The host galaxy/AGN connection in nearby early-type galaxies. Is there a miniature radio-galaxy in every "core" galaxy?

NASA Astrophysics Data System (ADS)

Balmaverde, B.; Capetti, A.

2006-02-01

This is the second of a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. We selected two samples with 5 GHz VLA radio flux measurements down to 1 mJy, reaching levels of radio luminosity as low as 1036 erg s-1. In Paper I we presented a study of the surface brightness profiles for the 65 objects with available archival HST images out of the 116 radio-detected galaxies. We classified early-type galaxies into "core" and "power-law" galaxies, discriminating on the basis of the slope of their nuclear brightness profiles, following the Nukers scheme. Here we focus on the 29 core galaxies (hereafter CoreG). We used HST and Chandra data to isolate their optical and X-ray nuclear emission. The CoreG invariably host radio-loud nuclei, with an average radio-loudness parameter of Log R = L5 {GHz} / LB ˜ 3.6. The optical and X-ray nuclear luminosities correlate with the radio-core power, smoothly extending the analogous correlations already found for low luminosity radio-galaxies (LLRG) toward even lower power, by a factor of ˜ 1000, covering a combined range of 6 orders of magnitude. This supports the interpretation of a common non-thermal origin of the nuclear emission also for CoreG. The luminosities of the nuclear sources, most likely dominated by jet emission, set firm upper limits, as low as L/L_Edd ˜ 10-9 in both the optical and X-ray band, on any emission from the accretion process. The similarity of CoreG and LLRG when considering the distributions host galaxies luminosities and black hole masses, as well as of the surface brightness profiles, indicates that they are drawn from the same population of early-type galaxies. LLRG represent only the tip of the iceberg associated with (relatively) high activity levels, with CoreG forming the bulk of the population. We do not find any relationship between radio-power and black hole mass. A minimum black hole

THE ABUNDANCE OF X-SHAPED RADIO SOURCES. I. VLA SURVEY OF 52 SOURCES WITH OFF-AXIS DISTORTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roberts, David H.; Cohen, Jake P.; Lu, Jing

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

Radio emission from an ultraluminous x-ray source.

PubMed

Kaaret, Philip; Corbel, Stephane; Prestwich, Andrea H; Zezas, Andreas

2003-01-17

The physical nature of ultraluminous x-ray sources is uncertain. Stellar-mass black holes with beamed radiation and intermediate black holes with isotropic radiation are two plausible explanations. We discovered radio emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC 5408. The x-ray, radio, and optical fluxes as well as the x-ray spectral shape are consistent with beamed relativistic jet emission from an accreting stellar black hole. If confirmed, this would suggest that the ultraluminous x-ray sources may be stellar-mass rather than intermediate-mass black holes. However, interpretation of the source as a jet-producing intermediate-mass black hole cannot be ruled out at this time.

Radio Sources Associated with Intermediate X-ray Luminosity Objects in Merging Galaxy Systems

NASA Technical Reports Server (NTRS)

Neff, S. G.; Ulvestad, J. S.; Oegerle, William R. (Technical Monitor)

2002-01-01

We present new, high-resolution 6, 3.6, and 2 cm radio images of a time-ordered sequence of merging galaxy systems. The new data have a resolution of less than 100pc and a sensitivity comparable to a few x Cas A. We detect compact radio sources in all systems, generally embedded in more diffuse radio emission at the longer wavelengths. Several of the compact radio sources are coincident with compact Intermediate-luminosity X-ray Objects (IXOs) in these systems, and many more are within the 3$/sigma$ Chandra position errors for other IXOs. The fraction of radio identifications and the nature of the radio sources changes as a function of merger stage. These data suggest that the IXOs are associated with complexes of supernova remnants, and therefore with star formation that has occurred within the last $/sim$10$circumflex7$ yr, but are not located in HII regions where copious star formation is occurring currently.

Jet-ISM Interaction in the Radio Galaxy 3C 293: Jet-driven Shocks Heat ISM to Power X-Ray and Molecular H2 Emission

NASA Astrophysics Data System (ADS)

Lanz, L.; Ogle, P. M.; Evans, D.; Appleton, P. N.; Guillard, P.; Emonts, B.

2015-03-01

We present a 70 ks Chandra observation of the radio galaxy 3C 293. This galaxy belongs to the class of molecular hydrogen emission galaxies (MOHEGs) that have very luminous emission from warm molecular hydrogen. In radio galaxies, the molecular gas appears to be heated by jet-driven shocks, but exactly how this mechanism works is still poorly understood. With Chandra, we observe X-ray emission from the jets within the host galaxy and along the 100 kpc radio jets. We model the X-ray spectra of the nucleus, the inner jets, and the X-ray features along the extended radio jets. Both the nucleus and the inner jets show evidence of 107 K shock-heated gas. The kinetic power of the jets is more than sufficient to heat the X-ray emitting gas within the host galaxy. The thermal X-ray and warm H2 luminosities of 3C 293 are similar, indicating similar masses of X-ray hot gas and warm molecular gas. This is consistent with a picture where both derive from a multiphase, shocked interstellar medium (ISM). We find that radio-loud MOHEGs that are not brightest cluster galaxies (BCGs), like 3C 293, typically have LH2/LX˜ 1 and MH2/MX˜ 1, whereas MOHEGs that are BCGs have LH2/LX˜ 0.01 and MH2/MX˜ 0.01. The more massive, virialized, hot atmosphere in BCGs overwhelms any direct X-ray emission from current jet-ISM interaction. On the other hand, LH2/LX˜ 1 in the Spiderweb BCG at z = 2, which resides in an unvirialized protocluster and hosts a powerful radio source. Over time, jet-ISM interaction may contribute to the establishment of a hot atmosphere in BCGs and other massive elliptical galaxies.

Chandra Finds Most Distant X-ray Galaxy Cluster

NASA Astrophysics Data System (ADS)

2001-02-01

The most distant X-ray cluster of galaxies yet has been found by astronomers using NASA’s Chandra X-ray Observatory. Approximately 10 billion light years from Earth, the cluster 3C294 is 40 percent farther than the next most distant X-ray galaxy cluster. The existence of such a distant galaxy cluster is important for understanding how the universe evolved. "Distant objects like 3C294 provide snapshots to how these galaxy clusters looked billions of years ago," said Andrew Fabian of the Institute of Astronomy, Cambridge, England and lead author of the paper accepted for publication in the Monthly Notices of Britain’s Royal Astronomical Society. "These latest results help us better understand what the universe was like when it was only 20 percent of its current age." Chandra’s image reveals an hourglass-shaped region of X-ray emission centered on the previously known central radio source. This X-ray emission extends outward from the central galaxy for at least 300,000 light years and shows that the known radio source is in the central galaxy of a massive cluster. Scientists have long suspected that distant radio-emitting galaxies like 3C294 are part of larger groups of galaxies known as "clusters." However, radio data provides astronomers with only a partial picture of these distant objects. Confirmation of the existence of clusters at great distances - and, hence, at early stages of the universe - requires information from other wavelengths. Optical observations can be used to pinpoint individual galaxies, but X-ray data are needed to detect the hot gas that fills the space within the cluster. "Galaxy clusters are the largest gravitationally bound structures in the universe," said Fabian. "We do not expect to find many massive objects, such as the 3C294 cluster, in early times because structure is thought to grow from small scales to large scales." The vast clouds of hot gas that envelope galaxies in clusters are thought to be heated by collapse toward the

The BL LAC phenomenon: X-ray observations of transition objects and determination of the x-ray spectrum of a complete sample of flat-spectrum radio sources

NASA Technical Reports Server (NTRS)

Worrall, Diana M.

1994-01-01

This report summarizes the activities related to two ROSAT investigations: (1) x-ray properties of radio galaxies thought to contain BL Lac type nuclei; and (2) x-ray spectra of a complete sample of flat-spectrum radio sources. The following papers describing the research are provided as attachments: Multiple X-ray Emission Components in Low Power Radio Galaxies; New X-ray Results on Radio Galaxies; Analysis Techniques for a Multiwavelength Study of Radio Galaxies; Separation of X-ray Emission Components in Radio Galaxies; X-ray Emission in Powerful Radio Galaxies and Quasars; Extended and Compact X-ray Emission in Powerful Radio Galaxies; and X-ray Spectra of a Complete Sample of Extragalactic Core-dominated Radio Sources.

GIANT LOBES OF CENTAURUS A RADIO GALAXY OBSERVED WITH THE SUZAKU X-RAY SATELLITE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stawarz, L.; Gandhi, P.; Takahashi, T.

2013-03-20

We report on Suzaku observations of selected regions within the southern giant lobe of the radio galaxy Centaurus A. In our analysis we focus on distinct X-ray features detected with the X-ray Imaging Spectrometer within the range 0.5-10 keV, some of which are likely associated with fine structure of the lobe revealed by recent high-quality radio intensity and polarization maps. With the available photon statistics, we find that the spectral properties of the detected X-ray features are equally consistent with thermal emission from hot gas with temperatures kT > 1 keV, or with a power-law radiation continuum characterized by photonmore » indices {Gamma} {approx} 2.0 {+-} 0.5. However, the plasma parameters implied by these different models favor a synchrotron origin for the analyzed X-ray spots, indicating that a very efficient acceleration of electrons up to {approx}> 10 TeV energies is taking place within the giant structure of Centaurus A, albeit only in isolated and compact regions associated with extended and highly polarized radio filaments. We also present a detailed analysis of the diffuse X-ray emission filling the whole field of view of the instrument, resulting in a tentative detection of a soft excess component best fitted by a thermal model with a temperature of kT {approx} 0.5 keV. The exact origin of the observed excess remains uncertain, although energetic considerations point to thermal gas filling the bulk of the volume of the lobe and mixed with the non-thermal plasma, rather than to the alternative scenario involving a condensation of the hot intergalactic medium around the edges of the expanding radio structure. If correct, this would be the first detection of the thermal content of the extended lobes of a radio galaxy in X-rays. The corresponding number density of the thermal gas in such a case is n{sub g} {approx} 10{sup -4} cm{sup -3}, while its pressure appears to be in almost exact equipartition with the volume-averaged non

The IRAS galaxy 0421+040P06: An active spiral (?) galaxy with extended radio lobes

NASA Technical Reports Server (NTRS)

Beichman, C. A.; Wynn-Williams, C. G.; Lonsdale, C. J.; Persson, S. E.; Heasley, J. N.; Miley, G. K.; Soifer, B. T.; Neugebauer, G.; Becklin, E. E.; Houck, J. R.

1984-01-01

The infrared bright galaxy 0421+040P06 detected by IRAS at 25 and 60 microns was studied at optical, infrared, and radio wavelength. It is a luminous galaxy with apparent spiral structure emitting 4 x 10 to the 37th power from far-infrared to optical wavelengths. Optical spectroscopy reveals a Seyfert 2 emission line spectrum, making 0421+040P06 the first active galaxy selected from an unbiased infrared survey of galaxies. The fact that this galaxy shows a flatter energy distribution with more 25 micron emission than other galaxies in the infrared sample may be related to the presence of an intense active nucleus. The radio observations reveal the presence of a non-thermal source that, at 6 cm, shows a prominent double lobed structure 20 to 30 kpc in size extending beyond the optical confines of the galaxy. The radio source is three to ten times larger than structures previously seen in spiral galaxies.

FRESH ACTIVITY IN OLD SYSTEMS: RADIO AGNs IN FOSSIL GROUPS OF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hess, Kelley M.; Wilcots, Eric M.; Hartwick, Victoria L., E-mail: hess@ast.uct.ac.za, E-mail: ewilcots@astro.wisc.edu, E-mail: vhartwick@wisc.edu

2012-08-15

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from Sloan Digital Sky Survey Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L{sub 1.4GHz} > 10{sup 23} W Hz{sup -1}) active galactic nucleusmore » (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray-selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.« less

The difference between radio-loud and radio-quiet active galaxies

NASA Astrophysics Data System (ADS)

Wilson, A. S.; Colbert, E. J. M.

1995-01-01

The recent development of unified theories of active galactic nuclei (AGNs) has indicated that there are two physically distinct classes of these objects--radio-loud and radio-quiet. Despite differences, the (probable) thermal emissions from the AGNs (continua and lines from X-ray to infrared wavelengths) are quite similar to the two classes of object. We argue that this last result suggests that the black hole masses and mass accretion rates in the two classes are not greatly different, and that the difference between the classes is associated with the spin of the black hole. We assume that the normal process of accretion through a disk does not lead to rapidly spinning holes and propose that galaxies (e.g., spirals) which have not suffered a recent major merger event contain nonrotating or only slowly rotating black holes. When two such galaxies merge, the two black holes are known to form a binary and we assume that they eventually coalesce. The ratio of the number of radio-loud to radio-quiet AGNs at a given thermal (e.g., optical) luminosity is determined by the galaxy merger rate. Comparisons between the predicted and observed radio luminosity functions constrain the efficiencies with which jet power is extracted from the spinning hole and radio emission is produced by the jet.

Probing the Curious Case of a Galaxy Cluster Merger in Abell 115 with High-fidelity Chandra X-Ray Temperature and Radio Maps

NASA Astrophysics Data System (ADS)

Hallman, Eric J.; Alden, Brian; Rapetti, David; Datta, Abhirup; Burns, Jack O.

2018-05-01

We present results from an X-ray and radio study of the merging galaxy cluster Abell 115. We use the full set of five Chandra observations taken of A115 to date (360 ks total integration) to construct high-fidelity temperature and surface brightness maps. We also examine radio data from the Very Large Array at 1.5 GHz and the Giant Metrewave Radio Telescope at 0.6 GHz. We propose that the high X-ray spectral temperature between the subclusters results from the interaction of the bow shocks driven into the intracluster medium by the motion of the subclusters relative to one another. We have identified morphologically similar scenarios in Enzo numerical N-body/hydrodynamic simulations of galaxy clusters in a cosmological context. In addition, the giant radio relic feature in A115, with an arc-like structure and a relatively flat spectral index, is likely consistent with other shock-associated giant radio relics seen in other massive galaxy clusters. We suggest a dynamical scenario that is consistent with the structure of the X-ray gas, the hot region between the clusters, and the radio relic feature.

Chandra Observations of Dying Radio Sources in Galaxy Clusters

NASA Technical Reports Server (NTRS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-01-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions. We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from

The Mpc-scale radio source associated with the GPS galaxy B1144+352

NASA Astrophysics Data System (ADS)

Schoenmakers, A. P.; de Bruyn, A. G.; Röttgering, H. J. A.; van der Laan, H.

1999-01-01

We present the results of new observations of the enigmatic radio source B1144+352 with the WSRT at 1.4 GHz. This source is hosted by an m_r = 14.3 +/- 0.1 galaxy at a redshift of z=0.063 +/- 0.002 and is one of the lowest redshift Gigahertz Peaked Spectrum (GPS) sources known. It has been known to show radio structure on pc-scale in the radio core and on 20-60 kpc-scale in two jet-like radio structures. The WENSS and NVSS surveys have now revealed faint extended radio structures on an even much larger scale. We have investiga ted these large-scale radio components with new 1.4-GHz WSRT observations. Our radio data indicate that the eastern radio structure has a leading hotspot and we conclude that this structure is a radio lobe originating in the galaxy hosting the GPS source. The western radio structure contains two separate radio sources which are superposed on the sky. The first is a low-power radio source, hosted by a m_R = 15.3 +/- 0.5 galaxy at a similar redshift (z=0.065+/-0.001) to the GPS host galaxy; the second is an extended radio lobe, which we believe is associated with the GPS host galaxy and which contains an elongated tail. The total projected linear size of the extended radio structure associated with B1144+352 is ~ 1.2 Mpc. The core of B1144+353 is a known variable radio source: its flux density at 1.4 GHz has increased continuously between 1974 and 1994. We have measured the flux density of the core in our WSRT observations (epoch 1997.7) and find a value of 541+/-10 mJy This implies that its flux density has decreased by ~ 70 mJy between 1994 and 1997. Further, we have retrieved unpublished archival ROSAT HRI data of B1144+352. The source has been detected and appears to be slightly extended in X-rays. We find a luminosity of (1.26 +/- 0.15)*E(43) erg s(-1) between 0.1 and 2.4 keV, assumin that the X-ray emission is due to an AGN with a powerlaw spectrum with photon index 1.8, or (0.95 +/- 0.11) *E(43) erg s(-1) if it is due to thermal

Big Bangs in Galaxy Clusters: Using X-ray Temperature Maps to Trace Merger Histories in Clusters with Radio Halos/Relics

NASA Astrophysics Data System (ADS)

Burns, Jack O.; Datta, Abhirup; Hallman, Eric J.

2016-06-01

Galaxy clusters are assembled through large and small mergers which are the most energetic events ("bangs") since the Big Bang. Cluster mergers "stir" the intracluster medium (ICM) creating shocks and turbulence which are illuminated by ~Mpc-sized radio features called relics and halos. These shocks heat the ICM and are detected in x-rays via thermal emission. Disturbed morphologies in x-ray surface brightness and temperatures are direct evidence for cluster mergers. In the radio, relics (in the outskirts of the clusters) and halos (located near the cluster core) are also clear signposts of recent mergers. Our recent ENZO cosmological simulations suggest that around a merger event, radio emission peaks very sharply (and briefly) while the x-ray emission rises and decays slowly. Hence, a sample of galaxy clusters that shows both luminous x-ray emission and radio relics/halos are good candidates for very recent mergers. We are in the early stages of analyzing a unique sample of 48 galaxy clusters with (i) known radio relics and/or halos and (ii) significant archival x-ray observations (>50 ksec) from Chandra and/or XMM. We have developed a new x-ray data analysis pipeline, implemented on parallel processor supercomputers, to create x-ray surface brightness, high fidelity temperature, and pressure maps of these clusters in order to study merging activity. The temperature maps are made using three different map-making techniques: Weighted Voronoi Tessellation, Adaptive Circular Binning, and Contour Binning. In this talk, we will show preliminary results for several clusters, including Abell 2744 and the Bullet cluster. This work is supported by NASA ADAP grant NNX15AE17G.

An Unlikely Radio Halo in the Low X-Ray Luminosity Galaxy Cluster RXCJ1514.9-1523

NASA Technical Reports Server (NTRS)

Marketvitch, M.; ZuHone, J. A.; Lee, D.; Giacintucci, S.; Dallacasa, D.; Venturi, T.; Brunetti, G.; Cassano, R.; Markevitch, M.; Athreya, R. M.

2011-01-01

Aims: We report the discovery of a giant radio halo in the galaxy cluster RXCJ1514,9-1523 at z=0.22 with a relatively low X-ray luminosity, L(sub X) (0.1-2.4kev) approx. 7 x 10(exp 44) ergs/s. Methods: This faint, diffuse radio source is detected with the Giant Meterwave Radio Telescope at 327 MHz. The source is barely detected at 1.4 GHz in a NVSS pointing that we have reanalyzed. Results: The integrated radio spectrum of the halo is quite steep, with a slope alpha = 1.6 between 327 MHz and 1.4 GHz. While giant radio halos are common in more X-ray luminous cluster mergers, there is a less than 10% probability to detect a halo in systems with L(sub X) < 8 x 10(exp 44) ergs/s. The detection of a new giant halo in this borderline luminosity regime can be particularly useful for discriminating between the competing theories for the origin of ultrarelativistic electrons in clusters. Furthermore, if our steep radio spectral index is confirmed by future deeper radio observations, this cluster would provide another example of the very rare, new class of ultra-steep spectrum radio halos, predicted by the model in which the cluster cosmic ray electrons are produced by turbulent reacceleration.

Centaurus A galaxy, type EO peculiar elliptical, also radio source

NASA Technical Reports Server (NTRS)

2002-01-01

Centaurus A galaxy, type EO peculiar elliptical, also radio source. CTIO 4-meter telescope, 1975. NGC 5128, a Type EO peculiar elliptical galaxy in the constellation Centaurus. This galaxy is one of the most luminous and massive galaxies known and is a strong source of both radio and X-ray radiation. Current theories suggest that the nucleus is experiencing giant explosions involving millions of stars and that the dark band across the galactic disk is material being ejected outward. Cerro Toloto 4-meter telescope photo. Photo credit: National Optical Astronomy Observatories

H I absorption in nearby compact radio galaxies

NASA Astrophysics Data System (ADS)

Glowacki, M.; Allison, J. R.; Sadler, E. M.; Moss, V. A.; Curran, S. J.; Musaeva, A.; Deng, C.; Parry, R.; Sligo, M. C.

2017-05-01

H I absorption studies yield information on both active galactic nucleus (AGN) feeding and feedback processes. This AGN activity interacts with the neutral gas in compact radio sources, which are believed to represent the young or recently re-triggered AGN population. We present the results of a survey for H I absorption in a sample of 66 compact radio sources at 0.040 < z < 0.096 with the Australia Telescope Compact Array. In total, we obtained seven detections, five of which are new, with a large range of peak optical depths (3-87 per cent). Of the detections, 71 per cent exhibit asymmetric, broad (ΔvFWHM > 100 km s-1) features, indicative of disturbed gas kinematics. Such broad, shallow and offset features are also found within low-excitation radio galaxies which is attributed to disturbed circumnuclear gas, consistent with early-type galaxies typically devoid of a gas-rich disc. Comparing mid-infrared colours of our galaxies with H I detections indicates that narrow and deep absorption features are preferentially found in late-type and high-excitation radio galaxies in our sample. These features are attributed to gas in galactic discs. By combining XMM-Newton archival data with 21-cm data, we find support that absorbed X-ray sources may be good tracers of H I content within the host galaxy. This sample extends previous H I surveys in compact radio galaxies to lower radio luminosities and provides a basis for future work exploring the higher redshift universe.

The Radio Luminosity Function and Galaxy Evolution in the Coma Cluster

NASA Technical Reports Server (NTRS)

Miller, Neal A.; Hornschemeier, Ann E.; Mabasher, Bahram; Brudgesm Terrry J.; Hudson, Michael J.; Marzke, Ronald O.; Smith, Russell J.

2008-01-01

We investigate the radio luminosity function and radio source population for two fields within the Coma cluster of galaxies, with the fields centered on the cluster core and southwest infall region and each covering about half a square degree. Using VLA data with a typical rms sensitivity of 28 (mu)Jy per 4.4" beam, we identify 249 radio sources with optical counterparts brighter than r = 22 (equivalent to M(sub r) = -13 for cluster member galaxies). Comprehensive optical spectroscopy identifies 38 of these as members of the Coma cluster, evenly split between sources powered by an active nucleus and sources powered by active star formation. The radio-detected star-forming galaxies are restricted to radio luminosities between about 10(exp 21) and 10(exp 22) W/Hz, an interesting result given that star formation dominates field radio luminosity functions below about 10(exp 23) W/Hz. The majority of the radio-detected star-forming galaxies have characteristics of starbursts, including high specific star formation rates and optical spectra with strong emission lines. In conjunction with prior studies on post-starburst galaxies within the Coma cluster, this is consistent with a picture in which late-type galaxies entering Coma undergo a starburst prior to a rapid cessation of star formation. Optically bright elliptical galaxies (Mr less than or equals -20.5) make the largest contribution to the radio luminosity function at both the high (> approx. 3x10(exp 22) W/Hz) and low (< approx. 10(exp 21) W/Hz) ends. Through a stacking analysis of these optically-bright ellipticals we find that they continue to harbor radio sources down to luminosities as faint as 3x10(exp 19) W/Hz. However, contrary to published results for the Virgo cluster we find no evidence for the existence of a population of optically faint (M(sub r) approx. equals -14) dwarf ellipticals hosting strong radio AGN.

Chandra observations of dying radio sources in galaxy clusters

NASA Astrophysics Data System (ADS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-12-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims: We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods: We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results: The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions: We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from

Chandra X-Ray Observatory Image of the Distant Galaxy, 3C294

NASA Technical Reports Server (NTRS)

2000-01-01

This most distant x-ray cluster of galaxies yet has been found by astronomers using Chandra X-ray Observatory (CXO). Approximately 10 billion light-years from Earth, the cluster 3C294 is 40 percent farther than the next most distant x-ray galaxy cluster. The existence of such a faraway cluster is important for understanding how the universe evolved. CXO's image reveals an hourglass-shaped region of x-ray emissions centered on the previously known central radio source (seen in this image as the blue central object) that extends outward for 60,000 light- years. The vast clouds of hot gas that surround such galaxies in clusters are thought to be heated by collapse toward the center of the cluster. Until CXO, x-ray telescopes have not had the needed sensitivity to identify such distant clusters of galaxies. Galaxy clusters are the largest gravitationally bound structures in the universe. The intensity of the x-rays in this CXO image of 3C294 is shown as red for low energy x-rays, green for intermediate, and blue for the most energetic x-rays. (Photo credit: NASA/loA/A. Fabian et al)

3C 220.3: A Radio Galaxy Lensing a Submillimeter Galaxy

NASA Astrophysics Data System (ADS)

Haas, Martin; Leipski, Christian; Barthel, Peter; Wilkes, Belinda J.; Vegetti, Simona; Bussmann, R. Shane; Willner, S. P.; Westhues, Christian; Ashby, Matthew L. N.; Chini, Rolf; Clements, David L.; Fassnacht, Christopher D.; Horesh, Assaf; Klaas, Ulrich; Koopmans, Léon V. E.; Kuraszkiewicz, Joanna; Lagattuta, David J.; Meisenheimer, Klaus; Stern, Daniel; Wylezalek, Dominika

2014-07-01

Herschel Space Observatory photometry and extensive multiwavelength follow-up have revealed that the powerful radio galaxy (PRG) 3C 220.3 at z = 0.685 acts as a gravitational lens for a background submillimeter galaxy (SMG) at z = 2.221. At an observed wavelength of 1 mm, the SMG is lensed into three distinct images. In the observed near infrared, these images are connected by an arc of ~1''.8 radius forming an Einstein half-ring centered near the radio galaxy. In visible light, only the arc is apparent. 3C 220.3 is the only known instance of strong galaxy-scale lensing by a PRG not located in a galaxy cluster and therefore it offers the potential to probe the dark matter content of the radio galaxy host. Lens modeling rejects a single lens, but two lenses centered on the radio galaxy host A and a companion B, separated by 1''.5, provide a fit consistent with all data and reveal faint candidates for the predicted fourth and fifth images. The model does not require an extended common dark matter halo, consistent with the absence of extended bright X-ray emission on our Chandra image. The projected dark matter fractions within the Einstein radii of A (1''.02) and B (0''.61) are about 0.4 ± 0.3 and 0.55 ± 0.3. The mass to i-band light ratios of A and B, M/Li ˜ 8 +/- 4 M⊙ L⊙ -1, appear comparable to those of radio-quiet lensing galaxies at the same redshift in the CfA-Arizona Space Telescope LEns Survey, Lenses Structure and Dynamics, and Strong Lenses in the Legacy Survey samples. The lensed SMG is extremely bright with observed f(250 μm) = 440 mJy owing to a magnification factor μ ~ 10. The SMG spectrum shows luminous, narrow C IV λ1549 Å emission, revealing that the SMG houses a hidden quasar in addition to a violent starburst. Multicolor image reconstruction of the SMG indicates a bipolar morphology of the emitted ultraviolet (UV) light suggestive of cones through which UV light escapes a dust-enshrouded nucleus.

Connection Between X-Ray Dips and Superluminal Ejections in the Radio Galaxy 3C 120

NASA Technical Reports Server (NTRS)

Aller, Margo F.

2005-01-01

This work represents a part of a long-term study of the X-ray flux variability of 3C 120 and its relation to flux and structural changes in the radio jet of this galaxy. The grant included fiinding for the rediiction and analysis of data obt,ained during the time pwiod of Rossi XTE cycle 8 (March 1, 2003-February 29, 2004). Prior RXTE observations, combined with single dish monitoring at centimeter wavelengths and 43 GHz mapping (monthly until February 1999 and bimonthly thereafter) of the inner jet with the VLBA, had identified the presence of X-ray dips in the light curves and X-ray spectral hardening 4 weeks prior to the ejection of new VLBI components in the radio jet. This suggested a picture in which the radio jet was fed by accretion events near the black hole. The specific goals of the cycle 8 observations were to better define the relation between the X-ray dips and the radio events using higher sampling, to include more events in the correlation and hence improve the statistics, to look for a possible optical X-ray connection, and to search for quasi periodicities on timescales of 1-3 days. In cycle 8 this project was awarded time for 4 pointings weekly with RXTE.

On the Interaction of the PKS B1358-113 Radio Galaxy with the A1836 Cluster

DOE PAGES

Stawarz, L.; Szostek, A.; Cheung, C. C.; ...

2014-10-07

In this study, we present the analysis of multifrequency data gathered for the Fanaroff-Riley type-II (FR II) radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy in the center of A1836. The galaxy harbors one of the most massive black holes known to date, and our analysis of the acquired optical data reveals that this black hole is only weakly active, with a mass accretion ratemore » $$\\dot{M}_{\\rm acc} \\sim 2 \\times 10^{-4} \\, \\dot{M}_{\\rm Edd} \\sim 0.02 \\, M_{\\odot }$$ yr –1. Based on analysis of new Chandra and XMM-Newton X-ray observations and archival radio data, and assuming the well-established model for the evolution of FR II radio galaxies, we derive the preferred range for the jet kinetic luminosity L j ~ (1-6) × 10 –3 L Edd ~ (0.5-3) × 10 45 erg s –1. This is above the values implied by various scaling relations proposed for radio sources in galaxy clusters, being instead very close to the maximum jet power allowed for the given accretion rate. We also constrain the radio source lifetime as τ j ~ 40-70 Myr, meaning the total amount of deposited jet energy E tot ~ (2-8) × 10 60 erg. We argue that approximately half of this energy goes into shock heating of the surrounding thermal gas, and the remaining 50% is deposited into the internal energy of the jet cavity. The detailed analysis of the X-ray data provides indication for the presence of a bow shock driven by the expanding radio lobes into the A1836 cluster environment. We derive the corresponding shock Mach number in the range $$\\mathcal {M}_{\\rm sh} \\sim 2\\hbox{--}4$$, which is one of the highest claimed for clusters or groups of galaxies. This, together with the recently growing evidence that powerful FR II radio galaxies may not be uncommon in the centers of clusters at higher redshifts, supports the idea that jet-induced shock heating may indeed play an important role in shaping the properties of clusters, galaxy groups, and galaxies in formation. In this

Suzaku observations of γ-ray bright radio galaxies: Origin of the x-ray emission and broadband modeling

DOE PAGES

Fukazawa, Yasushi; Finke, Justin; Stawarz, Łukasz; ...

2014-12-24

Here, we performed a systematic X-ray study of eight nearby γ-ray bright radio galaxies with Suzaku in order to understand the origins of their X-ray emissions. The Suzaku spectra for five of those have been presented previously, while the remaining three (M87, PKS 0625–354, and 3C 78) are presented here for the first time. Based on the Fe-K line strength, X-ray variability, and X-ray power-law photon indices, and using additional information on the [O III] line emission, we argue for a jet origin of the observed X-ray emission in these three sources. We also analyzed five years of Fermi Largemore » Area Telescope (LAT) GeV gamma-ray data on PKS 0625–354 and 3C 78 to understand these sources within the blazar paradigm. We found significant γ-ray variability in the former object. Overall, we note that the Suzaku spectra for both PKS 0625–354 and 3C 78 are rather soft, while the LAT spectra are unusually hard when compared with other γ-ray detected low-power (FR I) radio galaxies. We demonstrate that the constructed broadband spectral energy distributions of PKS 0625–354 and 3C 78 are well described by a one-zone synchrotron/synchrotron self-Compton model. The results of the modeling indicate lower bulk Lorentz factors compared to those typically found in other BL Lacertae (BL Lac) objects, but consistent with the values inferred from modeling other LAT-detected FR I radio galaxies. Interestingly, the modeling also implies very high peak (~10 16 Hz) synchrotron frequencies in the two analyzed sources, contrary to previously suggested scenarios for Fanaroff-Riley (FR) type I/BL Lac unification. Finally, we discuss the implications of our findings in the context of the FR I/BL Lac unification schemes.« less

Particle content, radio-galaxy morphology, and jet power: all radio-loud AGN are not equal

NASA Astrophysics Data System (ADS)

Croston, J. H.; Ineson, J.; Hardcastle, M. J.

2018-05-01

Ongoing and future radio surveys aim to trace the evolution of black hole growth and feedback from active galactic nuclei (AGNs) throughout cosmic time; however, there remain major uncertainties in translating radio luminosity functions into a reliable assessment of the energy input as a function of galaxy and/or dark matter halo mass. A crucial and long-standing problem is the composition of the radio-lobe plasma that traces AGN jet activity. In this paper, we carry out a systematic comparison of the plasma conditions in Fanaroff & Riley class I and II radio galaxies to demonstrate conclusively that their internal composition is systematically different. This difference is best explained by the presence of an energetically dominant proton population in the FRI, but not the FRII radio galaxies. We show that, as expected from this systematic difference in particle content, radio morphology also affects the jet-power/radio-luminosity relationship, with FRII radio galaxies having a significantly lower ratio of jet power to radio luminosity than the FRI cluster radio sources used to derive jet-power scaling relations via X-ray cavity measurements. Finally, we also demonstrate conclusively that lobe composition is unconnected to accretion mode (optical excitation class): the internal conditions of low- and high-excitation FRII radio lobes are indistinguishable. We conclude that inferences of population-wide AGN impact require careful assessment of the contribution of different jet subclasses, particularly given the increased diversity of jet evolutionary states expected to be present in deep, low-frequency radio surveys such as the LOFAR Two-Metre Sky Survey.

Very-long-baseline radio interferometry observations of low power radio galaxies.

PubMed Central

Giovannini, G; Cotton, W D; Feretti, L; Lara, L; Venturi, T; Marcaide, J M

1995-01-01

The parsec scale properties of low power radio galaxies are reviewed here, using the available data on 12 Fanaroff-Riley type I galaxies. The most frequent radio structure is an asymmetric parsec-scale morphology--i.e., core and one-sided jet. It is shared by 9 (possibly 10) of the 12 mapped radio galaxies. One (possibly 2) of the other galaxies has a two-sided jet emission. Two sources are known from published data to show a proper motion; we present here evidence for proper motion in two more galaxies. Therefore, in the present sample we have 4 radio galaxies with a measured proper motion. One of these has a very symmetric structure and therefore should be in the plane of the sky. The results discussed here are in agreement with the predictions of the unified scheme models. Moreover, the present data indicate that the parsec scale structure in low and high power radio galaxies is essentially the same. PMID:11607596

Soft X-ray Emission from Large-Scale Galactic Outflows in Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Colbert, E. J. M.; Baum, S.; O'Dea, C.; Veilleux, S.

1998-01-01

Kiloparsec-scale soft X-ray nebulae extend along the galaxy minor axes in several Seyfert galaxies, including NGC 2992, NGC 4388 and NGC 5506. In these three galaxies, the extended X-ray emission observed in ROSAT HRI images has 0.2-2.4 keV X-ray luminosities of 0.4-3.5 x 10(40) erg s(-1) . The X-ray nebulae are roughly co-spatial with the large-scale radio emission, suggesting that both are produced by large-scale galactic outflows. Assuming pressure balance between the radio and X-ray plasmas, the X-ray filling factor is >~ 10(4) times as large as the radio plasma filling factor, suggesting that large-scale outflows in Seyfert galaxies are predominantly winds of thermal X-ray emitting gas. We favor an interpretation in which large-scale outflows originate as AGN-driven jets that entrain and heat gas on kpc scales as they make their way out of the galaxy. AGN- and starburst-driven winds are also possible explanations if the winds are oriented along the rotation axis of the galaxy disk. Since large-scale outflows are present in at least 50 percent of Seyfert galaxies, the soft X-ray emission from the outflowing gas may, in many cases, explain the ``soft excess" X-ray feature observed below 2 keV in X-ray spectra of many Seyfert 2 galaxies.

Diffuse radio emission in the complex merging galaxy cluster Abell2069

NASA Astrophysics Data System (ADS)

Drabent, A.; Hoeft, M.; Pizzo, R. F.; Bonafede, A.; van Weeren, R. J.; Klein, U.

2015-03-01

Context. Galaxy clusters with signs of a recent merger in many cases show extended diffuse radio features. This emission originates from relativistic electrons that suffer synchrotron losses due to the intracluster magnetic field. The mechanisms of particle acceleration and the properties of the magnetic field are still poorly understood. Aims: We search for diffuse radio emission in galaxy clusters. Here, we study the complex galaxy cluster Abell 2069, for which X-ray observations indicate a recent merger. Methods: We investigate the cluster's radio continuum emission by deep Westerbork Synthesis Radio Telescope (WSRT) observations at 346 MHz and Giant Metrewave Radio Telescope (GMRT) observations at 322 MHz. Results: We find an extended diffuse radio feature roughly coinciding with the main component of the cluster. We classify this emission as a radio halo and estimate its lower limit flux density at 25 ± 9 mJy. Moreover, we find a second extended diffuse source located at the cluster's companion and estimate its flux density at 15 ± 2 mJy. We speculate that this is a small halo or a mini-halo. If true, this cluster is the first example of a double-halo in a single galaxy cluster.

A Case for Radio Galaxies as the Sources of IceCube's Astrophysical Neutrino Flux

DOE PAGES

Hooper, Dan

2016-09-01

Here, we present an argument that radio galaxies (active galaxies with mis-aligned jets) are likely to be the primary sources of the high-energy astrophysical neutrinos observed by IceCube. In particular, if the gamma-ray emission observed from radio galaxies is generated through the interactions of cosmic-ray protons with gas, these interactions can also produce a population of neutrinos with a flux and spectral shape similar to that measured by IceCube. We present a simple physical model in which high-energy cosmic rays are confined within the volumes of radio galaxies, where they interact with gas to generate the observed diffuse fluxes ofmore » neutrinos and gamma rays. In addition to simultaneously accounting for the observations of Fermi and IceCube, radio galaxies in this model also represent an attractive class of sources for the highest energy cosmic rays.« less

High–frequency cluster radio galaxies: Luminosity functions and implications for SZE–selected cluster samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Nikhel; Saro, A.; Mohr, J. J.

We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; < z > = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg 2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, whichmore » is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. As a result, allowing for redshift evolution of the form (1 + z) 2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.« less

High–frequency cluster radio galaxies: Luminosity functions and implications for SZE–selected cluster samples

DOE PAGES

Gupta, Nikhel; Saro, A.; Mohr, J. J.; ...

2017-01-15

We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; < z > = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg 2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, whichmore » is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. As a result, allowing for redshift evolution of the form (1 + z) 2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.« less

Radio Selection of the Most Distant Galaxy Clusters

NASA Astrophysics Data System (ADS)

Daddi, E.; Jin, S.; Strazzullo, V.; Sargent, M. T.; Wang, T.; Ferrari, C.; Schinnerer, E.; Smolčić, V.; Calabró, A.; Coogan, R.; Delhaize, J.; Delvecchio, I.; Elbaz, D.; Gobat, R.; Gu, Q.; Liu, D.; Novak, M.; Valentino, F.

2017-09-01

We show that the most distant X-ray-detected cluster known to date, Cl J1001 at {z}{spec}=2.506, hosts a strong overdensity of radio sources. Six of them are individually detected (within 10\\prime\\prime ) in deep 0\\buildrel{\\prime\\prime}\\over{.} 75 resolution VLA 3 GHz imaging, with {S}3{GHz}> 8 μ {Jy}. Of the six, an active galactic nucleus (AGN) likely affects the radio emission in two galaxies, while star formation is the dominant source powering the remaining four. We searched for cluster candidates over the full COSMOS 2 deg2 field using radio-detected 3 GHz sources and looking for peaks in {{{Σ }}}5 density maps. Cl J1001 is the strongest overdensity by far with > 10σ , with a simple {z}{phot}> 1.5 preselection. A cruder photometric rejection of z< 1 radio foregrounds leaves Cl J1001 as the second strongest overdensity, while even using all radio sources Cl J1001 remains among the four strongest projected overdensities. We conclude that there are great prospects for future deep and wide-area radio surveys to discover large samples of the first generation of forming galaxy clusters. In these remarkable structures, widespread star formation and AGN activity of massive galaxy cluster members, residing within the inner cluster core, will ultimately lead to radio continuum as one of the most effective means for their identification, with detection rates expected in the ballpark of 0.1-1 per square degree at z≳ 2.5. Samples of hundreds such high-redshift clusters could potentially constrain cosmological parameters and test cluster and galaxy formation models.

Radio Galaxy Zoo: Machine learning for radio source host galaxy cross-identification

NASA Astrophysics Data System (ADS)

Alger, M. J.; Banfield, J. K.; Ong, C. S.; Rudnick, L.; Wong, O. I.; Wolf, C.; Andernach, H.; Norris, R. P.; Shabala, S. S.

2018-05-01

We consider the problem of determining the host galaxies of radio sources by cross-identification. This has traditionally been done manually, which will be intractable for wide-area radio surveys like the Evolutionary Map of the Universe (EMU). Automated cross-identification will be critical for these future surveys, and machine learning may provide the tools to develop such methods. We apply a standard approach from computer vision to cross-identification, introducing one possible way of automating this problem, and explore the pros and cons of this approach. We apply our method to the 1.4 GHz Australian Telescope Large Area Survey (ATLAS) observations of the Chandra Deep Field South (CDFS) and the ESO Large Area ISO Survey South 1 (ELAIS-S1) fields by cross-identifying them with the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. We train our method with two sets of data: expert cross-identifications of CDFS from the initial ATLAS data release and crowdsourced cross-identifications of CDFS from Radio Galaxy Zoo. We found that a simple strategy of cross-identifying a radio component with the nearest galaxy performs comparably to our more complex methods, though our estimated best-case performance is near 100 per cent. ATLAS contains 87 complex radio sources that have been cross-identified by experts, so there are not enough complex examples to learn how to cross-identify them accurately. Much larger datasets are therefore required for training methods like ours. We also show that training our method on Radio Galaxy Zoo cross-identifications gives comparable results to training on expert cross-identifications, demonstrating the value of crowdsourced training data.

A new method for finding and characterizing galaxy groups via low-frequency radio surveys

NASA Astrophysics Data System (ADS)

Croston, J. H.; Ineson, J.; Hardcastle, M. J.; Mingo, B.

2017-09-01

We describe a new method for identifying and characterizing the thermodynamic state of large samples of evolved galaxy groups at high redshifts using high-resolution, low-frequency radio surveys, such as those that will be carried out with LOFAR and the Square Kilometre Array. We identify a sub-population of morphologically regular powerful [Fanaroff-Riley type II (FR II)] radio galaxies and demonstrate that, for this sub-population, the internal pressure of the radio lobes is a reliable tracer of the external intragroup/intracluster medium (ICM) pressure, and that the assumption of a universal pressure profile for relaxed groups enables the total mass and X-ray luminosity to be estimated. Using a sample of well-studied FR II radio galaxies, we demonstrate that our method enables the estimation of group/cluster X-ray luminosities over three orders of magnitude in luminosity to within a factor of ˜2 from low-frequency radio properties alone. Our method could provide a powerful new tool for building samples of thousands of evolved galaxy groups at z > 1 and characterizing their ICM.

A representative survey of the dynamics and energetics of FR II radio galaxies

NASA Astrophysics Data System (ADS)

Ineson, J.; Croston, J. H.; Hardcastle, M. J.; Mingo, B.

2017-05-01

We report the first large, systematic study of the dynamics and energetics of a representative sample of Fanaroff-Riley type II (FR II) radio galaxies with well-characterized group/cluster environments. We used X-ray inverse-Compton and radio synchrotron measurements to determine the internal radio-lobe conditions, and these were compared with external pressures acting on the lobes, determined from measurements of the thermal X-ray emission of the group/cluster. Consistent with previous work, we found that FR II radio lobes are typically electron dominated by a small factor relative to equipartition, and are overpressured relative to the external medium in their outer parts. These results suggest that there is typically no energetically significant proton population in the lobes of FR II radio galaxies (unlike for FR Is), and so for this population, inverse-Compton modelling provides an accurate way of measuring total energy content and estimating jet power. We estimated the distribution of Mach numbers for the population of expanding radio lobes, finding that at least half of the radio galaxies are currently driving strong shocks into their group/cluster environments. Finally, we determined a jet power-radio luminosity relation for FR II radio galaxies based on our estimates of lobe internal energy and Mach number. The slope and normalization of this relation are consistent with theoretical expectations, given the departure from equipartition and environmental distribution for our sample.

Radio Identifications of UGC Galaxies - Starbursts and Monsters

NASA Astrophysics Data System (ADS)

Condon, J. J.; Broderick, J. J.

1995-11-01

Radio identifications of galaxies in the Uppsala General Catalogue of Galaxies with delta < +82 degrees were made from the Green Bank 1400 MHz sky maps. Every source having peak flux density S(P) >= 150 mJy in the approximately 12 arcmin FWHM map point-source response and position < 5 arcmin in both coordinates from the optical position of any UGC galaxy was considered a candidate identification to ensure that very extended (up to 1 Mpc) and asymmetric sources would not be missed. Maps in the literature or new 1.49 GHz VLA C-array maps made with 18 arcsec FWHM resolution were used to confirm or reject candidate identifications. The maps in this directory include both confirmed identifications and candidates rejected because of confusion or low flux density. For more information on this study, please see the following reference: Condon, J. J., and Broderick, J. J., 1988, AJ, 96, 30. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

Accretion processes of radio galaxies at high energies

NASA Astrophysics Data System (ADS)

de Jong, Sandra

2013-10-01

AGN are the luminous (L>10^42 erg/s) cores of active galaxies, powered by accretion onto the central super massive black hole, either via an accretion disk or via a radiatively inefficient accretion flow. There are still several open questions, for example on the launching of jets, which are present in about 10% of the AGN. Another question appeared with the Fermi/LAT gamma-ray survey, which detected many blazars but also a small group of radio galaxies. Radio galaxies are postulated to be blazars where the observer sees the jet at an angle θ>10 degrees allowing a view of both jet and core, rather than only the jet as is the case with blazars. Radio galaxies are divided into two classes, depending on the radio luminosity of the jets. The Fanaroff-Riley I (FR-I) sources have jets that are bright near the core, where the FR-IIs display extended edge-brightened jets. The FR-I sources are connected to the BL Lacs, which are low-luminosity blazars. FR-II types are thought to be the parent population of the luminous FSRQ, which are also blazars. This thesis presents a study of gamma-ray bright radio galaxies. By analysing X-ray and gamma-ray data in addition to creating broad-band spectral energy distributions (SEDs), we studied two examples of this new class of sources. For the FR-II source 3C 111 we analysed Suzaku/XIS and PIN and INTEGRAL IBIS/ISGRI observations to create a X-ray spectrum. We also used a Swift/BAT spectrum from the 58-month survey. The 0.4-200 keV spectrum of the source shows both thermal, Seyfert-like signatures such as an iron K-α line, and non-thermal jet features. We also analysed gamma-ray data from Fermi/LAT. The gamma-ray and X-ray data are combined with historical radio, infrared and optical observations to build the SED, which can be well represented with a non-thermal jet model. The bolometric luminosity of 3C111 is rather low, and the SED model shows rather a BL Lac type than the expected FSRQ. The next source we studied is the nearby FR

Redshifts of twenty radio galaxies.

NASA Technical Reports Server (NTRS)

Burbidge, E. M.; Strittmatter, P. A.

1972-01-01

Spectroscopic observations and redshifts of 20 radio galaxies obtained with the Lick 120-inch telescope are presented. Ten of the radio galaxies are from the 3C R catalog, and the remainder are from the 4C, 5C, Ohio, and Parkes catalogs. The reported results represent a continuation of Burbidge's (1970) previously published data.

