4,142 research outputs found
Complete Treatment of Galaxy Two-Point Statistics: Gravitational Lensing Effects and Redshift-Space Distortions
We present a coherent theoretical framework for computing gravitational
lensing effects and redshift-space distortions in an inhomogeneous universe and
investigate their impacts on galaxy two-point statistics. Adopting the
linearized FRW metric, we derive the gravitational lensing and the generalized
Sachs-Wolfe effects that include the weak lensing distortion, magnification,
and time delay effects, and the redshift-space distortion, Sachs-Wolfe, and
integrated Sachs-Wolfe effects, respectively. Based on this framework, we first
compute their effects on observed source fluctuations, separating them as two
physically distinct origins: the volume effect that involves the change of
volume and is always present in galaxy two-point statistics, and the source
effect that depends on the intrinsic properties of source populations. Then we
identify several terms that are ignored in the standard method, and we compute
the observed galaxy two-point statistics, an ensemble average of all the
combinations of the intrinsic source fluctuations and the additional
contributions from the gravitational lensing and the generalized Sachs-Wolfe
effects. This unified treatment of galaxy two-point statistics clarifies the
relation of the gravitational lensing and the generalized Sachs-Wolfe effects
to the metric perturbations and the underlying matter fluctuations. For near
future dark energy surveys, we compute additional contributions to the observed
galaxy two-point statistics and analyze their impact on the anisotropic
structure. Thorough theoretical modeling of galaxy two-point statistics would
be not only necessary to analyze precision measurements from upcoming dark
energy surveys, but also provide further discriminatory power in understanding
the underlying physical mechanisms.Comment: 20 pages, 5 figures, Fig.4 corrected, appendix added, accepted for
publication in Physical Review
A photometricity and extinction monitor at the Apache Point Observatory
An unsupervised software ``robot'' that automatically and robustly reduces
and analyzes CCD observations of photometric standard stars is described. The
robot measures extinction coefficients and other photometric parameters in real
time and, more carefully, on the next day. It also reduces and analyzes data
from an all-sky camera to detect clouds; photometric data taken
during cloudy periods are automatically rejected. The robot reports its
findings back to observers and data analysts via the World-Wide Web. It can be
used to assess photometricity, and to build data on site conditions. The
robot's automated and uniform site monitoring represents a minimum standard for
any observing site with queue scheduling, a public data archive, or likely
participation in any future National Virtual Observatory.Comment: accepted for publication in A
Evaluation of Metals in a Defined Medium for \u3ci\u3ePichia pastoris\u3c/i\u3e Expressing Recombinant β-Galactosidase
Culture growth and recombinant protein yield of the Pichia pastoris GS115 methanol utilization positive system were studied in response to the types and levels of metals present in the growth medium and the supplemental salts typically used for these fermentations. Magnesium and zinc were both required to support cell growth but at significantly reduced levels compared to the control. However, supplementation with calcium, cobalt, iron, manganese, iodine, boron, and molybdenum were not required to sustain cell mass. When the medium was reformulated with only zinc and magnesium, the cells grew to 12–15 generations, which are expected for high cell density fed-batch fermentations. Product yields of the recombinant protein β-galactosidase were significantly influenced by the trace metal concentrations. By using response surface and full factorial designs, maximum protein yield occurred when the concentration of zinc salt was limited to the level necessary only to support cell mass while protein yield positively correlated to increasing levels of the remaining trace metal salts. These studies are the first to show that excess trace metals must be optimized when developing P. pastoris based fed-batch fermentations
Chandra Multiwavelength Project: Normal Galaxies at Intermediate Redshift
(abridged) We have investigated 136 Chandra extragalactic sources without
broad optical emission lines, including 93 galaxies with narrow emission lines
(NELG) and 43 with only absorption lines (ALG). Based on fx/fo, Lx, X-ray
spectral hardness and optical emission line diagnostics, we have conservatively
classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. We
found no statistically significant evolution in Lx/LB, within the limited z
range. We have built log(N)-log(S), after correcting for completeness based on
a series of simulations. The best-fit slope is -1.5 for both S and B energy
bands, which is considerably steeper than that of the AGN-dominated cosmic
background sources, but slightly flatter than the previous estimate, indicating
normal galaxies will not exceed the AGN population until fx ~ 2 x 10-18 erg s-1
cm-2 (a factor of ~5 lower than the previous estimate). A group of NELGs appear
