Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe optical luminosity function of LOFAR radio-selected quasars at $1.4leq zleq5.0$ in the NDWFS-Bootes field
71
0
0.0
(
0
)
Added by
E. Retana-Montenegro
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present an estimate of the optical luminosity function (OLF) of LOFAR radio-selected quasars (RSQs) at $1.4<z<5.0$ in the $9.3:textrm{deg}^{2}$ NOAO Deep Wide-field survey (NDWFS) of the Bootes field. The selection was based on optical/mid-ir photometry used to train three different machine learning (ML) algorithms. Objects taken as quasars by the ML algorithms are required to be detected at $5sigma$ significance in deep radio maps to be classified as candidate quasars. The optical imaging came from the SDSS and the PS1 $3pi$ survey; mid-ir photometry was taken from the SDWFS survey; and radio data was obtained from deep LOFAR imaging of the NDWFS-Bootes field. The requirement of a $5sigma$ LOFAR detection allowed us to reduce the stellar contamination in our sample by two orders of magnitude. The sample comprises 134 objects, including both photometrically selected candidate quasars (47) and spectroscopically confirmed quasars (83). The depth of our LOFAR observations allowed us to detect the radio-emission of quasars that would be otherwise classified as radio-quiet. Around $65%$ of the quasars in the sample are fainter than $M_{textrm{1450}}=-24.0$, a regime where the OLF of quasars selected through their radio emission, has not been investigated in detail. It has been demonstrated that in cases where mid-ir wedge-based AGN selection is not possible due to a lack of appropriate data, the selection of quasars using ML algorithms trained with optical/mid-ir photometry in combination with LOFAR data provides an excellent approach for obtaining samples of quasars. We demonstrate that RSQs show an evolution similar to that exhibited by faint quasars $(M_{textrm{1450}}leq-22.0)$. Finally, we find that RSQs may compose up to $sim20%$ of the whole faint quasar population (radio-detected plus radio-undetected).
rate research
Read More
We have combined data from the NOAO Deep Wide-Field Survey in Bootes and the Spitzer Space Telescope to determine basic properties for sixteen optically invisible MIPS 24um (OIMS) and thirty-five optically invisible radio (OIRS) soruces, including their spectral energy distributions (SED) and luminosities. Most OIMSs possess steep power-law SEDs over lambda(rest) = 1-10 um, indicating the presence of obscured AGN in agreement with Spitzer spectroscopy. These objects are extremely luminous at rest-frame near and mid-IR (nu L_nu(5um) ~ 10^{38}-10^{39} W), consistent with accretion near the Eddington limit and further implying that they host buried QSOs. The majority of the IRAC detected OIRSs have flat 3.6 to 24um SEDs, implying comparable emission from stellar photospheres and hot AGN illuminated dust. This may reflect relatively small amounts of dust close to the central engine or current low mass accretion rates. A small subset of OIRSs appear to be starburst dominated with photometric redshifts from 1.0 to 4.5. The OIMSs and OIRSs with significant starburst components have similar L_K and stellar masses (M* ~ 10^{11} M_solar) assuming minimal AGN contribution. Roughly half of the OIRSs are not detected by Spitzers IRAC or MIPS. These are most likely z > 2 radio galaxies. The IRAC detected OIRSs are more likely than OIMSs to appear non point-like in the 3.6um and 4.5um images, suggesting that interactions play a role in triggering their activity. The AGN powered OIMSs may represent sub-millimeter galaxies making the transition from starburst to accretion dominance in their evolution to current epoch massive ellipticals.
Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. Measuring the projected linear sizes of these sources provides an indication of their orientation. Steep-spectrum isotropic radio emission allows for orientation-free sample selection at low radio frequencies. We use a new radio survey of the Bootes field at 150 MHz made with the Low Frequency Array (LOFAR) to select a sample of radio sources. We identify 44 radio galaxies and 16 quasars with powers $P>10^{25.5}$ W Hz$^{-1}$ at 150 MHz using cross-matched multi-wavelength information from the AGN and Galaxy Evolution Survey (AGES), which provides spectroscopic redshifts. We find that LOFAR-detected radio sources with steep spectra have projected linear sizes that are on average 4.4$pm$1.4 larger than those with flat spectra. The projected linear sizes of radio galaxies are on average 3.1$pm$1.0 larger than those of quasars (2.0$pm$0.3 after correcting for redshift evolution). Combining these results with three previous surveys, we find that the projected linear sizes of radio galaxies and quasars depend on redshift but not on power. The projected linear size ratio does not correlate with either parameter. The LOFAR data is consistent within the uncertainties with theoretical predictions of the correlation between the quasar fraction and linear size ratio, based on an orientation-based unification scheme.
