scholarly journals How do bound star clusters form?

2020 ◽  
Vol 494 (1) ◽  
pp. 624-641 ◽  
Author(s):  
Mark R Krumholz ◽  
Christopher F McKee
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Conveyor Belt ◽  
Young Stellar Objects ◽  
Gas Removal ◽  
Gas Accretion

ABSTRACT Gravitationally bound clusters that survive gas removal represent an unusual mode of star formation in the Milky Way and similar spiral galaxies. While forming, they can be distinguished observationally from unbound star formation by their high densities, virialized velocity structures, and star formation histories that accelerate towards the present, but extend multiple free-fall times into the past. In this paper, we examine several proposed scenarios for how such structures might form and evolve, and carry out a Bayesian analysis to test these models against observed distributions of protostellar age, counts of young stellar objects relative to gas, and the overall star formation rate of the Milky Way. We show that models in which the acceleration of star formation is due either to a large-scale collapse or a time-dependent increase in star formation efficiency are unable to satisfy the combined set of observational constraints. In contrast, models in which clusters form in a ‘conveyor belt’ mode where gas accretion and star formation occur simultaneously, but the star formation rate per free-fall time is low, can match the observations.

scholarly journals Cloud fragmentation cascades and feedback: on reconciling an unfettered inertial range with a low star formation rate

2020 ◽  
Vol 493 (1) ◽  
pp. 815-820
Author(s):  
Eric G Blackman
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Dynamic Range ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
Star Forming ◽  
Cloud Complex

ABSTRACT Molecular cloud complexes exhibit both (i) an unfettered Larson-type spectrum over much of their dynamic range, whilst (ii) still producing a much lower star formation rate than were this cascade to remain unfettered all the way down to star-forming scales. Here we explain the compatibility of these attributes with minimalist considerations of a mass-conserving fragmentation cascade, combined with estimates of stellar feedback. Of importance is that the amount of feedback needed to abate fragmentation and truncate the complex decreases with decreasing scale. The scale at which the feedback momentum matches the free-fall momentum marks a transition scale below most of the cascade is truncated and the molecular cloud complex dissipated. For a 106 M⊙ giant molecular cloud (GMC) complex starting with radius of ∼50 pc, the combined feedback from young stellar objects, supernovae, radiation, and stellar winds for a GMC cloud complex can truncate the cascade within an outer free-fall time but only after the cascade reaches parsec scales.

scholarly journals Turbulence, feedback, and slow star formation

2006 ◽  
Vol 2 (S237) ◽  
pp. 378-383
Author(s):  
Mark R. Krumholz
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
Striking Result ◽  
Wide Range ◽  
Individual Cluster

AbstractOne of the outstanding puzzles about star formation is why it proceeds so slowly. Giant molecular clouds convert only a few percent of their gas into stars per free-fall time, and recent observations show that this low star formation rate is essentially constant over a range of scales from individual cluster-forming molecular clumps in the Milky Way to entire starburst galaxies. This striking result is perhaps the most basic fact that any theory of star formation must explain. I argue that a model in which star formation occurs in virialized structures at a rate regulated by supersonic turbulence can explain this observation. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks and keeps star-forming structures from wandering too far from virial balance. This model is able to reproduce observational results covering a wide range of scales, from the formation times of young clusters to the extragalactic IR-HCN correlation, and makes additional quantitative predictions that will be testable in the next few years.

scholarly journals Testing the star formation scaling relations in the clumps of the North American and Pelican nebulae cloud complex

2020 ◽  
Vol 500 (3) ◽  
pp. 3123-3141
Author(s):  
Swagat R Das ◽  
Jessy Jose ◽  
Manash R Samal ◽  
Shaobo Zhang ◽  
Neelam Panwar
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Free Fall ◽  
Scaling Relations ◽  
Time Model ◽  
Fall Time ◽  
The North ◽  
Crossing Time

