- ID:
- ivo://CDS.VizieR/J/MNRAS/438/796
- Title:
- Local radio-galaxy population at 20GHz
- Short Name:
- J/MNRAS/438/796
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made the first detailed study of the high-frequency radio-source population in the local Universe, using a sample of 202 radio sources from the Australia Telescope 20GHz (AT20G) survey identified with galaxies from the 6dF Galaxy Survey (6dFGS). The AT20G-6dFGS galaxies have a median redshift of z=0.058 and span a wide range in radio luminosity, allowing us to make the first measurement of the local radio luminosity function at 20GHz. Our sample includes some classical Fanaroff-Riley type I (FR I) and FR II radio galaxies, but most of the AT20G-6dFGS galaxies host compact (FR 0) radio active galactic nuclei which appear to lack extended radio emission even at lower frequencies. Most of these FR 0 sources show no evidence for relativistic beaming, and the FR 0 class appears to be a mixed population which includes young compact steep-spectrum and gigahertz peaked-spectrum radio galaxies. We see a strong dichotomy in the Wide-field Infrared Survey Explorer (WISE) mid-infrared colours of the host galaxies of FR I and FR II radio sources, with the FR I systems found almost exclusively in WISE 'early-type' galaxies and the FR II radio sources in WISE 'late-type' galaxies. The host galaxies of the flat- and steep-spectrum radio sources have a similar distribution in both K-band luminosity and WISE colours, though galaxies with flat-spectrum sources are more likely to show weak emission lines in their optical spectra. We conclude that these flat-spectrum and steep-spectrum radio sources mainly represent different stages in radio-galaxy evolution, rather than beamed and unbeamed radio-source populations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/2703
- Title:
- Local SDSS galaxies in Herschel Stripe 82
- Short Name:
- J/MNRAS/457/2703
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a set of 3319 galaxies in the redshift interval 0.04<z<0.15 Herschel/SPIRE 250{mu}m band. Total infrared (TIR) luminosities derived from HerS and Wide-field Infrared Survey Explorer (WISE) photometry allow us to compare infrared and optical estimates of SFR with unprecedented statistics for diverse classes of galaxies. We find excellent agreement between TIR-derived and emission line-based SFRs for H ii galaxies. Other classes, such as active galaxies and evolved galaxies, exhibit systematic discrepancies between optical and TIR SFRs. We demonstrate that these offsets are attributable primarily to survey biases and the large intrinsic uncertainties of the D_n_4000- and colour-based optical calibrations used to estimate the SDSS SFRs of these galaxies. Using a classification scheme which expands upon popular emission-line methods, we demonstrate that emission-line galaxies with uncertain classifications include a population of massive, dusty, metal-rich star-forming systems that are frequently neglected in existing studies. We also study the capabilities of infrared selection of star-forming galaxies. FIR selection reveals a substantial population of galaxies dominated by cold dust which are missed by the long-wavelength WISE bands. Our results demonstrate that Herschel large-area surveys offer the means to construct large, relatively complete samples of local star-forming galaxies with accurate estimates of SFR that can be used to study the interplay between nuclear activity and star formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/123
- Title:
- Local velocity substructures in the Milky Way disk
- Short Name:
- J/ApJ/847/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We confirm, quantify, and provide a table of the coherent velocity substructure of the Milky Way disk within 2kpc of the Sun toward the Galactic anticenter, with a 0.2kpc resolution. We use the radial velocities of ~340000 F-type stars obtained with the Guoshoujing Telescope (also known as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST), and proper motions derived from the PPMXL catalog. The PPMXL proper motions have been corrected to remove systematic errors by subtracting the average proper motions of galaxies and QSOs that have been confirmed in the LAMOST spectroscopic survey, and that are within 2.5{deg} of the star's position. We provide the resulting table of systematic offsets derived from the PPMXL proper motion measurements of extragalactic objects identified in the LAMOST spectroscopic survey. Using the corrected phase-space stellar sample, we find statistically significant deviations in the bulk disk velocity of 20km/s or more in the three-dimensional velocities of Galactic disk stars. The bulk velocity varies significantly over length scales of half a kiloparsec or less. The rotation velocity of the disk increases by 20km/s from the Sun's position to 1.5kpc outside the solar circle. Disk stars in the second quadrant, within 1kpc of the Sun, are moving radially toward the Galactic center and vertically toward a point a few tenths of a kiloparsec above the Galactic plane; looking down on the disk, the stars appear to move in a circular streaming motion with a radius of the order of 1kpc.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/1611
- Title:
- Local Volume H I Survey (LVHIS)
- Short Name:
