99 research outputs found
Infrared Spectroscopy of Nearby Radio Active Elliptical Galaxies
In preparation for a study of their circumnuclear gas we have surveyed 60% of a complete sample of elliptical galaxies within 75 Mpc that are radio sources. Some 20% of our nuclear spectra have infrared emission lines, mostly Paschen lines, Brackett Îł, and [Fe II]. We consider the influence of radio power and black hole mass in relation to the spectra. Access to the spectra is provided here as a community resource
The Clustering and Halo Masses of Star Forming Galaxies at z<1
We present clustering measurements and halo masses of star forming galaxies
at 0.2 < z < 1.0. After excluding AGN, we construct a sample of 22553 24 {\mu}m
sources selected from 8.42 deg^2 of the Spitzer MIPS AGN and Galaxy Evolution
Survey of Bo\"otes. Mid-infrared imaging allows us to observe galaxies with the
highest star formation rates (SFRs), less biased by dust obscuration afflicting
the optical bands. We find that the galaxies with the highest SFRs have optical
colors which are redder than typical blue cloud galaxies, with many residing
within the green valley. At z > 0.4 our sample is dominated by luminous
infrared galaxies (LIRGs, L_TIR > 10^11 Lsun) and is comprised entirely of
LIRGs and ultra-luminous infrared galaxies (ULIRGs, L_TIR > 10^12 Lsun) at z >
0.6. We observe weak clustering of r_0 = 3-6 Mpc/h for almost all of our star
forming samples. We find that the clustering and halo mass depend on L_TIR at
all redshifts, where galaxies with higher L_TIR (hence higher SFRs) have
stronger clustering. Galaxies with the highest SFRs at each redshift typically
reside within dark matter halos of M_halo ~ 10^12.9 Msun/h. This is consistent
with a transitional halo mass, above which star formation is largely truncated,
although we cannot exclude that ULIRGs reside within higher mass halos. By
modeling the clustering evolution of halos, we connect our star forming galaxy
samples to their local descendants. Most star forming galaxies at z < 1.0 are
the progenitors of L < 2.5L* blue galaxies in the local universe, but star
forming galaxies with the highest SFRs (L_TIR >10^11.7 Lsun) at 0.6<z<1.0 are
the progenitors of early-type galaxies in denser group environments.Comment: 18 pages, 16 figures, 2 tables. Accepted for publication in the
Astrophysical Journa
Disparate MgII Absorption Statistics towards Quasars and Gamma-Ray Bursts : A Possible Explanation
We examine the recent report by Prochter et al. (2006) that gamma-ray burst
(GRB) sight lines have a much higher incidence of strong MgII absorption than
quasar sight lines. We propose that the discrepancy is due to the different
beam sizes of GRBs and quasars, and that the intervening MgII systems are
clumpy with the dense part of each cloudlet of a similar size as the quasars,
i.e. < 10^16 cm, but bigger than GRBs. We also discuss observational
predictions of our proposed model. Most notably, in some cases the intervening
MgII absorbers in GRB spectra should be seen varying, and quasars with smaller
sizes should show an increased rate of strong MgII absorbers. In fact, our
prediction of variable MgII lines in the GRB spectra has been now confirmed by
Hao et al. (2007), who observed intervening FeII and MgII lines at z=1.48 to be
strongly variable in the multi-epoch spectra of z=4.05 GRB060206.Comment: 12 pages, 2 figures; substantially revised model calculation;
accepted for publication in Astrophysics & Space Science as a Lette
Bostonia: The Boston University Alumni Magazine. Volume 10
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Multi-wavelength landscape of the young galaxy cluster RX J1257.2+4738 at z = 0.866 I. The infrared view
Context. Many studies have shown how galaxy properties (e.g. colours, morphology, star-forming (SF) activity, active galactic nuclei population) change not only with redshift, but also with local galaxy density, revealing the important effect of the stellar/halo mass and the environment in the evolution of galaxies. A detailed analysis of the star formation activity in a representative sample of clusters will help us to understand the physical processes that cause the observed changes.
Aims. We performed a thorough analysis of the star formation activity in the young massive galaxy cluster RX J1257+4738 at z = 0.866, with emphasis on the relationship between the local environment of the cluster galaxies and their star formation activity. We present an optical and infrared (IR) study that benefited from the large amount of data available for this cluster, including new OSIRIS/GTC and Herschel imaging observations.
Methods. Using a multi-wavelength catalogue from the optical to the near-infrared, we measured photometric redshifts through a Ï2 spectral energy distribution fitting procedure. We implemented a reliable and carefully chosen cluster membership selection criterion including Monte Carlo simulations and derived a sample of 292 reliable cluster member galaxies for which we measured the following properties: optical colours, stellar masses, ages, ultraviolet luminosities and local densities. Using the MIPS 24âÎŒm and Herschel data, we measured total IR luminosities and star formation rates (SFRs).
