Unravelling the kinematics, dynamics and structure of galaxies using H I - 21cm observation
The advent of the multi-wavelength observations of galaxies in this recent era gives us the opportunity to study the details of the different pivotal facets of galactic astrophysics. Among the observations in different wavelengths, the H I interferometric observations are of immense importance and useful. Several extensive H I 21cm interferometric observations of nearby galaxies have been performed in the last few decades, and they comprise a large number of data sets. It has now become essential to appraise the existing archival data so that this large sample volume can be used to examine the completion and coverage of sources. To explore the potential of these archival data, we constructed a sample from all the galaxies observed in 21cm by the Giant Meter wave Radio Telescope (GMRT). This results in a total of 515 galaxies, the largest sample to date. We intend to analyse all this data uniformly and carry out different exciting science cases. In this regard, We have started carrying out this exercise of GMRT ARChIve Atomic gas survey (GARCIA) (Biswas et al. 2022) with a pilot sample of eleven galaxies and explored different science cases. As a first step in this regard, we use the data products of this pilot sample to identify the warm and cold phases of the interstellar medium (ISM) using Multi-Gaussian decomposition method. For all our galaxies, we observe a bimodality in the distribution of widths of the decomposed Gaussians of the spectra, indicating the two neutral phases of the ISM. Most of the previous studies of distinguishing these two phases were limited to spectra with a signal-to-noise ratio (SNR) of 10 or above. However, our method successfully distinguishes these two phases at a much lower SNR of 5, resulting in the detection of more cold gases inside these galaxies. We found that the outskirts are dominated by cold gas for most of our galaxies, whereas warm gas dominates the central region. This could happen because in the central region, star formation activity is higher, and hence, there exists an increased amount of turbulence. To comprehend the fundamental aspects of galaxy structures, dynamics, composition, formation and evolution; it is important to have proper understanding of the kinematics and distribution of different components of the galaxies. In this regard, we present the 3D kinematical models of these galaxies by fitting the Tilted-ring model to 3-dimensional data cubes and discuss the importance of doing 3D kinematic modelling over 2D kinematical modelling (fitting the Tilted-ring model to the 2D velocity field). Equipped with the rotation curve from 3D kinematical modelling, we build a robust technique for galaxy mass modelling. We model this observed H I rotation curve using 3.6 μm infrared data and SDSS r-band data for stellar contribution, H I surface density profile for gas, and Navarro-Frenk-White (NFW) profile (Navarro et al. 1996) for dark matter halo. We employ the Markov Chain Monte Carlo (MCMC) optimisation method for parameter estimation and model the rotation curve. This is for the first time when the 3D modelled rotation curve; stellar kinematics derived using the Multi-Gaussian Expansion (MGE) (Cappellari 2002) technique and Jeans Anisotropic Modelling (JAM) (Cappellari 2008); along with the contribution of gas derived from our own developed method that does not assume any profile beforehand; have been put together for doing the mass modelling of galaxies via MCMC optimisation method. Further, to validate our analysis, we compare the parameters derived from our method of 3D kinematic modelling and mass modelling with important scaling relations, i.e., the Mgas -Mstar, Mstar -Mhalo and Mgas -Mhalo relations and found that they are in good agreement with these relations. Further, it has been well observed that there exists a global non-axisymmetric lopsided mass distribution in approximately 30% of late-type galaxies within the nearby Universe (Varela-Lavin et al. 2022). The recent observations from Spitzer survey (Sheth et al. 2010) and studies with the disk galaxies from TNG50 simulation (Varela-Lavin et al.2022), it has been anticipated that lopsidedness is a generic trait of galaxies and does not typically depend on a rare event such as interactions or mergers. This phenomenon puts additional constraints on the existing galaxy formation and evolution models. Hence it is important to understand the origin of this lopsidedness. In this regard, we investigate both the kinematic and morphological lopsidedness of the galaxies from the GARCIA pilot sample. Through a theoretical consideration, Jog (2002) showed that both the kinematic lopsidedness and morphological lopsidedness can be explained by the response of a galactic disk to a lopsided halo potential. Previous studies by van Eymeren et al. (2011) showed that the values of the halo perturbation parameter found kinematically and morphologically by the Fourier decomposition method differ from each other depending upon the type of differences in rotation curves from both arms. However, we found that irrespective of the nature of differences in the rotation curves of the two arms, the halo perturbation parameter found kinematically and morphologically are both in the same range. Our results suggest that the perturbation parameter found kinematically and morphologically are consistent with the prediction from Jog(2002). Moreover, our robust techniques of 3D kinematic modelling and mass modelling are further applied for an extended number of sources from the CALIFA survey (Calar Alto Legacy Integral Field Area survey, Sánchez et al. 2012, 2016). We have observed a sample of 15 of the CALIFA galaxies, which are at different stages of quenching, through uGMRT, as a part of the MasQue (Mass Modelling and Star-formation Quenching of Nearby Galaxies) (Kalinova et al. 2021) project. Acceptable fits for the mass modelling were obtained for seven sources in this sample. The parameters found in the 3D kinematic modelling and mass modelling of GARCIA and CALIFA sources are used to revisit one of the most important scaling relations in Astrophysics, i.e., the Baryonic Tully-Fisher relation (BTFR). Most of the previous studies of this relation are based on the velocity widths from the single-dish spectra corrected for the optical inclinations (e.g, McGaugh et al. 2000) or with rotation velocity from 2D kinematic modelling (Lelli et al. 2019). As there are discrepancies in inclination and velocity found in 3D and 2D kinematic modelling, we revisit this relation with parameters from 3D kinematic modelling and compare the results with the existing literature. Although our sample size is moderate, our study shows the importance of revisiting this relation with the 3D kinematic data and with a larger sample of galaxies. To conclude, through our studies, we have shown the potential of archival data to extract various science cases; presented the robust method and the details of the kinematic and mass modelling for a number of 18 sources; showed the importance of revisiting BTFR through 3D kinematically modelled data and found that kinematic lopsidedness and morphological lopsidedness are comparable irrespective of the nature of the difference in the rotation curve. Though these studies are currently limited to the pilot sample of the GARCIA galaxies, the same will be done with the analysed data products of the next and successive batches of GARCIA. Besides that, in the upcoming era of big interferometers such as Square Kilometer Array (SKA), where the data will be saved in the image domain, these apprised archival saved in the visibility domain will be helpful to revisit the raw data and apply improved calibration techniques or investigating the instrumental and environmental effects or processing new algorithms as they become available.