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A 10-M YSO with a Keplerian disk and a nonthermal radio jet


In the last decade, high-angular-resolution observations have clearly indicated that the formation of low-mass up to intermediate-mass stars follows a common route, involving accretion disks and jets. However, towards high-mass (M ≥8 M) young stellar objects (YSO), the detection of both the disk and the associated jet is still relatively rare. Observing the full disk+jet system is fundamental to study the connection between accretion and ejection and, in particular, to determine the mechanism responsible for launching and collimating the protostellar jet.
In September 2016, an international group of astronomers employed the Atacama Large Millimeter Array (ALMA) to observe the star-forming region (SFR) G16.59-0.05 at high-angular resolution. The data obtained with ALMA have been recently published in an article [1] led by Luca Moscadelli  with the participation of Riccardo Cesaroni and Victor M. Rivilla (INAF – Arcetri Astrophysical Observatory).

Previous sensitive Jansky Very Large Array (JVLA) observations detected a radio jet emerging from a massive YSO in G16.59-0.05 (in the following referred to as Bm), elongated ≈3” along the E-W direction [2,3]. The recent ALMA data reveals that a well-defined SW-NE velocity (Vlsr) gradient is revealed at the position of Bm in all the observed high-density gas tracers. Looking at Fig.1 (left panel), the JVLA 22-GHz continuum, pinpointing the YSO, falls just between the SW blueshifted and the NE red-shifted line emission, and the direction of the Vlsr gradient forms a large (≈70o ) angle with the radio jet traced by the extended JVLA 13-GHz continuum. These findings suggest that the Vlsr gradient can be due to rotation of the gas in an envelope and/or disk surrounding the YSO.

mosca fig1
Fig.1: Left panel: the black contours and the color map show, respectively, the velocity-integrated intensity and the intensity-averaged velocity of the C34S J = 5─4 line (Eu = 28 K). The gray-scale filled and white contours show the JVLA 22 GHz and 13 GHz continuum emission, respectively.
Right panel: P-V plot of the C34S J = 5─4 line. The cut (at PA = 18 deg) along which positions are evaluated is indicated with the dashed black line in the left panel. The blue curve marks the Keplerian profile around a YSO of 10 M.

 

The P-V plot (Fig.1, right panel) produced along the axis (at PA = 18o ) of the Vlsr gradient confirms that envelope-disk rotation is actually observed. The P-V plot has a butterfly-like shape, with well-defined "spurs" at high absolute velocities and small offsets in the second and fourth quadrants. These spurs correspond to gas whose line of sight velocity increases with decreasing radius and are consistent with Keplerian rotation.
Since the molecular emission at high velocities is quite compact, it is possible to fit a 2D Gaussian profile and determine the peak position at each velocity channel. Figure 2 (left panel) shows that the spatial distribution of the high-velocity emission of CH3OH is elongated at PA = 18o ± 3o, which can be taken as the direction of the major axis of the molecular disk around the high-mass YSO Bm. Along the red-shifted side, ≈0.15” or ≈500 au in extent, the gas Vlsr increases monotonically approaching the YSO, ranging from ≈62 km s-1 up to ≈69 km s-1 .
Figure 2 (right panel) plots Vlsr versus positions projected along the disk major-axis, and shows the best-fit Keplerian curve. The derived value for the YSO mass is M sin2(i) = 10 ± 2 M , where i (60o ≤ i ≤ 120o) is the inclination of the disk rotation axis with the line of sight. Inside the disk radius of ≈500 au, the 1.2-mm continuum flux is 42 mJy, corresponding to ≈1 M. Since this value is much less than the YSO mass ≈10 M, the choice of fitting a Keplerian velocity profile appears to be well justified a posteriori.
In conclusion, through high-angular-resolution and sensitive ALMA and JVLA observations a disk+jet system around a 10-M YSO has been discovered in the SFR G16.59-0.05, and its geometrical properties (orientation and extension) determined. This is a promising target to study the interplay among a massive YSO, the disk and the jet..

