385 research outputs found
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500 (the pseudo-pressure YX has a consistent scatter of 22%+/-5%). The scatter
does not change when measured within a fixed physical radius of 1 Mpc. Clusters
with small BCG to X-ray peak offsets constitute a very regular population whose
members have the same gas mass fractions and whose even smaller <10% deviations
from regularity can be ascribed to line of sight geometrical effects alone.
Cool-core clusters, while a somewhat different population, also show the same
(<10%) scatter in the gas mass-lensing mass relation. There is a good
correlation and a hint of bimodality in the plane defined by BCG offset and
central entropy (or central cooling time). The pseudo-pressure YX does not
discriminate between the more relaxed and less relaxed populations, making it
perhaps the more even-handed mass proxy for surveys. Overall, hydrostatic
masses underestimate weak lensing masses by 10% on the average at r500; but
cool-core clusters are consistent with no bias, while non-cool-core clusters
have a large and constant 15-20% bias between r2500 and r500, in agreement with
N-body simulations incorporating unthermalized gas. For non-cool-core clusters,
the bias correlates well with BCG ellipticity. We also examine centroid shift
variance and and power ratios to quantify substructure; these quantities do not
correlate with residuals in the scaling relations. Individual clusters have for
the most part forgotten the source of their departures from self-similarity.Comment: Corrects an error in the X-ray luminosities (erratum
submitted)---none of the other results are affected. Go to
http://sfstar.sfsu.edu/jaco for an electronic fitter and updated quick data
download link
On the Energy Required to Eject Processed Matter from Galaxies
We evaluate the minimum energy input rate that starbursts require for
expelling their newly processed matter from their host galaxies. Special
attention is given to the pressure caused by the environment in which a galaxy
is situated, as well as to the intrinsic rotation of the gaseous component. We
account for these factors and for a massive dark matter distribution, and
develop a self-consistent solution for the interstellar matter gas
distribution. Our results are in excellent agreement with the results of Mac
Low & Ferrara (1999) for galaxies with a flattened disk-like ISM density
distribution and a low intergalactic gas pressure ( 1
cm K). However, our solution also requires a much larger energy input
rate threshold when one takes into consideration both a larger intergalactic
pressure and the possible existence of a low-density, non-rotating, extended
gaseous halo component.Comment: 7 pages, 4 figures, 1 table, Accepted for publication in Ap
Discovery of a Metal-Line Absorber Associated with a Local Dwarf Starburst Galaxy
We present optical and near-infrared images, H I 21 cm emission maps, optical
spectroscopy, and Hubble Space Telescope/Space Telescope Imaging Spectrograph
ultraviolet spectroscopy of the QSO/galaxy pair SBS 1122+594/IC 691. The QSO
sight line lies at a position angle of 27 degrees from the minor axis of the
nearby dwarf starburst galaxy IC 691 (cz_gal = 1204+-3 km/s, L_B ~ 0.09 L*,
current star formation rate = 0.08-0.24 solar masses per year) and 33 kpc (6.6
arcmin) from its nucleus. We find that IC 691 has an H I mass of M_HI =
(3.6+-0.1) x 10^8 solar masses and a dynamical mass of M_dyn = (3.1+-0.5) x
10^10 solar masses. The UV spectrum of SBS 1122+594 shows a metal-line
(Ly-alpha + C IV) absorber near the redshift of IC 691 at cz_abs = 1110+-30
km/s. Since IC 691 is a dwarf starburst and the SBS 1122+594 sight line lies in
the expected location for an outflowing wind, we propose that the best model
for producing this metal-line absorber is a starburst wind from IC 691. We
place consistent metallicity limits on IC 691 ([Z/Zsun] ~ -0.7) and the
metal-line absorber ([Z/Zsun] < -0.3). We also find that the galaxy's escape
velocity at the absorber location is v_esc = 80+-10 km/s and derive a wind
velocity of v_w = 160+-50 km/s. Thus, the evidence suggests that IC 691
produces an unbound starburst wind that escapes from its gravitational
potential to transport metals and energy to the surrounding intergalactic
medium.Comment: 31 pages, 8 figures; AJ in press; a version with high resolution
figures can be downloaded from
http://casa.colorado.edu/~keeney/research/papers/IC691.pd
Evolution of the Luminosity Density in the Universe: Implications for the Nonzero Cosmological Constant
We show that evolution of the luminosity density of galaxies in the universe
provides a powerful test for the geometry of the universe. Using reasonable
galaxy evolution models of population synthesis which reproduce the colors of
local galaxies of various morphological types, we have calculated the
luminosity density of galaxies as a function of redshift . Comparison of the
result with recent measurements by the Canada-France Redshift Survey in three
wavebands of 2800{\AA}, 4400{\AA}, and 1 micron at z<1 indicates that the
\Lambda-dominated flat universe with \lambda_0 \sim 0.8 is favored, and the
lower limit on \lambda_0 yields 0.37 (99% C.L.) or 0.53 (95% C.L.) if
\Omega_0+\lambda_0=1. The Einstein-de Sitter universe with (\Omega_0,
\lambda_0)=(1, 0) and the low-density open universe with (0.2, 0) are however
ruled out with 99.86% C.L. and 98.6% C.L., respectively. The confidence levels
quoted apply unless the standard assumptions on galaxy evolution are
drastically violated. We have also calculated a global star formation rate in
the universe to be compared with the observed rate beyond z \sim 2. We find
from this comparison that spiral galaxies are formed from material accretion
over an extended period of a few Gyrs, while elliptical galaxies are formed
from initial star burst at z >~ 5 supplying enough amount of metals and
ionizing photons in the intergalactic medium.Comment: 11 pages including 3 figures, LaTeX, uses AASTeX. To Appear in ApJ
Letter
