The Population of Compact Radio Sources in M17
Abstract: We present a catalog of radio sources of the M17 region based on deep X-band radio observations centered at 10 GHz obtained with the Jansky Very Large Array in the A configuration. We detect a total of 194 radio sources, 12 of them extended and 182 compact. We find that a significant fraction (at least 40% in our catalog) have suspected gyrosynchrotron emission associated with stellar coronal emission. By comparing the radio luminosities of our sources with their X-ray counterparts, when available, we find tha… Show more
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Cited by 3 publications
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The early evolution of young massive clusters
Context. Characterising the outcome of the star formation process is key to understand and predict the evolution of stellar populations. Especially the fraction of massive stars in young stellar clusters is of importance as they are the dominant sources of both mechanical and radiative feedback, strongly influencing the thermal and dynamical state of their birth environments, and beyond. Their supernovae may trigger the formation of new generations of stars in neighbouring regions. It turns out that a significant fraction of massive stars escape from their parent cluster via dynamical interactions of single stars and/or multiple stellar systems. Aims. M 17 is the nearest giant H II region hosting a very young and massive cluster: NGC 6618. Our aim is to identify stars brighter than G ≲ 21 mag that belong to NGC 6618, including the (massive) stars that may have escaped since its formation, and to determine the cluster distance and age. Methods. The Gaia DR3 database was used to identify members of NGC 6618 based on parallax and proper motion within 9′ from the cluster centre. We searched for nearby stars in a field of 5° around the cluster centre that may have originated from the cluster, and we determined their transverse velocity, kinematic age, and impact parameter. Results. We identified 42 members of NGC 6618 of which eight have a spectral type of O, with a mean distance of 1675−18+19 pc and a (transversal) velocity dispersion of about 3 km s−1, and a radial velocity dispersion of ∼6 km s−1. Another ten O stars are associated with NGC 6618, but they cannot be classified as members due to poor astrometry and/or high extinction. We have also identified six O star runaways. The relative transverse velocity of these runaways ranges from 10 to 70 km s−1 and their kinematic age ranges from about 100 to 750 kyr. Given the already established young age of NGC 6618 (≲1 Myr), this implies that massive stars are being ejected from the cluster already directly after (or during) the cluster formation process. Conclusions. When constructing the initial mass function, one has to take into account the massive stars that have already escaped from the cluster, that is, about 30% of the O stars of the original population of NGC 6618. The trajectories of the O runaways can be traced back to the central 0.2–0.3 pc region of NGC 6618. The good agreement between the evolutionary and kinematic age of the runaways implies that the latter provides an independent way to estimate (a lower limit to) the age of the cluster.
The early evolution of young massive clusters
Context. Characterising the outcome of the star formation process is key to understand and predict the evolution of stellar populations. Especially the fraction of massive stars in young stellar clusters is of importance as they are the dominant sources of both mechanical and radiative feedback, strongly influencing the thermal and dynamical state of their birth environments, and beyond. Their supernovae may trigger the formation of new generations of stars in neighbouring regions. It turns out that a significant fraction of massive stars escape from their parent cluster via dynamical interactions of single stars and/or multiple stellar systems. Aims. M 17 is the nearest giant H II region hosting a very young and massive cluster: NGC 6618. Our aim is to identify stars brighter than G ≲ 21 mag that belong to NGC 6618, including the (massive) stars that may have escaped since its formation, and to determine the cluster distance and age. Methods. The Gaia DR3 database was used to identify members of NGC 6618 based on parallax and proper motion within 9′ from the cluster centre. We searched for nearby stars in a field of 5° around the cluster centre that may have originated from the cluster, and we determined their transverse velocity, kinematic age, and impact parameter. Results. We identified 42 members of NGC 6618 of which eight have a spectral type of O, with a mean distance of 1675−18+19 pc and a (transversal) velocity dispersion of about 3 km s−1, and a radial velocity dispersion of ∼6 km s−1. Another ten O stars are associated with NGC 6618, but they cannot be classified as members due to poor astrometry and/or high extinction. We have also identified six O star runaways. The relative transverse velocity of these runaways ranges from 10 to 70 km s−1 and their kinematic age ranges from about 100 to 750 kyr. Given the already established young age of NGC 6618 (≲1 Myr), this implies that massive stars are being ejected from the cluster already directly after (or during) the cluster formation process. Conclusions. When constructing the initial mass function, one has to take into account the massive stars that have already escaped from the cluster, that is, about 30% of the O stars of the original population of NGC 6618. The trajectories of the O runaways can be traced back to the central 0.2–0.3 pc region of NGC 6618. The good agreement between the evolutionary and kinematic age of the runaways implies that the latter provides an independent way to estimate (a lower limit to) the age of the cluster.