The Biggest Bangs Since the Big Bang: Unveiling Mergers of Galaxy Clusters with Radio Halos/Relics Using X-ray Temperature Maps

NASA Astrophysics Data System (ADS)

Burns, Jack

Galaxy clusters are assembled through large and small mergers which are the most energetic events ( bangs ) since the Big Bang. Cluster mergers stir the ICM creating shocks and turbulence which are illuminated by Mpc-sized radio features called relics and halos. These shocks heat the ICM and are detected in x-rays via thermal emission. Disturbed morphologies in x-ray surface brightness and temperatures are direct evidence for cluster mergers. In the radio, relics (in the outskirts of the clusters) and halos (located near the cluster core) are clear signposts of recent mergers. Our recent cosmological simulations suggest that around a merger event, radio emission peaks very sharply (and briefly) while the x-ray emission rises and decays slowly. Hence, a sample of galaxy clusters that shows both luminous x-ray and radio relics/halos are clear candidates for very recent mergers. We propose to analyze a unique sample of 48 galaxy clusters with (i) known radio relics and/or halos and (ii) significant archival x-ray observations (e 50 ksec) from Chandra and/or XMM. We will use a new x-ray data analysis pipeline, implemented on a parallelprocessor supercomputer, to create x-ray surface brightness, high fidelity temperature, and pressure maps of these clusters in order to study merging activity. In addition, we will use a control sample of clusters from the HIFLUGCS catalog which do not show radio relics/halos or any significant x-ray surface brightness substructure, thus devoid of recent mergers. The temperature maps will be made using 3 different map-making techniques: Weighted Voronoi Tessellation, Adaptive Circular Binning, and Contour Binning. We also plan to use archival Suzaku data for 22 clusters in our sample and study the x-ray temperatures at the outskirts of the clusters. All 48 clusters have archival radio data at d1.4 GHz which will be re-analyzed using advanced algorithms in NRAO s CASA software. We also have new radio data on a subset of these clusters and

Banging Galaxy Clusters: High Fidelity X-ray Temperature and Radio Maps to Probe the Physics of Merging Clusters

NASA Astrophysics Data System (ADS)

Burns, Jack O.; Hallman, Eric J.; Alden, Brian; Datta, Abhirup; Rapetti, David

2017-06-01

We present early results from an X-ray/Radio study of a sample of merging galaxy clusters. Using a novel X-ray pipeline, we have generated high-fidelity temperature maps from existing long-integration Chandra data for a set of clusters including Abell 115, A520, and MACSJ0717.5+3745. Our pipeline, written in python and operating on the NASA ARC high performance supercomputer Pleiades, generates temperature maps with minimal user interaction. This code will be released, with full documentation, on GitHub in beta to the community later this year. We have identified a population of observable shocks in the X-ray data that allow us to characterize the merging activity. In addition, we have compared the X-ray emission and properties to the radio data from observations with the JVLA and GMRT. These merging clusters contain radio relics and/or radio halos in each case. These data products illuminate the merger process, and how the energy of the merger is dissipated into thermal and non-thermal forms. This research was supported by NASA ADAP grant NNX15AE17G.

New Members in the Galaxy Group Around Giant Radio Galaxy DA 240

NASA Astrophysics Data System (ADS)

Chen, Ru-Rong; Peng, Bo; Strom, Richard

2018-05-01

With new spectroscopic observations of group candidates around the giant radio galaxy DA 240, we have identified five new group members, increasing the number to twenty-five. While all the new members are located some distance from the host galaxy, two of them lie in one of the radio lobes, and the rest are found at a distance from the radio components. The new group members reinforce our earlier conclusion that the distribution of the DA 240 group with respect to the radio lobes is unusual among giant radio galaxy host environments.

A CHANDRA-VLA INVESTIGATION OF THE X-RAY CAVITY SYSTEM AND RADIO MINI-HALO IN THE GALAXY CLUSTER RBS 797

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doria, Alberto; Gitti, Myriam; Brighenti, Fabrizio

2012-07-01

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and Very Large Array (VLA) data. RBS 797 (z = 0.35) is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate a higher metallicity along the cavity directions. This is likely due to the active galactic nucleus outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than themore » surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally, we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow, as it nicely follows the trend P{sub radio} versus P{sub CF} predicted by the reacceleration model.« less

Radio/X-ray monitoring of the broad-line radio galaxy 3C 382. High-energy view with XMM-Newtonand NuSTAR

NASA Astrophysics Data System (ADS)

Ursini, F.; Petrucci, P.-O.; Matt, G.; Bianchi, S.; Cappi, M.; Dadina, M.; Grandi, P.; Torresi, E.; Ballantyne, D. R.; De Marco, B.; De Rosa, A.; Giroletti, M.; Malzac, J.; Marinucci, A.; Middei, R.; Ponti, G.; Tortosa, A.

2018-05-01

We present the analysis of five joint XMM-Newton/NuSTARobservations, 20 ks each and separated by 12 days, of the broad-line radio galaxy 3C 382. The data were obtained as part of a campaign performed in September-October 2016 simultaneously with VLBA. The radio data and their relation with the X-ray ones will be discussed in a following paper. The source exhibits a moderate flux variability in the UV/X-ray bands, and a limited spectral variability especially in the soft X-ray band. In agreement with past observations, we find the presence of a warm absorber, an iron Kα line with no associated Compton reflection hump, and a variable soft excess well described by a thermal Comptonization component. The data are consistent with a "two-corona" scenario, in which the UV emission and soft excess are produced by a warm (kT ≃ 0.6 keV), optically thick (τ ≃ 20) corona consistent with being a slab fully covering a nearly passive accretion disc, while the hard X-ray emission is due to a hot corona intercepting roughly 10% of the soft emission. These results are remarkably similar to those generally found in radio-quiet Seyferts, thus suggesting a common accretion mechanism.

Revisiting Scaling Relations for Giant Radio Halos in Galaxy Clusters

NASA Technical Reports Server (NTRS)

Cassano, R.; Ettori, S.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Venturi, T.; Kale, R.; Dolag, K.; Markevitch, Maxim L.

2013-01-01

Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. Correlations between the synchrotron power of radio halos and the thermal properties of the hosting clusters were established in the last decade, including the connection between the presence of a halo and cluster mergers. The X-ray luminosity and redshift-limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. We find that the radio power at 1.4 GHz scales with the cluster X-ray (0.1-2.4 keV) luminosity computed within R(sub 500) as P(sub 1.4) approx. L(2.1+/-0.2) - 500). Our bigger and more homogenous sample confirms that the X-ray luminous (L(sub 500) > 5 × 10(exp 44) erg/s)) clusters branch into two populations-radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. This bimodality remains if we excise cool cores from the X-ray luminosities. We also find that P(sub 1.4) scales with the cluster integrated SZ signal within R(sub 500), measured by Planck, as P(sub 1.4) approx. Y(2.05+/-0.28) - 500), in line with previous findings. However, contrary to previous studies that were limited by incompleteness and small sample size, we find that "SZ-luminous" Y(sub 500) > 6×10(exp -5) Mpc(exp 2) clusters show a bimodal behavior for the presence of radio halos, similar to that in the radio-X-ray diagram. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle acceleration.

Close entrainment of massive molecular gas flows by radio bubbles in the central galaxy of Abell 1795

NASA Astrophysics Data System (ADS)

Russell, H. R.; McNamara, B. R.; Fabian, A. C.; Nulsen, P. E. J.; Combes, F.; Edge, A. C.; Hogan, M. T.; McDonald, M.; Salomé, P.; Tremblay, G.; Vantyghem, A. N.

2017-12-01

We present new ALMA observations tracing the morphology and velocity structure of the molecular gas in the central galaxy of the cluster Abell 1795. The molecular gas lies in two filaments that extend 5-7 kpc to the N and S from the nucleus and project exclusively around the outer edges of two inner radio bubbles. Radio jets launched by the central active galactic nucleus have inflated bubbles filled with relativistic plasma into the hot atmosphere surrounding the central galaxy. The N filament has a smoothly increasing velocity gradient along its length from the central galaxy's systemic velocity at the nucleus to -370 km s^{-1}, the average velocity of the surrounding galaxies, at the furthest extent. The S filament has a similarly smooth but shallower velocity gradient and appears to have partially collapsed in a burst of star formation. The close spatial association with the radio lobes, together with the ordered velocity gradients and narrow velocity dispersions, shows that the molecular filaments are gas flows entrained by the expanding radio bubbles. Assuming a Galactic XCO factor, the total molecular gas mass is 3.2 ± 0.2 × 109 M⊙. More than half lies above the N radio bubble. Lifting the molecular clouds appears to require an infeasibly efficient coupling between the molecular gas and the radio bubble. The energy required also exceeds the mechanical power of the N radio bubble by a factor of 2. Stimulated feedback, where the radio bubbles lift low-entropy X-ray gas that becomes thermally unstable and rapidly cools in situ, provides a plausible model. Multiple generations of radio bubbles are required to lift this substantial gas mass. The close morphological association then indicates that the cold gas either moulds the newly expanding bubbles or is itself pushed aside and shaped as they inflate.

A search for extended radio emission from selected compact galaxy groups

NASA Astrophysics Data System (ADS)

Nikiel-Wroczyński, B.; Urbanik, M.; Soida, M.; Beck, R.; Bomans, D. J.

2017-07-01

Context. Studies on compact galaxy groups have led to the conclusion that a plenitude of phenomena take place in between galaxies that form them. However, radio data on these objects are extremely scarce and not much is known concerning the existence and role of the magnetic field in intergalactic space. Aims: We aim to study a small sample of galaxy groups that look promising as possible sources of intergalactic magnetic fields; for example data from radio surveys suggest that most of the radio emission is due to extended, diffuse structures in and out of the galaxies. Methods: We used the Effelsberg 100 m radio telescope at 4.85 GHz and NRAO VLA Sky Survey (NVSS) data at 1.40 GHz. After subtraction of compact sources we analysed the maps searching for diffuse, intergalactic radio emission. Spectral index and magnetic field properties were derived. Results: Intergalactic magnetic fields exist in groups HCG 15 and HCG 60, whereas there are no signs of them in HCG 68. There are also hints of an intergalactic bridge in HCG 44 at 4.85 GHz. Conclusions: Intergalactic magnetic fields exist in galaxy groups and their energy density may be comparable to the thermal (X-ray) density, suggesting an important role of the magnetic field in the intra-group medium, wherever it is detected.

The inevitable youthfulness of known high-redshift radio galaxies

NASA Astrophysics Data System (ADS)

Blundell, Katherine M.; Rawlings, Steve

1999-05-01

Some galaxies are very luminous in the radio part of the spectrum. These `radio galaxies' have extensive (hundreds of kiloparsecs) lobes of emission powered by plasma jets originating at a central black hole. Some radio galaxies can be seen at very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that, for any model of radio-galaxy evolution in which the luminosity decreases with time after an initial rapid increase (that is, essentially all reasonable models), all observable high-redshift radio galaxies must be seen when the lobes are less than 107 years old. This means that high-redshift radio galaxies can be used as a high-time-resolution probe of evolution in the early Universe. Moreover, this result explains many observed trends of radio-galaxy properties with redshift, without needing to invoke explanations based on cosmology or strong evolution of the surrounding intergalactic medium with cosmic time, thereby avoiding conflict with current theories of structure formation.

Neutralinos and the Origin of Radio Halos in Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Colafrancesco, S.; Mele, B.

2001-11-01

We assume that the supersymmetric lightest neutralino is a good candidate for the cold dark matter in the galaxy halo and explore the possibility to produce extended diffuse radio emission from high-energy electrons arising from the neutralino annihilation in galaxy clusters whose intracluster medium is filled with a large-scale magnetic field. We show that these electrons fit the population of seed relativistic electrons that is postulated in many models for the origin of cluster radio halos. For a uniform magnetic field of ~1-3 μG the population of seed relativistic electrons from neutralino annihilation can fit the radio halo spectra of two well-studied clusters: Coma and 1E 0657-56. In the case of a magnetic field that is radially decreasing from the cluster center, central values ~8 μG (for Coma) and ~50 μG (for 1E 0657-56) are required to fit the data. The radio halo data strongly favor a centrally peaked dark matter density profile (like a Navarro, Frenk, & White [NFW97] density profile). The shape and the frequency extension of the radio halo spectra are connected with the mass and physical composition of the neutralino. A pure gaugino neutralino with mass Mχ>=80 GeV can reasonably fit the radio halo spectra of both Coma and 1E 0657-56. The model we present here provides a number of extra predictions that make it definitely testable. On the one hand, it agrees quite well with the observations that (1) the radio halo is centered on the cluster dynamical center, usually coincident with the center of its X-ray emission; (2) the radio halo surface brightness is similar to the X-ray one; and (3) the monochromatic radio luminosity at 1.4 GHz correlates strongly with the intracluster (IC) gas temperature. On the other hand, the same model predicts that radio halos should be present in every cluster, which is not presently observed, although the predicted radio halo luminosities can change (decrease) by factors of up to ~102-106, depending on the amplitude and

The Spectacular Radio-Near-IR-X-Ray Jet of 3C 111: the X-Ray Emission Mechanism and Jet Kinematics

NASA Technical Reports Server (NTRS)

Clautice, Devon; Perlman, Eric S.; Georganopoulos, Markos; Lister, Matthew L.; Tombesi, Francesco; Cara, Mihai; Marshall, Herman L.; Hogan, Brandon M.; Kazanas, Demos

2016-01-01

Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the subparsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near- IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new, deep Chandra and Hubble Space Telescope (HST) observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray, and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical, and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR, HST, and Chandra will allow us to further constrain the emission mechanisms.

THE SPECTACULAR RADIO-NEAR-IR-X-RAY JET OF 3C 111: THE X-RAY EMISSION MECHANISM AND JET KINEMATICS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clautice, Devon; Perlman, Eric S.; Georganopoulos, Markos

2016-08-01

Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the sub-parsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near-IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new,more » deep Chandra and Hubble Space Telescope ( HST ) observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray, and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical, and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR , HST , and Chandra will allow us to further constrain the emission mechanisms.« less

LOFAR discovery of a 700-kpc remnant radio galaxy at low redshift

NASA Astrophysics Data System (ADS)

Brienza, M.; Godfrey, L.; Morganti, R.; Vilchez, N.; Maddox, N.; Murgia, M.; Orru, E.; Shulevski, A.; Best, P. N.; Brüggen, M.; Harwood, J. J.; Jamrozy, M.; Jarvis, M. J.; Mahony, E. K.; McKean, J.; Röttgering, H. J. A.

2016-01-01

Context. Remnant radio galaxies represent the final dying phase of radio galaxy evolution in which the jets are no longer active. Remnants are rare in flux-limited samples, comprising at most a few percent. As a result of their rarity and because they are difficult to identify, this dying phase remains poorly understood and the luminosity evolution is largely unconstrained. Aims: Here we present the discovery and detailed analysis of a large (700 kpc) remnant radio galaxy with a low surface brightness that has been identified in LOFAR images at 150 MHz. Methods: By combining LOFAR data with new follow-up Westerbork observations and archival data at higher frequencies, we investigated the source morphology and spectral properties from 116 to 4850 MHz. By modelling the radio spectrum, we probed characteristic timescales of the radio activity. Results: The source has a relatively smooth, diffuse, amorphous appearance together with a very weak central compact core that is associated with the host galaxy located at z = 0.051. From our ageing and morphological analysis it is clear that the nuclear engine is currently switched off or, at most, active at a very low power state. We find that the source has remained visible in the remnant phase for about 60 Myr, significantly longer than its active phase of 15 Myr, despite being located outside a cluster. The host galaxy is currently interacting with another galaxy located at a projected separation of 15 kpc and a radial velocity offset of ~ 300 km s-1. This interaction may have played a role in the triggering and/or shut-down of the radio jets. Conclusions: The spectral shape of this remnant radio galaxy differs from most of the previously identified remnant sources, which show steep or curved spectra at low to intermediate frequencies. Our results demonstrate that remnant radio galaxies can show a wide range of evolutionary paths and spectral properties. In light of this finding and in preparation for new-generation deep

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

NASA Technical Reports Server (NTRS)

Carilli, Chris; Conner, Sam; Dreher, John; Perley, Rick

1990-01-01

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy.

Radio active galactic nuclei in galaxy clusters: Feedback, merger signatures, and cluster tracers

NASA Astrophysics Data System (ADS)

Paterno-Mahler, Rachel Beth

Galaxy clusters, the largest gravitationally-bound structures in the universe, are composed of 50-1000s of galaxies, hot X-ray emitting gas, and dark matter. They grow in size over time through cluster and group mergers. The merger history of a cluster can be imprinted on the hot gas, known as the intracluster medium (ICM). Merger signatures include shocks, cold fronts, and sloshing of the ICM, which can form spiral structures. Some clusters host double-lobed radio sources driven by active galactic nuclei (AGN). First, I will present a study of the galaxy cluster Abell 2029, which is very relaxed on large scales and has one of the largest continuous sloshing spirals yet observed in the X-ray, extending outward approximately 400 kpc. The sloshing gas interacts with the southern lobe of the radio galaxy, causing it to bend. Energy injection from the AGN is insufficient to offset cooling. The sloshing spiral may be an important additional mechanism in preventing large amounts of gas from cooling to very low temperatures. Next, I will present a study of Abell 98, a triple system currently undergoing a merger. I will discuss the merger history, and show that it is causing a shock. The central subcluster hosts a double-lobed AGN, which is evacuating a cavity in the ICM. Understanding the physical processes that affect the ICM is important for determining the mass of clusters, which in turn affects our calculations of cosmological parameters. To further constrain these parameters, as well as models of galaxy evolution, it is important to use a large sample of galaxy clusters over a range of masses and redshifts. Bent, double-lobed radio sources can potentially act as tracers of galaxy clusters over wide ranges of these parameters. I examine how efficient bent radio sources are at tracing high-redshift (z>0.7) clusters. Out of 646 sources in our high-redshift Clusters Occupied by Bent Radio AGN (COBRA) sample, 282 are candidate new, distant clusters of galaxies based on

Radio Map of the Andromeda Galaxy.

PubMed

Macleod, J M

1964-07-24

The University of Illinois radio telescope has resolved the 610.5 Mcy/sec disk component of radio emission from the large galaxy M 31 into several discrete concentrations. In two cases, these correspond to the crossing of the optical major axis by spiral arms. A spur of emission extends southeast from the galaxy near the minor axis.

Radio and X-ray structure of Centaurus A

NASA Technical Reports Server (NTRS)

Feigelson, E. D.

1982-01-01

Recent studies of the nearby radio galaxy Centaurus A with the Very Large Array and the Einstein X-Ray Observatory reveal complex radio and X-ray structures. A prominent one-sided jet comprised of resolved knots located 0.2-6 kpc from the nucleus is seen in both radio and X-rays. The X-ray emission is probably synchrotron, requiring in situ reacceleration up to about ten million. Inverse Compton emission is not a likely explanation though a thermal model in which the nucleus ejects dense 100,000 solar mass clouds cannot be excluded. An elongated X-ray region is also found near the 'middle' radio lobe and optical HII regions about 30 kpc NE of the nucleus. Conditions around the active nucleus, the absence of X-rays from the inner radio lobes, and X-ray evidence for a hot interstellar medium are briefly discussed

The LOFAR window on star-forming galaxies and AGNs - curved radio SEDs and IR-radio correlation at 0

NASA Astrophysics Data System (ADS)

Calistro Rivera, G.; Williams, W. L.; Hardcastle, M. J.; Duncan, K.; Röttgering, H. J. A.; Best, P. N.; Brüggen, M.; Chyży, K. T.; Conselice, C. J.; de Gasperin, F.; Engels, D.; Gürkan, G.; Intema, H. T.; Jarvis, M. J.; Mahony, E. K.; Miley, G. K.; Morabito, L. K.; Prandoni, I.; Sabater, J.; Smith, D. J. B.; Tasse, C.; van der Werf, P. P.; White, G. J.

2017-08-01

We present a study of the low-frequency radio properties of star-forming (SF) galaxies and active galactic nuclei (AGNs) up to redshift z = 2.5. The new spectral window probed by the Low Frequency Array (LOFAR) allows us to reconstruct the radio continuum emission from 150 MHz to 1.4 GHz to an unprecedented depth for a radio-selected sample of 1542 galaxies in ˜ 7 deg2 of the LOFAR Boötes field. Using the extensive multiwavelength data set available in Boötes and detailed modelling of the far-infrared to ultraviolet spectral energy distribution (SED), we are able to separate the star formation (N = 758) and the AGN (N = 784) dominated populations. We study the shape of the radio SEDs and their evolution across cosmic time and find significant differences in the spectral curvature between the SF galaxy and AGN populations. While the radio spectra of SF galaxies exhibit a weak but statistically significant flattening, AGN SEDs show a clear trend to become steeper towards lower frequencies. No evolution of the spectral curvature as a function of redshift is found for SF galaxies or AGNs. We investigate the redshift evolution of the infrared-radio correlation for SF galaxies and find that the ratio of total infrared to 1.4-GHz radio luminosities decreases with increasing redshift: q1.4 GHz = (2.45 ± 0.04) (1 + z)-0.15 ± 0.03. Similarly, q150 MHz shows a redshift evolution following q150 GHz = (1.72 ± 0.04) (1 + z)-0.22 ± 0.05. Calibration of the 150 MHz radio luminosity as a star formation rate tracer suggests that a single power-law extrapolation from q1.4 GHz is not an accurate approximation at all redshifts.

Continuum radio emission from Virgo galaxies

NASA Technical Reports Server (NTRS)

Turner, Kenneth C.; Helou, George; Terzian, Yervant

1988-01-01

The paper presents single-antenna measurements of radio emission from 120 galaxies in the Virgo cluster at 2380 MHz using a 2.6 arc min beam (half-power beam width). It also presents interferometric measurements at the same frequency for 48 galaxies with less than or equal to 1 arc sec resolution. The relative concentration of the radio emission for these galaxies, particularly the emission from the galactic disk compared with that from the nucleus is discussed. It is found that the disk emission dominates in most cases. Some indications that the flux concentration is greater in elliptical and lenticular galaxies than it is in spirals are also found.

Enhanced X-ray Emission from Early Universe Analog Galaxies

NASA Astrophysics Data System (ADS)

Brorby, Matthew; Kaaret, Philip; Prestwich, Andrea H.; Mirabel, I. Felix; Feng, Hua

2016-04-01

X-rays from binaries containing compact objects may have played an important role in heating the early Universe. Here we discuss our findings from X-ray studies of blue compact dwarf galaxies (BCDs), Lyman break analogs (LBAs), and Green Pea galaxies (GP), all of which are considered local analogs to high redshift galaxies. We find enhanced X-ray emission per unit star-formation rate which strongly correlates with decreasing metallicity. We find evidence for the existence of a L_X-SFR-Metallicity plane for star-forming galaxies. The exact properties of X-ray emission in the early Universe affects the timing and morphology of reionization, both being observable properties of current and future radio observations of the redshifted 21cm signal from neutral hydrogen.

The Peculiar Radio-loud Narrow Line Seyfert 1 Galaxy 1H 0323+342

NASA Astrophysics Data System (ADS)

Paliya, Vaidehi S.; Sahayanathan, S.; Parker, M. L.; Fabian, A. C.; Stalin, C. S.; Anjum, Ayesha; Pandey, S. B.

2014-07-01

We present a multiwavelength study of the radio-loud narrow-line Seyfert 1 galaxy (NLSy1) 1H 0323+342, detected by the Fermi Gamma-Ray Space Telescope. Multiband light curves show many orphan X-ray and optical flares having no corresponding γ-ray counterparts. Such anomalous variability behavior can be due to different locations of the emission region from the central source. During a large flare, a γ-ray flux doubling timescale as small as ~3 hr is noticed. We built spectral energy distributions (SEDs) during different activity states and modeled them using a one-zone leptonic model. The shape of the optical/UV component of the SEDs is dominated by accretion disk emission in all the activity states. In the X-ray band, significant thermal emission from the hot corona is inferred during quiescent and first flaring states; however, during subsequent flares, the nonthermal jet component dominates. The γ-ray emission in all the states can be well explained by inverse-Compton scattering of accretion disk photons reprocessed by the broad-line region. The source showed violent intra-night optical variability, coinciding with one of the high γ-ray activity states. An analysis of the overall X-ray spectrum fitted with an absorbed power-law plus relativistic reflection component hints at the presence of an Fe Kα line and returns a high black hole spin value of a = 0.96 ± 0.14. We argue that 1H 0323+342 possesses dual characteristics, akin to both flat-spectrum radio quasars (FSRQs) and radio-quiet NLSy1 galaxies, though at a low jet power regime compared to powerful FSRQs.

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447. I. The X-ray View

NASA Astrophysics Data System (ADS)

Kreikenbohm, A.; Schulz, R.; Kadler, M.; Wilms, J.; Markowitz, A.; Chang, C. S.; Carpenter, B.; Elsässer, D.; Gehrels, N.; Mannheim, K.; Müller, C.; Ojha, R.; Ros, E.; Trüstedt, J.

2016-01-01

As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the γ-ray and radio-loud narrow line Seyfert 1 galaxy (γ-NLS1) PKS 2004-447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in γ-rays by the Fermi Large Area Telescope. It stands out for being the radio-loudest and the only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. Supplemented by archival data from 2004 and 2011, our data set allows for a careful analysis of the X-ray spectrum and variability of this peculiar source. The (0.5-10) keV spectrum is described well by a power law (Γ ~ 1.6), which can be interpreted as non-thermal emission from a relativistic jet. The source exhibits moderate flux variability on timescales of both months and years. Correlated brightness variations in the (0.5-2) keV and (2-10) keV bands are explained by a single variable spectral component, such as the one from the jet. A possible soft excess seen in the data from 2004 cannot be confirmed by the new XMM-Newton observations taken during low-flux states. Any contribution to the total flux in 2004 is less than 20% of the power-law component. The (0.5-10) keV luminosities of PKS 2004-447 are in the range of (0.5-2.7) × 1044 erg s-1. A comparison of the X-ray properties among the known γ-NLS1 galaxies shows that in four out of five cases the X-ray spectrum is dominated by a flat power law without intrinsic absorption. These objects are moderately variable in their brightness, while spectral variability is observed in at least two sources. The major difference across the X-ray spectra of γ-NLS1s is the luminosity, which spans a range of almost two orders of magnitude from 1044 erg s-1 to 1046 erg s-1 in the (0.5-10) keV band.

Radio emission in peculiar galaxies

NASA Technical Reports Server (NTRS)

Demellorabaca, Dulia F.; Abraham, Zulema

1990-01-01

During the last decades a number of surveys of peculiar galaxies have been carried out and accurate positions become available. Since peculiarities are a possible evidence of radio emission (Wright, 1974; Sulentic, 1976; Stocke et al., 1978), the authors selected a sample of 24 peculiar galaxies with optical jet-like features or extensions in different optical catalogues, mainly the Catalogue of Southern Peculiar Galaxies and Associations (Arp and Madore, 1987) and the ESO/Uppsala Survey of the ESO(B) Atlas (Lauberts, 1982) for observation at the radio continuum frequency of 22 GHz. The sample is listed in a table. Sol (1987) studied this sample and concluded that the majority of the jet-like features seem to admit an explanation in terms of interactive galaxies with bridges and/or tails due to tidal effects. Only in a few cases do the jets seem to be possibly linked to some nuclear activity of the host galaxy. The observations were made with the 13.7m-radome enclosed Itapetinga Radiotelescope (HPBW of 4.3 arcmin), in Brazil. The receiver was a 1 GHz d.s.b. super-heterodine mixer operated in total-power mode, with a system temperature of approximately 800 K. The observational technique consisted in scans in right ascention, centralized in the optical position of the galaxy. The amplitude of one scan was 43 arcmin, and its duration time was 20 seconds. The integration time was at least 2 hours (12 ten-minute observations) and the sensibility limit adopted was an antenna temperature greater than 3 times the r.m.s. error of the baseline determination. Virgo A was used as the calibrator source. Three galaxies were detected for the first time as radio sources and four other known galaxies at low frequencies had their flux densities measured at 22 GHz. The results for these sources are presented.

Mpc-scale diffuse radio emission in two massive cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Sommer, Martin W.; Basu, Kaustuv; Intema, Huib; Pacaud, Florian; Bonafede, Annalisa; Babul, Arif; Bertoldi, Frank

2017-04-01

Radio haloes are diffuse synchrotron sources on scales of ˜1 Mpc that are found in merging clusters of galaxies, and are believed to be powered by electrons re-accelerated by merger-driven turbulence. We present measurements of extended radio emission on similarly large scales in two clusters of galaxies hosting cool cores: Abell 2390 and Abell 2261. The analysis is based on interferometric imaging with the Karl G. Jansky Very Large Array, Very Large Array and Giant Metrewave Radio Telescope. We present detailed radio images of the targets, subtract the compact emission components and measure the spectral indices for the diffuse components. The radio emission in A2390 extends beyond a known sloshing-like brightness discontinuity, and has a very steep in-band spectral slope at 1.5 GHz that is similar to some known ultrasteep spectrum radio haloes. The diffuse signal in A2261 is more extended than in A2390 but has lower luminosity. X-ray morphological indicators, derived from XMM-Newton X-ray data, place these clusters in the category of relaxed or regular systems, although some asymmetric features that can indicate past minor mergers are seen in the X-ray brightness images. If these two Mpc-scale radio sources are categorized as giant radio haloes, they question the common assumption of radio haloes occurring exclusively in clusters undergoing violent merging activity, in addition to commonly used criteria for distinguishing between radio haloes and minihaloes.

The changing source of X-ray reflection in the radio-intermediate Seyfert 1 galaxy III Zw 2

NASA Astrophysics Data System (ADS)

Gonzalez, A. G.; Waddell, S. G. H.; Gallo, L. C.

2018-03-01

We report on X-ray observations of the radio-intermediate, X-ray bright Seyfert 1 galaxy, III Zw 2, obtained with XMM-Newton, Suzaku, and Swift over the past 17 yr. The source brightness varies significantly over yearly time-scales, but more modestly over periods of days. Pointed observations with XMM-Newton in 2000 and Suzaku in 2011 show spectral differences despite comparable X-ray fluxes. The Suzaku spectra are consistent with a power-law continuum and a narrow Gaussian emission feature at ˜6.4 keV, whereas the earlier XMM-Newton spectrum requires a broader Gaussian profile and soft-excess below ˜2 keV. A potential interpretation is that the primary power-law emission, perhaps from a jet base, preferentially illuminates the inner accretion disc in 2000, but the distant torus in 2011. The interpretation could be consistent with the hypothesized precessing radio jet in III Zw 2 that may have originated from disc instabilities due to an ongoing merging event.

X-ray Properties and the Environment of Compact Radio Sources.

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Malgorzata; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Lukasz

2018-01-01

Compact extragalactic radio sources provide important insights into the initial stages of radio source evolution and probe states of a black hole activity at the time of the formation of the relativistic outflow. Such outflows propagate out to hundreds kpc distances from the origin and impact environment on many scales, and thus influence evolution of structures in the universe. These compact sources show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Compact Symmetric Objects (CSOs, a subclass of GigaHertz Peaked spectrum radio sources) are symmetric and not affected by beaming. Their linear radio size can be translated into a source age if one measures the expansion velocity of the radio structures. Such ages has been measured for a small sample of CSOs. Using the Chandra X-ray Observatory and XMM-Newton we observed a pilot samples of 16 CSOs in X-rays (6 for the first time). Our results show heterogeneous nature of the CSOs X-ray emission indicating a range of AGN luminosities and a complex environment. In particular, we identified four Compton Thick sources with a dense medium (equivalent column > 1e24 cm^-2) capable of disturbing/slowing down the jet and confining the jet to a small region. Thus for the first time we gain the observational evidence in X-ray domain in favor of the hypothesis that in a sub-population of CSOs the radio jets may be confined by the dense X-ray obscuring medium. As a consequence, the kinematic ages of these CSOs may be underestimated.. We discuss the implications of our results on the emission models of CSOs, the earliest stages of the radio source evolution, jet interactions with the ISM, diversity of the environments in which the jets expand, and jet-galaxy co-evolution.Partial support for this work was provided by the NASA grants GO1-12145X, GO4-15099X, NNX10AO60G, NNX17AC23G and XMM AO15 project 78461. This work supported

Radio morphology and parent population of X-ray selected BL Lacertae objects

NASA Technical Reports Server (NTRS)

Laurent-Muehleisen, S. A.; Kollgaard, R. I.; Moellenbrock, G. A.; Feigelson, E. D.

1993-01-01

High-dynamic range (typically 1700:1) radio maps of 15 X-ray BL Lac (XBL) objects from the HEAO-1 Large Area Sky Survey are presented. Morphological characteristics of these sources are compared with Fanaroff-Riley (FR) class I radio galaxies in the context of unified schemes, with reference to one-sided kiloparsec-scale emission. Evidence that cluster membership of XBLs is significantly higher than previously thought is also presented. It is shown that the extended radio powers, X-ray emission, core-to-lobe ratios, and linear sizes of the radio selected BL Lac (RBL) and XBL populations are consistent with an FR I radio galaxy parent population. A source list and VLA observing log and map parameters are provided.

A Multi-Wavelength View of Radio Galaxy Hercules A

NASA Image and Video Library

2017-12-08

Spectacular jets powered by the gravitational energy of a super massive black hole in the core of the elliptical galaxy Hercules A illustrate the combined imaging power of two of astronomy's cutting-edge tools, the Hubble Space Telescope's Wide Field Camera 3, and the recently upgraded Karl G. Jansky Very Large Array (VLA) radio telescope in New Mexico. To view a video of this go to: bit.ly/Ue2ypS Some two billion light-years away, the yellowish elliptical galaxy in the center of the image appears quite ordinary as seen by Hubble in visible wavelengths of light. The galaxy is roughly 1,000 times more massive than the Milky Way and harbors a 2.5-billion-solar-mass central black hole that is 1,000 times more massive than the black hole in the Milky Way. But the innocuous-looking galaxy, also known as 3C 348, has long been known as the brightest radio-emitting object in the constellation Hercules. Emitting nearly a billion times more power in radio wavelengths than our Sun, the galaxy is one of the brightest extragalactic radio sources in the entire sky. Credit: NASA, ESA, S. Baum and C. O'Dea (RIT), R. Perley and W. Cotton (NRAO/AUI/NSF), and the Hubble Heritage Team (STScI/AURA) To read more about this image go to: 1.usa.gov/Yu7uvX NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Discovery of large-scale diffuse radio emission in low-mass galaxy cluster Abell 1931

NASA Astrophysics Data System (ADS)

Brüggen, M.; Rafferty, D.; Bonafede, A.; van Weeren, R. J.; Shimwell, T.; Intema, H.; Röttgering, H.; Brunetti, G.; Di Gennaro, G.; Savini, F.; Wilber, A.; O'Sullivan, S.; Ensslin, T. A.; De Gasperin, F.; Hoeft, M.

2018-07-01

Extended, steep-spectrum radio synchrotron sources are pre-dominantly found in massive galaxy clusters as opposed to groups. LOFAR Two-Metre Sky Survey images have revealed a diffuse, ultra-steep-spectrum radio source in the low-mass cluster Abell 1931. The source has a fairly irregular morphology with the largest linear size of about 550 kpc. The source is only seen in LOFAR observations at 143 MHz and Giant Metre Radio Telescope observations at 325 MHz. The spectral index of the total source between 143 and 325 MHz is α _{143}^{325} = -2.86 ± 0.36. The source remains invisible in Very Large Array (1-2 GHz) observations as expected given the spectral index. Chandra X-ray observations of the cluster revealed a bolometric luminosity of LX = (1.65 ± 0.39) × 1043 erg s-1 and a temperature of 2.92_{-0.87}^{+1.89} keV which implies a mass of around ˜1014 M⊙. We conclude that the source is a remnant radio galaxy that has shut off around 200 Myr ago. The brightest cluster galaxy, a radio-loud elliptical galaxy, could be the source for this extinct source. Unlike remnant sources studied in the literature, our source has a steep spectrum at low radio frequencies. Studying such remnant radio galaxies at low radio frequencies is important for understanding the scarcity of such sources and their role in feedback processes.

Particle acceleration areas in two radio galaxies.

NASA Astrophysics Data System (ADS)

Andernach, H.

1989-04-01

Two edge-darkened, tailed radio galaxies (PKS 0123-01 and PKS 2247+11) were mapped with the VLA at 1.4 and 5 GHz at sub-arcmin resolution as well as with the Effelsberg 100-m telescope at 2.7, 5 and 10.7 GHz at arcmin resolution. With additional use of existing low-frequency maps the shape of the radio spectrum is analyzed point by point across the source extent. The shape is found to be concave (i.e. having high-frequency excess) over major parts of the source extent, in the case of 2247+11 even for a region in the far radio tail. Possible mechanisms causing this feature are proposed. Using a subset of maps at higher angular resolution most of the regions with spectral flattening turn out to coincide with bends and wiggles of the radio jets and/or tails. Polarization data are available at four frequencies and some problems in their interpretation are discussed. The following one consists of a 1-page "extended abstract" including two small figures. I attach to this message the processed postscript file which I would be happy to offer in ADS as a "scanned" paper. I include here the full extended abstract text which you could also offer as HTML code. I converted the four references to bibcodes.

Phenomenological model for the evolution of radio galaxies such as Cygnus A

NASA Astrophysics Data System (ADS)

Artyukh, V. S.

2015-06-01

A phenomenological model for the evolution of classical radio galaxies such as Cygnus A is presented. An activity cycle of the host galaxy in the radio begins with the birth of radio jets, which correspond to shocks on scales ˜1 pc (the radio galaxy B0108+388). In the following stage of the evolution, the radio emission comes predominantly from formations on scales of 10-100 pc, whose physical parameters are close to those of the hot spots of Cygnus A (this corresponds to GHz-peaked spectrum radio sources). Further, the hot spots create radio lobes on scales of 103-104 pc (compact steep-spectrum radio sources). The fully formed radio galaxies have radio jets, hot spots, and giant radio lobes; the direction of the jets can vary in a discrete steps with time, creating new hot spots and inflating the radio lobes (as in Cygnus A). In the final stage of the evolutionary cycle, first the radio jets disappear, then the hot spots, and finally the radio lobes (similar to the giant radio galaxies DA 240 and 3C 236). A large fraction of radio galaxies with repeating activity cycles is observed. The close connection between Cygnus A-type radio galaxies and optical quasars is noted, as well as similarity in the cosmological evolution of powerful radio galaxies and optical quasars.

Observations of a nearby filament of galaxy clusters with the Sardinia Radio Telescope

NASA Astrophysics Data System (ADS)

Vacca, Valentina; Murgia, M.; Loi, F. Govoni F.; Vazza, F.; Finoguenov, A.; Carretti, E.; Feretti, L.; Giovannini, G.; Concu, R.; Melis, A.; Gheller, C.; Paladino, R.; Poppi, S.; Valente, G.; Bernardi, G.; Boschin, W.; Brienza, M.; Clarke, T. E.; Colafrancesco, S.; Enßlin, T.; Ferrari, C.; de Gasperin, F.; Gastaldello, F.; Girardi, M.; Gregorini, L.; Johnston-Hollitt, M.; Junklewitz, H.; Orrù, E.; Parma, P.; Perley, R.; Taylor, G. B.

2018-05-01

We report the detection of diffuse radio emission which might be connected to a large-scale filament of the cosmic web covering a 8° × 8° area in the sky, likely associated with a z≈0.1 over-density traced by nine massive galaxy clusters. In this work, we present radio observations of this region taken with the Sardinia Radio Telescope. Two of the clusters in the field host a powerful radio halo sustained by violent ongoing mergers and provide direct proof of intra-cluster magnetic fields. In order to investigate the presence of large-scale diffuse radio synchrotron emission in and beyond the galaxy clusters in this complex system, we combined the data taken at 1.4 GHz with the Sardinia Radio Telescope with higher resolution data taken with the NRAO VLA Sky Survey. We found 28 candidate new sources with a size larger and X-ray emission fainter than known diffuse large-scale synchrotron cluster sources for a given radio power. This new population is potentially the tip of the iceberg of a class of diffuse large-scale synchrotron sources associated with the filaments of the cosmic web. In addition, we found in the field a candidate new giant radio galaxy.

Discovery of large-scale diffuse radio emission in low-mass galaxy cluster Abell 1931

NASA Astrophysics Data System (ADS)

Brüggen, M.; Rafferty, D.; Bonafede, A.; van Weeren, R. J.; Shimwell, T.; Intema, H.; Röttgering, H.; Brunetti, G.; Di Gennaro, G.; Savini, F.; Wilber, A.; O'Sullivan, S.; Ensslin, T. A.; De Gasperin, F.; Hoeft, M.

2018-04-01

Extended, steep-spectrum radio synchrotron sources are pre-dominantly found in massive galaxy clusters as opposed to groups. LOFAR Two-Metre Sky Survey images have revealed a diffuse, ultra-steep spectrum radio source in the low-mass cluster Abell 1931. The source has a fairly irregular morphology with a largest linear size of about 550 kpc. The source is only seen in LOFAR observations at 143 MHz and GMRT observations at 325 MHz. The spectral index of the total source between 143 MHz and 325 MHz is α _{143}^{325} = -2.86 ± 0.36. The source remains invisible in Very Large Array (1-2 GHz) observations as expected given the spectral index. Chandra X-ray observations of the cluster revealed a bolometric luminosity of LX = (1.65 ± 0.39) × 1043 erg s-1 and a temperature of 2.92_{-0.87}^{+1.89} keV which implies a mass of around ˜1014M⊙. We conclude that the source is a remnant radio galaxy that has shut off around 200 Myr ago. The brightest cluster galaxy, a radio-loud elliptical galaxy, could be the source for this extinct source. Unlike remnant sources studied in the literature, our source has a steep spectrum at low radio frequencies. Studying such remnant radio galaxies at low radio frequencies is important for understanding the scarcity of such sources and their role in feedback processes.

Classifying Radio Galaxies with the Convolutional Neural Network

NASA Astrophysics Data System (ADS)

Aniyan, A. K.; Thorat, K.

2017-06-01

We present the application of a deep machine learning technique to classify radio images of extended sources on a morphological basis using convolutional neural networks (CNN). In this study, we have taken the case of the Fanaroff-Riley (FR) class of radio galaxies as well as radio galaxies with bent-tailed morphology. We have used archival data from the Very Large Array (VLA)—Faint Images of the Radio Sky at Twenty Centimeters survey and existing visually classified samples available in the literature to train a neural network for morphological classification of these categories of radio sources. Our training sample size for each of these categories is ˜200 sources, which has been augmented by rotated versions of the same. Our study shows that CNNs can classify images of the FRI and FRII and bent-tailed radio galaxies with high accuracy (maximum precision at 95%) using well-defined samples and a “fusion classifier,” which combines the results of binary classifications, while allowing for a mechanism to find sources with unusual morphologies. The individual precision is highest for bent-tailed radio galaxies at 95% and is 91% and 75% for the FRI and FRII classes, respectively, whereas the recall is highest for FRI and FRIIs at 91% each, while the bent-tailed class has a recall of 79%. These results show that our results are comparable to that of manual classification, while being much faster. Finally, we discuss the computational and data-related challenges associated with the morphological classification of radio galaxies with CNNs.

Twin radio relics in the nearby low-mass galaxy cluster Abell 168

NASA Astrophysics Data System (ADS)

Dwarakanath, K. S.; Parekh, V.; Kale, R.; George, L. T.

2018-06-01

We report the discovery of twin radio relics in the outskirts of the low-mass merging galaxy cluster Abell 168 (redshift=0.045). One of the relics is elongated with a linear extent ˜800 kpc and projected width of ˜80 kpc and is located ˜900 kpc towards the north of the cluster centre, oriented roughly perpendicular to the major axis of the X-ray emission. The second relic is ring-shaped with a size ˜220 kpc and is located near the inner edge of the elongated relic at a distance of ˜600 kpc from the cluster centre. These radio sources were imaged at 323 and 608 MHz with the Giant Meterwave Radio Telescope and at 1520 MHz with the Karl G. Jansky Very Large Array (VLA). The elongated relic was detected at all frequencies, with a radio power of 1.38 ± 0.14 × 1023 W Hz-1 at 1.4 GHz and a power law in the frequency range 70-1500 MHz (S ∝ να, α = -1.1 ± 0.04). This radio power is in good agreement with that expected from the known empirical relation between the radio powers of relics and host cluster masses. This is the lowest mass (M500 = 1.24 × 1014 M⊙) cluster in which relics due to merger shocks are detected. The ring-shaped relic has a steeper spectral index (α) of -1.74 ± 0.29 in the frequency range 100-600 MHz. We propose this relic to be an old plasma, revived due to adiabatic compression by the outgoing shock that produced the elongated relic.

X-rays from the radio halo of Virgo A = M87

NASA Technical Reports Server (NTRS)

1985-01-01

The purpose of this study is to investigate in more detail the associated X-ray and radio emission in the Virgo A halo discovered by SGF. Improved Einstein HRI data and new radio maps obtained with the Very Large Array are described and the relation between the X-ray and radio structures is carefully examined. Several possible explanations are presented for the X-ray emission. The inverse compton model is found to be viable only if the magnetic field is variable and substantially weaker than the equipartition value. The principal alternative is excess thermal X-rays due to compression of the intracluster medium by the radio lobe. In either case, the association of such prominent radio and X-ray structures is unique among known radio galaxies.

Infrared images of distant 3C radio galaxies

NASA Technical Reports Server (NTRS)

Eisenhardt, Peter; Chokshi, Arati

1990-01-01

J (1.2-micron) and K (2.2 micron) images have been obtained for eight 3CR radio galaxies with redshifts from 0.7 to 1.8. Most of the objects were known to have extended asymmetric optical continuum or line emission aligned with the radio lobe axis. In general, the IR morphologies of these galaxies are just as peculiar as their optical morphologies. For all the galaxies, when asymmetric structure is present in the optical, structure with the same orientation is seen in the IR and must be accounted for in any model to explain the alignment of optical and radio emission.

Radio emission in the directions of cD and related galaxies in poor clusters. III. VLA observations at 20 cm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burns, J.O.; White, R.A.; Hough, D.H.

1981-01-01

VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approx.70%). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approx.25% of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies ismore » seen from rich to poor clusters. We speculate that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. We briefly discuss galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and x-ray emission.« less

Radio emission in the directions of cD and related galaxies in poor clusters. III - VLA observations at 20 cm

NASA Technical Reports Server (NTRS)

Burns, J. O.; White, R. A.; Hough, D. H.

1981-01-01

VLA radio maps and optical identifications of a sample of sources in the directions of 21 Yerkes poor cluster fields are presented. The majority of the cluster radio sources are associated with the dominant D or cD galaxies (approximately 70 percent). Our analysis of dominant galaxies in rich and poor clusters indicates that these giant galaxies are much more often radio emitters (approximately 25 percent of cD's are radio active in the poor clusters), have steeper radio spectra, and have simpler radio morphologies (i.e., double or other linear structure) than other less bright ellipticals. A strong continuum of radio properties in cD galaxies is seen from rich to poor clusters. It is speculated that the location of these dominant galaxies at the cluster centers (i.e., at the bottom of a deep, isolated gravitational potential well) is the crucial factor in explaining their multifrequency activity. Galaxy cannibalism and gas infall models as fueling mechanisms for the observed radio and X-ray emission are discussed

A DISTANT RADIO MINI-HALO IN THE PHOENIX GALAXY CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Weeren, R. J.; Andrade-Santos, F.; Forman, W. R.

We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z = 0.596) with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observationsmore » show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of 17 ± 5 mJy, resulting in a 1.4 GHz radio power of (10.4 ± 3.5) × 10{sup 24} W Hz{sup –1}. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of –0.84 ± 0.12 for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.« less

Classifying Radio Galaxies with the Convolutional Neural Network

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aniyan, A. K.; Thorat, K.

