scholarly journals Radio Nuclei in Nearby Galaxies

1984 ◽  
Vol 110 ◽  
pp. 251-256
Author(s):  
E. Preuss
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Instrumental Performance ◽  
Nuclear Activity ◽  
Normal Galaxies ◽  
Nearby Galaxies ◽  
The Subject ◽  
5 Ghz ◽  
Work Done

This review is an attempt to summarize VLBI continuum observations at cm- and dm-wavelengths of active galactic nuclei at distances ≲ 100 Mpc (Ho = 50 km s−1 Mpc−1). ‘Nearby galaxies’, thus defined, are close enough for achieving the highest possible spatial resolution. Galaxies at these distances, however, typically do not show extreme and rare forms of nuclear activity such as powerful radio sources, the cores of which are relatively easy to map with VLBI, and which are therefore the subject of most of the VLBI work done so far (see e.g. Preuss, 1983). Nearby active galaxies show rather more ‘ordinary’ forms of nuclear activity; they include a few of the weaker classical ‘radio galaxies’, but most of them are Seyfert galaxies and mildly active ‘normal galaxies’. Their total radio emission is typically weak (P(5 GHz) ≲ 1031 erg s−1 Hz−1) and so are their compact radio nuclei (if any). The highest available sensitivity is therefore required for their study and the current instrumental performance is just becoming sufficient to tackle the strongest of them in the hope of obtaining maps.

scholarly journals Understanding the origin of radio outflows in Seyfert galaxies using radio polarimetry

2019 ◽  
Vol 15 (S356) ◽  
pp. 247-251
Author(s):  
Biny Sebastian ◽  
Preeti Kharb ◽  
Christopher P. O’ Dea ◽  
Jack F. Gallimore ◽  
Stefi A. Baum ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxy ◽  
Seyfert Galaxies ◽  
Starburst Galaxies ◽  
Galactic Magnetic Fields ◽  
5 Ghz

AbstractThe role of starburst winds versus active galactic nuclei (AGN) jets/winds in the formation of the kiloparsec scale radio emission seen in Seyferts is not yet well understood. In order to be able to disentangle the role of various components, we have observed a sample of Seyfert galaxies exhibiting kpc-scale radio emission suggesting outflows, along with a comparison sample of starburst galaxies, with the EVLA B-array in polarimetric mode at 1.4 GHz and 5 GHz. The Seyfert galaxy NGC 2639, shows highly polarized secondary radio lobes, not observed before, which are aligned perpendicular to the known pair of radio lobes. The additional pair of lobes represent an older epoch of emission. A multi-epoch multi-frequency study of the starburst-Seyfert composite galaxy NGC 3079, reveals that the jet together with the starburst superwind and the galactic magnetic fields might be responsible for the well-known 8-shaped radio lobes observed in this galaxy. We find that many of the Seyfert galaxies in our sample show bubble-shaped lobes, which are absent in the starburst galaxies that do not host an AGN.

scholarly journals Radio Emission from Low-Luminosity Active Galactic Nuclei

1998 ◽  
Vol 164 ◽  
pp. 205-206
Author(s):  
Schuyler D. Van Dyk ◽  
Luis C. Ho
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Physical Origin ◽  
Common Variety ◽  
Nearby Galaxies ◽  
Optical Evidence ◽  
Shed Light

AbstractMany nearby galaxies show optical evidence for low-luminosity AGNs that are far less luminous than classical Seyfert nuclei and QSOs. LINERs, the most common variety of such emission-line objects, comprise ~ 1/3 of nearby galaxies, and may serve as an important “missing link“ between normal and Seyfert galaxies. To shed light on the physical origin of LINERs, which remains controversial, we are conducting a high-resolution continuum survey of a representative sample of galaxies using the VLA to search for compact radio cores. We additionally discuss the dramatic radio variability in the LINER nucleus of M81.

