Galactic Molecular Ring Research Articles

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

ABSTRACT We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

Molecular gas in absorption and emission along the line of sight to W31C G10.62-0.38

We used the ARO 12m antenna to observe emission from the J=1-0 lines of carbon monoxide, \hcop\ and HNC and the J=2-1 line of CS toward and around the continuum peak used for absorption studies and we compare them with CH, HNC, C\p\ and other absorption spectra from PRISMAS. We develop a kinematic analysis that allows a continuous description of the spectral properties and relates them to viewing geometry in the Galaxy. As for CH, HF, C\p, \hcop\ and other species observed in absorption, mm-wave emission in CO, \hcop, HNC and CS is continuous over the full velocity range expected for material between the Sun and W31 4.95 kpc away. CO emission is much stronger than average in the Galactic molecular ring and the mean \HH\ density derived from CH, $4 \pccc \la$ 2$<$n(\HH)$>$ $\la 10 \pccc$ at 4 $\la$ R $\la$ 6.4 kpc, is similarly elevated. The CO-\HH\ conversion factor falls in a narrow range \XCO\ $= 1-2\times10^{20}~\HH\ \pcc~({\rm K}-\kms)^{-1}$ if the emitting gas is mostly on the near side of the sub-central point, as we suggest. The brightnesses of \hcop, HNC, and CS are comparable (0.83\%, 0.51\% and 1.1\% respectively relative to CO) and have no variation in galactocentric radius with respect to CO. Comparison of the profile-averaged \hcop\ emission brightness and optical depth implies local densities n(H) $\approx 135\pm25\pccc$ with most of excitation of \hcop\ from electrons. At such density, a consistent picture of the \HH-bearing gas, accounting also for the CO emission, has a volume filling factor 3\% and a 5 pc clump or cloud size.

Properties of the UCHII region G25.4NW and its associated molecular cloud

Ultra compact HII (UCHII) G25.4NW is a bright IR source in the region of the inner Galaxy. New HI images from the Very Large Array Galactic Plane Survey show clear absorption features associated with the UCHII region up to 95 km s−1, and there are no other absorptions up to the tangential velocity. This reveals that G25.4NW has a near-side distance of 5.7 kpc, and it is located in the region of the inner Galactic molecular ring. Using the new distance, the bolometric luminosity of G25.4NW is estimated as 105.6 L⊙, which corresponds to an O6 star. It contains 460 M⊙ of ionized gas. A high-resolution 13CO image from the Galactic Ring Survey reveals that G25.4NW is part of a more extended star-forming complex with about 104 M⊙ of molecular gas.

Applying the manifold theory to Milky Way models: First steps on morphology and kinematics

We present recent results obtained by applying invariant manifold techniques to analytical models of the Milky Way. It has been shown that invariant manifolds can reproduce successfully the spiral arms and rings in external barred galaxies. Here, for the first time, we apply this theory to Milky Way models. We select five different models from the literature and, using the parameters chosen by the authors of the papers, and three different cases, namely Case 1, where only the COBE/DIRBE bar is included in the potential; Case 2, when the COBE/DIRBE and the Long bar are aligned, and Case 3, when the COBE/DIRBE bar and the Long bar are misaligned. We compute in each case and for each model the orbits trapped by the manifolds. In general, the global morphology of the manifolds can account for the 3-kpc arms and for the Galactic Molecular Ring.

