Interacting Pair NGC Research Articles

A triple active galactic nucleus in the NGC 7733–7734 merging group

Context. Galaxy interactions and mergers can lead to supermassive black hole (SMBH) binaries, which become active galactic nucleus (AGN) pairs when the SMBHs start accreting mass. If there is a third galaxy involved in the interaction, then a triple-AGN system can form. Aims. Our goal is to investigate the nature of the nuclear emission from the galaxies in the interacting pair NGC 7733–NGC 7734 using archival VLT/MUSE integral field spectrograph data and study its relation to the stellar mass distribution traced by near-infrared (NIR) observations from the South African Astronomical Observatory (SAAO). Methods. We conducted NIR observations using the SAAO and identified the morphological properties of bulges in each galaxy. We used MUSE data to obtain a set of ionized emission lines from each galaxy and studied the ionization mechanism. We also examined the relation of the galaxy pair with any nearby companions with far-ultraviolet observations using the UVIT. Results. The emission line analysis from the central regions of NGC 7733 and NGC 7734 shows Seyfert and low ionization nuclear emission-line regions type AGN activity. The galaxy pair NGC 7733−34 also shows evidence of a third component, which has Seyfert-like emission. Hence, the galaxy pair NGC 7733−34 forms a triple-AGN system. We also detected an extended narrow-line region associated with the nucleus of NGC 7733.

A study of the ionized gas in Stephan's Quintet from integral field spectroscopy observations★

The Stephan's Quintet (SQ) is a famous interacting compact group of galaxies in an important stage of dynamical evolution, but surprisingly very few spectroscopic studies are found in the literature. We present optical integral field spectroscopy (IFS) observations of the SQ from the PPAK IFS Nearby Galaxies Survey (PINGS), that provide a powerful way of studying with spatial resolution the physical characteristics of the ionized gas within the group. The nature of the gas emission is analysed using 2D maps of continuum-subtracted, pure emission-line intensities, stacked spectra, diagnostic diagrams, and photoionization model predictions. In the case of NGC 7319, we study the galaxy-wide high-velocity outflow emission by comparing the emission properties with theoretical shock and AGN models. We conclude that the excitation mechanism of the gas in this galaxy is a mixture of AGN photoionization and shocks with a photoionizing precursor. The emission spectra from the large scale shock front in the interacting pair NGC 7318A/B is analysed, confirming the presence of several kinematic components. Comparison with predictions from theoretical shock models suggests that the gas emission is consistent with shocks without a photoionizing precursor, low pre-shock density, and velocities in the range of 200 - 400 km s-1. The gas oxygen abundance for NGC 7318B is determined using an updated O3N2 calibration. Although NGC 7317 shows no significant gas emission, an ionizing cluster is found southwest of this galaxy, probably the result of tidal interaction. As a by-product, we analyse the gas emission of the foreground galaxy NGC 7320.

Diffuse far-infrared and ultraviolet emission in the NGC 4435/4438 system: tidal stream or Galactic cirrus?

Abstract We report the discovery of diffuse far-infrared and far-ultraviolet emission projected near the interacting pair NGC 4435/4438, in the Virgo cluster. This feature spatially coincides with a well-known low surface-brightness optical plume, usually interpreted as tidal debris. If extragalactic, this stream would represent not only one of the clearest examples of intracluster dust, but also a rare case of intracluster molecular hydrogen and large-scale intracluster star formation. However, the ultraviolet, far-infrared, Hi and CO emission as well as the dynamics of this feature are extremely unusual for tidal streams but are typical of Galactic cirrus clouds. In support to the cirrus scenario, we show that a strong spatial correlation between far-infrared and far-ultraviolet cirrus emission is observed across the centre of the Virgo cluster, over a scale of several degrees. This study demonstrates how dramatic Galactic cirrus contamination can be, even at optical and ultraviolet wavelengths and at high galactic latitudes. If ignored, the presence of diffuse light scattered by Galactic dust clouds could significantly bias our interpretation of low surface-brightness features and diffuse light observed around galaxies and in clusters of galaxies.

Star Formation in the Interacting Pair NGC 7733/7734

The problem of star formation within the interacting pair NGC7733/34 has been studied, based on the UBVRI photometry of the source. The distribution of the colors of selected regions within the galaxies is used to infer an estimate for the age distribution of the star forming regions. The results seem to indicate the presence of numerous extended young star-forming regions in the disk of one of the two galaxies, NGC 7733, with ages in the range of $10^6$--$10^8$ yr. However, there exist no evidence for any violent star formation activity, in the past $10^8$ yr, in the nuclei of the two galaxies. The pair seems to be a merger bound system with the brightest, youngest, site of star forming activity lying at the disk interface.

Dynamical Interactions of Galaxy Pairs

As the dynamics of galaxy interactions is too broad a subject to be discussed in any depth in a single review, I will concentrate only on a few topics proposed to me by the organisers. Since a pair should be “two things of a kind”, I will not discuss merging and merger remnants. I will also leave out discussions on M/L and hence halo mass determinations. Good reviews covering these subjects, and some of the subjects treated here, have been given by Toomre (1977), Tremaine (1981), White (1982, 1983a), van Albada (1988), Barnes (1990) and others. Here I will briefly review the dynamics of sinking satellites and the effect of companions on elliptical galaxies, then discuss recent work on interacting disk systems, and finally focus on my favourite interacting pair NGC 5194/5195.

Shocked molecular hydrogen in NGC 4038/4039, 'the antennae'

The nuclei of the interacting pair NGC 4038/4039 have been observed in the 2.123-micron v = 1 to 0 S(1) line of excited molecular hydrogen. The observed S(1)-line luminosity/FIR luminosity ratios for NGC 4038 and NGC 4039 are found to be too high to be compatible with a model in which the H2 is excited by radiatively driven gas motions in the star-forming regions. Alternative excitation mechanisms considered include supernova explosions and collisions between the molecular clouds of the two galaxies. 49 refs.

Neutral hydrogen in the interacting pair NGC 4725/NGC 4747

view Abstract Citations (15) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral hydrogen in the interacting pair NGC 4725/NGC 4747. Haynes, M. P. Abstract Neutral hydrogen observations of the galaxy pair NGC 4725/NGC 4747, a subsystem within the Coma I cloud, reveal severe distortion in the HI distribution of NGC 4747. The ridge of the HI emission within the galaxy deviates from the optical major axis by about 30 deg and appears to coincide with a faint optical appendage. The companion NGC 4725, a supergiant spiral, is the most prominent member of the Coma I cloud and is almost twenty times more massive than its neighbor. NGC 4725 itself shows small but noticeable perturbations. A tidal encounter is invoked in order to explain the catastrophic events which have led to the distortion of NGC 4747 and the formation of its HI and optical tail. Publication: The Astronomical Journal Pub Date: December 1979 DOI: 10.1086/112613 Bibcode: 1979AJ.....84.1830H Keywords: Galactic Structure; Hydrogen Clouds; Interstellar Gas; Neutral Gases; Astronomical Photography; Galactic Evolution; Photographic Plates; Spiral Galaxies; Velocity Distribution; Astrophysics full text sources ADS | data products NED (14)