- ID:
- ivo://CDS.VizieR/J/ApJ/710/764
- Title:
- Extended radio emission in MOJAVE blazars
- Short Name:
- J/ApJ/710/764
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study on the kiloparsec-scale radio emission in the complete flux density limited MOJAVE sample, comprising 135 radio-loud active galactic nuclei. New 1.4GHz Very Large Array (VLA) radio images of six quasars and previously unpublished images of 21 blazars are presented, along with an analysis of the high-resolution (VLA A-array) 1.4GHz emission for the entire sample. While extended emission is detected in the majority of the sources, about 7% of the sources exhibit only radio core emission. We expect more sensitive radio observations, however, to detect faint emission in these sources, as we have detected in the erstwhile "core-only" source, 1548+056. The kiloparsec-scale radio morphology varies widely across the sample. Many BL Lac objects exhibit extended radio power and kiloparsec-scale morphology typical of powerful FRII jets, while a substantial number of quasars possess radio powers intermediate between FRIs and FRIIs.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/385/1656
- Title:
- Extragalactic radio-sources at 95GHz
- Short Name:
- J/MNRAS/385/1656
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used the Australia Telescope Compact Array (ATCA) at 95GHz to carry out continuum observations of 130 extragalactic radio sources selected from the Australia Telescope 20GHz (AT20G) survey. We use a triple-correlation method to measure simultaneous 20- and 95-GHz flux densities for these objects, and over 90 per cent of our target sources are detected at 95GHz. We demonstrate that the ATCA can robustly measure 95-GHz flux densities with an accuracy of ~10 per cent in a few minutes for sources stronger than about 50mJy. We measure the distribution of radio spectral indices in a flux-limited sample of extragalactic sources, and show that the median 20-95GHz spectral index does not vary significantly with flux density for S_20_>150mJy . This finding allows us to estimate the extragalactic radio source counts at 95GHz by combining our observed 20-95GHz spectral-index distribution with the accurate 20-GHz source counts measured in the AT20G survey.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/3806
- Title:
- Extragalactic radio sources with recurrent jet
- Short Name:
- J/MNRAS/471/3806
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 74 radio sources with recurrent jet activity. The sample consists of 67 galaxies, 2 quasars and 5 unidentified sources, selected from the published data or are newly recognized. The sample's redshift range is 0.002<z<0.7 and the size of inner and outer structures varies from 0.02 to 4248kpc. We analyse the optical and radio properties of the sample and compare them with the characteristics of ordinary one-off FRII radio sources. With the help of stellar population modelling, we derive black hole masses and stellar masses of host galaxies of 35 restarting radio sources, finding that the black hole masses in restarting radio sources are comparable to those of typical single-cycle FRII radio sources. The obtained median values of log M_BH_ are 8.58 and 8.62M_{sun}_. Unlike the black hole masses, the stellar masses in restarting radio sources tend to be smaller than in the FRII sources. Although the stellar populations of the hosts of recurrent activity sources are dominated by old stars, a significant fraction of young stars can be observed as well. Based on the Sloan Digital Sky Survey photometric observations, we also analyse the morphology of the host galaxies and obtained significantly smaller concentration indices for the restarting radio sources when compared to the classical FRII hosts. This effect can be interpreted as a result of frequent merger events in the history of host galaxies of restarting radio sources.
- ID:
- ivo://CDS.VizieR/J/A+A/427/769
- Title:
- Extragalactic sources at 22, 37 and 87GHz
- Short Name:
- J/A+A/427/769
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Long term monitoring results from mid 1995 to the end of 2000 of quasar observations at 22, 37 and 87GHz done at the Metsahovi radio observatory are presented. Approximately 15700 observations are published here.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/3431
- Title:
- Extremely red quasars in BOSS
- Short Name:
- J/MNRAS/464/3431
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Red quasars are candidate young objects in an early transition stage of massive galaxy evolution. Our team recently discovered a population of extremely red quasars (ERQs) in the Baryon Oscillation Spectroscopic Survey (BOSS) that has a suite of peculiar emission-line properties including large rest equivalent widths (REWs), unusual 'wingless' line profiles, large NV/Ly{alpha}, NV/CIV, SiIV/CIV and other flux ratios, and very broad and blueshifted [OIII] {lambda}5007. Here we present a new catalogue of CIV and NV emission-line data for 216188 BOSS quasars to characterize the ERQ line properties further. We show that they depend sharply on UV-to-mid-IR colour, secondarily on REW(CIV), and not at all on luminosity or the Baldwin Effect. We identify a 'core' sample of 97 ERQs with nearly uniform peculiar properties selected via i-W3>=4.6(AB) and REW(CIV)>=100{AA} at redshifts 2.0-3.4. A broader search finds 235 more red quasars with similar unusual characteristics. The core ERQs have median luminosity <logL(ergs/s)>~47.1, sky density 0.010deg^-2^, surprisingly flat/blue UV spectra given their red UV-to-mid-IR colours, and common outflow signatures including BALs or BAL-like features and large CIV emission-line blueshifts. Their SEDs and line properties are inconsistent with normal quasars behind a dust reddening screen. We argue that the core ERQs are a unique obscured quasar population with extreme physical conditions related to powerful outflows across the line-forming regions. Patchy obscuration by small dusty clouds could produce the observed UV extinctions without substantial UV reddening.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A24
