arXiv subjects

S. Kurapati

Publications and source records attributed to S. Kurapati.

8 recordsLinked to original sources

arXiv2026

The ultra-deep HI radial profiles of late-type galaxies from MHONGOOSE

Galaxy discs have a finite extent, yet how and where their neutral atomic hydrogen (HI) components end is not fully understood. The existence of a break in the HI disc at column densities of $\sim10^{19}$ cm$^{-2}$ has been debated since early 21-cm observations of the spiral galaxy NGC 3198. We present the HI radial profiles of 16 star-forming, late-type galaxies from the MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey spanning a range of HI mass from $10^{7}$ M$_\odot$ to $10^{10}$ M$_\odot$. We probed via spectral stacking their HI discs down to inclination-corrected column densities of a few times $10^{17}$ cm$^{-2}$ at kpc resolution. The HI radial profiles of high-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$) galaxies are characterised by a inner plateau, followed by a knee at column densities of $\sim5\times10^{20}$ cm$^{-2}$, but no edges are unambiguously identified. The HI radial profiles of low-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$) galaxies shows a steeper decline and also no edges. We found that the profiles are self-similar when normalised to the radius at which a mass surface density of 0.01 M$_\odot$ pc$^{-2}$ is reached, in agreement with recent literature results, but we also found a possible correlation between the normalisation radius and the environment, suggesting that environment contributes to the shaping of the HI distribution in galaxies. The emerging picture is that the diverse morphology of the HI radial profiles is difficult to interpret, and future studies with a larger sample are necessary for quantifying the contribution of internal and external processes acting at different levels for different galaxies.

astro-ph.GA↗

arXiv2026

HI absorption in MHONGOOSE -- Spin temperatures and cold neutral medium in nearby disk galaxies

Combined HI emission-absorption studies constrain the spin temperature and phase structure of the neutral atomic hydrogen interstellar medium (ISM), but have largely been limited to the Milky Way and the Local Group. We extend this technique to galaxies at distances of 7-22 Mpc using deep data from the MeerKAT HI Observations of Nearby Galactic Objects - Observing Southern Emitters (MHONGOOSE) survey, and quantify the detection fraction and Cold Neutral Medium (CNM) properties at these distances. We search for HI absorption toward 56 background continuum sources in 21 out of the 30 MHONGOOSE galaxies (with nine galaxies lacking suitable background sources), and detect absorption associated with the galaxies' HI disks in three cases: one sight line in NGC 289 and two in NGC 7424. This corresponds to detection rates of 3/56 (5 percent) for the full sample and 3/31 (10 percent) for a clean sub-sample of sight lines, considering only unresolved background sources behind 14 low-inclination galaxies. Detections occur only where both the continuum flux and the foreground \HI column density are high, with optical-depth sensitivity as the primary limiting factor. For the detected sight lines, we model the absorption and emission spectra to derive spin temperatures and CNM fractions using the standard combined emission-absorption method. The CNM spin temperatures and line widths are comparable to Local Group measurements, but the inferred CNM fractions are systematically lower. We argue that this difference is primarily a resolution effect: at the distances of our galaxies, the emission spectra average over several hundred parsecs, diluting structured CNM relative to the smoother Warm Neutral Medium (WNM). This demonstrates that emission-absorption analyses can be extended beyond the Local Group, provided that care is taken in constructing representative emission spectra.

astro-ph.GA↗

arXiv2026

MIGHTEE-HI: Mass Models and Dark Matter properties

Measuring galaxy rotation curves is critical for inferring the properties of dark-matter haloes in the Lambda Cold Dark Matter ($\Lambda$CDM) paradigm. We present HI rotation curves and mass models for 20 galaxies from the MIGHTEE survey. Using extended HI kinematics, we construct resolved mass models that include stellar, gaseous, and dark-matter components. Stellar masses are derived using 3.6 $\mu$m imaging under fixed mass-to-light ratio ($\Upsilon_{*} = M/L$) assumptions and are complemented, for the first time for a HI-selected sample, by spatially resolved $M/L$, obtained from multi-wavelength SED fitting. We examine the ratio of baryonic to observed rotation velocity ($V_{\rm bar}/V_{\rm obs}$) at the characteristic radius $R_{2.2}$. Adopting a fixed $\Upsilon_\star = 0.5\,M_\odot/L_\odot$ yields a clear dependence of $V_{2.2}/V_{\rm obs}$ on galaxy luminosity, while adopting $\Upsilon_\star = 0.2\,M_\odot/L_\odot$ substantially weakens this trend. In contrast, the resolved $M/L$ analysis preserves the luminosity dependence while modifying the stellar contribution on a galaxy-by-galaxy basis, providing a more accurate representation of the underlying relation. We model the dark-matter haloes using Navarro-Frenk-White profiles and find that the different assumptions for a fixed a $M/L$ systematically shift galaxies relative to the theoretical stellar-to-halo mass and baryonic-to-halo mass relations, while the spatially varying $M/L$ yields the closest agreement with theoretical benchmarks within $\Lambda$CDM. We therefore demonstrate that future investigations of the dark matter properties of galaxies using rotation curves need to account for varying $M/L$ across individual galaxy profiles and between galaxies in order to obtain accurate measurements of the dark matter, and therefore test $\Lambda$CDM.

