scholarly journals The nature and likely redshift of GLEAM J0917–0012

2021 ◽  
Vol 38 ◽  
Author(s):  
Guillaume Drouart ◽  
Nick Seymour ◽  
Jess W. Broderick ◽  
José Afonso ◽  
Rajan Chhetri ◽  
...  
Keyword(s):  
Radio Galaxy ◽  
Emission Lines ◽  
Optical Data ◽  
Space Observatory ◽  
Very Large Array ◽  
Murchison Widefield Array ◽  
Original Interpretation ◽  
Independent Confirmation ◽  
Infrared Survey

Abstract We previously reported a putative detection of a radio galaxy at $z=10.15$ , selected from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey. The redshift of this source, GLEAM J0917–0012, was based on three weakly detected molecular emission lines observed with the Atacama Large Millimetre Array (ALMA). In order to confirm this result, we conducted deep spectroscopic follow-up observations with ALMA and the Karl Jansky Very Large Array (VLA). The ALMA observations targeted the same CO lines previously reported in Band 3 (84–115 GHz) and the VLA targeted the CO(4-3) and [CI(1-0)] lines for an independent confirmation in Q-band (41 and 44 GHz). Neither observation detected any emission lines, removing support for our original interpretation. Adding publicly available optical data from the Hyper Suprime-Cam survey, Widefield Infrared Survey Explorer (WISE), and Herschel Space Observatory in the infrared, as well as $<$ 10 GHz polarisation and 162 MHz inter-planetary scintillation observations, we model the physical and observational characteristics of GLEAM J0917–0012 as a function of redshift. Comparing these predictions and observational relations to the data, we are able to constrain its nature and distance. We argue that if GLEAM J0917–0012 is at $z<3,$ then it has an extremely unusual nature, and that the more likely solution is that the source lies above $z=7$ .

scholarly journals The “Gravitational Lens” 3C 321: A Remarkable Impostor

1987 ◽  
Vol 124 ◽  
pp. 761-765
Author(s):  
Alexei V. Filippenko
Keyword(s):  
Radio Galaxy ◽  
Line Emission ◽  
Careful Analysis ◽  
Gravitational Lens ◽  
Emission Lines ◽  
Optical Data ◽  
High Ionization ◽  
Spectrum Radio ◽  
Hα Emission

Recent observations of the radio galaxy 3C 321 are presented. The optical nucleus consists of two components (A, B), separated by ∼ 4″ (∼ 6 kpc), whose low-resolution spectra strongly resemble those of high-ionization type 2 Seyfert nuclei. The relative intensities of the emission lines differ in A and B by less than 1%, and their profiles are almost identical. 3C 321 appears to be a convincing example of a gravitationally lensed object.Careful analysis of high-quality radio and optical data, however, reveals that the system is almost certainly not a lens. The equivalent widths of the emission lines are roughly twice as high in B than in A, and there are significant spatial offsets between regions of bright continuum and line emission. A slight, but fundamental, difference is visible in the two Hα emission profiles. The radial velocities of A and B are discrepant by 31 ± 10 km s−1. Finally, component A is nearly coincident with a flat-spectrum radio core, whereas B is next to an extended, steep-spectrum knot of radio emission.This object should serve as a warning to lens hunters: beware of impostors, whose true properties may be difficult to ascertain without extensive optical and radio observations.

scholarly journals Candidate radio supernova remnants observed by the GLEAM survey over 345° < l < 60° and 180° < l < 240°

2019 ◽  
Vol 36 ◽  
Author(s):  
N. Hurley-Walker ◽  
B. M. Gaensler ◽  
D. A. Leahy ◽  
M. D. Filipović ◽  
P. J. Hancock ◽  
...  
Keyword(s):  
Supernova Remnants ◽  
Supernova Remnant ◽  
Galactic Plane ◽  
Data Release ◽  
Murchison Widefield Array ◽  
Infrared Survey

Abstract We examined the latest data release from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey covering 345° < l < 60° and 180° < l < 240°, using these data and that of the Widefield Infrared Survey Explorer to follow up proposed candidate Supernova Remnant (SNR) from other sources. Of the 101 candidates proposed in the region, we are able to definitively confirm ten as SNRs, tentatively confirm two as SNRs, and reclassify five as H ii regions. A further two are detectable in our images but difficult to classify; the remaining 82 are undetectable in these data. We also investigated the 18 unclassified Multi-Array Galactic Plane Imaging Survey (MAGPIS) candidate SNRs, newly confirming three as SNRs, reclassifying two as H ii regions, and exploring the unusual spectra and morphology of two others.