scholarly journals SkyMapper colours of Seyfert galaxies and Changing-Look AGN

2020 ◽  
Vol 499 (1) ◽  
pp. 1005-1022
Author(s):  
Christian Wolf ◽  
Jacob Golding ◽  
Wei Jeat Hon ◽  
Christopher A Onken
Keyword(s):  
Active Galactic Nuclei ◽  
Power Law ◽  
Stellar Population ◽  
Broad Band ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Host Galaxy ◽  
Normal Galaxies ◽  
Mixing Sequences

ABSTRACT We study the utility of broad-band colours in the SkyMapper Southern Survey for selecting Seyfert galaxies at low luminosity. We find that the u − v index, built from the ultraviolet u and violet v filters, separates normal galaxies, starburst galaxies, and type-1 active galactic nuclei (AGNs). This u − v index is not sensitive to age or metallicity in a stellar population but is instead a quenching-and-bursting indicator in galaxies and detects power-law continua in type-1 AGNs. Using over 25 000 galaxies at z < 0.1 from 6dFGS, we find a selection cut based on u − v and central u band brightness that identifies type-1 AGNs. By eyeballing 6dFGS spectra we classify new Seyfert galaxies of type 1 to 1.8. Our sample includes eight known Changing-Look AGNs (CLAGNs), two of which show such strong variability that they move across the selection cut during the 5 yr of SkyMapper observations in DR3, along mixing sequences of nuclear and host galaxy light. We identify 46 CLAGN candidates in our sample, one of which has been reported as a Type IIn supernova. We show that this transient persists for at least 5 yr and marks a flare in a Seyfert-1 period of a new CLAGN.

scholarly journals A search for QSOs in the fields of nearby galaxies

1986 ◽  
Vol 119 ◽  
pp. 573-574
Author(s):  
A S Pocock ◽  
M V Penston ◽  
M Pettini ◽  
J C Blades
Keyword(s):  
High Resolution ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
High Resolution Spectroscopy ◽  
Nearby Galaxy ◽  
Physical Conditions ◽  
The Galaxy ◽  
External Galaxies ◽  
Nearby Galaxies ◽  
The Subject

The extent and physical conditions of diffuse gas in the outer regions of galaxies are currently the subject of considerable interest. A very sensitive way to probe the gas is by observing the absorption lines it produces in the spectra of background objects. However, a detailed investigation of the interstellar medium associated with external galaxies requires the availability, in the field of the galaxy under study, of several probes (QSOs, Active Galactic Nuclei, supernovae) which are: (a) sufficiently bright for high-resolution spectroscopy (B ≤ 17.5) and, (b) located over a range of projected distances from the galaxy, say from 10 to 200 kpc. As there are very few QSOs in the literature which meet these requirements, we have been carrying out a search of nearby galaxy fields for the specific purpose of finding a number of suitable background probes.

scholarly journals Optical Spectra of Radio-Loud and Radio-Quiet Active Galactic Nuclei

1982 ◽  
Vol 97 ◽  
pp. 369-371 ◽  
Author(s):  
Donald E. Osterbrock
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Radio Galaxies ◽  
Optical Spectra ◽  
Emission Lines ◽  
Radio Sources ◽  
Strong Emission ◽  
Normal Galaxies ◽  
Many Sources

Many radio galaxies have strong emission lines in their optical spectra. The fraction with such lines is much larger than in “normal” galaxies. Radio galaxies generally also have very bright nuclei; thus those with strong emission lines are similar in both respects to Seyfert galaxies. Hence radio and Seyfert galaxies are both generally considered to be similar physical objects: active galactic nuclei. Their observational properties show they are closely related to quasars (quasi-stellar radio sources) and (radio-quiet) QSOs. A short table of the space density of these objects, culled from many sources, chiefly Schmidt (1978) and Simkim, Su and Schwarz (1980) is given below. Although all the numbers are quite uncertain, there is no doubt that the radio-loud objects are relatively rare. With less certainty, it appears that the ratio of numbers of radio galaxies to Seyfert galaxies is about the same as the ratio of numbers of quasars to QSOs.

