5,666 research outputs found
A maximum-likelihood method for improving faint source flux and color estimates
Flux estimates for faint sources or transients are systematically biased high
because there are far more truly faint sources than bright. Corrections which
account for this effect are presented as a function of signal-to-noise ratio
and the (true) slope of the faint-source number-flux relation. The corrections
depend on the source being originally identified in the image in which it is
being photometered. If a source has been identified in other data, the
corrections are different; a prescription for calculating the corrections is
presented. Implications of these corrections for analyses of surveys are
discussed; the most important is that sources identified at signal-to-noise
ratios of four or less are practically useless.Comment: 9 pp., accepted for publication in PAS
The History of Galaxies and Galaxy Number Counts
(Abridged) A simple quantitative model is presented for the history of
galaxies to explain galaxy number counts, redshift distributions and some other
related observations. We first infer that irregular galaxies and the disks of
spiral galaxies are young, probably formed at from a
simultaneous consideration of colours and gas content under a moderate
assumption on the star formation history. Assuming that elliptical galaxies and
bulges of spiral galaxies, both called spheroids in the discussion, had formed
early in the universe, the resulting scenario is that spiral galaxies formed as
intergalactic gas accreting onto pre-existing bulges mostly at ;
irregular galaxies as seen today formed by aggregation of clouds at . Taking the formation epochs thus estimated into account, we construct
a model for the history of galaxies employing a stellar population synthesis
model. We assume that the number of galaxies does not change except that some
of them (irregulars) were newly born, and use a morphology-dependent local
luminosity function to constrain the number of galaxies. The predictions of the
model are compared with the observation of galaxy number counts and redshift
distributions for the , and colour bands. It is shown that young
irregular galaxies cause the steep slope of the -band counts. The fraction
of irregular galaxies increases with decreasing brightness: at mag, they
contribute as much as spiral galaxies. Thus, ``the faint blue galaxy problem''
is solved by invoking young galaxies. This interpretation is corroborated by a
comparison of our prediction with the morphologically-classified galaxy counts
in the band.Comment: 25 pages, LaTeX (aaspp4), 24 PostScript figures. Submitted to ApJ in
February 199
Measuring the Angular Correlation Function for Faint Galaxies in High Galactic Latitude Fields
A photometric survey of faint galaxies in three high Galactic latitude fields
(each ) with sub-arcsecond seeing is used to study the
clustering properties of the faint galaxy population. Multi-color photometry of
the galaxies has been obtained to magnitude limits of , and
. Angular correlation analysis is applied to magnitude-limited and
color-selected samples of galaxies from the three fields for angular
separations ranging from . General agreement is obtained with other
recent studies which show that the amplitude of the angular correlation
function, , is smoothly decreasing as a function of limiting
magnitude. The observed decline of rules out the viability of
``maximal merger'' galaxy evolution models. Using redshift distributions
extrapolated to faint magnitude limits, models of galaxy clustering evolution
are calculated and compared to the observed I-band . Faint
galaxies are determined to have correlation lengths and clustering evolution
parameters of either and ;
and ; or and
, assuming and with . The latter case is for clustering fixed in co-moving
coordinates and is probably unrealistic since most local galaxies are observed
to be more strongly clustered. No significant variations in the clustering
amplitude as a function of color are detected, for all the color-selected
galaxy samples considered. (Abridged)Comment: LaTeX (aaspp4.sty), 54 pages including 15 postscript figures; 3
additional uuencoded, gzipped postscript files (~300 kb each) of Figs. 1, 2
and 3 available at ftp://ftp.astro.ubc.ca/pub/woods ; To be published in the
Nov. 20, 1997 issue of The Astrophysical Journa
Tailoring the A and B site of Fe-based perovskites for high selectivity in the reverse water-gas shift reaction
Solving the woolly mammoth conundrum: amino acid 15N-enrichment suggests a distinct forage or habitat
