scholarly journals Radio continuum properties of OH megamaser galaxies

2021 ◽  
Author(s):  
Yu V Sotnikova ◽  
Wu Zhongzu ◽  
T V Mufakharov ◽  
A G Mikhailov ◽  
M G Mingaliev ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Spectral Index ◽  
Control Sample ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Radio Continuum ◽  
Ultraluminous Infrared Galaxy ◽  
Two Samples ◽  
Tight Correlation ◽  
And Control

Abstract We present a study of the radio continuum properties of two luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample (74 objects) and the control sample (128 objects) without detected maser emission. We carried out pilot observations for 140 objects with the radio telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019–2021. The OHM sample has two times more flat-spectrum sources (32 per cent) than the control sample. Steep radio spectra prevail in both samples. The median spectral index at 4.7 GHz α4.7 = −0.59 for the OHM sample, and α4.7 = −0.71 for the non-OHM galaxies. We confirm a tight correlation of the far-infrared (FIR) and radio luminosities for the OHM sample. We found correlations between isotropic OH line luminosity LOH and the spectral index α4.7 (ρ=0.26, p-val.=0.04) and between LOH and radio luminosity P1.4 (ρ=0.35, p-val.=0.005). Reviewing subsamples of masers powered by active galactic nuclei and star formation revealed insignificant differences for their FIR and radio properties. Nonetheless, AGN-powered galaxies exhibit larger scatter in a range of parameters and their standard deviations. The similarities in the radio and FIR properties in the two samples are presumably caused by the presence of a significant amount of AGN sources in both samples (47 and 30 per cent in the OHM and control samples) and/or possibly by the presence of undetected OH emission sources in the control sample.

scholarly journals OH Megamasers and Active Galactic Nuclei

1988 ◽  
Vol 129 ◽  
pp. 261-262
Author(s):  
R.P. Norris
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Disk ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Active Galaxies ◽  
Radio Continuum ◽  
Substantial Fraction ◽  
Continuum Source ◽  
Maser Amplifier ◽  
The Galaxy

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?

scholarly journals What Powers Ultra-Luminous IRAS Galaxies?

1996 ◽  
Vol 175 ◽  
pp. 215-216
Author(s):  
R.B. Partridge ◽  
J. Marr ◽  
T. Crawford ◽  
M. Strauss
Keyword(s):  
Active Galactic Nuclei ◽  
Thermal Emission ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Radio Flux ◽  
Very Large Array ◽  
Radio Wavelength ◽  
Tight Correlation ◽  
Galaxies Active

I report here centimeter–wavelength observations carried out at the Very Large Array (VLA) to help resolve two questions. First, what is the source of the far infrared (FIR) emission in infrared-luminous IRAS galaxies, active nuclei or more widely distributed star formation? And what physics underlies the tight correlation (Helou et al., 1985) between FIR and radio flux? To test potential answers to these questions, we believe it is important to study the most luminous IRAS galaxies. We selected 39 for study from the ultraluminous catalog of Strauss et al.(1990 and 1992). All sources had FIR luminosity ≥ 1011.4 L⊙. Radio wavelength observations of these systems provide several advantages. First, in the radio there is no obscuration, so we can “see” the active galactic nuclei, if present. Radio spectral indices can distinguish between synchrotron and thermal emission. And finally, observations at the VLA provide sub–kpc resolution. We observed these sources with the VLA in its C configuration. At 1460 MHz, the effective resolution was ≃ 15″; and ≃ 4″ at 4860 MHz. We made follow-up observations on 24 sources in the A configuration with resolution at 4860 MHz of ≃ 0″.5 (or 300–800 h–1 pc for these sources).

scholarly journals The Southern 2MASS Active Galactic Nuclei Survey: Spectroscopic Follow-up with Six Degree Field

2010 ◽  
Vol 27 (3) ◽  
pp. 302-320 ◽  
Author(s):  
Frank J. Masci ◽  
Roc M. Cutri ◽  
Paul J. Francis ◽  
Brant O. Nelson ◽  
John P. Huchra ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Type I ◽  
Galactic Latitude ◽  
Stellar Objects ◽  
Identification Rate ◽  
Near Ir ◽  
The Uk ◽  
Probable Type

