Vertical position of the Sun with γ-rays

We illustrate a method for estimating the vertical position of the Sun above the Galactic plane by γ-ray observations. Photons of γ-ray wavelengths are particularly well suited for geometrical and kinematic studies of the Milky Way because they are not subject to extinction by interstellar gas or dust. Here, we use the radioactive decay line of 26Al at 1.809 MeV to perform maximum likelihood fits to data from the spectrometer SPI on board the INTEGRAL satellite as a proof-of-concept study. Our simple analytic 3D emissivity models are line-of-sight integrated, and varied as a function of the Sun’s vertical position, given a known distance to the Galactic centre. We find a vertical position of the Sun of z0 = 15 ± 17 pc above the Galactic plane, consistent with previous studies, finding z0 in a range between 5 and 29 pc. Even though the sensitivity of current MeV instruments is several orders of magnitude below that of telescopes for other wavelengths, this result reveals once more the disregarded capability of soft γ-ray telescopes. We further investigate possible biases in estimating the vertical extent of γ-ray emission if the Sun’s position is set incorrectly, and find that the larger the true extent, the less is it affected by the observer position. In the case of 26Al with an exponential scale height of 150 pc (700 pc) in the inner (full) Galaxy, this may lead to misestimates of up to 25%.

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Interstellar gas in the central region of the Galaxy

Symposium - International Astronomical Union ◽

10.1017/s0074180900101032 ◽

1967 ◽

Vol 31 ◽

pp. 239-251 ◽

Cited By ~ 3

Author(s):

F. J. Kerr

Keyword(s):

Central Region ◽

Galactic Plane ◽

Neutral Hydrogen ◽

Continuum Emission ◽

Galactic Centre ◽

Interstellar Gas ◽

Hydrogen Recombination ◽

The Galaxy ◽

Centre Region ◽

The Relationship

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.

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Arcminute-scale studies of the interstellar gas towards HESS J1804−216: Still an unidentified TeV γ-ray source

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2020.47 ◽

2020 ◽

Vol 37 ◽

Author(s):

Kirsty Feijen ◽

Gavin Rowell ◽

Sabrina Einecke ◽

Catherine Braiding ◽

Michael G. Burton ◽

...

Keyword(s):

Supernova Remnant ◽

Galactic Plane ◽

Cosmic Ray ◽

Line Of Sight ◽

Dispersion Measure ◽

Molecular Gas ◽

Interstellar Gas ◽

Isotropic Diffusion ◽

Unidentified Source ◽

Using Data

Abstract The Galactic TeV ${\gamma}$ -ray source ${\mathrm{HESS\,J}1804{-}216}$ is currently an unidentified source. In an attempt to unveil its origin, we present here the most detailed study of interstellar gas using data from the Mopra Southern Galactic Plane CO Survey, 7- and 12-mm wavelength Mopra surveys and Southern Galactic Plane Survey of HI. Several components of atomic and molecular gas are found to overlap ${\mathrm{HESS\,J}1804{-}216}$ at various velocities along the line of sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both correlation and anti-correlation between the gas and TeV ${\gamma}$ -ray emission have been identified in various gas tracers, enabling several origin scenarios for the TeV ${\gamma}$ -ray emission from ${\mathrm{HESS\,J}1804{-}216}$ . For a hadronic scenario, ${\mathrm{SNR\,G}8.7{-}0.1}$ and the progenitor supernova remnant (SNR) of ${\mathrm{PSR\,J}1803{-}2137}$ require cosmic ray (CR) enhancement factors of ${\mathord{\sim} 50}$ times the solar neighbour CR flux value to produce the TeV ${\gamma}$ -ray emission. Assuming an isotropic diffusion model, CRs from both these SNRs require a slow diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM gas. The morphology of gas located at 3.8 kpc (the dispersion measure distance to ${\mathrm{PSR\,J}1803{-}2137}$ ) tends to anti-correlate with features of the TeV emission from ${\mathrm{HESS\,J}1804{-}216}$ , making the leptonic scenario possible. Both pure hadronic and pure leptonic scenarios thus remain plausible.