We present the application of a deep machine learning technique to classify radio images of extended sources on a morphological basis using convolutional neural networks (CNN). In this study, we have taken the case of the Fanaroff–Riley (FR) class of radio galaxies as well as radio galaxies with bent-tailed morphology. We have used archival data from the Very Large Array (VLA)—Faint Images of the Radio Sky at Twenty Centimeters survey and existing visually classified samples available in the literature to train a neural network for morphological classification of these categories of radio sources. Our training sample size for each of these categoriesmore » is ∼200 sources, which has been augmented by rotated versions of the same. Our study shows that CNNs can classify images of the FRI and FRII and bent-tailed radio galaxies with high accuracy (maximum precision at 95%) using well-defined samples and a “fusion classifier,” which combines the results of binary classifications, while allowing for a mechanism to find sources with unusual morphologies. The individual precision is highest for bent-tailed radio galaxies at 95% and is 91% and 75% for the FRI and FRII classes, respectively, whereas the recall is highest for FRI and FRIIs at 91% each, while the bent-tailed class has a recall of 79%. These results show that our results are comparable to that of manual classification, while being much faster. Finally, we discuss the computational and data-related challenges associated with the morphological classification of radio galaxies with CNNs.« less

Radio galaxies dominate the high-energy diffuse gamma-ray background

DOE PAGES

Hooper, Dan; Linden, Tim; Lopez, Alejandro

2016-08-09

It has been suggested that unresolved radio galaxies and radio quasars (sometimes referred to as misaligned active galactic nuclei) could be responsible for a significant fraction of the observed diffuse gamma-ray background. In this study, we use the latest data from the Fermi Gamma-Ray Space Telescope to characterize the gamma-ray emission from a sample of 51 radio galaxies. In addition to those sources that had previously been detected using Fermi data, we report here the first statistically significant detection of gamma-ray emission from the radio galaxies 3C 212, 3C 411, and B3 0309+411B. Combining this information with the radio fluxes,more » radio luminosity function, and redshift distribution of this source class, we find that radio galaxies dominate the diffuse gamma-ray background, generating 77.2(+25.4)(-9.4)% of this emission at energies above ~1 GeV . We discuss the implications of this result and point out that it provides support for scenarios in which IceCube's high-energy astrophysical neutrinos also originate from the same population of radio galaxies.« less

Galaxy Evolution in the Radio Band: The Role of Star-forming Galaxies and Active Galactic Nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mancuso, C.; Prandoni, I.; Lapi, A.

We investigate the astrophysics of radio-emitting star-forming galaxies and active galactic nuclei (AGNs) and elucidate their statistical properties in the radio band, including luminosity functions, redshift distributions, and number counts at sub-mJy flux levels, which will be crucially probed by next-generation radio continuum surveys. Specifically, we exploit the model-independent approach by Mancuso et al. to compute the star formation rate functions, the AGN duty cycles, and the conditional probability of a star-forming galaxy to host an AGN with given bolometric luminosity. Coupling these ingredients with the radio emission properties associated with star formation and nuclear activity, we compute relevant statisticsmore » at different radio frequencies and disentangle the relative contribution of star-forming galaxies and AGNs in different radio luminosity, radio flux, and redshift ranges. Finally, we highlight that radio-emitting star-forming galaxies and AGNs are expected to host supermassive black holes accreting with different Eddington ratio distributions and to occupy different loci in the galaxy main-sequence diagrams. These specific predictions are consistent with current data sets but need to be tested with larger statistics via future radio data with multiband coverage on wide areas, as will become routinely achievable with the advent of the Square Kilometre Array and its precursors.« less

Large scale structures around radio galaxies at z ~ 1.5

NASA Astrophysics Data System (ADS)

Galametz, A.; De Breuck, C.; Vernet, J.; Stern, D.; Rettura, A.; Marmo, C.; Omont, A.; Allen, M.; Seymour, N.

2009-11-01

We explore the environments of two radio galaxies at z ~ 1.5, 7C 1751+6809 and 7C 1756+6520, using deep optical and near-infrared imaging. Our data cover 15×15 arcmin2 fields around the radio galaxies. We develop and apply BzK color criteria to select cluster member candidates around the radio galaxies and find no evidence of an overdensity of red galaxies within 2 Mpc of 7C 1751+6809. In contrast, 7C 1756+6520 shows a significant overdensity of red galaxies within 2 Mpc of the radio galaxy, by a factor of 3.1±0.8 relative to the four MUSYC fields. At small separation (r < 6 arcsec), this radio galaxy also has one z > 1.4 evolved galaxy candidate, one z > 1.4 star-forming galaxy candidate, and an AGN candidate (at indeterminate redshift). This is suggestive of several close-by companions. Several concentrations of red galaxies are also noticed in the full 7C 1756+6520 field, forming a possible large-scale structure of evolved galaxies with a NW-SE orientation. We construct the color-magnitude diagram of red galaxies found near 7C 1756+6520 (r < 2 Mpc), and find a clear red sequence that is truncated at Ks ~ 21.5 (AB). We also find an overdensity of mid-infrared selected AGN in the surroundings of 7C 1756+6520. These results are suggestive of a proto-cluster at high redshift. Tables 2-6 are only available in electronic form at http://www.aanda.org

Low-frequency radio observations of poor clusters of galaxies

NASA Technical Reports Server (NTRS)

Hanisch, R. J.; White, R. A.

1981-01-01

Observations have been made at the Clark Lake Radio Observatory of 16 poor clusters of galaxies at 34.3 MHz. Four of the poor clusters were detected at flux densities greater than 20 Jy. The spectra of the four detected clusters are all rather steep. Two of the detected clusters, AWM 4 and AWM 5, are also known to be X-ray sources. The possibility that the X-ray-emitting gas is heated by Coulomb interactions with the relativistic electrons responsible for the radio emission is investigated, and it is found that the observed X-ray luminosities can be accounted for if the electron energy spectrum extends to very low energies (gamma approximately 1-10). Collective plasma effects may increase the heating efficiency and eliminate the need to extrapolate the electron energy spectrum to such low values.

Radio properties of type 1.8 and 1.9 Seyfert galaxies

NASA Technical Reports Server (NTRS)

Ulvestad, James S.

1986-01-01

A number of type 1.8 and 1.9 Seyfert galaxies have been observed at the VLA in order to compare their properties with those of the other types of Seyfert galaxy. The observed types have radio luminosities in the range of 10 to the 39th-40.5th args/s, with the median near 10 to the 40th ergs/s. Most of these galaxies have radio sources with diameters of about 500 pc or less. The ratio of radio luminosity to featureless optical continuum luminosity in the Seyfert 1.8/12.9 galaxies and Seyfert 1.2/1.5 galaxies is intermediate between the values for Seyfert 1 and Seyfert 2 galaxies. The infrared-to-radio ratio decreases along the sequence from Seyfert 1 galaxies, through intermediate Seyfert galaxies, to Seyfert 2 galaxies. This systematic statistical difference in the ratio of two aspect-independent quantities implies that the differences among the Seyfert classes cannot be attributed solely to differences in viewing angle.

Protoclusters with evolved populations around radio galaxies at z ~ 2.5

NASA Astrophysics Data System (ADS)

Kajisawa, Masaru; Kodama, Tadayuki; Tanaka, Ichi; Yamada, Toru; Bower, Richard

2006-09-01

We report the discovery of protocluster candidates around high-redshift radio galaxies at z ~ 2.5 on the basis of clear statistical excess of colour-selected galaxies around them seen in the deep near-infrared imaging data obtained with CISCO on the Subaru Telescope. We have observed six targets, all at similar redshifts at z ~ 2.5, and our data reach J = 23.5, H = 22.6 and K = 21.8 (5σ) and cover a 1.6 × 1.6 arcmin2 field centred on each radio galaxy. We apply colour cuts in JHK bands in order to exclusively search for galaxies located at high redshifts, z > 2. Over the magnitude range of 19.5 < K < 21.5, we see a significant excess of red galaxies with J - K > 2.3 by a factor of 2 around the combined radio galaxies fields compared to those found in the general field of the Great Observatories Origins Deep Survey-South (GOODS-S). The excess of galaxies around the radio galaxies fields becomes more than a factor of 3 around 19.5 < K < 20.5 when the two-colour cuts are applied with JHK bands. Such overdensity of the colour-selected galaxies suggests that those fields tend to host high-density regions at high redshifts, although there seems to be the variety of the density of the colour-selected galaxies in each field. In particular, two radio galaxies fields out of the six observed fields show very strong density excess and these are likely to be protoclusters associated with the radio galaxies which would evolve into rich clusters of galaxies dominated by old passively evolving galaxies.

Imaging the host galaxies of high-redshift radio-quiet QSOs

NASA Technical Reports Server (NTRS)

Lowenthal, James D.; Heckman, Timothy M.; Lehnert, Matthew, D.; Elias, J. H.

1995-01-01

We present new deep K-band and optical images of four radio-quiet QSOs at z approximately = 1 and six radio-quiet QSOs at z approximately = 2.5, as well as optical images only of six more at z approximately = 2.5. We have examined the images carefully for evidence of extended 'fuzz' from any putative QSO host galaxy. None of the z approximately = 2.5 QSOs shows any extended emission, and only two of the z approximately = 1 QSOs show marginal evidence for extended emission. Our 3 sigma detection limits in the K images, m(sub K) approximately = 21 for an isolated source, would correspond approximately to an unevolved L(sup star) elliptical galaxy at z = 2.5 or 2-3 mag fainter than an L(sup star) elliptical at z = 1, although our limits on host galaxy light are weaker than this due to the difficulty of separating galaxy light from QSO light. We simulate simple models of disk and elliptical host galaxies, and find that the marginal emission around the two z approximately = 1 QSOs can be explained by disks or bulges that are approximately 1-2 mag brighter than an unevolved L(sup star) galaxy in one case and approximately 1.5-2.5 mag brighter than L(sub star) in the other. For two other z approximately = 1 QSOs, we have only upper limits (L approximately = L(sup star)). The hosts of the high-redshift sample must be no brighter than about 3 mag above an unevolved L(sup star) galaxy, and are at least 1 magnitude fainter than the hosts of radio-loud QSOs at the same redshift. If the easily detected K-band light surrounding a previous sample of otherwise similar but radio-loud QSOs is starlight, then it must evolve on timescales of greater than or approximately equal to 10(exp 8) yr (e.g., Chambers & Charlot 1990); therefore our non-detection of host galaxy fuzz around radio-quiet QSOs supports the view that high-redshift radio-quiet and radio-loud QSOs inhabit different host objects, rather than being single types of objects that turn their radio emission on and off over

Radio jets and gamma-ray emission in radio-silent narrow-line Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Lähteenmäki, A.; Järvelä, E.; Ramakrishnan, V.; Tornikoski, M.; Tammi, J.; Vera, R. J. C.; Chamani, W.

2018-06-01

We have detected six narrow-line Seyfert 1 (NLS1) galaxies at 37 GHz that were previously classified as radio silent and two that were classified as radio quiet. These detections reveal the presumption that NLS1 galaxies labelled radio quiet or radio silent and hosted by spiral galaxies are unable to launch jets to be incorrect. The detections are a plausible indicator of the presence of a powerful, most likely relativistic jet because this intensity of emission at 37 GHz cannot be explained by, for example, radiation from supernova remnants. Additionally, one of the detected NLS1 galaxies is a newly discovered source of gamma rays and three others are candidates for future detections. 37 GHz data are only available in electronic form at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/L1

A Catalog Sample of Low-mass Galaxies Observed in X-Rays with Central Candidate Black Holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nucita, A. A.; Manni, L.; Paolis, F. De

We present a sample of X-ray-selected candidate black holes in 51 low-mass galaxies with z ≤ 0.055 and masses up to 10{sup 10} M {sub ⊙} obtained by cross-correlating the NASA-SLOAN Atlas with the 3XMM catalog. We have also searched in the available catalogs for radio counterparts of the black hole candidates and find that 19 of the previously selected sources also have a radio counterpart. Our results show that about 37% of the galaxies of our sample host an X-ray source (associated with a radio counterpart) spatially coincident with the galaxy center, in agreement with other recent works. Formore » these nuclear sources, the X-ray/radio fundamental plane relation allows one to estimate the mass of the (central) candidate black holes, which are in the range of 10{sup 4}–2 × 10{sup 8} M {sub ⊙} (with a median value of ≃3 × 10{sup 7} M {sub ⊙} and eight candidates having masses below 10{sup 7} M {sub ⊙}). This result, while suggesting that X-ray emitting black holes in low-mass galaxies may have had a key role in the evolution of such systems, makes it even more urgent to explain how such massive objects formed in galaxies. Of course, dedicated follow-up observations both in the X-ray and radio bands, as well as in the optical, are necessary in order to confirm our results.« less

`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C 35.06, a peculiar radio galaxy with dancing radio jets

NASA Astrophysics Data System (ADS)

Biju, K. G.; Bagchi, Joydeep; Ishwara-Chandra, C. H.; Pandey-Pommier, M.; Jacob, Joe; Patil, M. K.; Kumar, P. Sunil; Pandge, Mahadev; Dabhade, Pratik; Gaikwad, Madhuri; Dhurde, Samir; Abraham, Sheelu; Vivek, M.; Mahabal, Ashish A.; Djorgovski, S. G.

2017-10-01

We report the results of our radio, optical and infrared studies of a peculiar radio source 4C 35.06, an extended radio-loud active galactic nucleus (AGN) at the centre of galaxy cluster Abell 407 (z = 0.047). The central region of this cluster hosts a remarkably tight ensemble of nine galaxies, the spectra of which resemble those of passive red ellipticals, embedded within a diffuse stellar halo of ˜1 arcmin size. This system (named 'Zwicky's Nonet') provides unique and compelling evidence for a multiple-nucleus cD galaxy precursor. Multifrequency radio observations of 4C 35.06 with the Giant Meterwave Radio Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400-kpc scale helically twisted and kinked radio jets and outer diffuse lobes. The outer extremities of jets contain extremely steep-spectrum (spectral index -1.7 to -2.5) relic/fossil radio plasma with a spectral age of a few ×(107-108) yr. Such ultra-steep spectrum relic radio lobes without definitive hotspots are rare and they provide an opportunity to understand the life cycle of relativistic jets and physics of black hole mergers in dense environments. We interpret our observations of this radio source in the context of growth of its central black hole, triggering of its AGN activity and jet precession, all possibly caused by galaxy mergers in this dense galactic system. A slow conical precession of the jet axis due to gravitational perturbation between interacting black holes is invoked to explain the unusual jet morphology.

Ultra-high-energy cosmic rays from radio galaxies

NASA Astrophysics Data System (ADS)

Eichmann, B.; Rachen, J. P.; Merten, L.; van Vliet, A.; Becker Tjus, J.

2018-02-01

Radio galaxies are intensively discussed as the sources of cosmic rays observed above about 3 × 1018 eV, called ultra-high energy cosmic rays (UHECRs). We present a first, systematic approach that takes the individual characteristics of these sources into account, as well as the impact of the extragalactic magnetic-field structures up to a distance of 120 Mpc. We use a mixed simulation setup, based on 3D simulations of UHECRs ejected by observed, individual radio galaxies taken out to a distance of 120 Mpc, and on 1D simulations over a continuous source distribution contributing from beyond 120 Mpc. Additionally, we include the ultra-luminous radio galaxy Cygnus A at a distance of about 250 Mpc, as its contribution is so strong that it must be considered as an individual point source. The implementation of the UHECR ejection in our simulation setup, both that of individual radio galaxies and the continuous source function, is based on a detailed consideration of the physics of radio jets and standard first-order Fermi acceleration. This allows to derive the spectrum of ejected UHECR as a function of radio luminosity, and at the same time provides an absolute normalization of the problem involving only a small set of parameters adjustable within narrow constraints. We show that the average contribution of radio galaxies taken over a very large volume cannot explain the observed features of UHECRs measured at Earth. However, we obtain excellent agreement with the spectrum, composition, and arrival-direction distribution of UHECRs measured by the Pierre Auger Observatory, if we assume that most UHECRs observed arise from only two sources: the ultra-luminous radio galaxy Cygnus A, providing a mostly light composition of nuclear species dominating up to about 6 × 1019 eV, and the nearest radio galaxy Centaurus A, providing a heavy composition dominating above 6 × 1019 eV . Here we have to assume that extragalactic magnetic fields out to 250 Mpc, which we did not

A non cool-core 4.6-keV cluster around the bright nearby radio galaxy PKS B1416-493

NASA Astrophysics Data System (ADS)

Worrall, D. M.; Birkinshaw, M.

2017-05-01

We present new X-ray (Chandra) and radio (ATCA) observations of the z = 0.09 radio galaxy PKS B1416-493, a member of the southern equivalent of the 3CRR sample. We find the source to be embedded in a previously unrecognized bright kT = 4.6-keV non cool-core cluster. The discovery of new clusters of such high temperature and luminosity within z = 0.1 is rare. The radio source was chosen for observation based on its intermediate FR I/II morphology. We identify a cavity coincident with the northeast lobe, and excess counts associated with the southwest lobe that we interpret as inverse-Compton X-ray emission. The jet power, at 5.3 × 1044 erg s-1, when weighted by radio source density, supports suggestions that radio sources of intermediate morphology and radio power may dominate radio-galaxy heating in the local Universe.

SUZAKU X-RAY IMAGING OF THE EXTENDED LOBE IN THE GIANT RADIO GALAXY NGC 6251 ASSOCIATED WITH THE FERMI-LAT SOURCE 2FGL J1629.4+8236

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takeuchi, Y.; Kataoka, J.; Takahashi, Y.

2012-04-10

We report the results of a Suzaku X-ray imaging study of NGC 6251, a nearby giant radio galaxy with intermediate FR I/II radio properties. Our pointing direction was centered on the {gamma}-ray emission peak recently discovered with the Fermi Large Area Telescope (LAT) around the position of the northwest (NW) radio lobe 15 arcmin offset from the nucleus. After subtracting two 'off-source' pointings adjacent to the radio lobe and removing possible contaminants in the X-ray Imaging Spectrometer field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is wellmore » fitted by a power law with a photon index {Gamma} = 1.90 {+-} 0.15 and a 0.5-8 keV flux of 4 Multiplication-Sign 10{sup -13} erg cm{sup -2} s{sup -1}. We interpret this diffuse X-ray emission component as being due to inverse Compton upscattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broadband spectral modeling that the {gamma}-ray flux of the Fermi-LAT source 2FGL J1629.4+8236 may well be accounted for by the high-energy tail of the inverse Compton continuum of the lobe. Thus, this claimed association of {gamma}-rays from the NW lobe of NGC 6251, together with the recent Fermi-LAT imaging of the extended lobes of Centaurus A, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general.« less

The SAMI Galaxy Survey: the intrinsic shape of kinematically selected galaxies

NASA Astrophysics Data System (ADS)

Foster, C.; van de Sande, J.; D'Eugenio, F.; Cortese, L.; McDermid, R. M.; Bland-Hawthorn, J.; Brough, S.; Bryant, J.; Croom, S. M.; Goodwin, M.; Konstantopoulos, I. S.; Lawrence, J.; López-Sánchez, Á. R.; Medling, A. M.; Owers, M. S.; Richards, S. N.; Scott, N.; Taranu, D. S.; Tonini, C.; Zafar, T.

2017-11-01

Using the stellar kinematic maps and ancillary imaging data from the Sydney AAO Multi Integral field (SAMI) Galaxy Survey, the intrinsic shape of kinematically selected samples of galaxies is inferred. We implement an efficient and optimized algorithm to fit the intrinsic shape of galaxies using an established method to simultaneously invert the distributions of apparent ellipticities and kinematic misalignments. The algorithm output compares favourably with previous studies of the intrinsic shape of galaxies based on imaging alone and our re-analysis of the ATLAS3D data. Our results indicate that most galaxies are oblate axisymmetric. We show empirically that the intrinsic shape of galaxies varies as a function of their rotational support as measured by the 'spin' parameter proxy λ _{R_e}. In particular, low-spin systems have a higher occurrence of triaxiality, while high-spin systems are more intrinsically flattened and axisymmetric. The intrinsic shape of galaxies is linked to their formation and merger histories. Galaxies with high-spin values have intrinsic shapes consistent with dissipational minor mergers, while the intrinsic shape of low-spin systems is consistent with dissipationless multimerger assembly histories. This range in assembly histories inferred from intrinsic shapes is broadly consistent with expectations from cosmological simulations.

Coma cluster ultradiffuse galaxies are not standard radio galaxies

NASA Astrophysics Data System (ADS)

Struble, Mitchell F.

2018-02-01

Matching members in the Coma cluster catalogue of ultradiffuse galaxies (UDGs) from SUBARU imaging with a very deep radio continuum survey source catalogue of the cluster using the Karl G. Jansky Very Large Array (VLA) within a rectangular region of ∼1.19 deg2 centred on the cluster core reveals matches consistent with random. An overlapping set of 470 UDGs and 696 VLA radio sources in this rectangular area finds 33 matches within a separation of 25 arcsec; dividing the sample into bins with separations bounded by 5, 10, 20 and 25 arcsec finds 1, 4, 17 and 11 matches. An analytical model estimate, based on the Poisson probability distribution, of the number of randomly expected matches within these same separation bounds is 1.7, 4.9, 19.4 and 14.2, each, respectively, consistent with the 95 per cent Poisson confidence intervals of the observed values. Dividing the data into five clustercentric annuli of 0.1° and into the four separation bins, finds the same result. This random match of UDGs with VLA sources implies that UDGs are not radio galaxies by the standard definition. Those VLA sources having integrated flux >1 mJy at 1.4 GHz in Miller, Hornschemeier and Mobasher without SDSS galaxy matches are consistent with the known surface density of background radio sources. We briefly explore the possibility that some unresolved VLA sources near UDGs could be young, compact, bright, supernova remnants of Type Ia events, possibly in the intracluster volume.

Feeding and feedback in radio galaxies of the local universe

NASA Astrophysics Data System (ADS)

Couto, Guilherme dos Santos

2016-10-01

We present integral field spectroscopic data covering the inner kiloparsecs of four radio galaxies of the local Universe (z<0.07), Arp 102B, Pictor A, 3C 33 and 4C +29.30, obtained with the GMOS-IFU instrument of the Gemini telescopes. We use these data to analyze the gas excitation and kinematics via two-dimensional maps. Using the flux distributions of the emission lines, we identify extended emission in ionized gas up to the edges of the observed field, which corresponds to 1.7 kpc x 2.5 kpc for Arp 102B, 2.5 kpc x 3.4 kpc for Pictor A, 4.0 kpc x 5.8 kpc for 3C 33 and 4.3 kpc x 6.2 kpc for 4C +29.30. The extended line emitting gas displays structures resembling rotating disks, spiral arms and bars. Line ratios indicate that both photons from the nuclear source and shocks originated in the interaction of the radio jet with circumnuclear gas are ionizing mechanisms of the gas. Line ratio values are typical of Seyfert galaxies for 3C 33 and 4C +29.30, while intermediate values between Seyferts and LINERs are observed in Arp 102B. Pictor A galaxy, however, shows low values of [NII]/Ha=0.15-0.25, expected for HII regions. We suggest that these values are observed due to the low gas metallicity (12+log(O/H)=8.39). Centroid velocity maps show that the gas kinematics is dominated by rotation only in Arp 102B and 3C 33. Outflows are observed in the galaxies Arp 102B, 3C 33 and 4C +29.30. We obtain mass outflow rates of 0.32-0.49 Msun per year, but the outflow kinetic power is small, ranging 0.04-0.07% of the AGN bolometric luminosity, indicating that the feedback has little impact in the host galaxies evolution. The high masses of ionized gas, ranging from 7.4E7 to 4.6E8 Msun, and the fact that these galaxies are early-type, suggest an external origin of the gas. Indeed, it is observed evidence of interaction with companion galaxies in Arp 102B, Pictor A and 4C +29.30. We suggest that the capture of mass has triggered the nuclear activity in these galaxies, with the high

The X-Ray Weakness of GPS Radio Galaxies: A Volume-Limited Complete Sample

NASA Technical Reports Server (NTRS)

Mushotzky, Richard F. (Technical Monitor); Siemiginowska, Aneta (Principal Investigator)

2004-01-01

The XMM observations of Mkn 668 have been analyzed. We found soft X-ray signatures of a hot plasma (kT approximately 10^7 approximately K) and a hard X-ray emission from the nucleus. The X-ray spectrum above 2.5 approximately keV is characterized by a very flat (observed photon index, Gamma approximately 0.5) power-law continuum, alongside with a strong Fe-K-alpha neutral iron fluorescent line (EW approximately 600 approximately eV). The best explanation for the origin of this high energy X-ray emission is in terms of the Compton-reflection of the nuclear emission. The primary X-ray emission is obscured by a Compton-thick (N_H approximately 10^24 approximately cm-2) matter which becomes transparent at higher energies. The observed above 2.5-keV X-rays are mostly due to reflection which is indicated by a strong Fe-K-alpha line. This represents the second hard X-ray detection of the GPS galaxy ever (the first one being 1345+125; O Dea et al. 2000). Interestingly, the both such trend is confirmed by our on going XMM-Newton observations of a larger GPS sample, it would lead us to looking into the question on how the dense nuclear environment impacts the nature and evolution of a GPS source, and more generally, on the history of radio power in the universe. The paper summarizing the results has been submitted to Astronomy and Astrophysics in December 2003.

Fermi gamma-ray imaging of a radio galaxy.

PubMed

Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, Ł; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

2010-05-07

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.

SEARCH FOR GAMMA-RAY EMISSION FROM X-RAY-SELECTED SEYFERT GALAXIES WITH FERMI-LAT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Allafort, A.

We report on a systematic investigation of the {gamma}-ray properties of 120 hard X-ray-selected Seyfert galaxies classified as 'radio-quiet' objects, utilizing the three-year accumulation of Fermi Large Area Telescope (LAT) data. Our sample of Seyfert galaxies is selected using the Swift Burst Alert Telescope 58 month catalog, restricting the analysis to the bright sources with average hard X-ray fluxes F{sub 14-195keV} {>=} 2.5 Multiplication-Sign 10{sup -11} erg cm{sup -2} s{sup -1} at high Galactic latitudes (|b| > 10 Degree-Sign ). In order to remove 'radio-loud' objects from the sample, we use the 'hard X-ray radio loudness parameter', R{sub rX}, definedmore » as the ratio of the total 1.4 GHz radio to 14-195 keV hard X-ray energy fluxes. Among 120 X-ray bright Seyfert galaxies with R{sub rX} <10{sup -4}, we did not find a statistically significant {gamma}-ray excess (TS > 25) positionally coincident with any target Seyferts, with possible exceptions of ESO 323-G077 and NGC 6814. The mean value of the 95% confidence level {gamma}-ray upper limit for the integrated photon flux above 100 MeV from the analyzed Seyferts is {approx_equal} 4 Multiplication-Sign 10{sup -9} photons cm{sup -2} s{sup -1} , and the upper limits derived for several objects reach {approx_equal} 1 Multiplication-Sign 10{sup -9} photons cm{sup -2} s{sup -1} . Our results indicate that no prominent {gamma}-ray emission component related to active galactic nucleus activity is present in the spectra of Seyferts around GeV energies. The Fermi-LAT upper limits derived for our sample probe the ratio of {gamma}-ray to X-ray luminosities L{sub {gamma}}/L{sub X} < 0.1, and even <0.01 in some cases. The obtained results impose novel constraints on the models for high-energy radiation of 'radio-quiet' Seyfert galaxies.« less

On the origin of the Z-shaped narrow-line region in the Seyfert galaxy NGC 3516

NASA Technical Reports Server (NTRS)

Veilleux, Sylvain; Tully, R. B.; Bland-Hawthorn, Jonathan

1993-01-01

A kinematic study has been carried out of the line-emitting gas in the Seyfert galaxy NGC 3516. The existence of two curved filaments in the central 2.5 kpc of this galaxy, which give Z-shaped appearance to its NLR. A precessing twin-jet model in which the line-emitting material is entrained by a precessing radio jet and kept ionized by the nuclear ionization field can explain the kinematic data of the brightest emission rather well. If this model is valid, this would make NGC 3516 the least luminous known active galaxy with a precessing jet. An alternative scenario assumes that the curved inner filaments represent gas entrained by a radio jet which is deflected by ram pressure from the rotation interstellar medium of the galaxy.

A long-term space astrophysics research program: An x-ray perspective of the components and structure of galaxies

NASA Technical Reports Server (NTRS)

Fabbiano, G.

1995-01-01

X-ray studies of galaxies by the Smithsonian Astrophysical Observatory (SAO) and MIT are described. Activities at SAO include ROSAT PSPC x-ray data reduction and analysis pipeline; x-ray sources in nearby Sc galaxies; optical, x-ray, and radio study of ongoing galactic merger; a radio, far infrared, optical, and x-ray study of the Sc galaxy NGC247; and a multiparametric analysis of the Einstein sample of early-type galaxies. Activities at MIT included continued analysis of observations with ROSAT and ASCA, and continued development of new approaches to spectral analysis with ASCA and AXAF. Also, a new method for characterizing structure in galactic clusters was developed and applied to ROSAT images of a large sample of clusters. An appendix contains preprints generated by the research.

Barlenses and X-shaped features compared: two manifestations of boxy/peanut bulges

NASA Astrophysics Data System (ADS)

Laurikainen, E.; Salo, H.

2017-02-01

Aims: We study the morphological characteristics of boxy/peanut-shaped bulges. In particular, we are interested to determine whether most of the flux associated with bulges in galaxies with masses similar to those of the Milky Way at redshift z 0 might belong to the vertically thick inner part of the bar, in a similar manner as in the Milky Way itself. At high galaxy inclinations, these structures are observed as boxy/peanut/X-shaped features, and when the view is near to face-on, they are observed as barlenses. We also study the possibility that bulges in some fraction of unbarred galaxies might form in a similar manner as the bulges in barred galaxies. Methods: We used the Spitzer Survey of Stellar Structure in Galaxies (S4G) and the Near-IR S0 galaxy Survey (NIRS0S) to compile complete samples of galaxies with barlenses (N = 85) and X-shaped features (N = 88). A sample of unbarred galaxies (N = 41) is also selected. For all 214 galaxies unsharp mask images were created, used to recognize the X-shaped features and to measure their linear sizes. To detect possible boxy isophotes (using the B4-parameter), we also performed an isophotal analysis for the barlens galaxies. We use recently published N-body simulations: the models that exhibit boxy/peanut/X/barlens morphologies are viewed from isotropically chosen directions that cover the full range of galaxy inclinations in the sky. The synthetic images were analyzed in a similar manner as the observations. Results: This is the first time that the observed properties of barlenses and X-shaped features are directly compared across a wide range of galaxy inclinations. A comparison with the simulation models shows that the differences in their apparent sizes, a/rbar ≳ 0.5 for barlenses and a/rbar ≲ 0.5 for X-shapes, can be explained by projection effects. Observations at various inclinations are consistent with intrinsic abl ≈ aX ≈ 0.5rbar: here intrinsic size means the face-on semimajor axis length for bars and

Starburst Galaxies. II. Imaging and Spectroscopy of a Radio-selected Sample

NASA Astrophysics Data System (ADS)

Smith, Denise A.; Herter, Terry; Haynes, Martha P.; Beichman, C. A.; Gautier, T. N., III

1996-06-01

We present J-, H-, and K-band images and low-resolution K-band spectra of the 20 most luminous starburst galaxies from the survey of Condon, Frayer, & Broderick. Optical rotation curves are also shown for 10 of these galaxies. Near-infrared colors, optical depths, CO indices, and dynamical masses are calculated. The near-infrared colors of the starburst nuclei are significantly redder than those observed in "normal" galaxies. Together, the Brγ and radio fluxes available for five of the galaxies imply that the starbursts are heavily obscured; an average extinction of A_V_~ 25 is derived. Strong CO absorption features indicate that late-type evolved stars are present in many of the starbursts. The average dynamical mass of the starburst region is found to be (1.0 +/- 0.4) x 10^9^ M_sun_.

The host galaxy of a fast radio burst.

PubMed

Keane, E F; Johnston, S; Bhandari, S; Barr, E; Bhat, N D R; Burgay, M; Caleb, M; Flynn, C; Jameson, A; Kramer, M; Petroff, E; Possenti, A; van Straten, W; Bailes, M; Burke-Spolaor, S; Eatough, R P; Stappers, B W; Totani, T; Honma, M; Furusawa, H; Hattori, T; Morokuma, T; Niino, Y; Sugai, H; Terai, T; Tominaga, N; Yamasaki, S; Yasuda, N; Allen, R; Cooke, J; Jencson, J; Kasliwal, M M; Kaplan, D L; Tingay, S J; Williams, A; Wayth, R; Chandra, P; Perrodin, D; Berezina, M; Mickaliger, M; Bassa, C

2016-02-25

In recent years, millisecond-duration radio signals originating in distant galaxies appear to have been discovered in the so-called fast radio bursts. These signals are dispersed according to a precise physical law and this dispersion is a key observable quantity, which, in tandem with a redshift measurement, can be used for fundamental physical investigations. Every fast radio burst has a dispersion measurement, but none before now have had a redshift measurement, because of the difficulty in pinpointing their celestial coordinates. Here we report the discovery of a fast radio burst and the identification of a fading radio transient lasting ~6 days after the event, which we use to identify the host galaxy; we measure the galaxy's redshift to be z = 0.492 ± 0.008. The dispersion measure and redshift, in combination, provide a direct measurement of the cosmic density of ionized baryons in the intergalactic medium of ΩIGM = 4.9 ± 1.3 per cent, in agreement with the expectation from the Wilkinson Microwave Anisotropy Probe, and including all of the so-called 'missing baryons'. The ~6-day radio transient is largely consistent with the radio afterglow of a short γ-ray burst, and its existence and timescale do not support progenitor models such as giant pulses from pulsars, and supernovae. This contrasts with the interpretation of another recently discovered fast radio burst, suggesting that there are at least two classes of bursts.

A New Radio Loudness Diagnostic for Active Galaxies: A Radio-to-Mid-Infrared Parameter

NASA Technical Reports Server (NTRS)

Melendez, Marcio B.; Kraemer, S. B.; Schmitt, H. R.

2010-01-01

We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4GHz (3.6cm) and 1.4GHz (20cm), the [O IV) (gamma)25.89 micron, [Ne III] (gamma)l5.56 micron and [Ne II] (gamma)l2.81 micron emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4 GHz/[O IV] ratio, assuming that [0 IV] scales with the luminosity of the active galactic nuclei (AGN). From this we find that Seyfert 1 s (i.e. Seyfert 1.0s, 1.2s and 1.5s) and Seyfert 2s (i.e. Seyfert 1.8s, 1.9s and 2.0s) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne u] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more 'radio loud', by a factor of approx.2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4 GHz/[O IV], or alternatively, 1.4 GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables. Key words: Galaxy: stellar content - galaxies: Seyfert - infrared: galaxies

Fermi Gamma-Ray Imaging of a Radio Galaxy

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2010-04-01

The Fermi Gamma-ray Space Telescope has detected the γ-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved γ-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy γ-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The γ-ray emission from the lobes is interpreted as inverse Compton–scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. In conclusion, these measurements provide γ-raymore » constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.« less

LOFAR discovery of an ultra-steep radio halo and giant head-tail radio galaxy in Abell 1132

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Rafferty, D.; Mechev, A. P.; Intema, H.; Andrade-Santos, F.; Clarke, A. O.; Mahony, E. K.; Morganti, R.; Prandoni, I.; Brunetti, G.; Röttgering, H.; Mandal, S.; de Gasperin, F.; Hoeft, M.

2018-01-01

Low-Frequency Array (LOFAR) observations at 144 MHz have revealed large-scale radio sources in the unrelaxed galaxy cluster Abell 1132. The cluster hosts diffuse radio emission on scales of ∼650 kpc near the cluster centre and a head-tail (HT) radio galaxy, extending up to 1 Mpc, south of the cluster centre. The central diffuse radio emission is not seen in NRAO VLA FIRST Survey, Westerbork Northern Sky Survey, nor in C & D array VLA observations at 1.4 GHz, but is detected in our follow-up Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz. Using LOFAR and GMRT data, we determine the spectral index of the central diffuse emission to be α = -1.75 ± 0.19 (S ∝ να). We classify this emission as an ultra-steep spectrum radio halo and discuss the possible implications for the physical origin of radio haloes. The HT radio galaxy shows narrow, collimated emission extending up to 1 Mpc and another 300 kpc of more diffuse, disturbed emission, giving a full projected linear size of 1.3 Mpc - classifying it as a giant radio galaxy (GRG) and making it the longest HT found to date. The head of the GRG coincides with an elliptical galaxy (SDSS J105851.01+564308.5) belonging to Abell 1132. In our LOFAR image, there appears to be a connection between the radio halo and the GRG. The turbulence that may have produced the halo may have also affected the tail of the GRG. In turn, the GRG may have provided seed electrons for the radio halo.

The two-component giant radio halo in the galaxy cluster Abell 2142

NASA Astrophysics Data System (ADS)

Venturi, T.; Rossetti, M.; Brunetti, G.; Farnsworth, D.; Gastaldello, F.; Giacintucci, S.; Lal, D. V.; Rudnick, L.; Shimwell, T. W.; Eckert, D.; Molendi, S.; Owers, M.

2017-07-01

Aims: We report on a spectral study at radio frequencies of the giant radio halo in A 2142 (z = 0.0909), which we performed to explore its nature and origin. The optical and X-ray properties of the cluster suggest that A 2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. Methods: We performed deep radio observations of A 2142 with the Giant Metrewave Radio Telescope (GMRT) at 608 MHz, 322 MHz, and 234 MHz and with the Very Large Array (VLA) in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions, from the galaxy scale, I.e. 5'', up to 60'' to image the diffuse cluster-scale emission. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A 2142, about 1 Mpc away from the cluster centre. We studied the spectral index in two regions: the central part of the halo, where the X-ray emission peaks and the two brightest dominant galaxies are located; and a second region, known as the ridge (in the direction of the most distant south-eastern cold front), selected to follow the bright part of the halo and X-ray emission. We complemented our deep observations with a preliminary LOw Frequency ARray (LOFAR) image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. Results: The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, I.e. α1.78 GHz118 MHz = 1.33 ± 0.08 . The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, I.e. α1.78 GHz118 MHz 1.5. We propose that the brightest part of the radio halo is powered by the central sloshing in A 2142, in a process similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On

Discovery of Misaligned Radio Emission in Galaxy Cluster Zw CL 2971

NASA Astrophysics Data System (ADS)

Wallack, Nicole; Migliore, C.; Resnick, A.; White, T.; Liu, C.

2014-01-01

In a search for green valley galaxies with radio loud active galactic nuclei (AGN), we found one such object that may be associated with the cluster of galaxies Zw CL 2971 (z = 0.098). Serendipitously, we found in this cluster a strong bent-jet radio source associated with the cluster's central dominant (cD) elliptical galaxy. The center of the cD galaxy is coincident (0.35 arcsecond) with the second brightest spot of radio continuum emission (34.3 mJy as measured by FIRST), but the brightest radio hotspot (66.8 mJy) is offset by 4.6 arcseconds 9 kpc at the redshift of the cluster) and has no visible counterpart. Furthermore, the optical spectrum of the cD galaxy has only weak emission lines, suggesting the absence of a currently active nucleus. It is possible that the counterpart is optically faint (possibly due to a recently completed duty cycle) or is not visible due to movement or position. If the radio source is a distant background object, then the brighter jet is most likely magnified by gravitational lensing. If the radio source is located at the redshift of the cluster, then the brighter radio jet trails backward toward and past the cD galaxy to a distance of ~120 kpc, while the fainter jet is bent at a nearly orthogonal angle, ~40 kpc away from the brightest radio hotspot, in the opposite direction. These geometric offsets could be used to constrain the duty cycle history of the AGN creating the radio emission, as well as the dynamical properties of the intracluster medium.

Extremely red objects in the fields of high redshift radio galaxies

NASA Technical Reports Server (NTRS)

Persson, S. E.; Mccarthy, P. J.; Dressler, Alan; Matthews, Keith

1993-01-01

We are engaged in a program of infrared imaging photometry of high redshift radio galaxies. The observations are being done using NICMOS2 and NICMOS3 arrays on the DuPont 100-inch telescope at Las Campanas Observatory. In addition, Persson and Matthews are measuring the spectral energy distributions of normal cluster galaxies in the redshift range 0 to 1. These measurements are being done with a 58 x 62 InSb array on the Palomar 5-m telescope. During the course of these observations we have imaged roughly 20 square arcminutes of sky to limiting magnitudes greater than 20 in the J, H, and K passbands (3 sigma in 3 square arcseconds). We have detected several relatively bright, extremely red, extended objects during the course of this work. Because the radio galaxy program requires Thuan-Gunn gri photometry, we are able to construct rough photometric energy distributions for many of the objects. A sample of the galaxy magnitudes within 4 arcseconds diameter is given. All the detections are real; either the objects show up at several wavelengths, or in subsets of the data. The reddest object in the table, 9ab'B' was found in a field of galaxies in a rich cluster at z = 0.4; 9ab'A' lies 8 arcseconds from it.

Search For Gamma-Ray Emission From X-Ray-Selected Seyfert Galaxies With Fermi -LAT

DOE PAGES

Ackermann, M.

2012-02-23

We report on a systematic investigation of the γ-ray properties of 120 hard Xray– selected Seyfert galaxies classified as ‘radio-quiet’ objects, utilizing the threeyear accumulation of Fermi–LAT data. Our sample of Seyfert galaxies is selected using the Swift–BAT 58-month catalog, restricting the analysis to the bright sources with average hard X-ray fluxes F14-195 keV ≥ 2.5 × 10 -11 erg cm -2 s -1 at high Galactic latitudes (|b| > 10°). In order to remove ‘radio-loud’ objects from the sample, we use the ‘hard X-ray radio loudness parameter’, RrX , defined as the ratio of the total 1.4 GHz radiomore » to 14 - 195 keV hard X-ray energy fluxes. Among 120 X-ray bright Seyfert galaxies with RrX < 10-4, we did not find a statistically significant γ-ray excess (TS > 25) positionally coincident with any target Seyferts, with possible exceptions of ESO 323–G077 and NGC 6814. The mean value of the 95% confidence level γ-ray upper limit for the integrated photon flux above 100 MeV from the analyzed Seyferts is ≃ 4×10 -9 ph cm -2 s -1 , and the upper limits derived for several objects reach ≃ 1 × 10 -9 ph cm -2 s -1 . Our results indicate that no prominent γ-ray emission component related to active galactic nucleus activity is present in the spectra of Seyferts around GeV energies. The Fermi–LAT upper limits derived for our sample probe the ratio of γ-ray to X-ray luminosities L /LX < 0.1, and even < 0.01 in some cases. The obtained results impose novel constraints on the models for high energy radiation of ‘radio-quiet’ Seyfert galaxies.« less

The inner radio structure of Centaurus A - Clues to the origin of the jet X-ray emission

NASA Technical Reports Server (NTRS)

Burns, J. O.; Feigelson, E. D.; Schreier, E. J.

1983-01-01

VLA observations at 1.4 and 4.9 GHz of the jet and inner lobes of the nearby radio galaxy Centaurus A have been used to construct maps of total intensity and polarization at resolutions of 31 x 10 and 3.6 x 1.1 arcsec. Surface brightness and pressure distributions in the jet, combined with the apparent X-ray emission from the ISM of NGC 5128, indicate that it is thermally confined. A comparison of the radio structure and the optical galaxy shows that the jet in Cen A emerges nearly along the major axis of the elliptical stellar component that is parallel to the angular momentum vector of the dust lane. The outer radio structure bends toward the galaxy minor axis. Evidence is found for a common synchrotron radiation origin of the full spectrum jet emission.

The Cosmic History of Hot Gas Cooling and Radio AGN Activity in Massive Early-Type Galaxies

NASA Technical Reports Server (NTRS)

Danielson, A. L. R.; Lehmer, B. D.; Alexander, D. M.; Brandt, W. M.; Luo, B.; Miller, N.; Xue, Y. Q.; Stott, J. P.

2012-01-01

We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z approx equals 0.0-1.2 in the Chandra Deep Fields. To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z = 0.1-1.2 in the approx equals 4 Ms CDF-S and approx equals 2 Ms CDF-N and z = 0.1-0.6 in the approx equals 250 ks E-CDF-S where the contribution from individually undetected AGNs is expected to be negligible in our stacking. We find that 55 of the ETGs are detected individually in the X-rays, and 12 of these galaxies have properties consistent with being passive hot-gas dominated systems (i.e., systems not dominated by an X-ray bright Active Galactic Nucleus; AGN). On the basis of our analyses, we find little evolution in the mean 0.5-2 keY to B-band luminosity ratio (L(sub x) /L(sub Beta) varies as [1 +z]) since z approx equals 1.2, implying that some heating mechanism prevents the gas from cooling in these systems. We consider that feedback from radio-mode AGN activity could be responsible for heating the gas. We select radio AGNs in the ETG population using their far-infrared/radio flux ratio. Our radio observations allow us to constrain the duty cycle history of radio AGN activity in our ETG sample. We estimate that if scaling relations between radio and mechanical power hold out to z approx equals 1.2 for the ETG population being studied here, the average mechanical power from AGN activity is a factor of approx equals1.4 -- 2.6 times larger than the average radiative cooling power from hot gas over the redshift range z approx equals 0-1.2. The excess of inferred AGN mechanical power from these ETGs is consistent with that found in the local Universe for similar types of galaxies.

Average Heating Rate of Hot Atmospheres in Distant Galaxy Clusters by Radio AGN: Evidence for Continuous AGN Heating

NASA Astrophysics Data System (ADS)

Ma, Cheng-Jiun; McNamara, B.; Nulsen, P.; Schaffer, R.

2011-09-01

X-ray observations of nearby clusters and galaxies have shown that energetic feedback from AGN is heating hot atmospheres and is probably the principal agent that is offsetting cooling flows. Here we examine AGN heating in distant X-ray clusters by cross correlating clusters selected from the 400 Square Degree X-ray Cluster survey with radio sources in the NRAO VLA Sky Survey. The jet power for each radio source was determined using scaling relations between radio power and cavity power determined for nearby clusters, groups, and galaxies with atmospheres containing X-ray cavities. Roughly 30% of the clusters show radio emission above a flux threshold of 3 mJy within the central 250 kpc that is presumably associated with the brightest cluster galaxy. We find no significant correlation between radio power, hence jet power, and the X-ray luminosities of clusters in redshift range 0.1 -- 0.6. The detection frequency of radio AGN is inconsistent with the presence of strong cooling flows in 400SD, but cannot rule out the presence of weak cooling flows. The average jet power of central radio AGN is approximately 2 10^{44} erg/s. The jet power corresponds to an average heating of approximately 0.2 keV/particle for gas within R_500. Assuming the current AGN heating rate remained constant out to redshifts of about 2, these figures would rise by a factor of two. Our results show that the integrated energy injected from radio AGN outbursts in clusters is statistically significant compared to the excess entropy in hot atmospheres that is required for the breaking of self-similarity in cluster scaling relations. It is not clear that central AGN in 400SD clusters are maintained by a self-regulated feedback loop at the base of a cooling flow. However, they may play a significant role in preventing the development of strong cooling flows at early epochs.

Starburst galaxies

NASA Technical Reports Server (NTRS)

Weedman, Daniel W.

1987-01-01

The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution.

Contemporaneous observations of the radio galaxy NGC 1275 from radio to very high energy γ -rays

DOE PAGES

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; ...

