Galactic Longitude Research Articles

Position and Proper Motion of Sagittarius A* in the ICRF3 Frame from VLBI Absolute Astrometry

Sagittarius A* (Sgr A*) is a strong, compact radio source believed to be powered by a supermassive black hole at the galactic center. Extinction by dust and gas in the galactic plane prevents observing it optically, but its position and proper motion have previously been estimated using radio interferometry. We present new VLBI absolute astrometry measurements of its precise position and proper motion in the frame of the third realization of the International Celestial Reference Frame (ICRF3). The observations used were made at 52 epochs on the VLBA at K band (24 GHz) between 2006 June and 2022 August. We find the proper motion of Sgr A* to be −3.128 ± 0.042 mas yr−1 in R.A. and −5.584 ± 0.075 mas yr−1 in decl., or 6.400 ± 0.073 mas yr−1 at a position angle of 209.°26 ± 0.°51. We also find its J2000 ICRF3 coordinates at the 2015.0 proper motion epoch to be 17h45m40.ˢ034047 ± 0.ˢ000018, −29°00′28.″21601 ± 0.″00044. In galactic coordinates, Sgr A* shows proper motion of −6.396 ± 0.071 mas yr−1 in galactic longitude and −0.239 ± 0.045 mas yr−1 in galactic latitude, indicating solar motion of 248.0 ± 2.8 km s−1 in the galactic plane and 9.3 ± 1.9 km s−1 toward the north galactic pole.

The Mopra Southern Galactic Plane CO Survey – data release 4– complete survey

Abstract We present observations of the Mopra carbon monoxide (CO) survey of the Southern Galactic Plane, covering Galactic longitudes spanning $l = 250^{\circ}$ ( $-110^{\circ}$ ) to $l = 355^{\circ}$ ( $-5^{\circ}$ ), with a latitudinal coverage of at least $|b|<1^\circ$ , totalling an area of $>$ 210 deg $^{2}$ . These data have been taken at 0.6 arcmin spatial resolution and 0.1 km s $^{-1}$ spectral resolution, providing an unprecedented view of the molecular gas clouds of the Southern Galactic Plane in the 109–115 GHz $J = 1-0$ transitions of $^{12}$ CO, $^{13}$ CO, C $^{18}$ O, and C $^{17}$ O.

Detailed Analysis of the TeV γ-Ray Sources 3HWC J1928+178, 3HWC J1930+188, and the New Source HAWC J1932+192

The latest High Altitude Water Cherenkov (HAWC) point-like source catalog up to 56 TeV reported the detection of two sources in the region of the Galactic plane at galactic longitude 52° < ℓ < 55°, 3HWC J1930+188 and 3HWC J1928+178. The first one is associated with a known TeV source, the supernova remnant SNR G054.1+00.3. It was discovered by one of the currently operating Imaging Atmospheric Cherenkov Telescope (IACT), the Very Energetic Radiation Imaging Telescope Array System (VERITAS), detected by the High Energy Stereoscopic System (H.E.S.S), and identified as a composite SNR. However, the source 3HWC J1928+178, discovered by HAWC and coincident with the pulsar PSR J1928+1746, was not detected by any IACT despite their long exposure on the region, until a recent new analysis of H.E.S.S. data was able to confirm it. Moreover, no X-ray counterpart has been detected from this pulsar. We present a multicomponent fit of this region using the latest HAWC data. This reveals an additional new source, HAWC J1932+192, which is potentially associated with the pulsar PSR J1932+1916, whose γ-ray emission could come from the acceleration of particles in its pulsar wind nebula. In the case of 3HWC J1928+178, several possible explanations are explored, in an attempt to unveil the origins of the very-high-energy γ-ray emission.