- J/MNRAS/478/1611
- Date:
- 19 Jan 2022 11:54:59
- Publisher:
- CDS
- Description:
- The 'Local Volume HI Survey' (LVHIS) comprises deep HI spectral line and 20-cm radio continuum observations of 82 nearby, gas-rich galaxies, supplemented by multiwavelength images. Our sample consists of all galaxies with Local Group velocities v_LG_<550km/s or distances D<10Mpc that are detected in the HI Parkes All Sky Survey (HIPASS). Using full synthesis observations in at least three configurations of the Australia Telescope Compact Array (ATCA), we obtain detailed HI maps for a complete sample of gas-rich galaxies with {delta}~-30{deg}. Here we present a comprehensive LVHIS galaxy atlas, including the overall gas distribution, mean velocity field, velocity dispersion, and position-velocity diagrams, together with a homogeneous set of measured and derived galaxy properties. Our primary goal is to investigate the HI morphologies, kinematics, and environment at high resolution and sensitivity. LVHIS galaxies represent a wide range of morphologies and sizes; our measured HI masses range from ~10^7^ to 10^10^M_{sun}_, based on independent distance estimates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/2080
- Title:
- Lockman Hole 10C sources radio spectral indices
- Short Name:
- J/MNRAS/429/2080
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied a sample of 296 faint (>0.5mJy) radio sources selected from an area of the Tenth Cambridge (10C) survey at 15.7GHz in the Lockman Hole. By matching this catalogue to several lower frequency surveys (e.g. including a deep GMRT survey at 610MHz, a WSRT survey at 1.4GHz, NVSS, FIRST and WENSS) we have investigated the radio spectral properties of the sources in this sample; all but 30 of the 10C sources are matched to one or more of these surveys. We have found a significant increase in the proportion of flat spectrum sources at flux densities below 1mJy - the median spectral index between 15.7GHz and 610MHz changes from 0.75 for flux densities greater than 1.5mJy to 0.08 for flux densities less than 0.8mJy. This suggests that a population of faint, flat spectrum sources is emerging at flux densities around 1mJy. The spectral index distribution of this sample of sources selected at 15.7GHz is compared to those of two samples selected at 1.4GHz from FIRST and NVSS. We find that there is a significant flat spectrum population present in the 10C sample which is missing from the samples selected at 1.4GHz. The 10C sample is compared to a sample of sources selected from the SKADS Simulated Sky by Wilman et al. (2008MNRAS.388.1335W) and we find that this simulation fails to reproduce the observed spectral index distribution and significantly underpredicts the number of sources in the faintest flux density bin. It is likely that the observed faint, flat spectrum sources are a result of the cores of FRI sources becoming dominant at high frequencies. These results highlight the importance of studying this faint, high frequency population.
- ID:
- ivo://CDS.VizieR/J/MNRAS/463/2997
- Title:
- Lockman Hole low-frequency radio sources
- Short Name:
- J/MNRAS/463/2997
- Date:
- 02 Nov 2021 11:21:03
- Publisher:
- CDS
- Description:
- The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper, we present new 150-MHz observations carried out with the LOw-Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6x14.7-arcsec and reaches an rms of 160{mu}Jy/beam at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of {alpha}_150_^1400^=-0.78+/-0.015. The median spectral index becomes slightly flatter (increasing from {alpha}_150_^1400^=-0.84 to {alpha}_150_^1400^=-0.75) with decreasing flux density down to S_150_ ~10mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample, we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 ultra-steep-spectrum sources and 13 peaked-spectrum sources. We estimate that up to 21 per cent of these could have z>4 and are candidate high-z radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/2934
- Title:
- Lockman Hole North 3GHz catalogue
- Short Name:
- J/MNRAS/462/2934
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second of two papers describing the observations and source catalogues derived from sensitive $3$-GHz images of the Lockman Hole North using the Karl G. Jansky Very Large Array. We describe the reduction and cataloguing process, which yielded an image with 8-arcsec resolution and instrumental noise of {sigma}_n=1.01uJy/beam rms (before primary beam corrections) and a catalogue of 558 sources detected above 5{sigma}_n. We include details of how we estimate source spectral indices across the 2GHz VLA bandwidth, finding a median index of -0.76+/-0.04. Stacking of source spectra reveals a flattening of spectral index with decreasing flux density. We present a source count derived from the catalogue. We show a traditional count estimate compared with a completely independent estimate made via a P(D) confusion analysis, and find very good agreement. Cross-matches of the catalogue with X-ray, optical, infrared, radio, and redshift catalogues are also presented. The X-ray, optical and infrared data, as well as AGN selection criteria allow us to classify 10 per cent as radio-loud AGN, 28 percent as radio-quiet AGN, and 58 per cent as star-forming galaxies, with only 4 per cent unclassified.
