Mapping H <scp>i</scp> 21-cm in the Klemola 31 group at <i>z</i> = 0.029: emission and absorption towards PKS 2020−370

Maina, Eric; Mohapatra, Abhisek; Józsa, G. I. G.; Gupta, N.; Combes, F.; Deka, P.; Wagenveld, J.; Srianand, R.; Balashev, S. A.; Chen, Hsiao‐Wen; Krogager, Jens-Kristian; Momjian, Emmanuel; Noterdaeme, P.; Petitjean, P.

doi:10.1093/mnras/stac1752

Cited by 3 publications

(2 citation statements)

References 53 publications

(68 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For cube imaging of an SPW, the self-calibration solutions obtained from the continuum imaging are applied to the line data set, and continuum subtraction is performed using the model, i.e., CLEAN components obtained from the last round of self-calibration. The continuum subtracted visibilities are then inverted to obtain spectral line cubes, which may then be deconvolved for line emission (for example, see Boettcher et al 2021;Maina et al 2022). The wideband continuum imaging utilizing full L-band bandwidth would require the wprojection algorithm in combination with MTMFS for deconvolution, but with nterms = 2 (see Wagenveld et al 2023).…”

Section: Observations Calibration and Imagingmentioning

confidence: 99%

The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1–1.4 GHz

Deka,

Gupta,

Jagannathan

et al. 2024

ApJS

Self Cite

View full text Add to dashboard Cite

The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at the L band (900–1670 MHz) at δ ≲ +20°. We present radio continuum images and a catalog of 495,325 (240,321) radio sources detected at a signal-to-noise ratio (S/N) > 5 over an area of 2289 deg2 (1132 deg2) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source (S 1 GHz ≳ 0.2 Jy). The median spatial resolution is 12″ (8″). The median rms noise away from the pointing center is 25 μJy beam−1 (22 μJy beam−1) and is within ∼15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are <1% (8% scatter) and 1″, respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog’s accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and 0.″8, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices (α) of a subset of 125,621 sources (S/N > 8), confirm the flattening of spectral indices with decreasing flux density, and identify 140 ultra-steep-spectrum (α < −1.3) sources as prospective high-z radio galaxies (z > 2). We have identified 1308 variable and 122 transient radio sources comprising primarily active galactic nuclei that demonstrate long-term (26 yr) variability in their observed flux densities. The MALS catalogs and images are publicly available at https://mals.iucaa.in.

show abstract

Section: Observations Calibration and Imagingmentioning

confidence: 99%

The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1–1.4 GHz

Deka,

Gupta,

Jagannathan

et al. 2024

ApJS

Self Cite

View full text Add to dashboard Cite

show abstract

“…The absorption signal may be diluted either due to the presence of emission (Maina et al 2022) at low redshift or poor baseline subtraction as a result of fluctuations of the bandpass. In order to quantify how this affects our Hi absorption search, we estimated completeness by adding 1.67 × 10 8 mock absorption lines to real spectra and calculating the fraction detected using our search method and selection threshold.…”

Section: Completenessmentioning

confidence: 99%

Detections of 21 cm absorption with a blind FAST survey at z ≤ 0.09

Hu¹,

Wang²,

Li³

et al. 2023

A&A

View full text Add to dashboard Cite

We present the early science results from a blind search of the extragalactic H I 21 cm absorption lines at z ≤ 0.09 with the drift-scan observation of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We carried out the search using the data collected over 643.8 h by the ongoing Commensal Radio Astronomy FasT Survey (CRAFTS), which spans a sky area of 3155 deg2 (∼81% of CRAFTS sky coverage up to January 2022) and covers 44827 radio sources with a flux density greater than 12 mJy. Due to the radio frequency interference (RFI), only the relatively clean data in the frequency range of 1.3–1.45 GHz are used in the present work. Under the assumption of Ts/cf = 100 K, the total completeness-corrected comoving absorption path length spanned by our data and sensitive to Damped Lyman α Absorbers (DLAs; NH I ⩾ 2 × 1020 cm−2) is ΔXinv = 8.33 × 103 (Δzinv = 7.81 × 103) for intervening absorption. For associated absorption, the corresponding value is ΔXasc = 1.28 × 101 (Δzasc = 1.19 × 101). At each time point of the drift scan, a matched-filtering approach is used to search H I absorbers. Combining the information of observation mode and the distribution of the beams that detect the same candidates, spurious absorbers are successfully excluded. Three known H I absorbers (UGC 00613, 3C 293, and 4C +27.14) and two new H I absorbers (towards the direction of NVSS J231240–052547 and NVSS J053118+315412) are detected blindly. We fitted the H I profiles with multi-component Gaussian functions and calculated the redshift (0.063, 0.066), width, flux density, optical depth, and H I column densities for each absorption. Our results demonstrate the power of FAST in blindly searching H I absorbers. For absorption towards NVSS J231240–052547, the optical counterparts are faint and currently lack existing spectra. The most likely interpretation is that a radio-loud active galactic nucleus (AGN) is faint in the optical as the background source, with a faint optical absorber in between. NVSS J053118+315412 exhibits an associated absorption with a complex profile, which may suggest unsettled gas structures or gas accretion onto the supermassive black hole (SMBH). The expanding collection of blind radio detections in the ongoing CRAFTS survey offers a valuable opportunity to study AGNs, associated interstellar medium (ISM) interaction, and intervening absorbers optically without overwhelming quasi-stellar object (QSO) background light.

show abstract

The MeerKAT Absorption Line Survey Data Release 2: Wideband continuum catalogues and a measurement of the cosmic radio dipole

Wagenveld,

Klöckner,

Gupta

et al. 2024

A&A

View full text Add to dashboard Cite

We present the second data release of the MeerKAT Absorption Line Survey (MALS), consisting of wideband continuum catalogues of 391 pointings observed at L band. The full wideband catalogue covers 4344 deg$^2$ of sky, reaches a depth of 10 Jy $, and contains 971,980 sources. With its balance between survey depth and sky coverage, MALS DR2 covers five orders of magnitude of flux density, presenting a robust view of the extragalactic radio source population down to 200 Jy. Using this catalogue, we perform a measurement of the cosmic radio dipole, an anisotropy in the number counts of radio sources with respect to the cosmic background, analogous to the dipole found in the cosmic microwave background (CMB). For this measurement, we present the characterisation of completeness and noise properties of the catalogue, and show that a declination-dependent systematic affects the number density of faint sources. In the dipole measurement on the MALS catalogue, we recover reasonable dipole measurements once we model the declination systematic with a linear fit between the size of the major axis of the restoring beam and the amount of sources of each pointing. The final results are consistent with the CMB dipole in terms of direction and amplitude, unlike many recent measurements of the cosmic radio dipole made with other centimetre wavelength catalogues, which generally show a significantly larger amplitude. This result demonstrates the value of dipole measurements with deeper and more sparse radio surveys, as the population of faint sources probed may have had a significant impact on the measured dipole.

show abstract

Mapping H i 21-cm in the Klemola 31 group at z = 0.029: emission and absorption towards PKS 2020−370

Cited by 3 publications

References 53 publications

The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1–1.4 GHz

The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1–1.4 GHz

Detections of 21 cm absorption with a blind FAST survey at z ≤ 0.09

The MeerKAT Absorption Line Survey Data Release 2: Wideband continuum catalogues and a measurement of the cosmic radio dipole

Contact Info

Product

Resources

About