2014-03-27

The radio galaxy NGC 1275, recently identified as a very high energy (VHE, >100 GeV) γ-ray emitter by MAGIC, is one of the few non-blazar active galactic nuclei detected in the VHE regime. The purpose of this work is to better understand the origin of the γ-ray emission and locate it within the galaxy. We studied contemporaneous multifrequency observations of NGC 1275 and modeled the overall spectral energy distribution. We analyzed unpublished MAGIC observations carried out between October 2009 and February 2010, and the previously published observations taken between August 2010 and February 2011. Here, we studied the multiband variabilitymore » and correlations by analyzing data of Fermi-LAT in the 100 MeV–100 GeV energy band, as well as Chandra (X-ray), KVA (optical), and MOJAVE (radio) data taken during the same period. Using customized Monte Carlo simulations corresponding to early MAGIC stereoscopic data, we detect NGC 1275 also in the earlier MAGIC campaign. The flux level and energy spectra are similar to the results of the second campaign. The monthly light curve above 100 GeV shows a hint of variability at the 3.6σ level. In the Fermi-LAT band, both flux and spectral shape variabilities are reported. Furthermore, the optical light curve is also variable and shows a clear correlation with the γ-ray flux above 100 MeV. In radio, three compact components are resolved in the innermost part of the jet. One of these components shows a similar trend as the Fermi-LAT and KVA light curves. The γ-ray spectra measured simultaneously with MAGIC and Fermi-LAT from 100 MeV to 650 GeV can be well fitted either by a log-parabola or by a power-law with a subexponential cutoff for the two observation campaigns. A single-zone synchrotron-self-Compton model, with an electron spectrum following a power-law with an exponential cutoff, can explain the broadband spectral energy distribution and the multifrequency behavior of the source. But, this model suggests an

FR II radio galaxies in the Sloan Digital Sky Survey: observational facts

NASA Astrophysics Data System (ADS)

Kozieł-Wierzbowska, D.; Stasińska, G.

2011-08-01

Starting from the Cambridge Catalogues of radio sources, we have created a sample of 401 Fanaroff-Riley type II (FR II) radio sources that have counterparts in the main galaxy sample of the seventh Data release of the Sloan Digital Sky Survey (SDSS) and analyse their radio and optical properties. We find that the luminosity in the Hα line - which we argue gives a better measure of the total emission-line flux than the widely used luminosity in [O III]- is strongly correlated with the radio luminosity P1.4 GHz. We show that the absence of emission lines in about one third of our sample is likely due to a detection threshold and not to a lack of optical activity. We also find a very strong correlation between the values of LHα and P1.4 GHz when scaled by ‘MBH’, an estimate of the black hole mass. We find that the properties of FR II galaxies are mainly driven by the Eddington parameter LHα/‘MBH’ or, equivalently, P1.4 GHz/‘MBH’. Radio galaxies with hotspots are found among the ones with the highest values of P1.4 GHz/‘MBH’. Compared to classical active galactic nuclei (AGN) hosts in the main galaxy sample of the SDSS, our FR II galaxies show a larger proportion of objects with very hard ionizing radiation field and large ionization parameter. A few objects are, on the contrary, ionized by a softer radiation field. Two of them have double-peaked emission lines and deserve more attention. We find that the black hole masses and stellar masses in FR II galaxies are very closely related: ‘MBH’∝M1.13* with very little scatter. A comparison sample of line-less galaxies in the SDSS follows exactly the same relation, although the masses are, on average, smaller. This suggests that the FR II radio phenomenon occurs in normal elliptical galaxies, preferentially in the most massive ones. Although most FR II galaxies are old, some contain traces of young stellar populations. Such young populations are not seen in normal line-less galaxies, suggesting that

Soft γ-ray selected radio galaxies: favouring giant size discovery

NASA Astrophysics Data System (ADS)

Bassani, L.; Venturi, T.; Molina, M.; Malizia, A.; Dallacasa, D.; Panessa, F.; Bazzano, A.; Ubertini, P.

2016-09-01

Using the recent INTEGRAL/IBIS and Swift/BAT surveys we have extracted a sample of 64 confirmed plus three candidate radio galaxies selected in the soft gamma-ray band. The sample covers all optical classes and is dominated by objects showing a Fanaroff-Riley type II radio morphology; a large fraction (70 per cent) of the sample is made of `radiative mode' or high-excitation radio galaxies. We measured the source size on images from the NRAO VLA Sky Survey, the Faint Images of the Radio Sky at twenty-cm and the Sydney University Molonglo Sky Survey images and have compared our findings with data in the literature obtaining a good match. We surprisingly found that the soft gamma-ray selection favours the detection of large size radio galaxies: 60 per cent of objects in the sample have size greater than 0.4 Mpc while around 22 per cent reach dimension above 0.7 Mpc at which point they are classified as giant radio galaxies (GRGs), the largest and most energetic single entities in the Universe. Their fraction among soft gamma-ray selected radio galaxies is significantly larger than typically found in radio surveys, where only a few per cent of objects (1-6 per cent) are GRGs. This may partly be due to observational biases affecting radio surveys more than soft gamma-ray surveys, thus disfavouring the detection of GRGs at lower frequencies. The main reasons and/or conditions leading to the formation of these large radio structures are still unclear with many parameters such as high jet power, long activity time and surrounding environment all playing a role; the first two may be linked to the type of active galactic nucleus discussed in this work and partly explain the high fraction of GRGs found in the present sample. Our result suggests that high energy surveys may be a more efficient way than radio surveys to find these peculiar objects.

CONNECTION BETWEEN THE ACCRETION DISK AND JET IN THE RADIO GALAXY 3C 111

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chatterjee, Ritaban; Marscher, Alan P.; Jorstad, Svetlana G.

2011-06-10

We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 111 between 2004 and 2010 at X-ray (2.4-10 keV), optical (R band), and radio (14.5, 37, and 230 GHz) wave bands, as well as multi-epoch imaging with the Very Long Baseline Array (VLBA) at 43 GHz. Over the six years of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. This shows a clear connection between the radiative state near the black hole, where the X-rays are produced, and events in the jet. The X-ray continuummore » flux and Fe line intensity are strongly correlated, with a time lag shorter than 90 days and consistent with zero. This implies that the Fe line is generated within 90 lt-day of the source of the X-ray continuum. The power spectral density function of X-ray variations contains a break, with a steeper slope at shorter timescales. The break timescale of 13{sup +12}{sub -6} days is commensurate with scaling according to the mass of the central black hole based on observations of Seyfert galaxies and black hole X-ray binaries (BHXRBs). The data are consistent with the standard paradigm, in which the X-rays are predominantly produced by inverse Compton scattering of thermal optical/UV seed photons from the accretion disk by a distribution of hot electrons-the corona-situated near the disk. Most of the optical emission is generated in the accretion disk due to reprocessing of the X-ray emission. The relationships that we have uncovered between the accretion disk and the jet in 3C 111, as well as in the Fanaroff-Riley class I radio galaxy 3C 120 in a previous paper, support the paradigm that active galactic nuclei and Galactic BHXRBs are fundamentally similar, with characteristic time and size scales proportional to the mass of the central black hole.« less

Chandra X-ray observations of the hyper-luminous infrared galaxy IRAS F15307+3252

NASA Astrophysics Data System (ADS)

Hlavacek-Larrondo, J.; Gandhi, P.; Hogan, M. T.; Gendron-Marsolais, M.-L.; Edge, A. C.; Fabian, A. C.; Russell, H. R.; Iwasawa, K.; Mezcua, M.

2017-01-01

Hyper-luminous infrared galaxies (HyLIRGs) lie at the extreme luminosity end of the IR galaxy population with LIR > 1013 L⊙. They are thought to be closer counterparts of the more distant sub-millimeter galaxies, and should therefore be optimal targets to study the most massive systems in formation. We present deep Chandra observations of IRAS F15307+3252 (100 ks), a classical HyLIRG located at z = 0.93 and hosting a radio-loud AGN (L1.4 GHz ˜ 3.5 × 1025 W Hz-1). The Chandra images reveal the presence of extended (r = 160 kpc), asymmetric X-ray emission in the soft 0.3-2.0 keV band that has no radio counterpart. We therefore argue that the emission is of thermal origin originating from a hot intragroup or intracluster medium virializing in the potential. We find that the temperature (˜2 keV) and bolometric X-ray luminosity (˜3 × 1043 erg s-1) of the gas follow the expected LX-ray-T correlation for groups and clusters, and that the gas has a remarkably short cooling time of 1.2 Gyr. In addition, VLA radio observations reveal that the galaxy hosts an unresolved compact steep-spectrum (CSS) source, most likely indicating the presence of a young radio source similar to 3C186. We also confirm that the nucleus is dominated by a redshifted 6.4 keV Fe Kα line, strongly suggesting that the AGN is Compton-thick. Finally, Hubble images reveal an overdensity of galaxies and sub-structure in the galaxy that correlates with soft X-ray emission. This could be a snapshot view of on-going groupings expected in a growing cluster environment. IRAS F15307+3252 might therefore be a rare example of a group in the process of transforming into a cluster.

Stochastic Particle Acceleration in the Hot Spots of FRII Radio Galaxies

NASA Astrophysics Data System (ADS)

Liu, Siming; Fan, Z.; Wang, J.; Fryer, C. L.; Li, H.

2007-12-01

Chandra, XMM-Newton, and HST observations of FRII radio galaxies, in combination with traditional radio studies, have advanced our understanding of the nature of jets, hot spots, and lobes significantly. The observed radio to optical emission has been attributed to the synchrotron processes. The X-ray emission can be produced through synchrotron, synchrotron self-Comptonization, and inverse Comptonization of the CMB or other background photos. Phenomenologically modelings of the observed broadband spectra have led to good constraints on the magnetic field and electron distribution. However, the matter and energy contents of the relativistic outflows driven by the central black holes, which power these sources, are still not well-constrained, and we also lack an understanding of the physical processes that determine the energy partition between the electrons and the magnetic field, the low energy cutoff of the electron spectrum, and the electron acceleration rate in these strongly magnetized relativistic plasmas. In the context of stochastic particle acceleration, we propose a model for the hot spots of radio galaxies and show how it may help us to address the above issues. This work was funded in part under the auspices of the US Department of Energy, and supported by its contract W-7405-ENG-36 to Los Alamos National Laboratory.

Relics in galaxy clusters at high radio frequencies

NASA Astrophysics Data System (ADS)

Kierdorf, M.; Beck, R.; Hoeft, M.; Klein, U.; van Weeren, R. J.; Forman, W. R.; Jones, C.

2017-04-01

Aims: We investigated the magnetic properties of radio relics located at the peripheries of galaxy clusters at high radio frequencies, where the emission is expected to be free of Faraday depolarization. The degree of polarization is a measure of the magnetic field compression and, hence, the Mach number. Polarization observations can also be used to confirm relic candidates. Methods: We observed three radio relics in galaxy clusters and one radio relic candidate at 4.85 and 8.35 GHz in total emission and linearly polarized emission with the Effelsberg 100-m telescope. In addition, we observed one radio relic candidate in X-rays with the Chandra telescope. We derived maps of polarization angle, polarization degree, and Faraday rotation measures. Results: The radio spectra of the integrated emission below 8.35 GHz can be well fitted by single power laws for all four relics. The flat spectra (spectral indices of 0.9 and 1.0) for the so-called Sausage relic in cluster CIZA J2242+53 and the so-called Toothbrush relic in cluster 1RXS 06+42 indicate that models describing the origin of relics have to include effects beyond the assumptions of diffuse shock acceleration. The spectra of the radio relics in ZwCl 0008+52 and in Abell 1612 are steep, as expected from weak shocks (Mach number ≈2.4). Polarization observations of radio relics offer a method of measuring the strength and geometry of the shock front. We find polarization degrees of more than 50% in the two prominent Mpc-sized radio relics, the Sausage and the Toothbrush, which are among the highest percentages of linear polarization detected in any extragalactic radio source to date. This is remarkable because the large beam size of the Effelsberg single-dish telescope corresponds to linear extensions of about 300 kpc at 8.35 GHz at the distances of the relics. The high degree of polarization indicates that the magnetic field vectors are almost perfectly aligned along the relic structure, as expected for shock

A search for X-ray bright distant clusters of galaxies

NASA Technical Reports Server (NTRS)

Nichol, R. C.; Ulmer, M. P.; Kron, R. G.; Wirth, G. D.; Koo, D. C.

1994-01-01

We present the results of a search for X-ray luminous distant clusters of galaxies. We found extended X-ray emission characteristic of a cluster toward two of our candidate clusters of galaxies. They both have a luminosity in the ROSAT bandpass of approximately equals 10(exp 44) ergs/s and a redshift greater than 0.5; thus making them two of the most distant X-ray clusters ever observed. Furthermore, we show that both clusters are optically rich and have a known radio source associated with them. We compare our result with other recent searches for distant X-ray luminous clusters and present a lower limit of 1.2 x 10(exp -7)/cu Mpc for the number density of such high-redshift clusters. This limit is consistent with the expected abundance of such clusters in a standard (b = 2) cold dark matter universe. Finally, our clusters provide important high-redshift targets for further study into the origin and evolution of massive clusters of galaxies.

Multiwavelength observations of Active Galactic Nuclei from the radio to the hard X-rays

NASA Astrophysics Data System (ADS)

Beuchert, Tobias

2017-07-01

Active Galaxies form a peculiar type of galaxies. Their cores, the so-called "Active Galactic Nuclei" (AGN), are the most persistent luminous objects in the universe. Accretion of several solar masses per year onto black holes of Millions to Billions of solar masses drive the immense energy output of these systems, which can exceed that of the entire galaxy. The compact energy source, however, only measures about one over a Billion times that of the entire galaxy. Subject of my thesis are observations of the two main channels of energy release of selected AGN systems, both of which are encompassed by profound and yet unanswered questions. These channels are on the one hand the pronounced X-ray emission of the hot and compact accreting environment in close vicinity of the black hole, and on the other hand the radio synchrotron emission of magnetically collimated jets that are fed by portions of the accreted matter. These jets also function as effective accelerators and drive the injected matter deep into the intergalactic medium. As the circumnuclear environment of AGN is too compact to be spatially resolved in the X-rays, I show how X-ray spectroscopy can be used to: (1) understand the effects of strong gravity to trace the geometry and physics of the X-ray source and (2) more consistently quantify matter that surrounds and dynamically absorbs our direct line of sight towards the X-ray source. Second, I unveil the valuable information contained in the polarized radio light being emitted from magnetized jet outflows. In contrast to the X-ray emitting region, I am able to spatially resolve the inner parts of the jet of a prominent galaxy with help of the Very Long Baseline Array, a large network of radio telescopes. The resulting polarization maps turn out to be exceptionally promising in answering fundamental questions related to jet physics.

X-ray inverse Compton emission from the radio halo of M87

NASA Technical Reports Server (NTRS)

Feigelson, E. D.

1984-01-01

A significant fraction of known galaxies contain an active galactic nucleus (AGN) at their cores, the site of violent activity and non-stellar radiation seen across the entire electromagnetic spectrum. This activity is thought to be due to the accretion of gas onto a massive black hole. A fraction of AGNs also eject collimated beams of energetic material, usually seen by virtue of its synchrotron emission in the radio band. Efforts to study these jets from AGNs in the X-ray band with the Einstein Observatory has led to several detections, most notably the jets in the nearby radio galaxies Centaurus A and Virgo A = M87. In their study of M87, Schreier, Gorenstein and Feigelson (1982) noted that, in addition to the synchrotron jet 10"-20" from the nucleus, X-rays appear to be generated in the diffuse radio halo 2'-5' from the nucleus. This finding may be particularly important as it may constitute the first known case of X-ray inverse Compton emission from AGN ejecta, allowing for the first time direct determination of the magnetic field strengths.

The Physics of Cooling Flow Clusters with Central Radio Sources

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.

2005-01-01

Central galaxies in rich clusters are the sites of cluster cooling flows, with large masses of gas cooling through part of the X-ray band. Many of these galaxies host powerful radio sources. These sources can displace and compress the X-ray gas leading to enhanced cooling and star formation. We observed the bright cooling flow Abell 2626 with a strangely distorted central radio source. We wished to understand the interaction of radio and X-ray thermal plasma, and to determine the dynamical nature of this cluster. One aim was to constrain the source of additional pressure in radio "holes" in the X-ray emission needed to support overlying shells of X-ray gas. We also aimed to study the problem of the lack of kT < 1-2 keV gas in cooling flows by searching for abundance inhomogeneities, heating from the radio source, and excess absorption. We also have a Chandra observation of this cluster. There were problems with the pipeline processing of this data due to a telemetry dropout. We are publishing the Chandra and XMM data together. Delays with the Chandra data have slowed up the publication. At the center of the cluster, there is a complex interaction of the odd, Z-shaped radio source, and the X-ray plasma. However, there are no clear radio bubbles. Also, the cluster SO galaxy IC 5337, which is projected 1.5 arcmin west of the cluster center, has unusual tail-like structures in both the radio and X-ray. It appears to be falling into the cluster center. There is a hot, probably shocked region of gas to the southwest, which is apparently due to the merger of a subcluster in this part of the system. There is also a merging subcluster to the northeast. The axes of these two mergers agrees with a supercluster filament structure.

Radio emission from dusty galaxies observed by AKARI

NASA Astrophysics Data System (ADS)

Pepiak, A.; Pollo, A.; Takeuchi, T. T.; Solarz, A.; Jurusik, W.

2014-10-01

We probe radio-infrared correlation for two samples of extragalactic sources from the local Universe from the AKARI All-Sky Catalogue. The first, smaller sample (1053 objects) was constructed by the cross-correlation of the AKARI/FIS All-Sky Survey Bright Source Catalogue, the AKARI IRC All-Sky Survey Point Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the mid- and far-infrared by AKARI, and at the 1.4 GHz radio frequency by NRAO. The second, larger sample (13,324 objects) was constructed by the cross-correlation of only the AKARI/FIS All-Sky Survey Bright Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the far-infrared and radio, without a condition to be detected in the mid-infrared. Additionally, all objects in both samples were identified as galaxies in the NED and/or SIMBAD databases, and a part of them is known to host active galactic nuclei (AGNs). For the present analysis, we have restricted our samples only to sources with known redshift z. In this paper, we analyse the far-infrared-radio correlation for both of these samples. We compare the ratio of infrared and radio emission from normal star-forming dusty galaxies and AGNs in both samples. For the smaller sample we obtained =2.14 for AGNs and =2.27 for normal galaxies, while for the larger sample =2.15 for AGNs and =2.22 for normal galaxies. An average value of the slope in both samples is ~2.2, which is consistent with the previous measurements from the literature.

Chandra X-Ray Observatory Image of Andromeda Galaxy

NASA Technical Reports Server (NTRS)

1999-01-01

Chandra X-Ray Observatory took this first x-ray picture of the Andromeda Galaxy (M31) on October 13, 1999. The blue dot in the center of the image is a 'cool' million-degree x-ray source where a supermassive black hole with the mass of 30-million suns is located. The x-rays are produced by matter furneling toward the black hole. Numerous other hotter x-ray sources are also apparent. Most of these are probably due to x-ray binary systems, in which a neutron star or black hole is in close orbit around a normal star. While the gas falling into the central black hole is cool, it is only cool by comparison to the 100 other x-ray sources in the Andromeda Galaxy. To be detected by an x-ray telescope, the gas must have a temperature of more than a million degrees. The Andromeda Galaxy is our nearest neighbor spiral galaxy at a distance of two million light years. It is similar to our own Milky Way in size, shape, and also contains a supermassive black hole at the center. (Photo Credit: NASA/CXC/SAO/S. Murray, M. Garcia)

FR0CAT: a FIRST catalog of FR 0 radio galaxies

NASA Astrophysics Data System (ADS)

Baldi, R. D.; Capetti, A.; Massaro, F.

2018-01-01

With the aim of exploring the properties of the class of FR 0 radio galaxies, we selected a sample of 108 compact radio sources, called FR0CAT, by combining observations from the NVSS, FIRST, and SDSS surveys. We included in the catalog sources with redshift ≤0.05, with a radio size ≲5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their radio luminosities at 1.4 GHz are in the range 1038 ≲ νL1.4 ≲ 1040 erg s-1. The FR0CAT hosts are mostly (86%) luminous (-21 ≳ Mr ≳ -23) red early-type galaxies with black hole masses 108 ≲ MBH ≲ 109M⊙. These properties are similar to those seen for the hosts of FR I radio galaxies, but they are on average a factor 1.6 less massive. The number density of FR0CAT sources is 5 times higher than that of FR Is, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR 0s with respect to FR Is. An age-size scenario that considers FR 0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR 0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR 0s might be intrinsically different from those of the FR Is, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR 0s and FR I/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.

New Detections of Radio Minihalos in Cool Cores of Galaxy Clusters

NASA Technical Reports Server (NTRS)

Giacintucci, Simona; Markevitch, Maxim; Venturi, Tiziana; Clarke, Tracy E.; Cassano, Rossella; Mazzotta, Pasquale

2013-01-01

Cool cores of some galaxy clusters exhibit faint radio minihalos. Their origin is unclear, and their study has been limited by their small number. We undertook a systematic search for minihalos in a large sample of X-ray luminous clusters with high-quality radio data. In this article, we report four new minihalos (A 478, ZwCl 3146,RXJ 1532.9+3021, and A 2204) and five candidates found in the reanalyzed archival Very Large Array observations.The radio luminosities of our minihalos and candidates are in the range of 102325 W Hz1 at 1.4 GHz, which is consistent with these types of radio sources. Their sizes (40160 kpc in radius) are somewhat smaller than those of previously known minihalos. We combine our new detections with previously known minihalos, obtaining a total sample of 21 objects, and briefly compare the cluster radio properties to the average X-ray temperature and the total masses estimated from Planck.We find that nearly all clusters hosting minihalos are hot and massive. Beyond that, there is no clear correlation between the minihalo radio power and cluster temperature or mass (in contrast with the giant radio halos found in cluster mergers, whose radio luminosity correlates with the cluster mass). Chandra X-ray images indicate gas sloshing in the cool cores of most of our clusters, with minihalos contained within the sloshing regions in many of them. This supports the hypothesis that radio-emitting electrons are reaccelerated by sloshing. Advection of relativistic electrons by the sloshing gas may also play a role in the formation of the less extended minihalos.

Discovery of a Giant Radio Halo in a New Planck Galaxy Cluster PLCKG171.9-40.7

NASA Technical Reports Server (NTRS)

Giacintucci, Simona; Kale, Ruta; Wik, Daniel R.; Venturi, Tiziana; Markevitch, Maxim

2013-01-01

We report the discovery of a giant radio halo in a new, hot, X-ray luminous galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was found using Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz, and in the 1.4 GHz data from a NRAO Very Large Array Sky Survey pointing that we have reanalyzed. The diffuse radio emission is coincident with the cluster X-ray emission, has an extent of approx.1 Mpc and a radio power of approx. 5×10(exp 24)W/Hz at 1.4 GHz. Its integrated radio spectrum has a slope of alpha approx. = 1.8 between 235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of the archival XMMNewton X-ray data shows that the cluster is hot (approx. 10 keV) and disturbed, consistent with X-ray selected clusters hosting radio halos. This is the first giant radio halo discovered in one of the new clusters found by Planck.

A Radio Study of the Ultra-luminous FIR Galaxy NGC 6240

NASA Astrophysics Data System (ADS)

Colbert, E.; Wilson, A. S.; Bland-Hawthorn, J.

1993-05-01

A number of galaxies observed in the IRAS mission are noted to emit ~ 99% of their bolometric flux in the FIR, with FIR luminosities in excess of 10(11) Lsun. The interacting galaxy NGC 6240 has often been referred to as the ``proto-typical'' ultra-luminous (L_FIR >~ 10(12) Lsun) FIR galaxy. The origin of the FIR excess remains a disputed subject in the literature. New observations of NGC 6240 were taken with the VLA at 20cm in the B-configuration, and at 3.6cm in the A-configuration. No significant radio emission was detected from or near the possible ultra-massive ``dark core'' hypothesized by Bland-Hawthorn et. al. (1991); however, approximately 30% of Seyfert galaxies have 20 cm radio luminosities weaker than the upper limit derived from the radio maps. The non-thermal radio emission from luminous FIR galaxies is tightly correlated with the FIR emission. Previous radio observations of NGC 6240 revealed two compact, steep-spectrum nuclear sources, nearly coincident with the two nuclear sources seen in optical images. The 2 images from the new VLA observations and 5 images from previous VLA observations are used to identify the morphological and spectral features of the strong, compact components in the nuclear regions (<~ 1.5 kpc; D=100 Mpc) and of the weaker ``clumps'' of diffuse emission south and west (>~ 3 kpc) from the nucleus. Feasible explanations for the radio emission are discussed. The models that have been proposed in the literature for the FIR excess of NGC 6240 are evaluated for consistency with the observed radio emission.

Surprise: Dwarf Galaxy Harbors Supermassive Black Hole

NASA Astrophysics Data System (ADS)

2011-01-01

with the Hubble Space Telescope. They found a region near the center of the galaxy that strongly emits radio waves with characteristics of those emitted by super-fast "jets" of material spewed outward from areas close to a black hole. They then searched images from the Chandra X-Ray Observatory that showed this same, radio-bright region to be strongly emitting energetic X-rays. This combination, they said, indicates an active, black-hole-powered, galactic nucleus. "Not many dwarf galaxies are known to have massive black holes," Sivakoff said. While central black holes of roughly the same mass as the one in Henize 2-10 have been found in other galaxies, those galaxies all have much more regular shapes. Henize 2-10 differs not only in its irregular shape and small size but also in its furious star formation, concentrated in numerous, very dense "super star clusters." "This galaxy probably resembles those in the very young Universe, when galaxies were just starting to form and were colliding frequently. All its properties, including the supermassive black hole, are giving us important new clues about how these black holes and galaxies formed at that time," Johnson said. The astronomers reported their findings in the January 9 online edition of Nature, and at the American Astronomical Society's meeting in Seattle, WA. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. More information, including images and other multimedia, can be found at: http://chandra.harvard.edu and http://chandra.nasa.gov

Evolution of Extragalactic Radio Sources and Quasar/Galaxy Unification

NASA Astrophysics Data System (ADS)

Onah, C. I.; Ubachukwu, A. A.; Odo, F. C.; Onuchukwu, C. C.

2018-04-01

We use a large sample of radio sources to investigate the effects of evolution, luminosity selection and radio source orientation in explaining the apparent deviation of observed angular size - redshift (θ - z) relation of extragalactic radio sources (EGRSs) from the standard model. We have fitted the observed θ - z data with standard cosmological models based on a flat universe (Ω0 = 1). The size evolution of EGRSs has been described as luminosity, temporal and orientation-dependent in the form DP,z,Φ ≍ P±q(1 + z)-m sinΦ, with q=0.3, Φ=59°, m=-0.26 for radio galaxies and q=-0.5, Φ=33°, m=3.1 for radio quasars respectively. Critical points of luminosity, logPcrit=26.33 WHz-1 and logDc=2.51 kpc (316.23 kpc) of the present sample of radio sources were also observed. All the results were found to be consistent with the popular quasar/galaxy unification scheme.

Average radio spectral energy distribution of highly star-forming galaxies

NASA Astrophysics Data System (ADS)

Tisanić, K.; Smolčić, V.; Delhaize, J.; Novak, M.; Intema, H.; Delvecchio, I.; Schinnerer, E.; Zamorani, G.

2018-05-01

The infrared-radio correlation (IRRC) offers a way to assess star formation from radio emission. Multiple studies found the IRRC to decrease with increasing redshift. This may in part be due to the lack of knowledge about the possible radio spectral energy distributions (SEDs) of star-forming galaxies. We constrain the radio SED of a complete sample of highly star-forming galaxies (SFR > 100 M⊙/ yr) based on the VLA-COSMOS 1.4 GHz Joint and 3 GHz Large Project catalogs. We reduce archival GMRT 325 MHz and 610 MHz observations, broadening the rest-frame frequency range to 0.3-15 GHz. Employing survival analysis and fitting a double power law SED, we find that the slope steepens from a spectral index of α1 = 0.51+/-0.04 below 4.5 GHz to α2 = 0.98+/-0.07 above 4.5 GHz. Our results suggest that the use of a K-correction assuming a single power-law radio SED for star forming galaxies is likely not the root cause of the IRRC trend.

EVN observations of the radio galaxy M87 following a TeV flare

NASA Astrophysics Data System (ADS)

Giroletti, M.; Giovannini, G.; Beilicke, M.; Cesarini, A.; Krawczynski, H.

2010-02-01

We report on EVN observations of the radio galaxy M87, taken at 5 GHz on 2010 Feb 10. Data were acquired by 7 radio telescopes from 21:40 UT on Feb 10 to 8:30 UT on Feb 11, directly streamed to the central data processor at JIVE, and correlated in real-time (eVLBI). This permits us to promptly report on the status of the radio jet of the source, following the increase in gamma ray emission above 100GeV reported by MAGIC (ATel #2431) The observations have an angular resolution of about 7 mas x 3 mas and rms noise of 0.12 mJy/beam.

High-energy neutrinos from FR0 radio galaxies?

NASA Astrophysics Data System (ADS)

Tavecchio, F.; Righi, C.; Capetti, A.; Grandi, P.; Ghisellini, G.

2018-04-01

The sources responsible for the emission of high-energy (≳100 TeV) neutrinos detected by IceCube are still unknown. Among the possible candidates, active galactic nuclei with relativistic jets are often examined, since the outflowing plasma seems to offer the ideal environment to accelerate the required parent high-energy cosmic rays. The non-detection of single-point sources or - almost equivalently - the absence, in the IceCube events, of multiplets originating from the same sky position - constrains the cosmic density and the neutrino output of these sources, pointing to a numerous population of faint sources. Here we explore the possibility that FR0 radio galaxies, the population of compact sources recently identified in large radio and optical surveys and representing the bulk of radio-loud AGN population, can represent suitable candidates for neutrino emission. Modelling the spectral energy distribution of an FR0 radio galaxy recently associated with a γ-ray source detected by the Large Area Telescope onboard Fermi, we derive the physical parameters of its jet, in particular the power carried by it. We consider the possible mechanisms of neutrino production, concluding that pγ reactions in the jet between protons and ambient radiation is too inefficient to sustain the required output. We propose an alternative scenario, in which protons, accelerated in the jet, escape from it and diffuse in the host galaxy, producing neutrinos as a result of pp scattering with the interstellar gas, in strict analogy with the processes taking place in star-forming galaxies.

THE {gamma}-RAY EMISSION REGION IN THE FANAROFF-RILEY II RADIO GALAXY 3C 111

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grandi, P.; Torresi, E.; Stanghellini, C., E-mail: grandi@iasfbo.inaf.it, E-mail: torresi@iasfbo.inaf.it, E-mail: cstan@ira.inaf.it

The broad-line radio galaxy 3C 111, characterized by a Fanaroff-Riley II (FRII) radio morphology, is one of the sources of the misaligned active galactic nucleus sample, consisting of radio galaxies and steep spectrum radio quasars, recently detected by the Fermi Large Area Telescope (LAT). Our analysis of the 24 month {gamma}-ray light curve shows that 3C 111 was only occasionally detected at high energies. It was bright at the end of 2008 and faint, below the Fermi-LAT sensitivity threshold, for the rest of the time. A multifrequency campaign of 3C 111, ongoing in the same period, revealed an increase ofmore » the millimeter, optical, and X-ray fluxes in 2008 September-November, interpreted by Chatterjee et al. as due to the passage of a superluminal knot through the jet core. The temporal coincidence of the millimeter-optical-X-ray outburst with the GeV activity suggests a cospatiality of the events, allowing, for the first time, the localization of the {gamma}-ray dissipative zone in an FRII jet. We argue that the GeV photons of 3C 111 are produced in a compact region confined within 0.1 pc and at a distance of about 0.3 pc from the black hole.« less

The dust masses of powerful radio galaxies: clues to the triggering of their activity

NASA Astrophysics Data System (ADS)

Tadhunter, C.; Dicken, D.; Morganti, R.; Konyves, V.; Ysard, N.; Nesvadba, N.; Ramos Almeida, C.

2014-11-01

We use deep Herschel Space Observatory observations of a 90 per cent complete sample of 32 intermediate-redshift 2Jy radio galaxies (0.05 < z < 0.7) with strong emission lines to estimate the dust masses of their host galaxies and thereby investigate the triggering mechanisms for their quasar-like AGN. The dust masses derived for the radio galaxies (7.2 × 105 < Md < 2.6 × 108 M⊙) are intermediate between those of quiescent elliptical galaxies on the one hand, and ultraluminous infrared galaxies (ULIRGs) on the other. Consistent with simple models for the co-evolution of supermassive black holes and their host galaxies, these results suggest that most radio galaxies represent the late time re-triggering of AGN activity via mergers between the host giant elliptical galaxies and companion galaxies with relatively low gas masses. However, a minority of the radio galaxies in our sample (˜20 per cent) have high, ULIRG-like dust masses, along with evidence for prodigious star formation activity. The latter objects are more likely to have been triggered in major, gas-rich mergers that represent a rapid growth phase for both their host galaxies and their supermassive black holes.

Radio continuum of galaxies with H2O megamaser disks: 33 GHz VLA data

NASA Astrophysics Data System (ADS)

Kamali, F.; Henkel, C.; Brunthaler, A.; Impellizzeri, C. M. V.; Menten, K. M.; Braatz, J. A.; Greene, J. E.; Reid, M. J.; Condon, J. J.; Lo, K. Y.; Kuo, C. Y.; Litzinger, E.; Kadler, M.

2017-09-01

Context. Galaxies with H2O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H2O maser emission has been detected. Because their geometry is known, they provide a unique view into the properties of active galactic nuclei. Aims: The goal of this work is to investigate the nuclear environment of galaxies with H2O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy. Methods: The 33 GHz (9 mm) radio continuum properties of 24 galaxies with reported 22 GHz H2O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37 GHz Ka-band observations are made with the Karl Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of 0.2-0.5 arcsec. Hard X-ray data from the Swift/BAT survey and 22 μm infrared data from WISE, 22 GHz H2O maser data and 1.4 GHz data from NVSS and FIRST surveys are also included in the analysis. Results: Eighty-seven percent (21 out of 24) galaxies in our sample show 33 GHz radio continuum emission at levels of 4.5-240σ. Five sources show extended emission (deconvolved source size larger than 2.5 times the major axis of the beam), including one source with two main components and one with three main components. The remaining detected 16 sources (and also some of the above-mentioned targets) exhibit compact cores within the sensitivity limits. Little evidence is found for extended jets (>300 pc) in most sources. Either they do not exist, or our chosen frequency of 33 GHz is too high for a detection of these supposedly steep spectrum features. In NGC 4388, we find an extended jet-like feature that appears to be oriented perpendicular to the H2O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300 pc sized jets might also be present, as is suggested by the beam-deconvolved morphology of our

The Gamma-Ray Emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447 II. The Radio View

NASA Technical Reports Server (NTRS)

Schulz, R.; Kreikenbohm, A.; Kadler, M.; Ojha, R.; Ros, E.; Stevens, J.; Edwards, P. G.; Carpenter, B.; Elsaesser, D.; Gehrels, N.;

A search for faint high-redshift radio galaxy candidates at 150 MHz

NASA Astrophysics Data System (ADS)

Saxena, A.; Jagannathan, P.; Röttgering, H. J. A.; Best, P. N.; Intema, H. T.; Zhang, M.; Duncan, K. J.; Carilli, C. L.; Miley, G. K.

2018-04-01

Ultrasteep spectrum (USS) radio sources are good tracers of powerful radio galaxies at z > 2. Identification of even a single bright radio galaxy at z > 6 can be used to detect redshifted 21 cm absorption due to neutral hydrogen in the intervening intergalactic medium. Here we describe a new sample of high-redshift radio galaxy (HzRG) candidates constructed from the TIFR GMRT Sky Survey First Alternative Data Release survey at 150 MHz. We employ USS selection (α ≤ -1.3) in ˜10 000 deg2, in combination with strict size selection and non-detections in all-sky optical and infrared surveys. We apply flux density cuts that probe a unique parameter space in flux density (50 mJy < S150 < 200 mJy) to build a sample of 32 HzRG candidates. Follow-up Karl G. Jansky Very Large Array (VLA) observations at 1.4 GHz with an average beam size of 1.3 arcsec revealed ˜ 48 per cent of sources to have a single radio component. P-band (370 MHz) imaging of 17 of these sources revealed a flattening radio SED for 10 sources at low frequencies, which is expected from compact HzRGs. Two of our sources lie in fields where deeper multiwavelength photometry and ancillary radio data are available and for one of these we find a best-fitting photo-z of 4.8 ± 2.0. The other source has zphot = 1.4 ± 0.1 and a small angular size (3.7 arcsec), which could be associated with an obscured star-forming galaxy or with a `dead' elliptical. One USS radio source not part of the HzRG sample but observed with the VLA none the less is revealed to be a candidate giant radio galaxy with a host galaxy photo-z of 1.8 ± 0.5, indicating a size of 875 kpc.

Giant Metrewave Radio Telescope Observations of Head–Tail Radio Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sebastian, Biny; Lal, Dharam V.; Rao, A. Pramesh, E-mail: biny@ncra.tifr.res.in

We present results from a study of seven large known head–tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of multiple bends and wiggles in several head–tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailingmore » equipartition magnetic field also decreases along the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ∼10{sup 8} yr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.« less

Revealing the Faraday depth structure of radio galaxy NGC 612 with broad-band radio polarimetric observations

NASA Astrophysics Data System (ADS)

Kaczmarek, J. F.; Purcell, C. R.; Gaensler, B. M.; Sun, X.; O'Sullivan, S. P.; McClure-Griffiths, N. M.

2018-05-01

We present full-polarization, broad-band observations of the radio galaxy NGC 612 (PKS B0131-637) from 1.3 to 3.1 GHz using the Australia Telescope Compact Array. The relatively large angular scale of the radio galaxy makes it a good candidate with which to investigate the polarization mechanisms responsible for the observed Faraday depth structure. By fitting complex polarization models to the polarized spectrum of each pixel, we find that a single polarization component can adequately describe the observed signal for the majority of the radio galaxy. While we cannot definitively rule out internal Faraday rotation, we argue that the bulk of the Faraday rotation is taking place in a thin skin that girts the polarized emission. Using minimum energy estimates, we find an implied total magnetic field strength of 4.2 μG.

Understanding the radio spectral indices of galaxy cluster relics by superdiffusive shock acceleration

NASA Astrophysics Data System (ADS)

Zimbardo, Gaetano; Perri, Silvia

2018-06-01

Galaxy cluster merger shocks are the likely source of relativistic electrons, but many observations do not fit into the standard acceleration models. In particular, there is a long-standing discrepancy between the radio derived Mach numbers M_radio and the Mach numbers derived from X-ray measurements, M_X. Here, we show how superdiffusive electron transport and superdiffusive shock acceleration (SSA) can help to solve this problem. We present a heuristic derivation of the superlinear time growth of the mean square displacement of particles, ⟨Δx2⟩∝tβ, and of the particle energy spectral index in the framework of SSA. The resulting expression for the radio spectral index α is then used to determine the superdiffusive exponent β from the observed values of α and of the compression ratio for a number of radio relics. Therefore, the fact that M_radio>M_X can be explained by SSA without the need to make assumptions on the energy spectrum of the seed electrons to be re-accelerated. We also consider the acceleration times obtained in the diffusive case, based both on the Bohm diffusion coefficient and on the quasilinear diffusion coefficient. While in the latter case the acceleration time is consistent with the estimated electron energy loss time, the former case it is much shorter.

The Origin of Powerful Radio Sources

NASA Astrophysics Data System (ADS)

Wilson, A. S.; Colbert, E. J. M.

1995-05-01

Radio-loud active galaxies are associated with elliptical or elliptical-like galaxies, many of which appear to be the result of a recent merger. In contrast, radio-quiet active galaxies prefer spiral hosts. Despite the very large difference in radio luminosities between the two classes, their continua and line spectra from infrared through X-ray frequencies are very similar. In this paper, we describe recent developments of our model (Ap. J. 438, 62 1995) in which the radio-loud phenomenon is the result of a merger of two galaxies, with each galaxy nucleus containing a slowly (or non-) rotating supermassive black hole. It is envisaged that the two black holes eventually coalesce. For the small fraction of mergers in which the two holes are both massive and of comparable mass, a rapidly-spinning, high-mass hole results. The spin energy of a rapidly rotating 10(8-9) solar mass hole suffices to provide the ~ 10(60) ergs in relativistic particles and magnetic fields in the most energetic radio sources. Luminous radio-quiet active galaxies contain high-mass, slowly-rotating holes, with the infrared through X-ray emission of both classes being fuelled by accretion as commonly assumed. We discuss constraints on the model from the luminosity functions of radio-loud and radio-quiet galaxies and from the known cosmological evolution of the radio source population; this evolution is assumed to reflect higher galaxy merger rates in the past.

Stellar Dynamics and Star Formation Histories of z ∼ 1 Radio-loud Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barišić, Ivana; Van der Wel, Arjen; Chauké, Priscilla

We investigate the stellar kinematics and stellar populations of 58 radio-loud galaxies of intermediate luminosities ( L {sub 3} {sub GHz} > 10{sup 23} W Hz{sup −1}) at 0.6 < z < 1. This sample is constructed by cross-matching galaxies from the deep VLT/VIMOS LEGA-C spectroscopic survey with the VLA 3 GHz data set. The LEGA-C continuum spectra reveal for the first time stellar velocity dispersions and age indicators of z ∼ 1 radio galaxies. We find that z ∼ 1 radio-loud active galactic nucleus (AGN) occur exclusively in predominantly old galaxies with high velocity dispersions: σ {sub *} >more » 175 km s{sup −1}, corresponding to black hole masses in excess of 10{sup 8} M {sub ⊙}. Furthermore, we confirm that at a fixed stellar mass the fraction of radio-loud AGN at z ∼ 1 is five to 10 times higher than in the local universe, suggesting that quiescent, massive galaxies at z ∼ 1 switch on as radio AGN on average once every Gyr. Our results strengthen the existing evidence for a link between high black hole masses, radio loudness, and quiescence at z ∼ 1.« less

An Analysis Framework for Understanding the Origin of Nuclear Activity in Low-power Radio Galaxies

NASA Astrophysics Data System (ADS)

Lin, Yen-Ting; Huang, Hung-Jin; Chen, Yen-Chi

2018-05-01

Using large samples containing nearly 2300 active galaxies of low radio luminosity (1.4 GHz luminosity between 2 × 1023 and 3 × 1025 W Hz‑1, essentially low-excitation radio galaxies) at z ≲ 0.3, we present a self-contained analysis of the dependence of the nuclear radio activity on both intrinsic and extrinsic properties of galaxies, with the goal of identifying the best predictors of the nuclear radio activity. While confirming the established result that stellar mass must play a key role on the triggering of radio activities, we point out that for the central, most massive galaxies, the radio activity also shows a strong dependence on halo mass, which is not likely due to enhanced interaction rates in denser regions in massive, cluster-scale halos. We thus further investigate the effects of various properties of the intracluster medium (ICM) in massive clusters on the radio activities, employing two standard statistical tools, principle component analysis and logistic regression. It is found that ICM entropy, local cooling time, and pressure are the most effective in predicting the radio activity, pointing to the accretion of gas cooling out of a hot atmosphere to be the likely origin in triggering such activities in galaxies residing in massive dark matter halos. Our analysis framework enables us to logically discern the mechanisms responsible for the radio activity separately for central and satellite galaxies.

VLA Discovers Giant Rings Around Galaxy Cluster

NASA Astrophysics Data System (ADS)

2006-11-01

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope have discovered giant, ring-like structures around a cluster of galaxies. The discovery provides tantalizing new information about how such galaxy clusters are assembled, about magnetic fields in the vast spaces between galaxy clusters, and possibly about the origin of cosmic rays. Radio-Optical Image of Cluster Galaxy Cluster Abell 3376 (Radio/Optical) CREDIT: Joydeep Bagchi, IUCAA, NRAO/AUI/NSF Above, a combined radio/optical image shows the galaxy cluster Abell 3376 in visible light (blue) and radio (red) images. The giant radio arcs surrounding the cluster were discovered using the Very Large Array. The visible-light image is from the Digitized Sky survey. Below, an X-ray image of Abell 3376 made using the European Space Agency's XMM-Newton telescope shows a spectacular, bullet-shaped region of X-rays coming from gas heated to 60 million degrees Kelvin. The bullet shape results from the supersonic collision of a smaller smaller galaxy subcluster with the main body of the larger cluster. Click on images for larger version. X-Ray Image of Cluster Galaxy Cluster Abell 3376 (X-Ray) CREDIT: Joydeep Bagchi, IUCAA, ESA "These giant, radio-emitting rings probably are the result of shock waves caused by violent collisions of smaller groups of galaxies within the cluster," said Joydeep Bagchi, of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, who led an international research team. The scientists reported their findings in the November 3 edition of the journal Science. The newly-discovered ring segments, some 6 million light-years across, surround a galaxy cluster called Abell 3376, more than 600 million light-years from Earth. They were revealed because fast-moving electrons emitted radio waves as they spiraled around magnetic field lines in intergalactic space. "Even from this large distance, the feeble radio waves were easily picked up by the VLA

Non Thermal Emission from Clusters of Galaxies: the Importance of a Joint LOFAR/Simbol-X View

NASA Astrophysics Data System (ADS)

Ferrari, C.

2009-05-01

Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources (``halos'' and ``relics'') related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. I will outline our current knowledge about the presence and properties of this non-thermal cluster component. Despite the recent progress made in observational and theoretical studies of the non-thermal emission in galaxy clusters, a number of open questions about its origin and its effects on the thermo-dynamical evolution of galaxy clusters need to be answered. I will show the importance of combining galaxy cluster observations by new-generation instruments such as LOFAR and Simbol-X. A deeper knowledge of the non-thermal cluster component, together with statistical studies of radio halos and relics, will allow to test the current cluster formation scenario and to better constrain the physics of large scale structure evolution.

The γ-ray emission region in the Fanaroff-Riley II radio galaxy 3C 111

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grandi, P.; Torresi, E.; Stanghellini, C.

The broad-line radio galaxy 3C 111, characterized by a Fanaroff-Riley II (FRII) radio morphology, is one of the sources of the misaligned active galactic nucleus sample, consisting of radio galaxies and steep spectrum radio quasars, recently detected by the Fermi Large Area Telescope (LAT). In this analysis of the 24 month γ-ray light curve shows that 3C 111 was only occasionally detected at high energies. It was bright at the end of 2008 and faint, below the Fermi-LAT sensitivity threshold, for the rest of the time. A multifrequency campaign of 3C 111, ongoing in the same period, revealed an increasemore » of the millimeter, optical, and X-ray fluxes in 2008 September-November, interpreted by Chatterjee et al. as due to the passage of a superluminal knot through the jet core. Furthermore, the temporal coincidence of the millimeter-optical-X-ray outburst with the GeV activity suggests a cospatiality of the events, allowing, for the first time, the localization of the γ-ray dissipative zone in an FRII jet. Here, we argue that the GeV photons of 3C 111 are produced in a compact region confined within 0.1 pc and at a distance of about 0.3 pc from the black hole.« less

The γ-ray emission region in the Fanaroff-Riley II radio galaxy 3C 111

DOE PAGES

Grandi, P.; Torresi, E.; Stanghellini, C.

2012-04-30

The broad-line radio galaxy 3C 111, characterized by a Fanaroff-Riley II (FRII) radio morphology, is one of the sources of the misaligned active galactic nucleus sample, consisting of radio galaxies and steep spectrum radio quasars, recently detected by the Fermi Large Area Telescope (LAT). In this analysis of the 24 month γ-ray light curve shows that 3C 111 was only occasionally detected at high energies. It was bright at the end of 2008 and faint, below the Fermi-LAT sensitivity threshold, for the rest of the time. A multifrequency campaign of 3C 111, ongoing in the same period, revealed an increasemore » of the millimeter, optical, and X-ray fluxes in 2008 September-November, interpreted by Chatterjee et al. as due to the passage of a superluminal knot through the jet core. Furthermore, the temporal coincidence of the millimeter-optical-X-ray outburst with the GeV activity suggests a cospatiality of the events, allowing, for the first time, the localization of the γ-ray dissipative zone in an FRII jet. Here, we argue that the GeV photons of 3C 111 are produced in a compact region confined within 0.1 pc and at a distance of about 0.3 pc from the black hole.« less

Large-Scale Outflows in Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Colbert, E. J. M.; Baum, S. A.

