1,163 research outputs found
Formation and evolution of dusty starburst galaxies I. A new method for deriving spectral energy distribution
We present a new numerical code which is designed to derive a spectral energy
distribution (SED) for an arbitrary spatial distribution of stellar and gaseous
components in a dusty starburst galaxy. We apply a ray tracing method to
numerical simulations and thereby estimate extinction and reemission of stellar
light by dusty gas in an explicitly self-consistent manner. By using this code,
we can investigate simultaneously dynamical and photometric evolution of a
dusty galaxy based on stellar and gaseous dynamical simulations. As an example,
we demonstrate when and how a major galaxy merger with dusty starburst becomes
an ultra-luminous infrared galaxy owing to strong internal dust extinction. We
furthermore discuss advantages and disadvantages of the present new code in
clarifying the nature and the origin of low and high redshift dusty starburst
galaxies.Comment: 44 pages 19 figures (11 color), accepted by Ap
The irradiated ISM of ULIRGs
The nuclei of ULIRGs harbor massive young stars, an accreting central black
hole, or both. Results are presented for molecular gas that is exposed to
X-rays (1-100 keV, XDRs) and far-ultraviolet radiation (6-13.6 eV, PDRs).
Attention is paid to species like HCO+, HCN, HNC, OH, H2O and CO. Line ratios
of HCN/HCO+ and HNC/HCN discriminate between PDRs and XDRs. Very high J (>10)
CO lines, observable with HIFI/Herschel, discriminate very well between XDRs
and PDRs. In XDRs, it is easy to produce large abundances of warm (T>100 K) H2O
and OH. In PDRs, only OH is produced similarly well.Comment: 5 pages, 6 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
Canopy uptake dominates nighttime carbonyl sulfide fluxes in a boreal forest
Nighttime vegetative uptake of carbonyl sulfide (COS) can exist due to the incomplete closure of stomata and the light independence of the enzyme carbonic anhydrase, which complicates the use of COS as a tracer for gross primary productivity (GPP). In this study we derived nighttime COS fluxes in a boreal forest (the SMEAR II station in Hyytiälä, Finland; 61°51′ N, 24°17′ E; 181 m a.s.l.) from June to November 2015 using two different methods: eddy-covariance (EC) measurements (FCOS-EC) and the radon-tracer method (FCOS-Rn). The total nighttime COS fluxes averaged over the whole measurement period were −6.8 ± 2.2 and −7.9 ± 3.8 pmol m−2 s−1 for FCOS-Rn and FCOS-EC, respectively, which is 33–38 % of the average daytime fluxes and 21 % of the total daily COS uptake. The correlation of 222Rn (of which the source is the soil) with COS (average R2 = 0.58) was lower than with CO2 (0.70), suggesting that the main sink of COS is not located at the ground. These observations are supported by soil chamber measurements that show that soil contributes to only 34–40 % of the total nighttime COS uptake. We found a decrease in COS uptake with decreasing nighttime stomatal conductance and increasing vapor-pressure deficit and air temperature, driven by stomatal closure in response to a warm and dry period in August. We also discuss the effect that canopy layer mixing can have on the radon-tracer method and the sensitivity of (FCOS-EC) to atmospheric turbulence. Our results suggest that the nighttime uptake of COS is mainly driven by the tree foliage and is significant in a boreal forest, such that it needs to be taken into account when using COS as a tracer for GPP
Molecules as tracers of galaxy evolution: an EMIR survey. I. Presentation of the data and first results
We investigate the molecular gas properties of a sample of 23 galaxies in
order to find and test chemical signatures of galaxy evolution and to compare
them to IR evolutionary tracers. Observation at 3 mm wavelengths were obtained
with the EMIR broadband receiver, mounted on the IRAM 30 m telescope on Pico
Veleta, Spain. We compare the emission of the main molecular species with
