Towards the first detection of strongly lensed H i emission

Abstract

We report interferometric observations tuned to the redshifted neutral hydrogen (H i) 21cm emission line in three strongly lensed galaxies at z ∼ 0.4 with the Giant Metrewave Radio Telescope (GMRT). One galaxy spectrum (J1106+5228 at z=0.407) shows evidence of a marginal detection with an integrated signal-to-noise ratio of 3.8, which, if confirmed by follow-up observations, would represent the first strongly lensed and most distant individual galaxy detected in H i emission. Two steps are performed to transcribe the lensed integrated flux measurements into H i mass measurements for all three target galaxies. First, we calculate the H i magnification factor µ by applying general relativistic ray-tracing to a physical model of the source-lens system. The H i magnification generally differs from the optical magnification and depends largely on the intrinsic H i mass M HI due to the H i mass-size relation. Second, we employ a Bayesian formalism to convert the integrated flux, amplified by the M HI -dependent magnification factor µ, into a probability density for M HI , accounting for the asymmetric uncertainty due to the declining HI mass function (Eddington bias). In this way, we determine a value of log 10 (M HI /M ) = 10.2 +0.3 −0.7 for J1106+5228, consistent with the estimate of 9.4 ± 0.3 from the optical properties of this galaxy. The H i mass of the other two sources are consistent with zero within a 95 per cent confidence interval however we still provide upper limits for both sources and a 1σ lower limit for J1250-0135 using the same formalism.

WALLABY – an SKA Pathfinder H i survey

“…One of the highest redshift detections in H I emission from an individual galaxy, obtained in the COSMOS H I Large Extragalactic Survey (CHILES), is at z = 0.376 (Fernandez et al 2016), well surpassing previous detections at z ∼ 0.2 (Zwaan et al 2001;Verheijen et al 2007;Catinella et al 2008;Catinella and Cortese 2015). Recently, H I emission from a strongly lensed galaxy at z = 0.407 has been marginally detected by Blecher et al (2019). The dearth of detections at high redshift is mainly due to the intrinsic weakness of the 21-cm emission line, but is also affected by the available frequency ranges (e.g., Hess et al 2019), the presence of radio frequency interference (RFI), and limited observing time on current radio telescopes.…”

Deep Extragalactic VIsible Legacy Survey (DEVILS): DR1 Blended Spectra Search for Candidate Strong Gravitational Lenses

“…WAVES and ORCIDSS using the 4MOST instrument. Confirmation of these lenses may come in the form of magnified H rather (cf Deane et al 2015;Blecher et al 2019) than resolved imaging of the lensing arcs or high resolution imaging even with the Roman or Euclid space telescopes or targeted follow-up with JWST. Future data-releases from DEVILS promise to improve the numbers of strong lenses known at 𝑧 ∼ 1 in the immediate future.…”

“…Lipnicky et al (2018) report the first strongly lensed HI detection using a nearby edge-on spiral galaxy as the lens. The new H surveys, such as MIGHTEE (Jarvis et al 2016;Delhaize et al 2021;Maddox et al 2021) and LADUMA (Holwerda 2011;Blyth 2015;Blyth et al 2016;Baker et al 2018) using the MeerKAT radio telescope and WALLABY (Koribalski et al 2020) on ASKAP (Johnston et al 2008), promise a boon of H detections lensed by a closer galaxy (Deane et al 2015;Blecher et al 2019). A magnified H detection would allow these surveys to probe below their sensitivity limit to verify for example the results from stacking H spectra for a given galaxy population (cf Delhaize et al 2013;Healy et al 2021;Chowdhury et al 2020Chowdhury et al , 2021.…”

WALLABY -- An SKA Pathfinder HI Survey

“…One of the highest redshift detections in H i emission from an individual galaxy, obtained in the COSMOS H i Large Extragalactic Survey (CHILES), is at z = 0.376 (Fernandez et al 2016), well surpassing previous detections at z ∼ 0.2 (Zwaan et al 2001;Verheijen et al 2007;Catinella et al 2008;Catinella & Cortese 2015). Recently, H i emission from a strongly lensed galaxy at z = 0.407 has been marginally detected by Blecher et al (2019). The dearth of detections at high redshift is mainly due to the intrinsic weakness of the 21-cm emission line, but is also affected by the available frequency ranges (e.g., Hess et al 2019) and limited observing time on current radio telescopes.…”