H i in extremely metal deficient galaxies – III. Giant Metrewave Radio Telescope observations of blue compact galaxy HS 0822+3542 |
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| Authors: | Jayaram N Chengalur S A Pustilnik J-M Martin A Y Kniazev |
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| Institution: | ATNF/CSIRO, PO Box 76, Epping NSW 1710, Australia;NCRA (TIFR), Pune University Campus, Postbag 3, Ganeshkhind, Pune 411007, India;Special Astrophysical Observatory RAS, Nizhnij Arkhyz, Karachai-Circassia, 369167 Russia;Observatoire de Paris, 5, place J. Janssen, 92195 Meudon Cedex, France;South African Astronomical Observatory, Cape Town, South Africa |
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| Abstract: | We present the results of Giant Metrewave Radio Telescope H i 21-cm line observations of the extremely metal deficient (XMD) blue compact galaxy (BCG) HS 0822+3542. HS 0822+3542 is the smallest known XMD galaxy; from Hubble Space Telescope ( HST ) imaging, it has been suggested that it actually consists of two still smaller (～100 pc sized) ultra-compact dwarfs that are in the process of merging. The brighter of these two putative ultra-compact dwarfs has an ocular appearance, similar to that seen in galaxies that have suffered a penetrating encounter with a smaller companion. From our H i imaging, we find that the gas distribution and kinematics in this object are similar to that of other low-mass galaxies, albeit with some evidence for tidal disturbance. On the other hand, the H i emission has an angular size ～25 times larger than that of the putative ultra-compact dwarfs. The optical emission is also offset from the centre of the H i emission. HS 0822+3542 is located in the nearby Lynx–Cancer void, but has a nearby companion low surface brightness dwarf galaxy SAO 0822+3545. In light of all this, we also consider a scenario where the optical emission from HS 0822+3542 comes not from two merging ultra-compact dwarfs but from multiple star-forming regions in a tidally disturbed galaxy. In this model, the ocular appearance of the brighter star-forming region could be the result of triggered star formation. |
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| Keywords: | galaxies: individual: HS 0822+3542 galaxies: individual: SAO 0822+3545 galaxies: interaction galaxies: ISM galaxies: kinematics and dynamics |
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