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25 April 2024 |
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A Comprehensive Archival Search for Counterparts to Ultra-Compact High Velocity Clouds: Five Local Volume Dwarf Galaxies | | D.J. Sand
; D. Crnojević
; P. Bennet
; B. Willman
; J. Hargis
; J. Strader
; E. Olszewski
; E.J. Tollerud
; J.D. Simon
; N. Caldwell
; P. Guhathakurta
; B. L. James
; S. Koposov
; B. McLeod
; N. Morrell
; M. Peacock
; R. Salinas
; A.C. Seth
; D. P. Stark
; E. Toloba
; | | Date: |
2 Mar 2015 | | Abstract: | We report the discovery of five Local Volume dwarf galaxies uncovered during
a comprehensive archival search for optical counterparts to ultra-compact high
velocity clouds (UCHVCs). The UCHVC population of HI clouds are thought to be
candidate gas-rich, low mass halos at the edge of the Local Group and beyond,
but no comprehensive search for stellar counterparts to these systems has been
presented. Careful visual inspection of all publicly available optical and
ultraviolet imaging at the position of the UCHVCs revealed six blue, diffuse
counterparts with a morphology consistent with a faint dwarf galaxy beyond the
Local Group. Optical spectroscopy of all six candidate dwarf counterparts show
that five have an H$alpha$-derived velocity consistent with the coincident HI
cloud, confirming their association; the sixth diffuse counterpart is likely a
background object. The size and luminosity of the UCHVC dwarfs is consistent
with other known Local Volume dwarf irregular galaxies. The gas fraction
($M_{HI}/M_{star}$) of the five dwarfs are generally consistent with that of
dwarf irregular galaxies in the Local Volume, although ALFALFA-Dw1 (associated
with ALFALFA UCHVC HVC274.68+74.70$-$123) has a very high
$M_{HI}/M_{star}$$sim$40. Despite the heterogenous nature of our search, we
demonstrate that the current dwarf companions to UCHVCs are at the edge of
detectability due to their low surface brightness, and that deeper searches are
likely to find more stellar systems. If more sensitive searches do not reveal
further stellar counterparts to UCHVCs, then the dearth of such systems around
the Local Group may be in conflict with $Lambda$CDM simulations. | | Source: | arXiv, 1503.0720 | | Services: | Forum | Review | PDF | Favorites | |
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