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25261. X-shaped radio galaxies from FIRST
ID:
ivo://CDS.VizieR/J/ApJS/245/17
Title:
X-shaped radio galaxies from FIRST
Short Name:
J/ApJS/245/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs) extracted from the latest (2014 December 17) data release of the "Very Large Array Faint Images of the Radio Sky at Twenty centimeter". We have combined these radio images with their counterparts in the TIFR GMRT sky survey at 150MHz, in an attempt to identify any low surface brightness radio emission present in these sources. This has enabled us to assemble a sample of 106 "strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation needs to be verified by further observations. The present sample of 290 XRG candidates is almost twice as large as the number of XRGs currently known. Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are identified as quasars. Double-peaked narrow emission lines are seen in the optical spectra of three of the XRG candidates (two "strong" and one "probable"). Nearly 90% of the sample is located in the FR II domain of the Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat radio spectrum (spectral index {alpha} flatter than -0.3) between 150MHz and 1.4GHz, or between 1.4 and 5GHz. Since this is not expected for lobe-dominated extragalactic radio sources (like nearly all known XRGs), these sources are particularly suited for follow-up radio imaging and near-simultaneous measurement of the radio spectrum.
25262. X-shaped radio sources. II. New redshifts
ID:
ivo://CDS.VizieR/J/ApJS/181/548
Title:
X-shaped radio sources. II. New redshifts
Short Name:
J/ApJS/181/548
Date:
21 Oct 2021
Publisher:
CDS
Description:
We reported optical spectroscopic observations of X-shaped radio sources with the Hobby-Eberly Telescope and Multiple-Mirror Telescope, focused on the sample of candidates from the FIRST survey presented in Paper I (Cheung, 2007, Cat. <J/AJ/133/2097>). A total of 27 redshifts were successfully obtained, 21 of which are new, including a newly identified candidate source of this type which is presented here. With these observations, the sample of candidates from the previous paper is over 50% spectroscopically identified. Two new broad emission-lined X-shaped radio sources are revealed, while no emission lines were detected in about one-third of the observed sources; a detailed study of the line properties is deferred to a future paper. Finally, to explore their relation to the Fanaroff-Riley division, the radio luminosities and host galaxy absolute magnitudes of a spectroscopically identified sample of 50 X-shaped radio galaxies are calculated to determine their placement in the Owen-Ledlow plane.
25263. "X-shaped" radio sources. II. Sample properties
ID:
ivo://CDS.VizieR/J/ApJ/852/48
Title:
"X-shaped" radio sources. II. Sample properties
Short Name:
J/ApJ/852/48
Date:
21 Oct 2021
Publisher:
CDS
Description:
In an earlier paper, we presented Jansky Very Large Array multi-frequency, multi-array continuum imaging of a unique sample of low-axial ratio radio galaxies. In this paper, the second in the series, we examine the images to learn the phenomenology of how the off-axis emission relates to the main radio source. Inversion-symmetric offset emission appears to be bimodal and to originate from one of two strategic locations: outer ends of radio lobes (outer-deviation) or from inner ends (inner-deviation). The latter sources are almost always associated with edge-brightened sources. With S- and Z-shaped sources being a subset of outer-deviation sources, this class lends itself naturally to explanations involving black hole axis precession. Our data allow us to present a plausible model for the more enigmatic inner-deviation sources with impressive wings; as for outer-deviation sources these too require black hole axis shifts, although they also require plasma backflows into relic channels. Evolution in morphology over time relates the variety in structures in inner-deviation sources including XRGs. With features such as non- collinearities, central inner-S "spine," corresponding lobe emission peaks, double and protruding hotspots not uncommon, black hole axis precession, drifts, or flips could be active in a significant fraction of radio sources with prominent off-axis emission. At least 4% of radio galaxies appear to undergo black hole axis rotation. Quasars offer a key signature for recognizing rotating axes. With a rich haul of sources that have likely undergone axis rotation, our work shows the usefulness of low-axial ratio sources in pursuing searches for binary supermassive black holes.
25264. "X-shaped" radio sources. I. VLA imaging
ID:
ivo://CDS.VizieR/J/ApJ/852/47
Title:
"X-shaped" radio sources. I. VLA imaging
Short Name:
J/ApJ/852/47
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present archival and Jansky Very Large Array multi-frequency multi-array radio continuum imaging of a unique sample of 100 radio sources that have been selected to be candidate "X-shaped" radio galaxies (XRGs). The archival data were calibrated in AIPS (Bridle & Greisen 1994, NRAO AIPS Memo 87) and imaged using DIFMAP (Shepherd+ 1994BAAS...26..987S), while the new Very Large Array data were calibrated and imaged in CASA (McMullin+ 2007ASPC..376..127M). No attempt was made to re-image the archival data in CASA. Altogether we present images of 95 of the 100 sources. These observations give us the opportunity to study radio sources with synchrotron plasma that is significantly offset from the main radio axis and therefore to open a window into investigations of physical mechanisms responsible for depositing the plasma in off-axis regions. Here, we present the technical details of the observations and all of the total intensity images, while in subsequent papers we use them to examine critically various models for the formation of XRGs. Spectral index and linear polarization information is also presented and analyzed in further papers in this series.
