- ID:
- ivo://CDS.VizieR/J/ApJ/858/90
- Title:
- Radial profiles of 5 nearby galaxies
- Short Name:
- J/ApJ/858/90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use new ALMA observations to investigate the connection between dense gas fraction, star formation rate (SFR), and local environment across the inner region of four local galaxies showing a wide range of molecular gas depletion times. We map HCN(1-0), HCO^+^(1-0), CS(2-1), ^13^CO(1-0), and C^18^O(1-0) across the inner few kiloparsecs of each target. We combine these data with short-spacing information from the IRAM large program EMPIRE, archival CO maps, tracers of stellar structure and recent star formation, and recent HCN surveys by Bigiel+ (2016ApJ...822L..26B) and Usero+ (2015AJ....150..115U). We test the degree to which changes in the dense gas fraction drive changes in the SFR. I_HCN_/I_CO_ (tracing the dense gas fraction) correlates strongly with I_CO_ (tracing molecular gas surface density), stellar surface density, and dynamical equilibrium pressure, P_DE_ (Elmegreen 1989ApJ...338..178E). Therefore, I_HCN_/I_CO_ becomes very low and HCN becomes very faint at large galactocentric radii, where ratios as low as I_HCN_/I_CO_~0.01 become common. The apparent ability of dense gas to form stars, {Sigma}_SFR_/{Sigma}_dense_ (where {Sigma}_dense_ is traced by the HCN intensity and the star formation rate is traced by a combination of H{alpha} and 24{mu}m emission), also depends on environment. {Sigma}_SFR_/{Sigma}_dense_ decreases in regions of high gas surface density, high stellar surface density, and high P_DE_. Statistically, these correlations between environment and both {Sigma}_SFR_/{Sigma}_dense_ and I_HCN_/I_CO_ are stronger than that between apparent dense gas fraction (I_HCN_/I_CO_) and the apparent molecular gas star formation efficiency {Sigma}_SFR_/{Sigma}_mol_. We show that these results are not specific to HCN.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/901/51
- Title:
- Radio continuum param. of Galactic HII regions
- Short Name:
- J/ApJ/901/51
- Date:
- 15 Feb 2022 14:31:45
- Publisher:
- CDS
- Description:
- Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact HII regions. It is located at the intersection between the central molecular zone (CMZ) and the far dust lane of the Galactic bar, similar to "hot spots" seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its HII regions all have similar radio luminosities and angular extents, and they are deficient in ~10{mu}m emission from their photodissociation regions (PDRs). Our Green Bank Telescope radio recombination line observations increase the known membership of Sgr E to 19 HII regions. There are 43 additional HII region candidates in the direction of Sgr E, 26 of which are detected for the first time here using MeerKAT 1.28GHz data. Therefore, the true HII region population of Sgr E may number >60. Using APEX SEDIGISM ^13^CO 2->1 data we discover a 3.0x10^5^M_{sun}_ molecular cloud associated with Sgr E, but find few molecular or far-infrared concentrations at the locations of the Sgr E HII regions. Comparison with simulations and an analysis of its radio continuum properties indicate that Sgr E formed upstream in the far dust lane of the Galactic bar a few million years ago and will overshoot the CMZ, crashing into the near dust lane. We propose that the unusual infrared properties of the Sgr E HII regions are caused by their orbits about the Galactic center, which have possibly stripped their PDRs.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A21
- Title:
- Radio cubes of G82.65-2.00
- Short Name:
- J/A+A/608/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The combination of line and continuum observations can provide vital insight into the formation and fragmentation of filaments and the initial conditions for star formation. We have carried out line observations to map the kinematics of an evolved, actively star forming filament G82.65-2.00. The filament was first identified from the Planck data as a region of particularly cold dust emission and was mapped at 100-500m as a part of the Herschel key program Galactic Cold Cores. The Herschel observations cover the central part of the filament, corresponding to a filament length of ~12pc at the assumed distance of 620pc. CO observations show that the filament has an intriguing velocity field with several velocity components around the filament. In this paper, we study the velocity structure in detail, to quantify possible mass accretion rate onto the filament, and study the masses of the cold cores located in the filament. We have carried out line observations of several molecules, including CO isotopologues, HCO^+^, HCN, and CS with the Osaka 1.85m telescope and the Nobeyama 45m telescope. The spectral line data are used to derive velocity and column density information.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A69
- Title:
- Radio observations of G074.11+00.11
- Short Name:
- J/A+A/630/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H_2_O maser emission. We aim to determine the mass distribution and gas dynamics within the clump, to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate the global dynamical state of the clump, the role of filamentary inflows, filament fragmentation and core accretion. We use molecular line and continuum observations from single dish observatories and interferometry facilities to study the kinematics of the region. The molecular line observations show that the central clump may have formed as a result of a large-scale filament collision. The central clump contains three compact cores. Assuming a distance of 2.3kpc, based on Gaia observations and a three-dimensional extinction method of background stars, the mass of the central clump exceeds 700 solar masses, which is roughly 25% of the total mass of the cloud. Our virial analysis suggests that the central clump and all identified substructures are collapsing. We find no evidence for small-scale filaments associated with the cores. Our observations indicate that the clump is fragmented into three cores with masses in the range of [10,50] solar masses and that all three are collapsing. The presence of an H_2_O maser emission suggests active star formation. However the CO lines show only weak signs of outflows. We suggest that the region is young and any processes leading to star formation have just recently begun.