AbstractThe Two Micron All-Sky Survey (2MASS) has provided a uniform photometric catalog to search for previously unknown red active galactic nuclei (AGN) and Quasi-Stellar Objects (QSOs).We have extended the search to the southern equatorial sky by obtaining spectra for 1182 AGN candidates using the six degree field (6dF) multifibre spectrograph on the UK Schmidt Telescope. These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey. The candidates were selected using a single color cut of J – Ks > 2 to Ks ≲ 15.5 and a galactic latitude of lbl > 30°. 432 spectra were of sufficient quality to enable a reliable classification. 116 sources (∼27%) were securely classified as type I AGN, 20 as probable type I AGN, and 57 as probable type II AGN. Most of them span the redshift range 0.05 < z < 0.5 and only 8 (∼6%) were previously identified as AGN or QSOs. Our selection leads to a significantly higher AGN identification rate amongst local galaxies (>20%) than in any previous (mostly blue-selected) galaxy survey. A small fraction of the type I AGN could have their optical colors reddened by optically thin dust with AV < 2 mag relative to optically selected QSOs. A handful show evidence of excess far-infrared (IR) emission. The equivalent width (EW) and color distributions of the type I and II AGN are consistent with AGN unified models. In particular, the EW of the [Oiii] emission line weakly correlates with optical–near-IR color in each class of AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the optical properties of the 2MASS red AGN are not dramatically different from those of optically-selected QSOs. Our near-IR selection appears to detect the most near-IR luminous QSOs in the local universe to z≃0.6 and provides incentive to extend the search to deeper near-IR surveys.

scholarly journals 6.8. A multi wavelength study of the circumnuclear region of NGC 1365

1998 ◽  
Vol 184 ◽  
pp. 277-278
Author(s):  
H. Kristen ◽  
Aa. Sandqvist ◽  
P.O. Lindblad
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Nuclear Region ◽  
High Excitation ◽  
Multi Wavelength ◽  
Optical Wavelengths ◽  
Barred Spiral Galaxy ◽  
Seyfert Nucleus ◽  
Ngc 1365

The nuclear region of the supergiant barred spiral galaxy NGC 1365 contains bright “hot spots”, as seen at optical wavelengths, as well as a number of non-thermal radio continuum sources, some of which remain unresolved at 0.25” × 0.10” resolution (Sandqvist et al. 1995, A&A 295, 585).The distribution of [OIII] λ5007 emission from the nuclear region supports the scenario of an [OIII] cone emanating from the Seyfert nucleus. The velocity field of the high excitation gas in the cone has been modeled by Hjelm & Lindblad (1996, A&A 305, 727) in terms of an accelerated bipolar conical outflow. Such conical or biconical high-excitation emission-line structures extending from the position of the nucleus are found in several active galactic nuclei.

scholarly journals Radio properties of the OH megamaser galaxy IRAS 02524+2046

2020 ◽  
Vol 638 ◽  
pp. A78
Author(s):  
Hao Peng ◽  
Zhongzu Wu ◽  
Bo Zhang ◽  
Yongjun Chen ◽  
Xingwu Zheng ◽  
...  
Keyword(s):  
Flux Density ◽  
Spectral Index ◽  
Line Emission ◽  
Far Infrared ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Starburst Galaxy ◽  
Radio Flux ◽  
Vlbi Observations

We present results from VLBI observations of continuum and OH line emission in IRAS 02524+2046 as well as arcsecond-scale radio properties of this galaxy using VLA archive data. We found that there is no significant detection of radio continuum emission from VLBI observations. The arcsecond-scale radio images of this source show no clear extended emission. The total radio flux density at L and C bands are approximately 2.9 mJy and 1.0 mJy, respectively, which indicates a steep radio spectral index between the two bands. A steep spectral index, low brightness temperature, and high q-ratio (i.e., the far-infrared to the radio flux density), which are three critical indicators in the classification of radio activity in the nuclei of galaxies, are all consistent with the classification of this source as a starburst galaxy from its optical spectrum. The high-resolution line profile reveals that we detected both the 1665 MHz and 1667 MHz OH maser lines, which show two and three clear components, respectively. The channel maps show that the maser emission are distributed in a region of ∼210 pc × 90 pc. The detected maser components in different regions indicate similar double spectral features, which might be evidence that this galaxy is at a stage of major merger as seen from the optical morphology.

scholarly journals AKARI Infrared Views of AGNs

2009 ◽  
Vol 5 (S267) ◽  
pp. 129-129
Author(s):  
Shinki Oyabu
Keyword(s):  
Infrared Spectroscopy ◽  
Active Galactic Nuclei ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Sky Survey