mosca fig2
Fig. 2: Left panel: The disk around the high-mass YSO Bm. Colored dots indicate the peak positions of the most blue- and red-shifted velocity channels for the emission of nine unblended CH3OH lines with 20 K ≤ Eu ≤ 900 K. Colors represent Vlsr as coded on the right of the panel. The dashed black line, at PA = 18o, shows the linear fit to the spatial distribution of the channel peaks. The gray-scale filled and black contours represent the JVLA 22- and 13-GHz continuum, respectively, with the same levels as in Fig.1. Right panel: Black and red errorbars give, respectively, major-axis projected positions and Vlsr (together with the corresponding errors) for the highest-velocity emission peaks of six CH3OH lines with 20 K ≤ Eu ≤ 150 K. The blue curve is the best Keplerian fit to the data.

References:
[1] Moscadelli, L. et al. 2019, A&A in press

[2] Moscadelli, L. et al. 2013, A&A 558, A145

[3] Moscadelli, L. et al. 2016, A&A 585, A71.

 

Ionized and atomic outflows in the nearby merging system Mkn 848

The understanding of the mechanisms regulating the emergence and evolution of galaxies from the Big Bang, with their rich range of properties across cosmic time, constitutes a major goal of modern Astrophysics. During the last decades, important advances have been made from a theoretical viewpoint as well as from the observational side. However, important questions remain unanswered. Why the properties of the supermassive Black Holes (SMBH) found at the centre of galaxies are highly correlated with those of the host galaxies? Why models predict more massive galaxies than observed? How the intergalactic medium is enriched by metals?

Powerful gas outflows are routinely invoked to give answers to the above questions. They are originated either during the SMBH growth, when the nuclear object becomes visible as active galactic nucleus (AGN) and accretion disc winds are launched (AGN-driven outflows), or from stellar winds and supernovae explosions (star formation (SF)-driven outflows). Outflows are expected to affect the physical and dynamical conditions of the surrounding medium, hence regulating with a feedback mechanism the formation of new stars and the gas accretion onto the SMBH. However, we are still far from being able to include in detail the physics of outflows to galaxy models, and to understand their effects on galaxy evolution.

The recent work led by Michele Perna and with the participation, among others, of Giovanni Cresci, Alessandro Marconi and Filippo Mannucci from the Arcetri Astrophysical Observatory, focuses on the study of the kinematic and physical properties of powerful outflows in the nearby system Mkn 848, consisting of two merging galaxies at z ~ 0.04 (Fig. 1).

Mkn848 sdssFig.1: SDSS three-color image of the merging system Mkn 848. The two nuclei have a projected separation of 7.5 kpc. Merging signatures are identified in the two long, highly curved tidal tails of gas and stars emerging from the north-west (NW) and south-east (SE) galaxies.

The structure and multi-phase nature of the ejected material have been reconstructed thanks to a detailed analysis of integral field spectroscopy data from the survey MaNGA providing two-dimensional maps of stellar and gas velocities, as well as important physical properties of cool and warm gas. All these quantities have been used to constrain the outflows nature and their impact on the host galaxies. The authors revealed, for the first time, (emitting) ionised and (absorbing) neutral ejected gas in the two merging galaxies. They also detected the Na ID emission across the MaNGA field-of-view, so far detected in only other two galaxies. All these gas components are reasonably associated with strong AGN-driven outflows. The outflowing material reaches velocities as high as 600-1200 km/s, hence involving tremendous amount of energy that is transferred from the vicinity of the SMBH to kiloparsec scales (Fig. 2).

Mkn848 maps
Mkn848 spettro
Fig. 2: Upper panel: Line widths (W80) of the ionized [OIII] (left) and neutral NaID (right) gas. The broadening of the line features in the regions associated with orange/red colors (high velocities) is unequivocally due to outflows. Lower panel: Integrated spectra extracted from the red/orange regions in the upper panel showing very extended wings associated with the [OIII] emission line profiles and the very broad NaID absorption features. Figures taken from Perna et al 2019.