- ID:
- ivo://CDS.VizieR/J/ApJS/221/26
- Title:
- Radio observations of Galactic WISE HII regions
- Short Name:
- J/ApJS/221/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The WISE Catalog of Galactic H II Regions contains ~2000 H II region candidates lacking ionized gas spectroscopic observations. All candidates have the characteristic H II region mid-infrared morphology of WISE 12{mu}m emission surrounding 22{mu}m emission, and additionally have detected radio continuum emission. We here report Green Bank Telescope hydrogen radio recombination line (RRL) and radio continuum detections in the X-band (9GHz; 3cm) of 302 WISE H II region candidates (out of 324 targets observed) in the zone 225{deg}>=l>=-20{deg}, |b|<=6{deg}. Here we extend the sky coverage of our H II region Discovery Survey, which now contains nearly 800 HII regions distributed across the entire northern sky. We provide LSR velocities for the 302 detections and kinematic distances for 131 of these. Of the 302 new detections, 5 have (l, b, v) coordinates consistent with the Outer Scutum-Centaurus Arm (OSC), the most distant molecular spiral arm of the Milky Way. Due to the Galactic warp, these nebulae are found at Galactic latitudes >1{deg} in the first Galactic quadrant, and therefore were missed in previous surveys of the Galactic plane. One additional region has a longitude and velocity consistent with the OSC but lies at a negative Galactic latitude (G039.183-01.422; -54.9km/s). With Heliocentric distances >22kpc and Galactocentric distances >16kpc, the OSC H II regions are the most distant known in the Galaxy. We detect an additional three HII regions near ~=150{deg} whose LSR velocities place them at Galactocentric radii >19kpc. If their distances are correct, these nebulae may represent the limit to Galactic massive star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/641/L4
- Title:
- Radio source J1402+5347 1.4GHz light curves
- Short Name:
- J/A+A/641/L4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Propagation of the radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy leads to twinkling of these sources, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. intensity modulation of a few per cent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the Milky Way's interstellar plasma. So far, only three sources were known that show more extreme variations, with modulations at the level of tens of per cent on timescales less than an hour. This requires propagation through nearby (d<~10pc) anomalously dense (n_e_>10^2^cm^3^) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (~50%) and rapid variations on a timescale of just 6.5 minutes in the decimetre band (1.4GHz). The spatial scintillation pattern is highly anisotropic with a semi-minor axis of about 20,000 km. Canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sight-line to J1402+5347 however passes unusually close to the B3 star Alkaid (eta UMa) at a distance of 32pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor-axis of the scintels must be smaller than 10 microarcseconds yielding an apparent brightness temperature for an isotropic source of >10^14^K.
