scholarly journals A Global View of Molecule-Forming Clouds in the Galaxy

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Steven J. Gibson ◽  
Ward S. Howard ◽  
Christian S. Jolly ◽  
Jonathan H. Newton ◽  
Aaron C. Bell ◽  
...  
Keyword(s):  
Line Emission ◽  
Cloud Models ◽  
Global View ◽  
The Galaxy ◽  
Atomic Gas

AbstractWe have mapped cold atomic gas in 21cm line H i self-absorption (HISA) at arcminute resolution over more than 90% of the Milky Way's disk. To probe the formation of H2 clouds, we have compared our HISA distribution with CO J = 1-0 line emission. Few HISA features in the outer Galaxy have CO at the same position and velocity, while most inner-Galaxy HISA has overlapping CO. But many apparent inner-Galaxy HISA-CO associations can be explained as chance superpositions, so most inner-Galaxy HISA may also be CO-free. Since standard equilibrium cloud models cannot explain the very cold H i in many HISA features without molecules being present, these clouds may instead have significant CO-dark H2.

scholarly journals LIGHT SUPERCONDUCTING STRINGS IN THE GALAXY

2007 ◽  
Vol 16 (12b) ◽  
pp. 2399-2405 ◽  
Author(s):  
FRANCESC FERRER ◽  
TANMAY VACHASPATI
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Particle Physics ◽  
Milky Way ◽  
Gamma Ray ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Magnetic Field ◽  
The Galaxy ◽  
Intense Source

Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 keV gamma ray line emission from the bulge, which requires an intense source of positrons in the galactic center. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma ray background. Here we suggest that light superconducting strings could be the source of the observed 511 keV emission. The associated particle physics, at the ~ 1 TeV scale, is within the reach of planned accelerator experiments, while the distinguishing spatial distribution, proportional to the galactic magnetic field, could be mapped by SPI or by future, more sensitive satellite missions.

scholarly journals Multiwavelength Milky Way: An Educational Poster

1998 ◽  
Vol 179 ◽  
pp. 237-237 ◽  
Author(s):  
D. Leisawitz ◽  
S.W. Digel ◽  
S. Geitz
Keyword(s):  
Milky Way ◽  
Gamma Ray ◽  
Line Emission ◽  
Electromagnetic Spectrum ◽  
Data Sets ◽  
X Ray ◽  
Nasa Goddard Space ◽  
Broadband Emission ◽  
The Galaxy ◽  
Effective Use

The Astrophysics Data Facility at NASA Goddard Space Flight Center supports the processing, management, and dissemination of data obtained by past, current, and future NASA and international astrophysics missions, and promotes the effective use of those data by the astrophysics community, educators, and the public. Our Multiwavelength Milky Way poster was printed for broad distribution. It depicts the Galaxy at radio, infrared, optical, X-ray, and gamma-ray wavelengths. In particular, the poster contains images of the Galactic 21-cm and CO (J = 1 → 0) line emission, and IRAS 12, 60, and 100 μm, COBE/DIRBE 1.25, 2.2, and 3.5 μm, Digitized Sky Survey optical wavelength, ROSAT/PSPC 0.25, 0.75, and 1.5 keV X-ray, and CGRO/EGRET E > 100 MeV gamma ray broadband emission. All of the data sets are publicly available. Captions describe the Milky Way and what can be learned about the Galaxy from measurements made in each segment of the electromagnetic spectrum. The poster is intended to be an educational tool, one that will stimulate heightened awareness by laypersons of NASA's contribution to modern astronomy.Through an interface available on the World Wide Web at http://adf.gsfc.nasa.gov/adf/adf.html one may view the images that appear on the poster, read the poster captions, and locate the archived data and references.

scholarly journals What do Gamma Rays tell us about the ISM?: New Insight from the Compton Observatory

1996 ◽  
Vol 169 ◽  
pp. 437-446 ◽  
Author(s):  
Hans Bloemen
Keyword(s):  
Interstellar Medium ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Line Emission ◽  
Cosmic Ray ◽  
Gamma Ray Astronomy ◽  
Early Results ◽  
The Galaxy ◽  
Γ Ray ◽  
Insight Into

