scholarly journals Gas phase Elemental abundances in Molecular cloudS (GEMS)

2019 ◽  
Vol 624 ◽  
pp. A105 ◽  
Author(s):  
A. Fuente ◽  
D. G. Navarro ◽  
P. Caselli ◽  
M. Gerin ◽  
C. Kramer ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Hydrogen ◽  
Dense Phase ◽  
Dark Cloud ◽  
Chemical Modeling ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Two Phases ◽  
Strong Depletion

GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2 mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from AV ~ 3 to ~20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1−5 × 103 cm−3; and (ii) the dense phase, located at AV > 10 mag, with molecular hydrogen densities >104 cm−3. Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (AV ~ 3 mag) where C/H ~ 8 × 10−5 and C/O ~ 0.8−1, until the beginning of the dense phase at AV ~ 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S∕H ~ (0.4−2.2) × 10−6, an abundance ~7–40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S∕H ~ 8 × 10−8). Based on our chemical modeling, we constrain the value of ζH2 to ~(0.5–1.8) × 10−16 s−1 in the translucent cloud.

scholarly journals The Connection between Molecular Gas and Star Formation in XUV Disks

2016 ◽  
Vol 11 (S321) ◽  
pp. 214-216
Author(s):  
Linda C. Watson
Keyword(s):  
Star Formation ◽  
Molecular Hydrogen ◽  
Optical Disk ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions

AbstractWe found that star-forming regions in extended ultraviolet (XUV) disks are generally consistent with the molecular-hydrogen Kennicutt-Schmidt law that applies within the inner, optical disk. This is true for star formation rates based on Hα + 24 μm data or FUV + 24 μm data. We estimated that the star-forming regions have ages of 1 − 7 Myr and propose that the presence or absence of molecular gas provides an additional “clock” that may help distinguish between aging and stochasticity as the explanation for the low Hα-to-FUV flux ratios in XUV disks. This contribution is a summary of the work originally presented in Watson et al. (2016).

scholarly journals Shocked Molecular Hydrogen from Star Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 181-181 ◽  
Author(s):  
Adair P. Lane ◽  
John Bally
Keyword(s):  
Shock Waves ◽  
High Velocity ◽  
Molecular Hydrogen ◽  
Near Infrared ◽  
Young Stars ◽  
Emission Lines ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions ◽  
Post Shock

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.

Sardinia Radio Telescope (SRT) observations of Local Group dwarf galaxies

2017 ◽  
Vol 13 (S336) ◽  
pp. 109-112
Author(s):  
A. Tarchi ◽  
P. Castangia ◽  
G. Surcis ◽  
A. Brunthaler ◽  
K. M. Menten ◽  
...  
Keyword(s):  
Radio Telescope ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Radio Continuum ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Ngc 6822 ◽  
Almost All

AbstractThe dwarf galaxies in the Local Group (LG) reveal a surprising amount of spatial structuring. In particular, almost all non-satellite dwarfs belong to one of two planes that show a very pronounced symmetry. In order to determine if these structures in the LG are dynamically stable or, alternatively, if they only represent transient alignments, proper motion measurements of these galaxies are required. A viable method to derive proper motions is offered by VLBI studies of 22-GHz water (and 6.7-GHz methanol) maser lines in star-forming regions.In 2016, in the framework of the Early Science Program of the Sardinia Radio Telescope (SRT), we have conducted an extensive observational campaign to map the entire optical body of all the LG dwarf galaxies that belong to the two planes, at C and K band, in a search for methanol and water maser emission.Here, we outline the project and present its first results on 3 targets, NGC 6822, IC 1613, and WLM. While no luminous maser emission has been detected in these galaxies, a number of interesting weaker detections has been obtained, associated with particularly active star forming regions. In addition, we have produced deep radio continuum maps for these galaxies, aimed at investigating their star forming activity and providing an improved assessment of star formation rates in these galaxies.

