Journal articles: 'Radio intermediate galaxies'

1

Pierce, J. C. S., C. N. Tadhunter, and R. Morganti. "The radio properties of high-excitation radio galaxies with intermediate radio powers." Monthly Notices of the Royal Astronomical Society 494, no. 2 (February 24, 2020): 2053–67. http://dx.doi.org/10.1093/mnras/staa531.

Full text

Abstract:

ABSTRACT In the past decade, high-sensitivity radio surveys have revealed that the local radio active galactic nucleus population is dominated by moderate-to-low power sources with emission that is compact on galaxy scales. High-excitation radio galaxies (HERGs) with intermediate radio powers (22.5 < log (L1.4 GHz) < 25.0 W Hz−1) form an important sub-group of this population, since there is strong evidence that they also drive multiphase outflows on the scales of galaxy bulges. Here, we present high-resolution Very Large Array observations at 1.5, 4.5, and 7.5 GHz of a sample of 16 such HERGs in the local universe (z < 0.1), conducted in order to investigate the morphology, extent, and spectra of their radio emission in detail, down to sub-kpc scales. We find that the majority (56 per cent) have unresolved structures at the limiting angular resolution of the observations (∼0.3 arcsec). Although similar in the compactness of their radio structures, these sources have steep radio spectra and host galaxy properties that distinguish them from local low-excitation radio galaxies that are unresolved on similar scales. The remaining sources exhibit extended radio structures with projected diameters ∼1.4–19.0 kpc and a variety of morphologies: three double-lobed; two large-scale diffuse; one jetted and ‘S-shaped’; one undetermined. Only 19 per cent of the sample therefore exhibit the double-lobed/edge-brightened structures often associated with their counterparts at high and low radio powers: radio-powerful HERGs and Seyfert galaxies, respectively. Additional high-resolution observations are required to investigate this further, and to probe the ≲300 pc scales on which some Seyfert galaxies show extended structures.

APA, Harvard, Vancouver, ISO, and other styles

2

Heisler, C. A., R. P. Norris, D. L. Jauncey, J. E. Reynolds, and E. A. King. "Compact Radio Emission in 60 µm Peaker Galaxies." International Astronomical Union Colloquium 164 (1998): 211–12. http://dx.doi.org/10.1017/s0252921100045255.

Full text

Abstract:

AbstractWe present radio interferometric observations of a well defined sample of IRAS galaxies with warm far-infrared colors — 60 µm Peakers (60PKs). The core radio power of 60PKs is intermediate to that of “normal” Seyfert 2 galaxies and radio ellipticals, and follows the same relationship with respect to total radio emission as low and high power radio galaxies. This is consistent with the suggestion that 60PKs represent nascent radio elliptical galaxies.

APA, Harvard, Vancouver, ISO, and other styles

3

Venturi, T., W. D. Cotton, L. Feretti, G. Giovannini, L. Lara, and J. M. Marcaide. "VLBI Observations of FRI Radio Galaxies." Symposium - International Astronomical Union 175 (1996): 124–26. http://dx.doi.org/10.1017/s0074180900080281.

Full text

Abstract:

The Fanaroff-Riley type I radio galaxies (Fanaroff & Riley, 1974) presented in this paper belong to the complete sample of low-intermediate luminosity radio galaxies published in Giovannini, Feretti & Comoretto (1990). This sample includes radio galaxies with different morphologies on the arcsecond scale, such as compact sources, core-halos, FRIs and FRIIs.

APA, Harvard, Vancouver, ISO, and other styles

4

Brown, M. J. I., R. L. Webster, and B. J. Boyle. "The Evolution of Radio Galaxies at Intermediate Redshift." Astronomical Journal 121, no. 5 (May 2001): 2381–91. http://dx.doi.org/10.1086/320410.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Ronnback, J., E. van Groningen, I. Wanders, and E. Orndahl. "Host galaxies of intermediate redshift radio-loud and radio-quiet quasars." Monthly Notices of the Royal Astronomical Society 283, no. 1 (October 21, 1996): 282–96. http://dx.doi.org/10.1093/mnras/283.1.282.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Pierce, J. C. S., C. N. Tadhunter, Y. Gordon, C. Ramos Almeida, S. L. Ellison, C. O’Dea, L. Grimmett, L. Makrygianni, P. S. Bessiere, and P. Doña Girón. "Do AGN triggering mechanisms vary with radio power? – II. The importance of mergers as a function of radio power and optical luminosity." Monthly Notices of the Royal Astronomical Society 510, no. 1 (November 10, 2021): 1163–83. http://dx.doi.org/10.1093/mnras/stab3231.

Full text

Abstract:

ABSTRACT Investigation of the triggering mechanisms of radio active galactic nuclei (radio AGN) is important for improving our general understanding of galaxy evolution. In the first paper in this series, detailed morphological analysis of high-excitation radio galaxies (HERGs) with intermediate radio powers suggested that the importance of triggering via galaxy mergers and interactions increases strongly with AGN radio power and weakly with optical emission-line luminosity. Here, we use an online classification interface to expand our morphological analysis to a much larger sample of 155 active galaxies (3CR radio galaxies, radio-intermediate HERGs, and Type 2 quasars) that covers a broad range in both 1.4 GHz radio power and [O iii] λ5007 emission-line luminosity. All active galaxy samples are found to exhibit excesses in their rates of morphological disturbance relative to 378 stellar-mass- and redshift-matched non-active control galaxies classified randomly and blindly alongside them. These excesses are highest for the 3CR HERGs (4.7σ) and Type 2 quasar hosts (3.9σ), supporting the idea that galaxy mergers provide the dominant triggering mechanism for these subgroups. When the full active galaxy sample is considered, there is clear evidence to suggest that the enhancement in the rate of disturbance relative to the controls increases strongly with [O iii] λ5007 emission-line luminosity but not with 1.4 GHz radio power. Evidence that the dominant AGN host types change from early-type galaxies at high radio powers to late-type galaxies at low radio powers is also found, suggesting that triggering by secular, disc-based processes holds more importance for lower-power radio AGN.

APA, Harvard, Vancouver, ISO, and other styles

7

Pierce, J. C. S., C. N. Tadhunter, C. Ramos Almeida, P. S. Bessiere, and M. Rose. "Do AGN triggering mechanisms vary with radio power? – I. Optical morphologies of radio-intermediate HERGs." Monthly Notices of the Royal Astronomical Society 487, no. 4 (May 4, 2019): 5490–507. http://dx.doi.org/10.1093/mnras/stz1253.

Full text

Abstract:

ABSTRACT Active galactic nuclei (AGNs) with intermediate radio powers are capable of driving multiphase outflows in galaxy bulges, and are also more common than their high-radio-power counterparts. In-depth characterization of the typical host galaxies and likely triggering mechanisms for this population is therefore required in order to better understand the role of radio AGN feedback in galaxy evolution. Here, we use deep optical imaging data to study the detailed host morphologies of a complete sample of 30 local radio AGNs with high-excitation optical emission (HERG) spectra and intermediate radio powers [ z < 0.1; 22.5 < log($L_{\rm 1.4GHz}$) < 24.0 W Hz-1]. The fraction of hosts with morphological signatures of mergers and interactions is greatly reduced compared to the 2Jy radio-powerful galaxies [log($L_{\rm 1.4GHz}$) > 25.0 W Hz-1] with strong optical emission lines: 53 ± 9 per cent compared with 94 ± 4 per cent. In addition, the most radio-powerful half of the sample has a higher frequency of morphological disturbance than the least radio-powerful half (67 ± 12 per cent and 40 ± 13 per cent, respectively), including the eight most highly disturbed galaxies. This suggests that the importance of triggering nuclear activity in high-excitation radio galaxies (HERGs) through mergers and interactions reduces with radio power. Both visual inspection and detailed light profile modelling reveal a mixed population of early-type and late-type morphologies, contrary to the massive elliptical galaxy hosts of radio-powerful AGNs. The prevalence of late-type hosts could suggest that triggering via secular, disc-based processes has increased importance for HERGs with lower radio powers (e.g. disc instabilities and large-scale bars).