1995-12-01

\\catcode`\\@=11 \\ialign{m @th#1hfil ##hfil \\crcr#2\\crcr\\sim\\crcr}}} \\catcode`\\@=12 Highly collimated outflows extend out to Mpc scales in many radio-loud active galaxies. In Seyfert galaxies, which are radio-quiet, the outflows extend out to kpc scales and do not appear to be as highly collimated. In order to study the nature of large-scale (>~1 kpc) outflows in Seyferts, we have conducted optical, radio and X-ray surveys of a distance-limited sample of 22 edge-on Seyfert galaxies. Results of the optical emission-line imaging and spectroscopic survey imply that large-scale outflows are present in >~{{1} /{4}} of all Seyferts. The radio (VLA) and X-ray (ROSAT) surveys show that large-scale radio and X-ray emission is present at about the same frequency. Kinetic luminosities of the outflows in Seyferts are comparable to those in starburst-driven superwinds. Large-scale radio sources in Seyferts appear diffuse, but do not resemble radio halos found in some edge-on starburst galaxies (e.g. M82). We discuss the feasibility of the outflows being powered by the active nucleus (e.g. a jet) or a circumnuclear starburst.

Relativistic and Slowing Down: The Flow in the Hotspots of Powerful Radio Galaxies and Quasars

NASA Technical Reports Server (NTRS)

Kazanas, D.

2003-01-01

The 'hotspots' of powerful radio galaxies (the compact, high brightness regions, where the jet flow collides with the intergalactic medium (IGM)) have been imaged in radio, optical and recently in X-ray frequencies. We propose a scheme that unifies their, at first sight, disparate broad band (radio to X-ray) spectral properties. This scheme involves a relativistic flow upstream of the hotspot that decelerates to the sub-relativistic speed of its inferred advance through the IGM and it is viewed at different angles to its direction of motion, as suggested by two independent orientation estimators (the presence or not of broad emission lines in their optical spectra and the core-to-extended radio luminosity). This scheme, besides providing an account of the hotspot spectral properties with jet orientation, it also suggests that the large-scale jets remain relativistic all the way to the hotspots.

Surprise: Dwarf Galaxy Harbors Supermassive Black Hole

NASA Astrophysics Data System (ADS)

2011-01-01

with the Hubble Space Telescope. They found a region near the center of the galaxy that strongly emits radio waves with characteristics of those emitted by super-fast "jets" of material spewed outward from areas close to a black hole. They then searched images from the Chandra X-Ray Observatory that showed this same, radio-bright region to be strongly emitting energetic X-rays. This combination, they said, indicates an active, black-hole-powered, galactic nucleus. "Not many dwarf galaxies are known to have massive black holes," Sivakoff said. While central black holes of roughly the same mass as the one in Henize 2-10 have been found in other galaxies, those galaxies all have much more regular shapes. Henize 2-10 differs not only in its irregular shape and small size but also in its furious star formation, concentrated in numerous, very dense "super star clusters." "This galaxy probably resembles those in the very young Universe, when galaxies were just starting to form and were colliding frequently. All its properties, including the supermassive black hole, are giving us important new clues about how these black holes and galaxies formed at that time," Johnson said. The astronomers reported their findings in the January 9 online edition of Nature, and at the American Astronomical Society's meeting in Seattle, WA.

The VLA-COSMOS 3 GHz Large Project: The infrared-radio correlation of star-forming galaxies and AGN to z ≲ 6

NASA Astrophysics Data System (ADS)

Delhaize, J.; Smolčić, V.; Delvecchio, I.; Novak, M.; Sargent, M.; Baran, N.; Magnelli, B.; Zamorani, G.; Schinnerer, E.; Murphy, E. J.; Aravena, M.; Berta, S.; Bondi, M.; Capak, P.; Carilli, C.; Ciliegi, P.; Civano, F.; Ilbert, O.; Karim, A.; Laigle, C.; Le Fèvre, O.; Marchesi, S.; McCracken, H. J.; Salvato, M.; Seymour, N.; Tasca, L.

2017-06-01

We examine the behaviour of the infrared-radio correlation (IRRC) over the range 0 radio or in the infrared using a doubly-censored survival analysis. We find that the IRRC of star-forming galaxies, quantified by the infrared-to-1.4 GHz radio luminosity ratio (qTIR), decreases with increasing redshift: qTIR(z) = (2.88 ± 0.03)(1 + z)- 0.19 ± 0.01. This is consistent with several previous results from the literature. Moderate-to-high radiative luminosity AGN do not follow the same qTIR(z) trend as star-forming galaxies, having a lower normalisation and steeper decrease with redshift. We cannot rule out the possibility that unidentified AGN contributions only to the radio regime may be steepening the observed qTIR(z) trend of the star-forming galaxy population. We demonstrate that the choice of the average radio spectral index directly affects the normalisation, as well as the derived trend with redshift of the IRRC. An increasing fractional contribution to the observed 3 GHz flux by free-free emission of star-forming galaxies may also affect the derived evolution. However, we find that the standard (M82-based) assumption of the typical radio spectral energy distribution (SED) for star-forming galaxies is inconsistent with our results. This suggests a more complex shape of the typical radio SED for star-forming galaxies, and that imperfect K corrections in the radio may govern the derived trend of decreasing qTIR with increasing redshift. A more detailed understanding of the radio spectrum is therefore required for robust K corrections in the radio and to fully understand the

Occurrence of Radio Minihalos in a Mass-Limited Sample of Galaxy Clusters

NASA Technical Reports Server (NTRS)

Giacintucci, Simona; Markevitch, Maxim; Cassano, Rossella; Venturi, Tiziana; Clarke, Tracy E.; Brunetti, Gianfranco

2017-01-01

We investigate the occurrence of radio minihalos-diffuse radio sources of unknown origin observed in the cores of some galaxy clusters-in a statistical sample of 58 clusters drawn from the Planck Sunyaev-Zeldovich cluster catalog using a mass cut (M(sub 500) greater than 6 x 10(exp 14) solar mass). We supplement our statistical sample with a similarly sized nonstatistical sample mostly consisting of clusters in the ACCEPT X-ray catalog with suitable X-ray and radio data, which includes lower-mass clusters. Where necessary (for nine clusters), we reanalyzed the Very Large Array archival radio data to determine whether a minihalo is present. Our total sample includes all 28 currently known and recently discovered radio minihalos, including six candidates. We classify clusters as cool-core or non-cool-core according to the value of the specific entropy floor in the cluster center, rederived or newly derived from the Chandra X-ray density and temperature profiles where necessary (for 27 clusters). Contrary to the common wisdom that minihalos are rare, we find that almost all cool cores-at least 12 out of 15 (80%)-in our complete sample of massive clusters exhibit minihalos. The supplementary sample shows that the occurrence of minihalos may be lower in lower-mass cool-core clusters. No minihalos are found in non-cool cores or "warm cores." These findings will help test theories of the origin of minihalos and provide information on the physical processes and energetics of the cluster cores.

On the population of remnant Fanaroff-Riley type II radio galaxies and implications for radio source dynamics

NASA Astrophysics Data System (ADS)

Godfrey, L. E. H.; Morganti, R.; Brienza, M.

2017-10-01

The purpose of this work is two-fold: (1) to quantify the occurrence of ultrasteep spectrum remnant Fanaroff-Riley type II (FRII) radio galaxies in a 74 MHz flux-limited sample, and (2) perform Monte Carlo simulations of the population of active and remnant FRII radio galaxies to confront models of remnant lobe evolution, and to provide guidance for further investigation of remnant radio galaxies. We find that fewer than 2 per cent of FRII radio galaxies with S74 MHz > 1.5 Jy are candidate ultrasteep spectrum remnants, where we define ultrasteep spectrum as α _74 MHz^1400 MHz > 1.2. Our Monte Carlo simulations demonstrate that models involving Sedov-like expansion in the remnant phase, resulting in rapid adiabatic energy losses, are consistent with this upper limit, and predict the existence of nearly twice as many remnants with normal (not ultrasteep) spectra in the observed frequency range as there are ultrasteep spectrum remnants. This model also predicts an ultrasteep remnant fraction approaching 10 per cent at redshifts z < 0.5. Importantly, this model implies the lobes remain overpressured with respect to the ambient medium well after their active lifetime, in contrast with existing observational evidence that many FRII radio galaxy lobes reach pressure equilibrium with the external medium whilst still in the active phase. The predicted age distribution of remnants is a steeply decreasing function of age. In other words, young remnants are expected to be much more common than old remnants in flux-limited samples. For this reason, incorporating higher frequency data ≳5 GHz will be of great benefit to future studies of the remnant population.

When galaxies collide: understanding the broad absorption-line radio galaxy 4C +72.26

NASA Astrophysics Data System (ADS)

Smith, D. J. B.; Simpson, C.; Swinbank, A. M.; Rawlings, S.; Jarvis, M. J.

2010-05-01

We present a range of new observations of the `broad absorption-line radio galaxy' 4C +72.26 (z ~ 3.5), including sensitive rest-frame ultraviolet integral field spectroscopy using the Gemini/GMOS-N instrument and Subaru/CISCO K-band imaging and spectroscopy. We show that 4C +72.26 is a system of two vigorously star-forming galaxies superimposed along the line of sight separated by ~1300 +/- 200 km s-1 in velocity, with each demonstrating spectroscopically resolved absorption lines. The most active star-forming galaxy also hosts the accreting supermassive black hole which powers the extended radio source. We conclude that the star formation is unlikely to have been induced by a shock caused by the passage of the radio jet, and instead propose that a collision is a more probable trigger for the star formation. Despite the massive starburst, the ultraviolet-mid-infrared spectral energy distribution suggests that the pre-existing stellar population comprises ~1012Msolar of stellar mass, with the current burst only contributing a further ~2 per cent, suggesting that 4C +72.26 has already assembled most of its final stellar mass.

Magnetic fields in spiral galaxies

NASA Astrophysics Data System (ADS)

Krause, Marita

2015-03-01

The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

Circumnuclear gaseous kinematics and excitation of four local radio galaxies

NASA Astrophysics Data System (ADS)

Couto, G. S.; Storchi-Bergmann, T.; Axon, D. J.; Robinson, A.; Riffel, R. A.; Kharb, P.; Lena, D.; Schnorr-Müller, A.

2017-07-01

We present our results using optical integral field spectroscopy of four nearby (z<0.07) radio galaxies obtained with GMOS in Gemini North and South telescopes. The field-of-view probes a circumnuclear region of ≍3.5"×5", with average spatial resolution of ≍0.6". In this presentation, we will resume our results for two galaxies of our sample, Arp 102B and Pictor A, which are already published (Couto et al. 2013, 2016), as well as discuss the preliminary results for the other two, 3C 33 and 4C +29.30. While these galaxies present different characteristics, like radio jet morphology, they display in common signatures of interactions or merger events.

Giant Radio Jet Coming From Wrong Kind of Galaxy

NASA Astrophysics Data System (ADS)

2003-01-01

Giant jets of subatomic particles moving at nearly the speed of light have been found coming from thousands of galaxies across the Universe, but always from elliptical galaxies or galaxies in the process of merging -- until now. Using the combined power of the Hubble Space Telescope, the Very Large Array (VLA) and the 8-meter Gemini-South Telescope, astronomers have discovered a huge jet coming from a spiral galaxy similar to our own Milky Way. Radio-optical view of galaxy Combined HST and VLA image of the galaxy 0313-192. Optical HST image shows the galaxy edge-on; VLA image, shown in red, reveals giant jet of speeding particles. For more images, see this link below. CREDIT: Keel, Ledlow & Owen; STScI,NRAO/AUI/NSF, NASA "We've always thought spirals were the wrong kind of galaxy to generate these huge jets, but now we're going to have to re-think some of our ideas on what produces these jets," said William Keel, a University of Alabama astronomer who led the research team. Keel worked with Michael Ledlow of Gemini Observatory and Frazer Owen of the National Radio Astronomy Observatory. The scientists reported their findings at the American Astronomical Society's meeting in Seattle, Washington. "Further study of this galaxy may provide unique insights on just what needs to happen in a galaxy to produce these powerful jets of particles," Keel said. In addition, Owen said, "The loose-knit nature of the cluster of galaxies in which this galaxy resides may play a part in allowing this particular spiral to produce jets." Astronomers believe such jets originate at the cores of galaxies, where supermassive black holes provide the tremendous gravitational energy to accelerate particles to nearly the speed of light. Magnetic fields twisted tightly by spinning disks of material being sucked into the black hole are presumed to narrow the speeding particles into thin jets, like a nozzle on a garden hose. Both elliptical and spiral galaxies are believed to harbor supermassive

A young source of optical emission from distant radio galaxies.

PubMed

Hammer, F; Fèvre, O Le; Angonin, M C

1993-03-25

DISTANT radio galaxies provide valuable insights into the properties of the young Universe-they are the only known extended optical sources at high redshift and might represent an early stage in the formation and evolution of galaxies in general. This extended optical emission often has very complex morphologies, but the origin of the light is still unclear. Here we report spectroscopic observations for several distant radio galaxies (0.75≤ z ≤ 1.1) in which the rest-frame spectra exhibit featureless continua between 2,500 Å and 5,000 Å. We see no evidence for the break in the spectrum at 4,000 Å expected for an old stellar population 1-3 , and suggest that young stars or scattered emissions from the active nuclei are responsible for most of the observed light. In either case, this implies that the source of the optical emission is com-parable in age to the associated radio source, namely 10 7 years or less.

Complete identification of the Parkes half-Jansky sample of GHz peaked spectrum radio galaxies

NASA Astrophysics Data System (ADS)

de Vries, N.; Snellen, I. A. G.; Schilizzi, R. T.; Lehnert, M. D.; Bremer, M. N.

2007-03-01

Context: Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources. Statistically complete samples of GPS sources are vital for studying the early evolution of radio-loud AGN and the trigger of their nuclear activity. The "Parkes half-Jansky" sample of GPS radio galaxies is such a sample, representing the southern counterpart of the 1998 Stanghellini sample of bright GPS sources. Aims: As a first step of the investigation of the sample, the host galaxies need to be identified and their redshifts determined. Methods: Deep R-band VLT-FORS1 and ESO 3.6 m EFOSC II images and long slit spectra have been taken for the unidentified sources in the sample. Results: We have identified all twelve previously unknown host galaxies of the radio sources in the sample. Eleven have host galaxies in the range 21.0 < RC < 23.0, while one object, PKS J0210+0419, is identified in the near infrared with a galaxy with Ks = 18.3. The redshifts of 21 host galaxies have been determined in the range 0.474 < z < 1.539, bringing the total number of redshifts to 39 (80%). Analysis of the absolute magnitudes of the GPS host galaxies show that at z>1 they are on average a magnitude fainter than classical 3C radio galaxies, as found in earlier studies. However their restframe UV luminosities indicate that there is an extra light contribution from the AGN, or from a population of young stars. Based on observations collected at the European Southern Observatory Very Large Telescope, Paranal, Chile (ESO prog. ID No. 073.B-0289(B)) and the European Southern Observatory 3.6 m Telescope, La Silla, Chile (prog. ID No. 073.B-0289(A)). Appendices are only available in electronic form at http://www.aanda.org

Black Hole Demographics in and Nuclear Properties of Nearby Low Luminosity Radio Galaxies; Connections to Radio Activity?

NASA Technical Reports Server (NTRS)

Baum, S. A.; Kleijn, G. A. Verdoes; Xu, C.; ODea, C. P.; deZeeuw, P. T.

2004-01-01

We combine the results of an HST STIS and WFPC study of a complete sample of 21 nearby UGC low luminosity radio galaxies with the results of a radio VLA and VLBA study of the same sample. We examine the relationship between the stellar and gaseous properties of the galaxies on tens to hundreds of parsec scale with the properties of the radio jets on the same scale. From the VLA and VLBA data we constrain the physics of the outflowing radio plasma from the tens of parsecs to hundreds of kiloparsec scales. From the WFPC2 H alpha and dust images and the STIS kinematics of the near nuclear gas we obtain constraints on the orientation of near nuclear disks of gas and measures of the nuclear stellar, continuum point source, and line emission fluxes. Under the statistically supported assumption that the radio jet issues perpendicular to the disk, we use the orientation of the optical (large scale accretion?) disks to constrain the three-dimensional orientation of the radio ejection. From HST/STIS spectroscopy of the near-nuclear emission line gas we obtain measures/limits on the black hole masses. We examine correlations between the VLBA and VLA-scale radio emission, the nuclear line emission, and the nuclear optical and radio continuum emission. Though our sample is relatively small, it is uniquely well defined, spans a narrow range in redshift and we have a consistent set of high resolution data with which to carefully examine these relationships. We use the combined radio and optical data to: 1) Constrain the orientation, physics, and bulk outflow speed of the radio plasma; 2) Put limits on the mass accretion rate and study the relationship between black hole mass, radio luminosity, and near nuclear gaseous content; 3) Provide insight into the relationship between BL Lac objects and low luminosity radio galaxies.

THE X-SHAPED BULGE OF THE MILKY WAY REVEALED BY WISE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ness, Melissa; Lang, Dustin, E-mail: ness@mpia-hd.mpg.de

2016-07-01

The Milky Way bulge has a boxy/peanut morphology and an X-shaped structure. This X-shape has been revealed by the “split in the red clump” from star counts along the line of sight toward the bulge, measured from photometric surveys. This boxy, X-shaped bulge morphology is not unique to the Milky Way and such bulges are observed in other barred spiral galaxies. N -body simulations show that boxy and X-shaped bulges are formed from the disk via dynamical instabilities. It has also been proposed that the Milky Way bulge is not X-shaped, but rather, the apparent split in the red clumpmore » stars is a consequence of different stellar populations, in an old classical spheroidal bulge. We present a Wide-Field Infrared Survey Explorer ( WISE ) image of the Milky Way bulge, produced by downsampling the publicly available “unWISE” coadds. The WISE image of the Milky Way bulge shows that the X-shaped nature of the Milky Way bulge is self-evident and irrefutable. The X-shape morphology of the bulge in itself and the fraction of bulge stars that comprise orbits within this structure has important implications for the formation history of the Milky Way, and, given the ubiquity of boxy X-shaped bulges, spiral galaxies in general.« less

Connecting optical and X-ray tracers of galaxy cluster relaxation

NASA Astrophysics Data System (ADS)

Roberts, Ian D.; Parker, Laura C.; Hlavacek-Larrondo, Julie

2018-04-01

Substantial effort has been devoted in determining the ideal proxy for quantifying the morphology of the hot intracluster medium in clusters of galaxies. These proxies, based on X-ray emission, typically require expensive, high-quality X-ray observations making them difficult to apply to large surveys of groups and clusters. Here, we compare optical relaxation proxies with X-ray asymmetries and centroid shifts for a sample of Sloan Digital Sky Survey clusters with high-quality, archival X-ray data from Chandra and XMM-Newton. The three optical relaxation measures considered are the shape of the member-galaxy projected velocity distribution - measured by the Anderson-Darling (AD) statistic, the stellar mass gap between the most-massive and second-most-massive cluster galaxy, and the offset between the most-massive galaxy (MMG) position and the luminosity-weighted cluster centre. The AD statistic and stellar mass gap correlate significantly with X-ray relaxation proxies, with the AD statistic being the stronger correlator. Conversely, we find no evidence for a correlation between X-ray asymmetry or centroid shift and the MMG offset. High-mass clusters (Mhalo > 1014.5 M⊙) in this sample have X-ray asymmetries, centroid shifts, and Anderson-Darling statistics which are systematically larger than for low-mass systems. Finally, considering the dichotomy of Gaussian and non-Gaussian clusters (measured by the AD test), we show that the probability of being a non-Gaussian cluster correlates significantly with X-ray asymmetry but only shows a marginal correlation with centroid shift. These results confirm the shape of the radial velocity distribution as a useful proxy for cluster relaxation, which can then be applied to large redshift surveys lacking extensive X-ray coverage.

Galactic Starburst NGC 3603 from X-Rays to Radio

NASA Technical Reports Server (NTRS)

Moffat, A. F. J.; Corcoran, M. F.; Stevens, I. R.; Skalkowski, G.; Marchenko, S. V.; Muecke, A.; Ptak, A.; Koribalski, B. S.; Brenneman, L.; Mushotzky, R.;

The radio sources CTA 21 and OF+247: The hot spots of radio galaxies

NASA Astrophysics Data System (ADS)

Artyukh, V. S.; Tyul'bashev, S. A.; Chernikov, P. A.

2013-06-01

The physical conditions in the radio sources CTA 21 and OF+247 are studied assuming that the low-frequency spectral turnovers are due to synchrotron self-absorption. The physical parameters of the radio sources are estimated using a technique based on a nonuniform synchrotron source model. It is shown that the magnetic-field distributions in the dominant compact components of these radio sources are strongly inhomogeneous. The magnetic fields at the center of the sources are B ˜ 10-1 G, and the fields are two to three orders of magnitude weaker at the periphery. The magnetic field averaged over the compact component is B ˜ 10-3 G, and the density of relativistic electrons is n e ˜ 10-3 cm-3. Assuming that there is equipartition of the energies of the magnetic field and relativistic particles, averaged over the source, < E H > = < E e > ˜ 10-7-10-6 erg cm-3. The energy density of the magnetic field exceeds that of the relativistic electrons at the centers of the radio sources. The derived parameters of CTA 21 and OF+247 are close to those of the hot spots in the radio galaxy Cygnus A. On this basis, it is suggested that CTA 21 and OF+247 are radio galaxies at an early stage of their evolution, when the hot spots (dominant compact radio components) have appeared, and the radio lobes (weak extended components) are still being formed.

Superwind Outflows in Seyfert Galaxies? : Large-Scale Radio Maps of an Edge-On Sample

NASA Astrophysics Data System (ADS)

Colbert, E.; Gallimore, J.; Baum, S.; O'Dea, C.

1995-03-01

Large-scale galactic winds (superwinds) are commonly found flowing out of the nuclear region of ultraluminous infrared and powerful starburst galaxies. Stellar winds and supernovae from the nuclear starburst provide the energy to drive these superwinds. The outflowing gas escapes along the rotation axis, sweeping up and shock-heating clouds in the halo, which produces optical line emission, radio synchrotron emission, and X-rays. These features can most easily be studied in edge-on systems, so that the wind emission is not confused by that from the disk. We have begun a systematic search for superwind outflows in Seyfert galaxies. In an earlier optical emission-line survey, we found extended minor axis emission and/or double-peaked emission line profiles in >~30% of the sample objects. We present here large-scale (6cm VLA C-config) radio maps of 11 edge-on Seyfert galaxies, selected (without bias) from a distance-limited sample of 23 edge-on Seyferts. These data have been used to estimate the frequency of occurrence of superwinds. Preliminary results indicate that four (36%) of the 11 objects observed and six (26%) of the 23 objects in the distance-limited sample have extended radio emission oriented perpendicular to the galaxy disk. This emission may be produced by a galactic wind blowing out of the disk. Two (NGC 2992 and NGC 5506) of the nine objects for which we have both radio and optical data show good evidence for a galactic wind in both datasets. We suggest that galactic winds occur in >~30% of all Seyferts. A goal of this work is to find a diagnostic that can be used to distinguish between large-scale outflows that are driven by starbursts and those that are driven by an AGN. The presence of starburst-driven superwinds in Seyferts, if established, would have important implications for the connection between starburst galaxies and AGN.

RADIO DETECTION OF GREEN PEAS: IMPLICATIONS FOR MAGNETIC FIELDS IN YOUNG GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborti, Sayan; Yadav, Naveen; Ray, Alak

Green Peas are a new class of young, emission line galaxies that were discovered by citizen volunteers in the Galaxy Zoo project. Their low stellar mass, low metallicity, and very high star formation rates make Green Peas the nearby (z {approx} 0.2) analogs of the Lyman break galaxies which account for the bulk of the star formation in the early universe (z {approx} 2-5). They thus provide accessible laboratories in the nearby universe for understanding star formation, supernova feedback, particle acceleration, and magnetic field amplification in early galaxies. We report the first direct radio detection of Green Peas with lowmore » frequency Giant Metrewave Radio Telescope observations and our stacking detection with archival Very Large Array FIRST data. We show that the radio emission implies that these extremely young galaxies already have magnetic fields ({approx}> 30 {mu}G) even larger than that of the Milky Way. This is at odds with the present understanding of magnetic field growth based on amplification of seed fields by dynamo action over a galaxy's lifetime. Our observations strongly favor models with pregalactic magnetic fields at {mu}G levels.« less

Increased Prevalence of Bent Lobes for Double-lobed Radio Galaxies in Dense Environments

NASA Astrophysics Data System (ADS)

Silverstein, Ezekiel M.; Anderson, Michael E.; Bregman, Joel N.

2018-01-01

Double-lobed radio galaxies (DLRGs) often have radio lobes that subtend an angle of less than 180°, and these bent DLRGs have been shown to associate preferentially with galaxy clusters and groups. In this study, we utilize a catalog of DLRGs in SDSS quasars with radio lobes visible in VLA FIRST 20 cm radio data. We cross-match this catalog against three catalogs of galaxies over the redshift range 0< z< 0.70, obtaining 81 tentative matches. We visually examine each match and apply a number of selection criteria, eventually obtaining a sample of 44 securely detected DLRGs, which are paired to a nearby massive galaxy, galaxy group, or galaxy cluster. Most of the DLRGs identified in this manner are not central galaxies in the systems to which they are matched. Using this sample, we quantify the projected density of these matches as a function of projected separation from the central galaxy, finding a very steep decrease in matches as the impact parameter increases (for {{Σ }}\\propto {b}-m we find m={2.5}-0.3+0.4) out to b∼ 2 Mpc. In addition, we show that the fraction of DLRGs with bent lobes also decreases with radius, so that if we exclude DLRGs associated with the central galaxy in the system, the bent fraction is 78% within 1 Mpc and 56% within 2 Mpc, compared to just 29% in the field; these differences are significant at 3.6σ and 2.8σ , respectively. This behavior is consistent with ram pressure being the mechanism that causes the lobes to bend.

VLBA Observations of Low Luminosity Flat Spectrum Radio Galaxies and BL Lac Objects: Polarisation Properties

NASA Astrophysics Data System (ADS)

Bondi, M.; Dallacasa, D.; Stanghellini, C.; Marchã, M. J. M.

We obtained two-epoch VLBA observations at 5 GHz of a list of radio galaxies drawn from the 200 mJy sample (Marcha et al. 1996). The objects selected for milli-arcsecond scale observations are classified, on the basis of their optical spectroscopic and polarimetric properties, as BL Lac objects, normal weak line radio galaxies, broad line radio galaxies, and transition objects (those with intermediate properties). We present preliminary results on the radio polarization properties, on the milli-arcsecond scale, of objects with different optical properties and discuss structural variations detected from the two epochs.

FERMI Large Area Telescope Gamma-Ray Detection of the Radio Galaxy M87

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2009-11-17

Here, we report the Fermi Large Area Telescope (LAT) discovery of high-energy (MeV/GeV) γ-ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10σ in 10 months of all-sky survey data. Following the detections of Cen A and Per A, this makes M87 the third radio galaxy seen with the LAT. The faint point-like γ-ray source has a >100 MeV flux of 2.45 (±0.63) × 10 –8 photons cm –2 s –1 (photon index = 2.26 ± 0.13) with no significant variability detected within the LAT observation. This flux is comparable withmore » the previous EGRET upper limit (<2.18 × 10 –8 photons cm –2 s –1, 2σ), thus there is no evidence for a significant MeV/GeV flare on decade timescales. Contemporaneous Chandra and Very Long Baseline Array data indicate low activity in the unresolved X-ray and radio core relative to previous observations, suggesting M87 is in a quiescent overall level over the first year of Fermi-LAT observations. The LAT γ-ray spectrum is modeled as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the core. The resultant SSC spectrum extrapolates smoothly from the LAT band to the historical-minimum TeV emission. Lastly, alternative models for the core and possible contributions from the kiloparsec-scale jet in M87 are considered, and cannot be excluded.« less

Peanut-shaped metallicity distributions in bulges of edge-on galaxies: the case of NGC 4710

NASA Astrophysics Data System (ADS)

Gonzalez, Oscar A.; Debattista, Victor P.; Ness, Melissa; Erwin, Peter; Gadotti, Dimitri A.

2017-03-01

Bulges of edge-on galaxies are often boxy/peanut-shaped (B/PS), and unsharp masks reveal the presence of an X shape. Simulations show that these shapes can be produced by dynamical processes driven by a bar which vertically thickens the centre. In the Milky Way, which contains such a B/PS bulge, the X-shaped structure is traced by the metal-rich stars but not by the metal-poor ones. Recently, Debattista et al. interpreted this property as a result of the varying effect of the bar on stellar populations with different starting kinematics. This kinematic fractionation model predicts that cooler populations at the time of bar formation go on to trace the X shape, whereas hotter populations are more uniformly distributed. As this prediction is not specific to the Milky Way, we test it with Multi Unit Spectroscopic Explorer (MUSE) observations of the B/PS bulge in the nearby galaxy NGC 4710. We show that the metallicity map is more peanut-shaped than the density distribution itself, in good agreement with the prediction. This result indicates that the X-shaped structure in B/PS bulges is formed of relatively metal-rich stars that have been vertically redistributed by the bar, whereas the metal-poor stars have a more uniform, box-shaped distribution.

The radio emission from the ultraluminous far-infrared galaxy NGC 6240

NASA Technical Reports Server (NTRS)

Colbert, Edward J. M.; Wilson, Andrew S.; Bland-Hawthorn, Jonathan

1994-01-01

We present new radio observations of the 'prototypical' ultraluminous far-infrared galaxy NGC 6240, obtained using the Very Large Array (VLA) at lambda = 20 cm in B-configuration and at lambda = 3.6 cm in A-configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC 6240. Approximately 70% (approximately 3 x 10(exp 23) W/Hz) of the total radio power at 20 cm originates from the nuclear region (approximately less than 1.5 kpc), of which half is emitted by two unresolved (R approximately less than 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (alpha approximately equals 0.6; S(sub nu) proportional to nu(exp -alpha). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke et al. (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young (approximately less than 100 yr.) Nearly all of the remaining 30% of the total radio power comes from an 'armlike' region extending westward from the nuclear region. The western arm emission has a steep spectrum (alpha approximately equals 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of approximately 2 - 6 x 10(exp -14) ergs/s/sq cm in the 2 - 10 keV band. No significant radio emission is detected from or near the possible ultramassive 'dark core'.

Radio and X-ray properties of the source G29.37+0.1 linked to HESS J1844-030

NASA Astrophysics Data System (ADS)

Castelletti, G.; Supan, L.; Petriella, A.; Giacani, E.; Joshi, B. C.

2017-06-01

Aims: We report on the first detailed multiwavelength study of the radio source G29.37+0.1, which is an as-yet-unclassified object linked to the very-high-energy γ-emitting source HESS J1844-030. The origin of the multiwavelength emission toward G29.37+0.1 has not been clarified so far, leaving open the question about the physical relationship between these sources. Methods: Using observations carried out with the Giant Metrewave Radio Telescope (GMRT), we performed high-quality full-synthesis imaging at 610 MHz of the field containing G29.37+0.1. The obtained data, combined with observations at 1400 MHz from The Multi-Array Galactic Plane Imaging Survey (MAGPIS) were used to investigate in detail the properties of its radio emission. Additionally, we reprocessed archival data obtained with the XMM-Newton and Chandra observatories in order to get a multiwavelength view of this unusual source. Results: The radio source G29.37+0.1 mainly consists of a bright twisted structure, named the S-shaped feature. The high sensitivity of the new GMRT observations allowed the identification of potential lobes, jets, and a nuclear central region in the S-shaped morphology of G29.37+0.1. We also highlight the detection of diffuse and low surface brightness emission enveloping the brightest emitting regions. The brightest emission in G29.37+0.1 has a radio synchrotron spectral index α = 0.59 ± 0.09. Variations in the spectral behaviour are observed across the whole radio source with the flattest spectral features in the central nuclear and jets components (α 0.3). These results lead us to conclude that the brightest radio emission from G29.37+0.1 likely represents a newly recognized radio galaxy. The identification of optical and infrared counterparts to the emission arising from the core of G29.37+0.1 strengthens our interpretation of an extragalactic origin of the radio emission. We performed several tests to explain the physical mechanism responsible for the observed X

Fermi/LAT Observations of Swift/BAT Seyfert Galaxies: On the Contribution of Radio-Quiet Active Galactic Nuclei to the Extragalactic gamma-Ray Background

NASA Technical Reports Server (NTRS)

Teng, Stacy H.; Mushotzky, Richard F.; Sambruna, Rita M.; Davis, David S.; Reynolds, Christopher S.

2011-01-01

We present the analysis of 2.1 years of Fermi Large Area Telescope (LAT) data on 491 Seyfert galaxies detected by the Swift Burst Alert Telescope (BAT) survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi first year catalog, are detected. Using Swift/BAT and radio 20 cm fluxes, we define a new radio-loudness parameter R(sub X,BAT) where radio-loud objects have logR(sub X,BAT) > -4.7. Based on this parameter, only radio-loud sources are detected by Fermi/LAT. An upper limit to the flux of the undetected sources is derived to be approx.2x10(exp -11) photons/sq cm/s, approximately seven times lower than the observed flux of NGC 1068. Assuming a median redshift of 0.031, this implies an upper limit to the gamma-ray (1-100 GeV) luminosity of < approx.3x10(exp 41) erg/s. In addition, we identified 120 new Fermi/LAT sources near the Swift/BAT Seyfert galaxies with significant Fermi/LAT detections. A majority of these objects do not have Swift/BAT counterparts, but their possible optical counterparts include blazars, flat-spectrum radio quasars, and quasars.

An infrared jet in Centaurus A - A link to the extranuclear activity in distant radio galaxies?

NASA Technical Reports Server (NTRS)

Joy, Marshall; Harvey, P. M.; Tollestrup, E. V.; Sellgren, K.; Mcgregor, P. J.

1991-01-01

High-resolution NIR images of the visually obscured central region of Centaurus A (NGC 5128) were obtained with the University of Texas array camera on the AAT in June 1988, in order to investigate the effect of the active nucleus on the surrounding galaxy. The J (1.25 micron), H (1.65 micron), and K (2.2 micron) images of the central 40 arcsec of the galaxy revealed an emission feature extending about 10 arcsec northeast of the nucleus at the same position angle as the X-ray and radio jets. This jet is most prominent at the 1.25 micron wavelength, where its brightness was comparable to that of the nucleus. The observed properties of the 'infrared jet' were found to be similar to those seen in distant radio sources.

A catalogue of faint local radio AGN and the properties of their host galaxies

NASA Astrophysics Data System (ADS)

Lofthouse, E. K.; Kaviraj, S.; Smith, D. JB; Hardcastle, M. J.

2018-05-01

We present a catalogue of local (z < 0.1) galaxies that contain faint AGN. We select these objects by identifying galaxies that exhibit a significant excess in their radio luminosities, compared to what is expected from the observed levels of star-formation activity in these systems. This is achieved by comparing the optical (spectroscopic) star formation rate (SFR) to the 1.4 GHz luminosity measured from the FIRST survey. The majority of the AGN identified in this study are fainter than those in previous work, such as in the Best and Heckman (2012) catalogue. We show that these faint AGN make a non-negligible contribution to the radio luminosity function at low luminosities (below 1022.5 W Hz-1), and host ˜13 per cent of the local radio luminosity budget. Their host galaxies are predominantly high stellar-mass systems (with a median stellar mass of 1011M⊙), are found across a range of environments (but typically in denser environments than star-forming galaxies) and have early-type morphologies. This study demonstrates a general technique to identify AGN in galaxy populations where reliable optical SFRs can be extracted using spectro-photometry and where radio data are also available so that a radio excess can be measured. Our results also demonstrate that it is unsafe to infer SFRs from radio emission alone, even if bright AGN have been excluded from a sample, since there is a significant population of faint radio AGN which may contaminate the radio-derived SFRs.

Non-Gaussian shape discrimination with spectroscopic galaxy surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byun, Joyce; Bean, Rachel, E-mail: byun@astro.cornell.edu, E-mail: rbean@astro.cornell.edu

2015-03-01

We consider how galaxy clustering data, from Mpc to Gpc scales, from upcoming large scale structure surveys, such as Euclid and DESI, can provide discriminating information about the bispectrum shape arising from a variety of inflationary scenarios. Through exploring in detail the weighting of shape properties in the calculation of the halo bias and halo mass function we show how they probe a broad range of configurations, beyond those in the squeezed limit, that can help distinguish between shapes with similar large scale bias behaviors. We assess the impact, on constraints for a diverse set of non-Gaussian shapes, of galaxymore » clustering information in the mildly non-linear regime, and surveys that span multiple redshifts and employ different galactic tracers of the dark matter distribution. Fisher forecasts are presented for a Euclid-like spectroscopic survey of Hα-selected emission line galaxies (ELGs), and a DESI-like survey, of luminous red galaxies (LRGs) and [O-II] doublet-selected ELGs, in combination with Planck-like CMB temperature and polarization data.While ELG samples provide better probes of shapes that are divergent in the squeezed limit, LRG constraints, centered below z<1, yield stronger constraints on shapes with scale-independent large-scale halo biases, such as the equilateral template. The ELG and LRG samples provide complementary degeneracy directions for distinguishing between different shapes. For Hα-selected galaxies, we note that recent revisions of the expected Hα luminosity function reduce the halo bias constraints on the local shape, relative to the CMB. For galaxy clustering constraints to be comparable to those from the CMB, additional information about the Gaussian galaxy bias is needed, such as can be determined from the galaxy clustering bispectrum or probing the halo power spectrum directly through weak lensing. If the Gaussian galaxy bias is constrained to better than a percent level then the LSS and CMB data could

Compact radio sources in luminous infrared galaxies

NASA Astrophysics Data System (ADS)

Parra, Rodrigo

2007-08-01

Radio interferometry is an observational technique of high sensitivity and incomparably high spatial resolution. Moreover, because radio waves can freely propagate through interstellar dust and gas, it allows the study of regions of the universe completely obscured at other wavelengths. This thesis reports the observational and theoretical results of my research during the past four years which are mostly based on interferometric radio data. The COLA sample is an infrared selected sample of active star forming galaxies. We conducted 6 cm VLA and VLBI snapshot observations of the northern half of this sample. The radio emission seen at VLA scales is consistent with being powered by star formation activity because it follows the far infrared to radio correlation. We detect 22% of the sample sources in our VLBI snapshots. Based on luminosity arguments, we argue that these sub-parsec VLBI sources are powered by AGN activity. Furthermore, we find that VLBI detections are preferentially found in sources whose VLA scale structures have the highest peak brightnesses suggesting a strong correlation between compact starburst and AGN activity. This observational result is consistent with the theoretical picture of an Eddington-limited nuclear starburst acting as the last valve in the pipeline transporting the gas from kiloparsec scales onto the accretion disc of a buried AGN. Arp 220 is the archetypical ultra luminous infrared galaxy. For many years this source has been known to harbour a compact (~100 pc) cluster of unresolved 18 cm bright sources believed to be bright core collapse supernovae. Using multiwavelength VLBI observations, we obtained for the first time radio spectra for 18 of these sources. We find that over a half of them have spectra consistent with young supernovae. The rest can be better explained as older supernova remnants interacting with the high density starburst ISM. This finding allowed us to constrain the number of possible scenarios for the Arp 220

A new giant luminous arc gravitational lens associated with a z = 0.62 galaxy cluster, and the environments of distant radio galaxies

NASA Technical Reports Server (NTRS)

Dickinson, Mark

1993-01-01

In the course of a survey investigating the cluster environments of distant 3CR radio galaxies, I have identified a previously unknown 'giant luminous arc' gravitational lens. The lensing cluster is associated with the radio galaxy 3C 220.1 at z = 0.62 and is the most distant cluster now known to produce such arcs. I present imaging and spectroscopic observations of the cluster and the arc, and discuss the implications for the cluster mass. At z greater than 0.6 the cluster velocity dispersions implied by such giant arcs may provide an interesting constraint on theories of large scale structure formation. The parent investigation in which this arc was identified concerns galaxy clusters and radio galaxy environments at 0.35 less than z less than 0.8. At the present epoch, powerful FR 2 radio galaxies tend to be found in environments of poor or average galaxy density. In contrast, at the higher redshifts investigated here, richer group and cluster environments are common. I present additional data on other clusters from this survey, and discuss its extension to z greater than 1 through a program of near-infrared and optical imaging.

Proto-Clusters with Evolved Populations around Radio Galaxies at 2

NASA Astrophysics Data System (ADS)

Kodama, T.; Tanaka, M.; Tanaka, I.; Kajisawa, M.

2007-12-01

We present an on-going near-infrared survey of proto-clusters around high-z radio-loud galaxies at 2 ≲ z ≲ 3 with a new wide-field instrument MOIRCS on Subaru. Most of these field are known to show a large number of Lyα and/or Hα emitters at the same redshifts of the radio galaxies. We see a clear excess of near-infrared selected galaxies (JHK_s-selected galaxies as well as DRG) in these fields, and they are indeed proto-clusters with not only young emitters but also evolved populations. Spatial distribution of such NIR selected galaxies is filamentary and track similar structures traced by the emitters. There is an hint that the bright-end of the red sequence first appeared between z=3 and 2.

Chandra Observations of the Nuclei of Radio Galaxies: 3C 295 and Hydra A

NASA Technical Reports Server (NTRS)

Harris, D. E.; McNamara, B. R.; David, L. P.; Lavoie, Anthony R. (Technical Monitor)

2000-01-01

The angular resolution available with Chandra allows us to isolate the X-ray emission from the nucleus of many radio galaxies and obtain their spectra. As expected from unification schemes, spectra so far obtained can best be interpreted as heavily absorbed power laws. We present the spectral parameters so derived for 3C 295 and Hydra A and compare them to data obtained at other wavelengths.

Occurrence of Radio Minihalos in a Mass-limited Sample of Galaxy Clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giacintucci, Simona; Clarke, Tracy E.; Markevitch, Maxim

2017-06-01

We investigate the occurrence of radio minihalos—diffuse radio sources of unknown origin observed in the cores of some galaxy clusters—in a statistical sample of 58 clusters drawn from the Planck Sunyaev–Zel’dovich cluster catalog using a mass cut ( M {sub 500} > 6 × 10{sup 14} M {sub ⊙}). We supplement our statistical sample with a similarly sized nonstatistical sample mostly consisting of clusters in the ACCEPT X-ray catalog with suitable X-ray and radio data, which includes lower-mass clusters. Where necessary (for nine clusters), we reanalyzed the Very Large Array archival radio data to determine whether a minihalo is present.more » Our total sample includes all 28 currently known and recently discovered radio minihalos, including six candidates. We classify clusters as cool-core or non-cool-core according to the value of the specific entropy floor in the cluster center, rederived or newly derived from the Chandra X-ray density and temperature profiles where necessary (for 27 clusters). Contrary to the common wisdom that minihalos are rare, we find that almost all cool cores—at least 12 out of 15 (80%)—in our complete sample of massive clusters exhibit minihalos. The supplementary sample shows that the occurrence of minihalos may be lower in lower-mass cool-core clusters. No minihalos are found in non-cool cores or “warm cores.” These findings will help test theories of the origin of minihalos and provide information on the physical processes and energetics of the cluster cores.« less

The nature of radio emission from distant galaxies

NASA Astrophysics Data System (ADS)

Richards, Eric A.

I describe an observational program aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA centered on the Hubble Deep Field. Further MERLIN observations of the HDF region at 1.4 GHz provided an angular resolution of 0.2'' and when combined with the VLA data produced an image with an unprecedented rms noise of 4 μJy. All radio sources detected in the VLA complete sample are resolved with a median angular size of 1-2''. The differential count of the radio sources is marginally sub-Euclidean (γ = -2.4 +/- 0.1) and fluctuation analysis suggests nearly 60 sources per armin2 are present at the 1 μJy level. A correlation analysis indicates spatial clustering among the 371 radio sources on angular scales of 1-40 arcmin. Optical identifications are made primarily with bright (I = 22) disk systems composed of irregulars, peculiars, interacting/merging galaxies, and a few isolated field spirals. Available redshifts span the range 0.2-3. These clues coupled with the steep spectral index of the 1.4 GHz selected sample are indicative of diffuse synchrotron radiation in distant galactic disks. Thus the evolution in the microjansky radio population is driven principally by star-formation. I have isolated a number of optically faint radio sources (about 25% of the overall sample) which remain unidentified to I = 26-28 in the HDF and flanking optical fields. Several of these objects have extremely red counterparts and constitute a new class of radio sources which are candidate high redshift dusty protogalaxies.

Radio jet refraction in galactic atmospheres with static pressure gradients

NASA Technical Reports Server (NTRS)

Henriksen, R. N.; Vallee, J. P.; Bridle, A. H.

1981-01-01

A theory based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy, is proposed for double radio sources with a Z or S morphology. The model describes a collimated jet of supersonic material that bends self-consistently under the influence of external static pressure gradients, and may alternatively be seen as a continuous-jet version of the buoyancy model proposed by Gull (1973). Emphasis is placed on (1) S-shaped radio sources identified with isolated galaxies, such as 3C 293, whose radio structures should be free of distortions resulting from motion relative to a cluster medium, and (2) small-scale, galaxy-dominated rather than environment-dominated S-shaped sources such as the inner jet structure of Fornax A.

Fast radio burst tied to distant dwarf galaxy (Image 2)

NSF Multimedia

2017-06-07

Radio telescope at Arecibo only localized the fast radio burst to the area inside the two circles in this image, but the Very Large Array was able to pinpoint it as a dwarf galaxy within the square (shown at intersection of cross hairs in enlarged box)

Galaxy-wide radio-induced feedback in a radio-quiet quasar

NASA Astrophysics Data System (ADS)

Villar-Martín, M.; Emonts, B.; Cabrera Lavers, A.; Tadhunter, C.; Mukherjee, D.; Humphrey, A.; Rodríguez Zaurín, J.; Ramos Almeida, C.; Pérez Torres, M.; Bessiere, P.

2017-12-01

We report the discovery of a radio-quiet type 2 quasar (SDSS J165315.06+234943.0 nicknamed the 'Beetle' at z = 0.103) with unambiguous evidence for active galactic nucleus (AGN) radio-induced feedback acting across a total extension of ∼46 kpc and up to ∼26 kpc from the AGN. To the best of our knowledge, this is the first radio-quiet system where radio-induced feedback has been securely identified at ≫several kpc from the AGN. The morphological, ionization and kinematic properties of the extended ionized gas are correlated with the radio structures. We find along the radio axis (a) enhancement of the optical line emission at the location of the radio hotspots (b) turbulent gas kinematics (FWHM ∼ 380-470 km s-1) across the entire spatial range circumscribed by them (c) ionization minima for the turbulent gas at the location of the hot spots, (d) high temperature Te ≳ 1.9 × 104 K at the NE hotspot. Turbulent gas is also found far from the radio axis, ∼25 kpc in the perpendicular direction. We propose a scenario in which the radio structures have perforated the interstellar medium of the galaxy and escaped into the circumgalactic medium. While advancing, they have interacted with in situ gas modifying its properties. Our results show that jets of modest power can be the dominant feedback mechanism acting across huge volumes in radio-quiet systems, including highly accreting luminous AGNs, where radiative mode feedback may be expected.

