Double-nucleus Galaxy Research Articles

ALMA Observations of HCN and HCO+ Outflows in the Merging Galaxy NGC 3256

Abstract We report ∼2″ resolution Atacama Large Millimeter/submillimeter Array observations of the HCN (1–0), HCO+ (1–0), CO (1–0), CO (2–1), and CO (3–2) lines toward the nearby merging double-nucleus galaxy NGC 3256. We find that the high-density gas outflow traced in HCN (1–0) and HCO+ (1–0) emission is colocated with the diffuse molecular outflow emanating from the southern nucleus, where a low-luminosity active galactic nucleus (AGN) is believed to be the dominant source of the far-infrared luminosity. On the other hand, the same lines were undetected in the outflow region associated with the northern nucleus, whose primary heating source is likely related to starburst activity without obvious signs of an AGN. Both the HCO+ (1–0)/CO (1–0) line ratio (i.e., dense gas fraction) and the CO (3–2)/CO (1–0) line ratio are larger in the southern outflow (0.20 ± 0.04 and 1.3 ± 0.2, respectively) than in the southern nucleus (0.08 ± 0.01 and 0.7 ± 0.1, respectively). By investigating these line ratios for each velocity component in the southern outflow, we find that the dense gas fraction increases and the CO (3–2)/CO (1–0) line ratio decreases toward the largest velocity offset. This suggests the existence of a two-phase (diffuse and clumpy) outflow. One possible scenario to produce such a two-phase outflow is an interaction between the jet and the interstellar medium, which possibly triggers shocks and/or star formation associated with the outflow.

Photometry and Kinematics of Two Minor Merger Candidate Galaxies

We observationally investigate the properties of disk galaxies undergoing minor merger or capture events. In this context, the properties of two double-nucleus candidate galaxies, ESO 381-IG 23 and MCG -3-35-14, are analyzed. Both are disk-dominated Sc-Scd galaxies that show a bright knot superposed on their disk body. The size and surface brightness of these knots are in both cases comparable to those of the galaxy nucleus, which has led previous work to classify these galaxies as double-nucleus galaxies. We present results from observations made with the SOAR 4.1 m, CASLEO 2.15 m, and Bosque Alegre 1.54 m telescopes. We determined the values for the apparent and absolute magnitudes of the nuclei and the bright regions and analyzed the surface brightness profiles and colors. We also study the kinematics of the galaxies via their rotation curves. Analytical mass models were fitted under the constraints of both kinematic and photometric observational data. It is found that ESO 381-IG 23 has an absolute magnitude MB = -19.59 and mass = (3.0 ± 0.2) × 1010 ⊙, and its nuclear spectrum shows strong emission lines typical of starbursts. MCG -3-35-14 has MB = -19.97 and = (9.6 ± 0.5) × 1010 ⊙. Both galaxies are morphologically normal disk galaxies. They have a bulge-to-disk ratio of ~0.1 and show no significant signatures of dynamical perturbation in their rotation curves. The secondary nuclei candidates are found to be giant H II regions, rather than nuclei of captured companions. They have masses of (2.2 ± 0.2) × 106 ⊙ (ESO 381-IG 23) and (4.1 ± 0.2) × 106 ⊙ (MCG -3-35-14), and ages of 6.6 ± 0.1 and 8.0 ± 1.0 Myr, respectively.