APA, Harvard, Vancouver, ISO, and other styles

8

Gregorini, L., P. Parma, U. Klein, and K. H. Mack. "High-Frequency Study of Low and Intermediate Luminosity Radio Galaxies." Symposium - International Astronomical Union 175 (1996): 145–46. http://dx.doi.org/10.1017/s0074180900080359.

Full text

Abstract:

All the information on the morphology, spectral index and polarization properties of low and intermediate luminosity radio galaxies were collected in an intermediate frequency range, and some of the basic questions to be elucidated with such measurements are still unanswered. We therefore decided to extend the study of their characteristics towards higher frequencies. From the B2 and 4C catalogue we selected 26 radio galaxies for which VLA or WSRT data are available. These sources were observed at 10.6 GHz using the Effelsberg 100-m telescope (Gregorini & al. 1992; Mack & al. 1994; Klein & al. 1995).

APA, Harvard, Vancouver, ISO, and other styles

9

Brunthaler, A., H. Falcke, G. C. Bower, M. Aller, H. Aller, and H. Teräsranta. "III Zw 2: Superluminal Motion and Compact Lobe Expansion in a Seyfert Galaxy." Symposium - International Astronomical Union 205 (2001): 110–11. http://dx.doi.org/10.1017/s0074180900220627.

Full text

Abstract:

So far all relativistically boosted jets with superluminal motion have only been detected in normal radio galaxies that have early-type host galaxies. We have now discovered superluminal motion in the Seyfert 1 galaxy III Zw 2, classified as a spiral. Spectral and spatial evolution are closely linked. Since III Zw 2 is part of a sample of so-called radio-intermediate quasars (RIQ), it confirms earlier predictions of superluminal motion for this source, based on the argument that RIQs could be relativistically boosted jets in radio-weak quasars and Seyfert galaxies.

APA, Harvard, Vancouver, ISO, and other styles

10

Kuźmicz, A., B. Czerny, and C. Wildy. "Stellar populations in hosts of giant radio galaxies and their neighbouring galaxies." Astronomy & Astrophysics 624 (April 2019): A91. http://dx.doi.org/10.1051/0004-6361/201834653.

Full text

Abstract:

Context. Giant radio galaxies (with projected linear size of radio structure larger than 0.7 Mpc) are very rare and unusual objects. Only ∼5% of extended radio sources reach such sizes. Understanding of the processes responsible for their large sizes is crucial to further our knowledge about the radio source’s evolution. Aims. We check the hypothesis that giants become extremely large due to the specific history of their host galaxy formation, as well as in the context of the cluster or group of galaxies where they evolve. Therefore we study the star formation histories in their host galaxies and in galaxies located in their neighbourhood. Methods. We studied 41 giant-size radio galaxies as well as galaxies located within a radius of 5 Mpc around giants to verify whether the external conditions of the intergalactic medium somehow influence the internal evolution of galaxies in the group/cluster. We compared the results with a control sample of smaller-sized Fanaroff–Riley type II radio galaxies and their neighbouring galaxies. We fit stellar continua in all galaxy spectra using the spectral synthesis code STARLIGHT and provide statistical analysis of the results. Results. We find that hosts of giant radio galaxies have a larger amount of intermediate age stellar populations compared with smaller-sized FRII radio sources. The same result is also visible when we compare neighbouring galaxies located up to 1.5 Mpc around giants and FRIIs. This may be evidence that star formation in groups with giants was triggered due to global processes occurring in the ambient intergalactic medium. These processes may also contribute to mechanisms responsible for the extremely large sizes of giants.

APA, Harvard, Vancouver, ISO, and other styles

11

Worrall, Diana M., Ryan T. Duffy, and Mark Birkinshaw. "The intermediate-power population of radio galaxies: morphologies and interactions." Proceedings of the International Astronomical Union 14, A30 (August 2018): 90–93. http://dx.doi.org/10.1017/s1743921319003533.

Full text

Abstract:

AbstractRadio galaxies of intermediate power dominate the radio-power injection in the Universe as a whole, due to the break in the radio luminosity function, and so are of special interest. The population spans FR I, FR II, and hybrid morphologies, resides in a full range of environmental richness, and sources of all ages are amenable to study. We describe structures and interactions, with emphasis on sources with deep high-resolution Chandra X-ray data. As compared with low-power sources there is evidence that the physics changes, and the work done in driving shocks can exceed that in evacuating cavities. A range of morphologies and phenomena is identified.

APA, Harvard, Vancouver, ISO, and other styles

12

Jimenez-Gallardo, A., F. Massaro, A. Capetti, M. A. Prieto, A. Paggi, R. D. Baldi, R. Grossova, L. Ostorero, A. Siemiginowska, and S. Viada. "COMP2CAT: hunting compact double radio sources in the local Universe." Astronomy & Astrophysics 627 (July 2019): A108. http://dx.doi.org/10.1051/0004-6361/201935104.

Full text

Abstract:

We present a catalog of compact double radio galaxies (hereafter COMP2CAT) listing 43 edge-brightened radio sources whose projected linear size does not exceed 60 kpc, the typical size of their host galaxies. This is the fifth in a series of radio source catalogs recently created, namely: FRICAT, FRIICAT, FR0CAT, and WATCAT, each of which focuses on a different class of radio galaxies. The main aim of our analysis is to attain a better understanding of sources with intermediate morphologies between FR IIs and FR 0s. COMP2CAT sources were selected from an existing catalog of radio sources based on NVSS, FIRST and SDSS observations because they have (i) edge-brightened morphologies typical of FR IIs, (ii) redshifts z < 0.15, and (iii) projected linear sizes smaller than 60 kpc. With radio luminosities at 1.4 GHz 1038 ≲ L1.4 ≲ 1041 erg s−1, COMP2CAT sources appear as the low radio luminosity tail of FR IIs. However, their host galaxies are indistinguishable from those of large-scale radio sources: they are luminous (−21 ≳ Mr ≳ −24), red, early-type galaxies with black hole masses in the range 107.5 ≲ MBH ≲ 109.5 M⊙. Moreover, all but one of the COMP2CAT sources are optically classifiable as low-excitation radio galaxies, in agreement with being the low radio luminosity tail of FR Is and FR IIs. This catalog of compact double sources, which is ∼47% complete at z < 0.15, can potentially be used to clarify the role of compact double sources in the general evolutionary scheme of radio galaxies.

APA, Harvard, Vancouver, ISO, and other styles

13

Martínez-González, E., and N. Benítez. "Association Of Distant Radio Sources And Foreground Galaxies." Symposium - International Astronomical Union 173 (1996): 83–88. http://dx.doi.org/10.1017/s0074180900230970.

Full text

Abstract:

A statistically significant (99.1%) excess of red galaxies from the APM Sky Catalogue is found around a sample of z ∼ 1 1Jy radio sources. The most plausible explanation for this result seems to be the magnification bias caused by the weak gravitational lensing of large scale structures at intermediate redshifts.

APA, Harvard, Vancouver, ISO, and other styles

14

Radcliffe, J. F., P. D. Barthel, M. A. Garrett, R. J. Beswick, A. P. Thomson, and T. W. B. Muxlow. "The radio emission from active galactic nuclei." Astronomy & Astrophysics 649 (May 2021): L9. http://dx.doi.org/10.1051/0004-6361/202140791.

Full text

Abstract:

Context. For nearly seven decades, astronomers have been studying active galaxies, that is to say, galaxies with actively accreting central supermassive black holes: active galactic nuclei (AGN). A small fraction are characterized by luminous, powerful radio emission: This class is known as radio-loud AGN. A substantial fraction, the so-called radio-quiet AGN population, display intermediate or weak radio emission. However, an appreciable fraction of strong X-ray-emitting AGN are characterized by the absence of radio emission, down to an upper limit of about 10−7 times the luminosity of the most powerful radio-loud AGN. Aims. We wish to address the nature of these – seemingly radio-silent – X-ray-luminous AGN and their host galaxies to determine if there is any radio emission, and, if so, where it originates. Methods. Focusing on the GOODS-N field, we examine the nature of these objects, employing stacking techniques on ultra-deep radio data obtained with the JVLA. We combine these radio data with Spitzer far-infrared data. Results. We establish the absence, or totally insignificant contribution, of jet-driven radio emission in roughly half of the otherwise normal population of X-ray-luminous AGN, which appear to reside in normal star-forming galaxies. Conclusions. AGN- or jet-driven radio emission is simply a mechanism that may be at work or may be dormant in galaxies with actively accreting black holes. The latter cases can be classified as radio-silent AGN.

