Megamaser Galaxies Research Articles

A Search for 6.7 GH[CLC]z[/CLC] Methanol Masers in OH Megamaser Galaxies at 0.11 < [CLC][ITAL]z[/ITAL][/CLC] < 0.27

We report the results of a search for 6.7 GHz methanol (CH3OH) maser emission in OH megamaser galaxies at 0.11 < z < 0.27. No detections were made in the 25 objects observed down to rms noise levels of roughly 0.6 mJy in 150 kHz channels. The OH megamaser sample includes OH emission of all observed types: narrow and broad, physically compact and extended, variable and quiescent, and from simple single lines to multicomponent complexes to lines with high-velocity wings. Our null result indicates that, for the widest possible range of OH megamaser environments, methanol masing does not scale with OH from Galactic masers to megamasers. These observations, however, are not sensitive enough to rule out methanol masing that scales with star formation from Galactic compact H II regions to starbursts associated with major mergers. This and previous work suggest that OH megamasers do not represent large ensembles of individual masers associated with star-forming regions. Maser models combined with observational constraints on the physical settings of OH megamasers indicate that 6.7 GHz methanol megamasers will not be detected by this survey if Tdust < 100 K or if n ≤ nOH.

Continuum and spectral line observations of the OH Megamaser galaxy Arp 220

We present MERLIN observations of the continuum (both 1.6 and 5 GHz) and OH maser emission towards Arp220. the correct spatial configuration of the various componnents of the galaxy is revealed. In the eastern component the masers are shown to be generally coincident with the larger scale continuum emission; in the west, the masers and continuum do not generally arise from the same location. A velocity gradient (0.32+/-0.03km/s/pc) is found in the eastern nuclear region in MERLIN scales; this gradient is three times smaller than seen in OH and implies that the OH gas lies inside the HI. A re-analysis of previously presented global VLBI data (Lonsdale et al. 1998) reveals a very high velocity gradient (18.67+/-0.12km/s/pc) in one component, possibly the site of a heavily obscured AGN.

IR properties of H2O megamaser galaxies, pumping mechanisms, and central sources

The IR-properties of all the host galaxies which exhibit H2O megamaser emission have been studied in this paper. The most striking feature is the anticorrelation of the log[S(60)/S(100)] vs. log[S(12)/S(25)] and log[S(25)/S(60)] vs. log[S(12)/S(25)], and the correlation of log[S(60)/S(100)] vs. log[S(25)/S(60)]. These anticorrelations and the correlation in the flux density ratios can be explained by the coexistence of large and very small dust particles. The relationship between the luminosity of the H2O megamaser and the infrared luminosity vs. the flux density ratio of S(60)/S(100), S(25)/S(60), and S(12)/S(25) have been studied. The correlation of the luminosity vs. S(60)/S(100) and the luminosity vs. S(25)/S(60), and the anticorrelation of the lumonosity vs. S(12)/S(25) are obtained, respectively. The pumping mechanism of the H2O megamaser is discussed according to the these results. The characteristics of the central sources are also studied, according to these relationships.

Global VLBI Observations of the Compact OH Megamaser Emission from III Zw 35 and IRAS 17208−0014

We have performed global VLBI observations of the OH megamaser galaxies III Zw 35 and IRAS 17208-0014. We detect strong and compact 1667 MHz OH emission from each galaxy, but, apart from one weak detection of a single 1665 MHz OH feature in III Zw 35, no 1665, 1720 MHz, or continuum emission are detected, which indicates that they occur on size scales greater than 01. We surmise that the OH emission consists of two components. One is diffuse, has unsaturated masers pumped by far-infrared radiation, and is readily explained by the classical OH megamaser model. The second is compact, consists of saturated masers, is responsible for up to 65% of the 1667 MHz flux density, is not associated with any compact continuum emission, and may be pumped by a combination of collisional and radiative processes. One component in III Zw 35 exhibits a well-defined velocity gradient of 32±4 km s-1 pc-1 along a 5.5 pc line of masers. This indicates strong rotation of a molecular cloud with an enclosed mass density of ~6×104 M☉ pc-3.

Spectral energy distribution of OH megamaser galaxies

The properties of OH megamaser galaxies are analyzed. Using the linear dependence of LOHon LFIRand the luminosity function for IR galaxies, the expected number of megamasers is estimated. From observational data at many frequencies (from radio waves to x rays), the spectral energy distributions (SEDs) of 16 objects have been plotted and studied. The SEDs of megamasers have the same form from the radio to the x ray range. Considerable emission is observed in the 3 µm range, which evidently indicates the presence of red giants and supergiants in these objects. Possible reasons for the departure of the slope of the dependence of LOHon LFIRfrom unity are considered. The assumption that collisional pumping may play an important role in the inversion of ground levels of the OH molecule and the saturated gain mechanism in megamasers is confirmed.

