Galaxy with long extended arms or tidal streams

Here is a DECaLS image of a small galaxy with long arms or tidal trails. It is just below NGC 3580. As far as I can tell they haven’t been spotted before.

The arms can’t be seen in the visible part of the spectrum, they are invisible on SDSS images, but when the image is inverted you can see them.

It is an interesting object that raises a number of questions:

  1. Why do NGC 3580 and the part of the galaxy that can be seen in the visible part of the spectrum appear mainly undisturbed?

  2. What are the arms made out of? As they are mostly visible in the DECaLS Skyserver images (infrared) I would suspect they consist mainly of gas.

  3. Why two arms in opposite directions? You would think there would be only one pointing in the direction of NGC 3580. But there are two, one pointing away from NGC 3580. Is the southern arm the result of a previous meeting with NGC 3580?

  4. Does the northern stream belong to our galaxy or NGC 3580?

5.Is there still interaction going on between the two galaxies? I would say, yes.

I had someone do some calculations for me and preliminary estimates give this galaxy a size of 254.000 lightyears, which is bigger than the Andromeda Galaxy.

Maybe someone can take an interest in this object.

Cheers,
Abe

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http://legacysurvey.org/viewer?ra=168.33&dec=3.63&spectra

It looks like that little galaxy in the stream is at the same redshift as NGC 3580, so this is probably a typical tidal stream from their interaction.

Nice find!

–dustin

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Assuming this is the debris from the partial tidal disruption of a satellite, it’s expected that there is a leading and trailing stream: eg, the illustration at the top of this page:

The DECaLS imaging is g,r,z bands, so optical and near-infrared. The tidal stream would be made of typical galaxy material – the light is coming from stars. There will be gas mixed in there too of course, but it’s the stars that are emitting.

cheers,
–dustin

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That’s very interesting, Dustin, I didn’t know about the Milky Way and Andromeda streams.

Also a leading and trailing stream is new to me. Glad to have learned something new :-).

Cheers,
Abe

The tidal force (differential gravitational field) pulls more strongly on the closer side of the satellite galaxy and less strongly on the far side, causing leading and trailing arms/streams/trails.
cheers,
–dustin

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