in the post-acquisition organization depends on the balance
between the acquiring firmsâ incentives to retain the acquired CEOs and the acquired
CEOsâ opportunity costs to remain in the company. Specifically, we argue that both sides
increase with the cultural distance between the acquiring and acquired firms and that the
acquired CEOsâ personal characteristics and context-specific conditions also influence this
balance. We test our hypotheses using a sample of 447 cross-border acquisitions of small
high-tech firms by large listed firms between 2001 and 2014. Our findings confirm our
expectations and highlight the role of micro-foundational characteristics in shaping the
effect of key macro-level factors on the integration of high-tech acquisitions in international
contexts
AGN counts at 15um. XMM observations of the ELAIS-S1-5 sample
Context: The counts of galaxies and AGN in the mid infra-red (MIR) bands are
important instruments for studying their cosmological evolution. However, the
classic spectral line ratios techniques can become misleading when trying to
properly separate AGN from starbursts or even from apparently normal galaxies.
Aims: We use X-ray band observations to discriminate AGN activity in
previously classified MIR-selected starburst galaxies and to derive updated
AGN1 and (Compton thin) AGN2 counts at 15 um.
Methods: XMM observations of the ELAIS-S1 15um sample down to flux limits
~2x10^-15 erg cm^-2 s^-1 (2-10 keV band) were used. We classified as AGN all
those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that
~10^42 erg/s.
Results: We find that at least about 13(+/-6) per cent of the previously
classified starburst galaxies harbor an AGN. According to these figures, we
provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15
um. It turns out that at least 24% of the extragalactic sources brighter than
0.6 my at 15 um are AGN (~13% contribution to the extragalactic background
produced at fluxes brighter than 0.6 mJy).Comment: Accepted for publication on A&
X-ray absorption in Compton-thin AGN: the predictions of a model revisited
The evidence of a decrease with increasing luminosity of the fraction f_{abs}
of absorbed and Compton-thin among X-ray (2-10 keV) selected AGN is
observationally rather well supported, while that of an increase of f_{abs}
with redshift is rather controversial. In Lamastra, Perola & Matt (2006) the
gravitational effect of the SMBH on the molecular interstellar gas, in the
central region of the host galaxy, was shown to predict an anti-correlation
between f_{abs} and M_{BH}. The most recent findings on the distribution of the
Eddington ratio \lambda=L_b/L_E as a function of M_{BH} and z are used to
convert that relationship into one between f_{abs} and both bolometric (L_b)
and X-ray (L_X) luminosities at various values of z. The findings on
\lambda(M_{BH},z) are properly treated in order to ensure completeness in the
prediction of f_{abs} above a certain luminosity, at values of z=0.1, 0.35, 0.7
and >1. To verify the consequence of these findings alone, we adopted in a
first istance a distribution of gas surface density \Sigma, observed in a
sample of local spiral galaxies, irrespective of the galaxy morphological type
and z. Assuming in the \lambda(M_{BH},z) distribution the Eddington limit,
\lambda=1, as a ``natural'' cut-off, the predictions are consistent with the
existence of an anti-correlation between f_{abs} and L_X, but fail to reproduce
an increase of f_{abs} with z. Because the early type galaxies on average are
much poorer in molecular gas than late type ones, a quantitative agreement with
the local value of f_{abs} requires the existence of a correlation between
\Sigma and the central activity. An increase of typical values of \Sigma with
z, correlated with the activity, might explain an increase of f_{abs} with z.
However, at the highest luminosities f_{abs} could hardly exceed about 0.3.Comment: 12 pages, 12 figures, accepted for publication in A&
A possible bias on the estimate of Lbol/Ledd in AGN as a function of luminosity and redshift
The BH mass (and the related Eddington ratio) in broad line AGN is usually
evaluated by combining estimates (often indirect) of the BLR radius and of the
FWHM of the broad lines, under the assumption that the BLR clouds are in
Keplerian motion around the BH. Such an evaluation depends on the geometry of
the BLR. There are two major options for the BLR configuration: spherically
symmetric or ``flattened''. In the latter case the inclination to the line of
sight becomes a relevant parameter. This paper is devoted to evaluate the bias
on the estimate of the Eddington ratio when a spherical geometry is assumed
(more generally when inclination effects are ignored), while the actual
configuration is ``flattened'', as some evidence suggests. This is done as a
function of luminosity and redshift, on the basis of recent results which show
the existence of a correlation between the fraction of obscured AGN and these
two parameters up to at least z=2.5. The assumed BLR velocity field is akin to
the ``generalized thick disk'' proposed by Collin et al. (2006). Assuming an
isotropic orientation in the sky, the mean value of the bias is calculated as a
function of luminosity and redshift. It is demonstrated that, on average, the
Eddington ratio obtained assuming a spherical geometry is underestimated for
high luminosities, and overestimated for low luminosities. This bias converges
for all luminosities at z about 2.7, while nothing can be said on this bias at
larger redshifts due to the lack of data. The effects of the bias, averaged
over the luminosity function of broad line AGN, have been calculated. The
results imply that the bias associated with the a-sphericity of the BLR make
even worse the discrepancy between the observations and the predictions of
evolutionary models.Comment: 6 pages, 3 figures, accepted for publication in A&