APA, Harvard, Vancouver, ISO, and other styles

15

Tadhunter, C. N., S. M. Scarrott, P. Draper, and C. Rolph. "The optical polarizations of high- and intermediate-redshift radio galaxies." Monthly Notices of the Royal Astronomical Society 256, no. 1 (May 1992): 53P—58P. http://dx.doi.org/10.1093/mnras/256.1.53p.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Machalski, J., and J. J. Condon. "The GB/GB2 sample of 122 intermediate-strength radio galaxies." Astronomical Journal 90 (June 1985): 973. http://dx.doi.org/10.1086/113803.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Athreya, R. M., and V. K. Kapahi. "Cosmological Studies from the MRC/1Jy Radio Galaxy Sample: The Spectral Index – Redshift Correlation." Symposium - International Astronomical Union 183 (1999): 251. http://dx.doi.org/10.1017/s0074180900132681.

Full text

Abstract:

The MRC/1Jy sample of 559 radio sources with S408 MHz ≥ 0.95 Jy (McCarthy et al. 1996; Kapahi et al. in preparation) is a factor of 5 to 6 times deeper than the 3CRR sample; it is therefore, well suited for disentangling the redshift (z) and luminosity (P) dependence of several properties of extragalaxtic radio sources. Here we present results on the spectral index — redshift correlation for radio galaxies, based on a comparison of the well documented radio spectra (in the rest frame frequency range of about 1 to 16 GHz) of the following two matched-luminosity samples, (a) 14 high redshift radio galaxies (HRRG) from MRC with 2.0 < z < 3.2 and linear size i > 10 kpc, and (b) 21 intermediate z radio galaxies (IRRG) from 3CRR with 0.85 < z < 1.7 and l > 10 kpc. Both samples have P1.4 GHz in the range 1028 and 1028.8 WHz−1.

APA, Harvard, Vancouver, ISO, and other styles

18

Shen, Lu, Brian C. Lemaux, Lori M. Lubin, John McKean, Neal A. Miller, Debora Pelliccia, Christopher D. Fassnacht, et al. "The properties of radio and mid-infrared detected galaxies and the effect of environment on the co-evolution of AGN and star formation at z ∼ 1." Monthly Notices of the Royal Astronomical Society 494, no. 4 (April 15, 2020): 5374–95. http://dx.doi.org/10.1093/mnras/staa1005.

Full text

Abstract:

ABSTRACT In this study, we investigate 179 radio-infrared (IR) galaxies drawn from a sample of spectroscopically confirmed galaxies, which are detected in radio and mid-IR (MIR) in the redshift range of 0.55 ≤ z ≤ 1.30 in the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey. We constrain the active galactic nuclei (AGN) contribution to the total IR luminosity (fAGN), and estimate the AGN luminosity (LAGN) and the star formation rate (SFR). Based on the fAGN and radio luminosity, radio–IR galaxies are split into galaxies that host either high- or low-fAGN AGN (high-/low-fAGN), and star-forming galaxies (SFGs) with little to no AGN activity. We study the properties of the three radio–IR sub-samples comparing to an underlying parent sample. In the comparison of radio luminosity of three sub-samples, no significant difference was found, which could be due to the combined contribution of radio emission from AGN and star formation. We find a positive relationship between LAGN and specific SFR (sSFR) for both AGN sub-samples, strongly suggesting a co-evolution scenario of AGN and SF in these galaxies. A toy model is designed to demonstrate this co-evolution scenario, where we find that, in almost all cases, a rapid quenching time-scale is required, which we argue is a signature of AGN quenching. The environmental preference for intermediate/infall regions of clusters/groups remains across the co-evolution scenario, which suggests that galaxies might be in an orbital motion around the cluster/group during the scenario.

APA, Harvard, Vancouver, ISO, and other styles

19

Comoretto, G., L. Feretti, and G. Giovannini. "VLBI Cores in a Sample of Radio Galaxies." Symposium - International Astronomical Union 129 (1988): 75–76. http://dx.doi.org/10.1017/s0074180900133996.

Full text

Abstract:

We present the first results of a statistical study of the milliarcsec structure in a complete sample of radio galaxies. We have selected from the B2 and 3CR samples of galaxies the sources which present, at the VLA or WSRT angular resolution, an unresolved core with a flux density at 5 GHz Sc ≥ 100 mJy. The total sample consists of 30 radio galaxies, 17 from the B2 and 13 from the 3CR catalog. This complete sample covers a range of total radio power at 408 MHz log P = 23.5 – 26.5 W/Hz (low-intermediate luminosity). The radio structure of these sources on the arcsec-arcmin scale is well known, thanks to good dynamic range VLA and/or WSRT maps; a large variety of structures is present in the sample, from classical doubles to head-tail sources; flat, inverted and steep spectrum cores are also present.

APA, Harvard, Vancouver, ISO, and other styles

20

Varano, S., M. Chiaberge, F. D. Macchetto, and A. Capetti. "The nuclear radio-optical properties of intermediate-redshift FR II radio galaxies and quasars." Astronomy & Astrophysics 428, no. 2 (November 26, 2004): 401–8. http://dx.doi.org/10.1051/0004-6361:20040303.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Zanichelli, A., R. Scaramella, M. Vigotti, G. Vettolani, and G. Grueff. "Clusters of Galaxies at Intermediate Redshifts: a Sample Selected at Radio Wavelenghts." Symposium - International Astronomical Union 175 (1996): 325–26. http://dx.doi.org/10.1017/s0074180900080967.

Full text

Abstract:

In order to gather a sample of intermediate redshifts (z ≃ 0.1 ÷ 0.2) clusters avoiding evolutionary effects or biases induced by limited sensitivity of instruments and optical plates that affect samples selected through inspection of optical plates, color diagrams or X-ray emission properties, we plan to use radio galaxies as suitable tracers of dense environments (e.g. Allington-Smith et al., 1993). This would allow us to effectively test different environments and population properties, and would also give valuable information on the effect of environment on the radioemission phenomena. Moreover, it would not impact on the X–ray or optical properties of clusters, since there is no significant correlation between the radio properties of galaxies within a cluster with its LX (Feigelson, Maccacaro and Zamorani, 1982), or with richness of the cluster (Zhao, Burns, and Owen, 1989).

APA, Harvard, Vancouver, ISO, and other styles

22

Hammer, F., D. Crampton, S. Lilly, and O. LE Fèvre. "Redshift Distribution & Nature of μ-Jy Radio Sources." Symposium - International Astronomical Union 175 (1996): 559–60. http://dx.doi.org/10.1017/s0074180900081845.

Full text

Abstract:

During the preliminary deep imaging phase of our large spectroscopic survey of faint field galaxies (CFRS), one of our fields (10 arcmin × 10 arcmin) was chosen to coincide with the Fomalont et al (1991, A.J. 102,1258, hereafter FWKK) radio source field, including 36 S≃ 16μJy radio sources of their complete sample. All sources but two have been identified to V < 25 and/or IAB ≤ 24, and/or KAB ≤ 21.The microJy population is mainly constituted of three distinct populations of galaxies with different redshift regimes: early-type galaxies at z > 0.75 with a low powered AGN in their cores, post-starburst galaxies at intermediate redshifts (z = 0.375 to z = 0.8 or slightly > 1), and emission-line galaxies at z < 0.45 containing AGNs. The fraction of μJy sources with z > 1 could be as high as 30%. Most of the μJy radio sources (> 50%) are likely associated to AGNs, conversely to what is found at mJy levels (mostly starburst galaxies, Benn et al, 1993, MNRAS, 263, 98). Only one galaxy in our sample has a classical starburst spectrum.The strong decrease of the radio spectral index from sub-mJy to μJy counts appears to be due to a combination of three factors: (1) the emergence of an elliptical population at high redshifts with moderate radio emission (2) an increasing fraction of narrow emission-line AGNs (Seyfert 2 and LINER); (3) a higher contribution of the thermal radiation to the radio emission from spirals, and the almost complete disappearance of starburst galaxies. Details of the results summarized here can be found in Hammer et al (1995, MNRAS, 276, 1085).