25265. X-Shooter Spectral Library (XSL). DR2
ID:
ivo://CDS.VizieR/J/A+A/634/A133
Title:
X-Shooter Spectral Library (XSL). DR2
Short Name:
J/A+A/634/A133
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the second data release (DR2) of the X-Shooter Spectral Library (XSL), which contains all the spectra obtained over the six semesters of that program. This release supersedes our first data release from 2014, with a larger number of spectra (813 observations of 666 stars) and with a more extended wavelength coverage as the data from the near-infrared arm of the X-Shooter spectrograph are now included. The DR2 spectra then consist of three segments that were observed simultaneously and, if combined, cover the range between 300nm and 2.45um at a spectral resolving power close to R=10000. The spectra were corrected for instrument transmission and telluric absorption, and they were also corrected for wavelength-dependent flux-losses in 85% of the cases. On average, synthesized broad-band colors agree with those of the MILES library and of the combined IRTF and Extended IRTF libraries to within 1%. The scatter in these comparisons indicates typical errors on individual colors in the XSL of 2-4%. The comparison with 2MASS point source photometry shows systematics of up to 5% in some colors, which we attribute mostly to zero-point or transmission curve errors and a scatter that is consistent with the above uncertainty estimates. The final spectra were corrected for radial velocity and are provided in the rest-frame (with wavelengths in air). The spectra cover a large range of spectral types and chemical compositions (with an emphasis on the red giant branch), which makes this library an asset when creating stellar population synthesis models or for the validation of near-ultraviolet to near-infrared theoretical stellar spectra across the Hertzsprung-Russell diagram.
25266. X-Shooter Spectral Library (XSL). DR1
ID:
ivo://CDS.VizieR/J/A+A/565/A117
Title:
X-Shooter Spectral Library (XSL). DR1
Short Name:
J/A+A/565/A117
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first release of XSL, the X-Shooter Spectral Library observed at the European Southern Observatory (ESO). This release contains 237 stars spanning the wavelengths 3000-10200{AA} observed at a resolving power R~10000. Telluric standard stars used to correct the Earth atmospheric contamination are presented as well.
25267. X-shooter spectra of AGN and inactive galaxies
ID:
ivo://CDS.VizieR/J/A+A/654/A132
Title:
X-shooter spectra of AGN and inactive galaxies
Short Name:
J/A+A/654/A132
Date:
22 Feb 2022
Publisher:
CDS
Description:
The relation between nuclear (<~50pc) star formation and nuclear galactic activity is still elusive; theoretical models predict a link between the two, but it is unclear whether active galactic nuclei (AGNs) should appear at the same time, before, or after nuclear star formation activity. We present a study of this relation in a complete, volume-limited sample of nine of the most luminous (log_L14-195keV_>10^42.5^erg/s) local AGNs (the LLAMA sample), including a sample of 18 inactive control galaxies (six star-forming; 12 passive) that are matched by Hubble type, stellar mass (9.5<~logM*/M_{sun}_<~10.5), inclination, and distance. This allows us to calibrate our methods on the control sample and perform a differential analysis between the AGN and control samples. We performed stellar population synthesis on VLT/X-shooter spectra in an aperture corresponding to a physical radius of ~150pc. We find young (<~30Myr) stellar populations in seven out of nine AGNs and in four out of six star-forming control galaxies. In the non-star-forming control population, in contrast, only two out of 12 galaxies show such a population. We further show that these young populations are not indicative of ongoing star formation, providing evidence for models that see AGN activity as a consequence of nuclear star formation. Based on the similar nuclear star formation histories of AGNs and star-forming control galaxies, we speculate that the latter may turn into the former for some fraction of their time. Under this assumption, and making use of the volume completeness of our sample, we infer that the AGN phase lasts for about 5% of the nuclear starburst phase.
