486 research outputs found
VLA H92 Alpha and H53 Alpha Radio Recombination Line Observations of M82
We present high angular resolution (0.6'') observations made with the VLA of
the radio continuum at 8.3 and 43 GHz as well as H92 Alpha and H53 Alpha radio
recombination lines from the nearby (3 Mpc) starburst galaxy M82. In the
continuum we report 19 newly identified sources at 8.3 GHz and 5 at 43 GHz that
were unknown previously. The spatial distribution of the H92 Alpha line is
inhomogeneous; we identify 27 features. The line and continuum emission are
modeled using a collection of HII regions at different distances from the
nucleus assuming a single-density component and two-density components. The
high-density component has a density of 4 X 10^{4} cm^{-3}. However, the bulk
of the ionization is in regions with densities which are typically a factor 10
lower. The gas kinematics, using the H92 Alpha line, confirms the presence of
steep velocity gradient (26 km s^{-1} arcsec^{-1}) in the nuclear region. As
this steep gradient is observed not only on the major axis but also at large
distances along a band of PA of 150 degrees, the interpretation in terms of x2
orbits elongated along the minor axis of the bar, which would be observed at an
angle close to the inclination of the main disk, seems inadequate. Ad-hoc
radial motions must be introduced to reproduce the pattern of the velocity
field. Different families of orbits are indicated as we detect a signature in
the kinematics at the transition between the two plateaus observed in the NIR
light distribution. The H92 Alpha line also reveals the base of the outflow
where the injection towards the halo on the Northern side occurs. The
kinematical pattern suggests a connection between the gas flowing in the plane
of M82 towards the center; this behavior most likely originates due to the
presence of a bar and the outflow out of the plane.Comment: 45 pages, 11 figures and 6 tables. Accepted for publication in Ap
Very large array H92α and H53α radio recombination line observations of M82
We present high angular resolution (0".6) observations made with the Very Large Array of the radio continuum at 8.3 and 43 GHz, as well as H92α and H53α radio recombination lines from the nearby (~3 Mpc) starburst galaxy M82. In the continuum we identify 58 sources at 8.3 GHz, of which 19 have no counterparts in catalogs published at other frequencies. At 43 GHz we identify 18 sources, unresolved at 0".6 resolution, of which five were unknown previously. The spatial distribution of the H92α line is inhomogeneous; we identify 27 features; about half of them are associated with continuum emission sources. Their sizes are typically in the range 2-10 pc. Although observed with poorer signal-to-noise ratio, the H53α line is detected. The line and continuum emission are modeled using a collection of H II regions at different distances from the nucleus. The observations can be interpreted assuming a single-density component, but equally well with two components if constraints originating from previous high-resolution continuum observations are used. The high-density component has a density of ~4× 104 cm-3. However, the bulk of the ionization is in regions with densities that are typically a factor of 10 lower. The gas kinematics, using the H92α line, confirms the presence of steep velocity gradient (26 km s-1 arcsec-1) in the nuclear region, as previously reported, in particular from observations of the [Ne II] line at 12 µm. This gradient has about the same amplitude on both sides of the nucleus. Since this steep gradient is observed not only on the major axis but also at large distances along a band at P.A. ~ 150°, the interpretation in terms of x2 orbits elongated along the minor axis of the bar, which would be observed at an angle close to the inclination of the main disk, seems inadequate. The observed kinematics cannot be modeled using a simple model that consists of a set of circular orbits observed at different tilt angles. Ad hoc radial motions must be introduced to reproduce the pattern of the velocity field. Different families of orbits are indicated since we detect a signature in the kinematics at the transition between the two plateaus observed in the NIR light distribution. These H92α data also reveal the base of the outflow where the injection toward the halo on the northern side occurs. The outflow has a major effect on the observed kinematics, present even in the disk at distances close to the nucleus. The kinematic pattern suggests a connection between the gas flowing in the plane of M82 toward the center; this behavior most likely is due to the presence of a bar and the outflow out of the plane
Very large array H53α and H92α line observations of the central region of NGC 253