We present a new analysis of the widely used relation between cavity power and radio luminosity in clusters of galaxies with evidence for strong AGN feedback. We study the correlation at low radio frequencies using two new surveys - the First Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) at 148 MHz and LOFARs first all-sky survey, the Multifrequency Snapshot Sky Survey (MSSS) at 140 MHz. We find a scaling relation $P_{rm cav} propto L_{148}^{beta}$, with a logarithmic slope of $beta = 0.51 pm 0.14$, which is in good agreement with previous results based on data at 327 MHz. The large scatter present in this correlation confirms the conclusion reached at higher frequencies that the total radio luminosity at a single frequency is a poor predictor of the total jet power. We show that including measurements at 148 MHz alone is insufficient to reliably compute the bolometric radio luminosity and reduce the scatter in the correlation. For a subset of four well-resolved sources, we examine the detected extended structures at low frequencies and compare with the morphology known from higher frequency images and Chandra X-ray maps. In Perseus we discuss details in the structures of the radio mini-halo, while in the 2A 0335+096 cluster we observe new diffuse emission associated with multiple X-ray cavities and likely originating from past activity. For A2199 and MS 0735.6+7421, we confirm that the observed low-frequency radio lobes are confined to the extents known from higher frequencies. This new low-frequency analysis highlights the fact that existing cavity power to radio luminosity relations are based on a relatively narrow range of AGN outburst ages. We discuss how the correlation could be extended using low frequency data from the LOFAR Two-metre Sky Survey (LoTSS) in combination with future, complementary deeper X-ray observations.
We determine the 22$mu$m luminosity evolution and luminosity function for quasars from a data set of over 20,000 objects obtained by combining flux-limited Sloan Digital Sky Survey optical and Wide field Infrared Survey Explorer mid-infrared data. We apply methods developed in previous works to access the intrinsic population distributions non-parametrically, taking into account the truncations and correlations inherent in the data. We find that the population of quasars exhibits positive luminosity evolution with redshift in the mid-infrared, but with considerably less mid-infrared evolution than in the optical or radio bands. With the luminosity evolutions accounted for, we determine the density evolution and local mid-infrared luminosity function. The latter displays a sharp flattening at local luminosities below $sim 10^{31}$ erg sec$^{-1}$ Hz$^{-1}$, which has been reported previously at 15 $mu$m for AGN classified as both type-1 and type-2. We calculate the integrated total emission from quasars at 22 $mu$m and find it to be a small fraction of both the cosmic infrared background light and the integrated emission from all sources at this wavelength.
We present the first measurement of the spatial clustering of mid-infrared selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg^2 Bootes multiwavelength survey. Recently the Spitzer Space Telescope and X-ray observations have revealed large populations of obscured quasars that have been inferred from models of the X-ray background and supermassive black hole evolution. To date, little is known about obscured quasar clustering, which allows us to measure the masses of their host dark matter halos and explore their role in the cosmic evolution of black holes and galaxies. In this study we use a sample of 806 mid-infrared selected quasars and ~250,000 galaxies to calculate the projected quasar-galaxy cross-correlation function w_p(R). The observed clustering yields characteristic dark matter halo masses of log (M_halo [h^-1 M_sun]) = 12.7^+0.4_-0.6 and 13.3^+0.3_-0.4 for unobscured quasars (QSO-1s) and obscured quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent agreement with previous measurements for optically-selected quasars, while we conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We test for the effects of photometric redshift errors on the optically-faint Obs-QSOs, and find that our method yields a robust lower limit on the clustering; photo-z errors may cause us to underestimate the clustering amplitude of the Obs-QSOs by at most ~20%. We compare our results to previous studies, and speculate on physical implications of stronger clustering for obscured quasars.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
