- ID:
- ivo://CDS.VizieR/J/A+A/648/A3
- Title:
- LOFAR Two-metre Sky Survey Deep Fields DR1
- Short Name:
- J/A+A/648/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the source associations, cross-identifications, and multi-wavelength properties of the faint radio source population detected in the deep tier of the LOFAR Two Metre Sky Survey (LoTSS): the LoTSS Deep Fields. The first LoTSS Deep Fields data release consists of deep radio imaging at 150MHz of the ELAIS-N1, Lockman Hole, and Bootes fields, down to RMS sensitives of around 20, 22, and 32uJy/beam, respectively. These fields are some of the best studied extra-galactic fields in the northern sky, with existing deep, wide-area panchromatic photometry from X-ray to infrared wavelengths, covering a total of ~26 square degrees. We first generated improved multi-wavelength catalogues in ELAIS-N1 and Lockman Hole; combined with the existing catalogue for Bootes, we present forced, matched aperture photometry for over 7.2 million sources across the three fields. We identified multi-wavelength counterparts to the radio detected sources, using a combination of the Likelihood Ratio method and visual classification, which greatly enhances the scientific potential of radio surveys and allows for the characterisation of the photometric redshifts and the physical properties of the host galaxies. The final radio-optical cross-matched catalogue consists of 81951 radio-detected sources, with counterparts identified and multi-wavelength properties presented for 79820 (>97%) sources. We also examine the properties of the host galaxies, and through stacking analysis find that the radio population with no identified counterpart is likely dominated by AGN at z~3-4. This dataset contains one of the largest samples of radio-selected star-forming galaxies and active galactic nuclei (AGN) at these depths, making it ideal for studying the history of star-formation, and the evolution of galaxies and AGN across cosmic time.
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- ID:
- ivo://CDS.VizieR/J/A+A/622/A1
- Title:
- LOFAR Two-metre Sky Survey DR1 source catalog
- Short Name:
- J/A+A/622/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45{deg}00'00'' to 57{deg}00'00'') were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325694 sources are detected with a signal of at least five times the noise, and the source density is a factor of ~10 higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S_144MHz_=71{mu}Jy/beam and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6'' and the positional accuracy is within 0.2''. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further ~20 articles that highlight the scientific potential of LoTSS.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A108
- Title:
- LOFAR view of NGC 3998
- Short Name:
- J/A+A/634/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-power radio sources dominate the radio sky. They tend to be small in size and dominated by their cores, but the origin of their properties and the evolution of their radio plasma are not well constrained. Interestingly, there is mounting evidence that low-power radio sources can significantly aect their surrounding gaseous medium and may therefore be more relevant for galaxy evolution than previously thought. In this paper, we present low radio frequency observations obtained with LOFAR at 147MHz of the radio source hosted by NGC 3998. This is a rare example of a low-power source that is extremely dominated by its core, but that has two large scale lobes of low surface brightness. We combine the new 147MHz image with available 1400MHz data to derive the spectral index over the source. Despite the low surface brightness, reminiscent of remnant structures, the lobes show an optically thin synchrotron spectral index (~0.6). We interpret this as being due to rapid decollimation of the jets close to the core, to high turbulence of the plasma flow, and to entrainment of thermal gas. This could be the result of intermittent activity of the central active galactic nucleus, or, more likely, temporary disruption of the jet due to the interaction of the jet with the rich circumnuclear interstellar matter. Both would result in sputtering energy injection from the core, which would keep the lobes fed, albeit at a low rate.We discuss these results in connection with the properties of low-power radio sources in general. Our findings show that amorphous low surface brightness lobes should not be interpreted by default as remnant structures. Large deep surveys (in particular the LOFAR 150MHz LoTSS and the recently started 1400MHz Apertif survey) will identify a growing number of objects similar to NGC 3998 where these ideas can be further tested.
- ID:
- ivo://CDS.VizieR/VI/128
- Title:
- Log of CGPS exposures
- Short Name:
- VI/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Dominion Radio Astrophysical Observatory at Penticton (HIA/NRC), in collaboration with an international Consortium of astronomers, has begun a high-resolution survey of the atomic hydrogen and radio continuum emission from our Milky Way galaxy. By constructing a mosaic of 190 synthesis fields, the survey will cover Galactic longitudes from L=74.2 to 147.3 degrees and latitudes from B=-3.6 to +5.6 degrees, resolving features as small as 1 arcminute. For each mosaic (1024x1024 pixels), atomic hydrogen observations are presented as a data "cube" with 272 spectral channels having a velocity resolution of 1.3km/s. Stokes I continuum images at 1420MHz and 408MHz are produced, as well as selected Stokes Q, U and V images at 1420MHz. Complementary images in the four IRAS infrared bands and data cubes of CO (J=1-0) emission have also been created as part of the Survey. In addition to the 5x5{deg} mosaics, a series of nine 15x15{deg} mosaics of 408MHz emission, and possibly other lower radio frequencies, will be created. Mosaics are archived as they are processed and released to the Consortium. Archived data are in FITS format, except for the occasional text file. Imaging of the molecular phase of the ISM, traced by the CO molecule, has been realized at the Five College Radio Astronomy Observatory. High-resolution IRAS images of the dust component, seen through its infrared emission, have been completed at far-infrared wavelengths at the California Institute of Technology, and in the mid-infrared at the Canadian Institute for Theoretical Astrophysics at the University of Toronto. Complementary radio continuum images at frequencies below 408MHz are being contributed by the Mullard Radio Astronomy Observatory of the University of Cambridge and at the Beijing Astronomical Observatory.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A40
- Title:
- LoLSS-Deep Bootes 54MHz catalog
- Short Name:
- J/A+A/655/A40
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the first sub-mJy (~0.7mJy/beam) survey to be completed below 100 MHz, which is over an order of magnitude deeper than previously achieved for widefield imaging of any field at these low frequencies. The high-resolution (15x15arcsec) image of the Bootes field at 34-75MHz is made from 56 hours of observation with the LOw Frequency ARray (LOFAR) Low Band Antenna (LBA) system. We present a radio source catalogue containing 1,948 sources detected over an area of 23.6 sq. deg, with a peak flux density threshold of 5{sigma}. Using the available deep 144-MHz data, we identified 144-MHz counterparts to all the 54-MHz sources, and produced a matched catalogue within the deep optical coverage area containing 829 sources.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A11
- Title:
- LoTSS/HETDEX. Optical quasars. I.