scholarly journals 11.4. Demographics of nuclear activity in nearby galaxies

1998 ◽  
Vol 184 ◽  
pp. 463-464
Author(s):  
Luis C. Ho ◽  
Alexei V. Filippenko ◽  
Wallace L. W. Sargent
Keyword(s):  
Active Galactic Nuclei ◽  
Luminosity Function ◽  
Galactic Nuclei ◽  
Optical Spectra ◽  
Complete Sample ◽  
High Quality ◽  
Nuclear Activity ◽  
Moderate Resolution ◽  
Nearby Galaxies ◽  
Scientific Results

Between 1984 and 1990 we conducted a survey at Palomar Observatory (Filippenko and Sargent 1985) to quantify the luminosity function of nearby active galactic nuclei (AGNs). The Hale 5 m telescope was used to obtain high-quality, moderate-resolution optical spectra of a nearly statistically complete sample of about 500 bright (BT ≤ 12.5 mag), northern (δ > 0°) galaxies (see Ho et al. 1995 for details). The survey has now been completed, and the first scientific results are reported in a series of papers by Ho et al. (1997a, b, c).

scholarly journals Infrared-detected AGNs in the local Universe

2020 ◽  
Vol 640 ◽  
pp. A68
Author(s):  
T. İkiz ◽  
R. F. Peletier ◽  
P. D. Barthel ◽  
C. Yeşilyaprak
Keyword(s):  
Active Galactic Nuclei ◽  
Infrared Imaging ◽  
Galactic Nuclei ◽  
Morphological Type ◽  
Selection Method ◽  
Small Sample ◽  
Promising Technique ◽  
Nuclear Activity ◽  
Color Selection ◽  
Nearby Galaxies

Context. Spitzer/IRAC color selection is a promising technique to identify hot accreting nuclei, that is, active galactic nuclei (AGN), in galaxies. We demonstrate this using a small sample of SAURON galaxies and then explore this technique further. Aims. The goal of this study is to find a simple and efficient way to reveal optically obscured nuclear accretion in (nearby) galaxies. Methods. We applied an infrared selection method to the Spitzer Survey of Stellar Structures in Galaxies (S4G) sample of more than 2500 galaxies, together with its extension sample of more than 400 galaxies. We used the Spitzer colors to find galaxies in the S4G survey containing a hot core, suggesting the presence of a strong AGN, and we studied the detection fraction as a function of morphological type. We tested this infrared color selection method by examining the radio properties of the galaxies via the VLA NVSS and FIRST surveys. Results. Using the radio data, we demonstrate that galaxies displaying hot mid-infrared nuclei stand out as (candidate) active galaxies. We reproduce these results when using colors from the lower spatial resolution WISE mission instead of Spitzer. Hence multiband infrared imaging represents a useful tool to uncover optically obscured nuclear activity in galaxies.

scholarly journals The Ultraviolet Flare at the Center of the Elliptical Galaxy NGC 4278

2009 ◽  
Vol 5 (S267) ◽  
pp. 199-199
Author(s):  
A. Cardullo ◽  
E. Dalla Bontà ◽  
E. M. Corsini ◽  
A. Beifiori ◽  
L. Buson ◽  
...  
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Elliptical Galaxy ◽  
Large Fraction ◽  
Galactic Nuclei ◽  
Nuclear Activity ◽  
Normal Galaxies ◽  
Line Region ◽  
Liner Galaxies

A large fraction of otherwise normal galaxies shows weak nuclear activity. One of the signatures of the low-luminosity active galactic nuclei (LLAGNs) is the ultraviolet variability which was serendipitously discovered in the center of some low-ionization nuclear emission-line region (LINER) galaxies (see Ho 2008 for a review).

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