Among many other results, this work shows that detailed multi-phase studies are required to comprehensively characterise the outflows. Figure 3 shows a cartoon for Mkn 848, illustrating the reconstructd spatial configuration of the two merging galaxies and the mulit-phase outflows, as well as the gas ionization conditions. The authors found that the neutral outflow component might be related to outflow energetics similar to or even higher than those of the ionized component. This result further emphasises the need for follow-up observations aimed at detecting and characterising the different outflow phases in individual targets.

Mkn848 cartoonFig. 3: Cartoon illustration for Mkn 848. The blue ellipses and the black and yellow stars represent the galaxies and the central SMBHs, respectively, with the near edge-on orientation for the SE system and the almost face-on configuration of the NW galaxy. The cyan and grey areas refer to the tidal arms and the dust observed in the SDSS three-color image. The extended and tenuous yellow area indicates the regions associated with AGN ionization: in the SE system we observe an extended narrow-line-region (NLR) close to the plane of the sky; in the NW system the almost face-on configuration suggests that the NLR axis is close to the line-of-sight. The clouds indicate outflows and distinguish between ionized (yellow contour) and atomic (brown contour) gas, as well as between receding (red filled) and approaching (blue filled) material. The collected information suggest AGN-driven biconical outflows in the two merging galaxies. Figure taken from Perna et al 2019.

The results of this work are published in “Multi-phase outflows in Mkn 848 observed with SDSS-MaNGA Integral Field Spectroscopy”,M. Perna, G. Cresci, M. Brusa, G. Lanzuisi, A. Concas, V. Mainieri, F. Mannucci and A. Marconi, Astronomy and Astrophysics, in press.


 Edited by M. Perna and A. Gallazzi

An unprecedented view on ionized gas and outflows in the nearby active galaxy NGC 1365

All galaxies in the Universe are thought to host a supermassive black hole (BH) at their center. In some cases the BH can accrete large quantities of surrounding material and reprocess it in the form of energetic electromagnetic radiation, giving rise to a so-called active galactic nucleus (AGN), capable of accelerating fast winds and producing gas outflows. These outflows are believed to have an important role in shaping the formation and evolution of galaxies throughout the history of the Universe. Extended outflows of ionized gas are commonly observed in AGN but the low intrinsic spatial resolution of the observations has generally prevented a detailed characterization of their properties and impact on the host galaxies.

A team of astronomers from the Arcetri Astrophysical Observatory has started an observational campaign, called MAGNUM (Measuring Active Galactic Nuclei Under MUSE Microscope), to overcome these limitations by targeting the nearest galaxies hosting an AGN with the new-generation Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT) in Chile. MUSE provides a total of about 90000 spectra in the optical and near-infrared band on a wide area in the sky (1′⨉1′). This allowed the team to inspect theionized gas in the central kiloparsecs of nearby active galaxies in unprecedented detail, resolving its structure and kinematics down to the scale of single gas clouds (about 10 parsec). The first results of the MAGNUM survey are published in a work led by G. Venturi in collaboration with E. Nardini as well as A. Marconi, M. Mingozzi, G. Cresci, F. Mannucci, G. Risaliti, A. Gallazzi, M. Perna, P. Tozzi and S. Zibetti from the Arcetri Astrophysical Observatory. The paper (Venturi et al. 2018) focuses on the barred spiral galaxy NGC 1365 hosting an AGN.

