scholarly journals Density Bounding of Giant HII Regions and the Ionisation of the Diffuse Interstellar Medium

1998 ◽  
Vol 15 (1) ◽  
pp. 83-85 ◽  
Author(s):  
J. E. Beckman ◽  
M. Rozas ◽  
J. H. Knapen
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Intergalactic Medium ◽  
Hii Regions ◽  
Critical Value ◽  
Disk Galaxies ◽  
Lyman Continuum ◽  
Different Types

AbstractThree different types of evidence are presented in favour of the hypothesis that the HII regions in disk galaxies with Hα luminosities greater than a critical value of 1038·6 erg s−1 are density-bounded, and that the escaping Lyman continuum photons from these are the principal ionising agents for the diffuse ISM in disk galaxies. This has important implications for the ionisation of the intergalactic medium, and for computed star formation rates in spirals.

scholarly journals Star Formation in Disk Galaxies

1998 ◽  
Vol 15 (1) ◽  
pp. 118-122 ◽  
Author(s):  
Rosemary F. G. Wyse ◽  
Annette M. N. Ferguson ◽  
Jay S. Gallagher ◽  
Deidre A. Hunter
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Massive Stars ◽  
Broad Band ◽  
Hii Regions ◽  
Disk Galaxies ◽  
Chemical Enrichment

AbstractWe present results, some preliminary, from a major new study of the star formation properties of a sample of nearby disk galaxies (Ferguson 1997). Our emphasis is on the faint outer regions of disks. Hα images, combined with broad-band images and spectroscopy of HII regions, constrain the present and past star formation rates and chemical enrichment. These data also allow study of faint diffuse ionised gas, which traces the influence of massive stars on their environment, and the structure of the interstellar medium.

scholarly journals HII regions and star formation in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 139-144 ◽  
Author(s):  
Robert C. Kennicutt
Keyword(s):  
Star Formation ◽  
Interstellar Medium ◽  
Massive Star ◽  
Massive Stars ◽  
Hii Regions ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Distant Galaxies ◽  
Close Range ◽  
Mass Functions

The H II regions in the Magellanic Clouds provide an opportunity to characterize the global star formation properties of a galaxy at close range. They also provide a unique laboratory for testing empirical tracers of the massive star formation rates and initial mass functions in more distant galaxies, and for studying the dynamical interactions between massive stars and the interstellar medium. This paper discusses several current studies in these areas.

scholarly journals Star Clusters in Giant Extragalactic HII Regions

2002 ◽  
Vol 207 ◽  
pp. 439-444
Author(s):  
Yu Zhi-yao
Keyword(s):  
Star Formation ◽  
Key Words ◽  
Star Clusters ◽  
Hii Regions ◽  
Star Cluster ◽  
Continuum Radiation ◽  
Hii Region ◽  
Lyman Continuum ◽  
Formation Efficiency ◽  
The Relationship

In this paper we study the relationship between the star formation efficiency and luminosity of Hα emission, Lyman continuum radiation, and Hβ emission on 35 giant extragalactic HII regions in seven galaxies. Using the observational results we obtain the relationship, and find that the star formation efficiency is correlation with Halpha luminocity, and Lyman continuum luminosity, and Hβ lumonosity, respectively. Key words: external galaxy—giant HII region—star cluster

scholarly journals Warps and Accretion

2010 ◽  
Vol 6 (S277) ◽  
pp. 71-74 ◽  
Author(s):  
Gyula I. G. Józsa
Keyword(s):  
Star Formation ◽  
Intergalactic Medium ◽  
Ambient Medium ◽  
Basic Feature ◽  
Optical Disk ◽  
Disk Galaxies ◽  
Galactic Disks ◽  
Star Forming ◽  
Show Evidence ◽  
Excitation Mechanisms

AbstractWarps are a basic feature of disk galaxies. Usually they occur at radii where the optical disk fades and become most pronounced in the outermost gaseous disks.As such, warps present a massive reservoir to replenish star forming material in the inner, star forming disks. Furthermore, some possible excitation mechanisms for warps connect their formation to the accretion of extragalctic material. Interactions or mergers with gas-rich companions or the direct accretion of the ambient intergalactic medium might lead to the formation of warps, at the same time supplementing fuel to maintain star formation in galactic disks.Employing a number of H i studies of warped galaxies, including ultra-deep observations of the prototype warped galaxies NGC 5907 and NGC 4013, I discuss whether the observed kinematics may show evidence for a connection of warps and accretion from the ambient medium.

scholarly journals Star Formation in M81

1987 ◽  
Vol 115 ◽  
pp. 626-626
Author(s):  
Frank Bash ◽  
Michele Kaufman
Keyword(s):  
Shock Wave ◽  
Star Formation ◽  
Interstellar Medium ◽  
Thermal Radiation ◽  
Spiral Galaxy ◽  
Density Wave ◽  
Wave Theory ◽  
Hii Regions ◽  
Radio Continuum ◽  
Density Wave Theory

VLA observations of the spiral galaxy M81 in the radio continuum at wavelengths of 6 and 20-cm have been used to check the predictions of the density wave theory. The non-thermal radiation from the arms has been detected and the arms are found to be broader than the predictions of the classical density wave theory. Their width does seem to agree with that predicted by models which take the clumpy nature of the interstellar medium into account. These data are also able to separate giant HII regions from the non-thermal arms. Collaborators have furnished optical Hα data on the HII regions and HI 21-cm data, from the VLA, which will be used to find and measure the location of the HII regions with respect to the spiral shock wave and to measure the visual extinction in the disk of M81.

