Editing NGC 404 (section)

== Physical characteristics ==

[[New General Catalogue|NGC]] 404 is a very isolated dwarf [[lenticular galaxy]], a bit more luminous and smaller than the [[Small Magellanic Cloud]].<ref name="Karachentsev2004">{{cite journal
    | author=Karachentsev, Igor D. | author2=Karachentseva, Valentina E. | author3=Huchtmeier, Walter K. | author4=Makarov, Dmitry I.
    | title=A Catalog of Neighboring Galaxies
    | journal=The Astronomical Journal
    | date=2003
    | volume=127
    | issue=4
    | pages=2031–2068
    | bibcode=2004AJ....127.2031K
    | doi=10.1086/382905| doi-access=free
    }}</ref> Unlike many other early-type galaxies, it is very rich in [[neutral hydrogen]], most of it concentrated in a pair of large rings around it.<ref name="Rio2004">{{cite journal
    | author=del Río, M. S. | author2=Brinks, E. | author3=Cepa, J.
    | title=High-Resolution H I Observations of the Galaxy NGC 404: A Dwarf S0 with Abundant Interstellar Gas
    | journal=The Astronomical Journal
    | date=2004
    | volume=128
    | issue=1
    | pages=89–102
    | bibcode=2004AJ....128...89D
    | doi=10.1086/421358|arxiv = astro-ph/0403467 | s2cid=118900337 }}</ref> It also has [[star formation]] both in its center<ref name="Bouchard2010">{{cite journal
    | author=Bouchard, A. | author2=Prugniel, P. | author3=Koleva, M. | author4=Sharina, M.
    | title=Stellar population and kinematics of NGC 404
    | journal=Astronomy & Astrophysics
    | date=2010
    | volume=513
    | pages=A54 | id=A54
    | bibcode=2010A&A...513A..54B
    | doi=10.1051/0004-6361/200913137|arxiv = 1001.4087 | s2cid=54924295 }}</ref> and in its outermost regions, albeit at a low level.<ref name="Thilker2010">{{cite journal
    | author=Thilker, David A. | display-authors=4 | author2=Bianchi, Luciana | author3=Schiminovich, David | author4=Gil de Paz, Armando | author5=Seibert, Mark | author6=Madore, Barry F. | author7=Wyder, Ted | author8=Rich, R. Michael | author9=Yi, Sukyoung | author10=Barlow, Tom | author11=Conrow, Tim | author12=Forster, Karl | author13=Friedman, Peter | author14=Martin, Chris | author15=Morrissey, Patrick | author16=Neff, Susan | author17=Small, Todd
    | title=NGC 404: A Rejuvenated Lenticular Galaxy on a Merger-induced, Blueward Excursion Into the Green Valley
    | journal=The Astrophysical Journal Letters
    | date=2010
    | volume=714
    | issue=1
    | pages=L171–L175
    | bibcode=2010ApJ...714L.171T
    | doi=10.1088/2041-8205/714/1/L171|arxiv = 1003.4985 | s2cid=51511487 }}</ref>

Both the outer gas disk and its star formation are assumed to have been triggered by one or several [[galaxy merger|mergers]] with smaller galaxies roughly 1 billion years ago<ref name="Thilker2010" /> and it has been proposed [[New General Catalogue|NGC]] 404 is a former [[spiral galaxy]] that was transformed into a lenticular one by that event.<ref name="Bouchard2010" />