Optical Classification of Megamaser Galaxies

We have obtained spectroscopic observations of the nuclear regions of 42 galaxies known to harbor strong OH masers. These megamaser galaxies represent a subsample of FIR (ultra)luminous galaxies, which typically have FIR luminosities in excess of 1011 L☉. The primary goal of this study is to investigate the nuclear activity sources of OH megamaser galaxies. We are able to classify the nuclear emission-line of all but one of our sample, and we find that this class of galaxies is dominated by active galactic nuclei (AGNs), although starburst galaxies do make up an appreciable fraction of the megamasers as well. Fully 45% of the megamasers exhibit Seyfert or LINER spectra, predominantly of Seyfert 2 type, although two galaxies with broad lines are observed. This observation is consistent with the current unification models for the two types of Seyfert activity, since the assumed geometry necessary to detect a megamaser places the Seyfert nucleus behind a high column density of molecular gas (i.e., the molecular torus). Starburst-nucleus galaxies comprise 32.5% of our sample, while 22.5% are classified as composite nuclear spectra (CSN) sources, showing evidence of both AGN and starburst activity. A number of objects show unusual emission-line ratios, not surprising for a group of galaxies that are known a priori to possess substantial absorbing material along the line of sight to their nuclei. Our results are compared to previous studies of FIR-selected galaxy samples, as well as to radio-continuum observations of these galaxies. The activity classification obtained from the radio data disagrees with the optical classifications in roughly 25% of the sources; we discuss possible explanations for these discrepancies.

Properties of OH Megamaser Galaxies

AbstractAn analysis of a sample of OH megamaser galaxies is presented. It is shown that the dependence of OH luminosity on FIR (far infrared) luminosity is not quadratic, as previously assumed, but closer to linear. Using a luminosity function of the luminous infrared galaxies, as well as linear relationship between OH and FIR luminosities the expected number of OH megamaser galaxies has been estimated. Spectral energy distributions (SED) of 16 megamaser galaxies have been constructed using multiwavelength (from radio to X-ray) data. The SED of megamasers look closely similar from radio to X-ray. It is shown that the maser amplification coefficient depends both on the OH main line to 60 micron ratio and the main line to 2.2 micron ratio. The OH main lines ratio (f1667/f1665) decreases, while the flux density at 10 micron is increasing.

A Study of the Spectrum of the OH Megamaser in III Zw 35

III Zw 35 is an OH megamaser galaxy which is of great interest. In this paper, the spectrum has been fitted and the position map has been studied. A new model of multiple and distinct rotating and expanding rings in a thin disk is proposed in this paper.

OH Zeeman measurements of the magnetic fields in four megamaser galaxies

OH Zeeman measurements of the magnetic fields in four megamaser galaxies

Compact OH megamaser and probable quasar activity in the galaxy Arp 220

Arp 220 is the prototype far-infrared ultraluminous galaxy, and the origin of its luminosity—a burst of massive star formation or a quasar obscured by a layer of dense gas and dust—has been the subject of much debate. It also contains the prototypical OH megamaser—an extremely luminous version of masers (microwave lasers) commonly found in our own galaxy. It has been thought that the dense gas in the inner few hundred parsecs of megamaser galaxies acts as a low-gain masing screen, pumped by the far-infrared radiation, which amplifies background continuum emission from the nuclear regions. Here we show, using new very-long-baseline interferometry observations, that the OH line peak in Arp 220 originates in a structure ≤1 pc across, position-ally aligned with a weak continuum feature, and that most of the emission originates on scales of ≤10 pc. These results imply that the maser is physically 10–100 times smaller than previously thought, strongly suggesting that much of the far-infrared radia-tion from Arp 220 arises in a very small region, possibly a dense molecular torus, surrounding a quasar nucleus.

Velocity Field of Extragalactic OH Megamaser Clouds

As it has very strong and abnormal radiation, the external OH megamaser attracts many people. A lot of work has been done in searching for extragalactic OH megamaser and some observations of VLA-A, MERLIN and VLBI were conducted for the extragalactic OH megamaser galaxies which had been observed with single-antenna, e. g.

