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result(s) for
"Quasars"
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Peculiar Black Hole Accretion Rates in AGN with Highest Star Formation Rates in the Universe
Pouliasis et al. explored star formation rates, black hole accretion rates, and stellar mass of active galaxies at redshift above 3.5, uncovering a leveling off of the star formation rate at high stellar mass, which they consider to be evidence of AGN feedback. Their data shows that as AGN approach the flattening of the curve in the star formation rate—stellar mass plane, the accretion rates begin to drop. We describe the nature of the AGN feedback responsible for this in terms of powerful FRII jets enhancing star formation rates but eventually also triggering a shift in accretion from near-Eddington rates to advection dominated. These systems are on the cusp of a dramatic transition where the active galaxy goes from strong enhancement to large suppression of star formation in a way that produces the steeper slope for radio AGN at low redshift compared to radio AGN at higher redshift and to jetless AGN. We argue, therefore, that the data of Pouliasis et al. constitute the high redshift objects predicted by Singh et al. that connect to the low redshift behavior of radio AGN shown in Comerford et al.
Journal Article
The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
The All-Sky Automated Survey for Supernovae (ASAS-SN) is working toward imaging the entire visible sky every night to a depth of V ∼ 17 mag. The present data covers the sky and spans ∼2-5 years with ∼100-400 epochs of observation. The data should contain some ∼1 million variable sources, and the ultimate goal is to have a database of these observations publicly accessible. We describe here a first step, a simple but unprecedented web interface https://asas-sn.osu.edu/ that provides an up to date aperture photometry light curve for any user-selected sky coordinate. The V band photometry is obtained using a two-pixel (16 0) radius aperture and is calibrated against the APASS catalog. Because the light curves are produced in real time, this web tool is relatively slow and can only be used for small samples of objects. However, it also imposes no selection bias on the part of the ASAS-SN team, allowing the user to obtain a light curve for any point on the celestial sphere. We present the tool, describe its capabilities, limitations, and known issues, and provide a few illustrative examples.
Journal Article
Decoding the giant extragalactic radio sources
Giant radio sources (GRSs) defined to be >0.7 Mpc are the largest single objects in the Universe and can be associated with both galaxies (GRGs) and quasars (GRQs). They are important for understanding the evolution of radio galaxies and quasars whose sizes range from pc to Mpc scales and are also valuable probes of their environment. These radio-loud active galactic nuclei (RLAGN) interact with the interstellar medium of the host galaxy on small scales and the large-scale intracluster or intergalactic medium for the GRSs. With several new and sensitive surveys over the last few years, the number of known GRSs has increased many fold, which has led a resurgence of interest in the field. This review article summarises our current understanding of these sources based on nearly five decades of research, and discusses the importance of the Square Kilometer Array (SKA) in addressing some of the outstanding questions.
Journal Article
Probing the Structure of SDSS J1004+4112 through Microlensing Analysis of Spectroscopic Data
We aim to uncover the structure of the continuum and broad emission line (BEL) emitting regions in the gravitationally lensed quasar SDSS J1004+4112 through unique microlensing signatures. Analyzing 20 spectroscopic observations from 2003 to 2018, we study the striking deformations of various BEL profiles and determine the sizes of their respective emitting regions. We use the emission line cores as a baseline for no microlensing and then apply Bayesian methods to derive the sizes of the Lyα, Si IV, C IV, C III], and Mg II emitting regions, as well as of the underlying continuum-emitting sources. We find that the sizes of the emitting regions for the BELs are a few light-days across, notably smaller than in typical lensed quasars. The asymmetric distortions observed in the BELs suggest that the broad-line region lacks spherical symmetry and is likely confined to a plane. The inferred continuum emitting region sizes are larger than predictions based on standard thin-disk theory by a factor of ∼ 4. We find that the size-wavelength relation is in agreement with that of a geometrically thin and optically thick accretion disk.
