scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2019 ◽  
Vol 623 ◽  
pp. L3 ◽  
Author(s):  
A. Sanna ◽  
L. Moscadelli ◽  
C. Goddi ◽  
M. Beltrán ◽  
C. L. Brogan ◽  
...  
Keyword(s):  
Young Star ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Relativistic Electrons ◽  
Very Large Array ◽  
Star Forming ◽  
Nonthermal Radiation ◽  
Index Analysis ◽  
Protostellar Jets ◽  
The Magnetic Field

Centimeter continuum observations of protostellar jets have revealed knots of shocked gas where the flux density decreases with frequency. This spectrum is characteristic of nonthermal synchrotron radiation and implies both magnetic fields and relativistic electrons in protostellar jets. Here, we report on one of the few detections of a nonthermal jet driven by a young massive star in the star-forming region G035.02+0.35. We made use of the NSF’s Karl G. Jansky Very Large Array (VLA) to observe this region at C, Ku, and K bands with the A- and B-array configurations, and obtained sensitive radio continuum maps down to an rms of 10 μJy beam−1. These observations allow for a detailed spectral index analysis of the radio continuum emission in the region, which we interpret as a protostellar jet with a number of knots aligned with extended 4.5 μm emission. Two knots clearly emit nonthermal radiation and are found at similar distances, of approximately 10 000 au, at each side of the central young star, from which they expand at velocities of several hundred km s−1. We estimate both the mechanical force and the magnetic field associated with the radio jet, and infer a lower limit of 0.4 × 10−4 M⊙ yr−1 km s−1 and values in the range 0.7–1.3 mG.

scholarly journals Protostellar Outflows at the EarliesT Stages (POETS)

2018 ◽  
Vol 619 ◽  
pp. A107 ◽  
Author(s):  
A. Sanna ◽  
L. Moscadelli ◽  
C. Goddi ◽  
V. Krishnan ◽  
F. Massi
Keyword(s):  
Spectral Index ◽  
Young Stars ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Stellar Winds ◽  
Distance Measurements ◽  
Very Large Array ◽  
Star Forming ◽  
Continuum Source ◽  
Star Forming Regions

Context. Weak and compact radio continuum and H2O masers are preferred tracers of the outflow activity nearby very young stars. Aims. We want to image the centimeter free–free continuum emission in the range 1–7 cm (26–4 GHz), which arises in the inner few 1000 au from those young stars also associated with bright H2O masers. We seek to study the radio continuum properties in combination with the H2O maser kinematics to quantify the outflow energetics powered by single young stars. Methods. We made use of the Karl G. Jansky Very Large Array (VLA) in the B configuration at K band and the A configuration at both Ku and C bands in order to image the radio continuum emission toward 25 H2O maser sites with an angular resolution and thermal rms on the order of 0.′′1 and 10 μJy beam−1, respectively. These targets add to our pilot study of 11 maser sites previously presented. The sample of H2O maser sites was selected among those regions that have accurate distance measurements, obtained through maser trigonometric parallaxes, and H2O maser luminosities in excess of 10−6 L⊙. Results. We present high-resolution radio continuum images of 33 sources belonging to 25 star-forming regions. In each region, we detect radio continuum emission within a few 1000 au of the H2O masers’ position; 50% of the radio continuum sources are associated with bolometric luminosities exceeding 5 × 103 L⊙, including W33A and G240.32 + 0.07. We provide a detailed spectral index analysis for each radio continuum source, based on the integrated fluxes at each frequency, and produce spectral index maps with the multifrequency synthesis deconvolution algorithm of CASA. The radio continuum emission traces thermal bremsstrahlung in (proto)stellar winds and jets that have flux densities at 22 GHz below 3 mJy and spectral index values between − 0.1 and 1.3. We prove a strong correlation (r > 0.8) between the radio continuum luminosity (Lrad) and the H2O maser luminosity (LH2O) of (L8 GHz∕mJy kpc2) = 103.8 × (LH2O L⊙)0.74. This power-law relation is similar to that between the radio continuum and bolometric luminosities, which confirms earlier studies. Since H2O masers are excited through shocks driven by (proto)stellar winds and jets, these results provide support to the idea that the radio continuum emission around young stars is dominated by shock ionization, and this holds over several orders of magnitude of stellar luminosites (1–105 L⊙).