Galaxies with a Central Minimum in Stellar Luminosity Density

We used HST WFPC2 images to identify six early-type galaxies with surface- brightness profiles that decrease inward over a limited range of radii near their centers. The implied luminosity density profiles of these galaxies have local minima interior to their core break radii. NGC 3706 harbors a high surface brightness ring of starlight with radius ~20 pc. Its central structure may be related to that in the double-nucleus galaxies M31 and NGC 4486B. NGC 4406 and NGC 6876 have nearly flat cores that on close inspection are centrally depressed. Colors for both galaxies imply that this is not due to dust absorption. The surface brightness distributions of both galaxies are consistent with stellar tori that are more diffuse than the sharply defined system in NGC 3706. The remaining three galaxies are the brightest cluster galaxies in A260, A347, and A3574. Color information is not available for these objects, but they strongly resemble NGC 4406 and NGC 6876 in their cores. The thin ring in NGC 3706 may have formed dissipatively. The five other galaxies resemble the endpoints of some simulations of the merging of two gas-free stellar systems, each harboring a massive nuclear black hole. In one version of this scenario, diffuse stellar tori are produced when stars initially bound to one black hole are tidally stripped away by the second black hole. Alternatively, some inward-decreasing surface-brightness profiles may reflect the ejection of stars from a core during the hardening of the binary black hole created during the merger.

The Morphologies of Dwarf Markarian Galaxies

The morphologies of the 96 dwarf (M(B) ≥ -17m) galaxies in the Markarian catalog are determined from the digitized Schmidt plates obtained for the construction of the Hubble Space Telescope Guide Star Catalog. The fraction of double nucleus galaxies within the dwarf Markarian galaxies is determined to be twice that found for all galaxies in the Markarian catalog. In addition to the 12 previously known cases, four definite and two probable galaxies with double nuclei are identified. The fraction of dwarf Markarian galaxies with bright star forming regions is found to be twice that of Virgo cluster dwarf galaxies. No Elliptical galaxies are found in the sample. Galaxies with blue compact dwarf and S0 morphologies are more often found to contain unresolved regions of UV excess emission. Dwarf Markarian galaxies with different morphological structures and spectral classes are found to have similar FIR properties.

Properties of Host Galaxies of Powerful Radio Sources

This paper describes those properties of the host of powerful radio sources that are unique to radio galaxies. The radio have redshifts up to z = 0.5 and radio powers, P408 MHz, ranging from 1025 to 1028 W Hz–1 (H0 = 50 km s–1 Mpc–1 and q0 = 0.0). We find that the magnitudes, colors, and surface brightness profiles of these radio are very diverse. Their rest frame V magnitudes range from -24th to -20th magnitude and are 0.55 ± 0.06 mag fainter than those of brightest cluster members. Their (B - V) colors can be as red as those of brightest cluster members but may also be ~ 1 mag bluer. The optical structure of the low-redshift (0.03 < z < 0.25) radio may vary ranging from cD to N galaxy behavior. Although the host of the low-redshift radio sources are generally elliptical-like galaxies, a comparison of the overall structure of radio to those of radio-quiet generalized elliptical galaxies of Schombert shows that only 17% are genuine elliptical galaxies, 9% have elliptical profiles with truncated halos, 26% are roughly elliptical but have disturbed surface brightness profiles, 16% are cD or D galaxies, 7% have double nuclei, and 21% are N galaxies. The only property that radio galaxies, as a class, have in common is that their sizes are relatively larger than those of normal elliptical of the same absolute magnitude. At the 22d isophote (in V) radio are 11% larger, at the 24th isophote they are 15% larger, and at the 25th isophote they are 20% larger. The host of the low-redshift (0.03 < z < 0.25) FR I and FR II sources have different properties. Sixty-nine percent of all FR I's are associated with cD-like or double nucleus galaxies, 19% with smooth ellipticals, and 13% with disturbed ellipticals; no FR I's are associated with N galaxies. Forty-one percent of all FR II's are associated with N galaxies, 26% with smooth ellipticals, and 26% with disturbed ellipticals; no FR II's are associated with cD-like galaxies. The colors and color gradients are also different, with the FR II's having both bluer colors and a larger dispersion in their color gradients. Powerful FR I and FR II sources exhibit differing cosmological evolutions in their number counts. At low redshifts, almost all powerful sources are FR I's, and at high redshifts they are predominantly FR II's. We suggest that powerful FR I's prefer host that are the dominant central of relaxed groups and clusters, while FR II's are most often associated with violent galaxy encounters.

