The Clumpy Structure of Five Star-bursting Dwarf Galaxies in the MaNGA Survey

The star-forming clumps in star-bursting dwarf galaxies provide valuable insights into understanding the evolution of dwarf galaxies.In this paper,we focus on five star-bursting dwarf galaxies featuring off-centered clumps in the Mapping Nearby Galaxies at Apache Point Observatory survey.Using the stellar population synthesis software Fitting Analysis using Differential evolution Optimization,we obtain the spatially resolved distribution of the star formation history,which allows us to construct the g-band images of the five galaxies at different ages.These images can help us to probe the evolution of the morphological structures of these galaxies.While images of a stellar population older than 1 Gyr are typically smooth,images of a stellar population younger than 1 Gyr reveal significant clumps,including multiple clumps which appear at different locations and even different ages.To study the evolutionary connections of these five galaxies to other dwarf galaxies before their star-forming clumps appear,we construct the images of the stellar populations older than three age nodes,and define them to be the images of the"host"galaxies.We find that the properties such as the central surface brightness and the effective radii of the hosts of the five galaxies are in between those of dwarf ellipticals(dEs)and dwarf irregulars(dIrrs),with two clearly more similar to dEs and one more similar to dIrrs.Among the five galaxies,8257-3704 is particularly interesting,as it shows a previous starburst event that is not quite visible from its gri image,but only visible from images of the stellar population at a few hundred million years.The star-forming clump associated with this event may have appeared at around 600 Myr ago and disappeared at around 40 Myr ago.

Interacting system NGC 7805/6(Arp 112)and its tidal dwarf galaxy candidate

We present results from our Giant Metrewave Radio Telescope(GMRT)HⅠ,Himalayan Chandra Telescope(HCT)Hα,1 m Sampurnanand Telescope(ST)and 1.3 m Devasthal Fast Optical Telescope(DFOT)deep optical observations of the NGC 7805/6(Arp 112)system to test KUG 2359+311’s tidal dwarf galaxy(TDG)candidacy and explore the properties of the interacting system.Our GMRT HⅠmap shows no HⅠdetection associated with KUG 2359+311,nor any HⅠtail or bridge-like structure connecting KUG 2359+311 to the NGC 7805/6 system.Our HCT Hαimage,on the other hand,displays strong detections in KUG 2359+311,with net SFR0.035±0.009 M_(⊙)yr^(-1).The Hαdata constrain the redshift of KUG 2359+311 to 0.00≤z≤0.043,compared to the redshift of NGC 7806 of0.015.TDGs detected to date have all been HⅠrich,and displayed HⅠ,ionised gas and stellar tidal debris trails(bridges or tails)linking them to their parent systems.However,neither our HⅠdata nor our optical imaging,while three magnitudes deeper than SDSS,reveals a tidal trail connecting KUG 2359+311 to NGC 7805/6.Lack of HⅠ,presence of an old stellar population,ongoing star formation and reasonably high SFR compared to normal dwarf galaxies suggest that KUG 2359+311 may not be an Arp 112 TDG.It is most likely a case of a regular gas-rich dwarf galaxy undergoing a morphological transformation after having lost its entire gas content to an interaction with the Arp 112 system.Redshift and metallicity from future spectroscopic observations of KUG 2359+311 would help clarify the nature of this enigmatic structure.