- ID:
- ivo://CDS.VizieR/J/MNRAS/495/4071
- Title:
- Lockman Hole region 325MHz source catalogue
- Short Name:
- J/MNRAS/495/4071
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modelling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325-MHz data obtained from the Giant Metrewave Radio Telescope, a 6{deg}x6{deg} mosaiced map is produced with an rms reaching 50uJy per beam. A source catalogue containing 6186 sources is created, and the Euclidean normalized differential source counts have been derived from it, consistent with previous observations as well as simulations. A detailed comparison of the source catalogue is also made with previous findings - at both lower and higher frequencies. The angular power spectrum (APS) of the diffuse Galactic synchrotron emission is determined for three different Galactic latitudes using the tapered gridded estimator. The values of the APS lie between ~1 and ~100mK^2^. Fitting a power law of the form Al^-{beta}^ gives values of A and {beta} varying across the latitudes considered. This paper demonstrates, for the first time, the variation of the power-law index for diffuse emission at very high Galactic locations. It follows the same trend that is seen at locations near the Galactic plane, thus emphasizing the need for low-frequency observations for developing better models of the diffuse emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/793/82
- Title:
- LOFAR Bootes and 3C295 field sources
- Short Name:
- J/ApJ/793/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Low Frequency Array (LOFAR) Low Band observations of the Bootes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy/beam, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg^2^. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of -0.7. We find that a spectral index scaling of -0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum ({alpha}<-1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Bootes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7<~z<~2.5 range.
1020. LOFAR LBA Sky Survey. I.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A104
- Title:
- LOFAR LBA Sky Survey. I.
- Short Name:
- J/A+A/648/A104
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- LOFAR is the only radio telescope that is presently capable of high-sensitivity, high-resolution (i.e. <1mJy/b and <15") observations at ultra-low frequencies (<100MHz). To utilise these capabilities, the LOFAR Surveys Key Science Project is undertaking a large survey to cover the entire northern sky with Low Band Antenna (LBA) observations. The LOFAR LBA Sky Survey (LoLSS) aims to cover the entire northern sky with 3170 pointings in the frequency range 42-66MHz, at a resolution of 15-arcsec and at a sensitivity of 1mJy/beam (1{sigma}. Here we outline the survey strategy, the observational status, the current calibration techniques, and briefly describe several scientific motivations. We also describe the preliminary public data release. The preliminary images were produced using a fully automated pipeline that aims to correct all direction-independent effects in the data. Whilst the direction-dependent effects, such as those from the ionosphere, are not yet corrected, the images presented in this work are still 10 times more sensitive than previous surveys available at these low frequencies. The preliminary data release covers 740deg^2^ around the HETDEX spring field region at a resolution of 47" with a median noise level of 5mJy/beam. The images and the catalogue with 25247 sources are publicly released. We demonstrate that the system is capable of reaching an rms noise of 1mJy/beam and the resolution of 15" once direction-dependent effects are corrected for. LoLSS will provide the ultra-low-frequency information for hundreds of thousands of radio sources, providing critical spectral information and producing a unique dataset that can be used for a wide range of science topics such as: the search for high redshift galaxies and quasars, the study of the magnetosphere of exoplanets, and the detection of the oldest populations of cosmic-rays in galaxies, clusters of galaxies, and from AGN activity.