to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting
for intrinsic absorption, their X-ray luminosities could be Lx > 10^44 erg s-1,
making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG -
X-ray bright, optically normal galaxy candidates) do not appear to be
significantly absorbed, we found two heavily obscured objects, which could be
as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A
galaxy candidates with strong Balmer absorption lines, but no [OII] line. The
X-ray spectra of both galaxies are soft and one of them has a nearby close
companion galaxy, supporting the merger/interaction scenario rather than the
dusty starburst hypothesis.Comment: 31 pages, 9 figures, accepted for publication in ApJ (20 June 2006,
v644), replaced with minor correction
The Cepheid distance to the Local Group Galaxy NGC 6822
Recent estimates of the Cepheid distance modulus of NGC 6822 differ by 0.18
mag. To investigate this we present new multi-epoch JHKs photometry of
classical Cepheids in the central region of NGC 6822 and show that there is a
zero-point difference from earlier work. These data together with optical and
mid-infrared observations from the literature are used to derive estimates of
the distance modulus of NGC 6822. A best value of 23.40 mag is adopted, based
on an LMC distance modulus of 18.50 mag. The standard error of this quantity is
~0.05 mag. We show that to derive consistent moduli from Cepheid observations
at different wavelengths, it is necessary that the fiducial LMC
period-luminosity relations at these wavelengths should refer to the same
subsample of stars. Such a set is provided. A distance modulus based on RR
Lyrae variables agrees with the Cepheid result.Comment: accepted for publication in MNRA
Physical Properties of the X-ray Luminous SN 1978K in NGC 1313 from Multiwavelength Observations
We update the light curves from the X-ray, optical, and radio bandpasses
which we have assembled over the past decade, and present two observations in
the ultraviolet using the Hubble Space Telescope Faint Object Spectrograph. The
HRI X-ray light curve is constant within the errors over the entire observation
period. This behavior is confirmed in the ASCA GIS data obtained in 1993 and
1995. In the ultraviolet, we detected Ly-alpha, the [Ne IV] 2422/2424 A
doublet, the Mg II doublet at 2800 A, and a line at ~3190 A we attribute to He
I 3187. Only the Mg II and He I lines are detected at SN1978K's position. The
optical light curve is formally constant within the errors, although a slight
upward trend may be present. The radio light curve continues its steep decline.
The longer time span of our radio observations compared to previous studies
shows that SN1978K is in the same class of highly X-ray and radio-luminous
supernovae as SN1986J and SN1988Z. The [Ne IV] emission is spatially distant
from the location of SN1978K and originates in the pre-shocked matter. The Mg
II doublet flux ratio implies the quantity of line optical depth times density
of ~10^14 cm^-3 for its emission region. The emission site must lie in the
shocked gas.Comment: 32 pages, 13 figs; LaTeX with AASTEXv5; paper accepted, scheduled for
AJ, Dec 199
What Produced the Ultraluminous Supernova Remnant in NGC 6946?
The ultraluminous supernova remnant (SNR) in NGC 6946 is the brightest known
SNR in X-rays, ~1000 times brighter than Cas A. To probe the nature of this
remnant and its progenitor, we have obtained high-dispersion optical echelle
spectra. The echelle spectra detect H-alpha, [N II], and [O III] lines, and
resolve these lines into a narrow (FWHM ~20--40 km/s) component from un-shocked
material and a broad (FWHM ~250 km/s) component from shocked material. Both
narrow and broad components have unusually high [N II]/H-alpha ratios, ~1.
Using the echelle observation, archival HST images, and archival ROSAT X-ray
observations, we conclude that the SNR was produced by a normal supernova,
whose progenitor was a massive star, either a WN star or a luminous blue
variable. The high luminosity of the remnant is caused by the supernova ejecta
expanding into a dense, nitrogen-rich circumstellar nebula created by the
progenitor.Comment: 20 pages, 5 figures. To be published in The Astronomical Journal,
March 200
Eleven years of radio monitoring of the Type IIn supernova SN 1995N
We present radio observations of the optically bright Type IIn supernova SN
1995N. We observed the SN at radio wavelengths with the Very Large Array (VLA)
for 11 years. We also observed it at low radio frequencies with the Giant
Metrewave Radio Telescope (GMRT) at various epochs within years since
explosion. Although there are indications of an early optically thick phase,
most of the data are in the optically thin regime so it is difficult to
distinguish between synchrotron self absorption (SSA) and free-free absorption
(FFA) mechanisms. However, the information from other wavelengths indicates
that the FFA is the dominant absorption process. Model fits of radio emission
with the FFA give reasonable physical parameters. Making use of X-ray and
optical observations, we derive the physical conditions of the shocked ejecta
and the shocked CSM.Comment: 22 pages, 2 tables, 13 figures, Accepted for publication in
Astrophysical Journa
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