existing models of chemical evolution by means of line intensity ratios
diagrams and principal component analysis. We detect molecular emission in 19
galaxies in two 8 GHz-wide bands centred at 88 and 112 GHz. The main detected
transitions are the J=1-0 lines of CO, 13CO, HCN, HNC, HCO+, CN, and C2H. We
also detect HC3N J=10-9 in the galaxies IRAS 17208, IC 860, NGC 4418, NGC 7771,
and NGC 1068. The only HC3N detections are in objects with HCO+/HCN<1 and warm
IRAS colours. Galaxies with the highest HC3N/HCN ratios have warm IRAS colours
(60/100 {\mu}m>0.8). The brightest HC3N emission is found in IC 860, where we
also detect the molecule in its vibrationally excited state.We find low HNC/HCN
line ratios (<0.5), that cannot be explained by existing PDR or XDR chemical
models. Bright HC3N emission in HCO+-faint objects may imply that these are not
dominated by X-ray chemistry. Thus the HCN/HCO+ line ratio is not, by itself, a
reliable tracer of XDRs. Bright HC3N and faint HCO+ could be signatures of
embedded starformation, instead of AGN activity
The population of SNe/SNRs in the starburst galaxy Arp 220. A self-consistent analysis of 20 years of VLBI monitoring
The nearby ultra-luminous infrared galaxy (ULIRG) Arp 220 is an excellent
laboratory for studies of extreme astrophysical environments. For 20 years,
Very Long Baseline Interferometry (VLBI) has been used to monitor a population
of compact sources thought to be supernovae (SNe), supernova remnants (SNRs)
and possibly active galactic nuclei (AGNs). Using new and archival VLBI data
spanning 20 years, we obtain 23 high-resolution radio images of Arp 220 at
wavelengths from 18 cm to 2 cm. From model-fitting to the images we obtain
estimates of flux densities and sizes of all detected sources. We detect radio
continuum emission from 97 compact sources and present flux densities and sizes
for all analysed observation epochs. We find evidence for a LD-relation within
Arp 220, with larger sources being less luminous. We find a compact source LF
with , similar to SNRs in normal
galaxies. Based on simulations we argue that there are many relatively large
and weak sources below our detection threshold. The observations can be
explained by a mixed population of SNe and SNRs, where the former expand in a
dense circumstellar medium (CSM) and the latter interact with the surrounding
interstellar medium (ISM). Nine sources are likely luminous, type IIn SNe. This
number of luminous SNe correspond to few percent of the total number of SNe in
Arp 220 which is consistent with a total SN-rate of 4 yr as inferred
from the total radio emission given a normal stellar initial mass function
(IMF). Based on the fitted luminosity function, we argue that emission from all
compact sources, also below our detection threshold, make up at most 20\% of
the total radio emission at GHz frequencies.Comment: Accepted for publication in Astronomy and Astrophysic
New insights on the dense molecular gas in NGC253 as traced by HCN and HCO+
We have imaged the central ~1kpc of the circumnuclear starburst disk in the
galaxy NGC253 in the HCN(1-0), HCO+(1-0), and CO(1-0) transitions at 60pc
resolution using the Owens Valley Radio Observatory Millimeter-Wavelength Array
(OVRO). We have also obtained Atacama Pathfinder Experiment (APEX) observations
of the HCN(4-3) and the HCO+(4-3) lines of the starburst disk. We find that the
emission from the HCN(1-0) and HCO+(1-0) transitions, both indicators of dense
molecular gas, trace regions which are non-distinguishable within the
uncertainties of our observations. Even though the continuum flux varies by
more than a factor 10 across the starburst disk, the HCN/HCO+ ratio is constant
throughout the disk, and we derive an average ratio of 1.1+/-0.2. From an
excitation analysis we find that all lines from both molecules are subthermally
excited and that they are optically thick. This subthermal excitation implies
that the observed HCN/HCO+ line ratio is sensitive to the underlying chemistry.
