Low density ionized gas in the inner galaxy — Interpretation of recombination line observations at 325 MHz

1985 ◽  
Vol 6 (4) ◽  
pp. 203-226 ◽  
Author(s):  
K. R. Anantharamaiah
Keyword(s):  
Low Density ◽  
Recombination Line ◽  
Ionized Gas

Radio recombination line observations towards Spitzer infrared bubbles with the TianMa radio telescope

2019 ◽  
Vol 489 (4) ◽  
pp. 4862-4874
Author(s):  
L G Hou ◽  
X Y Gao
Keyword(s):  
Radio Telescope ◽  
Detection Rate ◽  
Milky Way ◽  
Absorption Method ◽  
Recombination Line ◽  
Ionized Gas ◽  
Radio Recombination Line ◽  
Warm Ionized Medium

ABSTRACT Many of the Spitzer infrared bubbles identified by the Milky Way Project (MWP) are suggested to be $\rm{H \small {II}} $ regions in nature. More than 70 per cent of the ∼5000 known bubbles do not have radio recombination line (RRL) observations, hence have not been confirmed as $\rm{H \small {II}} $ regions. A systematic RRL survey should be helpful to identify the nature of the bubbles. With the Shanghai TianMa 65-m radio telescope, we searched for RRLs towards 216 selected Spitzer bubbles by simultaneously observing 19 RRLs in the C band (4–8 GHz). RRLs are detected in the directions of 75 of the 216 targets. 31 of the 75 RRL sources are classified as new detections, which are possibly from new $\rm{H \small {II}} $ regions or diffuse warm ionized medium; 36 of them are probably from the outskirts of nearby bright $\rm{H \small {II}} $ regions, rather than bubble-encircled ionized gas; and the detected RRLs towards 8 bubbles are identified from known $\rm{H \small {II}} $ regions. For 58 of the 75 RRL sources, we obtained their distances after resolving the kinematic distance ambiguity by combining the results of the H2CO absorption method, the $\rm{H \small {I}} $ emission/absorption method, and the $\rm{H \small {I}} $ self-absorption method. The low detection rate of new $\rm{H \small {II}} $ regions implies that a number of MWP bubbles in the DR1 catalogue are too faint if they are $\rm{H \small {II}} $ regions.

Diffuse Ionized Gas in the β CMa Tunnel

1997 ◽  
Vol 166 ◽  
pp. 173-176
Author(s):  
Olivier Dupin ◽  
Cécile Gry
Keyword(s):  
Interstellar Medium ◽  
Low Density ◽  
Ionized Gas ◽  
Local Bubble ◽  
Diffuse Ionized Gas ◽  
Main Components ◽  
Collisional Ionization ◽  
Dust Grain

AbstractWe present HST observations of the interstellar medium toward the star β CMa known to be located in a low density extension of the Local Bubble. Most of the matter in the sight-line is ionized and clumped in two main components. One of them, as well as one of the components detected toward ϵ CMa, is mostly ionized and only slightly depleted. Their ionization ratios are compatible with collisional ionization at T~25 000 K. These clouds could have been ionized by shocks related to the Local Bubble creation and also responsible of some dust grain sputtering.

scholarly journals How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Takahiro Tsutsumi ◽  
Ryosuke Miyawaki ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Galactic Center ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Recombination Line ◽  
Intermediate Mass ◽  
Ionized Gas ◽  
Sagittarius A ◽  
Projection Distance ◽  
Spectroscopic Information ◽  
Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

scholarly journals Probing Sagittarius A* accretion with ALMA

2016 ◽  
Vol 11 (S322) ◽  
pp. 21-24
Author(s):  
Elena Murchikova
Keyword(s):  
Galactic Center ◽  
Accretion Rate ◽  
Recombination Line ◽  
Ionized Gas ◽  
X Ray ◽  
Sagittarius A ◽  
Hydrogen Recombination ◽  
Unique Probe ◽  
Cool Gas

