344,624 research outputs found
HST emission-line images of nearby 3CR radio galaxies: two photoionization, accretion and feedback modes
We present HST/ACS narrow-band images of a low-z sample of 19 3C radio
galaxies to study the H and [OIII] emissions from the narrow-line
region (NLR). Based on nuclear emission line ratios, we divide the sample into
High and Low Excitation Galaxies (HEGs and LEGs). We observe different line
morphologies, extended line emission on kpc scale, large [OIII]/H
scatter across the galaxies, and a radio-line alignment. In general, HEGs show
more prominent emission line properties than LEGs: larger, more disturbed, more
luminous, and more massive regions of ionized gas with slightly larger covering
factors. We find evidence of correlations between line luminosities and (radio
and X-ray) nuclear luminosities. All these results point to a main common
origin, the active nucleus, which ionize the surrounding gas. However, the
contribution of additional photoionization mechanism (jet shocks and star
formation) are needed to account for the different line properties of the two
classes. A relationship between the accretion, photoionization and feedback
modes emerges from this study. For LEGs (hot-gas accretors), the synchrotron
emission from the jet represents the main source of ionizing photons. The lack
of cold gas and star formation in their hosts accounts for the moderate
ionized-gas masses and sizes. For HEGs (cold-gas accretors), an ionizing
continuum from a standard disk and shocks from the powerful jets are the main
sources of photoionization, with the contribution from star formation. These
components, combined with the large reservoir of cold/dust gas brought from a
recent merger, account for the properties of their extended emission-line
regions.Comment: accepted for publication on ApJ (22 pages, 12 figures
EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with : Weak Feedback in Low-Mass Galaxies?
We study emission line profiles of 21 nearby low-mass
() galaxies in deep medium-high resolution spectra taken
with Magellan/MagE. These low-mass galaxies are actively star-forming systems
with high specific star-formation rates of
that are well above the
star-formation main sequence and its extrapolation. We identify broad-line
components of H and [OIII] emission in 14 out of the 21
galaxies that cannot be explained by the MagE instrumental profile or the
natural broadening of line emission. We conduct double Gaussian profile fitting
to the emission of the 14 galaxies, and find that the broad-line components
have line widths significantly larger than those of the narrow-line components,
indicative of galactic outflows. The board-line components have moderately
large line widths of km s. We estimate the maximum outflow
velocities and obtain values of km s,
which are found to be comparable to or slightly larger than the escape
velocities. Positive correlations of with star-formation
rates, stellar masses, and circular velocities, extend down into this low-mass
regime. Broad- to narrow-line flux ratios BNRs are generally found to be
smaller than those of massive galaxies. The small and BNRs
suggest that the mass loading factors can be as small as 0.1 - 1 or
below, in contrast to the large of energy-driven outflows predicted by
numerical simulations.Comment: 22 pages, 11 figures, Accepted for publication by Ap
Merging Filaments and Hub Formation in the G083.09703.270 Molecular Complex
We uncover a hub-filament system associated with massive star formation in
the G083.09703.270. Diagnosed with simultaneous CO, CO, and
CO line observations, the region is found to host two distinct and
elongated filaments having separate velocity components, interacting spatially
and kinematically, that appear to have seeded the formation of a dense hub at
the intersection. A large velocity spread at the hub in addition to clear
bridging feature connecting the filaments in velocity are indicating merging of
filaments. Along the filaments axis, the velocity gradient reveals a global gas
motion with an increasing velocity dispersion inward to the hub signifying
turbulence. Altogether, the clustering of Class I sources, a high excitation
temperature, a high column density, and presence of a massive outflow at the
central hub suggest enhanced star formation. We propose that merging of
large-scale filaments and velocity gradients along filaments are the driving
factors in the mass accumulation process at the hub that have sequentially led
to the massive star formation. With two giant filaments merging to coincide
with a hub therein with ongoing star formation, this site serves as a benchmark
for the `filaments to clusters' star-forming paradigm.Comment: 12 pages, 7 figures, 1 table, accepted for publication in Ap
High-Energy Emission From Millisecond Pulsars
The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is
investigated in a model for acceleration and pair cascades on open field lines
above the polar caps. Although these pulsars have low surface magnetic fields,
their short periods allow them to have large magnetospheric potential drops,
but the majority do not produce sufficient pairs to completely screen the
accelerating electric field. The accelerating particles maintain high Lorentz
factors and undergo cyclotron resonant absorption of radio emission, that
produces and maintains a large pitch angle, resulting in a strong synchrotron
component. The resulting spectra consist of several distinct components:
curvature radiation from primary electrons dominating from 1 - 100 GeV,
synchrotron radiation from primary and secondary electrons dominating up to
about 100 MeV, and much weaker inverse-Compton radiation from primary electrons
at 0.1 - 1 TeV. We find that the relative size of these components depends on
pulsar period, period derivative, and neutron star mass and radius with the
level of the synchrotron component also depending sensitively on the radio
emission properties. This model is successful in describing the observed X-ray
and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking
around 100 MeV and extending up to a turnover around several GeV. The predicted
curvature radiation components from a number of millisecond pulsars, as well as
the collective emission from the millisecond pulsars in globular clusters,
should be detectable with AGILE and GLAST. We also discuss a hidden population
of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the
pair death line, some of which may be detectable by telescopes sensitive above