A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters

NASA Technical Reports Server (NTRS)

Eskridge, Paul B.; Fabbiano, Giuseppina; Kim, Dong-Woo

1995-01-01

We have conducted bivariate and multivariate statistical analysis of data measuring the luminosity and interstellar medium of the Einstein sample of early-type galaxies (presented by Fabbiano, Kim, & Trinchieri 1992). We find a strong nonlinear correlation between L(sub B) and L(sub X), with a power-law slope of 1.8 +/- 0.1, steepening to 2.0 +/- if we do not consider the Local Group dwarf galaxies M32 and NGC 205. Considering only galaxies with log L(sub X) less than or equal to 40.5, we instead find a slope of 1.0 +/- 0.2 (with or without the Local Group dwarfs). Although E and S0 galaxies have consistent slopes for their L(sub B)-L(sub X) relationships, the mean values of the distribution functions of both L(sub X) and L(sub X)/L(sub B) for the S0 galaxies are lower than those for the E galaxies at the 2.8 sigma and 3.5 sigma levels, respectively. We find clear evidence for a correlation between L(sub X) and the X-ray color C(sub 21), defined by Kim, Fabbiano, & Trinchieri (1992b), which indicates that X-ray luminosity is correlated with the spectral shape below 1 keV in the sense that low-L(sub X) systems have relatively large contributions from a soft component compared with high-L(sub X) systems. We find evidence from our analysis of the 12 micron IRAS data for our sample that our S0 sample has excess 12 micron emission compared with the E sample, scaled by their optical luminosities. This may be due to emission from dust heated in star-forming regions in S0 disks. This interpretation is reinforced by the existence of a strong L(sub 12)-L(sub 100) correlation for our S0 sample that is not found for the E galaxies, and by an analysis of optical-IR colors. We find steep slopes for power-law relationships between radio luminosity and optical, X-ray, and far-IR (FIR) properties. This last point argues that the presence of an FIR-emitting interstellar medium (ISM) in early-type galaxies is coupled to their ability to generate nonthermal radio continuum, as

Deep HST imaging of distant weak radio and field galaxies

NASA Technical Reports Server (NTRS)

Windhorst, R. A.; Gordon, J. M.; Pascarelle, S. M.; Schmidtke, P. C.; Keel, W. C.; Burkey, J. M.; Dunlop, J. S.

1994-01-01

We present deep Hubble Space Telescope (HST) Wide-Field Camera (WFC) V- and I-band images of three distant weak radio galaxies with z = 0.311-2.390 and seven field galaxies with z = 0.131-0.58. The images were deconvolved with both the Lucy and multiresolution CLEAN methods, which yield a restoring Full Width at Half Maximum (FWHM) of less than or equal to 0.2 sec, (nearly) preserve photons and signal-to-noise ratio at low spatial frequencies, and produce consistent light profiles down to our 2 sigma surface brightness sensitivity limit of V approximately 27.2 and I approximately 25.9 mag/sq arcsec. Multi-component image modeling was used to provide deconvolution-independent estimates of structural parameters for symmetric galaxies. We present 12-band (m(sub 2750) UBVRIgriJHK) photometry for a subset of the galaxies and bootstrap the unknown FOC/48 zero point at 2750 A in three independent ways (yielding m(sub 2750) = 21.34 +/- 0.09 mag for 1.0 e(-)/s). Two radio galaxies with z = 0.311 and 0.528, as well as one field galaxy with z = 0.58, have the colors and spectra of early-type galaxies, and a(exp 1/4)-like light profiles in the HST images. The two at z greater than 0.5 have little or no color gradients in V - I and are likely giant ellipticals, while the z = 0.311 radio galaxy has a dim exponential disk and is likely an S0. Six of the seven field galaxies have light profiles that indicate (small) inner bulges following a(exp 1/4) laws and outer exponential disks, both with little or no color gradients. These are (early-type) spiral galaxies with z = 0.131-0.528. About half have faint companions or bars. One shows lumpy structure, possibly a merger. The compact narrow-line galaxy 53W002 at z = 2.390 has less than or = 30% +/- 10% of its HST V and I flux in the central kiloparsec (due to its weak Active Galactic Nucleus (AGN)). Most of its light (V approximately equal to 23.3) occurs in a symmetric envelope with a regular a(exp 1/4)-like profile of effective

A physical model of the infrared-to-radio correlation in galaxies

NASA Technical Reports Server (NTRS)

Helou, G.; Bicay, M. D.

1993-01-01

We explore the implications of the IR-radio correlation in star-forming galaxies, using a simple physical model constrained by the constant global ratio q of IR to radio emission and by the radial falloff of this ratio in disks of galaxies. The modeling takes into account the diffusion, radiative decay, and escape of cosmic-ray electrons responsible for the synchrotron emission, and the full range of optical depths to dust-heating photons. We introduce two assumptions: that dust-heating photons and radio-emitting cosmic-ray electrons are created in constant proportion to each other as part of the star formation activity, and that gas and magnetic field are well coupled locally, expressed as B proportional to n exp beta, with beta between 1/3 and 2/3. We conclude that disk galaxies would maintain the observed constant ratio q under these assumptions if the disk scale height h(0) and the escape scale length l(esc) for cosmic-ray electrons followed a relation of the form l(esc) proportional to h(0) exp 1/2; the IR-to-radio ratio will then depend very weakly on interstellar density, and, therefore, on magnetic field strength or mean optical depth.

Super-Sharp Radio "Vision" Measures Galaxy's Motion in Space

NASA Astrophysics Data System (ADS)

2005-03-01

Astronomers using the National Science Foundation's Very Long Baseline Array (VLBA) have measured the motion across the sky of a galaxy nearly 2.4 million light-years from Earth. While scientists have been measuring the motion of galaxies directly toward or away from Earth for decades, this is the first time that the transverse motion (called proper motion by astronomers) has been measured for a galaxy that is not a satellite of our own Milky Way Galaxy. M33 Radio/Optical Image of M33 CREDIT: NRAO/AUI/NSF, NOAO/AURA/NSF (Click on image for more files) An international scientific team analyzed VLBA observations made over two and a half years to detect minuscule shifts in the sky position of the spiral galaxy M33. Combined with previous measurements of the galaxy's motion toward Earth, the new data allowed the astronomers to calculate M33's movement in three dimensions for the first time. "A snail crawling on Mars would appear to be moving across the surface more than 100 times faster than the motion we measured for this galaxy," said Mark Reid, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. M33 is a satellite of the larger galaxy M31, the well-known Andromeda Galaxy that is the most distant object visible to the naked eye. Both are part of the Local Group of galaxies that includes the Milky Way. In addition to measuring the motion of M33 as a whole, the astronomers also were able to make a direct measurement of the spiral galaxy's rotation. Both measurements were made by observing the changes in position of giant clouds of molecules inside the galaxy. The water vapor in these clouds acts as a natural maser, strengthening, or amplifying, radio emission the same way that lasers amplify light emission. The natural masers acted as bright radio beacons whose movement could be tracked by the ultra-sharp radio "vision" of the VLBA. Reid and his colleagues plan to continue measuring M33's motion and also to make similar measurements of M31's motion

NuSTAR reveals the Comptonizing corona of the broad-line radio galaxy 3C 382

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ballantyne, D. R.; Bollenbacher, J. M.; Brenneman, L. W.

Broad-line radio galaxies (BLRGs) are active galactic nuclei that produce powerful, large-scale radio jets, but appear as Seyfert 1 galaxies in their optical spectra. In the X-ray band, BLRGs also appear like Seyfert galaxies, but with flatter spectra and weaker reflection features. One explanation for these properties is that the X-ray continuum is diluted by emission from the jet. Here, we present two NuSTAR observations of the BLRG 3C 382 that show clear evidence that the continuum of this source is dominated by thermal Comptonization, as in Seyfert 1 galaxies. The two observations were separated by over a year andmore » found 3C 382 in different states separated by a factor of 1.7 in flux. The lower flux spectrum has a photon-index of Γ=1.68{sub −0.02}{sup +0.03}, while the photon-index of the higher flux spectrum is Γ=1.78{sub −0.03}{sup +0.02}. Thermal and anisotropic Comptonization models provide an excellent fit to both spectra and show that the coronal plasma cooled from kT{sub e} = 330 ± 30 keV in the low flux data to 231{sub −88}{sup +50} keV in the high flux observation. This cooling behavior is typical of Comptonizing corona in Seyfert galaxies and is distinct from the variations observed in jet-dominated sources. In the high flux observation, simultaneous Swift data are leveraged to obtain a broadband spectral energy distribution and indicates that the corona intercepts ∼10% of the optical and ultraviolet emitting accretion disk. 3C 382 exhibits very weak reflection features, with no detectable relativistic Fe Kα line, that may be best explained by an outflowing corona combined with an ionized inner accretion disk.« less

Reflections on works by I.S.Shklovsky regarding the nature of radio galaxies

NASA Astrophysics Data System (ADS)

Komberg, B. V.; Zhuravlev, V. I.

The paper is a brief overview of the works by Iosif S. Shklovsky (1916-1985), carried out over almost 30 years (1955-1985), on the nature of activity (primarily in the radio frequency range) in nuclei of some galaxies. Worthy of note is Shklovsky's pioneering work of 1962, in which he made an attempt to consider possible evolutionary tracks of extragalactic radio sources by constructing an analog of the Herzsprung-Russel diagram for stars (radio luminosity at 160 MHz was taken instead of optical luminosity; total radio size at the same frequency, as the other parameter). Later works by other authors are also discussed, where similar diagrams were plotted using a larger observational material. Special attention is paid to the evolution of Shklovsky's views regarding the possible ways of gas getting into radio galaxies' central regions, followed by high-velocity ejections of magnetized plasmons from their nuclei. Shklovsky's assumptions were mainly based on the observational data for the properties of the closest radio galaxy, NGC 4486 (Virgo A, M87), which he believed to be the same reference standard for extragalactic radio astronomy as the Crab Nebula for galactic radio astronomy. Shklovsky's approach to the recurrence of the activity phenomenon in galactic nuclei and the one-sided character of radio ejections from them is discussed. Modern views on these issues are also briefly considered.

On the merging cluster Abell 578 and its central radio galaxy 4C+67.13

DOE PAGES

Hagino, K.; Stawarz, Ł.; Siemiginowska, A.; ...

2015-05-26

Here we analyze radio, optical, and X-ray data for the peculiar cluster Abell 578. This cluster is not fully relaxed and consists of two merging sub-systems. The brightest cluster galaxy (BCG), CGPG 0719.8+6704, is a pair of interacting ellipticals with projected separation ~10 kpc, the brighter of which hosts the radio source 4C+67.13. The Fanaroff–Riley type-II radio morphology of 4C+67.13 is unusual for central radio galaxies in local Abell clusters. Our new optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are active, albeit at low accretion rates corresponding to the Eddington ratiomore » $$\\sim {{10}^{-4}}$$ (for the estimated black hole masses of $$\\sim 3\\times {{10}^{8}}\\;{{M}_{\\odot }}$$ and $$\\sim {{10}^{9}}\\;{{M}_{\\odot }}$$). The gathered X-ray (Chandra) data allowed us to confirm and to quantify robustly the previously noted elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a large spatial offset (~60 kpc projected) between the position of the BCG and the cluster center inferred from the modeling of the X-ray surface brightness distribution. Detailed analysis of the brightness profiles and temperature revealed also that the cluster gas in the vicinity of 4C+67.13 is compressed (by a factor of about ~1.4) and heated (from $$\\simeq 2.0$$ keV up to 2.7 keV), consistent with the presence of a weak shock (Mach number ~1.3) driven by the expanding jet cocoon. As a result, this would then require the jet kinetic power of the order of $$\\sim {{10}^{45}}$$ erg s –1, implying either a very high efficiency of the jet production for the current accretion rate, or a highly modulated jet/accretion activity in the system.« less

Understanding Galaxy Shapes Across Cosmic Time Using The IllustrisTNG Simulation

NASA Astrophysics Data System (ADS)

Genel, Shy

2017-08-01

Legacy HST observations have enabled groundbreaking measurements of galaxy structure over cosmic time, measurements that still require theoretical interpretation in the context of a comprehensive galaxy evolution model. This proposed research aims at significantly promoting our understanding of the shapes of galaxies as quantified by their principal axes ratios. The main tool we propose to use is IllustrisTNG, a suite consisting of two of the largest cosmological hydrodynamical simulations run to date, which contain resolved galaxy populations (thousands of L* galaxies) that represent a state-of-the-art match to observed galaxies. In Part I of the program, we will use the simulations to create mock images and study the dependence of projected shape measurements on various factors: shape estimator, observed band, the presence of dust, radial and surface brightness cuts, and noise. We will then perform apples-to-apples comparison with observations (including HST), and provide predictions for archival as well as future observations. Further, we will quantify the intrinsic, three-dimensional, shape distribution of galaxies as a function of various galaxy parameters: redshift, mass, color, and size. In Part II of the program, we will develop theoretical insights into the physical mechanisms driving these results. We will study how galaxy shapes relate to angular momentum and merger history, and will follow the shape evolution of individual galaxies over time, looking for correlations to the evolution of other galaxy properties, e.g. size and SFR. We will also study galaxy shape relations to dark matter halo shape, thereby providing input for high-precision cosmic shear models.

Astronomers Discover Spectacular Structure in Distant Galaxy

NASA Astrophysics Data System (ADS)

1999-01-01

Researchers using the National Science Foundation's Very Large Array (VLA) radio telescope have imaged a "spectacular and complex structure" in a galaxy 50 million light-years away. Their work both resolves a decades-old observational mystery and revises current theories about the origin of X-ray emission coming from gas surrounding the galaxy. The new VLA image is of the galaxy M87, which harbors at its core a supermassive black hole spewing out jets of subatomic particles at nearly the speed of light and also is the central galaxy of the Virgo Cluster of galaxies. The VLA image is the first to show detail of a larger structure that originally was detected by radio astronomers more than a half-century ago. Analysis of the new image indicates that astronomers will have to revise their ideas about the physics of what causes X-ray emission in the cores of many galaxy clusters. Frazer Owen of the National Radio Astronomy Observatory (NRAO) in Socorro, NM; Jean Eilek of the New Mexico Institute of Mining and Technology (NM Tech) in Socorro, NM; and Namir Kassim of the Naval Research Laboratory in Washington, DC, announced their discovery at the American Astronomical Society's meeting today in Austin, TX. The new observations show two large, bubble-like lobes, more than 200,000 light-years across, that emit radio waves. These lobes, which are intricately detailed, apparently are powered by gravitational energy released from the black hole at the galaxy's center. "We think that material is flowing outward from the galaxy's core into these large, bright, radio-emitting 'bubbles,'" Owen said. The newly-discovered "bubbles" sit inside a region of the galaxy known to be emitting X-rays. Theorists have speculated that this X-ray emission arises when gas that originally was part of the Virgo Cluster of galaxies, cools and falls inwards onto M87 itself, at the center of the cluster. Such "cooling flows" are commonly thought to be responsible for strong X-ray emission in many

Measuring size evolution of distant, faint galaxies in the radio regime

NASA Astrophysics Data System (ADS)

Lindroos, L.; Knudsen, K. K.; Stanley, F.; Muxlow, T. W. B.; Beswick, R. J.; Conway, J.; Radcliffe, J. F.; Wrigley, N.

2018-05-01

We measure the evolution of sizes for star-forming galaxies as seen in 1.4 GHz continuum radio for z = 0-3. The measurements are based on combined VLA+MERLIN data of the Hubble Deep Field, and using a uv-stacking algorithm combined with model fitting to estimate the average sizes of galaxies. A sample of ˜1000 star-forming galaxies is selected from optical and near-infrared catalogues, with stellar masses M⊙ ≈ 1010-1011 M⊙ and photometric redshifts 0-3. The median sizes are parametrized for stellar mass M* = 5 × 1010 M⊙ as R_e = A× {}(H(z)/H(1.5))^{α _z}. We find that the median radio sizes evolve towards larger sizes at later times with αz = -1.1 ± 0.6, and A (the median size at z ≈ 1.5) is found to be 0.26^'' ± 0.07^'' or 2.3±0.6 kpc. The measured radio sizes are typically a factor of 2 smaller than those measure in the optical, and are also smaller than the typical H α sizes in the literature. This indicates that star formation, as traced by the radio continuum, is typically concentrated towards the centre of galaxies, for the sampled redshift range. Furthermore, the discrepancy of measured sizes from different tracers of star formation, indicates the need for models of size evolution to adopt a multiwavelength approach in the measurement of the sizes star-forming regions.

The Radio Spectral Energy Distribution and Star-formation Rate Calibration in Galaxies

NASA Astrophysics Data System (ADS)

Tabatabaei, F. S.; Schinnerer, E.; Krause, M.; Dumas, G.; Meidt, S.; Damas-Segovia, A.; Beck, R.; Murphy, E. J.; Mulcahy, D. D.; Groves, B.; Bolatto, A.; Dale, D.; Galametz, M.; Sandstrom, K.; Boquien, M.; Calzetti, D.; Kennicutt, R. C.; Hunt, L. K.; De Looze, I.; Pellegrini, E. W.

2017-02-01

We study the spectral energy distribution (SED) of the radio continuum (RC) emission from the Key Insight in Nearby Galaxies Emitting in Radio (KINGFISHER) sample of nearby galaxies to understand the energetics and origin of this emission. Effelsberg multi-wavelength observations at 1.4, 4.8, 8.4, and 10.5 GHz combined with archive data allow us, for the first time, to determine the mid-RC (1-10 GHz, MRC) bolometric luminosities and further present calibration relations versus the monochromatic radio luminosities. The 1-10 GHz radio SED is fitted using a Bayesian Markov Chain Monte Carlo technique leading to measurements for the nonthermal spectral index ({S}ν ˜ {ν }-{α {nt}}) and the thermal fraction ({f}{th}) with mean values of {α }{nt}=0.97 +/- 0.16(0.79 +/- 0.15 for the total spectral index) and {f}{th} = (10 ± 9)% at 1.4 GHz. The MRC luminosity changes over ˜3 orders of magnitude in the sample, 4.3× {10}2 {L}⊙ < MRC < 3.9× {10}5 {L}⊙ . The thermal emission is responsible for ˜23% of the MRC on average. We also compare the extinction-corrected diagnostics of the star-formation rate (SFR) with the thermal and nonthermal radio tracers and derive the first star-formation calibration relations using the MRC radio luminosity. The nonthermal spectral index flattens with increasing SFR surface density, indicating the effect of the star-formation feedback on the cosmic-ray electron population in galaxies. Comparing the radio and IR SEDs, we find that the FIR-to-MRC ratio could decrease with SFR, due to the amplification of the magnetic fields in star-forming regions. This particularly implies a decrease in the ratio at high redshifts, where mostly luminous/star-forming galaxies are detected.

Radio and X-ray variability of the nucleus of Centaurus A /NGC 5128/

NASA Technical Reports Server (NTRS)

Beall, J. H.; Rose, W. K.; Graf, W.; Price, K. M.; Dent, W. A.; Hobbs, R. W.; Dennis, B. R.; Crannell, C. J.; Conklin, E. K.; Ulich, B. L.

1978-01-01

Centaurus A (NGC 5128) has been observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. These observations, together with results reported by other workers, are interpreted in terms of models of the nucleus of this radio galaxy. The radio observations cover the period from 1973 through early 1977. The X-ray observations cover two 10-day intervals, one in July and August (1975) and the other in July and August 1976. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are shown to be consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons. Upper limits obtained with the model indicate that there may be sufficient energy available in the nucleus to form radio lobes with the same total energy as those already present.

Radio Galaxy Zoo: cosmological alignment of radio sources

NASA Astrophysics Data System (ADS)

Contigiani, O.; de Gasperin, F.; Miley, G. K.; Rudnick, L.; Andernach, H.; Banfield, J. K.; Kapińska, A. D.; Shabala, S. S.; Wong, O. I.

2017-11-01

We study the mutual alignment of radio sources within two surveys, Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and TIFR GMRT Sky Survey (TGSS). This is done by producing two position angle catalogues containing the preferential directions of respectively 30 059 and 11 674 extended sources distributed over more than 7000 and 17 000 deg2. The identification of the sources in the FIRST sample was performed in advance by volunteers of the Radio Galaxy Zoo (RGZ) project, while for the TGSS sample it is the result of an automated process presented here. After taking into account systematic effects, marginal evidence of a local alignment on scales smaller than 2.5 deg is found in the FIRST sample. The probability of this happening by chance is found to be less than 2 per cent. Further study suggests that on scales up to 1.5 deg the alignment is maximal. For one third of the sources, the RGZ volunteers identified an optical counterpart. Assuming a flat Λ cold dark matter cosmology with Ω _m = 0.31, Ω _Λ = 0.69, we convert the maximum angular scale on which alignment is seen into a physical scale in the range [19, 38] Mpc h_{70}^{-1}. This result supports recent evidence reported by Taylor and Jagannathan of radio jet alignment in the 1.4 deg2 ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The TGSS sample is found to be too sparsely populated to manifest a similar signal.

STAR FORMATION SUPPRESSION DUE TO JET FEEDBACK IN RADIO GALAXIES WITH SHOCKED WARM MOLECULAR GAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lanz, Lauranne; Ogle, Patrick M.; Appleton, Philip N.

2016-07-20

We present Herschel observations of 22 radio galaxies, selected for the presence of shocked, warm molecular hydrogen emission. We measured and modeled spectral energy distributions in 33 bands from the ultraviolet to the far-infrared to investigate the impact of jet feedback on star formation activity. These galaxies are massive, early-type galaxies with normal gas-to-dust ratios, covering a range of optical and infrared colors. We find that the star formation rate (SFR) is suppressed by a factor of ∼3–6, depending on how molecular gas mass is estimated. We suggest that this suppression is due to the shocks driven by the radiomore » jets injecting turbulence into the interstellar medium (ISM), which also powers the luminous warm H{sub 2} line emission. Approximately 25% of the sample shows suppression by more than a factor of 10. However, the degree of SFR suppression does not correlate with indicators of jet feedback including jet power, diffuse X-ray emission, or intensity of warm molecular H{sub 2} emission, suggesting that while injected turbulence likely impacts star formation, the process is not purely parameterized by the amount of mechanical energy dissipated into the ISM. Radio galaxies with shocked warm molecular gas cover a wide range in SFR–stellar mass space, indicating that these galaxies are in a variety of evolutionary states, from actively star-forming and gas-rich to quiescent and gas-poor. SFR suppression appears to have the largest impact on the evolution of galaxies that are moderately gas-rich.« less

A hot X-ray filament associated with A3017 galaxy cluster

NASA Astrophysics Data System (ADS)

Parekh, V.; Durret, F.; Padmanabh, P.; Pandge, M. B.

2017-09-01

Recent simulations and observations have shown large-scale filaments in the cosmic web connecting nodes, with accreting materials (baryonic and dark matter) flowing through them. Current high-sensitivity observations also show that the propagation of shocks through filaments can heat them up and make filaments visible between two or more galaxy clusters or around massive clusters, based on optical and/or X-ray observations. We are reporting here the special case of the cluster A3017 associated with a hot filament. The temperature of the filament is 3.4^{-0.77}_{+1.30} keV and its length is ∼1 Mpc. We have analysed its archival Chandra data and report various properties. We also analysed GMRT 235/610 MHz radio data. Radio observations have revealed symmetric two-sided lobes that fill cavities in the A3017 cluster core region, associated with central active galactic nucleus. In the radio map, we also noticed a peculiar linear vertical radio structure in the X-ray filament region which might be associated with a cosmic filament shock. This radio structure could be a radio phoenix or old plasma where an old relativistic population is re-accelerated by shock propagation. Finally, we put an upper limit on the radio luminosity of the filament region.

The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy

NASA Astrophysics Data System (ADS)

Ching, John H. Y.; Sadler, Elaine M.; Croom, Scott M.; Johnston, Helen M.; Pracy, Michael B.; Couch, Warrick J.; Hopkins, A. M.; Jurek, Russell J.; Pimbblet, K. A.

2017-01-01

We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ˜ 0.8. The catalogue covers ˜800 deg2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of Imod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radio-loud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc.

LeMMINGs - I. The eMERLIN legacy survey of nearby galaxies. 1.5-GHz parsec-scale radio structures and cores

NASA Astrophysics Data System (ADS)

Baldi, R. D.; Williams, D. R. A.; McHardy, I. M.; Beswick, R. J.; Argo, M. K.; Dullo, B. T.; Knapen, J. H.; Brinks, E.; Muxlow, T. W. B.; Aalto, S.; Alberdi, A.; Bendo, G. J.; Corbel, S.; Evans, R.; Fenech, D. M.; Green, D. A.; Klöckner, H.-R.; Körding, E.; Kharb, P.; Maccarone, T. J.; Martí-Vidal, I.; Mundell, C. G.; Panessa, F.; Peck, A. B.; Pérez-Torres, M. A.; Saikia, D. J.; Saikia, P.; Shankar, F.; Spencer, R. E.; Stevens, I. R.; Uttley, P.; Westcott, J.

2018-05-01

We present the first data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 103 nearby galaxies from the Palomar sample, observed with the eMERLIN array, as part of the LeMMINGs survey. This sample includes galaxies which are active (low-ionization nuclear emission-line regions [LINER] and Seyfert) and quiescent (H II galaxies and absorption line galaxies, ALGs), which are reclassified based upon revised emission-line diagrams. We detect radio emission ≳0.2 mJy for 47/103 galaxies (22/34 for LINERS, 4/4 for Seyferts, 16/51 for H II galaxies, and 5/14 for ALGs) with radio sizes typically of ≲100 pc. We identify the radio core position within the radio structures for 41 sources. Half of the sample shows jetted morphologies. The remaining half shows single radio cores or complex morphologies. LINERs show radio structures more core-brightened than Seyferts. Radio luminosities of the sample range from 1032 to 1040 erg s-1: LINERs and H II galaxies show the highest and lowest radio powers, respectively, while ALGs and Seyferts have intermediate luminosities. We find that radio core luminosities correlate with black hole (BH) mass down to ˜107 M⊙, but a break emerges at lower masses. Using [O III] line luminosity as a proxy for the accretion luminosity, active nuclei and jetted H II galaxies follow an optical Fundamental Plane of BH activity, suggesting a common disc-jet relationship. In conclusion, LINER nuclei are the scaled-down version of FR I radio galaxies; Seyferts show less collimated jets; H II galaxies may host weak active BHs and/or nuclear star-forming cores; and recurrent BH activity may account for ALG properties.

The radio-far infrared correlation: Spiral and blue compact dwarf galaxies opposed

NASA Technical Reports Server (NTRS)

Klein, U.; Wunderlich, E.

1987-01-01

The recently established correlation between radio continuum and far infrared emission in galaxies was further investigated by comparing normal spiral and blue compact dwarf galaxies. The puzzling result is that the ratio of radio to far infrared luminosity and its dispersion is the same for both samples, although their ratios of blue to far infrared luminosity, their radio spectral indices and their dust temperatures exhibit markedly different mean values and dispersions. This suggests that the amount of energy radiated in the two regimes is enhanced in the same way although the mechanisms responsible for the two components are rather different and complex. The fact that the blue light does not increase at the same proportion shows that both the radio and the far infrared emission are connected with the recent star formation history.

A Comparison of the Extra Nuclear X-ray and Radio Features in M87

NASA Technical Reports Server (NTRS)

Harris, D. E.; Owen, F.; Biretta, J. A.; Junor, W.

2000-01-01

ROSAT High Resolution Imager (HRI) data from eight observations have been co-added to obtain an effective exposure of 230 ksec. We have identified a number of features and regions with excess X-ray brightness over that from a circularly symmetric model of the well known hot gas component. A prominent 'spur' extends 4feet from the vicinity of knot A towards the south-west. The brightness to the south and east of this spur is significantly higher than that to the north and west. Excess brightness is also found to the East of the nucleus, with a local maximum centered on the eastern radio lobe 3 feet from the core. There are two well known relationships between radio and X-ray emission for radio galaxies in clusters: coincidence of emissions because the X-rays come from inverse Compton or synchrotron processes; and anti-coincidence caused by exclusion of hot gas from radio entities. We present a radio/X-ray comparison to determine if either of these relationships can be isolated in M87. The greatest obstacle we face is the unknown projection which affects both bands.

The spatial variation of the infrared-to-radio ratio in spiral galaxies

NASA Technical Reports Server (NTRS)

Marsh, K. A.; Helou, G.

1995-01-01

We have produced two-dimensional maps of the intensity ratio, Q(sub 60), of 60 micron infrared to 20 cm radio continuum emission, for a set of 25 nearby galaxies, mostly spirals. The ratio maps were obtained from infrared images made using IRAS data with the maximum correlation method, and radio images made using VLA data. Before taking the ratio, the radio images were processed so as to have the same resolution properties as the infrared images; the final spatial resolution in all cases is approximately 1 min, corresponding to 1 - 2 kpc for most galaxies. This resolution represents a significant improvement over previous studies. Our new high-resolution maps confirm the slow decrease of Q(sub 60) with increasing radial distance from the nucleus, but show additional structure which is probably associated with separate sites of active star formation in the spiral arms. The maps show Q(sub 60) to be more closely related to infrared surface brightness than to the radial distance r in the galaxy disk. We note also that the Q(sub 60) gradients are absent (or at least reduced) for the edge-on galaxies, a property which can be attributed to the dilution of contrast due to the averaging of the additional structure along the line of sight. The results are all in qualitative agreement with the suggestion that the radio image represents a smeared version of the infrared image, as would be expected on the basis of current models in which the infrared-radio correlation is driven by the formation of massive stars, and the intensity distribution of radio emission is smeared as a result of the propagation of energetic electrons accelerated during the supernova phase.

HIghZ: A search for HI absorption in high-redshift radio galaxies

NASA Astrophysics Data System (ADS)

Allison, J.; Callingham, J.; Sadler, E.; Wayth, R.; Curran, S.; Mahoney, E.

2017-01-01

We will use the unique low-frequency spectral capability of the MWA to carry out a pilot survey for neutral gas in the interstellar medium of the most distant (z>5) radio galaxies in the Universe. Through detection of the HI 21-cm line in absorption we aim to place stringent lower limits on the source redshift, confirming its location in the early Universe. Our sample makes use of the excellent wide-band spectral information available from the recently completed MWA GLEAM survey, from which we have selected a sample of ultra-steep peaked-spectrum radio sources that have a spectral turnover below 300 MHz. These sources should be ideal candidates for high-redshift compact radio galaxies since they have (a) spectral peaks that turnover below 1GHz and (b) very steep (alpha < -1.0) spectral indices that are consistent with the high density environments expected for radio galaxies in the early Universe. Using the MWA, we aim to verify this hypothesis through the detection of significant column densities of cold HI. This pathfinder project will provide important technical information that will inform future absorption surveys both with the MWA and, ultimately, the SKA-LOW telescope.

Discrete X-Ray Source Populations and Star-Formation History in Nearby Galaxies

NASA Technical Reports Server (NTRS)

Zezas, Andreas

2004-01-01

This program aims in understanding the connection between the discrete X-ray source populations observed in nearby galaxies and the history of star-formation in these galaxies. The ultimate goal is to use this knowledge in order to constrain X-ray binary evolution channels. For this reason although the program is primarily observational it has a significant modeling component. During the first year of this study we focused on the definition of a pilot sample of galaxies with well know star-formation histories. A small part of this sample has already been observed and we performed initial analysis of the data. However, the majority of the objects in our sample either have not been observed at all, or the detection limit of the existing observations is not low enough to probe the bulk of their young X-ray binary populations. For this reason we successfully proposed for additional Chandra observations of three targets in Cycle-5. These observations are currently being performed. The analysis of the (limited) archival data for this sample indicated that the X-ray luminosity functions (XLF) of the discrete sources in these galaxies may not have the same shape as is widely suggested. However, any solid conclusions are hampered by the small number of detected sources. For this reason during the second year of this study, we will try to extend the sample in order to include more objects in each evolutionary stage. In addition we are completing the analysis of the Chandra monitoring observations of the Antennae galaxies. The results from this work, apart from important clues on the nature of the most luminous sources (Ultra-luminous X-ray sources; ULXs) provide evidence that source spectral and/or temporal variability does not significantly affect the shape of their X-ray luminosity functions. This is particularly important for comparisons between the XLFs of different galaxies and comparisons with predictions from theoretical models. Results from this work have been

Gas kinematics in powerful radio galaxies at z 2: Energy supply from star formation, AGN, and radio jets⋆

NASA Astrophysics Data System (ADS)

Nesvadba, N. P. H.; Drouart, G.; De Breuck, C.; Best, P.; Seymour, N.; Vernet, J.

2017-04-01

We compare the kinetic energy and momentum injection rates from intense star formation, bolometric AGN radiation, and radio jets with the kinetic energy and momentum observed in the warm ionized gas in 24 powerful radio galaxies at z 2. These galaxies are among our best candidates for being massive galaxies near the end of their active formation period, when intense star formation, quasar activity, and powerful radio jets all co-exist. All galaxies have VLT/SINFONI imaging spectroscopy of the rest-frame optical line emission, showing extended emission-line regions with large velocity offsets (up to 1500 km s-1) and line widths (typically 800-1000 km s-1) consistent with very turbulent, often outflowing gas. As part of the HeRGÉ sample, they also have FIR estimates of the star formation and quasar activity obtained with Herschel/PACS and SPIRE, which enables us to measure the relative energy and momentum release from each of the three main sources of feedback in massive, star-forming AGN host galaxies during their most rapid formation phase. We find that star formation falls short by factors 10-1000 of providing the energy and momentum necessary to power the observed gas kinematics. The obscured quasars in the nuclei of these galaxies provide enough energy and momentum in about half of the sample, however, only if both are transferred to the gas relatively efficiently. We compare with theoretical and observational constraints on the efficiency of the energy and momentum transfer from jet and AGN radiation, which favors the radio jets as main drivers of the gas kinematics. Based on observations carried out with the Very Large Telescope of ESO under Program IDs 079.A-0617, 084.A-0324, 085.A-0897, and 090.A-0614.Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

NASA's Fermi Telescope Resolves Radio Galaxy Centaurus A

NASA Image and Video Library

2017-12-08

NASA release April 1, 2010 Fermi's Large Area Telescope resolved high-energy gamma rays from an extended region around the active galaxy Centaurus A. The emission corresponds to million-light-year-wide radio-emitting gas thrown out by the galaxy's supersized black hole. This inset shows an optical/gamma-ray composite of the galaxy and its location on the Fermi one-year sky map. Credit: NASA/DOE/Fermi LAT Collaboration, Capella Observatory To learn more about these images go to: www.nasa.gov/mission_pages/GLAST/news/smokestack-plumes.html NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Fermi large area telescope detection of extended gamma-ray emission from the radio galaxy fornax A

DOE PAGES

Ackermann, M.; Ajello, M.; Baldini, L.; ...

2016-07-14

Here, we report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to bemore » $$\\lt 14$$% of the total γ-ray flux. We also demonstrated a preferred alignment of the γ-ray elongation with the radio lobes by rotating the radio lobes template. We found no significant evidence for variability on ~0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. Furthermore, with the extended nature of the $$\\gt 100\\;{\\rm{MeV}}$$ γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ~2–3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton–proton collisions of cosmic rays with thermal plasma within the radio lobes.« less

Fermi Large Area Telescope Detection of Extended Gamma-Ray Emission from the Radio Galaxy Fornax A

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Cohen, J. M.; Cohen-Tanugi, J.; Costanza, F.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Georganopoulos, M.; Giglietto, N.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I. A.; Guiriec, S.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Jogler, T.; Jóhannesson, G.; Kensei, S.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mayer, M.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Negro, M.; Nuss, E.; Ohno, M.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Schmid, J.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; Wood, K. S.; Wood, M.; Zimmer, S.; Fermi LAT Collaboration

2016-07-01

We report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be < 14% of the total γ-ray flux. A preferred alignment of the γ-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on ˜0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. With the extended nature of the > 100 MeV γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ˜2-3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.

VLA observations of radio sources in interacting galaxy pairs in poor clusters

NASA Technical Reports Server (NTRS)

Batuski, David J.; Hanisch, Robert J.; Burns, Jack O.

1992-01-01

Observations of 16 radio sources in interacting galaxies in 14 poor clusters were made using the Very Large Array in the B configuration at lambda of 6 and 2 cm. These sources had been unresolved in earlier observations at lambda of 21 cm, and were chosen as a sample to determine which of three models for radio source formation actually pertains in interacting galaxies. From the analysis of this sample, the starburst model appears most successful, but the 'central monster' model could pertain in some cases.

Neutral hydrogen in elliptical galaxies with nuclear radio sources and optical emission lines

NASA Technical Reports Server (NTRS)

Dressel, L. L.; Bania, T. M.; Oconnell, R. W.

1982-01-01

An H I detection survey of eleven elliptical galaxies with powerful nuclear radio sources was conducted, using the 305 m antenna of Arecibo Observatory, to test the hypothesis that large H I mass is conductive to the formation of nuclear radio sources in elliptical galaxies. The H I was detected in emission in UGC 09114 and was possibly detected in absorption in UGC 06671. Observations of the remaining galaxies were not sensitive enough to support or refute the hypothesis. Data was combined from other H I surveys and spectroscopic surveys to search for correlations of H I mass with other galactic properties and environmental conditions. Strong correlations of (O II) lambda 3727 emission with H I content and with nuclear radio power were found. The latter two properties may simply indicate, respectively, whether a significant amount of gas is available to be ionized and whether energy is provided by nuclear activity for ionization. No dependence of H I content on optical luminosity or on degree of isolation from other galaxies was found.

Classifying bent radio galaxies from a mixture of point-like/extended images with Machine Learning.

NASA Astrophysics Data System (ADS)

Bastien, David; Oozeer, Nadeem; Somanah, Radhakrishna

2017-05-01

The hypothesis that bent radio sources are supposed to be found in rich, massive galaxy clusters and the avalibility of huge amount of data from radio surveys have fueled our motivation to use Machine Learning (ML) to identify bent radio sources and as such use them as tracers for galaxy clusters. The shapelet analysis allowed us to decompose radio images into 256 features that could be fed into the ML algorithm. Additionally, ideas from the field of neuro-psychology helped us to consider training the machine to identify bent galaxies at different orientations. From our analysis, we found that the Random Forest algorithm was the most effective with an accuracy rate of 92% for a classification of point and extended sources as well as an accuracy of 80% for bent and unbent classification.

LOFAR-Boötes: properties of high- and low-excitation radio galaxies at 0.5 < z < 2.0

NASA Astrophysics Data System (ADS)

Williams, W. L.; Calistro Rivera, G.; Best, P. N.; Hardcastle, M. J.; Röttgering, H. J. A.; Duncan, K. J.; de Gasperin, F.; Jarvis, M. J.; Miley, G. K.; Mahony, E. K.; Morabito, L. K.; Nisbet, D. M.; Prandoni, I.; Smith, D. J. B.; Tasse, C.; White, G. J.

2018-04-01

This paper presents a study of the redshift evolution of radio-loud active galactic nuclei (AGN) as a function of the properties of their galaxy hosts in the Boötes field. To achieve this we match low-frequency radio sources from deep 150-MHz LOFAR (LOw Frequency ARray) observations to an I-band-selected catalogue of galaxies, for which we have derived photometric redshifts, stellar masses, and rest-frame colours. We present spectral energy distribution (SED) fitting to determine the mid-infrared AGN contribution for the radio sources and use this information to classify them as high- versus low-excitation radio galaxies (HERGs and LERGs) or star-forming galaxies. Based on these classifications, we construct luminosity functions for the separate redshift ranges going out to z = 2. From the matched radio-optical catalogues, we select a sub-sample of 624 high power (P150 MHz > 1025 W Hz-1) radio sources between 0.5 ≤ z < 2. For this sample, we study the fraction of galaxies hosting HERGs and LERGs as a function of stellar mass and host galaxy colour. The fraction of HERGs increases with redshift, as does the fraction of sources in galaxies with lower stellar masses. We find that the fraction of galaxies that host LERGs is a strong function of stellar mass as it is in the local Universe. This, combined with the strong negative evolution of the LERG luminosity functions over this redshift range, is consistent with LERGs being fuelled by hot gas in quiescent galaxies.

COLA. III. Radio Detection of Active Galactic Nucleus in Compact Moderate Luminosity Infrared Galaxies

NASA Astrophysics Data System (ADS)

Parra, R.; Conway, J. E.; Aalto, S.; Appleton, P. N.; Norris, R. P.; Pihlström, Y. M.; Kewley, L. J.

2010-09-01

We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L IR = 1011.01 L sun) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores (~1021 W Hz-1) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whose VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.

The radio-X-ray relation as a star formation indicator: results from the Very Large Array-Extended Chandra Deep Field-South

NASA Astrophysics Data System (ADS)

Vattakunnel, S.; Tozzi, P.; Matteucci, F.; Padovani, P.; Miller, N.; Bonzini, M.; Mainieri, V.; Paolillo, M.; Vincoletto, L.; Brandt, W. N.; Luo, B.; Kellermann, K. I.; Xue, Y. Q.

2012-03-01

In order to trace the instantaneous star formation rate (SFR) at high redshift, and thus help in understanding the relation between the different emission mechanisms related to star formation, we combine the recent 4-Ms Chandra X-ray data and the deep Very Large Array radio data in the Extended Chandra Deep Field-South region. We find 268 sources detected both in the X-ray and radio bands. The availability of redshifts for ˜95 per cent of the sources in our sample allows us to derive reliable luminosity estimates and the intrinsic properties from X-ray analysis for the majority of the objects. With the aim of selecting sources powered by star formation in both bands, we adopt classification criteria based on X-ray and radio data, exploiting the X-ray spectral features and time variability, taking advantage of observations scattered across more than 10 years. We identify 43 objects consistent with being powered by star formation. We also add another 111 and 70 star-forming candidates detected only in the radio and X-ray bands, respectively. We find a clear linear correlation between radio and X-ray luminosity in star-forming galaxies over three orders of magnitude and up to z˜ 1.5. We also measure a significant scatter of the order of 0.4 dex, higher than that observed at low redshift, implying an intrinsic scatter component. The correlation is consistent with that measured locally, and no evolution with redshift is observed. Using a locally calibrated relation between the SFR and the radio luminosity, we investigate the LX(2-10 keV)-SFR relation at high redshift. The comparison of the SFR measured in our sample with some theoretical models for the Milky Way and M31, two typical spiral galaxies, indicates that, with current data, we can trace typical spirals only at z≤ 0.2, and strong starburst galaxies with SFRs as high as ˜100 M⊙ yr-1, up to z˜ 1.5.

A soft X-ray map of the Perseus cluster of galaxies

NASA Technical Reports Server (NTRS)

Cash, W.; Malina, R. F.; Wolff, R. S.

1976-01-01

A 0.5-3-keV X-ray map of the Perseus cluster of galaxies is presented. The map shows a region of strong emission centered near NGC 1275 plus a highly elongated emission region which lies along the line of bright galaxies that dominates the core of the cluster. The data are compared with various models that include point and diffuse sources. One model which adequately represents the data is the superposition of a point source at NGC 1275 and an isothermal ellipsoid resulting from the bremsstrahlung emission of cluster gas. The ellipsoid has a major core radius of 20.5 arcmin and a minor core radius of 5.5 arcmin, consistent with the values obtained from galaxy counts. All acceptable models provide evidence for a compact source (less than 3 arcmin FWHM) at NGC 1275 containing about 25% of the total emission. Since the diffuse X-ray and radio components have radically different morphologies, it is unlikely that the emissions arise from a common source, as proposed in inverse-Compton models.

Einstein observations of the X-ray structure of Centaurus A - Evidence for the radio-lobe energy source

NASA Technical Reports Server (NTRS)

Schreier, E. J.; Feigelson, E.; Delvaille, J.; Giacconi, R.; Grindlay, J.; Schwartz, D. A.; Fabian, A. C.

1979-01-01

The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.

Identification and properties of host galaxies of RCR radio sources

NASA Astrophysics Data System (ADS)

Zhelenkova, O. P.; Soboleva, N. S.; Majorova, E. K.; Temirova, A. V.

2013-01-01

FIRST and NVSS radio maps are used to cross identify the radio sources of the RCR catalog, which is based on observational data obtained in several runs of the "Cold" survey, with the SDSS and DPOSS digital optical sky surveys and the 2MASS, LAS UKIDSS, and WISE infrared surveys. Digital images in various filters and the coadded gri-band SDSS images, red and infrared DPOSS images, JHK-band UKIDSS images, and JHK-band 2MASS images are analyzed for the sources with no optical candidates found in the above catalogs. Our choice of optical candidates was based on the data on the structure of the radio source, its photometry, and spectroscopy (where available). We found reliable identifications for 86% of the radio sources; possible counterparts for 8% of the sources, and failed to find any optical counterparts for 6% of the sources because their host objects proved to be fainter than the limiting magnitude of the corresponding surveys. A little over half of all the identifications proved to be galaxies; about one quarter were quasars, and the types of the remaining objects were difficult to determine because of their faintness. A relation between the luminosity and the radioloudness index was derived and used to estimate the 1.4 and 3.94 GHz luminosities for the sources with unknown redshifts. We found 3% and 60% of all the RCR radio sources to be FRI-type objects ( L ≲ 1024 W/Hz at 1.4 GHz) and powerful FRII-type galaxies ( L ≳ 1026.5 W/Hz), respectively, whereas the rest are sources including objects of the FRI, FRII, and mixed FRI-FRII types. Unlike quasars, galaxies show a trend of decreasing luminosity with decreasing flux density. Note that identification would be quite problematic without the software and resources of the virtual observatory.

History of Chandra X-Ray Observatory

NASA Image and Video Library

2000-10-01

This most distant x-ray cluster of galaxies yet has been found by astronomers using Chandra X-ray Observatory (CXO). Approximately 10 billion light-years from Earth, the cluster 3C294 is 40 percent farther than the next most distant x-ray galaxy cluster. The existence of such a faraway cluster is important for understanding how the universe evolved. CXO's image reveals an hourglass-shaped region of x-ray emissions centered on the previously known central radio source (seen in this image as the blue central object) that extends outward for 60,000 light- years. The vast clouds of hot gas that surround such galaxies in clusters are thought to be heated by collapse toward the center of the cluster. Until CXO, x-ray telescopes have not had the needed sensitivity to identify such distant clusters of galaxies. Galaxy clusters are the largest gravitationally bound structures in the universe. The intensity of the x-rays in this CXO image of 3C294 is shown as red for low energy x-rays, green for intermediate, and blue for the most energetic x-rays. (Photo credit: NASA/loA/A. Fabian et al)

Radio haloes in nearby galaxies modelled with 1D cosmic ray transport using SPINNAKER

NASA Astrophysics Data System (ADS)

Heesen, V.; Krause, M.; Beck, R.; Adebahr, B.; Bomans, D. J.; Carretti, E.; Dumke, M.; Heald, G.; Irwin, J.; Koribalski, B. S.; Mulcahy, D. D.; Westmeier, T.; Dettmar, R.-J.

2018-05-01

We present radio continuum maps of 12 nearby (D ≤ 27 Mpc), edge-on (i ≥ 76°), late-type spiral galaxies mostly at 1.4 and 5 GHz, observed with the Australia Telescope Compact Array, Very Large Array, Westerbork Synthesis Radio Telescope, Effelsberg 100-m, and Parkes 64-m telescopes. All galaxies show clear evidence of radio haloes, including the first detection in the Magellanic-type galaxy NGC 55. In 11 galaxies, we find a thin and a thick disc that can be better fitted by exponential rather than Gaussian functions. We fit our SPINNAKER (SPectral INdex Numerical Analysis of K(c)osmic-ray Electron Radio-emission) 1D cosmic ray transport models to the vertical model profiles of the non-thermal intensity and to the non-thermal radio spectral index in the halo. We simultaneously fit for the advection speed (or diffusion coefficient) and magnetic field scale height. In the thick disc, the magnetic field scale heights range from 2 to 8 kpc with an average across the sample of 3.0 ± 1.7 kpc; they show no correlation with either star formation rate (SFR), SFR surface density (ΣSFR), or rotation speed (Vrot). The advection speeds range from 100 to 700 km s - 1 and display correlations of V∝SFR0.36 ± 0.06 and V∝ Σ _SFR^{0.39± 0.09}; they agree remarkably well with the escape velocities (0.5 ≤ V/Vesc ≤ 2), which can be explained by cosmic ray-driven winds. Radio haloes show the presence of disc winds in galaxies with ΣSFR > 10 - 3 M⊙ yr - 1 kpc - 2 that extend over several kpc and are driven by processes related to the distributed star formation in the disc.

