1,938 research outputs found
CN and HNC Line Emission in IR Luminous Galaxies
We have observed HNC 1-0, CN 1-0 and 2-1 line emission in a sample of 13 IR
luminous (LIRGs, L_IR > 10E11 Lo) starburst and Seyfert galaxies. HNC 1-0 is
detected in 9, CN 1-0 is detected in 10 and CN 2-1 in 7 of the galaxies. We
also report the first detection of HC3N (10-9) emission in Arp220. The
excitation of HNC and CN emission requires densities n > 10E4 cm-3. We compare
their intensities to that of the usual high density tracer HCN. The
I(HCN)/I(HNC}) and I(HCN)/I(CN) 1-0 line intensity ratios vary significantly,
from 0.5 to >6, among the galaxies. This implies that the actual properties of
the dense gas is varying among galaxies who otherwise have similar I(CO)/I(HCN)
line intensity ratios. We suggest that the HNC emission is not a reliable
tracer of cold (10 K) gas at the center of LIRGs, as it often is in the disk of
the Milky Way. Instead, the HNC abundance may remain substantial, despite high
gas temperatures, because the emission is emerging from regions where the HCN
and HNC formation and destruction processes are dominated by ion-neutral
reactions which are not strongly dependent on kinetic temperature. We find five
galaxies (four AGNs and one starburst) where the I(HCN)/I(HNC) intensity ratio
is close to unity. In other AGNs, however, I(HCN)/I(HNC}) is >4. The CN
emission is on average a factor of two fainter than HCN, but the variation is
large and there seems to be a trend of reduced relative CN luminosity with
increasing IR luminosity. One galaxy, NGC3690, has a CN luminosity twice that
of HCN and its ISM is thus strongly affected by UV radiation. We discuss the
I(HCN)/I(HNC) and I(HCN)/I(CN) line ratios as indicators of starburst
evolution.Comment: 12 pages, 4 figures. Accepted for publication in Astronomy and
Astrophysic
Arp 220 - IC 4553/4: understanding the system and diagnosing the ISM
Arp220 is a nearby system in final stages of galaxy merger with powerful
ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected
in HI absorption and OH Megamaser emission and later recognized as the nearest
ultra-luminous infrared galaxy also showing powerful molecular and X-ray
emissions. In this paper we review the available radio and mm-wave
observational data of Arp 220 in order to obtain an integrated picture of the
dense interstellar medium that forms the location of the powerful
star-formation at the two nuclei.Comment: 9 pages, 4 figures, to appear in: IAU Symposium 242 Astrophysical
Masers and their Environment
A Molecular Tidal Tail in the Medusa Minor Merger
We have detected CO 1-0 emission along the tidal tail of the NGC 4194 (the
Medusa) merger. It is the first CO detection in the optical tail of a minor
merger. Emission is detected both in the centre of the tail and at its tip. The
molecular mass in the 33'' Onsala 20m beam is estimated to be >= 8.5 x 10^7
M_{sun} which is at least 4% of the total molecular mass measured so far in
this system. We suggest that the emission is a molecular tidal tail which is
part of the extended structure of the main body, and that the molecular gas was
thrown out by the collision instead of having formed in situ from condensing
atomic material. We find it unlikely that the emission is associated with a
tidal dwarf galaxy (even if the future formation of such an object is
possible), but high resolution HI, CO and optical observations are necessary to
resolve the issue. The Medusa is very likely the result of an elliptical+spiral
collison and our detection supports the notion that molecular gas in minor
mergers can be found at great distances from the merger centre.Comment: 4 Pages, 2 figures included, accepted for A&A letter
Variation of Molecular Line Ratios and Cloud Properties in the Arp 299 Galaxy Merger
High resolution observations of 12CO (2.''3), 13CO (3.''9), and HCN (5.''4)
J=1--0 in the galaxy merger Arp 299 (IC 694 and NGC 3690) show the line ratios
vary dramatically across the system. The 12CO/13CO ratio is unusually large, 60
+- 15, at the IC 694 nucleus, where 12CO emission is very strong, and much
smaller, 10 +- 3, in the southern extended disk of that galaxy. Elsewhere, the
12CO/13CO line ratio is 5-20, typical of spiral galaxies. The line ratio
variation in the overlap between the two galaxies is smaller, ranging from 10
+- 3 in the east to 20 +- 4 in the west.
