HST resolves stars in a tiny body falling on the dwarf galaxy DDO 68. (arXiv:1904.01986v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Annibali_F/0/1/0/all/0/1">F. Annibali</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Bellazzini_M/0/1/0/all/0/1">M. Bellazzini</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Correnti_M/0/1/0/all/0/1">M. Correnti</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Sacchi_E/0/1/0/all/0/1">E. Sacchi</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Tosi_M/0/1/0/all/0/1">M. Tosi</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Cignoni_M/0/1/0/all/0/1">M. Cignoni</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Aloisi_A/0/1/0/all/0/1">A. Aloisi</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Calzetti_D/0/1/0/all/0/1">D. Calzetti</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Ciotti_L/0/1/0/all/0/1">L. Ciotti</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Cusano_F/0/1/0/all/0/1">F. Cusano</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Lee_J/0/1/0/all/0/1">J. Lee</a> (6), <a href="http://arxiv.org/find/astro-ph/1/au:+Nipoti_C/0/1/0/all/0/1">C. Nipoti</a> (5) ((1) INAF-Astrophysics and Space Science Observatory, Bologna, Italy (2) Space Telescope Science Institute, Baltimore, USA (3) Dipartimento di Fisica, Universita&#x27; di Pisa, Italy (4) Department of Astronomy, University of Massachusetts-Amherst, USA (5) Dipartimento di Fisica e Astronomia, Universita&#x27; di Bologna, Italy (6) Caltech-IPAC, USA)

We present new Hubble Space Telescope (HST) imaging of a stream-like system
associated with the dwarf galaxy DDO 68, located in the Lynx-Cancer Void at a
distance of D$sim$12.65 Mpc from us. The stream, previously identified in deep
Large Binocular Telescope images as a diffuse low surface brightness structure,
is resolved into individual stars in the F606W (broad V) and F814W ($sim$I)
images acquired with the Wide Field Camera 3. The resulting V, I
color-magnitude diagram (CMD) of the resolved stars is dominated by old
(age$gtrsim$1-2 Gyr) red giant branch (RGB) stars. From the observed RGB tip,
we conclude that the stream is at the same distance as DDO 68, confirming the
physical association with it. A synthetic CMD analysis indicates that the large
majority of the star formation activity in the stream occurred at epochs
earlier than $sim$1 Gyr ago, and that the star formation at epochs more recent
than $sim$500 Myr ago is compatible with zero. The total stellar mass of the
stream is $sim10^{6} M_{odot}$, about 1/100 of that of DDO~68. This is a
striking example of hierarchical merging in action at the dwarf galaxy scales.

We present new Hubble Space Telescope (HST) imaging of a stream-like system
associated with the dwarf galaxy DDO 68, located in the Lynx-Cancer Void at a
distance of D$sim$12.65 Mpc from us. The stream, previously identified in deep
Large Binocular Telescope images as a diffuse low surface brightness structure,
is resolved into individual stars in the F606W (broad V) and F814W ($sim$I)
images acquired with the Wide Field Camera 3. The resulting V, I
color-magnitude diagram (CMD) of the resolved stars is dominated by old
(age$gtrsim$1-2 Gyr) red giant branch (RGB) stars. From the observed RGB tip,
we conclude that the stream is at the same distance as DDO 68, confirming the
physical association with it. A synthetic CMD analysis indicates that the large
majority of the star formation activity in the stream occurred at epochs
earlier than $sim$1 Gyr ago, and that the star formation at epochs more recent
than $sim$500 Myr ago is compatible with zero. The total stellar mass of the
stream is $sim10^{6} M_{odot}$, about 1/100 of that of DDO~68. This is a
striking example of hierarchical merging in action at the dwarf galaxy scales.

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