APA, Harvard, Vancouver, ISO, and other styles

23

Vader, J. P., J. A. Frogel, F. C. Gillett, and M. H. K. de Grijp. "Dust-Embedded AGN in Unusually Warm IRAS Galaxies." Symposium - International Astronomical Union 134 (1989): 406–7. http://dx.doi.org/10.1017/s007418090014149x.

Full text

Abstract:

The IRAS Point Source Catalog contains only 61 sources identified as galaxies whose energy distribution peaks at 60 mμ. The scarcity of such galaxies has prompted a search for possible common properties. This sample of ‘60 mμ peakers’, 21 of which are previously identified galaxies, partially overlaps with that of warm IRAS galaxies studied by de Grijp et al. (1987) and contains similar percentages of Seyfert (65%) and starburst galaxies on the one hand, and of strong and weak radio sources on the other hand. A remarkable characteristic is, however, that about half of the 60 mμ peakers seem to be early-type galaxies. The fact that such galaxies are rarely IRAS sources and, if so, have FIR energy distributions peaking at 100 mμ similar to those of spirals, implies that we are sampling active or nuclear starburst early-type galaxies with a very large success rate. The observational data accumulated so far further show that: (i)objects with smaller FIR to near-IR flux ratios have redder J-K colors and warmer 60 to 25 mμ colors, i.e., an infared spectrum dominated by warmer dust and/or a nonthermal source (Figs. 1a,b);(ii)out of 32 objects with radio data, the 5 compact radio sources with luminosities intermediate between those af radio-quiet and radio-loud AGN have among the warmest 60 to 25 mμ colors (Fig. 2). Such warm FIR colors are not a common characteristic of radio galaxies and quasars (Golombek et al. 1987, Neugebauer et al. 1986).(iii)the 60 mμ luminosities range from 109 to 1012 L0, and are largest for Mkn 231, 2306+0505 (Hill et al. 1987) and 2046+1925 (Frogel et al. 1988). The latter 2 objects, along with 0052-7054 (Frogel and Elias 1987) which also belongs to our sample, are Seyfert 2 galaxies with evidence for the presence of a dust-obsured broad line region.

APA, Harvard, Vancouver, ISO, and other styles

24

Stroe, Andra, Victoria Catlett, Jeremy J. Harwood, Tessa Vernstrom, and Beatriz Mingo. "The Host Galaxies of Hybrid Morphology Radio Sources." Astrophysical Journal 941, no. 2 (December 1, 2022): 136. http://dx.doi.org/10.3847/1538-4357/ac9b1e.

Full text

Abstract:

Abstract Based on their differing radio morphologies, powerful radio galaxies can be separated into the Fanaroff–Riley I (FR I) and II (FR II) classes. Hybrid morphology radio sources (HyMoRS) contain morphologies consistent with each type of jet on either side: a powerful, highly relativistic FR I–like jet terminating in a hotspot on one side and an FR I–like plume on the other. HyMoRS present a unique opportunity to study the conditions that give rise to the dichotomy. Using host galaxy properties, we conduct the first multiwavelength investigation into whether orientation can explain HyMoRS morphology. Through optical spectroscopy and mid-infrared photometry, we analyze the emission characteristics, and evaluate the broad characteristics of five HyMoRS host galaxies at intermediate redshifts (0.4 < z < 1.5). The HyMoRS host galaxies in our sample have properties consistent with typical host galaxies of FR II sources, suggesting that the observed hybrid morphologies may be caused by a dense, cluster-like environment bending FR II jets combined with a favorable orientation that can make one side appear similar to an FR I jet. Our results thus support the hypothesis that HyMoRS are mainly caused by environment and orientation.

APA, Harvard, Vancouver, ISO, and other styles

25

Gregorini, L., M. Bondi, L. Feretti, G. Giovannini, and C. P. O'dea. "Magnetic Fields of Radio Galaxies in Abell Clusters 115 and 568." Symposium - International Astronomical Union 140 (1990): 495–96. http://dx.doi.org/10.1017/s0074180900190989.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Zajaček, Michal, Gerold Busch, Mónica Valencia-S., Andreas Eckart, Silke Britzen, Lars Fuhrmann, Jana Schneeloch, Nastaran Fazeli, Kevin C. Harrington, and J. Anton Zensus. "Radio spectral index distribution of SDSS-FIRST sources across optical diagnostic diagrams." Astronomy & Astrophysics 630 (September 24, 2019): A83. http://dx.doi.org/10.1051/0004-6361/201833388.

Full text

Abstract:

Context. The empirical relations between supermassive black holes and their host spheroids point towards the crucial role of galactic nuclei in affecting the properties of their hosts. A detailed understanding of how the activity of a galactic nucleus regulates the growth of its host is still missing. Aims. To understand the activity and the types of accretion of supermassive black holes in different hosts, it is essential to study the radio-optical properties of a large sample of extragalactic sources. In particular, we aim to study the radio spectral index trends across the optical emission line diagnostic diagrams to search for potential (anti)correlations. Methods. To this goal, we combined flux densities from the radio FIRST survey at 1.4 GHz (with the flux density range 10 mJy ≤ F1.4 ≤ 100 mJy) for 396 SDSS sources at intermediate redshift (0.04 ≤ z ≤ 0.4) with the Effelsberg radiotelescope measurements at 4.85 GHz and 10.45 GHz. The information about the optical emission-line ratios is obtained from the SDSS-DR7 catalogue. Results. Using the Effelsberg data, we were able to infer the two-point radio spectral index distributions for star-forming galaxies, composite galaxies (with a combined contribution to the line emission from the star formation and AGN activity), Seyferts, and low ionization narrow emission region (LINER) galaxies. Conclusions. While studying the distribution of steep, flat, and inverted sources across optical diagnostic diagrams, we found three distinct classes of radio emitters for our sample: (i) sources with a steep radio index, high ionization ratio, and high radio loudness, (ii) sources with a flat radio index, lower ionization ratio, and intermediate radio loudness, (iii) sources with an inverted radio index, low ionization ratio, and low radio loudness. The classes (i), (ii), and (iii) cluster mainly along the transition from Seyfert to LINER sources in the optical diagnostic (Baldwin, Phillips & Telervich; BPT) diagram. We interpret these groups as a result of the recurrent nuclear-jet activity.

APA, Harvard, Vancouver, ISO, and other styles

27

Kondratiev, Vladislav, Duncan Lorimer, Maura McLaughlin, and Scott Ransom. "A pulsar census of the Local Group." Proceedings of the International Astronomical Union 8, S291 (August 2012): 431. http://dx.doi.org/10.1017/s1743921312024398.

Full text

Abstract:

AbstractWe carried out a search for pulsars in nearby galaxies with the GBT and Arecibo radio telescopes at 820 and 327 MHz, correspondingly. Currently, the Magellanic Clouds are the only galaxies except for Milky Way known to harbor radio pulsars, with a total of 20 pulsars being discovered there to date. Discovery of pulsars in other galaxies can be used to trace the history of massive star formation and would allow to probe the intermediate intergalactic medium. We selected 22 galaxies of the Local Group at high galactic latitudes, |b| > 26 deg, with most of them being dwarf spheroidals with old star population. This makes them promising targets to search for giant pulses from recycled millisecond pulsars. Both single-pulse and periodicity searches were performed for trial dispersion measures up to 1000. No extragalactic pulsars are found in half of the selected targets processed so far. I will give the overview of our targetted searches, present potential candidates and discuss the obtained results.

APA, Harvard, Vancouver, ISO, and other styles

28

Dagkesamanskii, R. D. "Spectral Index - Redshift Relation for Radio Galaxies and Quasars." Symposium - International Astronomical Union 175 (1996): 569–70. http://dx.doi.org/10.1017/s0074180900081882.

