1,374 research outputs found
Evidence for a mass-dependent AGN Eddington ratio distribution via the flat relationship between SFR and AGN luminosity
The lack of a strong correlation between AGN X-ray luminosity (L X ; a proxy for AGN power) and the star formation rate (SFR) of their host galaxies has recently been attributed to stochastic AGNvariability. Studies using population synthesis models have incorporated this by assuming a broad, universal (i.e. does not depend on the host galaxy properties) probability distribution for AGN specific X-ray luminosities (i.e. the ratio of L X to host stellar mass; a common proxy for Eddington ratio). However, recent studies have demonstrated that this universal Eddington ratio distribution fails to reproduce the observed X-ray luminosity functions beyond z ~ 1.2. Furthermore, empirical studies have recently shown that the Eddington ratio distribution may instead depend upon host galaxy properties, such as SFR and/or stellarmass. To investigate this further, we develop a population synthesis model in which the Eddington ratio distribution is different for star-forming and quiescent host galaxies. We showthat, although this model is able to reproduce the observed X-ray luminosity functions out to z ~ 2, it fails to simultaneously reproduce the observed flat relationship between SFR and X-ray luminosity. We can solve this, however, by incorporating a mass dependency in the AGN Eddington ratio distribution for starforming host galaxies. Overall, our models indicate that a relative suppression of low Eddington ratios (λ Edd < ~0.1) in lower mass galaxies (M * < ~10 10-11 Mâ) is required to reproduce both the observed X-ray luminosity functions and the observed flat SFR/X-ray relationship
The Incidence of X-ray selected AGN in Nearby Galaxies
We present the identification and analysis of an unbiased sample of AGN that
lie within the local galaxy population. Using the MPA-JHU catalogue (based on
SDSS DR8) and 3XMM DR7 we define a parent sample of 25,949 local galaxies (). After confirming that there was strictly no AGN light
contaminating stellar mass and star-formation rate calculations, we identified
917 galaxies with central, excess X-ray emission likely originating from an
AGN. We analysed their optical emission lines using the BPT diagnostic and
confirmed that such techniques are more effective at reliably identifying
sources as AGN in higher mass galaxies: rising from 30% agreement in the lowest
mass bin to 93% in the highest. We then calculated the growth rates of the
black holes powering these AGN in terms of their specific accretion rates
(). Our sample exhibits a wide range of accretion rates, with
the majority accreting at rates of their Eddington luminosity.
Finally, we used our sample to calculate the incidence of AGN as a function of
stellar mass and redshift. After correcting for the varying sensitivity of
3XMM, we split the galaxy sample by stellar mass and redshift and investigated
the AGN fraction as a function of X-ray luminosity and specific black hole
accretion rate. From this we found the fraction of galaxies hosting AGN above a
fixed specific accretion rate limit of is constant (at ) over stellar masses of and increases
(from to ) with redshift.Comment: 18 pages, 10 figures, 2 appendices. Accepted for publication in MNRA
Cohort Profile: The Mater-University of Queensland Study of Pregnancy (MUSP)
How did the study come about? At the initiative of three hospital-based obstetricians one of the authors (JMN) and another sociologist attended a 1978 meeting to explore the potential for collaborative research. No specific project was proposed by the obstetricians. Two of the obstetricians had been trained in Scotland; one in Aberdeen where he had had some familiarity with the work of obstetrician Dugald Baird and sociologist Raymond Illsely. The obstetricians argued for an agenda which was clinically oriented. The two sociologists were more focussed on understanding how some social constructs (e.g. social class) might be relevant to explaining health outcomes. The initial year of the study was characterised by frequent (at least weekly) meetings at which the aims and substance of the proposed study were debated vigorously. As an initial decision the team focused on factors associated with adverse pregnancy outcomes. The first major project was to be a 3-5 year longitudinal study of pregnant women which would include a 6-month child post-natal follow-up as the main outcome of interest
PRIMUS + DEEP2: Clustering of X-ray, Radio and IR-AGN at z~0.7
We measure the clustering of X-ray, radio, and mid-IR-selected active
galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and
spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7
separate fields spanning ~10 square degrees. Using the cross-correlation of AGN
with dense galaxy samples, we measure the clustering scale length and slope, as
well as the bias, of AGN selected at different wavelengths. Similar to previous
studies, we find that X-ray and radio AGN are more clustered than
mid-IR-selected AGN. We further compare the clustering of each AGN sample with
matched galaxy samples designed to have the same stellar mass, star formation
rate, and redshift distributions as the AGN host galaxies and find no
significant differences between their clustering properties. The observed
differences in the clustering of AGN selected at different wavelengths can
therefore be explained by the clustering differences of their host populations,
which have different distributions in both stellar mass and star formation
