- ID:
- ivo://CDS.VizieR/J/ApJ/862/25
- Title:
- H{alpha} & UV emission scale heights for edge-on gal.
- Short Name:
- J/ApJ/862/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare vertical profiles of the extraplanar H{alpha} emission to those of the UV emission for 38 nearby edge-on late-type galaxies. It is found that detection of the "diffuse" extraplanar dust (eDust), traced by the vertically extended, scattered UV starlight, always coincides with the presence of the extraplanar H{alpha} emission. A strong correlation between the scale heights of the extraplanar H{alpha} and UV emissions is also found; the scale height at H{alpha} is found to be ~0.74 of the scale height at FUV. Our results may indicate the multiphase nature of the diffuse ionized gas and dust in the galactic halos. The existence of eDust in galaxies where the extraplanar H{alpha} emission is detected suggests that a larger portion of the extraplanar H{alpha} emission than that predicted in previous studies may be caused by H{alpha} photons that originate from HII regions in the galactic plane and are subsequently scattered by the eDust. This possibility raise an advantage in studying the extraplanar diffuse ionized gas. We also find that the scale heights of the extraplanar emissions normalized to the galaxy size correlate well with the star formation rate surface density of the galaxies. The properties of eDust in our galaxies is on a continuation line of that found through previous observations of the extraplanar polycyclic aromatic hydrocarbons emission in more active galaxies known to have galactic winds.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/656/A146
- Title:
- HCN and CN emission in Serpens Main region
- Short Name:
- J/A+A/656/A146
- Date:
- 21 Mar 2022 09:00:12
- Publisher:
- CDS
- Description:
- Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but its properties and significance in the immediate surroundings of low-mass protostars are still poorly understood. We aim to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime to trace and characterize the UV field around low-mass protostars on ~0.6x0.6pc scales. The spatial distribution of HCN and CS are well-correlated with CO 6-5 emission that traces outflows. The CN emission is extended from the central protostars to their immediate surroundings also tracing outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from ~1 to 12 corresponding to G_0_~10^1^-10^3^ for gas densities and temperatures typical for outflows of low-mass protostars. UV radiation associated with protostars and their outflows is indirectly identified in a significant part of the Serpens Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH and H_2_O ratios observed with Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint, the CN to HCN ratio is an excellent tracer of UV fields around low- and intermediate-mass star-forming regions.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A129
- Title:
- HCN, HNC and DNC spectra of 27 sources
- Short Name:
- J/A+A/609/A129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ratio between the two stable isotopes of nitrogen, ^14^N and ^15^N, is well measured in the terrestrial atmosphere (~272), and for the pre-solar nebula (~441, deduced from the solar wind). Interestingly, some pristine solar system materials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and how these enrichments are linked to the past chemical history because we have only a limited number of measurements in dense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and also contain intermediate- and high-mass stars, are important targets because the solar system was probably born within a rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations in such high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30m observations of the J=1-0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27 intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-mass starless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2-1) rotational transition in order to search for a relation between the isotopic ratios D/H and ^14^N/^15^N. We derive average ^14^N/^15^N ratios of 359+/-16 in HCN and of 438+/-21 in HNC, with a dispersion of about 150-200. We find no trend of the ^14^ N/^15^ N ratio with evolutionary stage. This result agrees with what has been found for N_2_H^+^ and its isotopologues in the same sources, although the ^14^N/^15^N ratios from N2H+ show a higher dispersion than in HCN/HNC, and on average, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and ^14^N/^15^N in HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation of nitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A4
- Title:
- HCN-to-HNC intensity ratio
- Short Name:
