Search

Start Over Subject quasars
1081. 12yrs of R-band photometry of the quasar 3C 454.3
ID:
ivo://CDS.VizieR/J/ApJS/253/10
Title:
12yrs of R-band photometry of the quasar 3C 454.3
Short Name:
J/ApJS/253/10
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this work, we present 8523 pairs of R-band optical photometry observations for the quasar 3C 454.3 made during the period of 2006 October - 2018 February on the 70cm meniscus telescope at Abastumani Observatory, Georgia, to study its intraday variabilities (IDVs) and long-term variations, and we have come to the following results. (1) We detected 10 outbursts, a {Delta}R=3.825mag variation, and some IDVs. The IDV timescales are from 4.1 to 285 minutes, with the corresponding variability amplitude being A=2.9%-43.67%. The amplitude increases with IDV timescale. (2) The largest variation over a 1 day timescale is {Delta}R=1.38mag. (3) The IDV timescales suggest that the emission sizes are from 8.9x10^13^cm to 6.20x10^15^cm, and the magnetic field strengths are B=0.18-0.79G. (4) Period analysis results show three possible long-term periods, p=3.04+/-0.02yr, p=1.66+/-0.06yr, and p=1.20+/-0.03yr in the optical light curve. We adopted the accretion disk models and the lighthouse models to period p=3.04+/-0.02yr: in the accretion disk models, the binary black holes have masses M=1.17x10^9^M_{sun}_; in the lighthouse models, we used two boosted jet flux densities to fit the observational light curve. (5) WWZ analysis gives some short-period (high-frequency) signals associated with strong bursts (JD2454302 and JD2454521) with variable frequencies and lasting for the entire observation time span (11.3yr).
1082. z<0.16 CIV absorbers from HST/COS QSOs spectra
ID:
ivo://CDS.VizieR/J/ApJ/815/91
Title:
z<0.16 CIV absorbers from HST/COS QSOs spectra
Short Name:
J/ApJ/815/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
To investigate the evolution of metal-enriched gas over recent cosmic epochs as well as to characterize the diffuse, ionized, metal-enriched circumgalactic medium, we have conducted a blind survey for CIV absorption systems in 89 QSO sightlines observed with the Hubble Space Telescope Cosmic Origins Spectrograph. We have identified 42 absorbers at z<0.16, comprising the largest uniform blind sample size to date in this redshift range. Our measurements indicate an increasing CIV absorber number density per comoving path length (dN/dX=7.5+/-1.1) and modestly increasing mass density relative to the critical density of the universe ({Omega}_CIV_=10.0+/-1.5x10^-8^) from z~1.5 to the present epoch, consistent with predictions from cosmological hydrodynamical simulations. Furthermore, the data support a functional form for the column density distribution function that deviates from a single power law, also consistent with independent theoretical predictions. As the data also probe heavy element ions in addition to CIV at the same redshifts, we identify, measure, and search for correlations between column densities of these species where components appear to be aligned in velocity. Among these ion-ion correlations, we find evidence for tight correlations between CII and SiII, CII and SiIII, and CIV and SiIV, suggesting that these pairs of species arise in similar ionization conditions. However, the evidence for correlations decreases as the difference in ionization potential increases. Finally, when controlling for observational bias, we find only marginal evidence for a correlation (86.8% likelihood) between the Doppler line width b(CIV) and column density N(CIV).