X-Ray Properties of the Youngest Radio Sources and Their Environments

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Małgosia; Migliori, Giulia; Guainazzi, Matteo; Hardcastle, Martin; Ostorero, Luisa; Stawarz, Łukasz

2016-05-01

We present the first results from our X-ray study of young radio sources classified as compact symmetric objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs already observed with XMM-Newton or BeppoSAX. We also included six other CSOs with archival data to built a pilot study of a sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, z\\lt 1, and the age of their radio structures (\\lt 3000 yr) has been derived from the expansion velocity of their hot spots. Our results show the heterogeneous nature of the CSOs’ X-ray emission, indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity, {L}2{--10{keV}}˜ {10}41-1045 erg s-1, and intrinsic absorbing column density of {N}{{H}}≃ {10}21-1022 cm-2. In particular, we detected extended X-ray emission in 1718-649 a hard photon index of {{Γ }}≃ 1 in 2021+614 and 1511+0518 consistent with either a Compton-thick absorber or non-thermal emission from compact radio lobes, and in 0710+439 an ionized iron emission line at {E}{rest}=(6.62+/- 0.04) keV and EW ˜ 0.15-1.4 keV, and a decrease by an order of magnitude in the 2-10 keV flux since the 2008 XMM-Newton observation in 1607+26. We conclude that our pilot study of CSOs provides a variety of exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and to study the interactions of young radio sources with the interstellar environment of their host galaxies.

On the Merging Cluster Abell 578 and Its Central Radio Galaxy 4C+67.13

NASA Astrophysics Data System (ADS)

Hagino, K.; Stawarz, Ł.; Siemiginowska, A.; Cheung, C. C.; Kozieł-Wierzbowska, D.; Szostek, A.; Madejski, G.; Harris, D. E.; Simionescu, A.; Takahashi, T.

2015-06-01

Here we analyze radio, optical, and X-ray data for the peculiar cluster Abell 578. This cluster is not fully relaxed and consists of two merging sub-systems. The brightest cluster galaxy (BCG), CGPG 0719.8+6704, is a pair of interacting ellipticals with projected separation ˜10 kpc, the brighter of which hosts the radio source 4C+67.13. The Fanaroff-Riley type-II radio morphology of 4C+67.13 is unusual for central radio galaxies in local Abell clusters. Our new optical spectroscopy revealed that both nuclei of the CGPG 0719.8+6704 pair are active, albeit at low accretion rates corresponding to the Eddington ratio ˜ {{10}-4} (for the estimated black hole masses of ˜ 3× {{10}8} {{M}⊙ } and ˜ {{10}9} {{M}⊙ }). The gathered X-ray (Chandra) data allowed us to confirm and to quantify robustly the previously noted elongation of the gaseous atmosphere in the dominant sub-cluster, as well as a large spatial offset (˜60 kpc projected) between the position of the BCG and the cluster center inferred from the modeling of the X-ray surface brightness distribution. Detailed analysis of the brightness profiles and temperature revealed also that the cluster gas in the vicinity of 4C+67.13 is compressed (by a factor of about ˜1.4) and heated (from ≃ 2.0 keV up to 2.7 keV), consistent with the presence of a weak shock (Mach number ˜1.3) driven by the expanding jet cocoon. This would then require the jet kinetic power of the order of ˜ {{10}45} erg s-1, implying either a very high efficiency of the jet production for the current accretion rate, or a highly modulated jet/accretion activity in the system. Based on service observations made with the WHT operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Hard X-ray Emission from Galaxy Clusters Observed with INTEGRAL and Prospects for Simbol-X

NASA Astrophysics Data System (ADS)

Eckert, D.; Paltani, S.; Courvoisier, T. J.-L.

2009-05-01

Some galaxy clusters are known to contain a large population of relativistic electrons, which produce radio emission through synchrotron radiation. Therefore, it is expected that inverse-Compton scattering of the relativistic electrons with the CMB produce non-thermal emission which should be observable in the hard X-ray domain. Here we focus on the recent results by INTEGRAL, which shed a new light on the non-thermal emission thanks to its angular resolution and sensitivity in the hard X-ray range. We also present the exciting prospects in this field for Simbol-X, which will allow us to detect the non-thermal emission in a number of clusters and map the magnetic field throughout the intra-cluster medium.

Multiwavelength Study of Active Galaxies

NASA Astrophysics Data System (ADS)

Singh, Veeresh

2010-08-01

Seyfert galaxies are a subclass of active galaxies and are categorized as nearby, low luminosity, radio-quiet Active Galactic Nuclei (AGN) hosted in spiral or lenticular galaxies. Demographically, Seyfert galaxies may account for ~ 10% of the entire population of active galaxies in the nearby universe. Seyfert galaxies are classified mainly into two subclasses named as `type 1' and `type 2' Seyferts, based on the presence and absence of broad permitted emission lines in their optical spectra, respectively. Detection of broad permitted emission lines in some Seyfert type 2s observed in the polarized light laid the foundation of the Seyfert unification scheme, which hypothesizes that Seyfert type 1s and type 2s belong to the same parent population and appear different solely due to the differing orientations of the obscuring material having a torus-like geometry around the AGN (Antonucci and Miller 1985; Antonucci 1993). The primary objective of this thesis work is to examine the validity and limitations of the orientation and obscuration based Seyfert unification scheme using multiwavelength (mainly X-ray and radio) observations. The key issue in testing the Seyfert unification scheme has been acquiring a well defined rigorously selected Seyfert sample. I have argued that the Seyfert samples based on flux limited surveys at optical, IR, UV and X-ray are likely to be biased against obscured and faint sources. In order to test the predictions of Seyfert unification scheme I use a sample based on properties (i.e., cosmological redshift, [OIII] emission line luminosity, absolute bulge magnitude, absolute stellar magnitude of the host galaxy and the Hubble stage of the host galaxy) that are independent to the orientation of the obscuring torus, host galaxy and the AGN axis. Furthermore, two Seyfert subtypes of our sample have matched distributions in the orientation-independent properties and this ensures the intrinsic similarity between two Seyfert subtypes within the

Stacking Searches for Greater Than 100 MeV Gamma Ray Emission from Radio Galaxies and Seyfert Galaxies

NASA Technical Reports Server (NTRS)

Cillis, A. N.; Hartman, R. C.; Bertsch, D. L.

2003-01-01

The EGRET telescope on CGRO detected more than sixty sources of high-energy gamma radiation associated with active galactic nuclei (AGN). All but one of those belong to the blazar subclass; the only exception is the nearby radio galaxy Centaurus A. Since there is no obvious reason other than proximity to expect Cen A to be the only non-blazar AGN emitting in high-energy gamma rays, we have utilized the "stacking" technique to search for $>100$-MeV emission from two non-blazar AGN subclasses, radio galaxies and Seyfert galaxies. Maps of gamma-ray counts, exposure, and diffuse background have been created, then co-added in varying numbers based on sorts by redshift, 5-GHZ flux density, and optical brightness, and finally tested for gamma-ray emission. No detection significance greater than $2\\sigma$ has been found for any subclass, sorting parameter, or number of objects co-added. Monte Carlo simulations have also been performed, to validate the technique and estimate the significance of the results.

Combining physical galaxy models with radio observations to constrain the SFRs of high-z dusty star-forming galaxies

NASA Astrophysics Data System (ADS)

Lo Faro, B.; Silva, L.; Franceschini, A.; Miller, N.; Efstathiou, A.

2015-03-01

We complement our previous analysis of a sample of z ˜ 1-2 luminous and ultraluminous infrared galaxies [(U)LIRGs], by adding deep Very Large Array radio observations at 1.4 GHz to a large data set from the far-UV to the submillimetre, including Spitzer and Herschel data. Given the relatively small number of (U)LIRGs in our sample with high signal-to-noise (S/N) radio data, and to extend our study to a different family of galaxies, we also include six well-sampled near-infrared (near-IR)-selected BzK galaxies at z ˜ 1.5. From our analysis based on the radtran spectral synthesis code GRASIL, we find that, while the IR luminosity may be a biased tracer of the star formation rate (SFR) depending on the age of stars dominating the dust heating, the inclusion of the radio flux offers significantly tighter constraints on SFR. Our predicted SFRs are in good agreement with the estimates based on rest-frame radio luminosity and the Bell calibration. The extensive spectrophotometric coverage of our sample allows us to set important constraints on the star formation (SF) history of individual objects. For essentially all galaxies, we find evidence for a rather continuous SFR and a peak epoch of SF preceding that of the observation by a few Gyr. This seems to correspond to a formation redshift of z ˜ 5-6. We finally show that our physical analysis may affect the interpretation of the SFR-M⋆ diagram, by possibly shifting, with respect to previous works, the position of the most dust obscured objects to higher M⋆ and lower SFRs.

The Shape of Extremely Metal-Poor Galaxies

NASA Astrophysics Data System (ADS)

Putko, Joseph; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce; Elmegreen, Debra

2018-01-01

This work is the first study on the 3D shape of starbursting extremely metal-poor galaxies (XMPs; a galaxy is said to be an XMP if its ionized gas-phase metallicity is less than 1/10 the solar value). A few hundred XMPs have been identified in the local universe primarily through mining the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS), and follow-up observations have shown that metallicity drops significantly at the starburst (compared to the quiescent component of the galaxy). As the timescale for gas mixing is short, the metal-poor gas triggering the starburst must have been accreted recently. This is strong observational evidence for the cold flow accretion predicted by cosmological models of galaxy formation, and, in this respect, XMPs seem to be the best local analogs of the very first galaxies.The ellipsoidal shape of a class of galaxies can be inferred from the observed axial ratio (q) distribution (q = minor axis/major axis) of a large sample of randomly-oriented galaxies. Fitting ellipses to 200 XMPs using r-band SDSS images, we observe that the axial ratio distribution falls off at q < ~0.4 and q > ~0.8, and we determine that these falloffs are not due to biases in the data. The falloff at low axial ratio indicates that the XMPs are thick for their size, and the falloff at high axial ratio suggests the vast majority of XMPs are triaxial. We also observe that smaller XMPs are thicker in proportion to their size, and it is expected that for decreasing galaxy size the ratio of random to rotational motions increases, which correlates with increasing relative thickness. The XMPs are low-redshift dwarf galaxies dominated by dark matter, and our results are compatible with simulations that have shown dark matter halos to be triaxial, with triaxial stellar distributions for low-mass galaxies and with triaxiality increasing over time. We will offer precise constraints on the 3D shape of XMPs via Bayesian analysis of our observed axial ratio

An XMM-Newton view of the radio galaxy 3C 411

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bostrom, Allison; Reynolds, Christopher S.; Tombesi, Francesco

We present the first high signal-to-noise XMM-Newton observations of the broad-line radio galaxy 3C 411. After fitting various spectral models, an absorbed double power-law (PL) continuum and a blurred relativistic disk reflection model (kdblur) are found to be equally plausible descriptions of the data. While the softer PL component (Γ = 2.11) of the double PL model is entirely consistent with that found in Seyfert galaxies (and hence likely originates from a disk corona), the additional PL component is very hard (Γ = 1.05); amongst the active galactic nucleus zoo, only flat-spectrum radio quasars (FSRQ) have such hard spectra. Togethermore » with the flat radio-spectrum displayed by this source, we suggest that it should instead be classified as an FSRQ. This leads to potential discrepancies regarding the jet inclination angle, with the radio morphology suggesting a large jet inclination but the FSRQ classification suggesting small inclinations. The kdblur model predicts an inner disk radius of at most 20 r {sub g} and relativistic reflection.« less

FERMI/LAT OBSERVATIONS OF SWIFT/BAT SEYFERT GALAXIES: ON THE CONTRIBUTION OF RADIO-QUIET ACTIVE GALACTIC NUCLEI TO THE EXTRAGALACTIC {gamma}-RAY BACKGROUND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teng, Stacy H.; Mushotzky, Richard F.; Reynolds, Christopher S.

2011-12-01

We present the analysis of 2.1 years of Fermi Large Area Telescope (LAT) data on 491 Seyfert galaxies detected by the Swift Burst Alert Telescope (BAT) survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi first year catalog, are detected. Using Swift/BAT and radio 20 cm fluxes, we define a new radio-loudness parameter R{sub X,BAT} where radio-loud objects have log R{sub X,BAT} > -4.7. Based on this parameter, only radio-loud sources are detected by Fermi/LAT. An upper limit to the flux of the undetected sources is derived to be {approx}2 Multiplication-Sign 10{supmore » -11} photons cm{sup -2} s{sup -1}, approximately seven times lower than the observed flux of NGC 1068. Assuming a median redshift of 0.031, this implies an upper limit to the {gamma}-ray (1-100 GeV) luminosity of {approx}< 3 Multiplication-Sign 10{sup 41} erg s{sup -1}. In addition, we identified 120 new Fermi/LAT sources near the Swift/BAT Seyfert galaxies with significant Fermi/LAT detections. A majority of these objects do not have Swift/BAT counterparts, but their possible optical counterparts include blazars, flat-spectrum radio quasars, and quasars.« less

Witnessing the Gradual Slowdown of Powerful Extragalactic Jets: The X-Ray-Optical-Radio Connection

NASA Technical Reports Server (NTRS)

Georganopoulos, Markos; Kazanas, Demosthenes

2004-01-01

A puzzling feature of the Chandra-detected quasar jets is that their X-ray emission decreases faster along the jet than their radio emission, resulting from an outward-increasing radio-to-X-ray ratio. In some sources this behavior is so extreme that the radio emission peak is located clearly downstream of that of the X-rays. This is a rather unanticipated behavior given that the inverse Compton nature of the X-rays and the synchrotron radio emission are attributed to roughly the same electrons of the jet's nonthermal electron distribution. In this letter we show that this morphological behavior can result from the gradual deceleration of a relativistic flow and that the offsets in peak emission at different wavelengths carry the imprint of this deceleration. This notion is consistent with another recent finding, namely, that the jets feeding the terminal hot spots of powerful radio galaxies and quasars are still relativistic with Lorentz factors GAMMA approximately 2-3. The picture of the kinematics of powerful jets emerging from these considerations is that they remain relativistic as they gradually decelerate from kiloparsec scales to the hot spots, where, in a final collision with the intergalactic medium, they slow down rapidly to the subrelativistic velocities of the hot spot advance speed.

COLA. III. RADIO DETECTION OF ACTIVE GALACTIC NUCLEUS IN COMPACT MODERATE LUMINOSITY INFRARED GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parra, R.; Conway, J. E.; Aalto, S.

2010-09-01

We present results from 4.8 GHz Very Large Array (VLA) and global very long baseline interferometry (VLBI) observations of the northern half of the moderate FIR luminosity (median L{sub IR} = 10{sup 11.01} L{sub sun}) COLA sample of star-forming galaxies. VLBI sources are detected in a high fraction (20/90) of the galaxies observed. The radio luminosities of these cores ({approx}10{sup 21} W Hz{sup -1}) are too large to be explained by radio supernovae or supernova remnants and we argue that they are instead powered by active galactic nuclei (AGNs). These sub-parsec scale radio cores are preferentially detected toward galaxies whosemore » VLA maps show bright 100-500 parsec scale nuclear radio components. Since these latter structures tightly follow the FIR to radio-continuum correlation for star formation, we conclude that the AGN-powered VLBI sources are associated with compact nuclear starburst environments. The implications for possible starburst-AGN connections are discussed. The detected VLBI sources have a relatively narrow range of radio luminosity consistent with models in which intense compact Eddington-limited starbursts regulate the gas supply onto a central supermassive black hole. The high incidence of AGN radio cores in compact starbursts suggests little or no delay between the starburst phase and the onset of AGN activity.« less

3C 159 - a double emission-line radio galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tytler, D.; Browne, I.

1985-09-01

An optical identification for 3C 159 is reported with a 19-mag emission-line radio galaxy at z = 0.482. Photometric measurements show it to be unusually bright and blue. The emission lines are of exceptionally high luminosity, and are split into two components separated by 598 + or - 13 km/s and 3 kpc along the spectrograph slit. A VLA may show that one of the radio lobes has two hot spots with tails of emission leading to both. 21 references.

Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC612 (PKS0131-36)

NASA Astrophysics Data System (ADS)

Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; van der Hulst, J. M.; Ojha, R.; Sadler, E. M.

2008-06-01

We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC612, which hosts one of the nearest powerful radio sources (PKS0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 × 109Msolar of HI emission-line gas that is distributed in a 140-kpc wide disc-like structure along the optical disc and dust lane of NGC612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850kms-1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC612 suggests that the total mass enclosed by the system is Menc ~ 2.9 × 1012 sin-2 iMsolar, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint HI bridge along a distance of 400kpc in between NGC612 and the gas-rich (MHI = 8.9 × 109Msolar) barred galaxy NGC619, indicating that likely an interaction between both systems occurred. From the unusual amounts of HI gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infrared luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first example of large-scale HI detected around a powerful Fanaroff-Riley type II (FR-II) radio galaxy. The HI properties of the FR-II radio galaxy NGC612 are very similar to those

Evidence for a Circum-Nuclear and Ionised Absorber in the X-ray Obscured Broad Line Radio Galaxy 3C 445

NASA Technical Reports Server (NTRS)

Braito, V.; Reeves, J. N.; Sambruna, R. M.; Gofford, J.

2012-01-01

Here we present the results of a Suzaku observation of the Broad Line Radio Galaxy 3C 445. We confirm the results obtained with the previous X-ray observations which unveiled the presence of several soft X-ray emission lines and an overall X-ray emission which strongly resembles a typical Seyfert 2 despite of the optical classification as an unobscured AGN. The broad band spectrum allowed us to measure for the first time the amount of reflection (R approximately 0.9) which together with the relatively strong neutral Fe Ka emission line (EW approximately 100 eV) strongly supports a scenario where a Compton-thick mirror is present. The primary X ray continuum is strongly obscured by an absorber with a column density of NH = 2 - 3 x 10(exp 23) per square centimeter. Two possible scenarios are proposed for the absorber: a neutral partial covering or a mildly ionised absorber with an ionisation parameter log xi approximately 1.0 erg centimeter per second. A comparison with the past and more recent X-ray observations of 3C 445 performed with XMM-Newton and Chandra is presented, which provided tentative evidence that the ionised and outflowing absorber varied. We argue that the absorber is probably associated with an equatorial diskwind located within the parsec scale molecular torus.

The correlation between far-IR and radio continuum emission from spiral galaxies

NASA Technical Reports Server (NTRS)

Dickey, John M.; Garwood, Robert W.; Helou, George

1987-01-01

A sample of 30 galaxies selected for their intense IRAS flux at 60 and 100 micron using the Arecibo telescope at 21 cm to measure the continuum and HI line luminosities were observed. The centimeter wave continuum correlates very well with the far-infrared flux, with a correlation coefficient as high as that found for other samples, and the same ratio between FIR and radio luminosities. Weaker correlations are seen between the FIR and optical luminosity and between the FIR and radio continuum. There is very little correlation between the FIR and the HI mass deduced from the integral of the 21 cm line. The strength of the radio continuum correlation suggests that there is little contribution to either the radio and FIR from physical processes not affecting both. If they each reflect time integrals of the star formation rate then the time constants must be similar, or the star formation rate must change slowly in these galaxies.

The 60 micron to 20 centimeter infrared-to-radio ratio within spiral galaxies

NASA Technical Reports Server (NTRS)

Bicay, M. D.; Helou, G.

1990-01-01

A detailed comparison is presented of the distribution of 60 micron IR and 20 cm radio continuum emission within 25 galaxies, mostly disk spirals. Local maxima in the thermal IR and nonthermal radio emission are found to be spatially coincident on scales of less than about 0.4 kpc in the nearest sample galaxies. The IR-red disk in normal spirals appears to be characterized by a shorter scale length than that of the radio continuum disk, suggesting that the IR-to-radio ratio should decrease as a function of radius. A model that successfully accounts for the observations is introduced which is based on the assumptions of steady-state star formation activity within the disk on kpc scales and a tight coupling between the origins of the dust-heating radiation and the radio-emitting cosmic-ray electrons. The underlying source is described as an exponential disk. The results also suggest that a random walk process cannot by itself describe the temporal evolution of cosmic rays.

CO detections and IRAS observations of bright radio spiral galaxies at cz equal or less than 9000 kilometers per second

NASA Technical Reports Server (NTRS)

Sanders, D. B.; Mirabel, I. F.

1985-01-01

CO emission has been detected from 20 of 21 bright radio spirals with strong extended nuclear sources, including the most distant (NGC 7674) and the most luminous (IC 4553 = Arp 220, NGC 6240) galaxies yet detected in CO. All of these galaxies are rich in molecular gas, with M total(H2) = 3 x 10 to the 8th - 2 x 10 to the 10th solar masses. IRAS observations show that they have a strong far-infrared (FIR) excess, with L(FIR)/L(B) approximately equal to 1-35 and L(FIR) (40-400 microns) approximately equal to 10 to the 10th - 10 to the 12th L solar masses. The primary luminosity source for these radio cores appears to be star formation in molecular clouds. A strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate. The ratio L(FIR)/M(H2) provides a measure of the current rate of star formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. At these rates their molecular gas will be depleted in about 10 to the 8th yr.

Modeling the spectral energy distribution of the radio galaxy IC310

NASA Astrophysics Data System (ADS)

Fraija, N.; Marinelli, A.; Galván-Gámez, A.; Aguilar-Ruiz, E.

2017-03-01

The radio galaxy IC310 located in the Perseus Cluster is one of the brightest objects in the radio and X-ray bands, and one of the closest active galactic nuclei observed in very-high energies. In GeV - TeV γ-rays, IC310 was detected in low and high flux states by the MAGIC telescopes from October 2009 to February 2010. Taking into account that the spectral energy distribution (SED) up to a few GeV seems to exhibit a double-peak feature and that a single-zone synchrotron self-Compton (SSC) model can explain all of the multiwavelength emission except for the non-simultaneous MAGIC emission, we interpret, in this work, the multifrequency data set of the radio galaxy IC310 in the context of homogeneous hadronic and leptonic models. In the leptonic framework, we present a multi-zone SSC model with two electron populations to explain the whole SED whereas for the hadronic model, we propose that a single-zone SSC model describes the SED up to a few GeVs and neutral pion decay products resulting from pγ interactions could describe the TeV - GeV γ-ray spectra. These interactions occur when Fermi-accelerated protons interact with the seed photons around the SSC peaks. We show that, in the leptonic model the minimum Lorentz factor of second electron population is exceedingly high γe ∼ 105 disfavoring this model, and in the hadronic model the required proton luminosity is not extremely high ∼1044 erg/s, provided that charge neutrality between the number of electrons and protons is given. Correlating the TeV γ-ray and neutrino spectra through photo-hadronic interactions, we find that the contribution of the emitting region of IC310 to the observed neutrino and ultra-high-energy cosmic ray fluxes are negligible.

Radio emission from the X-ray pulsar Her X-1: a jet launched by a strong magnetic field neutron star?

NASA Astrophysics Data System (ADS)

van den Eijnden, J.; Degenaar, N.; Russell, T. D.; Miller-Jones, J. C. A.; Wijnands, R.; Miller, J. M.; King, A. L.; Rupen, M. P.

2018-01-01

Her X-1 is an accreting neutron star (NS) in an intermediate-mass X-ray binary. Like low-mass X-ray binaries (LMXBs), it accretes via Roche lobe overflow, but similar to many high-mass X-ray binaries containing a NS; Her X-1 has a strong magnetic field and slow spin. Here, we present the discovery of radio emission from Her X-1 with the Very Large Array. During the radio observation, the central X-ray source was partially obscured by a warped disc. We measure a radio flux density of 38.7 ± 4.8 μJy at 9 GHz but cannot constrain the spectral shape. We discuss possible origins of the radio emission, and conclude that coherent emission, a stellar wind, shocks and a propeller outflow are all unlikely explanations. A jet, as seen in LMXBs, is consistent with the observed radio properties. We consider the implications of the presence of a jet in Her X-1 on jet formation mechanisms and on the launching of jets by NSs with strong magnetic fields.

The relationship between the carbon monoxide intensity and the radio continuum emission in spiral galaxies

NASA Technical Reports Server (NTRS)

Adler, David S.; Lo, K. Y.; Allen, Ronald J.

1991-01-01

The relationship between the velocity-integrated CO emission and the nonthermal radio continuum brightness in the disks of normal spiral galaxies is examined on a variety of length scales. On a global scale, the total CO intensity correlates strongly with the total radio continuum flux density for a sample of 31 galaxies. On scales of about 2 kpc or more in the disk of individual galaxies, it is found that the ratio I(CO)/T(20) remains fairly constant over the entire disk as well as from galaxy to galaxy. For the eight spirals in the sample, the disk-averaged values of I(CO)/T(20) range from 0.6-2.4, with the average over all eight galaxies being 1.3 +/- 0.6. It is concluded that what these various length scales actually trace are differences in the primary heating mechanism of the gas in the beam. The observed relationship between CO and nonthermal radio continuum emission can be explained by assuming that molecular gas in galactic disks is heated primarily by cosmic rays. The observed relationship is used to show that the brightness of synchrotron emission is proportional to n(cr) exp 0.4 - 0.9 in galactic disks.

A Repeating Fast Radio Burst: Radio and X-ray Follow-up Observations of FRB 121102

NASA Astrophysics Data System (ADS)

Scholz, Paul; Spitler, Laura; Hessels, Jason; Bogdanov, Slavko; Brazier, Adam; Camilo, Fernando; Chatterjee, Shami; Cordes, James M.; Crawford, Fronefield; Deneva, Julia S.; Ferdman, Robert; Freire, Paulo; Kaspi, Victoria M.; Lazarus, Patrick; Lynch, Ryan; Madsen, Erik; McLaughlin, Maura; Patel, Chitrang; Ransom, Scott M.; Seymour, Andrew; Stairs, Ingrid H.; Stappers, Benjamin; van Leeuwen, Joeri; Zhu, Weiwei

2016-04-01

A new phenomenon has emerged in high-energy astronomy in the past few years: the Fast Radio Burst. Fast Radio Bursts (FRBs) are millisecond-duration radio bursts whose dispersion measures imply that they originate from far outside of the Galaxy. Their origin is as yet unknown; their durations and energetics imply that they involve compact objects, such as neutron stars or black holes. Due to their extreme luminosities implied by their distances and the previous absence of any repeat burst in follow-up observations, many potential explanations involve one-time cataclysmic events. However, in our Arecibo telescope follow-up observations of FRB 121102 (discovered in the PALFA survey; Spitler et al. 2014), we find additional bursts at the same location and dispersion measure as the original burst. We also present the results of Swift and Chandra X-ray observations of the field. This result shows that, for at least a sub-set of the FRB population, the source can repeat and thus cannot be explained by a cataclysmic origin.

The Disk-Jet Connection in Radio-Loud AGN: The X-Ray Perspective

NASA Technical Reports Server (NTRS)

Sambruna, Rita

2008-01-01

Unification schemes assume that radio-loud active galactic nuclei (AGN) contain an accretion disk and a relativistic jet perpendicular to the disk, and an obscuring molecular torus. The jet dominance decreases with larger viewing angles from blazars to Broad-Line and Narrow-Line Radio Galaxies. A fundamental question is how accretion and ejecta are related. The X-rays provide a convenient window to study these issues, as they originate in the innermost nuclear regions and penetrate large obscuring columns. I review the data, using observations by Chandra but also from other currently operating high-energy experiments. Synergy with the upcoming GLAST mission will also be highlighted.

FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics.

PubMed

Harwood, Jeremy J; Croston, Judith H; Intema, Huib T; Stewart, Adam J; Ineson, Judith; Hardcastle, Martin J; Godfrey, Leith; Best, Philip; Brienza, Marisa; Heesen, Volker; Mahony, Elizabeth K; Morganti, Raffaella; Murgia, Matteo; Orrú, Emanuela; Röttgering, Huub; Shulevski, Aleksandar; Wise, Michael W

2016-06-01

Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.

Radio continuum survey of the Coma/A1367 supercluster. I - 610 MHz observations of CGCG galaxies in four groups

NASA Astrophysics Data System (ADS)

Jaffe, W.; Gavazzi, G.; Valentijn, E.

1986-02-01

Radio continuum observations obtained with the Westerbork Radio Synthesis Telescope at 0.6 GHz of four groups of galaxies in the Coma/A1367 supercluster area are presented. Ninety-nine CGCG galaxies were surveyed, yielding the detection of 21 objects. A wide-angle-tail radio galaxy, NGC 4061, is found in the NGC 4065 group. Analysis of this source suggests a relatively low value (neT ≡ 1000 cm-3K) for the intracluster gas pressure in this group.

NuSTAR observations of the powerful radio-galaxy Cygnus A

DOE PAGES

Reynolds, Christopher S.; Lohfink, Anne M.; Ogle, Patrick M.; ...

2015-07-29

Here, we present NuSTAR observations of the powerful radio galaxy Cygnus A, focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN and intracluster medium components. NuSTAR gives a source-dominated spectrum of the AGN out tomore » $$\\gt 70$$ keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law ($${\\rm{\\Gamma }}\\sim 1.6-1.7$$) absorbed by a neutral column density of $${N}_{{\\rm{H}}}\\sim 1.6\\times {10}^{23}\\;\\;{\\mathrm{cm}}^{-2}$$. However, we also detect curvature in the hard ($$\\gt 10$$ keV) spectrum resulting from reflection by Compton-thick matter out of our line of sight to the X-ray source. Compton reflection, possibly from the outer accretion disk or obscuring torus, is required even permitting a high-energy cut off in the continuum source; the limit on the cut-off energy is $${E}_{\\mathrm{cut}}\\gt 111$$ keV(90% confidence). Interestingly, the absorbed power law plus reflection model leaves residuals suggesting the absorption/emission from a fast ($$15,000-26,000\\;\\;\\mathrm{km}\\;\\;{{\\rm{s}}}^{-1}\\;$$), high column-density ($${N}_{W}\\gt 3\\times {10}^{23}\\;\\;{\\mathrm{cm}}^{-2}$$), highly ionized ($$\\xi \\sim 2500\\;\\mathrm{erg}\\;\\mathrm{cm}\\;{{\\rm{s}}}^{-1}$$) wind. A second, even faster ionized wind component is also suggested by these data. We show that the ionized wind likely carries a significant mass and momentum flux, and may carry sufficient kinetic energy to exercise feedback on the host galaxy. If confirmed, the simultaneous presence of a strong wind and powerful jets in Cygnus A demonstrates that feedback from radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN activity but can occur simultaneously.« less

THE TYPE Ia SUPERNOVA RATE IN RADIO AND INFRARED GALAXIES FROM THE CANADA-FRANCE-HAWAII TELESCOPE SUPERNOVA LEGACY SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, M. L.; Pritchet, C. J.; Balam, D.

2010-02-15

We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, Very Large Array 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is {approx}1-5 times the rate in all early-type galaxies, and that any enhancement is always {approx}<2{sigma}. Rates in these subsets are consistent with predictions of the two-component 'A+B' SN Ia rate model. Since infraredmore » properties of radio SN Ia hosts indicate dust-obscured star formation, we incorporate infrared star formation rates into the 'A+B' model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions (DTDs) for SNe Ia, although other DTDs cannot be ruled out based on our data.« less

X-ray detections of submillimetre galaxies: active galactic nuclei versus starburst contribution

NASA Astrophysics Data System (ADS)

Johnson, S. P.; Wilson, G. W.; Wang, Q. D.; Williams, C. C.; Scott, K. S.; Yun, M. S.; Pope, A.; Lowenthal, J.; Aretxaga, I.; Hughes, D.; Kim, M. J.; Kim, S.; Tamura, Y.; Kohno, K.; Ezawa, H.; Kawabe, R.; Oshima, T.

2013-05-01

We present a large-scale study of the X-ray properties and near-IR-to-radio spectral energy distributions (SEDs) of submillimetre galaxies (SMGs) detected at 1.1 mm with the AzTEC instrument across a ˜1.2 square degree area of the sky. Combining deep 2-4 Ms Chandra data with Spitzer IRAC/MIPS and Very Large Array data within the Great Observatories Origins Deep Survey North (GOODS-N), GOODS-S and COSMOS fields, we find evidence for active galactic nucleus (AGN) activity in ˜14 per cent of 271 AzTEC SMGs, ˜28 per cent considering only the two GOODS fields. Through X-ray spectral modelling and multiwavelength SED fitting using Monte Carlo Markov chain techniques to Siebenmorgen et al. (AGN) and Efstathiou, Rowan-Robinson & Siebenmorgen (starburst) templates, we find that while star formation dominates the IR emission, with star formation rates (SFRs) ˜100-1000 M⊙ yr-1, the X-ray emission for most sources is almost exclusively from obscured AGNs, with column densities in excess of 1023 cm-2. Only for ˜6 per cent of our sources do we find an X-ray-derived SFR consistent with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR, preventing significant contribution from the AGN template. Our SED modelling further shows that the AGN and starburst templates typically lack the required 1.1 mm emission necessary to match observations, arguing for an extended, cool dust component. The cross-correlation function between the full samples of X-ray sources and SMGs in these fields does not indicate a strong correlation between the two populations at large scales, suggesting that SMGs and AGNs do not necessarily trace the same underlying large-scale structure. Combined with the remaining X-ray-dim SMGs, this suggests that sub-mm-bright sources may evolve along multiple tracks, with X-ray-detected SMGs representing transitionary objects between periods of high star formation and AGN

Polarized radio emission from the edge-on spiral galaxies NGC 891 and NGC 4565

NASA Technical Reports Server (NTRS)

Sukumar, S.; Allen, R. J.

1991-01-01

Results are presented, at a resolution of 20 arcsec, of observations of the distribution of radio continuum intensity and linear polarization with the VLA in two nearby edge-on spiral galaxies, NGC 891 and NGC 4565, at 6 and 20 cm, respectively. A unified model is presented to account for the main features of the radio polarization in these two galaxies. The model geometry is determined from recent observations of face-on galaxies where the polarized emission is found to be strongest in the dark inter-arm and outer parts of the disks. A substantial Z-thickness is ascribed to this polarized emission. It is shown that the exceptionally strong wavelength dependence of this type of Faraday depolarization can result in edge-on galaxies becoming rapidly 'Faraday thick' at decimeter wavelengths, thereby obliterating the polarization from regions on the dark side of the disk. The degree of polarization observed in both galaxies increases strongly with increasing Z-distance from the plane.

Ultrahigh-energy Cosmic Rays from Fanaroff Riley class II radio galaxies

NASA Astrophysics Data System (ADS)

Rachen, Joerg; Biermann, Peter L.

1992-08-01

The hot spots of very powerful radio galaxies (Fanaroff Riley class II) are argued to be the sources of the ultrahigh energy component in Cosmic Rays. We present calculations of Cosmic Ray transport in an evolving universe, taking the losses against the microwave background properly into account. As input we use the models for the cosmological radio source evolution derived by radioastronomers (mainly Peacock 1985). The model we adopt for the acceleration in the radio hot spots has been introduced by Biermann and Strittmatter (1987), and Meisenheimer et al. (1989) and is based on first order Fermi theory of particle acceleration at shocks (see, e.g., Drury 1983). As an unknown the actual proportion of energy density in protons enters, which together with structural uncertainties in the hot spots should introduce no more than one order of magnitude in uncertainty: We easily reproduce the observed spectra of high energy cosmic rays. It follows that scattering of charged energetic particles in intergalactic space must be sufficiently small in order to obtain contributions from sources as far away as even the nearest Fanaroff Riley class II radio galaxies. This implies a strong constraint on the turbulent magnetic field in intergalactic space.

A search at the millijansky level for milli-arcsecond cores in a complete sample of radio galaxies

NASA Technical Reports Server (NTRS)

Wehrle, A. E.; Preston, R. A.; Meier, D. L.; Gorenstein, M. V.; Shapiro, I. I.; Rogers, A. E. E.; Rius, A.

1984-01-01

A complete sample of 26 extended radio galaxies was observed at 2.29 GHz with the Mark III VLBI system. The fringe spacing was about 3 milli-arcsec, and the detection limit was about 2 millijanskys. Half of the galaxies were found to possess milli-arcsec radio cores. In all but three sources, the nuclear flux density was less than 0.04 of the total flux density. Galaxies with high optical luminosity (less than -21.2) were more likely than less luminous galaxies to contain a detectable milliparcsec radio core (69 percent vs. 20 percent). For objects with arcsec cores, 80 percent were found to have a milli-arcsec core, even though the milli-arcsec object did not always contribute the greater part of the arcsec flux density.

Cluster candidates around low-power radio galaxies at z ∼ 1-2 in cosmos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castignani, G.; Celotti, A.; De Zotti, G.

2014-09-10

We search for high-redshift (z ∼1-2) galaxy clusters using low power radio galaxies (FR I) as beacons and our newly developed Poisson probability method based on photometric redshift information and galaxy number counts. We use a sample of 32 FR Is within the Cosmic Evolution Survey (COSMOS) field from the Chiaberge et al. catalog. We derive a reliable subsample of 21 bona fide low luminosity radio galaxies (LLRGs) and a subsample of 11 high luminosity radio galaxies (HLRGs), on the basis of photometric redshift information and NRAO VLA Sky Survey radio fluxes. The LLRGs are selected to have 1.4 GHzmore » rest frame luminosities lower than the fiducial FR I/FR II divide. This also allows us to estimate the comoving space density of sources with L {sub 1.4} ≅ 10{sup 32.3} erg s{sup –1} Hz{sup –1} at z ≅ 1.1, which strengthens the case for a strong cosmological evolution of these sources. In the fields of the LLRGs and HLRGs we find evidence that 14 and 8 of them reside in rich groups or galaxy clusters, respectively. Thus, overdensities are found around ∼70% of the FR Is, independently of the considered subsample. This rate is in agreement with the fraction found for low redshift FR Is and it is significantly higher than that for FR IIs at all redshifts. Although our method is primarily introduced for the COSMOS survey, it may be applied to both present and future wide field surveys such as Sloan Digital Sky Survey Stripe 82, LSST, and Euclid. Furthermore, cluster candidates found with our method are excellent targets for next generation space telescopes such as James Webb Space Telescope.« less

Steep radio spectra in high-redshift radio galaxies

NASA Technical Reports Server (NTRS)

Krolik, Julian H.; Chen, Wan

1991-01-01

The generic spectrum of an optically thin synchrotron source steepens by 0.5 in spectral index from low frequencies to high whenever the source lifetime is greater than the energy-loss timescale for at least some of the radiating electrons. Three effects tend to decrease the frequency nu(b) of this spectral bend as the source redshift increases: (1) for fixed bend frequency nu* in the rest frame, nu(b) = nu*/(1 + z); (2) losses due to inverse Compton scattering the microwave background rise with redshift as (1 + z) exp 4, so that, for fixed residence time in the radiating region, the energy of the lowest energy electron that can cool falls rapidly with increasing redshift; and (3) if the magnetic field is proportional to the equipartition field and the emitting volume is fixed or slowly varying, flux-limited samples induce a selection effect favoring low nu* at high z because higher redshift sources require higher emissivity to be included in the sample, and hence have stronger implied fields and more rapid synchrotron losses. A combination of these effects may explain the trend observed in the 3CR sample for higher redshift radio galaxies to have steeper spectra, and the successful use of ultrasteep spectrum surveys to locate high-redshift galaxies.

Radio Jets Clearing the Way Through a Galaxy: Watching Feedback in Action in the Seyfert Galaxy IC 5063

NASA Astrophysics Data System (ADS)

Morganti, R.; Oosterloo, T. A.; Oonk, J. B. R.; Frieswijk, W.; Tadhunter, C. N.

2015-12-01

High-resolution (0.5 arcsec) CO(2-1) observations performed with the Atacama Large Millimetre/submillimetre Array have been used to trace the kinematics of the molecular gas in the Seyfert 2 galaxy{IC 5063}. Although one of the most radio-loud Seyfert galaxy, IC 5063 is a relatively weak radio source (P1.4GHz=3 ×1023 W Hz-1). The data reveal that the kinematics of the gas is very complex. A fast outflow of molecular gas extends along the entire radio jet (˜ 1 kpc), with the highest outflow velocities about 0.5 kpc from the nucleus, at the location of the brighter hot-spot in the W lobe. All the observed characteristics can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the interstellar medium. This suggests that most of the observed cold molecular outflow is due to fast cooling of the gas after the passage of a shock and that it is the end product of the cooling process.

Binary model of Circinus X-1. I - Eccentricity from combined X-ray and radio observations

NASA Technical Reports Server (NTRS)

Murdin, P.; Jauncey, D. L.; Lerche, I.; Nicolson, G. D.; Kaluzienski, L. J.; Holt, S. S.; Haynes, R. F.

1980-01-01

A binary star model is used to account for the 16.59-d flaring behavior of the X-ray emission from Circinus X-1. The orbital eccentricity of 0.8 + or - 0.1 is derived from the X-ray light curve by assuming that the sharp X-ray cut-off every 16.59-d is a result of bound-free absorption in the primary star's stellar wind. The shape of the light curve has changed over the last eight years, and this is interpreted as due to orbital precession of the binary system. Simultaneous radio and X-ray observations of the flare from Circinus X-1 on February 1-5, 1978 are reported. These are accounted for within the framework of the model. The radio observations at 5 GHz are used independently to derive a high value of the orbital eccentricity (e = 0.7).

Detection of radio emission from the jet in Centaurus A

NASA Technical Reports Server (NTRS)

Schreier, E. J.; Burns, J. O.; Feigelson, E. D.

1981-01-01

The VLA has detected radio emission from the X-ray jet in Centaurus A, at 20 and 6 cm, whose radio morphology is similar to that of the X-ray jet. It is suggested that the same population of relativistic electrons is responsible for both radio and X-ray synchrotron emission, in which case in situ acceleration of electrons in the knots would be mandatory. The relativistic beam may alternatively heat the surrounding gas, resulting in X-ray emission. The static confinement of the knots of the jet seems to be accomplished by the presence of the ambient hot gas in the galaxy. The galaxy's nucleus has an inverted spectrum at radio frequencies, and it is noted that the jet is as bright as the nucleus at low frequencies.

Radio and infrared emission from Markarian starburst galaxies

NASA Technical Reports Server (NTRS)

Stine, Peter C.

1992-01-01

Radio and infrared emission were compared for a sample of 58 Markarian starburst galaxies, chosen to cover a wide range of 60-micron luminosity density. New radio observations were from the VLA at 6 and 20 cm in the B and A configurations. IRAS data were reanalyzed for 25 of the starbursts that were previously undetected at either 25 or 100 microns. The correlation between the global radio and IR emission for the starbursts in the sample is strongest at 25 and 60 microns, wavelengths in which the warm dust dominates. The radio spectral index steepens away from the center. This indicates that nonthermal emission leaks out of the starburst region. The change in the spectral index implies that while nonthermal sources dominate in the entire region, the bulk of the interior emission at 6 cm is thermal. The radio spectral index does not appear to vary as a function of the infrared luminosity or the infrared colors, which indicates that the slope of the initial mass function does not appear to be a function of either the mass or temperature of the starburst.

The Infrared-Radio Correlation of Dusty Star Forming Galaxies at High Redshift

NASA Astrophysics Data System (ADS)

Lower, Sidney; Vieira, Joaquin Daniel; Jarugula, Sreevani

2018-01-01

Far-infrared (FIR) and radio continuum emission in galaxies are related by a common origin: massive stars and the processes triggered during their birth, lifetime, and death. FIR emission is produced by cool dust, heated by the absorption of UV emission from massive stars, which is then re-emitted in the FIR. Thermal free-free radiation emitted from HII regions dominates the spectral energy density (SED) of galaxies at roughly 30 GHz, while non-thermal synchrotron radiation dominates at lower frequencies. At low redshift, the infrared radio correlation (IRC, or qIR) holds as a tight empirical relation for many star forming galaxy types, but until recently, there has not been sensitive enough radio observations to extend this relation to higher redshifts. Many selection biases cloud the results of these analyses, leaving the evolution of the IRC with redshift ambiguous. In this poster, I present CIGALE fitted spectral energy distributions (SEDs) for 24 gravitationally-lensed sources selected in the mm-wave from the South Pole Telescope (SPT) survey. I fit the IRC from infrared and submillimeter fluxes obtained with Herschel, Atacama Pathfinder Experiment (APEX), and SPT and radio fluxes obtained with ATCA at 2.1, 5.5, 9, and 30 GHz. This sample of SPT sources has a spectroscopic redshift range of 2.1

A multiparametric analysis of the Einstein sample of early-type galaxies. 2: Galaxy formation history and properties of the interstellar medium

NASA Technical Reports Server (NTRS)

Eskridge, Paul B.; Fabbiano, Giuseppina; Kim, Dong-Woo

1995-01-01

We have conducted bivariate and multivariate statistical analysis of data measuring the integrated luminosity, shape, and potential depth of the Einstein sample of early-type galaxies (presented by Fabbiano et al. 1992). We find significant correlations between the X-ray properties and the axial ratios (a/b) of our sample, such that the roundest systems tend to have the highest L(sub x) and L(sub x)/L(sub B). The most radio-loud objects are also the roundest. We confirm the assertion of Bender et al. (1989) that galaxies with high L(sub x) are boxy (have negative a(sub 4)). Both a/b and a(sub 4) are correlated with L(sub B), but not with IRAS 12 um and 100 um luminosities. There are strong correlations between L(sub x), Mg(sub 2), and sigma(sub nu) in the sense that those systems with the deepest potential wells have the highest L(sub x) and Mg(sub 2). Thus the depth of the potential well appears to govern both the ability to reatin an ISM at the present epoch and to retain the enriched ejecta of early star formation bursts. Both L(sub x)/L(sub B) and L(sub 6) (the 6 cm radio luminosity) show threshold effects with sigma(sub nu) exhibiting sharp increases at log sigma(sub nu) approximately = 2.2. Finally, there is clearly an interrelationship between the various stellar and structural parameters: The scatter in the bivariate relationships between the shape parameters (a/b and a(sub 4)) and the depth parameter sigma(sub nu) is a function of abundance in the sense that, for a given a(sub 4) or a/b, the systems with the highest sigma(sub nu) also have the highest Mg(sub 2). Furthermore, for a constant sigma(sun nu), disky galaxies tend to have higher Mg(sub 2) than boxy ones. Alternatively, for a given abundance, boxy ellipticals tend to be more massive than disky ellipticals. One possibility is that early-type galaxies of a given mass, originating from mergers (boxy ellipticals), have lower abundances than 'primordial' (disky) early-type galaxies. Another is that

Tracking Galaxy Evolution Through Low-Frequency Radio Continuum Observations using SKA and Citizen-Science Research using Multi-Wavelength Data

NASA Astrophysics Data System (ADS)

Hota, Ananda; Konar, C.; Stalin, C. S.; Vaddi, Sravani; Mohanty, Pradeepta K.; Dabhade, Pratik; Dharmik Bhoga, Sai Arun; Rajoria, Megha; Sethi, Sagar

2016-12-01

We present a brief review of progress in the understanding of general spiral and elliptical galaxies, through merger, star formation and AGN activities. With reference to case studies performed with the GMRT, we highlight the unique aspects of studying galaxies in the radio wavelengths where powerful quasars and bright radio galaxies are traditionally the dominating subjects. Though AGN or quasar activity is extremely energetic, it is extremely short-lived. This justify focussing on transitional galaxies to find relic-evidences of the immediate past AGN-feedback which decide the future course of evolution of a galaxy. Relic radio lobes can be best detected in low frequency observations with the GMRT, LOFAR and in future SKA. The age of these relic radio plasma can be as old as a few hundred Myr. There is a huge gap between this and what is found in optical bands. The very first relic-evidences of a past quasar activity (Hanny's Voorwerp) was discovered in 2007 by a Galaxy Zoo citizen-scientist, a school teacher, in the optical bands. This relic is around a few tens of thousand years old. More discoveries needed to match these time-scales with star formation time-scales in AGN host galaxies to better understand black hole galaxy co-evolution process via feedback-driven quenching of star formation. It is now well-accepted that discovery and characterization of such faint fuzzy relic features can be more efficiently done by human eye than a machine. Radio interferometry images are more complicated than optical and need the citizen-scientists to be trained. RAD@home, the only Indian citizen-science research project in astronomy, analysing TIFR GMRT Sky Survey (TGSS) 150 MHz data and observing from the Giant Meterwave Radio Telescope (GMRT), was launched in April 2013. Unique, zero-infrastructure zero-funded design of RAD@home as a collaboratory of 69 trained e-astronomers is briefly described. Some of the new-found objects like episodic radio galaxies, radio-jet and

Associating Fast Radio Bursts with Their Host Galaxies

NASA Astrophysics Data System (ADS)

Eftekhari, T.; Berger, E.

