Mosaic Imaging and 3D Distance Vectors

NGC 4088 and NGC 4085 – Interacting GalaxiesChelsea Braun

Image: Digitized Sky Survey

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OutlineIntroductionTheoryMosaic Image PlanCreating the ImagesFinal ImageDistance CalculationDiscussion

Image: Jeff Johnson, croppedhttp://jeffjastro.com/dso/NGC4088_30Jan09.htm

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IntroductionNGC 4088 is a weakly barred spiral galaxy

with morphological type SAB(rs)bcNGC 4085 is an Sc D galaxyFound in the Ursa Major constellationPart of the M109 group

Image: StellariumCredit: Simbad

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TheoryThe 3D distance vector

◦Calculating the distance between 2 galaxies

◦Not as simple as finding the distance in arc seconds on an image and then converting to parsecs

◦Requires knowing the distance to these objects

Geometry

Distance4 equations

Where the distance to the galaxies, d1 and d2,

can be determined using arcmins, is determined from the image with scale, S

ImagingSpent a night collecting 1hr

30mins of data30 mins for 3 7’x7’ imagesDifficulties?

◦Telescope moved a lot◦Provided difficulties when combining

the images

Mosaic Image PlanTake three 7’x7’ images, 30 mins at 60sec

exposuresNorth up and East right (for all images)Have common stars in each image to line

up the images

NGC 4088 MID NGC 4085Image: Digitized Sky Survey

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Mosaic Image Plan

Image: Digitized Sky Survey

15’x7’

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NGC 408830 images at 60sec exposures, 7’x7’

image◦Calibrated the images

Broke into 2 subgroups: 1-9, 10-30

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NGC 4088North: upEast: Left

NGC 4088Final NGC 4088 imageCombine the final averaged

images from the substacks into 1 stack

Register themCombine

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NGC 4088

Image: 6.7’x5.2’

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MID30 images at 60 second exposures,

7’x7’ imagesThe middle star image had the most

difficulties◦Most noise

First 5 frames removed (guide stars missing)

Broken down into 3 substacks:◦Substack 1: 6-15◦Substack 2:16-21◦Substack 3: 22-30

Substack 1Most difficult to register done for the 10 frames using

TurboReg: scaled rotation◦Pick 2 points on 2 different images◦Aligns those 2 points using translation

and rotation Rotation is a bad thing

Substack 1Slide 6

Slide 15

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Substack 1Crop all the manually registered

images and place in a stack◦PROBLEM: slight rotation in the

TurboReg plugin caused a very noisy averaged image

Substack 1North: upEast: Left

Substack 1North: upEast: Left

Substack 2 & 3 Final Images

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Mid – Final Image

Image: 6.5’ x 5.5’

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NGC 408530 images at 60 second exposures,

7’x7’No substacks neededAlthough 2 registrations were

necessary to align the images

NGC 4085 – Final ImageImage: 6.7’x5.8’

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Background LevelsBackground levels were matched to

create the mosaicMeasured the background levels of

the 3 final imagesTook the darkest background level

and matched them into the other images ◦Subtracted the differences in

background levels

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Background LevelsImage Background Level Difference

NGC 4088 1060.86 0

MID 1109.77 48.91

NGC 4085 1170.32 109.46

• Convert to 16 bit to use MosaicJ• Find the minimum and maximum pixel values for all three images and set the B & C min and max to these values over all 3 images• Then convert to 16 bit

Final Image

Image: 16.8’ x 7.6’

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Distance Between Galaxies

Measured a distance of 894.79 pixels between galaxies

Variable Value Error

d1 distance to NGC 4088

12.22 Mpc Given

d2 distance to NGC 4085

12.55 Mpc Given

D 894.79 pixels ±8 pixels

S, image scale 0.0136 arcmins/pixel

± 0.0003 arcmins/pixel

Distance Between Galaxies

Using the 4 equations

Darcmins = 12.2' ± 0.4'Drads = 0.0035 ± 0.0001Dparsecs = 0.043 ± 0.001 Mpcd1-d2 = 0.33 MpcD' = 0.33 ± 0.03 Mpc

DiscussionFixing the MID image

◦Save a ROI line between stars for substack 1 and use the same length distance Should eliminate rotation?

ENDTHANKS!!!!!!

References Association of Universities for Research in Astronomy, Inc.

1994. The Digitized Sky Survey http://stdatu.stsci.edu/cgi-bin/dss_form

Chereau F, Gates M, Kerr N, Marcos D, Marinov B. et al. 2010. Stellarium

Goldman, D. (2008). NGC 4088 in UMa. Last accessed 15th Nov. <http://dg-imaging.astrodon.com/gallery/display.cfm?imgID=135>

This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.