25268. X-shooter spectra of 43 metal-poor M dwarfs
ID:
ivo://CDS.VizieR/J/A+A/628/A61
Title:
X-shooter spectra of 43 metal-poor M dwarfs
Short Name:
J/A+A/628/A61
Date:
21 Oct 2021
Publisher:
CDS
Description:
The aim of the project is to define metallicity/gravity/temperature scales for different spectral types of metal-poor M dwarfs. We obtained intermediate-resolution ultraviolet (UVB), optical (VIS), and near-infrared (NIR) spectra of 43 metal-poor M dwarfs (16 sdMs, 16 esdMs, and 12 usdMs with the ESO VLT X-shooter spectrograph. We compared our atlas of spectra to the BT-Settl synthetic spectral energy distribution over a wide range of metallicities, gravities, and effective temperatures to infer the physical properties for the whole M dwarf sequence at sub-solar metallicities and constrain the latest atmospheric models. The BT-Settl models accurately reproduce the observed spectra across the 450--2500 nm wavelength range except for a few regions. We find that the best fits for gravities of log(g)=5.0-5.5 for the three metal classes. We infer metallicities of [Fe/H]=-0.5, -1.5, and -2.0+/-0.5dex and effective temperatures of 3700-2600K, 3800-2900K, and 3700-2900K for sdMs, esdMs, and usdMs, respectively.
25269. X-shooter spectra of 6 ~2.2 quasars
ID:
ivo://CDS.VizieR/J/A+A/603/A1
Title:
X-shooter spectra of 6 ~2.2 quasars
Short Name:
J/A+A/603/A1
Date:
21 Oct 2021
Publisher:
CDS
Description:
We studied the spectra of six z~2.2 quasars obtained with the X-shooter spectrograph at the Very Large Telescope. The redshift of these sources and X-shooter's spectral coverage allow us to cover the rest spectral range ~1200-7000{AA} for the simultaneous detection of optical and ultraviolet lines emitted by the Broad Line Region. Simultaneous measurements, avoiding issues related to quasars variability, help us understanding the connection between different Broad Line Region line profiles generally used as virial estimators of Black Holes masses in quasars. The goal of this work is comparing the emission lines from the same object to check on the reliability of H{alpha}, MgII and CIV with respect to H{beta}. H{alpha} and MgII linewidths correlate well with H{beta}, while CIV shows a poorer correlation, due to the presence of strong blueshifts and asymmetries in the profile. We compare our sample with the only other two whose spectra were taken with the same instrument and for all examined lines our results are in agreement with the ones obtained with X-shooter at z~1.5-1.7. We finally evaluate CIII] as a possible substitute of CIV in the same spectral range and find that its behaviour is more coherent with those of the other lines: we believe that, when a high quality spectrum such as the ones we present is available and a proper modelization with the FeII and FeIII emissions is performed, the use of this line is more appropriate than that of CIV if not corrected for the contamination by non-virialized components.
25270. X-shooter spectra of 12 young stellar objects
ID:
ivo://CDS.VizieR/J/A+A/548/A56
Title:
X-shooter spectra of 12 young stellar objects
Short Name:
J/A+A/548/A56
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high-quality, medium-resolution X-shooter/VLT spectra in the range 300-2500nm for a sample of 12 very low mass stars in the {sigma} Orionis cluster. The sample includes eight stars with evidence of disks from Spitzer and four without disks, with masses ranging from 0.08 to 0.3M_{sun}_. The aim of this first paper is to investigate the reliability of the many accretion tracers currently used to measure the mass accretion rate in low-mass young stars and the accuracy of the correlations between these secondary tracers (mainly accretion line luminosities) found in the literature. We use our spectra to measure the accretion luminosity from the continuum excess emission in the UV and visual; the derived mass accretion rates range from 10^-9^M_{sun}_/yr down to 5x10^-11^M_{sun}_/yr, allowing us to investigate the behavior of the accretion-driven emission lines in very low mass accretion rate regimes. We compute the luminosity of ten accretion-driven emission lines from the UV to the near-IR, which are all obtained simultaneously. In general, most of the secondary tracers correlate well with the accretion luminosity derived from the continuum excess emission. We recompute the relationships between the accretion luminosities and the line luminosities, and we confirm the validity of the correlations given in the literature, with the possible exception of H{alpha}. Metallic lines, such as the CaII IR triplet or the NaI line at 589.3nm, show a larger dispersion. When looking at individual objects, we find that the hydrogen recombination lines, from the UV to the near-IR, give good and consistent measurements of L_acc_ that often better agree than the uncertainties introduced by the adopted correlations. The average L_acc_ derived from several hydrogen lines, measured simultaneously, have a much reduced error. This suggests that some of the spread in the literature correlations may be due to the use of nonsimultaneous observations of lines and continuum. Three stars in our sample deviate from this behavior, and we discuss them individually.

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