437 research outputs found
A far-IR view of the starburst driven superwind in NGC 2146
NGC 2146, a nearby luminous infrared galaxy (LIRG), presents evidence for
outflows along the disk minor axis in all gas phases (ionized, neutral atomic
and molecular). We present an analysis of the multi-phase starburst driven
superwind in the central 5 kpc as traced in spatially resolved spectral line
observations, using far-IR Herschel PACS spectroscopy, to probe the effects on
the atomic and ionized gas, and optical integral field spectroscopy to examine
the ionized gas through diagnostic line ratios. We observe an increased ~250
km/s velocity dispersion in the [OI] 63 micron, [OIII] 88 micron, [NII] 122
micron and [CII] 158 micron fine-structure lines that is spatially coincident
with high excitation gas above and below the disk. We model this with a slow
~200 km/s shock and trace the superwind to the edge of our field of view 2.5
kpc above the disk. We present new SOFIA 37 micron observations to explore the
warm dust distribution, and detect no clear dust entrainment in the outflow.
The stellar kinematics appear decoupled from the regular disk rotation seen in
all gas phases, consistent with a recent merger event disrupting the system. We
consider the role of the superwind in the evolution of NGC 2146 and speculate
on the evolutionary future of the system. Our observations of NGC 2146 in the
far-IR allow an unobscured view of the wind, crucial for tracing the superwind
to the launching region at the disk center, and provide a local analog for
future ALMA observations of outflows in high redshift systems.Comment: 16 pages, 13 figures, accepted for publication in Ap
Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: NGC 628 and NGC 6946
We characterize the dust in NGC628 and NGC6946, two nearby spiral galaxies in
the KINGFISH sample. With data from 3.6um to 500um, dust models are strongly
constrained. Using the Draine & Li (2007) dust model, (amorphous silicate and
carbonaceous grains), for each pixel in each galaxy we estimate (1) dust mass
surface density, (2) dust mass fraction contributed by polycyclic aromatic
hydrocarbons (PAH)s, (3) distribution of starlight intensities heating the
dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR
luminosity originating in regions with high starlight intensity. We obtain maps
for the dust properties, which trace the spiral structure of the galaxies. The
dust models successfully reproduce the observed global and resolved spectral
energy distributions (SEDs). The overall dust/H mass ratio is estimated to be
0.0082+/-0.0017 for NGC628, and 0.0063+/-0.0009 for NGC6946, consistent with
what is expected for galaxies of near-solar metallicity. Our derived dust
masses are larger (by up to a factor 3) than estimates based on
single-temperature modified blackbody fits. We show that the SED fits are
significantly improved if the starlight intensity distribution includes a
(single intensity) "delta function" component. We find no evidence for
significant masses of cold dust T<12K. Discrepancies between PACS and MIPS
photometry in both low and high surface brightness areas result in large
uncertainties when the modeling is done at PACS resolutions, in which case
SPIRE, MIPS70 and MIPS160 data cannot be used. We recommend against attempting
to model dust at the angular resolution of PACS.Comment: To be published in Apj, September 2012. See the full version at
http://www.astro.princeton.edu/~ganiano/Papers
Connecting young star clusters to CO molecular gas in NGC 7793 with ALMA-LEGUS
We present an investigation of the relationship between giant molecular cloud (GMC) properties and the associated stellar clusters in the nearby flocculent galaxy NGC 7793. We combine the star cluster catalogue from the HST LEGUS (Legacy ExtraGalactic UV Survey) programme with the 15 pc resolution ALMA CO(2–1) observations. We find a strong spatial correlation between young star clusters and GMCs such that all clusters still associated with a GMC are younger than 11 Myr and display a median age of 2 Myr. The age distribution increases gradually as the cluster–GMC distance increases, with star clusters that are spatially unassociated with molecular gas exhibiting a median age of 7 Myr. Thus, star clusters are able to emerge from their natal clouds long before the time-scale required for clouds to disperse. To investigate if the hierarchy observed in the stellar components is inherited from the GMCs, we quantify the amount of clustering in the spatial distributions of the components and find that the star clusters have a fractal dimension slope of −0.35 ± 0.03, significantly more clustered than the molecular cloud hierarchy with slope of −0.18 ± 0.04 over the range 40–800 pc. We find, however, that the spatial clustering becomes comparable in strength for GMCs and star clusters with slopes of −0.44 ± 0.03 and −0.45 ± 0.06, respectively, when we compare massive (>105 M⊙) GMCs to massive and young star clusters. This shows that massive star clusters trace the same hierarchy as their parent GMCs, under the assumption that the star formation efficiency is a few per cent.Support for Program
13364 was provided by NASA through a grant from the Space
Telescope Science Institute. This research has made use of the
NASA/IPAC Extragalactic Database (NED) which is operated by
the Jet Propulsion Laboratory, California Institute of Technology,
under contract with NASA. This paper makes use of the following
ALMA data: ADS/JAO.ALMA #2015.1.00782.S. ALMA is a partnership
of ESO (representing its member states), NSF (USA) and
NINS (Japan), together with NRC (Canada) and NSC and ASIAA
(Taiwan) and KASI (Republic of Korea), in cooperation with the
Republic of Chile. The Joint ALMA Observatory is operated by
ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory
is a facility of the National Science Foundation operated
under cooperative agreement by Associated Universities, Inc.
