1,814 research outputs found
The Evolution of Post-Starburst Galaxies from to the Present
Post-starburst galaxies are in the transitional stage between blue,
star-forming galaxies and red, quiescent galaxies, and therefore hold important
clues for our understanding of galaxy evolution. In this paper, we
systematically searched for and identified a large sample of post-starburst
galaxies from the spectroscopic dataset of the Sloan Digital Sky Survey (SDSS)
Data Release 9. In total, we found more than 6000 objects with redshifts
between and , making this the largest sample of
post-starburst galaxies in the literature. We calculated the luminosity
function of the post-starburst galaxies using two uniformly selected
subsamples: the SDSS Main Galaxy Sample and the Baryon Oscillation
Spectroscopic Survey CMASS Sample. The luminosity functions are reasonably fit
by half-Gaussian functions. The peak magnitudes shift as a function of redshift
from at to at . This is
consistent with the downsizing trend, whereby more massive galaxies form
earlier than low-mass galaxies. We compared the mass of the post-starburst
stellar population found in our sample to the decline of the global
star-formation rate and found that only a small amount () of all
star-formation quenching in the redshift range results in
post-starburst galaxies in the luminosity range our sample is sensitive to.
Therefore, luminous post-starburst galaxies are not the place where most of the
decline in star-formation rate of the universe is happening.Comment: 26 pages, 24 figures, 8 tables. Accepted for publication in The
Astrophysical Journa
The near and mid-infrared photometric properties of known redshift z ≥ 5 quasars
We assemble a catalogue of 488 spectroscopically confirmed very high
() redshift quasars and report their near- () and mid-
(WISE W1234) infrared properties. 97\% of the VHQ sample is detected in one
or more NIR () band, with lack of coverage rather than lack of
depth being the reason for the non-detections. 389 (80\%) of the very high
redshift quasars are detected at 3.4m in the W1 band from the unWISE
catalog and all of the quasars are detected in both unWISE W1 and W2.
Using archival WFCAM/UKIRT and VIRCAM/VISTA data we check for photometric
variability that might be expected from super-Eddington accretion. We find 28
of the quasars have sufficient NIR measurements and signal-to-noise ratio to
look for variability. Weak variability was detected in multiple bands of SDSS
J0959+0227, and very marginally in the -band of MMT J0215-0529. Only one
quasar, SDSS J0349+0034, shows significant differences between WFCAM and VISTA
magnitudes in one band. With supermassive black hole accretion likely to be
redshift invariant up to very high-redshift, further monitoring of these
sources is warranted. All the data, analysis codes and plots used and generated
here can be found at: https://github.com/d80b2t/VHzQ}{\tt
github.com/d80b2t/VHzQ.Comment: Published in MNRAS, 2020, Vol. 494, pp.789-803. 15 pages; 12 figures;
6 tables. Databases available at WFCAM Science Archive and the VISTA Science
Archive. All data, analysis codes and plots can be found at
github.com/d80b2t/VHzQ. Play the Five Tone
An upper limit to the dry merger rate at <z> ~ 0.55
We measure the fraction of Luminous Red Galaxies (LRGs) in dynamically close
pairs (with projected separation less than 20 kpc and velocity
difference less than 500 km s) to estimate the dry merger rate for
galaxies with and
in the 2dF-SDSS LRG and QSO (2SLAQ) redshift survey. For galaxies with a
luminosity ratio of or greater we determine a upper limit to
the merger fraction of 1.0% and a merger rate of
Mpc Gyr (assuming that all pairs merge on the shortest possible
timescale set by dynamical friction). This is significantly smaller than
predicted by theoretical models and suggests that major dry mergers do not
contribute to the formation of the red sequence at .Comment: 8 pages emulateapj style, 3 figures, accepted by AJ (March 2010
Discretion in Felony Sentencing—A Study of Influencing Factors
The desirability and constitutionality of discretionary criminal sentencing can be ascertained only if the factors influencing sentencing decisions are known. The authors analyze data generated by a 1971 survey of Washington State superior court trial judges in order to identify the significant factors and to evaluate their relative importance in criminal sentencing. The results indicate that discretionary sentencing is influenced strongly by social biases in no way dependent upon the culpability of the offender, his personal behavior patterns, or circumstances of the crime
The Two-Point Correlation of 2QZ Quasars and 2SLAQ LRGs: From a Quasar Fueling Perspective
Public data from the 2dF quasar survey (2QZ) and 2dF/SDSS LRG & QSO (2SLAQ),
with their vast reservoirs of spectroscopically located and identified sources,
afford us the chance to more accurately study their real space correlations in
the hopes of identifying the physical processes that trigger quasar activity.
