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Hubble Sees the 'Teenage Years' of Quasars

Astronomers have used the Hubble Space Telescope's infrared vision to uncover the mysterious early formative years of quasars, the brightest objects in the universe. Hubble's sharp images unveil chaotic galaxy collisions that give birth to quasars by fuelling their energy source: a supermassive central black hole devouring infalling material.
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Title: A Hubble Diagram for Quasars
Author: Guido Risaliti, Elisabeta Lusso

We present a new method to test the cosmological model, and to estimate the cosmological parameters, based on the non-linear relation between ultraviolet and X-ray luminosity of quasars. We built a data set of ~1,250 quasars by merging several literature samples with X-ray measurements at 2 keV and SDSS photometry, which was used to estimate the extinction-corrected 2500~\AA\ flux. We obtained three main results: (1) we checked the non-linear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that it holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval, and extends the test of the cosmological model up to z~6; (3) we showed that this non-linear relation is a powerful tool to estimate cosmological parameters. With present data, assuming a Lambda CDM model, we obtain Omega_M=0.21^{+0.08}_{-0.10} and Omega_\Lambda=0.95^{+0.30}_{-0.20} (Omega_M=0.28±0.04 and Omega_\Lambda=0.74±0.08 from a joint quasar-SNe fit). However, much more precise measurements will be achieved in the future. A few thousands SDSS quasars already have serendipitous X-ray observations with Chandra or XMM-Newton, and at least 100,000 quasars with UV and X-ray data will be available from the eROSITA all-sky survey in a few years. Euclid, LSST, and Athena surveys will further increase the sample size to at least several hundred thousands. Our simulations show that these samples will provide tight constraints on the cosmological parameters, and will allow to test possible deviations from the standard model with higher precisions than available today.

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Existence of a group of "quiet" quasars confirmed

Apart from very distant, ultraluminous quasars -evolving rapidly and associated with galaxy mergers - there is likely another population of quasars that evolves slowly
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Title: The most luminous quasars do not live in the most massive dark matter haloes at any redshift
Authors: N. Fanidakis, A. V. Maccio, C. M. Baugh, C. G. Lacey, C. S. Frenk

Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing Black Holes (BHs), with luminosities as high as 10^48 erg/sec. It is often expected though that such an extremely energetic process will take place in the most massive bound structures in the dark matter (DM) distribution. We show that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, quasars are predicted to live in average DM halo environments with typical masses of a few times 10^12 solar masses. This fundamental prediction arises from the fact that quasar activity (i.e., BH accretion with luminosity greater than 10^46 erg/sec) is inhibited in DM haloes where AGN feedback operates. The galaxy hosts of quasars in our simulations are identified with over massive (in gas and stars) spheroidal galaxies, in which BH accretion is triggered via a galaxy merger or secular processes. We further show that the z=0 descendants of high redshift (z~6) QSOs span a wide range of morphologies, galaxy and halo masses. The z~6 BHs typically grow only by a modest factor by the present day. Remarkably, high redshift QSOs never inhabit the largest DM haloes at that time and their descendants are very seldom found in the most massive haloes at z=0. We also show that observationally it is very likely to find an enhancement in the abundance of galaxies around quasars at z~5. However, these enhancements are considerably weaker compared to the overdensities expected at the extreme peaks of the DM distribution. Thus, it is very unlikely that a quasar detected in the z\gtrsim5 Universe pinpoints the location of the progenitors of superclusters in the local Universe.

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Title: The Discovery of Quasars
Authors: K. I. Kellermann

Although the extragalactic nature of quasars was discussed as early as 1960, it was rejected largely because of preconceived ideas about what appeared to be an unrealistically high radio and optical luminosity. Following the 1962 occultations of the strong radio source 3C 273 at Parkes, and the subsequent identification with an apparent stellar object, Maarten Schmidt recognised that the relatively simple hydrogen line Balmer series spectrum implied a redshift of 0.16 Successive radio and optical measurements quickly led to the identification of other quasars with increasingly large redshifts and the general, although for some decades not universal, acceptance of quasars as being by far the most distant and the most luminous objects in the Universe. Curiously, 3C 273, which is one of the strongest extragalactic sources in the sky, was first catalogued in 1959 and the magnitude 13 optical counterpart was observed at least as early as 1887. Since 1960, much fainter optical counterparts were being routinely identified using accurate radio interferometer positions, measured primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded identification until the series of lunar occultation observations led by Cyril Hazard, although inexplicitly there was an earlier misidentification with a faint galaxy located about an arc minute away from the true position. Ironically, due to calculation error, the occultation position used by Schmidt to determine the redshift of 3C 273 was in error by 14 arcseconds, and a good occultation position was not derived until after Schmidt had obtained his 200 inch spectrum.

