scholarly journals How runaway stars boost galactic outflows

2020 ◽  
Vol 494 (3) ◽  
pp. 3328-3341 ◽  
Author(s):  
Eric P Andersson ◽  
Oscar Agertz ◽  
Florent Renaud
Keyword(s):  
Interstellar Medium ◽  
Large Scale ◽  
Ob Stars ◽  
Star Forming ◽  
Star Forming Regions ◽  
Order Of Magnitude ◽  
Hydrodynamical Simulations ◽  
Scale Properties ◽  
Energy And Momentum ◽  
Runaway Stars

ABSTRACT Roughly 10 per cent of OB stars are kicked out of their natal clusters before ending their life as supernovae. These so-called runaway stars can travel hundreds of parsecs into the low-density interstellar medium, where momentum and energy from stellar feedback is efficiently deposited. In this work, we explore how this mechanism affects large-scale properties of the galaxy, such as outflows. To do so we use a new model that treats OB stars and their associated feedback processes on a star-by-star basis. With this model, we compare two hydrodynamical simulations of Milky Way-like galaxies, one where we include runaways, and one where we ignore them. Including runaway stars leads to twice as many supernovae explosions in regions with gas densities ranging from $10^{-5}\, \mathrm{\,cm^{-3}}$ to $10^{-3}\, \mathrm{\,cm^{-3}}$. This results in more efficient heating of the inter-arm regions, and drives strong galactic winds with mass loading factors boosted by up to one order of magnitude. These outflows produce a more massive and extended multiphase circumgalactic medium, as well as a population of dense clouds in the halo. Conversely, since less energy and momentum is released in the dense star-forming regions, the cold phase of the interstellar medium is less disturbed by feedback effects.

scholarly journals First detection of NHD and ND2 in the interstellar medium

2020 ◽  
Vol 641 ◽  
pp. A153
Author(s):  
M. Melosso ◽  
L. Bizzocchi ◽  
O. Sipilä ◽  
B. M. Giuliano ◽  
L. Dore ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Column Density ◽  
Molecular Spectroscopy ◽  
Far Infrared ◽  
Chemical Model ◽  
Star Forming ◽  
Star Forming Regions ◽  
Submillimeter Wavelengths ◽  
Order Of Magnitude ◽  
Low Mass

Context. Deuterium fractionation processes in the interstellar medium (ISM) have been shown to be highly efficient in the family of nitrogen hydrides. To date, observations have been limited to ammonia (NH2D, NHD2, ND3) and imidogen radical (ND) isotopologues. Aims. We want to explore the high-frequency windows offered by the Herschel Space Observatory to search for deuterated forms of the amidogen radical NH2 and to compare the observations against the predictions of our comprehensive gas-grain chemical model. Methods. Making use of the new molecular spectroscopy data recently obtained at high frequencies for NHD and ND2, we searched for both isotopologues in the spectral survey toward the Class 0 protostar IRAS 16293-2422, a source in which NH3, NH, and their deuterated variants have previously been detected. We used the observations carried out with HIFI (Heterodyne Instrument for the Far-Infrared) in the framework of the key program “Chemical Herschel surveys of star forming regions” (CHESS). Results. We report the first detection of interstellar NHD and ND2. Both species are observed in absorption against the continuum of the protostar. From the analysis of their hyperfine structure, accurate excitation temperature and column density values are determined. The latter were combined with the column density of the parent species NH2 to derive the deuterium fractionation in amidogen. We find a high deuteration level of amidogen radical in IRAS 16293-2422, with a deuterium enhancement about one order of magnitude higher than that predicted by earlier astrochemical models. Such a high enhancement can only be reproduced by a gas-grain chemical model if the pre-stellar phase preceding the formation of the protostellar system has a long duration: on the order of one million years. Conclusions. The amidogen D/H ratio measured in the low-mass protostar IRAS 16293-2422 is comparable to that derived for the related species imidogen and much higher than that observed for ammonia. Additional observations of these species will provide more insights into the mechanism of ammonia formation and deuteration in the ISM. Finally, we indicate the current possibilities to further explore these species at submillimeter wavelengths.

scholarly journals Double trouble: Gaia reveals (proto)planetary systems that may experience more than one dense star-forming environment