rate. Selection biases inherent in AGN selection, therefore, determine the
clustering of observed AGN samples. We further find no significant difference
between the clustering of obscured and unobscured AGN, using IRAC or WISE
colors or X-ray hardness ratio.Comment: Accepted to ApJ. 23 emulateapj pages, 15 figures, 4 table
The Nustar Extragalactic Surveys: Initial Results and Catalog from the Extended Chandra Deep Field South
We present initial results and the source catalog from the NuSTAR survey of the Extended Chandra Deep Field South (hereafter, ECDFS) - currently the deepest contiguous component of the NuSTAR extragalactic survey program. The survey covers the full ~30 arcmin x 30 arcmin area of this field to a maximum depth of ~360 ks (~220 ks when corrected for vignetting at 3-24 keV), reaching sensitivity limits of ~1.3 x 10^-14 erg/cm2/s (3-8 keV), ~3.4 x 10^-14 erg/cm2/s (8-24 keV) and ~3.0 x 10^-14 erg/cm2/s (3-24 keV). Fifty four (54) sources are detected over the full field, although five of these are found to lie below our significance threshold once contaminating flux from neighboring (i.e., blended) sources is taken into account. Of the remaining 49 that are significant, 19 are detected in the 8-24 keV band. The 8-24 keV to 3-8 keV band ratios of the twelve sources that are detected in both bands span the range 0.39-1.7, corresponding to a photon index range of Gamma ~ 0.5-2.3, with a median photon index of 1.70 +/- 0.52. The redshifts of the 49 sources in our main sample span the range z = 0.21-2.7, and their rest-frame 10-40 keV luminosities (derived from the observed 8-24 keV fluxes) span the range L(10-40 keV) ~ (0.7-300) x 10^43 erg/s, sampling below the knee of the X-ray luminosity function out to z ~ 0.8-1. Finally, we identify one NuSTAR source that has neither a Chandra nor an XMM-Newton counterpart, but that shows evidence of nuclear activity at infrared wavelengths, and thus may represent a genuine, new X-ray source detected by NuSTAR in the ECDFS
PRIMUS: Galaxy Clustering as a Function of Luminosity and Color at 0.2<z<1
We present measurements of the luminosity and color-dependence of galaxy
clustering at 0.2<z<1.0 in the PRIsm MUlti-object Survey (PRIMUS). We quantify
the clustering with the redshift-space and projected two-point correlation
functions, xi(rp,pi) and wp(rp), using volume-limited samples constructed from
a parent sample of over 130,000 galaxies with robust redshifts in seven
independent fields covering 9 sq. deg. of sky. We quantify how the
scale-dependent clustering amplitude increases with increasing luminosity and
redder color, with relatively small errors over large volumes. We find that red
galaxies have stronger small-scale (0.1<rp<1 Mpc/h) clustering and steeper
correlation functions compared to blue galaxies, as well as a strong color
dependent clustering within the red sequence alone. We interpret our measured
clustering trends in terms of galaxy bias and obtain values between
b_gal=0.9-2.5, quantifying how galaxies are biased tracers of dark matter
depending on their luminosity and color. We also interpret the color dependence
with mock catalogs, and find that the clustering of blue galaxies is nearly
constant with color, while redder galaxies have stronger clustering in the
one-halo term due to a higher satellite galaxy fraction. In addition, we
measure the evolution of the clustering strength and bias, and we do not detect
statistically significant departures from passive evolution. We argue that the
luminosity- and color-environment (or halo mass) relations of galaxies have not
significantly evolved since z=1. Finally, using jackknife subsampling methods,
we find that sampling fluctuations are important and that the COSMOS field is
generally an outlier, due to having more overdense structures than other
fields; we find that 'cosmic variance' can be a significant source of
uncertainty for high-redshift clustering measurements.Comment: 22 pages, 21 figures, matches version published in Ap
Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties
We revisited the problem of the stability of the superconducting state in
RbxWO3 and identified the main causes of the contradictory data previously
published. We have shown that the ordering of the Rb vacancies in the
nonstoichiometric compounds have a major detrimental effect on the
superconducting temperature Tc.The order-disorder transition is first order
only near x = 0.25, where it cannot be quenched effectively and Tc is reduced
below 1K. We found that the high Tc's which were sometimes deduced from
resistivity measurements, and attributed to compounds with .25 < x < .30, are
to be ascribed to interfacial superconductivity which generates spectacular
non-linear effects. We also clarified the effect of acid etching and set more
precisely the low-rubidium-content boundary of the hexagonal phase.This work
makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we
approach this boundary (x = 0.20), if no ordering would take place - as its is
approximately the case in CsxWO3. This behaviour is reminiscent of the
tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism
is responsible for this large increase of Tc despite the considerable
associated reduction of the electron density of state ? By reviewing the other
available data on these bronzes we conclude that the theoretical models which
are able to answer this question are probably those where the instability of
the lattice plays a major role and, particularly, the model which call upon
local structural excitations (LSE), associated with the missing alkali atoms.Comment: To be published in Physical Review
- âŠ