Suzaku observation of the Phoenix Galaxy
In recent years, several Seyfert 2 galaxies have been discovered that change
state when observed in X-rays a few years apart, switching from Compton-thin to
reflection-dominated or viceversa. We observed a member of this class of
"Changing-look" sources, the Phoenix Galaxy, with Suzaku, with the aim of
better understanding the nature of the variations. The Suzaku spectrum was
analyzed, and the results compared with previous ASCA and XMM-Newton
observations. The source was caught in a Compton-thin state, as in XMM-Newton,
but differently from ASCA. Comparing the Suzaku and XMM-Newton observations, a
variation in the column density of the absorber on a time scale of years is
discovered. A similar change, but on much shorter time scales (i.e. ks) may
also explain the count-rate variations during the Suzaku observations. A soft
excess is also present, likely due to continuum and line emission from
photoionized circumnuclear matter.Comment: Accepted for publication in Astronomy & Astrophysic
On the Iwasawa-Taniguchi effect of radio-quiet AGN
The existence of an anti-correlation between the Equivalent Width (EW) of the
neutral narrow core of the iron Kalpha emission line and the 2-10 keV
luminosity (the so-called `X-ray Baldwin' or `Iwasawa-Taniguchi' effect) has
been debated in the last years. We aim at testing this claim on the largest
catalogue of radio quiet AGN high-quality X-ray spectra ever published. The
final sample comprises 157 objects. We search for a relation of the iron line
EW not only with the X-ray luminosity, but also with the Black Hole mass, the
Eddington ratio and the cosmological distance. The data presented here were
analyzed homogeneously, all spectra are from the same instrument and with high
Signal-to-Noise Ratio. A linear censored fit on the EW versus 2-10 keV
luminosity is highly significant and yields , where is the EW of the neutral iron
Kalpha line in eV and is the 2-10 keV X-ray luminosity in units of
erg s. The anti-correlation with the Eddington ratio is also
very significant, while no dependence of the iron EW on the BH mass is
apparent.Comment: 4 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics Letter
The bolometric luminosity of type 2 AGN from extinction-corrected [OIII]: no evidence for Eddington-limited sources
There have been recent claims that a significant fraction of type 2 AGN
accrete close or even above the Eddington limit. In type 2 AGN the bolometric
luminosity (L_b) is generally inferred from the [OIII] emission line luminosity
(L_OIII). The key issue, in order to estimate the bolometric luminosity in
these AGN, is therefore to know the bolometric correction to be applied to
L_OIII. A complication arises from the fact that the observed L_OIII is
affected by extinction, likely due to dust within the narrow line region. The
extinction-corrected [OIII] luminosity (L^c_OIII) is a better estimator of the
nuclear luminosity than L_OIII. However, so far only the bolometric correction
to be applied to the uncorrected L_OIII has been evaluated. This paper is
devoted to estimate the bolometric correction C_OIII=L_b/L^c_OIII in order to
derive the Eddington ratios for the type 2 AGN in a sample of SDSS objects. We
have collected from the literature 61 sources with reliable estimate of both
L^c_OIII and X-ray luminosities (L_X). To estimate C_OIII, we combined the
observed correlation between L^c_OIII and L_X with the X-ray bolometric
correction. We found, contrary to previous studies, a linear correlation
between L^c_OIII and L_X. We estimated C_OIII using the luminosity-dependent
X-ray bolometric correction of Marconi et al. (2004), and we found a mean value
of C_OIII in the luminosity ranges log L_OIII=38-40, 40-42, and 42-44 of 87,
142 and 454 respectively. We used it to calculate the Eddington ratio
distribution of type 2 SDSS AGN at 0.3<z<0.4 and we found that these sources
are not accreting near their Eddington limit, contrary to previous claims.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Average absorbed breast dose (2ABD): an easy radiation dose index for digital breast tomosynthesis
Background: To propose a practical and simple method to individually evaluate the average absorbed dose for digital breast tomosynthesis. Methods: The method is based on the estimate of incident air kerma (ka,i) on the breast surface. An analytical model was developed to calculate the ka,i from the tube voltage, tube load, breast thickness, x-ray tube yield, and anode-filter combination. A homogeneous phantom was employed to simulate the breast in experimental measurements and to assess the dose-depth relationship. The ka,i values were employed to calculate the âaverage absorbed breast doseâ (2ABD) index. Four mammographic units were used to develop and test our method under many conditions close to clinical settings. The average glandular dose (AGD) calculated following the method described by Dance et al., and the 2ABD computed through our method (i.e., from the exposure parameters) were compared in a number of conditions. Results: A good agreement was obtained between the ka,i computed through our model and that measured under different clinical conditions: discrepancies < 6% were found in all conditions. 2ABD matches with a good accuracy the AGD for a 100% glandular-breast: the minimum, maximum, and mean differences were < 0.1%, 7%, and 2.4%, respectively; the discrepancies increase with decreasing breast glandularity. Conclusions: The proposed model, based on only few exposure parameters, represents a simple way to individually calculate an index, 2ABD, which can be interpreted as the average absorbed dose in a homogeneous phantom, approximating a 100% glandular breast. The method could be easily implemented in any mammographic device performing DBT
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