Gamma-ray astronomy has become a rich field of research and matured significantly since the launch of NASA's Compton Gamma Ray Observatory in April 1991. Studies of the diffuse γ-ray emission of the Galaxy can now be performed in far more detail and extended into the MeV regime, including both continuum and line emission. These studies provide unique insight into various aspects of the interstellar medium, in particular of the cosmic-ray component. This paper gives a brief review on the diffuse Galactic γ-ray emission and summarizes early results and prospects from the Compton Observatory.

scholarly journals Bloated Stars as BLR Clouds: Numeric Results

1994 ◽  
Vol 159 ◽  
pp. 437-437
Author(s):  
Tal Alexander ◽  
Hagai Netzer
Keyword(s):  
Mass Loss ◽  
Stellar Population ◽  
Line Emission ◽  
Distribution Functions ◽  
Solar Neighborhood ◽  
High Mass ◽  
Line Spectrum ◽  
Edge Density ◽  
Cloud Models ◽  
Wide Range

The ‘Bloated Stars Scenario’ proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS) (see e.g. Kazanas 1989 and references therein). Its main advantage over BLR cloud models is the gravitational confinement of the gas and its major difficulty the large estimated number of BSs and the resulting high collisional and evolutionary mass loss rates (see e.g. Begelman & Sikura 1991). Previous work on this model did not include detailed calculations of the line spectrum, modeled solar neighborhood super giants (SG) and used very simplified stellar distribution functions for the nucleus. Here (Alexander & Netzer, 1993) we calculate the emission line ratios by applying a detailed numerical photoionization code (Rees, Netzer & Ferland, 1989) to the wind and by assuming a detailed nucleus model (Murphy, Cohn & Durisen, 1990). Allowing for the yet unknown effects of the AGN's extreme conditions on stars and stellar evolution, we study a wide range of simplified wind structures rather than confine ourselves to normal SGs. Our model consists of a spherically symmetric outflowing wind that emanates from the surface of the BS (R∗ = 1013 cm, M∗ = 0.8M⊙, M = 10−6M⊙/yr) whose size and edge density are determined by various processes: Comptonization by the central continuum source (calculated self consistently for our Lion = 1046 erg/s model continuum by the photoionization code), tidal disruption by the black hole (Mbh = 8 × 107M⊙) and the limit set by the assumption that the wind's mass ≤ 0.2M⊙. This results in a large range of wind sizes, from 1013 to 1016 cm. We find that the line emission spectrum is mainly determined by the conditions at the edge of the wind rather than by its internal structure. Comptonization results in a very high ionization parameter at the edge which produces an excess of unobserved broad high excitation forbidden lines. The finite mass constraint limits the wind's size, increases the edge density and thus improves the results. Studying power-law wind structures (v(R) = v∗(R/R∗)−α where v∗ is the wind's base velocity at the BS's surface), we find that slow, decelerating, mass-constrained flows (v∗ = 50 m/s, α = 0.5) with high gas densities (108 to 1012 cm−3) are as successful as cloud models in reproducing the overall observed line spectrum. The Mg II λ2798 and N V λ1240 lines are however under-produced in our models. The denser the winds, the more efficient they are as BLR clouds. By calculating the Lα emission from the wind we adjust the number of BSs so as to obtain the BLR's observed EW(Lα). We find that only ∼ 5 × 104 BSs with dense winds (v∗ = 50 m/s, α = 0.5) are required in the inner 1/3 pc (∼ 0.005 of the total stellar population). This small fraction approaches that of SGs in the solar neighborhood. The calculated mass loss from such a small number of BSs is consistent with the observational constraints. We find that the required number of BSs, and consequently their mass loss rate, are a very sensitive functions of the wind's density structure (a ∼ 104 factor between the slow v∗ = 50 m/s, α = 0.5 model and the fast v∗ = 50 km/s, α = −2 model). In particular, high mass loss rules out SG-like BSs (v∗ = 10 km/s, α = 0). We conclude that BSs with dense winds can reproduce the BLR line spectrum and be supported by the stellar population without excessive mass loss and collisional destruction rates. The question whether such hitherto unobserved stars actually exist in the BLR remains open.

