Non-Circular Gas Motions in the Inner Galaxy

1989 ◽  
Vol 136 ◽  
pp. 77-87 ◽  
Author(s):  
Robert H. Sanders
Keyword(s):  
Molecular Cloud ◽  
Near Infrared ◽  
Galactic Disk ◽  
Neutral Hydrogen ◽  
Infrared Emission ◽  
Massive Black Hole ◽  
Theoretical Understanding ◽  
Barred Galaxies ◽  
Normal Galaxies ◽  
The Galaxy

It is shown that the observed motion of neutral hydrogen in the inner 1000 pc of the Galaxy is, for the most part, consistent with flow on circular streamlines in the potential of the Galactic bulge as derived from the observed distribution of near infrared emission. The implied mass distribution is also consistent with recent kinematic determinations of the stellar mass in the inner few parsecs of the bulge. The non-circular gas motion seen between two and four kpc is most likely due to flow on elliptical streamlines in the presence of a weak bar distortion of the Galactic disk. Circular gas motion in the region of the bulge and elliptical streaming further out is an observed characteristic of flow in barred galaxies and is consistent with our present theoretical understanding of such systems. The implication is that non-circular motions of the molecular clouds in the inner 200 pc have a non-gravitational origin. A possible mechanism for exciting such motions is an accretion event resulting from an encounter of a molecular cloud with a massive black hole. A starburst leading to a high supernovae rate 107 years ago in the inner 50 pc is an alternative explanation. Observations of molecular cloud regions in the nuclei of external normal galaxies could distinguish between alternative mechanisms.

scholarly journals A new distance to the Brick, the dense molecular cloud G0.253+0.016

2021 ◽  
Vol 502 (1) ◽  
pp. 1246-1252
Author(s):  
M Zoccali ◽  
E Valenti ◽  
F Surot ◽  
O A Gonzalez ◽  
A Renzini ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Near Infrared ◽  
Formation Rate ◽  
Dynamical Evolution ◽  
Galactic Centre ◽  
The Galaxy ◽  
Centre Region ◽  
Order Of Magnitude ◽  
Red Clump

ABSTRACT We analyse the near-infrared colour–magnitude diagram of a field including the giant molecular cloud G0.253+0.016 (a.k.a. The Brick) observed at high spatial resolution, with HAWK-I@VLT. The distribution of red clump stars in a line of sight crossing the cloud, compared with that in a direction just beside it, and not crossing it, allow us to measure the distance of the cloud from the Sun to be 7.20, with a statistical uncertainty of ±0.16 and a systematic error of ±0.20 kpc. This is significantly closer than what is generally assumed, i.e. that the cloud belongs to the near side of the central molecular zone, at 60 pc from the Galactic centre. This assumption was based on dynamical models of the central molecular zone, observationally constrained uniquely by the radial velocity of this and other clouds. Determining the true position of the Brick cloud is relevant because this is the densest cloud of the Galaxy not showing any ongoing star formation. This puts the cloud off by one order of magnitude from the Kennicutt–Schmidt relation between the density of the dense gas and the star formation rate. Several explanations have been proposed for this absence of star formation, most of them based on the dynamical evolution of this and other clouds, within the Galactic centre region. Our result emphasizes the need to include constraints coming from stellar observations in the interpretation of our Galaxy’s central molecular zone.

scholarly journals Determination of the C/M5+ Ratio in the Galactic Disk

1995 ◽  
Vol 148 ◽  
pp. 276-279
Author(s):  
Francisco J. Fuenmayor
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Galactic Disk ◽  
Mean Value ◽  
Galactocentric Distance ◽  
The Galaxy ◽  
Metal Abundance ◽  
Objective Prism ◽  
M Stars

AbstractA determination of the C/M5+ ratio, as a function of the galactocentric distance, in the galactic disk is presented. These results are based upon previous determinations of the space density for cool carbon stars and for late giant M stars in the Milky Way. Most of these results were obtained from objective-prism surveys in the near infrared using mainly Schmidt-type telescopes. The ratio C/M5+ appears to increase from 0.05 to 0.25 in the galactic disk, from the galactic center outwards. A mean value of 0.15 of this ratio for the Galaxy is suggested. Correlations between the C/M5+ ratio and currently known metal abundance gradients in the galactic disk are discussed.

scholarly journals The Galaxy's Eating Habits

2004 ◽  
Vol 217 ◽  
pp. 406-411 ◽  
Author(s):  
M. E. Putman ◽  
C. Thom ◽  
B. K. Gibson ◽  
L. Staveley-Smith
Keyword(s):  
Eating Habits ◽  
Dwarf Galaxy ◽  
Galactic Disk ◽  
Neutral Hydrogen ◽  
Main Body ◽  
Gaseous Component ◽  
The Galaxy ◽  
Gaseous Stream ◽  
Gaseous Halo ◽  
Current Orbit

