اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدA Semi-automatic Search for Giant Radio Galaxy Candidates and their Radio-Optical Follow-up
88
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present results of a search for giant radio galaxies (GRGs) with a projected largest linear size in excess of 1 Mpc. We designed a computational algorithm to identify contiguous emission regions, large and elongated enough to serve as GRG candidates, and applied it to the entire 1.4-GHz NRAO VLA Sky survey (NVSS). In a subsequent visual inspection of 1000 such regions we discovered 15 new GRGs, as well as many other candidate GRGs, some of them previously reported, for which no redshift was known. Our follow-up spectroscopy of 25 of the brighter hosts using two 2.1-m telescopes in Mexico, and four fainter hosts with the 10.4-m Gran Telescopio Canarias (GTC), yielded another 24 GRGs. We also obtained higher-resolution radio images with the Karl G. Jansky Very Large Array for GRG candidates with inconclusive radio structures in NVSS.
قيم البحث
اقرأ أيضاً
Ultra-steep spectrum (USS) radio sources are good tracers of powerful radio galaxies at $z > 2$. Identification of even a single bright radio galaxy at $z > 6$ can be used to detect redshifted 21cm absorption due to neutral hydrogen in the intervenin
g IGM. Here we describe a new sample of high-redshift radio galaxy (HzRG) candidates constructed from the TGSS ADR1 survey at 150 MHz. We employ USS selection ($alpha le -1.3$) in $sim10000$ square degrees, in combination with strict size selection and non-detections in all-sky optical and infrared surveys. We apply flux density cuts that probe a unique parameter space in flux density ($50 < S_{textrm{150}} < 200$ mJy) to build a sample of 32 HzRG candidates. Follow-up Karl G. Jansky Very Large Array (VLA) observations at 1.4 GHz with an average beam size of $1.3$ arcseconds ($$) revealed $sim 48%$ of sources to have a single radio component. P-band (370 MHz) imaging of 17 of these sources revealed a flattening radio SED for ten sources at low frequencies, which is expected from compact HzRGs. Two of our sources lie in fields where deeper multi-wavelength photometry and ancillary radio data are available and for one of these we find a best-fit photo-z of $4.8 pm 2.0$. The other source has $z_{textrm{phot}}=1.4 pm 0.1$ and a small angular size ($3.7$), which could be associated with an obscured star forming galaxy or with a dead elliptical. One USS radio source not part of the HzRG sample but observed with the VLA nonetheless is revealed to be a candidate giant radio galaxy with a host galaxy photo-z of $1.8pm0.5$, indicating a size of 875 kpc.
The origin of fast radio bursts (FRBs), bright millisecond radio transients, is still somewhat of a mystery. Several theoretical models expect that the FRB accompanies an optical afterglow (e.g., Totani 2013; Kashiyama et al. 2013). In order to inves
tigate the origin of FRBs, we perform $gri$-band follow-up observations of FRB~151230 (estimated $z lesssim 0.8$) with Subaru/Hyper Suprime-Cam at $8$, $11$, and $14$~days after discovery. The follow-up observation reaches a $50%$ completeness magnitude of $26.5$~mag for point sources, which is the deepest optical follow-up of FRBs to date. We find $13$ counterpart candidates with variabilities during the observation. We investigate their properties with multicolor and multi-wavelength observations and archival catalogs. Two candidates are excluded by the non-detection of FRB~151230 in the other radio feed horns that operated simultaneously to the detection, as well as the inconsistency between the photometric redshift and that derived from the dispersion measure of FRB~151230. Eight further candidates are consistent with optical variability seen in AGNs. Two more candidates are well fitted with transient templates (Type IIn supernovae), and the final candidate is poorly fitted with all of our transient templates and is located off-center of an extended source. It can only be reproduced with rapid transients with a faint peak and rapid decline and the probability of chance coincidence is $sim3.6%$. We also find that none of our candidates are consistent with Type Ia supernovae, which rules out the association of Type Ia supernovae to FRB~151230 at $zleq0.6$ and limits the dispersion measure of the host galaxy to $lesssim300$~pc~cm$^{-3}$ in a Type Ia supernova scenario.
