Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~tghosh/stuff/arp220like_RM.ps Äàòà èçìåíåíèÿ: Thu May 20 23:39:08 2010 Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 12:47:49 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

Extending observations of Arp 220­like galaxies across the 1 -- 10 GHz range
1. Scientific Justification
Astro­chemistry is a growing field of interest, with many studies of molecular lines in the mm regime
being madeor planned with telescopes such as the GBT, the ARO 12­m telsecope, ALMA and the LMT. We
have recently used Arecibo to carry out a successful cm­wavelength spectral survey of Arp 220 (Salter et al.
2008) which included the first radio observations ever of the v 2 = 1 lines of HCN and the first detections of
methanimine (CH 2 NH) and methane (CH 3 OH) outside of the Local Volume (Figure 1).
In addition to the numerous molecular lines found in Arp 220, we were also able to detect a number of
hydrogen radio recombination lines (RRLs), particularly with the S­high receiver. The summed spectrum of
the RRLs in this band reached an RMS noise level of 80 µJy and represents the lowest frequency RRLs yet
detected in Arp 220. This helps to constrain models of the ionized gas in this galaxy.
Following this, we have been using the C­band receiver at Arecibo to observe a sample of Arp 220­like
starburst galaxies selected on the basis on their inclusion in samples of OH­megamaser galaxies (Chen et
al. 2007), starburst galaxies with detected formaldehyde (H 2 CO; Araya et al. 2004), ULIRGS with nuclear
starbursts (Armus et al. 1990), or FIR­luminous merging galaxies (Condon et al. 1991). C­band was
chosen for this initial study as it was possible to observe simultaneously one of the HCN lines, methanimine,
formaldehyde, and the 6­cm OH transitions. From these observations, two galaxies stand out as being
remarkably similar to Arp 220: IC 860 and Zw 049.057. Our observations of this pair of galaxies (Minchin et
al. 2009) demonstrated that both contained all the lines just listed (Figures 2 and 3) as well as confirming the
formaldehyde 4829 MHz masers previously seen in these galaxies. We also discovered a formaldehyde 4954
MHz maser in IC 860. The OH lines appear consistent with the 2:1 ratio predicted for thermal equilibrium
(although the second satellite line in IC 860 was obscured by RFI).
We now propose extending the spectral survey of IC 860 and Ze 049.057 to cover the full 1 -- 10 GHz range
observed for Arp 220 through observations with the L­wide, S­wide, S­high, C­high and X­band receivers as
well as with the higher frequencies (5 -- 6 GHz) of the C­band receiver that were not covered in our previous
project. This will give us the same coverage that we obtained for Arp 220, where many molecules were
found (Table 1). There are also many other interesting lines that were not seen or were only marginally
detected in Arp 220, despite there being good reasons to expect their presence (Table 2). These include the
HCN J=2 line, which appears to be attenuated by free­free emission in a foreground ionized screen in Arp
220, the 3­cm F=3­3 line of OH that should have been seen with 40 per cent higher flux than the detected
F=2­2 line were it to be in thermal equilibrium, and HNC and HCO+, which are often seen alongside HCN
in mm emission lines but have (like HCN prior to our Arp 220 observations) never yet been seen in cm­
wavelength absorption. Other potential lines are methylamine (CH 3 NH 2 ), which might be expected to be
found alongside methanimine, and transitions on the CH 2 # 3/2 ladder (only the most likely transitions have
been listed for these molecules).
This project will determine whether or not these two galaxies, which appear similar to Arp 220 in their
C­band properties, retain this similarity in their other cm­wavelength lines. If they do prove to be highly
similar, then this will give three examples of galaxies with the same spectral signature at cm­wavelengths
4800 000 00 400 00 800 000
00
000
00
00
00
004
4500 5000 5500 6000
Heliocentric Velocity (km/s)
­0.010
­0.005
0.000
0.005
Fractional
Absorption
CH OH: 5 - 6 A +
3 0
Fig. 1.--- Examples of lines seen in Arp 220: left: methanimine (CH 2 NH); center: methanol (CH 3 OH);
co­added radio recombination lines between H119alpha and H127# (3172.9 -- 3853.7 MHz)

-- 2 --
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.500
0.000
0.500
1.000
1.500
Intensity
(mJy/beam)
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.500
0.000
0.500
1.000
1.500
2.000
Intensity
(mJy/beam)
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.400
­0.200
­0.000
0.200
0.400
0.600
Intensity
(mJy/beam)
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.050
­0.040
­0.030
­0.020
­0.010
­0.000
0.010
0.020
Fractional
Absorption
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.060
­0.040
­0.020
0.000
0.020
Fractional
Absorption
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.040
­0.020
0.000
0.020
Fractional
Absorption
Fig. 2.--- Molecular lines detected in C­band in IC 860: top left: methanimine (CH 2 NH); top center:
formaldehyde (H 2 CO) at 4929 MHz; top right: formaldehye at 4954 MHz; bottom left: HCN; bottom center:
OH main line (left); bottom right: OH first satellite line.