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Gone, with the Wind

The case of the missing quasar gas clouds has been solved by a worldwide team of astronomers, and the answer is blowin' in the wind.
Astronomers Nurten Filiz Ak and Niel Brandt of the Pennsylvania State University led the team, which announced their results in a paper published in today's issue of The Astrophysical Journal. The paper describes 19 distant quasars in which giant clouds of gas seemed to disappear in just a few years.

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Spitzer, Hubble See Galaxy-Altering Quasars Ignite

NASA's Spitzer and Hubble Space Telescopes have caught sight of luminous quasars igniting after galaxies collide. Quasars are bright, energetic regions around giant, active black holes in galactic centers. 
The new observations shed light on a key early period of galactic evolution when quasars and their host galaxies begin to interact, but before the two have settled down after recent galactic smashups.

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 Most Quasars Live on Snacks, Not Large Meals

Astronomers are uncovering an underlying population of fainter quasars that thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such tasty treats as a batch of gas or the occasional small satellite galaxy.
A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, Hubble and Spitzer, has found that 26 of the host galaxies bear no telltale signs of collisions with neighbours, such as distorted shapes. Only one galaxy in the sample shows evidence of an interaction with another galaxy. The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth.
The study, led by Kevin Schawinski of Yale University, New Haven, Conn., bolsters evidence that the growth of most massive black holes in the early universe was fuelled by small, long-term events rather than dramatic short-term major mergers.

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 Most Quasars Live on Snacks, Not Large Meals

Black holes in the early universe needed a few snacks rather than one giant meal to fuel their quasars and help them grow, a new study shows. Quasars are the brilliant beacons of light that are powered by black holes feasting on captured material, and in the process, heating some of the matter to millions of degrees. The brightest quasars reside in galaxies distorted by collisions with other galaxies. These encounters send lots of gas and dust into the gravitational whirlpool of hungry black holes. Now, however, astronomers are uncovering an underlying population of fainter quasars that thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such tasty treats as a batch of gas or the occasional small satellite galaxy.
A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, the Hubble Space Telescope and Spitzer Space Telescope, has found that 26 of the host galaxies bear no tell-tale signs of collisions with neighbours, such as distorted shapes. Only one galaxy in the sample shows evidence of an interaction with another galaxy. The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth. The study bolsters evidence that the growth of most massive black holes in the early universe was fuelled by small, long-term events rather than dramatic short-term major mergers.

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Title: The Colour Variability of Quasars
Authors: Kasper B. Schmidt, Hans-Walter Rix, Joseph C. Shields, Matthias Knecht, David W. Hogg, Dan Maoz, Jo Bovy

We quantify quasar colour-variability using an unprecedented variability database - ugriz photometry of 9093 quasars from SDSS Stripe 82, observed over 8 years at ~60 epochs each. We confirm previous reports that quasars become bluer when brightening. We find a redshift dependence of this blueing in a given set of bands (e.g. g and r), but show that it is the result of the flux contribution from less-variable or decayed emission lines in the different SDSS bands at different redshifts. After correcting for this effect, quasar colour-variability is remarkably uniform, and independent not only of redshift, but also of quasar luminosity and black hole mass. The colour variations of individual quasars, as they vary in brightness on year timescales, are much more pronounced than the ranges in colour seen in samples of quasars across many orders of magnitude in luminosity. This indicates distinct physical mechanisms behind quasar variability and the observed range of quasar luminosities at a given black hole mass - quasar variations cannot be explained by changes in the mean accretion rate. We do find some dependence of the colour variability on the characteristics of the flux variations themselves, with fast, low-amplitude, brightness variations producing more colour variability. The observed behaviour could arise if quasar variability results from flares or ephemeral hot spots in an accretion disc.

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