Parts of this research were supported by the Australian Research
Council Centre of Excellence for All Sky Astrophysics in three
Dimensions (ASTRO 3D), through project number CE170100013.
AA acknowledges the support of the Swedish Research Council
(Vetenskapsradet) and the Swedish National Space Board (SNSB). ˚
MF acknowledges support by the Science and Technology Facilities
Council [grant number ST/P000541/1]. This project has received
funding from the European Research Council (ERC) under the European
Union’s Horizon 2020 research and innovation programme
(grant agreement number 757535
Cool Dust in the Outer Ring of NGC 1291
We examine Herschel Space Observatory images of one nearby prototypical outer ring galaxy, NGC 1291, and show that the ring becomes more prominent at wavelengths longer than 160 μm. The mass of cool dust in the ring dominates the total dust mass of the galaxy, accounting for at least 70% of it. The temperature of the emitting dust in the ring (T = 19.5 ± 0.3 K) is cooler than that of the inner galaxy (T = 25.7 ± 0.7 K). We discuss several explanations for the difference in dust temperature, including age and density differences in the stellar populations of the ring versus the bulge
Calibrating Extinction-Free Star Formation Rate Diagnostics with 33GHz Free-Free Emission in NGC6946
Abridged: Using free-free emission measured in the Ka-band (26-40GHz) for 10
star-forming regions in the nearby galaxy NGC6946, including its starbursting
nucleus, we compare a number of SFR diagnostics that are typically considered
to be unaffected by interstellar extinction: i.e., non-thermal radio (i.e.,
1.4GHz), total infrared (IR; 8-1000um), and warm dust (i.e., 24um) emission,
along with the hybrid (obscured + unobscured) indicators of H\alpha+24um and
UV+IR. The 33GHz free-free emission is assumed to provide the most accurate
measure of the current SFR. Among the extranuclear star-forming regions, the
24um, H\alpha+24um and UV+IR SFR calibrations are in good agreement with the
33GHz free-free SFRs. However, each of the SFR calibrations relying on some
form of dust emission overestimate the nuclear SFR by a factor of ~2. This is
more likely the result of excess dust heating through an accumulation of
non-ionizing stars associated with an extended episode of star formation in the
nucleus rather than increased competition for ionizing photons by dust. SFR
calibrations using the non-thermal radio continuum yield values which only
agree with the free-free SFRs for the nucleus, and underestimate the SFRs from
the extranuclear star-forming regions by a factor of ~2. This result likely
arises from the CR electrons decaying within the starburst region with
negligible escape compared to the young extranuclear star-forming regions.
