اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNew Insights on the z-alpha Correlation from Complete Radio Samples
108
0
0.0
(
0
)
تأليف
L. M. Ker
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The existence of a correlation between observed radio spectral index (alpha) and redshift (z) has long been used as a method for locating high-z radio galaxies. We use 9 highly spectroscopically complete radio samples, selected at different frequencies and flux limits, to determine the efficiency of this method, and compare consistently observed correlations between alpha, luminosity, linear size, and redshift. We observe a weak correlation between z and alpha which remains even when Malmquist bias is removed. The strength of this correlation depends on both the k-correction and sample selection frequency, in addition to the frequency at which alpha is measured, and consistent results for both high and low frequency selected samples are only seen if analysis is restricted to just extended radio galaxies. Many of the highest redshift radio galaxies are very compact and often display a negatively curved or peaked spectrum, and therefore the low-frequency radio spectrum as a whole should be studied; this is something for which the LOFAR will be crucial. We quantify both the efficiency and the completeness of various techniques used to select high-z radio galaxies. A steep-spectrum cut applied to low-frequency selected samples can more than double the fraction of high-z sources, but at a cost of excluding over half of the high-z sources present in the original sample. An angular size cut is an almost as equally effective method as a steep-spectrum cut, and works for both high and low frequency selected samples. In multi-wavelength data, selection first of infrared-faint radio sources remains by far the most efficient method of selecting high-z sources. We present a simple method for selecting high-z radio galaxies, based purely on combining their radio properties of alpha and angular size, with the addition of the K-band magnitude if available.[abridged]
قيم البحث
اقرأ أيضاً
We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Ly$alpha$-forest flux-transmission at a mean redshift $z=2.40$. The measurement uses the complete SDSS-III data sample: 168,889 forests and 23
4,367 quasars from the SDSS Data Release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level allowing a more accurate measurement of this cross-correlation. We also developed the first simulations of the cross-correlation allowing us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios $D_{H}(z=2.40)/r_{d} = 9.01 pm 0.36$ and $D_{M}(z=2.40)/r_{d} = 35.7 pm 1.7$, where the errors include marginalization over the non-linear velocity of quasars and the metal - quasar cross-correlation contribution, among other effects. These results are within $1.8sigma$ of the prediction of the flat-$Lambda$CDM model describing the observed CMB anisotropies. We combine this study with the Ly$alpha$-forest auto-correlation function [2017A&A...603A..12B], yielding $D_{H}(z=2.40)/r_{d} = 8.94 pm 0.22$ and $D_{M}(z=2.40)/r_{d} = 36.6 pm 1.2$, within $2.3sigma$ of the same flat-$Lambda$CDM model.
We present an analysis of four complete samples of radio-loud AGN (3CRR, 2Jy, 6CE and 7CE) using near- and mid-IR data taken by the Wide-Field Infrared Survey Explorer (WISE). The combined sample consists of 79 quasars and 273 radio galaxies, and cov
ers a redshift range 0.003<z<3.395. The dichotomy in the mid-IR properties of low- and high-excitation radio galaxies (LERGs - HERGs) is analysed for the first time using large complete samples. Our results demonstrate that a division in the accretion modes of LERGs and HERGs clearly stands out in the mid-IR-radio plane (L_(22 mu m) = 5x10^(43) erg s^(-1)). This means that WISE data can be effectively used to diagnose accretion modes in radio-loud AGN. The mid-IR properties of all objects were analysed to test the unification between quasars and radio galaxies, consistent with earlier work and we argue that smooth torus models best reproduce the observation. Quasars are found to have higher mid-IR luminosities than radio galaxies. We also studied all the sources in the near-IR to gain insights into evolution of AGN host galaxies. A relation found between the near-IR luminosity and redshift, well-known in the near-IR, is apparent in the two near-IR WISE bands, supporting the idea that radio sources are hosted by massive elliptical galaxies that formed their stars at high redshifts and evolved passively thereafter. Evaluation of the positions of the sample objects in WISE colour-colour diagrams shows that widely used WISE colour cuts are not completely reliable in selecting AGN.
We have observed a new, complete, cooling-core sample with the VLA, in order to understand how the massive black hole in the central galaxy interacts with the local cluster plasma. We find that every cooling core is currently being energized by an ac
tive radio jet, which has probably been destabilized by its interaction with the cooling core. We argue that current models of cooling-core radio galaxies need to be improved before they can be used to determine the rate at which the jet is heating the cooling core. We also argue that the extended radio haloes we see in many cooling-core clusters need extended, in situ re-energization, which cannot be supplied solely by the central galaxy.
From the spectral analysis of long Suzaku observations of five radio-loud AGNs we have been able to discover the presence of ultra-fast outflows with velocities ~0.1c in three of them, namely 3C 111, 3C 120 and 3C 390.3. They are consistent with bein
g accretion disk winds/outflows. We also performed a follow-up on 3C 111 to monitor its outflow on ~7days time-scales and detected an anti-correlated variability of a possible relativistic emission line with respect to blue-shifted Fe K features, following a flux increase. This provides the first direct evidence for an accretion disk-wind connection in an AGN. The mass outflow rate of these outflows can be comparable to the accretion rate and their mechanical power can correspond to a significant fraction of the bolometric luminosity and is comparable to their typical jet power. Therefore, they can possibly play a significant role in the expected feedback from AGNs and can give us further clues on the relation between the accretion disk and the formation of winds/jets.
We present NICMOS J110 (rest-frame 1200-2100 A) observations of the three z=5.7 Lyman Alpha emitters discovered in the blind multislit spectroscopic survey by Martin et al. (2008). These images confirm the presence of the two sources which were previ
ously only seen in spectroscopic observations. The third source, which is undetected in our J110 observations has been detected in narrowband imaging of the Cosmic Origins Survey (COSMOS), so our nondetection implies a rest frame equivalent width >146 Angstroms (3 sigma). The two J110-- detected sources have more modest rest frame equivalent widths of 30-40 Angstroms, but all three are typical of high-redshift LAEs. In addition, the J110- detected sources have UV luminosities that are within a factor of two of L*_{UV}, and sizes that appear compact (r_{hl} ~ 0.15) in our NIC2 images -- consistent with a redshift of 5.7. We use these UV-continuum and Lyman Alpha measurements to estimate the i-z colors of these galaxies, and show that at least one, and possibly all three would be missed by the i-dropout LBG selection. These observations help demonstrate the utility of multislit narrowband spectroscopy as a technique for finding faint emission line galaxies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
