NGC 5953/5954 - Arp 91
Object: NGC5953/5954, galaxies in Serpens, type SO-a 13.8m, 1.5' x 1.1' and type SBc 12.9m, 1.3' x 0.6' (source of data: PGC catalog). Click here for the Arp catalog image (Palomar 200inch) scaled to match my 4x image below. Orientation: North is down and East is to the right, frame is 8' x 5.3'.
Subimages: 43 frames x 600s (~7 hrs) using SD Mask combine after full
calibration (flats are camera with white t-shirt covering the nosecone, no OTA). Seeing
varied from mediocre (FWHM 4") to good (FWHM 2").
Scope: C11XLT, EFL=2936mm (f/10.5 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST7EI (0.63"/pixel) set to -15C
Guiding: SX716 camera on a Taurus Tracker III OAG
Acquisition and Processing: MaxIm DL/CCD v4.5
Taken over three weeks between 2006/05/27 and 06/20. DDP then a mild Curves command was applied to bring out the detail in the otherwise bright cores. The brighter of the pair is NGC 5953 which is a Seyfert type 2 galaxy, 5954 is a LINER (Low Ionisation Nuclear Emission-line Regions) galaxy. A bridge of material between 5953 and 5954 is clearly visible, this is most likely infall from 5954 to a supermassive blackhole in the core of 5953 (see below). The core of 5953 seems to have two main components, in addition, strange lobes are visible around the nucleus against the background of a smooth outer envelope. A faint extension is seen eminating from 5953 towards the NW, this may be a jet from the supermasive black hole?
Richard McDonald, a member of the OAFs yahoo group, offered this very good description of these types of objects, and a link to a paper he wrote on this topic:
Seyfert types 1 & 2 are part of the broad class of Active galaxies, whose nucleus is believed to be fueled by a supermassive black hole. There is a standard model for these objects that says they are all really the same kind of object, with the differences we see being a function of viewing angle.
Seyferts are spirals with bright nuclei, and strong emission lines on a featureless spectrum. Type-1 show narrow and broad emission lines and polarized light. Type-2 have only narrow lines, with broad lines sometimes dimly visible in polarized light.
The Unified Model has a supermassive black hole and accretion disk emitting synchrotron jets. Slow-moving clouds in these jets produce narrow emission lines. Fast-moving clouds orbit in the same plane as the accretion disk and their orbital speed doppler-spreads their emission lines. These are, in turn, orbited by an obscuring dust torus.
The torus of Type-1 Seyferts are seen from a high angle, revealing the jets and both the Broad and Narrow Line Regions (BNR and NLR). The torus of Type-2 Seyferts are seen nearly edge-on, and the obscuring torus hides the BLR, revealing only NLR lines. However, in polarized light we may see BLR light reflected off the NLR clouds (reflected light is often polarized). N.B. There is no relation between the orientation of the active galaxy nuclues and its torus to the orientation of the spiral arms of the galaxy, hence why NGC5953 appears as a face-on spiral, but the dust torus around the nucleus is maybe edge-on.
There's a better summary, a diagram of the standard model, and references to more credible works, here: http://www.themcdonalds.net/richard/astro/papers/604-smbh-agn.pdf
LINER (Low Ionisation Nuclear Emission-line Regions) galaxies are a broad class including both spirals and ellipticals. The classification is based on unusual ratios of certain emission lines suggesting a lower than usual amount of gas ionisation involved in the spectrum.
Here is a 4x close up of the galaxies where I have applied Lucy-Richardson deconvolution
before DDP stretching.
LR Settings: Bgd+Noise: Auto, PSF:Gaussian with r=1.8, Iterations=20. N.B. The auto PSF extract tool indicated the PSF radius to be 2.1, I have found from experimentation and reading on the net that reducing this value reduces the dark haloes around stars (Gibb's Rings), at the cost of less sharpening.
In order to bring out the detail around the core of NGC 5953 I applied a rotational
gradient to the image in MaxIm (Larson-Sekanina type, 0.5 deg rotation).
This technique is used to enhance jets emanating from the nucleus of comets,
I figured, why not try it on a galaxy nucleus. The rose petal pattern of the
dual core and 4 other lobes is plainly visible.