291 research outputs found
Understanding the Astrophysics of Galaxy Evolution: the role of spectroscopic surveys in the next decade
Over the last decade optical spectroscopic surveys have characterized the low
redshift galaxy population and uncovered populations of star-forming galaxies
back to z ~ 7. This work has shown that the primary epoch of galaxy building
and black hole growth occurs at redshifts of 2 to 3. The establishment of the
concordance LCDM cosmology shifted the focus of galaxy population studies from
constraining cosmological parameters to characterizing the processes which
regulate the formation and evolution of galaxies.In the next decade, high
redshift observers will attempt to formulate a coherent evolutionary picture
connecting galaxies in the high redshift Universe to galaxies today. In order
to link galaxy populations at different redshifts, we must not only
characterize their evolution in a systematic way, we must establish which
physical processes are responsible for it. Considerable progress has already
been made in understanding how galaxies evolved from z ~ 1 to the present day.
Large spectroscopic surveys in the near infrared are required to push these
studies back towards the main epoch of galaxy building. Only then will we
understand the full story of the formation of L* galaxies like our own Milky
Way. A large near-IR spectroscopic survey will also provide the calibration
needed to avoid systematics in the large photometric programs proposed to study
the nature of dark matter and dark energy. We provide an outline design for a
multi-object 0.4 to 1.8 micron spectrograph, which could be placed on an
existing telescope, and which would allow a full characterization of the galaxy
population out to z ~ 2. We strongly recommend a serious further study to
design a real instrument, which will be required for galaxy formation studies
to advance to the next frontier.Comment: White paper, primary author J.E. Gunn, submitted to Astro2010 Decadal
Survey, see http://www7.nationalacademies.org/bpa/Astro2010_SWP_byTitle.htm
Evolution of the Most Massive Galaxies to z=0.6: I. A New Method for Physical Parameter Estimation
We use principal component analysis (PCA) to estimate stellar masses, mean
stellar ages, star formation histories (SFHs), dust extinctions and stellar
velocity dispersions for ~290,000 galaxies with stellar masses greater than
$10^{11}Msun and redshifts in the range 0.4<z<0.7 from the Baryon Oscillation
Spectroscopic Survey (BOSS). We find the fraction of galaxies with active star
formation first declines with increasing stellar mass, but then flattens above
a stellar mass of 10^{11.5}Msun at z~0.6. This is in striking contrast to
z~0.1, where the fraction of galaxies with active star formation declines
monotonically with stellar mass. At stellar masses of 10^{12}Msun, therefore,
the evolution in the fraction of star-forming galaxies from z~0.6 to the
present-day reaches a factor of ~10. When we stack the spectra of the most
massive, star-forming galaxies at z~0.6, we find that half of their [OIII]
emission is produced by AGNs. The black holes in these galaxies are accreting
on average at ~0.01 the Eddington rate. To obtain these results, we use the
stellar population synthesis models of Bruzual & Charlot (2003) to generate a
library of model spectra with a broad range of SFHs, metallicities, dust
extinctions and stellar velocity dispersions. The PCA is run on this library to
identify its principal components over the rest-frame wavelength range
3700-5500A. We demonstrate that linear combinations of these components can
recover information equivalent to traditional spectral indices such as the
4000A break strength and HdA, with greatly improved S/N. This method is able to
recover physical parameters such as stellar mass-to-light ratio, mean stellar
age, velocity dispersion and dust extinction from the relatively low S/N BOSS
spectra. We examine the sensitivity of our stellar mass estimates to the input
parameters in our model library and the different stellar population synthesis
models.Comment: 20 pages, 18 Figures, submitted to MNRA
The Detection of Multimodal Oscillations on Alpha UMa
We have used the star camera on the WIRE satellite to observe the K0 III star
Alpha UMa, and we report the apparent detection of 10 oscillation modes. The
lowest frequency mode is at 1.82 microhertz, and appears to be the fundamental
mode. The mean spacing between the mode frequencies is 2.94 microhertz, which
implies that all detected modes are radial. The mode frequencies are consistent
with the physical parameters of a K0 III star, if we assume that only radial
modes are excited. Mode amplitudes are 100 -- 400 micromagnitudes, which is
consistent with the scaling relation of Kjeldsen & Beddinge (1995).Comment: ApJ Letters, in press. 14 pages, including 3 figure
The Vehicle, Fall 1985
Vol. 27, No. 1
Table of Contents
Satchel AssMichael D. Smithpage 3
PhotoDoug Andersonpage 7
CounselingChristy Dunphypage 8
Grave SiteJay D. Fiskpage 8
Sight-Seeing Outside PhoenixBob Zordanipage 9
PerformanceDan Von Holtenpage 10
NightmareKandy Bellpage 10
Photo (The Loft)Lawrence McGownpage 11
LaboringJanet Gracepage 12
Blood DonorDan Von Holtenpage 13
Photo (Pier)Lawrence McGownpage 14
ExamplesChristopher Albinpage 14
Three PoemsPatrick Peterspage 15
Sometimes I Dream in Cotton CandyKathy Graypage 16
One Day While BoatingF. Link Rapierpage 17
DepartureBob Zordanipage 17
140 Print That\u27s Life Peter Dowlingpage 18
Photo (Around the Bend)Mike Freckerpage 20
Light ConversationDan Hintzpage 22
She Waits For the WorldJim Harrispage 22
HoneyKathy Graypage 23
Photo AlbumPatrick Peterspage 24
Photo (Stairs)Lawrence McGownpage 25