The possibility of a gaseous halo stream which was stripped from the Sagittarius dwarf galaxy is presented. The total mass of the neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic Anti-Center is 4 − 10 × 106 M⊙ (at 36 kpc, the distance to the stellar debris in this region). Both the stellar and gaseous components have negative velocities in this part of the sky, but the gaseous component extends to higher negative velocities. We suggest this gaseous stream was stripped from the main body of the dwarf 0.2 – 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10−4 cm−3. The gas would then represent the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.

scholarly journals Surveying the Giant H ii Regions of the Milky Way with SOFIA. III. W49A

2021 ◽  
Vol 923 (2) ◽  
pp. 198
Author(s):  
James M. De Buizer ◽  
Wanggi Lim ◽  
Mengyao Liu ◽  
Nicole Karnath ◽  
James T. Radomski
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Physical Nature ◽  
Infrared Emission ◽  
Spectral Energy ◽  
H Ii Regions ◽  
Extended Radio ◽  
The Galaxy ◽  
Western Side

Abstract We present our third set of results from our mid-infrared imaging survey of Milky Way Giant H ii regions with our detailed analysis of W49A, one of the most distant, yet most luminous, GH ii regions in the Galaxy. We used the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) to obtain 20 and 37 μm images of the entire ∼5.′0 × 3.′5 infrared-emitting area of W49A at a spatial resolution of ∼3″. Utilizing these SOFIA data in conjunction with previous multiwavelength observations from the near-infrared to radio, including Spitzer-IRAC and Herschel-PACS archival data, we investigate the physical nature of individual infrared sources and subcomponents within W49A. For individual compact sources, we used the multiwavelength photometry data to construct spectral energy distributions (SEDs) and fit them with massive young stellar object (MYSO) SED models and find 22 sources that are likely to be MYSOs. Ten new sources are identified for the first time in this work. Even at 37 μm we are unable to detect infrared emission from the sources on the western side of the extremely extinguished ring of compact radio emission sources known as the Welch Ring. Utilizing multiwavelength data, we derived luminosity-to-mass ratio and virial parameters of the extended radio subregions of W49A to estimate their relative ages and find that overall the subcomponents of W49A have a very small spread in evolutionary state compared to our previously studied GH ii regions.

scholarly journals Broad view on hard X-ray background emission of the Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 810-810
Author(s):  
Roman Krivonos ◽  
Mikhail Revnivtsev ◽  
Sergey Tsygankov ◽  
Eugene Churazov ◽  
Rashid Sunyaev
Keyword(s):  
Near Infrared ◽  
Galactic Disk ◽  
Broad Band ◽  
Point Sources ◽  
X Rays ◽  
X Ray ◽  
Scientific Debate ◽  
The Galaxy ◽  
Background Emission ◽  
Galactic Background

AbstractThe nature of the Galactic Ridge X-Ray Emission (GRXE) has been under scientific debate since its discovery more than 30 years ago. It is observed as extended emission along the Galactic disk. The question was: is GRXE truly diffuse or is it composed from a large number of unresolved point sources? Using near-infrared Galaxy maps measured with the DIRBE experiment and data from the INTEGRAL observatory, we show that the galactic background in the energy range 20-60 keV originates from the stellar population of the Galaxy, which is in contrast to the diffuse nature believed before (Krivonos et al., 2007). Here we show preliminary results of studying the transition region from hard X-rays to gamma diffuse background of the Galaxy, revealing the broad band picture of Galactic Background emission.

scholarly journals Infrared Background Starlight: Observations and Galaxy Models

1990 ◽  
Vol 139 ◽  
pp. 35-47
Author(s):  
G. G. Fazio ◽  
T. M. Dame ◽  
S. Kent
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Galactic Disk ◽  
Dust Emission ◽  
Three Dimensional ◽  
Infrared Region ◽  
Global Scale ◽  
Three Dimensional Model ◽  
Infrared Telescope ◽  
The Galaxy

The near-infrared region of the spectrum is a particularly advantageous window for observing the distribution of old, evolved stars in the galactic disk and bulge. These stars are important because they provide an excellent tracer of the overall stellar mass distribution. At shorter wavelengths extinction is a serious problem, and at longer wavelengths the flux is dominated by dust emission. A summary of the large-scale diffuse near-infrared observations of the Galaxy is presented, as is a summary of the results obtained from these data on the structure of the galactic disk and bulge. The importance of combining CO and near-infrared maps of similar resolution to determine a three-dimensional model of galactic extinction is demonstrated. The Spacelab-2 Infrared Telescope (IRT) data are used in conjunction with a proposed galactic model to make preliminary measurements of the global scale parameters of the Galaxy.

scholarly journals The Luminosity of the Central Parsec of the Galaxy

1989 ◽  
Vol 136 ◽  
pp. 423-436
Author(s):  
M. W. Werner ◽  
J. A. Davidson
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Thermal Emission ◽  
Large Magellanic Cloud ◽  
Infrared Emission ◽  
Infrared Observations ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Central Parsec ◽  
30 Doradus

