Research Article
Investigating Star Formation Rate, Metallicity and Mass Relations in Dwarf Galaxies
Emenike Nwaokoro*
Issue:
Volume 13, Issue 3, September 2026
Pages:
88-96
Received:
8 June 2026
Accepted:
22 June 2026
Published:
22 July 2026
Abstract: Star formation rate (SFR), metallicity, and mass have been identified as the key to understanding how galaxies form and evolve. To show the actual contribution of star-formation to the growth of galaxies, specific star formation rate (SSFR) is used in place of SFR. SSFR is defined as a quantity that measures the SFR per unit galaxy stellar mass. It is the measure of time taken by a galaxy to form its stellar mass at its current star formation rate. The relation between SSFR and mass separates galaxies into two populations: those with active star formation and those with little or no star formation. Metallicity is the mass fraction of baryonic components in metals; it traces the fraction of baryonic mass already converted to stars. The purpose of this paper is to present results obtained from the investigation of mass, metallicity, and star formation rate relations in dwarf galaxies using data from Sloan Digital Sky Survey matched with Galaxy and Mass Assembly. 863 emission-line classified star-forming galaxies were used for this study. Stellar mass was estimated based on an empirical relation from the (g - i) band colour. Hα luminosity was used to estimate the star formation rate (SFR). Metallicities were estimated using three methods, namely Z94, T04 and D02, which are based on theoretical methods, empirical methods and a combination of both, respectively. Results obtained showed an increase in star formation rate with mass, with a lot of scatter, which is greater among dwarf galaxies. Towards normal galaxies, the star formation rate dropped, which may be due to AGN feedback. A decreasing SSFR with mass was obtained, with dwarf galaxies having higher SSFR than normal galaxies, indicating that star formation contributes more to the growth of dwarf galaxies, thereby rapidly increasing their stellar mass more than in the normal galaxies. Also, the downsizing effect can be used to explain this observation. Generally, the results for mass-metallicity (M-Z) relations showed that for all populations, metallicity increased with mass, with increased scatter in the dwarf galaxy region. The scatter observed in the dwarf galaxy region is due to the presence of lower metallicity objects. Z94 M-Z relation has more scatter than other M-Z relations and has higher metallicities. Even though the metallicity values for my dwarf galaxies are low compared with other galaxies, they are higher than those of dwarf irregular galaxies, suggesting that my dwarf galaxy sample is dominated by dwarf galaxies with different morphologies that have high metallicity, such as dwarf spirals.
Abstract: Star formation rate (SFR), metallicity, and mass have been identified as the key to understanding how galaxies form and evolve. To show the actual contribution of star-formation to the growth of galaxies, specific star formation rate (SSFR) is used in place of SFR. SSFR is defined as a quantity that measures the SFR per unit galaxy stellar mass. It...
Show More
Research Article
Morphology and Dynamics of Gas-dust Jets in Comet 67p/Churyumov-Gerasimenko from Ground-based Ccd Observations
Donish Kosimovich Ayubov*,
Abduljalol Ghafurovich Safarov
Issue:
Volume 13, Issue 3, September 2026
Pages:
97-105
Received:
27 April 2026
Accepted:
10 June 2026
Published:
6 November 2026
Abstract: Ground-based CCD observations of comet 67P/Churyumov-Gerasimenko were carried out during October 5-8, 2021 at the Sanglokh International Astronomical Observatory using the Zeiss-1000 reflector telescope equipped with an FLI ProLine 16803 CCD camera and broadband BVRI filters. The morphology and dynamics of gas-dust activity in the near-nucleus region were investigated using image-enhancement and photometric processing techniques. Application of the Larson-Sekanina rotational gradient filter revealed several asymmetric gas-dust jet structures whose morphology and orientation changed during the observing interval. Projected jet lengths, position angles, and particle ejection velocities were estimated from the processed CCD images. Dust-particle velocities were calculated using the Whipple and Jones dynamical models. The obtained results show that particle ejection velocities strongly depend on particle size and thermal conditions near the nucleus surface. According to the Whipple model, the derived velocities vary from approximately 35 m/s to 417 m/s, while the Jones model yielded lower characteristic velocities for larger particles. Thermal characteristics of several volatile species, including H2O, CO, O2, and CO2, were additionally investigated using simplified sublimation relations. Isophotal analysis revealed a pronounced asymmetry of the inner coma and confirmed the presence of anisotropic dust emission associated with localized active regions on the nucleus surface. Temporal variations in jet orientation allowed the rotational period of the nucleus to be estimated within the interval 11.5-12.5 h, which is consistent with previous Rosetta mission measurements. The obtained results demonstrate that medium-aperture ground-based telescopes combined with modern CCD image-processing techniques remain effective tools for investigating cometary activity and dust dynamics. The study also confirms that ground-based observations are capable of reproducing large-scale morphological features previously detected during spacecraft investigations of comet 67P/Churyumov-Gerasimenko.
Abstract: Ground-based CCD observations of comet 67P/Churyumov-Gerasimenko were carried out during October 5-8, 2021 at the Sanglokh International Astronomical Observatory using the Zeiss-1000 reflector telescope equipped with an FLI ProLine 16803 CCD camera and broadband BVRI filters. The morphology and dynamics of gas-dust activity in the near-nucleus regi...
Show More