Results. Of the sample of 292 cluster galaxies, 38 show far-infrared (FIR) emission with an SFR between 0.5 and 45âMââyr-1. The spatial distribution of the FIR emitters within the cluster density map and the filament-like overdensities observed suggest that RX J1257 is not virialised, but is in the process of assembly. The average star formation as a function of the cluster environment parametrised by the local density of galaxies does not show any clear trend. However, the fraction of SF galaxies unveils that the cluster intermediate-density regions is preferred for the SF activity to enhance, since we observe a significant increase of the FIR-emitter fraction in this environment. The analysis of the extinction distributions of the optically red and blue SF galaxies supports the assumption of the red SF galaxies as a dusty population
On the selection of AGN neutrino source candidates for a source stacking analysis with neutrino telescopes
The sensitivity of a search for sources of TeV neutrinos can be improved by
grouping potential sources together into generic classes in a procedure that is
known as source stacking. In this paper, we define catalogs of Active Galactic
Nuclei (AGN) and use them to perform a source stacking analysis. The grouping
of AGN into classes is done in two steps: first, AGN classes are defined, then,
sources to be stacked are selected assuming that a potential neutrino flux is
linearly correlated with the photon luminosity in a certain energy band (radio,
IR, optical, keV, GeV, TeV). Lacking any secure detailed knowledge on neutrino
production in AGN, this correlation is motivated by hadronic AGN models, as
briefly reviewed in this paper.
The source stacking search for neutrinos from generic AGN classes is
illustrated using the data collected by the AMANDA-II high energy neutrino
detector during the year 2000. No significant excess for any of the suggested
groups was found.Comment: 43 pages, 12 figures, accepted by Astroparticle Physic
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Pulse oximetry in the oesophagus
Pulse oximetry has been one of the most significant technological advances in clinical monitoring in the last two decades. Pulse oximetry is a non-invasive photometric technique that provides information about the arterial blood oxygen saturation (SpO(2)) and heart rate, and has widespread clinical applications. When peripheral perfusion is poor, as in states of hypovolaemia, hypothermia and vasoconstriction, oxygenation readings become unreliable or cease. The problem arises because conventional pulse oximetry sensors must be attached to the most peripheral parts of the body, such as finger, ear or toe, where pulsatile flow is most easily compromised. Since central blood flow may be preferentially preserved, this review explores a new alternative site, the oesophagus, for monitoring blood oxygen saturation by pulse oximetry. This review article presents the basic physics, technology and applications of pulse oximetry including photoplethysmography. The limitations of this technique are also discussed leading to the proposed development of the oesophageal pulse oximeter. In the majority, the report will be focused on the description of a new oesophageal photoplethysmographic/SpO(2) probe, which was developed to investigate the suitability of the oesophagus as an alternative monitoring site for the continuous measurement of SpO(2) in cases of poor peripheral circulation. The article concludes with a review of reported clinical investigations of the oesophageal pulse oximeter
AGES: The AGN and Galaxy Evolution Survey
The AGN and Galaxy Evolution Survey (AGES) is a redshift survey covering, in
its standard fields, 7.7 square degrees of the Bootes field of the NOAO Deep
Wide-Field Survey (NDWFS). The final sample consists of 23745 redshifts. There
are well-defined galaxy samples in ten bands (the Bw, R, I, J, K, IRAC 3.6,
4.5, 5.8 and 8.0 micron and MIPS 24 micron bands) to a limiting magnitude of
I<20 mag for spectroscopy. For these galaxies, we obtained 18163 redshifts from
a sample of 35200 galaxies, where random sparse sampling was used to define
statistically complete sub-samples in all ten photometric bands. The median
galaxy redshift is 0.31, and 90% of the redshifts are in the range
0.085<z<0.66. AGN were selected as radio, X-ray, IRAC mid-IR and MIPS 24 micron
sources to fainter limiting magnitudes (I<22.5 mag for point sources).
Redshifts were obtained for 4764 quasars and galaxies with AGN signatures, with
2926, 1718, 605, 119 and 13 above redshifts of 0.5, 1, 2, 3 and 4,
respectively. We detail all the AGES selection procedures and present the
complete spectroscopic redshift catalogs, spectra, and spectral energy
distribution decompositions. The photometric redshift estimates are for all
sources in the AGES samples.Comment: 49 pages, 9 figures, submitted to ApJS. Full data tables available
upon acceptanc
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