Stars seen forming in a far-off galaxy

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from Nature 522, 259 (18 June 2015) doi:10.1038/522259a


Astronomers have seen their best glimpse yet of stars forming in the early Universe.
The ALMA radio telescope in Chile explored the SDP.81 galaxy, which is 3.6 billion parsecs (11.7 billion light years) away from Earth. Its light was magnified and distorted by the gravitational pull of another galaxy between it and Earth, but a model developed by Yoichi Tamura of the University of Tokyo and his team corrected the distortions. Their images reveal many cold clouds of dust and gas that are driving a rapid rate of star formation.
Several research teams have analysed the ALMA data to characterize other aspects of this galaxy.

(a) ALMA 3-color image of SDP.81 (1.0, 1.15 and 1.3 mm for blue, green and red, respectively) overlaid with the Hubble WFC3/F160W (1.6 µm) image where the stellar light of SDSS J0903 is subtracted (contours). Two sets of counter-images of stellar peaks are indicated by filled and open stars, respectively. The synthesized beam size is indicated at the bottom-left corner. The origin of the image is taken at the position of a central compact non-thermal source. (b) The ALMA 1.0 mm image. Upper inset shows CO (5–4) spectra at the positions of the source A (upper) and E (lower). Bottom inset shows the spectral energy distribution of the central compact source, which is well fitted by a power-law function with a spectral index of −0.64 (solid line), suggesting the synchrotron emission. (c) The modeled brightness distribution on the image plane. The image is smoothed by a Gaussian with FWHM = 23 mas. The inner and outer ellipses represent radial and tangential critical curves, respectively. (d) The modeled brightness distribution on the source plane, which is 0.5′′ on a side. The star represents the source position of the stellar peaks denoted as filled stars in (a). The position of this panel is indicated as a dotted square in (c). The solid curves represent the caustics. The scale bar at the bottom-left corner shows a physical scale of 200 pc at z = 3.042.

(a) ALMA 3-color image of SDP.81 (1.0, 1.15 and 1.3 mm for blue, green and red, respectively) overlaid with the Hubble WFC3/F160W (1.6 µm) image where the stellar light of SDSS J0903 is subtracted (contours). Two sets of counter-images of stellar peaks are indicated by filled and open stars, respectively. The synthesized beam size is indicated at the bottom-left corner. The origin of the image is taken at the position of a central compact non-thermal source. (b) The ALMA 1.0 mm image. Upper inset shows CO (5–4) spectra at the positions of the source A (upper) and E (lower). Bottom inset shows the spectral energy distribution of the central compact source, which is well fitted by a power-law function with a spectral index of −0.64 (solid line), suggesting the synchrotron emission. (c) The modeled brightness distribution on the image plane. The image is smoothed by a Gaussian with FWHM = 23 mas. The inner and outer ellipses represent radial and tangential critical curves, respectively. (d) The modeled brightness distribution on the source plane, which is 0.5′′ on a side. The star represents the source position of the stellar peaks denoted as filled stars in (a). The position of this panel is indicated as a dotted square in (c). The solid curves represent the caustics. The scale bar at the bottom-left corner shows a physical scale of 200 pc at z = 3.042.

See paper/arXiv

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