Many bars in the red galaxy district

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PSA: Bars Kill Galaxies
Posted in: Astronomy, Citizen Science, galaxies by Jon Voisey (No Comments »)

Barred Spiral Galaxy NGC 6217

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<<Many spiral galaxies are known to harbor bars. Not the sort in which liquor is served as a social lubricant, but rather, the kind in which gas is served to the central regions of a galaxy. But just as recent studies have identified alcohol as one of the most risky drugs, a new study using results from the Galaxy Zoo 2 project have indicated galactic bars may be associated with dead galaxies as well.

The Galaxy Zoo 2 project is the continuation of the original Galaxy Zoo. Whereas the original project asked participants to categorize galaxies into Hubble Classifications, the continuation adds the additional layer of prompting users to provide further classification including whether or not the nearly quarter of a million galaxies showed the presence of a bar. While relying on only quickly trained volunteers may seem like a risky venture, the percentage of galaxies reported to have bars (about 30%) was in good agreement with previous studies using more rigorous methods.

The new study, led by Karen Masters of the Institute of Cosmology and Gravitation at the University of Portsmouth, analyzed the presence or lack of bars in relation to other variables, such as “colour, luminosity, and estimates of the bulge size, or prominence.” When looking to see if the percent of galaxies with bars evolved over the redshifts observed, the team found no evidence that this had changed in the sample (the GZ2 project contains galaxies to a lookback time of ~6 billion years).

When comparing the fraction with bars to the overall color of the galaxy, the team saw strong trends. In blue galaxies (which have more ongoing star formation) only about 20% of galaxies contained bars. Meanwhile, red galaxies (which contain more older stars) had as many as 50% of their members hosting bars. Even more striking, when the sample was further broken down into grouping by overall galaxy brightness, the team found that dimmer red galaxies were even more likely to harbor bars, peaking at ~70%!

Before considering the possible implications, the team stopped to consider whether or not there was some inherent biasing in the selection based on color. Perhaps bars just stood out more in red galaxies and the ongoing star formation in blue galaxies managed to hide their presence? The team referenced previous studies that determined visual identification for the presence of bars was not hindered in the wavelengths presented and only dipped in the ultraviolet regime which was not presented. Thus, the conclusion was deemed safe.

While the findings don’t establish a causal relationship, the connection is still apparent: If a galaxy has a bar, it is more likely to lack ongoing star formation. This discovery could help astronomers understand how bars form in the first place. Given both structure, such as bars and spiral arms, and star formation are associated with galactic interactions, the expectation would be that we should observe more bars in galaxies in which interactions have caused them to form as well as triggering star formation. As such, this study helps to constrain modes of bar formation. Another possible connection is the ability of bars to assist in movement of gas, potentially shuttling and shielding it from being accessible for formation. As Masters states, “It’s not yet clear whether the bars are some side effect of an external process that turns spiral galaxies red, or if they alone can cause this transformation. We should get closer to answering that question with more work on the Galaxy Zoo dataset.”>>

[bystander]

Bars kill spiral galaxies
Royal Astronomical Society | 09 Nov 2010

Two spiral galaxies from the Sloan Digital Sky Survey (SDSS). The red spiral on the left has a bar, whilst the blue spiral on the right does not. The red spiral is SDSS J083051.86+425544.8 and lies in the direction of the constellation Lynx, at a distance of 762 million light years. The blue spiral is SDSS J151132.83+093645.0 and is 465 million light years away, in the direction of the constellation Bootes. [i](Credit: SDSS)[/i]

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With the help of the army of volunteers working on the Galaxy Zoo 2 'citizen science' project, an international team of scientists have discovered that the bars found in many spiral galaxies could be helping to kill them off. The researchers present their results in the journal Monthly Notices of the Royal Astronomical Society.

The overwhelming majority of stars in the universe are found in galaxies like our own Milky Way. These vast stellar assemblies contain anything between a few hundred million and one million billion stars and come in a variety of shapes, from irregular to elliptical (shaped like rugby balls) to spirals, where spiral arms wind out in a disk from a central bulge.

About half of these spiral galaxies have a bar - a linear structure of stars crossing the centre (as shown in the galaxy in the left hand side of the image). Bars are important for the evolution of galaxies as they provide a way to move material in and out in the disk and possibly help to spark star formation in the central regions. They may even help feed the central massive black hole that seems to be present in almost all galaxies. But bars provide us with a great puzzle because we still don't understand why some galaxies have bars and others do not.

