Escaping Galaxies and Giant Halos:

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Jan 19, 2017.

  1. paddoboy Valued Senior Member

    Messages:
    27,543
    Struggle to escape distant galaxies creates giant halos of scattered photons
    January 11, 2017

    Please Register or Log in to view the hidden image!


    This artist's impression shows a Milky Way type galaxy in the local Universe, surrounded by a much larger halo of blue, faint light, made of Lyman-alpha photons. While these photons were produced around hot, young stars in much more central regions, they struggle to escape the galaxies, suffering many absorptions and re-emissions as they try to escape, and creating these giant haloes. For typical distant galaxies, only a few per cent actually make it out at all. This is what astronomers have now been able to see for similar galaxies that existed 11 billion years ago, in a very young, active Universe. This has important implications for studying the young Universe, where these photons are remarkably important, but are usually measured over only the very central component of each galaxy. Credit: ESO/L. Calçada
    Astronomers led by David Sobral and Jorryt Matthee, of the Universities of Lancaster in the UK and Leiden in the Netherlands have discovered giant halos around early Milky Way type galaxies, made of photons (elementary particles of light) that have struggled to escape them. The team reports its findings in the journal Monthly Notices of the Royal Astronomical Society.



    Read more at: https://phys.org/news/2017-01-struggle-distant-galaxies-giant-halos.html#jCp
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. paddoboy Valued Senior Member

    Messages:
    27,543
    https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw322


    The CALYMHA survey: Lyα escape fraction and its dependence on galaxy properties at z = 2.23


    Abstract
    We present the first results from our CAlibrating LYMan α with Hα (CALYMHA) pilot survey at the Isaac Newton Telescope. We measure Lyα emission for 488 Hα selected galaxies at z = 2.23 from High-z Emission Line Survey in the COSMOS and UDS fields with a specially designed narrow-band filter (λc = 3918 Å, Δλ = 52 Å). We find 17 dual Hα-Lyα emitters [fLyα > 5 × 10−17 erg s−1 cm−2, of which five are X-ray active galactic nuclei (AGN)]. For star-forming galaxies, we find a range of Lyα escape fractions (fesc, measured with 3 arcsec apertures) from 2 to 30 per cent. These galaxies have masses from 3 × 108 M⊙ to 1011 M⊙ and dust attenuations E(BV) = 0–0.5. Using stacking, we measure a median escape fraction of 1.6 ± 0.5 per cent (4.0 ± 1.0 per cent without correcting Hα for dust), but show that this depends on galaxy properties. The stacked fesc tends to decrease with increasing star formation rate and dust attenuation. However, at the highest masses and dust attenuations, we detect individual galaxies with fesc much higher than the typical values from stacking, indicating significant scatter in the values of fesc. Relations between fesc and UV slope are bimodal, with high fesc for either the bluest or reddest galaxies. We speculate that this bimodality and large scatter in the values of fesc is due to additional physical mechanisms such as outflows facilitating fesc for dusty/massive systems. Lyα is significantly more extended than Hα and the UV. fesc continues to increase up to at least 20 kpc (3σ, 40 kpc [2σ]) for typical star-forming galaxies and thus the aperture is the most important predictor of fesc.

     
  4. Google AdSense Guest Advertisement



    to hide all adverts.

Share This Page