NGC 4395, NGC 4399, NGC 4400 and NGC 4401 in H-alpha and continuum light

NGC 4395 is a low surface brightness galaxy in constellation Canes Venatici. NGC 4399, NGC 4400 and NGC 4401 are bright HII regions inside the galaxy.

NGC 4395, NGC 4399, NGC 4400 and NGC 4401 in H-alpha and continuum light
Click on the image to toggle H-alpha off (requires JavaScript, H-alpha: on)
In both images NIR (near infrared) is mapped to orange and blue is mapped to bluish cyan, but the first image additionally contains H-alpha light in the red channel. (The only difference is that in the H-alpha variant the NIR data in red channel was replaced by data taken with the H-alpha filter which contains about the same continuum information as the NIR data.)

By toggling between the images it can be seen that the HII regions correlate with bluish regions. That's because the HII gas clouds typically contain many young (blue) stars. Furthermore the HII regions probably also emit [OIII] and H-beta light which is collected by the blue filter.

The three brightest HII regions have their own NGC numbers: 4399, 4400 and 4401 (from east/left to west/right and south of/below the galaxy core. NGC 4399 and 4400 seem to be connected.) It is unclear whether the blue color in the continuum image comes from [OIII] and H-beta emissions or whether there are star formation regions.

Image data

FOV: 0.31° × 0.33°
Date: 2020-2021
Location: Pulsnitz, Germany
Instrument: 400mm Newton at f=1520mm
Camera Sensor: Panasonic MN34230
Orientation: North is up (approximately)
Scale: 0.8 arcsec/pixel (at full resolution)
Total exposure times:
H-alpha (3nm): 18.4 h
NIR: 3.2 h
Blue: 3.0 h

Image processing

All image processing steps are deterministic, i.e. there was no manual retouching or any other kind of non-reproducible adjustment. The software which was used can be downloaded here.

Image processing steps where:

  1. Bias correction, photon counting
  2. Dark current subtraction, flatfield correction, noise estimation
  3. Alignment and brightness calibration using stars from reference image
  4. Stacking with masking unlikely values and background correction
  5. Denoising and deconvolution
  6. RGB-composition
  7. Tonal curve correction

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