The constant line ratio thus implies that there are no strong abundance
gradients across the starburst disk of NGC253. This finding may also explain
the variations in L'(HCN)/L'(HCO+) between different star forming galaxies both
nearby and at high redshifts.Comment: 9 pages, 12 figures, ApJ in press (volume 666 September
Recommended from our members
Aerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn
Aerosol physics measurements made onboard the Swedish icebreaker Oden in the late Summer and early Autumn of 1991 during the International Arctic Ocean Expedition (IAOE-91) have provided the first data on the size distribution of particles in the Arctic marine boundary layer (MBL) that cover both the number and mass modes of the size range from 3 to 500 nm diameter. These measurements were made in conjunction with atmospheric gas and condensed phase chemistry measurements in an effort to understand a part of the ocean-atmosphere sulfur cycle. Analysis of the particle physics data showed that there were three distinct number modes in the submicrometric aerosol in the Arctic MBL. These modes had geometric mean diameters of around 170 nm. 45 nm and 14 nm referred to as accumulation, Aitken and ultrafine modes, respectively. There were clear minima in number concentrations between the modes that appeared at 20 to 30 nm and at 80 to 100 nm. The total number concentration was most frequently between 30 and 60 particles cm-3 with a mean value of around 100 particles cm-3, but the hourly average concentration varied over two to three orders of magnitude during the 70 days of the expedition. On average, the highest concentration was in the accumulation mode that contained about 45% of the total number, while the Aitken mode contained about 40%. The greatest variability was in the ultrafine mode concentration which is indicative of active, earby sources (nucleation from the gas phase) and sinks; the Aitken and accumulation mode concentrations were much less variable. The ultrafine mode was observed about two thirds of the time and was dominant 10% of the time. A detailed description and statistical analysis of the modal aerosol parameters is presented here
High-resolution imaging of the molecular outflows in two mergers: IRAS17208-0014 and NGC1614
Galaxy evolution scenarios predict that the feedback of star formation and
nuclear activity (AGN) can drive the transformation of gas-rich spiral mergers
into ULIRGs, and, eventually, lead to the build-up of QSO/elliptical hosts. We
study the role that star formation and AGN feedback have in launching and
maintaining the molecular outflows in two starburst-dominated advanced mergers,
NGC1614 and IRAS17208-0014, by analyzing the distribution and kinematics of
their molecular gas reservoirs. We have used the PdBI array to image with high
spatial resolution (0.5"-1.2") the CO(1-0) and CO(2-1) line emissions in
NGC1614 and IRAS17208-0014, respectively. The velocity fields of the gas are
analyzed and modeled to find the evidence of molecular outflows in these
sources and characterize the mass, momentum and energy of these components.
While most (>95%) of the CO emission stems from spatially-resolved
(~2-3kpc-diameter) rotating disks, we also detect in both mergers the emission
from high-velocity line wings that extend up to +-500-700km/s, well beyond the
estimated virial range associated with rotation and turbulence. The kinematic
major axis of the line wing emission is tilted by ~90deg in NGC1614 and by
~180deg in IRAS17208-0014 relative to their respective rotating disk major
axes. These results can be explained by the existence of non-coplanar molecular
outflows in both systems. In stark contrast with NGC1614, where star formation
alone can drive its molecular outflow, the mass, energy and momentum budget
requirements of the molecular outflow in IRAS17208-0014 can be best accounted
for by the existence of a so far undetected (hidden) AGN of L_AGN~7x10^11
L_sun. The geometry of the molecular outflow in IRAS17208-0014 suggests that
the outflow is launched by a non-coplanar disk that may be associated with a
buried AGN in the western nucleus.Comment: Final version in press, accepted by A&A. Reference list updated.
