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Title: HOST GALAXIES OF X-SHAPED RADIO SOURCES

Abstract

Most radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, active galaxies that emit much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies has an “X”-or winged-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being a realignment of the black hole within the AGN and the second positing that the radio jets are expanding into an asymmetric medium, causing backflow and producing secondary wings. By analyzing radio host galaxy shapes, the distribution of the stellar mass is compared to the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN. Results show elliptical host galaxies with an orthogonal offset between the semi-major axis ofmore » the host galaxy and the secondary radio wings, which lends support to the hydrodynamical model. However, results also show circular host galaxies with radio wings, making the realignment scenario a more likely model to describe the formation of these X-shaped radio sources.« less

Authors:
;
Publication Date:
Research Org.:
DOESC (USDOE Office of Science (SC) (United States))
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1052052
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Undergraduate Research; Journal Volume: 7
Country of Publication:
United States
Language:
English

Citation Formats

Springmann, A., and Cheung, C. HOST GALAXIES OF X-SHAPED RADIO SOURCES. United States: N. p., 2007. Web.
Springmann, A., & Cheung, C. HOST GALAXIES OF X-SHAPED RADIO SOURCES. United States.
Springmann, A., and Cheung, C. Mon . "HOST GALAXIES OF X-SHAPED RADIO SOURCES". United States. doi:. https://www.osti.gov/servlets/purl/1052052.
@article{osti_1052052,
title = {HOST GALAXIES OF X-SHAPED RADIO SOURCES},
author = {Springmann, A. and Cheung, C.},
abstractNote = {Most radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, active galaxies that emit much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies has an “X”-or winged-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being a realignment of the black hole within the AGN and the second positing that the radio jets are expanding into an asymmetric medium, causing backflow and producing secondary wings. By analyzing radio host galaxy shapes, the distribution of the stellar mass is compared to the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN. Results show elliptical host galaxies with an orthogonal offset between the semi-major axis of the host galaxy and the secondary radio wings, which lends support to the hydrodynamical model. However, results also show circular host galaxies with radio wings, making the realignment scenario a more likely model to describe the formation of these X-shaped radio sources.},
doi = {},
journal = {Journal of Undergraduate Research},
number = ,
volume = 7,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The majority of radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, the active galaxies emitting much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies have an ''X''-shaped morphology: in these, two pairsmore » of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being through the merger of a binary supermassive black hole system and the second being that the radio jets are expanding into an asymmetric medium. By analyzing radio host galaxy shapes, we probe the distribution of the stellar mass to compare the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN.« less
  • Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. Here, we present radio images of 52 of these sources that have been made from archival Very Large Array data with resolution of about 1″. Fifty-one of the 52 were observed at 1.4 GHz, 7 were observed at 1.4 and 5 GHz, and 1 was observed only at 5 GHz. We also present overlays of the Sloan Digital Sky Survey red images for 48 of the sources, and DSS II overlays for the remainder. Optical counterpartsmore » have been identified for most sources, but there remain a few empty fields. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% of sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories. The implications of this result for the gravitational wave background are discussed in Roberts et al.« less
  • We present new and archival Chandra X-ray Observatory observations of X-shaped radio galaxies (XRGs) within z {approx} 0.1 alongside a comparison sample of normal double-lobed FR I and II radio galaxies. By fitting elliptical distributions to the observed diffuse hot X-ray emitting atmospheres (either the interstellar or intragroup medium), we find that the ellipticity and the position angle of the hot gas follow that of the stellar light distribution for radio galaxy hosts in general. Moreover, compared to the control sample, we find a strong tendency for X-shaped morphology to be associated with wings directed along the minor axis ofmore » the hot gas distribution. Taken at face value, this result favors the hydrodynamic backflow models for the formation of XRGs which naturally explain the geometry; the merger-induced rapid reorientation models make no obvious prediction about orientation.« less
  • We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared (IR) wavebands. We study a sample of 585 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We select AGNs with observations in the radio at 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays from the Chandra XBooetes Survey, and mid-IR from the Spitzer IRAC Shallow Survey. The radio, X-ray, and IR AGN samplesmore » show only modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios, for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3-10 h {sup -1} Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red sequence galaxies, are strongly clustered (with M {sub halo} {approx} 3 x 10{sup 13} h {sup -1} M {sub sun}), and have very low Eddington ratios {lambda} {approx}< 10{sup -3}; (2) X-ray-selected AGNs are preferentially found in galaxies that lie in the 'green valley' of color-magnitude space and are clustered similar to the typical AGES galaxies (M {sub halo} {approx} 10{sup 13} h {sup -1} M {sub sun}), with 10{sup -3} {approx}< {lambda} {approx}< 1; (3) IR AGNs reside in slightly bluer, slightly less luminous galaxies than X-ray AGNs, are weakly clustered (M {sub halo} {approx}< 10{sup 12} h {sup -1} M {sub sun}), and have {lambda}>10{sup -2}. We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a 'quasar' phase and the growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a critical mass between {approx}10{sup 12} and 10{sup 13} M {sub sun}. After this event, star formation ceases and AGN accretion shifts from radiatively efficient (optical- and IR-bright) to radiatively inefficient (optically faint, radio-bright) modes.« less
  • Nuclear starbursts may contribute to the obscuration of active galactic nuclei (AGNs). The predicted star formation rates (SFRs) are modest, and, for the obscured AGNs that form the X-ray background at z < 1, the associated faint radio emission lies just beyond the sensitivity limits of the deepest surveys. Here, we search for this level of star formation by studying a sample of 359 X-ray-selected AGNs at z < 1 from the Cosmic Evolution Survey field that are not detected by current radio surveys. The AGNs are separated into bins based on redshift, X-ray luminosity, obscuration, and mid-infrared characteristics. Anmore » estimate of the AGN contribution to the radio flux density is subtracted from each radio image, and the images are then stacked to uncover any residual faint radio flux density. All of the bins containing 24 {mu}m detected AGNs are detected with a signal-to-noise >3{sigma} in the stacked radio images. In contrast, AGNs not detected at 24 {mu}m are not detected in the resulting stacked radio images. This result provides strong evidence that the stacked radio signals are likely associated with star formation. The estimated SFRs derived from the radio stacks range from 3 M{sub Sun} yr{sup -1} to 29 M{sub Sun} yr{sup -1}. Although it is not possible to associate the radio emission with a specific region of the host galaxies, these results are consistent with the predictions of nuclear starburst disks in AGN host galaxies.« less