Letter to the Editor

The host galaxy of the BL Lacertae object 1ES 0647+250 and its imaging redshift

¹ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
e-mail: jarkot@utu.fi
² Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
³ Osservatorio Astronomico di Padova, INAF, vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Dipartimento di Fisica e Matematica, Università dell’Insubria, via Valleggio 11, 22100 Como, affiliated to INAF and INFN, Italy
⁵ INAF-IASF Milano, via E. Bassini 15, 20133 Milano, Italy

Received: 31 July 2011
Accepted: 1 September 2011

Abstract

Aims. Since no spectroscopic redshift is available for the remarkable BL Lacertae object (BL Lac) 1ES 0647+250, we aim to derive an estimate of its distance from the properties of its host galaxy.

Methods. We obtained a deep, high-resolution near-infrared H-band image of the BL Lac object 1ES 0647+250.

Results. We are able to detect the underlying host galaxy in the near-infrared. The host galaxy has an H-band magnitude of 16.9  ±  0.2 and an effective radius of 16  ±  03. Using the imaging redshift method developed by Sbarufatti and collaborators, we estimate a redshift z = 0.41  ±  0.06. This redshift is consistent with the previously reported imaging redshift estimate from the optical i′-band of z = 0.45  ±  0.08, and with previously reported lower limits to the redshift. It agrees with constraints from its gamma-ray emission.

Conclusions. We encourage imaging searches in the near-infrared, even with moderately sized telescopes, of the host galaxies of BL Lac objects at unknown redshift, as well as optical spectroscopy studies of 1ES 0647+250 with large telescopes to determine its spectroscopic redshift.