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The Interstellar Media of the Luminous Infra-Red Galaxies, IC860 and Zw049.057 Yamil Nieves 1,2 , Christopher J. Salter 2 , Robert F. Minchin 2 , Tapasi Ghosh 2 1 University of Puerto Rico in Humacao, 2 Arecibo Observ atory (NAIC) Abstract Analyzing the Data Results Observations To reduce the standing-wave pattern due to the continuum emission from the target galaxy, we perform an ON/OFF observation on this source, yielding an (ON - OFF) spectrum. Then a further ON/OFF observation is made on a strong, nearby continuum (reference) source. Division of the (ON- OFF) target spectrum by that of the reference source cancels the residual standing wave. ( ) ( ) Acknowledgements: Rafael Muller, Arecibo Observatory, NASA Space Grant, UPR-Humacao Double Position Switching (DPS) If this cloud is under the condition of local thermodynamic equilibrium, we can show that the ratio of the two lines intensities are related to the energy levels as: = − To convert energy levels in cm -1 i nto Kelvin, we can use the equation: = Therefore: = ℎ λ ln = 58 From this, we derive a kinetic temperature of 58 K. Results (continued) T emperature of the Cloud We have observed the two LIRG galaxies, IC860 and Zw049.057. These two stand out as being almost identical in molecular content to Arp220 from a previous 4450 - 5300MHz spectral line survey of 20 “Arp220-like” galaxies. From a recent 4450-5300 MHz survey of 20 "Arp220-like" galaxies, the molecular spectra of two objects revealed remarkably similar interstellar media to that of Arp 220 (both in composition and physical state.) This is despite both galaxies having much lower FIR luminosities than Arp 220. Using the Double Position Switching (DPS) technique, we have now extended the spectral coverage for these two objects, IC860 and Zw049.057, to include the frequency ranges of 3.0 –4.4 and 5.3 –10 GHz. From the spectra of both galaxies, we detect the "pre-biotic" molecules, methanimine (CH 2 NH) in emission, and hydrogen cyanide (HCN v 2 =1) in absorption. We also detect formaldehyde (H 2 CO) in emission at 4.830 and 4.955 GHz, and hydroxyl (OH) in absorption at 4.7 and 6.0 GHz, as well as the 3.335-GHz emission line of methylidyne (CH) in Zw049.057. A nu mber o f other possibl e dete ctions are being further investigated. The detected pair of H 2 CO lines allowed us to determine a kinetic temperature of 58 K for the Luminous Infra-Red Galaxy, IC860. H 2 CO Formaldehyde Emission Line at 4829 MHz OH Two OH Absorption Lines at 4750 and 4765 MHz List of Detecte d Molecular Lines IC860 Zw049.057 Species ID Rest Frequency (z=0.012909) HCN v2=1 Hydrogen Cyanide 4489.13 MHz OH v=0 Hydroxyl 4660.08 MHz OH v=0 Hydroxyl 4750.18 MHz OH v=0 Hydroxyl 4764.96 MHz H2CO Formaldehyde 4829.23 MHz H 2 CO Formaldehyde 4954.76 MHz OH v=0 Hydroxyl 6030.75 MHz OH v=0 Hydroxyl 6034.49 MHz HCN v2=1 Hydrogen Cyanide 6731.60 MHz Species ID Rest Frequency (z=0.012999) CH 2 π 1/2 Methylidyne 3335.32 MHz HCN v2=1 Hydrogen Cyanide 4488.48 MHz OH v=0 Hydroxyl 4660.88 MHz OH v=0 Hydroxyl 4750.85 MHz OH v=0 Hydroxyl 4765.35 MHz H 2 CO Formaldehyde 4829.14 MHz OH v=0 Hydroxyl 6031.09 MHz OH v=0 Hydroxyl 6035.43 MHz Comparing Detected Molecular Lines with Arp 220 Lines Arp220 IC860 Zw049.057 HCN (v2=1) HCN (v2=1) HCN (v2=1) OH OH OH (Methanol)? H2CO H2CO H2CO CH CH CH 2 NH (CH 2 NH) (CH 2 NH) The ratio of the 4.7 GHz OH absorption lines in IC860 is 1:2:1, which tell us they are in thermal equilibrium. 0.0042 4660 MHz 0.0084 0.0042 4750 MHz 4765 MHz If two observed lines of the same species are seen to have the same radial velocities and velocity width, we can assume that they are originating in the same cloud. This is the case for H 2 CO in IC860. Same velocity width (61.3km/s) Two Formaldehyde (H 2 CO) transitions towards IC860 Spectra of Raw Data (Orthogonal Polarizations) Spectra of Processed DPS Data (Orthogonal Polarizations) In order to build up int egration time, and increase the sensitivity of the observations we accumulate the data by grading each board by the occurrence of RFI, and co-adding those boards with similar, or better, grades. We then average together the orthogonal polarizations to return the total intensity signal. Finally we boxcar smooth the data to a velocity resolution of 30 km/s. Molecules are detected as narrow, spectral features showing emission and/or absorption. References: • Salter, C. J., & Ghosh, T. (2002). Arecibo Spectral Baselines in the Presence of Continuum Emission. NAIC-NRAO School on Single-dish Astronomy: Techniques and Applications , 278 , 521. • Splatalogue. Database for Astronomical Spectroscopy . Retrieved July, 2012, from http://splatalogue.net/ • Sun Kwok, 2007, "Physics and Chemistry of the Interstellar Medium", University Science Books, Sausalito, CA. IC860 IC860 *White entries denote emission and red entries denote absorption. IC860 IC860
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