English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present results from deep HI and optical imaging of AGC 229101, an unusualHI source detected at v$_{\rm helio}$ = 7116 km/s in the ALFALFA survey.Initially classified as a candidate "dark" source because it lacks a clearoptical counterpart in SDSS or DSS2 imaging, AGC 229101 has $10^{9.31\pm0.05}$solar masses of HI, but an HI line width of only 43$\pm$9 km/s. Low resolutionWSRT imaging and higher resolution VLA B-array imaging show that the source issignificantly elongated, stretching over a projected length of ~80 kpc. The HIimaging resolves the source into two parts of roughly equal mass. WIYN pODIoptical imaging reveals a faint, blue optical counterpart coincident with thenorthern portion of the HI. The peak surface brightness of the optical sourceis only $\mu_{g}$ = 26.6 mag arcsec$^{-2}$, well below the typical cutoff thatdefines the isophotal edge of a galaxy, and its estimated stellar mass is only$10^{7.32\pm0.33}$ solar masses, yielding an overall neutral gas-to-stellarmass ratio of M$_{\rm HI}$/M$_*=$~98$_{+111}\atop^{-52}$. We demonstrate theextreme nature of this object by comparing its properties to those of otherHI-rich sources in ALFALFA and the literature. We also explore potentialscenarios that might explain the existence of AGC~229101, including a tidalencounter with neighboring objects and a merger of two dark HI clouds.

The ALFALFA Almost-Dark Galaxy AGC~229101: A Two Billion Solar Mass HI Cloud with a Very Low Surface Brightness Optical Counterpart