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Thread: NGC 3953 and UGC 6840 Classic and not so classic barred spiral galaxies

  1. #1
    Join Date
    Dec 2006

    NGC 3953 and UGC 6840 Classic and not so classic barred spiral galaxies

    NGC 3953 is a rather classic looking barred spiral in Ursa Major one and a third degrees south of Phecda (aka Phad and other aliases), the southeastern star in the bowl of the Big Dipper. It is thought to be about 60 million light-years away. Redshift data puts it at 57 million light-years so the various methods of measuring its distance tend to agree for a change. It is classed as a SBb spiral by the NGC project and SB(r)bc by NED. It is a LINER galaxy with HII emission though I didn't bring out any in my LRGB image. Probably too small for my resolution as the largest regions are said to be about 3" in size. I should think about adding some HII data to these to bring such regions out. The galaxy is about 114,000,000 light-years across, making it about the size of our galaxy. Except for the many arm segments it may be rather similar to our own galaxy in many respects.

    A note at NED reads: "NGC 3953 ... is notable for its extended, diffuse, polarized radio emission from the outer disc. No significant radio emission from the bar and the nucleus has been detected. Significant Faraday rotation between {lambda}22 cm and 6 cm occurs in the southern part of the galaxy (RM ~ +15 rad m^-2^)." Another note says: "The central region of NGC 3953 is more of an oval than a bar." While the core looks round from our perspective seen from "above" it would likely look oval. Still I see a rather well defined though short bar at either side of the core.

    A bit below and left of center is the very low surface brightness dwarf galaxy MCG +09-20-023. Unfortunately no distance data is available at NED for it. It sure is a ghost of a galaxy. Wish I knew more.

    UGC 6840/PGC 37164 is another low surface brightness galaxy, a spiral this time. I needed much more time than the hour I gave it to bring out its arms as they are so faint. Only the bar is easily seen. It has virtually the same redshift as NGC 3953 so too is about 55 to 60 million light years distant. It is classed as SB(rs)m. The m indicating it is similar to our Large Magellanic Cloud. If the distance is right it is about 31,500 light years across, about the same as the LMC as well.

    North of UGC 6840 is the quasar SDSS J115205.96+521114.2. Unusual for being only 3.3 billion light-years distant and for showing hints of the galaxy it is in. Two ansae are seen indicating it may be a disk galaxy. NED also classes it as a Bright Line AGN galaxy. It is also cataloged as an X-ray source (many AGN and quasars are). At magnitude 18.9 it isn't very bright for a quasar as I've imaged many at three times this distance that appeared even brighter than magnitude 18.9.

    North west of the quasar is a galaxy cluster. NED shows the Bright Cluster Galaxy anchoring the cluster to be a faint galaxy hiding in the glare of a much brighter one. It then uses the bright one as the position of the cluster. The distance to the cluster is based on a less accurate photographic method rather than actual spectral data so the two distances don't quite match. The cluster is listed with no size containing 13 galaxies. The bright galaxy, SDSS J115150.66+521250.1, is not listed by NED as being a BCG galaxy nor is a red shift value listed. While the much fainter one, MaxBCG J177.96111+52.21393 BCG, is. The cluster is MaxBCG J177.96111+52.21393, matching the fainter BCG. So does this mean the brighter galaxy just happens to be exactly at the same coordinates as the cluster? Quite possibly as the position of the cluster is rather vague with the error circle including both galaxies.

    14" LX200R @ f/10, L=6x10' RGB=2x10'x3, STL-11000XM, Paramount ME
    Attached Images Attached Images

  2. #2
    Hi Rick, love the close up of the spiral. Very nice!

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