Magnetic Field in some Selected Directions of the Galaxy: Sagittarius Spiral Arm

Faraday rotation data on 180 pulsars are used in a detail study of the magnetic field in the direction of galactic longitude 40◦ &lt; l &lt; 70◦, including the Sagittarius spiral arm region. The highly regular magnetic field in northern hemisphere of galaxy is directed to the Sun, when the magnetic field of southern hemisphere is directed from the Sun. We propose that the Sagittarius spiral arm lies mainly to the north of the Galactic plane, while the magnetic field with opposite direction below this plane is the field of the halo of the southern hemisphere of the Galaxy.

Spiral arms and the angular momentum gap in Milky Way Cepheids

ABSTRACT The angular momentum distribution of classical Cepheids in the outer Milky Way disc is bimodal with a gap at $L_\mathrm{gap}=2950\, \rm{km\,s^{-1}}$ kpc, corresponding to $R=13\,$ kpc, while no similar feature has been found in the general population of disc stars. We show that star formation in multiple spiral arm segments at the same azimuth leads to such multimodality that quickly dissolves and only shows in young stars. Unlike other explanations, such as a 1:1 orbital resonance with the Galactic bar, this also accounts for the observed steepening of the stellar warp at Lgap, since the adjacent spiral arms represent different parts of the warped gas disc, and for the predominance of the gap at negative Galactic longitude (ℓ &amp;lt; 0°), since for complex spiral structure this mechanism is limited in azimuth. In this scenario, the gap is clearly present only in young stars, as observed, while most purely stellar dynamical origins would affect all disc populations, including older disc stars.

MOCK OBSERVATIONS OF SIMULATED STAR CLUSTER ON SOLAR ORBIT

With the advent of the Gaia DR2 catalog, which contains astrometric and photometric parameters for a large number of stars, measured with a high degree of accuracy, data about the cosmos and the Universe, including Star clusters in our Galaxy, are growing. However, when observed, the cluster stars are lost against the background of stars in the dense Galactic field. In addition, observational data alone is not sufficient to study real clusters from birth to destruction. In this regard, a number of numerical simulations of star clusters have been running to explain the processes and to determine the membership of cluster stars. And for this, we need to conduct a mock observation of model clusters. In this paper, we performed analyses on the output data from numerical simulations and developed a method for conducting mock observations of model clusters. We took one model of a star cluster with an age of 350 Myr, with a mass of 6000 , and with a star formation efficiency SFE=0.25, and put it in different galactic longitudes and at different distances from the Sun. In conclusion, using this method, we can put a cluster at any point on the celestial sphere, and this in turn allows you to compare with the real observed clusters and evaluate the possibility of detecting physical parameters in them.

The origin of the Perseus-arm gap revealed with VLBI astrometry

AbstractThe Perseus arm has a gap in Galactic longitudes (l) between 50° and 80° where the arm has little star formation activity. To understand the gap, we conducted VERA (VLBI Exploration of Radio Astrometry) astrometry and analyzed archival H &lt;SC&gt;I&lt;/SC&gt; data. We report on parallax and proper motion results from four star-forming regions, of which G050.28–00.39 and G070.33+01.59 are associated with the gap. Perseus-arm sources G049.41+00.32 and G050.28–00.39 lag relative to a Galactic rotation by 77 ± 17 km s-1 and 31 ± 10 km s-1, respectively. The noncircular motion of G049.41+00.32 cannot be explained by the gravitational potential of the arm. We discovered rectangular holes with integrated brightness temperatures less than 30 K arcdeg in l vs. VLSR of the H &lt;SC&gt;I&lt;/SC&gt; data. Also, we found extended H &lt;SC&gt;I&lt;/SC&gt; emission on one side of the Galactic plane when integrating the H &lt;SC&gt;I&lt;/SC&gt; data over the velocity range covering the hole. G049.41+00.32 and G050.28–00.39 are moving toward the emission. The Galactic H &lt;SC&gt;I&lt;/SC&gt; disk at the same velocity range showed an arc structure, indicating that the disk was pushed from the lower side of the disk. All the observational results might be explained by a cloud collision with the Galactic disk.