We have used these two public databases to measure the projected cross
correlation, , between quasars and luminous red galaxies. We find the
projected two-point correlation to have a fitted clustering radius of and a slope, on scales from
0.7-27Mpc.
We attempt to understand this strong correlation by separating the LRG sample
into 2 populations of blue and red galaxies. We measure at the cross
correlation with each population. We find that these quasars have a stronger
correlation amplitude with the bluer, more recently starforming population in
our sample than the redder passively evolving population, which has a
correlation that is much more noisy and seems to flatten on scales Mpc. We compare this result to published work on hierarchical models.
The stronger correlation of bright quasars with LRGs that have undergone a
recent burst of starformation suggests that the physical mechanisms that
produce both activities are related and that minor mergers or tidal effects may
be important triggers of bright quasar activity and/or that bright quasars are
less highly biased than faint quasars.Comment: Accepted for publication in Ap
Sloan Digital Sky Survey III Photometric Quasar Clustering: Probing the Initial Conditions of the Universe using the Largest Volume
The Sloan Digital Sky Survey has surveyed 14,555 square degrees of the sky,
and delivered over a trillion pixels of imaging data. We present the
large-scale clustering of 1.6 million quasars between z = 0.5 and z = 2.5 that
have been classified from this imaging, representing the highest density of
quasars ever studied for clustering measurements. This data set spans ~11,000
square degrees and probes a volume of 80(Gpc/h)^3. In principle, such a large
volume and medium density of tracers should facilitate high-precision
cosmological constraints. We measure the angular clustering of photometrically
classified quasars using an optimal quadratic estimator in four redshift slices
with an accuracy of ~25% over a bin width of l ~10 - 15 on scales corresponding
to matter-radiation equality and larger (l ~ 2 - 30). Observational systematics
can strongly bias clustering measurements on large scales, which can mimic
cosmologically relevant signals such as deviations from Gaussianity in the
spectrum of primordial perturbations. We account for systematics by employing a
new method recently proposed by Agarwal et al. (2014) to the clustering of
photometrically classified quasars. We carefully apply our methodology to
mitigate known observational systematics and further remove angular bins that
are contaminated by unknown systematics. Combining quasar data with the
photometric luminous red galaxy (LRG) sample of Ross et al. (2011) and Ho et
al. (2012), and marginalizing over all bias and shot noise-like parameters, we
obtain a constraint on local primordial non-Gaussianity of fNL = -113+/-154
(1\sigma error). [Abridged]Comment: 35 pages, 15 figure
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Microstructures in Metasedimentary Rocks from the Neoproterozoic Bonahaven Formation, Scotland: Microconcretions, Impact Spherules, or Microfossils?
Microscopic spherules in relatively undeformed mudstones of the Neoproterozoic Bonahaven Formation, Islay, Scotland, are differentiated from their matrix by a sharp micron-scale, smoothly rounded boundary. These elongate spherules were earlier interpreted as hollow bodies filled penecontemporaneously by glauconite and subsequently metamorphosed to phengite, but their origin remains a matter of debate. Spherules observed in thin section are predominantly rounded (∼74%) but can exhibit a flat edge or protrusion at one end. In 11% of a sample population, two or more spherules are conjoined. X-ray diffraction indicates that spherule-bearing mudstones consist mainly of muscovite, with variable amounts of kaolin-group minerals and minor iron-chlorites. A range of physical origins for the spherules – including microconcretions or metamorphic microstructures; deposition from the sky as micrometeorites, microtektites/microkrystites, or accretionary volcanic ash particles; and detrital grains – is considered but rejected on distributional, morphological, and mineralogical evidence. Biological origins are considered most likely, especially protistan tests similar to the vase-shaped microfossils found in somewhat older Neoproterozoic rocks. If correct, this provides the first report of eukaryotic life in the Dalradian succession that passes critical tests for biogenicity and new evidence for testate microfossils in post-Sturtian but pre-Marinoan aged rocks.Earth and Planetary SciencesOrganismic and Evolutionary Biolog
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