Full text

Abstract:

Cosmological evolution of synchrotron spectra of the powerful extragalactic radio sources was studied by many authors. Some indications of such an evolution had been found firstly by analysis of ‘spectral index - flux density’ (α – S) relation for the sample of relatively strong radio sources. Later Gopal-Krishna and Steppe extended the analysis to weaker sources and found that the slope of αmed(S) curve changes dramatically at intermediate flux densities. Gopal-Krishna and Steppe pointed out that the maxima of the αmed(S) curve and of differential source counts are at almost the same flux density ranges (see, Fig. 2). It has to be noticed that the all mentioned results were obtained using the low-frequency spectral indices and on the basis of low frequency samples.

APA, Harvard, Vancouver, ISO, and other styles

29

Wu, Kinwah. "Multi-Messenger Astrophysics of a Millisecond Pulsar Orbiting around a Massive Black Hole." Universe 8, no. 2 (January 27, 2022): 78. http://dx.doi.org/10.3390/universe8020078.

Full text

Abstract:

Extreme-mass-ratio and intermediate-mass-ratio binaries with a millisecond pulsar are gravitational-wave sources that emit also electromagnetic radiation. The millisecond pulsars in these binaries have complex orbital and spin dynamics, which are observable because of spin–orbit and spin–spin coupling (through spin–curvature interaction). The strengths of the couplings generally depends on the mass ratio between the pulsar and the black hole. The narrow mass range of neutron stars gives an advantage in parameter extraction as it greatly reduces the search space, in particular, in the determination of the black-hole mass, in gravitational wave experiments and radio pulsar timing observations. Extreme-mass-ratio and intermediate-mass-ratio binaries with a millisecond pulsar will help to resolve the astrophysical problems, concerning the applicability of the M-σ relation for galactic spheroids extending to the very low-mass galaxies and whether or not low-mass dwarf galaxies and globular clusters would harbour a nuclear intermediate-mass black hole. The high-precision that can be achieved in gravitational wave experiments and radio pulsar timing observations will provide an opportunity to directly detect gravitational clock effects that are arisen from spin couplings. Radio monitoring of the orbital and spin evolution of the millisecond pulsar in an extreme-mass-ratio binary can be used as a bootstrap method for correcting the drifts in the phases in the gravitational waves from the extreme-mass-ratio and intermediate-mass-ratio binaries caused by self-force.

APA, Harvard, Vancouver, ISO, and other styles

30

Tadhunter, C., R. Dickson, R. Morganti, T. G. Robinson, K. Wills, M. Villar-Martin, and M. Hughes. "The origin of the UV excess in powerful radio galaxies: spectroscopy and polarimetry of a complete sample of intermediate-redshift radio galaxies." Monthly Notices of the Royal Astronomical Society 330, no. 4 (March 2002): 977–96. http://dx.doi.org/10.1046/j.1365-8711.2002.05153.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Zheng, X. C., H. J. A. Röttgering, P. N. Best, A. van der Wel, M. J. Hardcastle, W. L. Williams, M. Bonato, I. Prandoni, D. J. B. Smith, and S. K. Leslie. "Link between radio-loud AGNs and host-galaxy shape." Astronomy & Astrophysics 644 (November 24, 2020): A12. http://dx.doi.org/10.1051/0004-6361/202038646.

Full text

Abstract:

The morphology of quiescent galaxies has been found to be correlated with the activity of their central super massive black hole. In this work, we use data from the first data release of the LOFAR Two-Metre Sky Survey (LoTSS DR1) and the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) to select more than 15 000 quiescent galaxies at z < 0.3 to investigate the connection between radio-loud active galactic nuclei (RLAGNs) and the morphology of their host galaxy. Taking advantage of the depth of LoTSS, we find that the fraction of RLAGNs with L150 MHz > 1021 W Hz−1 at fixed stellar mass, velocity dispersion, or surface mass density does not depend on the galaxy projected axis ratio (q). However, the high-power (L150 MHz > 1023 W Hz−1) RLAGNs are more likely to be found in massive, round galaxies, while the low- and intermediate-power (L150 MHz ≤ 1023 W Hz−1) RLAGNs have similar distributions of q to non-RLAGN galaxies. We argue that our results support the picture that high-power RLAGNs are more easily triggered in galaxies with a merger-rich history, while low-power RLAGNs can be triggered in galaxies growing mainly via secular processes. Our work also supports the idea that the low-luminosity RLAGN may be sufficient for maintenance-mode feedback in low-mass quiescent galaxies with disc-like morphology, which is based on a simple extrapolation from the observed energy balance between cooling and RLAGN-induced cavities in massive clusters. We find no significant difference between the q distributions of RLAGNs likely to be found in clusters and those likely not found in clusters after controlling the radio luminosity and stellar mass of the two samples, indicating that the environment does not significantly influence the morphology–RLAGN correlation.

APA, Harvard, Vancouver, ISO, and other styles

32

Arshakian, Tigran G. "Kiloparsec Jet Speeds in Classical Double Radio Sources." Symposium - International Astronomical Union 205 (2001): 152–53. http://dx.doi.org/10.1017/s0074180900220810.

Full text

Abstract:

On the basis of an intrinsically symmetric relativistic jet model, analytical equations between the mean jet speed and the mean jet flux asymmetry, and between their variances are derived in the context of an orientation-based unification scheme. The mean jet speeds of classical double radio sources are estimated on kiloparsec scales by using the asymmetry of jet-counterjet flux densities taken from the 3CRR and B2 samples. For FRI radio sources the mean jet speed is ∼ (0.54 ± 0.03)c, while for FRII low-redshift radio galaxies and intermediate-redshift quasars the values found are ∼ (0.4 ± 0.06)c and ≳ 0.6c respectively.

APA, Harvard, Vancouver, ISO, and other styles

33

Petrosian, A. R., and M. Sh Karapetian. "Multivariate Statistical Analysis of the Sample of AGN." Symposium - International Astronomical Union 134 (1989): 43–46. http://dx.doi.org/10.1017/s0074180900140318.

Full text

Abstract:

Radio, FIR, spectral and X-ray data by 11 parameters for the AGNs samples of Sy1, Sy1.5, Sy2 types and LINERs are compiled. All samples are processed by the multivariate statistical methods including factor and discriminant analysises. The following results are obtained: –LINERs by principal factors, determining NLR and the central engine are clearly separated from the Seyfert galaxies.–All types of the Seyfert galaxies in all have the same NLR.–Intermediate Seyfert type is real. These AGNs are much more similar to Sy1 type objects than to Sy2.

APA, Harvard, Vancouver, ISO, and other styles

34

Lewis, Karen T., Rita M. Sambruna, Emmanouil Angelakis, Michael Eracleous, Chi C. Cheung, and Matthias Kadler. "MULTI-WAVELENGTH OBSERVATIONS OF A SAMPLE OF INTERMEDIATE-LUMINOSITY RADIO-LOUD ACTIVE GALAXIES." Astronomical Journal 142, no. 1 (May 27, 2011): 9. http://dx.doi.org/10.1088/0004-6256/142/1/9.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Chandola, Yogesh, D. J. Saikia, and Di Li. "H i absorption towards radio active galactic nuclei of different accretion modes." Monthly Notices of the Royal Astronomical Society 494, no. 4 (April 21, 2020): 5161–77. http://dx.doi.org/10.1093/mnras/staa1029.

Full text

Abstract:

ABSTRACT We present results of H i absorption experiment done using the Giant Metrewave Radio Telescope (GMRT) towards 27 low- and intermediate-luminosity ($P_{\rm 1.4 GHz}\, \sim 10^{23}$-1026 W Hz−1) radio active galactic nuclei (AGNs), classified as either low excitation radio galaxies (LERGs) or high excitation radio galaxies (HERGs) and with WISE colour W2[4.6 μm]−W3[12 μm]> 2. We report H i absorption detection towards seven radio AGNs, six of which are new. Combined with other sources from literature classified as LERGs or HERGs, we confirm our earlier result that compact radio AGNs with WISE colour W2−W3 > 2 have higher detection rates compared to those with W2−W3 < 2. We find that H i absorption detection rate is higher for HERGs (37.0$^{+15.8}_{-11.5}$ per cent) compared to LERGs (22.0$^{+3.9}_{-3.4}$ per cent), mainly due to a larger fraction of HERGs being gas and dust rich with a younger stellar population compared to LERGs. However, for similar compact radio structures and host galaxies with WISE colours W2−W3 > 2, we don’t find any significant difference in detection rates of two types of AGNs implying detection of H i gas may not necessarily mean high excitation mode AGN. We further analysed the kinematics towards these sources. We find that while LERGs show a wide range in the shift of centroid velocities ($\sim \, -$479 to +356 km s−1) relative to the optical systemic velocity, most of the HERGs have centroid velocity shift less than 200 km s−1, possibly due to differences in jet-interstellar medium interaction.