1 GeV.Comment: 34 pages, 6 figures, accepted for publication in Astrophysical
Journa
Characterization of methanol as a magnetic field tracer in star-forming regions
Magnetic fields play an important role during star formation. Direct magnetic
field strength observations have proven specifically challenging in the
extremely dynamic protostellar phase. Because of their occurrence in the
densest parts of star forming regions, masers, through polarization
observations, are the main source of magnetic field strength and morphology
measurements around protostars. Of all maser species, methanol is one of the
strongest and most abundant tracers of gas around high-mass protostellar disks
and in outflows. However, as experimental determination of the magnetic
characteristics of methanol has remained largely unsuccessful, a robust
magnetic field strength analysis of these regions could hitherto not be
performed. Here we report a quantitative theoretical model of the magnetic
properties of methanol, including the complicated hyperfine structure that
results from its internal rotation. We show that the large range in values of
the Land\'{e} g-factors of the hyperfine components of each maser line lead to
conclusions which differ substantially from the current interpretation based on
a single effective g-factor. These conclusions are more consistent with other
observations and confirm the presence of dynamically important magnetic fields
around protostars. Additionally, our calculations show that (non-linear) Zeeman
effects must be taken into account to further enhance the accuracy of
cosmological electron-to-proton mass ratio determinations using methanol.Comment: 23 pages, 3 figures, excluding Supplementary information. Author
manuscript version before editorial/copyediting by Nature Astronomy. Journal
version available via http://rdcu.be/FPeB . Supplementary material available
via
https://static-content.springer.com/esm/art%3A10.1038%2Fs41550-017-0341-8/MediaObjects/41550_2017_341_MOESM1_ESM.pd
Stellar and AGN Feedback Probed with Outflows in JWST Galaxies at z=3-9: Implications of Frequent Nearly-Spherical Galactic Fountains
We study outflows in 130 galaxies with -22<MUV<-16 at z=3-9 identified in
JWST NIRSpec and NIRCam WFSS data taken by the ERO, CEERS, FRESCO, GLASS, and
JADES programs. We identify 30 out of the 130 galaxies with broad components of
FWHM~200-700 km/s in the emission lines of H and [OIII] that trace
ionized outflows, and find no excesses from the star-formation main sequence.
Four out of the 30 outflowing galaxies are Type 1 AGN whose H
emission lines include line profile components as broad as FWHM>1000 km/s. With
the velocity shift and line widths of the outflow broad lines, we obtain
~80-500 km/s for the outflow velocities. We find that the outflow velocities as
a function of star-formation rate are comparable to or higher than those of
galaxies at z~1, accounting for the selection bias, while the outflow
velocities of AGN are large but not significantly different from the others.
Interestingly, these outflow velocities are typically not high enough to escape
from the galactic potentials, suggestive of fountain-type outflows, which are
concluded on the basis of thorough comparisons with recent JWST results. We
estimate mass loading factors to be 0.1-1 that are not particularly
large, but comparable with those of z~1 outflows. The large fraction of
galaxies with outflows (30% with high resolution data) provides constraints on
outflow parameters, suggesting a wide opening angle of >45 deg and a large
duty-cycle of >30%, which gives a picture of more frequent and spherical
outflows in high-z galaxies.Comment: 16 pages, 11 figures, submitted to the Astrophysical Journa
ISO spectroscopy of circumstellar dust in the Herbig Ae systems AB Aur and HD 163296
Using both the Short- and Long-wavelength Spectrometers on board the Infrared
Space Observatory (ISO), we have obtained infrared spectra of the Herbig Ae
systems AB Aur and HD 163296. In addition, we obtained ground-based N band
images of HD 163296. Our results can be summarized as follows: (1) The main
dust components in AB Aur are amorphous silicates, iron oxide and PAHs; (2) The
circumstellar dust in HD 163296 consists of amorphous silicates, iron oxide,
water ice and a small fraction of crystalline silicates; (3) The infrared
fluxes of HD 163296 are dominated by solid state features; (4) The colour
temperature of the underlying continuum is much cooler in HD 163296 than in AB
Aur, pointing to the existence of a population of very large (mm sized) dust
grains in HD 163296; (5) The composition and degree of crystallization of
circumstellar dust are poorly correlated with the age of the central star. The
processes of crystallization and grain growth are also not necessarily coupled.
This means that either the evolution of circumstellar dust in protoplanetary
disks happens very rapidly (within a few Myr), or that this evolution is
governed by factors other than stellar mass and age.Comment: 6 pages, 2 figures, accepted for publication in Astronomy &
Astrophysic
Principal Component Analysis of RR Lyrae light curves
In this paper, we analyze the structure of RRab star light curves using
Principal Component Analysis. We find this is a very efficient way to describe
many aspects of RRab light curve structure: in many cases, a Principal
Component fit with 9 parameters can describe a RRab light curve including bumps
whereas a 17 parameter Fourier fit is needed. As a consequence we show
statistically why the amplitude is also a good summary of the structure of a RR
Lyrae light curve. We also use our analysis to derive an empirical relation
relating absolute magnitude to light curve structure. In comparing this formula
to those derived from exactly the same dataset but using Fourier parameters, we
find that the Principal Component Analysis approach has disticnt advantages.
These advantages are, firstly, that the errors on the coefficients in such
formulae are smaller, and secondly, that the correlation between Principal
Components is significantly smaller than the correlation between Fourier
amplitudes. These two factors lead to reduced formal errors, in some cases
estimated to be a factor of 2, on the eventual fitted value of the absolute
magnitude. This technique will prove very useful in the analysis of data from
existing large scale survey projects concerning variable stars.Comment: 8 pages, 10 figures, revised version, accepted for publication to
MNRA
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