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Galactic ?-ray Lines Resulting from Interactions Between Low Energy Cosmic Rays and the Interstellar Medium

Australian Journal of Physics ◽

10.1071/ph790383 ◽

1979 ◽

Vol 32 (4) ◽

pp. 383 ◽

Cited By ~ 2

Author(s):

Masato Yoshimori

Keyword(s):

Cosmic Rays ◽

Supernova Remnants ◽

Galactic Plane ◽

Crab Nebula ◽

Cosmic Ray ◽

Low Energy ◽

Longitudinal Distribution ◽

Galactic Centre ◽

Interstellar Space ◽

Interstellar Gas

Calculated spectral profiles and galactic distributions are presented for y-ray lines resulting from interactions between low energy cosmic rays and the interstellar gas and dust. Calculated local intensities are also presented for y-ray lines from discrete sources such as supernova remnants and dense interstellar gas clouds. The y-ray lines from excited dust nuclei (which have long mean lifetimes) are sharp, having widths of the order of a few keV; the lines from excited gas nuclei are relatively narrow, having widths of the order of 100 keV; and the lines from excited cosmic ray nuclei are broad, having widths of the order of 1 MeV. The longitudinal distribution of y-ray lines in the galactic plane shows a significant concentration toward the galactic centre, and a rapid falloff beyond I;. 50�. The most intense y-ray lines arise from positron annihilation (0�511 MeV) and the deexcitation of 12C* (4�439 MeV) and 160* (6�131 MeV). In the direction of the galactic centre, these lines have estimated intensities of the order of 10-5 photons cm-2s-1rad- 1, and so they may be resolved from the diffuse y-ray background there by observing with a high resolution Ge(Li) detector. In the direction of several strong discrete sources, the estimated fluxes are generally lower: ~10-6 photons cm-2s-1 for the Crab Nebula and the Vela pulsar, ~10-8 photons cm-2 s-1 for the interstellar dense cloud pOph, but ~10-5 photons cm-2 s-1 for the ring cloud around the galactic centre. The calculated intensities of various other y-ray lines are compared with available experimental data, and their detectability is considered. The implication of the galactic distribution of low energy cosmic rays for the gas density of the interstellar space through which the cosmic rays propagate is also discussed.

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Magnetic field structure of the Galactic plane from differential analysis of interstellar polarization

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa001 ◽

2020 ◽

Vol 72 (2) ◽

Author(s):

Tetsuya Zenko ◽

Tetsuya Nagata ◽

Mikio Kurita ◽

Masaru Kino ◽

Shogo Nishiyama ◽

...

Keyword(s):

Magnetic Field ◽

Galactic Plane ◽

Color Change ◽

Field Structure ◽

Line Of Sight ◽

The Sun ◽

Differential Analysis ◽

Field Orientation ◽

Magnetic Field Structure ◽

The Magnetic Field

Abstract A new method for measuring the global magnetic field structure of the Galactic plane is presented. We have determined the near-infrared polarization of field stars around 52 Cepheids found in recent surveys toward the Galactic plane. The Cepheids are located at the galactic longitudes $-10^{\circ} \le l \le +10.^{\!\!\!\circ }5$ and latitudes $-0.^{\!\!\!\circ }22\le b \le +0.^{\!\!\!\circ }45$, and their distances are mainly in the range of 10 to 15 kpc from the Sun. Simple classification of the sightlines is made with the polarization behavior vs. $H-K_{\mathrm{S}}$ color of field stars, and typical examples of three types are presented. Then, division of the field stars in each line of sight into (a) foreground, (b) bulge, and (c) background is made with the Gaia DR2 catalog, the peak of the $H-K_{\mathrm{S}}$ color histogram, and $H-K_{\mathrm{S}}$ colors consistent with the distance of the Cepheid in the center, respectively. Differential analysis between them enables us to examine the magnetic field structure more definitely than just relying on the $H-K_{\mathrm{S}}$ color difference. In one line of sight, the magnetic field is nearly parallel to the Galactic plane and well aligned all the way from the Sun to the Cepheid position on the other side of the Galactic center. Contrary to our preconceived ideas, however, sightlines having such well-aligned magnetic fields in the Galactic plane are rather small in number. At least 36 Cepheid fields indicate random magnetic field components are significant. Two Cepheid fields indicate that the magnetic field orientation changes more than $45^{\circ }$ in the line of sight. The polarization increase per color change $\Delta P/\Delta (H-K_{\mathrm{S}})$ varies from region to region, reflecting the change in the ratio of the magnetic field strength and the turbulence strength.