Among the various ionized gas emission lines observable within MUSE wavelength range, Hα allows to trace star formation in the galaxy, while [OIII] emission is sensitive to the ionization from AGN photons. Moreover, from the Doppler shift of the emission lines it is possible to infer the kinematics of the ionized gas. Fig. 1 (left panel) displays the distribution of the ionized gas emission in the central 5 kpc of NGC 1365 covered by MUSE. Star formation predominantly occurs in an S-shaped region along the bar and in a circumnuclear ring (red), while the gas ionized by the energetic radiation from the spatially-unresolved AGN located in the nucleus (at the position of the cross) is distributed in a perpendicular double cone (green). The kinematics of the ionized gas reveals a bipolar outflow in correspondence of the ionization cones, with velocities up to about 200 km/s (Fig. 1 right panel). The biconical outflow approaches the observer to the bottom-left of the nucleus (negative velocities), while it recedes to the top-right (positive velocities). The former resides in fact above the disk of the galaxy, while the latter behind it, partially obscured by dust in the disk, as shown by their different brightness in the left panel.

NGC1365 maps
Figure 1: Ionized gas distribution and kinematics in the central 5 kpc of NGC 1365 obtained with MUSE at VLT. Left panel: Hα emission (red), tracing star formation in the galaxy, and [OIII] emission (green), due to the energetic ionizing radiation from the active galactic nucleus. Right panel: [OIII] velocity, revealing a biconical ionized outflow, approaching to the bottom-left (negative velocities), receding to the top-right (positive velocities).

Comparison with data from the Chandra X-ray space telescope, tracing the hot diffuse gas emitting in X-rays (with a temperature of about 106-107 K), shows that the diffuse X-ray emission predominantly arises from star-forming regions. However, the authors were able to isolate the hot gas component ionized by the AGN and show that this nicely matches the optical counterpart from MUSE emitting in [OIII], given by warm ionized gas (with a temperature of about 104 K). Moreover, the presence of a nuclear spatially-unresolved wind of hot, highly-ionized gas is traced by absorption lines in the X-rays, indicating a velocity of about 3000 km/s for this nuclear wind.

The spatially-resolved information provided by MUSE allowed the team to investigate the properties of the extended ionized outflow as a function of distance from the AGN. In particular, the radial profiles of the mass outflow rate and of the kinetic energy rate, that is, the rate at which the mass of ionized gas participating in the outflow and its associated kinetic energy flow away from the nucleus, are displayed in Fig. 2. After an initial peak at a radius of about 1 kpc, the mass outflow rate and the kinetic energy rate drop at larger distances, implying either that the outflow slows down with radius or that the AGN activity has intensified recently. Finally, the mass outflow rate of the nuclear X-ray wind is consistent with that of the extended ionized outflow within 1 kpc, suggesting that the nuclear and galactic-scale outflows are only two different phases of the same wind accelerated by the AGN.

NGC1365 profiles
Figure 2: Radial profiles of the mass outflow rate (left panel) and kinetic energy rate (right panel) of the galactic ionized outflow as a function of distance from the active galactic nucleus. Blue and red points indicate the approaching and the receding cone, respectively (see right panel of Fig. 1). The green dashed line marks the mass outflow rate of the fast nuclear wind measured from X-rays.

The results of this work are published in:

Venturi G. et al., ‘MAGNUM survey: A MUSE-Chandra resolved view on ionized outflows and photoionization in the Seyfert galaxy NGC1365’, 2018, A&A, 619, 74  (also available here)

Further MAGNUM publications on the topic:

Mingozzi M. et al., ‘The MAGNUM survey: different gas properties in the outflowing and disk components in nearby active galaxies with MUSE’, A&A, accepted (available here)

Venturi G. et al., 'Ionized gas outflows from the MAGNUM survey: NGC 1365 and NGC 4945’, 2017, FrASS, 4, 46 (also available here)


Edited by G. Venturi and A. Gallazzi

Synchrotron emission in molecular cloud cores: the SKA view

Understanding the role of magnetic fields in star-forming regions is of fundamental importance. In the near future, the exceptional sensitivity of the Square Kilometre Array (SKA) will offer a unique opportunity to evaluate the magnetic field strength in molecular clouds and cloud cores through synchrotron emission observations.

