110 research outputs found
High Latitude HI in NGC 2613: Buoyant Disk-Halo Outflow
We combine new VLA D array HI data of NGC 2613 with previous high resolution
data to show new disk-halo features in this galaxy. The global HI distribution
is modeled in detail using a technique which can disentangle the effects of
inclination from scale height and can also solve for the average volume density
distribution in and perpendicular to the disk. The model shows that the
galaxy's inclination is on the low end of the range given by Chaves & Irwin
(2001) and that the HI disk is thin (z_e = 188 pc), showing no evidence for
halo. Numerous discrete disk-halo features are observed, however, achieving z
heights up to 28 kpc from mid-plane. One prominent feature in particular, of
mass, 8X10^7 Msun and height, 22 kpc, is seen on the advancing side of the
galaxy at a projected galactocentric radius of 15.5 kpc. If this feature
achieves such high latitudes because of events in the disk alone, then input
energies of order ~ 10^{56} ergs are required. We have instead investigated the
feasibility of such a large feature being produced via buoyancy (with drag)
within a hot, pre-existing X-ray corona. Reasonable plume densities,
temperatures, stall height (~ 11 kpc), outflow velocities and ages can indeed
be achieved in this way. The advantage of this scenario is that the input
energy need only be sufficient to produce blow-out, a condition which requires
a reduction of three orders of magnitude in energy. If this is correct, there
should be an observable X-ray halo around NGC 2613.Comment: 32 pages 7 gif figures, accepted by Ap
CHANG-ES VI: Probing Supernova Energy Deposition in Spiral Galaxies Through Multi-Wavelength Relationships
How a galaxy regulates its SNe energy into different
interstellar/circumgalactic medium components strongly affects galaxy
evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz)
continuum observations, we perform statistical analysis comparing
multi-wavelength properties of the CHANG-ES galaxies. The high-quality JVLA
data and edge-on orientation enable us for the first time to include the halo
into the energy budget for a complete radio-flux-limited sample. We find tight
correlations of with the mid-IR-based SFR. The normalization of
our relation is 2-3 times of
those obtained for face-on galaxies, probably a result of enhanced IR
extinction at high inclination. We also find tight correlations between and the SNe energy injection rate , indicating
the energy loss via synchrotron radio continuum accounts for of
, comparable to the energy contained in CR electrons. The
integrated C-to-L-band spectral index is for non-AGN
galaxies, indicating a dominance by the diffuse synchrotron component. The
low-scatter /
relationships have super-linear logarithmic slopes at in L-band
(/) while consistent with linear in C-band
(/). The super-linearity could be naturally
reproduced with non-calorimeter models for galaxy disks. Using Chandra halo
X-ray measurements, we find sub-linear relations.
These results indicate that the observed radio halo of a starburst galaxy is
close to electron calorimeter, and a galaxy with higher SFR tends to distribute
an increased fraction of SNe energy into radio emission (than X-ray).Comment: 16 pages, 6 figures, 1 table, MNRAS in pres
CHANG-ES IV: Radio continuum emission of 35 edge-on galaxies observed with the Karl G. Jansky Very Large Array in D-configuration, Data Release 1
We present the first part of the observations made for the Continuum Halos in
Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES
project is to study and characterize the nature of radio halos, their
prevalence as well as their magnetic fields, and the cosmic rays illuminating
these fields. This paper reports observations with the compact D configuration
of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby
edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the
VLA, an unprecedented sensitivity was achieved for all polarization products.
The beam resolution is an average of 9.6" and 36" with noise levels reaching
approximately 6 and 30 microJy per beam for C- and L-bands, respectively
(robust weighting). We present intensity maps in these two frequency bands (C
and L), with different weightings, as well as spectral index maps, polarization
maps, and new measurements of star formation rates (SFRs). The data products
described herein are available to the public in the CHANG-ES data release
available at www.queensu.ca/changes. We also present evidence of a trend among
galaxies with larger halos having higher SFR surface density, and we show, for
the first time, a radio continuum image of the median galaxy, taking advantage
of the collective signal-to-noise ratio of 30 of our galaxies. This image shows
clearly that a typical spiral galaxy is surrounded by a halo of magnetic fields
and cosmic rays.Comment: 70 pages, of which 35 pages present the data of each galax
Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) -- I: Introduction to the Survey
We introduce a new survey to map the radio continuum halos of a sample of 35
edge-on spiral galaxies at 1.5 GHz and 6 GHz in all polarization products. The
survey is exploiting the new wide bandwidth capabilities of the Karl G. Jansky
Very Large Array (i.e. the Expanded Very Large Array, or EVLA) in a variety of
array configurations (B, C, and D) in order to compile the most comprehensive
data set yet obtained for the study of radio halo properties. This is the first
survey of radio halos to include all polarization products.
