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Register a new userTidal Dwarf Galaxies around a Post-merger Galaxy, NGC 4922
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One possible channel for the formation of dwarf galaxies involves birth in the tidal tails of interacting galaxies. We report the detection of a bright UV tidal tail and several young tidal dwarf galaxy candidates in the post-merger galaxy NGC 4922 in the Coma cluster. Based on a two-component population model (combining young and old stellar populations), we find that the light of tidal tail predominantly comes from young stars (a few Myr old). The Galaxy Evolution Explorer (GALEX) ultraviolet data played a critical role in the parameter (age and mass) estimation. Our stellar mass estimates of the tidal dwarf galaxy candidates are ~ 10^{6-7} M_sun, typical for dwarf galaxies.
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NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs. It is wreathed in an extraordinary neutral hydrogen (H I) complex, which includes rings, shells and a counter-rotating core, spanning 90 kiloparsecs. NGC 4449 is relatively isolated, although an interaction with its nearest known companion-the galaxy DDO 125, some 40 kpc to the south-has been proposed as being responsible for the complexity of its HI structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxys centre.
This work presents an extended, neutral Hydrogen emission map around Magellanic-type dwarf irregular galaxy (dIm) NGC 1569. In the Spring of 2010, the Robert C. Byrd Green Bank Telescope (GBT) was used to map a 9 degree x 2 degree region in HI line emission that includes NGC 1569 and IC 342 as well as two other dwarf galaxies. The primary objective for these observations was to search for structures potentially connecting NGC 1569 with IC 342 group members in order to trace previous interactions and thus, provide an explanation for the starburst and peculiar kinematics prevalent in NGC 1569. A large, half-degree diameter HI cloud was detected that shares the same position and velocity as NGC 1569. Also, two long structures were discovered that are reminiscent of intergalactic filaments extending out in a v-shaped manner from NGC 1569 toward UGCA 92, a nearby dwarf galaxy. These filamentary structures extend for about 1.5 degrees, which is 77 kpc at NGC 1569. There is a continuous velocity succession with the 0.5 degree HI cloud, filaments, and main body of the galaxy. The 0.5 degree HI cloud and filamentary structures may be foreground Milky Way, but are suggestive as possible remnants of an interaction between NGC 1569 and UGCA 92. The data also show two tidal tails extending from UGCA 86 and IC 342, respectively. These structures may be part of a continuous HI bridge but more data are needed to determine if this is the case.
We report the discovery of a UV-bright tidal dwarf galaxy candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas kinematics and stellar properties of this system. The HI morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M_sun yr^-1 from the FUV flux and measure a total HI mass of 3.8x10^8 M_sun for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object--whether it is tidal or pre-existing in origin--in the context of its metallicity being a factor of ten lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.
A starburst induced by a galaxy merger may create a relatively thin central stellar disk at radius $le 100$pc. We calculate the rate of tidal disruption events (TDEs) by the inspiraling secondary supermassive black (SMBH) through the disk. With a small enough stellar velocity dispersion ($sigma/v_c le 0.1$) in the disk, it is shown that $10^5-10^6$ TDEs of solar-type main sequence stars per post-starburst galaxy (PSB) can be produced to explain their dominance in producing observed TDEs. Although the time it takes to bring the secondary SMBH to the disk apparently varies in the range of $sim 0.1-1$Gyr since the starburst, depending on its landing location and subsequently due to dynamical friction with stars exterior to the central stellar disk in question, the vast majority of TDEs by the secondary SMBH in any individual PSB occurs within a space of time shorter than $sim 30$Myr. Five unique testable predictions of this model are suggested.
Tidal dwarf galaxies form during the interaction, collision or merger of massive spiral galaxies. They can resemble normal dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the missing baryons, known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem that can be significantly impacted if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today.
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