Fallen From Grace to SaturdayF. Link Rapierpage 26
Post MortemF. Link Rapierpage 27
ConfessionJohn Kayserpage 27
Child\u27s PlayChristopher Albinpage 27
Seeking A Friend\u27s Advice on DietingKathy Graypage 28
PhotoDoug Andersonpage 28
She Came Back to MeJim Harrispage 29
Farm BoyDiana Winsonpage 30
DilemmaJanet Wilhelmpage 31
In a Rock or StoneRichard Donnellypage 32
In November He Came To MeJean Kover Chandlerpage 33
EndingChristy Dunphypage 34
The Honor GradEddie Simpsonpage 35
Photo (Thirst)Mike Freckerpage 40https://thekeep.eiu.edu/vehicle/1046/thumbnail.jp
Consequences of Internet Use in College Students
The purposes of the research project were to explore how much time college students spend on the Internet and the consequences for college students who use the Internet
The Dependence of Star Formation History and Internal Structure on Stellar Mass for 10^5 Low-Redshift Galaxies
We study the relations between stellar mass, star formation history, size and
internal structure for a complete sample of 122,808 galaxies drawn from the
Sloan Digital Sky Survey. We show that low-redshift galaxies divide into two
distinct families at a stellar mass of 3 \times 10^10 M_sol. Lower mass
galaxies have young stellar populations, low surface mass densities and the low
concentrations typical of disks. A significant fraction of the lowest mass
galaxies in our sample have experienced recent starbursts. At given stellar
mass, the sizes of low mass galaxies are log- normally distributed with
dispersion sigma(ln R_50) \sim 0.5, in excellent agreement with the idea that
they form with little angular momentum loss through cooling and condensation in
a gravitationally dominant dark matter halo. Their median stellar surface mass
density scales with stellar mass as mu* propto M_*^0.54, suggesting that the
stellar mass of a disk galaxy is proprtional to the three halves power of its
halo mass. This suggests that the efficiency of the conversion of baryons into
stars in low mass galaxies increases in propor- tion to halo mass, perhaps as a
result of supernova feedback processes. At stellar masses above 3 \times 10^10
M_sol, there is a rapidly increasing frac- tion of galaxies with old stellar
populations, high surface mass densities and high concentrations typical of
bulges. In this regime, the size distribution is log-normal, but its dispersion
decreases rapidly with increasing stellar mass and the median mass surface
density is approximately constant. This suggests that the star formation
efficiency decreases in the highest mass halos, and that little star formation
occurs in massive galaxies once they have assembled.Comment: accepted by MNRAS, some changes to results as a result of
improvements in stellar mass estimates as decribed in Paper
Between a rock and a hard place: the need for and challenges to implementation of Rights Based Fisheries Management in small-scale fisheries of Southern Lake Malawi
There has been a decline in commercially valuable fish species, especially the Chambo (Oreochromis spp.), in southern Lake Malawi. Although there might be lack of reliable and scientifically backed evidence, most experts and experienced fishers concur that productivity of most fish stocks in the area is much below par compared to their productivity about two to three decades ago. This leads to the hypotheses that the fish stocks are generally over-exploited. This trend will continue or their productivity will remain at these depressed levels unless appropriate measures are taken. This article argues that Rights Based Management (RBM) could hold the best hope for moving towards sustainable fisheries management in the southern Lake Malawi (Southeast and Southwest Arms) area while recognizing the need for a broad human rights approach for fishing communities. Even then, the implementation of the RBM approach will not be easy given the historical developmental open access management approach and general unorganized characteristics of the small-scale fisheries sector. Of note is that co-management was introduced in area in the early millennium as part of attempts to strengthen user fishing rights, local accountability and stewardship—with mixed results
The Seventh Data Release of the Sloan Digital Sky Survey
This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)Comment: 20 pages, 10 embedded figures. Accepted to ApJS after minor
correction
An improved method for measuring muon energy using the truncated mean of dE/dx
The measurement of muon energy is critical for many analyses in large
Cherenkov detectors, particularly those that involve separating
extraterrestrial neutrinos from the atmospheric neutrino background. Muon
energy has traditionally been determined by measuring the specific energy loss
(dE/dx) along the muon's path and relating the dE/dx to the muon energy.
Because high-energy muons (E_mu > 1 TeV) lose energy randomly, the spread in
dE/dx values is quite large, leading to a typical energy resolution of 0.29 in
log10(E_mu) for a muon observed over a 1 km path length in the IceCube
detector. In this paper, we present an improved method that uses a truncated
mean and other techniques to determine the muon energy. The muon track is
divided into separate segments with individual dE/dx values. The elimination of
segments with the highest dE/dx results in an overall dE/dx that is more
closely correlated to the muon energy. This method results in an energy
resolution of 0.22 in log10(E_mu), which gives a 26% improvement. This
technique is applicable to any large water or ice detector and potentially to
large scintillator or liquid argon detectors.Comment: 12 pages, 16 figure
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