Sombrero Galaxy

Template:Short description {{#invoke:other uses|otheruses}} {{#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 }} The Sombrero Galaxy (also known as Messier Object 104, M104<ref name= "simbad"/> or NGC 4594) is a peculiar galaxy of unclear classification<ref name="scidaily2012" /> in the constellation borders of Virgo and Corvus, being about Template:Convert<ref name="McQuinn2016"/> from the Milky Way galaxy. It is a member of the Virgo II Groups, a series of galaxies and galaxy clusters strung out from the southern edge of the Virgo Supercluster.<ref name="atlas universe">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It has an isophotal diameter of approximately Template:Convert,<ref name="ned"/> making it slightly bigger in size than the Milky Way.

It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its outer disk, which from Earth is viewed almost edge-on. The dark dust lane and the bulge give it the appearance of a sombrero hat (thus the name). Astronomers initially thought the halo was small and light, indicative of a spiral galaxy; but the Spitzer Space Telescope found that the halo was significantly larger and more massive than previously thought, indicative of a giant elliptical galaxy.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The galaxy has an apparent magnitude of +8.0,<ref name="simbad"/> making it easily visible with amateur telescopes, and is considered by some authors to be the galaxy with the highest absolute magnitude within a radius of 10 megaparsecs of the Milky Way.<ref name="Karachentsev2004">Template:Cite journal</ref> Its large bulge, central supermassive black hole, and dust lane all attract the attention of professional astronomers.

Observation historyEdit

DiscoveryEdit

The Sombrero Galaxy was discovered on May 11, 1781 by Pierre Méchain, who described the object in a May 1783 letter to J. Bernoulli that was later published in the Berliner Astronomisches Jahrbuch.<ref name= "kepplesanner1998">Template:Cite book</ref><ref name="jones1991">Template:Cite book</ref> Charles Messier made a handwritten note about this and five other objects (now collectively recognized as M104 – M109) to his personal list of objects now known as the Messier Catalogue, but it was not "officially" included until 1921.<ref name= "jones1991"/> William Herschel independently discovered the object in 1784 and additionally noted the presence of a "dark stratum" in the galaxy's disc, what is now called a dust lane.<ref name= "kepplesanner1998"/><ref name= "jones1991"/> Later astronomers were able to connect Méchain's and Herschel's observations.<ref name="jones1991"/>

Designation as a Messier objectEdit

In 1921, Camille Flammarion found Messier's personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the New General Catalogue, and Flammarion declared that it should be included in the Messier Catalogue. Since this time, the Sombrero Galaxy has been known as M104.<ref name="jones1991"/>

Dust ringEdit

File:Sombrero Galaxy (MIRI Image) (2024-137).png

M104 captured by the James Webb Space Telescope's Mid-Infrared Instrument in 2024.

As noted above, this galaxy's most striking feature is the dust lane that crosses in front of the bulge of the galaxy. This dust lane is actually a symmetrical ring that encloses the bulge of the galaxy.<ref name="bendoetal2006">Template:Cite journal</ref> Most of the cold atomic hydrogen gas<ref name="bajajaetal1984">Template:Cite journal</ref> and the dust<ref name="bendoetal2006"/> lie within this ring. The ring might also contain most of the Sombrero Galaxy's cold molecular gas,<ref name="bendoetal2006"/> although this is an inference based on observations with low resolution and weak detections.<ref name="bajajaetal1988">Template:Cite journal</ref><ref name="youngetal1995">Template:Cite journal</ref> Additional observations are needed to confirm that the Sombrero galaxy's molecular gas is constrained to the ring. Based on infrared spectroscopy, the dust ring is the primary site of star formation within this galaxy.<ref name="bendoetal2006"/>

NucleusEdit

The nucleus of the Sombrero Galaxy is classified as a low-ionization nuclear emission-line region (LINER).<ref name="hoetal1997">Template:Cite journal</ref> These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.<ref name="bendoetal2006"/>

Central supermassive black holeEdit

In the 1990s, a research group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy.<ref name="kormendyetal1996">Template:Cite journal</ref> Using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of revolution of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times that of the Sun, Template:Solar mass, is present in the center.<ref name="kormendyetal1996"/> This is among the most massive black holes measured in any nearby galaxy, and is the nearest billion-solar-mass black hole to Earth.

Synchrotron radiationEdit

At radio and X-ray wavelengths, the nucleus is a strong source of synchrotron radiation.<ref name="debruynetal1996">Template:Cite journal</ref><ref name="hummeletal1984">Template:Cite journal</ref><ref name="theanetal2000">Template:Cite journal</ref><ref name="dimatteoetal2001">Template:Cite journal</ref><ref name="pellegrinietal2002">Template:Cite journal</ref><ref name="pellegrinietal2003">Template:Cite journal</ref><ref name="krauseetal2006">Template:Cite journal</ref> Synchrotron radiation is produced when high-velocity electrons oscillate as they pass through regions with strong magnetic fields. This emission is quite common for active galactic nuclei. Although radio synchrotron radiation may vary over time for some active galactic nuclei, the luminosity of the radio emission from the Sombrero Galaxy varies only 10–20%.<ref name="debruynetal1996"/>

Unidentified terahertz radiationEdit

In 2006, two groups published measurements of the terahertz radiation from the nucleus of the Sombrero Galaxy at a wavelength of Template:Val.<ref name="bendoetal2006"/><ref name="krauseetal2006"/> This terahertz radiation was found not to originate from the thermal emission from dust (which is commonly seen at infrared and submillimeter wavelengths), synchrotron radiation (which is commonly seen at radio wavelengths), bremsstrahlung emission from hot gas (which is uncommonly seen at millimeter wavelengths), or molecular gas (which commonly produces submillimeter spectral lines).<ref name="bendoetal2006"/> The source of the terahertz radiation remains unidentified.

