Green Bank NGC5044 HI Observation summary
- jackychc
- Aug 1, 2019
- 2 min read
Hi all,
Details of observation for proposal AGBT_19A_122 :
using L-band receiver, restfreq at 1407.3MHz , bandwidth of 187.5MHz, and number of channel 131072.
Flux calibrator : 3C286 , 5 mins allocated for ON-OFF on flux calibrator
Session 1:
May 13, 2019 19:15-22:30 ET
3 pairs of ON-OFF , each ON-OFF pair took 1 hour. i.e. 30 mins ON, 30 mins OFF
Last OFF scan is incomplete. calibrated using the previous OFF solution
Elevation : 18 degree above horizon at the start, 32 degree above horizon at the end
Session 2 :
May 15, 2019 22:15 - May 16, 2019 01:00 ET
26 pairs of ON-OFF , each ON-OFF pair took 4 mins. i.e. 2 mins ON, 2 mins OFF
Elevation is around 25-35 degree throughout the observation
The tenth pair (scan no.37/38) has poor calibration result, it is not used in producing final spectrum
Discussion can be found here:
________________________________________________________________________
Day 1:
Integration time for a scan is long, consequently, the overall calibration result it not good since the environment is changing.
The following is the final spectrum from -700 to 700 km/s (smooth to 20km/s) for the first session of observation
baseline fit : using -800 to 800 km/s , 4th order baseline is used.
while region of -200 to 200 km/s statistics shows RMS of 0.681mJy after smooth to 20km/s
Day 2:
Integration time for a scan is much shorter, and it is at a much more favorable elevation than 1st session
Final spectrum of -700km/s to 700 km/s for day 2: (smooth to 20km/s) [please ignore the green line]
baseline fit : using -800 to 800 km/s , 4th order baseline is used. [same as 1st session]
-200 to 200 km/s statistics shows RMS of 0.508mJy after smooth to 20km/s
________________________________________________________________________
Discussion:
Day1 RMS noise 0.681mJy over 20km/s would give the following upper limit for width of 400km/s :
0.681mJy / Sqrt(20) = 0.152276 mJy
integrated flux = 0.152276 * 400 = 60.9mJy
3-sigma limit : 3 (2.36e5) (31.2)^2 (60.9mJy) = 4.19e7 solar masses
Day2 RMS noise 0.508mJy over 20km/s would give the following upper limit for width of 400km/s :
0.508mJy / Sqrt(20) = 0.113592 mJy
integrated flux = 0.113592 mJy * 400 =45.44 mJy
3-sigma limit : 3 (2.36e5) (31.2)^2 (45.44mJy) = 3.13e7 solar masses
Other features
Gerrit and I agree that feature at 450kms-1 feature could be originated from both MCG-03-34-033 and 6dF J1315320-162851, two galaxies in NGC5044 group.
Details about these two galaxies can be found here page 24 :https://arxiv.org/pdf/astro-ph/0605279.pdf
Our observation covers GPS L3 band used by Nuclear Detonation Detection System , the signal is visible in our spectrum. The signal centered at 1381 MHz, and has bandwidth of around 2 MHz.
As discussed in our email conversation, this would made HI Astronomy for velocity approx. 8200 to 8600 kms-1 impossible.
We also discussed the possibility of receiver not functioning properly in the early stage, we compared the shape and relative strength of Gal-HI in ON and OFF scans with existing survey. We conclude the receiver is working properly, and pointing is right.
This is the GBT OFF scan
Survey result at the off-scan position
For GBT ON Scan:
Survey ON scan
Please tell me if you need any additional plots or anything you want me to check. thanks
Comments