AbstractThe submm Hydrogen recombination line technique can be used as a probe of the Galactic Center. We present the results of our H30α observations of ionized gas from within 0.015 pc around SgrA*. The observations were obtained on ALMA in cycle 3. The line was not detected, but we were able to set a limit on the mass of the cool gas (T~ 104 K) at 2 × 10−3M⊙. This is the unique probe of gas cooler than T ~106 K traced by X-ray emission. The total amount of gas near SgrA* gives us clues to understanding the accretion rate of SgrA*.

scholarly journals A Study of Low density Ionized Gas in the Galactic Plane

2002 ◽  
Vol 199 ◽  
pp. 335-338
Author(s):  
D. Anish Roshi ◽  
K. R. Anantharamaiah
Keyword(s):  
Radio Telescope ◽  
Radial Distribution ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Hii Regions ◽  
Low Density ◽  
Ionized Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Complete Survey

A complete survey of radio recombination lines (RRLs) near 327 MHz from the galactic plane (l = 330° − 0°-89°, b = 0°) was carried out using a section of the Ooty Radio Telescope (ORT) with an angular resolution of 2° × 2°. A subset of regions in the same area was observed using the whole telescope which has a beam of 2° × 6'. Hydrogen RRLs were detected in most of the positions that were observed. The lv diagram and radial distribution computed from the observed spectra and their comparison with other species in the galactic plane indicate that the low density gas detected in the survey is distributed similar to the star forming regions. For an assumed temperature of 7000 K, we estimate that the densities and sizes of the regions are in the range 1 — 10 cm−3 and 20 — 200 pc respectively. Our data suggests that the low density ionized gas is in the form of outer envelopes of normal HII regions.

scholarly journals Rotating ionized gas ring around the Galactic center IRS13E3

2019 ◽  
Vol 71 (5) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Takahiro Tsutsumi ◽  
Ryosuke Miyawaki ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Galactic Center ◽  
Mass Density ◽  
Angular Size ◽  
High Mass ◽  
Continuum Emission ◽  
Supporting Evidence ◽  
Recombination Line ◽  
Ionized Gas ◽  
Sgr A ◽  
The Continuum

Abstract We detected a compact ionized gas associated physically with IRS13E3, an intermediate mass black hole (IMBH) candidate in the Galactic center, in the continuum emission at 232 GHz and H30α recombination line using ALMA Cy.5 observation (2017.1.00503.S, P.I. M.Tsuboi). The continuum emission image shows that IRS13E3 is surrounded by an oval-like structure. The angular size is 0${^{\prime\prime}_{.}}$093 ± 0${^{\prime\prime}_{.}}$006 × 0${^{\prime\prime}_{.}}$061 ± 0${^{\prime\prime}_{.}}$004 (1.14 × 1016 cm × 0.74 × 1016 cm). The structure is also identified in the H30α recombination line. This is seen as an inclined linear feature in the position–velocity diagram, which is usually a defining characteristic of a rotating gas ring around a large mass. The gas ring has a rotating velocity of Vrot ≃ 230 km s−1 and an orbit radius of r ≃ 6 × 1015 cm. From these orbit parameters, the enclosed mass is estimated to be $M_{\mathrm{IMBH}}\simeq 2.4\times 10^{4}\, M_{\odot }$. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A*. Considering IRS13E3 has an X-ray counterpart, the large enclosed mass would be supporting evidence that IRS13E3 is an IMBH. Even if a dense cluster corresponds to IRS13E3, the cluster would collapse into an IMBH within τ < 107 yr due to the very high mass density of $\rho \gtrsim 8\times 10^{11}\, M_{\odot }\:$pc−3. Because the orbital period is estimated to be as short as T = 2πr/Vrot ∼ 50–100 yr, the morphology of the observed ionized gas ring is expected to be changed in the next several decades. The mean electron temperature and density of the ionized gas are $\bar{T}_{\mathrm{e}}=6800\pm 700\:$K and $\bar{n}_{\mathrm{e}}=6\times 10^{5}\:$cm−3, respectively. Then the mass of the ionized gas is estimated to be $M_{\mathrm{gas}}=4\times 10^{-4}\, M_{\odot }$.

