- ID:
- ivo://CDS.VizieR/J/A+A/608/A133
- Title:
- Gas and dust in star-forming region rho OphA
- Short Name:
- J/A+A/608/A133
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate to what degree local physical and chemical conditions are related to the evolutionary status of various objects in star-forming media. rho Oph A displays the entire sequence of low-mass star formation in a small volume of space. Using spectrophotometric line maps of H_2_, H_2_O, NH_3_, N_2_H^+^, O_2_, OI, CO, and CS, we examine the distribution of the atomic and molecular gas in this dense molecular core. The physical parameters of these species are derived, as are their relative abundances in rho Oph A. Using radiative transfer models, we examine the infall status of the cold dense cores from their resolved line profiles of the ground state lines of H_2_O and NH_3_, where for the latter no contamination from the VLA 1623 outflow is observed and line overlap of the hyperfine components is explicitly taken into account. The stratified structure of this photon dominated region (PDR), seen edge-on, is clearly displayed. Polycyclic aromatic hydrocarbons (PAHs) and OI are seen throughout the region around the exciting star S1. At the interface to the molecular core 0.05pc away, atomic hydrogen is rapidly converted into H_2_, whereas OI protrudes further into the molecular core. This provides oxygen atoms for the gas-phase formation of O_2_ in the core SM1, where X(O_2_)~5x10^-8^. There, the ratio of the O_2_ to H_2_O abundance [X(H_2_O)~5x10^-9^] is significantly higher than unity. Away from the core, O_2_ experiences a dramatic decrease due to increasing H_2_O formation. Outside the molecular core, on the far side as seen from S1, the intense radiation from the 0.5pc distant early B-type star HD147889 destroys the molecules. Towards the dark core SM1, the observed abundance ratio X(O_2_)/X(H_2_O)>1, which suggests that this object is extremely young, which would explain why O_2_ is such an elusive molecule outside the solar system.
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- ID:
- ivo://CDS.VizieR/J/A+A/578/A131
- Title:
- Gas and dust in the star-forming region rho OphA
- Short Name:
- J/A+A/578/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N_2_H^+^, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N_2_H^+^(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class-1 sources to low values close to 0 for the disk-dominated emission in ClassIII objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C^18^O, also N_2_H^+^ is frozen onto the grains.
- ID:
- ivo://CDS.VizieR/J/ApJS/131/47
- Title:
- Gas-rich dwarfs from the POSS-II. III.
- Short Name:
- J/ApJS/131/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Arecibo neutral hydrogen data on a sample of optically selected dwarf galaxies. The sample ranges in H I mass from 10^6^ to 5x10^9^M_{sun}_, with a mean of 7.9x10^8^M_{sun}_. Using estimated H I radii, the H I surface densities range from 0.6 to 20M_{sun}_/pc^2^, all well below the critical threshold for star formation (Kennicutt, 1998ApJ...498..541K). M_HI_/L values of the LSB dwarfs range from 0.3 to 12 with a mean value of 2.0. Dynamical masses, calculated from the H I profile widths, range from 10^8^ to 10^11^M_{sun}_. There is a strong correlation between optical luminosity and dynamical mass for LSB dwarfs implying that the dark matter (whether baryonic or nonbaryonic) follows the detectable baryonic matter.
- ID:
- ivo://CDS.VizieR/J/ApJ/688/290
- Title:
- GASS HI survey of the lower halo
- Short Name:
- J/ApJ/688/290
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have detected over 400 HI clouds in the lower halo of the Galaxy within the pilot region of the Galactic All-Sky Survey (GASS), a region of the fourth quadrant that spans 18{deg} in longitude, 40{deg} in latitude, and is centered on the Galactic equator. These clouds have a median peak brightness temperature of 0.6K, a median velocity width of 12.8km/s, and angular sizes <~1{deg}. The motion of these clouds is dominated by Galactic rotation with a random cloud-to-cloud velocity dispersion of 18km/s. A sample of clouds likely to be near tangent points was analyzed in detail. These clouds have radii on the order of 30pc and a median HI mass of 630M_{sun}_. The population has a vertical scale height of 400pc and is concentrated in Galactocentric radius, peaking at R=3.8kpc. This confined structure suggests that the clouds are linked to spiral features, while morphological evidence that many clouds are aligned with loops and filaments is suggestive of a relationship with star formation. The clouds might result from supernovae and stellar winds in the form of fragmenting shells and gas that has been pushed into the halo rather than from a galactic fountain.
- ID:
- ivo://CDS.VizieR/J/A+A/633/A14
- Title:
- GaussPy+ decomposition of Galactic Ring Survey
- Short Name:
- J/A+A/633/A14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of large molecular line surveys of the Galactic plane is essential for our understanding of the gas kinematics on Galactic scales and, in particular, its link with the formation and evolution of dense structures in the interstellar medium. An approximation of the emission peaks with Gaussian functions allows for an efficient and straightforward extraction of useful physical information contained in the shape and Doppler-shifted frequency of the emission lines contained in these enormous data sets. In this work, we present an overview and the first results of a Gaussian decomposition of the entire Galactic Ring Survey (GRS) ^13^CO (1-0) data that consists of about 2.3 million spectra. We performed the decomposition with the fully automated GaussPy+ algorithm and fitted about 4.6 million Gaussian components to the GRS spectra. These decomposition results enable novel and unexplored ways to interpret and study the gas velocity structure. We discuss the statistics of the fit components and relations between the fitted intensities, velocity centroids, and velocity dispersions. We find that the magnitude of the velocity dispersion values increase towards the inner Galaxy and around the Galactic midplane, which we speculate is partly due to the influence of the Galactic bar and regions with higher non-thermal motions located in the midplane, respectively. We also used our decomposition results to infer global properties of the gas emission and find that the number of fit components used per spectrum is indicative of the amount of structure along the line of sight. We find that the emission lines from regions located on the far side of the Galaxy show increased velocity dispersion values, which are likely due to beam averaging effects. We demonstrate how this trend has the potential to aid in characterising Galactic structure by disentangling emission that belongs to the nearby Aquila Rift molecular cloud from emission that is more likely associated with the Perseus and Outer spiral arms. With this work, we also make our entire decomposition results available.