- Title:
- Extremely strong damped Lyman-{alpha} systems
- Short Name:
- J/A+A/566/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of ~100 high redshift (z ~2-4) extremely strong damped Lyman-{alpha} systems (ESDLA, with N(HI)>=0.5x10^22^cm^-2^) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(HI) frequency distribution has a relatively shallow slope with power-law index -3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ~1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly{alpha} emission with <L_ESDLA_(Ly{alpha})>=~(0.6+/-0.2)x10^42^erg/s in the core of ESDLAs (corresponding to about 0.1L^*^ at z~2-3), obtained through stacking the fibre spectra (of radius 1" corresponding to ~8kpc at z~2.5). Statistical errors on the Ly{alpha} luminosity are of the order of 0.1x10^42^erg/s but we caution that the measured Ly{alpha} luminosity may be overestimated by ~35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2x10^42^erg/s. The properties of the Ly{alpha} line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-{alpha} emitting galaxies (LAEs) with L_LAE_(Ly{alpha})>=10^41^erg/s detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r_gas_=2.5kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly{alpha} luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M_{sun}_/yr)=~0.6/f_esc_, where f_esc_<1 is the Ly{alpha} escape fraction. Assuming the typical escape fraction of LAEs, f_esc_~0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r_gal_=~2.5kpc. Finally, we note that possible overestimation of the Ly{alpha} emission would result in both smaller r_gas_ and r_gal_. Our results support a close association between LAEs and strong DLA host galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/498/4033
- Title:
- Extreme quasar X-ray variability
- Short Name:
- J/MNRAS/498/4033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this investigation are all spectroscopically confirmed, optically bright (m_i_<=20.2), and contain no identifiable broad absorption lines in their optical/ultraviolet spectra. This sample includes quasars spanning z~0.1-4 and probes X-ray variability on timescales of up to ~12 rest-frame years. Variability amplitudes are computed between every epoch of observation for each quasar and are analyzed as a function of timescale and luminosity. The tail-heavy distributions of variability amplitudes at all timescales indicate that extreme X-ray variations are driven by an additional physical mechanism and not just typical random fluctuations of the coronal emission. Similarly, extreme X-ray variations of low-luminosity quasars seem to be driven by an additional physical mechanism, whereas high-luminosity quasars seem more consistent with random fluctuations. The amplitude at which an X-ray variability event can be considered extreme is quantified for different timescales and luminosities. Extreme X-ray variations occur more frequently at long timescales ({DELTA}t>=300-days) than at shorter timescales, and in low-luminosity quasars compared to high-luminosity quasars over a similar timescale. A binomial analysis indicates that extreme intrinsic X-ray variations are rare, with a maximum occurrence rate of <2.4% of observations. Finally, we present X-ray variability and basic optical emission-line properties of three archival quasars that have been newly discovered to exhibit extreme X-ray variability.
- ID:
- ivo://CDS.VizieR/J/ApJS/153/119
- Title:
- Faint blue objects at high galactic latitude
- Short Name:
- J/ApJS/153/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The US (UV-excess Starlike) survey has cataloged 3987 objects in 7 high Galactic latitude fields according to their optical colors, magnitudes, and morphologies using photographic techniques. This paper analyzes the effectiveness of the survey at producing finding lists for complete samples of hot stars and quasars that exhibit blue and/or ultraviolet excess (B-UVX) relative to the colors of halo F and G subdwarf stars. A table of 599 spectroscopic identifications summarizes the spectroscopic coverage of the US objects that has been accomplished to date.
- ID:
- ivo://CDS.VizieR/III/74
- Title:
- Faint Blue Stars near the South Galactic Pole
- Short Name:
- III/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search for faint blue stars conducted at the Observatories of Tonantzintla and Minnesota has yielded 8746 objects which are somewhat blue. The data file is organized into three sections with the same column format. The first 1569 records are for stars with U-V of -0.4 or bluer, which are very definitely blue (Table II of the paper). The next 2929 stars are somewhat blue, with U-V values of -0.3 or -0.2 (Table III of the paper). The final 4248 records give data for stars with U-V of -0.1 or 0.0 (Table IV of the paper). Photometric, spectroscopic, and proper-motion data have later been acquired for these objects, which revealed the great variety of the objects in this catalogue: white dwarfs, subdwarfs, QSOs (quasars), compact and active galaxies. Finding charts and details about the nature of these blue objects can be found in the following papers: Haro G., and Chavira E.: 1987RMxAA..15..107H ; Chavira E.: 1988RMxAA..16..123C, Chavira E., 1990RMxAA..20...47C, and 1992RMxAA..24..139C
- ID:
- ivo://CDS.VizieR/J/AJ/127/2565
- Title:
- Faint FIRST variable radio sources
- Short Name:
- J/AJ/127/2565
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 123 radio sources that exhibit significant variations at 1.4GHz on a 7 year baseline has been created using FIRST VLA B-configuration data from 1995 and 2002 on a strip at {delta}=0 near the south Galactic cap. This sample spans the range of radio flux densities from ~2 to 1000mJy. It presents both in size and radio flux density range a unique starting point for variability studies of galaxies and quasars harboring lower luminosity active galactic nuclei (AGNs).