scholarly journals Observations of H2O maser and continuum emission in AFGL 2591

2002 ◽  
Vol 206 ◽  
pp. 68-71
Author(s):  
Miguel A. Trinidad ◽  
Salvador Curiel ◽  
Jorge Cantó ◽  
José M. Torrelles ◽  
Luis F. Rodríguez ◽  
...  
Keyword(s):  
Radio Continuum ◽  
Continuum Emission ◽  
Molecular Flow ◽  
Large Array ◽  
Very Large Array ◽  
Star Forming ◽  
Bipolar Outflow ◽  
Maser Line ◽  
H Ii Region

We report results of radio continuum (1.3 and 3.6 cm) and H2O maser line observations, made with the Very Large Array (A configuration), toward the star-forming region AFGL 2591. We detected 85 maser spots toward this region, which are distributed in three main groups. Two of these groups spatially coincide with the radio continuum sources VLA 2 and VLA 3. The maser spots associated with VLA 3 are distributed along a shell-like structure of 0.01 and nearly perpendicular to the CO bipolar outflow. We propose that VLA 3 is the center of the observed molecular flow in this region. Finally, we confirm that AFGL 2591 region is a cluster of B type stars, each one with its own optically thin H II region.

The diagnostic power of radio spectra from star-forming galaxies

2019 ◽  
Vol 15 (S341) ◽  
pp. 177-186
Author(s):  
Eric J. Murphy
Keyword(s):  
Star Formation ◽  
Dust Emission ◽  
Cosmic Ray ◽  
Microwave Emission ◽  
Radio Continuum ◽  
Continuum Emission ◽  
H Ii Regions ◽  
Synchrotron Emission ◽  
Very Large Array ◽  
Star Forming

AbstractRadio continuum emission from galaxies is powered by a combination of distinct physical processes, each providing unique diagnostic information. Over frequencies spanning ∼ 1–120 GHz, radio spectra of star-forming galaxies are primarily comprised of: (1) non-thermal synchrotron emission powered by accelerated cosmic-ray electrons/positrons; (2) free-free emission from young massive star-forming (H ii) regions; (3) anomalous microwave emission, which is a dominant, but completely unconstrained, foreground in cosmic microwave background experiments; and (4) cold, thermal dust emission that accounts for most of the dust and total mass content in the interstellar medium in galaxies. In this proceeding, we discuss these key energetic processes that contribute to the radio emission from star-forming galaxies, with an emphasis on frequencies ≳30 GHz, where current investigations of star formation within nearby galaxies show that the free-free emission begins to dominate over non-thermal synchrotron emission. We also discuss how planned radio facilities that will access these frequencies, such as a next-generation Very Large Array (ngVLA), will be transformative to our understanding of the star formation process in galaxies.

scholarly journals A Highly-collimated Water Maser Bipolar Outflow in the Cepheus A HW3d Massive Protostellar Object

2012 ◽  
Vol 8 (S287) ◽  
pp. 141-145
Author(s):  
James O. Chibueze ◽  
Hiroshi Imai ◽  
Daniel Tafoya ◽  
Toshihiro Omodaka ◽  
Osamu Kameya ◽  
...  
Keyword(s):  
Strong Support ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Very Large Array ◽  
Star Forming ◽  
Bipolar Outflow ◽  
Long Baseline ◽  
Cepheus A ◽  
Continuum Data ◽  
Water Maser