- ID:
- ivo://CDS.VizieR/VIII/14
- Title:
- 87GB Catalog of radio sources
- Short Name:
- VIII/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- of paper: The 91m telescope in Green Blank was used during 1987 October to map 6.0sr of the sky in the [0,+75]degrees declination band at 4.85GHz. We present the 87GB catalog of 54579 discrete sources with angular sizes less than about 10.5arcmin and stronger than S about 25mJy derived from these maps. The catalog positions and flux densities have been corrected for known map biases. Their estimated rms uncertainties were verified by comparison with more accurate positions and flux densities available for some sources. The 4.85GHz normalized source counts S^5/2^.n(S) between 25mJy and 10Jy were obtained and agree well with evolutionary models based on independent data.
- ID:
- ivo://CDS.VizieR/VIII/40
- Title:
- GB6 catalog of radio sources
- Short Name:
- VIII/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Green Bank 4.85GHz (lambda~6cm) survey was made with the NRAO seven-beam receiver on the (former) 91m telescope during 1986 November and 1987 October. The final set of sky maps covering the declination band 0deg<Dec.<+75deg was constructed with data from both epochs. Its noise and position errors are nearly a factor of 2^(1/2)^ smaller than in the epoch 1987 maps, from which the 87GB catalog <VIII/14> of 54,579 sources stronger than S~25mJy was extracted. Therefore, we used the new maps to make the GB6 catalog of 75,162 discrete sources with angular sizes phi<=10.5arcmin and flux densities S>=18mJy. This catalog is available in machine-readable versions with either B1950 or J2000 positions and as a printed book with B1950 positions. The GB6 weighted differential source counts S^(5/2)n(S) between 18 mJy and 7Jy agree well with evolutionary models based on independent data.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/80
- Title:
- GBT 350MHz survey. I. 13 new pulsars
- Short Name:
- J/ApJ/763/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Over the summer of 2007, we obtained 1191hr of "drift-scan" pulsar search observations with the Green Bank Telescope at a radio frequency of 350MHz. Here we describe the survey setup, search procedure, and the discovery and follow-up timing of 13 pulsars. Among the new discoveries, one (PSR J1623-0841) was discovered only through its single pulses, two (PSRs J1327-0755 and J1737-0814) are millisecond pulsars, and another (PSR J2222-0137) is a mildly recycled pulsar. PSR J1327-0755 is a 2.7ms pulsar at a dispersion measure (DM) of 27.9pc/cm3 in an 8.7 day orbit with a minimum companion mass of 0.22M_{sun}_. PSR J1737-0814 is a 4.2ms pulsar at a DM of 55.3pc/cm3 in a 79.3 day orbit with a minimum companion mass of 0.06M_{sun}_. PSR J2222-0137 is a 32.8ms pulsar at a very low DM of 3.27pc/cm3 in a 2.4 day orbit with a minimum companion mass of 1.11M_{sun}_. It is most likely a white-dwarf-neutron-star system or an unusual low-eccentricity double neutron star system. Ten other pulsars discovered in this survey are reported in the companion paper Lynch et al. (2013ApJ...763...81L).
- ID:
- ivo://CDS.VizieR/J/ApJS/177/255
- Title:
- GBT multiwavelength survey of Galactic center
- Short Name:
- J/ApJS/177/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the results of a radio continuum survey of the central 4{deg}x1{deg} with the 100m Green Bank Telescope (GBT) at wavelengths of 3.5, 6, 20, and 90cm. The 3.5 and 6cm surveys are the most sensitive and highest resolution single-dish surveys made of the central degrees of our Galaxy. We present catalogs of compact and extended sources in the central 4{deg} of our Galaxy, including detailed spectral index studies of all sources. The analysis covers star-forming regions such as Sgr B and Sgr C, where we find evidence of a mixture of thermal and nonthermal emission. The analysis quantifies the relative contribution of thermal and nonthermal processes to the radio continuum flux density toward the Galactic center (GC) region. In the central 4{deg}x1{deg} of the GC, the thermal and nonthermal flux fractions for all compact and diffuse sources are 28%/72% at 3.5cm and 19%/81% at 6cm. The total flux densities from these sources are 783+/-52 and 1063+/-93Jy at 3.5 and 6cm, respectively, excluding the contribution of Galactic synchrotron emission.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A121
- Title:
- G203.7+11.5 21cm and 11cm intensity maps
- Short Name:
- J/A+A/641/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In soft X-rays, the Monogem ring is an object with a diameter of 25{deg} located in the Galactic anti-centre. It is believed to be a faint, evolved, local supernova remnant. It is not seen at radio wavelengths, as other large supernova remnants are. We study a narrow about 4.5D long, faint Halpha-filament, G203.7+11.5, that is seen towards the centre of the Monogem ring. It causes depolarisation and excessive Faraday rotation of radio polarisation data. Polarisation observations at 11cm and 21cm with the Effelsberg 100-m telescope were analysed.