New Data on the Peculiar Galaxy MRK 273

AbstractOn the basis of direct UBV and spectral observations at Tautenburg (DDR) 2m and Special Observatory (USSR) 6m telescopes respectively the colorimetric and spectral investigations of the megamaser galaxy MRK 273 are carried out. It is seen that: MRK 273 is in a physical group of galaxies, which contains at least five members. Two bright central condensations of MRK 273 are Seyfert nuclei. The area of the main body of MRK 273 which contains both Seyfert nuclei and from which comes out a straight tail, is redder than the remaining part of the galaxy. The tail has a pronounced blue color and most probably radiates in [OIII] λ5007 line. Observed radio continuum, OH and HI absorption features are related to bright “a” nucleus of galaxy. We come to the conclusion that MRK 273 which is the member of the group of the galaxies is itself a close system of two objects with AGNs. The tail, with radiation being of thermal origin, probably is the result of the interaction of these galaxies.

Megamasers in Young Active Galactic Nuclei

Megamaser emission provides new insights into the physics of active galactic nuclei. The megamaser phenomenon is consistent with a low-gain amplification model, where inverted foreground molecules amplify the radio continuum from the nucleus. The molecular gas seen in emission in the megamaser galaxies is located between 50 and 300 parsecs from the nucleus covering part of a possible NLR. Megamasers have been found for the molecules OH, H2CO and H2O. However, only OH megamasers form a clearly identifiable group of galaxies. They occur in prominent FIR galaxies and the FIR radiation field serves as a pumping agent for the OH molecules (Baan 1988). As a result only the ground state lines of OH are in emission, while the lines from excited states are in absorption (see Henkel, Güsten and Baan 1987).

The infrared color evolution of active nuclei

view Abstract Citations (14) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Infrared Color Evolution of Active Nuclei Baan, Willem A. Abstract The far-infrared color evolution is studied for galaxies with a nuclear starburst or an AGN. The nuclear source heats the surrounding dust to an effective blackbody temperature (T_d_ = 50-100 K). The color and luminosity evolution for such galaxies is simulated by letting the central heating source and the resulting warm dust emission (the primary source) decay exponentially in combination with a slower decaying secondary IR emission source. Secondary spectral components can be nonthermal or (hot or cold) thermal in nature and may be associated with the nuclear activity or with the rest of the galaxy. The evolving far-infrared (FIR) galaxy traverses the FIR color diagrams in a rather systematic fashion, and an FIR galaxy can be modeled very effectively with an appropriate mixture of primary and secondary luminosity contributions. The secondary components must have an initial strength of 0.1-0.005 relative to the primary source. Superluminous FIR sources with dominant nuclear sources lie at the start of the simulated evolutionary tracks in the color-color diagrams. While these sources evolve across the color diagram they will reveal more of their nuclear characteristics and eventually they may appear to the observer as normal Seyferts or quasars. The group of powerful FIR sources also incorporates the OH megamaser galaxies. A luminosity function is constructed for the family of nuclear FIR sources. A single distribution of nuclear FIR sources can account for the observed luminosity function at high L_IR_. Another distribution of nonnuclear sources is required to explain the low-luminosity end. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/166508 Bibcode: 1988ApJ...330..743B Keywords: Active Galactic Nuclei; Color-Color Diagram; Infrared Sources (Astronomy); Seyfert Galaxies; Far Infrared Radiation; Infrared Spectra; Interstellar Matter; Luminosity; Starburst Galaxies; Astrophysics; GALAXIES: NUCLEI; INFRARED: SOURCES; INTERSTELLAR: GRAINS full text sources ADS | data products SIMBAD (10) NED (6)

The megamaser galaxy Markarian 273. II - VLA observations of the neutral hydrogen absorption

The high-resolution A-array of the VLA was used to observe the wide neutral hydrogen absorption in the OH megamaser galaxy Mrk 273. The nuclear continuum of this galaxy is extended at 21 cm; Ulvestadt and Wilson (1984) find a double structure at 6 cm where the stronger component is resolved into a triple at 2 cm. The H I absorption is marginally resolved both spatially and spectrally and different features can be identified. These features are distinguishable as basically Gaussian components of the absorption but are probably not independent; several of these may form a rotating disk with a velocity gradient of 1.89 km/s per parsec. Assuming a typical rotational velocity of about 200 km/s, the radius of this disk would be R = 106 pc and the total internal mass can be estimated at M = 10 to the 9th solar masses. These parameters, when compared with the same values of other extragalactic H I absorption disks, are not highly unusual and are, possibly, quite believable.

OH Megamasers and Active Galactic Nuclei

OH megamasers are believed to be active galaxies in which a substantial fraction of the OH gas in the disk of the galaxy is stimulated by the intense far-infrared flux from the active nucleus. The result is that the galactic disk acts as a maser amplifier, producing in the OH line an amplified image of the radio continuum source in the nucleus. Megamasers promise to be powerful tools for the study of active galaxies, provided we can determine what it is that turns an active galaxy into a megamaser. Here I examine the archetypal megamaser galaxy Arp220 and ask the question: what makes it different from other active galaxies?

