Studies of the distinct regions due to CO selective dissociation in the Aquila molecular cloud

Aims. We investigate the role of selective dissociation in the process of star formation by comparing the physical parameters of protostellar-prestellar cores and the selected regions with the CO isotope distributions in photo-dissociation regions. We seek to understand whether there is a better connection between the evolutionary age of star forming regions and the effect of selective dissociation Methods. We used wide-field observations of the 12CO, 13CO, and C18O (J = 1–0) emission lines to study the ongoing star formation activity in the Aquila molecular region, and we used the 70 and 250 μm data to describe the heating of the surrounding material and as an indicator of the evolutionary age of the core. Results. The protostellar-prestellar cores are found at locations with the highest C18O column densities and their increasing evolutionary age coincides with an increasing 70μm/250μm emission ratio at their location. The evolutionary age of the cores may also follow from the 13CO versus C18O abundance ratio, which decreases with increasing C18O column densities. The original mass has been estimated for nine representative star formation regions and the original mass of the region correlates well with the integrated 70 μm flux density. Similarly, the X13CO/XC18O ratio, which provides the dissociation rate for these regions correlates with the 70 μm/250 μm flux density ratio and reflects the evolutionary age of the star formation activity.

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Investigations of dust heating in M81, M83 and NGC 2403 with Herschel and Spitzer

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312008812 ◽

2011 ◽

Vol 7 (S284) ◽

pp. 97-100

Author(s):

George J. Bendo ◽

Keyword(s):

Star Formation ◽

Flux Density ◽

Near Infrared ◽

Dust Emission ◽

Far Infrared ◽

Spectral Energy ◽

Star Forming ◽

Star Forming Regions ◽

Star Formation Activity ◽

Density Ratios

AbstractWe use Herschel Space Observatory and Spitzer Space Telescope 70-500 μm data along with ground-based optical and near-infrared data to understand how dust heating in the nearby face-on spiral galaxies M81, M83, and NGC 2403 is affected by the starlight from all stars and by the radiation from star-forming regions. We find that 70/160 μm flux density ratios tend to be more strongly influenced by star-forming regions. However, the 250/350 and 350/500 μm micron flux density ratios are more strongly affected by the light from the total stellar populations, suggesting that the dust emission at > 250 μm originates predominantly from a component that is colder than the dust seen at <160 μm and that is relatively unaffected by star formation activity. We conclude by discussing the implications of this for modelling the spectral energy distributions of both nearby and more distant galaxies and for using far-infrared dust emission to trace star formation.

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The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). IV. Star Formation Signatures in G023.477

The Astrophysical Journal ◽

10.3847/1538-4357/ac2365 ◽

2021 ◽

Vol 923 (2) ◽

pp. 147

Author(s):

Kaho Morii ◽

Patricio Sanhueza ◽

Fumitaka Nakamura ◽

James M. Jackson ◽

Shanghuo Li ◽

...

Keyword(s):

Star Formation ◽

Magnetic Fields ◽

Line Emission ◽

High Mass ◽

Mass Star ◽

Dark Cloud ◽

Early Stages ◽

Star Formation Activity ◽

Prestellar Cores ◽

The Masses

Abstract With a mass of ∼1000 M ⊙ and a surface density of ∼0.5 g cm−2, G023.477+0.114, also known as IRDC 18310-4, is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 μm Dark High-mass Clumps in Early Stages. We have conducted ∼1.″2 resolution observations with ALMA at 1.3 mm in dust continuum and molecular line emission. We have identified 11 cores, whose masses range from 1.1 to 19.0 M ⊙. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H2CO and CH3OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8–19 M ⊙). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.

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Multiwavelength dissection of a massive heavily dust-obscured galaxy and its blue companion at z∼2

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039577 ◽

2021 ◽

Vol 646 ◽

pp. A127

Author(s):

M. Hamed ◽

L. Ciesla ◽

M. Béthermin ◽

K. Małek ◽

E. Daddi ◽

...

