- ID:
- ivo://CDS.VizieR/J/A+A/658/A4
- Title:
- LOFAR imaging of Arp299 at 150MHz
- Short Name:
- J/A+A/658/A4
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the spatially resolved emission of Arp 299 revealed by 150 MHz international baseline Low-Frequency Array (LOFAR) and 1.4, 5.0, and 8.4GHz Very Large Array (VLA) observations. Nowadays, LOFAR allows to compare its resolution with the VLA ones. These will allow us to obtain pixel-by-pixel spectral imdex maps and local radio SEDs. With this information we recover the nature of the ISM around the main structures (either clumpy or continuous), as well as magnetic fields. The 150MHz image also shows structures never seen before, pointing out that these radio-frequencies observations are a perfect tool to detect them.
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- ID:
- ivo://CDS.VizieR/J/A+A/617/A136
- Title:
- LOFAR M51 field low-frequency polarized sources
- Short Name:
- J/A+A/617/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The new generation of broad-band radio continuum surveys will provide large data sets with polarization information. New algorithms need to be developed to extract reliable catalogs of linearly polarized sources that can be used to characterize those sources and produce a dense rotation measure (RM) grid to probe magneto-ionized structures along the line of sight via Faraday rotation. The aim of the paper is to develop a computationally efficient and rigorously defined source-finding algorithm for linearly polarized sources. We used a calibrated data set from the LOw Frequency ARray (LOFAR) at 150MHz centered on the nearby galaxy M51 to search for polarized background sources. With a new imaging software, we re-imaged the field at a resolution of 18''x15'' and cataloged a total of about 3000 continuum sources within 2.5{deg} of the center of M51. We made small Stokes Q and U images centered on each source brighter than 100mJy in total intensity (201 sources) and used RM synthesis to create corresponding Faraday cubes that were analyzed individually. For each source, the noise distribution function was determined from a subset of the measurements at high Faraday depths where no polarization is expected; the peaks in polarized intensity in the Faraday spectrum were identified and the p-value of each source was calculated. Finally, the false discovery rate method was applied to the list of p-values to produce a list of polarized sources and quantify the reliability of the detections. We also analyzed sources fainter than 100mJy but that were reported as polarized in the literature at at least another radio frequency. Of the 201 sources that were searched for polarization, six polarized sources were detected confidently (with a false discovery rate of 5%). This corresponds to a number density of one polarized source per 3.3 square degrees, or 0.3 source per square degree. Increasing the false discovery rate to 50% yields 19 sources. A majority of the sources have a morphology that is indicative of them being double-lobed radio galaxies, and the ones with literature redshift measurements have 0.5<z<1.0. We find that this method is effective in identifying polarized sources, and is well suited for LOFAR observations. In the future, we intend to develop it further and apply it to larger data sets such as the LOFAR Two-meter Survey of the whole northern sky, LOTSS, and the ongoing deep LOFAR observations of the GOODS-North field.
- ID:
- ivo://CDS.VizieR/J/A+A/628/A69
- Title:
- LOFAR 143MHz images of 3C 236
- Short Name:
- J/A+A/628/A69
- Date:
- 23 Mar 2022 16:28:49
- Publisher:
- CDS
- Description:
- We have examined the giant radio galaxy 3C 236 using LOFAR at 143MHz down to an angular resolution of 7 arcseconds, in combination with observations at higher frequencies. We used the low frequency data to derive spectral index maps with the highest resolution yet at these low frequencies. We confirm a previous detection of an inner hotspot in the north-west lobe and for the first time observe that the south-east lobe hotspot is in fact a triple hotspot, which may point to an intermittent source activity. Also, the spectral index map of 3C 236 shows that the spectral steepening at the inner region of the northern lobe is prominent at low frequencies. The outer regions of both lobes show spectral flattening, in contrast with previous high frequency studies. We derive spectral age estimates for the lobes, as well as particle densities of the IGM at various locations. We propose that the morphological differences between the lobes are driven by variations in the ambient medium density as well as the source activity history.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A4
- Title:
- LOFAR observations XMM-LSS field
- Short Name:
- J/A+A/622/A4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of the XMM Large-Scale Structure (XMM-LSS) field observed with the LOw Frequency ARray (LOFAR) at 120-168MHz. Centred at a J2000 declination of -4.5{deg}, this is a challenging field to observe with LOFAR because of its low elevation with respect to the array. The low elevation of this field reduces the effective collecting area of the telescope, thereby reducing sensitivity. This low elevation also causes the primary beam to be elongated in the north-south direction, which can introduce side lobes in the synthesised beam in this direction. However the XMM-LSS field is a key field to study because of the wealth of ancillary information, encompassing most of the electromagnetic spectrum. The field was observed for a total of 12 hours from three four-hour LOFAR tracks using the Dutch array. The final image presented encompasses ~27deg^2^, which is the region of the observations with a >50% primary beam response. Once combined, the observations reach a central rms of 280uJy/beam at 144MHz and have an angular resolution of 7.5x8.5". We present our catalogue of detected sources and investigate how our observations compare to previous radio observations. This includes investigating the flux scale calibration of these observations compared to previous measurements, the implied spectral indices of the sources, the observed source counts and corrections to obtain the true source counts, and finally the clustering of the observed radio sources.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A2
- Title:
- LOFAR Two-metre Sky Survey Deep Fields DR1
- Short Name:
- J/A+A/648/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The LOFAR Two-metre Sky Survey (LoTSS) will cover the full northern sky and, additionally, aims to observe the LoTSS deep fields to a noise level of <~10uJy/beam over several tens of square degrees in areas that have the most extensive ancillary data. This paper presents the ELAIS-N1 deep field, the deepest of the LoTSS deep fields to date. With an effective observing time of 163.7 hours, it reaches a root mean square (RMS) noise level of <~20uJy/beam in the central region (and below 30uJy/beam over 10 square degrees). The resolution is 6 arcsecs and 84862 radio sources were detected in the full area (68 square degrees) with 74127 sources in the highest quality area at less than 3 degrees from the pointing centre. The observation reaches a sky density of more than 5000 sources per square degree in the central region (5 square degrees).We present the calibration procedure, which addresses the special configuration of some observations and the extended bandwidth covered (115 to 177MHz; central frequency 146.2MHz) compared to standard LoTSS. We also describe the methods used to calibrate the flux density scale using cross-matching with sources detected by other radio surveys in the literature. We find the flux density uncertainty related to the flux density scale to be 6.5 per cent. By studying the variations of the flux density measurements between different epochs, we show that relative flux density calibration is reliable out to about a 3 degree radius, but that additional flux density uncertainty is present for all sources at about the 3 per cent level; this is likely to be associated with residual calibration errors, and is shown to be more significant in datasets with poorer ionosphere conditions. We also provide intra-band spectral indices, which can be useful to detect sources with unusual spectral properties. The final uncertainty in the flux densities is estimated to be 10 per cent for ELAIS-N1.