APA, Harvard, Vancouver, ISO, and other styles

36

Leslie, S. K., M. T. Sargent, E. Schinnerer, B. Groves, A. van der Wel, G. Zamorani, Y. Fudamoto, P. Lang, and V. Smolčić. "Probing star formation and ISM properties using galaxy disk inclination." Astronomy & Astrophysics 615 (July 2018): A7. http://dx.doi.org/10.1051/0004-6361/201732255.

Full text

Abstract:

Disk galaxies at intermediate redshift (z ~ 0.7) have been found in previous work to display more optically thick behaviour than their local counterparts in the rest-frame B-band surface brightness, suggesting an evolution in dust properties over the past ~6 Gyr. We compare the measured luminosities of face-on and edge-on star-forming galaxies at different wavelengths (Ultraviolet (UV), mid-infrared (MIR), far-infrared (FIR), and radio) for two well-matched samples of disk-dominated galaxies: a local Sloan Digital Sky Survey (SDSS)-selected sample at z ~ 0.07 and a sample of disks at z ~ 0.7 drawn from Cosmic Evolution Survey (COSMOS). We have derived correction factors to account for the inclination dependence of the parameters used for sample selection. We find that typical galaxies are transparent at MIR wavelengths at both redshifts, and that the FIR and radio emission is also transparent as expected. However, reduced sensitivity at these wavelengths limits our analysis; we cannot rule out opacity in the FIR or radio. Ultra-violet attenuation has increased between z ~ 0 and z ~ 0.7, with the z ~ 0.7 sample being a factor of ~3.4 more attenuated. The larger UV attenuation at z ~ 0.7 can be explained by more clumpy dust around nascent star-forming regions. There is good agreement between the fitted evolution of the normalisation of the SFRUV versus 1 − cos(i) trend (interpreted as the clumpiness fraction) and the molecular gas fraction/dust fraction evolution of galaxies found out to z < 1.

APA, Harvard, Vancouver, ISO, and other styles

37

Morganti, R., C. N. Tadhunter, T. A. Oosterloo, J. Holt, A. Tzioumis, and K. Wills. "The Impact of the Early Stages of Radio Source Evolution on the ISM of the Host Galaxies." Publications of the Astronomical Society of Australia 20, no. 1 (2003): 129–33. http://dx.doi.org/10.1071/as02056.

Full text

Abstract:

AbstractThe study of both neutral and ionised gas in young radio sources is providing key information on the effect the radio plasma has on the ISM of these objects. We present results obtained for the compact radio sources PKS 1549–79, 4C 12.50 and PKS 1814–63 and for the intermediate-size radio galaxy 3C 459. At least in the first two, low ionisation optical emission lines and HI absorption appear to be associated with the extended, but relatively quiescent, dusty cocoon surrounding the nucleus. The [OIII] lines are, on the other hand, mostly associated with the region of interaction between the radio plasma and the ISM, indicating a fast outflow from the centre. A case of fast outflow (up to ∼1000 km s-1) is also observed in HI in the radio source 4C 12.50. As the radio source evolves, any obscuring material along the radio axis is swept aside until, eventually, cavities (of the same kind as observed e.g. in Cygnus A) are hollowed out on either side of the nucleus. We may witness this phase in the evolution of a radio source in the radio galaxy 3C 459.

APA, Harvard, Vancouver, ISO, and other styles

38

Yang, Xiaolong, Prashanth Mohan, Jun Yang, Luis C. Ho, J. N. H. S. Aditya, Shaohua Zhang, Sumit Jaiswal, and Xiaofeng Yang. "Radio Observations of Four Active Galactic Nuclei Hosting Intermediate-mass Black Hole Candidates: Studying the Outflow Activity and Evolution." Astrophysical Journal 941, no. 1 (December 1, 2022): 43. http://dx.doi.org/10.3847/1538-4357/ac9e9d.

Full text

Abstract:

Abstract Observational searches for intermediate-mass black holes (IMBHs; 102–106 M ⊙) include relatively isolated dwarf galaxies. For those that host active galactic nuclei (AGNs), the IMBH nature may be discerned through the accretion–jet activity. We present radio observations of four AGN-hosting dwarf galaxies, which potentially harbor IMBHs. Very large array (VLA) observations indicate steep spectra (indices of −0.63 to −1.05) between 1.4 and 9 GHz. However, a comparison with the 9 GHz in-band spectral index shows a steepening for GH047 and GH158 (implying older/relic emission) and flattening for GH106 and GH163 (implying recent activity). Overlapping emission regions in the VLA 1.4 GHz and our very long baseline array (VLBA) 1.5 GHz observations, and possibly symmetric pc-scale extensions, are consistent with recent activity in the latter two. Using the compact VLBA radio luminosity, X-ray luminosity (probing the accretion activity), and the black hole masses, all AGNs are found to lie on the empirical fundamental plane relation. The four AGNs are radio-quiet with relatively higher Eddington ratios (0.04–0.32) and resemble X-ray binaries during spectral state transitions that entail an outflow ejection. Furthermore, the radio to X-ray luminosity ratio log R X of −3.9 to −5.6 in these four sources support the scenarios that include corona mass ejection from the accretion disk and wind activity. The growth to kpc-scales likely proceeds along a similar trajectory to young AGNs and peaked spectrum sources. These complex clues can thus aid in the detection and monitoring of IMBHs in the nearby universe.

APA, Harvard, Vancouver, ISO, and other styles

39

Delgado, R. M. González, R. Cid Fernandes, E. Pérez, J. Rodríguez-Zaurín, C. Tadhunter, O. Dors, V. Muñoz Marín, and M. Villar-Martín. "Stellar Populations in Luminous and Ultraluminous Infrared Galaxies." Proceedings of the International Astronomical Union 5, S262 (August 2009): 341–42. http://dx.doi.org/10.1017/s1743921310003145.

Full text

Abstract:

AbstractThe goal of this work is to determine the properties of the stellar populations in a sample of LIRGs and ULIRGs. Using the ages as a clock we investigate: a) whether LIRGs-ULIRGs evolve into Radio Galaxies and QSOs; b) whether cool LIRGs-ULIRGs can evolve into warm LIRGs-ULIRGs; c) the merger sequence deduced from the morphological studies is reflected in the properties of the stellar populations. Using evolutionary synthesis models with high spectral resolution stellar libraries we have found that the intermediate age stellar population dominates at optical wavelengths. The stellar population in LIRGs is similar to ULIRGs and ULIRGs-QSOs transition objects.

APA, Harvard, Vancouver, ISO, and other styles

40

Liodakis, I. "Detecting intermediate-mass black holes in midiquasars with current and future surveys." Monthly Notices of the Royal Astronomical Society 512, no. 1 (January 28, 2022): 291–95. http://dx.doi.org/10.1093/mnras/stac181.

Full text

Abstract:

ABSTRACT The lack of detected intermediate-mass black holes poses a gap in our understanding of the growth and evolution of the most exotic of astrophysical objects. Here, we investigate the possibility of low-luminosity relativistic jets launched by intermediate-mass black holes in the centres of dwarf galaxies. We built population models that allow us to make predictions for their radio emission and quantify their detectability by current and future surveys. We find that the upcoming instruments in optical and radio like the SKA, ngVLA, and the Vera C. Rubin Observatory will likely be able to detect a significant fraction ($\gt 38{{\,\rm per\,cent}}$) of such sources population if they exist. In addition, our results suggest that it is not unlikely that a small number of midiquasars, possibly masquerading as low-luminosity active galactic nuclei, may have already been detected by existing surveys.

