Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane

Chakraborty, Arnab; Roy, Nirupam; Wang, Y.; Datta, Abhirup; Beuther, H.; Medina, S.; Menten, K. M.; Urquhart, J. S.; Brunthaler, A.; Dzib, S. A.

doi:10.1093/mnras/stz3621

Cited by 10 publications

(8 citation statements)

References 25 publications

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“…Preliminary results of a study focused on the unresolved unidentified sources with negative spectral index (∼340 sources of the present catalog), such as was performed by Chakraborty et al (2020), indicated that differential source counts in the distribution trend of extragalactic sources result from other surveys or catalogs. However, we recall that the observed fields are in the surroundings of the Galactic plane, dense in Galactic sources, both of thermal and nonthermal nature.…”

Section: Search For Counterpartsmentioning

confidence: 66%

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

Benaglia

Ishwara‐Chandra

Intema

et al. 2020

A&A

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Context. Observations at the radio continuum band below the gigahertz band are key when the nature and properties of nonthermal sources are investigated because their radio radiation is strongest at these frequencies. The low radio frequency range is therefore the best to spot possible counterparts to very high-energy (VHE) sources: relativistic particles of the same population are likely to be involved in radio and high-energy radiation processes. Some of these counterparts to VHE sources can be stellar sources. Aims. The Cygnus region in the northern sky is one of the richest in this type of sources that are potential counterparts to VHE sources. We surveyed the central ∼15 sq deg of the Cygnus constellation at the 325 and 610 MHz bands with angular resolutions and sensitivities of 10″ and 6″, and 0.5 and 0.2 mJy beam−1, respectively. Methods. The data were collected during 172 h in 2013–2017, using the Giant Metrewave Radio Telescope with 32 MHz bandwidth, and were calibrated using the SPAM routines. The source extraction was carried out with the PyBDSF tool, followed by verification through visual inspection of every putative catalog candidate source in order to determine its reliability. Results. In this first paper we present the catalog of sources, consisting of 1048 sources at 325 MHz and 2796 sources at 610 MHz. By cross-matching the sources from both frequencies with the objects of the SIMBAD database, we found possible counterparts for 143 of them. Most of the sources from the 325-MHz catalog (993) were detected at the 610 MHz band, and their spectral index α was computed adopting S(ν) ∝ να. The maximum of the spectral index distribution is at α = −1, which is characteristic of nonthermal emitters and might indicate an extragalactic population.

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Section: Search For Counterpartsmentioning

confidence: 66%

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

Benaglia

Ishwara‐Chandra

Intema

et al. 2020

A&A

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“…In addition to many sources that are located in the Milky Way, there is also a large number of extragalactic sources in the survey. While these sources were not the main focus of the survey, they are an interesting by-product (e.g., Chakraborty et al 2020).…”

Section: Continuummentioning

confidence: 99%

A global view on star formation: The GLOSTAR Galactic plane survey

Brunthaler

Menten

Dzib

et al. 2021

A&A

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Aims. Surveys of the Milky Way at various wavelengths have changed our view of star formation in our Galaxy considerably in recent years. In this paper we give an overview of the GLOSTAR survey, a new survey covering large parts (145 square degrees) of the northern Galactic plane using the Karl G. Jansky Very Large Array (JVLA) in the frequency range 4 − 8 GHz and the Effelsberg 100m telescope. This provides for the first time a radio survey covering all angular scales down to 1.5 arcsecond, similar to complementary near-IR and mid-IR galactic plane surveys. We outline the main goals of the survey and give a detailed description of the observations and the data reduction strategy. Methods. In our observations we covered the radio continuum in full polarization, as well as the 6.7 GHz methanol maser line, the 4.8 GHz formaldehyde line, and seven radio recombination lines. The observations were conducted in the most compact D configuration of the VLA and in the more extended B configuration. This yielded spatial resolutions of 18" and 1.5" for the two configurations, respectively. We also combined the D configuration images with the Effelsberg 100-m data to provide zero spacing information, and we jointly imaged the D-and B-configuration data for optimal sensitivity of the intermediate spatial ranges. Results. Here we show selected results for the first part of the survey, covering the range of 28 • < l < 36 • and |b| < 1 • , including the full low-resolution continuum image, examples of high-resolution images of selected sources, and the first results from the spectral line data.

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“…For indices between −0.1 and 2, the emission corresponds to thermal emission that is associated with Hii regions or planetary nebulae (PNe). If it is steeply negative, that is ≤0.5, we consider it to be non-thermal, which means the emission is synchrotron in nature and could come from supernova remnants (SNR) or extra-galactic sources such as active galactic nuclei (AGN) (Condon 1984;Rodríguez et al 2012;Dzib et al 2013;Chakraborty et al 2020). We record the values of the spectral indices in Table A.1.…”

Section: Spectral Indexmentioning

confidence: 99%

A global view on star formation: The GLOSTAR Galactic plane survey

Nguyen

Rugel

Menten

et al. 2021

A&A

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Context. The Central Molecular Zone (CMZ), a ∼200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 μm infrared sources that have been identified as YSO candidates. Aims. Our goal is to investigate the presence of centimetre wavelength radio continuum counterparts to this sample of YSO candidates which we use to constrain the current SFR in the CMZ. Methods. As part of the GLObal view on STAR formation (GLOSTAR) survey, D-configuration Very Large Array data were obtained for the Galactic Centre, covering −2° < l < 2° and −1° < b < 1° with a frequency coverage of 4–8 GHz. We matched YSOs with radio continuum sources based on selection criteria and classified these radio sources as potential H II regions and determined their physical properties. Results. Of the 334 YSO candidates, we found 35 with radio continuum counterparts. We find that 94 YSOs are associated with dense dust condensations identified in the 870 μm ATLASGAL survey, of which 14 have a GLOSTAR counterpart. Of the 35 YSOs with radio counterparts, 11 are confirmed as H II regions based on their spectral indices and the literature. We estimated their Lyman continuum photon flux in order to estimate the mass of the ionising star. Combining these with known sources, the present-day SFR in the CMZ is calculated to be ∼0.068 M⊙ yr−1, which is ∼6.8% of the Galactic SFR. Candidate YSOs that lack radio counterparts may not have yet evolved to the stage of exhibiting an H II region or, conversely, are older and have dispersed their natal clouds. Since many lack dust emission, the latter is more likely. Our SFR estimate in the CMZ is in agreement with previous estimates in the literature.

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Characterization of unresolved and unclassified sources detected in radio continuum surveys of the Galactic plane

Cited by 10 publications

References 25 publications

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog

A global view on star formation: The GLOSTAR Galactic plane survey

A global view on star formation: The GLOSTAR Galactic plane survey

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