astro-ph.GA↗

arXiv2024

Searching for HI around MHONGOOSE Galaxies via Spectral Stacking

The observed star formation rates of galaxies in the Local Universe suggests that they are replenishing their gas reservoir across cosmic time. Cosmological simulations predict that this accretion of fresh gas can occur in a hot or a cold mode, yet the existence of low column density ($\sim10^{17}$ cm$^{-2}$) neutral atomic hydrogen (HI) tracing the cold mode has not been unambiguously confirmed by observations. We present the application of unconstrained spectral stacking to attempt to detect the emission from this HI in the Circum-Galactic Medium (CGM) and Inter-Galactic Medium (IGM) of 6 nearby star forming galaxies from the MHONGOOSE sample for which full-depth observations are available. Our stacking procedure consists of a standard spectral stacking algorithm coupled with a one-dimensional spectral line finder designed to extract reliable signal close to the noise level. In agreement with previous studies, we found that the amount of signal detected outside the HI disk is much smaller than implied by simulations. Furthermore, the column density limit that we achieve via stacking ($\sim10^{17}$ cm$^{-2}$) suggests that direct detection of the neutral CGM/IGM component might be challenging in the future, even with the next generation of radio telescopes.

astro-ph.GA↗

arXiv2024

MHONGOOSE -- A MeerKAT Nearby Galaxy HI Survey

The MHONGOOSE (MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters) survey maps the distribution and kinematics of the neutral atomic hydrogen (HI) gas in and around 30 nearby star-forming spiral and dwarf galaxies to extremely low HI column densities. The HI column density sensitivity (3 sigma over 16 km/s) ranges from ~ 5 x 10^{17} cm^{-2} at 90'' resolution to ~4 x 10^{19} cm^{-2} at the highest resolution of 7''. The HI mass sensitivity (3 sigma over 50 km/s) is ~5.5 X 10^5 M_sun at a distance of 10 Mpc (the median distance of the sample galaxies). The velocity resolution of the data is 1.4 km/s. One of the main science goals of the survey is the detection of cold, accreting gas in the outskirts of the sample galaxies. The sample was selected to cover a range in HI masses, from 10^7 M_sun to almost 10^{11} M_sun, to optimally sample possible accretion scenarios and environments. The distance to the sample galaxies ranges from 3 to 23 Mpc. In this paper, we present the sample selection, survey design, and observation and reduction procedures. We compare the integrated HI fluxes based on the MeerKAT data with those derived from single-dish measurement and find good agreement, indicating that our MeerKAT observations are recovering all flux. We present HI moment maps of the entire sample based on the first ten percent of the survey data, and find that a comparison of the zeroth- and second-moment values shows a clear separation between the physical properties of the HI in areas with star formation and areas without, related to the formation of a cold neutral medium. Finally, we give an overview of the HI-detected companion and satellite galaxies in the 30 fields, five of which have not previously been catalogued. We find a clear relation between the number of companion galaxies and the mass of the main target galaxy.

astro-ph.GA↗

arXiv2024

MHONGOOSE discovery of a gas-rich low-surface brightness galaxy in the Dorado Group

We present the discovery of a low-mass gas-rich low-surface brightness galaxy in the Dorado Group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen (HI) gas mass of $M_\star = 2.23\times10^6$ M$_\odot$ and $M_{\rm HI}=1.68\times10^6$ M$_\odot$, respectively. This low-surface brightness galaxy is the lowest mass HI detection found in a group beyond the Local Universe ($D\gtrsim 10$ Mpc). The dwarf galaxy has the typical overall properties of gas-rich low surface brightness galaxies in the Local group, but with some striking differences. Namely, the MHONGOOSE observations reveal a very low column density ($\sim 10^{18-19}$ cm$^{-2}$) HI disk with asymmetrical morphology possibly supported by rotation and higher velocity dispersion in the centre. There, deep optical photometry and UV-observations suggest a recent enhancement of the star formation. Found at galactocentric distances where in the Local Group dwarf galaxies are depleted of cold gas (at $390$ projected-kpc distance from the group centre), this galaxy is likely on its first orbit within the Dorado group. We discuss the possible environmental effects that may have caused the formation of the HI disk and the enhancement of star formation, highlighting the short-lived phase (a few hundreds of Myr) of the gaseous disk, before either SF or hydrodynamical forces will deplete the gas of the galaxy.

astro-ph.GA↗

arXiv2024

The SARAO MeerKAT 1.3 GHz Galactic Plane Survey

We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251°$\le l \le$ 358°and 2°$\le l \le$ 61°at $|b| \le 1.5°$). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8" and a broadband RMS sensitivity of $\sim$10--20 $μ$ Jy/beam. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908--1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE HII region candidates are not true HII regions; and a large sample of previously undiscovered background HI galaxies in the Zone of Avoidance.

astro-ph.GA↗

arXiv2022

Nearby voids and their galaxies: recent progress and prospects

Voids occupy about 3/4 of the volume of the Universe and contain about 15% of its mass. Due to various observational selection effects, these structure elements and galaxies populating voids, are highly under-explored. This especially relates to the lowest mass galaxies which comprise the main void population. Studying the nearby voids allows us to improve our understanding of the most elusive void objects. We present the brief overview of the current status and the prospects of the study of the nearest voids and their galaxies. First, we summarize the pioneer study of a hundred galaxies residing in the nearby Lynx-Cancer void which clearly evidence for the slower evolution of void galaxies and finds also the unusual very metal-poor and gas-rich dwarfs. Then we describe the recently defined sample of the nearby voids within the sphere with R = 25 Mpc and a sample of 1350 galaxies residing in these voids (~20% of all galaxies within this volume). We discuss the current results obtained for several directions of the study of this sample. They include: the search for Very Young Galaxies, the study of HI properties, the clustering of void galaxies and its relation to the void substructures, and the unbiased study of 260 void galaxies within the Local Volume (R < 11 Mpc). Altogether, this opens a perspective way to address the suggested peculiarities of the void galaxy formation and evolution. Finally, we briefly overview the expected advancements in the void galaxy studies related to the upcoming new facilities.

astro-ph.GA↗