Discovery of five new Galactic symbiotic stars in the VPHAS+ survey

2021 ◽  
Vol 502 (2) ◽  
pp. 2513-2517
Author(s):  
Stavros Akras ◽  
Denise R Gonçalves ◽  
Alvaro Alvarez-Candal ◽  
Claudio B Pereira
Keyword(s):  
Spectroscopic Data ◽  
Selection Criterion ◽  
Optical Spectra ◽  
Emission Lines ◽  
High Rate ◽  
Symbiotic Stars ◽  
Selection Of

ABSTRACT We report the validation of a recently proposed infrared (IR) selection criterion for symbiotic stars (SySts). Spectroscopic data were obtained for seven candidates, selected from the SySt candidates of Akras et al. by employing the new supplementary IR selection criterion for SySts in the VST/OmegaCAM Photometric H-Alpha Survey. Five of them turned out to be genuine SySts after the detection of H α, He ii, and [O iii] emission lines as well as TiO molecular bands. The characteristic O vi Raman-scattered line is also detected in one of these SySts. According to their IR colours and optical spectra, all five newly discovered SySts are classified as S-type. The high rate of true SySts detections of this work demonstrates that the combination of the H α emission and the new IR criterion improves the selection of target lists for follow-up observations by minimizing the number of contaminants and optimizing the observing time.

scholarly journals Thermal radio absorption as a tracer of the interaction of SNRs with their environments

2021 ◽  
Vol 653 ◽  
pp. A62
Author(s):  
G. Castelletti ◽  
L. Supan ◽  
W. M. Peters ◽  
N. E. Kassim
Keyword(s):  
Spectral Index ◽  
Supernova Remnants ◽  
Surrounding Medium ◽  
Low Frequency ◽  
Power Laws ◽  
Line Of Sight ◽  
Pulsar Wind Nebulae ◽  
Very Large Array ◽  
Murchison Widefield Array ◽  
Thermal Absorption

We present new images and continuum spectral analysis for 14 resolved Galactic supernova remnants (SNRs) selected from the 74 MHz Very Large Array Low-Frequency Sky Survey Redux (VLSSr). We combine new integrated measurements from the VLSSr with, when available, flux densities extracted from the Galactic and Extragalactic All-Sky Murchison Widefield Array Survey and measurements from the literature to generate improved integrated continuum spectra sampled from ~15 MHz to ~217 GHz. We present the VLSSr images. When possible we combine them with publicly available images at 1.4 GHz, to analyse the resolved morphology and spectral index distribution across each SNR. We interpret the results and look for evidence of thermal absorption caused by ionised gas either proximate to the SNR itself, or along its line of sight. Three of the SNRs, G4.5+6.8 (Kepler), G28.6−0.1, and G120.1+1.4 (Tycho), have integrated spectra which can be adequately fit with simple power laws. The resolved spectral index map for Tycho confirms internal absorption which was previously detected by the Low Frequency Array, but it is insufficient to affect the fit to the integrated spectrum. Two of the SNRs are pulsar wind nebulae, G21.5−0.9 and G130.7+3.1 (3C 58). For those we identify high-frequency spectral breaks at 38 and 12 GHz, respectively. For the integrated spectra of the remaining nine SNRs, a low frequency spectral turnover is necessary to adequately fit the data. In all cases we are able to explain the turnover by extrinsic thermal absorption. For G18.8+0.3 (Kes 67), G21.8−0.6 (Kes 69), G29.7−0.3 (Kes 75), and G41.1−0.3 (3C 397), we attribute the absorption to ionised gas along the line of sight, possibly from extended H II region envelopes. For G23.3−0.3 (W41) the absorption can be attributed to H II regions located in its immediate proximity. Thermal absorption from interactions at the ionised interface between SNR forward shocks and the surrounding medium were previously identified as responsible for the low frequency turnover in SNR G31.9+0.0 (3C 391); our integrated spectrum is consistent with the previous results. We present evidence for the same phenomenon in three additional SNRs G27.4+0.0 (Kes 73), G39.2–0.3 (3C 396), and G43.3–0.2 (W49B), and derive constraints on the physical properties of the interaction. This result indicates that interactions between SNRs and their environs should be readily detectable through thermal absorption by future low frequency observations of SNRs with improved sensitivity and resolution.

