1,592 research outputs found
CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer
We present new sensitive wide-band measurements of the fine structure line
3^P_1 -> 3^P_0 (J=1-0, 492GHz) of neutral atomic carbon (CI) in the two typical
Ultra Luminous Infrared Galaxies NGC6240 and Arp220. We then use them along
with several other CI measurements in similar objects found in the literature
to estimate their global molecular gas content under the assumption of a full
CI-H_2 concomitance. We find excellent agreement between the H_2 gas mass
estimated with this method and the standard methods using 12^CO. This may
provide a new way to measure H_2 gas mass in galaxies, and one which may be
very valuable in ULIRGs since in such systems the bright 12^CO emission is
known to systematically overestimate the gas mass while their 13^CO emission is
usually very weak. At redshifts z>=1 the CI J=1-0 line shifts to much more
favorable atmospheric windows and can become a viable alternative tracer of the
H_2 gas fueling starburst events in the distant Universe.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter
A Survey of HC3N in Extragalactic Sources - Is HC3N a Tracer of Activity in ULIRGs?
Context. HC3N is a molecule that is mainly associated with Galactic
star-forming regions, but it has also been detected in extragalactic
environments. Aims. To present the first extragalactic survey of HC3N, when
combining earlier data from the literature with six new single-dish detections,
and to compare HC3N with other molecular tracers (HCN, HNC), as well as other
properties (silicate absorption strength, IR flux density ratios, C II flux,
and megamaser activity). Methods. We present mm IRAM 30 m, OSO 20 m, and SEST
observations of HC3N rotational lines (mainly the J = 10-9 transition) and of
the J = 1-0 transitions of HCN and HNC. Our combined HC3N data account for 13
galaxies (excluding the upper limits reported for the non-detections), while we
have HCN and HNC data for more than 20 galaxies. Results. A preliminary
definition "HC3N-luminous galaxy" is made based upon the HC3N/HCN ratio. Most
(~80 %) HC3N-luminous galaxies seem to be deeply obscured galaxies and
(U)LIRGs. A majority (~60 % or more) of the HC3N-luminous galaxies in the
sample present OH mega- or strong kilomaser activity. A possible explanation is
that both HC3N and OH megamasers need warm dust for their excitation.
Alternatively, the dust that excites the OH megamaser offers protection against
UV destruction of HC3N. A high silicate absorption strength is also found in
several of the HC3N-luminous objects, which may help the HC3N to survive.
Finally, we find that a high HC3N/HCN ratio is related to a high dust
temperature and a low C II flux.Comment: 17 pages, 12 figures, to be published in Astronomy & Astrophysic
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
A survey of HC_3N in extragalactic sources: Is HC_3N a tracer of activity in ULIRGs?
Context. HC_3N is a molecule that is mainly associated with Galactic star-forming regions, but it has also been detected in extragalactic environments.
Aims. To present the first extragalactic survey of HC_3N, when combining earlier data from the literature with six new single-dish detections, and to compare HC_3N with other molecular tracers (HCN, HNC), as well as other properties (silicate absorption strength, IR flux density ratios, C_(II) flux, and megamaser activity).
Methods. We present mm IRAM 30 m, OSO 20 m, and SEST observations of HC_3N rotational lines (mainly the J = 10–9 transition) and of the J = 1–0 transitions of HCN and HNC. Our combined HC_3N data account for 13 galaxies (excluding the upper limits reported for the non-detections), while we have HCN and HNC data for more than 20 galaxies.
