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
(requires JavaScript, H-alpha: on)
In both images NIR (near infrared) is mapped to red, yellow is mapped to green and blue is mapped to blue. In the version with H-alpha that emission line is shown in reddish orange.

By toggling between the images (click on the button) it can be seen that the HII regions (reddish) correlate with bluish regions. That's because the HII gas clouds typically contain many young (blue) stars which are also responsible for the ionization. Furthermore the HII regions 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 (in the image from to right to left and below the galaxy core). NGC 4400 and 4401 seem to be connected. In the Javascript viewer annotations of these objects can be enabled by pressing the key '3' or via menu.

Image data

FOV: 0.44° × 0.42°
Date: 2020-2022
Location: Pulsnitz, Germany
Instrument: 400mm Newton at f=1520mm
Camera Sensor: Panasonic MN34230
Orientation: North is up (exactly)
Scale: 0.8 arcsec/pixel (at full resolution)
Total exposure times:
H-alpha (3nm): 20.5 h
NIR: 3.2 h
Yellow (540nm to 650nm): 8.0 h
Blue: 3.1 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, dark current subtraction, flatfield correction
  2. Alignment and brightness calibration using stars from reference image
  3. Stacking with masking unlikely values and background correction
  4. Denoising and deconvolution
  5. Color composition
  6. Dynamic range compression using non-linear high-pass filter
  7. Tonal curve correction

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