The luminosity of the central 5 pc of the Galaxy -encompassing the inner regions of the rotating ring of dust and gas which surrounds the galactic center - emerges primarily at infrared wavelengths in the form of thermal emission from heated dust. The nature and location of the sources which heat the dust can be inferred from the spatial and temperature distribution of the thermal infrared emission (λ>20um), from studies of the ionized gas in this region, and from direct imaging in the near infrared. These observations show that the principal heating sources within this 5-pc region are concentrated within the central parsec of the Galaxy and indicate that the luminosity of these sources is within a factor of two of 107 LO. The near-infrared observations of the compact sources at the galactic center do not reveal a single dominant source but suggest instead that the several components of the IRS-16 complex, taken together, may contribute the bulk of the luminosity; however, the data also permit a single object to dominate the energetics of this region. We draw attention to the striking morphological similarities between the galactic center and the innermost regions of the 30 Doradus nebula in the Large Magellanic Cloud and speculate that the luminosity sources in the galactic center may resemble the early-type supergiants in 30 Doradus.

scholarly journals The Diffuse Near- and Mid-Infrared Emission from the Galaxy

2001 ◽  
Vol 204 ◽  
pp. 35-46
Author(s):  
Martin Cohen
Keyword(s):  
Point Source ◽  
Surface Brightness ◽  
Near Infrared ◽  
Infrared Emission ◽  
Point Sources ◽  
Mid Infrared ◽  
Deep Point ◽  
Model Predictions ◽  
The Galaxy ◽  
Fundamental Stellar Parameters

Recognition of an isotropic cosmic near-infrared (NIR) and mid-infrared (MIR) background involves the removal of the zodiacal foreground (both scattered and reradiated), of the truly diffuse Galactic foreground (dominated by fluorescent bands of polcyclic aromatic hydrocarbons), and of resolved and unresolved Galactic point sources. I discuss model simulations of the near- and mid-infrared point source sky from which one can assess its particular contribution to the diffuse Galactic infrared foreground. I will also indicate the transitional stage which characterizes our knowledge of fundamental stellar parameters that are essential inputs to any such models. Using the latest version of the SKY model (Wainscoat et al. 1992; Cohen 1993; Cohen 1994; Cohen et al. 1994; Cohen 1995; Ruphy et al. 1997), I will demonstrate matches to deep point source counts for a variety of passbands and galactic latitudes, and will try to quantify the uncertainties achievable in model predictions of the integrated surface brightness due to the smearing of all these foreground point sources.

scholarly journals Using classical Cepheids to study the far side of the Milky Way disk

2020 ◽  
Vol 640 ◽  
pp. A92
Author(s):  
J. H. Minniti ◽  
L. Sbordone ◽  
A. Rojas-Arriagada ◽  
M. Zoccali ◽  
R. Contreras Ramos ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Galactic Disk ◽  
Variable Stars ◽  
Disk Rotation ◽  
Near Infrared Spectra ◽  
Classical Cepheids ◽  
The Galaxy ◽  
Bulge Region ◽  
First Time

Context. Much of what we know about the Milky Way disk is based on studies of the solar vicinity. The structure, kinematics, and chemical composition of the far side of the Galactic disk, beyond the bulge, are still to be revealed. Aims. Classical Cepheids (CCs) are young and luminous standard candles. We aim to use a well-characterized sample of these variable stars to study the present-time properties of the far side of the Galactic disk. Methods. A sample of 45 Cepheid variable star candidates were selected from near-infrared time series photometry obtained by the VVV survey. We characterized this sample using high quality near-infrared spectra obtained with VLT/X-shooter. The spectroscopic data was used to derive radial velocities and iron abundances for all the sample Cepheids. This allowed us to separate the CCs, which are metal rich and with kinematics consistent with the disk rotation, from type II Cepheids (T2Cs), which are more metal poor and with different kinematics. Results. We estimated individual distances and extinctions using VVV photometry and period-luminosity relations, reporting the characterization of 30 CCs located on the far side of the Galactic disk, plus 8 T2Cs mainly located in the bulge region, of which 10 CCs and 4 T2Cs are new discoveries. The remaining seven stars are probably misclassified foreground ellipsoidal binaries. This is the first sizeable sample of CCs in this distant region of our Galaxy that has been spectroscopically confirmed. We use their positions, kinematics, and metallicities to confirm that the general properties of the far disk are similar to those of the well-studied disk on the solar side of the Galaxy. In addition, we derive for the first time the radial metallicity gradient on the disk’s far side. Considering all the CCs with RGC < 17 kpc, we measure a gradient with a slope of −0.062 dex kpc−1 and an intercept of +0.59 dex, which is in agreement with previous determinations based on CCs on the near side of the disk.

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