1,696 research outputs found
The Spatial Clustering of ROSAT All-Sky Survey AGN: I. The cross-correlation function with SDSS Luminous Red Galaxies
We investigate the clustering properties of ~1550 broad-line active galactic
nuclei (AGNs) at =0.25 detected in the ROSAT All-Sky Survey (RASS) through
their measured cross-correlation function with ~46,000 Luminous Red Galaxies
(LRGs) in the Sloan Digital Sky Survey. By measuring the cross-correlation of
our AGN sample with a larger tracer set of LRGs, we both minimize shot noise
errors due to the relatively small AGN sample size and avoid systematic errors
due to the spatially varying Galactic absorption that would affect direct
measurements of the auto-correlation function (ACF) of the AGN sample.
The measured ACF correlation length for the total RASS-AGN sample
(=1.5 x 10^(44) erg/s) is r_0=4.3^{+0.4}_{-0.5} h^(-1) Mpc and
the slope \gamma=1.7^{+0.1}_{-0.1}. Splitting the sample into low and high L_X
samples at L_(0.5-10 keV)=10^(44) erg/s, we detect an X-ray luminosity
dependence of the clustering amplitude at the ~2.5 \sigma level. The low L_X
sample has r_0=3.3^{+0.6}_{-0.8} h^(-1) Mpc (\gamma=1.7^{+0.4}_{-0.3}), which
is similar to the correlation length of blue star-forming galaxies at low
redshift. The high L_X sample has r_0=5.4^{+0.7}_{-1.0} h^(-1) Mpc
(\gamma=1.9^{+0.2}_{-0.2}), which is consistent with the clustering of red
galaxies. From the observed clustering amplitude, we infer that the typical
dark matter halo (DMH) mass harboring RASS-AGN with broad optical emission
lines is log (M_DMH/(h^(-1) M_SUN)) =12.6^{+0.2}_{-0.3}, 11.8^{+0.6}_{-\infty},
13.1^{+0.2}_{-0.4} for the total, low L_X, and high L_X RASS-AGN samples,
respectively.Comment: The Astrophysical Journal, 713, 558 (2010), 16 pages, 11 figures, 4
table
X-rays across the galaxy population - III. The incidence of AGN as a function of star formation rate
We map the co-eval growth of galaxies and their central supermassive black
holes in detail by measuring the incidence of Active Galactic Nuclei (AGN) in
galaxies as a function of star formation rate (SFR) and redshift (to z~4). We
combine large galaxy samples with deep Chandra X-ray imaging to measure the
probability distribution of specific black hole accretion rates (LX relative to
stellar mass) and derive robust AGN fractions and average specific accretion
rates. First, we consider galaxies along the main sequence of star formation.
We find a linear correlation between the average SFR and both the AGN fraction
and average specific accretion rate across a wide range in stellar mass () and to at least z~2.5, indicating that AGN in
main-sequence galaxies are driven by the stochastic accretion of cold gas. We
also consider quiescent galaxies and find significantly higher AGN fractions
than predicted, given their low SFRs, indicating that AGN in quiescent galaxies
are fuelled by additional mechanisms (e.g. stellar winds). Next, we bin
galaxies according to their SFRs relative to the main sequence. We find that
the AGN fraction is significantly elevated for galaxies that are still
star-forming but with SFRs below the main sequence, indicating further
triggering mechanisms enhance AGN activity within these sub-main-sequence
galaxies. We also find that the incidence of high-accretion-rate AGN is
enhanced in starburst galaxies and evolves more mildly with redshift than
within the rest of the galaxy population, suggesting mergers play a role in
driving AGN activity in such high-SFR galaxies.Comment: 19 pages, 15 figures. This is a pre-copyedited, author-produced
version of an article accepted for publication in MNRAS following peer revie
Clustering Measurements of broad-line AGNs: Review and Future
Despite substantial effort, the precise physical processes that lead to the
growth of super-massive black holes in the centers of galaxies are still not
well understood. These phases of black hole growth are thought to be of key
importance in understanding galaxy evolution. Forthcoming missions such as
eROSITA, HETDEX, eBOSS, BigBOSS, LSST, and Pan-STARRS will compile by far the
largest ever Active Galactic Nuclei (AGNs) catalogs which will allow us to
measure the spatial distribution of AGNs in the universe with unprecedented
accuracy. For the first time, AGN clustering measurements will reach a level of
precision that will not only allow for an alternative approach to answering
open questions in AGN/galaxy co-evolution but will open a new frontier,
allowing us to precisely determine cosmological parameters. This paper reviews
the large-scale clustering measurements of broad line AGNs. We summarize how
clustering is measured and which constraints can be derived from AGN clustering
measurements, we discuss recent developments, and we briefly describe future
projects that will deliver extremely large AGN samples which will enable AGN
clustering measurements of unprecedented accuracy. In order to maximize the
scientific return on the research fields of AGN/galaxy evolution and cosmology,
we advise that the community develop a full understanding of the systematic
uncertainties which will, in contrast to today's measurement, be the dominant
source of uncertainty.Comment: referred review article, paper is in print in Acta Polytechnica, 7
pages, 3 figure
Draft Genome Sequence of Rhizobium rhizogenes Strain ATCC 15834.