2017-11-01

The first precise localization of a fast radio burst (FRB) sheds light on the nature of these mysterious bursts and the physical mechanisms that power them. Increasing the sample of FRBs with robust host galaxy associations is the key impetus behind ongoing and upcoming searches and facilities. Here, we quantify the robustness of FRB host galaxy associations as a function of localization area and galaxy apparent magnitude. We also explore the use of FRB dispersion measures to constrain the source redshift, thereby reducing the number of candidate hosts. We use these results to demonstrate that even in the absence of a unique association, a constraint can be placed on the maximum luminosity of a host galaxy as a function of localization and dispersion measure (DM). We find that localizations of ≲ 0.5\\text{'}\\text{'} are required for a chance coincidence probability of ≲ 1 % for dwarf galaxies at z≳ 0.1; if some hosts have luminosities of ˜ {L}\\ast , then localizations of up to ≈ 5\\prime\\prime may suffice at z˜ 0.1. Constraints on the redshift from the DM only marginally improve the association probability unless the DM is low, ≲ 400 pc cm-3. This approach also relies on the determination of galaxy redshifts, which is challenging at z≳ 0.5 if the hosts are dwarf galaxies. Finally, interesting limits on the maximum host luminosity require localizations of ≲ 5\\prime\\prime at z≳ 0.1. Even a few such localizations will explain the nature of FRB progenitors, their possible diversity, and their use as cosmological tools.

Search for low-frequency diffuse radio emission around a shock in the massive galaxy cluster MACS J0744.9+3927

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Rafferty, D.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Botteon, A.; Cassano, R.; Brunetti, G.; De Gasperin, F.; Wittor, D.; Hoeft, M.; Birzan, L.

2018-05-01

Merging galaxy clusters produce low-Mach-number shocks in the intracluster medium. These shocks can accelerate electrons to relativistic energies that are detectable at radio frequencies. MACS J0744.9+3927 is a massive [M500 = (11.8 ± 2.8) × 1014 M⊙], high-redshift (z = 0.6976) cluster where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich maps from MUSTANG indicate that a shock, with Mach number M = 1.0-2.9 and an extension of ˜200 kpc, sits near the centre of the cluster. The shock is also detected as a brightness and temperature discontinuity in X-ray observations. To search for diffuse radio emission associated with the merger, we have imaged the cluster with the LOw Frequency ARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previously undetected AGN emission, but do not show clear cluster-scale diffuse emission in the form of a radio relic nor a radio halo. The region of the shock is on the western edge of AGN lobe emission from the brightest cluster galaxy. Correlating the flux of known shock-induced radio relics versus their size, we find that the radio emission overlapping the shocked region in MACS J0744.9+3927 is likely of AGN origin. We argue against the presence of a relic caused by diffusive shock acceleration and suggest that the shock is too weak to accelerate electrons from the intracluster medium.

Chandra Discovers X-ray Source at the Center of Our Galaxy

NASA Astrophysics Data System (ADS)

2000-01-01

Culminating 25 years of searching by astronomers, researchers at Massachusetts Institute of Technology say that a faint X-ray source, newly detected by NASA's Chandra X-ray Observatory, may be the long-sought X-ray emission from a known supermassive black hole at the center of our galaxy. Frederick K. Baganoff and colleagues from Pennsylvania State University, University Park, and the University of California, Los Angeles, will present their findings today in Atlanta at the 195th national meeting of the American Astronomical Society. Baganoff, lead scientist for the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer (ACIS) team's "Sagittarius A* and the Galactic Center" project and postdoctoral research associate at MIT, said that the precise positional coincidence between the new X-ray source and the radio position of a long-known source called Sagittarius A* "encourages us to believe that the two are the same." Sagittarius A* is a point-like, variable radio source at the center of our galaxy. It looks like a faint quasar and is believed to be powered by gaseous matter falling into a supermassive black hole with 2.6 million times the mass of our Sun. Chandra's remarkable detection of this X-ray source has placed astronomers within a couple of years of a coveted prize: measuring the spectrum of energy produced by Sagittarius A* to determine in detail how the supermassive black hole that powers it works. "The race to be the first to detect X-rays from Sagittarius A* is one of the hottest and longest-running in all of X-ray astronomy," Baganoff said. "Theorists are eager to hear the results of our observation so they can test their ideas." But now that an X-ray source close to Sagittarius A* has been found, it has taken researchers by surprise by being much fainter than expected. "There must be something unusual about the environment around this black hole that affects how it is fed and how the gravitational energy released from the infalling matter is

X-Ray Emission from Ultraviolet Luminous Galaxies and Lyman Break Galaxies

NASA Technical Reports Server (NTRS)

Hornschemeier, Ann; Ptak, A. F.; Salim, S.; Heckman, T. P.; Overzier, R.; Mallery, R.; Rich, M.; Strickland, D.; Grimes, J.

2009-01-01

We present results from an XMM mini-survey of GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs) that appear to include an interesting subset that are analogs to the distant (3Galaxies (LBGs). The 2-10 kev X-ray emission of LBGs appear to be broadly similar to that of galaxies in the local Universe, possibly indicating similarity in the production of accreting binaries over large evolutionary timescales in the Universe. We have detected luminous X-ray emission from one UVLG that permits basic X-ray spectroscopic analysis, and have direct X-ray constraints on a total of 6 UVLGs. We find evidence for likely large scatter in the assumed X-ray/star-formation rate relation for LBGs.

Compact radio sources in the starburst galaxy M82 and the Sigma-D relation for supernova remnants

NASA Technical Reports Server (NTRS)

Huang, Z. P.; Thuan, T. X.; Chevalier, R. A.; Condon, J. J.; Yin, Q. F.

1994-01-01

We have obtained an 8.4 GHz Very Large Array (VLA) A-array map of the starburst galaxy M82 with a resolution Full Width at Half Maximum (FWHM) approximately 0.182 sec. About 50 compact radio sources in the central region of M82 were detected with a peak surface brightness approximately greater than 10(exp -17) W/Hz/sq m/sr. Comparison with previous observations shows that most sources are declining in flux. Three previously visible sources have faded into the background of our map (approximately less than 0.2 mJy/beam), while a few sources, including the second and third brightest radio sources in M82, may have increased slightly in flux over the last decade. No new radio supernova was found. The birth rate of the compact radio sources is estimated to be 0.11 + or - 0.05/yr. We attribute the population of such bright, small supernova remnants (SNRs) in M82 to the high pressure in the central region that can truncate the mass loss during a red supergiant phase or allow dense ionized clouds to be present. The compact radio sources obey a Sigma(radio surface brightness) - D(diameter) relation which is remarkably similar to that followed by supernova remnants in the Galaxy and the Magellanic Clouds and by two of the strongest known extragalactic radio supernovae: SN 1986J and SN 1979C. A least-squares fit to the SNR data gives: Sigma(sub 8.4 GHz) (W/Hz/sq m/sr) = 4.4 x 10(exp -16) D(sub pc)(exp -3.5 +/- 0.1) covering seven orders of magnitude in Sigma. Possible selection effects are discussed and a theoretical discussion of the correlation is presented.

a Snapshot Survey of X-Ray Selected Central Cluster Galaxies

NASA Astrophysics Data System (ADS)

Edge, Alastair

1999-07-01

Central cluster galaxies are the most massive stellar systems known and have been used as standard candles for many decades. Only recently have central cluster galaxies been recognised to exhibit a wide variety of small scale {<100 pc} features that can only be reliably detected with HST resolution. The most intriguing of these are dust lanes which have been detected in many central cluster galaxies. Dust is not expected to survive long in the hostile cluster environment unless shielded by the ISM of a disk galaxy or very dense clouds of cold gas. WFPC2 snapshot images of a representative subset of the central cluster galaxies from an X-ray selected cluster sample would provide important constraints on the formation and evolution of dust in cluster cores that cannot be obtained from ground-based observations. In addition, these images will allow the AGN component, the frequency of multiple nuclei, and the amount of massive-star formation in central cluster galaxies to be ass es sed. The proposed HST observatio ns would also provide high-resolution images of previously unresolved gravitational arcs in the most massive clusters in our sample resulting in constraints on the shape of the gravitational potential of these systems. This project will complement our extensive multi-frequency work on this sample that includes optical spectroscopy and photometry, VLA and X-ray images for the majority of the 210 targets.

The Complete Local-Volume Groups Sample (CLoGS): Early results from X-ray and radio observations

NASA Astrophysics Data System (ADS)

Vrtilek, Jan M.; O'Sullivan, Ewan; David, Laurence P.; Giacintucci, Simona; Kolokythas, Konstantinos

2017-08-01

Although the group environment is the dominant locus of galaxy evolution (in contrast to rich clusters, which contain only a few percent of galaxies), there has been a lack of reliable, representative group samples in the local Universe. In particular, X-ray selected samples are strongly biased in favor of the X-ray bright, centrally-concentrated cool-core systems. In response, we have designed the Complete Local-Volume Groups Sample (CLoGS), an optically-selected statistically-complete sample of 53 groups within 80 Mpc which is intended to overcome the limitations of X-ray selected samples and serve as a representative survey of groups in the local Universe. We have supplemented X-ray data from Chandra and XMM (70% complete to date, using both archival and new observations, with a 26-group high richness subsample 100% complete) with GMRT radio continuum observations (at 235 and 610 MHz, complete for the entire sample). CLoGS includes groups with a wide variety of properties in terms of galaxy population, hot gas content, and AGN power. We here describe early results from the survey, including the range of AGN activity observed in the dominant galaxies, the relative fraction of cool-core and non-cool-core groups in our sample, and the degree of disturbance observed in the IGM.

From Radio with Love: An Overview of the Role of Radio Observations in Understanding High-Energy Emission from Active Galaxies

NASA Technical Reports Server (NTRS)

Ojha, Roopesh

2012-01-01

The gamma-ray satellite Fermi and the ground based TeV facilities MAGIC, VERITAS and HESS have ushered in a new era in the observation of high-energy emission from active galaxies. The energy budgets of these objects have a major contribution from gamma-rays and it is simply not possible to understand their physics without high-energy observations. Though the exact mechanisms for high-energy production in galaxies remains an open question, gamma-rays typically result from interactions between high-energy particles. Via different interactions these same particles can produce radio emission. Thus the non-thermal nature of gamma-ray emission practically guarantees that high-energy emitters are also radio loud. Aside from their obvious role as a component of multiwavelength analysis, radio observations provide two crucial elements essential to understanding the source structure and physical processes of high-energy emitters: very high timing resolution and very high spatial resolution. A brief overview of the unique role played by radio observations in unraveling the mysteries of the high energy Universe as presented here.

Shocking features in the merging galaxy cluster RXJ0334.2-0111

NASA Astrophysics Data System (ADS)

Dasadia, Sarthak; Sun, Ming; Morandi, Andrea; Sarazin, Craig; Clarke, Tracy; Nulsen, Paul; Massaro, Francesco; Roediger, Elke; Harris, Dan; Forman, Bill

2016-05-01

We present a 66 ks Chandra X-ray observation of the galaxy cluster RXJ0334.2-0111. This deep observation revealed a unique bow shock system associated with a wide angle tail (WAT) radio galaxy and several intriguing substructures. The temperature across the bow shock jumps by a factor of ˜1.5 (from 4.1 to 6.2 keV), and is consistent with the Mach number M = 1.6_{-0.3}^{+0.5}. A second inner surface brightness edge is a cold front that marks the border between infalling subcluster cool core and the intracluster medium of the main cluster. The temperature across the cold front increases from 1.3_{-0.8}^{+0.3} to 6.2_{-0.6}^{+0.6} keV. We find an overpressurized region ˜250 kpc east of the cold front that is named `the eastern extension (EE)'. The EE may be a part of the third subcluster in the ongoing merger. We also find a tail shaped feature that originates near the bow shock and may extend up to a distance of ˜1 Mpc. This feature is also likely overpressurized. The luminous FR-I radio galaxy, 3C89, appears to be the cD galaxy of the infalling subcluster. We estimated 3C89's jet power from jet bending and the possible interaction between the X-ray gas and the radio lobes. A comparison between the shock stand-off distance and the Mach number for all known shock front/cold front combinations suggests that the core is continuously shrinking in size by stripping.

High levels of absorption in orientation-unbiased, radio-selected 3CR Active Galaxies

NASA Astrophysics Data System (ADS)

Wilkes, Belinda J.; Haas, Martin; Barthel, Peter; Leipski, Christian; Kuraszkiewicz, Joanna; Worrall, Diana; Birkinshaw, Mark; Willner, Steven P.

2014-08-01

A critical problem in understanding active galaxies (AGN) is the separation of intrinsic physical differences from observed differences that are due to orientation. Obscuration of the active nucleus is anisotropic and strongly frequency dependent leading to complex selection effects for observations in most wavebands. These can only be quantified using a sample that is sufficiently unbiased to test orientation effects. Low-frequency radio emission is one way to select a close-to orientation-unbiased sample, albeit limited to the minority of AGN with strong radio emission.Recent Chandra, Spitzer and Herschel observations combined with multi-wavelength data for a complete sample of high-redshift (1radio sources show that about half the sample is significantly obscured with ratios of unobscured: Compton thin (22 24.2) = 2.5:1.4:1 in these high-luminosity (log L(0.3-8keV) ~ 44-46) sources. These ratios are consistent with current expectations based on modelingthe Cosmic X-ray Background. A strong correlation with radio orientation constrains the geometry of the obscuring disk/torus to have a ~60 degree opening angle and ~12 degree Compton-thick cross-section. The deduced ~50% obscured fraction of the population contrasts with typical estimates of ~20% obscured in optically- and X-ray-selected high-luminosity samples. Once the primary nuclear emission is obscured, AGN X-ray spectra are frequently dominated by unobscured non-nuclear or scattered nuclear emission which cannot be distinguished from direct nuclear emission with a lower obscuration level unless high quality data is available. As a result, both the level of obscuration and the estimated instrinsic luminosities of highly-obscured AGN are likely to be significantly (*10-1000) underestimated for 25-50% of the population. This may explain the lower obscured fractions reported for optical and X-ray samples which have no independent measure of the AGN

Multiwavelength Study of the Bright X-ray Source Population in the Interacting Galaxies NGC 5774/NGC 5775

NASA Technical Reports Server (NTRS)

Ghosh, Kajal K.; Swartz, Douglas A.; Tennant, Allyn F.; Saripalli, Lakshmi; Gandhi, Poshak; Foellmi, Cedric; Gutierrez, Carlos M.; Lopez-Corredoira, Martin

2006-01-01

The X-ray source population in the field of the interacting pair of galaxies NGC 5774/5775 is reported. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates with lum inosities above 10(exp 39)erg/s in the 0.5 - 8.0 keV X-ray band. Several of these latter are transient X-ray sources that fall below detect ion levels in one of two X-ray observations spaced 15 months apart. X-ray source positions are mapped onto optical and radio images to sear ch for potential counterparts. Eleven sources have optically-bright c ounterparts. Optical colors are used to differentiate these sources, which are mostly located outside the optical extent of the interacting galaxies, as potential globular clusters (3 sources) and quasars (5) . Follow-up optical spectroscopy confirms two of the latter are background quasars.

Extreme Gaseous Outflows in Radio-Loud Narrow-Line Seyfert 1 Galaxies

NASA Astrophysics Data System (ADS)

Komossa, S.; Xu, D. W.; Wagner, A. Y.

2018-04-01

We present four radio-loud NLS1 galaxies with extreme emission-line shifts, indicating radial outflow velocities of the ionized gas of up to 2450 km/s, above the escape velocity of the host galaxies. The forbidden lines show strong broadening, up to 2270 km/s. An ionization stratification (higher line shift at higher ionization potential) implies that we see a large-scale outflow rather than single, localized jet-cloud interactions. Similarly, the paucity of zero-velocity [OIII]λ5007 emitting gas implies the absence of a second narrow-line region (NLR) component at rest, and therefore a large part of the high-ionization NLR is affected by the outflow. Given the radio loudness of these NLS1 galaxies, the observations are consistent with a pole on view onto their central engines, so that the effects of polar outflows are maximized. In addition, a very efficient driving mechanism is required, to reach the high observed velocities. We explore implications from recent hydrodynamic simulations of the interaction between fast winds or jets with the large-scale NLR. Overall, the best agreement with observations (and especially the high outflow speeds of the [NeV] emitting gas) can be reached if the NLS1 galaxies are relatively young sources with lifetimes not much exceeding 1 Myr. These systems represent sites of strong feedback at NLR scales at work, well below redshift one.

The case for electron re-acceleration at galaxy cluster shocks

NASA Astrophysics Data System (ADS)

van Weeren, Reinout J.; Andrade-Santos, Felipe; Dawson, William A.; Golovich, Nathan; Lal, Dharam V.; Kang, Hyesung; Ryu, Dongsu; Brìggen, Marcus; Ogrean, Georgiana A.; Forman, William R.; Jones, Christine; Placco, Vinicius M.; Santucci, Rafael M.; Wittman, David; Jee, M. James; Kraft, Ralph P.; Sobral, David; Stroe, Andra; Fogarty, Kevin

2017-01-01

On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found1,2 . Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster-cluster merger events 3 . A long-standing problem is how low-Mach-number shocks can accelerate electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411-3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. It also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.

The case for electron re-acceleration at galaxy cluster shocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

van Weeren, Reinout J.; Andrade-Santos, Felipe; Dawson, William A.

On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found. Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster–cluster merger events. A long-standing problem is how low-Mach-number shocks can acceleratemore » electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411–3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. Lastly, it also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.« less

The case for electron re-acceleration at galaxy cluster shocks

DOE PAGES

van Weeren, Reinout J.; Andrade-Santos, Felipe; Dawson, William A.; ...

2017-01-04

On the largest scales, the Universe consists of voids and filaments making up the cosmic web. Galaxy clusters are located at the knots in this web, at the intersection of filaments. Clusters grow through accretion from these large-scale filaments and by mergers with other clusters and groups. In a growing number of galaxy clusters, elongated Mpc-sized radio sources have been found. Also known as radio relics, these regions of diffuse radio emission are thought to trace relativistic electrons in the intracluster plasma accelerated by low-Mach-number shocks generated by cluster–cluster merger events. A long-standing problem is how low-Mach-number shocks can acceleratemore » electrons so efficiently to explain the observed radio relics. Here, we report the discovery of a direct connection between a radio relic and a radio galaxy in the merging galaxy cluster Abell 3411–3412 by combining radio, X-ray and optical observations. This discovery indicates that fossil relativistic electrons from active galactic nuclei are re-accelerated at cluster shocks. Lastly, it also implies that radio galaxies play an important role in governing the non-thermal component of the intracluster medium in merging clusters.« less

Galaxies in the X-Ray Band

NASA Technical Reports Server (NTRS)

Hornschemeier, Ann

2008-01-01

This talk will provide a brief review of progress an X-ray emission from normal (non-AGN) galaxy populations, including important constraints on the evolution of accreting binary populations over important cosmological timescales. We will also look to the future, anticipating constraints from near-term imaging hard X-ray missions such as NuSTAR, Simbol-X and NeXT and then the longer-term prospects for studying galaxies with the Generation-X mission,

Galaxies in the X-ray Band

NASA Technical Reports Server (NTRS)

Hornschemeier, Ann

2008-01-01

This talk will provide a brief review of progress on X-ray emission from normal (non-AGN) galaxy populations, including important constraints on the evolution of accreting binary populations over important cosmological timescales. We will also look to the future, anticipating constraints from near-term imaging hard X-ray missions such as NuSTAR, Simbol-X and NeXT and then the longer-term prospects for studying galaxies with the Generation-X mission.

Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio

NASA Astrophysics Data System (ADS)

Vardoulaki, E.; Charmandaris, V.; Murphy, E. J.; Diaz-Santos, T.; Armus, L.; Evans, A. S.; Mazzarella, J. M.; Privon, G. C.; Stierwalt, S.; Barcos-Muñoz, L.

2015-02-01

Context. Luminous infrared galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. Aims: The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z< 0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of active galactic nuclei (AGN). Methods: We used the archival data at 1.49 and 8.44 GHz to create radio-spectral-index maps using the standard relation between flux density Sν and frequency ν, Sν ~ ν- α, where α is the radio spectral index. By studying the spatial variations in α, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2 μm PAH feature) and optical (BPT diagram) AGN diagnostics. Results: We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on

Galaxy-galaxy and galaxy-cluster lensing with the SDSS and FIRST surveys

NASA Astrophysics Data System (ADS)

Demetroullas, C.; Brown, M. L.

2018-01-01

We perform a galaxy-galaxy lensing study by correlating the shapes of ∼2.7 × 105 galaxies selected from the VLA FIRST (Faint Images of the Radio Sky at Twenty centimetres) radio survey with the positions of ∼38.5 million Sloan Digital Sky Survey (SDSS) galaxies, ∼132 000 Brightest Cluster Galaxies (BCGs) and ∼78 000 SDSS galaxies that are also detected in the VLA FIRST survey. The measurements are conducted on angular scales θ ≲ 1200 arcsec. On scales θ ≲ 200 arcsec, we find that the measurements are corrupted by residual systematic effects associated with the instrumental beam of the VLA data. Using simulations, we show that we can successfully apply a correction for these effects. Using the three lens samples (the SDSS DR10 sample, the BCG sample and the SDSS-FIRST matched object sample), we measure a tangential shear signal that is inconsistent with 0 at the 10.2σ, 3.8σ and 9σ levels, respectively. Fitting an NFW model to the detected signals, we find that the ensemble mass profile of the BCG sample agrees with the values in the literature. However, the mass profiles of the SDSS DR10 and the SDSS-FIRST matched object samples are found to be shallower and steeper than results in the literature, respectively. The best-fitting Virial masses for the SDSS DR10, BCG and SDSS-FIRST matched samples, derived using an NFW model and allowing for a varying concentration factor, are M_{200}^SDSS-DR10 = (1.2 ± 0.4) × 10^{12} M_{⊙}, M_{200}^BCG = (1.4 ± 1.3) × 10^{13} M_{⊙} and M_{200}^SDSS-FIRST =8.0 ± 4.2 × 10^{13} M_{⊙}, respectively. These results are in good agreement (within ∼2σ) with values in the literature. Our findings suggest that for galaxies to be bright both in the radio and in the optical, they must be embedded in very dense environment on scales R ≲ 1 Mpc.

The Nuclear Spectrum of the Radio Galaxy NGC 5128 (Centaurus A)

NASA Technical Reports Server (NTRS)

Simpson, C.; Meadows, V.

1998-01-01

We present near-infrared spectra of the nucleus of the nearby radio galaxy NGC 5128 (Centaurus A). The observed emission line strengths suggest that NGC 5128 should be classified as a LINER, and appear to be powered by shocks.

Testing the Merger Paradigm: X-ray Observations of Radio-Selected Sub-Galactic-Scale Binary AGNs

NASA Astrophysics Data System (ADS)

Fu, Hai

2016-09-01

Interactions play an important role in galaxy evolution. Strong gas inflows are expected in the process of gas-rich mergers, which may fuel intense black hole accretion and star formation. Sub-galactic-scale binary/dual AGNs thus offer elegant laboratories to study the merger-driven co-evolution phase. However, previous samples of kpc-scale binaries are small and heterogeneous. We have identified a flux-limited sample of kpc-scale binary AGNs uniformly from a wide-area high-resolution radio survey conducted by the VLA. Here we propose Chandra X-ray characterization of a subset of four radio-confirmed binary AGNs at z 0.1. Our goal is to compare their X-ray properties with those of matched control samples to test the merger-driven co-evolution paradigm.

The shell galaxy NGC4104 in an X-ray group

NASA Astrophysics Data System (ADS)

Lima Neto, G. B.; Durret, F.; Laganá, T.; Machado, R. E. G.; Martinet, N.

2017-07-01

Groups of galaxies are expected to collapse early in the history of the universe, in particular the so-called Fossil Groups, with a central galaxy that grows at the bottom of the gravitational potential well by cannibalizing smaller galaxies and/or by major mergers. An evidence of galactic cannibalism is the feature known as shells or ripples in early-type galaxies Shell galaxies are believed to be the result of a minor merger of a dwarf with an elliptical galaxy, resulting in a series of faint concentric ripples in surface brightness observed throughout the main stellar component. This contribution presents very deep r and g imaging of NGC 4104 - the brightest galaxy of an X-ray emitting group - obtained with MegaCam on the 3.6 m CFHT. Using both iraf/ellipse and galfit 2D image-fitting programs, we show the presence of strong shell features and an extended stellar halo around the group brightest galaxy. We have run a series of N-body simulations in order to gain insight on the dynamical process that shaped NGC 4104. Numerical modeling suggests a recent (around 5 Gyrs ago) collision occurred with a dwarf galaxy, which may have also led to a central absorption feature observed in the galaxy center. Moreover, given the magnitude gap between the first and second brightest galaxies, it seems that we are witnessing the formation of an object that falls within the fossil group classification.

Gamma-Ray Emission from the Broad-Line Radio Galaxy 3C 111

NASA Technical Reports Server (NTRS)

Hartman, Robert C.; Kadler, M.; Tueller, Jack

2008-01-01

The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the y-ray source 3EG J0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright flat-spectrum radio core and a blazar-like broadband SED, in the Third EGRET Catalog, the large positional offset of about 1.5' put 3C 111 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available archival data for 3C 111 from the EGRET archives, resulting in detection of variable hard-spectrum high-energy gamma-ray emission above 1000 MeV from a position close to the nominal position of 3C 111, in three separate viewing periods (VPs), at a 3sigma level in each. A second variable hard-spectrum source is present nearby. At >100 MeV, one variable soft-spectrum source seems to account for most of the EGRET-detected emission of 3EG J0416+3650. A follow-up Swift UVOT/XRT observation reveals one moderately bright X-ray source in the error box of 3EG J0416+3650, but because of the large EGRET position uncertainty, it is not certain that the X-ray and gamma-ray sources are associated. Another Swift observation near the second (unidentified) hard gamma-ray source detected no X-ray source nearby.

A New Method to Separate Star-forming from AGN Galaxies at Intermediate Redshift: The Submillijansky Radio Population in the VLA-COSMOS Survey

NASA Astrophysics Data System (ADS)

Smolčić, V.; Schinnerer, E.; Scodeggio, M.; Franzetti, P.; Aussel, H.; Bondi, M.; Brusa, M.; Carilli, C. L.; Capak, P.; Charlot, S.; Ciliegi, P.; Ilbert, O.; Ivezić, Ž.; Jahnke, K.; McCracken, H. J.; Obrić, M.; Salvato, M.; Sanders, D. B.; Scoville, N.; Trump, J. R.; Tremonti, C.; Tasca, L.; Walcher, C. J.; Zamorani, G.

2008-07-01

We explore the properties of the submillijansky radio population at 20 cm by applying a newly developed optical color-based method to separate star-forming (SF) from active galactic nucleus (AGN) galaxies at intermediate redshifts (zlesssim 1.3). Although optical rest-frame colors are used, our separation method is shown to be efficient and not biased against dusty starburst galaxies. This classification method has been calibrated and tested on a local radio-selected optical sample. Given accurate multiband photometry and redshifts, it carries the potential to be generally applicable to any galaxy sample where SF and AGN galaxies are the two dominant populations. In order to quantify the properties of the submillijansky radio population, we have analyzed ~2,400 radio sources, detected at 20 cm in the VLA-COSMOS survey; 90% of these have submillijansky flux densities. We classify the objects into (1) star candidates, (2) quasi-stellar objects, (3) AGN, (4) SF, and (5) high-redshift (z > 1.3) galaxies. We find, for the composition of the submillijansky radio population, that SF galaxies are not the dominant population at submillijansky flux levels, as previously often assumed, but that they make up an approximately constant fraction of 30%-40% in the flux density range of ~50 μJy to 0.7 mJy. In summary, based on the entire VLA-COSMOS radio population at 20 cm, we find that the radio population at these flux densities is a mixture of roughly 30%-40% of SF and 50%-60% of AGN galaxies, with a minor contribution (~10%) of QSOs.

X-Ray Characteristics of Megamaser Galaxies

NASA Astrophysics Data System (ADS)

Leiter, K.; Kadler, M.; Wilms, J.; Braatz, J.; Grossberger, C.; Krauss, F.; Kreikenbohm, A.; Langejahn, M.; Litzinger, E.; Markowitz, A.

2017-10-01

Water megamaser galaxies are a rare subclass of Active Galactic Nuclei (AGN). They play a key role in modern cosmology, providing a significant improvement for measuring geometrical distances with high precision. Megamaser studies presently measure H_{0} to about 5%. The goal of modern programs is to reach 3%, which strongly constrains the equation of state of dark energy. An increasing number of independent measurements of suitable water masers is providing the statistics necessary to decrease the uncertainties. X-ray studies of maser galaxies yield important constraints on target-selection criteria for future surveys, increasing their detection rate. We studied the X-ray properties of a homogeneous sample of Type 2 AGN with water maser activity observed by XMM-Newton to investigate the properties of megamaser-hosting galaxies compared to a control sample of non-maser galaxies. Comparing the luminosity distributions confirm previous results that water maser galaxies appear more luminous than non-maser sources. The maser phenomenon goes along with more complex X-ray spectra, higher column densities and higher equivalent widths of the Fe Kα line. Both a sufficiently luminous X-ray source and a high absorbing column density in the line of sight are necessary prerequisites to favour the appearance of the water megamaser phenomenon in AGN.

CAVITIES AND SHOCKS IN THE GALAXY GROUP HCG 62 AS REVEALED BY CHANDRA, XMM-NEWTON, AND GIANT METREWAVE RADIO TELESCOPE DATA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gitti, Myriam; O'Sullivan, Ewan; Giacintucci, Simona

2010-05-01

We report on the results of an analysis of Chandra, XMM-Newton, and new Giant Metrewave Radio Telescope (GMRT) data of the X-ray bright compact group of galaxies HCG 62, which is one of the few groups known to possess clear, small X-ray cavities in the inner regions. This is part of an ongoing X-ray/low-frequency radio study of 18 groups, initially chosen for the availability of good-quality X-ray data and evidence for active galactic nucleus/hot gas interaction. At higher frequency (1.4 GHz), the HCG 62 cavity system shows minimal if any radio emission, but the new GMRT observations at 235 MHzmore » and 610 MHz clearly detect extended low-frequency emission from radio lobes corresponding to the cavities. By means of the synergy of X-ray and low-frequency radio observations, we compare and discuss the morphology, luminosity, and pressure of the gas and of the radio source. We find that the radio source is radiatively inefficient, with a ratio of radio luminosity to mechanical cavity power of {approx}10{sup -4}, and that the radio pressure of the lobes is about 1 order of magnitude lower than the X-ray pressure of the surrounding thermal gas. Thanks to the high spatial resolution of the Chandra surface brightness and temperature profiles, we also identify a shock front located at 36 kpc to the southwest of the group center, close to the southern radio lobe, with a Mach number {approx}1.5 and a total power which is about 1 order of magnitude higher than the cavity power. Such a shock may have heated the gas in the southern region, as indicated by the temperature map. The shock may also explain the arc-like region of enriched gas seen in the iron abundance map, as this may be produced by a non-Maxwellian electron distribution near its front.« less

The Red Radio Ring: a gravitationally lensed hyperluminous infrared radio galaxy at z = 2.553 discovered through the citizen science project SPACE WARPS

NASA Astrophysics Data System (ADS)

Geach, J. E.; More, A.; Verma, A.; Marshall, P. J.; Jackson, N.; Belles, P.-E.; Beswick, R.; Baeten, E.; Chavez, M.; Cornen, C.; Cox, B. E.; Erben, T.; Erickson, N. J.; Garrington, S.; Harrison, P. A.; Harrington, K.; Hughes, D. H.; Ivison, R. J.; Jordan, C.; Lin, Y.-T.; Leauthaud, A.; Lintott, C.; Lynn, S.; Kapadia, A.; Kneib, J.-P.; Macmillan, C.; Makler, M.; Miller, G.; Montaña, A.; Mujica, R.; Muxlow, T.; Narayanan, G.; O'Briain, D.; O'Brien, T.; Oguri, M.; Paget, E.; Parrish, M.; Ross, N. P.; Rozo, E.; Rusu, Cristian E.; Rykoff, E. S.; Sanchez-Argüelles, D.; Simpson, R.; Snyder, C.; Schloerb, F. P.; Tecza, M.; Wang, W.-H.; Van Waerbeke, L.; Wilcox, J.; Viero, M.; Wilson, G. W.; Yun, M. S.; Zeballos, M.

2015-09-01

We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (intrinsic LIR ≈ 1013 L⊙) with strong radio emission (intrinsic L1.4 GHz ≈ 1025 W Hz-1) at z = 2.553. The source was identified in the citizen science project SPACE WARPS through the visual inspection of tens of thousands of iJKs colour composite images of luminous red galaxies (LRGs), groups and clusters of galaxies and quasars. Appearing as a partial Einstein ring (re ≈ 3 arcsec) around an LRG at z = 0.2, the galaxy is extremely bright in the sub-millimetre for a cosmological source, with the thermal dust emission approaching 1 Jy at peak. The redshift of the lensed galaxy is determined through the detection of the CO(3→2) molecular emission line with the Large Millimetre Telescope's Redshift Search Receiver and through [O III] and Hα line detections in the near-infrared from Subaru/Infrared Camera and Spectrograph. We have resolved the radio emission with high-resolution (300-400 mas) eMERLIN L-band and Very Large Array C-band imaging. These observations are used in combination with the near-infrared imaging to construct a lens model, which indicates a lensing magnification of μ ≈ 10. The source reconstruction appears to support a radio morphology comprised of a compact (<250 pc) core and more extended component, perhaps indicative of an active nucleus and jet or lobe.

Radio Observations of Ultra-Luminous X-Ray Sources ---Microblazars or Intermediate-Mass Black Holes?---

NASA Astrophysics Data System (ADS)

Körding, E.; Colbert, E.; Falcke, H.

In recent years Ultra-Luminous X-Ray sources (ULXs) received wide attention, however, their true nature is not yet understood. Many explanations have been suggested, including intermediate-mass black holes, super-Eddington accretion flows, anisotropic emission, and relativistic beaming of microquasars. We model the logN-logS distribution of ULXs assuming that each neutron star or black hole XRB can be described by an accretion disk plus jet model, where the jet is relativistically beamed. The distribution can be either fit by intermediate-mass black holes or by stellar mass black holes with mildly relativistic jets. Even though the jet is intrinsically weaker than the accretion disk, relativistic beaming can in the latter approach lead to the high fluxes observed. To further explore the possibility of microblazars contributing to the ULX phenomenon, we have embarked on a radio-monitoring study of ULXs in nearby galaxies with the VLA. However, up to now no radio flare has been detected. Using the radio/X-ray correlation the upper limits on the radio flux can be converted into upper limits for the black hole masses of MBH ≲ 10^3 M⊙.

The X-Ray Reflection Spectrum of the Radio-Loud Quasar 4C 74.26

NASA Technical Reports Server (NTRS)

Lohfink, Ann M.; Fabian, Andrew C.; Ballantyne, David R.; Boggs, S. E.; Boorman, Peter; Christensen, F. E.; Craig, W. W.; Farrah, Duncan; Garcia, Javier; Hailey, C. J.;

The X-Ray Reflection Spectrum of the Radio-loud Quasar 4C 74.26

NASA Astrophysics Data System (ADS)

Lohfink, Anne M.; Fabian, Andrew C.; Ballantyne, David R.; Boggs, S. E.; Boorman, Peter; Christensen, F. E.; Craig, W. W.; Farrah, Duncan; García, Javier; Hailey, C. J.; Harrison, F. A.; Ricci, Claudio; Stern, Daniel; Zhang, W. W.

2017-06-01

The relativistic jets created by some active galactic nuclei are important agents of AGN feedback. In spite of this, our understanding of what produces these jets is still incomplete. X-ray observations, which can probe the processes operating in the central regions in the immediate vicinity of the supermassive black hole, the presumed jet launching point, are potentially particularly valuable in illuminating the jet formation process. Here, we present the hard X-ray NuSTAR observations of the radio-loud quasar 4C 74.26 in a joint analysis with quasi-simultaneous, soft X-ray Swift observations. Our spectral analysis reveals a high-energy cutoff of {183}-35+51 keV and confirms the presence of ionized reflection in the source. From the average spectrum we detect that the accretion disk is mildly recessed, with an inner radius of R in = 4-180 R g. However, no significant evolution of the inner radius is seen during the three months covered by our NuSTAR campaign. This lack of variation could mean that the jet formation in this radio-loud quasar differs from what is observed in broad-line radio galaxies.

Extreme gaseous outflows in radio-loud narrow-line Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Komossa, S.; Xu, D. W.; Wagner, A. Y.

2018-07-01

We present four radio-loud narrow-line Seyfert 1 (NLS1) galaxies with extreme emission-line shifts, indicating radial outflow velocities of the ionized gas of up to 2450 km s-1, above the escape velocity of the host galaxies. The forbidden lines show strong broadening, up to 2270 km s-1. An ionization stratification (higher line shift at higher ionization potential) implies that we see a large-scale outflow rather than single, localized jet-cloud interactions. Similarly, the paucity of zero-velocity [O III] λ5007 emitting gas implies the absence of a second narrow-line region (NLR) component at rest, and therefore a large part of the high-ionization NLR is affected by the outflow. Given the radio loudness of these NLS1 galaxies, the observations are consistent with a pole on view onto their central engines, so that the effects of polar outflows are maximized. In addition, a very efficient driving mechanism is required to reach the high observed velocities. We explore implications from recent hydrodynamic simulations of the interaction between fast winds or jets with the large-scale NLR. Overall, the best agreement with observations (and especially the high outflow speeds of the [Ne V] emitting gas) can be reached if the NLS1 galaxies are relatively young sources with lifetimes not much exceeding 1 Myr. These systems represent sites of strong feedback at NLR scales at work, well below redshift one.

Jets, hotspots and lobes: what X-ray observations tell us about extra-galactic radio sources.

PubMed

Hardcastle, Martin J

2005-12-15

The brightest and most numerous discrete radio sources in the sky, radio galaxies and quasars, are powered by twin jets of plasma which emerge at relativistic speeds from very small regions at the centre of large elliptical galaxies, powered by mass infall on to supermassive black holes. The jets can carry material out to very large distances (millions of light years) where it forms balloon-like lobes. Until recently it has been impossible to make definite statements about the energy or the nature of the matter supplied by the jets, or the dynamics of the lobes as they expand into the external medium. This has meant that crucial questions about the generation of radio sources and their effect on their environment have gone unanswered. The situation has been revolutionized by the launch at the start of this decade of a new generation of X-ray observatories, Chandra and XMM-Newton. In this article, I explain why observations with these instruments have made such a difference, what we have learned as a result and why the community remains divided on some important features of the interpretation of the data.

The Host Galaxy and Redshift of the Repeating Fast Radio Burst FRB 121102

NASA Astrophysics Data System (ADS)

Tendulkar, S. P.; Bassa, C. G.; Cordes, J. M.; Bower, G. C.; Law, C. J.; Chatterjee, S.; Adams, E. A. K.; Bogdanov, S.; Burke-Spolaor, S.; Butler, B. J.; Demorest, P.; Hessels, J. W. T.; Kaspi, V. M.; Lazio, T. J. W.; Maddox, N.; Marcote, B.; McLaughlin, M. A.; Paragi, Z.; Ransom, S. M.; Scholz, P.; Seymour, A.; Spitler, L. G.; van Langevelde, H. J.; Wharton, R. S.

2017-01-01

The precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability p ≲ 3 × 10-4) of an FRB with an optical and persistent radio counterpart. We report on optical imaging and spectroscopy of the counterpart and find that it is an extended (0.″6-0.″8) object displaying prominent Balmer and [O III] emission lines. Based on the spectrum and emission line ratios, we classify the counterpart as a low-metallicity, star-forming, m r‧ = 25.1 AB mag dwarf galaxy at a redshift of z = 0.19273(8), corresponding to a luminosity distance of 972 Mpc. From the angular size, the redshift, and luminosity, we estimate the host galaxy to have a diameter ≲4 kpc and a stellar mass of M * ˜ (4-7) × 107 M ⊙, assuming a mass-to-light ratio between 2 to 3 M ⊙ L ⊙ -1. Based on the Hα flux, we estimate the star formation rate of the host to be 0.4 M ⊙ yr-1 and a substantial host dispersion measure (DM) depth ≲324 pc cm-3. The net DM contribution of the host galaxy to FRB 121102 is likely to be lower than this value depending on geometrical factors. We show that the persistent radio source at FRB 121102’s location reported by Marcote et al. is offset from the galaxy’s center of light by ˜200 mas and the host galaxy does not show optical signatures for AGN activity. If FRB 121102 is typical of the wider FRB population and if future interferometric localizations preferentially find them in dwarf galaxies with low metallicities and prominent emission lines, they would share such a preference with long gamma-ray bursts and superluminous supernovae.

The SINFONI survey of powerful radio galaxies at z 2: Jet-driven AGN feedback during the Quasar Era

NASA Astrophysics Data System (ADS)

Nesvadba, N. P. H.; De Breuck, C.; Lehnert, M. D.; Best, P. N.; Collet, C.

2017-03-01

We present VLT/SINFONI imaging spectroscopy of the rest-frame optical emission lines of warm ionized gas in 33 powerful radio galaxies at redshifts z ≳ 2, which are excellent sites to study the interplay of rapidly accreting active galactic nuclei and the interstellar medium of the host galaxy in the very late formation stages of massive galaxies. Our targets span two orders of magnitude in radio size (2-400 kpc) and kinetic jet energy (a few 1046- almost 1048 erg s-1). All sources have complex gas kinematics with broad line widths up to 1300 km s-1. About half have bipolar velocity fields with offsets up to 1500 km s-1 and are consistent with global back-to-back outflows. The others have complex velocity distributions, often with multiple abrupt velocity jumps far from the nucleus of the galaxy, and are not associated with a major merger in any obvious way. We present several empirical constraints that show why gas kinematics and radio jets seem to be physically related in all galaxies of the sample. The kinetic energy in the gas from large scale bulk and local outflow or turbulent motion corresponds to a few 10-3 to 10-2 of the kinetic energy output of the radio jet. In galaxies with radio jet power ≳ 1047 erg s-1, the kinetic energy in global back-to-back outflows dominates the total energy budget of the gas, suggesting that bulk motion of outflowing gas encompasses the global interstellar medium. This might be facilitated by the strong gas turbulence, as suggested by recent analytical work. We compare our findings with recent hydrodynamic simulations, and discuss the potential consequences for the subsequent evolution of massive galaxies at high redshift. Compared with recent models of metal enrichment in high-z AGN hosts, we find that the gas-phase metallicities in our galaxies are lower than in most low-z AGN, but nonetheless solar or even super-solar, suggesting that the ISM we see in these galaxies is very similar to the gas from which massive low

Spectral Energy Distribution and Radio Halo of NGC 253 at Low Radio Frequencies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kapińska, A. D.; Staveley-Smith, L.; Meurer, G. R.

We present new radio continuum observations of NGC 253 from the Murchison Widefield Array at frequencies between 76 and 227 MHz. We model the broadband radio spectral energy distribution for the total flux density of NGC 253 between 76 MHz and 11 GHz. The spectrum is best described as a sum of a central starburst and extended emission. The central component, corresponding to the inner 500 pc of the starburst region of the galaxy, is best modeled as an internally free–free absorbed synchrotron plasma, with a turnover frequency around 230 MHz. The extended emission component of the spectrum of NGCmore » 253 is best described as a synchrotron emission flattening at low radio frequencies. We find that 34% of the extended emission (outside the central starburst region) at 1 GHz becomes partially absorbed at low radio frequencies. Most of this flattening occurs in the western region of the southeast halo, and may be indicative of synchrotron self-absorption of shock-reaccelerated electrons or an intrinsic low-energy cutoff of the electron distribution. Furthermore, we detect the large-scale synchrotron radio halo of NGC 253 in our radio images. At 154–231 MHz the halo displays the well known X-shaped/horn-like structure, and extends out to ∼8 kpc in the z -direction (from the major axis).« less

Fermi-LAT and Suzaku Observations of the Radio Galaxy Centaurus B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsuta, Junichiro; /Stanford U., HEPL /KIPAC, Menlo Park; Tanaka, Y.T.

2012-08-17

CentaurusB is a nearby radio galaxy positioned in the Southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months accumulation of Fermi-LAT data and of newly acquired Suzaku X-ray data for Centaurus B. The source is detected at GeV photon energies, although we cannot completely exclude the possibility that it is an artifact due to incorrect modeling of the bright Galactic diffuse emission in the region. The LAT image provides a weak hint of a spatial extension of the {gamma} rays along the radio lobes, which is consistent with the lack of sourcemore » variability in the GeV range. We note that the extension cannot be established statistically due to the low number of the photons. Surprisingly, we do not detect any diffuse emission of the lobes at X-ray frequencies, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. The broad-band modeling shows that the observed {gamma}-ray flux of the source may be produced within the lobes, if the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. This association would imply that efficient in-situ acceleration of the ultrarelativistic particles is occurring and that the lobes are dominated by the pressure from the relativistic particles. However, if the diffuse X-ray emission is much below the Suzaku upper limits, the observed {gamma}-ray flux is not likely to be produced within the lobes, but instead within the unresolved core of Centaurus B. In this case, the extended lobes could be dominated by the pressure of the magnetic field.« less

A Multi-Frequency Study of the Milky Way-Like Spiral Galaxy NGC 6744

NASA Astrophysics Data System (ADS)

Yew, Miranda; Filipović, Miroslav D.; Roper, Quentin; Collier, Jordan D.; Crawford, Evan J.; Jarrett, Thomas H.; Tothill, Nicholas F. H.; O'Brien, Andrew N.; Pavlović, Marko Z.; Pannuti, Thomas G.; Galvin, Timothy J.; Kapińska, Anna D.; Cluver, Michelle E.; Banfield, Julie K.; Schlegel, Eric M.; Maxted, Nigel; Grieve, Kevin R.

2018-03-01

We present a multi-frequency study of the intermediate spiral SAB(r)bc type galaxy NGC 6744, using available data from the Chandra X-Ray telescope, radio continuum data from the Australia Telescope Compact Array and Murchison Widefield Array, and Wide-field Infrared Survey Explorer infrared observations. We identify 117 X-ray sources and 280 radio sources. Of these, we find nine sources in common between the X-ray and radio catalogues, one of which is a faint central black hole with a bolometric radio luminosity similar to the Milky Way's central black hole. We classify 5 objects as supernova remnant (SNR) candidates, 2 objects as likely SNRs, 17 as H ii regions, 1 source as an AGN; the remaining 255 radio sources are categorised as background objects and one X-ray source is classified as a foreground star. We find the star-formation rate (SFR) of NGC 6744 to be in the range 2.8-4.7 M⊙ yr - 1 signifying the galaxy is still actively forming stars. The specific SFR of NGC 6744 is greater than that of late-type spirals such as the Milky Way, but considerably less that that of a typical starburst galaxy.

VizieR Online Data Catalog: Radio haloes in nearby galaxies (Heesen+, 2018)