A Swept-Up Molecular Bubble in L1551

1989 ◽  
Vol 120 ◽  
pp. 260-263
Author(s):  
Saeko S. Hayashi ◽  
Masahiko Hayashi ◽  
Norio Kaifu
Keyword(s):  
Uv Radiation ◽  
Spectral Type ◽  
Stellar Wind ◽  
Shell Structures ◽  
The Sun ◽  
Dark Cloud ◽  
Star Forming ◽  
Star Forming Regions ◽  
Molecular Outflow ◽  
Dominant Activity

The environment of the young stellar object IRS5 in L1551 dark cloud is a representative of the “protostellar disk and outflow” systems found in star forming regions. The bipolar molecular outflow there was discovered as the first of its kind a decade ago (Snell, Loren, and Plambeck 1980). Its location in the sky, that is, its proximity (160 pc), isolation, and its almost edge-on inclination have favored the observation in great detail. IRS5 is thought to have the spectral type G - K (Mundt et al. 1985) similar to the Sun, with its dominant activity in the stellar wind, and not in the UV radiation as in massive protostars. The blueshifted and redshifted outflow lobes are clearly resolved into a pair of shell structures. The successive studies, mostly in CO lines, have led to a model of the outflow in which the molecular material is accelerated at the edge of a cavity evacuated by the protostellar wind (e.g. Uchida et al. 1987, Rainey et al. 1987, Moriarty-Schieven and Snell 1988).

scholarly journals Ices in star forming regions

1997 ◽  
Vol 178 ◽  
pp. 45-60 ◽  
Author(s):  
A.G.G.M. Tielens ◽  
D.C.B. Whittet
Keyword(s):  
Ir Spectra ◽  
Gas Phase ◽  
Molecular Cloud ◽  
Oxidation Reactions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Interstellar Ice ◽  
Simple Molecules ◽  
Absorption Features ◽  
Cloud Material

IR spectra of sources associated with molecular cloud material show a variety of absorption features attributed to simple molecules, such as H2O, CO, CH3OH, CO2, CH4, and OCS in icy grain mantles. These identifications are reviewed. These molecules are formed through accretion and reaction of gas phase species on grain surfaces. The high abundance of CH3OH and CO2 point towards the importance of hydrogenation and oxidation reactions in this process. Observations also show that thermal outgassing is of great importance for the composition of interstellar ice mantles. Both these processes are discussed in some detail.

scholarly journals The ALMA-PILS survey: propyne (CH3CCH) in IRAS 16293–2422

2019 ◽  
Vol 631 ◽  
pp. A137 ◽  
Author(s):  
H. Calcutt ◽  
E. R. Willis ◽  
J. K. Jørgensen ◽  
P. Bjerkeli ◽  
N. F. W. Ligterink ◽  
...  
Keyword(s):  
Gas Phase ◽  
Spatial Scales ◽  
Excitation Temperature ◽  
Gas Phase Reactions ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Chemical Modelling ◽  
Low Mass ◽  
Grain Surface

Context. Propyne (CH3CCH), also known as methyl acetylene, has been detected in a variety of environments, from Galactic star-forming regions to extragalactic sources. These molecules are excellent tracers of the physical conditions in star-forming regions, allowing the temperature and density conditions surrounding a forming star to be determined. Aims. This study explores the emission of CH3CCH in the low-mass protostellar binary, IRAS 16293–2422, and examines the spatial scales traced by this molecule, as well as its formation and destruction pathways. Methods. Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey (PILS) were used to determine the abundances and excitation temperatures of CH3CCH towards both protostars. This data allows us to explore spatial scales from 70 to 2400 au. This data is also compared with the three-phase chemical kinetics model MAGICKAL, to explore the chemical reactions of this molecule. Results. CH3CCH is detected towards both IRAS 16293A and IRAS 16293B, and is found the hot corino components, one around each source, in the PILS dataset. Eighteen transitions above 3σ are detected, enabling robust excitation temperatures and column densities to be determined in each source. In IRAS 16293A, an excitation temperature of 90 K and a column density of 7.8 × 1015 cm−2 best fits the spectra. In IRAS 16293B, an excitation temperature of 100 K and 6.8 × 1015 cm−2 best fits the spectra. The chemical modelling finds that in order to reproduce the observed abundances, both gas-phase and grain-surface reactions are needed. The gas-phase reactions are particularly sensitive to the temperature at which CH4 desorbs from the grains. Conclusions. CH3CCH is a molecule whose brightness and abundance in many different regions can be utilised to provide a benchmark of molecular variation with the physical properties of star-forming regions. It is essential when making such comparisons, that the abundances are determined with a good understanding of the spatial scale of the emitting region, to ensure that accurate abundances are derived.

