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Posts: 131433
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PGC 64413
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Title: Star Formation Histories Across the Interacting Galaxy NGC 6872, the Largest-Known Spiral
Author: Rafael T. Eufrasio (1,2), Eli Dwek (2), Richard G. Arendt (2,3), Duilia F. de Mello (1,2,4), Dimitri Gadotti (5), Fernanda Urrutia-Viscarra (6), Claudia Mendes de Oliveira (6), Dominic Benford (2) ((1) The Catholic University of America, (2) NASA Goddard Space Flight Center, (3) CRESST, University of Maryland Baltimore County, (4) Johns Hopkins University, (5) European Southern Observatory, (6) Universidade de São Paulo)

NGC 6872, hereafter the Condor, is a large spiral galaxy that is interacting with its closest companion, the S0 galaxy IC 4970. The extent of the Condor provides an opportunity for detailed investigation of the impact of the interaction on the current star formation rate and its history across the galaxy, on the age and spatial distribution of its stellar population, and on the mechanism that drive the star formation activity. To address these issues we analysed the far-ultraviolet (FUV) to near-infrared (near-IR) spectral energy distribution (SED) of 17, 10 kpc diameter, regions across the galaxy, and derived their star formation history, current star formation rate, and stellar population and mass. We find that most of the star formation takes place in the extended arms, with very little star formation in the central 5 kpc of the galaxy, in contrast to what was predicted from previous numerical simulations. There is a trend of increasing star formation activity with distance from the nucleus of the galaxy, and no evidence for a recent increase in the current star formation rate (SFR) due to the interaction. The nucleus itself shows no significant current star formation activity. The extent of the Condor also provides an opportunity to test the applicability of a single standard prescription for conversion of the FUV + IR (22 micron) intensities to a star formation rate for all regions. We find that the conversion factor differs from region to region, arising from regional differences in the stellar populations.

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Posts: 131433
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Condor Galaxy
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NGC 6872 (also Condor Galaxy, ESO 73-32, IRAS 20115-7055 and PGC 64413)is a magnitude +12.7  interacting spiral galaxy located 212 million light-years away in the constellation Pavo. 

The galaxy was discovered by British astronomer John Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector at the Cape of Good Hope on the 27th June 1835.

Right Ascension 20h 16m 56.5s, Declination -70° 46' 04"

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NGC6872
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Largest Spiral Galaxy in Universe Revealed

Astronomers have crowned the universe's largest known spiral galaxy, a spectacular behemoth five times bigger than our own Milky Way.
The title-holder is now NGC 6872, a barred spiral found 212 million light-years away in the southern constellation Pavo, researchers announced today (Jan. 10). The distance between NGC 6872's two huge spiral arms is 522,000 light-years, compared to about 100,000 light-years for the Milky Way.

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Ed ~ As of February 2015, Malin 1 is the largest known spiral galaxy so far discovered.



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NGC 6872
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Galaxy crash sparks large spiral

Astronomers have spotted the largest known spiral galaxy - by accident.
A team was looking through data from the Galaxy Evolution Explorer (Galex) satellite for star-forming regions around a galaxy called NGC 6872.
But they were shocked to see a vast swathe of ultraviolet light from young stars, indicating that the galaxy is actually big enough to accommodate five of our Milky Way galaxies within it.

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Posts: 131433
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RE: NGC6872
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Australian Students Capture Dancing Galaxies

For the second consecutive year, high school students from across Australia joined in a competition to obtain scientifically useful (and aesthetically pleasing) images using the Gemini Observatory. The spectacular result of this contest, organized by the Australian Gemini Office (AusGO), is revealed here. As the 2010 winning student team suggested, Gemini targeted an interacting galaxy pair which, they assured, "would be more than just a pretty picture."
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Posts: 131433
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NGC 6872 and IC 4970
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NGC 6872 and IC 4970

ngc6872_w1.jpg
Credit       X-ray: NASA/CXC/SAO/M.Machacek; Optical: ESO/VLT; Infrared: NASA/JPL/Caltech

This composite image of data from three different telescopes shows an ongoing collision between two galaxies, NGC 6872 and IC 4970 (roll your mouse over the image above). X-ray data from NASA's Chandra X-ray Observatory is shown in purple, while Spitzer Space Telescope's infrared data is red and optical data from ESO's Very Large Telescope (VLT) is coloured red, green and blue.
Astronomers think that supermassive black holes exist at the center of most galaxies. Not only do the galaxies and black holes seem to co-exist, they are apparently inextricably linked in their evolution. To better understand this symbiotic relationship, scientists have turned to rapidly growing black holes - so-called active galactic nucleus (AGN) - to study how they are affected by their galactic environments.

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Position(2000):      RA 20h 16m 57s, Dec -70° 46' 06

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NGC6872
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Title: The Active Nucleus of IC4970: A Nearby Example of Merger-Induced Cold-Gas Accretion
Authors: M.E. Machacek, R.P. Kraft, M.L.N. Ashby, D.A. Evans, C. Jones, W.R. Forman (CfA)
(Version v2)

We present results from Chandra X-ray and Spitzer mid-infrared observations of the interacting galaxy pair NGC6872/IC4970 in the Pavo galaxy group and show that the smaller companion galaxy IC4970 hosts a highly obscured active galactic nucleus (AGN). The 0.5-10 keV X-ray luminosity of the nucleus is variable, increasing by a factor 2.9 to 1.7 x 10^{42} erg/s (bright state) on ~100 ks timescales. The X-ray spectrum of the is heavily absorbed (N_H = 3 x 10^{23} cm^{-2}) for power law models with Gamma = 1.5-2.0 and shows a clear 6.4 keV Fe Kalpha line with equivalent width of 144-195 eV. Limits on the diffuse emission in IC4970 from Chandra X-ray data suggest that the available power from Bondi accretion of hot interstellar gas may be an order of magnitude too small to power the AGN. Spitzer images show that 8 micron nonstellar emission is concentrated in the central 1 kpc of IC4970, consistent with high obscuration in this region. The mid-infrared colours of the nucleus are consistent with those expected for a highly obscured AGN. Taken together these data suggest that the nucleus of IC4970 is a Seyfert 2, triggered and fuelled by cold material supplied to the central supermassive black hole as a result of the off-axis collision of IC4970 with the cold-gas rich spiral galaxy NGC6872.

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