In this first paper, we outline the scientific motivation of the survey, the
specific science goals, and the expected improvements in noise levels and
spatial coverage from the survey. Our goals include investigating the physical
conditions and origin of halos, characterizing cosmic ray transport and wind
speed, measuring Faraday rotation and mapping the magnetic field, probing the
in-disk and extraplanar far-infrared - radio continuum relation, and
reconciling non-thermal radio emission with high-energy gamma-ray models. The
sample size allows us to search for correlations between radio halos and other
properties, including environment, star formation rate, and the presence of
AGNs. In a companion paper (Paper II) we outline the data reduction steps and
present the first results of the survey for the galaxy, NGC 4631.Comment: 17 pages, 1 figure, accepted to the Astronomical Journal, Version 2
changes: added acknowledgement to NRA
NMA CO (J=1-0) Observations of the Halpha/Radio Lobe Galaxy NGC 3079: Gas Dynamics in a Weak Bar Potential and Central Massive Core
within 24 lines with 80 characters) We present ^12CO (1-0) observations in
the central 4.5 kpc (1 arcmin) of the Halpha/Radio lobe galaxy NGC 3079 with
the Nobeyama Millimeter Array. The molecular gas shows four components: a main
disk, spiral arms, a nuclear disk, and a nuclear core. The main disk extends
beyond our spatial coverage. The spiral arms are superimposed on the main disk.
The nuclear disk with about 600 pc radius has an intense concentration of
molecular gas. Its appearance on PV diagrams is indicative of oval motions of
the gas, rather than circular. The nuclear core is more compact than our
resolution. Though it is unresolved, the nuclear core shows a very high
velocity about 200 km/s even at the radius of about 100 pc on the PV diagram.
We propose a model that NGC 3079 contains a weak bar. This model explains the
observed features: the main disk and spiral arms result from gaseous x1-orbits
and associated crowding respectively. The nuclear disk arises from gaseous
x2-orbits. From the appearance of the spiral arms on the PV diagram, the
pattern speed of the bar is estimated to be 55+-10 km/s/kpc. The high velocity
of the nuclear core cannot be explained by our model for a bar. Thus we
attribute it to a central massive core with a dynamical mass of 10^9 Msun
within the central 100 pc. This mass is three orders of magnitude more massive
than that of a central black hole in this galaxy.Comment: 43 pages, 17 figures; ApJ, 573, 105, 200
Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES) -- II: First Results on NGC 4631
We present the first results from the CHANG-ES survey, a new survey of 35
edge-on galaxies to search for both in-disk as well as extra-planar radio
continuum emission. The motivation and science case for the survey are
presented in a companion paper (Paper I). In this paper (Paper II), we outline
the observations and data reduction steps required for wide-band calibration
and mapping of EVLA data, including polarization, based on C-array test
observations of NGC 4631.
With modest on-source observing times (30 minutes at 1.5 GHz and 75 minutes
at 6 GHz for the test data) we have achieved best rms noise levels of 22 and
3.5 Jy beam at 1.5 GHz and 6 GHz, respectively. New disk-halo
features have been detected, among them two at 1.5 GHz that appear as loops in
projection. We present the first 1.5 GHz spectral index map of NGC 4631 to be
formed from a single wide-band observation in a single array configuration.
This map represents tangent slopes to the intensities within the band centered
at 1.5 GHz, rather than fits across widely separated frequencies as has been
done in the past and is also the highest spatial resolution spectral index map
yet presented for this galaxy. The average spectral index in the disk is
indicating that the emission is
largely non-thermal, but a small global thermal contribution is sufficient to
explain a positive curvature term in the spectral index over the band. Two
specific star forming regions have spectral indices that are consistent with
thermal emission. Polarization results (uncorrected for internal Faraday
rotation) are consistent with previous observations and also reveal some new
features. On broad scales, we find strong support for the notion that magnetic
fields constrain the X-ray emitting hot gas.Comment: Accepted to the Astronomical Journal, Version 2 changes: Added
acknowledgement to NRA
Water maser emission and the parsec-scale jet in NGC 3079
We have conducted VLBI observations of water maser and radio continuum
emission in the nucleus of NGC 3079. The 22 GHz maser emission arises in
compact clumps, distributed along an axis that is aligned with the major axis
of the galactic disk. The velocities of the masers are consistent with their
lying in the inner parsec of a molecular disk rotating in the same sense as the
rest of the galaxy. However, the velocity field has a significant
non-rotational component, which may indicate supersonic turbulence. The bright
maser emission is not coincident with any detected compact 22 GHz continuum
source, suggesting the high apparent luminosity of the maser may not due to
beamed amplification of continuum emission. We observed two compact continuum
sources that have inverted spectra between 5 and 8 GHz, and steep spectra
between 8 and 22 GHz. NGC 3079 may be a nearby, low-luminosity example of the
class of compact symmetric gigahertz-peaked spectrum (GPS) radio sources. We
detected a third continuum component that lies along the same axis as the other