WFPC2 Images of Multiple Nuclei in Nearby Active Galactic Nuclei

High-resolution images have been made with the Hubble Space Telescope of the cores of three active galaxies: Mrk 348, Mrk 516, and Mrk 789. The 500 s images were taken using the WFPC2 camera with the F606W filter. Each galaxy exhibits structure which may be interpreted as multiple nuclei. Mrk 348 appears to have two nuclei, although it is possible that they may be bipolar ejecta from the core. The optical image was compared to a VLBI image showing a linear triple source. Though there are similarities between the two images, there is no direct one-to-one correspondence between the sources. The optical polarization angle for Mrk 348 (168°) is almost perpendicular to the position angle of its nuclei (84°). Mrk 516 is a spiral with a warped disk which may be evidence of a recent merger. One of its two nuclei is resolved. Mrk 789 was identified as a double nucleus galaxy from the ground and is a merger in which three sources were detected within one of the previously identified nuclei. However, it is possible that the knots may be very bright H II regions.

Observations of Multiple Nucleus Galaxies

Disturbed Galaxies with two nuclei display the final state of the interaction process of two galaxies (Kollatschny et al., 1986; Fricke and Kollatschny, 1989). A few of these double nucleus galaxies contain Seyfert nuclei.

Activity of Interacting Galaxies Mkn 673: A Close-By “E+A” Galaxy

The close-by double nucleus galaxy Mkn 673 shows spectra and colors which are typical for “E+A” cluster galaxies.

The Twin-Nucleus Merging Galaxy MKN 266

We present results of observations of the double-nucleus galaxy Markarian 266 (NGC 5256) from 3 principal sources. These are 1:CCD imaging with the Canada-France-Hawaii telescope in broad and narrow bands. These indicate that the galaxy has extended, complex, faint outer plumes which indicate that a recent merger has occurred. The narrow-band images reveal remarkable knotty structure of the [O III] emitting gas, extending over the whole central part of the galaxy. This is not seen in Hα (see figure 1).2:21cm imaging with the VLA, covering velocity space near that of the optical nuclei. The continuum image reveals resolved triple structure, with the two outer peaks coincident with the optical nuclei. The 21cm velocity profiles indicate the presence of considerable H I absorption near the optical emission line velocities.3:Spatially resolved optical spectroscopy with the DAO 1.8m telescope. These data reveal the details of the [O III] velocity field and some of the physical parameters of the gas. The complexity and extended nature of the gas explains some conflicting redshift measurements in the literature. Together with the imaging data, we derive estimates of nuclear reddening and luminosity.

Multifrequency observations of the double-nucleus galaxy Markarian 266 - Enhanced synchrotron emission induced by a merger

Presentation d'observations CCD optiques et radio a synthese d'ouverture de la galaxie a noyau double Mkn 266 (NGC 5256). Cette radiogalaxie est en fait constituee de 3 sources continuum non thermique. On suppose que l'emission synchrotron est stimulee par la collision de deux galaxies dont les disques entrent en coalescence

Double Nucleus Galaxies

Double nucleus galaxies may represent late stages of galaxy mergers and may therefore be key objects for understanding galaxy evolution and activity. Here we present spectroscopic data on these objects and their individual nuclei.

Investigation of the galaxy Markaryan 306

Spectra obtained with the 6-m telescope of the Special Astrophysical Observatory of the USSR Academy of Sciences and the 2.72-m telescope at the McDonald Observatory have been used to make a spectroscopic and spectrophotometric investigation of the double-nucleus galaxy Markaryan 306. For both nuclei and the condensation in the northern spiral arm of the galaxy, the relative intensities of the observed emission lines are used to estimate the values of T /sub e/ and n /sub e/, the abundances of the elements O, N, S, the masses and volumes of the ionized gas, and the number of 09 stars. All three formations are objects of the type of H II regions. The possibility of regarding the northern spiral arm of Markaryan 306 as an individual galaxy whose nuclear region is the condensation in it is discussed. The reality of the double-nucleus structure of the galaxy is also considered.