Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/~tghosh/stuff/arp220like_RM.pdf
Дата изменения: Mon May 31 00:25:12 2010
Дата индексирования: Sun Apr 10 17:14:00 2016
Кодировка:

Поисковые слова: arp 220
Extending observations of Arp 220-like galaxies across the 1 ­ 10 GHz range

1.

Scientific Justification

Astro-chemistry 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 12-m telsecope, ALMA and the LMT. We have recently used Arecibo to carry out a successful cm-wavelength spectral survey of Arp 220 (Salter et al. 2008) which included the first radio observations ever of the v2 = 1 lines of HCN and the first detections of methanimine (CH2 NH) and methane (CH3 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 S-high 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 C-band receiver at Arecibo to observe a sample of Arp 220-like starburst galaxies selected on the basis on their inclusion in samples of OH-megamaser galaxies (Chen et al. 2007), starburst galaxies with detected formaldehyde (H2 CO; Araya et al. 2004), ULIRGS with nuclear starbursts (Armus et al. 1990), or FIR-luminous merging galaxies (Condon et al. 1991). C-band was chosen for this initial study as it was possible to observe simultaneously one of the HCN lines, methanimine, formaldehyde, and the 6-cm 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 L-wide, S-wide, S-high, C-high and X-band receivers as well as with the higher frequencies (5 ­ 6 GHz) of the C-band receiver that were not covered in our previous pro ject. 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 free-free emission in a foreground ionized screen in Arp 220, the 3-cm F=3-3 line of OH that should have been seen with 40 per cent higher flux than the detected F=2-2 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 cmwavelength absorption. Other potential lines are methylamine (CH3 NH2 ), 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 pro ject will determine whether or not these two galaxies, which appear similar to Arp 220 in their C-band properties, retain this similarity in their other cm-wavelength lines. If they do prove to be highly similar, then this will give three examples of galaxies with the same spectral signature at cm-wavelengths
0. 4 00

CH 3 OH: 51 - 6
0. 3 00
Fractional Absorption

0

A

+

0.005

Fu D ni ( ) l esy J x ty

0. 2 00

0.000

0. 1 00

-0.005

-. 0 0 00
-0.010

-. 1 0 00 4800 500 0 500 2 500 4 500 6 H l cn iV l i (m s eoetc e cy k / ir ot ) 500 8 600 0

4500

5000

5500 Heliocentric Velocity (km/s)

6000

Fig. 1.-- Examples of lines seen in Arp 220: left: methanimine (CH2 NH); center: methanol (CH3 OH); co-added radio recombination lines between H119alpha and H127 (3172.9 ­ 3853.7 MHz)


1.500 2.000 0.600

1.000 Intensity (mJy/beam) Intensity (mJy/beam)

1.500 Intensity (mJy/beam) 3500 4000 Heliocentric Velocity (km/s) 4500

0.400

1.000

0.200

0.500

0.500

-0.000

0.000 0.000

-0.200

-0.400 -0.500 3000 3500 4000 Heliocentric Velocity (km/s) 4500 -0.500 3000 3000 3500 4000 Heliocentric Velocity (km/s) 4500

0.020 0.010 -0.000 -0.010 -0.020 -0.030 -0.040 -0.050 3000

0.020

0.020

0.000 Fractional Absorption Fractional Absorption 3500 4000 Heliocentric Velocity (km/s) 4500

0.000

Fractional Absorption

-0.020

-0.020

-0.040

-0.040 -0.060 3500 4000 Heliocentric Velocity (km/s) 4500 3000 3000 3500 4000 Heliocentric Velocity (km/s) 4500

Fig. 2.-- Molecular lines detected in C-band in IC 860: top left: methanimine (CH 2 NH); top center: formaldehyde (H2 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.

2.000

0.010 0.005

2.000

1.500 Fractional Absorption Intensity (mJy/beam)

1.500 Intensity (mJy/beam) 3500 4000 Heliocentric Velocity (km/s) 4500

0.000

1.000

1.000

-0.005

0.500

0.500

-0.010

0.000

-0.015 -0.020 3000

0.000

-0.500 3000

3500

4000 Heliocentric Velocity (km/s)

4500

-0.500 3000

3500

4000 Heliocentric Velocity (km/s)

4500

0.010 0.010 -0.000 -0.000 0.000 Fractional Absorption 3500 4000 Heliocentric Velocity (km/s) 4500 -0.010 -0.020 -0.030 -0.040 -0.050 -0.100 3000 3500 4000 Heliocentric Velocity (km/s) 4500 -0.050 3000 3000 3500 4000 Heliocentric Velocity (km/s) 4500

Fractional Absorption

-0.040

Fractional Absorption

-0.020

-0.010

-0.020

-0.060

-0.030

-0.080

-0.040

Fig. 3.-- Molecular lines detected in C-band in Zw 049.057: top left: methanimine (CH 2 NH); top center: HCN; topright: formaldehyde (H2 CO); bottom row: OH main line (left); OH satellite lines (center and right).