- J/A+A/635/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The gas kinetic temperature (TK) determines the physical and chemical evolution of the interstellar medium (ISM). However, obtaining reliable TK estimates usually requires expensive observations including the combination of multi-line analysis and dedicated radiative transfer calculations. This work explores the use of HCN and HNC observations, and particularly the I(HCN)-to-I(HNC) intensity ratio (I(HCN)/I(HNC)) of their J=1-0 lines, as direct probe of the gas kinetic temperature in the molecular ISM. We obtained a new set of large-scale observations of the HCN and HNC (1-0) lines throughout the Integral Shape Filament (ISF) in Orion. In combination with ancillary gas and dust temperature measurements, we find a systematic temperature dependence of the observed I(HCN)-to-I(HNC) intensity ratio throughout our maps. Additional comparisons with chemical models demonstrate that these observed I(HCN)/I(HNC) variations are driven by the effective destruction and isomerization mechanisms of HNC under low-energy barriers. The observed variations of I(HCN)/I(HNC) with TK can be described with a two-part linear function. This empirical calibration is then used to create a temperature map of the entire ISF. Comparisons with similar dust temperature measurements in this cloud, as well as in other regions and galactic surveys, validate this simple technique for obtaining direct estimates of the gas kinetic temperature in a wide range of physical conditions and scales with an optimal working range between 15K<TK<=40K. Both observations and models demonstrate the strong sensitivity of the I(HCN)/I(HNC) ratio to the gas kinetic temperature. Since these lines are easily obtained in observations of local and extragalactic sources, our results highlight the potential use of this observable as new chemical thermometer for the ISM.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/1230
- Title:
- H_2_CO absorption toward Galactic anticenter
- Short Name:
- J/ApJ/652/1230
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have carried out a blind search in the general direction of the Galactic anticenter for absorption of the cosmic microwave background (CMB) radiation near 4.83GHz by molecular clouds containing gaseous ortho-formaldehyde (H_2_CO). The observations were done using the 25m radio telescope at Onsala in Sweden and covered strips in Galactic latitude, 1{deg}<=b<=+1{deg}, at several longitudes in the region 170{deg}<=l<=190{deg}. Spectra were obtained in these strips with a grid spacing corresponding to the telescope resolution of 10'. We have detected H_2_CO CMB absorption at 10% of the survey pointings.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A130
- Title:
- HCO and CH_3_O in prestellar cores
- Short Name:
- J/A+A/587/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent unexpected detection of terrestrial complex organic molecules in the cold (~10K) gas has cast doubts on the commonly accepted formation mechanisms of these species. Standard gas-phase mechanisms are inefficient and tend to underproduce these molecules, and many of the key reactions involved are unconstrained. Grain-surface mechanisms, which were presented as a viable alternative, suffer from the fact that they rely on grain surface diffusion of heavy radicals, which is not possible thermally at very low temperatures. One of the simplest terrestrial complex organic molecules, methanol is believed to form on cold grain surfaces following from successive H atom additions on CO. Unlike heavier species, H atoms are very mobile on grain surfaces even at 10K. Intermediate species involved in grain surface methanol formation by CO hydrogenation are the radicals HCO and CH_3_O, as well as the stable species formaldehyde H_2_CO. These radicals are thought to be precursors of complex organic molecules on grain surfaces. We present new observations of the HCO and CH_3_O radicals in a sample of prestellar cores and carry out an analysis of the abundances of the species HCO, H_2_CO, CH_3_O, and CH_3_OH, which represent the various stages of grain- surface hydrogenation of CO to CH_3_OH. The abundance ratios between the various intermediate species in the hydrogenation reaction of CO on grains are similar in all sources of our sample, HCO:H_2_CO:CH_3_O:CH_3_OH~10:100:1:100. We argue that these ratios may not be representative of the primordial abundances on the grains but, rather, suggest that the radicals HCO and CH_3_O are gas-phase products of the precursors H_2_CO and CH_3_OH, respectively. Various gas-phase pathways are considered, including neutral-neutral and ion-molecule reactions, and simple estimates of HCO and CH_3_O abundances are compared to the observations. Critical reaction rate constants, branching ratios, and intermediate species are finally identified.