- 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.
- 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/532/A78
- Title:
- Long-period variables in NGC 147 and NGC 185
- Short Name:
- J/A+A/532/A78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous studies on the stellar content of the two nearby dwarf galaxies NGC 147 and NGC 185 reveal a rich population of late-type giants in both systems, including a large number of carbon-rich objects. These stars are known to show pronounced photometric variability, which can be used for a more detailed characterisation of these highly evolved stars. Owing to their well-studied parameters, these Local Group members are ideal candidates for comparative studies. Through photometric monitoring, we attempt to provide a catalogue of long-period variables (LPVs), including Mira variables, semi-regular variables, and even irregular variables in NGC 147 and NGC 185. We investigate the light variations and compare the characteristics of these two LPV populations with the results found for other galaxies, such as the LMC.
- ID:
- ivo://CDS.VizieR/J/A+A/509/A61
- Title:
- Long slit spectroscopy in M31
- Short Name:
- J/A+A/509/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new optical long-slit data along six position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5-arcmin from the center, where the disk light contribution is always less than 30%, and out to 8-arcmin along the major axis, where the disk provides 55% of the total light. We show that the velocity dispersions of McElroy (1983ApJ...270..485M) are severely underestimated (by up to 50km/s). As a consequence, previous dynamical models have underestimated the stellar mass of M31's bulge by a factor of 2. As a further consequence, the light-weighted velocity dispersion of the galaxy grows to 166km/s and to 170km/s if rotation is also taken into account, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31 from a factor of 3 to a factor of 2. The kinematic position angle varies with distance, pointing to triaxiality, but a quantitative conclusion can be reached only after simultaneous proper dynamical modeling of the bulge and disk components is performed. We detect gas counter-rotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. Using simple stellar population models we derive the age, metallicity and {alpha}-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (>=12Gyr, with many best-fit ages at the model grid limit of 15Gyr), slightly {alpha}-elements overabundant ([{alpha}/Fe]~0.2) and of solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match the dust-corrected observations reasonably well, within the known limitations of current simple stellar population models. The stellar populations have approximately radially constant mass-to-light ratios (M/L_R~4-4.5M_{sun}_/L_{sun}_ for a Kroupa IMF), which is in agreement with the stellar dynamical estimates based on our new velocity dispersions. In the inner arcsecs the luminosity-weighted age drops to 4-8Gyr, while the metallicity increases to above three times the solar value. Starting from 6-arcmin from the center along the major axis, the mean age drops to >=8Gyr with slight supersolar metallicity (~+0.1dex) and {alpha}-element overabundance (~+0.2dex) for a mass-to-light ratio M/L_R<=3M_{sun}_/L_{sun}_. Diagnostic diagrams based on the [OIII]/H{beta} and [NI]H{beta} emission line equivalent widths (EWs) ratios indicate that the gas is ionized by shocks outside 10-arcsec, but an AGN-like ionizing source could be present near the center. We speculate that a gas-rich minor merger happened some 100Myr ago, causing the observed minor axis gas counter-rotation, the recent star formation event and possibly some nuclear activity.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/67
- Title:
- Longslit spectroscopy of local bulges
- Short Name:
- J/ApJ/754/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Marcario Low Resolution Spectrograph (LRS) at the Hobby-Eberly- Telescope (HET) to study the kinematics of pseudobulges and classical bulges in the nearby universe. We present major-axis rotational velocities, velocity dispersions, and h3 and h4 moments derived from high-resolution (39km/s) spectra for 45 S0 to Sc galaxies; for 27 of the galaxies we also present minor axis data. We combine our kinematics with bulge-to-disk decompositions. We demonstrate for the first time that purely kinematic diagnostics of the bulge dichotomy agree systematically with those based on Sersic index. Low Sersic index bulges have both increased rotational support (higher v/sigma values) and on average lower central velocity dispersions. Further- more, we confirm that the same correlation also holds when visual morphologies are used to diagnose bulge type. The previously noted trend of photometrically flattened bulges to have shallower velocity dispersion profiles turns to be significant and systematic if the Sersic index is used to distinguish between pseudobulges and classical bulges. The anti-correlation between h3 and v/sigma observed in elliptical galaxies is also observed in intermediate type galaxies, irrespective of bulge type. Finally, we present evidence for formerly undetected counter rotation in the two systems NGC 3945 and NGC 4736.