Astrometric observations of water maser sources toward the Galactic Center with VLBI

AbstractThe Central Molecular Zone (CMZ) in the Galactic Center region shows outstanding non-circular motion unlike the Galactic disk. While several models describing this non-circular motion have been proposed, a uniform kinematic model of the CMZ orbit has not yet emerged. To uncover the dynamics of the Galactic center region, we conducted VLBI astrometric observations of 22GHz water maser sources towards the Galactic center using VERA. By measuring parallaxes and proper motions, we can determine whether each source is actually located in the CMZ or not, and identify the three-dimensional positions and velocities in the non-circular orbit if the source is indeed located in the CMZ. We present the results of our astrometric study for several maser sources associated with molecular clouds towards the Galactic center. The astrometric observations toward Sgr B2(M) indicated that Sgr B2 complex is moving toward the positive Galactic longitude relative to Sgr A*.

Peering into the Milky Way by FAST: III. Magnetic fields in the Galactic halo and farther spiral arms revealed by the Faraday effect of faint pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive radio telescope for pulsar observations. We make polarimetric measurements of a large number of faint and distant pulsars using the FAST. We present the new measurements of Faraday rotation for 134 faint pulsars in the Galactic halo. Significant improvements are also made for some basic pulsar parameters for 15 of them. We analyse the newly determined rotation measures (RMs) for the Galactic magnetic fields by using these 134 halo pulsars, together with previously available RMs for pulsars and extragalactic radio sources and also the newly determined RMs for another 311 faint pulsars which are either newly discovered in the project of the Galactic Plane Pulsar Snapshot (GPPS) survey or previously known pulsars without RMs. The RM tomographic analysis in the first Galactic quadrant gives roughly the same field strength of around 2~$\mu$G for the large-scale toroidal halo magnetic fields. The scale height of the halo magnetic fields is found to be at least 2.7$\pm$0.3~kpc. The RM differentiation of a large number of pulsars in the Galactic disk in the Galactic longitude range of $26^{\circ}<l<90^{\circ}$ gives evidence for the clockwise magnetic fields (viewed from the north Galactic pole) in two interarm regions inside the Scutum arm and between the Scutum and Sagittarius arm, and the clockwise fields in the Local-Perseus interarm region and field reversals in the Perseus arm and beyond.

Population study of astrophysical false positive detections in the southern plato field

ABSTRACT For the upcoming PLAnetary Transits and Oscillation of stars (PLATO) satellite mission, a large number of target stars are required to yield a statistically significant number of planet transits. Locating the centres of the long duration observational phase (LOP) fields closer to the Galactic plane will increase the target star numbers but also the astrophysical false positives (FPs) from blended eclipsing binary systems. We utilize the Binary Stellar Evolution and Population Synthesis code, to create a complete synthetic stellar and planetary population for the proposed southern LOP field (LOPS0), as well as for a representative portion of the northern LOP field (LOPN-sub). For LOPS0, we find an overall low FP rate for planets smaller than Neptunes. The FP rate generally shows little variation with Galactic longitude (l), and a modest increase with decreasing Galactic latitude (|b|). The location of the LOPS field centre within the current allowed region is not strongly constrained by FPs. Analysis of LOPN-sub suggests a markedly increased number of FPs across the full range of planet radii at low |b| resulting in approximately twice the percentage of FP detection rate in the LOPN-sub compared to the corresponding southern field segment in the planet radius range −0.2 &amp;lt; log (R/R⊕) ≤ 0.4. However, only a few per cent of fully eclipsing FPs in LOPS0 in this radius range have periods between 180 and 1000 d so the vast majority of FPs are expected to be outside the period range of interest for PLATO.