2020 ◽  
Vol 501 (1) ◽  
pp. L12-L17
Author(s):  
Christina Schoettler ◽  
Richard J Parker
Keyword(s):  
Planetary Systems ◽  
Young Star ◽  
Young Stars ◽  
Orion Nebula ◽  
External Effects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Ejection Process ◽  
Runaway Stars

ABSTRACT Planetary systems appear to form contemporaneously around young stars within young star-forming regions. Within these environments, the chances of survival, as well as the long-term evolution of these systems, are influenced by factors such as dynamical interactions with other stars and photoevaporation from massive stars. These interactions can also cause young stars to be ejected from their birth regions and become runaways. We present examples of such runaway stars in the vicinity of the Orion Nebula Cluster (ONC) found in Gaia DR2 data that have retained their discs during the ejection process. Once set on their path, these runaways usually do not encounter any other dense regions that could endanger the survival of their discs or young planetary systems. However, we show that it is possible for star–disc systems, presumably ejected from one dense star-forming region, to encounter a second dense region, in our case the ONC. While the interactions of the ejected star–disc systems in the second region are unlikely to be the same as in their birth region, a second encounter will increase the risk to the disc or planetary system from malign external effects.

scholarly journals X-Ray Coronae from Stars

1998 ◽  
Vol 188 ◽  
pp. 13-16
Author(s):  
R. Pallavicini
Keyword(s):  
Open Clusters ◽  
Temperature Structure ◽  
List Type ◽  
Star Forming ◽  
Spectroscopic Observations ◽  
Star Forming Regions ◽  
Complete Mapping ◽  
Sky Survey ◽  
Order Of Magnitude ◽  
Age Range

A number of major advances in stellar coronal physics have occurred since 1990 mainly as a consequence of imaging observations by ROSAT and spectroscopic observations by ASCA. These can be summarised as follows: 1.an all-sky survey has been performed by ROSAT at a sensitivity of ~ 2 × 10−13 erg cm−2 s−1, complemented by pointed observations an order of magnitude deeper;2.complete mapping and deeper pointings have been obtained for virtually all open clusters closer than ~ 500 pc, and covering the age range from ~ 30 Myr to ~ 700 Myr;3.complete mapping and deeper paintings have been obtained for several Star Forming Regions (SFRs) covering the age range ~ 1 to ~ 10 Myr;4.spectroscopic observations of bright coronal sources have been obtained with EUVE and ASCA allowing the derivation of the temperature structure and elemental abundances.

scholarly journals The Violent Interstellar Medium of Nearby Dwarf Galaxies

1999 ◽  
Vol 16 (1) ◽  
pp. 106-112 ◽  
Author(s):  
Fabian Walter
Keyword(s):  
Interstellar Medium ◽  
Gamma Ray ◽  
Dwarf Galaxies ◽  
Young Star ◽  
Stellar Winds ◽  
Star Forming ◽  
Star Forming Regions ◽  
Supernova Explosions ◽  
High Velocity Clouds ◽  
Ob Associations

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.

scholarly journals Luminous IR Galaxies: Evolution and Molecular Gas

1997 ◽  
Vol 159 ◽  
pp. 439-440 ◽  
Author(s):  
Yu Gao
Keyword(s):  
Molecular Gas ◽  
Infrared Galaxies ◽  
Galaxy Interactions ◽  
Merging Galaxies ◽  
Star Forming ◽  
Luminous Infrared Galaxies ◽  
Star Forming Regions ◽  
Ir Sources ◽  
Order Of Magnitude ◽  
The Universe

Luminous infrared galaxies (LIRGs), denned by the criterion LIR ≳ 2 × 1011L⊙ (for H0=75 kms−1 Mpc−1), are the most powerful IR sources in the Universe, with most of their emission (~ 90%) in the far-IR. Most LIRGs are interacting/merging galaxies with large amounts of molecular gas as revealed by CO surveys (Sanders et al. 1991; Solomon et al. 1996). However, whether starbursts or dust-enshrouded AGNs/QSOs dominate the IR luminosity is not resolved.CO may not trace the active star-forming regions where gas density is more than one order of magnitude higher than the average. Dense molecular gas is better traced by high dipole-moment molecules like HCN and CS (e.g., Nguyen-Q-Rieu et al. 1992; Gao & Solomon 1996). Therefore, it is essential to survey HCN emission in a large sample of LIRGs to better reveal the nature of LIRGs. We here study IR and molecular gas properties vs. galaxy-galaxy interactions in LIRGs over various merging phases to trace their evolution and explore some links among interactions, starbursts, and AGN phenomena.