Keyword(s):

Star Formation ◽

Spectral Energy Distribution ◽

Gas Content ◽

Spectral Energy ◽

Physical Parameters ◽

Molecular Gas ◽

Star Forming ◽

Attenuation Law ◽

Star Formation Activity ◽

Attenuation Laws

Aims. We study a system of two galaxies, Astarte and Adonis, at z ∼ 2. At this time, the Universe was undergoing the peak of its star formation activity. Astarte is a dusty star-forming galaxy at the massive end of the main sequence (MS), and Adonis is a less massive companion galaxy that is bright in the ultraviolet and has an optical spectroscopic redshift. We investigate whether this ultramassive galaxy is quenching, and whether it has always been on the MS of star-forming galaxies. Methods. We used the code CIGALE to model the spectral energy distribution. The code relies on the energetic balance between the ultraviolet and the infrared. We derived some of the key physical properties of Astarte and Adonis, mainly their star formation rates (SFRs), stellar masses, and dust luminosities. We inspected the variation of the physical parameters depending on the assumed dust-attenuation law. We also estimated the molecular gas mass of Astarte from its CO emission, using different αCO and transition ratios (r31), and we discuss the implication of the various assumptions on the gas-mass derivation. Reults. We find that Astarte exhibits a MS-like star formation activity, and Adonis is undergoing a strong starburst phase. The molecular gas mass of Astarte is far lower than the gas fraction of typical star-forming galaxies at z = 2. This low gas content and high SFR result in a depletion time of 0.22 ± 0.07 Gyr, which is slightly shorter than expected for a MS galaxy at this redshift. The CO luminosity relative to the total infrared luminosity suggests a MS-like activity when we assume a galactic conversion factor and a low transition ratio. The SFR of Astarte is on the same order when different attenuation laws are used, unlike its stellar mass, which increases when shallow attenuation laws are used (∼1 × 1011 M⊙ assuming a Calzetti relation, versus ∼4 × 1011 M⊙ assuming a shallow attenuation law). We discuss these properties and suggest that Astarte might be experiencing a recent decrease in star formation activity and is quenching through the MS following a starburst epoch.

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The Herschel view of the dense core population in the Ophiuchus molecular cloud

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936442 ◽

2020 ◽

Vol 638 ◽

pp. A74 ◽

Cited By ~ 10

Author(s):

B. Ladjelate ◽

Ph. André ◽

V. Könyves ◽

D. Ward-Thompson ◽

A. Men’shchikov ◽

...

Keyword(s):

Star Formation ◽

Dynamic Range ◽

Far Infrared ◽

High Dynamic Range ◽

Young Stellar Objects ◽

Mass Star ◽

Decomposition Algorithms ◽

Dense Cores ◽

Star Formation Activity ◽

Prestellar Cores

Context. Herschel observations of nearby clouds in the Gould Belt support a paradigm for low-mass star formation, starting with the generation of molecular filaments, followed by filament fragmentation, and the concentration of mass into self-gravitating prestellar cores. In the case of the Ophiuchus molecular complex, a rich star formation activity has been documented for many years inside the clumps of L1688, the main and densest cloud of the complex, and in the more quiescent twin cloud L1689 thanks to extensive surveys at infrared and other wavelengths. Aims. With the unique far-infrared and submillimeter continuum imaging capabilities of the Herschel Space observatory, the closeby (d = 139 pc) Ophiuchus cloud was extensively mapped at five wavelengths from 70 to 500 μm with the aim of providing a complete census of dense cores in this region, including unbound starless cores, bound prestellar cores, and protostellar cores. Methods. Taking full advantage of the high dynamic range and multi-wavelength nature of the Herschel data, we used the multi-scale decomposition algorithms getsources and getfilaments to identify an essentially complete sample of dense cores and filaments in the cloud and study their properties. Results. The densest clouds of the Ophiuchus complex, L1688 and L1689, which thus far are only indirectly described as filamentary regions owing to the spatial distribution of their young stellar objects, are now confirmed to be dominated by filamentary structures. The tight correlation observed between prestellar cores and filamentary structures in L1688 and L1689 supports the view that solar-type star formation occurs primarily in dense filaments. While the sub clouds of the complex show some disparities, L1689 being apparently less efficient than L1688 at forming stars when considering their total mass budgets, both sub clouds share almost the same prestellar core formation efficiency in dense molecular gas. We also find evidence in the Herschel data for a remarkable concentric geometrical configuration in L1688 which is dominated by up to three arc-like compression fronts and has presumably been created by shockwave events emanating from the Sco OB2 association, including the neighboring massive (O9V) star σ Sco. Conclusions. Our Herschel study of the well-documented Ophiuchus region has allowed us to further analyze the influence of several early-type (OB) stars surrounding the complex, thus providing positive feedback and enhancing star formation activity in the dense central part of the region, L1688.