Star and Cluster Formation in the Sh2-112 Filamentary Cloud Complex

We present the star formation activity around the emission nebula Sh2-112. At a distance of ∼2.1 kpc, this H ii complex, itself 3 pc in radius, is illuminated by the massive star (O8 V) BD+45 3216. The associated molecular cloud extends in angular scales of 2.°0 × 0.°83, corresponding to linear sizes of 73 pc by 30 pc, along the Galactic longitude. The high-resolution (30″) extinction map reveals a chain of dust clumps aligned with the filament-like structure with an average extinction of A V ∼ 2.78 mag, varying up to a maximum of ∼17 mag. Our analysis led to identification of a rich population (∼500) of young (average age of ∼1 Myr) stars, plus a numerous number (∼350) of Hα emitters, spatially correlated with the filamentary clouds. Located near the edge of the cloud, the luminous star BD+45 3216 has created an arc-like pattern as the ionizing radiation encounters the dense gas, forming a blister-shaped morphology. We found three distinct young stellar groups, all coincident with relatively dense parts of the cloud complex, signifying ongoing star formation. Moreover, the cloud filament (excitation temperature ∼10 K) traced by the CO isotopologues and extending nearly ∼80 pc is devoid of ionized gas except at the dense cores (excitation temperature ∼28–32 K) wherein significant ionized emission excited by OB stars (dynamical age ∼0.18–1.0 Myr) pertains. The radial velocity is dynamic (median ∼−3.65 km s−1) along the main filament, increasing from Galactic east to west, indicating mass flow to form the massive stars/clusters at the central hubs.

Structure in the Magnetic Field of the Milky Way Disk and Halo Traced by Faraday Rotation

Magnetic fields in the ionized medium of the disk and halo of the Milky Way impose Faraday rotation on linearly polarized radio emission. We compare two surveys mapping the Galactic Faraday rotation, one showing the rotation measures of extragalactic sources seen through the Galaxy, and one showing Faraday depth of the diffuse Galactic synchrotron emission from the Global Magneto-Ionic Medium Survey. Comparing the two data sets in 5° × 10° bins shows good agreement at intermediate latitudes, 10° < ∣b∣ < 50°, and little correlation between them at lower and higher latitudes. Where they agree, both tracers show clear patterns as a function of Galactic longitude, ℓ; in the northern hemisphere a strong pattern; and in the southern hemisphere a pattern. Pulsars with height above or below the plane ∣z∣ > 300 pc show similar ℓ dependence in their rotation measures. Nearby nonthermal structures show rotation measure shadows as does the Orion–Eridanus superbubble. We describe families of dynamo models that could explain the observed patterns in the two hemispheres. We suggest that a field reversal, known to cross the plane a few hundred parsecs inside the solar circle, could shift to positive z with increasing Galactic radius to explain the pattern in the northern hemisphere. Correlation shows that rotation measures from extragalactic sources are one to two times the corresponding rotation measure of the diffuse emission, implying Faraday complexity along some lines of sight, especially in the southern hemisphere.

Age-morphology dependence of the Milky Way boxy/peanut bulge seen in Mira variables

ABSTRACT We analyse the distribution of Mira variable stars in the central region of the Milky Way. We find that with increasing period, i.e. decreasing age, the Miras shift towards negative Galactic longitudes ℓ. Comparing to a cosmological zoom simulation of a barred galaxy, we find that this shift with age can be explained by an age-morphology dependence of the boxy peanut/bulge. Owing to a combination of projection effects and the limitation of the range of Galactic longitudes, the near hump at ℓ &amp;gt; 0 is more truncated for younger populations, and the far hump at ℓ &amp;lt; 0 dominates the observed distributions.

A global view on star formation: The GLOSTAR Galactic plane survey

Class II methanol (CH3OH) masers are amongst the clearest signposts of recent high-mass star formation (HMSF). A complete catalogue outlines the distribution of star formation in the Galaxy, the number of young star-forming cores, and the physical conditions of their environment, made possible by the Global View on Star Formation (GLOSTAR) survey. This blind survey of the radio regime of 4–8 GHz maps the Galactic mid-plane in the radio continuum, 6.7 GHz methanol line, the 4.8 GHz formaldehyde line, and several radio recombination lines. We present an analysis of the observations of the 6.7 GHz CH3OH maser transition using data from the D-configuration of the Very Large Array (VLA). We analysed data covering Galactic longitudes from –2° &lt; l &lt; 60° and Galactic latitudes of |b| &lt; 1°. We detected a total of 554 methanol masers, out of which 84 are new, and we catalogued their positions, velocity components, and integrated fluxes. With a typical noise level of ~18 mJy beam−1, this is the most sensitive unbiased methanol survey for methanol masers to date. We also searched for dust continuum and radio continuum associations, finding that 97% of the sources are associated with dust and 12% are associated with radio continuum emission.