1083. z<1 3CR radio galaxies and quasars star formation
ID:
ivo://CDS.VizieR/J/AJ/151/120
Title:
z<1 3CR radio galaxies and quasars star formation
Short Name:
J/AJ/151/120
Date:
16 Dec 2021 13:37:06
Publisher:
CDS
Description:
Using the Herschel Space Observatory we have observed a representative sample of 87 powerful 3CR sources at redshift z<1. The far-infrared (FIR, 70-500 {mu}m) photometry is combined with mid-infrared (MIR) photometry from the Wide-Field Infrared Survey Explorer and cataloged data to analyze the complete spectral energy distributions (SEDs) of each object from optical to radio wavelength. To disentangle the contributions of different components, the SEDs are fitted with a set of templates to derive the luminosities of host galaxy starlight, dust torus emission powered by active galactic nuclei (AGNs), and cool dust heated by stars. The level of emission from relativistic jets is also estimated to isolate the thermal host galaxy contribution. The new data are in line with the orientation-based unification of high-excitation radio-loud AGN, in that the dust torus becomes optically thin longwards of 30 {mu}m. The low-excitation radio galaxies and the MIR-weak sources represent an MIR- and FIR-faint AGN population that is different from the high-excitation MIR-bright objects; it remains an open question whether they are at a later evolutionary state or an intrinsically different population. The derived luminosities for host starlight and dust heated by star formation are converted to stellar masses and star-formation rates (SFR). The host-normalized SFR of the bulk of the 3CR sources is low when compared to other galaxy populations at the same epoch. Estimates of the dust mass yield a 1-100 times lower dust/stellar mass ratio than for the Milky Way, which indicates that these 3CR hosts have very low levels of interstellar matter and explains the low level of star formation. Less than 10% of the 3CR sources show levels of star formation above those of the main sequence of star-forming galaxies.
1084. z>3 damped Ly{alpha} absorption systems
ID:
ivo://CDS.VizieR/J/ApJ/543/552
Title:
z>3 damped Ly{alpha} absorption systems
Short Name:
J/ApJ/543/552
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have completed spectroscopic observations using LRIS on the Keck 1 telescope of 30 very high redshift quasars, 11 selected for the presence of damped Ly{alpha} absorption systems and 19 with redshifts z>3.5 not previously surveyed for absorption systems. We have surveyed an additional 10 QSOs with the Lick 120" and the Anglo-Australian Telescope. We have combined these with previous data, resulting in a statistical sample of 646 QSOs and 85 damped Ly{alpha} absorbers with column densities N_HI_>=2 10^20^atoms/cm^2^ covering the redshift range 0.008<=z<=4.694. Four main features of how the neutral gas in the universe evolves with redshift are evident from these data.
1085. Zn measurements in sub-DLAs and DLAs QSOs
ID:
ivo://CDS.VizieR/J/ApJ/661/88
Title:
Zn measurements in sub-DLAs and DLAs QSOs
Short Name:
J/ApJ/661/88
Date:
21 Oct 2021
Publisher:
CDS
Description:
Observations of low mean metallicity of damped Ly{alpha} (DLA) quasar absorbers at all redshifts studied appear to contradict the predictions for the global mean interstellar metallicity in galaxies from cosmic chemical evolution models. On the other hand, a number of metal-rich sub-DLA systems have been identified recently, and the fraction of metal-rich sub-DLAs appears to be considerably larger than that of metal-rich DLAs, especially at z<1.5. In view of this, here we investigate the evolution of metallicity in sub-DLAs. We find that the mean Zn metallicity of the observed sub-DLAs may be higher than that of the observed DLAs, especially at low redshifts, reaching a near-solar level at z<~1. This trend does not appear to be an artifact of sample selection, the use of Zn, the use of N_HI_ weighting, or observational sensitivity.
1086. z<0.5 PG quasars IR energy distributions
ID:
ivo://CDS.VizieR/J/ApJ/854/158
Title:
z<0.5 PG quasars IR energy distributions
Short Name:
J/ApJ/854/158
Date:
21 Oct 2021
Publisher:
CDS
Description:
The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. However, direct gas measurements are limited by sensitivity and other uncertainties. Dust provides an efficient indirect probe of the total gas. We apply this technique to a large sample of quasars, whose total gas content would be prohibitively expensive to measure. We present a comprehensive study of the full (1 to 500{mu}m) infrared spectral energy distributions of 87 redshift <0.5 quasars selected from the Palomar-Green sample, using photometric measurements from 2MASS, WISE, and Herschel, combined with Spitzer mid-infrared (5-40{mu}m) spectra. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated spectral energy distribution, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass. Most (90%) quasar hosts have gas fractions similar to those of massive, star-forming galaxies, although a minority (10%) seem genuinely gas-deficient, resembling present-day massive early-type galaxies. This result indicates that "quasar mode" feedback does not occur or is ineffective in the host galaxies of low-redshift quasars. We also find that quasars can boost the interstellar radiation field and heat dust on galactic scales. This cautions against the common practice of using the far-infrared luminosity to estimate the host galaxy star formation rate.