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.500
0.000
0.500
1.000
1.500
2.000
Intensity
(mJy/beam)
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.020
­0.015
­0.010
­0.005
0.000
0.005
0.010
Fractional
Absorption
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.500
0.000
0.500
1.000
1.500
2.000
Intensity
(mJy/beam)
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.100
­0.080
­0.060
­0.040
­0.020
­0.000
Fractional
Absorption
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.050
­0.040
­0.030
­0.020
­0.010
­0.000
0.010
Fractional
Absorption
3000 3500 4000 4500
Heliocentric Velocity (km/s)
­0.050
­0.040
­0.030
­0.020
­0.010
0.000
0.010
Fractional
Absorption
Fig. 3.--- Molecular lines detected in C­band in Zw 049.057: top left: methanimine (CH 2 NH); top center:
HCN; topright: formaldehyde (H 2 CO); bottom row: OH main line (left); OH satellite lines (center and
right).

-- 3 --
-- Arp 220, the prototypical ULIRG, and these two much more moderate galaxies (log (LF IR /L# ) = 11.14
for IC 860, 11.27 for Zw 049.057 and 12.15 for Arp 220; Sanders et al. 2003). If they are markedly di#erent
from Arp 220 outside of C­band, then the question naturally arises as to why the similarity is constrained
to omly a few molecular species. Either way, this will advance our understanding of the conditions that give
rise to the di#erent transitions. Radio recombination lines will also enable models of the ionized gas in these
galaxies to be much better constrained, giving information on the mass of ionized gas and on the formation
rate of massive stars.
2. Technical Details
We intend to employ the Mock spectrometers in their new single­pixel mode. This will allow us to
observe the full 1 GHz available through the current IF, rather than the 680 MHz of useable spectrum
delivered by the WAPP spectrometers. This will reduce the necessary observing time by around 30 per cent
by allowing us to cover the 2 GHz bandwidth of the higher frequency receivers in two shots rather than
three. The planned observing bands are: L­band (1.1 ­ 1.8 GHz), S­wide (2 ­ 3 GHz), S­high (3 ­ 4 GHz)
C­band (5 ­ 6 GHz), C­high (6 ­ 7 GHz and 7 ­ 8 GHz) and X­band (8 ­ 9 GHz and 9 ­ 10 GHz). Note that
the lower part of C­band has already been observed and so is not included in this proposal.
In order to reach the same sensitivity as in Arp 220, we require 1 hour on­source in each band per target.
Using the DPS observing technique, this equates to 3 hours per band per target. Over our 8 bands, this is
therefore 24 hours per target or 48 hours in total. Including a slewing overhead and set­up time of 10%, our
total observing request is for 53 hours. As the two sources are so placed in the sky to allow for consecutive
observing from 11:55 to 16:20 (LST), it should be possible to do this in 12 sessions. Only Arecibo has the
sensitivity and the frequency coverage to be able to c carry out this survey -- reaching similar levels with the
GBT would take considerably longer and the frequency ranges 2.6 -- 3.8 GHz and 6.1 -- 8.0 GHz would not
be available, making observations of many of the lines impossible.
REFERENCES
Salter C. J., Ghosh T., Catinella B., Lebron M,, Lerner M. S., Minchin R., Momjian E., 2008, AJ, 136, 389
Chen P. S., Shan H. G., Gau Y. F., 2007, AJ, 133, 496
Araya E, Baan W. A., Hofner P., 2004, ApJ, 154, 541
Armus L., Heckmen T. M., Miley G. K., 1990, ApJ, 364, 471
Condon J. J., Huang Z.­P., Yin Q. F., Thuan T. X., 1991, ApJ, 378, 471
Minchin R. F., Catinella B., Ghosh T., Lebron M., Lerner M. S., Momjian E., O'Neil K., Salter C. J., 2009,
AAS, 215, 445.02
Sanders D. B., Mazzarella J. M., Kim D.­C., Surace J. A., Soifer B. T., 2003, AJ, 126, 1607
This preprint was prepared with the AAS L A T E X macros v5.2.

