NGC 3445 - Arp 24
Object: NGC 3445 galaxy in Ursa Major, also known as Arp 24 which is classified as "One armed spirals". The small galaxy PGC32784 is interacting with the much larger but distorted galaxy NGC 3445. The available redshifts for these two objects and their associated uncertainties are somewhat at odds with the cropped and enlarged monochrome image below, a bridge of material definitively connects the two galaxies. See NGC 3432 for another case like this one.
Calibration L: 30 bias, 45 darks and 40 tshirt flats.
Calibration RGB: 12 darks, 18 tshirt flats and aggressive bad pixel map.
Darks are combined with SD mask and no normalization, flats are SD mask with linear normalization.
Subimages L: 138 x 120 sec (4.6 hrs), Input FWHM = 2.8 +/- 0.4", Flatness = 0.09
Subimages RGB: 10 x 300 sec binned 2x2 (0.8 hrs each)
Scope: C11XLT EFL=2940mm (f/10.5 effective)
Mount: Losmandy G11 with Gemini L4
Camera: ST8XME+CFW10 (0.63"/pixel) set to -30C for L and -25C for RGB
Guiding L: Self-guide, ExpTime = 5 sec, dithered.
Guiding RGB: RGH on TT3 OAG, ExpTime = 4 sec, forgot to dither for first 6 frames, doh!
Acquisition and Processing: MaxIm DL/CCD v4.5
Imaged L on: March 30, 31 and April 1, 2007
Imaged RGB on: May 22, 2007
Data for the 3 galaxies in the center of the field from TheSky and NED:
NGC 3445; 12.3m, 1.6' x 1.4', type SAB(s)m, distance 30.6 +/- 2.2 Mpc (~100 Mly)
E from 3445 - PGC 32784 16.6m (Bmag), 0.7' x 0.2' type Sc, distance 26.0 +/- 1.9 Mpc
NE from 3445 - 2MASX J10544552+5659588 17.2m, 0.3'x0.1', type unknown, distance 198 Mpc
Comparing the relative brightness of the three galaxies in my image to the published
magnitudes made me wonder. So calibrated on a star on the W edge of the frame I
measured the integrated flux from each galaxy which resulted in the following magnitude
Cropped, enlarged by a factor of 2 and aggressively stretched to reveal a faint
light bridge from NGC 3445 to PGC 32784.
Image from the Arp's catalog acquired with the Palomar 200" telescope and 103a-D film.
Cropped and resized to match the image scale of the previous image.
- Combine L: SD Mask (normalization type unknown) with auto star math and bilinear interpolation.
- Flatten Bgd L: Auto complex.
- Combine RGB: SD Mask (delta level normalization) with auto star math and bilinear interpolation. Linear normalization did not preserve the relative intensity between the stars and the galaxy nucleus. In addition delta level normalization had better noise reduction in this case. However black splotches were more apparent (due to lower noise level?).
- Flatten Bgd RGB: manual complex region for all three planes.
- Bgd equalization: Backgrounds around main galaxy G=654.3, R=573.2 and B=441.5, subtract to set all to 100 ADU.
- Color combine: RGB coeffs 1:1.022:1.259, auto bgd, and Lweight=100%, Lab space
- Stretch: gamma = 0.85, low = -0.5, high = 15, dest = 8 bit
- Crop: x,y,w,h = 150,125,800,800
- Clone: Overwrote red/blue hot pixel clusters with adjacent bgd noise.
I tried three other color combine methods which did not produce as nice a result.
Processing steps after SD Mask combine of subframes:
- Flatten bgd: manual complex region for B, G and R planes
- Bgd equalize: Set Bgd to 100 counts with pixel math.
- Green frame 04a-fbgd-beq-G: bgd was 654.5 around galaxy
- Red frame 04a-fbgd-beq-R: bgd was 573.2 around galaxy
- Blue frame 04a-fbgd-beq-B: bgd was 441.5 around galaxy
- Color combine: Using three 04a-fbgd-beq-x color frames and fbgd-02XC clear frame
|RGB: coeffs 1:1.022:1.259, bgd auto
||LRGB coeffs 1:1.022:1.259, bgd auto, Lweight=100%, RGB space
| LxRGB with pixel math: clear frame times RGB frame:
02XC * 04X-fbgd-beq-RGB * 0.2
|Lab coeffs 1:1.022:1.259, bgd auto, Lweight=100%, Lab space
Download compressed FITS file, stretched into 16bit integer.
NGC3445_C11f10_1x1-04X-fbgd-beq-RGB-crop.16.fit (307 KB)
NGC3445_C11f10_1x1-04X-fbgd-beq-LRGB-crop.16.fit (626 KB)
NGC3445_C11f10_1x1-04X-fbgd-beq-LxRGB-crop.16.fit (674 KB)
NGC3445_C11f10_1x1-04X-fbgd-beq-Lab-crop.16.fit (331 KB)