AbstractWe report the results of multi-epoch very long baseline interferometry (VLBI) water (H2O) maser observations carried out with the VLBI Exploration of Radio Astrometry (VERA) toward the HW3d object within the Cepheus A star-forming region. We measured proper motions of 30 water maser features, tracing a compact bipolar outflow. This outflow is highly collimated, extending through ~400 mas (290 AU), and having a typical proper motion velocity of ~6 mas yr−1 (~21 km s−1). The dynamical timescale of the outflow was estimated to be ~100 years, showing that the outflow is tracing a very early star-formation phase. Our results provide strong support that the HW3d object harbors an internal massive protostar, as previous observations suggested. In addition, we have analyzed Very Large Array (VLA) archive 1.3 cm continuum data of the 1995 and 2006 epochs obtained towards Cepheus A. These results indicate possible different protostars around HW3d and/or strong variability in its radio continuum emission.

scholarly journals The ram pressure stripped radio tails of galaxies in the Coma cluster

2020 ◽  
Vol 496 (4) ◽  
pp. 4654-4673 ◽  
Author(s):  
Hao Chen ◽  
Ming Sun ◽  
Masafumi Yagi ◽  
Hector Bravo-Alfaro ◽  
Elias Brinks ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Infrared Emission ◽  
Radio Continuum ◽  
Relativistic Electrons ◽  
Coma Cluster ◽  
Very Large Array ◽  
Star Forming ◽  
Upper Limits ◽  
Ram Pressure ◽  
The Galaxy

ABSTRACT Previous studies have revealed a population of galaxies in galaxy clusters with ram pressure stripped (RPS) tails of gas and embedded young stars. We observed 1.4 GHz continuum and H i emission with the Very Large Array in its B-configuration in two fields of the Coma cluster to study the radio properties of RPS galaxies. The best continuum sensitivities in the two fields are 6 and 8 µJy per 4 arcsec beam, respectively, which are 4 and 3 times deeper than those previously published. Radio continuum tails are found in 10 (8 are new) out of 20 RPS galaxies, unambiguously revealing the presence of relativistic electrons and magnetic fields in the stripped tails. Our results also hint that the tail has a steeper spectrum than the galaxy. The 1.4 GHz continuum in the tails is enhanced relative to their H α emission by a factor of ∼7 compared to the main bodies of the RPS galaxies. The 1.4 GHz continuum of the RPS galaxies is also enhanced relative to their infrared emission by a factor of ∼2 compared to star-forming galaxies. The enhancement is likely related to ram pressure and turbulence in the tail. We furthermore present H i detections in three RPS galaxies and upper limits for the other RPS galaxies. The cold gas in D100’s stripped tail is dominated by molecular gas, which is likely a consequence of the high ambient pressure. No evidence of radio emission associated with ultra-diffuse galaxies is found in our data.

scholarly journals HCO+and Radio Continuum Emission from the Star Forming Region G75.78+0.34

2014 ◽  
Vol 2014 ◽  
pp. 1-5
Author(s):  
Rogemar A. Riffel ◽  
Everton Lüdke
Keyword(s):  
Massive Star ◽  
Emission Measure ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Ionized Gas ◽  
Very Large Array ◽  
Star Forming ◽  
Molecular Outflows ◽  
H Ii Region ◽  
The Continuum

We present 1.3 and 3.6 cm radio continuum images and a HCO+spectrum of the massive star forming region G75.78+0.34 obtained with the Very Large Array (VLA) and with the Berkley Illinois Maryland Association (BIMA) interferometer. Three structures were detected in the continuum emission: one associated with the well-known cometary H ɪɪ region, plus two more compact structures located at 6′′ east and at 2′′ south of cometary H ɪɪ region. Using the total flux and intensity peak we estimated an electron density of≈1.5 × 104 cm−3, an emission measure of≈6 × 107 cm−6 pc, a mass of ionized gas of≈3 M⊙, and a diameter of 0.05 pc for the cometary H ɪɪ region, being typical values for an ultracompact H ɪɪ region. The HCO+emission probably originates from the molecular outflows previously observed in HCN and CO.

scholarly journals High-sensitivity radio study of the non-thermal stellar bow shock EB27

2021 ◽  
Author(s):  
Paula Benaglia ◽  
Santiago del Palacio ◽  
Christopher Hales ◽  
Marcelo E Colazo
Keyword(s):  
Radio Emission ◽  
Massive Star ◽  
High Sensitivity ◽  
Bow Shock ◽  
Relativistic Electrons ◽  
Polarimetric Observation ◽  
Very Large Array ◽  
Thermal Radio Emission ◽  
The Magnetic Field ◽  
Linear Polarisation