Globular clustersEdit

The Sombrero Galaxy has a relatively large number of globular clusters, observational studies of which have produced population estimates in the range of 1,200 to 2,000.<ref name="wakamatsu1977">Template:Cite journal</ref><ref name="harrisetal1984">Template:Cite journal</ref><ref name="bridgeshaynes1992">Template:Cite journal</ref> The ratio of globular clusters to the galaxy's total luminosity is high compared to the Milky Way and similar galaxies with small bulges, but comparable to other galaxies with large bulges. These results have often been used to demonstrate that the number of a galaxy's globular clusters is thought to be related to the size of its bulge. The surface density of the globular clusters generally follows the bulge's light profile, except near the galaxy's center.<ref name="wakamatsu1977"/><ref name="bridgeshaynes1992"/><ref>Template:Cite journal</ref>

Distance, mass and brightnessEdit

At least two methods have been used to measure the distance to the Sombrero Galaxy.

The first method relies on comparing the measured fluxes from the galaxy's planetary nebulae to the known luminosity of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as Template:Cvt.<ref name="fordetal1996">Template:Cite journal</ref>

The second method is the surface brightness fluctuations method, which uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges appear very grainy, while more distant bulges appear smooth. Early measurements using this technique gave distances of Template:Cvt.<ref name="ajharetal1997">Template:Cite journal</ref> Later, after some refinement of the technique, a distance of Template:Cvt was measured.<ref name="tonryetal2001">Template:Cite journal</ref> This was even further refined in 2003 to Template:Cvt.<ref name="jensenetal2003">Template:Cite journal</ref>

The average distance measured through these two techniques is Template:Cvt.Template:Efn

The mass of M104 is estimated to be 800 billions solar masses<ref>https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-104/</ref>

The galaxy's absolute magnitude (in the blue) is estimated as −21.9 at Template:Cvt (−21.8 at the average distance of above)—which, as stated above, makes it the brightest galaxy in a radius of Template:Cvt around the Milky Way.<ref name="Karachentsev2004"/>

A 2016 report used the Hubble Space Telescope to measure the distance to M104 based on the tip of the red-giant branch method, yielding 9.55 ± 0.13 ± 0.31 Mpc.<ref name="McQuinn2016"/>

Nearby galaxies and galaxy group informationEdit

The Sombrero Galaxy lies within a complex, filament-like cloud of galaxies that extends to the south of the Virgo Cluster.<ref name="nbg">Template:Cite book</ref> However, it is unclear whether it is part of a formal galaxy group. Hierarchical methods for identifying groups, which determine group membership by considering whether individual galaxies belong to a larger aggregate of galaxies, typically produce results showing that the Sombrero Galaxy is part of a group that includes NGC 4487, NGC 4504, NGC 4802, UGCA 289, and possibly a few other galaxies.<ref name="nbg"/><ref name="fouqueetal1992">Template:Cite journal</ref><ref name="giuricinetal2002">Template:Cite journal</ref> However, results that rely on the percolation method (also known as the friends-of-friends method), which links individual galaxies together to determine group membership, indicate that either the Sombrero Galaxy is not in a group<ref name="garcia1993">Template:Cite journal</ref> or that it may be only part of a galaxy pair with UGCA 287.<ref name="giuricinetal2002"/>

Besides that, M104 is also accompanied by an ultra-compact dwarf galaxy, discovered in 2009, with an absolute magnitude of −12.3, an effective radius of just Template:Convert, and a mass of 3.3×Template:Solar mass<ref name="Hau2009">Template:Cite journal</ref>

Amateur astronomyEdit

The Sombrero Galaxy is 11.5° west of Spica<ref name="jones1991"/> and 5.5° north-east of Eta Corvi.<ref name="omeara1998">Template:Cite book</ref> Although it is visible with 7×35 binoculars or a Template:Convert amateur telescope,<ref name="omeara1998"/> an Template:Convert telescope is needed to distinguish the bulge from the disk,<ref name="jones1991"/> and a 10- or 12-inch (250 or 300 mm) telescope to see the dark dust lane.<ref name="jones1991"/>

In cultureEdit

One artistic work referencing the Sombrero Galaxy is the song South of the Sombrero Galaxy by St. Louis folk metal band Ars Arcanum. The gritty sci-fi Western piece is told from the perspective of a man on the run, from both the law and his own troubled past. The Sombrero Galaxy serves as a backdrop for the song’s narrative, blending cosmic imagery with themes of pursuit and regret.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

GalleryEdit

Sombrero Galaxy in infrared (Ssc2005-11a3).jpg

M104 in infrared by the Spitzer Space Telescope

NotesEdit

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ReferencesEdit

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External linksEdit

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