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The Effect of Crossing Times Through the Solar Neighbourhood on the Observed Stellar Age and Metallicity Distributions

International Astronomical Union Colloquium ◽

10.1017/s0252921100067701 ◽

1977 ◽

Vol 45 ◽

pp. 301-302

Author(s):

C. Turon Lacarrieu ◽

M. Mayor ◽

L. Martinet

Keyword(s):

High Velocity ◽

Approximate Formula ◽

Galactic Plane ◽

Stellar Populations ◽

Oscillation Period ◽

Linear Term ◽

Solar Neighbourhood ◽

Galactic Centre ◽

Quadratic Term ◽

The Sun

The effect of crossing times through the solar neighbourhood on the observed stellar age and metallicity distributions due to the oscillations perpendicular to the galactic plane is well known. Stars with high z-velocity are under-represented since they stay much longer far from the galactic plane than near the sun. Since the age and metallicity distributions of these high velocity stars are quite different from the age and metallicity distributions of all the stars moving at a mean distance10 kpc from the galactic centre, a weighting procedure has to be adopted. The weight to be assigned to each star should be proportional to the ratio of the oscillation period in z, i.e. Tz, to the time spent within a sphere centered on the sun, i.e. τz. An approximate formula has been given by Woolley (1970):. The effect of such a weighting procedure is very important : the ratio Tz/Tzvaries from 1 to more than A between young and old stellar populations. It has to be noted that the quadratic term of weighting (often neglected) is equal to the linear term for a |w| velocity of about 55 km/s.

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2D kinematics of massive stars near the Galactic Centre

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3329 ◽

2020 ◽

Vol 500 (3) ◽

pp. 3213-3239

Author(s):

Mattia Libralato ◽

Daniel J Lennon ◽

Andrea Bellini ◽

Roeland van der Marel ◽

Simon J Clark ◽

...

Keyword(s):

Moving Objects ◽

Hubble Space Telescope ◽

Massive Stars ◽

Line Of Sight ◽

Galactic Centre ◽

Harsh Environment ◽

Proper Motions ◽

Sgr A ◽

Better Than ◽

Rule Out

ABSTRACT The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.

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The evolutionary status of protostellar clumps hosting class II methanol masers

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa233 ◽

2020 ◽

Vol 493 (2) ◽

pp. 2015-2041 ◽

Cited By ~ 1

Author(s):

B M Jones ◽

G A Fuller ◽

S L Breen ◽

A Avison ◽

J A Green ◽

...

Keyword(s):

