3,112 research outputs found
A 20 Thousand Solar Mass Black Hole in the Stellar Cluster G1
We present the detection of a 2.0(+1.4,-0.8)x10^4 solar mass black hole (BH)
in the stellar cluster G1 (Mayall II), based on data taken with the Space
Telescope Imaging Spectrograph onboard the Hubble Space Telescope. G1 is one of
the most massive stellar clusters in M31. The central velocity dispersion (25
kms) and the measured BH mass of G1 places it on a linear extrapolation of the
correlation between BH mass and bulge velocity dispersion established for
nearby galaxies. The detection of a BH in this low-mass stellar system suggests
that (1) the most likely candidates for seed massive BHs come from stellar
clusters, (2) there is a direct link between massive stellar clusters and
normal galaxies, and (3) the formation process of both bulges and massive
clusters is similar due to their concordance in the M_BH/sigma relation.
Globular clusters in our Galaxy should be searched for central BHs.Comment: 4 pages, accepted in The Astrophysical Journal Letters, October 200
Organization of phenylalanine ammonia lyase (PAL), acidic PR-5 and osmotin-like (OSM) defence-response gene families in the potato genome
A Stellar Dynamical Measurement of the Black Hole Mass in the Maser Galaxy NGC 4258
We determine the mass of the black hole at the center of the spiral galaxy
NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These
models are constrained by high spatial resolution imaging and long-slit
spectroscopy of the nuclear region obtained with the {\em Hubble Space
Telescope}, complemented by ground-based observations extending to larger
radii. Our best mass estimate is \MBH = (3.3 \pm 0.2) \times 10^7 \MSun for
a distance of 7.28 Mpc (statistical errors only). This is within 15% of
(3.82\pm 0.01) \times 10^7 \MSun, the mass determined from the kinematics of
water masers (rescaled to the same distance) assuming they are in Keplerian
rotation in a warped disk. The construction of accurate dynamical models of NGC
4258 is somewhat compromised by an unresolved active nucleus and color
gradients, the latter caused by variations in the stellar population and/or
obscuring dust. These problems are not present in the other black
hole mass determinations from stellar dynamics that have been published by us
and other groups; thus, the relatively close agreement between the stellar
dynamical mass and the maser mass in NGC 4258 enhances our confidence in the
black hole masses determined in other galaxies from stellar dynamics using
similar methods and data of comparable quality.Comment: 58 pages, submitted to ApJ. Some figures excluded due to size. The
entire paper is at http://www.noao.edu/noao/staff/lauer/nuker_papers.htm
An Intermediate-Mass Black Hole in the Globular Cluster G1: Improved Significance from New Keck and Hubble Space Telescope Observations
We present dynamical models for the massive globular cluster G1. The goal is
to measure or place a significant upper limit on the mass of any central black
hole. Whether or not globular clusters contain central massive black holes has
important consequences for a variety of studies. We use new kinematic data
obtained with Keck and new photometry from the Hubble Space Telescope. The Keck
spectra allow us to obtain kinematics out to large radii that are required to
pin down the mass-to-light ratio of the dynamical model and the orbital
structure. The Hubble Space Telescope observations give us a factor of two
better spatial resolution for the surface brightness profile. By fitting
non-parametric, spherical, isotropic models we find a best-fit black hole mass
of 1.7(+-0.3)e4 Msun. Fully general axisymmetric orbit-based models give
similar results, with a black hole mass of 1.8(+-0.5)e4 Msun. The no-black hole
model has Delta_chi^2=5 (marginalized over mass-to-light ratio), implying less
than 3% significance. We have taken into account any change in the
mass-to-light ratio in the center due to stellar remnants. These results are
consistent with our previous estimate in Gebhardt, Rich & Ho (2002), and
inconsistent with the analysis of Baumgardt et al. (2003) who claim that G1
does not show evidence for a black hole. These new results make G1 the best
example of a cluster that contains an intermediate-mass black hole.Comment: accepted for publication in the Astrophysical Journa
Deep Photometry in a Remote M31 Major Axis Field Near G1