scholarly journals Separating line emission from star formation, shocks, and AGN ionization in NGC 1068

2019 ◽  
Vol 487 (3) ◽  
pp. 4153-4168 ◽  
Author(s):  
Joshua J D’Agostino ◽  
Lisa J Kewley ◽  
Brent A Groves ◽  
Anne M Medling ◽  
Enrico Di Teodoro ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Three Dimensional ◽  
Line Emission ◽  
X Ray ◽  
Diagnostic Diagram ◽  
The Galaxy ◽  
Ngc 1068 ◽  
Many Sources

ABSTRACT In the optical spectra of galaxies, the separation of line emission from gas ionized by star formation and an active galactic nucleus (AGN), or by star formation and shocks, are very well-understood problems. However, separating line emission between AGN and shocks has proven difficult. With the aid of a new three-dimensional diagnostic diagram, we show the simultaneous separation of line emission from star formation, shocks, and AGN in NGC 1068, and quantify the ratio of star formation, shocks, and AGN in each spaxel. The AGN, shock, and star formation luminosity distributions across the galaxy accurately align with X-ray, radio, and CO(3–2) observations, respectively. Comparisons with previous separation methods show that the shocked emission heavily mixes with the AGN emission. We also show that if the H α flux is to be used as a star formation rate indicator, separating line emission from as many sources as possible should be attempted to ensure accurate results.

scholarly journals Hidden or missing outflows in highly obscured galaxy nuclei?

2019 ◽  
Vol 623 ◽  
pp. A29 ◽  
Author(s):  
N. Falstad ◽  
F. Hallqvist ◽  
S. Aalto ◽  
S. König ◽  
S. Muller ◽  
...  
Keyword(s):  
Line Emission ◽  
Far Infrared ◽  
Spectral Lines ◽  
Absorption Lines ◽  
Wide Angle ◽  
Vibrationally Excited ◽  
Molecular Outflows ◽  
Luminous Infrared Galaxies ◽  
The Galaxy ◽  
Central Regions

Context. Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission from vibrationally excited HCN (HCN-vib), which is thought to trace warm and highly enshrouded galaxy nuclei. It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. Aims. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (ultra)luminous infrared galaxies ((U)LIRGs). Methods. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 μm OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. Results. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission have fast and collimated outflows that can be seen in spectral lines at longer wavelengths, including in millimeter emission lines of CO and HCN (in its vibrational ground state) and in radio absorption lines of OH. Conclusions. We conclude that the galaxy nuclei with the highest LHCN − vib/LIR do not drive wide-angle outflows that are detectable using the median velocities of far-infrared OH absorption lines. This is possibly because of an orientation effect in which sources oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed.

scholarly journals Warm Gas and Spatial Variations of Molecular Excitation in the Nuclear Region of IC342

1989 ◽  
Vol 8 ◽  
pp. 589-590
Author(s):  
A. Eckart ◽  
D. Downes ◽  
R. Genzel ◽  
A.I. Harris ◽  
D.T. Jaffe ◽  
...  
Keyword(s):  
Line Emission ◽  
Molecular Gas ◽  
Kinetic Temperature ◽  
Nuclear Region ◽  
Model Calculations ◽  
Physical Conditions ◽  
North East ◽  
The Galaxy ◽  
Molecular Excitation ◽  
North And South

Using the IRAM 30m millimeter radio telescope we mapped the line emission of the J=1-0 and J=2-1 transitions of 12C0, 13C0, and C180 in the nuclear region of the spiral galaxy IC342. This study demonstrates the value of multi line studies to investigate the neutral interstellar medium in extragalactic sources. Our observations as well as calculations of simple models of CO excitation and radiative transport show that the molecular gas in the nucleus is warm and that physical conditions vary with position in the galaxy. The molecular gas in the central kiloparsec of IC342 has a kinetic temperature of at least 30K and a molecular hydrogen density of about 3xl03 cm”3. At distances more than 500pc north and south of the center the kinetic temperature is significantly less (≥13K). About 500 pc north east of the center we find evidence for optically thin CO emission originating in a component of warm gas with a temperature of at least 40 K. Our model calculations result in conversion factors between the H2 column density and the 12CO (1-0) line intensity close to the value of 3–4×1020 cm-2/K km s-1 derived for molecular clouds in the Galaxy. The molecular mass contained in the central two kpc of IC342 is of the order of 2×108 M⊙.

