22 research outputs found
Constraining halo occupation properties of X-ray AGNs using clustering of Chandra sources in the Bootes survey region
We present one of the most precise measurement to date of the spatial
clustering of X-ray selected AGNs using a sample derived from the Chandra X-ray
Observatory survey in the Bootes field. The real-space two-point correlation
function over a redshift interval from z=0.17 to z~3 is well described by the
power law, xi(r)=(r/r0)^-gamma, for comoving separations r<~20h^-1 Mpc. We find
gamma=1.84+-0.12 and r0 consistent with no redshift trend within the sample
(varying between r0=5.5+-0.6 h^-1 Mpc for =0.37 and r0=6.9+-1.0 h^-1 Mpc for
=1.28). Further, we are able to measure the projections of the two-point
correlation function both on the sky plane and in the line of sight. We use
these measurements to show that the Chandra/Bootes AGNs are predominantly
located at the centers of dark matter halos with the circular velocity Vmax>320
km/s or M_200 > 4.1e12 h^-1 Msun, and tend to avoid satellite galaxies in halos
of this or higher mass. The halo occupation properties inferred from the
clustering properties of Chandra/Bootes AGNs --- the mass scale of the parent
dark matter halos, the lack of significant redshift evolution of the clustering
length, and the low satellite fraction --- are broadly consistent with the
Hopkins et al. scenario of quasar activity triggered by mergers of
similarly-sized galaxies.Comment: Accepted to ApJ. The revision matches the accepted version. The most
significant changes include the recalculation of uncertainties using mock
catalogs and explicit comparison with the AGN HOD studies based on projected
correlation function, w(rp
Evolution of active galactic nuclei
[Abriged] Supermassive black holes (SMBH) lurk in the nuclei of most massive
galaxies, perhaps in all of them. The tight observed scaling relations between
SMBH masses and structural properties of their host spheroids likely indicate
that the processes fostering the growth of both components are physically
linked, despite the many orders of magnitude difference in their physical size.
This chapter discusses how we constrain the evolution of SMBH, probed by their
actively growing phases, when they shine as active galactic nuclei (AGN) with
luminosities often in excess of that of the entire stellar population of their
host galaxies. Following loosely the chronological developments of the field,
we begin by discussing early evolutionary studies, when AGN represented beacons
of light probing the most distant reaches of the universe and were used as
tracers of the large scale structure. This early study turned into AGN
"Demography", once it was realized that the strong evolution (in luminosity,
number density) of the AGN population hindered any attempt to derive
cosmological parameters from AGN observations directly. Following a discussion
of the state of the art in the study of AGN luminosity functions, we move on to
discuss the "modern" view of AGN evolution, one in which a bigger emphasis is
given to the physical relationships between the population of growing black
holes and their environment. This includes observational and theoretical
efforts aimed at constraining and understanding the evolution of scaling
relations, as well as the resulting limits on the evolution of the SMBH mass
function. Physical models of AGN feedback and the ongoing efforts to isolate
them observationally are discussed next. Finally, we touch upon the problem of
when and how the first black holes formed and the role of black holes in the
high-redshift universe.Comment: 75 pages, 35 figures. Modified version of the chapter accepted to
appear in "Planets, Stars and Stellar Systems", vol 6, ed W. Keel
(www.springer.com/astronomy/book/978-90-481-8818-5). The number of references
is limited upon request of the editors. Original submission to Springer: June
201
Skin Ulcer: A Long-Term Complication After Massive Liquid Silicone Oil Infiltration
Despite scientific literature replete with stories of disastrous results and disfigurement, illicit subcutaneous injections of highly viscous fluids in massive quantities still are performed, often by unqualified persons. The authors present a devastating long-term outcome from a massive volume of silicone oil injected subcutaneously into the buttocks of a 48-year-old transsexual patient and its ulceration treated only through regular medications. The therapeutic protocol consisted of wound disinfection with iodopovidone, washing with saline solution, disinfection with sodium hypochlorite 0.05 %, and application of ointment containing Vibrio alginolyticus collagenase and hyaluronan. The follow-up evaluation was at 1 and 2 weeks and then at 1, 2, and 3 months. Weekly photographs were taken, and measurements of the lesion and evolution were estimated every 7 days. After 3 months of regular medications, the authors succeeded in closing the ulcer, avoiding invasive therapeutic options. In the presence of the cutaneous ulceration above a massively infiltrated area, if the removal of all the injected oil is surgically definitely impossible, other conservative procedures should be considered. Our experience demonstrated how it is possible to manage a so prickly a case with a noninvasive approach such as periodic medications. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266