We present photometry from Hubble Space Telescope (HST)/Wide Field Planetary
Camera 2 parallel imagery of a remote M31 field at a projected distance of
about 34 kpc from the nucleus near the SW major axis. This field is near the
globular cluster G1, and near one of the candidate tidal plumes identified by
Ferguson et al. (2002). The F606W (V) and F814W (I) images were obtained in
parallel with Space Telescope Imaging Spectrograph spectroscopy of G1 (GO-9099)
and total 7.11 hours of integration time -- the deepest HST field in the outer
disk of M31 to date, reaching to V ~ 28. The color-magnitude diagram of the
field shows a clearly-defined red clump at V = 25.25 and a red giant branch
consistent with [Fe/H] ~ -0.7. The lack of a blue horizontal branch contrasts
with other M31 halo fields, the Andromeda dwarf spheroidals, and with the
nearby globular cluster G1. Comparing the observed luminosity function to the
Padova models, we find that at least some of the stellar population must be
younger than 6 - 8 Gyr. The outermost detected neutral hydrogen gas disk of M31
lies only 2 kpc in projection from our field. The finding that some giants in
the field have radial velocities close to that of the neutral hydrogen gas
(Reitzel, Guhathakurta, & Rich 2003) leads us to conclude that our field
samples the old, low-surface-brightness disk rather than the true Population II
spheroid.Comment: 15 pages, 3 figures. accepted for publication in the A
A Frontal Dust Storm in the Northern Hemisphere at Solar Longitude 97 : An Unusual Observation by the Emirates Mars Mission
Funding Information: Funding for the development of the EMM mission was provided by the United Arab Emirates Government, and to coâauthors outside of the United Arab Emirates by the Mohammed Bin Rashid Space Centre. This work was also supported by a joint research agreement between the Mohammed Bin Rashid Space Centre and the National Space Science and Technology Center in the United Arab Emirates University. CG, BKG, and RMBY were supported by the United Arab Emirates University Grant âMars and Earth atmospheric science research at the National Space Science and Technology Center,â G00003407. RMBY was also supported by UAE University grant G00003322.Peer reviewe
Stillbirth risk across pregnancy by size for gestational age in Western Cape Province, South Africa: Application of the fetuses-at-risk approach using perinatal audit data
Background. There is little published work on the risk of stillbirth across pregnancy for small-for-gestational-age (SGA) and large-for-gestational (LGA) pregnancies in low-resource settings.Objectives. To compare stillbirth risk across pregnancy between SGA and appropriate-for-gestational-age (AGA) pregnancies in Western Cape Province, South Africa (SA).Methods. A retrospective audit of perinatal mortality data using data from the SA Perinatal Problem Identification Program was conducted. All audited stillbirths with information on size for gestational age (N=677) in the Western Cape between October 2013 and August 2015 were included in the study. The Western Cape has antenatal care (ANC) appointments at booking and at 20, 26, 32, 34, 36, 38 and 41 (if required) weeksâ gestation. A fetuses-at-risk approach was adopted to examine stillbirth risk (28 - 42 weeksâ gestation, â„1Â 000 g) across gestation by size for gestational age (SGA <10th centile Theron growth curves, LGA >90th centile). Stillbirth risk was compared between SGA/LGA and AGA pregnancies.Results. SGA pregnancies were at an increased risk of stillbirth compared with AGA pregnancies between 30 and 40 weeksâ gestation, with the relative risk (RR) ranging from 3.5 (95% confidence interval (CI) 1.6 - 7.6) at 30 weeksâ gestation to 15.3 (95% CI 8.8 - 26.4) at 33 weeksâ gestation (p<0.001). The risk for LGA babies increased by at least 3.5-fold in the later stages of pregnancy (from 37 weeks) (p<0.001). At 38 Â weeks, the greatest increased risk was seen for LGA pregnancies (RR 6.6, 95% CI 3.1 - 14.2; p<0.001).Conclusions. There is an increased risk of stillbirth for SGA pregnancies, specifically between 33 and 40 weeksâ gestation, despite fortnightly ANC visits during this time. LGA pregnancies are at an increased risk of stillbirth after 37 weeksâ gestation. This high-risk period highlights potential issues with the detection of fetuses at risk of stillbirth even when ANC is frequent.
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