6,103 research outputs found
Credentials for Dr. R. Farley
The Faculty Senate based upon evidence and documentation presented at the August 8, 1969 meeting finds the credentials for Dr. Rawle E.G. Farley to be in order
Star formation in the massive cluster merger Abell 2744
We present a comprehensive study of star-forming (SF) galaxies in the HST
Frontier Field recent cluster merger A2744 (z=0.308). Wide-field,
ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total
star formation rate (SFR) for 53 cluster galaxies, with SFR{UV+IR}=343+/-10
Msun/yr. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is
complete, yielding a total SFR{UV+IR}=201+/-9 Msun/yr. Focussing on obscured
star formation, this core region exhibits a total SFR{IR}=138+/-8 Msun/yr, a
mass-normalised SFR{IR} of Sigma{SFR}=11.2+/-0.7 Msun/yr per 10^14 Msun and a
fraction of IR-detected SF galaxies f{SF}=0.080(+0.010,-0.037). Overall, the
cluster population at z~0.3 exhibits significant intrinsic scatter in IR
properties (total SFR{IR}, Tdust distribution) apparently unrelated to the
dynamical state: A2744 is noticeably different to the merging Bullet cluster,
but similar to several relaxed clusters. However, in A2744 we identify a trail
of SF sources including jellyfish galaxies with substantial unobscured SF due
to extreme stripping (SFR{UV}/SFR{IR} up to 3.3). The orientation of the trail,
and of material stripped from constituent galaxies, indicates that the passing
shock front of the cluster merger was the trigger. Constraints on star
formation from both IR and UV are crucial for understanding galaxy evolution
within the densest environments.Comment: Accepted by MNRAS. 12 pages, 7 figures (high resolution versions of
Figs. 1 & 2 are available in the published PDF
Color and stellar population gradients in galaxies. Correlation with mass
We analyze the color gradients (CGs) of ~50000 nearby SDSS galaxies. From
synthetic spectral models based on a simplified star formation recipe, we
derive the mean spectral properties, and explain the observed radial trends of
the color as gradients of the stellar population age and metallicity (Z). The
most massive ETGs (M_* > 10^{11} Msun) have shallow CGs in correspondence of
shallow (negative) Z gradients. In the stellar mass range 10^(10.3-10.5) < M_*
< 10^(11) Msun, the Z gradients reach their minimum of ~ -0.5 dex^{-1}. At M_*
~ 10^{10.3-10.5} Msun, color and Z gradient slopes suddenly change. They turn
out to anti-correlate with the mass, becoming highly positive at the very low
masses. We have also found that age gradients anti-correlate with Z gradients,
as predicted by hierarchical cosmological simulations for ETGs. On the other
side, LTGs have gradients which systematically decrease with mass (and are
always more negative than in ETGs), consistently with the expectation from gas
infall and SN feedback scenarios. Z is found to be the main driver of the trend
of color gradients, especially for LTGs, but age gradients are not negligible
and seem to play a significant role too. We have been able to highlight that
older galaxies have systematically shallower age and Z gradients than younger
ones. Our results for high-mass galaxies are in perfect agreement with
predictions based on the merging scenario, while the evolution of LTGs and
younger and less massive ETGs seems to be mainly driven by infall and SN
feedback. (Abridged)Comment: 20 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's report
The kiloparsec-scale star formation law at redshift 4: wide-spread, highly efficient star formation in the dust-obscured starburst galaxy GN20
We present high-resolution observations of the 880 m (rest-frame FIR)
continuum emission in the z4.05 submillimeter galaxy GN20 from the IRAM
Plateau de Bure Interferometer (PdBI). These data resolve the obscured star
formation in this unlensed galaxy on scales of
0.30.2 (2.11.3 kpc).
The observations reveal a bright (161 mJy) dusty starburst centered on the
cold molecular gas reservoir and showing a bar-like extension along the major
axis. The striking anti-correlation with the HST/WFC3 imaging suggests that the
copious dust surrounding the starburst heavily obscures the rest-frame
UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no
evidence for variations in the dust properties across the source within the
uncertainties, consistent with extended star formation, and the peak star
formation rate surface density (1198 M yr kpc)
implies that the star formation in GN20 remains sub-Eddington on scales down to
3 kpc. We find that the star formation efficiency is highest in the central
regions of GN20, leading to a resolved star formation law with a power law
slope of , and that
GN20 lies above the sequence of normal star-forming disks, implying that the
dispersion in the star formation law is not due solely to morphology or choice
of conversion factor. These data extend previous evidence for a fixed star
formation efficiency per free-fall time to include the star-forming medium on
kpc-scales in a galaxy 12 Gyr ago.Comment: 6 pages, 5 figures, accepted to ApJ
Stellar population gradients from cosmological simulations: dependence on mass and environment in local galaxies
The age and metallicity gradients for a sample of group and cluster galaxies
from N-body+hydrodynamical simulation are analyzed in terms of galaxy stellar
mass. Dwarf galaxies show null age gradient with a tail of high and positive
values for systems in groups and cluster outskirts. Massive systems have
generally zero age gradients which turn to positive for the most massive ones.
Metallicity gradients are distributed around zero in dwarf galaxies and become
more negative with mass; massive galaxies have steeper negative metallicity
gradients, but the trend flatten with mass. In particular, fossil groups are
characterized by a tighter distribution of both age and metallicity gradients.