Here, we present the draft genome of Rhizobium rhizogenes strain ATCC 15834. The genome contains 7,070,307 bp in 43 scaffolds. R. rhizogenes, also known as Agrobacterium rhizogenes, is a plant pathogen that causes hairy root disease. This hairy root induction has been used in biotechnology for the generation of transgenic root cultures
Teaching science to deaf students: resources for teachers in kindergarten to fifth grade
Research indicates that many new teachers encounter hindrances to implementing the type of researched-based, state-of-the-art teaching methodologies for science instruction in the elementary grades, which they had learned about in their teacher preparation programs (Kane, 1994). Concerns have also been expressed about teacher preparation in the science education of deaf students (Lang & Propp, 1982; Lang, 1994, 1996). The present project is designed to assist new and inexperienced teachers in minimizing constraints to the implementation of an effective K-5 science curriculum, particularly in educational programs serving deaf students. In the present paper, some ofthe hindrances to implementing the best practices in K-5 science are described, including five critical issues for science education presented at a national conference held in 1994 (Lang, 1994& Egelston-Dodd, 1994). Secondly, some research-based considerations for effective teaching practices in general, in the field of science, and in the field of deaf education are presented. Finally, the results of a personal, mentored investigation of resources for new and current teachers interested in implementing research-based instructional programs in the K-5 classroom are offered as a supplementary web page to an educational web resource for teachers of both hearing and deaf students
Rebuilding Trust in the Financial Services Industry: Lessons for Human Resource Professionals
[Excerpt] Roger W. Ferguson, Jr., President and CEO of TIAA-CREF, delivered the Lewis H. Durland Memorial Lecture at the ILR School last October. Hosted by Cornell University’s S.C. Johnson Graduate School of Management, Ferguson’s lecture, entitled “Rebuilding Trust in the Financial Services Industry: The Way Forward,” highlighted a number of weaknesses concerning internal corporate governance that led to the financial crisis in 2008. To remedy these weaknesses and rebuild trust in the financial and service sectors, Ferguson outlined five key areas where HR can take a leading role: culture, compensation, communication to regulators, shareholder vs. customer interests, and retirement schemes
AGN clustering in the local Universe: an unbiased picture from Swift-BAT
We present the clustering measurement of hard X-ray selected AGN in the local
Universe. We used a sample of 199 sources spectroscopically confirmed detected
by Swift-BAT in its 15-55 keV all-sky survey. We measured the real space
projected auto-correlation function and detected a signal significant on
projected scales lower than 200 Mpc/h. We measured a correlation length of
r0=5.56+0.49-0.43 Mpc/h and a slope {\gamma}=1.64-0.08 -0.07. We also measured
the auto-correlation function of Type I and Type II AGN and found higher
correlation length for Type I AGN. We have a marginal evidence of luminosity
dependent clustering of AGN, as we detected a larger correlation length of
luminous AGN than that of low luminosity sources. The corresponding typical
host DM halo masses of Swift-BAT are log(MDMH) 12-14 h^-1 M/M_sun, depending on
the subsample. For the whole sample we measured log(MDMH)\sim 13.15 h-1 M/M_sun
which is the typical mass of a galaxy group. We estimated that the local AGN
population has a typical lifetime tau_AGN \sim 0.7 Gyr, it is powered by SMBH
with mass MBH \sim 1-10x10^8 M_\odot and accreting with very low efficiency,
log(epsilon)-2.0. We also conclude that local AGN host galaxies are typically
red-massive galaxies with stellar mass of the order 2-80x10^10 h^-1 M_sun. We
compared our results with clustering predictions of merger-driven AGN
triggering models and found a good agreement.Comment: 13 pages 3 figures, accepted by ApJ Letter
Tracing the Filamentary Structure of the Galaxy Distribution at z~0.8
We study filamentary structure in the galaxy distribution at z ~ 0.8 using
data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey
and its evolution to z ~ 0.1 using data from the Sloan Digital Sky Survey
(SDSS). We trace individual filaments for both surveys using the Smoothed
Hessian Major Axis Filament Finder, an algorithm which employs the Hessian
matrix of the galaxy density field to trace the filamentary structures in the
distribution of galaxies. We extract 33 subsamples from the SDSS data with a
geometry similar to that of DEEP2. We find that the filament length
distribution has not significantly changed since z ~ 0.8, as predicted in a
previous study using a \LamdaCDM cosmological N-body simulation. However, the
filament width distribution, which is sensitive to the non-linear growth of
structure, broadens and shifts to smaller widths for smoothing length scales of
5-10 Mpc/h from z ~ 0.8 to z ~ 0.1, in accord with N-body simulations.Comment: 10 pages, 8 figures, accepted for the publication in MNRA
- …