…but that’s not the really cool news. The cool news resides in ALMA itself!
Credit: ALMA (ESO/NAOJ/NRAO)
The past week this headline (or variations of it) has been floating around the twitter-verse. And, while this headline is cool, I don’t think it addresses the awesome-ness of the topic.
To stat, the Atacama Large Millimeter/Submillimeter Array (or ALMA) is an array of radio telescopes in the Atacama desert of northern Chile. This array consists of 66 12-meter and 7-meter diameter telescopes observing at the millimeter and sub-millimeter wavelengths. Due to the large number of telescopes this array contains, it has a much higher sensitivity and resolution that the existing telescopes of it’s kind (James Clerk Maxwell Telescope, Submillimeter Array, etc.).
The main science goals of ALMA as as follows (from their website):
- The ability to detect spectral line emission from CO or [CII] in a normal galaxy like the Milky Way at a redshift of z=3, in less than 24 hours,
- The ability to image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars in the nearest molecular clouds (150 pc),
- The ability to provide precise high dynamic range images at an angular resolution of 0.1 arcsec.
To summarize the first of the science goals above, ALMA will be used as a tool for studying star-formation in galaxies billions of years in the past. So, due to their distance away, most of the light from a wide range redshifted objects are observed in the millimeter and submillimeter wavelengths. Due to the unprecedented sensitivity and resolution of this telescope, it’s projected to offer a fantastic look into the distant universe to reveal loads about star-formation in the distance universe.
And, following this, ALMA became operational this month (March 2013) and though it is not fully operational has already released some very interesting results!
The new survey announced the observation of the most distance star-forming galaxy at 12.65 billion light-years (z = 5.7) as well as additional observations of a large number of other star-forming galaxies at high redshifts. These discovers are not out of the blue. An international team of researchers first discovered these distant star-forming galaxies with the National Science Foundations 10-meter South Pole Telescope (SPT; observes in microwave, millimeter-wave, and submillimeter-wave wavelengths), though an independent observation of redshifts was needed. ALMA provided a followup observation of these galaxies in order to preform an accurate redshift calculation of these sources.
The observation of these galaxies was made using gravitational lensing where the light from a distance galaxy is able to be observed due to the presence of a foreground gravitational source (such as a galaxy). Below shows a schematic for such an event.
Artist’s impression of one of the South Pole Telescope-discovered sources based on observation by ALMA and Hubble Space Telescope (HST). The massive central galaxy (in blue, seen by HST) bends the light of a more distant, submillimeter-bright galaxy, forming a ring-like image of the background galaxy which is observed by ALMA (red). (ALMA)
The light from the distant object is both distorted and magnified due to the gravitational force of the foreground object. The background object forms an Einstein ring around the foreground object. Astronomers are able to correct for the magnification and distortion to calculate various properties of the galaxies.
Of the galaxies found by the SPT, ALMA imaged 47 galaxies and collected spectra on 26. Due to the sensitivity of ALMA, astronomers were able to calculate the redshift of these 26 galaxies straight from the spectra rather than relying on independent visual or IR observations from other telescopes (which is not always possible due to the due to the dust obscuring the galaxy). Because of it’s precision it’s able to detect much more faint spectral lines and be able to determine the redshift out to these galaxies without requiring any multi-wavelength identifications!
From the spectra, ALMA was able to detect strong carbon monoxide lines (CO) in the spectra of these galaxies indicating intense star formation in the galaxy. These results were surprising as only a few starburst (intently star-forming) galaxies had been detected at these distances. It is still not clear how these galaxies could produce stars at such a furious rate so early in the Universe as these galaxies are forming 1,000 stars per year (for comparison the Milky Way galaxy has a star-forming rate of about 1 star per year). Overall, these discovered galaxies may be what today’s massive galaxies looked like in the past. These galaxies create stars many thousands of times faster than galaxies like our own!
Also, many of these galaxies have shown emission form water molecules, which is the most distance detection of water in the universe to date! How neat is that?!
They also found a higher sample mean redshift for these sources. Previously this value was found to be at z = 2.3 (10.76 Gyr), but new study has found the redshift mean to be at z = 3.5 (11.83 Gyr). This indicates that previous samples were biased towards lower redshift galaxies and may have missed a large fraction (≥ 50%) of these galaxies at redshift z>3.
This data is one of the first (if not the first?) data being released from an operational ALMA. And though it is only using 16 of its 66 planned telescopes and is only focusing on brighter galaxies, this study has almost doubled the number of star-forming galaxies seen at high redshifts (within the first 1.5 billion years of the universe). In addition, these observations only took 2 minutes to take, about one hundred times faster than before! Previously, a measurement of redshift for these sources would have to combine data from both visible-light and radio telescopes.
So more than the result, this study shows the capabilities of ALMA and the potential for exciting results to be found in the future. Due to its unprecedented resolution and sensitivity, this telescope should lead astronomers to understand much more about the formation of the early universe.