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Extended sources

Page last updated by CK on 2-Mar-2016

NGC891

Run 1

Observations

See TAPAS 28-Oct-2015 till 9-Nov-2015. Typical observing script used:

• @nkotf 7 7 0 0 20 40 azel ! OTF map, xSize=ySize=7arcmin, posAngle=0 and 90deg, tiltAngle=0deg,
• @nkotf 7 7 90 0 20 40 azel ! Step=20", Scan-Speed=40"/sec, System=Azimuth-Elevation
• ! 22 subscans, 10.5sec/subscan, 4.9min

IDL data processing by X.Desert

An offline data reduction was made using the 16 scans performed during good weather. The nk pipeline Rev 9881 was used with a single point source as a mask and a single common mode removal. Both 1mm arrays are used and coadded in a single map. Here are the data : say V1

The data will soon be reprocessed by masking the whole edge-on galaxy. Here they are : say V2

Greg plots by C.Kramer

NIKA2 maps of NGC891 at 1mm (Upper) and at 2mm (Lower), after correction for the position angle of 22.5deg. The maps cover 12'x2'. Half-power beamwidths of 12" and 18" are shown. Contours are at 10% (dashed), and 20% to 80% in steps of 20% (drawn) of the peak flux densities (82mJy/beam at 1mm and 18mJy/beam at 2mm). Peak 1.3mm flux density of Guelin et al. (1996) is 62mJy/beam. The surroundings of the galaxy still show somewhat negative flux densities, as a histogram of all flux densities would show more clearly. The vertical structure seen in the NIKA2 maps looks very smooth, qualitatively similar to the Herschel maps shown in Hughes et al.. NGC891 is at 9.6Mpc distance; 1arcmin corresponds to 2.8kpc. The 1mm map has an rms of 3mJy/beam, the 2mm map 1mJy/beam. Guelin et al. had 4mJy/beam rms.

Left: Cut along the major axis of NGC891, through the center position. Right: Vertical profile of NGC891, averaged between +4' and -4' (cf. with Herschel profiles shown in Fig. 2 of Hughes et al.). Negative features are still visible. Hughes et al. show the presence of extraplanar dust out to vertical offsets +-6'. We would need to go much deeper to compare with their results. (CK 18-Jan-2016)

Reduction with scanamorphos by H. Roussel

• Scanam NIKA2 Feb2016 V2 presented at the Data Reduction Workshop

Run 4

Planned observations of NGC891

• Mapping:
  • NIKA2 observations of NGC891 should be done alternating between two perpendicular scans, both 45deg relative to the source position angle. Maps should be repeated as often as possible, to fetch also the extraplanar dust, which has never before been mapped at 1mm/2mm with NIKA2 resolutions:
  • Check the z-Focus !

  • @ nkotf 20 20 -22.5 0 20 40 radec

  • @ nkotf 20 20 +67.5 0 20 40 radec

  • Mapsize = 20' = 10'/sqrt(2) source + 2x 6.5' FoV (based on recommendations by H.Roussel. See also here)

  • 20'x20', 20" step size, 40"/sec scanning speed
  • Total observing time per scan = 34 Minutes (without overheads, 61subscans, 30sec/subscan)

• NGC891 is observable above 30deg between 11:00 and 16:00 local time, given the Source visibility and observing schedule.

Observations of NGC891

• 2016-03-04 Scans 97, 98 (tau=0.22) using nkotf as described above

• 2016-03-14 Scans 213 & 214 in Polarimetry mode using ngc891_pol.pako (Two maps out of three done as the source became too high.)

References

• Guelin et al. 1996: 7-channel/30m 1.3mm observations

• Hughes et al. 2014: Herschel observations