two, strongly suggesting that this galaxy possesses a nuclear jet. Faint maser
emission was detected near this axis, which may indicate a second population of
masers associated with the jet.Comment: 31 pages, includes 8 figures. To appear in ApJ, Vol 495, 10 March
1998. Full-resolution figures and color plate available at
http://cfa-www.harvard.edu/~trotter/ngc3079.htm
Tuberculosis mortality and the male survival deficit in rural South Africa:An observational community cohort study
BACKGROUND: Women live on average five years longer than men, and the sex difference in longevity is typically lower in populations with high mortality. South Africa-a high mortality population with a large sex disparity-is an exception, but the causes of death that contribute to this difference are not well understood. METHODS: Using data from a demographic surveillance system in rural KwaZulu-Natal (2000-2014), we estimate differences between male and female adult life expectancy by HIV status. The contribution of causes of death to these life expectancy differences are computed with demographic decomposition techniques. Cause of death information comes from verbal autopsy interviews that are interpreted with the InSilicoVA tool. RESULTS: Adult women lived an average of 10.4 years (95% confidence Interval 9.0-11.6) longer than men. Sex differences in adult life expectancy were even larger when disaggregated by HIV status: 13.1 (95% confidence interval 10.7-15.3) and 11.2 (95% confidence interval 7.5-14.8) years among known HIV negatives and positives, respectively. Elevated male mortality from pulmonary tuberculosis (TB) and external injuries were responsible for 43% and 31% of the sex difference in life expectancy among the HIV negative population, and 81% and 16% of the difference among people living with HIV. CONCLUSIONS: The sex differences in adult life expectancy in rural KwaZulu-Natal are exceptionally large, atypical for an African population, and largely driven by high male mortality from pulmonary TB and injuries. This is the case for both HIV positive and HIV negative men and women, signalling a need to improve the engagement of men with health services, irrespective of their HIV status
TOI-2285b: A 1.7 Earth-radius planet near the habitable zone around a nearby M dwarf
We report the discovery of TO1-2285b, a sub-Neptune-sized planet transiting a nearby (42 pc) M dwarf with a period of 27.3 d. We identified the transit signal from the Transiting Exoplanet Survey Satellite photometric data, which we confirmed with ground-based photometric observations using the multiband imagers MuSCAT2 and MuSCAT3. Combining these data with other follow-up observations including high-resolution spectroscopy with the Tillinghast Reflector Echelle Spectrograph, high-resolution imaging with the SPeckle Polarimeter, and radial velocity (RV) measurements with the InfraRed Doppler instrument, we find that the planet has a radius of 1.74 +/- 0.08 R-circle plus, a mass of <19.5 M-circle plus + (95% c.I.), and an insolation flux of 1.54 +/- 0.14 times that of the Earth. Although the planet resides just outside the habitable zone for a rocky planet, if the planet harbors an H2O layer under a hydrogen-rich atmosphere, then liquid water could exist on the surface of the H2O layer depending on the planetary mass and water mass fraction. The bright host star in the near-infrared (K-s = 9.0) makes this planet an excellent target for further RV and atmospheric observations to improve our understanding of the composition, formation, and habitability of sub-Neptune-sized planets
TOI-969: a late-K dwarf with a hot mini-Neptune in the desert and an eccentric cold Jupiter
Context. The current architecture of a given multi-planetary system is a key fingerprint of its past formation and dynamical evolution history. Long-term follow-up observations are key to complete their picture. Aims. In this paper, we focus on the confirmation and characterization of the components of the TOI-969 planetary system, where TESS detected a Neptune-size planet candidate in a very close-in orbit around a late K-dwarf star. Methods. We use a set of precise radial velocity observations from HARPS, PFS, and CORALIE instruments covering more than two years in combination with the TESS photometric light curve and other ground-based follow-up observations to confirm and characterize the components of this planetary system. Results. We find that TOI-969 b is a transiting close-in (Pb ∼ 1.82 days) mini-Neptune planet (Formula Presented), placing it on the lower boundary of the hot-Neptune desert (Teq,b = 941 \ub1 31 K). The analysis of its internal structure shows that TOI-969 b is a volatile-rich planet, suggesting it underwent an inward migration. The radial velocity model also favors the presence of a second massive body in the system, TOI-969 c, with a long period of (Formula Presented) days, a minimum mass of (Formula Presented), and a highly eccentric orbit of (Formula Presented). Conclusions. The TOI-969 planetary system is one of the few around K-dwarfs known to have this extended configuration going from a very close-in planet to a wide-separation gaseous giant. TOI-969 b has a transmission spectroscopy metric of 93 and orbits a moderately bright (G = 11.3 mag) star, making it an excellent target for atmospheric studies. The architecture of this planetary system can also provide valuable information about migration and formation of planetary systems
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