­ Arp 220, the prototypical ULIRG, and these two much more moderate galaxies (log (L F I R /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 different from Arp 220 outside of C-band, 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 different 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 single-pixel 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: L-band (1.1 - 1.8 GHz), S-wide (2 - 3 GHz), S-high (3 - 4 GHz) C-band (5 - 6 GHz), C-high (6 - 7 GHz and 7 - 8 GHz) and X-band (8 - 9 GHz and 9 - 10 GHz). Note that the lower part of C-band 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 on-source 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 set-up 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

A This preprint was prepared with the AAS L TEX macros v5.2.


Table 1: Molecular transitions seen in Arp 220
Molecule HCN Transition v2 =1 J=0 J=3 v2 =1 J=0 J=4 v2 =1 J=0 J=5 v2 =1 J=0 J=6 2 1/2 J=1/2 F=0-1 2 1/2 J=1/2 F=1-1 2 1/2 J=1/2 F=1-0 2 3/2 J=5/2 F=2-3 2 3/2 J=5/2 F=2-2 2 3/2 J=5/2 F=3-3 2 3/2 J=5/2 F=3-2 2 1/2 J=3/2 F=1-1 2 1/2 J=3/2 F=2-2 2 1/2 J=5/2 F=2-2 2 3/2 J=3/2 F=2-2 1(1,0) - 1(1,1) 5 1 - 6 0 A+ 2 1/2 J=1/2 F=0-1 2 1/2 J=1/2 F=1-1 2 1/2 J=1/2 F=1-0 l10 -l11 F=0 ± 1 1(1,0) - 1(1,1) 6(2,4) - 6(2,5) Rest Frequency (MHz) 2693.339 4488.472 6731.910 9423.334 4660.242 4750.656 4765.562 6016.746 6030.747 6035.092 6049.084 7761.747 7820.125 8135.870 1639.503 1638.805 6668.519 3263.794 3335.481 3349.193 5289.812 4829.660 4954.760 Frequency in IC 860 (MHz) 2663.603 4438.916 6657.585 9319.293 4608.789 4698.205 4712.947 5950.317 5964.163 5968.460 5982.298 7676.052 7733.785 8046.044 1621.402 1620.711 6594.894 3227.759 3298.655 3312.215 5231.410 4776.337 4900.056 Frequency in Zw 049.057 (MHz) 2658.778 4430.875 6645.525 9302.412 4600.441 4689.695 4704.409 5939.538 5953.359 5957.649 5971.461 7662.147 7719.776 8031.469 1618.465 1617.776 6582.947 3221.912 3292.679 3306.216 5221.933 4767.685 4891.180

OH

18

OH HCOOH CH3 OH CH

CH2 NH H2 CO

Table 2: Selected interesting molecular transitions not seen or marginally detected in Arp 220
Molecule HCN HCO+ Transition v2 =1 J=0 J=2 v2 =1 J=0 J=2 v2 =1 J=0 J=3 v2 =1 J=0 J=4 v2 =1 J=0 J=5 v2 =1 J=0 J=6 v2 =1 J=0 J=2 v2 =1 J=0 J=3 v2 =1 J=0 J=4 v2 =1 J=0 J=5 2 1/2 J=5/2 F=3-3 23/2 N=2 J=5/2-5/2 F=2-2 23/2 N=2 J=5/2-5/2 F=3-3 23/2 N=2 J=3/2-3/2 F=1-2 23/2 N=2 J=3/2-3/2 F=1-1 23/2 N=2 J=3/2-3/2 F=2-2 2 + 3/2 N=2 J=3/2-3/2 F=2-1 1(1)A2 - 2(0)A1 2(1)A1 - 2(1)A2 2(1)B1 - 2(1)B2 2(0)E1+1 - 1(1)E1+1 2(1)E1+1 - 2(1)E1-1 2(0)E2+1 - 1(1)E2+1 2(0)B1 - 1(1)B2 2(0)E1+1 - 1(1)E1-1 Rest Frequency (MHz) 1346.765 1270.413 2540.711 4234.261 6350.908 8890.452 1945.938 3891.372 6484.488 9724.645 8189.587 4847.740 4870.120 7275.004 7325.203 7348.419 7398.618 2166.305 2639.492 2644.074 4364.348 5669.477 6437.552 8777.826 9459.230 Frequency in IC 860 (MHz) 1331.896 1256.386 2512.659 4187.512 6280.789 8792.295 1924.453 3848.408 6412.894 9617.278 8099.168 4794.217 4816.350 7194.683 7244.327 7267.287 7316.932 2142.387 2610.350 2614.881 4316.162 5606.882 6366.477 8680.912 9354.793 Frequency in Zw 049.057 (MHz) 1329.483 1254.110 2508.108 4179.926 6269.412 8776.368 1920.967 3841.437 6401.278 9599.856 8084.497 4785.533 4807.626 7181.650 7231.205 7254.123 7303.677 2138.507 2605.622 2610.145 4308.344 5596.725 6354.944 8665.187 9337.847

HNC

OH CH

CH3 NH

2