Minor typos correcte
On carbon and oxygen isotope ratios in starburst galaxies: New data from NGC253 and Mrk231 and their implications
Using the IRAM 30-m telescope, CN and CO isotopologues have been measured
toward the central regions of the nearby starburst galaxy NGC253 and the
prototypical ultraluminous infrared galaxy Mrk231. In NGC253, the 12C/13C ratio
is 40+-10. Assuming that the ratio also holds for the CO emitting gas, this
yields 16O/18O = 145+-36 and 16O/17O = 1290+-365 and a 32S/34S ratio close to
that measured for the local interstellar medium (20-25). No indication for
vibrationally excited CN is found. Peak line intensity ratios between NGC253
and Mrk231 are ~100 for 12C16O and 12C18O J=1-0, while the ratio for 13C16O
J=1-0 is ~250. This and similar 13CO and C18O line intensities in the J=1-0 and
2-1 transitions of Mrk231 suggest 12C/13C ~ 100 and 16O/18O ~ 100, in agreement
with values obtained for the less evolved ultraluminous merger Arp220. Also
accounting for other extragalactic data, 12C/13C ratios appear to vary over a
full order of magnitude, from >100 in ultraluminous high redshift galaxies to
~100 in more local such galaxies to ~40 in weaker starbursts not undergoing a
large scale merger to 25 in the Central Molecular Zone of the Milky Way. With
12C being predominantly synthesized in massive stars, while 13C is mostly
ejected by longer lived lower mass stars at later times, this is qualitatively
consistent with our results of decreasing carbon isotope ratios with time and
rising metallicity. It is emphasized, however, that both infall of poorly
processed material, initiating a nuclear starburst, as well as the ejecta from
newly formed massive stars (in particular in case of a top-heavy stellar
initial mass function) can raise the carbon isotope ratio for a limited amount
of time.Comment: Accepted by Astronomy & Astrophysics, 6 figures, 4 table
The analysis of size-segregated cloud condensation nuclei counter (CCNC) data and its implications for cloud droplet activation
Ambient aerosol, CCN (cloud condensation nuclei) and hygroscopic properties were measured with a size-segregated CCNC (cloud condensation nuclei counter) in a boreal environment of southern Finland at the SMEAR (Station for Measuring Ecosystem-Atmosphere Relations) II station. The instrumental setup operated at five levels of supersaturation <i>S</i> covering a range from 0.1–1% and measured particles with a size range of 20–300 nm; a total of 29 non-consecutive months of data are presented. The median critical diameter <i>D</i><sub>c</sub> ranged from 150 nm at <i>S</i> of 0.1% to 46 nm at <i>S</i> of 1.0%. The median aerosol hygroscopicity parameter κ ranged from 0.41 at <i>S</i> of 0.1% to 0.14 at <i>S</i> of 1.0%, indicating that ambient aerosol in Hyytiälä is less hygroscopic than the global continental or European continental averages. It is, however, more hygroscopic than the ambient aerosol in an Amazon rainforest, a European high Alpine site or a forested mountainous site. A fairly low hygroscopicity in Hyytiälä is likely a result of a large organic fraction present in the aerosol mass comparative to other locations within Europe. A considerable difference in particle hygroscopicity was found between particles smaller and larger than ~100 nm in diameter, possibly pointing out to the effect of cloud processing increasing κ of particles > 100 nm in diameter. The hygroscopicity of the smaller, ~50 nm particles did not change seasonally, whereas particles with a diameter of ~150 nm showed a decreased hygroscopicity in the summer, likely resulting from the increased VOC emissions of the surrounding boreal forest and secondary organic aerosol (SOA) formation. For the most part, no diurnal patterns of aerosol hygroscopic properties were found. Exceptions to this were the weak diurnal patterns of small, ~50 nm particles in the spring and summer, when a peak in hygroscopicity around noon was observed. No difference in CCN activation and hygroscopic properties was found on days with or without atmospheric new particle formation. During all seasons, except summer, a CCN-inactive fraction was found to be present, rendering the aerosol of 75–300 nm in diameter as internally mixed in the summer and not internally mixed for the rest of the year
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