scholarly journals Discovery of Superstrong, Fading, Iron Line Emission and Double-peaked Balmer Lines of the Galaxy SDSS J095209.56+214313.3: The Light Echo of a Huge Flare

2008 ◽  
Vol 678 (1) ◽  
pp. L13-L16 ◽  
Author(s):  
S. Komossa ◽  
H. Zhou ◽  
T. Wang ◽  
M. Ajello ◽  
J. Ge ◽  
...  
Keyword(s):  
Line Emission ◽  
Iron Line ◽  
The Galaxy ◽  
Balmer Lines

scholarly journals Power Spectrum of the Density of Cold Atomic Gas in the Galaxy toward Cassiopeia A and Cygnus A

2000 ◽  
Vol 543 (1) ◽  
pp. 227-234 ◽  
Author(s):  
A. A. Deshpande ◽  
K. S. Dwarakanath ◽  
W. M. Goss
Keyword(s):  
Power Spectrum ◽  
Cassiopeia A ◽  
Cygnus A ◽  
The Galaxy ◽  
Atomic Gas

scholarly journals A Possible Detection of CO (J = 3–2) Emission From the Host Galaxy of GRB 980425 with Atacama Submillimeter Telescope Experiment

2006 ◽  
Vol 2 (S235) ◽  
pp. 312-312
Author(s):  
Bunyo Hatsukade ◽  
Kotaro Kohno ◽  
Akira Endo ◽  
Tomoka Tosaki ◽  
Kouji Ohta ◽  
...  
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
Line Emission ◽  
Emission Feature ◽  
Star Formation History ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Long Duration ◽  
The Galaxy ◽  
Multi Wavelength

AbstractLong-duration gamma-ray bursts (GRBs) are considered to be due to the death of massive stars. Therefore, GRBs are closely associated with the star formation of host galaxies. Since GRBs can be detected at cosmological distances, they are expected to be probes of the star formation history of the Universe. In order to determine the use of GRBs, it is essential to understand the star formation of their hosts. Multi-wavelength observations have shown that the star formation rates (SFRs) of GRB hosts derived from submillimeter/radio observations are generally higher than those from optical/UV observations (Berger et al. 2003). This implies that GRB hosts have a large amount of molecular gas and massive star formation obscured by dust. In order to solve this problem, it is necessary to derive the SFRs in a method which is independent of existing methods and not affected by dust extinction.We observed 12CO (J = 3–2) line emission from the host galaxy of GRB 980425 using the Atacama Submillimeter Telescope Experiment (ASTE). Five points were observed covering the entire region of the galaxy, and we find possible emission features (S/N ~ 3 σ) at the velocity range corresponding to the redshift of the galaxy. By combining all spectra of five points, we obtain a global spectrum with a ~4 σ emission feature. If the features are real, this is the first detection of CO among GRB hosts. We derive the total gas mass of M(H2)=7 ± 2× 108M⊙ assuming a CO-to-H2 conversion factor of αCO = 8.0M⊙ (K km s−1 pc2)−1, which is deduced using the correlation between the αCO and the metallicity. The dynamical mass is calculated to be Mdyn=2× 1010M⊙, and M(H2)/Mdyn~3% is consistent with those of nearby dwarfs and normal spirals. The derived SFR is 0.5 ± 0.1 M⊙ yr−1 based on the Schmidt law. This SFR agrees with the results of previous Hα observations, suggesting that there is no significant obscured star formation in this host galaxy. This result implies that there is a variety of GRB hosts in terms of the presence of obscured star formation.

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