Modelling the inner disc of the Milky Way with manifolds - I. A first step

We study the bar-driven dynamics in the inner part of the Milky Way by using invariant manifolds. This theory has been successfully applied to describe the morphology and kinematics of rings and spirals in external galaxies, and now, for the first time, we apply it to the Milky Way. We compute the orbits confined by the invariant manifolds of the unstable periodic orbits located at the ends of the bar. We discuss whether the COBE/DIRBE bar and the Long bar compose a single bar or two independent bars and perform a number of comparisons which, taken together, argue strongly in favour of the former. More specifically, we favour the possibility that the so-called COBE/DIRBE bar is the boxy/peanut bulge of a bar whose outer thin parts are the so-called Long bar. This possibility is in good agreement both with observations of external galaxies, with orbital structure theory and with simulations. We then analyse in detail the morphology and kinematics given by five representative Galactic potentials. Two have a Ferrers bar, two have a quadrupole bar and the last one a composite bar. We first consider only the COBE/DIRBE bar and then extend it to include the effect of the Long bar. We find that the large-scale structure given by the manifolds describes an inner ring, whose size is similar to the near and far 3-kpc arm, and an outer ring, whose properties resemble those of the Galactic Molecular Ring. We also analyse the kinematics of these two structures, under the different galactic potentials, and find they reproduce the main over-densities found in the galactic longitude-velocity CO diagram. Finally, we consider for what model parameters, the global morphology of the manifolds may reproduce the two outer spiral arms. We conclude that this would necessitate either more massive and more rapidly rotating bars, or including in the potential an extra component describing the spiral arms.

Gas flow models in the Milky Way embedded bars

The gas distribution and dynamics in the inner Galaxy present many unknowns as the origin of the asymmetry of the longitude-velocity (lv) diagram of the Central Molecular Zone (CMZ). On the other hand, there are recent evidences in the stellar component of the presence of a nuclear bar that could be slightly lopsided. Our goal is to characterize the nuclear bar observed in 2MASS maps and to study the gas dynamics in the inner Milky Way taking into account this secondary bar. We have derived a realistic mass distribution by fitting 2MASS star counts maps with three components (disk, bulge and nuclear bar) and we have simulated the gas dynamics, in the deduced gravitational potential, using a sticky-particles code. Our simulations of the gas dynamics reproduce successfully the main characteristics of the Milky Way for a bulge orientation of 20-35 deg with respect to the Sun-Galactic Center (GC) line and a pattern speed of 30-40 km/s/kpc. In our models the Galactic Molecular Ring (GMR) is not an actual ring but the inner parts of the spiral arms, while the 3-kpc arm and its far side counterpart are lateral arms that contour the bar. Our simulations reproduce, for the first time, the parallelogram shape of the lv-diagram of the CMZ as the gas response to the nuclear bar. This bar should be oriented by an angle of ~60-75 deg with respect to the Sun-GC line and its mass amounts to (2-5.5)10e9 Msun. We show that the observed asymmetry of the CMZ cannot be due to lopsidedness of the nuclear bar as suggested by the 2MASS maps. We do not find clear evidences of lopsidedness in the stellar potential. We propose that the observed asymmetry of the central gas layer can be due to the infalling of gas into the CMZ in the l=1.3-complex

A Catalog ofMidcourse Space ExperimentInfrared Dark Cloud Candidates

We use 8.3 μm mid-infrared images acquired with the Midcourse Space Experiment satellite to identify and catalog infrared dark clouds (IRDCs) in the first and fourth quadrants of the Galactic plane. Because IRDCs are seen as dark extinction features against the diffuse Galactic infrared background, we identify them by first determining a model background from the 8.3 μm images and then searching for regions of high decremental contrast with respect to this background. IRDC candidates in our catalog are defined by contiguous regions bounded by closed contours of a 2 σ decremental contrast threshold. Although most of the identified IRDCs are actual cold dark clouds, some as yet unknown fraction may be spurious identifications. For large high-contrast clouds, we estimate the reliability to be 82%. Low-contrast clouds should have lower reliabilities. Verification of the reality of individual clouds will require additional data. We identify 10,931 candidate IRDCs. For each IRDC, we also catalog cores. These cores, defined as localized regions with at least 40% higher extinction than the cloud's average extinction, are found by iteratively fitting two-dimensional elliptical Gaussian functions to the contrast peaks. We identify 12,774 cores. The catalog contains the position, angular size, orientation, area, peak contrast, peak contrast signal-to-noise, and integrated contrast of the candidate IRDCs and their cores. The distribution of IRDCs closely follows the Galactic diffuse mid-infrared background and peaks toward prominent star-forming regions, spiral arm tangents, and the so-called 5 kpc Galactic molecular ring.

