'Population census' of galaxies buried in dust

May 31, 2013
'Population census' of galaxies buried in dust
Figure 1. This figure shows number density (red squares) for each brightness of the galaxies derived from observation this time. Compared to past observation results (blue squares), galaxies approximately ten times as dark were detected. The curve shows the prediction by the theories of galaxy formation. Credit: ALMA (ESO/NAOJ/NRAO) / Kyoto University

A research team led by Bunyo Hatsukade, a postdoc researcher, and Kouji Ohta, a professor, both from the Graduate School of Science, Kyoto University, revealed that approximately 80% of the unidentifiable millimeter wave signals from the universe is actually emitted from galaxies, based on the observations with ALMA (Atacama Large Millimeter/submillimeter Array). ALMA's high resolving power and sensitivity enables us to pinpoint the locations of those galaxies rich in fine solid particles (dust).

With the ALMA telescope, the research team observed the "Subaru/ Deep Survey Field" in the direction of the , and succeeded in identifying 15 extremely dark galaxies which had been previously unknown. In addition, they also successfully measured the number density of galaxies with 10 times less luminosity than ones previously observed with the conventional millimeter instruments. Their densities well match the prediction by theories of galaxy formation. Therefore, the researchers consider that they managed to capture more like "normal" galaxies, which had been impossible to detect up to now, than extremely bright "submillimeter-". Using ALMA and the , the research team is now seeking to uncover the overall picture of galaxy formation and evolution while conducting observations of much darker galaxies.

Research background

Conventional research on distant galaxies have been carried out mainly with visible light and near infrared light. However, it is possible that many galaxies in the universe have been overlooked as much of that radiation is largely absorbed by . That is why millimeter and submillimeter wave observations are important. Stellar light absorbed by dust is reradiated from the dust as millimeter/submillimeter waves. Therefore galaxies, even those which it has not been possible to observe with , can be detected using these wavebands. Furthermore, millimeter/submillimeter waves are suitable for observation of distant galaxies. This is because the more distant the galaxy is, the more luminous part of light we can see due to the shift of wavelength of light by the expansion of the universe. This effect is called "negative K correction" and it compensates the source dimming in the distant universe.

In past observations, gigantic galaxies deeply covered in dust, where several hundreds to thousands of stars are actively forming per year, have been detected with millimeter/submillimeter waves. To capture the overall picture of galaxies in the universe, it is important to observe "general galaxies" which have moderate star-formation activities. However, it has not been possible to detect faint galaxies due to the low sensitivity of existing observation instruments.

Observations with ALMA

The research team observed a field named "Subaru/XMM-Newtown Deep Survey Field," located in the direction of the constellation Cetus, with the ALMA telescope. As a result, they succeeded in finding 15 extremely dark galaxies that were unidentified until now. "It is thanks to the high performance of ALMA, which is proudly said to be the best in the world, that observations like this have been made possible," said Hatsukade.

With the ALMA observations the team successfully measured the number density of galaxies approximately 10 times darker than the research results up to now. The new results agree well with the prediction by the theories of . That means, the galaxies detected in this research are the faint but dust-rich galaxies and they are most likely to be similar in type to normal galaxies not detected before.. In regards to this, Professor Ohta commented, "This is a big step towards getting the big picture of galaxy evolution as the objects connecting especially bright galaxies in millimeter/submillimeter waves and normal galaxies were detected with ALMA."

Figure 2. Artist's illustration of the observed field. In each close-up view, left is the illustration of the optical (blue) and conventional millimeter/submillimeter (red) image and right is the optical and ALMA image. Existing millimeter/submillimeter telescopes could not identify the sources of the emission due to their low resolution, however, ALMA pinpoints the galaxies which emit the emission. These objects were not detected in the optical observations, which indicate that they are heavily embedded in dust. Credit: ALMA (ESO/NAOJ/NRAO) / Kyoto University

Furthermore, the team concluded that approximately 80% of the sources of the cosmic background radiation within the millimeter/submillimeter wavebands are more "normal galaxies" like those detected by ALMA this time.. Past observations showed the total power of signals emitted from the universe with the millimeter/submillimeter wavebands. However, spatial resolution was not sufficient to identify the sources of all the signals; only 10 - 20% of them were identified.

To gain an overall picture of galaxies in the universe requires a much higher sensitivity for observation. For this research, only a part of the ALMA telescope, 23~25 antennas, were used. As the number of antennas in the ALMA telescope increases, its observation ability will also improve. Hatsukade expressed his hopes, saying "I want to clarify the overall picture of galaxy evolution. So, using ALMA, I would like to make observations of much fainter galaxies, and also study star formation activities and the amount of dust in those galaxies in detail." Professor Ohta also mentioned, "We are also planning to make thorough observations with visible light and infrared radiation, using the Subaru Telescope. This is in order to explore the nature of galaxies become darker due to light-absorbing dust. But for observations of extremely dark , we might need the Thirty Meter Telescope with much larger light-gathering power."

Explore further: POLARBEAR detects curls in the universe's oldest light

More information: The research is described in the paper "FAINT END OF 1.3 mm NUMBER COUNTS REVEALED BY ALMA" in the Astrophysical Journal Letters published on June 1st, 2013.