Gas Column Density Distribution of Molecular Clouds in the Third Quadrant of the Milky Way

We have obtained column density maps for an unbiased sample of 120 molecular clouds in the third quadrant of the Milky Way midplane (b ≤ ∣5∣°) within the Galactic longitude range from 195° to 225°, using the high-sensitivity 12CO and 13CO (J = 1 − 0) data from the Milky Way Imaging Scroll Painting (MWISP) project. The probability density functions of the molecular hydrogen column density of the clouds, N-pdfs, are fitted with both a lognormal (LN) function and a lognormal plus power-law (LN+PL) function. The molecular clouds are classified into three categories according to their shapes of N-pdfs, i.e., LN, LN+PL, and UN (unclear). About 72% of the molecular clouds fall into the LN category, while 18% and 10% fall into the LN+PL and UN categories, respectively. A PL scaling relation, , exists between the width of the N-pdf, σ s , and the average column density, , of the molecular clouds. However, σ s shows no correlation with the mass of the clouds. A correlation is found between the dispersion of normalized column density, σ N/〈N〉, and the sonic Mach number, , of molecular clouds. Overall, as predicted by numerical simulations, the N-pdfs of the molecular clouds with active star formation activity tend to have N-pdfs with PL high-density tails.

Catalog of spiral arm tangents (Galactic longitudes) in the Milky Way, and the age gradient based on various arm tracers

An updated catalog of 205 observed tangents to the spiral arms (in Galactic longitudes) since 1980 is presented. This represents an addition of 80 arm tangents in 6 years (since 2016). Most arm tangents are observed at telescopes in the radio régime.In this study, the separation of each arm tracer from the dust lane is analysed to obtain the relative speed away from the dust lane (an age gradient). Each arm tracer is observed to be separated from the dust lane, showing an age gradient of about 11.3 ±2 Myr/kpc across the spiral arm – a relative speed away from the dust lane of about 87 ±10 km/s.

Metallicity Properties of the Galactic Bulge Stars Near and Far: Expectations from the Auriga Simulation

Using the high-resolution Milky Way–like model from Auriga simulation we study the chemical properties of the Galactic bulge, focusing on the metallicity difference between stars on the near side (in front of the Galactic center) and the far side (behind the Galactic center). In general, along certain sight lines the near side is more metal-rich than the far side, consistent with the negative vertical metallicity gradient of the disk, since the far side is located higher above the disk plane than the near side. However, at the region l < 0° and ∣b∣ ≤ 6°, the near side is even more metal-poor than the far side, and their difference changes with the Galactic longitude. This is mainly due to the fact that stars near the minor axis of the bar are more metal-poor than that around the major axis. Since the bar is tilted, in the negative longitude region, the near side is mainly populated by stars close to the minor-axis region rather than the far side resulting in such a metallicity difference. We extract stars in the X-shape structure by identifying the overdensities in the near and far sides. Their metallicity properties are consistent with the results of the whole Galactic bulge. The boxy/peanut-shaped bulge can naturally explain the metallicity difference of the double red clump stars in the observation. There is no need to involve a classical bulge component with different stellar populations.