Radio survey of the stellar population in the infrared dark cloud G14.225-0.506
The infrared dark cloud (IRDC) G14.225-0.506 is part of the extended and massive molecular cloud located to the southwest of the region M17. The cloud is associated with a network of filaments, which result in two different dense hubs, as well as with several signposts of star formation activity and a rich population of protostars and young stellar objects (YSOs). The aim of this work is to study the centimeter continuum emission in order to characterize the stellar population in both regions, as well as to study the evolutionary sequence across the IRDC G14.225-0.506. We performed deep ($ mu radio continuum observations at 6 and 3.6 cm toward the IRDC G14.225-0.506 using the Karl G.\ Jansky Very Large Array (VLA) in its most extended A configuration (sim prime $). Data at both C and X bands were imaged using the same (u,v) range in order to derive spectral indices. We have also made use of observations taken during different days to study the presence of variability at short timescales toward the detected sources. We detected a total of 66 sources, 32 in the northern region G14.2-N and 34 in the southern region G14.2-S. Ten of the sources are found to be variable, with three located in G14.2-N and seven in G14.2-S. Based on their spectral index, the emission in G14.2-N is mainly dominated by nonthermal sources while G14.2-S contains more thermal emitters. Approximately 75<!PCT!> of the sources present a counterpart at other wavelengths. When considering the inner 0.4 pc region around the center of each hub, the number of infrared (IR) sources in G14.2-N is larger than in G14.2-S by a factor of 4. We also studied the relation between the radio luminosity and the bolometric luminosity, finding that the thermal emission of the studied sources is compatible with thermal radio jets. For our sources with X-ray counterparts, the nonthermal emitters follow a Güdel-Benz relation with $ = 0.03$, as previously suggested for other similar regions. We found similar levels of fragmentation between G14.2-N and G14.2-S, suggesting that both regions are most likely twin hubs. The nonthermal emission found in the less evolved objects, mainly coming from G14.2-N, suggests that G14.2-N may be composed of more massive YSOs as well as being in a more advanced evolutionary stage, consistent with the "filament-halo" gradient in age and mass from previous works. Overall, our results confirm a wider evolutionary sequence from the southwest to northeast starting in G14.2-S as the youngest part, followed by G14.2-N, and ending with the most evolved region M17.
A global view on star formation: The GLOSTAR Galactic plane survey
The GLObal view on STAR formation in the Milky Way (GLOSTAR) survey studies star formation with the Very Large Array (VLA) and the Effelsberg 100 meter radio telescope in the Galactic plane between $-2 and $|b| < 1 and the Cygnus\,X region ($76 and $-1 < b< 2 with unprecedented sensitivity in both flux density ($1 $) and the capability of detecting emission with angular scales in the range from 1 $''$0 to the largest radio structures in the Galaxy on the order of a few degrees in size. Here, we provide a complete GLOSTAR-VLA D-configuration radio source catalog for the part of the Galactic disk covered. A catalog for the ``pilot region'' between $28 has been published in a previous paper and here we present the complementary catalog for the area within $2 and $|b| < 1 degr$. Observations were taken with the VLA in a 4 -- 8 GHz band to image 100 square degrees of the inner Galactic disk at a reference frequency of 5.8 GHz, using a total of 260 hours of telescope time. We determined spectral indices (alpha ; $S_ inside the observed band and in the frequency range of 1.4 -- 5.8 GHz by complementing our results with those from The HI/OH/Recombination line survey of the inner Milky Way (THOR), which covers 1 -- 2 GHz. The final images have an angular resolution of $18''$ and an average sensitivity of 123\,mu $. The sensitivity is better ($ $) in areas free of extended emission. The complementary Galactic disk catalog presented in this work consists of radio sources. Of these are known large-scale structure sources such as star-forming region complexes, well-known supernova remnants (SNRs), SNR candidates, or parts thereof. The remaining are discrete individual sources. Source parameters --- namely flux densities, sizes, spectral indices, and classifications --- are reported. We identify 769 region candidates, 359 of which have been newly classified as such. The mean value of spectral indices of 225 regions is $+0.14 consistent with most of them emitting optically thin thermal radio emission. Combining our results with the previously published catalog of the pilot region, the final GLOSTAR-VLA D-configuration catalog contains 12\,981 radio sources.
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