Search

We present the first measurement of H i mass of star-forming galaxies in different large scale structure environments from a blind survey at z ∼ 0.37. In particular, we carry out a spectral line stacking analysis considering 2875 spectra of colour-selected star-forming galaxies undetected in H i at 0.23 < z < 0.49 in the COSMOS field, extracted from the MIGHTEE-H i Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large-scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust H i detection yielding an average galaxy H i mass of |$M_{\rm H \, {\small I}}=(8.12\pm 0.75)\times 10^9\, {\rm M}_\odot$| at ∼11.8σ. Next, we investigate the different subsamples finding a negligible difference in M H i as a function of the galaxy overdensity. We report an H i excess compared to the full sample in satellite galaxies (M H i  = (11.31 ± 1.22) × 109, at ∼10.2σ) and in filaments (M H i  = (11.62 ± 0.90) × 109. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be H i -deficient. We find the same qualitative results also when stacking in units of H i fraction (f H i ). We conclude that the H i amount in star-forming galaxies at the studied redshifts correlates with the large-scale structure environment. [ABSTRACT FROM AUTHOR]

Here we report the discovery with the Giant Metrewave Radio Telescope of an extremely large (∼115 kpc in diameter) H  i ring, located around a massive quenched galaxy, AGC 203001, but off-centred with respect to it. This ring does not have any bright extended optical counterpart unlike several other known ring galaxies. Our deep g -, r- , and i -band optical imaging of the H  i ring, using the MegaCam instrument on the Canada–France–Hawaii Telescope, shows however several regions with faint optical emission at a surface brightness level of ∼28 mag arcsec−2. Such an extended H  i structure is very rare with only one other case known so far – the Leo ring. Conventionally, off-centred rings have been explained by a collision with an 'intruder' galaxy leading to expanding density waves of gas and stars in the form of a ring. However, in such a scenario the impact also leads to large amounts of star formation in the ring that is not observed in the ring presented in this paper. We discuss possible scenarios for the formation of such H  i -dominated rings. [ABSTRACT FROM AUTHOR]

We present high resolution H  i 21 cm Giant Meterwave Radio Telescope observations of the superthin galaxy FGC 1540 with a spatial resolution of 10 arcsec × 8 arcsec and a spectral resolution of 1.73 km s−1 and an rms noise of 0.9 mJy per beam. We obtain its rotation curve as well as deprojected radial H  i surface density profile by fitting a 3D tilted-ring model directly to the H  i data cubes using the publicly available software, Fully Automated tirrific. We also present the rotation curve of FGC 1540 derived from its optical spectroscopy study using the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We use the rotation curve, the H  i surface density profile together with Spitzer 3.6  $$\mu$$ m, and the SDSS i -band data to construct the mass models for FGC 1540. We find that both the Pseudo-isothermal () as well as Navarro–Frenk–White dark matter (DM) haloes, fit the observed rotation curve equally well. The PIS model indicates a compact DM halo (R C/ R D < 2), with the best-fitting core radius (R C) approximately half the exponential stellar disc scale length (R D), which is in agreement with the mass models of superthin galaxies studied earlier in the literature. Since the vertical thickness of the galactic stellar disc is determined by a balance between the net gravitational field and the velocity dispersion in the vertical direction, the compact DM halo may be primarily responsible in regulating the superthin vertical structure of the stellar disc in FGC 1540 as was found in case of the superthin galaxy UGC7321. [ABSTRACT FROM AUTHOR]

We report results from a Giant Metrewave Radio Telescope search for 'associated' redshifted HI 21 cm absorption from 24 active galactic nuclei (AGNs), at 1.1 < z < 3.6, selected from the Caltech-Jodrell Bank Flat-spectrum (CJF) sample. 22 out of 23 sources with usable data showed no evidence of absorption, with typical 3σ optical depth detection limits of ≈0.01 at a velocity resolution of ≈30 km s-1. A single tentative absorption detection was obtained at z ≈ 3.530 towards TXS 0604+728. If confirmed, this would be the highest redshift at which HI 21 cm absorption has ever been detected. Including 29 CJF sources with searches for redshifted HI 21 cm absorption in the literature, mostly at z < 1, we construct a sample of 52 uniformly selected flat-spectrum sources. A Peto-Prentice two-sample test for censored data finds (at ≈3σ significance) that the strength of HI 21 cm absorption is weaker in the high-z sample than in the low-z sample; this is the first statistically significant evidence for redshift evolution in the strength of HI 21 cm absorption in a uniformly selected AGN sample. However, the two-sample test also finds that the HI 21 cm absorption strength is higher in AGNs with low ultraviolet or radio luminosities, at ≈3.4σ significance. The fact that the higher luminosity AGNs of the sample typically lie at high redshifts implies that it is currently not possible to break the degeneracy between AGN luminosity and redshift evolution as the primary cause of the low HI 21 cm opacities in high-redshift, high-luminosity AGNs. [ABSTRACT FROM AUTHOR]