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On the Star-formation History in the LMC: Observations of the Interstellar C18O/C17O Ratio

Symposium - International Astronomical Union ◽

10.1017/s0074180900118029 ◽

1999 ◽

Vol 190 ◽

pp. 275-276

Author(s):

Arto Heikkilä ◽

Lars E.B. Johansson ◽

Hans Olofsson

Keyword(s):

Star Formation ◽

Massive Stars ◽

Density Ratio ◽

Abundance Ratio ◽

Initial Mass Function ◽

Star Formation History ◽

Intermediate Mass ◽

Stellar Nucleosynthesis ◽

Intermediate Mass Stars ◽

Formation History

The re-cycling of gas between stars and the interstellar medium (ISM) leads to a gradual metal-enrichment of a galaxy. Accordingly, information on the chemical evolution of a galaxy, e.g., its star-formation history (SFH), is contained in the chemical composition of the ISM. In this context, the abundance ratio of the rare oxygen isotopes, 18O/17O (usually taken as the C18O/C17O column density ratio), appears to be a particularly promising probe of the SFH. According to present understanding of stellar nucleosynthesis, 17O is mainly produced in intermediate-mass stars (say a few to ten M⊙) while 18O is synthesised in massive stars (say >10M⊙) (e.g., Prantzos et al. 1996). Thus, the 18O/17O abundance ratio possibly reflects the relative number of massive stars compared to intermediate-mass stars, and thereby (qualitatively) constrains the SFH in terms of the average star-formation rate (SFR) and the initial mass-function (IMF). However, it should be remembered that the stellar nucleosynthesis of 17,18O is not yet fully understood, leaving room for other interpretations of the 18O/17O ratio.

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The EDGE-CALIFA Survey: The Resolved Star Formation Efficiency and Local Physical Conditions

The Astrophysical Journal ◽

10.3847/1538-4357/ac2b29 ◽

2021 ◽

Vol 923 (1) ◽

pp. 60

Author(s):

V. Villanueva ◽

A. Bolatto ◽

S. Vogel ◽

R. C. Levy ◽

S. F. Sánchez ◽

...

Keyword(s):

Star Formation ◽

High Surface ◽

Formation Rate ◽

Radial Dependence ◽

Clear Correlation ◽

Physical Parameters ◽

Equilibrium Pressure ◽

Star Formation Activity ◽

Formation Efficiency ◽

Co Emission

Abstract We measure the star formation rate (SFR) per unit gas mass and the star formation efficiency (SFEgas for total gas, SFEmol for the molecular gas) in 81 nearby galaxies selected from the EDGE-CALIFA survey, using 12CO (J = 1–0) and optical IFU data. For this analysis we stack CO spectra coherently by using the velocities of Hα detections to detect fainter CO emission out to galactocentric radii r gal ∼ 1.2r 25 (∼3R e) and include the effects of metallicity and high surface densities in the CO-to-H2 conversion. We determine the scale lengths for the molecular and stellar components, finding a close to 1:1 relation between them. This result indicates that CO emission and star formation activity are closely related. We examine the radial dependence of SFEgas on physical parameters such as galactocentric radius, stellar surface density Σ⋆, dynamical equilibrium pressure P DE, orbital timescale τ orb, and the Toomre Q stability parameter (including star and gas Q star+gas). We observe a generally smooth, continuous exponential decline in the SFEgas with r gal. The SFEgas dependence on most of the physical quantities appears to be well described by a power law. Our results also show a flattening in the SFEgas–τ orb relation at log [ τ orb ] ∼ 7.9 – 8.1 and a morphological dependence of the SFEgas per orbital time, which may reflect star formation quenching due to the presence of a bulge component. We do not find a clear correlation between SFEgas and Q star+gas.

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Fragmentation and filaments at the onset of star and cluster formation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935410 ◽

2019 ◽

Vol 631 ◽

pp. A72 ◽

Cited By ~ 2

Author(s):

Y. Lin ◽

T. Csengeri ◽

F. Wyrowski ◽

J. S. Urquhart ◽

F. Schuller ◽

...

Keyword(s):