VLA Observations of a Sample of Low-Brightness 6.7 GHz Methanol Masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 311-312
Author(s):  
Luca Olmi ◽  
Esteban D. Araya ◽  
Jason Armstrong
Keyword(s):  
New Mexico ◽  
Star Formation ◽  
Far Infrared ◽  
Large Array ◽  
Very Large Array ◽  
Early Stages ◽  
Methanol Masers ◽  
Infrared Sources ◽  
Massive Cores

AbstractIn 2014 we conducted a survey for 6.7 GHz methanol masers with the Arecibo Telescope toward far infrared sources selected from the Hi-GAL catalog of massive cores. We found a number of sources with weak 6.7 GHz methanol masers, possibly indicating regions in early stages of star formation. Here we describe the results of follow-up observations that were conducted with the Very Large Array in New Mexico to characterize this new population of “weak” 6.7 GHz methanol masers.

scholarly journals Spectroscopic characterization of the protocluster of galaxies around 7C 1756+6520 at z ~ 1.4

2018 ◽  
Vol 618 ◽  
pp. A128 ◽  
Author(s):  
V. Casasola ◽  
L. Magrini ◽  
F. Combes ◽  
E. Sani ◽  
J. Fritz ◽  
...  
Keyword(s):  
Near Infrared ◽  
Radio Galaxy ◽  
High Redshift ◽  
Theoretical Models ◽  
Spectroscopic Characterization ◽  
Emission Lines ◽  
Peculiar Velocities ◽  
Long Time ◽  
High Fraction

Aims. The aim of this paper is the spectroscopic study of 13 galaxies belonging to the field of the protocluster associated with the radio galaxy 7C 1756+6520 at z = 1.4156. In particular, we focus on the characterization of the nuclear activity. Methods. This analysis has been performed on rest-frame optical spectra taken with the Large Binocular Telescope, using the spectrograph LUCI, which is operative in the near-infrared domain. The adopted spectral coverage allowed us to observe emission lines such as Hα, Hβ, [O III]λ 5007 Å, and [N II]λ 6583 Å at the redshift of the central radio galaxy. We observed the central part of the protocluster, which is suitable to include the radio galaxy, several spectroscopically confirmed active galactic nuclei (AGN) belonging to the protocluster, and other objects that might be members of the protocluster. Results. For four previously identified protocluster members, we derived the redshift by detecting emission lines that have never detected before for these galaxies. We identified a new protocluster member and eight new possible protocluster members. The stacked spectrum of the galaxies in which we detected the [O III]λ 5007 Å emission line revealed the second line of the [O III] doublet at 4959 Å and the Hβ line, which confirms that they belong to the protocluster. By collecting all members identified so far in this work and other members from the literature, we defined 31 galaxies, including the central radio galaxy, around the redshift 1.4152 ± 0.056. This corresponds to peculiar velocities ≲5000 km s−1 with respect to the radio galaxy. The position versus velocity phase-space diagram suggests that three AGN of the protocluster and the central radio galaxy might be a virialized population that has been coexisting for a long time in the densest core region of this forming structure. This protocluster is characterized by a high fraction of AGN (~23%). For one of them, AGN1317, we produced two so-called Baldwin, Phillips & Terlevich (BPT) diagrams. The high fraction of AGN and their distribution within the protocluster seem to be consistent with predictions of some theoretical models on AGN growth and feedback. These models are based on galaxy interactions and ram pressure as triggers of AGN activity. Conclusions. The high fraction of AGN belonging to the protocluster suggests that they were likely triggered at the same time, maybe by the ongoing formation of the protocluster. Observations of AGN in this protocluster and in other distant clusters will help clarifying whether the resulting high fraction of AGN is unusual or typical for such structures at high redshift. Our next step will be analyses of previously acquired high-resolution radio data of the central radio galaxy to derive information on the nature of the radio galaxy and connect it with its cosmic evolution.