Rapid In Vitro Multiplication of Non-Runnering \u3cem\u3eFragaria vesca\u3c/em\u3e Genotypes from Seedling Shoot Axillary Bud Explants
Fragaria vesca L. has become a model species for genomic studies relevant to important crop plant species in the Rosaceae family, but generating large numbers of plants from non-runner-producing genotypes is slow. To develop a protocol for the rapid generation of plants, leaf explants were compared to single axillary bud shoot explants, both from in vitro-grown Fragaria vesca seedlings, as sources of shoots for new plant production in response to benzyladenine (BA) or thidiazuron (TDZ) combined with indolebutyric acid (IBA) on Murashige and Skoogâs Basal Salt (MS) medium. BA at 2.0 and 4.0 mg Lâ1 and TDZ at 1.5 mg Lâ1 promoted the greatest number of shoots produced per shoot explant. There were no IBA effects or IBA interactions with BA or TDZ. Significant interactions between BA and IBA, but not TDZ and IBA, occurred in leaf explant callus formation and % explants with callus at 6 and 9 weeks of culture and on shoots per leaf explant at 9 weeks. TDZ treatments produced uniformly high levels of callus but low numbers of shoots. The treatment generating the most shoot production was BA at 4.0 mg Lâ1 plus IBA at 0.50 mg Lâ1. After 9 weeks of culture, leaf explants of the non-runner-producing genotype Baron Solemacher had generated 4.6 shoots per explant with the best treatment, while axillary bud explants had generated 30.8 shoots with the best treatment. Thus, in vitro culture of shoot axillary bud explants can generate high numbers of clonal shoots from a single seedling plant in vitro
An Old Cluster in NGC 6822
We present spectroscopy of two clusters in the dwarf irregular galaxy NGC
6822. From these we deduce an age for Cluster VII of 11 Gyr and [Fe/H] = -1.95
+/- 0.15 dex. Cluster VII appears to be an analog of the metal-poor galactic
globular clusters. Cluster VI is found to be much younger and more metal rich,
with an age of approximately 2 Gyr. Its derived metallicity, [Fe/H], of
approximately -1.0 dex is comparable to that of the gas seen today in NGC 6822.
The existence of a metal-poor old cluster in NGC 6822 rules out models for the
chemical evolution of this galaxy with significant prompt initial enhancement.
We find that a star formation rate which is constant with time and is within a
factor of two of the present star formation rate can reproduce the two points
on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined
by these two clusters.Comment: 8 pages; accepted for publication in A
Evidence for Non-Hydrostatic Gas from the Cluster X-ray to Lensing Mass Ratio
Using a uniform analysis procedure, we measure spatially resolved weak
gravitational lensing and hydrostatic X-ray masses for a sample of 18 clusters
of galaxies. We find a radial trend in the X-ray to lensing mass ratio: at
r2500 we obtain a ratio MX/ML=1.03+/-0.07 which decreases to MX/ML=0.78+/-0.09
at r500. This difference is significant at 3 sigma once we account for
correlations between the measurements. We show that correcting the lensing mass
for excess correlated structure outside the virial radius slightly reduces, but
does not eliminate this trend. An X-ray mass underestimate, perhaps due to
nonthermal pressure support, can explain the residual trend. The trend is not
correlated with the presence or absence of a cool core. We also examine the
cluster gas fraction and find no correlation with ML, an important result for
techniques that aim to determine cosmological parameters using the gas
fraction.Comment: 8 pages, minor modifications, accepted for publication in MNRA
Discovery of a Dwarf Post-Starburst Galaxy Near a High Column Density Ly-alpha Absorber
We report the discovery of a dwarf (M_B = -13.9) post-starburst galaxy
coincident in recession velocity (within uncertainties) with the highest column
density absorber (N_HI = 10^15.85 cm^{-2} at cz = 1586 km/s) in the 3C~273
sightline. This galaxy is by far the closest galaxy to this absorber, projected
just 71 kpc on the sky from the sightline. The mean properties of the stellar
populations in this galaxy are consistent with a massive starburst ~3.5 Gyrs
ago, whose attendant supernovae, we argue, could have driven sufficient gas
from this galaxy to explain the nearby absorber. Beyond the proximity on the
sky and in recession velocity, the further evidence in favor of this conclusion
includes both a match in the metallicities of absorber and galaxy, and the fact
that the absorber has an overabundance of Si/C, suggesting recent type II
supernova enrichment. Thus, this galaxy and its ejecta are the expected
intermediate stage in the fading dwarf evolutionary sequence envisioned by
Babul & Rees to explain the abundance of faint blue galaxies at intermediate
redshifts.Comment: 33 pages, 4 figures, ApJ in pres
Strong Clustering of Faint Galaxies at Small Angular Scales
The 2-point angular correlation function of galaxies, \wt, has been computed
on equatorial fields observed with the CTIO 4m prime focus, within a total area
of 2.31 deg. In the magnitude range , corresponding to
, we find an excess of power in \wt at scales over what would be expected from an extrapolation of \wt measured at
larger . The significance of this excess is . At
larger scales, , the amplitude of \wt is 1.6 times
smaller than the standard no evolutionary model. At these scales there is
remarkable agreement between the present data and Infante \& Pritchet (1995).
At large angular scales () the data is best described
by a model where clustering evolution in has taken place. Strong
luminosity evolution cannot be ruled out with the present data. At smaller
scales, , our data are formally fit by models where
Mpc) or Mpc
. If the mean redshift of our sample is 0.35 then our
data show a clear detection of the scale () where the
clustering evolution approaches a highly non linear regime, i.e., .
The rate at which galaxies merge has been computed. If this rate is
proportional to , then .Comment: 10 pages, LaTeX text, 2 Postscript figures, To appear in ApJ Let
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