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erdave
5 / 5 (2) Jun 01, 2013
Can anyone help me with this question. In what fraction of a second or number of seconds after the big bang did all baryonic matter exist from which this vast number of galaxies came into being.
Fleetfoot
5 / 5 (2) Jun 01, 2013
The details of baryogenesis will not really be clear until we understand how matter/anti-matter asymmetry came about but all galaxies and other matter evolved out of the hydrogen helium mix which formed between roughly one minute and fifteen minutes after the start. There's a graph on the right hand side about half way down this page showing the fraction of various elements:

http://www.astro....BNS.html

The model is built from data from lab accelerators and fit what is observed to better than 1% with the exception of lithium. That's out by about a factor of 3 but lithium is destroyed in stars and we have to use stellar atmospheres to measure it :-(
erdave
not rated yet Jun 01, 2013
Thank you Fleetfoot. Can you help with this one. Clearly the universe is distributed in real time as in a "god's eye view", with no current quasars etc.. Presumably in a one universe scenario this is perfectly spherical. Leaving aside problems concerning the observable universe, do we assume galactic distribution is homogeneous as in a rubber ball, or say orange like, or even balloon like. If homogeneous it seems logically possible though unlikely that we are at the centre.
Fleetfoot
5 / 5 (1) Jun 01, 2013
Presumably in a one universe scenario this is perfectly spherical. .. do we assume galactic distribution is homogeneous as in a rubber ball, or say orange like, or even balloon like. If homogeneous it seems logically possible though unlikely that we are at the centre.


I think you are picturing the Big Bang like an explosion in space creating a ball of matter in a void. If so, that's wrong.

Start by thinking of the old "Asteroids" arcade game where the screen wrapped round, there is no centre. In that picture, superclusters of galaxies are spread roughly homogeneously. In four dimensions, that looks like the balloon model (radius = time) with galaxies scattered over the surface creating gravitational dimples like an orange skin.

The picture also depends on whether the universe is closed or open and we don't know that, it's right on the boundary. If the universe is open, puncture the balloon then spread the rubber into an infinite, homogeneous but dimpled flat sheet.
ValeriaT
1 / 5 (3) Jun 01, 2013
In dense aether model the Universe is infinite, steady state and it appears like the rough landscape under the haze. The red shift is caused with scattering of light with CMBR noise in similar way, like for ripples at the water surface. At the sufficient distance all ripples are closely packed each other and scattered into underwater, which creates an illusion of the Big Bang explosion for us. The recent findings already indicate that the volume of Universe is much larger than the visible area of it.
erdave
not rated yet Jun 01, 2013
I completely appreciate your response, however I cannot subscribe to the notion that a snapshot, (ie a gods eye view that pays no mind to the speed of light), of the current universe, occupies more than three dimensions. I will happily concede I may be out of my depth.
Fleetfoot
5 / 5 (1) Jun 01, 2013
I will happily concede I may be out of my depth.


No, I just had to be economical with my wording to fit into 1000 characters.

I cannot subscribe to the notion that a snapshot, (ie a gods eye view that pays no mind to the speed of light), of the current universe, occupies more than three dimensions.


It doesn't. The universe has 4 dimensions, three spatial and one temporal, setting say t=13.7Ga defines a 3D 'snapshot' within the 4D whole. The surface of a balloon is 2D, you can think of that as a 'snapshot' with a given radius within a 3D block of rubber. The analogy drops one spatial dimension to make it easier to visualise.

If you had a gun whose bullet could travel any distance without the universe aging, in a closed universe it would eventually hit you on the back of the head (ignoring gravitational deflections along its course). In the open universe, it would travel an unlimited distance, always through new regions and all with the same density of galaxies.
ValeriaT
1 / 5 (3) Jun 01, 2013
The universe exhibits a much more dimensions, than just three or four - but the light is spreading most slowly in 3 dimensions, so that the volume of observable universe is largest in just 3D. But every gravitational lensing is the evidence of extradimensions. And the lensing within lens are evidence of another additional dimensions. The massive bodies do appear like myriads of tiny gravitational lenses (particles) embedded into another ones (atoms), etc, so that the number of their dimensions is very high. The massive bodies composed of particles therefore do behave like the slices of hyperdimensional objects embedded into 3D space. The residual dimensions manifest itself with various forces violating the inverse square law (Cassimir force, various dipole forces, macroscopic forces etc.)
Fleetfoot
5 / 5 (4) Jun 01, 2013
But every gravitational lensing is the evidence of extradimensions. And the lensing within lens are evidence of another additional dimensions.


More of your usual rubbish, gravitational lensing is described perfectly by GR in the usual 4 dimensions, 3 spatial and one temporal.
GSwift7
not rated yet Jun 03, 2013
Can anyone help me with this question. In what fraction of a second or number of seconds after the big bang did all baryonic matter exist from which this vast number of galaxies came into being.


42

google "The answer to everything". hehe

On a serious note, if I'm reading the original story correctly, it seems that they are saying that before this work we have only observed the extremes on both ends of the galaxy type spectrum?

Getting time on ALMA is like a guarantee of discovering something new.

The original story says:

As the number of antennas in the ALMA telescope increases, its observation ability will also improve


They completed the entire 66 antena array in March 2013, so that must be an old quote or a goofed up translation.