10 research outputs found
Star formation and UV colors of the brightest Cluster Galaxies in the representative XMM-Newton Cluster Structure Survey
We present UV broadband photometry and optical emission-line measurements for
a sample of 32 Brightest Cluster Galaxies (BCGs) in clusters of the
Representative XMM-Newton Cluster Structure Survey (REXCESS) with z =
0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters
of galaxies, have X-ray measurements of high quality. The trends of star
formation and BCG colors with BCG and host properties can be investigated with
this sample. The UV photometry comes from the XMM Optical Monitor, supplemented
by existing archival GALEX photometry. We detected H\alpha and forbidden line
emission in 7 (22%) of these BCGs, in optical spectra. All of the emission-line
BCGs occupy clusters classified as cool cores, for an emission-line incidence
rate of 70% for BCGs in cool core clusters. Significant correlations between
the H\alpha equivalent widths, excess UV production in the BCG, and the
presence of dense, X-ray bright intracluster gas with a short cooling time are
seen, including the fact that all of the H\alpha emitters inhabit systems with
short central cooling times and high central ICM densities. Estimates of the
star formation rates based on H\alpha and UV excesses are consistent with each
other in these 7 systems, ranging from 0.1-8 solar masses per year. The
incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat
lower than in other X-ray selected samples (-35%), and somewhat higher than but
statistically consistent with optically selected, slightly lower redshift BCG
samples (-10-15%). The UV-optical colors (UVW1-R-4.7\pm0.3) of REXCESS BCGs
without strong optical emission lines are consistent with those predicted from
templates and observations of ellipticals dominated by old stellar populations.
We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray
temperature, redshift, or offset between X-ray centroid and X-ray peak ().Comment: 19 pages, 18 figures, 6 tables. Submitted, with minor revisions, to
ApJ
The FIRST-Optical-VLA Survey for Lensed Radio Lobes
We present results from a survey for gravitationally lensed radio lobes.
Lensed lobes are a potentially richer source of information about galaxy mass
distributions than lensed point sources, which have been the exclusive focus of
other recent surveys. Our approach is to identify radio lobes in the FIRST
catalog and then search optical catalogs for coincident foreground galaxies,
which are candidate lensing galaxies. We then obtain higher-resolution images
of these targets at both optical and radio wavelengths, and obtain optical
spectra for the most promising candidates. We present maps of several radio
lobes that are nearly coincident with galaxies. We have not found any new and
unambiguous cases of gravitational lensing. One radio lobe in particular, FOV
J0743+1553, has two hot spots that could be multiple images produced by a
z=0.19 spiral galaxy, but the lensing interpretation is problematic.Comment: 38 pages, 18 figures, aastex, accepted to A
The Central Component of Gravitational Lens Q0957+561
In 1981, a faint radio source (G') was detected near the center of the
lensing galaxy of the famous "twin quasar" Q0957+561. It is still unknown
whether this central radio source is a third quasar image or an active nucleus
of the lensing galaxy, or a combination of both. In an attempt to resolve this
ambiguity, we observed Q0957+561 at radio wavelengths of 13cm, 18cm, and 21cm,
using the Very Long Baseline Array in combination with the phased Very Large
Array and the Green Bank Telescope. We measured the spectrum of G' for the
first time and found it to be significantly different from the spectra of the
two bright quasar images. This finding suggests that the central component is
primarily or entirely emission from the foreground lens galaxy, but the
spectrum is also consistent with the hypothesis of a central quasar image
suffering free-free absorption. In addition, we confirm the previously-reported
VLBI position of G' just north of the optical center of the lens galaxy. The
position slightly favors the hypothesis that G' originates in the lens, but is
not conclusive. We discuss the prospects for further clarification of this
issue.Comment: 18 pages, accepted for publication in A
The problem of natural divine causation and the benefits of partial causation : a response to Skogholt
In this article, I defend my previous argument that natural divine causation suffers under the problem of causal overdetermination and that it cannot serve as a line of demarcation between theistic evolution (TE) and intelligent design (ID). I do this in light of Christoffer Skogholt's critique of my article. I argue that Skogholt underestimates the naturalistic ambitions of some current thinkers in TE and fails, therefore, to adequately respond to my main argument. I also outline how partial causation better serves as a model for the relationship between God's providence and evolution.PostprintPeer reviewe
Radio Astronomy
Contains table of contents for Section 4 and reports on five research projects.National Science Foundation Grant AST 92-24191MIT Lincoln Laboratory Agreement BX-4975National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAS 5-31376National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAG5-10MIT Leaders for Manufacturing Progra
Radio Astronomy
Contains table of contents for Section 4 and reports on seven research projects.National Science Foundation Grant AST 92-24191MIT Class of 1948/Career Development ChairNational Science Foundation Presidential Young Investigator AwardDavid and Lucile Packard FellowshipMIT Lincoln Laboratory Agreement BX-4975National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAS5-31276National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAG5-10MIT Leaders for Manufacturing Progra