We present new VLA observations toward NGC 253 of the recombination line H53α (43 GHz) at an angular resolution of 1".5 × 1".0. The free-free emission at 43 GHz is estimated to be ~140 mJy, implying a star formation rate of 2 M⊙ yr-1 in the nuclear region of this starburst galaxy. A reanalysis is made for previously reported H92α observations carried out with angular resolution of 1".5 × 1".0 and 0".36 × 0".21. Based on the line and continuum emission models used for the 1".5 × 1".0 angular resolution observations, the RRLs H53α and H92α are tracers of the high-density (~105 cm-3) and low-density (~103 cm-3) thermally ionized gas components in NGC 253, respectively. The velocity fields observed in the H53α and H92α lines (1".5 × 1".0) are consistent. The velocity gradient in the central ~18 pc of the NE component, as observed in both the H53α and H92α lines, is in the opposite direction to the velocity gradient determined from the CO observations. The enclosed virial mass, as deduced from the H53α velocity gradient over the NE component, is ~5 × 106 M⊙ in the central ~18 pc region. The H92α line observations at high angular resolution (0".36 × 0".21) reveal a larger velocity gradient, along a P.A. ~ -45° on the NE component, of ~110 km s-1 arcsec-1. The dynamical mass estimated using the high angular resolution H92α data (~7 × 106 M⊙) supports the existence of an accreted massive object in the nuclear region of NGC 253
VLA H53alpha observations of the central region of the Super Star Cluster Galaxy NGC 5253
We present observations in the H53alpha line and radio continuum at 43 GHz
carried out with the VLA in the D array (2'' angular resolution) toward the
starburst galaxy NGC 5253. VLA archival data have been reprocessed to produce a
uniform set of 2, 1.3 and 0.7 cm high angular (0.''2 X 0.''1) radio continuum
images. The RRL H53alpha, a previously reported measurement of the H92alpha RRL
flux density and the reprocessed high angular resolution radio continuum flux
densities have been modeled using a collection of HII regions. Based on the
models, the ionized gas in the nuclear source has an electron density of ~6 X
10^4 cm^-3 and an volume filling factor of 0.05. A Lyman continuum photon
production rate of 2 X 10^52 s^-1 is necessary to sustain the ionization in the
nuclear region. The number of required O7 stars in the central 1.5 pc of the
supernebula is ~ 2000. The H53alpha velocity gradient 10 km s^-1 arcsec^-1)
implies a dynamical mass of ~3X10^5 Msun; this mass suggests the supernebula is
confined by gravity.Comment: Accepted in Astrophysical Journal 7 figure
VLA H53alpha and H92alpha line observations of the central region of NGC 253
We present new Very Large Array (VLA) observations toward NGC 253 of the
recombination line H53alpha (43 GHz) at an angular resolution of 1.''5 X 1.''0.
The free-free emission at 43 GHz is estimated to be ~100 mJy, implying a star
formation rate of ~1.3 Msun/yr in the nuclear region of this starburst galaxy.
A reanalysis is made for previously reported H92alpha observations carried out
with angular resolution of 1.''5 X 1.''0 and 0.''36 X 0.''21. Based on the line
and continuum emission models used for the 1.''5 X 1.''0 angular resolution
observations, the RRLs H53alpha and H92alpha are tracers of the high-density
(~10^5 cm-3) and low-density (~10^3 cm^-3) thermally ionized gas components in
NGC 253, respectively. The velocity fields observed in the H53alpha and
H92alpha lines 1.''5 X 1.''0) are consistent. The velocity gradient in the
central ~18 pc of the NE component, as observed in both the H53alpha and
H92alpha lines, is in the opposite direction to the velocity gradient
determined from the CO observations. The enclosed virial mass, as deduced from
the H53alpha velocity gradient over the NE component, is ~5 X 10^6 Msun in the
central ~18 pc region. The H92alpha line observations at high angular
resolution (0.''36 X 0.''21) reveal a larger velocity gradient, along a P.A. ~
-45 deg on the NE component, of ~110 km/s/arcsec. The dynamical mass estimated
using the high angular resolution H92alpha data (~7 X 10^6 Msun) supports the
existence of an accreted massive object in the nuclear region of NGC 253.Comment: Accepted for publication in Ap
VLA H53alpha radio recombination line observations of the ultraluminous infrared galaxy Arp 220
We present high angular resolution (0.7'') observations made with the Very
Large Array (VLA) of the radio recombination line (RRL) H53alpha and radio
continuum emission at 43 GHz from the ultraluminous infrared galaxy (ULIRG) Arp
220. The 43 GHz continuum emission shows a compact structure (~2'') with two
peaks separated by ~1'', the East (E) and West (W) components, that correspond
to each galactic nucleus of the merger. The spectral indices for both the E and
W components, using radio continuum images at 8.3 and 43 GHz are typical of
synchrotron emission (alpha ~ -1.0). Our 43 GHz continuum and H53alpha line
observations confirm the flux densities predicted by the models proposed by
Anantharamaiah et al. This agreement with the models implies the presence of
high-density (~ 100,000 cm^-3) compact HII regions (~ 0.1 pc) in Arp 220. The
integrated H53alpha line emission is stronger toward the non-thermal radio
continuum peaks, which are also coincident with the peaks of molecular emission
of the H2CO. The coincidence between the integrated H53alpha and the H2CO maser
line emission suggests that the recent star forming regions, traced by the high
density gas, are located mainly in regions that are close to the two radio
continuum peaks. A velocity gradient of ~ 0.30 km/s/pc in the H53alpha RRL is
observed toward the E component and a second velocity gradient of ~ 0.15
km/s/pc is detected toward the W component. The orientations of these velocity
gradients are in agreement with previous CO, HI and OH observations. The
kinematics of the high-density ionized gas traced by the H53alpha line are
