Are the Milky Way and Andromeda unusual? A comparison with Milky Way and Andromeda Analogs. (arXiv:2009.02576v2 [astro-ph.GA] UPDATED)

Are the Milky Way and Andromeda unusual? A comparison with Milky Way and Andromeda Analogs. (arXiv:2009.02576v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Boardman_N/0/1/0/all/0/1">Nicholas Fraser Boardman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zasowski_G/0/1/0/all/0/1">Gail Zasowski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Newman_J/0/1/0/all/0/1">Jeffrey Newman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Andrews_B/0/1/0/all/0/1">Brett Andrews</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fielder_C/0/1/0/all/0/1">Catherine Fielder</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bershady_M/0/1/0/all/0/1">Matthew Bershady</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brinkmann_J/0/1/0/all/0/1">Jonathan Brinkmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Drory_N/0/1/0/all/0/1">Niv Drory</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krishnarao_D/0/1/0/all/0/1">Dhanesh Krishnarao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lane_R/0/1/0/all/0/1">Richard Lane</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mackereth_T/0/1/0/all/0/1">Ted Mackereth</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Masters_K/0/1/0/all/0/1">Karen Masters</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stringfellow_G/0/1/0/all/0/1">Guy Stringfellow</a>

Our Milky Way provides a unique test case for galaxy evolution models, thanks
to our privileged position within the Milky Way’s disc. This position also
complicates comparisons between the Milky Way and external galaxies, due to our
inability to observe the Milky Way from an external point of view. Milky Way
analog galaxies offer us a chance to bridge this divide by providing the
external perspective that we otherwise lack. However, over-precise definitions
of “analog” yield little-to-no galaxies, so it is vital to understand which
selection criteria produce the most meaningful analog samples. To address this,
we compare the properties of complementary samples of Milky Way analogs
selected using different criteria. We find the Milky Way to be within 1$sigma$
of its analogs in terms of star-formation rate and bulge-to-total ratio in most
cases, but we find larger offsets between the Milky Way and its analogs in
terms of disc scale length; this suggests that scale length must be included in
analog selections in addition to other criteria if the most accurate analogs
are to be selected. We also apply our methodology to the neighbouring Andromeda
galaxy. We find analogs selected on the basis of strong morphological features
to display much higher star-formation rates than Andromeda, and we also find
analogs selected on Andromeda’s star-formation rate to over-predict Andromeda’s
bulge extent. This suggests both structure and star-formation rate should be
considered when selecting the most stringent Andromeda analogs.

Our Milky Way provides a unique test case for galaxy evolution models, thanks
to our privileged position within the Milky Way’s disc. This position also
complicates comparisons between the Milky Way and external galaxies, due to our
inability to observe the Milky Way from an external point of view. Milky Way
analog galaxies offer us a chance to bridge this divide by providing the
external perspective that we otherwise lack. However, over-precise definitions
of “analog” yield little-to-no galaxies, so it is vital to understand which
selection criteria produce the most meaningful analog samples. To address this,
we compare the properties of complementary samples of Milky Way analogs
selected using different criteria. We find the Milky Way to be within 1$sigma$
of its analogs in terms of star-formation rate and bulge-to-total ratio in most
cases, but we find larger offsets between the Milky Way and its analogs in
terms of disc scale length; this suggests that scale length must be included in
analog selections in addition to other criteria if the most accurate analogs
are to be selected. We also apply our methodology to the neighbouring Andromeda
galaxy. We find analogs selected on the basis of strong morphological features
to display much higher star-formation rates than Andromeda, and we also find
analogs selected on Andromeda’s star-formation rate to over-predict Andromeda’s
bulge extent. This suggests both structure and star-formation rate should be
considered when selecting the most stringent Andromeda analogs.

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