Abstract We present a deep radio-polarimetric observation of the stellar bow shock EB27 associated to the massive star BD+43○3654. This is the only stellar bow shock confirmed to have non-thermal radio emission. We used the Jansky Very Large Array in S band (2–4 GHz) to test whether this synchrotron emission is polarised. The unprecedented sensitivity achieved allowed us to map even the fainter regions of the bow shock, revealing that the more diffuse emission is steeper and the bow shock brighter than previously reported. No linear polarisation is detected in the bow shock above 0.5%, although we detected polarised emission from two southern sources, probably extragalactic in nature. We modeled the intensity and morphology of the radio emission to better constrain the magnetic field and injected power in relativistic electrons. Finally, we derived a set of more precise parameters for the system EB27–BD+43○3654 using Gaia Early Data Release 3, including the spatial velocity. The new trajectory, back in time, intersects the core of the Cyg OB2 association.

scholarly journals Radio continuum size evolution of star-forming galaxies over 0.35 < z < 2.25

2019 ◽  
Vol 625 ◽  
pp. A114 ◽  
Author(s):  
E. F. Jiménez-Andrade ◽  
B. Magnelli ◽  
A. Karim ◽  
G. Zamorani ◽  
M. Bondi ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Gaussian Model ◽  
Cosmic Time ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Selection Function ◽  
Star Forming ◽  
Size Evolution ◽  
Galaxy Population

To better constrain the physical mechanisms driving star formation, we present the first systematic study of the radio continuum size evolution of star-forming galaxies (SFGs) over the redshift range 0.35 <  z <  2.25. We use the VLA COSMOS 3 GHz map (noise rms = 2.3 μJy beam−1, θbeam = 0.75 arcsec) to construct a mass-complete sample of 3184 radio-selected SFGs that reside on and above the main sequence (MS) of SFGs. We constrain the overall extent of star formation activity in galaxies by applying a 2D Gaussian model to their radio continuum emission. Extensive Monte Carlo simulations are used to validate the robustness of our measurements and characterize the selection function. We find no clear dependence between the radio size and stellar mass, M⋆, of SFGs with 10.5 ≲ log(M⋆/M⊙) ≲ 11.5. Our analysis suggests that MS galaxies are preferentially extended, while SFGs above the MS are always compact. The median effective radius of SFGs on (above) the MS of Reff = 1.5 ± 0.2 (1.0 ± 0.2) kpc remains nearly constant with cosmic time; a parametrization of the form Reff ∝ (1 + z)α yields a shallow slope of only α = −0.26 ± 0.08 (0.12 ± 0.14) for SFGs on (above) the MS. The size of the stellar component of galaxies is larger than the extent of the radio continuum emission by a factor ∼2 (1.3) at z = 0.5 (2), indicating star formation is enhanced at small radii. The galactic-averaged star formation rate surface density (ΣSFR) scales with the distance to the MS, except for a fraction of MS galaxies (≲10%) that harbor starburst-like ΣSFR. These “hidden” starbursts might have experienced a compaction phase due to disk instability and/or a merger-driven burst of star formation, which may or may not significantly offset a galaxy from the MS. We thus propose to use ΣSFR and distance to the MS in conjunction to better identify the galaxy population undergoing a starbursting phase.

scholarly journals Quasi-simultaneous Radio/X-Ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6−1125 during its Low-luminosity Accretion-disk State

2021 ◽  
Vol 923 (1) ◽  
pp. 3
Author(s):  
Amruta D. Jaodand ◽  
Adam T. Deller ◽  
Nina Gusinskaia ◽  
Jason W. T. Hessels ◽  
James C. A. Miller-Jones ◽  
...  
Keyword(s):  
Accretion Disk ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Large Array ◽  
Millisecond Pulsar ◽  
Very Large Array ◽  
X Ray ◽  
Upper Limit ◽  
5 Ghz ◽  
Variable Radio