The team, led by Dr Karen Masters of the Institute of Cosmology and Gravitation at the University of Portsmouth, drew on the work of the volunteers taking part in Galaxy Zoo 2, the follow on from the highly successful Galaxy Zoo project. In this second phase users were asked to make detailed classifications of the galaxies they looked at, including information on the presence of a bar.

With these data – the largest ever sample of galaxies with visual bar identifications – they have shown that red spirals are about twice as likely to host bars as blue spirals. These colours are significant. Blue galaxies get their hue from the hot young stars they contain, implying that they are forming stars in large numbers. In red galaxies, this star formation has stopped, leaving behind the cooler, long-lived stars that give them their red colour.

The astronomers conclude that bars might help to kill spiral galaxies, although how they do it remains a mystery. But the Milky Way has a bar too, so this discovery may be telling us something about its future.

Galaxy Zoo: Bars in Disk Galaxies - KL Masters et al

• arXiv.org > astro-ph > arXiv:1003.0449 > 01 Mar 2010 (v1), 09 Oct 2010 (v2)

Click to view full size image

Hubble Heritage Image of the Prototypical Barred Spiral Galaxy NGC 1300

The Hubble telescope has captured a display of starlight, glowing gas, and silhouetted dark clouds of interstellar dust in this grand image of the barred spiral galaxy NGC 1300. NGC 1300 is considered to be prototypical of barred spiral galaxies. Barred spirals differ from normal spiral galaxies in that the arms of the galaxy do not spiral all the way into the center, but are connected to the two ends of a straight bar of stars containing the nucleus at its center.

The image was constructed from exposures taken in four filters in September 2004 by the Advanced Camera for Surveys onboard Hubble. Starlight and dust are seen in blue, visible, and infrared light. Bright star clusters are highlighted in red by their associated emission from glowing hydrogen gas. Due to the galaxy's large size, two adjacent pointings of the telescope were necessary to cover the extent of the spiral arms. The galaxy lies roughly 69 million light-years away (21 megaparsecs) in the direction of the constellation Eridanus.

Credit: NASA, ESA, The Hubble Heritage Team (STScI/AURA)
Acknowledgment: P. Knezek (WIYN)

Astronomers Describe The Bar Scene At The Beginning Of The Universe | Science Daily | 31 July 2008

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Infrared image of the core of the Milky Way

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Infer read image of the wrapper of a Milky Way

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<<The Milky Way bar is a chocolate bar distributed by the Mars confectionery company. The American version of the Milky Way bar is made of chocolate-malt nougat topped with caramel and covered with milk chocolate and is very similar to the Mars bar sold in other countries. The non-US Milky Way bar, on the other hand, is not topped with caramel and is therefore similar to the American 3 Musketeers bar.

The Milky Way bar was created in 1923 by Frank C. Mars and originally manufactured in Minneapolis, Minnesota. It was the first commercially distributed filled chocolate bar. The name and taste was taken from a famed malted milk drink (milkshake) of the day – not the Earth’s galaxy, as many contend. By 1926 Milky Way had two flavours, chocolate and vanilla, each for a nickel. In 1935, the slogan was "The sweet you can eat between meals." In 1991, the Health Education Authority and anti-sugar lobbyists both complained, without success, that such advertising encouraged children to eat sweets between meals.

In June 1932, the Milky Way bar was sold as a two piece bar, but just four years later, in 1936, the chocolate and vanilla flavors forever parted. The vanilla Milky Way bar, which was covered in dark chocolate rather than milk chocolate, was renamed the Forever Yours bar. The Forever Yours bar remained available until 1979 when it was discontinued. Due to popular demand, the Forever Yours bar returned in 1989 renamed as the Milky Way Dark bar. In 2000, it was renamed again, creating the now-popular Milky Way Midnight bar.

A popular child-oriented derivative of the Milky Way bar known as 'Milky Way Magic Stars' consists of small aerated chocolate star shapes. Originally, every star was engraved with a different smiley face, each representing one of the magic star characters portrayed on the packaging. The characters were: Pop Star, Jess Star, Bright Star, Super Star, Happy Star, Sport Star and Baby Star.>>

[Ann]

Yes indeed, many barred galaxies are red and dead!

Click to view full size image

This is NGC 2859. It has an outer ring, and you can see the remnants of the bar, the bar ends enhancements.

Ann

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Yes indeed, many barred galaxies are red and dead!

Many of us prefer to say: "Liberal leaning and past our child bearing years."