July 2016
Powerful Ionizing Sources in the Nearby Universe
An international team of astronomers using GMOS on each of the Gemini telescopes has obtained the first ever closeup images of Lyman-alpha blobs ( LABs ) at low redshifts of z = 0.3 ( Figure 8 ). LABs may extend up to 100 kiloparsecs , and emit copious amounts of Lyman-alpha radiation . They are landmarks of massive galaxy formation and have , so far , only been found at high redshifts of about 1.5 or higher . Gemini astronomer Mischa Schirmer and collaborators have shown that LABs may still exist in the low redshift Universe , 4 - 7 billion years later than previously known , based on far-ultraviolet measurements with the GALEX satellite .
One of the biggest mysteries of LABs is their ionizing power source . Various mechanisms have been suggested , such as cold accretion streams , hidden active galactic nuclei ( AGN ), star bursts , and supernovae ; however , many LABs show no ionizing continuum source at all . The researchers found weak AGN at the cores of the discovered lowredshift LABs . Their low redshifts allowed the astronomers to study these objects in much more detail than their high-redshift cousins .
The very luminous and extended nebulae observed require that the AGN must have been in a very powerful state until a few 1,000- 10,000 years ago . Such episodic duty cycles are typical for AGN , but are difficult to recognize otherwise because they last much longer than a human lifetime . One of the team ’ s main results is that even a short burst of high AGN activity is sufficient to power the LAB ’ s Lyman-alpha emission for a very long time .
This work is featured on the Gemini website and is published in Monthly Notices of the Royal Astronomical Society .
January 2017 | 2016 Year in Review
July 2016
A 17-Billion-Solar-Mass Black Hole Surprise
Astronomers using the Gemini Multi-Object Spectrograph ( GMOS ) integral field unit on the Gemini North telescope have measured a 17-billion-solar-mass black hole dominating the core of NGC 1600 , a large galaxy in the low-density environment of a galaxy group . This is a surprise , given that we expect to find monster black holes in very massive galaxies at the centers of large galaxy clusters . Astronomers have also observed luminous quasars hosting very massive black holes in the distant Universe , and this result sheds light on large black holes in the more local Universe , suggesting they are likely relics , the descendants of luminous quasars at higher redshift .
In the high-mass regime , Jens Thomas ( Max Planck Institute for Extraterrestrial Physics ,
GeminiFocus
Figure 8 . Gemini / GMOS images of four of the new lowredshift Lyman-alpha blobs , using g , r , and i filters . From upper left to lower right : J1505 + 1944 , J1455 + 0446 , J1155 – 0147 and J0113 + 0106 . These objects are among the most powerful [ OIII ] 5007 emitters known in the Universe , causing the green color in these optical images . Note that the far-UV Lyman-alpha radiation is not visible in these optical images .
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