Galactic Plane ◽

Dust Emission ◽

Principal Component ◽

Far Infrared ◽

Class Ii ◽

Young Stellar Objects ◽

Galactic Centre ◽

Evolutionary Status ◽

Methanol Maser ◽

Methanol Masers

ABSTRACT The Methanol MultiBeam survey (MMB) provides the most complete sample of Galactic massive young stellar objects (MYSOs) hosting 6.7 GHz class II methanol masers. We characterize the properties of these maser sources using dust emission detected by the Herschel Infrared Galactic Plane Survey (Hi-GAL) to assess their evolutionary state. Associating 731 (73 per cent) of MMB sources with compact emission at four Hi-GAL wavelengths, we derive clump properties and define the requirements of an MYSO to host a 6.7 GHz maser. The median far-infrared (FIR) mass and luminosity are 630 M⊙ and 2500 L⊙ for sources on the near side of Galactic centre and 3200 M⊙ and 10000 L⊙ for more distant sources. The median luminosity-to-mass ratio is similar for both at ∼4.2 L⊙ M⊙−1. We identify an apparent minimum 70 μm luminosity required to sustain a methanol maser of a given luminosity (with $L_{70} \propto L_{6.7}\, ^{0.6}$). The maser host clumps have higher mass and higher FIR luminosities than the general Galactic population of protostellar MYSOs. Using principal component analysis, we find 896 protostellar clumps satisfy the requirements to host a methanol maser but lack a detection in the MMB. Finding a 70 μm flux density deficiency in these objects, we favour the scenario in which these objects are evolved beyond the age where a luminous 6.7 GHz maser can be sustained. Finally, segregation by association with secondary maser species identifies evolutionary differences within the population of 6.7GHz sources.

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Unbound Close Stellar Encounters in the Solar Neighborhood

The Astronomical Journal ◽

10.3847/1538-3881/ac3a8b ◽

2022 ◽

Vol 163 (2) ◽

pp. 44

Author(s):

Bradley M. S. Hansen

Keyword(s):

Spectral Type ◽

Main Sequence ◽

Radial Distance ◽

Solar Neighborhood ◽

Limiting Factors ◽

Line Of Sight ◽

The Sun ◽

Finite Set ◽

Host Stars ◽

Migration Event

Abstract We present a catalog of unbound stellar pairs, within 100 pc of the Sun, that are undergoing close, hyperbolic, encounters. The data are drawn from the GAIA EDR3 catalog, and the limiting factors are errors in the radial distance and unknown velocities along the line of sight. Such stellar pairs have been suggested to be possible events associated with the migration of technological civilizations between stars. As such, this sample may represent a finite set of targets for a SETI search based on this hypothesis. Our catalog contains a total of 132 close passage events, featuring stars from across the entire main sequence, with 16 pairs featuring at least one main-sequence star of spectral type between K1 and F3. Many of these stars are also in binaries, so that we isolate eight single stars as the most likely candidates to search for an ongoing migration event—HD 87978, HD 92577, HD 50669, HD 44006, HD 80790, LSPM J2126+5338, LSPM J0646+1829 and HD 192486. Among host stars of known planets, the stars GJ 433 and HR 858 are the best candidates.

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A Multi-Wavelength View of the XMM-Newton Galactic Plane

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2014.01.0123 ◽

2014 ◽

Vol 1 (1) ◽

pp. 123-126

Author(s):

Ada Nebot Gómez-Morán ◽

Christian Motch

Keyword(s):

Surface Density ◽

Binary Systems ◽

Galactic Plane ◽

Galactic Centre ◽

Galactic Latitude ◽

X Ray ◽

Model Predictions ◽

Science Centre ◽

Multi Wavelength ◽

Galactic Longitude

We present an X-ray survey of the Galactic Plane conducted by the Survey Science Centre of the XMM-Newton satellite. The survey contains more than 1300 X-ray detections at low and intermediate Galactic latitudes and covering 4 deg<sup>2</sup> well spread in Galactic longitude. From a multi-wavelength analysis, using optical spectra and helped by optical and infrared photometry we identify and classify about a fourth of the sources. The observed surface density of soft X-ray (<2 keV) sources decreases with Galactic latitude and although compatible with model predictions at first glance, presents an excess of stars, likely due to giants in binary systems. In the hard band (>2 keV) the surface density of sources presents an excess with respect to the expected extragalactic contribution. This excess highly concentrates towards the direction of the Galactic Centre and is compatible with previous results from Chandra observations around the Galactic Centre. The nature of these sources is still unknown.

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