Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Galaxies
Type of Medium
Language
Year
  • 1
    In: Nature, Volume 468, Issue 7325, pp. 796-798 (2010)
    Description: Observations of the 21-centimetre line of atomic hydrogen in the early Universe directly probe the history of the reionization of the gas between galaxies. The observations are challenging, though, because of the low expected signal strength (~10 mK), and contamination by strong (〉100 K) foreground synchrotron emission in the Milky Way and extragalactic continuum sources2. If reionization happened rapidly, there should be a characteristic signature visible against the smooth foreground in an all-sky spectrum. Here we report an all-sky spectrum between 100 and 200 MHz, corresponding to the redshift range 6 〈 z 〈 13 for the 21-centimetre line. The data exclude a rapid reionization timescale of dz 〈 0.06 at the 95% confidence level. Comment: 8 pages, 2 figures, Published in Nature, Volume 468, Issue 7325, pp. 796-798 (2010)
    Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics
    Source: Cornell University
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    In: Monthly Notices of the Royal Astronomical Society, 2012, Vol. 419(2), pp.1070-1084
    Description: Efforts are being made to observe the 21-cm signal from the ‘cosmic dawn’ using sky-averaged observations with individual radio dipoles. In this paper, we develop a model of the observations accounting for the 21-cm signal, foregrounds and several major instrumental effects. Given this model, we apply Markov Chain Monte Carlo techniques to demonstrate the ability of these instruments to separate the 21-cm signal from foregrounds and quantify their ability to constrain properties of the first galaxies. For concreteness, we investigate observations between 40 and 120 MHz with the proposed  Dark Ages Radio Explorer  mission in lunar orbit, showing its potential for science return.
    Keywords: Methods: Statistical ; Cosmology: Theory ; Diffuse Radiation ; Radio Lines: General
    ISSN: 0035-8711
    E-ISSN: 1365-2966
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Description: We report absolutely calibrated measurements of diffuse radio emission between 90 and 190 MHz from the Experiment to Detect the Global EoR Signature (EDGES). EDGES employs a wide beam zenith-pointing dipole antenna centred on a declination of -26.7$^\circ$. We measure the sky brightness temperature as a function of frequency averaged over the EDGES beam from 211 nights of data acquired from July 2015 to March 2016. We derive the spectral index, $\beta$, as a function of local sidereal time (LST) and find -2.60 〉 $\beta$ 〉 -2.62 $\pm$0.02 between 0 and 12 h LST. When the Galactic Centre is in the sky, the spectral index flattens, reaching $\beta$ = -2.50 $\pm$0.02 at 17.7 h. The EDGES instrument is shown to be very stable throughout the observations with night-to-night reproducibility of $\sigma_{\beta}$ 〈 0.003. Including systematic uncertainty, the overall uncertainty of $\beta$ is 0.02 across all LST bins. These results improve on the earlier findings of Rogers & Bowman (2008) by reducing the spectral index uncertainty from 0.10 to 0.02 while considering more extensive sources of errors. We compare our measurements with spectral index simulations derived from the Global Sky Model (GSM) of de Oliveira-Costa et al. (2008) and with fits between the Guzm\'an et al. (2011) 45 MHz and Haslam et al. (1982) 408 MHz maps. We find good agreement at the transit of the Galactic Centre. Away from transit, the GSM tends to over-predict (GSM less negative) by 0.05 〈 $\Delta_{\beta} = \beta_{\text{GSM}}-\beta_{\text{EDGES}}$ 〈 0.12, while the 45-408 MHz fits tend to over-predict by $\Delta_{\beta}$ 〈 0.05.
    Keywords: Astrophysics - Instrumentation And Methods For Astrophysics ; Astrophysics - Astrophysics Of Galaxies
    ISSN: 00358711
    E-ISSN: 13652966
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: The Astrophysical Journal, 2018, Vol.863(1), p.11 (11pp)
    Description: We use the sky-average spectrum measured by EDGES High-band (90–190 MHz) to constrain parameters of early galaxies independent of the absorption feature at 78 MHz reported by Bowman et al. These parameters represent traditional models of cosmic dawn and the epoch of reionization produced with the 21cmFAST simulation code. The parameters considered are (1) the UV ionizing efficiency ( ζ ); (2) minimum halo virial temperature hosting efficient star-forming galaxies ( ); (3) integrated soft-band X-ray luminosity ( ); and (4) minimum X-ray energy escaping the first galaxies ( E 0 ), corresponding to a typical H i column density for attenuation through the interstellar medium. The High-band spectrum disfavors high values of and ζ , which correspond to signals with late absorption troughs and sharp reionization transitions. It also disfavors intermediate values of , which produce relatively deep and narrow troughs within the band. Specifically, we rule out (95% C.L.). We then combine the EDGES High-band data with constraints on the electron-scattering optical depth from Planck and the hydrogen neutral fraction from high- z quasars. This produces a lower degeneracy between ζ and than that reported by Greig & Mesinger using the Planck and quasar constraints alone. Our main result in this combined analysis is the estimate (95% C.L.). We leave the evaluation of 21 cm models using simultaneously data from EDGES Low- and High-band for future work.
    Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics ; Astrophysics - Astrophysics Of Galaxies;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Conference Proceeding
    Conference Proceeding
    Language: English
    In: The Evolution Of Galaxies Through The Neutral Hydrogen Window, Arecibo Observatory (Puerto Rico) (1–3 February 2008):
    In: AIP Conference Proceedings, 01 August 2008, Vol.1035(1), pp.296-302
    Description: There are three distinct regimes in which radio observations of the redshifted 21 cm line of H I can contribute directly to cosmology in unique ways. The regimes are naturally divided by redshift, from high to low, into: inflationary physics, the Dark Ages and reionization, and galaxy evolution and Dark Energy. Each measurement presents its own set of technical, theoretical, and observational challenges, making “what we need to know” not so much an astrophysical question at this early stage as a comprehensive experimental question. A wave of new pathfinder projects are exploring the fundamental aspects of what we need to know (and what we should expect to learn in the coming years) in order to achieve the goals of the Square Kilometer Array (SKA) and beyond.
    Keywords: Astronomy and Astrophysics
    ISBN: 978-0-7354-0558-5
    ISSN: 0094-243X
    E-ISSN: 1551-7616
    Source: © 2008 American Institute of Physics (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: The Astrophysical Journal, 2014, Vol.782(2), p.66 (25pp)
    Description: A number of experiments are currently working toward a measurement of the 21 cm signal from the epoch of reionization (EoR). Whether or not these experiments deliver a detection of cosmological emission, their limited sensitivity will prevent them from providing detailed information about the astrophysics of reionization. In this work, we consider what types of measurements will be enabled by the next generation of larger 21 cm EoR telescopes. To calculate the type of constraints that will be possible with such arrays, we use simple models for the instrument, foreground emission, and the reionization history. We focus primarily on an instrument modeled after the 0.1 km 2 collecting area Hydrogen Epoch of Reionization Array concept design and parameterize the uncertainties with regard to foreground emission by considering different limits to the recently described wedge footprint in k space. Uncertainties in the reionization history are accounted for using a series of simulations that vary the ionizing efficiency and minimum virial temperature of the galaxies responsible for reionization, as well as the mean free path of ionizing photons through the intergalactic medium. Given various combinations of models, we consider the significance of the possible power spectrum detections, the ability to trace the power spectrum evolution versus redshift, the detectability of salient power spectrum features, and the achievable level of quantitative constraints on astrophysical parameters. Ultimately, we find that 0.1 km 2 of collecting area is enough to ensure a very high significance ( 30) detection of the reionization power spectrum in even the most pessimistic scenarios. This sensitivity should allow for meaningful constraints on the reionization history and astrophysical parameters, especially if foreground subtraction techniques can be improved and successfully implemented.
