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| Main Authors: | , , , , |
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| Format: | Preprint |
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2026
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2604.02831 |
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| _version_ | 1866911618133131264 |
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| author | Mao, Ye-Wei Ho, Luis C. Moiseev, Alexei V. Egorov, Oleg V. Sobolev, Andrej M. |
| author_facet | Mao, Ye-Wei Ho, Luis C. Moiseev, Alexei V. Egorov, Oleg V. Sobolev, Andrej M. |
| contents | In this Letter, we report a novel discovery of unique characteristics for the tidal dwarf galaxy (candidate) Holmberg IX via a multiwavelength investigation. New observations are taken for deeply mapping Hα emission and combined with archival/published data for comprehensively probing dust, gas, and stellar populations in this galaxy. We find in Holmberg IX a dearth of dust incompatible with its rich gas and metal; globally young stellar populations with prominent far-ultraviolet but deficient and marginal Hα emissions, distinct from other tidal dwarf galaxies ever known. By assuming a normal initial mass function (IMF), Holmberg IX is suggested to be born ~130 Myr ago from a bursty star formation event, which then rapidly ceased, with very few stars formed in the past ~80 Myr that demarcates a lower age limit for the galactic mainbody; current star formation occurs only in outskirts, bringing a conundrum about the reason for the recent quenching in such a gas-rich environment. Contradicting the general expectation for tidal dwarf galaxies hosting continuous star formation, the present quiescence implies Holmberg IX currently staying in a rarely-seen transient period. Without star formation continuing, Holmberg IX is likely transforming into a dwarf spheroidal galaxy, or oppositely into a(n) (ultra-)diffuse system which will probably dissolve in the end. Instead, if Holmberg IX possesses peculiar IMF and hosts low-mass, weak-Hα star formation, it is able to maintain long-term survival in its current status. On whichever evolutionary pathway in reality, Holmberg IX appears as a special case updating conventional understandings of tidal dwarf galaxies and hinting potential existence of similar analogs in the Universe. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_02831 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Holmberg IX: A Unique, Infant but Inactive Galaxy as Revealed via a Multiwavelength Approach Mao, Ye-Wei Ho, Luis C. Moiseev, Alexei V. Egorov, Oleg V. Sobolev, Andrej M. Astrophysics of Galaxies In this Letter, we report a novel discovery of unique characteristics for the tidal dwarf galaxy (candidate) Holmberg IX via a multiwavelength investigation. New observations are taken for deeply mapping Hα emission and combined with archival/published data for comprehensively probing dust, gas, and stellar populations in this galaxy. We find in Holmberg IX a dearth of dust incompatible with its rich gas and metal; globally young stellar populations with prominent far-ultraviolet but deficient and marginal Hα emissions, distinct from other tidal dwarf galaxies ever known. By assuming a normal initial mass function (IMF), Holmberg IX is suggested to be born ~130 Myr ago from a bursty star formation event, which then rapidly ceased, with very few stars formed in the past ~80 Myr that demarcates a lower age limit for the galactic mainbody; current star formation occurs only in outskirts, bringing a conundrum about the reason for the recent quenching in such a gas-rich environment. Contradicting the general expectation for tidal dwarf galaxies hosting continuous star formation, the present quiescence implies Holmberg IX currently staying in a rarely-seen transient period. Without star formation continuing, Holmberg IX is likely transforming into a dwarf spheroidal galaxy, or oppositely into a(n) (ultra-)diffuse system which will probably dissolve in the end. Instead, if Holmberg IX possesses peculiar IMF and hosts low-mass, weak-Hα star formation, it is able to maintain long-term survival in its current status. On whichever evolutionary pathway in reality, Holmberg IX appears as a special case updating conventional understandings of tidal dwarf galaxies and hinting potential existence of similar analogs in the Universe. |
| title | Holmberg IX: A Unique, Infant but Inactive Galaxy as Revealed via a Multiwavelength Approach |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2604.02831 |