We report the discovery of four Fast Radio Bursts (FRBs) in the ongoing SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) at the Parkes Radio Telescope: FRBs 150610, 151206, 151230 and 160102. Our real-time discoveries have enabled us to con
duct extensive, rapid multi-messenger follow-up at 12 major facilities sensitive to radio, optical, X-ray, gamma-ray photons and neutrinos on time scales ranging from an hour to a few months post-burst. No counterparts to the FRBs were found and we provide upper limits on afterglow luminosities. None of the FRBs were seen to repeat. Formal fits to all FRBs show hints of scattering while their intrinsic widths are unresolved in time. FRB 151206 is at low Galactic latitude, FRB 151230 shows a sharp spectral cutoff, and FRB 160102 has the highest dispersion measure (DM = $2596.1pm0.3$ pc cm$^{-3}$) detected to date. Three of the FRBs have high dispersion measures (DM >$1500$ pc cm$^{-3}$), favouring a scenario where the DM is dominated by contributions from the Intergalactic Medium. The slope of the Parkes FRB source counts distribution with fluences $>2$ Jyms is $alpha=-2.2^{+0.6}_{-1.2}$ and still consistent with a Euclidean distribution ($alpha=-3/2$). We also find that the all-sky rate is $1.7^{+1.5}_{-0.9}times10^3$FRBs/($4pi$ sr)/day above $sim2$ Jyms and there is currently no strong evidence for a latitude-dependent FRB sky-rate.
Here we present new red sequence overdensity measurements for 77 fields in the high-$z$ Clusters Occupied by Bent Radio AGN (COBRA) survey, based on $r$- and $i$-band imaging taken with Lowell Observatorys Discovery Channel Telescope. We observe 38 C
OBRA fields in $r$-band and 90 COBRA fields in $i$-band. By combining the $r$- and $i$-band photometry with our 3.6$mu$m and 4.5$mu$m $Spitzer$ IRAC observations, we identify 39 red sequence cluster candidates that host a strong overdensity of galaxies when measuring the excess of red sequence galaxies relative to a background field. We initially treat the radio host as the cluster center and then determine a new cluster center based on the surface density of red sequence sources. Using our color selection, we identify which COBRA cluster candidates have strong red sequence populations. By removing foreground and background contaminants, we more securely determine which fields include cluster candidates with a higher significance than our single-band observations. Additionally, of the 77 fields we analyze with a redshift estimate, 26 include newly estimated photometric redshifts.
We present the composite optical spectrum for the largest sample of giant radio quasars (GRQs). They represent a rare subclass of radio quasars due to their large projected linear sizes of radio structures, which exceed 0.7 Mpc. To construct the comp
osite spectrum, we combined 216 GRQs optical spectra from Sloan Digital Sky Survey (SDSS). As a result, we obtained the composite spectrum covering the wavelength range from 1400 {AA} to 7000 {AA}. We calculated the power-law spectral slope for GRQs composite, obtaining $alpha_{lambda}=-1.25$ and compared it with that of the smaller-sized radio quasars, as well as with the quasar composite spectrum obtained for large sample of SDSS quasars. We obtained that the GRQs continuum is flatter (redder) than the continuum of comparison quasar samples. We also show that the continuum slope depends on core and total radio luminosity at 1.4 GHz, being steeper for higher radio luminosity bin. Moreover, we found the flattening of the continuum with an increase of the projected linear size of radio quasar. We show that $alpha_{lambda}$ is orientation-dependent, being steeper for a higher radio core-to-lobe flux density ratio which is consistent with AGN unified model predictions. For two GRQs, we fit the spectral energy distribution using X-CIGALE code to compare the consistency of results obtained in the optical part of the electromagnetic spectrum with broad-band emission. The parameters obtained from the SED fitting confirmed the larger dust luminosity for the redder optical continuum.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