1087. z~5 QSO luminosity function from SDSS Stripe 82
ID:
ivo://CDS.VizieR/J/ApJ/768/105
Title:
z~5 QSO luminosity function from SDSS Stripe 82
Short Name:
J/ApJ/768/105
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a measurement of the Type I quasar luminosity function at z=5 using a large sample of spectroscopically confirmed quasars selected from optical imaging data. We measure the bright end (M_1450_<-26) with Sloan Digital Sky Survey (SDSS) data covering ~6000deg^2^, then extend to lower luminosities (M_1450_<-24) with newly discovered, faint z~5 quasars selected from 235deg^2^ of deep, coadded imaging in the SDSS Stripe 82 region (the celestial equator in the Southern Galactic Cap). The faint sample includes 14 quasars with spectra obtained as ancillary science targets in the SDSS-III Baryon Oscillation Spectroscopic Survey, and 59 quasars observed at the MMT and Magellan telescopes. We construct a well-defined sample of 4.7<z<5.1 quasars that is highly complete, with 73 spectroscopic identifications out of 92 candidates. Our color selection method is also highly efficient: of the 73 spectra obtained, 71 are high-redshift quasars. These observations reach below the break in the luminosity function (M_1450_^*^~-27). The bright-end slope is steep ({beta}<~-4), with a constraint of {beta}<-3.1 at 95% confidence. The break luminosity appears to evolve strongly at high redshift, providing an explanation for the flattening of the bright-end slope reported previously. We find a factor of ~2 greater decrease in the number density of luminous quasars (M_1450_<-26) from z=5 to z=6 than from z=4 to z=5, suggesting a more rapid decline in quasar activity at high redshift than found in previous surveys. Our model for the quasar luminosity function predicts that quasars generate ~30% of the ionizing photons required to keep hydrogen in the universe ionized at z=5.
1088. z~6 QSOs CIV doublet absorption systems
ID:
ivo://CDS.VizieR/J/MNRAS/435/1198
Title:
z~6 QSOs CIV doublet absorption systems
Short Name:
J/MNRAS/435/1198
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z~6. This paper focuses on the properties of metals at high redshift traced, in particular, by the CIV doublet absorption systems. Six objects were observed with resolutions =~27 and 34km/s in the visual, and 37.5 and 53.5km/s in the near-infrared. We detected 10^2^ CIV lines in the range: 4.35<z<6.2 of which 27 are above z~5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 SiIV doublets associated with the CIV at z>~5. The column density distribution function of the CIV line sample is observed to evolve in redshift for z>~5.3, with respect to the normalization defined by low-redshift (1.5<z<4) CIV lines. This behaviour is reflected in the redshift evolution of the CIV cosmic mass density, {Omega}_CIV_, of lines with column density in the range 13.4<logN(CIV)<15, which is consistent with a drop of a factor of ~2 for z>~5.3. Considering only the stronger CIV lines (13.8<logN(CIV)<15), {Omega}_CIV_ gently rises by a factor of ~10 between z=~6.2 and z=~1.5 with a possible flattening towards z~0. The increase is well fitted by a power law: {Omega}_CIV=(2+/-1)x10^-8^[(1+z)/4]^-3.1+/-0.1^. An insight into the properties of the CIV absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated CIV, SiIV and CII absorptions with the output of a set of cloudy photoionization models. As already claimed by cosmological simulations, we find that CIV is a good tracer of the metallicity in the low-density intergalactic medium (IGM) gas at z~5-6 while at z~3 it arises in gas with overdensity {delta}~100.
