44 research outputs found
Distant X-ray Galaxies: Insights from the Local Population
A full understanding of the origin of the hard X-ray background requires a
complete and accurate census of the distant galaxies that produce it.
Unfortunately, distant X-ray galaxies tend to be very faint at all wavelengths,
which hinders efforts to perform this census. This chapter discusses the
insights that can be obtained through comparison of the distant population to
local X-ray galaxies, whose properties are well characterized. Such comparisons
will ultimately aid investigations into the cosmic evolution of supermassive
black holes and their environments.Comment: 19 pages, 10 figures, to appear as Chapter 7 in "Supermassive Black
Holes in the Distant Universe" (2004), ed. A. J. Barger, Kluwer Academic
Publishers, in pres
Core-collapse supernovae missed by optical surveys
We estimate the fraction of core-collapse supernovae (CCSNe) that remain
undetected by optical SN searches due to obscuration by large amounts of dust
in their host galaxies. This effect is especially important in luminous and
ultraluminous infrared galaxies, which are locally rare but dominate the star
formation at redshifts of z~1-2. We perform a detailed investigation of the SN
activity in the nearby luminous infrared galaxy Arp 299 and estimate that up to
83% of the SNe in Arp 299 and in similar galaxies in the local Universe are
missed by observations at optical wavelengths. For rest-frame optical surveys
we find the fraction of SNe missed due to high dust extinction to increase from
the average local value of ~19% to ~38% at z~1.2 and then stay roughly constant
up to z~2. It is therefore crucial to take into account the effects of
obscuration by dust when determining SN rates at high redshift and when
predicting the number of CCSNe detectable by future high-z surveys such as
LSST, JWST, and Euclid. For a sample of nearby CCSNe (distances 6-15 Mpc)
detected during the last 12 yr, we find a lower limit for the local CCSN rate
of 1.5 +0.4/-0.3 x 10^-4 yr^-1 Mpc^-3, consistent with that expected from the
star formation rate. Even closer, at distances less than ~6 Mpc, we find a
significant increase in the CCSN rate, indicating a local overdensity of star
formation caused by a small number of galaxies that have each hosted multiple
SNe.Comment: 16 pages, 5 figures, 11 tables, minor changes to match the published
versio
The [OIII] emission line luminosity function of optically selected type-2 AGN from zCOSMOS
We present a catalog of 213 type-2 AGN selected from the zCOSMOS survey. The
selected sample covers a wide redshift range (0.15<z<0.92) and is deeper than
any other previous study, encompassing the luminosity range 10^{5.5} < Lsun<
L[OIII] < 10^{9.1} Lsun. We explore the intrinsic properties of these AGN and
the relation to their X-ray emission (derived from the XMM-COSMOS
observations). We study their evolution by computing the [OIII]5007A line
luminosity function (LF) and we constrain the fraction of obscured AGN as a
function of luminosity and redshift. The sample was selected on the basis of
the optical emission line ratios, after applying a cut to the signal-to-noise
ratio (S/N) of the relevant lines. We used the standard diagnostic diagrams
[OIII]/Hbeta versus [NII]/Halpha and ([OIII]/Hbeta versus [SII]/Halpha) to
isolate AGN in the redshift range 0.15<z<0.45 and the diagnostic diagram
[OIII]/Hbeta versus [OII]/Hbeta to extend the selection to higher redshift
(0.5<z<0.92). Combining our sample with one drawn from SDSS, we found that the
best description of the evolution of type-2 AGN is a luminosity-dependent
density evolution model. Moreover, using the type-1 AGN LF we were able to
constrain the fraction of type-2 AGN to the total (type-1 + type-2) AGN
population. We found that the type-2 fraction decreases with luminosity, in
agreement with the most recent results, and shows signs of a slight increase
with redshift. However, the trend with luminosity is visible only after
combining the SDSS+zCOSMOS samples. From the COSMOS data points alone, the
type-2 fraction seems to be quite constant with luminosity.Comment: 20 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Primary chronic cold agglutinin disease: An update on pathogenesis, clinical features and therapy
Chronic cold agglutinin disease (CAD) is a subgroup of autoimmune hemolytic anemia. Primary CAD has traditionally been defined by the absence of any underlying or associated disease. The results of therapy with corticosteroids, alkylating agents and interferon-a have been poor. Cold reactive immunoglobulins against erythrocyte surface antigens are essential to pathogenesis of CAD. These cold agglutinins are monoclonal, usually IgMκ auto antibodies with heavy chain variable regions encoded by the VH4-34 gene segment. By flowcytometric and immunohistochemical assessments, a monoclonal CD20+κ+B-lymphocyte population has been demonstrated in the bone marrow of 90% of the patients, and lymphoplasmacytic lymphoma is a frequent finding. Novel attempts at treatment for primary CAD have mostly been directed against the clonal B-lymphocytes. Phase 2 studies have shown that therapy with the chimeric anti-CD20 antibody rituximab produced partial response rates of more than 50% and occasional complete responses. Median response duration, however, was only 11 months. In this review, we discuss the clinical and pathogenetic features of primary CAD, emphasizing the more recent data on its close association with clonal lymphoproliferative bone marrow disorders and implications for therapy. We also review the management and outline some perspectives on new therapy modalities