We find a good agreement with both local observations and independent
simulations. The results are also discussed in terms of the central age and
metallicity, as well as the total colour, specific star formation and velocity
dispersion.Comment: 9 pages, 5 figures, accepted for publication on MNRA
ALMA detection of [CII] 158 micron emission from a strongly lensed z=2 star-forming galaxy
Our objectives are to determine the properties of the interstellar medium
(ISM) and of star-formation in typical star-forming galaxies at high redshift.
Following up on our previous multi-wavelength observations with HST, Spitzer,
Herschel, and the Plateau de Bure Interferometer (PdBI), we have studied a
strongly lensed z=2.013 galaxy, the arc behind the galaxy cluster MACS
J0451+0006, with ALMA to measure the [CII] 158 micron emission line, one of the
main coolants of the ISM. [CII] emission from the southern part of this galaxy
is detected at 10 . Taking into account strong gravitational lensing,
which provides a magnification of , the intrinsic lensing-corrected
[CII]158 micron luminosity is . The observed
ratio of [CII]-to-IR emission, , is found to be similar to that in nearby galaxies. The same also
holds for the observed ratio , which is
comparable to that of star-forming galaxies and active galaxy nuclei (AGN) at
low redshift. We utilize strong gravitational lensing to extend diagnostic
studies of the cold ISM to an order of magnitude lower luminosity () and SFR than previous work at high redshift.
While larger samples are needed, our results provide evidence that the cold ISM
of typical high redshift galaxies has physical characteristics similar to
normal star forming galaxies in the local Universe.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy &
Astrophysics, Letter
Stellar Metallicity Gradients in SDSS galaxies
We infer stellar metallicity and abundance ratio gradients for a sample of
red galaxies in the Sloan Digital Sky Survey (SDSS) Main galaxy sample. Because
this sample does not have multiple spectra at various radii in a single galaxy,
we measure these gradients statistically. We separate galaxies into stellar
mass bins, stack their spectra in redshift bins, and calculate the measured
absorption line indices in projected annuli by differencing spectra in
neighboring redshift bins. After determining the line indices, we use stellar
population modeling from the EZ\_Ages software to calculate ages,
metallicities, and abundance ratios within each annulus. Our data covers the
central regions of these galaxies, out to slightly higher than . We
find detectable gradients in metallicity and relatively shallow gradients in
abundance ratios, similar to results found for direct measurements of
individual galaxies. The gradients are only weakly dependent on stellar mass,
and this dependence is well-correlated with the change of with mass.
Based on this data, we report mean equivalent widths, metallicities, and
abundance ratios as a function of mass and velocity dispersion for SDSS
early-type galaxies, for fixed apertures of 2.5 kpc and of 0.5 .Comment: 19 pages; 8 tables, 12 figures. Submitted to ApJ for publicatio
Infrared Galaxies in the Field of the Massive Cluster Abell S1063: Discovery of a Luminous Kiloparsec-Sized HII Region in a Gravitationally Lensed IR-Luminous Galaxy at
Using the Spitzer Space Telescope and Herschel Space Observatory, we have
conducted a survey of infrared galaxies in the field of the galaxy cluster
Abell S1063 (AS1063) at , which is one of the most massive clusters
known and a target of the HST CLASH and Frontier-Field surveys. The
Spitzer/MIPS 24 m and Herschel/PACS & SPIRE images revealed that the core
of AS1063 is surprisingly devoid of infrared sources, showing only a few
detectable sources within the central r. There is, however, one
particularly bright source (2.3 mJy at 24 m; 106 mJy at 160 m), which
corresponds to a background galaxy at . The modest magnification factor
(4.0) implies that this galaxy is intrinsically IR-luminous (L). What is particularly interesting about
this galaxy is that HST optical/near-infrared images show a remarkably bright
and large (1 kpc) clump at one edge of the disk. Our follow-up
optical/near-infrared spectroscopy shows Balmer (H-H8) and forbidden
emission from this clump ([OII] 3727, [OIII]
4959,5007, [NII] 6548,6583), indicating that it
is a HII region. The HII region appears to have formed in-situ, as
kinematically it is part of a rotating disk, and there is no evidence of nearby
interacting galaxies. With an extinction correction of A mag, the
star formation rate of this giant HII region is 10 M yr,
which is exceptionally large, even for high redshift HII regions. Such a large
and luminous HII region is often seen at but quite rare in the nearby
Universe.Comment: Accepted for publication in the Astrophysical Journal. 29 pages, 15
figure
George Washington’s Attorneys: The Political Selection of United States Attorneys at the Founding
This Article examines the relationship between the Nation’s first President and the selection of United States Attorneys. It argues that politics played an important, if not primary, role in the President’s selections. George Washington sought those who would represent the government’s interests, adhere to the government’s policies, and advance Washington’s political goals. His selections also demonstrated Washington’s requirement of loyalty to America. In this respect, the politicization of United States Attorneys occurred at the outset. Part I of this Article defines politicization and identifies its four aspects. Part II describes the United States Attorney position as understood through the 1789 Judiciary Act and state experience. Part III examines how Washington’s selections and selection process included three of the four politicization categories. The concluding Section briefly explores the ramifications of politicization and its potential benefits in today’s prosecutorial environmen
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