1. The document describes a student experiment to observe the 21 cm hydrogen line from different locations in the Milky Way galaxy using a radio telescope. 2. Spectra were obtained from 6 sources and 1 calibrated source at different galactic longitudes between 150-210 degrees. 3. By measuring the Doppler shift in the observed hydrogen line, the relative line-of-sight velocity was calculated and found to agree with the expected rotation of the Milky Way.

1. H I E M I S S I O N F R O M T H E M I L K Y WAY
G R O U P 6
1 . A I N D R I L A S A H A
2 . F E N I L S H A H
3 . H I M A N G S H U S E K H A R S A R M A H
4 . S A M YA K
5 . S H R U T I M A L I A K A L

2. I N T R O D U C T I O N
• What is HI ?
HI is the cold (10-100K) neutral atomic
hydrogen which is found in abundance in
the interstellar medium.
• Why does it emit in radio ?
This is the result of the hyperfine splitting of
the ground state (2S1/2 ) resulting in the
transition between the antiparallel and
parallel spin states .
An HI atom, after being excited, typically
waits 12 million years before spontaneously
decaying .
• The signature wavelength
21 cm or the 1420 MHz line.
Source: Wikipedia

3. E Q U I P M E N T
• The 4 m parabolic SMRT
• Feed
• Low-Noise Amplifier
• RF Filter
• Mixers, Bandpass filter, IF amplifier
• Detector and Integrator
• Recorder

4. E X P E R I M E N T
• The telescope was initialised and directed to the sources.
• The spectrum was obtained between 1418 and 1422 MHz.
• The background was fitted and subtracted with a fourth order
polynomial.
• Gaussians were then appropriately fitted for the peaks.
• The relative line-of-sight velocity was calculated using Doppler shifts.

5. S O U R C E : P 1 0 , G A L A C T I C L O N G I T U D E : 1 5 0 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

6. S O U R C E : P 1 0 , G A L A C T I C L O N G I T U D E : 1 5 0 O
( A N A LY S I S )
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

7. S O U R C E : P 1 1 , G A L A C T I C L O N G I T U D E : 1 6 5 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

8. S O U R C E : P 1 2 , G A L A C T I C L O N G I T U D E : 1 8 0 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

9. S O U R C E : P 1 3 , G A L A C T I C L O N G I T U D E : 1 9 5 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

10. S O U R C E : P 1 4 , G A L A C T I C L O N G I T U D E : 2 1 0 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

11. C A L I B R A T E D S O U R C E : S 0 8 , G A L A C T I C L O N G I T U D E : ~ 2 0 7 O
x axis: Frequency shift from 1420 MHz (in KHz)
y axis: Voltage (in V)

12. Relative line-of-sight velocity measured
from fit
Relativeline-of-
sightvelocity(km
s-1)
-22.5
-7.5
7.5
22.5
sin(l)
-0.6 -0.3 0 0.3 0.6
Relative line-of-sight velocity measured
from peakRelativeline-of-
sightvelocity(km
s-1)
-20
0
20
40
sin(l)
-0.6 -0.3 0 0.3 0.6
Relative line-of-sight velocity measured from fit
Source l = Galactic longitude (in degrees) sin(l) Doppler Shift frequency (kHz) Relative line-of-sight velocity (km s-1)
P10 150 0.5 124 26.1971830985915
P11 165 0.258819045102521 76 16.056338028169
P12 180 0.000000000000000122464679914735 11 2.32394366197183
P13 195 -0.258819045102521 -43 -9.08450704225352
P14 210 -0.5 -44 -9.29577464788732
S08 207.99 -0.469317452210033 -67 -14.1549295774648
Relative line-of-sight velocity measured from peak-1
Source Doppler Shift frequency (kHz) l = Galactic longitude (in degrees) sin(l) Relative line-of-sight velocity (km s-1)
P10 170 150 0.5 35.9154929577465
P11 70 165 0.258819045102521 14.7887323943662
P12 0 180 0.000000000000000122464679914735 0
P13 -30 195 -0.258819045102521 -6.33802816901408
P14 -50 210 -0.5 -10.5633802816901
S08 -70 206.99 -0.453834982850628 -14.7887323943662
C A L C U L A T I O N O F R E L A T I V E L I N E - O F - S I G H T V E L O C I T Y

13. C O N C L U S I O N S F R O M P R E V I O U S P L O T S
• All observed sources were in the outer galactic region
i.e. 90o
<l<270o
• At l = 180o
, no definitive Doppler shift was observed
G A L A C T I C L O N G I T U D E
S I G N O F R E L A T I V E L I N E -
O F - S I G H T V E L O C I T Y
N A T U R E O F S H I F T
9 0 o
< l < 1 8 0 o
+ V E B L U E
1 8 0 o
< l < 2 7 0 o
- V E R E D

14. T H E M I L K Y WA Y I N G A L A C T I C C O O R D I N A T E S
Source: NASA

15. R O TAT I O N
C U R V E

16. R O TAT I O N C U R V E
cos(l) = (Ro
2 + x2 - R2 )/(2xRo)
l (degrees) Dist from sun (ly) R0 Distance of cloud from centre of galaxy (ly)
150 7500 23000 ly 29732.621214848
165 7500 23000 ly 30306.6726987594
180 7500 23000 ly 30500
195 8500 23000 ly 31287.8090968196
210 10000 23000 ly 32052.6392944613

17. R O TAT I O N
C U R V E
• The distances from the centre of the galaxy was
calculated using the previous image
• The orbital velocity was calculated using
v=-(vr/sin(l) -vo)R/Ro
Distance of cloud from centre of galaxy (ly)
Orbital velocity (km/s);
Uncertainty in measurement:
50 km/s
29733 216
30307 207
31288 291
32053 251
Doppler shift velocity(km/sec)
0
75
150
225
300
29000 30000 31000 32000 33000
Orbital velocity (km/s)

18. E R R O R A N A LY S I S
S O U R C E
S TA N D A R D
D E V I A T I O N
P 1 0 1 . 3 7 4
P 1 1 0 . 8 7 4
P 1 2 0 . 8 4 2
P 1 3 1 . 0 1 5
P 1 4 1 . 1 6 6
S 0 8 0 . 9 3 0
Sources of Error
• System temperature
• External Interferences
• Feed response
• Pointing errors
• Limited sensitivity

19. R E F E R E N C E S
• www.cloud.sagemath.com, MS Excel for plotting and fitting
• Wikipedia
• www.convertalot.com
• www.cv.nrao.edu
• Radiative Processes - Rybicki and Lightman
• Galactic and Intergalactic Radio Astronomy - M. Harwit, R.
Kippenhahn, J.-P. Zahn

20. A C K N O W L E D G E M E N T S
• Subhashis Sir
• Neeraj Sir
• Joshi Sir
• Jesu Sir
• NCRA and IUCAA faculty and facilities.

21. C O N T R I B U T I O N S
• Aindrila: Data assembly and analysis, error analysis and
experimentation.
• Fenil: Experimentation, data interpretation and the “Google
Guy”.
• Himangshu: Experimentation, curve fitting, Rotation curve.
• Samyak: Plotting and presentation outline, experimentation,
rotation curve.
• Shruti: Presentation, Plotting (coding and fitting),
experimentation, error analysis, rotation curve.

22. G R O U P 6 , R A W S C 2 0 1 5 .
THANK YOU.