The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar
F00183-7111 is one of the most extreme Ultra-Luminous Infrared Galaxies
known. Here we present a VLBI image which shows that F00183-7111 is powered by
a combination of a radio-loud Active Galactic Nucleus surrounded by vigorous
starburst activity. Although already radio-loud, the quasar jets are only 1.7
kpc long, boring through the dense gas and starburst activity that confine
them. We appear to be witnessing this remarkable source in the brief transition
period between merging starburst and radio-loud "quasar-mode" accretion.Comment: Submitted to MNRA
Spin temperatures and covering factors for HI 21-cm absorption in damped Lyman-alpha systems
We investigate the practice of assigning high spin temperatures to damped
Lyman-alpha absorption systems (DLAs) not detected in HI 21-cm absorption. In
particular, Kanekar & Chengaulr (2003) have attributed the mix of 21-cm
detections and non-detections in low redshift (z<2.04) DLAs to a mix of spin
temperatures, while the non-detections at high redshift were attributed to high
spin temperatures. Below z=0.9, where some of the DLA host galaxy morphologies
are known, we find that 21-cm absorption is normally detected towards large
radio sources when the absorber is known to be associated with a large
intermediate (spiral) galaxy. Furthermore, at these redshifts, only one of the
six 21-cm non-detections has an optical identification and these DLAs tend to
lie along the sight-lines to the largest background radio continuum sources.
For these and many of the high redshift DLAs occulting large radio continua, we
therefore expect covering factors of less than the assumed/estimated value of
unity. This would have the effect of introducing a range of spin temperatures
considerably narrower than the current range of >9000 K, while still supporting
the hypothesis that the high redshift DLA sample comprises a larger proportion
of compact galaxies than the low redshift sample.Comment: Submitted to MNRAS, 11 pages, 6 figure
Molecular gas in the centre of nearby galaxies from VLT/SINFONI integral field spectroscopy - II. Kinematics(star)
We present an analysis of the H2 emission-line gas kinematics in the inner ≲4 arcsec radius of six nearby spiral galaxies, based on adaptive optics-assisted integral-field observations obtained in the K band with SINFONI/VLT. Four of the six galaxies in our sample display ordered H2 velocity fields, consistent with gas moving in the plane of the galaxy and rotating in the same direction as the stars. However, the gas kinematics is typically far from simple circular motion. We can classify the observed velocity fields into four different types of flows, ordered by increasing complexity: (1) circular motion in a disc (NGC 3351); (2) oval motion in the galaxy plane (NGC 3627 and NGC 4536); (3) streaming motion superimposed on circular rotation (NGC 4501); and (4) disordered streaming motions (NGC 4569 and NGC 4579). The H2 velocity dispersion in the galaxies is usually higher than 50 km s−1 in the inner 1–2 arcsec radii. The four galaxies with ordered kinematics have v/σ < 1 at radii less than 40–80 pc. The radius at which v/σ = 1 is independent of the type of nuclear activity. While the low values of v/σ could be taken as an indication of a thick disc in the innermost regions of the galaxies, other lines of evidence (e.g. H2 morphologies and velocity fields) argue for a thin disc interpretation in the case of NGC 3351 and NGC 4536. We discuss the implications of the high values of velocity dispersion for the dynamics of the gaseous disc and suggest caution when interpreting the velocity dispersion of ionized and warm tracers as being entirely dynamical. Understanding the nature and role of the velocity dispersion in the gas dynamics, together with the full 2D information of the gas, is essential for obtaining accurate black hole masses from gas kinematics
Host-Bacterial Symbiosis in Health and Disease
All animals live in symbiosis. Shaped by eons of co-evolution, host bacterial associations have developed into prosperous relationships creating mechanisms for mutual benefits to both microbe and host. No better example exists in biology than the astounding numbers of bacteria harbored by the lower gastrointestinal tract of mammals. The mammalian gut represents a complex ecosystem consisting of an extraordinary number of resident commensal bacteria
existing in homeostasis with the host’s immune system. Most
impressive about this relationship may be the concept that the host not only tolerates, but has evolved to require colonization by beneficial microorganisms, known as commensals, for various aspects of immune development and function. The microbiota provides critical signals that promote maturation of immune cells and tissues, leading to protection from infections by pathogens. Gut bacteria also appear to contribute to non-infectious immune disorders such as inflammatory bowel disease and autoimmunity.
How the microbiota influences host immune responses is an active area of research with important implications for human health. This review synthesizes emerging findings and concepts that describe the mutualism between the microbiota and mammals, specifically emphasizing the role of gut bacteria in shaping an immune response that mediates the balance between health and disease. Unlocking how beneficial bacteria affect the development of the immune
system may lead to novel and natural therapies based on harnessing the immunomodulatory properties of the microbiota