Widespread strong methanol masers near H II regions

view Abstract Citations (57) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Widespread Strong Methanol Masers near H II Regions Norris, R. P. ; Caswell, J. L. ; Gardner, F. F. ; Wellington, K. J. Abstract A strong (up to 1000 Jy) methanol maser transition has recently been discovered by Batrla et al. (1987). Here a search of southern sources for masers in this transition is reported, with the aim of establishing how common the masers are, where they might be found, and the extent to which their observation might be hindered by interference. Methanol masers were found in 25 of the 106 star-formation regions searched, predominantly those with associated OH masers. A number of other types of object were searched, including OH/IR stars and OH/H2O megamaser galaxies, but no methanol masers were detected in any of these. Publication: The Astrophysical Journal Pub Date: October 1987 DOI: 10.1086/185024 Bibcode: 1987ApJ...321L.159N Keywords: H Ii Regions; Interstellar Masers; Maser Outputs; Methyl Alcohol; Molecular Gases; Stellar Evolution; Absorption Spectra; Acetaldehyde; Hydrocarbons; Molecular Clouds; Population Inversion; Astrophysics; INTERSTELLAR: MOLECULES; MASERS; NEBULAE: H II REGIONS full text sources ADS | data products SIMBAD (34) NED (9)

ZW 15107 + 0724 and the family of OH megamasers

view Abstract Citations (30) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS ZW 15107+0724 and the Family of OH Megamasers Baan, Willem A. ; Henkel, Christian ; Haschick, Aubrey D. Abstract The galaxy Zw 15107 + 0724 exhibits broad H I absorption at its systematic velocity of 3902 km/s and emission in the two main ground-state transitions of OH. The isotropic luminosity of the 1667 MHz OH emission line is 10.8 solar, which makes it the weakest megamaser yet found. The optical depth of the OH line is approximately -0.37. An assessment of the infrared properties of OH megamasers indicates that these sources have an approximately thermal IR spectrum with a temperature between 50 and 90 K. The OH absorbing galaxies, which have an edge-on molecular disk as do the megamaser galaxies, do not distinguish themselves significantly from a much larger sample of strong infrared sources. Megamaser galaxies appear to be a very early phase of Seyfert 2 or H II nuclear activity, when much dust is still present close to the nucleus. Publication: The Astrophysical Journal Pub Date: September 1987 DOI: 10.1086/165531 Bibcode: 1987ApJ...320..154B Keywords: Electron Transitions; Emission Spectra; Ground State; H I Regions; Line Spectra; Masers; Hydroxyl Compounds; Infrared Lasers; Molecular Gases; Radiation Distribution; Radio Sources (Astronomy); Seyfert Galaxies; Astrophysics; GALAXIES: INDIVIDUAL ALPHANUMERIC: ZW 15107; 0724; GALAXIES: SEYFERT; MASERS full text sources ADS | data products NED (18) SIMBAD (14)

A new OH megamaser galaxy: IRAS 11506–3851

A new megamaser galaxy has been discovered as part of an OH survey of selected IRAS galaxies. This increases the number of known megamaser galaxies to seven, and extends the range of their infrared luminosity and colour temperature. The new megamaser differs from the others in that it appears optically as a spiral galaxy with a bright core, although the megamaser emission itself indicates that this core must contain an active nucleus. Both the infrared luminosity and the 60/100 K colour temperature are below those of any other OH megamaser galaxies, but the OH/infrared luminosity ratio is close to the median value, lending support to the suggested relationship between OH and infrared luminosities.

Formaldehyde absorption and maser emisson in galaxies

A sensitive search for the 1(10)-1(11)(6.2 cm) H2CO transition toward eight galaxies with prominent H I absorption and OH absorption or emission has resulted in the detection of three weak absorption lines (NGC 660, NGC 3079, and NGC 3628) and, in addition, of H2CO emission toward the OH megamaser galaxy IC 4553 (= Arp 220). This feature is the first extragalactic H2CO maser, and is at least 7 orders of magnitudes more powerful than the two known Galactic maser sources. The maser is likely due to amplification of the strong nonthermal radiation field from IC 4553 by foreground material with inverted level populations. In terms of a radiative transfer model, it is suggested that strong pumping between the J = 2 levels (at 14.5 GHz) causes, via the J = 2-1 millimeter transition, a population inversion in the ground-state doublet. Although the inversion processes are different for these molecules, the scenario for this maser emission is very similar to that proposed for the extragalactic OH and H2O megamasers. 37 references.