COMAP Early Science. VI. A First Look at the COMAP Galactic Plane Survey

We present early results from the CO Mapping Array Project (COMAP) Galactic Plane Survey conducted between 2019 June and 2021 April, spanning 20° < ℓ < 40° in Galactic longitude and ∣b∣ < 1.°5 in Galactic latitude with an angular resolution of 4.′5. We present initial results from the first part of the survey, including the diffuse emission and spectral energy distributions of H ii regions and supernova remnants (SNRs). Using low- and high-frequency surveys to constrain free–free and thermal dust emission contributions, we find evidence of excess flux density at 30 GHz in six regions, which we interpret as anomalous microwave emission. Furthermore we model ultracompact H ii contributions using data from the 5 GHz CORNISH catalog and reject these as the cause of the 30 GHz excess. Six known SNRs are detected at 30 GHz, and we measure spectral indices consistent with the literature or show evidence of steepening. The flux density of the SNR W44 at 30 GHz is consistent with a power-law extrapolation from lower frequencies with no indication of spectral steepening in contrast with recent results from the Sardinia Radio Telescope. We also extract five hydrogen radio recombination lines (RRLs) to map the warm ionized gas, which can be used to estimate electron temperatures or to constrain continuum free–free emission. The full COMAP Galactic Plane Survey, to be released in 2023/2024, will span ℓ ∼ 20°–220° and will be the first large-scale radio continuum and RRL survey at 30 GHz with 4.′5 resolution.

The Relative Orientation between Local Magnetic Field and Galactic Plane in Low Latitude Dark Clouds

In this work, we study the magnetic field morphology of selected star-forming clouds spread over the galactic latitude (b) range −10° to 10°. The polarimetric observations of clouds CB24, CB27 and CB188 are conducted to study the magnetic field geometry of those clouds using the 104 cm Sampurnanand Telescope (ST) located at ARIES, Manora Peak, Nainital, India. These observations are combined with those of 14 further low latitude clouds available in the literature. Most of these clouds are located within a distance range 140–500 pc except for CB3 (∼2500 pc), CB34 (∼1500 pc), CB39 (∼1500 pc) and CB60 (∼1500 pc). Analyzing the polarimetric data of 17 clouds, we find that the alignment between the envelope magnetic field () and galactic plane (GP) (θ GP) of the low-latitude clouds varies with their galactic longitudes (l). We observe a strong correlation between the longitude (l) and the offset () which shows that is parallel to the GP when the clouds are situated in the region 115° < l < 250°. However, has its own local deflection irrespective of the orientation of θ GP when the clouds are at l < 100° and l > 250°. To check the consistency of our results, the stellar polarization data available in the Heiles catalog are overlaid on the DSS image of the clouds having mean polarization vector of field stars. The results are almost consistent with the Heiles data. A systematic discussion is presented in the paper. The effect of turbulence in the cloud is also studied which may play an important role in causing the misalignment phenomenon observed between and θ GP. We have used Herschel (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.) SPIRE 500 μm and SCUBA 850 μm dust continuum emission maps in our work to understand the density structure of the clouds.

The Diffuse X-Ray Background of the Insight-HXMT/LE Telescope in the Galactic Plane

Accurately estimating of diffuse X-ray background (DXB) is essential for the investigation of sources in the Galactic plane observed with Insight-HXMT/LE, which is a collimated telescope in the soft X-ray energy band with a relatively large field of view. In the high-Galactic-latitude region, DXB is dominated by the cosmic X-ray background, which is almost uniform, but DXB in the Galactic plane region is more complex due to the Galactic H i absorption and the contribution of the Galactic ridge X-ray emission. This study, as a part of background estimation of LE, focuses on estimating the contribution of DXB in the Galactic plane to Insight-HXMT/LE observations. We calculate DXB confined in a region of 0° < l < 360° and ∣b∣ < 10°, where l and b denote Galactic longitude and latitude, respectively, with the first 3 yr of Galactic-plane-scanning survey data of Insight-HXMT/LE. The Galactic plane is divided into 360 × 20 small pixels (1° × 1° per pixel), and a DXB spectrum is obtained for each pixel. An indirect method is developed for the pixels of the bright source regions, which brings a systematic error of ∼10%. The systematic error brought by the satellite attitude is ∼7% on average for all the pixels in the Galactic plane. The LE DXB spectrum obtained in this study is consistent with that reported by RXTE’s Proportional Counter Array.