consistent with two counter rotating disks as suggested by the CO and HI
observations.Comment: The original version was published in the ApJ,633,198,2005. This new
version is submitted with the corrected velocity scal
From 10 Kelvin to 10 TeraKelvin: Insights on the Interaction Between Cosmic Rays and Gas in Starbursts
Recent work has both illuminated and mystified our attempts to understand
cosmic rays (CRs) in starburst galaxies. I discuss my new research exploring
how CRs interact with the ISM in starbursts. Molecular clouds provide targets
for CR protons to produce pionic gamma rays and ionization, but those same
losses may shield the cloud interiors. In the densest molecular clouds, gamma
rays and Al-26 decay can provide ionization, at rates up to those in Milky Way
molecular clouds. I then consider the free-free absorption of low frequency
radio emission from starbursts, which I argue arises from many small, discrete
H II regions rather than from a "uniform slab" of ionized gas, whereas
synchrotron emission arises outside them. Finally, noting that the hot
superwind gas phase fills most of the volume of starbursts, I suggest that it
has turbulent-driven magnetic fields powered by supernovae, and that this phase
is where most synchrotron emission arises. I show how such a scenario could
explain the far-infrared radio correlation, in context of my previous work. A
big issue is that radio and gamma-ray observations imply CRs also must interact
with dense gas. Understanding how this happens requires a more advanced
understanding of turbulence and CR propagation.Comment: Conference proceedings for "Cosmic-ray induced phenomenology in
star-forming environments: Proceedings of the 2nd Session of the Sant Cugat
Forum of Astrophysics" (April 16-19, 2012). 16 pages, 5 figure
Discovery, Photometry, and Kinematics of Planetary Nebulae in M 82
Using an [OIII]5007 on-band/off-band filter technique, we identify 109
planetary nebulae (PNe) candidates in M 82, using the FOCAS instrument at the
8.2m Subaru Telescope. The use of ancillary high-resolution HST ACS H-alpha
imaging aided in discriminating PNe from contaminants such as supernova
remnants and compact HII regions. Once identified, these PNe reveal a great
deal about the host galaxy; our analysis covers kinematics, stellar
distribution, and distance determination. Radial velocities were determined for
94 of these PNe using a method of slitless spectroscopy, from which we obtain a
clear picture of the galaxy's rotation. Overall, our results agree with those
derived by CO(2-1) and HI measurements that show a falling, near-Keplerian
rotation curve. However, we find a subset of our PNe that appear to lie far
above the plane (~1 kpc), yet these objects appear to be rotating as fast as
objects close to the plane. These objects will require further study to
determine if they are members of a halo population, or if they can be
interpreted as a manifestation of a thickened disk as a consequence of a past
interaction with M 81. In addition, [OIII]5007 emission line photometry of the
PNe allows the construction of a planetary nebula luminosity function (PNLF).
Our PNLF distance determination for M 82 yields a larger distance than those
derived using the TRGB, using Cepheid variable stars in nearby group member M
81, or using the PNLF of M 81. We show that this inconsistency most likely
stems from our inability to completely correct for internal extinction imparted
by this dusty, starburst galaxy. (Abridged)Comment: 16 pages, 13 figures, Accepted by Ap
Adaptive remodeling of the bacterial proteome by specific ribosomal modification regulates Pseudomonas infection and niche colonisation
Post-transcriptional control of protein abundance is a highly important, underexplored regulatory process by which organisms respond to their environments. Here we describe an important and previously unidentified regulatory pathway involving the ribosomal modification protein RimK, its regulator proteins RimA and RimB, and the widespread bacterial second messenger cyclic-di-GMP (cdG). Disruption of rimK affects motility and surface attachment in pathogenic and commensal Pseudomonas species, with rimK deletion significantly compromising rhizosphere colonisation by the commensal soil bacterium P. fluorescens, and plant infection by the pathogens P. syringae and P. aeruginosa. RimK functions as an ATP-dependent glutamyl ligase, adding glutamate residues to the C-terminus of ribosomal protein RpsF and inducing specific effects on both ribosome protein complement and function. Deletion of rimK in P. fluorescens leads to markedly reduced levels of multiple ribosomal proteins, and also of the key translational regulator Hfq. In turn, reduced Hfq levels induce specific downstream proteomic changes, with significant increases in multiple ABC transporters, stress response proteins and non-ribosomal peptide synthetases seen for both ΔrimK and Δhfq mutants. The activity of RimK is itself controlled by interactions with RimA, RimB and cdG. We propose that control of RimK activity represents a novel regulatory mechanism that dynamically influences interactions between bacteria and their hosts; translating environmental pressures into dynamic ribosomal changes, and consequently to an adaptive remodeling of the bacterial proteome
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