ABSTRACT The processes that regulate star formation within molecular clouds are still not well understood. Various star formation scaling relations have been proposed as an explanation, one of which is to formulate a relation between the star formation rate surface density $\rm \Sigma _{SFR}$ and the underlying gas surface density $\rm \Sigma _{gas}$. In this work, we test various star formation scaling relations, such as the Kennicutt–Schmidt relation, the volumetric star formation relation, the orbital time model, the crossing time model and the multi free-fall time-scale model, towards the North American Nebula and Pelican Nebula and in the cold clumps associated with them. Measuring stellar mass from young stellar objects and gaseous mass from CO measurements, we estimate the mean $\rm \Sigma _{SFR}$, the star formation rate per free-fall time and the star formation efficiency for clumps to be 1.5 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.009 and 2.0 per cent, respectively, while for the whole region covered by both nebulae (which we call the ‘NAN’ complex) the values are 0.6 $\rm M_{\odot}\, yr^{-1}\, kpc^{-2}$, 0.0003 and 1.6 per cent, respectively. For the clumps, we notice that the observed properties are in line with the correlation obtained between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$, and between $\rm \Sigma _{SFR}$ and $\rm \Sigma _{gas}$ per free-fall time and orbital time for Galactic clouds. At the same time, we do not observe any correlation with $\rm \Sigma _{gas}$ per crossing time and multi free-fall time. Even though we see correlations in the former cases, however, all models agree with each other within a factor of 0.5 dex. It is not possible to discriminate between these models because of the current uncertainties in the input observables. We also test the variation of $\rm \Sigma _{SFR}$ with the dense gas but, because of low statistics, a weak correlation is seen in our analysis.

scholarly journals The link between solenoidal turbulence and slow star formation in G0.253+0.016

2016 ◽  
Vol 11 (S322) ◽  
pp. 123-128 ◽  
Author(s):  
C. Federrath ◽  
J. M. Rathborne ◽  
S. N. Longmore ◽  
J. M. D. Kruijssen ◽  
J. Bally ◽  
...  
Keyword(s):  
Star Formation ◽  
Mach Number ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Dust Emission ◽  
Volume Density ◽  
Galactic Centre ◽  
Galactic Disc ◽  
Density Variance

AbstractStar formation in the Galactic disc is primarily controlled by gravity, turbulence, and magnetic fields. It is not clear that this also applies to star formation near the Galactic Centre. Here we determine the turbulence and star formation in the CMZ cloud G0.253+0.016. Using maps of 3 mm dust emission and HNCO intensity-weighted velocity obtained with ALMA, we measure the volume-density variance σρ /ρ 0=1.3±0.5 and turbulent Mach number $\mathcal{M}$ = 11±3. Combining these with turbulence simulations to constrain the plasma β = 0.34±0.35, we reconstruct the turbulence driving parameter b=0.22±0.12 in G0.253+0.016. This low value of b indicates solenoidal (divergence-free) driving of the turbulence in G0.253+0.016. By contrast, typical clouds in the Milky Way disc and spiral arms have a significant compressive (curl-free) driving component (b > 0.4). We speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this may reduce the star formation rate by a factor of 7 compared to nearby clouds.

scholarly journals Lessons from comparisons between the nuclear region of the Milky Way and those in nearby spirals

2013 ◽  
Vol 9 (S303) ◽  
pp. 61-65
Author(s):  
John S. Gallagher ◽  
Tova M. Yoast-Hull ◽  
Ellen G. Zweibel
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Molecular Gas ◽  
Nuclear Region ◽  
Stellar Content ◽  
Nuclear Regions ◽  
Stellar Masses

AbstractThe Milky Way appears as a typical barred spiral, and comparisons can be made between its nuclear region and those of structurally similar nearby spirals. Maffei 2, M83, IC 342 and NGC 253 are nearby systems whose nuclear region properties contrast with those of the Milky Way. Stellar masses derived from NIR photometery, molecular gas masses and star formation rates allow us to assess the evolutionary states of this set of nuclear regions. These data suggest similarities between nuclear regions in terms of their stellar content while highlighting significant differences in current star formation rates. In particular current star formation rates appear to cover a larger range than expected based on the molecular gas masses. This behavior is consistent with nuclear region star formation experiencing episodic variations. Under this hypothesis the Milky Way's nuclear region currently may be in a low star formation rate phase.

