The Deuterium Abundance In The Galactic Center 50 km/s Molecular Cloud: Evidence For A Cosmological Origin Of D

We confirm that deuterium exists in the Galactic Center (GC) and estimate that D/H = 3 × 10−6 using a new 5192-chemical reaction model. This is the lowest D/H ratio observed in the Galaxy, five times lower than the local ISM D/H = 1.5 × 10−5 but 106 × larger than D/H predicted by GC models. We detected DCN in the GC Sgr A 50 km/s molecular cloud located 10 pc from the GC with the NRAO 12m telescope and obtained T*R = 0.061 ± 0.007 K and 0.04 ± 0.02 K for the J = 1-0 and 2-1 lines. The most likely source of the GC D is continuous injection from the infall of primordial matter with D/H = 5 × 10−5 with the D/H determined by astration and mixing. Thus there are no significant Galactic sources of D and no recent quasar or AGN activity in the GC. This primordial D/H implies that the baryon density is less than the density necessary to close the Universe; most of the baryons are in dark matter; and there are fewer than four ν families.

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The Nature, Location and Environment of Sgr A East

Symposium - International Astronomical Union ◽

10.1017/s0074180900186723 ◽

1989 ◽

Vol 136 ◽

pp. 345-356 ◽

Cited By ~ 1

Author(s):

W. M. Goss ◽

K. R. Anantharamaiah ◽

J. H. van Gorkom ◽

R. D. Ekers ◽

A. Pedlar ◽

...

Keyword(s):

Spiral Galaxy ◽

Molecular Cloud ◽

Supernova Remnant ◽

Galactic Center ◽

Hii Regions ◽

Active Nucleus ◽

The Galaxy ◽

Sgr A ◽

Turn Over ◽

Unique Variation

We have observed SgrA at 332 MHz (92 cm) with a resolution of 12 arcsec (0.6 pc) using the four configurations of the VIA. These results illustrate the dramatic and almost unique variation of radio spectral index within the central 3–4 arcmin of the galactic center. SgrA East is a non-thermal shell source that could be a supernova remnant or a very low-luminosity example of a radio component associated with the active nucleus of a spiral galaxy. The most dramatic aspect of the new 332 MHz observations is the appearance of the the SgrA West spiral features in absorption against SgrA East. Based on these results, SgrA East is situated behind SgrA West, the center of the galaxy. The halo is in front of or surrounds the former sources. The HII regions to the east of SgrA East (1 = −0°.02, b = −0°.07) are probably associated with the 50 km/s molecular cloud. The 7 arcmin halo (20 pc) has a non-thermal spectrum with turn-over below 1 GHz.

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Deuterium in the Galaxy

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000014910 ◽

1977 ◽

Vol 3 (2) ◽

pp. 100-101 ◽

Cited By ~ 1

Author(s):

R. D. Brown

Keyword(s):

Great Majority ◽

Big Bang ◽

Baryon Density ◽

The Galaxy ◽

Mass Fractions ◽

Expansion Of The Universe ◽

Sensitive Function ◽

The Big Bang ◽

Deuterium Production ◽

The Universe

There have been a number of attempts made in the last decade or two to observe deuterium in parts of the universe other than here in Earth. It is of interest merely to detect deuterium elsewhere just as it is to detect the occurrence of any nuclide. However in the case of deuterium there is a special interest because in big-bang cosmologies the great majority of deuterium in the universe is considered to have been formed in the initial fireball (Wagoner, 1973). Any observation of the present abundance of deuterium thus might give information about the very early stages of the creation of the universe. Detailed studies of nucleosynthesis during the early expansion of hot big-bang universes have however indicated a particular feature of deuterium production. (Fig. 1) The mass fraction produced X(D) is a very sensitive function of the size of the universe, as measured say by the present baryon density ϱb. Other nuclides that are mainly produced in the early expansion, such as 4He, have mass fractions less dependent on ϱb. Thus if we adopt the big-bang model for our universe we can determine ϱb from observations of X(D). Apart from any intrinsic interest in the present density of the’universe, there is considerable interest in whether the value is great enough for the present expansion to halt and go over to a collapse — or so small that the expansion of the universe will go on forever.

