scholarly journals An early transition to magnetic supercriticality in star formation

Nature ◽  
2022 ◽  
Vol 601 (7891) ◽  
pp. 49-52
Author(s):  
T.-C. Ching ◽  
D. Li ◽  
C. Heiles ◽  
Z.-Y. Li ◽  
L. Qian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Neutral Medium ◽  
Molecular Gas ◽  
Number Density ◽  
Central Temperature ◽  
Molecular Envelope ◽  
Classical Picture ◽  
Early Transition

AbstractMagnetic fields have an important role in the evolution of interstellar medium and star formation1,2. As the only direct probe of interstellar field strength, credible Zeeman measurements remain sparse owing to the lack of suitable Zeeman probes, particularly for cold, molecular gas3. Here we report the detection of a magnetic field of +3.8 ± 0.3 microgauss through the H I narrow self-absorption (HINSA)4,5 towards L15446,7—a well-studied prototypical prestellar core in an early transition between starless and protostellar phases8–10 characterized by a high central number density11 and a low central temperature12. A combined analysis of the Zeeman measurements of quasar H I absorption, H I emission, OH emission and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope. The molecular envelope traced by the HINSA is found to be magnetically supercritical, with a field strength comparable to that of the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, which is necessary for star formation, thus seems to have already happened during the transition from the diffuse CNM to the molecular gas traced by the HINSA. This is earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes13,14.

scholarly journals Multi-Scale Coherent Magnetic Field from Atomic Medium to L1544 Molecular Core

2021 ◽  
Author(s):  
Tao-Chung Ching ◽  
Di Li ◽  
Carl Heiles ◽  
Zhi-Yun Li ◽  
Lei Qian ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Zeeman Effect ◽  
Spectral Lines ◽  
Neutral Medium ◽  
Molecular Gas ◽  
Multi Scale ◽  
Molecular Core ◽  
Molecular Envelope

Abstract Magnetic fields play an important role in the evolution of interstellar medium and star formation. As the only direct tracer of interstellar field strength, credible Zeeman measurements remain sparse due to rather limited number of spectral lines with discernible Zeeman effect, particularly for cold, molecular gas. Here we report the detection of a magnetic field of 3.8 ± 0.3 μG through a new tracer, the HI narrow self-absorption (HINSA), toward the prestellar core L1544 of the Taurus molecular cloud using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). A combined analysis of the Zeeman measurements of quasar HI absorption, HI emission, OH emission, and HINSA reveals a coherent magnetic field from the atomic cold neutral medium (CNM) to the molecular envelope of the L1544. We find that the molecular envelope traced by HINSA is already magnetically supercritical, with a field strength comparable to that in the surrounding diffuse, magnetically subcritical CNM despite a large increase in density. The reduction of the magnetic flux relative to the mass, necessary for star formation, thus seems to happen during the transition from the diffuse CNM to the molecular gas traced by HINSA, earlier than envisioned in the classical picture where magnetically supercritical cores capable of collapsing into stars form out of magnetically subcritical envelopes. The HINSA Zeeman effect opens up a new window on the interstellar magnetic field that is poised for rapid growth in the era of Square Kilometer Array and its precursors.

scholarly journals Survival of molecular gas in a stellar feedback-driven outflow witnessed with the MUSE TIMER project and ALMA

2019 ◽  
Vol 488 (3) ◽  
pp. 3904-3928 ◽  
Author(s):  
Ryan Leaman ◽  
Francesca Fragkoudi ◽  
Miguel Querejeta ◽  
Gigi Y C Leung ◽  
Dimitri A Gadotti ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Mechanical Energy ◽  
Molecular Gas ◽  
Ionized Gas ◽  
Star Forming ◽  
Stellar Feedback ◽  
Dominant Component ◽  
The Galaxy ◽  
Field Lines

ABSTRACT Stellar feedback plays a significant role in modulating star formation, redistributing metals, and shaping the baryonic and dark structure of galaxies – however, the efficiency of its energy deposition to the interstellar medium is challenging to constrain observationally. Here we leverage HST and ALMA imaging of a molecular gas and dust shell ($M_{\mathrm{ H}_2} \sim 2\times 10^{5}\, {\rm M}_{\odot }$) in an outflow from the nuclear star-forming ring of the galaxy NGC 3351, to serve as a boundary condition for a dynamical and energetic analysis of the outflowing ionized gas seen in our MUSE TIMER survey. We use starburst99 models and prescriptions for feedback from simulations to demonstrate that the observed star formation energetics can reproduce the ionized and molecular gas dynamics – provided a dominant component of the momentum injection comes from direct photon pressure from young stars, on top of supernovae, photoionization heating, and stellar winds. The mechanical energy budget from these sources is comparable to low luminosity active galactic neuclei, suggesting that stellar feedback can be a relevant driver of bulk gas motions in galaxy centres – although here ≲10−3 of the ionized gas mass is escaping the galaxy. We test several scenarios for the survival/formation of the cold gas in the outflow, including in situ condensation and cooling. Interestingly, the geometry of the molecular gas shell, observed magnetic field strengths and emission line diagnostics are consistent with a scenario where magnetic field lines aided survival of the dusty ISM as it was initially launched (with mass-loading factor ≲1) from the ring by stellar feedback. This system’s unique feedback-driven morphology can hopefully serve as a useful litmus test for feedback prescriptions in magnetohydrodynamical galaxy simulations.