Understanding woolly mammoth ecology is key to understanding Pleistocene community dynamics and evaluating the roles of human hunting and climate change in late Quaternary megafaunal extinctions. Previous isotopic studies of mammoths’ diet and physiology have been hampered by the ‘mammoth conundrum’: woolly mammoths have anomalously high collagen δ15N values, which are more similar to coeval carnivores than herbivores and which could imply a distinct diet and (or) habitat, or a physiological adaptation. We analyzed individual amino acids from collagen of adult woolly mammoths and coeval species and discovered greater 15N enrichment in source amino acids of woolly mammoths than in most other herbivores or carnivores. Woolly mammoths consumed an isotopically distinct food source, reflective of extreme aridity, dung fertilization and (or) plant selection. This dietary signal suggests that woolly mammoths occupied a distinct habitat or forage niche relative to other Pleistocene herbivores
The Calar Alto Deep Imaging Survey: K-band Galaxy Number Counts
We present K-band number counts for the faint galaxies in the Calar Alto Deep
Imaging Survey (CADIS). We covered 4 CADIS fields, a total area of 0.2deg^2, in
the broad band filters B, R and K. We detect about 4000 galaxies in the K-band
images, with a completeness limit of K=19.75mag, and derive the K-band galaxy
number counts in the range of 14.25 < K < 19.75mag. This is the largest medium
deep K-band survey to date in this magnitude range. The B- and R-band number
counts are also derived, down to completeness limits of B=24.75mag and
R=23.25mag. The K-selected galaxies in this magnitude range are of particular
interest, since some medium deep near-infrared surveys have identified breaks
of both the slope of the K-band number counts and the mean B-K color at
K=17\sim18mag. There is, however, a significant disagreement in the K-band
number counts among the existing surveys. Our large near-infrared selected
galaxy sample allows us to establish the presence of a clear break in the slope
at K=17.0mag from dlogN/dm = 0.64 at brighter magnitudes to dlogN/dm = 0.36 at
the fainter end. We construct no-evolution and passive evolution models, and
find that the passive evolution model can simultaneously fit the B-, R- and
K-band number counts well. The B-K colors show a clear trend to bluer colors
for K > 18mag. We also find that most of the K=18-20mag galaxies have a B-K
color bluer than the prediction of a no-evolution model for an L_* Sbc galaxy,
implying either significant evolution, even for massive galaxies, or the
existence of an extra population of small galaxies.Comment: Accepted for A&A, 10 pages, 7 figure
J- and Ks-band Galaxy Counts and Color Distributions in the AKARI North Ecliptic Pole Field
We present the J- and Ks-band galaxy counts and galaxy colors covering 750
square arcminutes in the deep AKARI North Ecliptic Pole (NEP) field, using the
FLoridA Multi-object Imaging Near-ir Grism Observational Spectrometer
(FLAMINGOS) on the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
limiting magnitudes with a signal-to-noise ratio of three in the deepest
regions are 21.85 and 20.15 in the J- and Ks-bands respectively in the Vega
magnitude system. The J- and Ks-band galaxy counts in the AKARI NEP field are
broadly in good agreement with those of other results in the literature,
however we find some indication of a change in the galaxy number count slope at
J~19.5 and over the magnitude range 18.0 < Ks < 19.5. We interpret this feature
as a change in the dominant population at these magnitudes because we also find
an associated change in the B - Ks color distribution at these magnitudes where
the number of blue samples in the magnitude range 18.5 < Ks < 19.5 is
significantly larger than that of Ks < 17.5
Cosmological Constraints from Measurements of Type Ia Supernovae discovered during the first 1.5 years of the Pan-STARRS1 Survey
We present griz light curves of 146 spectroscopically confirmed Type Ia
Supernovae () discovered during the first 1.5 years of the
Pan-STARRS1 Medium Deep Survey. The Pan-STARRS1 natural photometric system is
determined by a combination of on-site measurements of the instrument response
function and observations of spectrophotometric standard stars. We find that
the systematic uncertainties in the photometric system are currently 1.2\%
without accounting for the uncertainty in the HST Calspec definition of the AB
system. A Hubble diagram is constructed with a subset of 113 out of 146 SNe Ia
that pass our light curve quality cuts. The cosmological fit to 310 SNe Ia (113
PS1 SNe Ia + 222 light curves from 197 low-z SNe Ia), using only SNe and
assuming a constant dark energy equation of state and flatness, yields
.
When combined with BAO+CMB(Planck)+, the analysis yields and including all
identified systematics (see also Scolnic et al. 2014). The value of is
inconsistent with the cosmological constant value of at the 2.3
level. Tension endures after removing either the BAO or the constraint,
though it is strongest when including the constraint. If we include WMAP9
CMB constraints instead of those from Planck, we find
, which diminishes the discord to . We
cannot conclude whether the tension with flat CDM is a feature of dark
energy, new physics, or a combination of chance and systematic errors. The full
Pan-STARRS1 supernova sample with 3 times as many SNe should provide
more conclusive results.Comment: 38 pages, 16 figures, 14 tables, ApJ in pres
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