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Radio Continuum Emission from the Nuclei of Normal Galaxies

Highlights of Astronomy ◽

10.1017/s1539299600003877 ◽

1980 ◽

Vol 5 ◽

pp. 177-184 ◽

Cited By ~ 2

Author(s):

J. M. van der Hulst

Keyword(s):

Radio Emission ◽

Galactic Center ◽

Galactic Nuclei ◽

Radio Continuum ◽

Continuum Emission ◽

Thermal Source ◽

Very Large Array ◽

Normal Galaxies ◽

The Galaxy ◽

Sgr A

During the last few years detailed and sensitive observations of the radio emission from the nuclei of many normal spiral galaxies has become available. Observations from the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO1), in particular, enable us to distinguish details on a scale of ≤100 pc for galaxies at distances less than 21 Mpc. The best studied nucleus, however, still is the center of our own Galaxy (see Oort 1977 and references therein). Its radio structure is complex. It consists of an extended non-thermal component 200 × 70 pc in size, with embedded therein several giant HII regions and the central source Sgr A (˜9 pc in size). Sgr A itself consists of a thermal source, Sgr A West, located at the center of the Galaxy, and a weaker, non-thermal source, Sgr A East. Sgr A West moreover contains a weak, extremely compact (≤10 AU) source. The radio morphology of several other galactic nuclei is quite similar to that of the Galactic Center, as will be discussed in section 2. Recent reviews of the radio properties of the nuclei of normal galaxies have been given by Ekers (1978a,b) and De Bruyn (1978). The latter author, however, concentrates on galaxies with either active nuclei or an unusual radio morphology. In this paper I will describe recent results from the Westerbork Synthesis Radio Telescope (WSRT, Hummel 1979), the NRAO 3-element interferometer (Carlson, 1977; Condon and Dressel 1978), and the VLA (Heckman et al., 1979; Van der Hulst et al., 1979). I will discuss the nuclear radio morphology in section 2, the luminosities in section 3, and the spectra in section 4. In section 5 I will briefly comment upon the possible implications for the physical processes in the nuclei that are responsible for the radio emission.

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10.2. High proper motions in the vicinity of Sgr A∗: unambiguous evidence for a massive central black hole

Symposium - International Astronomical Union ◽

10.1017/s0074180900085478 ◽

1998 ◽

Vol 184 ◽

pp. 433-434

Author(s):

A. M. Ghez ◽

B. L. Klein ◽

C. McCabe ◽

M. Morris ◽

E. E. Becklin

Keyword(s):

Black Hole ◽

Milky Way ◽

Galactic Center ◽

Robust Method ◽

Proper Motions ◽

Central Black Hole ◽

Milky Way Galaxy ◽

The Galaxy ◽

Sgr A

Although the notion that the Milky Way galaxy contains a supermassive central black hole has been around for more than two decades, it has been difficult to prove that one exists. The challenge is to assess the distribution of matter in the few central parsecs of the Galaxy. Assuming that gravity is the dominant force, the motion of the stars and gas in the vicinity of the putative black hole offers a robust method for accomplishing this task, by revealing the mass interior to the radius of the objects studied. Thus objects located closest to the Galactic Center provide the strongest constraints on the black hole hypothesis.

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The Compact Nonthermal Radio Source at the Galactic Center: an Update

Symposium - International Astronomical Union ◽

10.1017/s0074180900187030 ◽

1989 ◽

Vol 136 ◽

pp. 527-534

Author(s):

K. Y. Lo

Keyword(s):

Radio Source ◽

Galactic Center ◽

Central Star ◽

Radio Sources ◽

Stellar Objects ◽

Nonthermal Radio ◽

Compact Radio Source ◽

The Galaxy ◽

Observational Status ◽

Sgr A

We review the current observational status of Sgr A∗, the compact nonthermal radio source at the galactic center. Sgr A∗ is a unique radio source at a unique location of the Galaxy. It is unlike any compact radio source associated with known stellar objects, but it is similar to extragalactic nuclear compact radio sources. The positional offset between Sgr A∗ and IRS16 places little constraint on the nature of the underlying energy source, since IRS16 need not be the core of the central star cluster. Sgr A∗ is still the best candidate for marking the location of a massive collapsed object.