-- 4 --
Table 1: Molecular transitions seen in Arp 220
Molecule Transition Rest Frequency Frequency in IC 860 Frequency in Zw 049.057
(MHz) (MHz) (MHz)
HCN v 2 =1 #J=0 J=3 2693.339 2663.603 2658.778
v 2 =1 #J=0 J=4 4488.472 4438.916 4430.875
v 2 =1 #J=0 J=5 6731.910 6657.585 6645.525
v 2 =1 #J=0 J=6 9423.334 9319.293 9302.412
OH 2 # 1/2 J=1/2 F=0­1 4660.242 4608.789 4600.441
2 # 1/2 J=1/2 F=1­1 4750.656 4698.205 4689.695
2 # 1/2 J=1/2 F=1­0 4765.562 4712.947 4704.409
2 # 3/2 J=5/2 F=2­3 6016.746 5950.317 5939.538
2 # 3/2 J=5/2 F=2­2 6030.747 5964.163 5953.359
2 # 3/2 J=5/2 F=3­3 6035.092 5968.460 5957.649
2 # 3/2 J=5/2 F=3­2 6049.084 5982.298 5971.461
2 # 1/2 J=3/2 F=1­1 7761.747 7676.052 7662.147
2 # 1/2 J=3/2 F=2­2 7820.125 7733.785 7719.776
2 # 1/2 J=5/2 F=2­2 8135.870 8046.044 8031.469
18 OH 2 # 3/2 J=3/2 F=2­2 1639.503 1621.402 1618.465
HCOOH 1(1,0) ­ 1(1,1) 1638.805 1620.711 1617.776
CH 3 OH 5 1 - 6 0 A + 6668.519 6594.894 6582.947
CH 2 # 1/2 J=1/2 F=0­1 3263.794 3227.759 3221.912
2 # 1/2 J=1/2 F=1­1 3335.481 3298.655 3292.679
2 # 1/2 J=1/2 F=1­0 3349.193 3312.215 3306.216
CH 2 NH l 10 ­l 11 #F=0 ± 1 5289.812 5231.410 5221.933
H 2 CO 1(1,0) ­ 1(1,1) 4829.660 4776.337 4767.685
6(2,4) ­ 6(2,5) 4954.760 4900.056 4891.180
Table 2: Selected interesting molecular transitions not seen or marginally detected in Arp 220
Molecule Transition Rest Frequency Frequency in IC 860 Frequency in Zw 049.057
(MHz) (MHz) (MHz)
HCN v 2 =1 #J=0 J=2 1346.765 1331.896 1329.483
HCO+ v 2 =1 #J=0 J=2 1270.413 1256.386 1254.110
v 2 =1 #J=0 J=3 2540.711 2512.659 2508.108
v 2 =1 #J=0 J=4 4234.261 4187.512 4179.926
v 2 =1 #J=0 J=5 6350.908 6280.789 6269.412
v 2 =1 #J=0 J=6 8890.452 8792.295 8776.368
HNC v 2 =1 #J=0 J=2 1945.938 1924.453 1920.967
v 2 =1 #J=0 J=3 3891.372 3848.408 3841.437
v 2 =1 #J=0 J=4 6484.488 6412.894 6401.278
v 2 =1 #J=0 J=5 9724.645 9617.278 9599.856
OH 2 # 1/2 J=5/2 F=3­3 8189.587 8099.168 8084.497
CH 2# 3/2 N=2 J=5/2­5/2 F=2­2 4847.740 4794.217 4785.533
2# 3/2 N=2 J=5/2­5/2 F=3­3 4870.120 4816.350 4807.626
2# 3/2 N=2 J=3/2­3/2 F=1­2 7275.004 7194.683 7181.650
2# 3/2 N=2 J=3/2­3/2 F=1­1 7325.203 7244.327 7231.205
2# 3/2 N=2 J=3/2­3/2 F=2­2 7348.419 7267.287 7254.123
2# + 3/2 N=2 J=3/2­3/2 F=2­1 7398.618 7316.932 7303.677
CH 3 NH 2 1(1)A2 ­ 2(0)A1 2166.305 2142.387 2138.507
2(1)A1 ­ 2(1)A2 2639.492 2610.350 2605.622
2(1)B1 ­ 2(1)B2 2644.074 2614.881 2610.145
2(0)E1+1 ­ 1(1)E1+1 4364.348 4316.162 4308.344
2(1)E1+1 ­ 2(1)E1­1 5669.477 5606.882 5596.725
2(0)E2+1 ­ 1(1)E2+1 6437.552 6366.477 6354.944
2(0)B1 ­ 1(1)B2 8777.826 8680.912 8665.187
2(0)E1+1 ­ 1(1)E1­1 9459.230 9354.793 9337.847