scholarly journals Radio Recombination Lines from Starburst Galaxies: High and Low Density Ionized Gas

2002 ◽  
Vol 199 ◽  
pp. 243-244
Author(s):  
N.R. Mohan ◽  
K.R. Anantharamaiah ◽  
W.M. Goss
Keyword(s):  
Flux Density ◽  
Hii Regions ◽  
Starburst Galaxies ◽  
High Density ◽  
The Other ◽  
Low Density ◽  
Ionized Gas ◽  
Density Measurements ◽  
Radio Recombination Lines ◽  
Upper Limits

Radio recombination lines (RRL) at 8 GHz and 15 GHz detected from four starburst galaxies are shown to arise in compact high density HII regions, which are undetectable below ∼4 GHz. Detection of an RRL at 1.4 GHz towards one galaxy and upper limits in the other three are consistent with the presence of an equal amount of low density diffuse gas. Continuum flux density measurements using the GMRT will be important in constraining the properties of the diffuse gas.

Molecular Clouds

1977 ◽  
Vol 75 ◽  
pp. 37-54 ◽  
Author(s):  
P. Thaddeus
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Molecular Clouds ◽  
Physical State ◽  
Molecular Gas ◽  
Spectroscopic Techniques ◽  
Low Density ◽  
Recombination Line ◽  
Interstellar Gas ◽  
Impossible Task

To attempt to understand star formation without knowing the physical state of the dense interstellar molecular gas from which stars are made is an almost impossible task. Star formation has developed late as a branch of astrophysics largely for lack of observational data, and in particular, has lagged badly behind the study of the atomic and ionized components of the interstellar gas because spectroscopic techniques which work well at low density have an unfortunate tendency to fail when the density is high. Optical spectroscopy, which has been applied to the interstellar medium for over 70 years, has made little progress in regions of high density because of obscuration, and the same is true a fortiori of spacecraft spectroscopy in the UV; radio 21-cm and recombination line observations, although unhampered by obscuration, are unsatisfactory because the dense condensations are almost entirely molecular in composition.

scholarly journals Recombination-line observations of the Galactic Centre

1985 ◽  
Vol 106 ◽  
pp. 371-376 ◽  
Author(s):  
J.H. van Gorkom ◽  
U. J. Schwarz ◽  
J. D. Bregman
Keyword(s):  
Velocity Field ◽  
Line Width ◽  
Intensity Distribution ◽  
Large Scale ◽  
Aperture Synthesis ◽  
Galactic Centre ◽  
Recombination Line ◽  
Ionized Gas

Aperture-synthesis observations of the H76α and H110α recombination lines are presented for the inner (3pc) region of the Galactic Nucleus. The large line width measured with single dishes (Pauls et al., 1974) is caused by well-ordered large-scale motions of the ionized gas. The velocities of the NeII clumps (Lacy et al., 1980) fit well into our smooth velocity field and smooth intensity distribution. We suggest therefore that the cloud picture of the NeII gas is (at least partly) invalid.

scholarly journals A hidden class of Be stars?

1994 ◽  
Vol 162 ◽  
pp. 420-421
Author(s):  
P.A. Zaal ◽  
L.B.F.M. Waters ◽  
J.M. Marlborough ◽  
T.R. Geballe
Keyword(s):  
Infrared Spectrum ◽  
Low Density ◽  
Be Stars ◽  
Recombination Line ◽  
B Stars

Recently, Brα and Brγ emission was detected in the infrared spectrum of the B0.2V star τ Scorpii, without noticeable emission in Hα (Waters et al. A&A 272, L9-L12, 1993). Here we present simple HI recombination line calculations in the infrared and in the optical that demonstrate that there could be a class of B stars with low-density discs, a factor of 100 lower in density compared to normal Be stars, which may have escaped detection so far.

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