Finally, we find that the SFRs estimated using the total 33GHz emission agree
well with the free-free SFRs due to the large thermal fractions present at
these frequencies even when local diffuse backgrounds are not removed. Thus,
rest-frame 33GHz observations may act as a reliable method to measure the SFRs
of galaxies at increasingly high redshift without the need of ancillary radio
data to account for the non-thermal emission.Comment: 18 pages, 7 Figures, Accepted for publication in Ap
Resolving Giant Molecular Clouds in NGC 300: : A First Look with the Submillimeter Array
Christopher M. Faesi, et al, 'RESOLVING GIANT MOLECULAR CLOUDS IN NGC 300: A FIRST LOOK WITH THE SUBMILLIMETER ARRAY', The Astrophysical Journal, Vol. 821(2) (16 pp), April 2016. doi:10.3847/0004-637X/821/2/125. © 2016. The American Astronomical Society. All rights reserved.We present the first high angular resolution study of giant molecular clouds (GMCs) in the nearby spiral galaxy NGC 300, based on observations from the Submillimeter Array (SMA). We target eleven 500 pc-sized regions of active star formation within the galaxy in the CO(J=2-1) line at 40 pc spatial and 1 km/s spectral resolution and identify 45 individual GMCs. We characterize the physical properties of these GMCs, and find that they are similar to GMCs in the disks of the Milky Way and other nearby spiral galaxies. For example, the GMC mass spectrum in our sample has a slope of 1.80+/-0.07. Twelve clouds are spatially resolved by our observations, of which ten have virial mass estimates that agree to within a factor of two with mass estimates derived directly from CO integrated intensity, suggesting that the majority of these GMCs are bound. The resolved clouds show consistency with Larson's fundamental relations between size, linewidth, and mass observed in the Milky Way. We find that the linewidth scales with the size as DeltaV ~ R^(0.52+/-0.20), and the median surface density in the subsample is 54 Msun/pc^(-2). We detect 13CO in four GMCs and find a mean 12CO/13CO flux ratio of 6.2. Our interferometric observations recover between 30% and 100% of the integrated intensity from the APEX single dish CO observations of Faesi et al. 2014, suggesting the presence of low-mass GMCs and/or diffuse gas below our sensitivity limit. The fraction of APEX emission recovered increases with the SMA total intensity as well as with the star formation rate.Peer reviewe
Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA
Events with a (2+1) jet topology in deep-inelastic scattering at HERA are
studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet
events has been determined with the modified JADE jet algorithm as a function
of the jet resolution parameter and is compared with the predictions of Monte
Carlo models. In addition, the event rate is corrected for both hadronization
and detector effects and is compared with next-to-leading order QCD
calculations. A value of the strong coupling constant of alpha_s(M_Z^2)=
0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is
extracted. The systematic error includes uncertainties in the calorimeter
energy calibration, in the description of the data by current Monte Carlo
models, and in the knowledge of the parton densities. The theoretical error is
dominated by the renormalization scale ambiguity.Comment: 25 pages, 6 figures, 3 tables, submitted to Eur. Phys.
Multi-Jet Event Rates in Deep Inelastic Scattering and Determination of the Strong Coupling Constant
Jet event rates in deep inelastic ep scattering at HERA are investigated
applying the modified JADE jet algorithm. The analysis uses data taken with the
H1 detector in 1994 and 1995. The data are corrected for detector and
hadronization effects and then compared with perturbative QCD predictions using
next-to-leading order calculations. The strong coupling constant alpha_S(M_Z^2)
is determined evaluating the jet event rates. Values of alpha_S(Q^2) are
extracted in four different bins of the negative squared momentum
transfer~\qq in the range from 40 GeV2 to 4000 GeV2. A combined fit of the
renormalization group equation to these several alpha_S(Q^2) values results in
alpha_S(M_Z^2) = 0.117+-0.003(stat)+0.009-0.013(syst)+0.006(jet algorithm).Comment: 17 pages, 4 figures, 3 tables, this version to appear in Eur. Phys.
J.; it replaces first posted hep-ex/9807019 which had incorrect figure 4
Multiplicity Structure of the Hadronic Final State in Diffractive Deep-Inelastic Scattering at HERA
The multiplicity structure of the hadronic system X produced in
deep-inelastic processes at HERA of the type ep -> eXY, where Y is a hadronic
system with mass M_Y< 1.6 GeV and where the squared momentum transfer at the pY
vertex, t, is limited to |t|<1 GeV^2, is studied as a function of the invariant
mass M_X of the system X. Results are presented on multiplicity distributions
and multiplicity moments, rapidity spectra and forward-backward correlations in
the centre-of-mass system of X. The data are compared to results in e+e-
annihilation, fixed-target lepton-nucleon collisions, hadro-produced
diffractive final states and to non-diffractive hadron-hadron collisions. The
comparison suggests a production mechanism of virtual photon dissociation which
involves a mixture of partonic states and a significant gluon content. The data
are well described by a model, based on a QCD-Regge analysis of the diffractive
structure function, which assumes a large hard gluonic component of the
colourless exchange at low Q^2. A model with soft colour interactions is also
successful.Comment: 22 pages, 4 figures, submitted to Eur. Phys. J., error in first
submission - omitted bibliograph
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