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CHE15 - Detection of a Methanol Megamaser in a Major-Merger Galaxy

Short title: Chen et al. (2015)
Authors: Chen, Xi Ellingsen, Simon P. Baan, Willem A. Qiao, Hai-Hua Li, Juan An, Tao Breen, Shari L.
Journal: The Astrophysical Journal Letters, Volume 800, Issue 1, article id. L2, 5 pp. (2015).
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Abstract
We have detected emission from both the {{4}_-1}\to {{3}₀} E (36.2 GHz) class I and {{7}_-2}\to {{8}_-1} E (37.7 GHz) class II methanol transitions toward the center of the closest ultra-luminous infrared galaxy Arp 220. The emission in both methanol transitions shows narrow spectral features and has luminosities approximately 8 orders of magnitude stronger than those observed from typical class I methanol masers observed in Galactic star formation regions. The emission is also orders of magnitude stronger than the expected intensity of thermal emission from these transitions and based on these findings we suggest that the emission from the two transitions are masers. These observations provide the first detection of a methanol megamaser in the 36.2 and 37.7 GHz transitions and represent only the second detection of a methanol megamaser, following the recent report of an 84 GHz methanol megamaser in NGC 1068. We find that the methanol megamasers are significantly offset from the nuclear region and arise toward regions where there is Halpha emission, suggesting that they are associated with starburst activity. The high degree of correlation between the spatial distribution of the 36.2 GHz methanol and X-ray plume emission suggests that the production of strong extragalactic class I methanol masers is related to galactic-outflow-driven shocks and perhaps cosmic rays. In contrast to OH and H₂O megamasers which originate close to the nucleus, methanol megamasers provide a new probe of feedback (e.g., outflows) processes on larger scales and of star formation beyond the circumnuclear starburst regions of active galaxies. eprintid: arXiv:1501.05412

Abstract

We have detected emission from both the {{4}_-1}\to {{3}₀} E (36.2 GHz) class I and {{7}_-2}\to {{8}_-1} E (37.7 GHz) class II methanol transitions toward the center of the closest ultra-luminous infrared galaxy Arp 220. The emission in both methanol transitions shows narrow spectral features and has luminosities approximately 8 orders of magnitude stronger than those observed from typical class I methanol masers observed in Galactic star formation regions. The emission is also orders of magnitude stronger than the expected intensity of thermal emission from these transitions and based on these findings we suggest that the emission from the two transitions are masers. These observations provide the first detection of a methanol megamaser in the 36.2 and 37.7 GHz transitions and represent only the second detection of a methanol megamaser, following the recent report of an 84 GHz methanol megamaser in NGC 1068. We find that the methanol megamasers are significantly offset from the nuclear region and arise toward regions where there is Halpha emission, suggesting that they are associated with starburst activity. The high degree of correlation between the spatial distribution of the 36.2 GHz methanol and X-ray plume emission suggests that the production of strong extragalactic class I methanol masers is related to galactic-outflow-driven shocks and perhaps cosmic rays. In contrast to OH and H₂O megamasers which originate close to the nucleus, methanol megamasers provide a new probe of feedback (e.g., outflows) processes on larger scales and of star formation beyond the circumnuclear starburst regions of active galaxies. eprintid:

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IRAS source	IRAS coordinates (RA, Dec)	IRAS flux density (F12,F25,F60,F100)
2MASS source	2MASS coordinates (RA, Dec)	2MASS magnituted (J,H,K)

Variable star	Variable star parameters	Star Formation Region name	Star Formation Region parameters
WISE source	WISE coordinates (RA, Dec)	WISE magnitudes (w1, w2, w3, w4)
Akari IRC source	Akari IRC coordinates (RA, Dec)	Akari IRC fluxes (S09, S18)
Akari FIS source	Akari FIS coordinates (RA, Dec)	Akari FIS fluxes (S65, S90, S140, S160)

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DSS (optical)	2MASS (JHK)	WISE (4-22 um)	IRAC (3-8 um)	GLIMPSE 360 (3.6-4.5 um)	PACS color (70-160 um)	SPIRE color (250-500 um)
AKARI color (60-160 um)	NVSS (1.4 GHz)	SDSS (optical+NIR)	Image size: arcsec (default is 120 arcsec)
			Image size: arcsec (default is 120 arcsec)

Position of H₂O maser detection

DSS colored	2MASS colored	WISE colored
SDSS color	IRAC color I1,I2,I4	GLIMPSE 360
PACS color (70-160 um)	SPIRE color (250-500 um)	NVSS (1.4GHz)
UKIDSS K	2MASS K

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CHE15 - Detection of a Methanol Megamaser in a Major-Merger Galaxy

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Detection table from Chen et al. (2015)