- ID:
- ivo://CDS.VizieR/J/ApJ/820/37
- Title:
- HCO+ and HCN obs. toward Planck Galactic Cold Clumps
- Short Name:
- J/ApJ/820/37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first survey of dense gas toward Planck Galactic Cold Clumps (PGCCs). Observations in the J=1-0 transitions of HCO^+^ and HCN toward 621 molecular cores associated with PGCCs were performed using the Purple Mountain Observatory's 13.7m telescope. Among them, 250 sources were detected, including 230 cores detected in HCO^+^ and 158 in HCN. Spectra of the J=1-0 transitions from ^12^CO, ^13^CO, and C^18^O at the centers of the 250 cores were extracted from previous mapping observations to construct a multi-line data set. The significantly low detection rate of asymmetric double-peaked profiles, together with the good consistency among central velocities of CO, HCO^+^, and HCN spectra, suggests that the CO-selected Planck cores are more quiescent than classical star-forming regions. The small difference between line widths of C^18^O and HCN indicates that the inner regions of CO-selected Planck cores are no more turbulent than the exterior. The velocity-integrated intensities and abundances of HCO^+^ are positively correlated with those of HCN, suggesting that these two species are well coupled and chemically connected. The detected abundances of both HCO^+^ and HCN are significantly lower than values in other low- to high-mass star-forming regions. The low abundances may be due to beam dilution. On the basis of an inspection of the parameters given in the PGCC catalog, we suggest that there may be about 1000 PGCC objects that have a sufficient reservoir of dense gas to form stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/143
- Title:
- HCO+ and N2D+ dense cores in Perseus
- Short Name:
- J/ApJ/819/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of an HCO^+^ (3-2) and N_2_D^+^ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO^+^ asymmetry using a dimensionless asymmetry parameter {delta}_v_, and identify 20 cores with significant blue or red line asymmetries in optically thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO^+^ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the {delta}_v_ and collapse model results, we find that {delta}_v_ is a good tracer of core contraction if the optically thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03km/s) to supersonic (0.40km/s), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/M_J_>1) are somewhat more likely to show contraction motions. We find no trend of optically thin non-thermal line width with M/M_J_, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.
- ID:
- ivo://CDS.VizieR/J/ApJ/874/172
- Title:
- H_2_CO & H110{alpha} obs. toward Aquila
- Short Name:
- J/ApJ/874/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formaldehyde H_2_CO(1_10_-1_11_) absorption line and H110{alpha} radio recombination line have been observed toward the Aquila Molecular Cloud using the Nanshan 25m telescope operated by the Xinjiang Astronomical Observatory CAS. These first observations of the H_2_CO (1_10_-1_11_) absorption line determine the extent of the molecular regions that are affected by the ongoing star formation in the Aquila molecular complex and show some of the dynamic properties. The distribution of the excitation temperature Tex for H_2_CO identifies the two known star formation regions W40 and Serpens South as well as a smaller new region Serpens 3. The intensity and velocity distributions of H_2_CO and ^13^CO(1-0) do not agree well with each other, which confirms that the H_2_CO absorption structure is mostly determined by the excitation of the molecules resulting from the star formation rather than by the availability of molecular material as represented by the distribution. Some velocity-coherent linear ^13^CO(1-0) structures have been identified in velocity channel maps of H2CO and it is found that the three star formation regions lie on the intersect points of filaments. The H110{alpha} emission is found only at the location of the W40 HII region and spectral profile indicates a redshifted spherical outflow structure in the outskirts of the HII region. Sensitive mapping of H_2_CO absorption of the Aquila Complex has correctly identified the locations of star formation activity in complex molecular clouds and the spectral profiles reveal the dominant velocity components and may identify the presence of outflows.
- ID:
- ivo://CDS.VizieR/J/ApJ/779/119
- Title:
- HCOOCH_2_D detection in Orion KL
- Short Name:
- J/ApJ/779/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on new measurements carried out in the laboratory from 0.77 to 1.2THz and on a line-frequency analysis of these new data, along with previously published data, we build a line list for HCOOCH_2_D that leads to its first detection in the Orion KL nebula. The observed lines, both in space and in the laboratory, involve the cis D-in-plane and trans D-out-of-plane conformations of HCOOCH_2_D and the two tunneling states arising from the large-amplitude motion connecting the two trans configurations. The model used in the line position calculation accounts for both cis and trans conformations, as well as the large-amplitude motion.