During the last decades, many observational techniques have been developed to gather information on the magnetic field strength and geometry in molecular clouds and star-forming regions such as Zeeman splitting of hyperfine molecular transitions, optical and near-infrared polarisation of starlight, polarisation of sub-millimetre thermal dust emission, maser emission polarisation, Goldreich–Kylafis effect, and Faraday rotation. Together, all these techniques contribute to elucidating the still controversial role of magnetic fields in the process of star formation.

An additional method to probe magnetic fields in molecular clouds is via synchrotron radiation produced by relativistic electrons braked by a cloud’s magnetic fields. The intensity of the emission depends only on the electron density per unit energy and the projection of the magnetic field on the plane perpendicular to the line of
sight. However, this technique was constrained by two limitations: the poor knowledge of the interstellar flux of cosmic-ray electrons below about 500 MeV and the limited sensitivity of current radio telescopes.

Today, thanks to the latest data release of the Voyager 1 spacecraft, the flux of cosmic-ray electrons down to about 3 MeV is well known (see Fig. 1). On the instrumental side, with the advent of the Square Kilometre Array (SKA),we are now approaching a new important era for high resolution observations at radio frequencies.

Marco Padovani and Daniele Galli of the INAF-Osservatorio Astrofisico di Arcetri, in a recenlty published paper (Padovani & Galli 2018)  explored the capability of SKA in detecting synchrotron emission in two starless molecular cloud cores in the southern hemisphere, Barnard 68 in Ophiuchus and FeSt 1-457 in the Pipe Nebula, finding that it will be possible to reach signal-to-noise ratios of the order of 2−23 at the lowest frequencies observable by SKA (60−218 MHz) with one hour of integration (see Fig. 2).

They also found a typical spectral index alpha=(pi−1)/2 ~0.6, intermediate between the values 0.2 and 1.1 resulting from the low- and high-energy asymptotic slopes p of the primary cosmic-ray electron flux. Since in starless cores the interstellar cosmic-ray electron flux is not attenuated by losses, the authors expect alpha ~ 0.6 to be a universal quantity, weakly dependent on density and magnetic field strength profiles at SKA1-Low frequencies.

Esyn jespectrum new

Fig.1: Flux of interstellar cosmic-ray electrons (black solid line) as a function of energy. Data: Voyager 1 (solid purple squares) at low energies, AMS-02 (solid cyan circles) at high energies. The red, blue, and green thick lines show the energy range that mostly contributes to synchrotron emission in the frequency range of SKA for the values of the magnetic field strength listed in the legend. The orange dashed line shows the cosmic-ray electron-positron flux obtained from Galactic synchrotron emission.

Snupaperfinal_highlight.png

Fig.2:  Radial flux density profiles for Barnard 68 (B68) and FeSt 1-457. The observing frequency is shown in black at the top of each column, while numbers in the upper-right corner of each subplot represent the radius-averaged signal-to-noise depending on the assumption on the magnetic field strength profile. The telescope beam is shown in the leftmost column for B68 (short-dashed black line, 330") and FeSt 1-457 (long-dashed black line, 284"). Hatched areas display SKA sensitivities for one hour of integration at different frequencies. The rightmost panel shows the flux density as a function of frequency. Empty (solid) circles refer to a signal-to-noise smaller (larger) than 3, respectively. The spectral index alpha is shown on the right of each curve.

 

Marco Padovani acknowledges funding from the European Unions Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 664931.

Complex starts with simple:

First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293-2422

An international group of scientists from the Arcetri Astrophysical Observatory (INAF-OAA, Florence, Italy), the Ural Federal University (Russia), the Max-Planck Institute for Extraterrestrial Physics (MPE, Garching, Germany) and the University College of London (UK) has obtained for the first time maps of the emission of the formyl radical, HCO, towardsa Solar-type protostellar binary. This simple molecule is the basic precursor of more complex organic molecules related to the origin of Life.