scholarly journals Stellar Explosions in High-surface Density Galaxies

2015 ◽  
Vol 11 (A29B) ◽  
pp. 232-232
Author(s):  
Evan Scannapieco ◽  
Sharanya Sur ◽  
Eve C. Ostriker
Keyword(s):  
Star Formation ◽  
Surface Density ◽  
Energy Input ◽  
Large Scale ◽  
Star Formation Rate ◽  
High Surface ◽  
Formation Rate ◽  
Three Dimensional ◽  
Velocity Dispersions ◽  
The Impact

AbstractHigh surface density, rapidly star-forming galaxies are observed to have ≈ 50 - 100 km s−1 line-of-sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae.We find that such motions lead to strong global outflows in the highly-compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds -35 km s−1, as occurs in the dense disks that have star formation rate densities above ≈ 0.1 M⊙ yr−1 kpc−2. These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the star-formation rate density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from stellar explosions.These results are explained in more detailed in Sur, Scannapieco, & Ostriker (2015).

scholarly journals From the outside looking in: what can Milky Way analogues tell us about the star formation rate of our own galaxy?

2019 ◽  
Vol 489 (4) ◽  
pp. 5030-5036 ◽  
Author(s):  
Amelia Fraser-McKelvie ◽  
Michael Merrifield ◽  
Alfonso Aragón-Salamanca
Keyword(s):  
Star Formation ◽  
Standard Deviation ◽  
Milky Way ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Structural Features ◽  
Mid Infrared ◽  
Recent Estimate ◽  
The Mean

ABSTRACT The Milky Way has been described as an anaemic spiral, but is its star formation rate (SFR) unusually low when compared to its peers? To answer this question, we define a sample of Milky Way analogues (MWAs) based on stringent cuts on the best literature estimates of non-transient structural features for the Milky Way. This selection yields only 176 galaxies from the whole of the SDSS DR7 spectroscopic sample which have morphological classifications in Galaxy Zoo 2, from which we infer SFRs from two separate indicators. The mean SFRs found are $\log (\rm {SFR}_{SED}/\rm {M}_{\odot }~\rm {yr}^{-1})=0.53$ with a standard deviation of 0.23 dex from SED fits, and $\log (\rm {SFR}_{W4}/\rm {M}_{\odot }~\rm {yr}^{-1})=0.68$ with a standard deviation of 0.41 dex from a mid-infrared calibration. The most recent estimate for the Milky Way’s SFR of $\log (\rm {SFR}_{MW}/\rm {M}_{\odot }~\rm {yr}^{-1})=0.22$ fits well within 2$\sigma$ of these values, where $\sigma$ is the standard deviation of each of the SFR indicator distributions. We infer that the Milky Way, while being a galaxy with a somewhat low SFR, is not unusual when compared to similar galaxies.

scholarly journals Low-redshift quasars in the SDSS Stripe 82 – II. Associated companion galaxies and signature of star formation

2020 ◽  
Vol 501 (1) ◽  
pp. 419-439
Author(s):  
M B Stone ◽  
D Bettoni ◽  
R Falomo ◽  
J K Kotilainen ◽  
K Karhunen ◽  
...  
Keyword(s):  
Star Formation ◽  
Emission Line ◽  
Large Scale ◽  
Strong Influence ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Host Galaxy ◽  
Starburst Galaxy ◽  
Published Paper ◽  
Larger Sample

ABSTRACT We present optical spectroscopy of the close companions of 22 low-redshift (z < 0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host galaxy and the large-scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; ∼44 per cent) have at least one associated galaxy. Many (12 galaxies; ∼67 per cent) of the associated companions exhibit [O ii] 3727 Å emission line as signature of recent star formation. The star formation rate (SFR) of these galaxies is modest (median SFR ∼ 4.3 M⊙ yr−1). For eight QSO, we are also able to detect the starlight of the host galaxy from which three have a typical spectrum of a post-starburst galaxy. Our results suggest that quasars do not have a strong influence on the star formation of their companion galaxies.

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