Results. A preliminary definition “HC_3N-luminous galaxy” is made based upon the HC_3N/HCN ratio. Most (~80%) HC_3N-luminous galaxies seem to be deeply obscured galaxies and (U)LIRGs. A majority (~60% or more) of the HC3N-luminous galaxies in the sample present OH mega- or strong kilomaser activity. A possible explanation is that both HC_3N and OH megamasers need warm dust for their excitation. Alternatively, the dust that excites the OH megamaser offers protection against UV destruction of HC_3N. A high silicate absorption strength is also found in several of the HC_3N-luminous objects, which may help the HC3N to survive. Finally, we find that a high HC_3N/HCN ratio is related to a high dust temperature and a low C_(II) flux
COLA. III. Radio Detection of Active Galactic Nucleus in Compact Moderate Luminosity Infrared Galaxies
We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L_(IR) = 10^(11.01) L_☉) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (~10^(21) W Hz^(–1)) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity
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
Bilateral Vestibular Hypofunction in Quantitative Head Impulse Test : Clinical Characteristics in 23 Patients
OBJECTIVE: To explore clinical features of patients with bilateral vestibular hypofunction (BVH) verified in motorized head impulse test (MHIT). MATERIALS and METHODS: We examined clinical records of 23 adult patients (10 males and 13 females), whose gain of the vestibulo-ocular reflex in the MHIT was bilaterally lowered. Fifteen of 62 unilateral cochlear implant (CI) recipients routinely tested both pre-and postoperatively with the MHIT had BVH. Eight of 198 vestibular outpatients selected to the MHIT due to clinical causes had BVH. Clinical characteristics and a questionnaire regarding current sensations were analyzed. RESULTS: The mean gain +/- SD in the MHIT was 0.26 +/- 0.17 on the right and 0.26 +/- 0.14 on the left side. The mean gain in the CI recipients did not differ from that of vestibular outpatients (p>0.05). All outpatients with BVH suffered from oscillopsia, whereas only 46% of CI recipients experienced oscillopsia (p=0.048). Instability was more prominent (p=0.004) and quality of life further decreased (p=0.012) among vestibular outpatients compared with CI patients. Most common etiology for the BVH was meningitis. Other causes were either sudden or progressive loss of labyrinthine function, bilateral Meniere's disease, and ototoxicity. CONCLUSION: BVH is rare even in a specialized clinic. Vestibular outpatients were more disabled than CI recipients with the BVH.Peer reviewe
HNC, HCN and CN in Seyfert galaxies
Bright HNC 1--0 emission has been found towards several Seyfert galaxies.
This is unexpected since traditionally HNC is a tracer of cold (10 K) gas, and
the molecular gas of luminous galaxies like Seyferts is thought to have bulk
kinetic temperatures surpassing 50 K. In this work we aim to distinguish the
cause of the bright HNC and to model the physical conditions of the HNC and HCN
emitting gas. We have used SEST, JCMT and IRAM 30m telescopes to observe HNC
3-2 and HCN 3-2 line emission in a selection of 5 HNC-luminous Seyfert
galaxies. We estimate and discuss the excitation conditions of HCN and HNC in
NGC 1068, NGC 3079, NGC 2623 and NGC 7469, based on the observed 3-2/1-0 line
intensity ratios. We also observed CN 1-0 and 2-1 emission and discuss its role
in photon and X-ray dominated regions. HNC 3-2 was detected in 3 galaxies (NGC
3079, NGC 1068 and NGC 2623). HCN 3-2 was detected in NGC 3079, NGC 1068 and
NGC 1365. The HCN 3-2/1-0 ratio is lower than 0.3 only in NGC 3079, whereas the
HNC 3-2/1-0 ratio is larger than 0.3 only in NGC 2623. The HCN/HNC 1-0 and 3-2
line ratios are larger than unity in all the galaxies. The HCN/HNC 3-2 line
ratio is lower than unity only in NGC 2623, similar to Arp 220, Mrk 231 and NGC
4418. In three of the galaxies the HNC emissions emerge from gas of densities
n<10^5 cm^3, where the chemistry is dominated by ion-neutral reactions. In NGC
1068 the emission of HNC emerges from lower (<10^5 cm^3) density gas than HCN
(>10^5 cm^3). Instead, the emissions of HNC and HCN emerge from the same gas in
NGC 3079. The observed HCN/HNC and CN/HCN line ratios favor a PDR scenario,
rather than an XDR one. However, the N(HNC)/N(HCN) column density ratios
obtained for NGC 3079 can be found only in XDR environments.Comment: Accepted for publication in A&A. A selection of this paper will be
presented as a poster in the FIR workshop 2007, held at Bad Honnef, Germany.
High resolution figures in original paper. 16 pages, 8 figure
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
A high resolution CO map of the inner region of M51
M51, the Whirlpool Galaxy, at a distance of ≈ 9,6 Mpc and a systemic velocity of 465 km s^(−1), is the closest “Grand Design” spiral galaxy. Its low inclination (20°) makes it an excellent target for structural studies, e.g. the formation of arms in response to a spiral density wave causing gas streaming motions. We have obtained a high resolution, sensitive map of the inner 2.5′ of M51 using the Caltech six-element OVRO array. The map consists of a 19-field mosaic, taken using three different telescope configurations. The resolution is 2.5″, (corresponding to 115 pc linear size) and 3.5” for the robustly and naturally weigthed maps, respectively
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