APA, Harvard, Vancouver, ISO, and other styles

41

Ward, Charlotte, Suvi Gezari, Peter Nugent, Eric C. Bellm, Richard Dekany, Andrew Drake, Dmitry A. Duev, et al. "Variability-selected Intermediate-mass Black Hole Candidates in Dwarf Galaxies from ZTF and WISE." Astrophysical Journal 936, no. 2 (September 1, 2022): 104. http://dx.doi.org/10.3847/1538-4357/ac8666.

Full text

Abstract:

Abstract While it is difficult to observe the first black hole seeds in the early universe, we can study intermediate-mass black holes (IMBHs) in local dwarf galaxies for clues about their origins. In this paper we present a sample of variability-selected active galactic nuclei (AGN) in dwarf galaxies using optical photometry from the Zwicky Transient Facility (ZTF) and forward-modeled mid-IR photometry of time-resolved Wide-field Infrared Survey Explorer (WISE) co-added images. We found that 44 out of 25,714 dwarf galaxies had optically variable AGN candidates and 148 out of 79,879 dwarf galaxies had mid-IR variable AGN candidates, corresponding to active fractions of 0.17% ± 0.03% and 0.19% ± 0.02%, respectively. We found that spectroscopic approaches to AGN identification would have missed 81% of our ZTF IMBH candidates and 69% of our WISE IMBH candidates. Only nine candidates have been detected previously in radio, X-ray, and variability searches for dwarf galaxy AGN. The ZTF and WISE dwarf galaxy AGN with broad Balmer lines have virial masses of 105 M ⊙ < M BH < 107 M ⊙, but for the rest of the sample, BH masses predicted from host galaxy mass range between 105.2 M ⊙ < M BH < 107.25 M ⊙. We found that only 5 of 152 previously reported variability-selected AGN candidates from the Palomar Transient Factory in common with our parent sample were variable in ZTF. We also determined a nuclear supernova fraction of 0.05% ± 0.01% yr−1 for dwarf galaxies in ZTF. Our ZTF and WISE IMBH candidates show the promise of variability searches for the discovery of otherwise hidden low-mass AGN.

APA, Harvard, Vancouver, ISO, and other styles

42

Liu, Xiang, Ning Chang, Zhenhua Han, and Xin Wang. "The Jet-Disk Coupling of Seyfert Galaxies from a Complete Hard X-ray Sample." Universe 6, no. 5 (May 10, 2020): 68. http://dx.doi.org/10.3390/universe6050068.

Full text

Abstract:

We analyze the jet-disk coupling for different subsamples from a complete hard X-ray Seyfert sample to study the coupling indices and their relation to accretion rate. The results are: (1) the power-law coupling index ranges from nearly unity (linear correlation) for radio loud Seyferts to significantly less than unity for radio quiet ones. This decline trend of coupling index also holds from larger sources to compact ones; (2) the Seyferts with intermediate to high accretion rate (Eddington ratio λ ∼ 0.001 to 0.3) show a linear jet-disk coupling, but it shallows from near to super Eddington ( λ ∼ 0.3 to 10), and the former is more radio loud than the latter; (3) the Seyfert 1s are slightly steeper than the Seyfert 2s, in the jet-disk correlation. In the linear coupling regime, the ratio of jet efficiency to radiative efficiency ( η / ε ) is nearly invariant, but in low accretion or super accretion regime, η / ε varies with λ in our model. We note that a radio-active cycle of accretion-dominated active galactic nuclei would be: from a weaker jet-disk coupling in λ < 0 . 001 for low luminosity Seyferts, to a linear coupling in 0 . 001 < λ < 0 . 3 for radio-loud luminous Seyferts and powerful radio galaxies/quasars, and to a weaker coupling in 0 . 3 < λ < 10 ones.

APA, Harvard, Vancouver, ISO, and other styles

43

Macconi, D., E. Torresi, P. Grandi, B. Boccardi, and C. Vignali. "Radio morphology–accretion mode link in Fanaroff–Riley type II low-excitation radio galaxies." Monthly Notices of the Royal Astronomical Society 493, no. 3 (February 27, 2020): 4355–66. http://dx.doi.org/10.1093/mnras/staa560.

Full text

Abstract:

ABSTRACT Fanaroff–Riley type II (FR II) low-excitation radio galaxies (LERGs) are characterized by weak nuclear excitation on parsec-scales and properties typical of powerful FR IIs (defined as high-excitation radio galaxies, hereafter HERGs/BLRGs) on kiloparsec-scales. Since a link between the accretion properties and the power of the produced jets is expected both from theory and observations, their nature is still debated. In this work, we investigate the X-ray properties of a complete sample of 19 FR II-LERGs belonging to the 3CR catalogue, exploiting Chandra and XMM–Newton archival data. We also analyse 32 FR II-HERGs/BLRGs with Chandra data as a control sample. We compared FR II-LERG and FR II-HERG/BLRG X-ray properties and optical data available in literature to obtain a wide outlook of their behaviour. The low accretion rate estimates for FR II-LERGs, from both X-ray and optical bands, allow us to firmly reject the hypothesis as they are the highly obscured counterpart of powerful FR II-HERGs/BLRGs. Therefore, at least two hypothesis can be invoked to explain the FR II-LERG nature: (i) they are evolving from classical FR IIs because of the depletion of accreting cold gas in the nuclear region, while the extended radio emission is the heritage of a past efficiently accreting activity; and (ii) they are an intrinsically distinct class of objects with respect to classical FR Is/FR IIs. Surprisingly, in this direction, a correlation between accretion rates and environmental richness is found in our sample. The richer the environment is, the more inefficient is the accretion. In this framework, the FR II-LERGs are intermediate between FR Is and FR II-HERGs/BLRGs both in terms of accretion rate and environment.

APA, Harvard, Vancouver, ISO, and other styles

44

Yang, Jun, Leonid I. Gurvits, Zsolt Paragi, Sándor Frey, John E. Conway, Xiang Liu, and Lang Cui. "A parsec-scale radio jet launched by the central intermediate-mass black hole in the dwarf galaxy SDSS J090613.77+561015.2." Monthly Notices of the Royal Astronomical Society: Letters 495, no. 1 (April 7, 2020): L71—L75. http://dx.doi.org/10.1093/mnrasl/slaa052.

Full text

Abstract:

ABSTRACT The population of intermediate-mass black holes (IMBHs) in nearby dwarf galaxies plays an important ‘ground truth’ role in exploring black hole formation and growth in the early Universe. In the dwarf elliptical galaxy SDSS J090613.77+561015.2 (z = 0.0465), an accreting IMBH has been revealed by optical and X-ray observations. Aiming to search for possible radio core and jet associated with the IMBH, we carried out very long baseline interferometry (VLBI) observations with the European VLBI Network at 1.66 GHz. Our imaging results show that there are two 1-mJy components with a separation of about 52 mas (projected distance 47 pc) and the more compact component is located within the 1σ error circle of the optical centroid from available Gaia astrometry. Based on their positions, elongated structures and relatively high brightness temperatures, as well as the absence of star-forming activity in the host galaxy, we argue that the radio morphology originates from the jet activity powered by the central IMBH. The existence of the large-scale jet implies that violent jet activity might occur in the early epochs of black hole growth and thus help to regulate the co-evolution of black holes and galaxies.

APA, Harvard, Vancouver, ISO, and other styles

45

Tisanić, K., G. De Zotti, A. Amiri, A. Khoram, S. Tavasoli, and Z. Vidović-Tisanić. "Infrared-radio relation in the local Universe." Astronomy & Astrophysics 658 (January 26, 2022): A21. http://dx.doi.org/10.1051/0004-6361/202140402.

Full text

Abstract:

Context. The Square Kilometer Array (SKA) is expected to detect high-redshift galaxies with star formation rates (SFRs) up to two orders of magnitude lower than Herschel surveys and will thus boost the ability of radio astronomy to study extragalactic sources. The tight infrared-radio correlation offers the possibility of using radio emission as a dust-unobscured star formation diagnostic. However, the physics governing the link between radio emission and star formation is poorly understood, and recent studies have pointed to differences in the exact calibration required when radio is to be used as a star formation tracer. Aims. We improve the calibration of the relation of the local radio luminosity–SFR and to test whether there are nonlinearities in it. Methods. We used a sample of Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) sources and investigated their radio luminosity, which was derived using the NRAO VLA Sky Survey (NVSS) and Faint Images of the Radio Sky at Twenty-cm (FIRST) maps. We stacked the bins of infrared luminosity and SFR and accounted for bins with no detections in the stacked images using survival analysis fitting. This approach was tested using Monte Carlo simulations. Results. After removing sources from the sample that have excess radio emission, which is indicative of nuclear radio activity, we found no deviations from linearity of the mean relations between radio luminosity and either SFR or infrared luminosity. Concluisions. We analyzed the link between radio emission and SFR or infrared luminosity using a local sample of star-forming galaxies without evidence of nuclear radio activity and found no deviations from linearity, although our data are also consistent with the small nonlinearity reported by some recent analyses. The normalizations of these relations are intermediate between those reported by earlier works.

APA, Harvard, Vancouver, ISO, and other styles

46

Clark, N. E., D. J. Axon, C. N. Tadhunter, A. Robinson, and P. O'Brien. "Jet‐induced Shocks in 3C 171: An Intermediate‐Redshift Analog of High‐Redshift Radio Galaxies." Astrophysical Journal 494, no. 2 (February 20, 1998): 546–66. http://dx.doi.org/10.1086/305225.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Augusto, P., P. N. Wilkinson, and I. W. A. Browne. "A VLA/Merlin/VLBA For Intermediate Scale Lenses and the Discovery of a New Lens System?" Symposium - International Astronomical Union 173 (1996): 399–400. http://dx.doi.org/10.1017/s0074180900231884.

Full text

Abstract:

We are searching for small lens systems (50-250 mas or 108–109M⊙) in a sample of ∼ 1800 flat spectrum radio sources. This is the first time a systematic search has been made “between” the VLA and VLBI resolutions. Finding any would indicate the existence of other than the “conventional” spiral/elliptical lenses (only ∼ 0.01% chance - Turner et al. (1984)). For example, faint galaxies are numerous (∼ 106 gal/deg2 - Lilly (1993), Glazebrook et al. 1995), compact (HST Medium Deep Survey (MDS) - Griffiths et al. 1994) and ideally placed for lensing (< z >∼ 0.6 - MDS, Smail et al. (1994); c.f. Turner et al. 1984). Early-type dwarf galaxies (dE,N and cE), if extant at intermediate-z as favored by MDS are also obvious lens candidates. If no lenses are found, a limit 400 times better than the current one (Surdej et al. 1993), ΩL < 0.001, will be placed on the cosmological density of compact objects (e.g. black holes) for the above mass range.

APA, Harvard, Vancouver, ISO, and other styles

48

Kornecki, P., E. Peretti, S. del Palacio, P. Benaglia, and L. J. Pellizza. "Exploring the physics behind the non-thermal emission from star-forming galaxies detected in γ rays." Astronomy & Astrophysics 657 (January 2022): A49. http://dx.doi.org/10.1051/0004-6361/202141295.

Full text

Abstract:

Context. Star-forming galaxies emit non-thermal radiation from radio to γ rays. Observations show that their radio and γ-ray luminosities scale with their star formation rates, supporting the hypothesis that non-thermal radiation is emitted by cosmic rays produced by their stellar populations. However, the nature of the main cosmic-ray transport processes that shape the emission in these galaxies is still poorly understood, especially at low star formation rates. Aims. Our aim is to investigate the main mechanisms of global cosmic-ray transport and cooling in star-forming galaxies. The way they contribute to shaping the relations between non-thermal luminosities and star formation rates could shed light onto their nature, and allow us to quantify their relative importance at different star formation rates. Methods. We developed a model to compute the cosmic-ray populations of star-forming galaxies, taking into account their production, transport, and cooling. The model is parametrised only through global galaxy properties, and describes the non-thermal emission in radio (at 1.4 GHz and 150 MHz) and γ rays (in the 0.1−100 GeV band). We focused on the role of diffusive and advective transport by galactic winds, either driven by turbulent or thermal instabilities. We compared model predictions to observations, for which we compiled a homogeneous set of luminosities in these radio bands, and updated those available in γ rays. Results. Our model reproduces reasonably well the observed relations between the γ-ray or 1.4 GHz radio luminosities and the star formation rate, assuming a single power-law scaling of the magnetic field (with index β = 0.3) and winds blowing either at Alfvenic speeds (∼tens of km s−1, for ≲5 M⊙ yr−1) or typical starburst wind velocities (∼hundreds of km s−1, for ≳5 M⊙ yr−1). Escape of cosmic rays is negligible for ≳30 M⊙ yr−1. A constant ionisation fraction of the interstellar medium fails to reproduce the 150 MHz radio luminosity throughout the whole star formation rate range. Conclusions. Our results reinforce the idea that galaxies with high star formation rates are cosmic-ray calorimeters, and that the main mechanism driving proton escape is diffusion, whereas electron escape also proceeds via wind advection. They also suggest that these winds should be cosmic-ray or thermally driven at low and intermediate star formation rates, respectively. Our results globally support that magneto-hydrodynamic turbulence is responsible for the dependence of the magnetic field strength on the star formation rate and that the ionisation fraction is strongly disfavoured to be constant throughout the whole range of star formation rates.

APA, Harvard, Vancouver, ISO, and other styles

49

Holt, J., C. N. Tadhunter, R. M. González Delgado, K. J. Inskip, J. Rodriguez, B. H. C. Emonts, R. Morganti, and K. A. Wills. "The properties of the young stellar populations in powerful radio galaxies at low and intermediate redshifts." Monthly Notices of the Royal Astronomical Society 381, no. 2 (October 2007): 611–39. http://dx.doi.org/10.1111/j.1365-2966.2007.12140.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Sanz, J. L., J. M. Martín-Mirones, E. Martínez-González, and J. I. González-Serrano. "Intermediate Resolution Spectroscopy of the Radio Galaxy B2 0902+34 at Z ≈ 3.4." Symposium - International Astronomical Union 168 (1996): 499–500. http://dx.doi.org/10.1017/s0074180900110484.

Full text

Abstract:

We have carried out optical spectroscopic observations at intermediate spectral resolution of the massive high redshift radio galaxy 0902+34 atz≈ 3.39. This source was first identified by Lilly (1988) (from hereafter L88). The study of high redshift radio galaxies is interesting to analyze the physical conditions of the early universe and the galaxy evolution at cosmological redshifts. It has been claimed that some of these systems may be protogalaxies in the process of formation. Indications for this are the flat spectrum and the absence of the 4000 Å break, features which have already been observed in many cases. In particular, observations in the spectral range fromVtoKsuggest that 0902+34 is a young galaxy (Eisenhardt and Dickinson 1992). Recent radio observations of the 21 cm line of neutral hydrogen have detected (Uson et al. 1991) an absorption against the radio continuum source. This absorption could also leave a track in the optical, redwards the Lyα line. Our observations were carried out with the ISIS spectrograph at the 4.2 m William Herschel Telescope (seeing ≈ 1.2–1.6 arcsec). A spectral dispersion of 0.78 Å/pixel (blue arm) and 1.38 Å/pixel (red arm) was obtained. Å long slit of width 3′ was used providing a spectral resolution of ≈ 5.4 Å in the blue arm and of ≈ 9.5 Å in the red one. Both resolutions are a clear improvement over that achieved by L88 of 20 Å, allowing us to resolve the Lyα line (and its possible structure) and any other possible strong features appearing in the spectral range observed (e. g., C iv λ1549, He ii λ1640, …). Six different observations of 2700 s of the radio galaxy 0902+34 were carried out. The slit was rotated to coincide with the parallactic angle at the beginning of each exposure. This will allow us to map spectroscopically different regions of the galaxy (for more details see Martín-Mirones et al. 1994).

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Radio intermediate galaxies'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles