observing proposals for evla and vlba time due radio … · 2011-01-24 · 1 astronomy 423 at unm...

1

Astronomy 423 at UNM Radio Astronomy

Radio Astronomy Intro, part 2 Greg Taylor University of New Mexico Jan 24, 2011

2

G. Taylor, Astr 423 at UNM

Announcements

• Observing proposals for EVLA and VLBA time due tomorrow, Jan 25 by 3pm MT. Just one paragraph (references optional) – I want at least one from everybody (can use today’s suggestions) – Strongly advise against “detection experiments”

• Graduate credit for properly enrolled Graduate students should happen automatically. If not, then turn in green card to OGS

Astronomy 423 at UNM Radio Astronomy

More Science with the EVLA Some Possible EVLA Observing Projects

4


What are the benefits to doing radio astronomy?

1. can do it easily from the ground, day and night!

2. some objects/processes are easier to detect in the radio compared to other wavelengths

cheap, easy to repair, upgrade round the clock observations – efficient observatories

- some distant, active galaxies are dominated by radio emission

- jets from accretion onto a black hole

- interstellar gas clouds between interacting galaxies - magnetic fields

5


6


Name that planet observed in the radio with the VLA

detection of the magnetic belts around Jupiter

synchrotron emission from energetic particles in magnetic fields

2

7


Solar activity in the radio 8



3. radio waves can propagate (fairly easily, sometimes affected) through the interstellar medium

unprecedented views of distant parts of our Galaxy reveal details of visibly obscured regions – star formation

9


• Our Galactic center (GC) is 25,000 ly away (8000 pc) • GC lies behind 30 visual magnitudes of dust and gas

10


VLA image at λ=90 cm

~45” resolution inner few degrees

of the Galaxy

11


“Mini-spiral” of gas spiraling around (and onto) the central supermassive (~4 x 106 Mo black hole), SgrA*

6 cm VLA image (Ekers et al. 1983)

10’=25 pc

12


VLA 20 cm Lang, Morris & Echevarria 1999

3

13


14


Possible VLA project #1

• Look at 21cm observations of some compact galaxies – Look at rotation curves to learn about kinematics – Measure the HI content of some galaxy or group of galaxies – Look for HI deficiency in clusters of galaxies

15



4. radio emission provides a wide variety of quantitative physical information about the source

radio continuum emission - spectral index (flux as a fxn. of frequency) = energetics - brightness/flux = density, strength of magnetic field number of illuminating stars

radio spectral line emission - width, amplitude of the line = temperature, density - velocity = kinematic motions of gas, distance

16


0218+35

17



• Look at new transitions (5 GHz OH, lines ~30 GHz) – Look at a Gravitational Lens to study ISM of distant galaxy – Look at a star forming region in our own galaxy

18


Differences between optical and radio observing

Optical

direct detection via CCD of the cosmic photon, strikes CCD DETECTION

Radio

- radio wave (cosmic signal) is so weak that it needs to be amplified in order to be processed radio hardware

- measure the wave properties of the radio wave, then reconstruct radio signal

4

19


20


Parkes 64-m in New South Wales, Australia

21


Arecibo Radio Telescope, Puerto Rico

22


• Frequencies ranging from 330 MHz to 86 GHz

• Angular resolution to 100 microarcseconds at highest frequency

Very Long Baseline Array (VLBA)

Dedicated in 1993

10 antennas recording to tape

Correlator in Socorro, NM

Combinable with Global Arrays

23


VLBA Time Lapse Movie

courtesy Enno Middelberg and the NRAO site Techs

24


Primary Beam

l=sin(θ), D = antenna diameter in contours: at factors of 3 increments wavelengths dB = 10log(power ratio) For VLA: θ3dB = 1.02/D, First null = 1.22/D

πDl

Antenna Performance Parameters

5

25


The VLBA 10 antennas each 25 m in diameter

Synthesised aperature over 8 hours.

VLBA Synthesised Aperture 26


image courtesy Lincoln Greenhill (see Miyoshi et al 1995 Herrnstein et al 1999)

27

G. Taylor, Astr 423 at UNM (Peck et al 2003) (today…)

28


(Peck et al 2003)

29


Possible EVLA/VLBA project #3

• Search for water masers – In the galactic center or in star forming regions – Measure line widths, kinematics – Consider physical conditions for any detected masers

30


Hydra A

Taylor (1996)

core:

τ ~ 0.8

FWHM = 80 km/s

NH = 1 x 1024 cm-2

for Tspin = 8000 K

Virial Mass

M ~ R v2 / G

M ~ 2 x 107 Msun for r=50 pc

6

31


HI absorption in PKS 2322-123

Taylor et al. (2000)

core:

τ ~ 0.26 FWHM = 735 km/s NH = 3 x 1024 cm-2

for Tspin = 8000 K

M ~ 109 Msun for r=50 pc

32


Gas in 4C31.04

size pc67 1−h

Perlman et al

2001

HST imaging

4C31.04

Z=0.06

Conway 1996

VLBA 1.4GHz

33


HI absorption in 1946+708

Peck & Taylor (2001)

“Global” VLBI observations

core:

τ ~ 0.2 FWHM = 350 km/s NH = 3 x 1023 cm-2

for Tspin = 8000 K

M ~ 108 Msun

34


0402+379

Rodriguez et al. 2006

35


0402+379

v ~ 600 km/s r ~ 7 pc

M(C2) ~ 7 x 108 Msun

Rodriguez et al. 2009

36



• Measure large scale HI in 0402+379 – Determine extent of HI absorption in space/velocity – Measure line widths, kinematics

7

37


38


Peck & Taylor (2001)

Spectral index map from 1.3/5 GHz VLBI observations

free-free optical depth:

τff ~ T-3/2 ne2ν-2 d

Ne ~ 3 x 1022 cm-2

ionization ~ 10%

Free-free absorption in 1946+708

39


Centaurus A – a peculiar galaxy with extensive radio lobes

40


(Peck 1999)

41


42



• Search for HI absorption against newly discovered CSOs – Determine extent of HI absorption in space/velocity – Measure line widths, kinematics

8

43


44


45


Further Reading 46


Blackbody Radiation

• Next class: To the chalk board

observing proposals for evla and vlba time due radio … · 2011-01-24 · 1 astronomy 423 at unm...

Documents