scholarly journals Discovery and follow-up of the unusual nuclear transient OGLE17aaj

2019 ◽  
Vol 622 ◽  
pp. L2 ◽  
Author(s):  
M. Gromadzki ◽  
A. Hamanowicz ◽  
L. Wyrzykowski ◽  
K. V. Sokolovsky ◽  
M. Fraser ◽  
...  
Keyword(s):  
Light Curve ◽  
Black Body ◽  
Emission Lines ◽  
First Year ◽  
Tidal Disruption ◽  
Massive Black Holes ◽  
X Ray ◽  
New Type ◽  
Narrow Emission

Aims. We report on the discovery and follow-up of a peculiar transient, OGLE17aaj, which occurred in the nucleus of a weakly active galaxy. We investigate whether it can be interpreted as a new candidate for a tidal disruption event (TDE). Methods. We present the OGLE-IV light curve that covers the slow 60-day-long rise to maximum along with photometric, spectroscopic, and X-ray follow-up during the first year. Results. OGLE17aaj is a nuclear transient exhibiting some properties similar to previously found TDEs, including a long rise time, lack of colour-temperature evolution, and high black-body temperature. On the other hand, its narrow emission lines and slow post-peak evolution are different from previously observed TDEs. Its spectrum and light-curve evolution is similar to F01004-2237 and AT 2017bgt. Signatures of historical low-level nuclear variability suggest that OGLE17aaj may instead be related to a new type of accretion event in active super-massive black holes.

scholarly journals The strength of the low-ionization emission lines in Type I PNe

1997 ◽  
Vol 180 ◽  
pp. 273-273
Author(s):  
A. Riera
Keyword(s):  
Statistical Analysis ◽  
Emission Line ◽  
Emission Lines ◽  
Optical Data ◽  
Type I

I have performed a statistical analysis on a group of emission line ratios of a sample of PNe. The optical data was taken from ELCAT2 Catalogue (http://www.stsci.edu/pub/elcat). Some observations of H–H objects were also included for comparison.

scholarly journals Supernova Optical Observations and Theory

2013 ◽  
Vol 9 (S296) ◽  
pp. 77-85
Author(s):  
Keiichi Maeda ◽  
Melina C. Bersten ◽  
Takashi J. Moriya ◽  
Gaston Folatelli ◽  
Ken'ichi Nomoto
Keyword(s):  
Radioactive Decay ◽  
Compton Effect ◽  
Optical Observations ◽  
Optical Data ◽  
Frequency Data ◽  
Inverse Compton Effect ◽  
Inverse Compton ◽  
Γ Ray ◽  
Synthesized Materials

AbstractWe review emission processes within the supernova (SN) ejecta. Examples of the application of the theory to observational data are presented. The emission processes and thermal condition within the SN ejecta change as a function of time, and multi-epoch observations are important to obtain comprehensive views. Through the analyses, we can constrain the progenitor radius, compositions as a function of depth, ejecta properties, explosion asymmetry and so on. Multi-frequency follow-up is also important, including radio synchrotron emissions and the inverse Compton effect, γ-ray emissions from radioactive decay of newly synthesized materials. The optical data are essential to make the best use of the multi-frequency data.

scholarly journals The FLAIR–DENIS Redshift Survey

1997 ◽  
Vol 14 (1) ◽  
pp. 125-126 ◽  
Author(s):  
Q. A. Parker ◽  
M. Colless ◽  
G. Mamon
Keyword(s):  
Near Infrared ◽  
Local Universe ◽  
Redshift Survey ◽  
Infrared Survey

AbstractThe DEep Near-Infrared Survey of the southern sky (DENIS) will produce an important by-product: a clean, complete view of the local Universe to z ∼ 0·07 for 105 galaxies. We identify the FLAIR multi-fibre system on the UKST as an extremely competitive facility to undertake follow-up spectroscopy for this sample due to the need to cover wide areas of sky and observe thousands of objects to a relatively bright (B < 17·5) magnitude.

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