1089. 1.4<=z<=5.0 QSOs luminosity function
ID:
ivo://CDS.VizieR/J/A+A/636/A12
Title:
1.4<=z<=5.0 QSOs luminosity function
Short Name:
J/A+A/636/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an estimate of the optical luminosity function (OLF) of LOFAR radio-selected quasars (RSQs) at 1.4<z<5.0 in the 9.3deg^2^ NOAO Deep Wide-field survey (NDWFS) of the Bootes field. The selection was based on optical and mid-infrared photometry used to train three different machine learning (ML) algorithms (Random forest, SVM, Bootstrap aggregation). Objects taken as quasars by the ML algorithms are required to be detected at >=5{sigma} significance in deep radio maps to be classified as candidate quasars. The optical imaging came from the Sloan Digital Sky Survey and the Pan-STARRS1 3{PI} survey; mid-infrared photometry was taken from the Spitzer Deep, Wide-Field Survey; and radio data was obtained from deep LOFAR imaging of the NDWFS-Bootes field. The requirement of a 5{sigma} LOFAR detection allowed us to reduce the stellar contamination in our sample by two orders of magnitude. The sample comprises 130 objects, including both photometrically selected candidate quasars (47) and spectroscopically confirmed quasars (83). The spectral energy distributions calculated using deep photometry available for the NDWFS-Bootes field confirm the validity of the photometrically selected quasars using the ML algorithms as robust candidate quasars. 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_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-infrared wedge-based AGN selection is not possible due to a lack of appropriate data, the selection of quasars using ML algorithms trained with optical and infrared photometry in combination with LOFAR data provides an excellent approach for obtaining samples of quasars. The OLF of RSQs can be described by pure luminosity evolution at z<2.4, and a combined luminosity and density evolution at z>2.4. The faint-end slope, {alpha}, becomes steeper with increasing redshift. This trend is consistent with previous studies of faint quasars (M_1450_<=-22.0). We demonstrate that RSQs show an evolution that is very similar to that exhibited by faint quasars. By comparing the spatial density of RSQs with that of the total (radio-detected plus radio-undetected) faint quasar population at similar redshifts, we find that RSQs may compose up to ~20% of the whole faint quasar population. This fraction, within uncertainties, is constant with redshift. Finally, we discuss how the compactness of the RSQs radio-morphologies and their steep spectral indices could provide valuable insights into how quasar and radio activity are triggered in these systems.
1090. z>4.5 QSOs with SDSS and WISE. I. Opt. spectra
ID:
ivo://CDS.VizieR/J/ApJ/819/24
Title:
z>4.5 QSOs with SDSS and WISE. I. Opt. spectra
Short Name:
J/ApJ/819/24
Date:
21 Oct 2021
Publisher:
CDS
Description:
High-redshift quasars are important tracers of structure and evolution in the early universe. However, they are very rare and difficult to find when using color selection because of contamination from late-type dwarfs. High-redshift quasar surveys based on only optical colors suffer from incompleteness and low identification efficiency, especially at z>~4.5. We have developed a new method to select 4.7<~z>~5.4 quasars with both high efficiency and completeness by combining optical and mid-IR Wide-field Infrared Survey Explorer (WISE) photometric data, and are conducting a luminous z~5 quasar survey in the whole Sloan Digital Sky Survey (SDSS) footprint. We have spectroscopically observed 99 out of 110 candidates with z-band magnitudes brighter than 19.5, and 64 (64.6%) of them are quasars with redshifts of 4.4<~z<~5.5 and absolute magnitudes of -29<~M_1450_<~-26.4. In addition, we also observed 14 fainter candidates selected with the same criteria and identified 8 (57.1%) of them as quasars with 4.7<z<5.4. Among 72 newly identified quasars, 12 of them are at 5.2<z<5.7, which leads to an increase of ~36% of the number of known quasars at this redshift range. More importantly, our identifications doubled the number of quasars with M_1450_<-27.5 at z>4.5, which will set strong constraints on the bright end of the quasar luminosity function. We also expand our method to select quasars at z>~5.7. In this paper we report the discovery of four new luminous z>~5.7 quasars based on SDSS-WISE selection.