Fueling Nuclear Starbursts

1999 ◽  
Vol 186 ◽  
pp. 213-216
Author(s):  
Jeroen P.E. Gerritsen ◽  
Vincent Icke
Keyword(s):  
Numerical Simulation ◽  
Star Formation ◽  
Interstellar Medium ◽  
Negative Feedback ◽  
Equal Mass ◽  
Young Stars ◽  
Disk Galaxies ◽  
Accurate Treatment

We present a numerical simulation of two merging equal-mass, gas-rich disk galaxies. Special emphasis is given to an accurate treatment of the interstellar medium physics and star formation with its feedback. We will explain how the negative feedback from young stars restricts the bulk of the star formation during the merger-induced starburst to the nucleus.

scholarly journals Non-stellar sources of turbulence in the interstellar medium

2006 ◽  
Vol 2 (S237) ◽  
pp. 70-75
Author(s):  
Eve C. Ostriker
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Milky Way ◽  
Hii Regions ◽  
Disk Galaxies ◽  
Magnetorotational Instability ◽  
Energy Inputs ◽  
Stellar Energy ◽  
Alternative Sources ◽  
Stellar Sources

AbstractTurbulence is believed to be important to star formation both within GMCs (affecting the IMF and the SFE), and on larger scales in the ISM (affecting GMC formation rates and properties). The traditional view of the ISM attributes most of the turbulent driving to stellar sources – in particular, supernovae and HII regions. However, evidence suggests that sources other than star formation must contribute significantly to large-scale turbulent driving in the diffuse ISM, thus also affecting the turbulence that GMCs inherit. I review recent investigations of alternative sources proposed for driving ISM turbulence, including thermal instabilities, the magnetorotational instability, large-scale self-gravitating modes, and instabilities in spiral shocks. I summarize results based on numerical simulations regarding the levels of turbulence that can be driven, and how these amplitudes depend on galactic conditions. This recent work shows that, under certain circumstances, very large-amplitude (trans-sonic with respect to the warm gas) motions and magnetic fields can be driven even without stellar energy inputs. Since turbulence can either trigger or limit star formation, understanding these potentially large non-stellar driving sources is crucial for a developing a theory of star formation regulation in the Milky Way and other disk galaxies.

scholarly journals The Warm Ionised Medium in Spiral Galaxies: A View from Above

1998 ◽  
Vol 15 (1) ◽  
pp. 99-102 ◽  
Author(s):  
René A. M. Walterbos
Keyword(s):  
Interstellar Medium ◽  
Reasonable Agreement ◽  
Spiral Galaxies ◽  
Hii Regions ◽  
Solar Neighborhood ◽  
Current Understanding ◽  
Unexpected Result ◽  
Ob Stars ◽  
Lyman Continuum ◽  
External Galaxies

AbstractThe warm ionised medium (WIM), also referred to as diffuse ionised gas (DIG), contains most of the mass of interstellar medium in ionised form, contributing as much as 30% of the total atomic gas mass in the solar neighborhood. The advent of CCDs has enabled unprecedented study of this medium in external galaxies, probing a variety of environments. In particular, we can derive the morphology of the WIM, its distribution across disks, and the correlation with other Population I material. Spectroscopy of the WIM makes it possible to test various ionisation models. I will review here our current understanding of the properties of the WIM in spiral galaxies. A perhaps unexpected result is that the Hα emission from the WIM contributes about 40% of the total observed Hα luminosity from spirals. This places severe constraints on possible sources of ionisation, since only photoionisation by OB stars meets this requirement. Spectroscopic measurements of forbidden line strengths appear in reasonable agreement with photoionisation models. It is not yet clear if the Lyman continuum photons that ionise the WIM are mostly from OB stars located inside traditional HII regions, or from field OB stars.

scholarly journals Anemic Galaxies: Evidence for a Threshold in Star Formation Processes

1987 ◽  
Vol 115 ◽  
pp. 633-633
Author(s):  
B. Guiderdoni
Keyword(s):  
Star Formation ◽  
Spiral Galaxies ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Critical Value ◽  
Virgo Cluster ◽  
Disk Galaxies ◽  
Formation Processes ◽  
The Galaxy ◽  
Gas Consumption

From a sample of Virgo Cluster and “field” disk galaxies, it is shown that a critical value of the HI surface density discriminates between RDDO anemic and “healthy” spirals. Below this threshold, at least massive stars do not form any more and the galaxy gets the anemic appearance. The influence of the HI content on the global star formation rate is discussed in the context of present models (Elmegreen 1979, Seiden and Gerola 1979, Dopita 1985), as well as the fate of disks in cluster and “field” environments. The existence of this threshold is an issue for the problem caused by the short gas consumption time scales derived from the observations of spiral galaxies.

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