Journal Article
The Zwicky Transient Facility: Science Objectives
The Zwicky Transient Facility (ZTF), a public-private enterprise, is a new time-domain survey employing a dedicated camera on the Palomar 48-inch Schmidt telescope with a 47 deg2 field of view and an 8 second readout time. It is well positioned in the development of time-domain astronomy, offering operations at 10% of the scale and style of the Large Synoptic Survey Telescope (LSST) with a single 1-m class survey telescope. The public surveys will cover the observable northern sky every three nights in g and r filters and the visible Galactic plane every night in g and r. Alerts generated by these surveys are sent in real time to brokers. A consortium of universities that provided funding (\"partnership\") are undertaking several boutique surveys. The combination of these surveys producing one million alerts per night allows for exploration of transient and variable astrophysical phenomena brighter than r ∼ 20.5 on timescales of minutes to years. We describe the primary science objectives driving ZTF, including the physics of supernovae and relativistic explosions, multi-messenger astrophysics, supernova cosmology, active galactic nuclei, and tidal disruption events, stellar variability, and solar system objects.
Journal Article
Study on Variability and Spectral Properties of Blazar 3C 273 with Long-term Multi-band Optical Monitoring from 2006 to 2015
We present long-term optical multi-band photometric monitoring of blazar 3C 273, from 2006 May 19 to 2015 March 31 with high temporal resolution in the BVRI bands. The source is in a steady state and showed very small variability, with the values of the fractional variability amplitude of F var = 0.457 0.014 % , 0.391 0.012 % , 0.264 0.043 % and 0.460 0.014 % in B, V, R and I, respectively. The intra-night point-to-point fractional variability (Fpp) in each band is below 1.0%, and the Fpp variation amplitude increase from the B-band to the I-band. We find a variability with the timescale of 5.8 2.9 minutes in the I-band on 2009 March 11. This fast variability requires the comoving magnetic field strength in the jet above 18 G with a Doppler factor δ D ∼ 10 . Using the discrete correlation function (DCF), the B- and I-band light curves are examined for correlation on whole campaign. Low significance (∼99.73 percent confidence) correlations with the I-band lags the B-band variations are observed. The spectral behaviors in the different variability episodes are studied. \"Bluer-when-brighter\" spectral behavior is presented for the whole campaign, while there is an opposite tendency when F V > 30.2 mJy . The weak of the correlation between B- and I-band and the spectrum analysis indicate that the optical radiation consists of two variable components.
Journal Article
Evidence for Radio Loud to Radio Quiet Evolution from Red and Blue Quasars
Recent work on red and blue quasi-stellar objects (QSOs) has identified peculiar number distributions as a function of radio-loudness that we explore and attempt to explain from the perspective of a picture in which a subset of the population of active galaxies evolves from the radio-loud to the radio-quiet state. Because the time evolution is slowed down by an order of magnitude or more for the radio-quiet phase, the numbers of red and blue QSOs approach each other at the extreme end of the radio-quiet range of radio-loudness with larger numbers. The rapid time evolution of most radio-loud phases, instead, makes the numbers similar but lower at the far radio-loud end. At the midpoint of radio-loudness, instead, the differences between red and blue QSOs experience their largest values which results from accretion rapidly spinning black holes down but subsequently spinning them up more slowly. Recovering these basic features of the observations is evidence for rapid evolution away from radio-loudness and slow evolution in radio-quiet states.
Journal Article
Most of the photons that reionized the Universe came from dwarf galaxies
The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600–800 Myr after the Big Bang
1
–
3
, has been a matter of debate
4
. Some models suggest that high ionizing emissivity and escape fractions (
f
esc
) from quasars support their role in driving cosmic reionization
5
,
6
. Others propose that the high
f
esc
values from bright galaxies generate sufficient ionizing radiation to drive this process
7
. Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and
f
esc
, can effectively dominate cosmic reionization
8
,
9
. However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between
M
UV
≈ −17 mag and −15 mag (down to 0.005
L
⋆
(refs.
10
,
11
)). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[
ξ
ion
(Hz erg
−1
)] = 25.80 ± 0.14, a factor of 4 higher than commonly assumed values
12
. If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%.
An analysis of eight ultra-faint galaxies during the epoch of reionization with absolute magnitudes between −17 mag and −15 mag shows that most of the photons that reionized the Universe come from dwarf galaxies.
Journal Article