NGC 404 is a field galaxy located about 10 million light years away in the constellation Andromeda. It was discovered by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline ...

in 1784, and is visible through small telescopes.Mirach's Ghost (NGC 404)
''The Internet Encyclopedia of Science'', David Darling. Accessed on line August 15, 2008. NGC 404 lies just beyond the

Local Group The Local Group is the galaxy group that includes the Milky Way. It has a total diameter of roughly , and a total mass of the order of . It consists of two collections of galaxies in a "dumbbell" shape: the Milky Way and its satellites form ...

and does not appear gravitationally bound to it. It is located within 7

arc-minute A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

s of second magnitude star Mirach, making it a difficult target to observe or photograph and granting it the nickname "Mirach's Ghost".

Physical characteristics

NGC 404 is a very isolated dwarf

lenticular galaxy A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. ...

, a bit more luminous and smaller than the Small Magellanic Cloud. 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. It also has star formation both on its center and on its outermost regions, albeit at a low level 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 and it has been proposed NGC 404 is a former spiral galaxy that was transformed into a lenticular one by that event

LINER emission

NGC 404 contains a low-ionization nuclear emission-line region (LINER), a type of region that is characterized by

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

emission from weakly

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

ized atoms. A nuclear star cluster is also present as well as -likely- a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical ob ...

, with a mass of several tens of thousands solar masses

Distance measurements

At least two techniques have been used to measure distances to NGC 404. The infrared

surface brightness fluctuation Surface brightness fluctuation (SBF) is a secondary distance indicator used to estimate distances to galaxies. It is useful to 100 Mpc (parsec). The method measures the variance in a galaxy's light distribution arising from fluctuations in the n ...

s 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 A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

(3.03 ± 0.15 Mpc). However, NGC 404 is close enough that

red supergiants Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelgeuse and Anta ...

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 The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

galaxy allows for direct measurement of the distance to the galaxy. This method is referred to as the

tip of the red giant branch Tip of the red-giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy. It has been used in conj ...

(TRGB) method. The estimated distance to NGC 404 using this technique is 10.0 ± 1.2 Mly (3.1 ± 0.4 Mpc). Averaged together, these distance measurements give a distance estimate of 10.0 ± 0.7 Mly (3.07 ± 0.21 Mpc).

Possible satellite

In 2018 a possible satellite designated Donatiello I was identified. Donatiello I is a

dwarf spheroidal galaxy A dwarf spheroidal galaxy (dSph) is a term in astronomy applied to small, low-luminosity galaxies with very little dust and an older stellar population. They are found in the Local Group as companions to the Milky Way and to systems that are com ...

with little recent star formation. Difficulty in establishing the exact distance to the galaxy leaves its status as a satellite unconfirmed.

Gallery

File:NGC 404 PanS.jpg,

Pan-STARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; obs. code: F51 and Pan-STARRS2 obs. code: F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical cameras, telescopes and a computing facility that is ...

image of NGC 404

Notes

average(3.03 ± 0.15, 3.1 ± 0.4) = ((3.03 + 3.1) / 2) ± ((0.15² + 0.4²)^0.5 / 2) = 3.07 ± 0.21

References

External links

Encyclopedia of Astrobiology, Astronomy & Spaceflight Entry

* * {{DEFAULTSORT:NGC 0404 Lenticular galaxies Field galaxies LINER galaxies Andromeda (constellation) 0404 00718 04126 17840913 Virgo Supercluster Discoveries by William Herschel