Far-Infrared Emission of the ISM in Galaxies of Varying Morphology and Star Formation
Observations of far-infrared emission lines can be used to infer the physical conditions of the ISM in galaxies.
galaxies ism star formation↗
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The IRAS2 and IRAS4 Outflows and Star Formation i NGC 1333
We report the first detection of the western bowshock component from IRAS2 in NGC 1333 along with observations of previously detected shocks and outflow winds from this source and those from IRAS4. We compare the shock and outflow distributions from these two young stellar objects, and the locations of other YSOs, with the overall distribution of the dense molecular gas in the star forming core using high spatial resolution observations of CS (J=2-->1, 3-->2, and 5-->4) emission made with the IRAM 30m antenna.
stars star formation outflows ISM↗
Clustering in High Mass Star Formation
We have undertaken a systematic study to identify a sample of massive protostellar candidates. We have now started a pilot program to observe these objects by means of millimeter interferometry.
clusters star formation high-mass↗
The energetics and mass structure of regions of star formation - S201
Theoretical predictions about dust and gas in star-forming regions are tested by observing a 4-arcmin region surrounding the radio continuum source in S201. The object was mapped in two far-infrared wavelengths and found to show significant extended emission. Under the assumption that the molecular gas is heated solely via thermal coupling with the dust, the volume density was mapped in S201. The ratios of infrared optical depth to CO column density were calculated for a number of positions in the source. Near the center of the cloud the values are found to be in good agreement with other determinations for regions with lower column density. In addition, the observations suggest significant molecular destruction in the outer parts of the object. Current models of gas heating were used to calculate a strong limit for the radius of the far-infrared emitting grains, a equal to or less than 0.15 micron. Grains of about this size are required by the observation of high temperature (T equal to or greater than 20 K) gas in many sources.
Thronson, H. A., Jr.↗
Star formation in IC 1848 A
Recent far-infrared photometric and near-infrared spectroscopic observations of IC 1848 A/W5 East are reported. The source appears to be excited by a star of spectral type near B0, which can explain the far-infrared luminosity, 2 micron spectrum, radio continuum, and radio molecular observations. Although this star appears surrounded by a local very compact H II region, the density over a large scale is relatively low. This puts constraints on models for the formation of this star.
Thronson, H. A., Jr.↗
Massive star formation in a gravitationally-lensed H II galaxy at z=3.357
The Lynx arc, with a redshift of 3.357, was discovered during spectroscopic follow-up of the z=0.570 cluster RX J0848+4456 from the ROSAT Deep Cluster Survey. The arc is characterized by a very red R - K color and strong, narrow emission lines.
star formation gravitationally-lensed↗
Star formation in the M17 SW giant molecular cloud
The first high-sensitivity, high-resolution far-IR survey of an entire molecular cloud complex is presented. The 20 km/s M17 SW complex, in addition to the three luminous M17 sources, contains 10 sources spread over 110 pc. The 10 lower luminosity sources divide into two groups: small blister sources powered by late O stars and compact sources powered by clusters of early B stars. No compact far-IR sources with luminosities between the detection limit and 10,000 solar luminosities were detected. Three possible formation mechanisms for the stars that power the far-IR sources in the M17 SW complex are examined. Sequential formation cannot explain the sources seen throughout the complex. Some type of stochastic formation mechanism or collapse induced by a spiral density wave could explain the observations.
Jaffe, D. T.↗
Neutron-star formation in the carbon-detonation supernova.
Neutrino losses, such as those driven by the convective Urca process, may affect the evolution of stars in the mass range from 4 to 8 solar masses so as to lead to collapse of their degenerate carbon/oxygen cores. A corresponding hydrodynamic model is computed which leads to the formation of a 1.3 to 1.4 solar mass neutron star with the expulsion of a small fraction of the mass, about 0.l solar mass at about 20,000 km/sec into the overlying hydrogen envelope. This sets the stage for the Ostriker-Gunn mechanism in which Type II supernovae and pulsars are formed.
Wheeler, J. C.↗
Star formation - A theoretician's view
The present evaluation of the hypothesis that the birth of a sunlike star occurs in four stages, with a critical bipolar outflow phase, notes that observed molecular outflows cannot be initiated from circumstellar disks and must instead represent swept-up shells of gas that are driven by strong protostellar winds. The star can resolve its growing angular-momentum problem only by rejecting a fraction of the material that is fed through the disk in a powerful, magnetocentrifugally-driven wind. Empirical properties measured for well-collimated outflow sources can be accounted for by the interaction of this anisotropic wind with the ambient molecular cloud core.
Shu, Frank H.↗
Effect of Population III Multiplicity on Dark Star Formation
We numerically study the mutual interaction between dark matter (DM) and Population III (Pop III) stellar systems in order to explore the possibility of Pop III dark stars within this physical scenario. We perform a cosmological simulation, initialized at z approx. 100, which follows the evolution of gas and DM. We analyze the formation of the first mini halo at z approx. 20 and the subsequent collapse of the gas to densities of 10(exp 12)/cu cm. We then use this simulation to initialize a set of smaller-scale 'cut-out' simulations in which we further refine the DM to have spatial resolution similar to that of the gas. We test multiple DM density profiles, and we employ the sink particle method to represent the accreting star-forming region. We find that, for a range of DM configurations, the motion of the Pop III star-disk system serves to separate the positions of the protostars with respect to the DM density peak, such that there is insufficient DM to influence the formation and evolution of the protostars for more than approx. 5000 years. In addition, the star-disk system causes gravitational scattering of the central DM to lower densities, further decreasing the influence of DM over time. Any DM-powered phase of Pop III stars will thus be very short-lived for the typical multiple system, and DM will not serve to significantly prolong the life of Pop III stars.
Stacy, Athena↗
The problem of life in the universe and the mode of star formation.
Theoretical predictions that 3 out of 42 known stellar systems may support life if planets have evolved for these stars
STELLAR EVOLUTION↗
Infrared galaxies - Evolutionary stages of massive star formation
We cite evidence which indicates that infrared galaxies may represent evolutionary stages during which a large number of massive stars are being formed. The lifetimes of these stars would be rather short (1-10 million years), and the resulting supernova explosions could account for the level of nonthermal activity which often accompanies the thermal infrared emission.
Harwit, M.↗
Central star formation in early-type galaxies: Images and implications
We are reporting on an on-going study of strong central star-bursts in early type galaxies. These galaxies are brighter than m(pg) = 14.5 and are classified as type SO, SO/a, or Sa in the Uppsala General Catalog. All of them have unusually warm, bright far infrared sources for early-type galaxies, with F(100 microns)/F(60 microns) less than 2.0 and F(60 microns) greater than 2.5 Jy. Much of the infrared emission comes from the central few arcsec. Most of the galaxies were detected at 2380 MHz at Arecibo, with flux densities between 15 and 33 mJy. They have diffuse radio sources with a variety of morphologies, typically a few kpc in extent. Long slit spectra through the nucleus show that all have Balmer absorption lines, signifying a large B or A star population, and (O2) 3727 and Balmer emission lines, consistent with ionization by hot young stars. We have made optical continuum and emission line images of the galaxies to use in combination with the above data to study the causes and evolution of strong central star-bursts in early-type disk systems.
Dressel, L. L.↗
HST Observations of Star Formation in Interacting Galaxies: NGC 4194, the "Medusa"
Ultraviolet and visible imaging of the blue compact galaxy NGC4194 was obtained to survey the star-forming knots in the center of this galaxy. Photometry and image analysis were performed on these regions. Comparison with evolutionary tracks indicates many of the knots are reddened with a typical E(B-V)approx.0.3. The knot ages range from 10(exp 6-10(exp 8)years. Some of the knots may have masses 3-5x10(exp 5) solar mass. The FUV fluxes correspond to the flux from 60-3.8x10(exp 3) O5V stars.
Weistrop, D.↗
On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?
IRAS19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS19312+1950 in the range 5-550 microns using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 microns, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: approx. = 0.22 Stellar Mass of material at 280+/-18 K, and ≈1.6 Me of material at 157+/-3 K. The OI 63 micron line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 microns and CO2 at 15 microns. The spectral energy distribution is consistent with a massive, luminous (approx. 2 × 10(exp 4) Stellar Luminosity) central source surrounded by a dense, warm circumstellar disk and envelope of total mass approx. 500-700 Stellar Mass with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.
ISM: molecules aEuro" masers aEuro" stars↗
Submillimeter astronomy and the problem of star formation
Sources that have traditionally been called 'protostars,' because they were strong emitters of infrared radiation embedded in dust clouds, are now recognized to be 'newly formed' stars instead. Recent developments in submillimeter astronomy should permit a redoubling of efforts to find bodies that are the actual predecessors of newly formed stars. This renewed search for true protostars will be aided by advances that have occurred in submillimeter spectroscopy; these will permit an analysis of the physical conditions and chemical constitution of cooler protostellar clouds, and may provide insight into circumstances favoring protostellar collapse.
Harwit, M.↗
Competition of neutrino and gravitational radiation in neutron star formation
An investigation is conducted concerning the possibility that neutrino radiation rather than gravitational radiation may be the dominant way by which nonradial pulsations are damped out in a collapsing star. The effects of neutrino radiation on the nonradial oscillations of such objects are examined and damping times corresponding to a particular neutrino production mechanism are evaluated. The obtained results imply that neutrino radiation, by more rapid damping of the nonradial oscillations of a newly formed neutron star in a supernova explosion, would hinder gravitational radiation, thus reducing the possibility of its detection.
Kazanas, D.↗
Submillimeter astronomy and low mass star formation
Surveys made at wavelengths shorter than 100 microns are criticized in that they are biased against finding the coldest, most deeply obscured, and possibly youngest protostars. Large scale mapping of star forming regions in the submillimeter continuum and in lines such as CS H2CO and NH3, that are excited at high density, is identified as crucial in order to find clouds in the earliest stages of collapse into stars. The use of photometry from 1 to 1000 microns in characterizing the disks around embedded stars and T Tauri stars is outlined.
Beichman, Charles A.↗