AbstractThe Japanese infrared satellite AKARI has unique capabilities for near-infrared spectroscopy and an all-sky survey in the mid- and far-infrared. We present the recent results on active galactic nuclei that use the unique capabilities of AKARI.

scholarly journals Mid- to far-infrared properties of star-forming galaxies and active galactic nuclei

2013 ◽  
Vol 558 ◽  
pp. A136 ◽  
Author(s):  
G. E. Magdis ◽  
D. Rigopoulou ◽  
G. Helou ◽  
D. Farrah ◽  
P. Hurley ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Far Infrared ◽  
Star Forming

scholarly journals Radiation pressure confinement – V. The predicted free–free absorption and emission in active galactic nuclei

2021 ◽  
Vol 508 (1) ◽  
pp. 680-697
Author(s):  
Alexei Baskin ◽  
Ari Laor
Keyword(s):  
Active Galactic Nuclei ◽  
Radiation Pressure ◽  
Galactic Nuclei ◽  
Radio Continuum ◽  
Absorption Frequency ◽  
Absorption And Emission ◽  
Scale Free ◽  
Spatially Resolved ◽  
Ngc 1068 ◽  
5 Ghz

ABSTRACT The effect of radiation pressure compression (RPC) on ionized gas in active galactic nuclei (AGNs) likely sets the photoionized gas density structure. The photoionized gas free–free absorption and emission are therefore uniquely set by the incident ionizing flux. We use the photoionization code cloudy RPC model results to derive the expected relations between the free–free emission and absorption properties and the distance from the AGN centre, for a given AGN luminosity. The free–free absorption frequency of RPC gas is predicted to increase from ∼100 MHz on the kpc scale to ∼100 GHz on the sub-pc scale, consistent with observations of spatially resolved free–free absorption. The free–free emission at 5 GHz is predicted to yield a radio loudness (R) of ∼0.03, below the typical observed values of R ∼ 0.1–1 in radio-quiet AGNs. However, the flat free–free radio continuum may become dominant above 100 GHz. The suggested detection of optically thin free–free emission in NGC 1068, on the sub-pc torus scale, is excluded as the brightness temperature is too high for optically thin free–free emission. However, excess emission observed with Atacama Large Millimeter/submillimeter Array (ALMA) above 150 GHz in NGC 1068 is consistent with the predicted free–free emission from gas just outside the broad-line region, a region that overlaps the hot dust disc resolved with GRAVITY. Extended ∼100 pc-scale free–free emission is also likely present in NGC 1068. Future sub-mm observation of radio-quiet AGNs with ALMA may allow to image the free–free emission of warm photoionized gas in AGNs down to the 30 mas scale, including highly absorbed AGNs.

scholarly journals MID- AND FAR-INFRARED PROPERTIES OF LOCAL ACTIVE GALACTIC NUCLEI

2012 ◽  
Vol 27 (4) ◽  
pp. 275-279
Author(s):  
Kohei Ichikawa ◽  
Yoshihiro Ueda ◽  
Yuichi Terashima ◽  
Shinki Oyabu ◽  
Poshak Gandhi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Far Infrared

scholarly journals Identifying quasars with astrometric and mid-infrared methods from APOP and ALLWISE

2018 ◽  
Vol 618 ◽  
pp. A144 ◽  
Author(s):  
Sufen Guo ◽  
Zhaoxiang Qi ◽  
Shilong Liao ◽  
Zihuang Cao ◽  
Mario G. Lattanzi ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Proper Motion ◽  
Reference Frames ◽  
Galactic Nuclei ◽  
Linear Boundary ◽  
Mid Infrared ◽  
Two Samples ◽  
Infrared Methods

Context. Quasars are spatially stationary, and they are essential objects in astrometry when defining reference frames. However, the census of quasars is far from complete. Mid-infared colors can be used to find quasar candidates because active galactic nuclei (AGNs) show a peculiar appearance in mid-infrared color, but these methods are incapable of separating quasars from AGNs. Aims. The aim of our study is to use astrometric and mid-infrared methods to select quasars and get a reliable quasar candidates catalog. Methods. We used a near-zero proper motion criterion in conjuction with WISE [W1–W2] color to select quasar candidates. The [W1–W2] color criterion is defined by the linear boundary of two samples: LAMOST DR5 quasars, which serve as the quasar sample, and LAMOST DR5 stars and galaxies, which serve as the non-quasar sample. The contamination and completeness are evaluated. Results. We present a catalog of 662 753 quasar candidates, with a completeness of about 75% and a reliability of 77.2%.

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