NGC 404

Template:Short description {{#invoke:Infobox|infobox}}Template:Template other{{#invoke:Check for unknown parameters|check|unknown=Template:Main other|preview=Page using Template:Infobox galaxy with unknown parameter "_VALUE_"| ignoreblank=y | name | image | image_scale | caption | alt | epoch | pronounce | constellation name | ra | dec | z | h_radial_v | gal_v | dist_pc | dist_ly | group_cluster | type | mass | mass_light_ratio | size | stars | appmag_v | appmag_b | absmag_v | absmag_b | mag_j | mag_h | mag_k| size_v | sbrightness | half_light_radius_pc | half_light_radius_arcminsec | h1_scale_length_pc | h1_scale_length_arcminsec | xray_radius_pc | xray_radius_arcminsec | notes | names | references }}

NGC 404 is a field galaxy<ref name=1979A&A....74..235M>Template:Cite journal</ref> located about 10 million light years away in the constellation Andromeda. It was discovered by William Herschel in 1784, and is visible through small telescopes.<ref name="EncSci">Mirach's Ghost (NGC 404), The Internet Encyclopedia of Science, David Darling. Accessed on line August 15, 2008.</ref> NGC 404 lies just beyond the Local Group and does not appear gravitationally bound to it. It is located within 7 arc-minutes of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".<ref name="EncSci" /><ref name="jpl">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Physical characteristics

NGC 404 is a very isolated dwarf lenticular galaxy, a bit more luminous and smaller than the Small Magellanic Cloud.<ref name="Karachentsev2004">Template:Cite journal</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">Template:Cite journal</ref> It also has star formation both in its center<ref name="Bouchard2010">Template:Cite journal</ref> and in its outermost regions, albeit at a low level.<ref name="Thilker2010">Template:Cite journal</ref>

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

LINER emission

NGC 404 contains a low-ionization nuclear emission-line region (LINER), a type of region that is characterized by spectral line emission from weakly ionized atoms.<ref name="hoetal1997">Template:Cite journal</ref> A nuclear star cluster is also present as well as (likely) a supermassive black hole, with a mass of several tens of thousands solar masses.<ref name="Seth2010">Template:Cite journal</ref>

Distance measurements

At least two techniques have been used to measure distances to NGC 404. The infrared surface brightness fluctuations distance measurement technique estimates distances to spiral galaxies based on the graininess of the appearance of their bulges. The distance measured to NGC 404 using this technique in 2003 is 9.9 ± 0.5 Mly (3.03 ± 0.15 Mpc).<ref name="jensenetal2003">Template:Cite journal</ref>

However, NGC 404 is close enough that red supergiants can be imaged as individual stars. The light from these stars and knowledge of how they should compare to nearby stars within the Milky Way galaxy allows for direct measurement of the distance to the galaxy. This method is referred to as the tip of the red giant branch (TRGB) method. The estimated distance to NGC 404 using this technique is 10.0 ± 1.2 Mly (3.1 ± 0.4 Mpc).<ref name="karachentsevetal2004">Template:Cite journal</ref> Averaged together, these distance measurements give a distance estimate of 10.0 ± 0.7 Mly (3.07 ± 0.21 Mpc).Template:Ref label

Possible satellite

In 2018 a possible satellite designated Donatiello I was identified.<ref name=ForbesDonatiello /> Donatiello I is a dwarf spheroidal galaxy with little recent star formation.<ref name=ForbesDonatiello /> Difficulty in establishing the exact distance to the galaxy leaves its status as a satellite unconfirmed.<ref name=ForbesDonatiello>Template:Cite journal</ref>

Gallery

• NGC 404 PanS.jpg

  Pan-STARRS image of NGC 404

Notes

1. Template:Note labelaverage(3.03 ± 0.15, 3.1 ± 0.4) = ((3.03 + 3.1) / 2) ± ((0.15² + 0.4²)^0.5 / 2) = 3.07 ± 0.21

External links

• Encyclopedia of Astrobiology, Astronomy & Spaceflight Entry
• Curdridge Observatory article
• Template:APOD
• Template:WikiSky