Constraining The Redshift Of Featureless Blazar 1ES 1553+113 And Implications For The WHIM
Abstract
Observations of the warm-hot (T > 105 K) phase of the intergalactic medium provide an important test of our understanding of galaxy evolution and help to verify our general cosmological paradigm. Simulations of structure growth predict that a substantial portion of baryonic matter is shock-heated to form the elusive warm-hot intergalactic medium (WHIM); however, with current facilities, very few blazars and AGN are bright enough to probe the WHIM in X-ray absorption. The bright blazar 1ES 1553+113 provides a unique opportunity to study the WHIM in X-ray absorption over a large redshift pathlength due to investment of 1.8 megaseconds of XMM-Newton grating spectroscopy. Despite numerous attempts with large telescopes across the electromagnetic spectrum, observers have been unable to directly constrain the redshift of 1ES 1553+113, limiting the utility of the archival X-ray spectra. Here, we present the near-UV (NUV) spectrum of 1ES 1553+113 obtained by the Cosmic Origins Spectrograph (COS) on HST and perform a blind search for absorption lines to constrain its redshift indirectly. We find that the Lyα forest toward this blazar does not extend past z = 0.413. To infer an independent redshift constraint from this, we carry out a robust characterization of the edge of the observed HI Lyα forest by identifying the highest-redshift Lyα lines (max(zLyα)) in the high-quality COS FUV spectra of 192 AGN that have accurate spectroscopic systemic redshifts (zsys). We use the observed cumulative distribution of zsys - max(zLyα) to infer a new 95% confidence interval for the redshift of 1ES 1553+113 of 0.408 < z < 0.434. This redshift constraint rules out a WHIM origin for the stronger X-ray absorber detected toward 1ES 1553+113, perhaps suggesting that the WHIM is not sufficiently metal enriched to be confidently detected in O VII or O VIII with current facilities. Finally, we apply our redshift constraint technique to other well-known blazars with difficult-to-measure redshifts, demonstrating its utility for future X-ray missions that aim to study the WHIM and also for constraints on the extragalactic background light.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- June 2021
- Bibcode:
- 2021AAS...23811602D