- Short Name:
- J/A+A/622/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio-loud/radio-quiet (RL/RQ) dichotomy in quasars is still an open question. Although it is thought that accretion onto supermassive black holes in the centre the host galaxies of quasars is responsible for some radio continuum emission, there is still a debate as to whether star formation or active galactic nuclei (AGN) activity dominate the radio continuum luminosity. To date, radio emission in quasars has been investigated almost exclusively using high-frequency observations in which the Doppler boosting might have an important effect on the measured radio luminosity, whereas extended structures, best observed at low radio frequencies, are not affected by the Doppler enhancement. We used a sample of quasars selected by their optical spectra in conjunction with sensitive and high-resolution low-frequency radio data provided by the LOw Frequency ARray (LOFAR) as part of the LOFAR Two-Metre Sky Survey (LoTSS) to investigate their radio properties using the radio loudness parameter (R=L_144MHz_/L_iband_). The examination of the Li band radio continuum emission and RL/RQ dichotomy in quasars exhibits that quasars show a wide continuum of radio properties (i.e. no clear bimodality in the distribution of R). Radio continuum emission at low frequencies in low-luminosity quasars is consistent with being dominated by star formation. We see a significant albeit weak dependency of R on the source nuclear parameters. For the first time, we are able to resolve radio morphologies of a considerable number of quasars. All these crucial results highlight the impact of the deep and high-resolution low-frequency radio surveys that foreshadow the compelling science cases for the Square Kilometre Array (SKA).
- ID:
- ivo://CDS.VizieR/J/ApJS/235/40
- Title:
- Low-mass black holes in Sy1 galaxies. II. SDSS-DR7
- Short Name:
- J/ApJS/235/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new sample of 204 low-mass black holes (LMBHs) in active galactic nuclei (AGNs) is presented with black hole masses in the range of (1-20)x10^5^M_{sun}_. The AGNs are selected through a systematic search among galaxies in the Seventh Data Release (DR7) of the Sloan Digital Sky Survey (SDSS), and careful analyses of their optical spectra and precise measurement of spectral parameters. Combining them with our previous sample selected from SDSS DR4 makes it the largest LMBH sample so far, totaling over 500 objects. Some of the statistical properties of the combined LMBH AGN sample are briefly discussed in the context of exploring the low-mass end of the AGN population. Their X-ray luminosities follow the extension of the previously known correlation with the [OIII] luminosity. The effective optical-to-X-ray spectral indices {alpha}_OX_, albeit with a large scatter, are broadly consistent with the extension of the relation with the near-UV luminosity L_2500{AA}_. Interestingly, a correlation of {alpha}_OX_ with black hole mass is also found, with {alpha}OX being statistically flatter (stronger X-ray relative to optical) for lower black hole masses. Only 26 objects, mostly radio loud, were detected in radio at 20cm in the FIRST survey, giving a radio-loud fraction of 4%. The host galaxies of LMBHs have stellar masses in the range of 10^8.8^-10^12.4^M_{sun}_ and optical colors typical of Sbc spirals. They are dominated by young stellar populations that seem to have undergone continuous star formation history.
478. Low-z BQS Quasars
- ID:
- ivo://CDS.VizieR/J/MNRAS/263/425
- Title:
- Low-z BQS Quasars
- Short Name:
- J/MNRAS/263/425
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/846/44
- Title:
- Luminous persistent sources in nearby galaxies search
- Short Name:
- J/ApJ/846/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities >10% of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within <108Mpc, in a footprint of 10600deg^2^. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1" of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of <~5x10^-5^Mpc^-3^, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source (<~10^-3^L_*_^-1^). Assuming a persistent source lifetime of 100 years, this implies a birth rate of <~5x10^-7^yr^-1^Mpc^-3^. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of >~0.8yr^-1^. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/12
- Title:
- Luminous X-ray candidates within D25 of galaxies
- Short Name:
- J/ApJS/222/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using Chandra archive data we conduct a thorough survey of luminous X-ray sources. We directly analyze about 9400 ACIS Observations and cross-correlate the X-ray sources with 77000 galaxies within 250Mpc. The final catalog includes 119 unique luminous X-ray source candidates with L_X_>3x10^40^erg/s from 93 galaxies or 41 HLX candidates with L_X_>1x10^41^erg/s from 35 galaxies. We derive a moderate contamination rate due to foreground or background sources. We also cross-correlate the catalog with FIRST, perform variability and periodicity tests, and analyze one HLX candidate in particular. Our catalog could be a starting point to perform follow-up observations.