Magnetic Fields and Star Formation for the ANS Sample of Galaxies

1990 ◽  
Vol 140 ◽  
pp. 233-234
Author(s):  
J. Stryczynski
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Field Data ◽  
Spiral Galaxies ◽  
Magnetic Field Data ◽  
Uv Range

From the literature we collected radio and magnetic field data for the ANS spiral galaxies. We suggest that the groups of objects, as revealed in the UV range, do not differ in magnetic field strength, although statistics of the sample are very poor.

scholarly journals Magnetic Fields in Dark Cloud Cores and H2O Masers

1990 ◽  
Vol 140 ◽  
pp. 305-308
Author(s):  
Rolf Güsten ◽  
Dirk Fiebig
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Kinetic Temperature ◽  
Dark Cloud ◽  
Dense Cores ◽  
Low Mass ◽  
Cloud Cores ◽  
First Time ◽  
The Magnetic Field

We present results of recent circular polarization experiments with the MPIfR 100-m telescope, revealing for the first time, the magnetic field strength towards interstellar H2O masers and the dense cores of local dark cloud complexes. Weak Zeeman splittings of a few 10 kHz only in the 22.235 GHz maser transition of the non-paramagnetic H2O molecule imply magnetic field strengths of ~ 50 mG in the dense (n ~ 1010 cm−3) masing layer. With the recently identified CCS radical it became possible to study the magnetic field associated with dense (~ 105 cm−3) dark cloud cores, the potential sites of future star formation. We report the detection of a −110μG field towards TMC-1C, a low-mass core associated with the Taurus Molecular Cloud. From complementary gas density and kinetic temperature probing measurements, we derive approximate equipartition between magnetic, gravitational and thermal energy for this clump.

scholarly journals Magnetic fields in spiral galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 399-399 ◽  
Author(s):  
Marita Krause
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Field Strength ◽  
Radio Emission ◽  
Magnetic Field Strength ◽  
Thin Disk ◽  
Total Magnetic Field ◽  
Galactic Wind ◽  
Plane Parallel

The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 ± 50 pc for the thin disk and 1.8 ± 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime tsyn at a single frequency is proportional to the total magnetic field strength Bt−1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as vCR = hCR/tsyn = 2 hz/tsyn, where hCR and hz are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: vCR∝ Bt1.5 ∝ SFR≈ 0.5 (Niklas & Beck 1997).

scholarly journals Molecular gas and triggered star formation surrounding Wolf-Rayet stars

2012 ◽  
Vol 8 (S292) ◽  
pp. 48-48
Author(s):  
Tie Liu ◽  
Yuefang Wu ◽  
Huawei Zhang
Keyword(s):  
Star Formation ◽  
Stellar Wind ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Number Density ◽  
Stellar Objects ◽  
Molecular Emission ◽  
Wind Velocities ◽  
Expanding Shells

AbstractThe environments surrounding nine Wolf-Rayet stars were studied in molecular emission. Expanding shells were detected surrounding these WR stars (see left panels of Figure 1). The average masses and radii of the molecular cores surrounding these WR stars anti-correlate with the WR stellar wind velocities (middle panels of Figure 1), indicating the WR stars has great impact on their environments. The number density of Young Stellar Objects (YSOs) is enhanced in the molecular shells at ∼5 arcmin from the central WR star (lower-right panel of Figure 1). Through detailed studies of the molecular shells and YSOs, we find strong evidences of triggered star formation in the fragmented molecular shells (Liu et al. 2010).

scholarly journals GMC Collisions as Triggers of Star Formation. VII. The Effect of Magnetic Field Strength on Star Formation