The formation of complex organic molecules (COMs) − carbon-based compounds with more than 5 atoms - is being intensively debated in astrochemistry. COMs play a central role in prebiotic chemistry and are thought to be directly linked to the origin of life. Numerous efforts have been done in the last years to understand how COMs are formed in the interstellar medium (ISM), by combining observations, chemical models and laboratory experiments. However, despite all efforts, our understanding about the synthesis of COMs in the ISM is still very limited. Two  paradigms have been proposed: i) gas-phase chemistry triggered by the evaporation (thermal or non-thermal) of interstellar ices; and ii) hydrogenation and/or radical-radical reactions on dust grain surfaces.

A key step to understand how complex molecules are built up in the ISM is to study their molecular precursors, namely, the basic pieces that lead to their formation. Many chemical models and laboratory experiments have suggested that the simple formyl radical, HCO, is the precursor of COMs like e.g. methanol, the sugar-like molecule glycolaldehyde, the sugar-alcohol ethylene glycol, or formamide. However, despite the importance of HCO to build-up chemical complexity, little is known so far about its formation.

To better understand the role of HCO in the formation of COMs, an international group of astronomers have studied this molecule towards the Solar-type protostellar binary IRAS 16293−2422 using the Atacama Large Millimeter/submillimeter Array (ALMA). The work is led by the Marie Skłodowska-Curie fellow Víctor M. Rivilla, and includes also the participation of Maite Beltrán, Francesco Fontani and Riccardo Cesaroni(INAF-Arcetri Astrophysical observatory). The high angular resolution (∼1′′, ∼150 au) maps reveal compact HCO emission arising from the two protostars (see Figure 1). The line profiles also show redshifted absorption produced by foreground material of a circumbinary envelope that is infalling towards the protostars. Additionally, IRAM 30m single-dish data revealed a more extended HCO component arising from the common circumbinary envelope.

   fig rivilla1

 Fig. 1: ALMA maps of the HCO emission and absorption towards the two members, A and B, of theSolar-type protostellar binary IRAS 16293−2422.

The comparison between the observed molecular abundances and the chemical model  (see Figure 2) suggests that whereas the extended HCO from the envelope can be formed via gas-phase reactions during the cold collapse of the natal core, the HCO in the hot corinos surrounding the protostars is predominantly formed by the hydrogenation of CO on the surface of dust grains and subsequent thermal desorption during the protostellar phase (see Figure 3).The derived abundance of HCO in the dust grains is high enough to produce efficiently more complex species such as formaldehyde (H2CO), methanol (CH3OH), and glycolaldehyde (CH2OHCHO) by surface chemistry

fig rivilla2
Fig. 2: Chemical routes discussed in the article and implemented in the chemical model to study the formation and HCO (in white) and glycoladehyde, CH2OHCHO (in green). The solid and dashed arrows indicate gas-phase and grain surface reactions, respectively.

fig rivilla3

Fig. 3:  Results of the different chemical models (I, II and III) developed to investigate the formation of HCO during the warm-up phase of a protostar. The evolution of the molecular abundance of HCO is represented as a function of temperature. The area within the dotted curves delimit the uncertainty of the chemical model. Model I (blue) includes only gas-phase reactions; model II (red) includes gas-phase reactions and the surface hydrogenation of CO; and model III (green) includes gas-phase reactions and the surface reaction H2CO + OH HCO + H2CO. The horizontal light gray band indicates the range of HCO abundances found in the ALMA observations.

Publication:First ALMA maps of HCO, an important precursor of complex organic molecules, towards IRAS 16293-2422V. M. Rivilla, M. T. Beltrán, A. Vasyunin, P. Caselli, S. Viti, F. Fontani, R. Cesaroni, article accepted in Monthly Notices of the Royal Astronomical Society, in press, arXiv:1811.01650, https://arxiv.org/abs/1811.01650

Contact:  

Víctor M. Rivilla Rodríguez

Marie Sklodowska-Curie ASTROFIT2 Fellow

Osservatorio Astrofisico di Arcetri, Florence, Italy

Website:http://www.arcetri.astro.it/~rivilla/

e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Acknowledgments: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 664931