scholarly journals A New Molecular Core in L1641

1987 ◽  
Vol 115 ◽  
pp. 81-82
Author(s):  
H. Takaba ◽  
Y. Fukui
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
Hot Spots ◽  
Orion Nebula ◽  
Dark Cloud ◽  
Star Forming ◽  
Star Forming Regions ◽  
The North ◽  
Molecular Core ◽  
A Site

L1641 is a large dark cloud which extends 6.3 degree2 to the south of the Orion nebula (Lynds 1962). This region contains a reflection nebula, NGC 1999, several emission line stars and Herbig-Haro objects and is thought to be a site of on-going star formation. A CO(J = 1-0) map obtained with the Nagoya 1.5 m telescope (Takano 1983) revealed that CO hot spots extend further to the north by ∼ 30′ from NGC 1999. This suggests that L1641 may contain other regions of recent star formation. Therefore, we have mapped the L1641 cloud to investigate if there are other star-forming regions in it.

scholarly journals Resolved Spectroscopy of Gravitationally Lensed Galaxies at z≃2

2014 ◽  
Vol 10 (S309) ◽  
pp. 247-250
Author(s):  
Tucker Jones
Keyword(s):  
Gas Phase ◽  
Gravitational Lensing ◽  
Gravitational Interaction ◽  
Interstellar Gas ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Integral Field Spectroscopy ◽  
Isolated Galaxies ◽  
Spatially Resolved Spectroscopy

AbstractSpatially resolved spectroscopy is even more powerful when combined with magnification by gravitational lensing. I discuss observations of lensed galaxies at z≃2 with spatial resolution reaching 100 parsecs. Near-IR integral field spectroscopy reveals the kinematics, distribution and physical properties of star forming regions, and gas-phase metallicity gradients. Roughly two thirds of observed galaxies are isolated systems with coherent velocity fields, large velocity dispersion, multiple giant star-forming regions, and negative gas-phase metallicity gradients, suggestive of inside-out growth in gravitationally unstable disks. The remainder are undergoing mergers and have shallower metallicity gradients, indicating mixing of the interstellar gas via gravitational interaction. The metallicity gradients in isolated galaxies are consistent with simulations using standard feedback prescriptions, whereas simulations with enhanced feedback predict shallower gradients. These measurements therefore constrain the growth of galaxies from mergers and star formation as well as the regulatory feedback.

scholarly journals First Results from ATCA at Millimetre Wavelengths

2004 ◽  
Vol 221 ◽  
pp. 275-282
Author(s):  
Vincent Minier
Keyword(s):  
Star Formation ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Dust Emission ◽  
Protoplanetary Disks ◽  
High Angular Resolution ◽  
Star Forming ◽  
Star Forming Regions ◽  
First Results ◽  
Excellent Tool

The newly upgraded Australia Telescope Compact Array (ATCA) at millimetre wavelengths is the first millimetre interferometer to be built in the Southern Hemisphere. The full array will be operational in 2004-2005 and will provide arcsec angular resolution at 3 mm and 12 mm. This will be a unique instrument to study at high angular resolution the interstellar chemistry and more generally the star formation process, especially in the bulk of the galactic plane and in the Magellanic Clouds. The upgraded ATCA will also be an excellent tool to detect dust emission from nearby protoplanetary disks. In this paper I will present the first results from the upgraded ATCA at 3 mm and 12 mm. The result review will cover the topics of massive star formation and hot molecular cores dust emission from star-forming regions and detection of protoplanetary disks.

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