2020 ◽  
Vol 891 (2) ◽  
pp. 168 ◽  
Author(s):  
Benjamin Wu ◽  
Jonathan C. Tan ◽  
Duncan Christie ◽  
Fumitaka Nakamura
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Magnetic Field Strength

scholarly journals Magnetic Fields in Molecular Clouds

2010 ◽  
Vol 6 (S271) ◽  
pp. 187-196 ◽  
Author(s):  
Paolo Padoan ◽  
Tuomas Lunttila ◽  
Mika Juvela ◽  
Åke Nordlund ◽  
David Collins ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Molecular Clouds ◽  
Large Scale ◽  
Small Scale ◽  
Mhd Turbulence ◽  
Turbulence Simulation ◽  
The Magnetic Field

AbstractSupersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds (MCs) plays an important role in the process of star formation. The effect of the turbulence on the cloud fragmentation process depends on the magnetic field strength. In this work we discuss the idea that the turbulence is super-Alfvénic, at least with respect to the cloud mean magnetic field. We argue that MCs are likely to be born super-Alfvénic. We then support this scenario based on a recent simulation of the large-scale warm interstellar medium turbulence. Using small-scale isothermal MHD turbulence simulation, we also show that MCs may remain super-Alfvénic even with respect to their rms magnetic field strength, amplified by the turbulence. Finally, we briefly discuss the comparison with the observations, suggesting that super-Alfvénic turbulence successfully reproduces the Zeeman measurements of the magnetic field strength in dense MC clouds.

scholarly journals Magnetic fields in the non-masing ISM

2007 ◽  
Vol 3 (S242) ◽  
pp. 47-54
Author(s):  
Richard M. Crutcher
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Linear Polarization ◽  
Formation Process ◽  
Molecular Clouds ◽  
Zeeman Effect ◽  
Flux Ratio

AbstractObservations of the Zeeman effect in OH and H2O masers provide valuable information about magnetic field strength and direction, but only for the very high density gas in which such masers are found. In order to understand the role of magnetic fields in the evolution of the interstellar medium and in the star formation process, it is essential to consider the maser results in the broader context of magnetic fields in lower density gas. This contribution will (very briefly) summarize the state of observational knowledge of magnetic fields in the non-masing gas. Magnetic fields in H I and molecular clouds may be observed via the Zeeman effect, linear polarization of dust emission, and linear polarization of spectral-line emission. Useful parameters that can be inferred from observations are the mass-to-flux ratio and the scaling of field strength with density. The former tells us whether magnetic fields exert sufficient pressure to provide support against gravitational contraction; the latter tells whether or not magnetic fields are sufficiently strong to determine the nature (spherical or disk geometry) of the contraction. Existing observations will be reviewed. Results are that the strength of interstellar magnetic fields remains roughly invariant at 5-10 microgauss between densities of 0.1 cm−3 < n(H) < 1,000 cm−3 but increases proportional to approximately the square root of density at higher densities. Moreover, the mass-to-flux ratio is significantly subcritical (strong magnetic support with respect to gravity) in diffuse H I clouds that are not self-gravitating, but becomes approximately critical in high-density molecular cloud cores. This suggests that MCs and GMCs form primarily by accumulation of matter along magnetic field lines, a process that will increase density but not magnetic field strength. How clumps in GMCs evolve will then depend crucially on the mass-to-flux ratio in each clump. Present data suggest that magnetic fields play a very significant role in the evolution of molecular clouds and in the star formation process.

scholarly journals A statistical measurement of the H i spin temperature in DLAs at cosmological distances

2021 ◽  
Author(s):  
James R Allison
Keyword(s):  
Star Formation ◽  
Atomic Hydrogen ◽  
Milky Way ◽  
Star Formation Rate ◽  
Mass Density ◽  
Formation Rate ◽  
Neutral Medium ◽  
Molecular Gas ◽  
Spin Temperature ◽  
Order Of Magnitude

Abstract Evolution of the cosmic star formation rate (SFR) and molecular mass density is expected to be matched by a similarly strong evolution of the fraction of atomic hydrogen (H i) in the cold neutral medium (CNM). We use results from a recent commissioning survey for intervening 21-cm absorbers with the Australian Square Kilometre Array Pathfinder (ASKAP) to construct a Bayesian statistical model of the NHI-weighted harmonic mean spin temperature (Ts) at redshifts between z = 0.37 and 1.0. We find that Ts ≤ 274 K with 95 per cent probability, suggesting that at these redshifts the typical H i gas in galaxies at equivalent DLA column densities may be colder than the Milky Way interstellar medium (Ts, MW ∼ 300 K). This result is consistent with an evolving CNM fraction that mirrors the molecular gas towards the peak in SFR at z ∼ 2. We expect that future surveys for H i 21-cm absorption with the current SKA pathfinder telescopes will be able to provide constraints on the CNM fraction that are an order of magnitude greater than presented here.

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