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Micro-arcsecond astrometry with the VLBA

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308018929 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 141-147 ◽

Cited By ~ 2

Author(s):

M. J. Reid

Keyword(s):

Galactic Center ◽

Galactic Plane ◽

Proper Motions ◽

Star Forming ◽

Star Forming Regions ◽

The Galaxy ◽

Trigonometric Parallaxes ◽

Sgr A ◽

Definition Of ◽

Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

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SiO and H2O Masers in the Central Parsec of the Galaxy

International Astronomical Union Colloquium ◽

10.1017/s0252921100045334 ◽

1998 ◽

Vol 164 ◽

pp. 229-230 ◽

Cited By ~ 1

Author(s):

Karl M. Menten ◽

Mark J. Reid

Keyword(s):

Galactic Center ◽

Radio Continuum ◽

Continuum Emission ◽

Proper Motions ◽

Infrared Images ◽

Evolved Stars ◽

The Galaxy ◽

Sgr A ◽

Central Parsec ◽

Infrared Sources

AbstractWe have discovered maser emission from SiO and H2O molecules toward a number of evolved stars within the central parsec of our Galaxy. The maser positions can be registered with milliarcsecond precision relative to the radio continuum emission of the nonthermal Galactic center source Sgr A*. Since the masing stars are prominent infrared sources, our data can be used to locate the position of Sgr A* on infrared images of the Galactic center region. Using VLBA observations it will be possible to measure proper motions of the maser stars, which can be used to put constraints on the mass distribution in the central parsec.

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Tidally-disrupted Molecular Clouds falling to the Galactic Center

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316012047 ◽

2016 ◽

Vol 11 (S322) ◽

pp. 115-118 ◽

Cited By ~ 1

Author(s):

Masato Tsuboi ◽

Yoshimi Kitamura ◽

Kenta Uehara ◽

Ryosuke Miyawaki ◽

Atsushi Miyazaki

Keyword(s):

Molecular Cloud ◽

Molecular Clouds ◽

Galactic Center ◽

Outer Region ◽

Recombination Line ◽

Ionized Gas ◽

Boundary Area ◽

Gas Streams ◽

Uv Emission ◽

Sgr A

AbstractWe found a molecular cloud connecting from the outer region to the “Galactic Center Mini-spiral (GCMS)” which is a bundle of the ionized gas streams adjacent to Sgr A*. The molecular cloud has a filamentary appearance which is prominent in the CSJ=2-1 emission line and is continuously connected with the GCMS. The velocity of the molecular cloud is also continuously connected with that of the ionized gas in the GCMS observed in the H42α recombination line. The morphological and kinematic relations suggest that the molecular cloud is falling from the outer region to the vicinity of Sgr A*, being disrupted by the tidal shear of Sgr A* and ionized by UV emission from the Central Cluster. We also found the SiOJ=2-1 emission in the boundary area between the filamentary molecular cloud and the GCMS. There seems to exist shocked gas in the boundary area.

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Is Sgr A∗ Underfed, Underefficient, or Underdone?

Symposium - International Astronomical Union ◽

10.1017/s0074180900229665 ◽

1996 ◽

Vol 169 ◽

pp. 181-187 ◽

Cited By ~ 1

Author(s):

Leonid M. Ozernoy ◽

Reinhard Genzel

Keyword(s):

Black Hole ◽

Galactic Center ◽

Lower Mass ◽

Lower Efficiency ◽

The Galaxy ◽

Sgr A

We argue that the wind from IRS 16 and He I stars in the central 1 pc of the Galaxy is responsible for the peculiar features of accretion onto a putative black hole at the Galactic center. What makes Sgr A∗ unique is not that it is just underfed but, in addition, it has a much lower efficiency of accretion and possibly a lower mass, compared to the AGN case.

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The Herschel view of the Galactic center

Proceedings of the International Astronomical Union ◽

10.1017/s174392131400009x ◽

2013 ◽

Vol 9 (S303) ◽

pp. 1-14

Author(s):

John Bally ◽

Keyword(s):

Star Formation ◽

Massive Star ◽

Galactic Center ◽

Galactic Plane ◽

Formation Rate ◽

Asymmetric Distribution ◽

The Galaxy ◽

Sgr A ◽

Almost All

AbstractThe 3.5 meter diameter Herschel Space Observatory conducted a ∼720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm−3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s−1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally ‘blow-out’ a portion of the gas on these x2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest ‘superbubble’ in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of the SMBH.

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