Abstract 3FGL J1544.6−1125 is a candidate transitional millisecond pulsar (tMSP). Similar to the well-established tMSPs—PSR J1023+0038, IGR J18245−2452, and XSS J12270−4859—3FGL J1544.6−1125 shows γ-ray emission and discrete X-ray “low” and “high” modes during its low-luminosity accretion-disk state. Coordinated radio/X-ray observations of PSR J1023+0038 in its current low-luminosity accretion-disk state showed rapidly variable radio continuum emission—possibly originating from a compact, self-absorbed jet, the “propellering” of accretion material, and/or pulsar moding. 3FGL J1544.6−1125 is currently the only other (candidate) tMSP system in this state, and can be studied to see whether tMSPs are typically radio-loud compared to other neutron star binaries. In this work, we present a quasi-simultaneous Very Large Array and Swift radio/X-ray campaign on 3FGL J1544.6−1125. We detect 10 GHz radio emission varying in flux density from 47.7 ± 6.0 μJy down to ≲15 μJy (3σ upper limit) at four epochs spanning three weeks. At the brightest epoch, the radio luminosity is L 5 GHz = (2.17 ± 0.17) × 1027 erg s−1 for a quasi-simultaneous X-ray luminosity L 2–10 keV = (4.32 ± 0.23) × 1033 erg s−1 (for an assumed distance of 3.8 kpc). These luminosities are close to those of PSR J1023+0038, and the results strengthen the case that 3FGL J1544.6−1125 is a tMSP showing similar phenomenology to PSR J1023+0038.

scholarly journals Investigation of the cosmic ray population and magnetic field strength in the halo of NGC 891

2018 ◽  
Vol 615 ◽  
pp. A98 ◽  
Author(s):  
D. D. Mulcahy ◽  
A. Horneffer ◽  
R. Beck ◽  
M. Krause ◽  
P. Schmidt ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Low Frequency ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Low Frequencies ◽  
Very Large Array ◽  
Field Strengths

Context. Cosmic rays and magnetic fields play an important role for the formation and dynamics of gaseous halos of galaxies. Aims. Low-frequency radio continuum observations of edge-on galaxies are ideal to study cosmic-ray electrons (CREs) in halos via radio synchrotron emission and to measure magnetic field strengths. Spectral information can be used to test models of CRE propagation. Free–free absorption by ionized gas at low frequencies allows us to investigate the properties of the warm ionized medium in the disk. Methods. We obtained new observations of the edge-on spiral galaxy NGC 891 at 129–163 MHz with the LOw Frequency ARray (LOFAR) and at 13–18 GHz with the Arcminute Microkelvin Imager (AMI) and combine them with recent high-resolution Very Large Array (VLA) observations at 1–2 GHz, enabling us to study the radio continuum emission over two orders of magnitude in frequency. Results. The spectrum of the integrated nonthermal flux density can be fitted by a power law with a spectral steepening towards higher frequencies or by a curved polynomial. Spectral flattening at low frequencies due to free–free absorption is detected in star-forming regions of the disk. The mean magnetic field strength in the halo is 7 ± 2 μG. The scale heights of the nonthermal halo emission at 146 MHz are larger than those at 1.5 GHz everywhere, with a mean ratio of 1.7 ± 0.3, indicating that spectral ageing of CREs is important and that diffusive propagation dominates. The halo scale heights at 146 MHz decrease with increasing magnetic field strengths which is a signature of dominating synchrotron losses of CREs. On the other hand, the spectral index between 146 MHz and 1.5 GHz linearly steepens from the disk to the halo, indicating that advection rather than diffusion is the dominating CRE transport process. This issue calls for refined modelling of CRE propagation. Conclusions. Free–free absorption is probably important at and below about 150 MHz in the disks of edge-on galaxies. To reliably separate the thermal and nonthermal emission components, to investigate spectral steepening due to CRE energy losses, and to measure magnetic field strengths in the disk and halo, wide frequency coverage and high spatial resolution are indispensable.

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