The KOSMA large-scale CO survey of clouds in the Galactic Molecular Ring

The KOSMA large-scale CO survey of clouds in the Galactic Molecular Ring

GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy

ABSTRACTThe Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of 2/3 of the inner Galactic disk with a pixel resolution of ∼1.″2 using the Infrared Array Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will cover Galactic latitudes |b|≤1° and longitudes |l| = 10°–65° (both sides of the Galactic center). The survey area contains the outer ends of the Galactic bar, the Galactic molecular ring, and the inner spiral arms. The GLIMPSE team will process these data to produce a point‐source catalog, a point‐source data archive, and a set of mosaicked images. We summarize our observing strategy, give details of our data products, and summarize some of the principal science questions that will be addressed using GLIMPSE data. Up‐to‐date documentation, survey progress, and information on complementary data sets are available on the GLIMPSE Web site.

Aperture synthesis observations of H I and CO in the early type starburst galaxy NGC 3928

view Abstract Citations (7) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Aperture Synthesis Observations of HI and CO in the Early Type Starburst Galaxy NGC 3928 Li, Jonathan G. ; Seaquist, E. R. ; Wang, Zhong ; Sage, L. J. Abstract Aperture synthesis observations of the 21 cm H I and the ^12^C0 J = 1 _0 lines with spatial resolutions of 24" X 22" and 11" X 6", respectively, are presented to study the gas distribution and kinematics in the blue compact early type starburst galaxy NGC 3928. The CO emission is partially resolved and is confined to a rotating disk with FWHM~11" in the nucleus of the galaxy. There is evidence to suggest that CO (and possibly H I) is deficient in the central few hundred pc. The average H_2_ surface density of the molecular disk of ~400M_sun_/pc^2^ is much higher than found in the Galactic molecular ring. The H I emission is centrally concentrated and most of the emission is within its de Vaucouleurs' radius, features not shared by most of the gas-rich S0/Sa galaxies studied so far. The H I displays a regular velocity field and is consistent with a disk in nearly solid body rotation out to r~3.7 kpc if no warp occurs within the optical radius, suggesting a dark halo surrounding the galaxy. There is good agreement between the kinematics of the CO and that of the H I where the two overlap in the inner part. The relatively unperturbed gas morphology argues against a recent interaction/merger being the cause of the nuclear starburst. Publication: The Astronomical Journal Pub Date: January 1994 DOI: 10.1086/116836 Bibcode: 1994AJ....107...90L Keywords: Carbon Monoxide; Compact Galaxies; Disk Galaxies; Emission Spectra; Galactic Halos; H I Regions; Starburst Galaxies; Synthetic Apertures; Galactic Evolution; Galactic Rotation; Galactic Structure; Spatial Resolution; Spectrum Analysis; Star Formation; Velocity Distribution; Astrophysics; GALAXIES: INDIVIDUAL: NGC 3928; GALAXIES: STARBURST; GALAXIES: ABUNDANCES full text sources ADS | data products SIMBAD (3) NED (1)

The CO distribution around L = 30 deg, B = 0 deg

The 4.6 millimeter-wave telescope at the University of British Columbia has been used to map a region about 1/2 /sup 0/ in diameter centered on l=30 /sup 0/, b=0 /sup 0/ in the J=1..-->..0 transition of /sup 12/C/sup 16/O. This study of the inner edge of the galactic molecular ring has revealed two well-defined giant molecular clouds with diameters in the range 25--45 pc and masses in the range (1.5--3.5) x 10/sup 5/ M/sub sun/. Values obtained for the internal kinetic and potential energies of these clouds are similar, indicating that they may be stable. In addition, our analysis indicates that a substantial fraction, amounting to approximately 30%, of the integrated CO intensity comes from a feature covering the entire field observed. This suggests that at the inner edge of the molecular ring there is a clumpy medium of molecular material with a smoothed average density n/sub H2/=4 cm/sup -3/. We have also found a complex of four clouds whose line widths are a little more than a factor of 2 greater than those of the standard giant molecular clouds. The nature of these clouds is at present uncertain. The total number of clouds detected in our survey, 10, givesmore » a number density of CO clouds of 3 x 10/sup -7/ pc/sup -3/.« less