Star Formation ◽

Physical Properties ◽

Structure Formation ◽

Point Sources ◽

High Mass ◽

Small Scale ◽

Physical Parameters ◽

Star Formation Activity ◽

Self Gravity ◽

Compact Sources

Context. The structure formation of the dense interstellar material and the fragmentation of clumps into cores is a fundamental step for understanding how stars and stellar clusters form. Aims. We aim to establish a statistical view of clump fragmentation at subparsec scales based on a large sample of massive clumps selected from the ATLASGAL survey. Methods. We used the APEX/SABOCA camera at 350 μm to image clumps at a resolution of 8.″5, corresponding to physical scales of < 0.2 pc at a distance < 5 kpc. The majority of the sample consists of massive clumps that are weak or in absorption at 24 μm. We resolved spherical and filamentary structures and identified the population of compact sources. Complemented with archival Herschel data, we derived the physical properties, such as dust temperature, mass, and bolometric luminosity of clumps and cores. We used association with mid-infrared 22−24 μm and 70 μm point sources to determine the star formation activity of the cores. We then statistically assessed their physical properties and the fragmentation characteristics of massive clumps. Results. We detect emission at 350 μm toward all targets and find that it typically exhibits a filamentary (-like) morphology and hosts a population of compact sources. Using Gaussclumps, we identify 1120 compact sources and derive the physical parameters and star formation activity for 971 of these, 874 of which are associated with 444 clumps. We find a moderate correlation between the clump fragmentation levels with the clump gas density and the predicted number of fragments with a pure Jeans fragmentation scenario. We find a strong correlation between the mass of the most massive fragment and the total clump mass, suggesting that self-gravity may play an important role in the small-scale structure formation of the clumps. Finally, due to the improved angular resolution compared to ATLASGAL, we are able to identify 27 massive quiescent cores with Mcore > 100 M⊙ within 5 kpc; these are massive enough to be self-gravitating, but do not yet show any sign of star formation. This sample therefore comprises promising candidates of massive prestellar cores or deeply embedded high-mass protostars. Conclusions. The submillimeter observations of the massive clumps that are weak or completely dark at 24 μm reveal rich filamentary structures and an embedded population of compact cores. The maximum core mass is likely determined by the self-gravity of the clump. The rarity of massive prestellar core candidates implies short collapse timescales for dense structures.

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The history of star formation in the Galactic young open cluster NGC 6231

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307002736 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 485-485

Author(s):

Mario E. van den Ancker

Keyword(s):

Star Formation ◽

Open Cluster ◽

Mass Function ◽

Star Formation History ◽

Wide Field ◽

Star Formation Activity ◽

Formation History ◽

Young Open Cluster ◽

History Of ◽

Low Mass

AbstractWe study the star formation history of the galactic young open cluster NGC 6231 using new, deep, wide-field BVRI imaging. Contrary to previous suggestions, we do not find a lack of low-mass cluster members; our derived mass function is compatible with a Salpeter IMF. The star formation history of NGC 6231 appears to be bi-modal, with a first wave of star formation activity 3–5 Myr ago, followed by a new generation of stars forming ~ 1 Myr ago.

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The evolution of star formation in QSOs according to WISE

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320001659 ◽

2020 ◽

Vol 15 (S359) ◽

pp. 33-34

Author(s):

K. A. Cutiva-Alvarez ◽

R. Coziol ◽

J. P. Torres-Papaqui ◽

H. Andernach ◽

A. C. Robleto-Orús

Keyword(s):

Star Formation ◽

Gradual Increase ◽

A Value ◽

Star Formation Activity ◽

The Mean ◽

Lower Redshift

AbstractUsing WISE data, we calibrated the W2-W3 colors in terms of star formation rates (SFRs) and applied this calibration to a sample of 1285 QSOs with the highest flux quality, covering a range in redshift from z ˜ 0.3 to z ˜ 3.8. According to our calibration, the SFR increases continuously, reaching a value at z ˜ 3.8 about 3 times higher on average than at lower redshift. This increase in SFR is accompanied by an increase of the BH mass by a factor 100 and a gradual increase of the mean Eddington ratio from 0.1 to 0.3 up to z ˜ 1.5 – 2.0, above which the ratio stays constant, despite a significant increase in BH mass. Therefore, QSOs at high redshifts have both more active BHs and higher levels of star formation activity.

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Modelling H2 and its effects on star formation using a joint implementation of gadget-3 and KROME

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab1015 ◽

2021 ◽

Vol 504 (2) ◽

pp. 2325-2345

Author(s):

Emanuel Sillero ◽

Patricia B Tissera ◽

Diego G Lambas ◽

Stefano Bovino ◽

Dominik R Schleicher ◽

...

Keyword(s):

Star Formation ◽

Formation Rate ◽

Physical Parameters ◽

Density Profiles ◽

Star Forming ◽

Chemical Enrichment ◽

Numerical Resolution ◽

Stellar Radiation ◽

Wide Range ◽

The Impact

ABSTRACT We present p-gadget3-k, an updated version of gadget-3, that incorporates the chemistry package krome. p-gadget3-k follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H2 and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H2 dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of star formation rate (SFR) and H2 are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H2 as a function of gas density and temperature. A star formation algorithm that takes into account the H2 fraction together with a treatment for the local stellar radiation field improves the agreement with observed H2 abundances over a wide range of gas densities and with the molecular Kennicutt–Schmidt law, implying a more realistic modelling of the star formation process.

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