scholarly journals The ACCELERATION programme: I. Cosmology with the redshift drift

2019 ◽  
Vol 492 (2) ◽  
pp. 2044-2057
Author(s):  
Ryan Cooke
Keyword(s):  
Local Density ◽  
Current Data ◽  
Cosmological Redshift ◽  
Star Forming ◽  
Star Forming Regions ◽  
Neutral Gas ◽  
Small Correction ◽  
Redshift Drift ◽  
Universal Expansion ◽  
Order Of Magnitude

ABSTRACT Detecting the change of a cosmological object’s redshift due to the time evolution of the Universal expansion rate is an ambitious experiment that will be attempted with future telescope facilities. In this paper, we describe the ACCELERATION programme, which aims to study the properties of the most underdense regions of the Universe. One of the highlight goals of this programme is to prepare for the redshift drift measurement. Using the EAGLE cosmological hydrodynamic simulations, we estimate the peculiar acceleration of gas in galaxies and the Lyα forest. We find that star-forming ‘cold neutral gas’ exhibits large peculiar acceleration due to the high local density of baryons near star-forming regions. We conclude that absorption by cold neutral gas is unlikely to yield a detection of the cosmological redshift drift. On the other hand, we find that the peculiar accelerations of Lyα forest absorbers are more than an order of magnitude below the expected cosmological signal. We also highlight that the numerous low H i column density systems display lower peculiar acceleration. Finally, we propose a new ‘Lyα cell’ technique that applies a small correction to the wavelength calibration to secure a relative measurement of the cosmic drift between two unrelated cosmological sources at different redshifts. For suitable combinations of absorption lines, the cosmological signal can be more than doubled, while the affect of the observer peculiar acceleration is mitigated. Using current data of four suitable Lyα cells, we infer a limit on the cosmological redshift drift to be $\dot{v}_{\rm obs}\lt 65~{\rm m~s}^{-1}~{\rm yr}^{-1}$ (2σ).

scholarly journals The atomic hydrogen/molecular cloud association: an unavoidable relationship

1991 ◽  
Vol 147 ◽  
pp. 37-40
Author(s):  
G. Joncas
Keyword(s):  
Atomic Hydrogen ◽  
Molecular Clouds ◽  
Large Scale ◽  
Young Stars ◽  
Physical Processes ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
The Impact

The presence of HI in the interstellar medium is ubiquitous. HI is the principal actor in the majority of the physical processes at work in our Galaxy. Restricting ourselves to the topics of this symposium, atomic hydrogen is involved with the formation of molecular clouds and is one of the byproducts of their destruction by young stars. HI has different roles during a molecular cloud's life. I will discuss here a case of coexisting HI and H2 at large scale and the origin of HI in star forming regions. For completeness' sake, it should be mentionned that there are at least three other aspects of HI involvement: HI envelopes around molecular clouds, the impact of SNRs (see work on IC 443), and the role of HI in quiescent dark clouds (see van der Werf's work).

scholarly journals Distribution of star-forming complexes and the structure of our Galaxy

2003 ◽  
Vol 212 ◽  
pp. 431-440 ◽  
Author(s):  
Delphine Russeil
Keyword(s):  
Large Scale ◽  
Stellar Population ◽  
Line Of Sight ◽  
H Ii Regions ◽  
Spiral Arms ◽  
Ob Stars ◽  
Star Forming ◽  
Optical Images ◽  
External Galaxies

