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ARP 302
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VV 340:  A Cosmic Exclamation Point

vv340_w1.jpg

VV 340, also known as Arp 302, provides a textbook example of colliding galaxies seen in the early stages of their interaction. The edge-on galaxy near the top of the image is VV 340 North and the face-on galaxy at the bottom of the image is VV 340 South. Millions of years later these two spirals will merge - much like the Milky Way and Andromeda will likely do billions of years from now. Data from NASA's Chandra X-ray Observatory (purple) are shown here along with optical data from the Hubble Space Telescope (red, green, blue). VV 340 is located about 450 million light years from Earth.
Because it is bright in infrared light, VV 340 is classified as a Luminous Infrared Galaxy (LIRG). These observations are part of the Great Observatories All-Sky LIRG Survey (GOALS) combining data from Chandra, Hubble, NASA's Spitzer Space Telescope and Galaxy Evolution Explorer (GALEX) and ground-based telescopes. The survey includes over two hundred LIRGs in the local Universe. A chief motivation of this study is to understand why LIRGs emit so much infrared radiation. These galaxies generate energy at a rate this is tens to hundreds of times larger than that emitted by a typical galaxy. An actively growing supermassive black hole or an intense burst of star formation is often invoked as the most likely source of the energy.

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Position (J2000):     R.A. 14 57 00.68  |  Dec. +24° 37' 02.7''



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Title: Molecular Gas and Star formation in ARP 302
Authors: Yiping Ao, Dinh-V-Trung, Jeremy Lim, Ji Yang, Satoki Matsu****a

We present the Submillimeter Array observation of the CO J=2-1 transition towards the northern galaxy, ARP 302N, of the early merging system, ARP 302. Our high angular resolution observation reveals the extended spatial distribution of the molecular gas in ARP 302N. We find that the molecular gas has a very asymmetric distribution with two strong concentrations on either side of the centre together with a weaker one offset by about 8 kpc to the north. The molecular gas distribution is also found to be consistent with that from the hot dust as traced by the 24 micro continuum emission observed by the Spitzer. The line ratio of CO J=2-1/1-0 is found to vary strongly from about 0.7 near the galaxy centre to 0.4 in the outer part of the galaxy. Excitation analysis suggests that the gas density is low, less than 10^3 cm^{-3}, over the entire galaxy. By fitting the SED of ARP 302N in the far infrared we obtain a dust temperature of T
m_d=26-36 K and a dust mass of M
m _{dust}=2.0--3.6 x10^8 M
m_\odot. The spectral index of the radio continuum is around 0.9. The spatial distribution and spectral index of the radio continuum emission suggests that most of the radio continuum emission is synchrotron emission from the star forming regions at the nucleus and ARP302N-cm. The good spatial correspondence between the 3.6 cm radio continuum emission, the Spitzer 8 & 24 \mu m data and the high resolution CO J=2-1 observation from the SMA shows that there is the asymmetrical star forming activities in ARP 302N.

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Position(2000): RA 14h57m15.8s, Dec  +24°34'56"

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