- ID:
- ivo://CDS.VizieR/J/A+A/602/A61
- Title:
- Radio spectra of globulettes in Carina nebula
- Short Name:
- J/A+A/602/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Carina nebula hosts a large number of globulettes. An optical study of these tiny molecular clouds shows that the majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. We seek to search for, and hopefully detect, molecular line emission from some of the more massive objects; in case of successful detection we aim to map their motion in the Carina nebula complex and derive certain physical properties. Methods.We carried out radio observations of molecular line emission in ^12^CO and ^13^CO (2-1) and (3-2) of 12 globulettes in addition to positions in adjacent shell structures using APEX. All selected objects were detected with radial velocities shifted relative to the emission from related shell structures and background molecular clouds. Globulettes along the western part of an extended dust shell show a small spread in velocity with small velocity shifts relative to the shell. This system of globulettes and shell structures in the foreground of the bright nebulosity surrounding the cluster Trumpler 14 is expanding with a few km/s relative to the cluster. A couple of isolated globulettes in the area move at similar speed. Compared to similar studies of the molecular line emission from globulettes in the Rosette nebula, we find that the integrated line intensity ratios and line widths are very different. The results show that the Carina objects have a different density/temperature structure than those in the Rosette nebula. In comparison the apparent size of the Carina globulettes is smaller, owing to the larger distance, and the corresponding beam filling factors are small. For this reason we were unable to carry out a more detailed modelling of the structure of the Carina objects in the way as performed for the Rosette objects. The Carina globulettes observed are compact and denser than objects of similar mass in the Rosette nebula. The distribution and velocities of these globulettes suggest that they have originated from eroding shells and elephant trunks. Some globulettes in the Trumpler 14 region are quite isolated and located far from any shell structures. These objects move at a similar speed as the globulettes along the shell, suggesting that they once formed from cloud fragments related to the same foreground shell.
- ID:
- ivo://CDS.VizieR/J/ApJ/872/56
- Title:
- R-band linear polarization of Gaia stars
- Short Name:
- J/ApJ/872/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The availability of large data sets with stellar distance and polarization information will enable a tomographic reconstruction of the (plane-of-the-sky-projected) interstellar magnetic field in the near future. We demonstrate the feasibility of such a decomposition within a small region of the diffuse interstellar medium (ISM). We combine measurements of starlight (R-band) linear polarization obtained using the RoboPol polarimeter with stellar distances from the second Gaia data release. The stellar sample is brighter than 17mag in the R-band and reaches out to several kiloparsecs from the Sun. HI emission spectra reveal the existence of two distinct clouds along the line of sight. We decompose the line-of-sight-integrated stellar polarizations to obtain the mean polarization properties of the two clouds. The two clouds exhibit significant differences in terms of column density and polarization properties. Their mean plane-of-the-sky magnetic field orientation differs by 60{deg}. We show how our tomographic decomposition can be used to constrain our estimates of the polarizing efficiency of the clouds as well as the frequency dependence of the polarization angle of polarized dust emission. We also demonstrate a new method to constrain cloud distances based on this decomposition. Our results represent a preview of the wealth of information that can be obtained from a tomographic map of the ISM magnetic field.
- ID:
- ivo://CDS.VizieR/J/ApJ/748/99
- Title:
- Reactions of acetic acid with hydroxylamine
- Short Name:
- J/ApJ/748/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A computational study of the reactions of hydroxylamine and its ionized and protonated derivatives with acetic acid is provided. The reaction of neutral hydroxylamine with acetic acid, despite being clearly exothermic, involves a very large energy barrier. The reaction of ionized hydroxylamine with acetic acid is also clearly exothermic, but again a significant energy barrier is found (around 24 kcal/mol at the CCSD(T) level). The reaction of the most stable protonated isomer of hydroxylamine, NH_3_OH^+^, with acetic acid also involves a high barrier (more than 27 kcal/mol at the CCSD(T) level). Only the higher energy isomer, NH_2_OH^+^_2_, leads to a sensibly lower energy barrier (about 2.3 kcal/mol at the CCSD(T) level). Nevertheless, an estimate of the reaction coefficient at low temperatures such as those reigning in the interstellar medium gives very low values. Therefore, it seems that precursors of interstellar glycine could not be efficiently produced from the reactions of hydroxylamine-derived ions with acetic acid.
- ID:
- ivo://CDS.VizieR/J/ApJ/623/897
- Title:
- Reddening and extinction at high galactic latitude
- Short Name:
- J/ApJ/623/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near-infrared (JHKL) photometry of 103 southern stars located behind translucent interstellar clouds at high Galactic latitude. Our data are combined with visual photometry and spectral type information from the literature in a detailed analysis of the wavelength dependence of interstellar extinction by dust in these high-latitude clouds. We investigate the shape of the near-infrared extinction curve and evaluate the total line-of-sight extinction (A_V_) and ratio of total-to-selective extinction (R_V_) in each line of sight.