The 12CO/HCN line ratio also varies across Arp 299, although to a lesser
degree. HCN emission is bright towards each galaxy nucleus and in the
extranuclear region of active star formation; it was not detected in the IC 694
disk, or the eastern part of the overlap region, leading to lower limits of 25
and 20 respectively. By contrast, at the nuclei of IC 694 and NGC 3690 the
ratios are 9 +- 1 and 14 +- 3 respectively. In the western part of the overlap
region it is 11 +- 3.Comment: 16 pages, 4 postscript figures, to appear in ApJ Letter
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
Radio continuum and X-ray emission from the most extreme FIR-excess galaxy NGC 1377: An extremely obscured AGN revealed
Galaxies which strongly deviate from the radio-far IR correlation are of
great importance for studies of galaxy evolution as they may be tracing early,
short-lived stages of starbursts and active galactic nuclei (AGNs). The most
extreme FIR-excess galaxy NGC1377 has long been interpreted as a young dusty
starburst, but millimeter observations of CO lines revealed a powerful
collimated molecular outflow which cannot be explained by star formation alone.
We present new radio observations at 1.5 and 10 GHz obtained with the Jansky
Very Large Array (JVLA) and Chandra X-ray observations towards NGC1377. The
observations are compared to synthetic starburst models to constrain the
properties of the central energy source. We obtained the first detection of the
cm radio continuum and X-ray emission in NGC1377. We find that the radio
emission is distributed in two components, one on the nucleus and another
offset by 4.5 to the South-West. We confirm the extreme FIR-excess of the
galaxy, with a 4.2, which deviates by more than
7- from the radio-FIR correlation. Soft X-ray emission is detected on
the off-nucleus component. From the radio emission we estimate for a young
( Myr) starburst a star formation rate SFR0.1 M yr. Such
a SFR is not sufficient to power the observed IR luminosity and to drive the CO
outflow. We find that a young starburst cannot reproduce all the observed
properties of the nucleus of NGC1377. We suggest that the galaxy may be
harboring a radio-quiet, obscured AGN of 10M, accreting at
near-Eddington rates. We speculate that the off-nucleus component may be
tracing an hot-spot in the AGN jet.Comment: 14 pages, accepted for publication on Astronomy and Astrophysics on
08/07/201
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
Sub-arcsecond imaging of the radio continuum and neutral hydrogen in the Medusa merger
We present sub-arcsecond, Multi-Element Radio Linked Interferometer (MERLIN)
observations of the decimetre radio continuum structure and neutral hydrogen
(HI) absorption from the nuclear region of the starburst galaxy NGC 4194 (the
Medusa Merger). The continuum structure of the central kiloparsec of the Medusa
has been imaged, revealing a pair of compact radio components surrounded by
more diffuse, weak radio emission. Using the constraints provided by these
observations and those within the literature we conclude that the majority of
this radio emission is related to the ongoing star-formation in this merger
system.
With these observations we also trace deep HI absorption across the detected
radio continuum structure. The absorbing HI gas structure exhibits large
variations in column densities. The largest column densities are found toward
the south of the nuclear radio continuum, co-spatial with both a nuclear dust
lane and peaks in CO (1->0) emission. The dynamics of the HI absorption,
which are consistent with lower resolution CO emission observations,
trace a shallow north-south velocity gradient of ~320km/s/kpc. This gradient is
interpreted as part of a rotating gas structure within the nuclear region. The
HI and CO velocity structure, in conjunction with the observed gas column
densities and distribution, is further discussed in the context of the fuelling
and gas physics of the ongoing starburst within the centre of this merger.Comment: 12 pages, 5 figures, to appear in A&
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
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