    Keywords: Astrophysics - Cosmology And Nongalactic Astrophysics;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Description: Above redshift 6, the dominant source of neutral hydrogen in the Universe shifts from localized clumps in and around galaxies and filaments to a pervasive, diffuse component of the intergalactic medium (IGM). This transition tracks the global neutral fraction of hydrogen in the IGM and can be studied, in principle, through the redshifted 21 cm hyperfine transition line. During the last half of the reionization epoch, the mean (global) brightness temperature of the redshifted 21 cm emission is proportional to the neutral fraction, but at earlier times (10 〈 z 〈 25), the mean brightness temperature should probe the spin temperature of neutral hydrogen in the IGM. Measuring the (of order 10 mK) mean brightness temperature of the redshifted 21 cm line as a function of frequency (and hence redshift) would chart the early evolution of galaxies through the heating and ionizing of the IGM by their stellar populations. Experiments are already underway to accomplish this task or, at least, provide basic constraints on the evolution of the mean brightness temperature. We provide a brief overview of one of these projects, the Experiment to the Detect the Global EOR Signature (EDGES), and discuss prospects for future results. Comment: From AIP Conference Proceedings, Volume 1035, 2008, "The Evolution of Galaxies through the Neutral Hydrogen Window". 3 pages
    Keywords: Astrophysics - Galaxy Astrophysics
    Source: Cornell University
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Language: English
    In: The Astrophysical Journal, 2004, Vol.617(1), pp.81-101
    Description: Observational measurements of the relationship between supermassive black holes (SMBHs) and the properties of their host galaxies are an important method for probing theoretical hierarchical growth models. Gravitational lensing is a unique mechanism for acquiring this information in systems at cosmologically significant redshifts. We review the calculations required to include SMBHs in two standard galactic lens models, a cored isothermal sphere and a broken power law. The presence of the SMBH produces two primary effects depending on the lens configuration, either blocking the "core" image that is usually predicted to form from a softened lens model or adding an extra, highly demagnified image to the predictions of the unaltered lens model. The magnitudes of these effects are very sensitive to galaxy core sizes and SMBH masses. Therefore, observations of these lenses would probe the properties of the inner regions of galaxies, including their SMBHs. Lensing cross sections and optical depth calculations indicate that to fully observe these characteristic signatures, flux ratios of order 10 6 or more between the brightest and faintest images of the lens must be detectable, and thus, the next generation of radio telescope technology offers the first opportunity for a serious observational campaign. Core images, however, are already detectable, and with additional observations their statistics may be used to guide future SMBH searches.
    Keywords: Astrophysics;
    ISSN: 0004-637X
    E-ISSN: 1538-4357
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    In: Monthly Notices of the Royal Astronomical Society, 2015, Vol. 447(3), pp.2468-2478
    Description: Recent observations with the Murchison Widefield Array at 185 MHz have serendipitously unveiled a heretofore unknown giant and relatively nearby ( z  = 0.0178) radio galaxy associated with NGC 1534. The diffuse emission presented here is the first indication that NGC 1534 is one of a rare class of objects (along with NGC 5128 and NGC 612) in which a galaxy with a prominent dust lane hosts radio emission on scales of ∼700 kpc. We present details of the radio emission along with a detailed comparison with other radio galaxies with discs. NGC 1534 is the lowest surface brightness radio galaxy known with an estimated scaled 1.4-GHz surface brightness of just 0.2 mJy arcmin −2 . The radio lobes have one of the steepest spectral indices yet observed: α = −2.1 ± 0.1, and the core to lobe luminosity ratio is 〈0.1 per cent. We estimate the space density of this low brightness (dying) phase of radio galaxy evolution as 7 × 10 −7  Mpc −3 and argue that normal AGN cannot spend more than 6 per cent of their lifetime in this phase if they all go through the same cycle.
    Keywords: Techniques: Interferometric ; Galaxies: Active ; Galaxies: General ; Galaxies: Individual:Ngc 1534 ; Radio Continuum: Galaxies
    ISSN: 0035-8711
    E-ISSN: 1365-2966
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    Language: English
    In: The Evolution Of Galaxies Through The Neutral Hydrogen Window, Arecibo Observatory (Puerto Rico) (1–3 February 2008):
    In: AIP Conference Proceedings, 01 August 2008, Vol.1035(1), pp.87-89
    Description: Above redshift 6, the dominant source of neutral hydrogen in the Universe shifts from localized clumps in and around galaxies and filaments to a pervasive, diffuse component of the intergalactic medium (IGM). This transition tracks the global neutral fraction of hydrogen in the IGM and can be studied, in principle, through the redshifted 21 cm hyperfine transition line. During the last half of the reionization epoch, the mean (global) brightness temperature of the redshifted 21 cm emission is proportional to the neutral fraction, but at earlier times (10〈z〈25), the mean brightness temperature should probe the spin temperature of neutral hydrogen in the IGM. Measuring the (of order 10 mK) mean brightness temperature of the redshifted 21 cm line as a function of frequency (and hence redshift) would chart the early evolution of galaxies through the heating and ionizing of the IGM by their stellar populations. Experiments are already underway to accomplish this task or, at least, provide basic constraints on the evolution of the mean brightness temperature. We provide a brief overview of one of these projects, the Experiment to the Detect the Global EOR Signature (EDGES), and discuss prospects for future results.
    Keywords: Astronomy and Astrophysics
    ISBN: 978-0-7354-0558-5
    ISSN: 0094-243X
    E-ISSN: 1551-7616
    Source: © 2008 American Institute of Physics (AIP)〈img src=http://exlibris-pub.s3.amazonaws.com/AIP_edited.gif style="vertical-align:middle;margin-left:7px"〉
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages