Journal articles: 'AGN galaxies'

1

Veilleux, Sylvain. "AGN host galaxies." New Astronomy Reviews 52, no. 6 (August 2008): 289–306. http://dx.doi.org/10.1016/j.newar.2008.06.011.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Turatto, Massimo, Enrico Cappellaro, and Artashes R. Petrosian. "Supernova Types, Star Formation and AGN." Symposium - International Astronomical Union 194 (1999): 364–72. http://dx.doi.org/10.1017/s0074180900162308.

Full text

Abstract:

New values of the frequencies of SNe are presented and discussed in relation to their use as SF indicators. The rate of core-collapse SNe is correlated to the colors and the FIR excesses of the parent galaxies in the sense that galaxies with blue colors and strong infrared excess have higher occurrence of type II and Ib/c SNe than other galaxies. This is in agreement with the expectation that they contain a higher fraction of massive stars. Instead no correlation is present for SNIa. The SN frequency does not correlate with the galaxy activity probably because searches are unable to discover SNe in the nuclear regions of galaxies.A number of SNe with spectra similar to those of AGN exist. Their characteristic features are explained with explosion of SNe in dense environments, reminding of cSNR's invoked in the starburst model for AGNs. Some recent, peculiar SNe seem linked to GRB's opening the possibility that at least some GRB's arise from this kind of stellar explosion.

APA, Harvard, Vancouver, ISO, and other styles

3

Shabala, Stanislav, Sugata Kaviraj, and Joseph Silk. "Effects of large-scale AGN feedback in local galaxies." Proceedings of the International Astronomical Union 8, S292 (August 2012): 375. http://dx.doi.org/10.1017/s1743921313001762.

Full text

Abstract:

AbstractThe effects of active galactic nucleus (AGN) feedback on group and cluster galaxies are investigated. We examine the colors of non-AGN hosts (i.e. satellite galaxies) by comparing galaxies overrun by radio AGN with similar galaxies located outside the radio AGN contours. We find that powerful Fanaroff-Riley type II (edge-brightened) radio AGN truncate star formation in the galaxies overrun by AGN-driven bow shocks. On the other hand, the ubiquitous Fanaroff-Riley type I (core-dominated) AGN do not affect neighboring galaxies. This result shows that, despite their rarity, feedback from powerful radio AGN is an important factor in the evolution of group/cluster galaxies.

APA, Harvard, Vancouver, ISO, and other styles

4

Barthel, Peter. "Star-forming AGN host galaxies." New Astronomy Reviews 45, no. 9-10 (October 2001): 591–99. http://dx.doi.org/10.1016/s1387-6473(01)00139-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Greene, Jenny E., Aaron J. Barth, and Luis C. Ho. "The smallest AGN host galaxies." New Astronomy Reviews 50, no. 9-10 (November 2006): 739–42. http://dx.doi.org/10.1016/j.newar.2006.06.080.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Dashyan, Gohar, Joseph Silk, Gary A. Mamon, Yohan Dubois, and Tilman Hartwig. "AGN feedback in dwarf galaxies?" Monthly Notices of the Royal Astronomical Society 473, no. 4 (October 23, 2017): 5698–703. http://dx.doi.org/10.1093/mnras/stx2716.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Kaviraj, Sugata, Stanislav S. Shabala, Adam T. Deller, and Enno Middelberg. "Radio AGN in spiral galaxies." Monthly Notices of the Royal Astronomical Society 454, no. 2 (October 6, 2015): 1595–604. http://dx.doi.org/10.1093/mnras/stv1957.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Väisänen, Petri. "AGN, host galaxies, and starbursts." Proceedings of the International Astronomical Union 15, S356 (October 2019): 169. http://dx.doi.org/10.1017/s1743921320002811.

Full text

Abstract:

AbstractAGN by definition live in galaxies. Despite a long history of studies, there is still much ongoing research into the interplay of the nucleus and the host galaxy, how do they affect each other, how is their evolution intertwined. This review will briefly go over the historical developments behind the current understanding of AGN host galaxies, their types and characteristics. It will discuss the starburst and AGN connection in particular, and how these phenomena may be connected or influence each other by means of e.g. gas flows. Finally, some examples of AGN/starburst evolution studies from SALT and other large telescopes will be presented.

APA, Harvard, Vancouver, ISO, and other styles

9

Erastova, L. K. "Byurakan Surveys: Density of Bright AGN." International Astronomical Union Colloquium 184 (2002): 92–93. http://dx.doi.org/10.1017/s0252921100030529.

Full text

Abstract:

It is clear now that morphological criteria don’t divide galaxies from QSOs. Many galaxies are stellar-like objects and, conversely, quasars have host galaxies of various luminosities. For instance, two objects - SBS 1120+586A and SBS 1123+598 - absolutely do not differ from stars on the charts of the POSS and were classified as BSO-type. But they turned out to be galaxies with moderate luminosities (Markarian et al. 1988). Erastova (2000) produced a list of stellar-like galaxies from the SBS. Out of 339 KUV objects, 107 (31.6%) are emission-line galaxies of various luminosities (Darling & Wegner 1996). A considerable number of active galaxies appear among CSO - Case stellar objects. Conversely, objects having extended images on low-dispersion spectral plates turned out to be QSOs. SBS 1520+530 is a gravitationally lensed QSO with z=1.855 and on our low-dispersion plates appears as a galaxy (Chavushyan et al., 1997).

APA, Harvard, Vancouver, ISO, and other styles

10

de Vries, Nathan, I. A. G. Snellen, R. T. Schilizzi, M. D. Lehnert, and M. N. Bremer. "Massive galaxies with very young AGN." Proceedings of the International Astronomical Union 3, S245 (July 2007): 261–62. http://dx.doi.org/10.1017/s1743921308017870.

Full text

Abstract:

AbstractGigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources and live in massive ellipticals. GPS sources are vital for studying the early evolution of radio-loud AGN, the trigger of their nuclear activity, and the importance of feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS radio galaxies of which now all host galaxies have been identified and 80% has their redshifts determined (0.122 < z < 1.539). 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. This suggests that the AGN in young radio galaxies have not yet much influenced the overall properties of the host galaxy. However their restframe UV luminosities indicate that there is a low level of excess as compared to passive evolution models.

APA, Harvard, Vancouver, ISO, and other styles

11

Kristensen, Mikkel T., Kevin Pimbblet, and Samantha Penny. "Environments of dwarf galaxies with optical AGN characteristics." Monthly Notices of the Royal Astronomical Society 496, no. 3 (June 17, 2020): 2577–90. http://dx.doi.org/10.1093/mnras/staa1719.

Full text

Abstract:

ABSTRACT This study aims to explore the relation between dwarf galaxies (M* ≤ 5 × 109 M⊙) with active galactic nuclei (AGNs) and their environment by comparing neighbourhood parameters of AGN and non-AGN samples. Using the NASA-Sloan Atlas, both the local environment and the immediate environment of dwarf galaxies with z ≤ 0.055 are analysed. Of the 145 155 galaxies in the catalogue, 62 258 of them are classified as dwarf galaxies, and by employing two AGN selection methods based on emission-line fluxes (BPT and WHAN), 4476 are found to have AGN characteristics in their optical spectra. Regardless of selection method, this study finds no discernible differences in environment between AGN and non-AGN host dwarf galaxies and these results indicate that environment is not an important factor in triggering AGN activity in dwarf galaxies. This is in line with existing literature on environments of regular galaxies with AGNs and suggests universality in terms of reaction to environment across the mass regime. The biases of AGN selection in low-mass galaxies, and the biases of different measures of environment are also considered. It is found that there are several mass trends in emission-line ratios and that the SDSS fibre covers galaxies non-uniformly with redshift. These biases should be accounted for in future work by possibly including other wavelength regimes or mass weighting of emission-line ratios. Lastly, a discussion of the environment estimation methods is included since they may not gauge the desired properties due to factors such as time delay or using loosely constrained proxy parameters.

APA, Harvard, Vancouver, ISO, and other styles

12

Feltre, Anna, Evanthia Hatziminaoglou, Antonio Hernán-Caballero, Jacopo Fritz, and Alberto Franceschini. "AGN and Star Formation in HerMES-IRS sources." Proceedings of the International Astronomical Union 9, S304 (October 2013): 52–55. http://dx.doi.org/10.1017/s1743921314003305.

Full text

Abstract:

AbstractOne of the remaining open issues in the context of the analysis of Active Galactic Nuclei (AGN) is the evidence that nuclear gravitational accretion is often accompanied by a concurrent starburst activity. We developed a spectral energy distribution (SED) fitting technique to derive simultaneously the physical properties of active galaxies and coexisting starbursts making the best use of Spitzer and Herschel IR observations. We apply the SED fitting procedure to a large sample of extragalactic sources representing the HerMES (Herschel/Multi-tiered Extragalactic Survey) population with IRS spectra with a plethora of multi-wavelength data in order to study the impact of a possible presence of an AGN on the host galaxy's properties. We analyze the star formation rate (SFR) in conncetion to the presence of an AGN and compared the properties of the hot (AGN) and cold (starburst) dust component. Our findings are consistent with no evidence for the presence of an AGN affecting the star formation processes of the host galaxies.

APA, Harvard, Vancouver, ISO, and other styles

13

Krishnan, Charutha, Omar Almaini, Nina A. Hatch, Aaron Wilkinson, David T. Maltby, Christopher J. Conselice, Dale Kocevski, Hyewon Suh, and Vivienne Wild. "The clustering of X-ray AGN at 0.5 < z < 4.5: host galaxies dictate dark matter halo mass." Monthly Notices of the Royal Astronomical Society 494, no. 2 (March 27, 2020): 1693–704. http://dx.doi.org/10.1093/mnras/staa815.

Full text

Abstract:

ABSTRACT We present evidence that active galactic nuclei (AGN) do not reside in ‘special’ environments, but instead show large-scale clustering determined by the properties of their host galaxies. Our study is based on an angular cross-correlation analysis applied to X-ray selected AGN in the COSMOS and UDS fields, spanning redshifts from $z$ ∼ 4.5 to $z$ ∼ 0.5. Consistent with previous studies, we find that AGN at all epochs are on average hosted by galaxies in dark matter haloes of 1012–1013 M⊙, intermediate between star-forming and passive galaxies. We find, however, that the same clustering signal can be produced by inactive (i.e. non-AGN) galaxies closely matched to the AGN in spectral class, stellar mass, and redshift. We therefore argue that the inferred bias for AGN lies in between the star-forming and passive galaxy populations because AGN host galaxies are comprised of a mixture of the two populations. Although AGN hosted by higher mass galaxies are more clustered than lower mass galaxies, this stellar mass dependence disappears when passive host galaxies are removed. The strength of clustering is also largely independent of AGN X-ray luminosity. We conclude that the most important property that determines the clustering in a given AGN population is the fraction of passive host galaxies. We also infer that AGN luminosity is likely not driven by environmental triggering, and further hypothesize that AGN may be a stochastic phenomenon without a strong dependence on environment.

APA, Harvard, Vancouver, ISO, and other styles

14

Hicks, Erin K. S., Francisco Müller-Sánchez, Matthew A. Malkan, and Po-Chieh Yu. "The Keck OSIRIS Nearby AGN (KONA) Survey: AGN Fueling and Feedback." Proceedings of the International Astronomical Union 11, S319 (August 2015): 59. http://dx.doi.org/10.1017/s1743921315010893.

Full text

Abstract:

In an effort to better constrain the relevant physical processes dictating the co-evolution of supermassive black holes and the galaxies in which they reside we turn to local Seyfert AGN. It is only with these local AGN that we can reach the spatial resolution needed to adequately characterize the inflow and outflow mechanisms thought to be the driving forces in establishing the relationship between black holes and their host galaxies at higher redshift. We present the first results from the KONA (Keck OSIRIS Nearby AGN) survey, which takes advantage of the integral field unit OSIRIS plus laser and natural guide star adaptive optics to probe down to scales of 5-30 parsecs in a sample of 40 local Seyfert galaxies. With these K-band data we measure the two-dimensional distribution and kinematics of the nuclear stars, molecular gas, and ionized gas within the central few hundred parsecs.

APA, Harvard, Vancouver, ISO, and other styles

15

Symeonidis, M., and M. J. Page. "AGN and star formation across cosmic time." Monthly Notices of the Royal Astronomical Society 503, no. 3 (March 3, 2021): 3992–4007. http://dx.doi.org/10.1093/mnras/stab598.

Full text

Abstract:

ABSTRACT We investigate the balance of power between stars and AGN across cosmic history, based on the comparison between the infrared (IR) galaxy luminosity function (LF) and the IR AGN LF. The former corresponds to emission from dust heated by stars and AGN, whereas the latter includes emission from AGN-heated dust only. We find that at all redshifts (at least up to z ∼ 2.5), the high-luminosity tails of the two LFs converge, indicating that the most IR-luminous galaxies are AGN-powered. Our results shed light to the decades-old conundrum regarding the flatter high-luminosity slope seen in the IR galaxy LF compared to that in the UV and optical. We attribute this difference to the increasing fraction of AGN-dominated galaxies with increasing total IR luminosity (LIR). We partition the LIR−z parameter space into a star formation-dominated and an AGN-dominated region, finding that the most luminous galaxies at all epochs lie in the AGN-dominated region. This sets a potential ‘limit’ to attainable star formation rates, casting doubt on the abundance of ‘extreme starbursts’: if AGN did not exist, LIR > 1013 L⊙ galaxies would be significantly rarer than they currently are in our observable Universe. We also find that AGN affect the average dust temperatures (Tdust) of galaxies and hence the shape of the well-known LIR−Tdust relation. We propose that the reason why local ULIRGs are hotter than their high-redshift counterparts is because of a higher fraction of AGN-dominated galaxies amongst the former group.

APA, Harvard, Vancouver, ISO, and other styles

16

Vergani, D., B. Garilli, M. Polletta, P. Franzetti, M. Scodeggio, G. Zamorani, C. P. Haines, et al. "The VIMOS Public Extragalactic Redshift Survey (VIPERS)." Astronomy & Astrophysics 620 (December 2018): A193. http://dx.doi.org/10.1051/0004-6361/201732495.

Full text

Abstract:

Aims. We analyse the properties of the host galaxies of a [NeV]-selected sample to investigate whether and how they are affected by the AGN. Methods. We have selected a sample of galaxies at 0.62 < z < 1.2 from the VIMOS Public Extragalactic Redshift Survey (VIPERS) and divided it in blue cloud galaxies, red passive galaxies and green valley galaxies using the NUVrK diagram. Within each category, galaxies with AGN activity were identified based on the detection of the high-ionisation [NeV]λ3426 emission line. For each galaxy we derived several properties (stellar age and mass, the (r−K) colour, the [OII] luminosity) and compared them between active and inactive galaxies matched in stellar mass and redshift. Results. We find statistically significant differences in the properties between active and inactive galaxies. These differences imply that the AGN is more often found in galaxies with younger stellar populations and more recent star-forming activity than their parent samples. Interestingly, the AGN identified through the [NeV]λ3426 emission line is not commonly found by traditional AGN-selection techniques based on shallow X-ray data, mid-IR colours, and classical line diagnostic diagrams, and might thus reveal a specific evolutionary phase. The spectral analysis reveals a sub-set of AGN within the blue cloud that has spectral signatures implying a sudden suppression of star formation activity similar to post-starburst galaxies. Conclusion. Using the rich dataset of the large VIPERS sample we identify a novel class of active post-starburst galaxies that would be missed by traditional selection techniques. These galaxies belong to the blue cloud, but their star-formation activity has been recently suppressed, possibly by the AGN identified through the presence of the [NeV]λ3426 emission line in their spectra. Our results support the idea that AGN feedback may be responsible for halting star-formation in active blue galaxies and for their transition into the red sequence, at least in the 0.6–1.2 redshift range and for stellar masses greater than 5 × 1010 ℳ⊙. Our results are based on a complete spectroscopic sample and limited by the [NeV] observability, and the AGN can be variable and with a relatively short duty cycle. Considering this, AGN feedback that makes blue galaxies quickly transition to the red sequence may be even more common than previously believed.

APA, Harvard, Vancouver, ISO, and other styles

17

Man, Zhong-yi, Ying-jie Peng, Xu Kong, Ke-xin Guo, Cheng-peng Zhang, and Jing Dou. "The dependence of AGN activity on environment in SDSS." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 20, 2019): 89–98. http://dx.doi.org/10.1093/mnras/stz1706.

Full text

Abstract:

ABSTRACT Environment is one of the key external drivers of the galaxies, while active galactic nucleus (AGN) is one of the key internal drivers. Both of them play fundamental roles in regulating the formation and evolution of galaxies. We explore the interrelationship between environment and AGN in SDSS. At a given stellar mass, the specific star formation rate distribution of the AGN host galaxies remains unchanged with overdensity, with the peak of the distribution around the Green Valley. We show that, at a given stellar mass, the AGN fraction that has been commonly used in previous studies (defined as the number of AGNs relative to all galaxies including passive and star forming ones) does decrease with increasing overdensity for satellites. This is largely due to the fact that the fraction of passive galaxies strongly depends on environment. In order to investigate the intrinsic correlation between AGN and environment, especially under the assumption that AGN feedback is responsible for star formation quenching, the AGN fraction should be defined as the number of AGNs relative to the star-forming galaxies only. With the new definition, we find little dependence of AGN fraction on overdensity, central/satellite, and group halo mass. There is only marginal evidence that AGN may prefer denser regions, which is possibly due to more frequent interaction of galaxies or higher merger rate in groups. Our results support the scenario that internal secular evolution is the predominant mechanism of triggering AGN activity, while external environment related processes only play a minor role.

APA, Harvard, Vancouver, ISO, and other styles

18

Juneau, Stéphanie. "AGN Absorption Linked to Host Galaxies." Proceedings of the International Astronomical Union 9, S304 (October 2013): 319–22. http://dx.doi.org/10.1017/s1743921314004165.

Full text

Abstract:

AbstractMultiwavelength identification of AGN is crucial not only to obtain a more complete census, but also to learn about the physical state of the nuclear activity (obscuration, efficiency, etc.). A panchromatic strategy plays an especially important role when the host galaxies are star-forming. Selecting far-Infrared galaxies at 0.3<z<1, and using AGN tracers in the X-ray, optical spectra, mid-infrared, and radio regimes, we found a twice higher AGN fraction than previous studies, thanks to the combined AGN identification methods and in particular the recent Mass-Excitation (MEx) diagnostic diagram. We furthermore find an intriguing relation between AGN X-ray absorption and the specific star formation rate (sSFR) of the host galaxies, indicating a physical link between X-ray absorption and either the gas fraction or the gas geometry in the hosts. These findings have implications for our current understanding of both the AGN unification model and the nature of the black hole-galaxy connection.

APA, Harvard, Vancouver, ISO, and other styles

19

Amiri, Amirnezam. "Role of environment on AGN activity." Proceedings of the International Astronomical Union 15, S356 (October 2019): 171. http://dx.doi.org/10.1017/s1743921320002835.

Full text

Abstract:

AbstractMotivated by the apparently conflicting results reported in the literature on the effect of environment on nuclear activity, we have carried out a new analysis by comparing the fraction of galaxies hosting active galactic nuclei (AGNs) in the most overdense regions (rich galaxy clusters) and the most underdense ones (voids) in the local universe. Exploiting the classical BPT diagnostics, we have extracted volume limited samples of star forming and AGN galaxies. We find that, at variance with star-forming galaxies, AGN galaxies have similar distributions of specific star formation rates and of galactic ages (as indicated by the Dn4000 parameter) both in clusters and in voids. In both environments galaxies hosting AGNs are generally old, with low star formation activity. The AGN fraction increases faster with stellar mass in clusters than in voids, especially above 1010.2 M⊙. Our results indicate that, in the local universe, the nuclear activity correlates with stellar mass and galaxy morphology and is weakly, if at all, affected by the local galaxy density.

APA, Harvard, Vancouver, ISO, and other styles

20

Tarchi, Andrea. "AGN and Megamasers." Proceedings of the International Astronomical Union 8, S287 (January 2012): 323–32. http://dx.doi.org/10.1017/s1743921312007259.

Full text

Abstract:

AbstractLuminous extragalactic masers are traditionally referred to as the ‘megamasers’. Those produced by water molecules are associated with accretion disks, radio jets, or outflows in the nuclear regions of active galactic nuclei (AGN). The majority of OH maser sources are instead driven by intense star formation in ultra-luminous infrared galaxies, although in a few cases the OH maser emission traces rotating (toroidal or disk) structures around the nuclear engines of AGN. Thus, detailed maser studies provide a fundamental contribution to our knowledge of the main nuclear components of AGN, constitute unique tools to measure geometric distances of host galaxies, and have a great impact on probing the, so far, paradigmatic Unified Model of AGN.

APA, Harvard, Vancouver, ISO, and other styles

21

Benson, Andrew J. "AGN and the necessity of feedback." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1828 (January 12, 2005): 695–704. http://dx.doi.org/10.1098/rsta.2004.1519.

Full text

Abstract:

There is now good observational evidence that some type of feedback process must operate within galaxies. Such a process has long been thought to exist on the basis of theoretical studies of galaxy formation. This feedback is responsible for regulating the rate of star formation and thereby preventing the formation of an overabundance of low–mass galaxies. There is gathering evidence that this feedback process must somehow involve the supermassive black holes thought to dwell in the centres of galaxies.

APA, Harvard, Vancouver, ISO, and other styles

22

Wang, Tao, D. Elbaz, D. M. Alexander, Y. Q. Xue, J. M. Gabor, S. Juneau, C. Schreiber, et al. "AGN-host connection at 0.5 < z < 2.5: A rapid evolution of AGN fraction in red galaxies during the last 10 Gyr." Astronomy & Astrophysics 601 (May 2017): A63. http://dx.doi.org/10.1051/0004-6361/201526645.

Full text

Abstract:

We explore the dependence of the incidence of moderate-luminosity (L0.5−8 keV = 1041.9−43.7 erg s-1) active galactic nuclei (AGNs) and the distribution of their accretion rates on host color at 0.5 <z < 2.5. Based on the deepest X-ray and UV-to-far-infrared data in the two The Great Observatories Origins Deep Survey (GOODS) fields, we identify 221 AGNs within a mass-complete parent galaxy sample down to M∗ > 1010 M⊙. We use extinction-corrected rest-frame U−V colors to divide both AGN hosts and non-AGN galaxies into red sequence (red), green valley (green), and blue cloud (blue) populations. We find that the fraction of galaxies hosting an AGN at fixed X-ray luminosity increases with stellar mass and redshift for all the three galaxy populations, independent of their colors. However, both the AGN fraction at fixed stellar mass and its evolution with redshift are clearly dependent on host colors. Most notably, red galaxies have the lowest AGN fraction (~5%) at z ~ 1 yet with most rapid evolution with redshift, increasing by a factor of ~5 (24%) at z ~ 2. Green galaxies exhibit the highest AGN fraction across all redshifts, which is most pronounced at z ~ 2 with more than half of them hosting an AGN at M∗ > 1010.6 M⊙. Together with the high AGN fraction in red galaxies at z ~ 2, this indicates that (X-ray) AGNs could be important in both transforming (quenching) star-forming galaxies into quiescent ones and subsequently maintaining their quiescence at high redshift. Furthermore, consistent with previous studies at lower redshifts, we show that the probability of hosting an AGN for the total galaxy population can be characterized by a universal Eddington ratio (as approximated by LX/M∗) distribution (p(λEdd) ~ λEdd-0.4), which is independent on host mass. Yet consistent with their different AGN fractions, galaxies with different colors appear to also have different p(λEdd) with red galaxies exhibiting more rapid redshift evolution compared with that for green and blue galaxies. Evidence for a steeper power-law distribution of p(λEdd) in red galaxies (p(λEdd) ~ λEdd-0.6) is also presented, though larger samples are needed to confirm. These results suggest that the AGN accretion or the growth of supermassive black holes is related to their host properties, and may also influence their hosts in a different mode dependent on the host color.

APA, Harvard, Vancouver, ISO, and other styles

23

Amirkhanian, A. S., A. del Olmo, A. G. Egikian, H. Tiersch, D. Stoll, and J. Perea. "AGN populations in compact groups of galaxies." Proceedings of the International Astronomical Union 9, S304 (October 2013): 337–38. http://dx.doi.org/10.1017/s1743921314004219.

Full text

Abstract:

AbstractCompact groups of galaxies (CGG) have revealed some interesting problems from their origin and lifetime to the evolution of their members in such dense configurations. Some authors suppose that CGG probably are the best location for AGNs in the local Universe. According to our preliminary data about 7–10% of member galaxies in Shahbazian compact groups (SHCGs) are emission-line galaxies including the broad-line AGN and the narrow emission-line galaxies. Shahbazian 355/4 is a classical Seyfert 1 galaxy at the same redshift as host group. Moreover Shahbazian 278/4 is also a broad-line AGN in an early-type galaxy. This is the first emission-line object in SHCGs. Meanwhile there is no Seyfert 1 galaxy among the spectroscopically investigated galaxies in the South compact groups, although more than 70% of the member galaxies in these groups probably have an active nucleus. The UZC- compact groups have an excess of Seyfert 2s (but not Seyfert 1s!). Further observational studies are necessary to understand such and many other questions related to the puzzle of CGG.

APA, Harvard, Vancouver, ISO, and other styles

24

Williams, Wendy L., Huub Röttgering, and Reinout van Weeren. "LOFAR and Radio Loud AGN." Proceedings of the International Astronomical Union 9, S304 (October 2013): 86–92. http://dx.doi.org/10.1017/s1743921314003408.

Full text

Abstract:

AbstractAt very low frequencies, the new pan-European radio telescope, LOFAR, is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. LOFAR will deeply survey the northern sky from ~ 10 up to 240 MHz. In this contribution we briefly describe some of the capabilities of LOFAR and the surveys planned to study fundamental issues related to the formation and evolution of galaxies and clusters of galaxies. We describe some of the challenges of low frequency observations with LOFAR and our progress in overcoming them. Further, we present some recent results from the ongoing imaging commissioning efforts. In the second part we discuss our studies of Low Excitation and High Excitation Radio Galaxies in the Boötes field and how LOFAR Surveys will help in studying their evolution.

APA, Harvard, Vancouver, ISO, and other styles

25

Manzano-King, Christina M., Gabriela Canalizo, and Laura V. Sales. "AGN-Driven Outflows in Dwarf Galaxies." Astrophysical Journal 884, no. 1 (October 11, 2019): 54. http://dx.doi.org/10.3847/1538-4357/ab4197.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Lutz, D., R. Genzel, E. Sturm, D. Tran, D. Rigopoulou, H. W. W. Spoon, and A. F. M. Moorwood. "Ultraluminous infrared galaxies: Starburst vs. AGN." Advances in Space Research 23, no. 5-6 (January 1999): 1061–64. http://dx.doi.org/10.1016/s0273-1177(99)00248-3.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Filho, Mercedes, Peter Barthel, and Luis Ho. "The AGN Population in Nearby Galaxies." Journal of Physics: Conference Series 54 (December 1, 2006): 342–48. http://dx.doi.org/10.1088/1742-6596/54/1/054.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Dashyan, Gohar, Ena Choi, Rachel S. Somerville, Thorsten Naab, Amanda C. N. Quirk, Michaela Hirschmann, and Jeremiah P. Ostriker. "AGN-driven quenching of satellite galaxies." Monthly Notices of the Royal Astronomical Society 487, no. 4 (June 28, 2019): 5889–901. http://dx.doi.org/10.1093/mnras/stz1697.

Full text

Abstract:

ABSTRACT We explore the effect of active galactic nucleus (AGN) feedback from central galaxies on their satellites by comparing two sets of cosmological zoom-in runs of 27 haloes with masses ranging from 1012 to 1013.4$\rm {M}_{\odot}$ at z = 0, with (wAGN) and without (noAGN) AGN feedback. Both simulations include stellar feedback from multiple processes, including powerful winds from supernovae, stellar winds from young massive stars, AGB stars, radiative heating within Strömgren spheres and photoelectric heating. Our wAGN model is identical to the noAGN model except that it also includes a model for black hole seeding and accretion, as well as AGN feedback via high-velocity broad absorption line winds and Compton/photoionization heating. We show that the inclusion of AGN feedback from the central galaxy significantly affects the star formation history and the gas content of the satellite galaxies. AGN feedback starts to affect the gas content and the star formation of the satellites as early as z = 2. The mean gas-rich fraction of satellites at z = 0 decreases from 15 per cent in the noAGN simulation to 5 per cent in the wAGN simulation. The difference between the two sets extends as far out as five times the virial radius of the central galaxy at z = 1. We investigate the quenching mechanism by studying the physical conditions in the surroundings of pairs of satellites matched across the wAGN and noAGN simulations and find an increase in the temperature and relative velocity of the intergalactic gas.

APA, Harvard, Vancouver, ISO, and other styles

29

Best, P. N., C. R. Kaiser, T. M. Heckman, and G. Kauffmann. "AGN-controlled cooling in elliptical galaxies." Monthly Notices of the Royal Astronomical Society: Letters 368, no. 1 (May 1, 2006): L67—L71. http://dx.doi.org/10.1111/j.1745-3933.2006.00159.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Cervantes-Sodi, Bernardo, X. Hernandez, Changbom Park, and Yun-Young Choi. "THE GALACTIC SPIN OF AGN GALAXIES." Astrophysical Journal 735, no. 1 (June 14, 2011): L25. http://dx.doi.org/10.1088/2041-8205/735/1/l25.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Karouzos, Marios, Myungshin Im, Markos Trichas, Tomogotsu Goto, Matthew Malkan, Angel Ruiz, Yiseul Jeon, et al. "GALAXIES ON DIET: FEEDBACK SIGNATURES IN RADIO-AGN HOST GALAXIES." Publications of The Korean Astronomical Society 32, no. 1 (March 31, 2017): 201–3. http://dx.doi.org/10.5303/pkas.2017.32.1.201.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Kollatschny, W., and A. Goerdt. "1.8. Evolutionary population synthesis of AGN host galaxy spectra." Symposium - International Astronomical Union 184 (1998): 31–32. http://dx.doi.org/10.1017/s007418090008387x.

Full text

Abstract:

We compute the stellar population of nearby Seyfert host galaxies and non-active galaxies using population and evolutionary synthesis methods. We find indication of enhanced star formation rates in the host-galaxies of AGN - especially in the circumnuclear regions of Seyfert 2 galaxies.

APA, Harvard, Vancouver, ISO, and other styles

33

Florez, Jonathan, Shardha Jogee, Sydney Sherman, Matthew L. Stevans, Steven L. Finkelstein, Casey Papovich, Lalitwadee Kawinwanichakij, et al. "Exploring AGN and star formation activity of massive galaxies at cosmic noon." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 29, 2020): 3273–96. http://dx.doi.org/10.1093/mnras/staa2200.

Full text

Abstract:

ABSTRACT We investigate the relation between active galactic nucleus (AGN) and star formation (SF) activity at 0.5 < z < 3 by analysing 898 galaxies with X-ray luminous AGNs (LX > 1044 erg s−1) and a large comparison sample of ∼320 000 galaxies without X-ray luminous AGNs. Our samples are selected from a large (11.8 deg2) area in Stripe 82 that has multiwavelength (X-ray to far-IR) data. The enormous comoving volume (∼0.3 Gpc3) at 0.5 < z < 3 minimizes the effects of cosmic variance and captures a large number of massive galaxies (∼30 000 galaxies with M* > 1011 M⊙) and X-ray luminous AGNs. While many galaxy studies discard AGN hosts, we fit the SED of galaxies with and without X-ray luminous AGNs with Code Investigating GALaxy Emission and include AGN emission templates. We find that without this inclusion, stellar masses and star formation rates (SFRs) in AGN host galaxies can be overestimated, on average, by factors of up to ∼5 and ∼10, respectively. The average SFR of galaxies with X-ray luminous AGNs is higher by a factor of ∼3–10 compared to galaxies without X-ray luminous AGNs at fixed stellar mass and redshift, suggesting that high SFRs and high AGN X-ray luminosities may be fuelled by common mechanisms. The vast majority ($\gt 95 {{\ \rm per\ cent}}$) of galaxies with X-ray luminous AGNs at z = 0.5−3 do not show quenched SF: this suggests that if AGN feedback quenches SF, the associated quenching process takes a significant time to act and the quenched phase sets in after the highly luminous phases of AGN activity.

APA, Harvard, Vancouver, ISO, and other styles

34

Drouart, Guillaume, Carlos De Breuck, Joël Vernet, Brigitte Rocca Volmerange, and Nicholas Seymour. "Revealing AGN, young and old stellar populations in HzRGs with PEGASE.3." Proceedings of the International Astronomical Union 9, S304 (October 2013): 307–10. http://dx.doi.org/10.1017/s174392131400413x.

Full text

Abstract:

AbstractThe HeRGÉ (Herschel Radio Galaxy Evolution) project consists of a sample of 70 radio galaxies in the range 1 < z < 5.2. They benefit from continuous coverage from 3 to 870μm with Spitzer, Herschel and sub-mm ground-based instruments (SCUBA, LABOCA). As a calorimeter, IR is an excellent proxy to estimate the contribution of both AGN and starburst, making of radio galaxies perfect candidates to provide new insights into the relationship between AGN and their host galaxies. The IR SED fitting with empirical templates reveals that radio galaxies are luminous and that their black holes and their host galaxies are not growing simultaneously. Extending the SED to optical/near-IR on a subsample of 12 radio galaxies spanning 1 < z < 4 reveal the necessity of three components to reproduce the observations. Making use of the evolutionary code PEGASE.3 and an AGN torus model, we are able to estimate parameters from the AGN torus, the evolved stellar population and the starburst (SB). They reveal that radio galaxies are massive, evolved, forming the bulk of their mass at very high redshift in a short timescale, but experience episodic, strong SB events, often associated with an AGN activity.

APA, Harvard, Vancouver, ISO, and other styles

35

Williams, Wendy L., and Huub J. A. Röttgering. "LOFAR and Radio-Loud AGN." Proceedings of the International Astronomical Union 10, S309 (July 2014): 137–40. http://dx.doi.org/10.1017/s1743921314009478.

Full text

Abstract:

AbstractAt very low frequencies, the new pan-European radio telescope, LOFAR, is opening the last unexplored window of the electromagnetic spectrum for astrophysical studies. Operating at frequencies from 15 to 240 MHz, its superb sensitivity, high angular resolution, large field of view and flexible spectroscopic capabilities represent a dramatic improvement over previous facilities at these wavelengths. LOFAR will carry out a broad range of fundamental astrophysical studies in a number of key science topics including the formation and evolution of clusters, galaxies and black holes. In this contribution we describe some of the capabilities of LOFAR and present some recent results from the ongoing imaging efforts. We also discuss the impact of LOFAR on our studies of radio-loud AGN. Our recent study of the evolution of radio-loud AGN as a function of host stellar mass shows a clear increase in the fraction of lower mass galaxies which host radio-loud AGN at 1 < z < 2 while the fraction for higher mass galaxies remains the same. This shows that the upturn in the radio luminosity function is driven by increasing AGN activity among low mass galaxies at higher redshifts. New LOFAR observations will allow us to build statistically large samples at high redshifts to constrain this evolution for the different accretion modes of AGN.

APA, Harvard, Vancouver, ISO, and other styles

36

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

37

Kauffmann, Guinevere, and Timothy M. Heckman. "The formation of bulges and black holes: lessons from a census of active galaxies in the SDSS." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1828 (January 12, 2005): 621–43. http://dx.doi.org/10.1098/rsta.2004.1516.

Full text

Abstract:

We examine the relationship between galaxies, supermassive black holes and AGN using a sample of 23 000 narrow–emission–line (‘type 2’) active galactic nuclei (AGN) drawn from a sample of 123 000 galaxies from the Sloan Digital Sky Survey. We have studied how AGN host properties compare with those of normal galaxies and how they depend on the luminosity of the active nucleus. We find that AGN reside in massive galaxies and have distributions of sizes and concentrations that are similar to those of the early–type galaxies in our sample. The host galaxies of low–luminosity AGN have stellar populations similar to normal early types. The hosts of highluminosity AGN have much younger mean stellar ages, and a significant fraction have experienced recent starbursts. High–luminosity AGN are also found in lower–density environments. We then use the stellar velocity dispersions of the AGN hosts to estimate black hole masses and their [OIII]λ5007 emission–line luminosities to estimate black hole accretion rates.We find that the volume averaged ratio of star formation to black hole accretion is ∼1000 for the bulge–dominated galaxies in our sample. This is remarkably similar to the observed ratio of stellar mass to black hole mass in nearby bulges. Most of the present–day black hole growth is occurring in black holes with masses less than 3 × 10 7 M ⊙. Our estimated accretion rates imply that low–mass black holes are growing on a time–scale that is comparable with the age of the Universe. Around 50% this growth takes place in AGN that are radiating within a factor of five of the Eddington luminosity. Such systems are rare, making up only 0.2% of the lowmass black hole population at the present day. The remaining growth occurs in lower luminosity AGN. The growth time–scale increases by more than an order of magnitude for the most massive black holes in our sample. We conclude that the evolution of the AGN luminosity function documented in recent optical and X–ray surveys is driven by a decrease in the characteristic mass scale of actively accreting black holes.

APA, Harvard, Vancouver, ISO, and other styles

38

Izotov, Yuri I. "Broad line emission in dwarf galaxies: the first detection of low-metallicity AGN." Proceedings of the International Astronomical Union 4, S255 (June 2008): 370–74. http://dx.doi.org/10.1017/s174392130802509x.

Full text

Abstract:

AbstractObservations of AGN show that they generally possess a high metallicity, varying from solar to supersolar metallicities. This is the case since AGN are usually found in massive, bulge-dominated galaxies that have converted most of their gas into stars by the present epoch. Since AGN metallicity is strongly correlated with stellar mass, low-metallicity AGN are expected to be in low-mass dwarf galaxies. However, until now, searches in low-mass galaxies have only turned up AGN with metallicities around half that of typical AGN, i.e. with solar or slightly subsolar values. We report the discovery of four low-metallicity dwarf galaxies in the Data Release 6 of the Sloan Digital Sky survey, with 12 + log O/H in the range 7.4–8.0, and that appear to harbor an AGN. In the course of a long-range program to search for extremely metal-deficient emission-line dwarf galaxies, we have come across four galaxies with very unusual spectra: the strong permitted emission lines, mainly the Hα line, show very prominent broad components, with full widths at zero intensity corresponding to velocities varying between 2200 and 3500 km s−1, and extraordinarily large broad Hα luminosities, varying from 3×1041 to 2×1042 erg s−1. The Balmer lines show a very steep decrement, suggesting collisional excitation and that the broad emission comes from very dense gas (Ne ≫ 104 cm−3). Only the presence of an accretion disk around an intermediate-mass black hole in the dwarf galaxies appears to account for these properties.

APA, Harvard, Vancouver, ISO, and other styles

39

Gioia, Isabella M., T. Maccacaro, S. L. Morris, R. Schild, J. T. Stocke, and A. Wolter. "X-ray Selected AGN from the Extended Medium Sensitivity Survey." Symposium - International Astronomical Union 134 (1989): 203–4. http://dx.doi.org/10.1017/s0074180900140847.

Full text

Abstract:

The spectroscopic identification of the Extended Medium Sensitivity Survey (EMSS) sources now provides ∼350 X-ray selected QSOs and Seyfert galaxies (AGN in our working definition) and 30 BL Lac objects. Almost all of the AGN are spectroscopically similar to AGN found by other means but a few resemble normal galaxies so closely that they would not be identified as AGN easily by any other method.

APA, Harvard, Vancouver, ISO, and other styles

40

Das, M., S. S. McGaugh, N. Kantharia, and S. N. Vogel. "Radio Observations of AGN in Low Surface Brightness Galaxies." Proceedings of the International Astronomical Union 3, S244 (June 2007): 352–53. http://dx.doi.org/10.1017/s1743921307014238.

Full text

Abstract:

AbstractWe present preliminary results of a study of the low frequency radio continuum emission from the nuclei of Giant Low Surface Brightness (LSB) galaxies. We have mapped the emission and searched for extended features such as radio lobes/jets associated with AGN activity. LSB galaxies are poor in star formation and generally less evolved compared to nearby bright spirals. This paper presents low frequency observations of 3 galaxies; PGC 045080 at 1.4 GHz, 610 MHz, 325MHz, UGC 1922 at 610 MHz and UGC 6614 at 610 MHz. The observations were done with the GMRT. Radio cores as well as extended structures were detected and mapped in all three galaxies; the extended emission may be assocated with jets/lobes associated with AGN activity. Our results indicate that although these galaxies are optically dim, their nuclei can host AGN that are bright in the radio domain.

APA, Harvard, Vancouver, ISO, and other styles

41

Joh, Kazuma, Tohru Nagao, Keiichi Wada, Koki Terao, and Takuji Yamashita. "Do gas clouds in narrow-line regions of Seyfert galaxies come from their nuclei?" Publications of the Astronomical Society of Japan 73, no. 4 (June 30, 2021): 1152–65. http://dx.doi.org/10.1093/pasj/psab065.

Full text

Abstract:

Abstract The narrow-line region (NLR) consists of gas clouds ionized by the strong radiation from the active galactic nucleus (AGN), distributed in the spatial scale of AGN host galaxies. The strong emission lines from the NLR are useful to diagnose physical and chemical properties of the interstellar medium in AGN host galaxies. However, the origin of the NLR is unclear; the gas clouds in NLRs may originally be in the host and photoionized by the AGN radiation, or they may be transferred from the nucleus with AGN-driven outflows. In order to study the origin of the NLR, we systematically investigate the gas density and velocity dispersion of NLR gas clouds using a large spectroscopic data set taken from the Sloan Digital Sky Survey. The [S ii] emission-line flux ratio and [O iii] velocity width of 9571 type-2 Seyfert galaxies and 110041 star-forming galaxies suggest that the gas density and velocity dispersion of NLR clouds in Seyfert galaxies (ne ≈ 194 cm−3 and $\sigma _{\rm [O\,{\small III}]} \approx 147\:$km s−1) are systematically larger than those of clouds in H ii regions of star-forming galaxies (ne ≈ 29 cm−3 and $\sigma _{\rm [O\,{\small III}]} \approx 58\:$km s−1). Interestingly, the electron density and velocity dispersion of NLR gas clouds are larger for Seyfert galaxies with a higher [O iii]/Hβ flux ratio, i.e., with a more active AGN. We also investigate the spatially-resolved kinematics of ionized gas clouds using the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey data for 90 Seyfert galaxies and 801 star-forming galaxies. We find that the velocity dispersion of NLR gas clouds in Seyfert galaxies is larger than that in star-forming galaxies at a fixed stellar mass, at both central and off-central regions. These results suggest that gas clouds in NLRs come from the nucleus, probably through AGN outflows.

APA, Harvard, Vancouver, ISO, and other styles

42

Mickaelian, A. M., H. V. Abrahamyan, G. S. Harutyunyan, and G. M. Paronyan. "Revised activity types for Markarian galaxies." Proceedings of the International Astronomical Union 9, S304 (October 2013): 41–42. http://dx.doi.org/10.1017/s1743921314003263.

Full text

Abstract:

AbstractThe sample of Markarian galaxies consists of 1515 UV-excess galaxies containing many active galaxies, both AGN and Starburst (SB). Several catalogs of Markarian galaxies have been published; however activity types are based on old spectroscopic data. The SDSS spectroscopy and some other recent spectral observations allow classify or re-classify many of Markarian galaxies, altogether we have retrieved and studied 779 SDSS and 300 other spectra. Out of 779 SDSS spectra, we have classified 533 HII, 31 Composites, 12 LINERs, 4 S2.0, 5 S1.9, 8 S1.8, 5 NLS1.5, 11 S1.5, 8 NLS1.2, 21 S1.2, 4 NLS1, 4 S1.0, 2 QSO, 11 AGN (without an exact class), 52 Em (HII or AGN), 65 Abs, and 3 Stars. On the other hand, the galaxies are being classified depending on the fact in which wavelength range they have been observed and studied. E.g. some Sy2 type galaxies turn to be Sy1 when classified in IR. Many hidden AGN (in X-ray and IR) appear to be normal galaxies in optical range. So for better understanding, IR spectra are necessary as well.

APA, Harvard, Vancouver, ISO, and other styles

43

Ineson, Judith, Judith Croston, Martin Hardcastle, Ralph Kraft, Daniel Evans, and Matt Jarvis. "The cluster environments of radio-loud AGN." Proceedings of the International Astronomical Union 10, S313 (September 2014): 299–300. http://dx.doi.org/10.1017/s1743921315002367.

Full text

Abstract:

AbstractRadio-loud AGN play an important rôle in galaxy evolution. We need to understand their properties, and the processes that affect their behaviour in order to model galaxy formation and development. We here present preliminary results of an investigation into the cluster environments of radio galaxies. We have found evidence of a strong correlation between radio luminosity and environment richness for low excitation radio galaxies, and no evidence of evolution of the environment with redshift. Conversely, for high excitation radio galaxies, we found no correlation with environment richness, and tentative evidence of evolution of the cluster environment.

APA, Harvard, Vancouver, ISO, and other styles

44

Xu, Dawei, and S. Komossa. "Low-Mass AGN at High Accretion Rates." Proceedings of the International Astronomical Union 5, S267 (August 2009): 338. http://dx.doi.org/10.1017/s174392131000668x.

Full text

Abstract:

AbstractGalaxies with low-mass black holes and high accretion rates, i.e., narrow-line Seyfert 1 (NLS1) galaxies, are important objects when addressing the issues of black hole growth and evolution, and of feeding and feedback. We have studied a sample of such objects, and find (1) that the locus of NLS1 galaxies on the MBH–σ plane appears to follow the relation of non-active galaxies after removing objects obviously dominated by outflows, (2) the presence of “blue outliers” that hint at extreme outflows as predicted by recent merger models, and (3) more subtle evidence for winds/outflows across the whole NLS1 population.

APA, Harvard, Vancouver, ISO, and other styles

45

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

46

Wamsteker, W., and R. Vio. "Multiwavelength Experiments on AGN: Reverberation Experiments." Symposium - International Astronomical Union 159 (1994): 159–62. http://dx.doi.org/10.1017/s0074180900174959.

Full text

Abstract:

The nature of the successful reverberation campaigns on variable active galaxies is summarized. A general summary of the completed campaigns is given. A discussion of the results of the first order (CCF) analysis is given and some comments are made on the directions needed to obtain more physcally meaningful solutions to the inversion problem presented by such observations of the sources of activity in the centers of active galaxies

APA, Harvard, Vancouver, ISO, and other styles

47

Yi, Sukyoung K. "GALEX Constraints on AGN Feedback in Early-Type Galaxies." Proceedings of the International Astronomical Union 5, S267 (August 2009): 442–44. http://dx.doi.org/10.1017/s1743921310006976.

Full text

Abstract:

AbstractThe absence of vigorous star formation in early-type galaxies is a mystery because early-type galaxies do have a copious supply of cold gas. Various heating mechanisms have been put forward to explain this, and AGN feedback is one of the most widely suspected culprits. The GALEX UV telescope detects even a small amount of star formation and allows an estimate of the current and recent star formation. We find that star formation is still common in early-type galaxies with low velocity dispersion where the black hole mass is believed to be small. We compare the star-formation rates of the galaxies with predictions from various semi-analytic models with different feedback prescriptions. We find that the passive behavior of central galaxies in groups and clusters is reproduced by semi-analytic models with AGN feedback. However, the same prescriptions causes satellite (i.e., non-central) galaxies to be quenched as well, much more than observed by GALEX, leading to a “satellite over-quenching problem.”

APA, Harvard, Vancouver, ISO, and other styles

48

Jones, Christine, William Forman, Akos Bogdan, Scott Randall, Ralph Kraft, and Eugene Churazov. "Hot Gas and AGN Feedback in Galaxies and Nearby Groups." Proceedings of the International Astronomical Union 8, S295 (August 2012): 257–60. http://dx.doi.org/10.1017/s1743921313004961.

Full text

Abstract:

AbstractMassive galaxies harbor a supermassive black hole at their centers. At high redshifts, these galaxies experienced a very active quasar phase, when, as their black holes grew by accretion, they produced enormous amounts of energy. At the present epoch, these black holes still undergo occasional outbursts, although the mode of their energy release is primarily mechanical rather than radiative. The energy from these outbursts can reheat the cooling gas in the galaxy cores and maintain the red and dead nature of the early-type galaxies. These outbursts also can have dramatic effects on the galaxy-scale hot coronae found in the more massive galaxies. We describe research in three areas related to the hot gas around galaxies and their supermassive black holes. First we present examples of galaxies with AGN outbursts that have been studied in detail. Second, we show that X-ray emitting low-luminosity AGN are present in 80% of the galaxies studied. Third, we discuss the first examples of extensive hot gas and dark matter halos in optically faint galaxies.

APA, Harvard, Vancouver, ISO, and other styles

49

De Breuck, Carlos, Wil van Breugel, Huub Röttgering, and Chris Carilli. "Radio AGN Surveys." International Astronomical Union Colloquium 184 (2002): 275–80. http://dx.doi.org/10.1017/s0252921100030827.

Full text

Abstract:

AbstractWe present a short overview of radio surveys for AGN, including the ‘complete’ flux limited surveys and ‘filtered’ surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z = 5.19) and the most luminous z <2 radio galaxy known.

APA, Harvard, Vancouver, ISO, and other styles

50

Singh, R., G. van de Ven, and K. Jahnke. "The nature of LINER galaxies: Ubiquitous hot old stars and rare accreting black holes." Proceedings of the International Astronomical Union 9, S304 (October 2013): 280–81. http://dx.doi.org/10.1017/s1743921314004074.

Full text

Abstract:

AbstractGalaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus or AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher AGN-luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN. Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN. For 48 galaxies with LINER-like emission we show, that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with gas present and with stars older than ~1 Gyr, unless a stronger radiation field from young hot stars or an AGN outshines them. This means, that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'AGN galaxies'

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