The determination of the external galaxies morphology is generally based on their appearance on optical images. At these wavelengths young stellar population and their associated H ii regions, which can be grouped into star-forming complexes, appear preferentially located along spiral arms. Hence, it is naturally to use the same tracers to delineate the arms of our own Galaxy. But, where for external galaxies the distribution of star-forming complexes along the spiral arms is generally evident from direct imaging, for our Galaxy the spiral arms are strung out along the line of sight, leading to the superposition and mixing of information from the different complexes in the spiral arms making it difficult to distinguish them. Thus to access to the spatial distribution of young objects, hence to the large scale structure of our Galaxy, it is required first to identify and collect star-forming complexes (molecular clouds – H ii regions – OB stars) and then to determine their distance. In this framework I review the observational results and difficulties concerning the distribution of star-forming complexes and the determination of the structure of our Galaxy.

scholarly journals Direct estimation of electron density in the Orion Bar PDR from mm-wave carbon recombination lines

2019 ◽  
Vol 625 ◽  
pp. L3 ◽  
Author(s):  
S. Cuadrado ◽  
P. Salas ◽  
J. R. Goicoechea ◽  
J. Cernicharo ◽  
A. G. G. M. Tielens ◽  
...  
Keyword(s):  
Electron Density ◽  
Critical Role ◽  
Elemental Abundance ◽  
Hyperfine Line ◽  
Line Profiles ◽  
Star Forming ◽  
Star Forming Regions ◽  
Trace Species ◽  
Order Of Magnitude ◽  
Uv Photons

Context. A significant fraction of the molecular gas in star-forming regions is irradiated by stellar UV photons. In these environments, the electron density (ne) plays a critical role in the gas dynamics, chemistry, and collisional excitation of certain molecules. Aims. We determine ne in the prototypical strongly irradiated photodissociation region (PDR), the Orion Bar, from the detection of new millimeter-wave carbon recombination lines (mmCRLs) and existing far-IR [13C II] hyperfine line observations. Methods. We detect 12 mmCRLs (including α, β, and γ transitions) observed with the IRAM 30 m telescope, at ∼25″ angular resolution, toward the H/H2 dissociation front (DF) of the Bar. We also present a mmCRL emission cut across the PDR. Results. These lines trace the C+/C/CO gas transition layer. As the much lower frequency carbon radio recombination lines, mmCRLs arise from neutral PDR gas and not from ionized gas in the adjacent H II region. This is readily seen from their narrow line profiles (Δv = 2.6 ± 0.4 km s−1) and line peak velocities (vLSR = +10.7 ± 0.2 km s−1). Optically thin [13C II] hyperfine lines and molecular lines – emitted close to the DF by trace species such as reactive ions CO+ and HOC+ – show the same line profiles. We use non-LTE excitation models of [13C II] and mmCRLs and derive ne = 60–100 cm−3 and Te = 500–600 K toward the DF. Conclusions. The inferred electron densities are high, up to an order of magnitude higher than previously thought. They provide a lower limit to the gas thermal pressure at the PDR edge without using molecular tracers. We obtain Pth ≥ (2−4) × 108 cm−3 K assuming that the electron abundance is equal to or lower than the gas-phase elemental abundance of carbon. Such elevated thermal pressures leave little room for magnetic pressure support and agree with a scenario in which the PDR photoevaporates.

scholarly journals Dusty magnetohydrodynamics in star-forming regions

2010 ◽  
Vol 76 (3-4) ◽  
pp. 569-578
Author(s):  
S. VAN LOO ◽  
S. A. E. G. FALLE ◽  
T. W. HARTQUIST ◽  
O. HAVNES ◽  
G. E. MORFILL
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Number Density ◽  
Star Forming ◽  
Star Forming Regions ◽  
Neutral Gas ◽  
Gas Phase Ions ◽  
Fractional Ionization ◽  
Magnetohydrodynamic Models ◽  
The Magnetic Field

AbstractStar formation occurs in dark molecular regions where the number density of hydrogen nuclei nH exceeds 104 cm−3 and the fractional ionization is 10−7 or less. Dust grains with sizes ranging up to tenths of microns and perhaps down to tens of nanometers contain just less than 1% of the mass. Recombination on grains is important for the removal of gas-phase ions, which are produced by cosmic rays penetrating the dark regions. Collisions of neutrals with charged grains contribute significantly to the coupling of the magnetic field to the neutral gas. Consequently, the dynamics of the grains must be included in the magnetohydrodynamic models of large-scale collapse, the evolution of waves and the structures of shocks important in star formation.

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