NGC 2273 is a
barred spiral galaxy located in the constellation
Lynx. It is located at a distance of circa 95 million
light years from Earth, which, given its apparent dimensions, means that NGC 2273 is about 100,000 light years across. It was discovered by
Nils Dunér on September 15, 1867.[3]
Characteristics
NGC 2273 has a
multiring structure. The galaxy has an inner ring and two outer pseudorings formed by two sets of
spiral arms. The galaxy is seen with an inclination of 41 degrees. The galaxy hosts about 1.1×109M☉ of
hydrogen gas (HI), with most of it lying at the outer pseudoring. The galaxy also hosts large amounts of molecular gas, as indicated by the CO lines, which is regarded as an indicator of active
star formation.[4] The total infrared luminosity of the galaxy is 1010.25L☉.[5] The galaxy has a bar whose radius is 40 arcseconds.[6]
Observations of the central 20 arcseconds of the galaxy by the
Hubble Space Telescope showed spiral arms that corresponded to the inner ring. The central ovoid of the galaxy was found to feature a bar-like structure and two arc structures that form a partial nuclear ring. Its emission is associated with the presence of
HII regions.[7] Around the nucleus lies a dusty ring-like structure, with a radius of 7 arcseconds, better seen at its northwest part. Another dusty ring is observed with 20 arcseconds radius.[8]
Nucleus
Based on the
emission lines that are present in its
spectrum, the nucleus of NGC 2273 has been characterised as
active and it has been categorised as a type II
Seyfert galaxy.[9][10] Also, a water
kilomaser has been detected in the nuclear region of the galaxy. It could be created either by the active nucleus or by a prominent site of star formation.[11]
Observations by
BeppoSAX,
XMM Newton, and
Chandra X-Ray Observatory suggested that the nucleus of NGC 2273 is obscured by a Compton thick column, with high
column density,[12][13] estimated to be 1.1×1024 cm−2 as measured by
ASCA,[14] or 1.5×1024 cm−2 as measured by
Suzaku.[15] The harder X-Rays manage to get through and are dominated by reflection from cold material, as the Fe-K line indicates.[14] The spectrography of the nuclear regions is weakly
polarised, more prominent in
H-alpha.[16] The broad X-ray spectrum of NGC 2273 has been found to be composed of a thermal or scattered soft component, a reflected component, and an absorbed power law component. The 2–10 keV X-ray flux of the galaxy is estimated to be 1.7×1042 ergs−1.[15]
The nucleus also emits
radiowaves. The radio source has been found to be linear and is composed of two unequal radio features separated by about 170
parsecs.[17] These two radio features have been identified as
radio jets. A linear jet-like feature extending for 2 arcseconds east of the nucleus was observed in [O III] λ5007 images. It is aligned with the radio jets and is possibly of nuclear origin.[7]
The most accepted theory for the energy source of active galactic nuclei is the presence of an
accretion disk around a
supermassive black hole. The mass of the black hole in the centre of NGC 2273 is estimated to be between (7.5±0.4)×106M☉ based on kinematics of the water maser circumnuclear disk. The disk appears warped.[18]
Nearby galaxies
NGC 2273 is the brightest galaxy in a
galaxy group known as the NGC 2273 group. Other members of the group include the galaxies NGC 2237B and UGC 3504.[19][20] NGC 2237B lies 40 arcminutes to the south.[21]
^van Driel, W.; Buta, R. J. (1 May 1991). "A study of the ringed galaxies NGC2273, 4826, and 6217. I - H I line observations". Astronomy and Astrophysics. 245: 7–26.
Bibcode:
1991A&A...245....7V.
ISSN0004-6361.
^Yankulova, I. M. (1 April 1999). "The circumnuclear gas and dust environment of the ringed Seyfert 2 galaxy MKN 620". Astronomy and Astrophysics. 344: 36–42.
Bibcode:
1999A&A...344...36Y.
ISSN0004-6361.
^Ho, Luis C.; Filippenko, Alexei V.; Sargent, Wallace L. W. (October 1997). "A Search for "Dwarf Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". The Astrophysical Journal Supplement Series. 112 (2): 315–390.
arXiv:astro-ph/9704107.
Bibcode:
1997ApJS..112..315H.
doi:
10.1086/313041.
S2CID17086638.
^Maiolino, R.; Salvati, M.; Bassani, L.; Dadina, M.; della Ceca, R.; Matt, G.; Risaliti, G.; Zamorani, G. (1 October 1998). "Heavy obscuration in X-ray weak AGNs". Astronomy and Astrophysics. 338: 781–794.
arXiv:astro-ph/9806055.
Bibcode:
1998A&A...338..781M.
ISSN0004-6361.
^
abAwaki, Hisamitsu; Terashima, Yuichi; Higaki, Yuusuke; Fukazawa, Yasushi (30 January 2009). "Detection of Hard X-Rays from the Compton-Thick Seyfert 2 Galaxy NGC 2273 with Suzaku". Publications of the Astronomical Society of Japan. 61 (sp1): S317–S325.
arXiv:0810.4570.
Bibcode:
2009PASJ...61S.317A.
doi:
10.1093/pasj/61.sp1.S317.
S2CID12846803.
^de Vaucouleurs, G.; de Vaucouleurs, A.; Corwin, J. R. (1976). "Second reference catalogue of bright galaxies". Second Reference Catalogue of Bright Galaxies. 1976.
Bibcode:
1976RC2...C......0D.